HomeMy WebLinkAboutCT 02-28; La Costa Condominiums; Storm Water Management Plan; 2008-04-16STORM WATER MANAGEMENT PLAN FOR
LA COSTA CONDOMINIUMS
CARLSBAD, CA CO
Job No. 981027-5
Prepared: October 7,2002
Revised: May 20,2003
Revised: September 22,2003
Revised: July 31,2007
Revised: October 1,2007
CONSULTA SI T S
O'Day Consultants, Inc.
2710 Loker Avenue West, Suite 100
Carlsbad, CA 92010
Tel: (760) 93 1-7700
Fax:(760)931-8680
John P. Strohminger, RCE 55187
Expires 6-30-08
Date
Prepared by: BRL
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TABLE OF CONTENTS
1.0 PROJECT DESCRIPTION 2
1.1 Hydrologic Unit Contribution 2
1.2 Beneficial Uses 2
2.0 CHARACTERIZATION OF PROJECT RUNOFF 3
2.1 Soil Characteristics 3
2.2 Potential Discharges 4
3.0 MITIGATION MEASURES TO PROTECT WATER QUALITY... .4
3.1 Site Design BMPs 4
3.2 Source Control BMPs 5
3.3 Treatment Control BMPs 6
4.0 MONITORING, INSPECTION, AND REPORTING 6
Attachments:
1. Vicinity map
2. Beneficial uses for the hydrologic unit
3. 303(D) list for impaired water bodies
4. SUSMP Appendix A checklist
5. Table 2: Anticipated and potential pollutants
6. Table 1: Storm Water BMP Requirements Matrix
7. Project site plan & BMP map
8. CASQA treatment control BMP datasheets
9. Inlet Filter Datasheets
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STORM WATER MANAGEMENT PLAN
Federal, state and local agencies have established goals and objectives for storm water quality in
the region. The proposed project, prior to the start of construction activities, will comply with all
federal, state and local permits including the Stormwater Management Plan (SWMP) required
under the County of San Diego Watershed Protection, Stormwater Management, and Discharge
Control Ordinance (WPO) (section 67.871), and the National Pollution Discharge Elimination
System (NPDES) from the Regional Water Quality Control Board (RWQCB).
The purpose of this SWMP is to address the water quality impacts from the proposed
improvements as shown on the Tentative Map. This project will provide guidelines in
developing and implementing Best Management Practices (BMPs) for storm water quality
during construction and post construction. Priori-issuance of a grading permit from the City of
Carlsbad, the applicant will be required to filerapcf^lotice of Intent with the State Water Quality
Control Board and prepare a Storm Water Polluncm Prevention Plan (SWPPP).
1.0 PROJECT DESCRIPTION
The project site is approximately 8.2 acres of land located on the south side of La Costa Avenue,
about 1 mile east of El Camino Real, see vicinity map Attachment 1. Currently the site is graded,
but it contains no structures. This project proposes a multi-family development with a total of 58
units.
1.1 Hydrologic Unit Contribution
The project is located in the Batiquitos Hydrologic Subarea (904.51) of the San Marcos
Watershed in the Carlsbad Hydrologic Unit in the San Diego Region. The site drains north to La
Costa Avenue where most of the runoff enters an existing drainage inlet. The site also takes on
runoff from a portion of the residential development to the south. The storm drain flows across
La Costa Avenue into a drainage channel, then about 1 mile west to Batiquitos Lagoon. This
project represents less than 0.01% of the Batiquitos Hydrologic Subarea.
The proposed project will not significantly alter the drainage patterns on-site. A detention basin
at the south end of the site will limit peak discharge to pre-development levels.
1.2 Beneficial Uses
The beneficial uses for the hydrologic unit are included in Attachment 2, and the definitions are
listed below. This information comes from the Water Quality Control Plan for the San Diego
Basin.
••
REC 1 -Contact Recreation: Includes uses of water for recreational activities involving body
contact with water, where ingestion of water is reasonably possible. These uses include, but are
not limited to, swimming, wading, water-skiing, skin and SCUBA diving, surfing, white water
activities, fishing, or use of natural hot springs.
REC 2 -Non-Contact Recreation: Includes the uses of water for recreational activities
involving proximity to water, but not normally involving body contact with water, where
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I
ingestion of water is reasonably possible. These include, but are not limited to, picnicking,
sunbathing, hiking, camping, boating, tide pool and marine life study, hunting, sightseeing, or
aesthetic enjoyment in conjunction with the above activities.
BIOL - Preservation of Biological Habitats of Special Significance: Includes uses of water
that support designated areas or habitats, such as established refuges, parks, sanctuaries,
ecological reserves, or Areas of Special Biological Significance (ASBS), where the preservation
or enhancement of natural resources requires special protection.
EST -Estuarine Habitat: Includes uses of water that support estuarine ecosystems including,
but not limited to, preservation or enhancement of estuarine habitats, vegetation, fish, shellfish,
or wildlife (e.g., estuarine mammals, waterfowl, shorebirds).
WILD -Wildlife Habitat: Includes uses of water that support terrestrial ecosystems including
but not limited to, preservation and enhancement of terrestrial habitats, vegetation, wildlife, (e.g.,
mammals, birds, reptiles, amphibians, invertebrates), or wildlife water food and sources.
RARE -Rare, Threatened, or Endangered Species: Includes uses of water that support
habitats necessary, at least in part, for the survival and successful maintenance of plant or animal
species established under state or federal law as rare, threatened, or endangered.
MAR -Marine Habitat: Includes uses of water that support marine ecosystems including, but
not limited to, preservation or enhancement or marine habitats, vegetation such as kelp, fish,
shellfish, or wildlife (e.g., marine mammals, shorebirds).
MIGR -Migration of Aquatic Organisms: Includes uses of water that support habitats
necessary for migration, acclimatization between fresh and salt water, or other temporary
activities by aquatic organisms, such as anadromous fish.
2.0 CHARACTERIZATION OF PROJECT RUNOFF
According to the California 2002 303d list published by the RWQCB and approved by the
USEPA July 2003, the Pacific Ocean Shoreline, San Marcos HA has a Low priority for bacteria.
This impairment is nonpoint/point source affecting 0.5 miles located at Moonlight State Beach,
see Attachment 3. (
The total disturbed area for this project is approximately 5.6 acres. The pre-development peak
runoff from this area is 32. 1 cfs, and the post-development peak runoff (ignoring detention) is
37.7 cfs. The time of concentration decreases from 10.0 minutes existing to 8.8 minutes proposed
(taking detention into consideration). The detention basin at the south end of the site will limit
the peak discharge to 32.4 cfs. Please see the Hydrology, Hydraulics, and Detention Study for La
Costa Condominiums by O'Day Consultants dated November 1, 2007 on file at the City of
Carlsbad.
According to the Storm Water Requirements Applicability Checklist, the project is considered
high priority, see Attachment 4.
2.1 Soil Characteristics
The project area consists entirely of soil group D.
