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STORM WATER MANAGEMENT PLAN
For
GREEN DRAGON COLONIAL VILLAGE
DWG. 464-7A
S.D.P. 08-03
C.U.P. 08-08
C.D.P. 08-13
SWMP#0927
Prepared: August 20, 2009
Updated: November 10, 2009
Updated: December 15, 2009
JN: 081240-5
Prepared For:
Bruce R. Bartlett
P.O. Box 9714
Rancho Santa Fe, CA 92067
LCORD COPY
]£
Date
Prepared By:
O'DAY CONSULTANTS
2710 Loker Avenue West, Suite 100
Carlsbad, CA 92010
George QTDay RCE 32014
Declaration of Responsible Charge
I hereby declare that I am the Engineer of Work for this project, that I have exercised responsible
charge over the design of this project as defined in section 6703 of the Business and Professions
Code, and that the design is consistent with current standards.
I understand that the check of project drawings and specifications by the City of Carlsbad is
confined to a review only and does not relieve me, as the Engineer of Work, of my
responsibilities for the project design.
O'Day Consultants, Inc.
2710 Loker Avenue West, Suite 100
Carlsbad, CA 92010
(760)931-7700
Date:
George O'ay
R.C.E. No. 32014 Exp.
Table of Contents
Section 1.0 - Introduction and Vicinity Map
Section 2.0 - Project Description
Section 3.0 - Site Map (pocket)
Section 4.0 - Pollutants and Conditions of Concern
Section 5.0 - Low Impact Development (LID) Site Design BMPS
Section 6.0 - Source Control BMPs
Section 7.0 - BMPs for Individual Priority Project Categories
Section 8.0 - Structural Treatment BMPs
Section 9.0 - Post Construction BMPs Maintenance Cost Responsibilities
Attachments:
1. Vicinity map
2. Soils Group Map
3. San Diego Region Hydrologic Boundary Map
4. Beneficial uses for the hydrologic unit
5. 2006 CWA Section 303(d) list for impaired water bodies
6. Table 1: Storm Water BMP Requirements Matrix
7. Table 2: Anticipated and Potential Pollutants
Table 3: Numeric Sizing Treatment Standards
Table 4: Structural Treatment Control BMP Selection Matrix
8. Project Storm Water Management Plan & BMP Exhibit
9. LID Site Design BMPs
10. Source Control BMPs
11. Treatment Control BMPs
12. Curb Inlet Filter Sizing Calculations
13. Applicable Manufacturer's BMP Information
BioClean Environmental Services, Inc.
Grate Inlet Skimmer Box, Curb Inlet Basket, Nutrient Separating Baffle Box
Report & Data
BioClean Environmental Services, Inc.
Flume Filter - Boom Box Type - Report & Data
14. Section 6: Long-term Maintenance of BMPs
15. Storm Water Standards Questionnaire (City of Carlsbad, Form E-34)
Section 1.0 Introduction and Vicinity Map
This Storm Water Management Plan was prepared to support the application for construction
plans of Green Dragon Colonial Village, a remodel of the existing building and parking lot,
C.D.P. 08-13, in the City of Carlsbad, County of San Diego, State of California.
See Attachment 1 for Vicinity Map.
Section 2.0 Project Description
The 3.08 acre site currently consists of a food market building with a footprint of approximately
18,400 square-feet (0.42 acres) and on-grade parking lot. The proposed project will remodel the
existing building and parking lot to a single building with a restaurant, museum, tavern, and
conference rooms along with an on-grade parking lot.
Several studies have been prepared for this project as follows:
1. Reference 1: Drainage Study for Green Dragon Colonial Village, C.D.P. 08-13
dated August 17, 2009 updated October 29, 2009 by O'Day Consultants; and,
2. Reference 2: Grading Plans for Green Dragon Colonial Village, C.D.P. 08-13, City
of Carlsbad Dwg. 464-7A; and,
Existing Conditions
The project is located in the Encinas Hydrologic Area (904.4) of the Carlsbad Hydrologic Unit in
the San Diego Region (See Attachment 3). Under existing conditions, the site consists of two
distinct drainage basins, Basin 'A' and Basin 'B'. Runoff generated in Basin 'A' is conveyed via
overland flow across the existing parking lot to a concrete ditch located at the northwest corner
of the site. The concrete ditch then conveys the runoff off site to an existing catch basin located
in the right-of-way of Interstate 5. Runoff generated in Basin 'B' is conveyed via overland flow
to the southeast corner onto Paseo Del Norte through two existing driveways
Proposed Conditions
In the proposed condition, the drainage patterns will remain relatively the same as currently
exist. Runoff from both Basin 'A' and Basin 'B' will be directed into vegetated swales for storm
water treatment before leaving the site. Runoff from Basin 'A' will enter the right-of-way of
Interstate 5 through a concrete ditch as in the existing condition. Runoff from Basin 'B' will
enter Paseo Del Norte through a proposed curb outlet. See Reference 1 above for the Drainage
Study for this site and Attachment 8 for the Storm Water Management Plan Exhibit.
Priority Project Determination
The City of Carlsbad SUSMP dated June 2008 provides a Storm Water Standards Questionnaire
to determine a project's permanent and construction storm water BMP requirements (See
Attachment 14). The results are summarized below:
This project meets Priority Project Requirements. Must comply with the priority project
standards and must prepare a Storm Water Management Plan for submittal at the time of
application.
Storm Water Pollution Prevention Plan
Federal, state and local agencies have established goals and objectives for storm water quality in
the region. The project, prior to the start of construction activities, will comply with all federal,
state and local permits including the National Pollution Discharge Elimination System (NPDES)
from the Regional Water Quality Control Board and the erosion control requirements from the
City of Carlsbad grading ordinance. Compliance with the NPDES requires the applicant to file a
Notice of Intent (NOI) with the State Water Quality Control Board (SWQCB), apply Best
Management Practices (BMPs) and develop a storm water pollution prevention plan (SWPPP).
A Notice of Intent has been filed, WDID 9 37C356496, and a SWPPP has been prepared by
O'Day Consultants dated August 17, 2009 and updated October 29, 2009. The SWPPP shall be
kept on site during construction.
Section 3.0
Attachment 8 - Site Map
Section 4.0 Pollutants and Conditions of Concern
Pollutants of Concern
In the 2006 CWA Section 303(d) List of Water Quality Limited Segments, Encinas Creek is not
an impaired water body, but it is in an environmentally sensitive area (Attachment 5). Portions
of Carlsbad where construction sites have the potential to discharge into a tributary of a 303 (d) or
directly into a 303 (d) water body or sites located within 200 feet of an ESA require additional
BMP implementation.
Soil Characteristics
A soils report for the site has been prepared by GeoSoils, Inc. titled "Preliminary Geotechnical
Investigation Proposed Green Dragon Colonial Village (Formerly Hadley's), Paseo Del Norte,
Carlsbad, San Diego County, California." dated June 30, 2009.
The Soil Hydrologic Group for this site is mainly Type 'D' soil as determined by using the
County of San Diego Soil Hydrologic Group Map (See Attachment 2).
Potential Discharges
The project will contain some pollutants commonly found on similar developments that could
affect water quality. The following list is taken from Table 2: Anticipated and Potential
Pollutants Generated by Land Use of the City of Carlsbad's Storm Water Standards Manual (See
Attachment 7).
Anticipated:
1. Heavy metals
2. Trash and debris
3. Oil and grease from paved areas
Potential:
4. Sediment discharge
5. Nutrients from fertilizers
6. Organic compounds
7. Oxygen demanding substances
8. Bacteria & Viruses
9. Pesticides from landscaping and home use
Conditions of Concern
The hydrologic analysis for this project (Reference 1) indicates that the project will generate the
following flow rates for pre- and post-development conditions:
Location
Basin 'A'
Basin 'B'
Total
Qioo (cfs)
Pre-development
6.7
8.8
15.5
Post-development
6.7
8.6
15.3
Section 5.0 Low Impact Development (LID) Site Design BMPs
To address water quality for the project, BMPs will be implemented during construction and post
construction. Required BMPs are selected from Table 1: Storm Water BMP requirements Matrix,
of the City of Carlsbad's Storm Water Standards Manual (Attachment 6).
Control of post-development peak storm water runoff discharge rates and velocities is desirable
in order to maintain or reduce pre-development downstream erosion. The following list provides
LID site design measures chosen for this site to help avoid or reduce potential impacts. These
measures will control post-development peak storm water runoff discharge rates and velocities to
maintain or reduce pre-development downstream erosion and to protect stream habitat. The
major principles for site design BMP's are 1) to maintain pre-development rainfall runoff
characteristics and 2) to protect slopes and channels. (See Attachment 9 for details):
Maintain Pre-Development Rainfall Runoff Characteristics:
This Site Design BMP entails controlling post construction peak storm water discharge at the
rate and velocities of the pre-developed condition.
Drain Runoff from Impervious Surfaces to Pervious Areas:
To the maximum extent practicable, parking lots, sidewalks, patios, roof top drains, rain gutters,
and other impervious surfaces shall drain into adjacent landscaping prior to discharging to the
storm water conveyance system. The project will utilize this LID Site Design BMP according to
the County of San Diego LID Handbook, Section 2.2.5 (Attachment 9).
Biofilters:
Biofilters, vegetated swales or bioswales as it is referred to here, have be incorporated into as
much of the landscaped areas as possible. See Section 8.0 for further discussion. The project
will utilize this LID Site Design BMP according to the County of San Diego LID Handbook,
Section 3.1.3.1, Fact Sheet 4. Vegetated Swale / Rock Swale (Attachment 9).
Drain Runoff from Impervious Surfaces to Pervious Areas:
To the maximum extent practicable, parking lots, sidewalks, patios, roof top drains, rain gutters,
and other impervious surfaces shall drain into adjacent landscaping prior to discharging to the
storm water conveyance system. The project will utilize this LID Site Design BMP according to
the County of San Diego LID Handbook, Section 2.2.5 (Attachment 9).
Curb-cuts:
Curb-cuts have been located along the parking curb line to direct drainage from the parking lot
into the vegetated swales, bioswales and bioretention areas that have been incorporated into the
design of the parking area. The project will utilize this LID Site Design BMP according to the
County of San Diego LID Handbook, Section 3.3.3, Fact Sheet 17: Curb-cuts (Attachment 9).
Downspouts to Swale:
Roof drains have been designed to outlet to and undersidewalk drain, crossing the parking area
via concrete swale which will outlet into the closest vegetated swale or otherwise landscaped
area. The project will utilize this LID Site Design BMP according to the County of San Diego
LID Handbook, Section 3.6.4, Fact Sheet 28: Downspout to Swale (Attachment 9).
Protect Slopes and Channels:
All runoff will be safely conveyed away from the tops of slopes. All slopes and landscape areas
will have permanent landscaping consistent with the Carlsbad Landscape Manual to prevent
erosion of sediment. Each top and bottom of slope has been designed so that runoff will safely
be conveyed away from the slope.
Vegetate Slopes with Natural or Drought Tolerant Vegetation:
The project will utilize this BMP by having the landscaping designer utilize the applicable City
of Carlsbad Landscape Manual and any other applicable City of Carlsbad Standards.
Section 6.0 Source Control BMPs
Source Control BMPs help minimize the introduction of pollutants and sedimentation into storm
water in order to maintain or reduce pre-development levels of pollutants by applying the
following concepts (See Attachment 10):
Street Sweeping:
City maintained streets will be swept routinely in order to reduce introduction of trash, debris,
sediment and siltation into drainage systems.
Use Efficient Irrigation Systems & Landscape Design:
This Source Control BMP entails employing rain shutoff devices to prevent irrigation during
precipitation and this requires all landscaping aspects to be designed per the Carlsbad Landscape
Manual. The project will utilize this Source Control BMP by having the landscaping designer
utilize the applicable City of Carlsbad Landscape Manual and any other applicable City of
Carlsbad Standards. In addition, site irrigation will also be designed in accordance with CASQA
SD-10: Site Design and Landscape Planning & SD-12: Efficient Irrigation.
Provide Storm Water Conveyance System Stenciling and Signage:
This Source Control BMP entails providing storm drain conveyance system stenciling and
signage. This shall be done by providing concrete stamping, porcelain tile, insert permanent
marking or approved equivalent as approved by the City of Carlsbad, of all storm drain
conveyance system inlets and catch basins within the project area with prohibitive language (i.e.
"No Dumping - I Live Downstream') satisfactory to the City Engineer. The project will utilize
this Source Control BMP in accordance with CASQA SD-13: Storm Drain Signage.
Trash Storage Areas to Reduce Pollution Introduction:
This Source Control BMP entails designing trash storage areas to reduce pollution introduction.
Trash Storage Areas shall be paved with an impervious surface, designed not to allow runoff
from adjoining areas, screened or walled to prevent off-site transportation of trash, and contain
attached lids on all trash containers that protects them from precipitation. Alternatively, the trash
enclosure can contain a roof or awning to minimize direct contact with precipitation. The project
will utilize this Source Control BMP by designing and building the trash storage areas according
to the City of Carlsbad Standard Drawing GS-16 and in accordance with CASQA SD-32: Trash
Enclosures. These areas will be paved with an impervious surface, graded to drain away from the
enclosure, and screened and walled to prevent off-site transport of trash. Trash containers will
contain attached lids that exclude rain to minimize direct precipitation.
Section 7.0 BMPs for Individual Priority Project Categories
Where identified in Table 1 of the City Standards (Attachment 6), the following requirements
shall be incorporated into priority projects:
Surface Parkins Areas:
Surface parking areas (covered and uncovered) where landscaping is proposed shall incorporate
landscape areas into the drainage design. Parking that is in excess of the project's minimum
requirements (overflow parking) may be constructed with permeable paving subject to the City
Engineer's approval. This project will utilize this Individual Priority Project Category BMP by
incorporating the proposed landscaping areas in the drainage pattern as much as feasibly
possible.
Section 8.0 Structural Treatment BMPs
Where identified in Table 1 of the City Standards (Attachment 6), and after L.I.D. site design and
source control BMPs have been incorporated into the project design, treatment control BMPs
may then be utilized.
Treatment Control BMPs shall be designed to infiltrate, filter, and/or treat runoff from the project
footprint per Table 3: Numeric Sizing Treatment Standards. A copy of Table 3 is provided in
Attachment 7. There are four guidelines that need to be followed for Treatment Control BMPs:
• All Structural Treatment Control BMPs shall infiltrate, filter, and/or treat the
required runoff volume or flow prior to discharging to any receiving water body
supporting beneficial uses.
• Multiple post construction Structural Treatment Control BMPs for a single
priority project shall collectively be designed to comply with the numeric sizing
treatment standards.
• Shared BMPs shall be operational prior to the use of any dependent development
or phase of development. The shared BMPs shall only be required to treat the
dependent developments or phases of development that are in use.
• Interim storm water BMPs that provide equivalent or greater treatment than is
required may be implemented by a dependant development until each shared
BMP is operational. If interim BMPs are selected, the BMPs shall remain in use
until permanent BMPs are operational.
Based on the pollutants of concern present from the project site and the removal efficiencies
listed in Table 4: Structural Treatment Control BMP Selection Matrix, the Structural Treatment
Control BMP with the most efficient removal efficiencies for the project are as follows (listed
most to least efficient):
• Bioretention
• Vegetated Swale/Buffer
• Media Filters
Based on the above mentioned removal efficiencies and limited space on site, the project shall
incorporate a combination of bioretention areas vegetated swales/buffers and drainage inserts on
site.
Vegetated Swale:
As mentioned in Section 6, vegetated swales, or bioswales as referred to on the BMP Exhibit
(Attachment 8), have been incorporated to all of the landscape areas large enough to facilitate
such swales. The project will utilize this Treatment Control BMP by utilizing CASQA TC-30:
Vegetated Swale (Attachment 11).
Bioretention Areas:
Bioretention areas are incorporated through the design of the parking areas by the use of
infiltration planters, flow-through planters and swales as much as feasibly possible. See sizing
calculations in Attachment 12. The project will utilize this Treatment Control BMP by utilizing
CASQA TC-32: Bioretention (Attachment 11).
Inlet filters:
Although not numerically required as a treatment train, the drainage inserts will be grate inlet
skimmer baskets by Suntree Technologies, Inc. The inlet baskets will also include hydrocarbon
absorption booms to collect oil and grease. Drainage inserts will be installed at four locations as
shown on the SWMP Exhibit (Attachment 8). See Attachment 13 for product information and
sample data and CASQA MP-52: Drain Inserts (Attachment 11).
The combination of these BMPs together with the site and source control BMPs sited above
maximizes pollutant removal efficiency for the particular pollutants of concern to the maximum
extent practicable.
Section 9.0 Post Construction BMPs Maintenance Cost Responsibilities
The following post-construction BMPs shall be owner maintained:
1. All planted slopes and landscaped areas
2. Efficient irrigation systems & landscape design
3. Storm drain inlet stenciling and signage
4. Storm drain inlets fitted with "Bio Clean" grated basket inserts with hydrocarbon
absorption booms
5. Vegetated swale
The table that follows lists post-construction BMPs, maintenance responsibility and estimated
cost.
BMPs
Source Control
Maintenance Cost
Efficient Irrigation and
Landscape Design (SD-12)
Owner responsibility
Storm Drain Signage (SD-13) Owner yearly inspection
and repaint or replace
Treatment Control
Budget by the
Owner
Est. $500.00
Drain Inserts (MP-52)
Vegetated Swale (TC-30)
Bioretention (TC-32)
Owner responsibility
Inspect 2 times per year (min)
(before rain season, and after major
storm events)
Clean screen and replace
hydro-carbon filter at least once
per year before rainy season
Owner responsibility
Owner responsibility
Est. $200 per insert
Budget by the Owner
Budget by the Owner
Attachment 1
STORM WATER MANAGEMENT PLAN
GREEN DRAGON COLONIAL VILLAGE
ATTACHMENT 1: VICINITY MAP
CITY OF OCEAN SIDE
CITY OF VISTA
CITY OF
SAN MARCOS
CITY OF EMCINITAS
VICINITY MAP
NO SCALE
VICINITY M4P
SCALE: 1" = 80'
G:\081240\0840VlC.dwg Nov 03. 2009 9:44am
Xrefs: 0840MAP; 0840GRD; 0840TP01
Attachment 2
STORM WATER MANAGEMENT PLAN
GREEN DRAGON COLONIAL VILLAGE
ATTACHMENT 2: COUNTY OF SAN DIEGO HYDROLOGY MANUAL
SOIL HYDROLOGIC GROUP MAP
Please see attached.
117°30'0"W 117°15'0"W 116°30'0"W
ti i i i i
Orange
County Riverside County
)CEANSIDE
CARLSBAD
ENCINITAS
\f "It :?i!?S.. .
HULA VISTA
RIAL BEACH
County of San Diego
Hydrology Manual
Soil Hydrologic Group
Legend
~ Major Roads
Incorporated City Bdy
HYDROLOGIC SOIL GROUP
Hydrologic Group Undefined
" Hydrologic Group A
Hydrologic Group B
Hydrologic Group C
* Hydrologic Group D
" No Soil Data
Note: Soil Data Source
USDA7NRCS
SSURGO Soils 2007
N
A 31.50 3 Miles
DPW
THIS MAP IS PROVIDED WITHOUT WARRANTY OF ANY KIND,
EITHER EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE.
Copyright SanGIS. All Rights Reserved.
This product may contain information from the SANDAG Regional
Information System which cannot be reproduced without the written
permission of SANDAG.
This product may contain information which has been reproduced
with permission granted by Thomas Brothers Maps.
117°3010"W 117°15'0"W 117°0'0"W 116°45'0"W 116030'0"W 116°15'0"W
Attachment 3
Attachment 4
STORM WATER MANAGEMENT PLAN
GREEN DRAGON COLONIAL VILLAGE
ATTACHMENT 4: BENEFICIAL USES FOR THE HYDROLOGIC UNIT
Please see attached.
Table 2-2. BENEFICIAL USES OF INLAND SURFACE WATERS
1,2
Inland Surface Waters Hydrologic Unit
Basin Number
BENEFICIAL USE
M
U
N
A
G
R
I
N
D
P
R
0
C
G
W
R
F
R
S
H
P
O
W
R
E
C
1
R
E
C
2
B
I
O
L
W
A
R
M
C
0
L
D
W
I
L
D
R
A
R
E
S
P
W
N
San Diego County Coastal Streams - continued
Buena Vista Lagoon
Buena Vista Creek
Buena Vista Creek
Agua Hedlonda
Agua Hedionda Creek
Buena Creek
Agua Hedionda Creek
Letterbox canyon
Canyon de las Encinas
4.21
4.22
4.21
4.31
4.32
4.32
4.31
4.31
4.40
See Coastal Waters- Table 2-3
+
+
•
•
•
•
•
•
•
•
•
•
•
••
See Coastal Waters- Table 2-3
•
•
•
•
+
•
•
•
•
•
•
•
•
•
•
•
•
0
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
San Marcos Creek Watershed
Batiquitos Lagoon
San Marcos Creek
unnamed intermittent streams
4.51
4.52
4.53
See Coastal Waters- Table 2-3
+
+
•
•
•
•
•
•
•
•
•
•
San Marcos Creek Watershed
San Marcos Creek
Encinitas Creek
4.51
4.51
+
+
•
•
•
•
•
•
•
•
•
•
• Existing Beneficial Use
O Potential Beneficial Use
+ Excepted From MUN (See Text)
1 Waterbodies are listed multiple times if they cross hydrologic area or sub area boundaries.
Beneficial use designations apply to all tributaries to the indicated waterbody, if not listed separately.
Table 2-2
BENEFICIAL USES 2-27
March 12, 1997
r
Table 2-3. BENEFICIAL USES OF COASTAL WATERS
Coastal Waters
Pacific Ocean
Dana Point Harbor
Del Mar Boat Basin
Mission Bay
Oceanside Harbor
San Diego Bay
Hydrologic
Unit Basin
Number
BENEFICIAL USE
1
N
D
•
N
A
V
R
E
C
1
•
R
E
C
2
•
C
0
M
M
•
B
I
0
L
E
S
T
•
W
I
L
D
•
•
•
•
R
A
R
E
•
•
•
•
M
A
R
•
•
•
•
A
Q
U
A
M
I
G
R
•
•
•
•
•
S
P
W
N
•
•
•
•
•
W
A
R
M
S
H
E
L
L
•
•
•
•
•
•
Coastal Lagoons
Tijuana River Estuary
Mouth of San Diego River
2Los Penasquitos Lagoon
San Dieguito Lagoon
Batiquitos Lagoon
San Elijo Lagoon
Aqua Hedionda Lagoon
11. 11
7.11
6.10
5.11
4.51
5.61
4.31 •
•
•
•
•
•
•
•
•
•
•
•
•
•
•
••••
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
1 Includes the tidal prisms of the Otay and Sweetwater Rivers.
2 Fishing from shore or boat permitted, but other water contact recreational (REC-1) uses are prohibited.
• Existing Beneficial Use
Table 2-3
BENEFICIAL USES
March 12, 1997
2-47
Table 2-3. BENEFICIAL USES OF COASTAL WATERS
Coastal Waters Hydrologic
Unit Basin
Number
BENEFICIAL USE
I
N
D
N
A
V
R
E
C
1
R
E
C
2
C
0
M
M
B
I
0
L
E
S
T
w
I
L
D
R
A
R
E
M
A
R
A
Q
U
A
M
I
G
R
S
P
W
N
W
A
R
M
S
H
E
L
L
Coastal Lagoons - continued
2Buena Vista Lagoon
Loma Alta Slough
Mouth of San Luis Rey River
Santa Margarita Lagoon
Aliso Creek Mouth
San Juan Creek Mouth
San Mateo Creek Mouth
San Onofre Creek Mouth
4.21
4.10
3.11
2.11
1.13
1.27
1.40
1.51
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
0
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
1 Includes the tidal prisms of the Otay and Sweetwater Rivers.
2 Fishing from shore or boat permitted, but other water contact recreational (REC-1) uses are prohibited.
• Existing Beneficial Use
0 Potential Beneficial Use
Table 2-3
BENEFICIAL USES 2-48
March 12, 1997
Table 2-5. BENEFICIAL USES OF GROUND WATERS
Ground Water
CARLSBAD HYDROLOGIC UNIT
Loma Alta HA 2
Buena Vista Creek HA
El Salto HSA 2
Vista HSA
Aqua Hedionda HA
Los Monos HSA 2
Los Monos HSA 5
Los Monos HSA 6
Buena HSA
Encinas HA
Hydrologic
Unit Basin
Number
4.00
4.10
4.20
4.21
4.22
4.30
4.31
4.31
4.31
4.32
4.40
BENEFICIAL USE
M
U
N
A
G
R
I
N
D
+•
p
R
0
C
F
R
S
H
G
W
R
•
•
•
•
O
•
•
0
0
•
+
•
O
•
•
•
0
0
•
2 These beneficial uses do not apply westerly of the easterly boundary of the right-of-way of Interstate Highway 5 and
this area is excepted from the sources of drinking water policy. The beneficial uses for the remainder
of the hydrologic area are as shown.
5 These beneficial use designations apply to the portion of HSA 4.31 bounded on the west by the easterly boundary of Interstate Highway 6 right-of-way; on the east by the
easterly boundary of El Camino Real; and on the north by a line extending along the southerly edge of Agua Hedionda Lagoon to the easterly end of the lagoon, thence in
an easterly direction to Evans Point, thence easterly to El Camino Real along the ridge lines separating Letterbox Canyon and the area draining to the Marcario Canyon.
6 These beneficial use designations apply to the portion of HSA 4.31 tributary to Agua Hedionda Creek downstream from the El Camino Real crossing, except lands tributary to
Marcario Canyon (located directly southerly of Evans Point), land directly south of Agua Hedionda Lagoon, and areas west of Interstate Highway 5.
0 Existing Beneficial Use
0 Potential Beneficial Use
+ Excepted From MUN (see text)
Table 2-5
BENEFICIAL USES 2-53 September 8, 1994
Attachment 5
STORM WATER MANAGEMENT PLAN
GREEN DRAGON COLONIAL VILLAGE
ATTACHMENT 5: 2006 CWA SECTION 303(d) LIST FOR IMPAIRED WATER
BODIES
Please see attached.
20! CWA SECTION 303(d) LIST OF WATER QUA TY LIMITED SEGMENTS REQUIRING TMD
SAN DIEGO REGIONAL WATER QUALITY CONTROL BOARD
USEPA APPROVAL DATE: JUNE 28, 2007
REGION TYPE NAME
CALWATER POTENTIAL
WATERSHED POLLUTANT/STRESSOR SOURCES
ESTIMATED PROPOSED TMDL
SIZE AFFECTED COMPLETION
9 B Dana Point Harbor
9 R De Luz Creek
9 L El Capitan Lake
9 R Encinitas Creek
90114000
90221000
90731000
90451000
Phosphorus
Sediment Toxicity
Source Unknown
Source Unknown
Indicator bacteria
Impairment located at Baby Beach.
Urban Runoff/Storm Sewers
Marinas and Recreational Boating
Unknown Nonpoint Source
Unknown point source
Iron
Manganese
Color
Manganese
Phosphorus
Source Unknown
Source Unknown
Source Unknown
Source Unknown
Source Unknown
Source Unknown
1.9 Miles
1.9 Miles
119 Acres
14 Miles
14 Miles
1454 Acres
1454 Acres
1454 Acres
3 Miles
2019
2019
2006
2019
2019
2019
2019
2019
2019
Page 4 of 27
Attachment 6
Table 1
Standard Development Project & Priority Project Storm Water BMP Requirements Matrix
•**,..
Standard Projects
LID
Site
Design
BMPs(1)
R
Source
Control
BMPs(2)
R
BMPs Applicable to Individual
Priority Project Categories'3'a. Private RoadsR b. ResidentialDriveways & GuestParkingR
(/>co
1.*:8
Q
d
R d. Maintenance BaysR e. Vehicle Wash AreasR f. Equipment WashAreasR g. Outdoor ProcessingAreasR h. Surface ParkingAreasR
wCD
£
<
D)
"co
LU
R j. Hillside LandscapingR
Treatment
Control
BMPs(4)
O
Priority Projects:
Detached Residential
Development
Attached Residential
Development
Commercial Development
greater than 100,000ft2
Heavy industry /industrial
Automotive Repair Shop
Restaurants
Steep Hillside
Development greater than
5,000 ft2
Parking Lots
Retail Gasoline Outlets
Streets, Highways &
Freeways
R
R
R*
R
R
R
R
R*
R
R
R
R
R*
R
R
R
R
R *
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R R
R<5>*
R
R
R
R
R
S
S
S*
S
S
S
S
s*
S
S
R = Required; select one or more applicable and appropriate BMPs from the applicable steps in Section III.2.A-D, or
equivalent as identified in Appendix B.
O = Optional/ or may be required by City staff. As appropriate, applicants are encouraged to incorporate treatment
control BMPs and BMPs applicable to individual priority project categories into the project design. City staff may
require one or more of these BMPs, where appropriate.
S = Select one or more applicable and appropriate treatment control BMPs from Appendix B.
(1) Refer to Chapter 2.3.3.1. LID = Low Impact Development.
(2) Refer to Chapter 2.3.3.2.
(3) Priority project categories must apply specific storm water BMP requirements, where applicable. Priority projects
are subject to the requirements of all priority project categories that apply. Refer to Chapter 2.3.3.3
(4) Refer to Chapter 2.3.3.4
(5) Applies if the paved area totals >5,000 square feet or with >15 park ng spaces and is potentially exposed to urban
runoff.
