HomeMy WebLinkAboutSDP 05-18; ECR CORPORATE CENTER; STORM WATER MITIGATION PLAN AND PRELIMINARY HYDROLOGY STUDY; 2006-04-12Storm Water Mitigation Plan
And
Preliminary Hydrology Study
LA COSTA GREENS - LOT I
CITY OF CARLSBAD
SAN DIEGO COUNTY, CALIFORNIA
(MAP NO. 14543)
December 13, 2005
Revised January 31, 2006
Revised March 16, 2006
Revised April 12, 2006
Prepared for:
CARLTAS DEVELOPMENT COMPANY
5600 AVENIDA ENCINAS, SUITE 100
CARLSBAD, CA 92008
JOHN C. WHITE, PRESIDENT
Prepared by:
RBF CONSULTING
5050 Avenida Encinas, Suite 260
Carlsbad, CA 92008 F&MM 760.476.9193
CONSULTING
Contact Person:
89 Richard Lucera, P.E.
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STORM WATER MITIGATION PLAN
TABLE OF CONTENTS
TABLE OF CONTENTS..................................................................................................
IPURPOSE OF SCOPE...............................................................................2 2 PROJECT INFORMATION ........ ................................................................. 2 2.1 Project Description ............... ....................................................................... 2 2.2 Project Activities .........................................................................................2
3 WATER QUALITY CONDITIONS OF CONCERN......................................4
3.1.1 Potential Pollutants.....................................................................................4 3.1.2 Pollutants of Concern .................................................. ................................. 6 3.1.3 Conditions of Concern ................................................................................7 4 POST-CONSTRUCTION BEST MANAGEMENT PRACTICE PLAN..........8 4.1 Site Design BMPs ....................................................................................... 8 4.2 Source Control BMPs .................................................................................9 4.3 BMPs for Individual Project Categories.....................................................12 4.4 Treatment Control BMPs ...................................................... . ............ . ........ 12 4.5 Construction-Phase BMPs ........................................................................ 15 5 MAINTENANCE .......................................................................................16 POST-CONSTRUCTION BMP SITE MAP ..................................................................... 17
TABLE OF FIGURES
Figure2-1 Vicinity Map ................................................................................................3
Figure 4-1 Kristar Floguard Plus® Inlet Insert .............................................................15
LIST OF TABLES
Table 3-1 Anticipated and potential pollutants by project type (San Diego County, 2002a) ........................................................................................................4 Table 3-2 Summary of 303(d) impairments of downsteam water bodies ...................... 7 Table 4-1 Site design BMPs alternatives.....................................................................8 Table 4-2 Source-control BMP alternatives .................. ...............................................9 Table 4-3 Carlsbad SUSMP Individual Project Categories........................................12
Table 4-4 Treatment Control BMP Selection Matrix (San Diego County, 2002a).......13 Table 4-5 Treatment-Control BMP alternatives ..................... ....................................13
APPENDIX
A STORM WATER REQUIREMENTS APPICABILITY CHECKLIST
B BMP CALCULATIONS
PRELIMINARY HYDROLOGY STUDY
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I PURPOSE AND SCOPE
This report presents the water quality measures required for the development of Lot I of• the La Costa Greens Development, in order to fulfill the requirements of the City of
Carlsbad. This report also describes the implementation and maintenance of water
quality Best-Management Practices that will be installed on the site.
2 PROJECT INFORMATION
2.1 Project Description
The project is located within the City-of Carlsbad in the La Costa Greens Development
(CT-99-03). The project is adjacent to El Camino Real, just south of Town Garden Road
(see Figure 2-1). The site will be rough graded per City Drawing No. 397-2Y and is
currently vacant.
Existing site conditions inclUde one 7.7 acre graded pad with a vegetated parkway along
El Camino Real. The project site contains side slopes of 2:1 or less. The project is not
located within the Coastal Zone. Its existing land use designation is Light Industrial, but
the designation is subject to ôhange to Medical for the proposed project. There are no
water bodies, sanitary landfills, historical, archaeological or paleontolOgical resources
located within a half-mile of the project site. A conservation easement (within La Costa
Greens Lot 20) borders the project area to the east.