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2.2 Potential Discharges
There are no sampling data available for the existing site condition. The project will contain
some pollutants commonly found on similar developments that could affect water quality. The
following list is taken from Table 2 of the City of Carlsbad's SUSMP, see Attachment 5. The
anticipated and potential pollutants for attached residential developments and streets are:
1. Sediment discharge due to construction activities
2. Nutrients from fertilizers
3. Trash and debris
4. Oxygen demanding substances
5. Oil and grease from cars
6. Bacteria and viruses
7. Pesticides from landscaping and home use
8. Heavy metals from streets and driveways
The primary pollutant of concern is a low priority for bacteria. All other pollutants are secondary
pollutants. Incorporating multiple BMP systems will mitigate for both primary and secondary
pollutants.
3.0 MITIGATION MEASURES TO PROTECT WATER QUALITY
To address water quality for the project, BMPs will be implemented during construction and post
construction. Table 1 of the City of Carlsbad's SUSMP shows the requirements for the
permanent storm water BMPs, see Attachment 6.
A detailed description of the construction phase BMPs are in the Storm Water Pollution
Prevention Plan (SWPPP) by O'Day Consultants dated October 1, 2007 on file at the City of
Carlsbad.
3.1 Site Design BMPs
All Site Design BMPs will be designed to CASQA standards. Control of post-development peak
storm water runoff discharge rates and velocities are desirable in order to maintain or reduce pre-
development downstream erosion by applying the following concepts:
Minimize Impervious Footprint:
The following measures have been incorporated to minimize the impervious footprint to the
maximum extent practicable:
• Increase building density
• Construct streets, sidewalks, and parking lot aisles to the minimum acceptable widths
• Minimize impervious surfaces, such as decorative concrete, in the landscape design.
Conserve Natural Areas:
The project has been designed to conserve natural areas by concentrating development on the
least environmentally sensitive portions of the site while leaving the remaining land in a natural
condition. Natural drainage systems have been incorporated to the maximum extent practicable.
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Minimize Directly Connected Impervious Areas:
To the maximum extent practicable, parking lots, sidewalks, patios, roof top drains, rain gutters,
and other impervious surfaces shall drain into adjacent landscaping or vegetated swales prior to
discharging to the storm water conveyance system.
Maximize Canopy Interception:
The project will maximize canopy interception by preserving existing native trees and shrubs as
well as planting native or drought tolerant trees and large shrubs.
Protect Slopes and Channels:
All runoff will be safely conveyed away from the tops of slopes. Energy dissipaters shall be
installed at the outlets of new storm drains, culverts, or channels that enter unlined channels in
accordance with applicable standards and specifications to minimize erosion. Energy dissipaters
will be installed in such a way as to minimize impacts on receiving waters. Slopes shall be
planted with native or drought tolerant vegetation.
3.2 Source Control BMPs
Trash Storage Areas to Reduce Pollution Introduction:
All trash containers shall contain attached lids that exclude rain or contain a roof or awning to
minimize direct precipitation. Storage areas shall be paved, screened or walled to prevent off-site
transport of trash, and designed not to allow run-on from adjoining areas.
Use Efficient Irrigation Systems & Landscape Design:
Irrigation systems shall employ rain shutoff devices to prevent irrigation during precipitation and
be designed to each landscape area's specific water requirements consistent with the Carlsbad's
Landscape Manual. Irrigation of landscaped areas will use flow reducers or shutoff valves
triggered by a pressure drop top control water loss in the event of a broken sprinkler heads or
lines. Bubblers and or drip irrigation will be installed in the parking lot planters. Maintenance of
common areas will be performed by contract with a professional maintenance company. The
Home Owner's Association will enforce landscape and irrigation standards for operation and
maintenance of watering systems on critical slopes.
Provide Storm Water Conveyance System Stenciling and Signage:
All storm drain inlets and catch basins within the project shall have a tile that reads: "NO
DUMPING - DRAINS TO BATIQUITOS LAGOON." Legibility of the tiles will be maintained,
and the tiles placed flush with the top of concrete to reduce tripping by pedestrians.
Trash Management:
The Home Owner's Association will enforce trash management standards and provide for debris
removal at storm drain inlets.
Dry Street Sweeping:
Periodic street sweeping will be performed prior to the rainy season and when significant time
has elapsed between rains. This will help prevent large amounts of trash and silt from washing
into the storm drain system. All street areas will be swept, including access roads and
driveways.
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3.3 Treatment Control BMPs
Treatment control BMPs have been selected to mitigate for the primary and secondary pollutants
as identified in Section 2.2 of this report. Attachment 7 shows the project site plan and BMP
map. Treatment Control datasheets per CASQA are provided for reference, see Attachment 8.
Vegetated Swale (TC-30):
Much of the runoff from the site will pass through vegetated swales before discharging off the
property. These swales will slow storm flows, increase infiltration, and provide filtration for the
first flush runoff.
Drain Inserts (MP-52)
All of the runoff from the site enters the storm drain system and will pass through a filtration
insert, see Attachment 9 for datasheets. The Home Owner's Association will be responsible for
inspecting the inserts every 3 months and performing any necessary maintenance.
Infiltration Basin (TC-11)
Much of the runoff from the site enters a grass-lined detention basin before discharging off the
property. The basin will provide additional biofiltration and allow for infiltration of runoff.
4.0 MONITORING, INSPECTION, AND REPORTING
I The BMP Summary table on the SWMP & BMP Summary Map (Attachment 3) shows a
summary of the BMPs to be used and their corresponding monitoring and maintenance
frequency. The Owner/Developer will be responsible for the monitoring and maintenance of the
BMPs until the CC&Rs are executed.
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Attachment 1
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4
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1
1
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1
CITY OF OCEAHS.M
*
OH OTVBTA
MARCOS
PACIFIC
OCEAH
HO SCALE
Attachment 2
li I i li § i 11 if iA ftl
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 1'3
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
Tijuana River Estuary
Mouth of San Diego River
Famosa Slough and Channel
Los Penasquitos Lagoon 2
San Dieguito Lagoon
Batiquitos Lagoon
San Elijo Lagoon
Agua Hedionda Lagoon
11.11
7.11
7.11
6.10
5.11
4.51
4.61
4.31 •
•
•
•
•
•
•
•
•
•
•
•
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•
•
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•
•
•
•
•
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•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
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.
3 The Shelter Island Yacht Basin portion of San Diego Bay is designated as an impaired water body for dissolved copper pursuant to Clean Water Act
section 303(d). A Total Maximum Daily Load (TMDL) has been adopted to address this impairment. See Chapter 3, Water Quality Objectives for Pesticides,
Toxicity and Toxic Pollutants and Chapter 4, Total Maximum Daily Loads.