SWMP Rev 6/4/08
Attachment 7
2.3 PERMANENT BEST MANAGEMENT PRACTICES SELECTION PROCEDURE
2.3.1 INTRODUCTION
The following process should be followed to determine the permanent BMPs for the applicant's project.
2.3.2 IDENTIFY POLLUTANTS AND CONDITIONS OF CONCERN
2.3.2.1 Identify Pollutants from the Project Area
Using Table 2 below, identify the project's anticipated pollutants. Pollutants associated with any
hazardous material sites that have been remediated or are not threatened by the proposed project are not
considered a pollutant of concern. Projects meeting the definition of more than one project category shall
identify all general pollutant categories that apply. Descriptions of the general pollutant categories listed
in Table 2 are defined in Appendix F under the definition of "pollutants of concern."
Table 2
Anticipated and Potential Pollutants Generated by Land Use Type
Project
Categories
Detached
Residential
Development
Attached
Residential
Development
Commercial
Development
>100,000ft2
Heavy industry
/industrial
development
Automotive
Repair Shops
Restaurants
Steep Hillside
Development
>5,000 ft2
Parking Lots
Retail Gasoline
Outlets
Streets,
Highways &
Freeways
General Pollutant Categories
Sediments
X
X
p(D
X
X
p(1)
X
Nutrients
X
X
p(i)
X
p(1)
p(1>
Heavy
Metals
X
X
X
X
X
Organic
Compounds
p(2)
X
X<4)(5)
X
XW
Trash
&
Debris
X
X
X
X
X
X
X
X
X
X
Oxygen
Demanding
Substances
X
p(i)
p(5)
X
X
X
p(1)
X
p(5)
Oil&
Grease
X
p(2)
X
X
X
X
X
X
X
X
Bacteria
&
Viruses
X
p(i)
p(3)
X
Pesticides
X
X
p(5)
X
p(1)
X = anticipated
P = potential
(1) A potential pollutant if landscaping exists on-site.
(2) A potential pollutant if the project includes uncovered parking areas.
(3) A potential pollutant if land use involves food or animal waste products.
(4) Including petroleum hydrocarbons.
(5) Including solvents.
SWMP Rev 6/4/08
Table 3
Numeric Sizing Treatment Standards
Volume
1.
IV.
Volume-based BMPs shall be designed to mitigate (infiltrate, filter, or treat) either:
The volume of runoff produced from a 85th percentile storm event, as determined from isopluvial maps
contained in the County of San Diego Hydrology Plan (0.6 inch approximate average for the San Diego
County area) [Note: Applicants may calculate the 85th percentile storm event using local rain data, when
available. See the County of San Diego's isopluvial map at
http://www.sdcountv.ca.gov/dpw/engineer/flood.htm1: or
The volume of runoff produced by the 85tn percentile storm event, determined as the maximized capture
urban runoff volume for the area, from the formula recommended in Urban Runoff Quality Management,
WEF Plan of Practice No. 23/ASCE Plan of Practice No. 87, page 175 Equation 5.2; (1998); or
The volume of annual runoff based on unit basin storage volume, to achieve 90 percent or more volume
treatment by the method recommended in the latest edition of the California Stormwater Best Management
Practices Handbook, or
The volume of runoff, as determined from the local historical rainfall record, that achieves approximately
the same reduction in pollutant loads and flows as achieved by mitigation of the 85th percentile 24-hour
runoff event.
OR
Flow
2. Flow-based BMPs shall be designed to mitigate (infiltrate, filter, or treat) either:
3.0 The maximum flow rate of runoff produced from a rainfall intensity of 0.2 inch of rainfall per hour for each
hour of a storm event; or
4.0 The maximum flow rate of runoff produced by the 85th percentile hourly rainfall intensity, as determined
from the local historical rainfall record, multiplied by a factor of two; or
5.0 The maximum flow rate of runoff, as determined from the local historical rainfall record, that achieves
approximately the same reduction in pollutant loads and flows as achieved by mitigation of the 85th
percentile hourly rainfall intensity multiplied by a factor of two.
Notes on Structural Treatment Limited Exclusions
Proposed restaurants, where the land area for development or redevelopment is less than 5,000 square
feet, are excluded from the numerical sizing criteria requirements listed in Table 3.
Where significant redevelopment results in an increase of less than 50 percent of the impervious surfaces
of a previously existing development, and the existing development was not subject to priority project
requirements, the numeric sizing criteria apply only to the addition, and not to the entire development.
15 SWMP Rev 6/4/08
2.3.3.5 Structural Treatment BMP Selection Procedure
Priority projects shall select a single or combination of treatment BMPs from the categories in Table 4 that
maximize pollutant removal for the particular pollutant(s) of concern.
1. Determine if the project would discharge to a Clean Water Act Section 303(d) impaired receiving
water. If any receiving waters for the project are impaired, identify the specific type of pollutant(s)
for which the receiving water(s) is/are impaired.
2. If the project is anticipated to generate a pollutant (per Table 2) for which the receiving water is
impaired, select one or more BMPs from Table 4 that maximize the pollutant removal for that
pollutant. Any pollutants the project is expected to generate that are also causing a Clean Water
Act section 303(d) impairment of the downstream receiving waters of the project shall be given
top priority in selecting treatment BMPs
3. If none of the project's receiving waters are listed as impaired, select one or more BMPs from
Table 4 that maximize the removal of the pollutants the project is anticipated to generate.
Alternative storm water BMPs not identified in Table 4 may be approved at the discretion of the City
Engineer, provided the alternative BMP is as effective in removal of pollutants of concern as other
feasible BMPs listed in Table 4.
Table 4. Structural Treatment Control BMP Selection Matrix
Pollutants of
Concern
Coarse Sediment
and Trash
Pollutants that
tend to associate
with fine particles
during treatment
Pollutants that
tend to be
dissolved
following
treatment
Bioretention^
Facilities
(LID)
High
High
Medium
Settling
Basins
(Dry Ponds)
High
High
Low
Wet Ponds
and
Wetlands
High
High
Medium
Infiltration
Facilities or
Practices
(LID)
High
High
High
Media
Filters
High
High
Low
High-rate
biofilters
High
Medium
Low
High-rate
media
filters
High
Medium
Low
Trash Racks &
Hydro
-dynamic
Devices
High
Low
Low
2.3.3.6 Notes on Pollutants of Concern
In Table 4 above, Pollutants of Concern are grouped as gross pollutants, pollutants that tend to associate
with fine particles, and pollutants that remain dissolved. The table below distinguishes the pollutant types
associated with each of these three groupings.
Pollutant
Sediment
Nutrients
Heavy Metals
Organic Compounds
Trash & Debris
Oxygen Demanding
Bacteria
Oil & Grease
Pesticides
Coarse Sediment
and Trash
X
X
Pollutants that tend
to associate with
fine particles during
treatment
X
X
X
X
X
X
X
X
Pollutants that tend
to be dissolved
following treatment
X
16 SWMP Rev 6/4/08
Attachment 8
Attachment 9
The County of San Diego LID Handbook
2.2.5. Drain Runoff from Impervious Surfaces to Pervious Areas5
When planning for stormwater
management and designing the
project to meet stormwater
requirements, the permeability of
the project site should be retained
or improved. Projects planned
with landscaped areas or other
pervious areas (lawns) are required
to be designed and constructed to
receive stormwater runoff (from
rooftops, parking lots, sidewalks,
walkways, patios, etc.)". These
pervious areas help slow, retain,
filter, and treat runoff in the first
few inches of the soil before
discharging into the municipal
stormwater system. In rural
situations these pervious areas
should be designed to infiltrate
and/or percolate stormwater on site
where appropriate. In areas that
have stormwater infrastructure, /,/,,.,,/,.,, i ,,/,,/,
pervious areas must receive runoff
before it drains into the municipal
stormwater system. As required,
the amount of runoff directed from impervious areas shall correspond with the pervious
area's capacity to treat that runoff5. When directly infiltrating into the ground using pure
infiltration BMPs (infiltration trench, infiltration basin, dry wells, permeable pavements
without an under-drain) the soil conditions, slope and other pertinent factors must be
addressed by a qualified licensed geotechnical, civil or professional engineer.
Urban and infill developments may have limited opportunities to maximize permeability,
in which case LID techniques such as the application of permeable pavements, vegetated
roofs/modules/walls, raised sidewalks, street trees, etc., may be more appropriate.
LID techniques for stormwater infiltration and/or filtration attempt to work with land uses
and natural land features to become a major design element of the development plan. By
applying LID techniques early in the site plan development, these stormwater techniques
can be utilized more efficiently. When applying LID strategies in the stonmvater
management plan and the drainage plan, the project can include optimal pathway
alignment, optimum locations for usable open space, pocket parks and play areas, and
building sites. In this way, the stormwater management plan helps the project convey a
' Order No. R9-2007-0001, Pgl9. Section: D.!.d.(4)(a)i.. ii.
FINAL -25-12/31/2007
The County of San Diego LID Handbook
more aesthetically pleasing and integrated relationship to the natural features of the site
and the project's surroundings. In redevelopment and other site-constrained projects
where the opportunities for surface drainage and surface infiltration systems are limited,
it may be possible to create underground storage systems to promote retention and/or
slow infiltration (e.g. permeable pavements, recharge bed, etc.) prior to releasing runoff
into the municipal stormwater system.
Important Note: Proposed stormwater "Infiltration BMPs", including permeable
pavements, shall be reviewed by a qualified, licensed professional to provide a
professional opinion regarding the potential adverse geotechnical conditions created by
the implementation of the plans. Geotechnical conditions such as slope stability,
expansive soils, compressible soils, seepage, groundwater, and loss of foundation or
pavement subgrade strength should be addressed, and where appropriate, mitigation
recommendations should be provided. The impact on existing, proposed, and future
improvements should be included in the review.
Mission Valley Library Photograph Courtesy ot'C.Sloan
FINAL -26-12/31/2007
The County of San Diego LID Handbook
2.3.2.2.Commercial Office buildings
Office buildings can
integrate storniwater
management
techniques in many
ways.
benign roofing,
materials \
roof drainage directed
to landscape /swale
"landscape reserve"
employee amenity area/
iire parking area
notches in curb to
direct nmojfto swale
Landscape areas for
employee use and
perimeter screening
can be designed as
extended dry
detention basins or
biofilters (swales) to
infiltrate and detain
runoff, while drying
up shortly after a
rain event. These
areas can also be
designed as
fountains or entry
statements to add aesthetic enhancement.
vegetated s\vale
with chf
infiltration islands pervious overflow
parking stalls
Parking can be treated in a variety of ways with the use of permeable materials.
Impervious parking stalls can be designed to drain onto landscape infiltration areas.
A portion of the required parking may be allowed to be held in "landscape reserve," until
a need for the full parking supply is established. This means that the original
construction only builds parking to meet anticipated staff needs. If the parking demand
increases, the area held in landscape reserve can be modified to accommodate parking.
In this way, parking is held to a minimum based on actual use, rather than by a zoning
formula that may not apply to the office building's actual parking need.
The techniques illustrated in this example are:
• Catch basin runoff directed to infiltration area1
• Vegetated swale with check dams
• Landscaped "parking reserve"
• Concave landscape areas to infiltrate runoff1
• Pervious overflow parking stalls'
• Roof drainage directed to landscape
• Rain harvesting
Technique requires Qualified, licensed professional's approval.
FINAL -35-12/31/2007
The County of San Diego LID Handbook
2.3.2.3.Commercial Restaurant
M'gt'ti'tritiii (-it ifrij. >iinc
Restaurants offer a strong contrast between infiltration opportunities and special activity
areas. Careful selection of materials such as brick or stone paving for outdoor patios can
enhance the restaurant's aesthetic appeal while allowing for infiltration as appropriate.
Landscape plantings can also be selected for stormwater infiltration.
Parking can be provided in a variety of ways, with hybrid parking lots for staff, who stay
for long shifts, or with landscaped infiltration islands in lots with conventional paving for
patrons, who stay for shorter periods.
In contrast to these infiltration opportunities, restaurants have special activity areas that
need to be isolated from the storm drain system. Grease, stored items, trash, and other
food waste must be kept in properly designed and maintained special activity areas.
Local ordinances may have design guidelines for allowable square footage of covered
and uncovered areas.
The techniques illustrated in this example are:
• Permeable pavement patio1
• Catch basin runoff directed to infiltration area1
• Hybrid parking lot
• Vegetation at drip line
• Concave landscape areas to infiltrate runoff1
• Rain harvesting
• Covered outdoor work area (trash, food waste, storage, equipment wash)
Technique requires Qualified, licensed professional's approval.
FINAL - 36 -12/31/2007
The County of San Diego LID Appendix
Fact Sheet 4. Vegetated Swale / Rock Swale
w wifiw
Upper limit mater Jevel
nothw soil Intel
B.ta,
Bqutdtere - efieroy dissfoatoraBelow cJieck tor
Freaboond
iKrtte %»3 with
^•lIMll llrf'hllli III IHa Itf ^M I »*li • VWIKtatAM f
Section Al Check Dam
Vegetated / rock swales are vegetated or rock lined earthen channels that collect, convey,
and filter site water runoff and remove pollutants. Swales are an alternative to lined
channels and pipes; configuration and setting are unique to each site.
CHARACTERISTICS
• If properly designed and maintained, swales can last for at least 50 years.
• Can be used in all soil types, natural or amended.
• When swales are not holding water, they appear as a typical landscaped area.
• Water is filtered by vegetation/rocks and pollutants are removed by
infiltration into the subsurface of the soil.
• Swales also serve to delay runoff peaks by reducing flow velocities.
APPLICATION
• Swales are most effective in removing coarse to medium sized sediments.
• Parking lot medians, perimeters of impervious pavements.
• Street and highway medians, edges (in lieu of curb and gutter, where appropriate).
• In combination with constructed treatment systems or sand filters.
DESIGN
• Vegetation of each swale is unique to the setting, function, climate, geology, and
character of each site and climatic condition.
• Can be designed with natural or amended soils, depending on the infiltration rate
provided by the natural condition versus the rate needed to reduce surface runoff.
• Grass swales move water more quickly than vegetated swales. A grass swale
is planted with salt grass; a vegetated swale is planted with bunch grass, shrubs or
trees.
• Rocks, gravel, boulders, and/or cobbles help slow peak velocity, allow
sedimentation, and add aesthetic value.
Final -36- 12/31/2007
The County of San Diego LID Appendix
• Pollutant removal effectiveness can be maximized by increasing residence time of
water in swale using weirs or check dams.
• Swales are often used as an alternative to curbs and gutters along roadways, but
can also be used to convey stormwater flows in recreation areas and parking lots.
• Calculations should also be provided proving the swale capable of safely
conveying the 100-year flow to the swale without flooding adjacent property or
infrastructure.
• See County of San Diego Drainage Design Manual for design criteria, (section
5.5) hjt|2l//v£w^
MAINTENANCE
• Swale maintenance includes mowing and removing clippings and litter. Vegetated
swales may require additional maintenance of plants.
• Periodically remove sediment accumulation at top of bank, in swale bed,
or behind check dams.
• Monitor for erosion and reseed grass or replace plants, erosion control netting and
mulch as necessary. Fertilize and replace vegetation well in advance of rainy
season to minimize water quality degradation.
• Regular inspections and maintenance is required during the establishment period.
LIMITATIONS
• Only suitable for grades between 1% and 6%; when greater than 2.5% should be
paired with weir or check dam.
• "Turf swales will commonly require irrigation and may not meet State water
conservation goals.
• Irrigated vegetation is not appropriate in certain sites. Xeriscape techniques,
natural stone and rock linings should be used as an alternative to turf.
• Wider road corridors may be required to incorporate swales.
• Contributing drainage areas should be sized to meet the stormwater management
objective given the amount of flow that will be produced.
• When contributing flow could cause formation of low-flow channel, channel
dividers must be constructed to direct flow and prevent erosion.
ECONOMICS
• Estimated grass swale construction cost per linear foot $4.50-$8.50 (from seed)
to $15-20 (from sod), compare to $2 per inch of diameter underground pipe e.g., a
12" pipe would cost $24 per linear foot).
• $0.75 annual maintenance cost per linear foot
REFERENCES
• CALTRANS - Storm Water Handbook (cabmphandbooks.com)
• For additional information pertaining to Swales, see the works cited in the San
Diego County LID Literature Index.
Final -37- 12/31/2007
The County of San Diego LID Appendix
Fact Sheet 17. Curb-cuts
Suaiisa
Concrete ewfc beyond
inlet
Suction
Cobbiws (bury 1/3 rnin,)
Notch in curb
Concrete curb
Boulders / cobbles todisslpete energy
Forebfly/setBement basin
swobs/ biofilter
Mortar setting bsd (optional}
On streets where a more urban character is desired or where a rigid pavement edge
is required, curb and gutter systems can be designed to empty into drainage swales.
These swales can run parallel to the street, in the parkway between the curb and the
sidewalk, or can intersect the street at cross angles, and run between residences,
depending on topography. Runoff travels along the gutter, but instead of being emptied
into a catch basin and underground pipe, multiple openings in the curb direct runoff into
surface swales or infiltration/detention basins. If lined with ground cover or
gravel/rock and gently sloped, these swales function as biofilters. Because concentration
of flow will be highest at the curb opening, erosion control must be provided, which may
include a settlement basin for ease of debris removal.
Urban curb/swale systems are a hybrid of standard urban curb and gutter with a more
rural or suburban swale drainage system. It provides a rigid pavement edge for vehicle
control, street sweeping, and pavement protection, while still allowing surface flow in
landscaped areas for stormwater quality protection.
CHARACTERISTICS
• Runoff travels along the gutter, but instead of being emptied directly into catch
basins and underground pipes, it flows into surface swales.
• Stormwater can be directed into swales either through conventional catch
basins with outfall to the swale or notches in the curb with flow line leading to the
swale.
• Swales remove dissolved pollutants, suspended solids (including heavy metals,
nutrients), oil and grease by infiltration.
APPLICATION
• Can be created in existing and new residential developments, commercial office
parks, arterial streets, concave median islands.
Final -66-12/31/2007
The County of San Diego LID Appendix
• Swale system can run either parallel to roadway or perpendicular to it,
depending on topography and adjacent land uses.
DESIGN
• Size curb-openings or catch basins for design storm.
• Multiple curb openings closely spaced are better than fewer openings
widely spaced because it allows for greater dissipation of flow and pollutants.
• Provide energy dissipaters at curb notches or catch basin outfall into swale.
• Provide settlement basin at bottom of energy dissipater to allow for
sedimentation before water enters swale.
• Curb cuts should be at least 12 inches wide to prevent clogging.
• Curb cuts should have a vertical drop in addition to sufficient width to prevent
clogging.
MAINTENANCE
• Annual removal of built-up sediment in settlement basin may be required.
• Catch basins require periodic cleaning.
• Inspect system prior to rainy season and during or after large storms.
LIMITATIONS
• Parking requirements and codes
ECONOMICS
• Cobble-lined curb opening may add marginal cost compared to standard catch
basin.
• Swale system requires periodic landscape maintenance.
REFERENCES
• Village Homes subdivision, Davis, CA. Residential street network,
• Folsom, CA. Dual-drainage system,
• For additional information pertaining to Curb-cuts, see the works cited in the San
Diego County LID Literature Index.
Final -67- 12/31/2007
The County of San Diego LID Appendix
Fact Sheet 28. Downspout to Swale
Discharging a roof downspout to landscaped areas
via swales allows for polishing and infiltration of
the runoff.
CHARACTERISTICS
• Runoff from the roof is directed into a
rocky or vegetated swale area.
• The water flows through swale with
overflow continuing to the storm drain.
APPLICATIONS
• Appropriate for most buildings with
landscaped areas adjacent to the building
where soil drainage is appropriate and
water infiltration does not pose a risk to
the foundation.
Photograph Courtesy of EGA, Inc.
DESIGN
• The downspout can be directly connected to a pipe which daylights some distance
from the building foundation, releasing the roof runoff into a rock lined swale
towards a landscaped area.
• The roof runoff is slowed by the rocks, absorbed by the soils and vegetation, and
remaining runoff flows away from the building foundation into the storm drain.
• Xeriscape techniques, natural stone and rock linings should be used as an
alternative to turf.
MAINTENANCE
• Maintenance is similar to that necessary for other swale areas and will depend on
the specific style chosen.
LIMITATIONS
• Only suitable for grades between 1% and 6%
• When a vegetated swale is used, the site requires adequate sunlight for vegetation
growth
• Avoid infiltrating too close to foundations and underground utilities.
ECONOMICS
• Costs are similar to those associated with other swale devices.
REFERENCES
• For additional information pertaining to the Downspout to Swale technique, see
the works cited in the San Diego County LID Literature Index.
Final -88-12/31/2007
The County of San Diego LID Handbook
3.3.3. Curb-Cuts
On streets where a more urban
character is desired or where a
rigid pavement edge is required,
curb and gutter systems can be
designed to empty into drainage
swales. These swales can run
parallel to the street, in the
parkway between the curb and the
sidewalk, or can intersect the street
at cross angles, and run between
residences, depending on
topography. Runoff travels along Photograph courtesy of Mike Campbell (RBF consulting)
the gutter, but instead of being emptied into a catch basin and underground pipe, multiple
openings in the curb direct runoff into surface swales or infiltration/detention basins. If
lined with vegetation or gravel/rock and gently sloped, these swales function as biofilters.
Because concentration of flow will be highest at the curb opening, erosion control must
be provided, which may include a settlement basin for ease of debris removal.
For more information on Curb-Cuts please see Fact Sheet 17 in Appendix 4.
3.3.4. Rural Swale Systems
On streets where a more rural character is desired, concrete curb and gutter need not be
required. Since there is no hard edge to the street, the pavement margins can be protected
by a rigid header of steel, wood or a concrete band poured flush with the street surface.
Parking can be permitted on a gravel shoulder. If the street is crowned in the middle, this
gravel shoulder also can serve as a linear swale (with appropriate slopes),
permitting infiltration of stormwater along its entire length. Because runoff from the
street is not concentrated, but dispersed along its entire length, the buildup of pollutants
in the soil is reduced. If parking is not desired on the shoulder, signage or striping can
be installed along the shoulder to prevent vehicle trespass. In these ways edge treatments
other than continuous concrete curb and gutters with underground drainage systems can
be integrated into street design to create a headwaters street system that reduces impact
on stormwater quality and that captures the most attractive elements of traditional
neighborhood design. [9]
For more information on Rural Swale Systems please see Fact Sheet 18 in Appendix 4.
Road drainage considerations. The perception that surface swale systems require a
great deal of maintenance is a barrier to their acceptance. In practice, maintenance is
required for all drainage systems, and surface systems can require comparable or less
maintenance than underground systems. Design factors for low maintenance include:
• Erosion control at curb openings
• Shallow side slopes and flat bottoms (as opposed to ditches which erode)
FINAL -56-12/31/2007
The County of San Diego LID Handbook
• Design non-circulation element streets for the minimum required
pavement widths
• Minimize the number of residential street cul-de-sacs and incorporate
landscaped areas to reduce impervious cover
• Urban curb/swale system: street slopes to curb, periodic swale inlets drain
to vegetated swale biofilter
For more information on LID Street Design please see Fact Sheet 14 in Appendix 4.
3.3.1. Public Road Standards
Current Public and Private Road standards mandate 60-80% impervious land coverage in
the public right-of-way and/or the Private road easement. Runoff from these impervious
surfaces is a principal concern regarding stormwater quality objectives unless the directly
connected impervious areas are sufficiently reduced. Road standards that allow a
hierarchy of road sizes according to average daily traffic volumes yields a wide variety of
benefits: improved aesthetics from street trees and green parkways, reduced impervious
land coverage, and reduced heat island effect. If the reduction in road width is
accompanied by a drainage system that allows for infiltration of runoff, the impact of
roads on stormwater quality can be effectively mitigated.
Public roads may utilize curbs and gutters, though the gutter may be tied to a biofilter or
swale rather than an underground storm drain. Sidewalks may be provided on one side of
the road, though usually preferable on both sides [35].
For more information on Public Road Standards please see Fact Sheet 15 in Appendix 4.
3.3.2. Private Road Standards
A Private Road is used where required by Subdivision and Zoning Ordinance
requirements. Curbs and gutters are replaced by gravel shoulders that are graded to form
a drainage way, with opportunities for biofiltration and landscaping. Road sheet flow
drains to a vegetated swale or gravel shoulder. Other characteristics of a private road
standard include, curbs at street corners, and the placement of culverts under driveways
and road crossings.
Typically, a narrow two-lane paved roadway is provided at approximately 24' wide.
Most of the time single vehicles use the center of the paved roadway. Protection of the
roadway edge and organization of parking are two significant issues in rural street design.
Roadway edge protection can be achieved by flush concrete bands, steel edge, or wood
headers. Upon recommendation of the local Fire Authority parking can be restricted by
use of signage and/or striping.
For more information on Private Road Standards please see Fact Sheet 16 in
Appendix 4.
FINAL -55- 12/31/2007
Section 3
Site and Facility Design for Water
Quality Protection
3.1 Introduction
Site and facility design for stormwater quality protection employs a multi-level strategy. The
strategy consists of: i) reducing or eliminating post-project runoff; 2) controlling sources of
pollutants; and 3), if still needed after deploying i) and 2), treating contaminated stormwater
runoff before discharging it to the storm drain system or to receiving waters.
This section describes how elements i), 2), and 3) of the strategy can be incorporated into the
site and facility planning and design process, and by doing so, eliminating or reducing the
amount of stormwater runoff that may require treatment at the point where stormwater runoff
ultimately leaves the site. Elements i) and 2) may be referred to as "source controls" because
they emphasize reducing or eliminating pollutants in stormwater runoff at their source through
runoff reduction and by keeping pollutants and stormwater segregated. Section 4 provides
detailed descriptions of the BMPs related to elements i) and 2) of the strategy. Element 3) of
the strategy is referred to as "treatment control" because it utilizes treatment mechanisms to
remove pollutants that have entered stormwater runoff. Section 5 provides detailed
descriptions of BMPs related to element 3) of the strategy. Treatment controls integrated into
and throughout the site usually provide enhanced benefits over the same or similar controls
deployed only at the "end of the pipe" where runoff leaves the project site.
3.2 Integration of BMPs into Common Site
Features
Many common site features can achieve stormwater management goals by incorporating one or
more basic elements, either alone or in combination, depending on site and other conditions.
The basic elements include infiltration,
retention/detention, biofilters, and
structural controls. This section first
describes these basic elements, and then
describes how these elements can be
incorporated into common site features.
Infiltration
Infiltration is the process where water enters
the ground and moves downward through
the unsaturated soil zone. Infiltration is
ideal for management and conservation of
runoff because it filters pollutants through
the soil and restores natural flows to
groundwater and downstream water bodies.
See Figure 3-1. Figure 3-1
Infiltration Basin
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The infiltration approach to stormwater management seeks to "preserve and restore the
hydrologic cycle." An infiltration stormwater system seeks to infiltrate runoff into the soil by
allowing it to flow slowly over permeable surfaces. The slow flow of runoff allows pollutants to
settle into the soil where they are naturally mitigated. The reduced volume of runoff that
remains takes a long time to reach the outfall, and when it empties into a natural water body or
storm sewer, its pollutant load is greatly reduced.
Infiltration basins can be either open or closed. Open infiltration basins, include ponds, swales
and other landscape features, are usually vegetated to maintain the porosity of the soil structure
and to reduce erosion. Closed infiltration basins can be constructed under the land surface with
open graded crushed stone, leaving the surface to be used for parking or other uses. Subsurface
closed basins are generally more difficult to maintain and more expensive than open filtration
systems, and are used primarily where high land costs demand that the land surface be
reclaimed for economic use.
Infiltration systems are often designed to capture the "first flush" storm event and used in
combination with a detention basin to control peak hydraulic flows. They effectively remove
suspended solids, participates, bacteria, orgauics and soluble metals and nutrients through the
vehicle of filtration, absorption and mierobial decomposition. Groundwater contamination
should be considered as a potential adverse effect and should be considered where shallow
groundwater is a source of drinking water. In cases where groundwater sources are deep, there
is a very low chance of contamination from normal concentrations of typical urban runoff.
Retention and Detention
Retention and detention systems differ from infiltration systems primarily in intent. Detention
systems are designed to capture and retain runoff temporarily and release it to receiving waters
at predevelopraent flow rates. Permanent pools of water are not held between storm events.
Pollutants settle out and are removed from the water column through physical processes. See
Figure 3-2.
Retention systems capture runoff and retain it
between storms as shown in Figure 3-3.
Water held in the system is displaced by the
next significant rainfall event. Pollutants
settle out and are thereby removed from the
water column. Because the water remains in
the system for a period of time, retention * ' ,
systems benefit from biological and »'. -
biochemical removal mechanisms provided by , - *
aquatic plants and microorganisms. See
Figure 3-3.
Figure 3-2
Simple Detention System
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Retention/detention systems may release runoff
slowly enough to reduce downstream peak flows
"'"'" to their pre-development levels, allow fine
sediments to settle, and uptake dissolved
nutrients in the runoff where wetland vegetation
• -. is included.
,->•-' ^ f T"f Bioretention facilities have the added benefit of
~~.*£ „ t Ivi^s fj. v aesthetic appeal. Tliese systems can be placed in
\ ^ parking lot islands, landscaped areas surrounding
- / ( buildings, perimeter parking lots, and other open
*• '\ * space sections. Placing bioretentioii facilities on
\ land that city regulations require developers to
devote to open space efficiently uses the land. An
experienced landscape architect can choose plant
Figure 3-3 species and planting materials that are easy to
Retention System maintain, aesthetically pleasing, and capable of
effectively reducing pollutants in runoff from the
site.
Constructed wetland systems retain and release stonnwater in a manner that is similar to
retention or detention basins. The design mimics natural ecological functions and uses wetland
vegetation to filter pollutants. The system needs a permanent water source to function properly
and must be engineered to remove coarse sediment, especially construction related sediments,
from entering the pond. Stonnwater has the potential to negatively affect natural wetland
functions and constructed wetlands can be used to buffer sensitive resources.
Biofilters
Biofilters, also known as vegetated swales and '",', ^'','"'"" '"""*
filter strips, are vegetated slopes and channels
designed and maintained to transport shallow
depths of runoff slowly over vegetation.
Biofilters are effective if flows are slow and / , l %, > ' t f
* *»»*,«&*depths are shallow (3% slope max.). The slow |. .' ^ .* j l^S," *
movement of runoff through the vegetation ' T* ••**{ ;V J*/" ^
provides an opportunity'for sediments and ' **j
participates to be filtered and degraded through
biological activity7. In most soils, the biofilter
also provides an opportunity7 for stonnwater " ' "
infiltration, which further removes pollutants Figure 3-4
and reduces runoff volumes. See Figure 3-4. Vegetated Swale
Swales intercept both sheet and concentrated flows and convey these flows in a concentrated,
vegetation-lined channel. Grass filter strips intercept sheet runoff from the impervious network
of streets, parking lots, and rooftops and divert stonnwater to a uniformly graded meadow,
buffer zone, or small forest. Typically, the vegetated swale and grass strip-planting palette can
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Site and Facility Design for Water Quality Protection
comprise a wide range of possibilities from dense vegetation to turf grass. Grass strips and
vegetated swales can function as pretreatment systems for water entering bioretentiou systems
or other BMPs. If biofilters are to succeed in filtering pollutants from the water column, the
planting design must consider the hydrology, soils, and maintenance requirements of the site.
Appropriate plantings not only improve water quality, they provide habitat and aesthetic
benefits. Selected plant materials must be able to adapt to variable moisture regimes. Turf
grass is acceptable if it can be watered in the dry season, and if it is not inundated for long
periods. Species such as willows, dogwoods, sedge, rush, lilies, and bulrush tolerate varying
degrees of soil moisture and can provide an attractive plant palette year round.
Structural Controls
Structural controls in the context of this section include a range of measures that prevent
pollutants from coming into contact with storniwater. In this context, these measures may be
referred to as "structural source controls" meaning that they utilize structural features to
prevent pollutant sources and stormwater from coming into contact with one another, thus
reducing the opportunity for stormwater to become contaminated. Examples of structural
source controls include covers, impermeable surfaces, secondary containment facilities, runoff
diversion berms, and diversions to wastewater treatment plants.
3.2.1 Streets
More than any other single element, street design has a powerful impact on stormwater quality.
Street and other transportation-related structures typically can comprise between 60 and 70%
of the total impervious coverage in urban areas and, unlike rooftops, streets are almost always
directly connected to an underground stormwater system.
Recognizing that street design can be the greatest factor in development's impact on stormwater
quality, it is important that designers, municipalities and developers employ street standards
that reduce impervious land coverage. Directing runoff to biofilters or swales rather than
underground storm drains produces a street system that conveys stormwater efficiently while
providing both water quality and aesthetic benefits.
On streets where a more urban character is desired, or where a rigid pavement edge is required,
curb and gutter systems can be designed to empty into drainage swales. These swales can run
parallel to the street, in the parkway between the curb and the sidewalk, or can intersect the
street at cross-angles, and run between residences, depending on topography or site planning.
Runoff travels along the gutter, but instead of being emptied into a catch basin and underground
pipe, multiple openings in the curb direct runoff into surface swales or infiltration/detention
basins.
In recent years, new street standards have been gaining acceptance that meets the access
requirements of local residential streets while reducing impervious land coverage. These
standards create a new class of street that is narrower and more interconnected than the current
local street standard, called an "access" street. An access street is at the lowest end of the street
hierarchy and is intended only to provide access to a limited number of residences.
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Street design is usually mandated by local municipal standards. Officials must consider the
scale of the land use as they select stonnwater and water quality design solutions. Traffic
volume and speeds, bicycle lane design criteria; and residential and business densities influence
the willingness of decision makers to permit the narrow streets that include curbless design
alternatives.
Emergency sendee providers often raise objections to reduced street widths. Street designs
illustrated here meet national Fire Code standards for emergency access. An interconnected
grid system of narrow streets also allows emergency sendee providers with multiple access
routes to compensate for the unlikely possibility that a street may be blocked.
Many municipal street standards mandate 80 to 100% impervious land coverage in the public
right-of-way, and are a principal contributor to the environmental degradation caused by
development.
A street standard that allows an interconnected system of narrow access streets for residential
neighborhoods has the potential to achieve several complimentary environmental and social
benefits. A hierarchy of streets sized according to average daily traffic volumes yields a wide
variety of benefits: improved safety from lower speeds and volumes, improved aesthetics from
street trees and green parkways, reduced impervious land coverage, less heat island effect, and
lower development costs. If the reduction in street width is accompanied by a drainage system
that allows for infiltration of runoff, the impact of streets on stonnwater quality can be greatly
mitigated.
There are many examples of narrow streets, from both newly constructed and older
communities, which demonstrate the impact of street design on neighborhood character and
environmental quality. See Table 3-1.
Table 3-1 Adopted Narrow Street Standards (Typ. Cross-Sections, two-way
traffic)
City of Santa Rosa
CityofPalmdale
City of San Jose
City ofNovato
Counts,- of San Mateo
30 ft wide with parking permitted both sides, <iooo Average Daily
Traffic (ADT)
26 - 28 ft with parking permitted one side
20 ft - no parking permitted
20 ft neck downs at intersections
28 ft wide with parking permitted both sides
30 ft wide with parking permitted both sides, <2i Dwelling Units (DU)
34 ft wide with parking permitted both sides, <121 DU
24 ft wide with parking permitted both sides, 2-4 DU
28 ft with parking permitted both sides, 5-15 DU
19 ft wide rural pavement cross-section with parking permitted on adjacent gravel
shoulders
A comparison of street cross-sections is shown in Figure 3-5.
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Site and Facility Design for Water Quality Protection
I—': V-M |' i -I --r,- •-- I,-- '
t==±r n
v
T-^I|/T
'L -I « L I I L
t "i- f f C
f i jt it i ^ i
Figure 3-5
Comparison of Street Cross-Sections (two-way traffic, residential access streets)
3.2.2 Parking Lots
Iu any development, storage space for stationary vehicles can consume many acres of land area,
often greater than the area covered by streets or rooftops. In a neighborhood of single-family
homes, this parking area is generally located on private driveways or along the street. In higher
density residential developments, parking is often consolidated in parking lots.
The space for storage of the automobile, the standard parking stall, occupies only 160 ft2, but
when combined with aisles, driveways, curbs, overhang space, and median islands, a parking lot
can require up to 400 ft2 per vehicle, or nearly one acre per 100 cars. Since parking is usually
accommodated on an asphalt or concrete surface with conventional underground storm drain
systems, parking lots typically generate a great deal of DCIA.
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There are many ways to both reduce the impervious land coverage of parking areas and to filter
runoff before it reaches the storm drain system.
Hybrid Parking Lot
Hybrid lots work on the principle that
pavement use differs between aisles and
stalls. Aisles must be designed for
speeds between 10 and 20 mph, and
durable enough to support the
concentrated traffic of all vehicles using
the lot. The stalls, on the other hand,
need only be designed for the 2 or 3 mph
speed of vehicles maneuvering into
place. Most of the time the stalls are in
use, vehicles are stationary. Hybrid lots
reduce impervious surface coverage in
parking areas by differentiating the
paving between aisles and stalls, and
combining impervious aisles with
permeable stalls, as shown in Figure 3-6.
impervious aisle
Figure 3-6
Hybrid Parking Lot
If aisles are constructed of a more conventional, impermeable material suitable for heavier
vehicle use, such as asphalt, stalls can be constructed of permeable pavement. This can reduce
the overall impervious surface coverage of a typical double loaded parking lot by 60% and avoid
the need for an underground drainage system.
Permeable stalls can be constructed of a number of materials including pervious concrete, unit
pavers such as brick or stone spaced to expose a permeable joint and set on a permeable base,
crushed aggregate, porous asphalt, tuif block, and cobbles in low traffic areas. Turf blocks and
permeable joints are shown in Figures 3-7 and 3-8.
Figure 3-7
Turf Blocks
rises'
Figure 3-8
Permeable Joints
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Parking Grove
A variation on the permeable stall design, a grid of trees and bollards can be used to delineate
parking stalls and create a "parking grove." If the bollard and tree grids are spaced
approximately 19 ft apart, two vehicles can park between each row of the grid. This 9.5 ft stall
spacing is slightly more generous than the standard 8.5 to 9 ft stall, and allows for the added
width of the tree trucks and bollards. A benefit of this design is that the parking grove not only
shades parked cars, but also presents an attractive open space when cars are absent. Examples
of parking groves are shown in Figures 3-9 and 3-10.
Figure 3-9
Parking Grove
Figure 3-10
Parking Grove
Overflow Parking
Parking lot design is often required to
accommodatepeak demand, generating a high
proportion of impervious land coverage of
very limited usefulness. An alternative is to
differentiate between regular and peak
parking demands, and to construct the peak
parking stalls of a different, more permeable,
material. This "overflow parking" area can be
made of a turf block, which appears as a green
lawn when not occupied by vehicles, or
crushed stone or other materials. See Figure
3-11. The same concept can be applied to
areas with temporary parking needs, such as
emergency access routes, or in residential
applications, RV, or trailer parking.
Figure 3-11
Overflows Parking
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Porous Pavement Recharge Bed *In some cases, parking lots can be designed to '
perform more complex stormwater management ,
functions. Constructing a stone-filled reservoir below ,> \
the pavement surface and directing runoff ^ » . ••' ^ » ~
underground by means of perforated distribution ^ ^ ' ^ ,., *
pipes can achieve subsurface stormwater storage and *
infiltration as shown in Figure 3-12. Subsurface * ~* ^ ,. ?
infiltration basins eliminate the possibilities of mud, ^ ' *\~ * - \
mosquitoes and safety hazards sometimes perceived ^*"
to be associated with ephemeral surface drainage.
They also can provide for storage of large volumes of
runoff, and can be incorporated with roof runoff
collection systems. Figure 3-12
Porous Pavement Recharge Bed
3.2.3 Driveways
Driveways can comprise up to 40% of the total transportation network in a conventional
development, with streets, turn-arounds, and sidewalks comprising the remaining 60%.
Driveway length is generally determined by garage setback requirements, and width is usually
mandated by municipal codes and ordinances. If garages are setback from the street, long
driveways are required, unless a rear alley system is included to provide garage access. If
parking for two vehicles side by side is required, a 20 ft minimum width is required. Thus, if a
20 ft setback and a two-car-wide driveway are required, a minimum of 400 ft2 of driveway will
result, or 4% of a typical 10,000 ft2 residential lot. If the house itself is compact, and the
driveway is long, wide, and paved with an impervious material such as asphalt or concrete, it can
become the largest component of impervious land coverage on the lot.
Municipalities can reduce the area dedicated to driveways by allowing for tandem parking (one
vehicle in front of another on a narrow driveway). In addition, if shared driveways are
permitted, then two or more garages can be accessed by a single driveway, further reducing
required land area. Rear alley access to the garage can reduce driveway length, but overall
impervious surface coverage may not be reduced if the alleys are paved with impervious
materials and the access streets remain designed to conventional municipal standards.
.Alternative solutions that work to reduce the impact of water quality problems associated with
impervious land coverage on city streets also work on driveways. Sloping the driveway so that it
drains onto an adjacent turf or groundcover area prevents driveways from draining directly to
storm drain systems. This concept is shown in Figures 3-13 and 3-14. Use of turf-block or unit
pavers on sand creates attractive, low maintenance, permeable driveways that filter stormwater.
See Figure 3-1.5. Crushed aggregate can serve as a relatively smooth pavement with minimal
maintenance as shown in Figure 3-16. Paving only under wheels (Figure 3-17) is a viable,
inexpensive design if the driveway is straight between the garage and the street, and repaying
temporary parking areas with permeable unit pavers such as brick or stone can significantly
reduce the percentage of impervious area devoted to the driveway.
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•"'*
Figure 3-13
Traditional Design
Drains Flow Directly to Storm Drain
Figure 3-14
Alternative Solution
Slopes Flow to Groundcover
Figure 3-15
Unit Pavers
Figure 3-16
Crushed Aggregate
Figure 3-17
Paving Only Under Wheels
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3.2.4 Landscape and Open Space
In the natural landscape, most soils infiltrate a high percentage of rainwater through a complex
web of organic and biological activities that build soil porosity and permeability. Roots reach
into the soil and separate particles of clay, insects excavate voids in the soil mass, roots decay
leaving networks of macro pores, leaves fall and form a mulch over the soil surface, and
earthworms burrow and ingest organic detritus to create richer, more porous soil. These are
just a few examples of the natural processes that occur within the soil.
Maintenance of a healthy soil structure through the practice of retaining or restoring native soils
where possible and using soil amendments where appropriate can improve the land's ability to
filter and slowly release stormwater into drainage networks. Construction practices such as
decreasing soil compaction, storing topsoil on-site for use after construction, and chipping wood
for mulch as it is cleared for the land can improve soil quality and help maintain healthy
watersheds. Practices that reduce erosion and help retain water oil-site include incorporating
organic amendments into disturbed soils after construction, retaining native vegetation, and
covering soil during revegetation.
Subtle changes in grading can also improve infiltration. Landscape surfaces are conventionally
graded to have a slight convex slope. This causes water to ran off a central high point into a
surrounding drainage system, creating increased runoff. If a landscape surface is graded to have
a slightly concave slope, it will hold water. The infiltration value of concave vegetated surfaces is
greater in permeable soils. Soils of heavy clay or underlain with hardpaii provide less
**** infiltration value. In these cases, concave vegetated surfaces must be designed as
retention/detention basins, with proper outlets or under drains to an interconnected system.
Multiple Small Basins
Biofilters, infiltration, retention/detention basins are the basic elements of a landscape designed
for stormwater management. The challenge for designers is to integrate these elements
creatively and attractively in the landscape - either within a conventional landscape aesthetic or
by presenting a different landscape image that emphasizes the role of water and drainage.
Multiple small basins can provide a great deal of water storage and infiltration capacity. These
small basins can fit into the parkway planting strip or shoulders of street rights-of-way. If
connected by culverts under walks and driveways, they can create a continuous linear
infiltration system. Infiltration and retention/detention basins can be placed under wood decks,
in parking lot planter islands, and at roof downspouts. Outdoor patios or seating areas can be
sunken a few steps, paved with a permeable pavement such as flagstone or gravel, and designed
to hold a few inches of water collected from surrounding rooftops or paved areas for a few hours
after a rain.
All of these are examples of small basins that can store water for a brief period, allowing it to
infiltrate into the soil, slowing its release into the drainage network, and filtering pollutants. An
ordinary lawn can be designed to hold a few inches of water for a few hours after a storm,
attracting birds and creating a landscape of diversity. Grass/vegetated swales can be integrated
***•" with landscaping, providing an attractive, low maintenance, linear biofilter. Extended detention
(dry ponds) store water during storms, holding runoff to predevelopment levels. Pollutants
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settle and are removed from the water column before discharging to streams. Wet ponds serve a
similar purpose and can increase property values by providing a significant aesthetic, and
passive recreation opportunity.
Plant species selection is critical for proper functioning of infiltration areas. Proper selection of
plant materials can improve the infiltration potential of landscape areas. Deep-rooted plants
help to build soil porosity. Plant leaf-surface area helps to collect rainwater before it lands on
the soil, especially in light rains, increasing the overall water-holding potential of the landscape.
A large number of plant species will survive moist soils or periodic inundation. These plants
provide a wide range of choices for planted infiltration/detention basins and drainage swales.
Most inundated plants have a higher survival potential on well-drained alluvial soils than on fine
textured shallow soils or clays.
Maintenance Needs for Stormwnter Systems
All landscape treatments require maintenance. Landscapes designed to perform stormwater
management functions are not necessarily more maintenance intensive than highly manicured
conventional landscapes. A concave lawn requires the same mowing, fertilizing, and weeding as
a convex one and often less irrigation because more rain is filtered into the underlying soil.
Sometimes infiltration basins may require a different kind of maintenance than conventionally
practiced.
Typical maintenance activities include periodic inspection of surface drainage systems to ensure
clear flow lines, repair of eroded surfaces, adjustment or repair of drainage structures, soil
cultivation or aeration, care of plant materials, replacement of dead plants, replenishment of
mulch cover, irrigation, fertilizing, priming and mowing. In addition, dead or stressed
vegetation may indicate chemical dumping. Careful observation should be made of these areas
to determine if such a problem exists.
Landscape maintenance can have a significant impact on soil permeability and its ability to
support plant growth. Most plants concentrate the majority of their small absorbing roots in the
upper 6 in. of the soil surface if a mulch or forest litter protects the surface. If the soil is exposed
or bare, it can become so hot that surface roots will not grow in the upper 8 to 10 in. The
common practice of removing all leaf litter and detritus with leaf blowers creates a hard-crusted
soil surface of low permeability and high heat conduction. Proper mulching of the soil surface
improves water retention and infiltration, while protecting the surface root zone from
temperature extremes.
In addition to impacting permeability, landscape maintenance practices can have adverse effects
on water quality. Because commonly used fertilizers and herbicides are a source of organic
compounds, it is important to keep these practices to a minimum, and prevent overwatering.
When well maintained and designed, landscaped concave surfaces, infiltration basins, swales
and bioretention areas can add aesthetic value while providing the framework for
environmentally sound, comprehensive stormwater management systems.
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Street Trees
Trees improve water quality by intercepting and storing rainfall on leaves and branch surfaces,
thereby reducing runoff volumes and delaying the onset of peak flows. A single street tree can
have a total leaf surface area of several hundred to several thousand ft2, depending on species
and size. This aboveground surface area created by trees and other plants greatly contributes to
the water holding capacity of the land. They attenuate conveyance by increasing the soil's
capacity to filter rainwater and reduce overland flow rates. By diminishing the impact of
raindrops on uu-vegetated soil, trees reduce soil erosion. Street trees also have the ability to
reduce ambient temperature of stormwater runoff and absorb surface water pollutants.
When using street trees to achieve storniwater management goals, it is important to use tree
species with wide canopies. Street tree design criteria should specify species expected to attain
20 to 30 ft canopies at maturity. Planter strips with adequate width and depth of soil volume
are necessary to ensure tree vitality and reduce future maintenance. Structural soils also
provide rooting space for large trees and can be specified along narrow planter strips and
underneath sidewalks to enable continuous belowground soil and root connections.
3.2.5 Outdoor Work Areas
The site design and landscape details listed in previous sections are appropriate for uses where
low concentrations of pollutants can be mitigated through infiltration, retention, and detention.
Often iu commercial and industrial sites, there are outdoor work areas in which a higher
concentration of pollutants exists, and thus a higher potential of pollutants infiltrating the soil.
These work areas often involve automobiles, equipment machinery, or other commercial and
industrial uses, and require special consideration.
Outdoor work areas are usually isolated elements in a larger development. Infiltration and
detention strategies are still appropriate for and can be applied to other areas of the site, such as
parking lots, landscape areas, employee use areas, and bicycle path. It is only the outdoor work
area within the development - such as the loading dock, fueling area, or equipment wash area -
that requires a different drainage approach. This drainage approach is often precisely the
opposite from the infiltration/detention strategy - in other words, collect and convey.
In these outdoor work areas, infiltration is discouraged and runoff is often routed directly to the
sanitary sewer, not the storm drain. Because this runoff is being added to the loads normally
received by the water treatment plants (publicly owned treatment works - POTWs), it raises
several concerns that must be addressed in the planning and design stage. These include:
• Higher flows that could exceed the sewer system capacity
• Catastrophic spills that may cause harm to POTW operation
• A potential increase in pollutants
These concerns can be addressed at policy, management, and site planning levels.
January 2003 California Stormwater BMP Handbook 3-13
Errata 9-04 New Development and Redevelopment
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Section 3
Site and Facility Design for Water Quality Protection
Policy
Piping runoff and process water from outdoor work areas directly to the sanitaiy sewer for
treatment by a downstream POTW displaces the problem of reducing stormwater pollution.
Municipal stormwater programs and/or private developers can work with the local POTW to
develop solutions that minimize effects on the treatment facility. It should be noted that many
POTWs have traditionally prohibited the discharge of stormwater to their systems. However,
these prohibitions are being reviewed in light of the benefits possible from such diversions.
Management
Commercial and industrial sites that host special activities need to implement a pollution
prevention program minimizing hazardous material use and waste. For example, if restaurant
grease traps are directly connected to the sanitaiy sewer, proper management programs can
mitigate the amount of grease that escapes from the trap, clogging sewer systems and causing
overflows or damage to downstream systems.
Site Planning
Outdoor work areas can be designed in particular ways to reduce their impacts on both
stormwater quality and sewage treatment plants.
• Create an impermeable surface such as concrete or asphalt, or a prefabricated metal drip
pan, depending on the use.
• Cover the area with a roof. This prevents rain from falling on the work area and becoming
polluted runoff.
• Berm or mound around the perimeter of the area to prevent water from adjacent areas to
flow on to the surface of the work area.
• Directly connect runoff. Unlike other areas, runoff from these work areas is directly
connected to the sanitary sewer or other specialized containment systems. This allows the
more highly concentrated pollutants from these areas to receive special treatment that
removes particular constituents. Approval for this connection must be obtained from the
appropriate sanitaiy sewer agency.
• Locate the work area away from storm drains or catch basins. If the work area is adjacent to,
or directly upstream from a storm drain or landscape drainage feature (e.g., bioswales),
debris or liquids from the work area can migrate into the stonnwater system.
• Plan the work area to prevent run-on. This can be accomplished by raising the work area or
by diverting run-on around the work area.
These design elements are general considerations for work areas. In designing any outdoor
work area, evaluate local ordinances affecting the type of work area, as many local jurisdictions
have specific requirements.
Some activities are common to many commercial and industrial sites. These include garbage
and recycling, maintenance and storage, and loading. These activities can have a significant
3-14 California Stormwater BMP Handbook January 2003
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Section 3
Site and Facility Design for Water Quality Protection
negative impact on stormwater quality, and require
special attention to the siting and design of the activity
area. -' ~""">\, '
3.2.6 Maintenance and Storage , *
Areas ~~7\
To reduce the possibility of contact with stormwater
runoff, maintenance and storage areas can be sited
away from drainage paths and waterways, and covered. ^
Implementing a regular maintenance plan for ^ft <*' , •
sweeping, litter control, and spill cleanup also helps ( ** ,' T
prevent stormwater pollution. ,H „
Specifying impermeable surfaces for vehicle and \ . .• <
equipment maintenance areas will reduce the chance of ,, ,
pollutant infiltration. A concrete surface will usually
last much longer than an asphalt one, as vehicle fluids Figure 3-18
can either dissolve asphalt or be absorbed by the Material Storage
asphalt and released later. See Figure 3-18.
3.2.7 Vehicle and Equipment Washing Areas
It is generally advisable to cover areas used for regular washing of vehicles, trucks, or
equipment, surround them with a perimeter berm, and clearly mark them as a designated
washing area. Sumps or drain lines can be installed to collect wash water, which may be treated
for reuse or recycling, or for discharge to the sanitary sewer. The POTW may require some form
of pretreatment, such as a trap, for these areas.
Fueling and maintenance activities must be isolated from the vehicle washing facilities. These
activities have specific requirements, described later in this section.
Storage of bulk materials, fuels, oils, solvents, other chemicals, and process equipment should
be accommodated on an impervious surface covered with a roof. To reduce the chances of
corrosion, materials should not be stored directly on the ground, but supported by a wire mesh
or other flooring above the impervious pavement. In uncovered areas, drums or other
containers can be stored at a slight angle to prevent ponding of rainwater from rusting the lids.
Liquid containers should be stored in a designated impervious area that is roofed, fenced within
a berm, to prevent spills from flowing into the storm drain.
If hazardous materials are being used or stored, additional specific local, state, or federal
requirements may apply.
3.2.8 Loading Area
Loading areas and docks can be designed with a roof or overhang, and a surrounding curb or
berm. See Figure 3-19. The area should be graded to direct flow toward an inlet with a shut off
valve or dead-end sump. The sump must be designed with enough capacity to hold a spill while
the valve is closed. If the sump has a valve, it must be kept in the closed position and require an
January 2003 California Stormwater BMP Handbook 3-15
Errata 9-04 Mew Development and Redevelopment
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Section 3
Site and Facility Design for Water Quality Protection
action to open it. All sumps must have a sealed bottom so they cannot infiltrate water.
Contaminated accumulated waste and liquid must not be discharged to a storm drain and may
be discharged to the sanitary sewer only with the POTW's permission. If the waste is not
approved for discharge to the sanitary sewer, it must be conveyed to a hazardous waste (or other
offsite disposal) facility, and may require pretreatment. Some specific uses have unique
requirements.
3.2.9 Trash Storage Areas
Areas designated for trash storage can be covered to protect containers from rainfall. Where
covering the trash storage area is not feasible, the area can be protected from run on using
grading and berms, and connected to the sanitary sewer to prevent leaks from leaving the
designated trash storage area enclosure.
3.2.10 Wash Areas
Areas designated for washing of floor mats, containers, exhaust filters, and similar items can be
covered and enclosed to protect the area from rainfall and from overspray leaving the area.
These areas can also be connected to the sanitary sewer to prevent wash waters from leaving the
designated enclosures. A benefit of covering and enclosing these areas is that vectors may be
reduced and aesthetics of the area improved.
3.2.11 Fueling Areas
In all vehicle and equipment fueling areas, plans must be developed for cleaning near fuel
dispensers, emergency spill cleanup, and routine inspections to prevent leaks and ensure
properly functioning equipment.
If the fueling activities are minor, fueling can be performed in a designated, covered, and
bermed area that will not allow rim-on of stormwater or runoff of spills.
Retail gasoline outlets and vehicle fueling areas have specific design guidelines. These are
described in a Best Management Practice Guide for retail gasoline outlets developed by the
California Stormwater Quality Task Force, in cooperation with major gasoline corporations. The
practice guide addresses standards for existing, new, or substantially remodeled facilities. In
addition, some municipal stormwater permits require RGOs to provide appropriate runoff
treatment.
Fuel dispensing areas are defined as extending 6.5 ft from the corner of each fuel dispenser or
the length at which the hose and nozzle assembly may be operated plus i ft, whichever is less.
These areas must be paved with smooth impervious surfaces, such as Portland cement concrete,
with a 2-4% slope to prevent ponding, and must be covered. The cover must not drain onto the
work area. The rest of the site must separate the fuel dispensing area by a grade break that
prevents run-on of stormwater.
Within the gas station, the outdoor trash receptacle area (garbage and recycling), and the
air/water supply area must be paved and graded to prevent stormwater run-on. Trash
receptacles should be covered.
3-16 California Stormwater BMP Handbook January 2003
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Attachment 10
STORM WATER MANAGEMENT PLAN
GREEN DRAGON COLONIAL VILLAGE
ATTACHMENT 10: SOURCE CONTROL BMP FACT SHEETS
Please see attached.
Source Control BMPs
4.1 Introduction
This section describes specific source control Best Management Practices (BMPs) to be
considered for incorporation into newly developed public and private infrastructure, as well as
retrofit into existing facilities to meet stormwater management objectives.
4.2 BMP Fact Sheets
Source control fact sheets for design are listed in
Table 4-1. The fact sheets detail planning
methods and concepts that should be taken into
consideration by developers during project
design. The fact sheets are arranged in three
categories: those that have to do with landscape,
irrigation, and signage considerations; those that
have to do with use of particular materials, those
hat have to do with design of particular areas.
»w
4.3 Fact Sheet Format
A BMP fact sheet is a short document that
provides information about a particular BMP.
Typically each fact sheet contains the information
outlined in Figure 4-1. Supplemental information
is provided if it is available. The fact sheets also
contain side bar presentations with information
on BMP design objectives. Completed fact sheets
for each of the above activities are provided in
Section 4.4.
Table 4-1 Source Control BMPs for
Design
Design
SD-io
SD-li
SD-12
SD-J3
Site Design and Landscape Planning
Roof Runoff Controls
Efficient Irrigation
Storm Drain System Signs
Materials
SD-2O
SD-zi
Pervious Pavements
Alternative Building Materials
Areas
SD-30
SD-31
SD-32
SD-33
SD-34
SD-35
SD-36
Fueling Areas
Maintenance Bays and Docks
Trash Enclosures
Vehicle Washing Areas
Outdoor Material Storage Areas
Outdoor Work Areas
Outdoor Processing Areas
SDxx Example Fact Sheet
Description of the BMP
Approach
Suitable Applications
Design Considerations
• Designing New Installations
• Redeveloping Existing Installations
Supplemental Information
Examples
m Other Resources
4.4 BMP Fact Sheets
Source Control BMP Fact Sheets for design follow.
The BMP fact sheets are individually page numbered
and are suitable for photocopying and inclusion in
stormwater quality management plans. Fresh copies
of the fact sheets can be individually downloaded from
the California Stormwater BMP Handbook website at
www.cabmphandbooks.com.