• Existing Beneficial Use
Table 2-3
BENEFICIAL USES
2 - 52
Attachment 3
I i ii i t i i i i i i I i i
2002 CWA SECTION 303(d) LIST OF WATER QUALITY LIMITED SEGMENT
SAN DIEGO REGIONAL WATER QUALITY CONTROL BOARD
Approved by USEPA:
Julv 2003
REGION TYPE NAME
CALWATER
WATERSHED POLLUTANT/STHESSOR
POTENTIAL
SOURCES
TMDL ESTIMATED PROPOSED TMDL
PRIORITY SIZE AFFECTED COMPLETION
9 C Pacific Ocean Shoreline, San Diequito HU 90511000
9 C Pacific Ocean Shoreline, San Joaquin Hills
HSA
9 C Pacific Ocean Shoreline, San Marcos HA
9 C Pacific Ocean Shoreline, Scripps HA
9 C Pacific Ocean Shoreline, Tijuana HU
9 R Pine Valley Creek (Upper)
90111000
9 C Pacific Ocean Shoreline, San Luis Rey HU 90311000
90451000
90630000
91111000
91141000
Bacteria Indicators Low 0.86 Miles
Impairment located at San Dieguito Lagoon Mouth, Solana Beach.
Nonpoint/Point Source
Bacteria Indicators Low 0.63 Miles
Impairment located at Cameo Cove at Irvine Cove Dr./Riviera Way, Heisler Park-North
Urban Runoff/Storm Sewers
Unknown Nonpoint Source
Unknown point source
Bacteria Indicators Low 0.49 Miles
Impairment located at San Luis Rey River Mouth.
Nonpoint/Point Source
Bacteria Indicators Low 0.5 Miles
Impairment located at Moonlight State Beach.
Nonpoint/Point Source
Bacteria Indicators Medium 3.9 Miles
Impairment located at La Jolla Shores Beach at El Paseo Grande, La Jolla Shores Beach at Caminito Del Oro, La Jolla
Shores Beach at Vallecitos, La Jolla Shores Beach atAve de la Play a, Casa Beach (Childrens Pool), South Casa Beach at
Coast Blvd., Whispering Sands Beach at Ravina St., Windansea Beach at Vista de la Playa, Windansea Beach at Bonair St.,
Windansea Beach at Playa del None, Windansea Beach at Palomar Ave., Tourmaline Surf Park, Pacific Beach at Grand
Ave.
Nonpoint/Point Source
Bacteria Indicators Low
Impairment located from the border, extending north along the shore.
Nonpoint/Point Source
Enterococci Medium
Grazing-Related Sources
Concentrated Animal Feeding Operations
(permitted, point source)
Transient encampments
3 Miles
2.9 Miles
Page 7 of 16
Attachment 4
STORM WATER REQUIREMENTS APPLICABILITY CHECKLIST
Project Address Assessors Parcel Number(s):
La Costa Avenue, Carlsbad, CA 216-160-27
Project # (city use only):
Complete Sections 1 and 2 of the following checklist to determine your project's permanent and
construction storm water best management practices requirements. This form must be completed
and submitted with your permit application.
Section 1. Permanent Storm Water BMP Requirements:
If any answers to Part A are answered "Yes," your project is subject to the "Priority Project
Permanent Storm Water BMP Requirements," and "Standard Permanent Storm Water BMP
Requirements" in Section III, "Permanent Storm Water BMP Selection Procedure" in the Storm
Water Standards manual.
If all answers to Part A are "No," and any answers to Part B are "Yes," your project is only subject
to the "Standard Permanent Storm Water BMP Requirements". If every question in Part A and B
is answered "No," your project is exempt from permanent storm water requirements.
Part A: Determine Priority Project Permanent Storm Water BMP Requirements.
Does the project meet the definition of one or more of the priority project categories?*
1 . Detached residential development of 10 or more units.
2. Attached residential development of 10 or more units.
3. Commercial development greater than 100,000 square feet.
4. Automotive repair shop.
5. Restaurant.
6. Steep hillside development greater than 5,000 square feet.
7. Project discharging to receiving waters within Environmentally Sensitive Areas.
2
8. Parking lots greater than or equal to 5,000 ft or with at least 15
potentially exposed to urban runoff.
parking spaces, and
9. Streets, roads, highways, and freeways which would create a new paved surface that is
5,000 square feet or greater
* Refer to the definitions section in the Storm Water Standards for
priority project categories.
Yes
/
No
/
/
/
/
/
/
/
/
expanded definitions of the
Limited Exclusion: Trenching and resurfacing work associated with utility projects are not
considered priority projects. Parking lots, buildings and other structures associated with utility
projects are priority projects if one or more of the criteria in Part A is met. If all answers to Part A
are "No", continue to Part B.
Part B: Determine Standard Permanent Storm Water Requirements.
Does the project propose:
1 . New impervious areas, such as rooftops, roads, parking lots, driveways, paths and
sidewalks?
2. New pervious landscape areas and irrigation systems?
3. Permanent structures within 100 feet of any natural water body?
4. Trash storage areas?
5. Liquid or solid material loading and unloading areas?
6. Vehicle or equipment fueling, washing, or maintenance areas?
7. Require a General NPDES Permit for Storm Water Discharges Associated with Industrial
Activities (Except construction)?*
8. Commercial or industrial waste handling or storage, excluding typical office or household
waste?
9. Any grading or ground disturbance during construction?
10. Any new storm drains, or alteration to existing storm drains?
Yes
/
/
/
/
/
No
/
/
/
\A
W
*To find out if your project is required to obtain an individual General NPDES Permit for Storm Water
Discharges Associated with Industrial Activities, visit the State Water Resources Control Board web site
at, www.swrcb.ca.gov/stormwtr/industrial.html
Section 2. Construction Storm Water BMP Requirements:
If the answer to question 1 of Part C is answered "Yes," your project is subject to Section IV, "Construction
Storm Water BMP Performance Standards," and must prepare a Storm Water Pollution Prevention Plan
(SWPPP). If the answer to question 1 is "No," but the answer to any of the remaining questions is "Yes,"
your project is subject to Section IV, "Construction Storrn Water BMP Performance Standards," and must
prepare a Water Pollution Control Plan (WPCP). If every question in Part C is answered "No," your project
is exempt from any construction storm water BMP requirements. If any of the answers to the questions in
Part C are "Yes," complete the construction site prioritization in Part D, below.
Part C: Determine Construction Phase Storm Water Requirements.
Would the project meet any of these criteria during construction?
1 . Is the project subject to California's statewide General NPDES Permit for Storm Water
Discharges Associated With Construction Activities?
2. Does the project propose grading or soil disturbance?
3. Would storm water or urban runoff have the potential to contact any portion of the
construction area, including washing and staging areas?
4. Would the project use any construction materials that could negatively affect water quality
if discharged from the site (such as, paints, solvents, concrete, and stucco)?
Yes
/
/
/
/
No
Part D: Determine Construction Site Priority
In accordance with the Municipal Permit, each construction site with construction storm water BMP
requirements must be designated with a priority: high, medium or low. This prioritization must be
completed with this form, noted on the plans, and included in the SWPPP or WPCP. Indicate the project's
priority in one of the check boxes using the criteria below, and existing and surrounding conditions of the
project, the type of activities necessary to complete the construction and any other extenuating
circumstances that may pose a threat to water quality. The City reserves the right to adjust the priority of
the projects both before and during construction. [Note: The construction priority does NOT change
construction BMP requirements that apply to projects; all construction BMP requirements must be
identified on a case-by-case basis. The construction priority does affect the frequency of inspections that
will be conducted by City staff. See Section IV. 1 for more details on construction BMP requirements.]