Figure 4-1
Example Fact Sheet
Site Design & Landscape Planning SD-10
Design Objectives
0 Maximize Infiltration
0 Provide Retention
0 Slow Runoff
r* Minimize Impervious Land
Coverage
Prohibit Dumping of Improper
Materials
Contain Pollutants
Collect and Convey
Description
Each project site possesses unique topographic, hydrologic, and vegetative features, some of
which are more suitable for development than others. Integrating and incorporating
appropriate landscape planning methodologies into the project design is the most effective
action that can be done to minimize surface and groundwater contamination from stormwater.
Approach
Landscape planning should couple consideration of land suitability for urban uses with
consideration of community goals and projected growth. Project plan designs should conserve
natural areas to the extent possible, maximize natural water storage and infiltration
opportunities, and protect slopes and channels.
Suitable Applications
Appropriate applications include residential, commercial and industrial areas planned for
development or redevelopment.
Design Considerations
Design requirements for site design and landscapes planning
should conform to applicable standards and specifications of
agencies \vith jurisdiction and be consistent with applicable
General Plan and Local Area Plan policies.
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
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1 of 4
SD-10 Site Design & Landscape Planning
Designing Neiv Installations
Begin the development of a plan for the landscape unit with attention to the following general
principles:
• Formulate the plan on the basis of clearly articulated community goals. Carefully identify
conflicts and choices between retaining and protecting desired resources and community
growth.
• Map and assess land suitability for urban uses. Include the following landscape features in
the assessment: wooded land, open unwooded land, steep slopes, erosion-prone soils,
foundation suitability, soil suitability for waste disposal, aquifers, aquifer recharge areas,
wetlands, floodplains, surface waters, agricultural lands, and various categories of urban
land use. When appropriate, the assessment can highlight outstanding local or regional
resources that the community determines should be protected (e.g., a scenic area,
recreational area, threatened species habitat, farmland, fish run). Mapping and assessment
should recognize not only these resources but also additional areas needed for their
sustenance.
Project plan designs should conserve natural areas to the extent possible, maximize natural
water storage and infiltration opportunities, and protect slopes and channels.
Conserve Natural Areas during Landscape Planning
If applicable, the following items are required and must be implemented in the site layout
during the subdivision design and approval process, consistent with applicable General Plan and
Local Area Plan policies:
• Cluster development on least-sensitive portions of a site while leaving the remaining land in
a natural undisturbed condition.
• Omit clearing and grading of native vegetation at a site to the minimum amount needed to
build lots, allow access, and provide fire protection.
» Maximize trees and other vegetation at each site by planting additional vegetation, clustering
tree areas, and promoting the use of native and/or drought tolerant plants.
» Promote natural vegetation by using parking lot islands and other landscaped areas.
• Preserve riparian areas and wetlands.
Maximize Natural Water Storage and Infiltration Opportunities Within the Landscape Unit
» Promote the conservation of forest cover. Building on laud that is already deforested affects
basin hydrology to a lesser extent than converting forested land. Loss of forest cover reduces
interception storage, detention in the organic forest floor layer, and water losses by
evapotranspiratioii, resulting in large peak runoff increases and either their negative effects
or the expense of countering them with structural solutions.
» Maintain natural storage reservoirs and drainage corridors, including depressions, areas of
permeable soils, swales, and intermittent streams. Develop and implement policies and
2 of 4 California Stormwater BMP Handbook January 2003
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Site Design & Landscape Planning SD-10
•^.t,.-
regulations to discourage the clearing, filling, and channelization of these features. Utilize
them in drainage networks in preference to pipes, culverts, and engineered ditches.
• Evaluating infiltration opportunities by referring to the stormwater management manual for
the jurisdiction and pay particular attention to the selection criteria for avoiding
groundwater contamination, poor soils, and hydrogeological conditions that cause these
facilities to fail. If necessary, locate developments with large amounts of impervious
surfaces or a potential to produce relatively contaminated runoff away from groundwater
recharge areas.
Protection of Slopes and Channels during Landscape Design
m Convey runoff safely from the tops of slopes.
• Avoid disturbing steep or unstable slopes.
• Avoid disturbing natural channels.
• Stabilize disturbed slopes as quickly as possible.
• Vegetate slopes with native or drought tolerant vegetation.
• Control and treat flows in landscaping and/or other controls prior to reaching existing
natural drainage systems.
• Stabilize temporary and permanent channel crossings as quickly as possible, and ensure that
increases in run-off velocity and frequency caused by the project do not erode the channel.
• Install energy dissipaters, such as riprap, at the outlets of new storm drains, culverts,
conduits, or channels that enter unlined channels in accordance with applicable
specifications to minimize erosion. Energy dissipaters shall be installed in such a way as to
minimize impacts to receiving waters.
• Line on-site conveyance channels where appropriate, to reduce erosion caused by increased
flow velocity due to increases in tributary impervious area. The first choice for linings
should be grass or some other vegetative surface, since these materials not only reduce
runoff velocities, but also provide water quality benefits from filtration and infiltration. If
velocities in the channel are high enough to erode grass or other vegetative linings, riprap,
concrete, soil cement, or geo-grid stabilization are other alternatives.
• Consider other design principles that are comparable and equally effective.
Redeveloping Existing Installations
Various jurisdictional stormwater management and mitigation plans (SUSMP, WQMP, etc.)
define "redevelopment" in terms of amounts of additional impervious area, increases in gross
floor area and/or exterior construction, and land disturbing activities with structural or
impervious surfaces. The definition of * redevelopment" must be consulted to determine
whether or not the requirements for new development apply to areas intended for
redevelopment. If the definition applies, the steps outlined under "designing new installations'*
above should be followed.
January 2003 California Stormwater BMP Handbook 3 of 4
New Development and Redevelopment
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SD-10 Site Design & Landscape Planning
Redevelopment may present significant opportunity to add features which had not previously
been implemented. Examples include incorporation of depressions, areas of permeable soils,
and swales in newly redeveloped areas. While some site constraints may exist due to the status
of already existing infrastructure, opportunities should not be missed to maximize infiltration,
slow runoff, reduce impervious areas, disconnect directly connected impervious areas.
Other Resources
A Manual for the Standard Urban Stormwater Mitigation Plan (SUSMP), Los Angeles County
Department of Public Works, May 2002.
Stormwater Management Manual for Western Washington, Washington State Department of
Ecology, August 2001.
Model Standard Urban Storm Water Mitigation Plan (SUSMP) for San Diego County, Port of
San Diego f and Cities in San Diego County, February 14, 2002.
Model Water Quality Management Plan (WQMP) for County of Orange, Orange County Flood
Control District, and the Incorporated Cities of Orange County, Draft February 2003.
Ventura Countywide Technical Guidance Manual for Stormwater Quality Control Measures,
July 2002.
4 of 4 California Stormwater BMP Handbook January 2003
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Efficient Irrigation SD-12
Design Objectives
J Maximize Infiltration
J Provide Retention
/ Slow Runoff
Minimize Impervious Land
Coverage
Prohibit Dumping of Improper
Materials
Contain Pollutants
Collect and Convey
Description "™~"———
Irrigation water provided to landscaped areas may result in excess irrigation water being
conveyed into stormwater drainage systems.
Approach
Project plan designs for development and redevelopment should include application methods of
irrigation water that minimize runoff of excess irrigation water into the stormwater conveyance
system.
Suitable Applications
Appropriate applications include residential, commercial and industrial areas planned for
development or redevelopment. (Detached residential single-family homes are typically
excluded from this requirement.)
Design Considerations
Designing New Installations
The following methods to reduce excessive irrigation runoff should be considered, and
incorporated and implemented where determined applicable and feasible by the Permittee:
• Employ rain-triggered shutoff devices to prevent irrigation after precipitation.
• Design irrigation systems to each landscape area's specific water requirements.
• Include design featuring flow reducers or shutoff valves triggered by a pressure drop to
control water loss in the event of broken sprinkler heads or lines.
• Implement landscape plans consistent with County or City water conservation resolutions,
which may include provision of water sensors, programmable
irrigation times (for short cycles), etc. -f " C f\ OL
California
Stormwater
Quality
Association
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
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Iof2
SD-12 Efficient Irrigation
• Design timing and application methods of irrigation water to minimize the runoff of excess
irrigation water into the storm water drainage system.
• Group plants with similar water requirements in order to reduce excess irrigation runoff and
promote surface filtration. Choose plants with low irrigation requirements (for example,
native or drought tolerant species). Consider design features such as:
Using mulches (such as wood chips or bar) in planter areas without ground cover to
minimize sediment in runoff
Installing appropriate plant materials for the location, in accordance with amount of
sunlight and climate, and use native plant materials where possible and/or as
recommended by the landscape architect
Leaving a vegetative barrier along the property boundary and interior watercourses, to
act as a pollutant filter, where appropriate and feasible
Choosing plants that minimize or eliminate the use of fertilizer or pesticides to sustain
growth
• Employ other comparable, equally effective methods to reduce irrigation water runoff.
Redeveloping Existing Installations
Various jurisdictional stormwater management and mitigation plans (SUSMP, WQMP, etc.)
define "redevelopment" in terms of amounts of additional impervious area, increases in gross
floor area and/or exterior construction, and land disturbing activities with structural or
impervious surfaces. The definition of " redevelopment" must be consulted to determine
whether or not the requirements for new development apply to areas intended for
redevelopment. If the definition applies, the steps outlined under "designing new installations"
above should be followed.
Other Resources
A Manual for the Standard Urban Stormwater Mitigation Plan (SUSMP), Los Angeles County
Department of Public Works, May 2002.
Model Standard Urban Storm Water Mitigation Plan (SUSMP) for San Diego County, Port of
San Diego, and Cities in San Diego County, February 14, 2002.
Model Water Quality Management Plan (WQMP) for County of Orange, Orange County Flood
Control District, and the Incorporated Cities of Orange County, Draft February 2003.
Ventura Countywide Technical Guidance Manual for Stormwater Quality Control Measures,
July 2002.
2 of 2 California Stormwater BMP Handbook January 2003
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Storm Drain Signage SD-13
Design Objectives
Maximize Infiltration
Provide Retention
Slow Runoff
Minimize Impervious Land
Coverage
e Prohibit Dumping of Improper
Materials
Contain Pollutants
Collect and Convey
Description
Waste materials dumped into storm drain inlets can have severe impacts on receiving and
ground waters. Posting notices regarding discharge prohibitions at storm drain inlets can
prevent waste dumping. Storm drain signs and stencils are highly visible source controls that
are typically placed directly adjacent to storm drain inlets.
Approach
The stencil or affixed sign contains a brief statement that prohibits dumping of improper
materials into the urban runoff conveyance system. Storm drain messages have become a
popular method of alerting the public about the effects of and the prohibitions against waste
disposal.
Suitable Applications
Stencils and signs alert the public to the destination of pollutants discharged to the storm drain.
Signs are appropriate in residential, commercial, and industrial areas, as well as any other area
where contributions or dumping to storm drains is likely.
Design Considerations
Storm drain message markers or placards are recommended at all storm drain inlets within the
boundary of a development project. The marker should be placed in clear sight facing toward
anyone approaching the inlet from either side. All storm drain inlet locations should be
identified on the development site map.
Designing New Installations
The following methods should be considered for inclusion in the project design and show on
project plans:
Provide stenciling or labeling of all storm drain inlets and catch
basins, constructed or modified, within the project area with
prohibitive language. Examples include "NO DUMPING -
SJ5LA
California
Stormwater
Quality
Association
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
www.cabmphandbooks.com
lof 2
SD-13 Storm Drain Signage
DRAINS TO OCEAN" and/or other graphical icons to discourage illegal dumping.
• Post signs with prohibitive language and/or graphical icons, which prohibit illegal dumping
at public access points along channels and creeks within the project area.
Note - Some local agencies have approved specific signage and/or storm drain message placards
for use. Consult local agency stormwater staff to determine specific requirements for placard
types and methods of application.
Redeveloping Existing Installations
Various jurisdictional stormwater management and mitigation plans (SUSMP, WQMP, etc.)
define "redevelopment" in terms of amounts of additional impervious area, increases in gross
floor area and/or exterior construction, and land disturbing activities with structural or
impervious surfaces. If the project meets the definition of "redevelopment", then the
requirements stated under " designing new installations" above should be included in all project
design plans.
Additional Information
Maintenance Considerations
m Legibility of markers and signs should be maintained. If required by the agency with
jurisdiction over the project, the owner/operator or homeowner's association should enter
into a maintenance agreement with the agency or record a deed restriction upon the
property title to maintain the legibility of placards or signs.
Placement
• Signage on top of curbs tends to weather and fade.
• Signage on face of curbs tends to be worn by contact with vehicle tires and sweeper brooms.
Supplemental Information
Examples
m Most MS4 programs have storm drain signage programs. Some MS4 programs will provide
stencils, or arrange for volunteers to stencil storm drains as part of their outreach program.
Other Resources
A Manual for the Standard Urban Stormwater Mitigation Plan (SUSMP), Los Angeles County
Department of Public Works, May 2002.
Model Standard Urban Storm Water Mitigation Plan (SUSMP) for San Diego County, Port of
San Diego, and Cities in San Diego County, February 14, 2002.
Model Water Quality Management Plan (WQMP) for County of Orange, Orange County Flood
Control District, and the Incorporated Cities of Orange County, Draft February 2003.
Ventura Countywide Technical Guidance Manual for Stormwater Quality Control Measures,
July 2002.
2 of 2 California Stormwater BMP Handbook January 2003
New Development and Redevelopment
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Trash Storage Areas SD-32
. . Design ObjectivesDescription ,.»»«™™_™=^^^™^^«___,«!«™,
Trash storage areas are areas where a trash receptacle (s) are Maximize Infiltration
located for use as a repository for solid wastes. Stormwater Provide Retention
runoff from areas where trash is stored or disposed of can be qi R ff
polluted. In addition, loose trash and debris can be easily
transported by water or wind into nearby storm drain inlets, Minimize Impervious Land
channels, and/or creeks. Waste handling operations that may be Coverage
sources of stormwater pollution include dumpsters, litter control, Prohibit Dumping of Improper
and waste piles. Materials
J Contain Pollutants
Appr°ach Collect and ConveyThis fact sheet contains details on the specific measures required
to prevent or reduce pollutants in stormwater runoff associated
with trash storage and handling. Preventative measures
including enclosures, containment structures, and impervious
pavements to mitigate spills, should be used to reduce the
likelihood of contamination. ---—_--——»~--—~_.
Suitable Applications
Appropriate applications include residential, commercial and industrial areas planned for
development or redevelopment. (Detached residential single-family homes are typically
excluded from this requirement.)
Design Considerations
Design requirements for waste handling areas are governed by Building and Fire Codes, and by
current local agency ordinances and zoning requirements. The design criteria described in this
fact sheet are meant to enhance and be consistent with these code and ordinance requirements.
Hazardous waste should be handled in accordance with legal requirements established in Title
22, California Code of Regulation.
Wastes from commercial and industrial sites are typically hauled by either public or commercial
carriers that may have design or access requirements for waste storage areas. The design
criteria in this fact sheet are recommendations and are not intended to be in conflict with
requirements established by the waste hauler. The waste hauler should be contacted prior to the
design of your site trash collection areas. Conflicts or issues should be discussed with the local
agency.
Designing New Installations
Trash storage areas should be designed to consider the following structural or treatment control
BMPs:
• Design trash container areas so that drainage from adjoining roofs and pavement is diverted
around the area(s) to avoid run-on. This might include berming
or grading the waste handling area to prevent run-on of
stormwater. ^ 5 Q./|
• Make sure trash container areas are screened or walled to .' stormwater
prevent off-site transport of trash. \ Quality
. Association
January 2003 California Stormwater BMP Handbook 1 of 2
New Development and Redevelopment
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SD-32 Trash Storage Areas
• Use lined bins or dumpsters to reduce leaking of liquid waste.
• Provide roofs, awnings, or attached lids on all trash containers to minimize direct
precipitation and prevent rainfall from entering containers.
• Pave trash storage areas with an impervious surface to mitigate spills.
• Do not locate storm drains in immediate vicinity of the trash storage area.
• Post signs on all dumpsters informing users that hazardous materials are not to be disposed
of therein.
Redeveloping Existing Installations
Various jurisdictional stormwater management and mitigation plans (SUSMP, WQMP, etc.)
define "redevelopment" in terms of amounts of additional impervious area, increases in gross
floor area and/or exterior construction, and land disturbing activities with structural or
impervious surfaces. The definition of " redevelopment" must be consulted to determine
whether or not the requirements for new development apply to areas intended for
redevelopment. If the definition applies, the steps outlined under "designing new installations"
above should be followed.
Additional Information
Maintenance Considerations
The integrity of structural elements that are subject to damage (i.e., screens, covers, and signs)
must be maintained by the owner/operator. Maintenance agreements between the local agency
and the owner/operator may be required. Some agencies will require maintenance deed
restrictions to be recorded of the property title. If required by the local agency, maintenance
agreements or deed restrictions must be executed by the owner/operator before improvement
plans are approved.
Other Resources
A Manual for the Standard Urban Stormwater Mitigation Plan (SUSMP), Los Angeles County
Department of Public Works, May 2002.
Model Standard Urban Storm Water Mitigation Plan (SUSMP) for San Diego County, Port of
San Diego, and Cities in San Diego County, February 14, 2002.
Model Water Quality Management Plan (WQMP) for County of Orange, Orange County Flood
Control District, and the Incorporated Cities of Orange County, Draft February 2003.
Ventura Countywide Technical Guidance Manual for Stormwater Quality Control Measures,
July 2002.
2 of 2 California Stormwater BMP Handbook January 2003
New Development and Redevelopment
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Attachment 11
STORM WATER MANAGEMENT PLAN
GREEN DRAGON COLONIAL VILLAGE
ATTACHMENT 11: TREATMENT CONTROL BMP FACT SHEETS
Please see attached.
Section 5
Treatment Control BMPs
5.1 Introduction
This section describes treatment control Best Management Practices (BMPs) to be considered
for incorporation into newly developed public and private infrastructure, as well as retrofit into
existing facilities to meet stormwater management objectives. BMP fact sheets are divided into
two groups: public domain BMPs and manufactured (proprietary) BMPs. In some cases, the
same BMP may exist in each group, for example, media filtration. However, treatment BMPs
are typically very different between the two groups.
Brand names of manufactured BMPs are not stated. Descriptions of manufactured BMPs in this
document should not be inferred as endorsement by the authors.
5.2 Treatment Control BMPs
Public domain and manufactured BMP controls are listed in Table 5-1.
Table 5-1 Treatment Control BMPs
Public Domain
Infiltration
TC-io Infiltration Trench
TC-ii Infiltration Basin
TC-12 Retention/Irrigation
Detention and Settling
TC-20 Wet Pond
TC-21 Constructed Wetland
TC-22 Extended Detention Basin
Biofiltration
TC-30 Vegetated Swale
TC-31 Vegetated Buffer Strip
TC-32 Bioretention
Filtration
TC-40 Media Filter
Flow Through Separation
TC-so Water Quality Inlet
Other
TC-6o Multiple Systems
Manufactured (Proprietary)
Infiltration
Detention and Settling
MP-2Q Wetland
Biofiltration
Filtration
MP-40 Media Filter
Flow Through Separation
MP-50 Wet Vault
MP-5I Vortex Separator
MP-52 Drain Inserts
Other
January 2003
Errata 9-04
California Stormwater BMP Handbook
New Development and Redevelopment
www.cabmphandbooks.com
5-1
Section 5
Treatment Control BMPs
5.3 Fact Sheet Format
A BMP fact sheet is a short document that gives
all the information about a particular BMP.
Typically, each public domain and
manufactured BMP fact sheet contains the
information outlined in Figure 5-1. The fact
sheets also contain side bar presentations with
information on BMP design considerations,
targeted constituents, and removal
effectiveness (if known).
Treatment BMP performance, design criteria,
and other selection factors are discussed in 5.4
- 5.6 below. BMP Fact sheets are included in 5.7.
TCxx/MPxx Example Fact Sheet
Description
California Experience
Advantages
Limitations
Design and Sizing Guidelines
Performance
Siting Criteria
Design Guidelines
Maintenance
Cost
Rgferepces and Sources of Additional Information
Figure 5-1
Example Fact Sheet
5.4 Comparing Performance of Treatment BMPs
With a myriad of storrawater treatment BMPs from which to choose, a question commonly
asked is "which one is best". Particularly when considering a manufactured treatment system,
the engineer wants to know if it provides performance that is reasonably comparable to the
typical public-domain BMPs like wet ponds or grass swales. With so many BMPs, it is not likely
that they perform equally for all pollutants. Thus, the question that each local jurisdiction faces
is which treatment BMPs will it allow, and under what circumstances. What level of treatment
is desired or reasonable, given the cost? Which BMPs are the most cost-effective? Current
municipal stonnwater permits specify the volume or rate of stormwater that must be treated,
but not the specific level or efficiency of treatment: These permits usually require performance
to the specific maximum extent practicable (MEP), but this does not translate to an easy to apply
specific design criteria.
Methodology for comparing BMP performance may need to be expanded to include more than
removal effectiveness. Many studies have been conducted on the performance of stormwater
treatment BMPs. Several publications have provided summaries of performance (ASCE, 1998;
ASCE, 2001; Brown and Schueler, 1997; Shoemaker et al., 2000; Winter, 2001). These
summaries indicate a wide variation in the performance of each type of BMP, making
effectiveness comparisons between BMPs problematic.
5.4.1 Variation in Performance
There are several reasons for the observed variation.
The Variability of Stormwater Quality
Stormwater quality is highly variable during a storm, from storm to storm at a site, and between
sites even of the same land use. For pollutants of interest, maximum observed concentrations
commonly exceed the average concentration by a factor of 100. The average concentration of a
storm, known as the event mean concentration (EMC) commonly varies at a site by a factor of 5.
One aspect of stormwater quality that is highly variable is the particle size distribution (PSD) of
o
o
5-2 California Stormwater BMP Handbook
New Development and Redevelopment
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January 2003
Errata 9-04
Section 5
Treatment Control BMPs
the suspended sediments. This results in variation in the settle ability of these sediments and
the pollutants that are attached. For example, several performance studies of manufactured
BMPs have been conducted in the upper Midwest and Northeast where deicing sand is
commonly used. Hie sand, washed off during spring and summer storms, skews the PSD to
larger sizes not commonly found in stormwater from California sites except in mountainous
areas. Consequently, a lower level efficiency may be observed if the same treatment system is
used in California.
Most Field Studies Monitor Too Few Storms
High variability of stormwater quality requires that a large number of storms be sampled to
discern if there is a significant difference in performance among BMPs. Hie smaller the actual
difference in performance between BMPs, the greater the number of storms that must be
sampled to statistically discern the difference between them. For example, a researcher
attempting to determine a difference in performance between two BMPs of 10% must monitor
many more storms than if the interest is to define the difference within 50%. Given the expense
and difficulty, few studies have monitored enough storms to determine the actual performance
with a high level of precision.
Different Design Criteria
Performance of different systems within the same group (e.g., wet ponds) differs significantly in
part because of differing design criteria for each system. This in turn can make it problematic to
compare different groups of treatment BMPs to each other (e.g., wet ponds to vortex
separators).
Differing Influent Concentrations and Analytical Variability
With most treatment BMPs, efficiency decreases with decreasing influent concentration. This is
illustrated in Figure 5-2. Tims, a low removal efficiency may be observed during a study not
because the device is inherently a poorer performer, but possibly because the influent
concentrations for the site were unusually low. In addition, as the concentration of a particular
constituent such as TSS approaches its analytical detection limit, the effect of the variability of
the laboratory technique becomes more significant. This factor also accounts for the wide
variability of observations on the left of Figure 5-2.
The variability of the laboratory results as the TSS approaches its analytical detection limit may
also account for negative efficiencies at very low influent concentrations (e.g., TSS less than 10
nig/L). However, some negative efficiencies observed at higher concentrations may not
necessarily be an artifact of laboratory analysis. The cause varies to some extent with the type of
treatment BMP. Negative efficiencies may be due to the re-suspension of previously deposited
pollutants, a change in pH that dissolves precipitated or sorbed pollutants, discharge of algae in
the case of BMPs with open wet pools, erosion of unprotected basin side or bottom, and the
degradation of leaves that entered the system the previous fall.
January 2003 California Stormwater BMP Handbook 5-3
Errata 9-04 New Development and Redevelopment
www.cabmphandbooks.com
Section 5
Treatment Control BMPs
Different Methods of
Calculating Efficiency
Researchers (i) have used
different methods to
calculate efficiency, (2) do
not always indicate which
method they have used, and
(3) often do not provide
sufficient information in
their report to allow others
to recalculate the efficiency
using a common method.
One approach to quantifying
BMP efficiency is to
determine first if the BMP is
providing treatment (that
the influent and effluent
mean event mean concentrations are statistically different from one another) and then examine
either a cumulative distribution function of influent and effluent quality or a standard parallel
probability plot. This approach is called the Effluent Probability Method. While this approach
has been used in the past by EPA and ASCE, some researchers have experienced problems with
the general applicability of this method. A discussion of these issues is included in Appendix B.
100% -|
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Figure 5-2
Removal Efficiency Versus Influent Concentration
A second approach to comparing
performance among BMPs is to compare
effluent concentrations, using a box-whisker
plot, the basic form of which is illustrated in
Figure 5-3. The plot represents all of the
data points, of one study, several studies, or
of individual storms. The plots provide
insight into the variability of performance
within each BMP type, and possible
differences in performance among the types.
To explain the plot: 50% of the data points as
well as the median value of all the data
points is represented by the box. That is, the
median falls within the 75th and 2§th
perceiitile of data (top and bottom of the
box). The whisker extends to the highest
point within a range of 1.5 times the
difference between the first and third
quartiles. Individual points beyond this
range are shown as asterisks.
Whisker extends to
the highest value
of data points
Third Quartile --
First Quartile -
Median
Whisker extends to
the lowest value
of data points
A line is drawn across the box at the median, The bo/ton of the
box is at the 25th percentile and the top is at the 75th psrcsntiie. I,
The whiskers are the lines that extend from thatop and feoftom I-
of the box. ;
Figure 5-3
Box-Whisker Plot
O
5-4 California Stormwater BMP Handbook
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January 2003Errata 9-04
Section 5
Treatment Control BMPs
Recognizing the possible effect of influent concentration on efficiency, an alternative is to
compare effluent concentrations. The reasoning is that regardless of the influent concentration,
a particular BMP will generate a narrower range of effluent concentrations. Figure 5-4 shows
observed effluent concentrations for several different types of BMPs. These data were generated
in an extensive field program conducted by the California Department of Transportation
(Caltrans). As this program is the most extensive effort to date in the entire United States, the
observations about performance in this Handbook rely heavily on these data. The Caltrans
study is unique in that many of the BMPs were tested under reasonably similar conditions
(climate, storms, freeway stormwater quality), with each type of BMP sized with the same design
criteria.
An additional factor to consider when comparing BMPs is the effect of infiltration. BMPs with
concrete or metal structures will have no infiltration, whereas the infiltration in earthen BMPs
will vary from none to substantial. For example, in the Caltrans study, infiltration in vegetated
swales averaged nearly 50%. This point is illustrated with Figure 5-4 where effluent quality of
several BMPs is compared. As seen in Figure 5-4, effluent concentration for grass swales is
higher than, either filters or wet basins (30 vs. 10 to 15 mg/L), suggesting that swales in
comparison are not particularly effective. However, surface water entering swales may infiltrate
into the ground, resulting in a loading reduction (flow times concentration) that is similar to
those BMPs with minimal or no infiltration.
200 T —
TC-22
Extended
Detention
Basin
TC-30
Vegetated
Swale
TC-31
Vegetated
Buffer
TC-40 Media
F liter {Austin
Sand Filter)
TC-40 Media
Fitter
(Delaware
Lineal Sand
Filter)
TC-40 Media
filter (Multi-
chamber
Treatment
Train)
Figure 5-4
Observed Effluent Concentrations for Several Different Public Domain BMPs
January 2003
Errata 9-04
California Stormwater BMP Handbook
New Development and Redevelopment
www .cabmpha ndbooks. com
5-5
Section 5
Treatment Control BMPs
With equation shown below, it is possible using the data from Figure 5-4 to estimate different
levels of loading reduction as a function of the fraction of stormwater that is infiltrated.
EEC = (i-I)(EC) + (I)(GC)
Where:
EEC = the effective effluent concentration
I = fraction of stormwater discharged by infiltration
EC = the median concentration observed in the effluent
GC = expected concentration of stormwater when it reaches the groundwater
To illustrate the use of the equation above, the effect of infiltration is considered on the effective
effluent concentration of TSS from swales. From Figure 5-4, the median effluent concentration
for swales is about 30 mg/L. Infiltration of 50% is assumed with an expected concentration of 5
mg/L when the stormwater reaches the groundwater. This gives:
EEC = (1-0.5X30) + (0.5X5) = 17-5 mg/L.
The above value can be compared to other BMPs that may directly produce a lower effluent
concentration, but do not exhibit infiltration, such as concrete wet vaults.
5.4.2 Other Issues Related to Performance Comparisons
A further consideration related to performance comparisons is whether or not the treatment
BMP removes dissolved pollutants. Receiving water standards for most metals are based on the
dissolved fraction; the form of nitrogen or phosphorus of most concent as a nutrient is the
dissolved fraction.
The common practice of comparing the performance of BMPs using TSS may not be considered
sufficient by local governments and regulatory agencies, as there is not always a strong,
consistent relationship between TSS and the pollutants of interest, particularly those identified
in the 3O3d list for specific water bodies in California. These pollutants frequently include
metals, nitrogen, nutrients (but often nutrients without specifying nitrogen or phosphorus),
indicator bacteria (i.e., fecal coliform), pesticides, and trash. Less commonly cited pollutants
include sediment, PAHs, PCBs, and dioxin. With respect to metals, typically, only the general
term is used. In some cases, a specific metal is identified. The most commonly listed metals are
mercury, copper, lead, selenium, zinc, and nickel. Less frequently listed metals are cadmium,
arsenic, silver, chromium, molybdenum, and thallium. Commonly, only the general term
"metals" is indicated for a water body without reference to a particular metal.
It is desirable to know how each of the treatment BMPs performs with respect to the removal of
the above pollutants. Unfortunately, the performance data are non-existent or very limited for
many of the cited pollutants, particularly trash, PAHs, PCBs, dioxin, mercury, selenium, and
pesticides. Furthermore, the concentrations of these constituents are very low, often below the
5-6 California Stormwater BMP Handbook January 2003
New Development and Redevelopment Errata 9-04
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Section 5
Treatment Control BMPs
detection limit. This prevents the determination of which BMPs are most effective. However,
with the exception of trash and possibly dioxin, these pollutants readily sorb to sediments in
stormwater, and therefore absent data at this time can be considered to be removed in
proportion to the removal of TSS (i.e., sediment.) Therefore, in general, those treatment
systems that are most effective at removing TSS will be most effective at removing pollutants
noted above.
While there is little data on the removal of trash, those treatment BMPs that include a basin
such as a wet pond or vault, or extended detention basin should be similarly effective at
removing trash as long as the design incorporates a means of retaining the floating trash in the
BMP. Whether or not manufactured products that are configured as a basin (e.g., round vaults
or vortex separators) are as effective as public domain BMPs is unknown. However, their ability
to retain floating debris may be limited by the fact that many of these products are relatively
small and therefore may have limited storage capacity. Only one manufactured BMP is
specifically designed to remove floating debris.
There are considerable amounts of performance data for zinc, copper, and lead, with a less
substantial database for nickel, cadmium, and chromium. An exception is high-use freeways
where metals in general are at higher concentrations than residential and commercial
properties. Lead sorbs easily to the sediments in stormwater, with typically only 10% in the
dissolved phase. Hence, its removal is generally in direct proportion to the removal of TSS. In
contrast, zinc, copper, and cadmium are highly soluble with 50% or more in the dissolved phase.
Hence, two treatment BMPs may remove TSS at the same level, but if one is capable of removing
dissolved metals, it provides better treatment overall for the more soluble metals.
5.4.3 Comparisons of Treatment BMPs for Nitrogen, Zinc,
Bacteria, and TSS
Presented in Figures 5-5 through 5-8 are comparisons of the effluent concentrations produced
by several types of treatment BMPs for nitrogen, zinc, and fecal coliform, respectively (TSS is
represented in Figure 5-4). Graphs for other metals are provided in Appendix C. These data are
from the Caltrans study previously cited. Total and the dissolved effluent concentrations are
shown for zinc. (Note that while box-whisker plots are used here to compare BMPs, other
methodologies, such as effluent cumulative probability distribution plots, are used by others.)
January 2003 California Stormwater BMP Handbook 5-7
Errata 9-04 New Development and Redevelopment
www.cabmphandbooks.com
Section 5
Treatment Control BMPs
TC 20 Wet Pond 1C-22 Extended TC -30 Vegetated TC 31 Vegetated TC-40 Media TC 40 Media TC-40 Media
Detention Basin Swate Buffer Filter (Austin Fitter (Delaware filler (Mtilti-
Sand Filter] Unea! Sand chamber
Fitter) Treatment Train;
Figure 5-5
Total Nitrogen in Effluent
300 -T
ocn
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g 20°
1Ul-, -i en .
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I I
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I ™ I
TC-20Wet TC-22 TC-30 TC-31 TC-40 Media TC-40 Media TC-40 Media
Pond Extended Vegetated Vegetated Filter (Austin Filter Filter (M ulti-
Detention Swale Buffer Sand Filter) (Delaware chamber
Basin Lineal Sand Treatment
Filter) Train)
O
Figure 5-6
Total Dissolved Zinc in Effluent
5-8 California Stormwater BMP Handbook
New Development and Redevelopment
www.cabmphandbooks.com
January 2003
Errata 9-04
Section 5
Treatment Control BMPs
Jrf"»fc
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Pond Extended Vegetated Vegetated Filter (Austin Filter Filter (Multi-
Detention Swale Buffer Sand Filter) (Delaware chamber
Basin Lineal Sand Treatment
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Figure 5-7
Total Zinc in Effluent
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Pond Extended Vegetated Vegetated filter Fitter Filter {Molti-
Detenfion Swale Buffer (Austin Sand (Delaware chamber
Basin Filter) Lineal Sand Treatment
Filter) Train}
Figure 5-8
Total Fecal Coliforms in Effluent
January 2003
Brata 9-04
California Stormwater BMP Handbook
New Development and Redevelopment
www .cabmphandbooks.com
5-9
Section 5
Treatment Control BMPs
While a figure is provided for fecal coliform, it is important to stress that the performance
comparisons between BMPs is problematic. Some California BMP studies have shown excellent
removal of fecal conform through constructed wetlands and other BMPs, However, BMP
comparisons are complicated by the fact that several BMPs attract wildlife and pets, thereby
elevating bacteria levels. As bacteria sorb to the suspended sediments, a significant fraction may
be removed by settling or filtration. A cautionary note regarding nitrogen: when comparing
nitrogen removal between treatment systems it is best to use the parameter total nitrogen. It
consists of Total Kjeldahl Nitrogen - TKN (organic nitrogen plus ammonia) plus nitrate.
Comparing TKN removal rates is misleading in that in some treatment systems the ammonia is
changed to nitrate but not removed. Examination of the performance data of many systems
shows that while TKN may decrease dramatically, the nitrate concentration increases
correspondingly. Hence, the overall removal of nitrogen is considerably lower than implied
from looking only at Kjeldahl Nitrogen.
5.4.4 General Performance of Manufactured BMPs
An important question is how the performance of manufactured treatment BMPs compares to
those in the public domain, illustrated previously in Figures 5-4 through 5-8. Figure 5-9 (and
Figure 5-10 in log format) presents box-whisker plots of the removal of TSS for the
manufactured systems. Data are presented for five general types of manufactured BMPs: wet
vaults, drain inserts, constructed wetlands, media filters, and vortex separators. The figures
indicate wide ranges in effluent concentrations, reflecting in part the different products and
design criteria within each type. Comparing Figures 5-4 and 5-9 suggests that manufactured
products may perform as well as the less effective publicdomain BMPs such as swales and
extended detention basins (excluding the additional benefits of infiltration with the latter).
Manufactured wetlands may perform as well as the most effective publicdomain BMPs;
however, the plot presented in Figure 5-9 for the manufactured wetlands represents only five
data points. It should be noted that each type of BMP illustrated in Figure 5-9 contains data
from more than one product. Performance of particular products within that grouping may not
perform as well as even the least effective publicdomain BMPs. This observation is implied by
the greater spread within some boxes in Figure 5-9, for example, manufactured wet vaults and
vortex separators.
Product performance within each grouping of manufactured BMPs vary as follows:
• Filters - TSS effluent concentrations range from 2 to 280 mg/L, with a median value of 29
mg/L
• Inserts - TSS effluent concentrations range from 4 to 248 mg/L with a median value of 27
mg/L
m Wetlands - TSS effluent concentrations vary little, and have a median value of 1.2 mg/L
• Vaults - TSS effluent concentrations range from i to 467 mg/L, with a median value of 36
mg/L
• Vortex - TSS effluent concentrations range from 13 to 359 mg/L, with a median value of 32 mg/L
5-10 California Stormwater BMP Handbook January 2003
New Development and Redevelopment Errata 9-04
www.cabmphandbooks.com
Section 5
Treatment Control BMPs
800-,
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Figure 5-9
Total Suspended Solids in Effluent
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Filter
inlet
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Figure 5-10
Total Suspended Solids in Effluent (log-format)
January 2003
Errata 9-04
California Stormwater BMP Handbook
New Development and Redevelopment
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5-11
Section 5
Treatment Control BMPs
oAs noted earlier, performance of particular products in a grouping may be due to different ^""^
design criteria within the group. For example, wet vault products differ with respect to the
volume of the permanent wet pool to the design event volume; filter products differ with
respect to the type of media.
5.4.5 Technology Certification
This Handbook does not endorse proprietary products, although many are described. It is left to
each community to determine which proprietary products may be used, and under what
circumstances. When considering a proprietary product, it is strongly advised that the
community consider performance data, but only performance data that have been collected
following a widely accepted protocol. Protocols have been developed by the American Society of
Civil Engineering (ASCE BMP Data Base Program), and by the U.S.Environraental Protection
Agency (Environmental Technology Certification Program). The local jurisdiction should ask
the manufacturer of the product to submit a report that describes the product and protocol that
was followed to produce the performance data.
It can be expected that subsequent to the publishing of this Handbook, new public-domain
technologies will be proposed (or design criteria for existing technologies will be altered) by
development engineers. As with proprietary products, it is advised that new public-domain
technologies be considered only if performance data are available and have been collected
following a widely accepted protocol.
5.5 BMP Design Criteria for Flow and Volume
Many municipal stormwater discharge permits in California contain provisions such as
Standard Urban Stormwater Mitigation Plans, Stormwater Quality Urban Impact Mitigation
Plans, or Provision C.3 New and Redevelopment Performance Standards, commonly referred to
as SUSMPs, SQUIMPs, or C.3 Provisions, respectively. What these and similar provisions have
in common is that they require many new development and redevelopment projects to capture
and then infiltrate or treat runoff from the project site prior to being discharged to storm drains.
These provisions include minimum standards for sizing these treatment control BMPs. Sizing
standards are prescribed for both volume-based and flow-based BMPs.
A key point to consider when developing, reviewing, or complying with requirements for the
sizing of treatment control BMPs for stormwater quality enhancement is that BMPs are most
efficient and economical when they target small, frequent storm events that over time produce
more total runoff than the larger, infrequent storms targeted for design of flood control
facilities. The reason for this can be seen by examination of Figure 5-11 and Figure 5-12.
Figure 5-11 shows the distribution of storm events at San Jose, California where most storms
produce less than 0.50 in. of total rainfall. Figure 5-12 shows the distribution of rainfall
intensities at San Jose, California, where most storms have intensities of less than 0.25 in/hr.
The patterns at San Jose, California are typical of other locations throughout the state. Figures
5-11 and 5-12 show that as storm sizes increase, the number of events decrease. Therefore, when
BMPs are designed for increasingly larger storms (for example, storms up to i in. versus storms
of up to 0.5 in.), the BMP size and cost increase dramatically, while the number of additional
5-12 California Stormwater BMP Handbook January 2003
New Development and Redevelopment Errata 9-04
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Section 5
Treatment Control BMPs
treated storm events are small. Table 5-2 shows that doubling the design storm depth from 0.50
in. to l.oo in. only increases the number of events captured by 23%. Similarly, doubling the
design rainfall intensity from 0.25 in/hr to 0.50 in/hr only increases the number of events
captured by 7%.
1200-j 1067
Rain Storms at San Jose, CA
1948-2000
Storm Depth, Inches
Figure 5-11
Rain Storms at San Jose, CA
3000
<a 2500
•*•*
| 2000
IU
"5 1500 -w
A 1000
7 500 4
Rain Intensity at San Jose, CA
2963 1948-2000
10
9,335 hourly readings
less than 0.10 in/hr
are not shown
Rainfall intensity, inches per Hour
Figure 5-12
Rain Intensity at San Jose, CA
January 2003
Errata 9-04
California Stormwater BMP Handbook
New Development and Redevelopment
www.cabmphandbooks.com
5-13
Section 5
Tmafmenf Control BMPs
Table 5-2 Incremental Design Criteria VS Storms Treated at San Jose, CA
Proposed
BMP Design Target
Storm Depth
o.oo to 0.50 in.
Storm Depth
0.51 to i.oo in.
Rainfall Intensity
o.iotoo.25in/hr
Rainfall Intensity
0.26 to 0,50 in/hr
Number of
Historical Events
in Range
1,067
242
2,963
207
Incremental
Increase in
Design Criteria
+100%
+100%
Incremental
Increase in
Storms Treated
+23%
+7%
Due to economies of scale, doubling the capture and treatment requirements for a BMP are not
likely to double the cost of many BMPs, but the incremental cost per event will increase, making
increases beyond a certain point generally unattractive. Typically, design criteria for water
quality control BMPs are set to coincide with the "knee of the curve," that is, the point of
inflection where the magnitude of the event increases more rapidly than number of events
captured. Figure 5-13 shows that the "knee of the curve" or point of diminishing returns for San
Jose, California is in the range of 0.75 to i.oo in. of rainfall. In other words, targeting design
storms larger than this will produce gains at considerable incremental cost. Similar curves can
be developed for rainfall intensity and runoff volume.
k.
9
1600
1400
1200
ffI s5 uu•«"•(0
U
1000 -
800
600
400 -
200
Rain Storms at San Jose, CA
1948-2000
"Knee of the Curve"
is in this vicinity
1 - i - 1 - 1 - 1 - 1 - r— — i — — i - 1 - 1
Storm Depth, Inches
Figure 5-13
Rain Storms at San Jose, CA
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Section 5
Treatment Control BMPs
It is important to note that arbitrarily targeting large, infrequent storm events can actually
reduce the pollutant removal capabilities of some BMPs. This occurs when outlet structures,
detention times, and drain down times are designed to accommodate unusually large volumes
and high flows. When BMPs are over-designed, the more frequent, small storms that produce
the most annual runoff pass quickly through the over-sized BMPs and therefore receive
inadequate treatment. For example, a detention basin might normally be designed to capture
0.5 in. of runoff and to release that runoff over 48 hrs, providing a high level of sediment
removal. If the basin were to be oversized to capture i.o in. of runoff and to release that runoff
over 48 hrs, a more common 0.5 inch runoff event entering basin would drain in approximately
24 hrs, meaning the smaller, more frequent storm that is responsible for more total runoff
would receive less treatment than if the basin were designed for the smaller event. Therefore,
efficient and economical BMP sizing criteria are usually based 011 design criteria that correspond
to the "knee of the curve" or point of diminishing returns.
5.5.1 Volume-Based BMP Design
Volume-based BMP design standards apply to BMPs whose primary mode of pollutant removal
depends on the volumetric capacity of the BMP. Examples of BMPs in this category include
detention basins, retention basins, and infiltration. Typically, a volume-based BMP design
criteria calls for the capture and infiltration or treatment of a certain percentage of the runoff
from the project site, usually in the range of the 75th to 85th perceutile average annual runoff
volume. The 75th to 85th percentile capture range corresponds to the "knee of the curve" for
many sites in California for sites whose composite runoff coefficient is in the 0.50 to 0.95 range.
The following are examples of volume-based BMP design standards from current municipal
stormwater permits. The permits require that volume-based BMPs be designed to capture and
then to infiltrate or treat stormwater runoff equal to one of the following:
• Eighty (80) percent of the volume of annual runoff, determined in accordance with the
methodology set forth in Appendix D of the California Storm Water Best Management
Practices Handbook (Stormwater Quality Task Force, 1993), using local rainfall data.
• The maximized stormwater quality capture volume for the area, based on historical rainfall
records, determined using the formula and volume capture coefficients set forth in Urban
Runoff Quality Management (WEF Manual of Practice No. 23/ASCE Manual of Practice No.
87, (1998), pages 175-178)-
The reader is referred to the municipal stormwater program manager for the jurisdiction
processing the new development or redevelopment project application to determine the specific
requirements applicable to a proposed project.
California Stormwater BMP Handbook Approach
The volume-based BMP sizing methodology included in. the first edition of the California Storm
Water Best Management Practice Handbook (Stormwater Quality Task Force, 1993) has been
included in this second edition of the handbook and is the method recommended for use.
January 2003 California Stormwater BMP Handbook 5-15
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Section 5
Treatment Control BMPs
The California Stonnwater BMP Handbook approach is based on results of a continuous
simulation model, the STORM model, developed by the Hydrologic Engineering Center of the
U.S. Army Corps of Engineers (COE-HEC, 1977). The Storage, Treatment, Overflow, Runoff
Model (STORM) was applied to long-term hourly rainfall data at numerous sites throughout
California, with sites selected throughout the state representing a wide range of municipal
stormwater permit areas, climatic areas, geography, and topography. STORM translates rainfall
into runoff, then routes the runoff through detention storage. The volume-based BMP sizing
curves resulting from the STORM model provide a range of options for choosing a BMP sizing
curve appropriate to sites in most areas of the state. The volume-based BMP sizing curves are
included in Appendix D. Key model assumptions are also documented in Appendix D.
o
100
San Jose |?821) - Santa Clara County, California
Capture / Treatment Anaii
RunoB Coefficient = 0.25
RunoB Coefficient - 0.50
Runoff Coefficient = 0.7S
Runolf Coefficient -1.00
8.3 0.4 0.5 0.6 0.7Unit Basin Storage Volume (inches)
Figure 5-14
Capture/Treatment Analysis at San Jose, CA
The California Stormwater BMP Handbook approach is simple to apply, and relies largely on
commonly available information about a project. The following steps describe the use of the
BMP sizing curves contained in Appendix D.
1. Identify the "BMP Drainage Area" that drains to the proposed BMP. This includes all areas
that will contribute runoff to the proposed BMP, including pervious areas, impervious areas,
and off-site areas, whether or not they are directly or indirectly connected to the BMP.
2. Calculate the composite runoff coefficient "C" for the area identified in Step i.
3. Select a capture curve representative of the site and the desired drain down time using
Appendix D. Curves are presented for 24-hour and 48-hour draw down times. The 48-hour
curve should be used in most areas of California. Use of the 24-hour curve should be limited
5-16 California Stormwater BMP Handbook
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Treatment Control BMPs
to drainage areas with coarse soils that readily settle and to watersheds where warming may
be detrimental to downstream fisheries. Draw down times in excess of 48 hours should be
used with caution, as vector breeding can be a problem after water has stood in excess of 72
hours.
4. Determine the applicable requirement for capture of runoff (Capture, % of Runoff).
5. Enter the capture curve selected in Step 3 on the vertical axis at the "Capture, % Runoff'
value identified in Step 4. Move horizontally to the right across capture curve until the curve
corresponding to the drainage area's composite runoff coefficient "C" determined in Step 2 is
intercepted. Interpolation between curves may be necessary. Move vertically down from
this point until the horizontal axis is intercepted. Read the "Unit Basin Storage Volume"
along the horizontal axis. If a local requirement for capture of runoff is not specified, enter
the vertical axis at the "knee of the curve" for the curve representing composite runoff
coefficient "C." The "knee of the curve" is typically in the range of 75 to 85% capture.
6. Calculate the required capture volume of the BMP by multiplying the "BMP Drainage Area"
from Step i by the "Unit Basin Storage Volume" from Step 5 to give the BMP volume. Due to
the mixed units that result (e.g., ac-in., ac-ft) it is recommended that the resulting volume be
converted to cubic feet for use during design.
Urban Runoff Quality Management Approach
The volume-based BMP sizing methodology described in Urban Runoff Quality Management
(WEF Manual of Practice No. 23/ASCE Manual of Practice No. 87, (1998), pages 175-178) has
been included in this edition of the handbook as an alternative to the California Stormwater
BMP Handbook approach described above. The Urban Runoff Quality Management Approach
is suitable for planning level estimates of the size of volume-based BMPs (WEF/ASCE, 1998,
page 175).
The Urban Runoff Quality Management approach is similar to the California Stormwater BMP
Handbook approach in that it is based on the translation of rainfall to runoff. The Urban Runoff
Quality Management approach is based on two regression equations. The first regression
equation relates rainfall to runoff. The rainfall to runoff regression equation was developed
using 2 years of data from more than 60 urban watersheds nationwide. The second regression
equation relates mean annual runoff-producing rainfall depths to the "Maximized Water Quality
Capture Volume" which corresponds to the "knee of the cumulative probability curve". This
second regression was based on analysis of long-term rainfall data from seven rain gages
representing climatic zones across the country. The Maximized Water Quality Capture Volume
corresponds to approximately the 85th percentile runoff event, and ranges from 82 to 88%.
The two regression equations that form the Urban Runoff Quality Management approach are as
follows:
C = 0.858/3 - o.78ia + 0.7741 + 0.04
P0 = (a • C) • P$
January 2003 California Stormwater BMP Handbook 5-17
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Section 5
Treatment Control BMPs
Where
C= runoff coefficient
i = watershed imperviousness ratio which is equal to the percent total iraperviousness
divided by 100
Po = Maximized Detention Volume, in watershed inches
a = regression constant, a= 1.582 and a= 1.963 for 24 and 48 hour draw down,
respectively
PS = mean annual runoff-producing rainfall depths, in watershed inches, Table #-i. See
Appendix D.
The Urban Runoff Quality Management Approach is simple to apply. The following steps
describe the use of the approach.
1. Identify the "BMP Drainage Area" that drains to the proposed BMP. This includes all areas
that will contribute runoff to the proposed BMP, including pervious areas, impervious areas,
and off-site areas, whether or not they are directly or indirectly connected to the BMP.
2. Calculate the "Watershed Imperviousness Ratio" (i), which is equal to the percent of total
impervious area in the "BMP Drainage Area" divided by 100.
3. Calculate the "Runoff Coefficient" (C) using the following equation:
C = 0.858/3 - o.ySi2 + 0.7741 + 0.04
4. Determine the "Mean Annual Runoff (P6) for the "BMP Drainage Area" using Table #-i in
Appendix D.
5. Determine the "Regression Constant" (a) for the desired BMP drain down time. Use 3=1.582
for 24 hrs and 8=1.963 for 48 hr draw down.
6. Calculate the "Maximized Detention Volume" (Po) using the following equation:
Po = (a • C) • P6
7. Calculate the required capture volume of the BMP by multiplying the "BMP Drainage Area"
from Step i by the "Maximized Detention Volume" from Step 6 to give the BMP volume.
Due to the mixed units that result (e.g., ac-in., ac-ft) it is recommended that the resulting
volume be converted to fts for use during design.
5.5.2 Flow-Based BMP Design
Flow-based BMP design standards apply to BMPs whose primary mode of pollutant removal
depends on the rate of flow of runoff through the BMP. Examples of BMPs in this category
5-18 California Stormwater BMP Handbook January 2003
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o
Section 5
Treatment Control BMPs
include swales, sand filters, screening devices, and many proprietary products. Typically, a
flow-based BMP design criteria calls for the capture and infiltration or treatment of the flow
runoff produced by rain events of a specified magnitude.
The following are examples of flow-based BMP design standards from current municipal
stormwater permits. The permits require that flow-based BMPs be designed to capture and
then to infiltrate or treat stormwater runoff equal to one of the following:
• 10% of the 5O-yr peak flow rate (Factored Flood Flow Approach)
• The flow of runoff produced by a rain event equal to at least two times the 85th percentile
hourly rainfall intensity for the applicable area, based on historical records of hourly rainfall
depths (California Stormwater BMP Handbook Approach)
• The flow of runoff resulting from a rain event equal to at least 0.2 in/hr intensity (Uniform
Intensity Approach)
The reader is referred to the municipal stormwater program manager for the jurisdiction
processing the new development or redevelopment project application to determine the specific
requirements applicable to a proposed project.
The three typical requirements shown above all have in common a rainfall intensity element.
That is, each criteria is based treating a flow of runoff produced by a rain event of specified
rainfall intensity.
In the first example, the Factored Flood Flow Approach, the design rainfall intensity is a
function of the location and time of concentration of the area discharging to the BMP. The
intensity in this case is determined using Intensity-Duration-Frequency curves published by the
flood control agency with jurisdiction over the project or available from climatic data centers.
This approach is simple to apply when the 5O-yr peak flow has already been determined for
either drainage system design or flood control calculations.
In the second example, the California Stormwater BMP Handbook Approach (so called because
it is recommended in this handbook), the rainfall intensity is a function of the location of the
area discharging to the BMP. The intensity in this case can be determined using the rain
intensity cumulative frequency curves developed for this Handbook based on analysis of long-
term hourly rainfall data at numerous sites throughout California, with sites selected throughout
the state representing a wide range of municipal stormwater permit areas, climatic areas,
geography, and topography. These rain intensity cumulative frequency curves are included in
Appendix D. This approach is recommended as it reflects local conditions throughout the state.
The flow-based design criteria in some municipal permits require design based on two times the
85* percentile hourly rainfall intensity. The factor of two included in these permits appears to
be provided as a factor of safety: therefore, caution should be exercised when applying
additional factors of safety during the design process so that over design can be avoided.
January 2003 California Stormwater BMP Handbook 5-19
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Section 5
Treatment Control BMPs
In the third example, the Uniform Intensity Approach, the rainfall intensity is specified directly,
and is not a function of the location or time of concentration of the area draining to the BMP.
This approach is very simple to apply., but it is not reflective of local conditions.
Hie three example flow-based BMP design criteria are easy to apply and can be used in
conjunction with the Rational Formula, a simplified, easy to apply formula that predicts flow
rates based on rainfall intensity and drainage area characteristics. The Rational Formula is as
follows:
o
= CiA
where
Q = flow in ft3/s
i = rain intensity in in/hr
A = drainage area in acres
C= runoff coefficient
The Rational Formula is widely used for hydrologic calculations, but it does have a number of
limitations. For stormwater BMP design, a key limitation is the ability of the Rational Formula
to predict runoff from undeveloped areas where runoff coefficients are highly variable with
storm intensity and antecedent moisture conditions. This limitation is accentuated when
predicting runoff from frequent, small storms used in stormwater quality BMP design because
many of the runoff coefficients in common use were developed for predicting runoff for drainage
design where larger, infrequent storms are of interest. Table 5-3 provides some general
guidelines on use of the Rational Equation.
Table 5-3 Use of Rational Formula for Stormwater BMP Design
BMP Drainage Area
(Acres)
Ot025
26 to 50
51 to 75
76 to 100
Composite Riinoff Coefficient, "C"
o.oo to 0.25
Caution
High Caution
Not
Recommended
Not
Recommended
0.26 to 0.50
Yes
Caution
High Caution
High Caution
0.51 to 0.73
Yes
Yes
Caution
Caution
0.76 to i.oo
Yes
Yes
Yes
Yes
In summary, the Rational Formula, when used with commonly tabulated runoff coefficients in
undeveloped drainage areas, will likely result in predictions higher than will be experienced
under actual field conditions. However, given the simplicity of the equation, its use remains
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practical and is often the standard method specified by local agencies. In general, use of
alternative formulas for predicting BMP design flows based on the intensity criteria above is
acceptable if the formula is approved by the local flood control agency or jurisdiction where the
project is being developed.
The following steps describe the approach for application of the flow-based BMP design criteria:
1. Identify the "BMP Drainage Area" that drains to the proposed BMP. This includes all areas
that will contribute runoff to the proposed BMP, including pervious areas, impervious areas,
and off-site areas, whether or not they are directly or indirectly connected to the BMP.
2. Determine rainfall intensity criteria to apply and the corresponding design rainfall intensity.
a. Factored Flood Flow Approach: Determine the time of concentration for "BMP
Drainage Area" using procedures approved by the local flood control agency or using
standard hydrology methods. Identify an Intensity-Duration-Frequency Curve
representative of the drainage area (usually available from the local flood control agency
or climatic data center). Enter the Intensiry-Duration-Frequency Curve with the time of
concentration and read the rainfall intensity corresponding to the 5O-yr return period
rainfall event. This intensity is the "Design Rainfall Intensity."
b. California Stonnwater BMP Handbook Approach: Select a rain intensity cumulative
frequency curve representative of the "BMP Drainage Area." See Appendix D. Read the
rainfall intensity corresponding to the cumulative probability specified in the criteria,
usually 85%. Multiply the intensity by the safety factor specified in the criteria, usually
2, to get the "Design Rainfall Intensity."
c. Uniform Intensity Approach: The "Design Rainfall Intensity" is the intensity specified
in the criteria, usually 0.2 in/hr.
3. Calculate the composite runoff coefficient" "C" for the "BMP Drainage Area" identified in
Step i.
4. Apply the Rational Formula to calculate the "BMP Design Flow"
a. Factored Flood Flow Approach: Using the "BMP Drainage Area" from Step i, the
"Design Rainfall Intensity" from Step za, and "C" from Step 3, apply the Rational
Formula and multiply the result by o.i. The result is the "BMP Design Flow."
b. California Stormwater BMP Handbook Approach: Using the "BMP Drainage Area"
from Step i, the "Design Rainfall Intensity" from Step ab, and "C" from Step 3, apply the
Rational Formula. The result is the "BMP Design Flow."
c. Uniform Intensity Approach: Using the "BMP Drainage Area" from Step 1, the "Design
Rainfall Intensity" from Step 2c, and "C" from Step 3, apply the Rational Formula. The
result is the "BMP Design Flow."
January 2003 California Stonnwater BMP Handbook 5-21
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Section 5
Treatment Control BMPs
5.5.3 Combined Volume-Based and Flow-Based BMP
Design
Volume-based BMPs and flow-based BMPs do not necessarily treat precisely the same
stormwater runoff. For example, an on-line volume-based BMP such as a detention basin will
treat the design runoff volume and is essentially unaffected by runoff entering the basin at an
extremely high rate, say from a very short, but intense storm that produces the design volume of
runoff. However, a flow-based BMP might be overwhelmed by the same short, but intense
storm if the storm intensity results in runoff rates that exceed the flow-based BMP design flow
rate. By contrast, a flow-based BMP such as a swale will treat the design flow rate of runoff and
is essentially unaffected by the duration of the design flow, say from a long, low intensity storm.