/\A) High Priority
1) Projects where the site is 50 acres or more and grading will occur during the rainy season
2) Projects 1 acre or more.
3) Projects 1 acre or more within or directly adjacent to or discharging directly to a coastal lagoon or
other receiving water within an environmentally sensitive area
4) Projects, active or inactive, adjacent or tributary to sensitive water bodies
|B; Medium Priority
5) Capital Improvement Projects where grading occurs, however a Storm Water Pollution Prevention
Plan (SWPPP) is not required under the State General Construction Permit (i.e., water and sewer
replacement projects, intersection and street re-alignments, widening, comfort stations, etc.)
6) Permit projects in the public right-of-way where grading occurs, such as installation of sidewalk,
substantial retaining walls, curb and gutter for an entire street frontage, etc. , however SWPPPs are
not required.
7) Permit projects on private property where grading permits are required, however, Notice Of Intents
(NOIs) and SWPPPs are not required.
C) Low Priority
8) Capital Projects where minimal to no grading occurs, such as signal light and loop installations,
street light installations, etc.
9) Permit projects in the public right-of-way where minimal to no grading occurs, such as pedestrian
ramps, driveway additions, small retaining walls, etc.
10) Permit projects on private property where grading permits are not required, such as small retaining
walls, single-family homes, small tenant improvements, etc.
Owner/Agent/Engineer Name (Please Print):
John F?. Strohmipger,
Title:
Project Manager
Sigtjat Date:'\0-\-oJ_
Attachment 5
Storm Water Standards
4/03/03
III. PERMANENT BEST MANAGEMENT PRACTICES SELECTION PROCEDURE
When referred to this Section, by Step 2 of Section II, complete the analysis required for
your project in the subsections of Section 111.1 below.
1. IDENTIFY POLLUTANTS & CONDITIONS OF CONCERN
A. Identify Pollutants from the Project Area
Using Table 1, 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.
Table 2. Anticipated and Potential Pollutants Generated by Land Use Type.
Project
Categories
Detached
Residential
Development
Attached
Residential
Development
Commercial
Development
>1 00,000 ft2
Automotive
Repair
Restaurants
Hillside
Development
>5,000ft2
Parking Lots
Streets,
Highways &
Freeways
General Pollutant Categories
Sediments
X
X
Pd)
X
P(i)
X
Nutrients
X
X
p(i)
X
P(1)
P0)x
Heavy
Metals
X
X
X
Organic
Compounds
P(2)
XW<5)
xw
Trash
&
Debris
X
X
X
X
X
X
X
X
Oxygen
Demanding
Substances
X
p(i)
P(5)
X
X
p(1)
P(5)
OII&
Grease
X
P(2)
X
X
X
X
X
X
Bacteria
&
Viruses
X
P(i)
P(3)
X
Pesticides
X
X
P(5)
X
PO)
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.
12
Attachment 6
Storm Water Standards
4/03/03
Table 1. Standard Development Project & Priority Project Storm Water BMP Requirements Matrix.
Standard Projects
Site
Design
BMPsW
R
Source
Control
BMPs®
R
BMPs Applicable to Individual
Priority Project Categories^
tn
QL
BCO
cZ
cc
0 b. Residential Driveways &Guest Parking0 c. Dock Areas0
1
§coJic
'CD
"D
0 e. Vehicle Wash Areas0 f. Equipment Wash Areas0
0)CO1en
'§
2Q.
O
o>
0 h. Surface Parking Areas0 i. Fueling Areas0 j. Hillside Landscaping0
Treatment
Control
BMPsM
0
Priority Projects:
Detached Residential
Development
Attached Residential
Development
Commercial Development
>1 00,000 ft2
Automotive Repair Shop
Restaurants
Hillside Development
>5,000 ft2
Parking Lots
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(5)
R
R
R
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 C.
0 = 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 C.
(1) Refer to Section III.2.A.
(2) Refer to Section III.2.B.
(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.
(4) Refer to Section III.2.D.
(5) Applies if the paved area totals >5,000 square feet or with >15 parking spaces and is potentially exposed to urban runoff.
8
Attachment 7
Attachment 8
Infiltration Basin TC-11
I
Design Considerations
• Soil for Infiltration
• Slope
• Aesthetics
Targeted Constituents
Description
An infiltration basin is a shallow impoundment that is designed
to infiltrate stormwater. Infiltration basins use the natural
filtering ability of the soil to remove pollutants in stormwater
runoff. Infiltration facilities store runoff until it gradually
exfiltrates through the soil and eventually into the water table.
This practice has high pollutant removal efficiency and can also
help recharge groundwater, thus helping to maintain low flows in
stream systems. Infiltration basins can be challenging to apply
on many sites, however, because of soils requirements. In
addition, some studies have shown relatively high failure rates
compared with other management practices.
California Experience
Infiltration basins have a long history of use in California,
especially in the Central Valley. Basins located in Fresno were
among those initially evaluated in the National Urban Runoff
Program and were found to be effective at reducing the volume of
runoff, while posing little long-term threat to groundwater
quality (EPA, 1983; Schroeder, 1995). Proper siting of these
devices is crucial as underscored by the experience of Caltrans in
siting two basins in Southern California. The basin with
marginal separation from groundwater and soil permeability
failed immediately and could never be rehabilitated.
Advantages
• Provides 100% reduction in the load discharged to surface
waters.
• The principal benefit of infiltration basins is the
approximation of pre-development hydrology during which a
/ Sediment
/ Nutrients
/ Trash
/ Metals
J Bacteria
/ Oil and Grease
/ Organics
Legend (Removal Effectiveness)
• Low • High
A Medium
California
Stormwater
Quality
Association
January 2003 California Stormwater BMP Handbook
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1 of 8
TO 11 Infiltration Basin
significant portion of the average annual rainfall runoff is infiltrated and evaporated rather
than flushed directly to creeks.
• If the water quality volume is adequately sized, infiltration basins can be useful for providing
control of channel forming (erosion) and high frequency (generally less than the 2-year)
flood events.
Limitations
• May not be appropriate for industrial sites or locations where spills may occur.
• Infiltration basins require a minimum soil infiltration rate of 0.5 inches/hour, not
appropriate at sites with Hydrologic Soil Types C and D.
• If infiltration rates exceed 2.4 inches/hour, then the runoff should be fully treated prior to
infiltration to protect groundwater quality.
• Not suitable on fill sites or steep slopes.
• Risk of groundwater contamination in very coarse soils.
• Upstream drainage area must be completely stabilized before construction.
• Difficult to restore functioning of infiltration basins once clogged.
Design and Sizing Guidelines
• Water quality volume determined by local requirements or sized so that 85% of the annual
runoff volume is captured.
• Basin sized so that the entire water quality volume is infiltrated within 48 hours.
• Vegetation establishment on the basin floor may help reduce the clogging rate.
Construction/Inspection Considerations
m Before construction begins, stabilize the entire area draining to the facility. If impossible,
place a diversion berm around the perimeter of the infiltration site to prevent sediment
entrance during construction or remove the top 2 inches of soil after the site is stabilized.