However, a volume-based detention basin subjected to this same rainfall and runoff event will
begin to provide less treatment or will go into bypass or overflow mode after the design runoff
volume is delivered.
Therefore, there may be some situations where designers need to consider both volume-based
and flow-based BMP design criteria. An example of where both types of criteria might apply is
an off-line detention basin. For an off-line detention basin, the capacity of the diversion
structure could be designed to comply with the flow-based BMP design criteria while the
detention basin itself could be designed to comply with the volume-based criteria.
When both volume-based and flow based criteria apply, the designer should determine which of
the criteria apply to each element of the BMP system, and then size the elements accordingly.
5.6 Other BMP Selection Factors
Other factors that influence the selection of BMPs include cost, vector control issues, and
endangered species issues. Each of these is discussed briefly below.
5.6.1 Costs
The relative costs for implementing various public domain and manufactured BMPs based on
flow and volume parameters are shown in Tables 5-4 and 5-5 below:
Table 5-4 Economic
Comparison Matrix -
Flow
BMP
Strip
Swale
Wet Vault
Media Filter
Vortex
Drain Insert
Cost/cfe
$$
$$
Not available
$$$$
Not available
Not available
Table 5-5 Economic Comparison Matrix
- Volume
BMP
Austin Sand Filter Basin
Delaware Lineal Sand Filter
Extended Detention Basin (EDB)
Multi Chamber Treatment Train
(MCTT)
Wet Basin
Manufactured Wetland
Infiltration Basin
Wet Pond and Constructed Wetland
Cost/acre-ft
<&<%%<£H**?*?*?
$$$$
$$
$$$$
4j**t4i*£*?<B*p*|»
Not available
$
$$$$
o
o
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5.6.2 Vector Breeding Considerations
The potential of a BMP to create vector breeding habitat and/or harborage should be considered
when selecting BMPs. Mosquito and other vector production is a nuisance and public health
threat. Mosquitoes can breed in standing water almost immediately following a BMP
installation and may persist at unnaturally high levels and for longer seasonal periods in created
habitats. BMP siting, design, construction, and maintenance must be considered in order to
select a BMP that is least conducive to providing habitat for vectors. Tips for minimizing
vector-breeding problems in the design and maintenance of BMPs are presented in the BMP fact
sheets. Certain BMPs, including ponds and wetlands and those designed with permanent water
sumps, vaults, and/or catch basins (including below ground installations), may require routine
inspections and treatments by local mosquito and vector control agencies to suppress vector
production.
5.6.3 Threatened and Endangered Species Considerations
The presence or potential presence of threatened and endangered species should also be
considered when selecting BMPs. Although preservation of threatened endangered species is
crucial, treatment BMPs are not intended to supplement or replace species habitat except under
special circumstances. The presence of threatened or endangered species can hinder timely and
routine maintenance, which in turn can result in reduced BMP performance and an increase in
vector production. In extreme cases, jurisdictional rights to the treatment BMP and
surrounding land may be lost if threatened or endangered species utilize or become established
in the BMP.
When considering BMPs where there is a presence or potential presence of threatened or
endangered species, early coordination with the California Department of Fish and Game and
the U.S. Fish and Wildlife service is essential. During this coordination, the purpose and the
long-term operation and maintenance requirements of the BMPs need to be clearly established
through written agreements or memorandums of understanding. Absent firm agreements or
understandings, proceeding with BMPs under these circumstances is not recommended.
5.7 BMP Fact Sheets
BMP fact sheets for public domain and manufactured BMPs follow. The BMP fact sheets are
individually page numbered and are suitable for photocopying and inclusion in stormwater
quality management plans. Fresh copies of the fact sheets can be individually downloaded from
the Caltrans Stormwater BMP Handbook website at www.cabmphandbooks.com.
January 2003 California Stormwater BMP Handbook 5-23
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Vegetated Swale TC-30
Description
Vegetated swales are open, shallow channels with vegetation
covering the side slopes and bottom that collect and slowly
convey runoff flow to downstream discharge points. They are
designed to treat runoff through filtering by the vegetation in the
channel, filtering through a subsoil matrix, and/or infiltration
into the underlying soils. Swales can be natural or mamnade.
They trap particulate pollutants (suspended solids and trace
metals), promote infiltration, and reduce the flow velocity of
stormwater runoff. Vegetated swales can serve as part of a
stomiwater drainage system and can replace curbs, gutters and
storm sewer systems.
California Experience
Caltrans constructed and monitored six vegetated swales in
southern California. These swales were generally effective in
reducing the volume and mass of pollutants in runoff. Even in
the areas where the annual rainfall was only about 10 inches/yr,
the vegetation did not require additional irrigation. One factor
that strongly affected performance was the presence of large
numbers of gophers at most of the sites. The gophers created
earthen mounds, destroyed vegetation, and generally reduced the
effectiveness of the controls for TSS reduction.
Advantages
• If properly designed, vegetated, and operated, swales can
serve as an aesthetic, potentially inexpensive urban
development or roadway drainage conveyance measure with
significant collateral water quality benefits.
Design Considerations
Tributary Area
Area Required
Slope
Water Availability
Targeted Constituents
^wratwsmwssw&wsstH'fc'
0 Sediment
0 Nutrients
El Trash
El Metals
0 Bacteria
El Oil and Grease A
El Organics A
Legend {Removal Effectiveness)
• Low • High
A Medium
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1 of 13
TC-30 Vegetated Swale
• Roadside ditches should be regarded as significant potential swale/buffer strip sites and
should be utilized for this purpose whenever possible.
Limitations
• Can be difficult to avoid channelization.
• May not be appropriate for industrial sites or locations where spills may occur
• Grassed swales cannot treat a very large drainage area. Large areas may be divided and
treated using multiple swales.
• A thick vegetative cover is needed for these practices to function properly.
• They are impractical in areas with steep topography.
• They are not effective and may even erode when flow velocities are high, if the grass cover is
not properly maintained.
• In some places, their use is restricted by law: many local municipalities require curb and
gutter systems in residential areas.
• Swales are mores susceptible to failure if not properly maintained than other treatment
BMPs.
Design and Sizing Guidelines
• Flow rate based design determined by local requirements or sized so that 85% of the annual
runoff volume is discharged at less than the design rainfall intensity.
• Swale should be designed so that the water level does not exceed 2/3rds the height of the
grass or 4 inches, which ever is less, at the design treatment rate.
• Longitudinal slopes should not exceed 2.5%
• Trapezoidal channels are normally recommended but other configurations, such as
parabolic, can also provide substantial water quality improvement and may be easier to mow
than designs with sharp breaks in slope.
• Swales constructed in cut are preferred, or in fill areas that are far enough from an adjacent
slope to minimize the potential for gopher damage. Do not use side slopes constructed of
fill, which are prone to structural damage by gophers and other burrowing animals.
• A diverse selection of low growing, plants that thrive under the specific site, climatic, and
watering conditions should be specified. Vegetation whose growing season corresponds to
the wet season are preferred. Drought tolerant vegetation should be considered especially
for swales that are not part of a regularly irrigated landscaped area.
• The width of the swale should be detennined using Manning's Equation using a value of
0.25 for Manning's n.o
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Vegetated Swale TO30
Construction/Inspection Considerations
m Include directions in the specifications for use of appropriate fertilizer and soil amendments
based on soil properties determined through testing and compared to the needs of the
vegetation requirements.
• Install swales at the time of the year when there is a reasonable chance of successful
establishment without irrigation; however, it is recognized that rainfall in a given year may
not be sufficient and temporary irrigation may be used.
• If sod tiles must be used, they should be placed so that there are no gaps between the tiles;
stagger the ends of the tiles to prevent the formation of channels along the swale or strip.
• Use a roller on the sod to ensure that no air pockets form between the sod and the soil.
• Where seeds are used, erosion controls will be necessary to protect seeds for at least 75 days
after the first rainfall of the season.
Performance
The literature suggests that vegetated swales represent a practical and potentially effective
technique for controlling urban runoff quality. While limited quantitative performance data
exists for vegetated swales, it is known that check dams, slight slopes, permeable soils, dense
grass cover, increased contact time, and small storm events all contribute to successful pollutant
removal by the swale system. Factors decreasing the effectiveness of swales include compacted
soils, short runoff contact time, large storm events, frozen ground, short grass heights, steep
slopes, and high runoff velocities and discharge rates.
Conventional vegetated swale designs have achieved mixed results in removing particulate
pollutants. A study performed by the Nationwide Urban Runoff Program (NURP) monitored
three grass swales in the Washington, D.C., area and found no significant improvement in urban
runoff quality for the pollutants analyzed. However, the weak performance of these swales was
attributed to the high flow velocities in the swales, soil compaction, steep slopes, and short grass
height.
Another project in Durham, NC, monitored the performance of a carefully designed artificial
swale that received runoff from a commercial parking lot. Hie project tracked 11 storms and
concluded that particulate concentrations of heavy metals (Cu, Pb, Zn, and Cd) were reduced by
approximately 50 percent. However, the swale proved largely ineffective for removing soluble
nutrients.
The effectiveness of vegetated swales can be enhanced by adding check dams at approximately
17 meter (50 foot) increments along their length (See Figure i). These dams maximize the
retention time within the swale, decrease flow velocities, and promote particulate settling.
Finally, the incorporation of vegetated filter strips parallel to the top of the channel banks can
help to treat sheet flows entering the swale.
Only 9 studies have been conducted on all grassed channels designed for water quality (Table i).
The data suggest relatively high removal rates for some pollutants, but negative removals for
some bacteria, and fair performance for phosphorus.
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TC-30 Vegetated Swale
Table 1 Grassed swale pollutant removal efficiency data
Removal Efficiencies (% Removal)
Study
Caltrans 2002
Goldberg 1993
Seattle Metro and Washington
Department of Ecology 1992
Seattle Metro and Washington
Department of Ecology, 1992
Wang et al., 1981
Domian et al., 1989
Harper, 1988
Kercheretal., 1983
Harper. 1988.
Koon, 1995
TSS
77
67.8
60
83
80
98
87
99
81
' 67
TP
8
4-5
45
29
-
18
83
99
17
39
TN
67
-
-
-
-
-
84
99
40
-
N03
66
31-4
-25
-25
-
45
80
99
52
9
Metals
83-90
42-62
2-16
46-73
70-80
37-81
88-90
99
37-69
-35 to 6
Bacteria
-33
-100
-25
-25
-
-
-
-
-
-
Type
dry swales
grassed channel
grassed channel
grassed channel
dry swale
dry swale
dry swale
dry swale
wet swale
wet swale
O
While it is difficult to distinguish between different designs based on the small amount of
available data, grassed channels generally have poorer removal rates than wet and dry swales,
although some swales appear to export soluble phosphorus (Harper, 1988; Koon, 1995). It is not
clear why swales export bacteria. One explanation is that bacteria thrive in the warm swale
soils.
Siting Criteria
The suitability of a swale at a site will depend on land use, size of the area serviced, soil type,
slope, imperviousness of the contributing watershed, and dimensions and slope of the swale
system (Schueler et al., 1992). In general, swales can be used to serve areas of less than 10 acres,
with slopes no greater than 5 %. Use of natural topographic lows is encouraged and natural
drainage courses should be regarded as significant local resources to be kept in use (Young et al.,
1996).
Selection Criteria (NCTCOG, 1993)
m Comparable performance to wet basins
• Limited to treating a few acres
• Availability of water during dry periods to maintain vegetation
• Sufficient available land area
Research in the Austin area indicates that vegetated controls are effective at removing pollutants
even when dormant. Therefore, irrigation is not required to maintain growth during dry
periods, but may be necessary only to prevent the vegetation from dying.
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Vegetated Swale TC-30
The topography of the site should permit the design of a channel with appropriate slope and
cross-sectional area. Site topography may also dictate a need for additional structural controls.
Recommendations for longitudinal slopes range between 2 and 6 percent. Flatter slopes can be
used, if sufficient to provide adequate conveyance. Steep slopes increase flow velocity, decrease
detention time, and may require energy dissipating and grade check. Steep slopes also can be
managed using a series of check dams to terrace the swale and reduce the slope to within
acceptable limits. The use of check dams with swales also promotes infiltration.
Additional Design Guidelines
Most of the design guidelines adopted for swale design specify a minimum hydraulic residence
time of 9 minutes. This criterion is based on the results of a single study conducted in Seattle,
Washington (Seattle Metro and Washington Department of Ecology, 1992), and is not well
supported. Analysis of the data collected in that study indicates that pollutant removal at a
residence time of 5 minutes was not significantly different, although there is more variability in
that data. Therefore, additional research in the design criteria for swales is needed. Substantial
pollutant removal has also been observed for vegetated controls designed solely for conveyance
(Barrett et al, 1998); consequently, some flexibility in the design is warranted.
Many design guidelines recommend that grass be frequently mowed to maintain dense coverage
near the ground surface. Recent research (Colwell et al., 2000) has shown mowing frequency or
grass height has little or no effect on pollutant removal.
Summary of Design Recommendations
1) The swale should have a length that provides a minimum hydraulic residence time of
at least 10 minutes. The maximum bottom width should not exceed 10 feet unless a
dividing berm is provided. The depth of flow should not exceed 2/3rds the height of
the grass at the peak of the water quality design storm intensity. The channel slope
should not exceed 2.5%.
2) A design grass height of 6 inches is recommended.
3) Regardless of the recommended detention time, the swale should be not less than
100 feet in length.
4) The width of the swale should be determined using Manning's Equation, at the peak
of the design storm, using a Manning's n of 0.25.
5) The swale can be sized as both a treatment facility for the design storm and as a
conveyance system to pass the peak hydraulic flows of the loo-year storm if it is
located "on-line." The side slopes should be no steeper than 3:1 (H:V).
6) Roadside ditches should be regarded as significant potential swale/buffer strip sites
and should be utilized for this purpose whenever possible. If flow is to be introduced
through curb cuts, place pavement slightly above the elevation of the vegetated areas.
Curb cuts should be at least 12 inches wide to prevent clogging.
7) Swales must be vegetated in order to provide adequate treatment of runoff. It is
important to maximize water contact with vegetation and the soil surface. For
general purposes, select fine, close-growing, water-resistant grasses. If possible,
divert runoff (other than necessary irrigation) during the period of vegetation
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TC-30 Vegetated Swale
Oestablishment. Where runoff diversion is not possible, cover graded and seeded
areas with suitable erosion control materials.
Maintenance
The useful life of a vegetated swale system is directly proportional to its maintenance frequency.
If properly designed and regularly maintained, vegetated swales can last indefinitely. The
maintenance objectives for vegetated swale systems include keeping up the hydraulic and
removal efficiency of the channel and maintaining a dense, healthy grass cover.
Maintenance activities should include periodic mowing (with grass never cut shorter than the
design flow depth), weed control, watering during drought conditions, reseeding of bare areas,
and clearing of debris and blockages. Cuttings should be removed from the channel and
disposed in a local composting facility. Accumulated sediment should also be removed
manually to avoid concentrated flows in the swale. The application of fertilizers and pesticides
should be minimal.
Another aspect of a good maintenance plan is repairing damaged areas within a channel. For
example, if the channel develops ruts or holes, it should be repaired utilizing a suitable soil that
is properly tamped and seeded. The grass cover should be thick; if it is not, reseed as necessary.
Any standing water removed during the maintenance operation must be disposed to a sanitary
sewer at an approved discharge location. Residuals (e.g., silt, grass cuttings) must be disposed
in accordance with local or State requirements. Maintenance of grassed swales mostly involves
maintenance of the grass or wetland plant cover. Typical maintenance activities are
summarized below:
• Inspect swales at least twice annually for erosion, damage to vegetation, and sediment and
debris accumulation preferably at the end of the wet season to schedule summer
maintenance and before major fall runoff to be sure the swale is ready for winter. However,
additional inspection after periods of heavy runoff is desirable. The swale should be checked
for debris and litter, and areas of sediment accumulation.
• Grass height and mowing frequency may not have a large impact on pollutant removal.
Consequently, mowing may only be necessary once or twice a year for safety or aesthetics or
to suppress weeds and woody vegetation.
• Trash tends to accumulate in swale areas, particularly along highways. The need for litter
removal is determined through periodic inspection, but litter should always be removed
prior to mowing.
• Sediment accumulating near culverts and in channels should be removed when it builds up
to 75 mm (3 in.) at any spot, or covers vegetation.
• Regularly inspect swales for pools of standing water. Swales can become a nuisance due to
mosquito breeding in standing water if obstructions develop (e.g. debris accumulation,
invasive vegetation) and/or if proper drainage slopes are not implemented and maintained.
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Vegetated Swale TC-30
Cost
Construction Cost
Little data is available to estimate the difference in cost between various swale designs. One
study (SWRPC, 1991) estimated the construction cost of grassed channels at approximately
$0.25 per ft2. This price does not include design costs or contingencies. Brown and Schueler
(1997) estimate these costs at approximately 32 percent of construction costs for most
stormwater management practices. For swales, however, these costs would probably be
significantly higher since the construction costs are so low compared with other practices. A
more realistic estimate would be a total cost of approximately $0.50 per ft2, which compares
favorably with other stormwater management practices.
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TC-30 Vegetated Swale
Table 2 Swaie Cost Estimate (SEWRPC, 1991)
Component
Mobilization /
Demobilization -Light
Site Preparation
Clearing6
Grubbingf
General
Excavation"
Level and Till4
Sites Development
Salvaged Topsoii
Seed, and Mulch'..
Sod3
Subtotal
Contingencies
Total
Unit
Swale
Acre
Yd3
Yd2
Yd*
Yd2
_
Swaie
--
Extent
1
0 6
0.2S
372
1,210
1,210
1,210
-
1
-
LOW
$107
$2200
$3,800
12.10
SQ.2G
10,40
$1.20
--
25%
-
Unit Cost
Moderate
$274
$3800
$5.200
$3,70
$0.35
$1.00
$2.40
-
25%
~
High
$441
$5400
$6,4500
$5.30
$0.50
$1.60
$3.30
,,
25%
--
Low
$107
$1 100
$950
$781
$242
$484
$1,452
$5,118
$1578
$6.395
Total Cost
Moderate
$274
$1 800
$1 ,300
$1,376
$424
$1,210
$2,804
19,388
$2,347
$11,735
High
$441
$2700
$1 ,650
$1,872
$605
$1,936
$4356
$13,660
$3,415
$17,076
Source; (SEWRPC, 1891)
Note: Mobiiization/dernoDiiizatran refers to the organization and planning involved in establishing a vsgeiatvs swale.
8 Swale has a bottom width of 1.0 foot, a top width of 10 feet wtth 1:3 side slopes, and a 1,000-foot length.
15 Area cleaned = (top width + 10 feetj x swale length.
" Area grubbed = {top width x swale length).
'Volume excavated = (0.87 x top width x swale depth) x swale length (parabolic cross-section),
e Area tilled = (top width + & swale deMirlx swale length (parabolic cross-section).
3<top width)
' Area seeded = area cleared x 0,5.
8 Area sodded = ares cleared x Q.6.
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o
Vegetated Swale TC-3U
Table 3 Estimated Maintenance Costs fSEWRPC, 1991)
Component
lawn Mowing
General Lawn Care
Swale Debris and Litter
Removal
Grass Reseeding with
Mulch and Fertilizer
Program Administration and
Swale Inspection
Total
Unit Cost
$0.85 / 1,000 ft*'/ mowing
$9.00 / 1,000 #/ year
$0.10 /linear foot /year
$0.30 /yd2
$0. 1 6 / linear foot / year,
plus $25 /inspection
«
Swale Size
{Depth and Top Width)
1.5 Foot Depth, One-
Foot Bottom Width,
UO-Foot Top Width
$0.14 / lin aarfoot
$a.18/linsarfoot
$0.10 /linear foot
$0.01 / lin earfoot
$0,15 /lin earfoot
JJD.58 / finear foot
3-Foot Depth, 3-Foot
Bottom Width, 21-Foot
Top Width
10.21 /linear foot
$0.28 /linear foot
$0.10 /linear foot
$0.01 /linear foot
$0.15 /linear foot
$0.75 /linear foot
Comment
Lawn maintenance arsa=(top
width + 10 test)* length. Mow
eight times per year
Lawn maintenance area = {top
width + 10 fset) x length
_
Area rev^getatad equals 1 %
of lawn maintenance area per
year
Inspect four times per par
-
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9 of 13
TC-30 Vegetated Swale
Maintenance Cost
Caltrans (2002) estimated the expected annual maintenance cost for a swale with a tributary
area of approximately 2 ha at approximately $2,700. Since almost all maintenance consists of
mowing, the cost is fundamentally a function of the mowing frequency. Unit costs developed by
SEWRPC are shown in Table 3. In many cases vegetated channels would be used to convey
runoff and would require periodic mowing as well, so there may be little additional cost for the
water quality component. Since essentially all the activities are related to vegetation
management, no special training is required for maintenance personnel.
References and Sources of Additional Information
Barrett, Michael E., Walsh, Patrick M., Malina, Joseph F., Jr., Gharbeneau, Randall J, 1998,
"Performance of vegetative controls for treating highway runoff," ASCE Journal of
Environmental Engineering, Vol. 124, No. 11, pp. 1121-1128.
Brown, W., and T. Sehueler. 1997. The Economics ofStormwater BMPs in the Mid-Atlantic
Region. Prepared for the Chesapeake Research Consortium, Edgewater, MD, by the Center for
Watershed Protection, Ellicott City, MD.
Center for Watershed Protection (CWP). 1996. Design of Stormwater Filtering Systems.
Prepared for the Chesapeake Research Consortium, Solomons, MD, and USEPA Region V,
Chicago, IL, by the Center for Watershed Protection, Ellicott City, MD.
Colwell, Shanti R., Homer, Richard R., and Booth, Derek B., 2000. Characterization of
Performance Predictors and Evaluation of Mowing Practices in Biqfiltration Swales. Report
to King County Land And Water Resources Division and others by Center for Urban Water
Resources Management, Department of Civil and Environmental Engineering, University of
Washington, Seattle, WA
Dorman, M.E., J. Hartigan, R.F. Steg, and T. Quasebarth. 1989. Retention, Detention and
Overland Flow for Pollutant Removal From Highway Stormwater Runoff. Vol. i. FHWA/RD
89/202. Federal Highway Administration, Washington, DC.
Goldberg. 1993. Dayton Avenue Swale Biqfiltration Study. Seattle Engineering Department,
Seattle, WA.
Harper, H. 1988. Effects of Stormwater Management Systems on Groundwater Quality.
Prepared for Florida Department of Environmental Regulation, Tallahassee, FL, by
Environmental Research and Design, Inc., Orlando, FL.
Kercher, W.C., J.C. Laudon, and R. Massarelli. 1983. Grassy swales prove cost-effective for
water pollution control. Public Works, 16: 53-55.
Koon, J. 1995. Evaluation of Water Quality Ponds and Swales in the Issaqitah/East Lake
Sammamish Basins. King County Surface Water Management, Seattle, WA, and Washington
Department of Ecology, Olympia, WA.
Metzger, M. E., D. F. Messer, C. L. Beitia, C. M. Myers, and V. L. Kramer. 2002. The Dark Side
Of Stormwater Runoff Management: Disease Vectors Associated With Structural BMPs.
Stormwater 3(2): 24-39-Oakland, P.H. 1983. An evaluation of Stormwater pollutant removal
10 of 13 California Stormwater BMP Handbook January 2003
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Vegetated Swale TO30
through grassed swale treatment. In Proceedings of the International Symposium of Urban
Hydrology, Hydraulics and Sediment Control, Lexington, K¥. pp. 173-182.
Occoquan Watershed Monitoring Laboratory. 1983. Final Report: Metropolitan Washington
Urban Runoff Project. Prepared for the Metropolitan Washington Council of Governments,
Washington, DC, by the Occoquan Watershed Monitoring Laboratory, Manassas, VA.
Pitt, R., and J. McLean. 1986. Toronto Area Watershed Management Strategy Study: Humber
River Pilot Watershed Project. Ontario Ministry of Environment, Toronto, ON.
Schueler, T. 1997. Comparative Pollutant Removal Capability of Urban BMPs: A reanalysis.
Watershed Protection Techniques 2(a):379-383.
Seattle Metro and Washington Department of Ecology. 1992. Biojiltration Swale Performance:
Recommendations and Design Considerations. Publication No. 657. Water Pollution Control
Department, Seattle, WA.
Southeastern Wisconsin Regional Planning Commission (SWRPC). 1991. Costs of Urban
Nonpoint Source Water Pollution Control Measures. Technical report 110. 31. Southeastern
Wisconsin Regional Planning Commission, Waukesha, WI.
U.S. EPA, 1999, Stormwater Fact Sheet: Vegetated Swales, Report # 832^-99-006
http://mvw.epa.gov/owm/mtb/vegswale.pdf. Office of Water, Washington DC.
Wang, T., D. Spyridakis, B. Mar, and R. Homer. 1981. Transport, Deposition and Control of
Heavy Metals in Highway Runoff. FHWA-WA-RD-39-io. University of Washington,
Department of Civil Engineering, Seattle, WA.
Washington State Department of Transportation, 1995, Highway Runoff Manual, Washington
State Department of Transportation, Olympia, Washington.
Welborn, C., and J. Veenhuis. 1987. Effects of Runoff Controls on the Quantity and Quality of
Urban Runoff in Two Locations in Austin, TX. USGS Water Resources Investigations Report
No. 87-4004. U.S. Geological Survey, Reston, VA.
Yousef, Y., M. Wanielista, H. Harper, D. Pearce, and R. Tolbert. 1985. Best Management
Practices: Removal of Highway Contaminants By Roadside Swales. University of Central
Florida and Florida Department of Transportation, Orlando, FL.
Yu, S., S. Barnes, and V. Gerde. 1993. Testing of Best Management Pi'acticesfor Controlling
Highway Runoff. FHWTA/VA-93-Ri6. Virginia Transportation Research Council,
Charlottesville, VA.
Information Resources
Maryland Department of the Environment (MDE). 2000. Maryland Stormwater Design
Manual. \v\v\v.mde.state.md.us/environment/wma/stormwatermanual. Accessed May 22,
2001.
Reeves, E. 1994. Performance and Condition of Biofilters in the Pacific Northwest. Watershed
Protection Techniques 1(3): 117-119.
January 2003 California Stormwater BMP Handbook 11 of 13
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TC-30 Vegetated Swale
Seattle Metro and Washington Department of Ecology. 1992. Biofiltration Swale Performance.
Recommendations and Design Considerations. Publication No. 657. Seattle Metro and
Washington Department of Ecology, Olympia, WA.
USEPA1993. Guidance Specifying Management Measures for Sources ofNonpoint Pollution in
Coastal Waters. EPA-84O-B-92-OO2. U.S. Environmental Protection Agency, Office of Water.
Washington, DC.
Watershed Management Institute (WMI). 1997. Operation, Maintenance, and Management of
Stormwater Management Systems. Prepared for U.S. Environmental Protection Agency, Office
of Water. Washington, DC, by the Watershed Management Institute, Ingleside, MD.
O
O
12 of 13 California Stormwater BMP Handbook January 2003
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Vegetated Swale TC-30
(a) Crow «•«««.!!» of *« ate with die** Jam.
x-
Notation:
L. =
Os - 0<?p«)i c( check <!*m fftj
S» » Bottom *4>e of sv*3l@
VV = Top «Wfl!i«f check d
Wj, = Bsttem aWih of eteefe dam <it>
^«<" - "•ilf* «f hwitontal to v«rti«rt
wtt 1
p«; (It'tC
vkw of *
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13 of 13
Bioretention TC-32
Description
Tlie bioretention best management practice (BMP) functions as a
soil and plant-based filtration device that removes pollutants
through a variety of physical, biological, and chemical treatment
processes. These facilities normally consist of a grass buffer
strip, sand bed, ponding area, organic layer or mulch layer,
planting soil, and plants. The runoffs velocity is reduced by
passing over or through buffer strip and subsequently distributed
evenly along a ponding area. Exfiltration of the stored water in
the bioretention area planting soil into the underlying soils
occurs over a period of days.
California Experience
None documented. Bioretention has been used as a stormwater
BMP since 1992. In addition to Prince George's County, MD and
Alexandria, VA, bioretention has been used successfully at urban
and suburban areas in Montgomery County, MD; Baltimore
County, MD; Chesterfield County, VA; Prince William County,
VA; Smith Mountain Lake State Park, VA; and Cary, NC.
Advantages
• Bioretention provides stormwater treatment that enhances
the quality of downstream water bodies by temporarily
storing runoff in the BMP and releasing it over a period of
four days to the receiving water (EPA, 1999).
• The vegetation provides shade and wind breaks, absorbs
noise, and improves an area's landscape.
Limitations
• The bioretention BMP is not recommended for areas with
slopes greater than 0.0% or where mature tree removal would
Design Considerations
• Soil for Infiltration
• Tributary Area
• Slope
• Aesthetics
• Environmental Side-effects
Targeted Constituents
0 Sediment
El Nutrients
El Trash
El Metals
El Bacteria
El Oil and Grease
El Organics
Legend (Removal Effectiveness)
• Low • High
A Medium
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Iof8
TC-32 Bioretention
Obe required since clogging may result, particularly if the BMP receives runoff with high
sediment loads (EPA, 1999).
• Bioretention is not a suitable BMP at locations where the water table is within 6 feet of the
ground surface and where the surrounding soil stratum is unstable.
• By design, bioretention BMPs have the potential to create very attractive habitats for
mosquitoes and other vectors because of highly organic, often heavily vegetated areas mixed
with shallow water.
• In cold climates the soil may freeze, preventing runoff from infiltrating into the planting soil.
Design and Sizing Guidelines
• The bioretention area should be sized to capture the design storm runoff.
• In areas where the native soil permeability is less than 0,5 in/hr an underdrain should be
provided.
• Recommended minimum dimensions are 15 feet by 40 feet, although the preferred width is
25 feet. Excavated depth should be 4 feet.
• Area should drain completely within 72 hours.
• Approximately i tree or shrub per 50 ft2 of bioretention area should be included. ,^N
• Cover area with about 3 inches of mulch.
Construction/Inspection Considerations
Bioretention area should not be established until contributing watershed is stabilized.
Performance
Bioretention removes stormwater pollutants through physical and biological processes,
including adsorption, filtration, plant uptake, microbial activity, decomposition, sedimentation
and volatilization (EPA, 1999). Adsorption is the process whereby particulate pollutants attach
to soil (e.g., clay) or vegetation surfaces. Adequate contact time between the surface and
pollutant must be provided for in the design of the system for this removal process to occur.
Thus, the infiltration rate of the soils must not exceed those specified in the design criteria or
pollutant removal may decrease. Pollutants removed by adsorption include metals, phosphorus,
and hydrocarbons. Filtration occurs as runoff passes through the bioretention area media, such
as the sand bed, ground cover, and planting soil.
Common particulates removed from stormwater include particulate organic matter,
phosphorus, and suspended solids. Biological processes that occur in wetlands result in
pollutant uptake by plants and microorganisms in the soil. Plant growth is sustained by the
uptake of nutrients from the soils, with woody plants locking up these nutrients through the
seasons. Microbial activity within the soil also contributes to the removal of nitrogen and
organic matter. Nitrogen is removed by nitrifying and denitrifying bacteria, while aerobic
bacteria are responsible for the decomposition of the organic matter. Microbial processes <<m\
require oxygen and can result in depleted oxygen levels if the bioretention area is not adequately N"*^
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Bioretention TC-32
aerated. Sedimentation occurs in the swale or ponding area as the velocity slows and solids fall
out of suspension.
The removal effectiveness of bioretention has been studied during field and laboratory studies
conducted by the University of Maryland (Davis et al, 1998). During these experiments,
synthetic stormwater runoff was pumped through several laboratory and field bioretention areas
to simulate typical storm events in Prince George's County, MD. Removal rates for heavy metals
and nutrients are shown in Table i.
Table 1 Laboratory and Estimated
Bioretention Davis et al. (1998);
PGDER(1993)
Pollutant
Total Phosphorus
Metals (Ca, Zn, Pb)
TKN
Total Suspended Solids
Organics
Bacteria
Removal Rate
70-83%
93-98%
68-80%
90%
90%
90%
Results for both the laboratory and field experiments were similar for each of the pollutants
analyzed. Doubling or halving the influent pollutant levels had little effect on the effluent
pollutants concentrations (Davis et al, 1998).
Hie microbial activity and plant uptake occurring in the bioreteution area will likely result in
higher removal rates than those determined for infiltration BMPs.
Siting Criteria
Bioretention BMPs are generally used to treat stormwater from impervious surfaces at
commercial, residential, and industrial areas (EPA, 1999). Implementation of bioretention for
stormwater management is ideal for median strips, parking lot islands, and swales. Moreover,
the runoff in these areas can be designed to either divert directly into the bioretention area or
convey into the bioretention area by a curb and gutter collection system.
The best location for bioretention areas is upland from inlets that receive sheet flow from graded
areas and at areas that will be excavated (EPA, 1999). In order to maximize treatment
effectiveness, the site must be graded in such a way that minimizes erosive conditions as sheet
flow is conveyed to the treatment area. Locations where a bioretention area can be readily
incorporated into the site plan without further environmental damage are preferred.
Furthermore, to effectively minimize sediment loading in the treatment area, bioretention only
should be used in stabilized drainage areas.
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TC-32 Bioretention
Additional Design Guidelines
The layout of the bioretention area is determined after site constraints such as location of
utilities, underlying soils, existing vegetation, and drainage are considered (EPA, 1999). Sites
with loamy sand soils are especially appropriate for bioretention because the excavated soil can
be backfilled and used as the planting soil, tlms eliminating the cost of importing planting soil.
The use of bioretention may not be feasible given an unstable surrounding soil stratum, soils
with clay content greater than 25 percent, a site with slopes greater than 20 percent, and/or a
site with mature trees that would be removed during construction of the BMP.
Bioretention can be designed to be off-line or on-line of the existing drainage system (EPA,
1999). The drainage area for a bioretention area should be between o.i and 0.4 hectares (0.25
and i.o acres). Larger drainage areas may require multiple bioretention areas. Furthermore,
the maximum drainage area for a bioretention area is determined by the expected rainfall
intensity and runoff rate. Stabilized areas may erode when velocities are greater than 5 feet per
second (1.5 meter per second). The designer should determine the potential for erosive
conditions at the site,
The size of the bioretention area, which is a function of the drainage area and the runoff
generated from the area is sized to capture the water quality volume.
Hie recommended minimum dimensions of the bioretention area are 15 feet (4.6 meters) wide
by 40 feet (12.2 meters) long, where the minimum width allows enough space for a dense,
randomly-distributed area of trees and shrubs to become established. Thus replicating a natural
forest and creating a microclimate, thereby enabling the bioretention area to tolerate the effects
of heat stress, acid rain, runoff pollutants, and insect and disease infestations which landscaped
areas in urban settings typically are unable to tolerate. The preferred width is 25 feet (7.6
meters), with a length of twice the width. Essentially, any facilities wider than 20 feet (6.1
meters) should be twice as long as they are wide, which promotes the distribution of flow and
decreases the chances of concentrated flow.
In order to provide adequate storage and prevent water from standing for excessive periods of
time the ponding depth of the bioretention area should not exceed 6 inches (15 centimeters).
Water should not be left to stand for more than 72 hours. A restriction on the type of plants that
can be used may be necessary due to some plants' water intolerance. Furthermore, if water is
left standing for longer than 72 hours mosquitoes and other insects may start to breed.
The appropriate planting soil should be backfilled into the excavated bioretention area. Planting
soils should be sandy loam, loamy sand, or loam texture with a clay content ranging from 10 to
25 percent.
Generally the soil should have infiltration rates greater than 0.5 inches (1.25 centimeters) per
hour, which is typical of sandy loams, loamy sands, or loams. The pH of the soil should range
between 5.5 and 6.5, where pollutants such as organic nitrogen and phosphorus can be adsorbed
by the soil and microbial activity can flourish. Additional requirements for the planting soil
include a 1.5 to 3 percent organic content and a maximum 500 ppm concentration of soluble
salts.
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Bioretention TC-32
Soil tests should be performed for every 500 cubic yards (382 cubic meters) of planting soil,
with the exception of pH and organic content tests, which are required only once per
bioretention area (EPA, 1999). Planting soil should be 4 inches (10.1 centimeters) deeper than
the bottom of the largest root ball and 4 feet (1.2 meters) altogether. This depth will provide
adequate soil for the plants' root systems to become established, prevent plant damage due to
severe wind, and provide adequate moisture capacity. Most sites will require excavation in
order to obtain the recommended depth.
Planting soil depths of greater than 4 feet (1.2 meters) may require additional construction
practices such as shoring measures (EPA, 1999). Planting soil should be placed in 18 inches or
greater lifts and lightly compacted until the desired depth is reached. Since high canopy trees
may be destroyed during maintenance the bioretention area should be vegetated to resemble a
terrestrial forest community ecosystem that is dominated by understory trees. Three species
each of both trees and shrubs are recommended to be planted at a rate of 2500 trees and shrubs
per hectare (1000 per acre). For instance, a 15 foot (4.6 meter) by 40 foot (12.2 meter)
bioretention area (600 square feet or 55.75 square meters) would require 14 trees and shrubs.
The shrub-to-tree ratio should be 2:1 to 3:1.
Trees and shrubs should be planted when conditions are favorable. Vegetation should be
watered at the end of each day for fourteen days following its planting. Plant species tolerant of
pollutant loads and varying wet and dry conditions should be used in the bioretention area.
The designer should assess aesthetics, site layout, and maintenance requirements when
selecting plant species. Adjacent non-native invasive species should be identified and the
designer should take measures, such as providing a soil breach to eliminate the threat of these
species invading the bioretention area. Regional landscaping manuals should be consulted to
ensure that the planting of the bioretention area meets the landscaping requirements
established by the local authorities. The designers should evaluate the best placement of
vegetation within the bioretention area. Plants should be placed at irregular intervals to
replicate a natural forest. Trees should be placed on the perimeter of the area to provide shade
and shelter from the wind. Trees and shrubs can be sheltered from damaging flows if they are
placed away from the path of the incoming runoff. In cold climates, species that are more
tolerant to cold winds, such as evergreens, should be placed in windier areas of the site.
Following placement of the trees and shrubs, the ground cover and/or mulch should be
established. Ground cover such as grasses or legumes can be planted at the beginning of the
growing season. Mulch should be placed immediately after trees and shrubs are planted. Two
to 3 inches (5 to 7.6 cm) of commercially-available fine shredded hardwood mulch or shredded
hardwood chips should be applied to the bioretention area to protect from erosion.
Maintenance
The primary maintenance requirement for bioretention areas is that of inspection and repair or
replacement of the treatment area's components. Generally, this involves nothing more than the
routine periodic maintenance that is required of any landscaped area. Plants that are
appropriate for the site, climatic, and watering conditions should be selected for use in the
bioretention cell. Appropriately selected plants will aide in reducing fertilizer, pesticide, water,
and overall maintenance requirements. Bioretention system components should blend over
time through plant and root growth, organic decomposition, and the development of a natural
January 2003 California Stormwater BMP Handbook 5 of 8
New Development and Redevelopment
www.cabmphandbooks.com
TC-32 Bioretention
Osoil horizon. Tliese biologic and physical processes over time will lengthen the facility's life span
and reduce the need for extensive maintenance.
Routine maintenance should include a biannual health evaluation of the trees and shrubs and
subsequent removal of any dead or diseased vegetation (EPA, 1999}. Diseased vegetation
should be treated as needed using preventative and low-toxic measures to the extent possible.
BMPs have the potential to create very attractive habitats for mosquitoes and other vectors
because of highly organic, often heavily vegetated areas mixed with shallow water. Routine
inspections for areas of standing water within the BMP and corrective measures to restore
proper infiltration rates are necessary to prevent creating mosquito and other vector habitat. In
addition, bioretention BMPs are susceptible to invasion by aggressive plant species such as
cattails, which increase the chances.of water standing and subsequent vector production if not
routinely maintained.
In order to maintain the treatment area's appearance it may be necessary to prune and weed.
Furthermore, mulch replacement is suggested when erosion is evident or when the site begins to
look unattractive. Specifically, the entire area may require mulch replacement every two to
three years, although spot mulching may be sufficient when there are random void areas. Mulch
replacement should be done prior to the start of the wet season.
New Jersey's Department of Environmental Protection states in their bioretention systems
standards that accumulated sediment and debris removal (especially at the inflow point) will
normally be the primary maintenance function. Other potential tasks include replacement of
dead vegetation, soil pH regulation, erosion repair at inflow points, mulch replenishment,
uuclogging the underdrain, and repairing overflow structures. There is also the possibility that
the cation exchange capacity of the soils in the cell will be significantly reduced over time.
Depending on pollutant loads, soils may need to be replaced within 5-10 years of construction
(LID, 2000).
Cost
Construction Cost
Construction cost estimates for a bioreteution area are slightly greater than those for the
required landscaping for a new development (EPA, 1999). A general rule of thumb (Coffman,
1999) is that residential bioretention areas average about $3 to $4 per square foot, depending on
soil conditions and the density and types of plants used. Commercial, industrial and
institutional site costs can range between $10 to $40 per square foot, based on the need for
control structures, curbing, storm drains and underdrains.
Retrofitting a site typically costs more, averaging $6,500 per bioretention area. The higher costs
are attributed to the demolition of existing concrete, asphalt, and existing structures and the
replacement of fill material \vith planting soil. Hie costs of retrofitting a commercial site in
Maryland, Kettering Development, with 15 bioretentiou areas were estimated at $111,600.
In any bioreteution area design, the cost of plants varies substantially and can account for a
significant portion of the expenditures. While these cost estimates are slightly greater than
those of typical landscaping treatment (due to the increased number of plantings, additional soil
excavation, backfill material, use of underdraws etc.), those landscaping expenses that would be
required regardless of the bioretention installation should be subtracted when determining the
net cost.
6 of 8 California Storrnwater BMP Handbook January 2003
New Development and Redevelopment
www.cabmphandbooks.com
Bioretention TC-32
Perhaps of most importance, however, the cost savings compared to the use of traditional
structural stormwater conveyance systems makes bioretentiou areas quite attractive financially.
For example, the use of bioretentiou can decrease the cost required for constructing stormwater
conveyance systems at a site. A medical office building in Maryland was able to reduce the
amount of storm drain pipe that was needed from 800 to 230 feet - a cost savings of $24,000
(PGDER, 1993). And a new residential development spent a total of approximately $100,000
using bioreteiition cells on each lot instead of nearly $400,000 for the traditional stormwater
ponds that were originally planned (Rappahauock, ). Also, in residential areas, stormwater
management controls become a part of each property owner's landscape, reducing the public
burden to maintain large centralized facilities.
Maintenance Cost
The operation and maintenance costs for a bioretention facility will be comparable to those of
typical landscaping required for a site. Costs beyond the normal landscaping fees will include
the cost for testing the soils and may include costs for a sand bed and planting soil.
References and Sources of Additional Information
Coffman, L.S., R. Goo and R. Frederick, 1999: Low impact development: an innovative
alternative approach to stormwater management. Proceedings of the 26th Annual Water
Resources Planning and Management Conference ASCE, June 6-9, Tempe, Arizona.
Davis, A.P., Shokouliian, M., Sharma, H. and Minami, C., "Laboratory Study of Biological
Retention (Bioretention) for Urban Stormwater Management," Water Environ. Res., 73(1), 5-14
(2001).
Davis, A.P., Shokouliian, M., Sharma, H., Minami, C., and Winogradoff, D. "Water Quality
Improvement through Bioretention: Lead, Copper, and Zinc," Water Environ. Res., accepted for
publication, August 2002.
Kim, H., Seagren, E.A., and Davis, A.P., "Engineered Bioretention for Removal of Nitrate from
Stormwater Runoff," WEFTECsooo Conference Proceedings on CDROM Research
Symposium, Nitrogen Removal, Session 19, Anaheim CA, October 2000.
Hsieh, C.-h. and Davis, A.P. "Engineering Bioretention for Treatment of Urban Stormwater
Runoff," Watersheds 2002, Proceedings on CDROM Research Symposium, Session 15, Ft.
Lauderdale, FL, Feb. 2002.
Prince George's County Department of Environmental Resources (PGDER), 1993. Design
Manual for Use of Bioretention in Stormwater Management. Division of Environmental
Management, Watershed Protection Branch. Laudover, MD.
U.S. EPA Office of Water, 1999. Stormwater Technology Fact Sheet: Bioretention. EPA 832-F-
99-012.
Weinstein, N. Davis, A.P. and Veeramachaneni, R. "Low Impact Development (LID) Stormwater
Management Approach for the Control of Diffuse Pollution from Urban Roadways," §th
International Conference Dijfiise/Nonpoint Pollution and Watershed Management
Proceedings, C.S. Melching and Erare Alp, Eds. 2001 International Water Association
January 2003 California Stormwater BMP Handbook 7 of 8
New Development and Redevelopment
www.cabmphandbooks.com
TC-32 Bioretention
CURB STOPS-
PARKING tOT SHEET HOW
i i { -i i
- STONE DIAPHRAGM
GRASS FILTER
STRIP« ^ ^ VVV ^-> ¥ V- V tf V i- ^ * * * * t V * •*•
*-*.ft ft.*.*...* *.*J» t.*.fc.§.*Jt.*.t*.«».-».*.*..»..*:*-**.* ft.*-*.*.*..*.*.*.*
OVERFLOW
"CATCH BASIN'
UNOERORAIN COLLECTION SYSTEM
GRAVEL CURTAIN
DRAIN OVERFLOW
PLAN VIEW
6" PONDING
2"-3" MULCHJ
4'PI ANTING SOIL
5" PERFORATED
PIPE IN 8" BRAVI-L
. JACKET
-FILTER FABRIC
TYPICAL SECTION PROFILE
Schematic of a Bioretention Facility (MDE, 2000)
8 of 8 California Stormwater BMP Handbook
New Development and Redevelopment
vvM/w.cabmphandbooks.com
January 2003
Drain Inserts MP-52
Description
Drain inserts are manufactured filters or fabric placed in a drop
inlet to remove sediment and debris. There are a multitude of
inserts of various shapes and configurations, typically falling into
one of three different groups: socks, boxes, and trays. The sock
consists of a fabric, usually constructed of polypropylene. The
fabric may be attached to a frame or the grate of the inlet holds
the sock. Socks are meant for vertical (drop) inlets. Boxes are
constructed of plastic or wire mesh. Typically a polypropylene
"bag" is placed in the wire mesh box. The bag takes the form of
the box. Most box products are one box; that is, the setting area
and filtration through media occur in the same box. Some
products consist of one or more trays or mesh grates. The trays
may hold different types of media. Filtration media vary by
manufacturer. Types include polypropylene, porous polymer,
treated cellulose, and activated carbon.
California Experience
The number of installations is unknown but likely exceeds a
thousand. Some users have reported that these systems require
considerable maintenance to prevent plugging and bypass.
Advantages
• Does not require additional space as inserts as the drain
inlets are already a component of the standard drainage
systems.
• Easy access for inspection and maintenance.
• As there is no standing water, there is little concern for
mosquito breeding.
• A relatively inexpensive retrofit option.
Limitations
Performance is likely significantly less than treatment systems
that are located at the end of the drainage system such as ponds
and vaults. Usually not suitable for large areas or areas with
trash or leaves than can plug the insert.
Design and Sizing Guidelines
Refer to manufacturer's guidelines. Drain inserts come any
many configurations but can be placed into three general groups:
socks, boxes, and trays. The sock consists of a fabric, usually
constructed of polypropylene. The fabric may be attached to a
frame or the grate of the inlet holds the sock. Socks are meant
for vertical (drop) inlets. Boxes are constructed of plastic or wire
mesh. Typically a polypropylene "bag" is placed in the wire mesh
box. The bag takes the form of the box. Most box products are
Design Considerations
• Use with other BMPs
• Fit and Seal Capacity within Inlet
Targeted Constituents
/ Sediment
</ Nutrients
/ Trash
V Metals
Bacteria
/ Oil and Grease
•S Organics
Removal Effectiveness
See New Development and
Redevelopment Handbook-Section 5.
California
Storntwater
Quality
.,.,- Association
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
www.cabmphandbooks.com
lof 3
MP-52 Drain Inserts
one box; that is, the setting area and filtration through media occurs in the same box. One
manufacturer has a double-box, Stormwater enters the first box where setting occurs. The
stormwater flows into the second box where the filter media is located. Some products consist
of one or more trays or mesh grates. The trays can hold different types of media. Filtration
media vary with the manufacturer: types include polypropylene, porous polymer, treated
cellulose, and activated carbon.
Construction/Inspection Considerations
Be certain that installation is done in a manner that makes certain that the stormwater enters
the unit and does not leak around the perimeter. Leakage between the frame of the insert and
the frame of the drain inlet can easily occur with vertical (drop) inlets.
Performance
Few products have performance data collected under field conditions.
Siting Criteria
It is recommended that inserts be used only for retrofit situations or as pretreatment where
other treatment BMPs presented in this section area used.
Additional Design Guidelines
Follow guidelines provided by individual manufacturers.
Maintenance
Likely require frequent maintenance, on the order of several times per year.
Cost
• The initial cost of individual inserts ranges from less than $100 to about $2,000. The cost of
using multiple units in curb inlet drains varies with the size of the inlet.
• The low cost of inserts may tend to favor the use of these systems over other, more effective
treatment BMPs. However, the low cost of each unit may be offset by the number of units
that are required, more frequent maintenance, and the shorter structural life (and therefore
replacement).
References and Sources of Additional Information
Hrachovec, R., and G. Minton, 2001, Field testing of a sock-type catch basin insert, Planet CPR,
Seattle, Washington
Interagency Catch Basin Insert Committee, Evaluation of Commercially-Available Catch Basin
Inserts for the Treatment of Stormwater Runoff from Developed Sites, 1995
Larry Walker Associates, June 1998, NDMP Inlet/In- Line Control Measure Study Report
Manufacturers literature
Santa Monica (City), Santa Monica Bay Municipal Stormwater/Urban Runoff Project -
Evaluation of Potential Catch basin Retrofits, Woodward Clyde, September 24, 1998
2 of 3 California Stormwater BMP Handbook January 2003
New Development and Redevelopment
www.cabmphandbooks.com
Drain Inserts MP-52
Woodward Clyde, June 11,1996, Parking Lot Monitoring Report, Santa Clara Valley Nonpoint
Source Pollution Control Program.
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
www.cabmphandbooks.com
3 of 3
Multiple System Fact Sheet TC-60
Description
A multiple treatment system uses two or more BMPs in series.
Some examples of multiple systems include: settling basin
combined with a sand filter; settling basin or biofilter combined
with an infiltration basin or trench; extended detention zone on a
wet pond.
California Experience
The research wetlands at Fremont, California are a combination
of wet ponds, wetlands, and vegetated controls.
Advantages
• BMPs that are less sensitive to high pollutant loadings,
especially solids, can be used to pretreat runoff for sand
filters and infiltration devices where the potential for
clogging exists.
• BMPs which target different constituents can be combined to
provide treatment for all constituents of concern.
• BMPs which use different removal processes (sedimentation,
filtration, biological uptake) can be combined to improve the
overall removal efficiency for a given constituent.
• BMPs in series can provide redundancy and reduce the
likelihood of total system failure.
Limitations
• Capital costs of multiple systems are higher than for single
devices.
• Space requirements are greater than that required for a
single technology.
Design and Sizing Guidelines
Refer to individual treatment control BMP fact sheets.
Performance
• Be aware that placing multiple BMPs in series does not
necessarily result in combined cumulative increased
performance. This is because the first BMP may already
achieve part of the gain normally achieved by the second
BMP. On the other hand, picking the right combination can
often help optimize performance of the second BMP since the
influent to the second BMP is of more consistent water quality,
and thus more consistent performance, thereby allowing the
BMP to achieve its highest performance.
Design Considerations
• Area Required
• Slope
» Water Availability
• Hydraulic Head
• Environmental Side-effects
Targeted Constituents
0 Sediment I
0 Nutrients <
0 Trash I
0 Metals i
0 Bacteria I
0 Oil and Grease i
0 Organics i
Legend (Removal Effectiveness)
• Low » High
A Medium
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
www.cabmphandbooks.com
1 of 2
TC-60 Multiple System Fact Sheet
• When addressing multiple constituents through multiple BMPs, one BMP may optimize
removal of a particular constituent, while another BMP optimizes removal of a different
constituent or set of constituents. Therefore, selecting the right combination of BMPs can
be very constructive in collectively removing multiple constituents.
Siting Criteria
Refer to individual treatment control BMP fact sheets.
Additional Design Guidelines
• When using two or more BMPs in series, it may be possible to reduce the size of BMPs.
• Existing pretreatment requirements may be able to be avoided when using some BMP
combinations.
Maintenance
Refer to individual treatment control BMP fact sheets.
Cost
Refer to individual treatment control BMP fact sheets.
Resources and Sources of Additional Information
Refer to individual treatment control BMP fact sheets.o
2 of 2 California Stormwater BMP Handbook January 2003
New Development and Redevelopment
www.cabmphandbooks.com
Attachment 12
STORM WATER MANAGEMENT PLAN
GREEN DRAGON COLONIAL VILLAGE
ATTACHMENT 12: BIORETENTION SIZING CALCS.
Please see attached.
STORM WATER MANAGEMENT PLAN
GREEN DRAGOM COLONIAL VILLAGE
BIORETENTION SIZING CALCULATIONS:
Sub-Basin
A1
A2
A3
A4
B1
B2
B3
B4
B5
B6
B7
B8
A(ac.)
0.42
0.57
0.23
0.15
0.94
0.21
0.15
0.14
0.05
0.07
0.05
0.1
C
0.82
0.82
0.82
0.82
0.82
0.82
0.82
0.82
0.82
0.82
0.82
0.82
1 (in./hr.)
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
Q (treat) = CIA
0.07
0.09
0.04
0.02
0.15
0.03
0.02
0.02
0.01
0.01
0.01
0.02
Required Surface Area
(sq.-ft.) = C*A*4%
600
814
329
214
1343
300
214
200
71
100
71
143
Provided Surface Area (sq.
ft.)
2740
1630
n/a
n/a
2500
n/a
360
310
100
100
340
150
G:\081240\SWMP\SWMP-GREEN DRAGON091105\Bioretention.xls
Part / GISB-24-24-12
24
24
TOP VIEW
FLOW SCHEMATIC
STORM BOOM
SKIMMER
THROAT
TURBULENCE
DEFLECTOR
Flow Specifications
Description
of filter
opening
SkimmerprotectedBy— Pass
Coarse Screen-3/4" x 1-3/4"stainless stoolflattened expanded
Medium Screen1Ox1O meshstainless steel
Fine screen14 x 13 meshstain/ass steel
Percent
Open
aMrfoiSmnOtmnbM
100X
62X
56X
68X
Total
Square
Inches
per Unit
72.0
72.0
143.5
144.0
Square
Inches
of Total
Unobstructed
Openings
72.0
44.6
80.4
97.9
Flow
Rate
(Cubic
Feet per
Second)
2.9 cfs
2.1 cfs
4.3 cfs
5.8 cfs
THROAT FLOW RATE TREATED FLOW RATE
Total:4.4cfs Total: 12.2cfs
FLOW RATES BASED ON UNOBSTRUCTED OPENINGS
GRATE
SIDE VIEW
SKIMMER PROTECTED
BYPASS
COARSE SCREEN
FINE SCREEN
1 '..*' «'* .' -.-.*• .• •-•
-.':*•*
' • •* • " .
' .'• : ••*<«« «
<•' .' . - •'
• • : .* «»• .' •".
* • •»«
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_•''*"*
4. ' - .
1 *
\&BJI\nf j
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••.*«'••'.. '. "« •'* ' •- • ' *
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'••- . '• ' ;
*.*' *'.'
>* \«
^ : " .*
**•* ' *•.. ' «
•. * • **• * ' '.
CONCRETE STRUCTURE
BOX MANUFACTURED FROM
MARINE GRADE FIBERGLASS & GEL
COATED FOR UV PROTECTION
5 YEAR MANUFACTURERS WARRANTY
PATENTED
•ALL FILTER SCREENS ARE STAINLESS STEEL
REMOVE GRATE
INSERT GISB
REINSTALL GRATE
EXCLUSIVE CALIFORNIA DISTRIBUTOR:
BIO CLEAN/ ENVIRONMENTAL. SERVICE
F>.O. BOX 369. OCEANSIDE. CA. 92O-4-9
TEL.. 7GO—+33—7G+O F~AX:7SO — '433 — 31
Email: lnfo<9t>locloananvlronmantal.not
SMWBEF QUHJTf PRODUCTS MS BOLT FOR EfSf CLEWING AND M£
DESKNEO TO BE PtWNEM ItMSmKrUK HID SHOUU)
UST FOR OECHXS.
793 CLEARLAKE RD. SUITE #2COCOA FL. 32023
TEL. 321 —837—7332 FAX 32t—O37—7SS4
GRATE INLET SKIMMER BOX
GISB—24—24— 12
DATE: 04-/1 2/O-*
DRAFTER: N.R.B.
SCAL.E.-SF — IS
UNITS —INCHES
Grate Inlet Skimmer Box - Removal Efficiencies
Numeric Reductions (mg/L)
Location
Site Evaluation - Reedy Creek
Creech Engineering Report
Witman's Pond
UC Irvine
Total Suspended Solids mg/L
Inlet
978
Outlet
329
Removal
Efficiency
74%
73%
66%
53%
Total Phosphorus mg/L
Inlet
18.6
Outlet
0.452
Removal
Efficiency
57%
79%
98%
Total Nitrogen mg/L
Inlet
24.3
48.08
Outlet
10.4
9.86
Removal
Efficiency
57%
79%
79%
Location
UC Irvine
Longo Toyota
Zinc mg/L
Inlet
13.7
Outlet
0.73
Removal
Efficiency
11%
95%
Lead mg/L
Inlet
1.5
Outlet
0.2
Removal
Efficiency
99%
87%
Copper mg/L
Inlet
1.9
Outlet
0.1
Removal
Efficiency
95%
Location
Site Evaluation - Reedy Creek
UC Irvine
Ammonia, Salicylate mg/L
Inlet
0.38
Outlet
0.23
Removal
Efficiency
39%
Fecal Collform CFU/100 mL
Inlet Outlet
Removal
Efficiency
33%
Cadmium
Inlet Outlet
Removal
Efficiency
94%
Location
Site Evaluation - Reedy Creek
Witman's Pond
UC Irvine
Longo Toyota
Hydrocarbons mg/L
Inlet
110
199
Outlet
so
10.43
Removal
Efficiency
54%
55%
90%
95%
COD (mg/L)
Inlet
2670
Outlet
1490
Removal
Efficiency
44%
Reedy Creek - Site Evaluation of a Grate Inlet Skimmer Box for Debris, Sediment, and Oil & Grease Removal -1999 - Independent Test
Creech Engineering Report • Pollutant Removal Testing for a Grate Inlet Skimmer Box - 2001
Witman's Pond - Restoration Project - Massachusetts Dept of Environmental Management -1998 - Independent Test
UC Irvine - Optimization of Stormwater Filtration at the Urban/Watershed Interface - Dept of Environmental Health - 2005 - Independent Test
Longo Toyota - Field Test - City of El Monte - 2002 - Independent Test
B N
Environmental Laboratories, Inc.