Stabilize the entire contributing drainage area, including the side slopes, before allowing any
runoff to enter once construction is complete.
• Place excavated material such that it can not be washed back into the basin if a storm occurs
during construction of the facility.
• Build the basin without driving heavy equipment over the infiltration surface. Any
equipment driven on the surface should have extra-wide ("low pressure") tires. Prior to any
construction, rope off the infiltration area to stop entrance by unwanted equipment.
• After final grading, till the infiltration surface deeply.
• Use appropriate erosion control seed mix for the specific project and location.
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Infiltration Basin TO 11
^^••••••••••••••^•^^•^^^^^^^^^^^^^•••••••^^^•^^^^^^^^^^^^^^^^^^^^^^^^^^^^••••^•^•••^^•••i^HHH^HH^H^^^^^^^^^^HHHMHBHHI^^^^^^^^^^^^^^^Hi
Performance
As water migrates through porous soil and rock, pollutant attenuation mechanisms include
precipitation, sorption, physical filtration, and bacterial degradation. If functioning properly,
this approach is presumed to have high removal efficiencies for particulate pollutants and
moderate removal of soluble pollutants. Actual pollutant removal in the subsurface would be
expected to vary depending upon site-specific soil types. This technology eliminates discharge to
surface waters except for the very largest storms; consequently, complete removal of all
stormwater constituents can be assumed.
There remain some concerns about the potential for groundwater contamination despite the
findings of the NURP and Nightingale (1975; I98ya,b,c; 1989). For instance, a report by Pitt et
al. (1994) highlighted the potential for groundwater contamination from intentional and
unintentional stormwater infiltration. That report recommends that infiltration facilities not be
sited in areas where high concentrations are present or where there is a potential for spills of
toxic material. Conversely, Schroeder (1995) reported that there was no evidence of
groundwater impacts from an infiltration basin serving a large industrial catchment in Fresno,
CA.
•
Siting Criteria
The key element in siting infiltration basins is identifying sites with appropriate soil and
hydrogeologic properties, which is critical for long term performance. In one study conducted in
Prince George's County, Maryland (Galli, 1992), all of the infiltration basins investigated clogged
within 2 years. It is believed that these failures were for the most part due to allowing infiltration
at sites with rates of less than 0.5 in/hr, basing siting on soil type rather than field infiltration
tests, and poor construction practices that resulted in soil compaction of the basin invert.-
A study of 23 infiltration basins in the Pacific Northwest showed better long-term performance
in an area with highly permeable soils (Hilding, 1996). In this study, few of the infiltration
basins had failed after 10 years. Consequently, the following guidelines for identifying
appropriate soil and subsurface conditions should be rigorously adhered to.
• Determine soil type (consider RCS soil type 'A, B or C' only) from mapping and consult
USDA soil survey tables to review other parameters such as the amount of silt and clay,
presence of a restrictive layer or seasonal high water table, and estimated permeability. The
soil should not have more than 30% clay or more than 40% of clay and silt combined.
Eliminate sites that are clearly unsuitable for infiltration.
• Groundwater separation should be at least 3 m from the basin invert to the measured
ground water elevation. There is concern at the state and regional levels of the impact on
groundwater quality from infiltrated runoff, especially when the separation between
groundwater and the surface is small.
Location away from buildings, slopes and highway pavement (greater than 6 m) and wells
and bridge structures (greater than 30 m). Sites constructed of fill, having a base flow or
with a slope greater than 15% should not be considered.
Ensure that adequate head is available to operate flow splitter structures (to allow the basin
to be offline) without ponding in the splitter structure or creating backwater upstream of the
splitter.
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TC-11 Infiltration Basin
• Base flow should not be present in the tributary watershed.
Secondary Screening Based on Site Geotechnical Investigation
m At least three in-hole conductivity tests shall be performed using USER 7300-89 or Bouwer-
Rice procedures (the latter if groundwater is encountered within the boring), two tests at
different locations within the proposed basin and the third down gradient by no more than
approximately 10 m. The tests shall measure permeability in the side slopes and the bed
within a depth of 3 m of the invert.
• The minimum acceptable hydraulic conductivity as measured in any of the three required
test holes is 13 mm/hr. If any test hole shows less than the minimum value, the site should
be disqualified from further consideration.
• Exclude from consideration sites constructed in fill or partially in fill unless no silts or clays
are present in the soil boring. Fill tends to be compacted, with clays in a dispersed rather
than flocculated state, greatly reducing permeability.
• The geotechnical investigation should be such that a good understanding is gained as to how
the stormwater runoff will move in the soil (horizontally or vertically) and if there are any
geological conditions that could inhibit the movement of water.
Additional Design Guidelines
(1) Basin Sizing - The required water quality volume is determined by local regulations
or sufficient to capture 85% of the annual runoff.
(2) Provide pretreatment if sediment loading is a maintenance concern for the basin.
(3) Include energy dissipation in the inlet design for the basins. Avoid designs that
include a permanent pool to reduce opportunity for standing water and associated
vector problems.
(4) Basin invert area should be determined by the equation:
_WQV
A —to
where A = Basin invert area (m2)
WQV = water quality volume (m3)
k = 0.5 times the lowest field-measured hydraulic conductivity
(m/hr)
t = drawdown time (48 hr)
(5) The use of vertical piping, either for distribution or infiltration enhancement shall
not be allowed to avoid device classification as a Class V injection well per 40
CFRi46.5(e)(4).
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Infiltration Basin TC-11
Maintenance
Regular maintenance is critical to the successful operation of infiltration basins. Recommended
operation and maintenance guidelines include:
• Inspections and maintenance to ensure.
• Observe drain time for the design storm after completion or modification of the facility to
confirm that the desired drain time has been obtained.
• Schedule semiannual inspections for beginning and end of the wet season to identify
potential problems such as erosion of the basin side slopes and invert, standing water, trash
and debris, and sediment accumulation.
• Remove accumulated trash and debris in the basin at the start and end of the wet season.
• Inspect for standing water at the end of the wet season.
• Trim vegetation at the beginning and end of the wet season to prevent establishment of
woody vegetation and for aesthetic and vector reasons.
• Remove accumulated sediment and regrade when the accumulated sediment volume
exceeds 10% of the basin.
• If erosion is occurring within the basin, revegetate immediately and stabilize with an erosion
control mulch or mat until vegetation cover is established.
• To avoid reversing soil development, scarification or other disturbance should only be
performed when there are actual signs of clogging, rather than on a routine basis. Always
remove deposited sediments before scarification, and use a hand-guided rotary tiller, if
possible, or a disc harrow pulled by a very light tractor.
Cost
Infiltration basins are relatively cost-effective practices because little infrastructure is needed
when constructing them. One study estimated the total construction cost at about $2 per ft
(adjusted for inflation) of storage for a o.25-acre basin (SWRPC, 1991). As with other BMPs,
these published cost estimates may deviate greatly from what might be incurred at a specific
site. For instance, Caltrans spent about $i8/ft3 for the two infiltration basins constructed in
southern California, each of which had a water quality volume of about 0.34 ac.-ft. Much of the
higher cost can be attributed to changes in the storm drain system necessary to route the runoff
to the basin locations.