10926 Rush St, Suite A-168 • South El MorrtjgCA 91733 * Tel: (626) 575-5137 • Fax: (626) 575-7467
Client: CITY OF EL MONTE
PUBLIC WORKS/ENGINEERING DEPARTMENT
1133 3 Valley Boulevard
ElMonte,CA91731-3293
Report based on Analyses Results.
The city of El Monte provided ABN Environmental Laboratories, Inc. with four runoff samples
which were collected from Longo Toyota. Only one sample was collected before filtration and three
samples were collected after filtration. Three samples (after filtration) were collected on three separate
dates. All four samples were tested for metals, oil & grease, and MBAS (soap )
Based on the analyses results, the following can be deduced:
The filtration is efficient in retaining the tested metals as well as oil & grease. However, filtration is
unable to retain MBAS (soap) as indicated by the test results. This report is prepared based on limited
runoff samples.
Respectfully submitted,
-
Tredrick Bet-Pera, Ph. D.
Laboratory Director
Jacob (Hacop) Nercessian
Technical Director
LAB TESr RESULTS-RUNOFF WATER SAMPLES
COLLECTED AT LONGO TOYOTA
BETWEEN 09/23/02 AND 11/07/02
(BIO CLEAN FILTERS)
TESTING BY ABN ENV. LABS,, SOUTH EL MONTE, CA
No.
1
2
3
A
5
6
7
8
9
POLLUTANT
OtLftGREASe
SOAP
CHROMIUM
LEAD
COPPER
IRON
ALUMINUM
ZINC
NtCKEL
DETECTION
LIMIT
«**2.70
17.00
0.06
0.10
<WJ6
0.05
0.20
a 10
0.10
TE8T1
NOHLT6R
"f
199.00
102.00
0.47
1.50
1.90
218.00
103.00
13.70
0.70
TEST 2
AFTER! WEEK WALTER
ra?fl
<2J
166,00
<O.Q5
0.40
0.13
3.70
1.90
1.10
0.30
TEST 3
AFTB* 3 WEEKS WRLTER
mgfl
20.00
161JM
<0.05
<aio
0^6
1.63
120
0.34
<0.10
TB8T4
AFTER 5 WEEKS WWLTER
ran
B.QO
106.00
<0.06
<0.10
0.11
1.25
0.80
0.76
0.16
STORM WATER FILTRATION SYSTEMS
(760)433-7640 FAX (760) 433-3176
SAIES A SSW7OF A INFORMATION
STORM WATER MANAGEMENT PLAN
GREEN DRAGON COLONIAL VILLAGE
APPENDIX J: MAP EXHIBITS
Please see attached.
STORM WATER MANAGEMENT PLAN
GREEN DRAGOM COLONIAL VILLAGE
BIORETENTION SIZING CALCULATIONS:
Sub-Basin
A1
A2
A3
A4
B1
B2
B3
B4
B5
B6
B7
B8
A(ac.)
0.42
0.57
0.23
0.15
0.94
0.21
0.15
0.14
0.05
0.07
0.05
0.1
C
0.82
0.82
0.82
0.82
0.82
0.82
0.82
0.82
0.82
0.82
0.82
0.82
1 (in./hr.)
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
Q (treat) = CIA
0.07
0.09
0.04
0.02
0.15
0.03
0.02
0.02
0.01
0.01
0.01
0.02
Required Surface Area
(sq.-ft.) = C*A*4%
600
814
329
214
1343
300
214
200
71
100
71
143
Provided Surface Area (sq.
ft)
2740
1630
n/a
n/a
2500
n/a
360
310
100
100
340
150
G:\081240\SWMP-GREEN DRAGON090824\Bioretention.xls
FLUME FILTER
A Stormwater Pollution Control Device
FLUME FILTER -
Boom Box Type
Captures Trash & Litter
Captures Hydrocarbons
Captures Grass & Leaves
Various Sizes Available
Custom Configurations
Easy to Maintain
Heavy Duty Construction
FLUME FILTER
Trash Type
Easy Access for Cleaning
Durable- Fiberglass for Strength
Storm Booms - For Filtering Hydrocarbons
Mesh Screen - For Filtering out Sediments
Diamond Plate for Strength and Filtering
Large Debris
BIO CLEAN
ENVIRONMENTAL SERVICES, INC
P O Box 869, Oceanside, CA 92049
(760)433-7640 • Fax (760) 433-3176
www.biocleanenvironmental.net "The Stormwater Standard"
Bio Clean Flume Filter - Removal Efficiencies
Numeric Reductions (mg/L)
I Total Suspended Solids mg/Ll Total Phosphorus mg/L Nitrate-N mg/L
Location Inlet Outlet
Removal
Efficiency Inlet Outlet
Removal
Efficiency B Inlet Outlet
Removal
Efficiency
Waves Environmental 73 51.6 29%5.12 5.42 -6%5.43 5.02 8%
Zinc mg/L Lead mg/L Copper mg/L
Location Inlet Outlet
Removal
Efficiency B Inlet Outlet
Removal
Efficiency B Inlet Outlet
Removal
Efficiency
Waves Environmental 1.33 1.28 4%0.201 0.17 15%0.951 0.93 2%
Silver mg/L Mercury mg/L Cadmium mg/L
Location Inlet Outlet
Removal
Efficiency Inlet Outlet
Removal
Efficiency B Inlet Outlet
Removal
Efficiency
Waves Environmental 0.04 0.03 25%'0 0.009 0.007 22%0.584 0.55 6%
Oil & Grease mg/L TPH (mg/L)
Location Inlet Outlet
Removal
Efficiency Inlet Outlet
Removal
Efficiency |
Waves Environmental 360 62.2 83%223 29.57 87%
Waves Environmental - Bio Clean Flume Filter Pollutant Removal Testing - 2007
SPECIFICATIONS
Flume Filter/ Boom Box
1. Specifications
Coverage: The Flume Filter provides full coverage of flume such that all influent, at rated flows, is conveyed to the filter.
The filter will retain all windblown and swept debris entering the flume or channel.
Non-Corrosive Materials: All components of the filter system, including mounting hardware, fasteners, support
brackets, filtration material, and support frame are constructed of non-corrosive materials: 316 stainless steel, aluminum
and starboard. Fasteners are stainless steel. Primary filter screen is W flattened expanded aluminum metal and 316
stainless steel welded 10 x 10 mesh screen.
Durability: The Flume Filter is constructed of an all starboard frame and stainless steel screens backed by 3A" flattened
expanded aluminum metal. Filter (excluding oil absorbent media) and support structures are of proven durability, with an
expected service life of 10 to 15 years. The filter and mounting structures are of sufficient strength to support water,
sediment, and debris loads when full without breaking, or tearing. All filters are warranted for a minimum of five (5) years.
Oil Absorbent Media: The Flume Filter is fitted with an absorbent media for removal of petroleum hydrocarbons from
influent, and so placed in the filter assembly to treat influent at rated flow. Absorbent media is easily replaceable in the
filter, without the necessity of removing fixed mounting brackets or mounting hardware. Hydrocarbon media is placed in
the bottom of the filter unit. The hydrocarbon media encompasses the total bottom area of the unit and lie horizontal for
maximum absorption. No polypropylene, monofilament netting or fabrics shall be used in the product.
Overflow Protection: The Flume Filter is designed so that it does not inhibit storm flows entering the flume/channel or
obstruct flow through the flume/channel during peak storm flows.
s^^Jter Bypass: Water will not bypass the filter at low flows, nor bypass through contact surfaces(hydrocarbon boom) at
low flows.
Pollutant Removal Efficiency: The Flume Filter is designed to capture high levels of trash and litter, grass and foliage,
sediments, hydrocarbons, grease and oil. The filter has a multistage filtration system, which incorporates durable screen
and steel mesh filtering.
II. Installation
Installation: The Flume Filter will be securely installed within the flume/channel, with contact surfaces sufficiently joined
together so that no filter bypass can occur at low flow. All anchoring devices and fasteners are installed within the interior
of the flume/channel.
Installation Notes:
1 . Bio Clean Environmental Services, Inc. Flume Filter shall be installed pursuant to the manufacturer's
recommendations and the details on this sheet.
2. Flume Filter shall provide coverage of entire flume/channel opening to direct all flow through the filter.
3. Attachments to flume/channel walls shall be made of non-corrosive hardware.
4. Place filter in flume/channel, attach the scribe strips to the filter with pop rivets, and then attach the same scribe strips
with concrete drive pins to the side of the flume/channel.
5. Place hydrocarbon booms in bottom of unit in a horizontal manner.
6. Close lid and latch when applicable.
"I. Maintenance
^Maintenance: The Flume filter is readily serviceable without removing. Debris accumulated in front of the filter should be
swept up and disposed of appropriately. The filter's front screen should be inspected and cleaned if necessary to maintain
proper flow through the filter. This screen can easily be cleaned by brushing of its surface with a broom. To service the
media booms, open the top hatch, clean and inspect and/or replace hydrocarbon booms.
Maintenance Notes:
1. Bio Clean Environmental Services, Inc. recommends cleaning and debris removal maintenance a minimum of four
times per year, and replacement of hydrocarbon booms a minimum of twice per year.
B ,. Following maintenance and/or inspection, the maintenance operator shall prepare a maintenance/inspection record.
The record shall include any maintenance activities performed, amount and description of debris collected, and
condition of filter.
3. The owner shall retain the maintenance/inspection record for a minimum of five years from the date of maintenance.
These records shall be made available to the governing municipality for inspection upon request at any time.
4. Remove all trash, debris, organics, and sediments collected in front of the filter, then open the lid and remove trash
and debris within the filter.
5. Evaluation of the hydrocarbon boom shall be performed at each cleaning. If the boom is filled with hydrocarbons and
oils it should be replaced. Remove hydrocarbon booms and replace.
6. Transport all debris, trash, organics and sediments to approved facility for disposal in accordance with local and state
requirements.
7. The hydrocarbon boom is classified as hazardous material and will have to be picked up and disposed of as
hazardous waste. Hazardous material can only be handled by a certified hazardous waste trained person (minimum
24-hour hazwoper).
jHk m g*± f* 1 1? A ikf 1^ P O Box 869, Oceanside, CA 92049
01%jP %»fcBC^%Ill jijB (760433-7640 Fax (760)433-3176
ENVIRONMENTAL SERVICES, INC.HI^^ www.biocleanenvironmental.net
Attachment 13
STORM WATER MANAGEMENT PLAN
GREEN DRAGON COLONIAL VILLAGE
ATTACHMENT 13: APPLICABLE MANUFACTURER'S BMP INFORMATION
Please see attached.
Attachment 14
Section 6
Long-term Maintenance of BMPs
6.1 Introduction
The long-term performance of BMPs hinges on ongoing and proper maintenance. In order for
this to occur detailed maintenance plans are needed that include specific maintenance activities
and frequencies for each type of BMP. In addition, these should include indicators for assessing
when "as needed" maintenance activities are required. The fact sheets included in this volume
contain the basic information needed to develop these maintenance plans, but municipalities
and other regulatory agencies also need to identify the responsible party and potentially to
address funding requirements. The following discussion is based primarily on data developed
by Horner et al. (1994) and information available at http://www.stormwatercenter.net/
6.2 Critical Regulatory Components
Critical regulatory components identified by Horner et al. (1994) include:
• Regulations should officially designate a responsible party, frequently the development site
owner, to have ultimate responsibility for the continued maintenance of stormwater
facilities. This official designation provides the opportunity for appropriate preparation and
budgeting prior to actually assuming responsibilities. It also facilitates enforcement or other
legal remedies necessary to address compliance or performance problems once the facility
has been constructed.
• Regulations should clearly state the inspection and maintenance requirements. Inspection
and maintenance requirements should also comply with all applicable statutes and be based
on the needs and priorities of the individual measure or facility. A clear presentation will
help owners and builders comply and inspectors enforce requirements.
• Regulations should contain comprehensive requirements for documenting and detailing
maintenance. A facility operation and maintenance manual should be prepared containing
accurate and comprehensive drawings or plans of the completed facility and detailed
descriptions and schedules of inspection and maintenance.
• The regulations should delineate the procedure for maintenance noncompliance. This
process should provide informal, discretionary measures to deal with periodic, inadvertent
noncompliance and formal and severe measures to address chronic noncompliance or
performance problems. In either case, the primary goal of enforcement is to maintain an
effective BMP - the enforcement action should not become an end in itself.
• Regulations should also address the possibility of total default by the owner or builder by
providing a way to complete construction and continue maintenance. For example, the
public might assume maintenance responsibility. If so, the designated public agency must
be alerted and possess the necessary staffing, equipment, expertise, and funding to assume
this responsibility. Default can be addressed through bonds and other performance
January 2003 California Stormwater BMP Handbook 6-1
New Development and Redevelopment
www.cabmphandbooks.com
Section 6
Long-term Maintenance ofBMPs
guarantees obtained before the project is approved and construction begins. These bonds
can then be used to fund the necessary maintenance activities.
• The regulations must recognize that adequate and secure funding is needed for facility
inspection and maintenance and provide for such funding.
6.3 Enforcement Options
A public agency will sometimes need to compel those responsible for facility construction or
maintenance to fulfill their obligations. Therefore, the maintenance program must have
enforcement options for quick corrective action. Rather than a single enforcement measure, the
program should have a variety of techniques, each with its own degree of formality and legal
weight. The inspection program should provide for nonconforming performance and even
default, and contain suitable means to address all stages.
Prior to receiving construction approval, the developer or builder can be forced to provide
performance guarantees. The public agency overseeing the construction can use these
guarantees, usually a performance bond or other surety in an amount equal to some fraction of
the facility's construction cost, to fund maintenance activities.
Enforcement of maintenance requirements can be accomplished through a stormwater
maintenance agreement, which is a formal contract between a local government and a property
owner designed to guarantee that specific maintenance functions are performed in exchange for
permission to develop that properly (http://www.storniwatercenter.net/). Local governments
benefit from these agreements in that responsibility for regular maintenance of the BMPs can be
placed upon the property owner or other legally recognized party, allowing agency staff more
time for plan review and inspection.
6.4 Maintenance Agreements
Maintenance agreements can be an effective tool for ensuring long-term maintenance of on-site
BMPs. The most important aspect of creating these maintenance agreements is to clearly define
the responsibilities of each party entering into the agreement. Basic language that should be
incorporated into an agreement includes the following:
1. Performance of Routine Maintenance
Local governments often find it easier to have a property owner perform all maintenance
according to the requirements of a Design Manual. Other communities require that property
owners do aesthetic maintenance (i.e., mowing, vegetation removal) and implement pollution
prevention plans, but elect to perform structural maintenance and sediment removal
themselves.
2. Maintenance Schedules
Maintenance requirements may vary, but usually governments require that all BMP owners
perform at least an annual inspection and document the maintenance and repairs performed.
An annual report must then be submitted to the government, who may then choose to perform
an inspection of the facility.
6-2 California Stormwater BMP Handbook January 2003
New Development and Redevelopment
www.cabmphandbooks.com
Section 6
Long-term Maintenance of BMPs
3. Inspection Requirements
Local governments may obligate themselves to perform an annual inspection of a BMP, or may
choose to inspect when deemed necessary instead. Local governments may also wish to include
language allowing maintenance requirements to be increased if deemed necessary to ensure
proper functioning of the BMP.
4. Access to BMPs
The agreement should grant permission to a local government or its authorized agent to enter
onto property to inspect BMPs. If deficiencies are noted, the government should then provide a
copy of the inspection report to the property owner and provide a timeline for repair of these
deficiencies.
5. Failure to Maintain
In the maintenance agreement, the government should repeat the steps available for addressing
a failure to maintain situation. Language allowing access to BMPs cited as not properly
maintained is essential, along with the right to charge any costs for repairs back to the property
owner. The government may wish to include deadlines for repayment of maintenance costs, and
provide for liens against property up to the cost of the maintenance plus interest.
6. Recording Of The Maintenance Agreement
An important aspect to the recording of the maintenance agreement is that the agreement be
recorded into local deed records. This helps ensure that the maintenance agreement is bound to
the property in perpetuity.
Finally, some communities elect to include easement requirements into their maintenance
agreements. While easement agreements are often secured through a separate legal agreement,
recording public access easements for maintenance in a maintenance agreement reinforces a
local government's right to enter and inspect a BMP.
Examples of maintenance agreements include several available on the web at:
http: //www.stormwatercenter.net/
6.5 Public Funding Sources
If local agencies are willing to assume responsibility for stormwater BMPs, it is essential to
identify the long-term funding sources. Several of these are described below:
General Tax Revenues
Tax revenues are an obvious source of funding, particularly for the long-term inspection and
maintenance of existing runoff and drainage facilities. The benefits and protection to the public
from continued safe and effective operation of the facility justifies using revenues from general
funds.
To use tax revenues, particularly from a general fund, the inspection and maintenance program
must annually compete with all other programs included in the government's annual operating
budget. This inconsistent and unreliable funding makes securing a long-term financial
January 2003 California Stormwater BMP Handbook 6-3
New Development and Redevelopment
www.cabmphandbooks.com
Section 6
Long-term Maintenance of BMPs
commitment to inspection and maintenance difficult and subject to political pressures.
Nevertheless, tax revenues remain a popular funding source because the collection and
disbursement system is already in place and familiar.
Utility Charges
Using utility charges to fund inspection and maintenance is a somewhat recent application of an
already established financing technique. In addition, several municipalities and counties
throughout the country have runoff management, drainage, and flood control authorities or
districts to provide residents with runoff related services.
Using utility charge financing has several advantages. By addressing only runoff needs and
benefits, utility funding avoids competing with other programs and needs. Utility funding also
demonstrates a direct link between the funding and the services it provides. This approach can
require an entirely new operating system and organization that needs legal authorization to
exist, operate, and assess charges. The effort required to create such an entity can deter many,
although the continued success of established authorities and growth of new ones have done
much to allay concerns over the effort required.
In a runoff utility, the user charges are often based on the need for services rather than the
benefits derived from them. While charges are based on actual costs to inspect and maintain
runoff facilities and measures within the service area, the assessed rate structure should relate to
site characteristics. These include property area size, extent of impervious coverage, and other
factors with a direct and demonstrable effect on runoff. To be fair, the rate structure should also
remain simple and understandable to the ratepayer.
To finance the stormwater utility in Prince William County, Virginia, residential and
nonresidential owners of developed property pay based on the amount of impervious area
(rooftops, paved areas, etc.) on their property. Residents pay $10.38 billed twice a year ($20.76
total annual fee) for detached singe-family homes. Town home and condominium owners will
pay $7.785 billed twice a year ($15.57 total annual fee). Nonresidential property owners pay
$0.84 per 1,000 ft2 of impervious area per month. Fee adjustments or credits may be available
if a stormwater management system is already in place. The fee will be on the real estate bills.
Fees for the stormwater utility in Austin, Texas are higher with residential users billed
$5.79/mo, while commercial users pay $94.62/mo/acre of impervious cover. These fees cover
not only maintenance of existing BMPs, but also capital improvement projects related to the
drainage infrastructure.
Permit Fees
Collecting permit fees to finance runoff inspection and maintenance is a long standing funding
procedure. Most governmental entities local, county, and state can establish and collect fees
and other charges to obtain operating funds for programs and services. Many inspection
services, most notably the construction inspection of both ESC measures and permanent
drainage and runoff management facilities, are financed at least in part through fees collected by
permitting agencies. Unlike taxes or some utility charges, inspection costs are borne by those
who need them.
6-4 California Stormwater BMP Handbook January 2003
New Development and Redevelopment
www.cabmphandbooks.com
Section 6
Long-term Maintenance ofBMPs
The permit fee collection program should have a demonstrable link to the runoff management
or drainage systems. The public agency should demonstrate a direct link between the permit
fees collected and the permitted project one method is using dedicated accounts for individual
projects and facilities. Finally, the rate structure should reflect site characteristics such as area
size or imperviousness that directly relate to the measure or facility by affecting runoff or
erosion.
Dedicated Contributions
Public agencies at times have used developer contributions to fund long-term facility
maintenance. This approach is particularly appropriate in single-family residential
subdivisions, where numerous individual property owners served by a single runoff facility can
result in confusion over who has maintenance responsibility.
The exact funding technique depends on many factors, including community attitude and
knowledge, economic and political viability, and program needs and costs. Some techniques,
including permit fees and dedicated contributions, may be more appropriate for short-term
activities, such as construction inspection. Others utility charges and specialized tax revenues
may apply to all phases of an inspection and maintenance program but require considerable
effort and special legal authorization to operate.
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
www.cabmphandbooks.com
6-5
Attachment 15
STORM WATER MANAGEMENT PLAN
GREEN DRAGON COLONIAL VILLAGE
ATTACHMENT 15: STORM WATER STANDARDS QUESTIONNAIRE
Please see attached.
Vi
APPENDIX A
STORM WATER STANDARDS QUESTIONNAIRE
INSTRUCTIONS:
This questionnaire must be completed by the applicant in advance of submitting for a development application
(subdivision and land use planning approvals and construction permits). The results of the questionnaire determine
the level of storm water pollution prevention standards applied to a proposed development or redevelopment
project. Many aspects of project site design are dependent upon the storm water pollution protection standards
applied to a project.
Applicant responses to the questionnaire represent an initial assessment of the proposed project conditions and
impacts. City staff has responsibility for making the final assessment after submission of the development
application. A staff determination that the development application is subject to more stringent storm water
standards, than initially assessed by the applicant, will result in the return of the development application as
incomplete.
If applicants are unsure about the meaning of a question or need help in determining how to respond to one or
more of the questions, they are advised to seek assistance from Engineering Department Development Services
staff.
A separate completed and signed questionnaire must be submitted for each new development application
submission. Only one completed and signed questionnaire is required when multiple development applications for
the same project are submitted concurrently. In addition to this questionnaire, applicants for construction permits
must also complete, sign and submit a Construction Activity Storm Water Standards Questionnaire.
To address pollutants that may be generated from new development, the City requires that new development and
significant redevelopment priority projects incorporate Permanent Storm Water Best Management Practices
(BMPs) into the project design, which are described in Chapter 2 of the City's Storm Water Standards Manual This
questionnaire should be used to categorize new development and significant redevelopment projects as priority or
non-priority, to determine what level of storm water standards are required or if the project is exempt.
| 1. Is your project a significant redevelopment?
Definition:
Significant redevelopment is defined as the creation, addition or replacement of at least 5,000 square feet of
impervious surface on an already existing developed site.
Significant redevelopment includes, but is not limited to: the expansion of a building footprint; addition to or
replacement of a structure; structural development including an increase in gross floor area and/or exterior
construction remodeling; replacement of an impervious surface that is not part of a routine maintenance activity;
and land disturbing activities related with structural or impervious surfaces. Replacement of impervious surfaces
includes any activity that is not part of a routine maintenance activity where impervious material(s) are removed,
exposing underlying soil during construction.
Note: If the Significant Redevelopment results in an increase of less than fifty percent of the impervious surfaces of
a previously existing development, and the existing development was not subject to SUSMP requirements, the
numeric sizing criteria discussed in Table 3 of 2.3.3.4 applies only to the addition, and not to the entire
development.
2. If your project IS considered significant redevelopment, then please skip Section 1 and proceed with Section
2.
3. If your project IS NOT considered significant redevelopment, then please proceed to Section 1.
21 SWMP Rev 6/4/08
SECTION 1
NEW DEVELOPMENT
PRIORITY PROJECT TYPE
Does you project meet one or more of the following criteria:
1. Home subdivision of 100 units or more.
Includes SFD, MFD, Condominium and Apartments
2. Residential development of 10 units or more.
Includes SFD, MFD, Condominium and Apartments
3. Commercial and industrial development greater than 100.000 sauare feet including parking areas.
Any development on private land that is not for heavy industrial or residential uses. Example: Hospitals,
Hotels, Recreational Facilities, Shopping Malls, etc.
4. Heavy Industrial / Industry greater than 1 acre (NEED SIC CODES FOR PERMIT BUSINESS TYPES)
SIC codes 5013, 5014, 5541, 7532-7534, and 7536-7539
5. Automotive repair shop.
SIC codes 5013, 5014, 5541 , 7532-7534, and 7536-7539
6. A New Restaurant where the land area of development is 5.000 sauare feet or more including parking
areas.
SIC code 5812
7. Hillside development
(1) greater than 5,000 square feet of impervious surface area and (2) development will grade on any
natural slope that is 25% or greater
8. Environmentally Sensitive Area (ESA).
Impervious surface of 2,500 square feet or more located within, "directly adjacent"2 to (within 200 feet),
or "discharging directly to"3 receiving water within the ESA1
9. Parking lot.
Area of 5,000 square feet or more, or with 15 or more parking spaces, and potentially exposed to urban
runoff
10. Retail Gasoline Outlets - serving more than 100 vehicles per day
Serving more than 100 vehicles per day and greater than 5,000 square feet
11. Streets, roads, driveways, highways, and freeways.
Project would create a new paved surface that is 5,000 square feet or greater.
12. Coastal Development Zone.
Within 200 feet of the Pacific Ocean and (1) creates more than 2500 square feet of impermeable
surface or (2) increases impermeable surface on property by more than 10%.
YES
X
y^
X
NO
X
X
X
X
X
X
X
x:
X
1 Environmentally Sensitive Areas include but are not limited to all Clean Water Act Section 303(d) impaired water bodies;
areas designated as Areas of Special Biological Significance by the State Water Resources Control Board (Water Quality
Control Plan for the San Diego Basin (1994) and amendments); water bodies designated with the RARE beneficial use by
the State Water Resources Control Board (Water Quality Control Plan for the San Diego Basin (1994) and amendments);
areas designated as preserves or their equivalent under the Multi Species Conservation Program within the Cities and Count
of San Diego; and any other equivalent environmentally sensitive areas which have been identified by the Copermittees.
2 "Directly adjacent" means situated within 200 feet of the environmentally sensitive area.
3 "Discharging directly to" means outflow from a drainage conveyance system that is composed entirely of flows from the
subject development or redevelopment site, and not commingled with flow from adjacent lands.
Section 1 Results:
If you answered YES to ANY of the questions above you have a PRIORITY project and PRIORITY project requirements DO
apply. A Storm Water Management Plan, prepared in accordance with City Storm Water Standards, must be submitted at
time of application. Please check the "MEETS PRIORITY REQUIREMENTS" box in Section 3.
If you answered NO to ALL of the questions above, then you are a NON-PRIORITY project and STANDARD requirements
apply. Please check the "DOES NOT MEET PRIORITY Requirements" box in Section 3.
SVVMP Rev 6/4/08
SECTION 2
SIGNIFICANT REDEVELOPMENT:
1 . Is the project redeveloping an existing priority project type? (Priority projects
are defined in Section 1 )
(YES^
K6
NO
If you answered YES, please proceed to question 2.
If you answered NO, then you ARE NOT a significant redevelopment and you ARE NOT subject to
PRIORITY project requirements, only STANDARD requirements. Please check the "DOES NOT MEET
PRIORITY Requirements" box in Section 3 below.
2. Is the project solely limited to one of the following:
a. Trenching and resurfacing associated with utility work?
b. Resurfacing and reconfiguring existing surface parking lots?
c. New sidewalk construction, pedestrian ramps, or bike lane on public
and/or private existing roads?
d. Replacement of existing damaged pavement?
(N/O
If you answered NO to ALL of the questions, then proceed to Question 3.
If you answered YES to ONE OR MORE of the questions then you ARE NOT a significant redevelopment
and you ARE NOT subject to PRIORITY project requirements, only STANDARD requirements. Please
check
the "DOES NOT MEET PRIORITY Requirements" box in Section 3 below.
3. Will the development create, replace, or add at least 5,000 square feet of
impervious surfaces on an existing development or, be located within 200
feet of the Pacific Ocean and (1)create more than 2500 square feet of
impermeable surface or (2) increases impermeable surface on property by
more than 10%?
<f^
If you answered YES, you ARE a significant redevelopment, and you ARE subject to PRIORITY project
requirements. Please check the "MEETS PRIORITY REQUIREMENTS" box in Section 3 below.
If you answered NO, you ARE NOT a significant redevelopment, and you ARE NOT subject to
PRIORITY project requirements, only STANDARD requirements. Please check the "DOES NOT MEET
PRIORITY Requirements" box in Section 3 below.
SECTION 3
Questionnaire Results:
MY PROJECT MEETS PRIORITY REQUIREMENTS, MUST COMPLY WITH PRIORITY
PROJECT STANDARDS AND MUST PREPARE A STORM WATER MANAGEMENT PLAN FOR
SUBMITTAL AT TIME OF APPLICATION.
MY PROJECT DOES NOT MEET PRIORITY REQUIREMENTS AND MUST ONLY COMPLY
WITH STANDARD STORM WATER REQUIREMENTS.
Applicant Information and Signature Box /7i/» Km fui-L ifr t. v (Inly
Address:Assessors Parcel Nuinbcr(s):
Applicant Name:
Applicant Signature:
Applicant Title:
Date:
City Concurrence:
By:
SWMPRev6/4,08