Infiltration basins typically consume about 2 to 3% of the site draining to them, which is
relatively small. Additional space may be required for buffer, landscaping, access road, and
fencing. Maintenance costs are estimated at 5 to 10% of construction costs.
One cost concern associated with infiltration practices is the maintenance burden and longevity.
If improperly maintained, infiltration basins have a high failure rate. Thus, it may be necessary
to replace the basin with a different technology after a relatively short period of time.
January 2003 California Stormwater BMP Handbook 5 of 8
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TO 11 Infiltration Basin
Caltrans, 2002, BMF Retrofit Filot Program Proposed Final Report, Rpt. (JTSW-RT-oi-oso,
California Dept. of Transportation, Sacramento, CA.
Galli, J. 1992. Analysis of Urban BMP Performance and Longevity in Prince George's County,
Maryland. Metropolitan Washington Council of Governments, Washington, DC.
Hilding, K. 1996. Longevity of infiltration basins assessed in Puget Sound. Watershed Protection
Techniques i(3):i24~i25.
Maryland Department of the Environment (MDE). 2000. Maryland Stormwater Design
Manual, http://www.mde.state.md.us/environment/wma/stormwatermanual. Accessed May
22, 2002.
Nightingale, H.I., 1975, "Lead, Zinc, and Copper in Soils of Urban Storm-Runoff Retention
Basins," American Water Works Assoc. Journal. Vol. 67, p. 443-446.
Nightingale, H.I., I987a, "Water Quality beneath Urban Runoff Water Management Basins,"
Water Resources Bulletin, Vol. 23, p. 197-205.
Nightingale, H.I., I987b, "Accumulation of As, Ni, Cu, and Pb in Retention and Recharge Basin
Soils from Urban Runoff," Water Resources Bulletin, Vol. 23, p. 663-672.
Nightingale, H.I., 1987C, "Organic Pollutants in Soils of Retention/Recharge Basins Receiving
Urban Runoff Water," Soil Science Vol. 148, pp. 39-45.
Nightingale, H.I., Harrison, D., and Salo, J.E., 1985, "An Evaluation Technique for Ground-
water Quality Beneath Urban Runoff Retention and Percolation Basins," Ground Water
Monitoring Review, Vol. 5, No. i, pp. 43-50.
Oberts, G. 1994. Performance of Stormwater Ponds and Wetlands in Winter. Watershed
Protection Techniques 1(2): 64-68.
Pitt, R., et al. 1994, Potential Groundwater Contamination from Intentional and
Nonintentional Stormwater Infiltration, EPA/6oo/R-94/osi, Risk Reduction Engineering
Laboratory, U.S. EPA, Cincinnati, OH.
Schueler, T. 1987. Controlling Urban Runoff: A Practical Manual for Planning and Designing
Urban BMPs. Metropolitan Washington Council of Governments, Washington, DC.
Schroeder, R.A., 1995, Potential For Chemical Transport Beneath a Storm-Runoff Recharge
(Retention) Basin for an Industrial Catchment in Fresno, CA, USGS Water-Resource
Investigations Report 93-4140.
Southeastern Wisconsin Regional Planning Commission (SWRPC). 1991. Costs of Urban
Nonpoint Source Water Pollution Control Measures. Southeastern Wisconsin Regional
Planning Commission, Waukesha, WI.
U.S. EPA, 1983, Results of the Nationwide Urban Runoff Program: Volume i - Final Report,
WH-554, Water Planning Division, Washington, DC.
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Infiltration Basin TC-11
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.
Information Resources
Center for Watershed Protection (CWP). 1997. Stormwater BMP Design Supplement for Cold
Climates. Prepared for U.S. Environmental Protection Agency Office of Wetlands, Oceans and
Watersheds. Washington, DC.
Ferguson, B.K., 1994. Stormwater Infiltration. CRC Press, Ann Arbor, MI.
USEPA. 1993. Guidance to Specify Management Measures for Sources of Nonpoint Pollution in
Coastal Waters. EPA-84O-B-92-OO2. U.S. Environmental Protection Agency, Office of Water,
Washington, DC.
January 2003 California Stormwater BMP Handbook 7 of 8
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TO 11 Infiltration Basin
STILLING
BASIN
EMERGENCY
SPILLWAY
CONCRETE
LEVEL
SPREADER
****** **~~vv*** **************************** jw*********** * A ******************************************************************I*********************************»*»****»»»**»***»»*»»»**»»*»»»*»
*»»»*»»*» FLATBASIN FLOOR WITH ********r»»***»»»*»
»»*»»**»»**
**
*******************************
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*****************************
* * * *
* **************************************************************»*»********
RISER/
BARREL
PLAN VIEW
INFLOW -STILLING BASIN EMBANKMENT -
RISER-
EMERGENCY
SPILLWAY
INFILTRATION
BACKUP UNOERDRAIN PIPE IN CASE OF
STANDING WATER PROBLEMS ANTI-SEEP COLLAR or -
FILTER DIAPHRAGM
PROFILE
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Vegetated Swale TC-30
Bt''x .
Design Considerations
• Tributary Area
• Area Required
• Slope
• Water Availability
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 manmade.
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
stormwater 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.
Targeted Constituents
/ Sediment A
/ Nutrients •
/ Trash •
/ Metals A
/ Bacteria •
/ Oil and Grease A
J Organics A
Legend (Removal Effectiveness)
• Low • High
A Medium
CASQA
California
Stormwater
Quality
Association
January 2003 California Stormwater BMP Handbook
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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. ^f~ ^-T "*~ a ^
• 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 determined using Manning's Equation using a value of
Ck2"5 for Manning's n.
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Vegetated Swale TC-30
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. The 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
Dorman et al., 1989
Harper, 1988
Kercher et al., 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
Brassed channel
grassed channel
grassed channel
dry swale
dry swale
dry swale
dry swale
wet swale
wet swale
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)
• 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
"^i-" The topography of the site should permit the design of a channel with appropriate slope and
,i 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
m 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
MI 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.
"t<*t
M 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%.
i,**«
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.
m 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
January 2003 California Stormwater BMP Handbook 5 of 13
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TC-30 Vegetated Swale
establishment. 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.
6 of 13 California Stormwater BMP Handbook January 2003
New Development and Redevelopment
www.cabmphandbooks.com
Vegetated Swale TC-30
f" 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.
January 2003 California Stormwater BMP Handbook 7 of 13
New Development and Redevelopment
www.cabmphandbooks.com
TC-30 Vegetated Swale
Table 2 Swale Cost Estimate (SEWRPC, 1991)
Component
Mobilization/
Demobilization -light
Site Preparation
Clearing...
Grubbing*.
General
aeration"
La¥BlandTr.
Sites Development
Salvaged Tojnoi
Seed, and Mutch1..
Soo?.
Subtotal
Contingencies
Total
Unit
Swale
Arra
Aero
Yd»
Yd*
Yd'
Yd*
--
Swato
-
Extant
1
ns
0.25
372
1,210
1,210
1,210
-
1
-
LOW
$107
to yon
$3.800
$2.10
$0.20
$0.40
$120
~
25%
--
Unit Cost
Moderate
$274
S3Rnn
$5,200
$3.70
$0.35
$1.00
$240
-
2SK
-
High
$441
tKAM
$6,600
$5.30
$0.60
$1.60
$3.60
-
25%
-
Low
$107
ti inn
$950
$781
$242
$4B4
$1452
$5,116
$1,279
$6.395
Total Cott
Moderate
1274
$1 BOO
$1,300
$1,376
$424
$1,210
$2.904
$8,388
$2,347
$11.735
High
$441
$2.700
$1,650
$1,072
$605
$1,936
$4,366
$13,660
$3,415
$17.075
source: pstWRPC, luBl)
Note: MobilizBionAJemobilzalion raiaratotheoiganizrtiGn and planning involved in establishing • vegetative swate.
•Swale has a bottom width of 1.0 foot, a top width or 10 feet wth 1:3 side slopes, and a 1,000-foot length.
"Area cleared = (top width +10 feet) xswale length.c Area grubbed = (top width x swale length).
'Volume excavated = (0.67 x top width x swale depth) x swale length (parabolic cross-section).
* Area tilled = (top width + 8f swate depth2) x swale length (parabolic cross-section).
3(top width)
'Area seeded = area cleared x 0.5.
1 Area sodded = area cleared x 0.5.
8 of 13 California Stormwater BMP Handbook
New Development and Redevelopment
www.cabm,'"J~~vadbooks.corn
January 2003
p i 11 PI
I . i. I i k i If ti i i I t I i i I i I i---,. i i i <
Vegetated Swale TC-30
Table 3 Estimated Maintenance Costs fSEWRPC. 1991)
Component
Lawn Mowing
General Lawn Cam
Swato Debris and Lifer
Removal
Mulch and Fertilizer
program AtxrwHwrauon and
Swato Inspadon
Total
Unit Cost
$0.86/ 1,000 IP/ mowing
$9.00 / 1,000 ff/ year
$0.10 /inaar foot/ yav
saao/yd1
$0.1 5 /linear loot /year,
pluB$2S/inapaclon
-
Swale Size
(D«pthar>dTopVWcJth)
1.5 Foot Depth, One-
Foot Bottom Width,
It-Foot Top Width
$0.14 /Ifeittrfoot
$0.18 /Ihaar foot
$0.10 /linear foot
$051 /linear foot
$0.16 /linair foot
(0.fiS/Hnearfoot
3^oo< Depth, 3-Foot
Bottom Width, 21 -Foot
Top Width
$0.21 /inear foot
1028 /Inaar foot
$0.10 /Inear foot
$0X11 /Inaar foot
$0.15 /Inaar foot
$0.75 /linear foot
Comment
.Lawn maintananoe 8raa>(iop
wtdti-f10fa0f)Ktongtti. Mow
algMtknaaoftryaar
Lawn mahtananoe area - (top
widti + 10feet)xlengti
-
AIM nwagaWad aquata 1K
of lawn mantenancaaraa par
year
Inspect four times per year
—
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
www.cabmphandbooks.com
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., Charbeneau, 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. Schueler. 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 ofStormwater 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., Horner, Richard R., and Booth, Derek B., 2000. Characterization of
Performance Predictors and Evaluation of Mowing Practices in Biofiltration 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 Biofiltration 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. Landon, 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 Issaquah/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
New Development and Redevelopment
www.cabmphandbooks.com
Vegetated Swale TC-30
through grassed swale treatment. In Proceedings of the International Symposium of Urban
Hydrology, Hydraulics and Sediment Control, Lexington, KY. 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(2):379~383.
Seattle Metro and Washington Department of Ecology. 1992. Bicfiltration 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 no. 31. Southeastern
Wisconsin Regional Planning Commission, Waukesha, WI.
U.S. EPA, 1999, Stormwater Fact Sheet: Vegetated Swales, Report # 832^-99-006
http://www.epa.gov/owm/mtb/vegswale.pdf. Office of Water, Washington DC.
Wang, T., D. Spyridakis, B. Mar, and R. Horner. 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 Practices for Controlling
Highway Runoff. FHWA/VA-93-Ri6. Virginia Transportation Research Council,
Charlottesville, VA.
Information Resources
Maryland Department of the Environment (MDE). 2000. Maryland Stormwater Design
Manual, www.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
New Development and Redevelopment
www.cabmphandbooks.com
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.
12 of 13 California Stormwater BMP Handbook January 2003
New Development and Redevelopment
www.cabmphandbooks.com
Vegetated Swale TC-30
Providi far scour
protection.
<«) CroMMctiraofnrakwithcfMCkdu.
Notation:
L * Length of iwtalmix dnwntMMiMrclwcfcttamm (b) Dteta*k>**lvieworswalelnp<MMj»«Man*.
0, * DeptheldMckdnt(ft)
St "Bottomtip*oftwtto(Ml)W »TopwkHhofetwekd»m(fl)
W, » Bottom wtdth of chw*<tain (ft)
Ztu " "*•» <* horiion« to vwttcal dunga In swato ilda slope (Wft)
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
www.cabmphandbooks.com
13 of 13
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
S Nutrients
/ Trash
/ Metals
Bacteria
<f Oil and Grease
*/ Organics
Removal Effectiveness
See New Development and
Redevelopment Handbook-Section 5.
CASQA
California
Stormwater
Quality
Association
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
www.cabmphandbooks.com
1 of 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
T 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
Attachment 9
'me*
798 Clearlake Road, Cocoa, FL 32922
Ph: 321 -637-7552 FAX: 321 -637-7554
www.suntreetech.com
V
Remove the grate
Drop in the filter
Replace the grate
\\
Patented
Ready For Action
Page 3
Jooo
Grate Inlet Skimmer Box
Special Features
Ami
O Bypass Openings.
*
O Coarse Sieve Size Screen.
O Medium Sieve Size Screen
O Fine Sieve Size Screen
(Fine sieve size screen also on bottom)
or/
L
O Storm Boom
O Zip Tie
O Skimmer Tray
O Deflection Shield
O Flange is reinforced
with knitted 1808 ±45°
biaxial fiberglass
Screens
on all four
sides
Fiberglass
components have
gelcoated finish +
^ UV filter
Storm Boom
absorbs
hydrocarbons\ I
Page 4
Grate Inlet Skimmer Box — Functional Description
Stage 1: As stormwater enters the inlet
through the grate it comes in contact with and
passes through a Storm Boom located around
the top perimeter of the Grate Inlet Skimmer
Box. After making contact with the Storm
Boom, the stormwater flows down into the
lower filtration chamber which is equipped with
3 different sieve size filtration screens and
bypass openings.
Typical Low Flow Storm Event
•<— Coarse Screen
r~
Medium Screen—
As Stormwater Enters The Inlet
Stage 2: Throughout the entire storm event,
stormwater continues to come in contact with
the Storm Boom and then flow into the lower
filtration chamber, adjacent to the fine sieve
size screens. The fine sieve size screens are
sized to be able to capture sediment such as
sand, clay, phosphates, etc. A sand filter
quickly forms across the bottom which has the
potential to capture the finest of particles.
Stage 3: As the storm event increases in
intensity the water level in the Grate Inlet
Skimmer box rises to a level adjacent to the
medium sieve size screens and the turbulence
deflector. The medium screen provides
additional flow with less chance of obstruction
than the fine screen. The turbulence deflector
dramatically reduces the turbulence in the
lower filtration chamber,
which allows sediment to
continue to settle, without
re-suspending sediment
that has previously been
captured.
PageS
Typical Medium Flow Storm Event
Stage 4: As the storm event increases in intensity to that of high flow storm event,
the water level in the Grate Inlet Skimmer box rises to a level adjacent to the coarse
sieve size screens above turbulence deflector.
Stage 4
Typical High Flow Storm Event
The coarse screen provides additional filtered
flow with less chance for obstruction than
either the medium or fine screen. The coarse
screen is sized to capture floatables like
foliage and litter. At this stage water is flowing
through all the different sieve size screens, the
turbulence deflector continues to dramatically
reduce the turbulence in the lower filtration
chamber, and sediment continues to settle and
collect toward the bottom.
Stage 5: If the storm event creates an
extremely high flow rate into the inlet which
exceeds the flow through all the screens, the
water flow can bypass the filtration screens
through skimmer protected bypass openings near
the top of the Grate Inlet Skimmer Box. As
water flows through the bypass openings, it also
continues to flow through all the other screens.
Storm events that produce such high flow rates
are rare and typically don't last very long.
stormwatj«>.mmi\\""L^^-
Typical Super High Flow Storm Event
After The Storm Event
Parking Lot Parking Lot
Foliage &-«__ Litter _^—
1 I I
Can Hold Hundreds of Pounds of Debris
After The Storm Event: The stormwater
drains completely out of the Grate Inlet
Skimmer Box after the storm event. The
debris collected in the unit is stored in a dry
state which helps to contain the nutrient
pollutant load, prevents the filter from going
septic, and prevents mosquitoes from
breeding in the unit. After each storm event
more debris is collected, which can ultimately
weigh many hundreds of pounds.
Page6
Grate Inlet Skimmer Box - Captured Debris
I/te
4 ¥1®
The picture to the right shows an inlet with
a Grate Inlet Skimmer Box immediately
after the grate was removed, just 45 days
after it was installed. Because this inlet is
adjacent to a wash down area, it
experiences a simulated storm event
every day. The filter is full to capacity and
has been operating in bypass mode for
some time.
The picture to the left shows the Grate Inlet
Skimmer Box immediately after the
removal of booms and skimmer tray. Notice
the bypass openings around the top are
completely unobstructed. The filter is full to
capacity and is operating in bypass mode.
Because this inlet experiences an extra
heavy hydrocarbon pollutant load it is fitted
with extra Storm Booms.
^m^Mmftm
n (trite
Although the inlet is relatively small with
a grate that measures 24" x 24", debris
weighing 232 pounds with a volume of
78 quarts was removed during this
servicing. To the right is a photo of the
same Grate Inlet Skimmer Box after
being serviced.
Page 7
P
Grate Inlet Skimmer Box - Sizing and Flow Rates
Filter Openings
Medium Screen"*'
-Fine Screen —
Allow for water flow
under filter.
The maximum flow rate of a Grate Inlet
Skimmer Box is determined by the amount of
flow that can pass through the throat, the
exception is found only in very large units.
To determine the minimum flow rate of
a Grate Inlet Skimmer Box, consider only the
potential flow through the throat and bypass. If
the potential flow through the throat is less than
the potential flow through the bypass, then the
throat determines the minimum flow. If the
potential water flow through the bypass is less
than that of the throat, then the bypass
determines the minimum flow. Filtered Flow
represents the potential flow rate through all screens, and does not include the potential
flow through the bypass. Water flow through the bypass happens only when the flow rate
through the grate exceeds the flow rate through all the screens.
Flow Rate Table For 8 different Models
Model
Number
GISB-I-24-24-25
GISB-A-24-37-25
GISB-C-28-37-25
GISB-J-24-41-25
GISB-NK-32-32-25
GISB-36-36-25
GISB-D-36-48-18
GISB-G-52-58-18
Dimensions of the flange
around the top of the Grate
Inlet Skimmer Box
Width
(inches)
24
24
28
24
32
36
36
52
Length
(inches)
24
37
37
41
32
36
48
58
Depth
(inches)
25
25
25
25
25
25
18
18
Flow Rate
(cubic feet per second)
Throat
4.4
10.2
12.2
12
12.5
18.8
33.2
89.3
Filtered
Flow
14.9
21.1
19.4
24.6
19.1
23.4
26.3
40.1
Bypass
Flow
6.7
8.7
7.4
10
10.3
13.4
13.3
25
• The yellow blocks represent the minimum flow rates.
• Filtered flow is based on unobstructed screens.
Drawings and flow specifications for any size Grate Inlet
Skimmer Box is available upon request.
PageS
798 Clearlake Road, Cocoa, FL 32922
Ph: 321 -637-7552 FAX: 321 -637-7554
www.suntreetech.com
For grated curb inlets
Standard Capacity
Patented
For inlets where the only
access is through a manhole.
,
Coarse Screen
Up High For Capturing
Foliage and Litter
Storm Boom For
Collecting
Hydrocarbons
Fine Screen In
Back and Bottom
For Collecting
Sediment
Durable
Fiberglass Body
Page 9
Curb Inlet Basket
Multi-stage Filtration Captures
Everything From
Hydrocarbons, To Sediment, To
Grass Clippings, To
Litter...Everything!
To Service:
* Remove the manhole lid
* Reach in by hand or with a manhole
hook and remove the basket
* Empty the contents of the basket and
replace the Storm Boom
» Replace the basket and manhole lid
ill
Page 10
mc,
798 Clearlake Road, Cocoa, FL 32922
Ph: 321 -637-7552 FAX: 321 -637-7554
www.suntreetech.com
High Capacity
Patented
O Coarse Sieve Size Screen
O Medium Sieve Size Screen
O Fine Sieve Size Screen-
(Fine sieve size screen also on bottom)
Installation Schematic
O Storm Boom
FEemdlf
For use in inlets where the only
access is through a manhole.
A shelf system directs water flow
into the filtration basket and
positions the basket directly
under the manhole for easy
access. If necessary, the water
flow can bypass the entire
filtration system simply by flowing
past the filter and into the
catchbasin.
Page 11
Capmtbme T<a> Cmptaiare MmmHf(A Of PC
Above: View of the curb inlet showing
that the only access is through a
manhole.
Right: View of full High Capacity
Curb Inlet Basket immediately after
the manhole lid was removed.
\ >S-
Lakeland, Florida
Umlet
South Side of Hibriten Way & Lake
Hollingsworth DR
November 5, 2002
A total of 200.5 pounds of debris
was removed having a volume of
123 quarts. The foliage weighed
140.4 pounds and the sediment
weighed 56.2 pounds. A large
quantity of palm nuts was captured
by this unit.
Left: The Curb Inlet Basket has been
removed and can be easily emptied by
hand without the need of a vacuum truck.
Page 12