2.2 Project Activities
The project will consist of two medical office buildings (42,500 sq. ft) with adjacent
parking lots (152,150 sq.' if). Landscaping will be incorporated into the planter medians
and parkway strips surrounding. each lot. There are two private driveways proposed as
part of this project. The driveways will provide access to the site from El Camino Real
and from Metropolitan Street. Drainage from the project will be directed into a proposed
storm drain system and connected to an existing piping system that will outlet to open
space located directly south of the project area on La Costa Greens Lot 2. Although the
site is to be rough graded, approximately 90% of the site will be re-graded as part of this
project. -
The project is considered a high priority project by the City of Carlsbad. (See Appendix
-A - "Storm Water Requirements Applicability Checklist") Therefore, the project will
incorporate all applicable permanent storm water management requirements.. These
include the site design and source control BMPs, BMPs applicable to individual priority
project categories, and treatment control BMP requirements.
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Figure 2-1
Vicinity Map (Reference Thomas Bros. 1086)
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Th
3.1.5 Trash and Debris
Trash (such as paper, plastic, polystyrene packing foam, and aluminum materials) and
biodegradable organic matter (such as leaves, grass cuttings, and food waste) are
general waste products on the landscape. The presence of trash and debris may have a
significant impact on the recreational value of a water body and aquatic habitat. Excess
organic matter can create a high biochemical oxygen demand in a stream and thereby
lower its water quality. Also, in areas where stagnant water exists, the presence of I excess organic matter can promote septic conditions resulting in the growth of
I undesirable organisms and the release of odorous and hazardous compounds such as
hydrogen sulfide.
1
3.1.6 Oxygen-Demanding Substances
- This category includes biodegradable organic material as well as chemicals that react
with dissolved oxygen in water to form other compounds. Proteins, carbohydrates, and
fats are examples of biodegradable organic compounds. Compounds such as ammonia
and hydrogen sulfide are examples of oxygen-demanding compounds. The oxygen
demand of. a substance can lead to depletion of dissolved oxygen in a water body and
possibly the development of septic conditions.
3.1.7 Oil and Grease
Oil and grease are characterized as high-molecular weight organic compounds. The
primary sources of oil and grease are petroleum hydrocarbon products, motor products
from leaking vehicles, esters, oils, fats, waxes, and high molecular-weight fatty acids.
Introduction of these pollutants to the water bodies are very possible due to the wide
uses and applications of some of these products in municipal, residential, commercial,
industrial, and construction areas. Elevated oil and grease content can decrease the
aesthetic value of the water body, as well as the water quality.
3.1.8 Pesticides
Pesticides (including herbicides) are chemical compounds commonly used to control
nuisance growth of organisms. Excessive application of a pesticide may result in runoff
containing toxic levels of its active component.
3.2 Pollutants of Concern
The Environmental Protection Agency (EPA) is the primary federal agency responsible
for management of .water quality in the United States. The Clean Water Act (CWA) is
the federal law that governs water quality control activities initiated by the EPA and
others. Section 303 of the CWA requires the adoption of water quality standards for all
surface water in the United States. Under Section 303(d), individual states are required
to develop lists of water bodies that do not meet water quality objectives after required
levels of treatment by point source dischargers. Total maximum daily loads (TMDLs) for
all pollutants for which these water bodies are listed must be developed in order to bring
them into compliance with water quality objectives.
The project is located within the San Marcos hydrologic area of the Carlsbad hydrologic
unit. Receiving waters for the project site include the Pacific Ocean. According to the
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California 2002 303(d) list published by the San Diego Regional Water Quality Control
Board (RWQCB Region 9), the project is not impaired by any of the potential sources.
Table 3-2 summarizes the receiving waters and their classification by the RWQCB
- Region 9.
Table 3-2 Summary of 303(d) impairments of downstream water bodies.
Hydrologic Approximate 303 Receiving Water Unit Distance Impairment(s) Code From Site
Pacific Ocean Shoreline— San Marcos HA 904.50 3.5 mi Bacteria Indicators
3.3 Conditions of Concern
According to the City of Carlsbad SUSMP, a change to a priority project site's hydrologic
regime would be considered a condition of concern if the change would impact
downstream channels and habitat integrity. However, the changes in hydrologic
characteristics resulting from the development of this site have already. been
incorporated into the downstream storm drain system design. Runoff from this site will
discharge into open space located south of the project area on La Costa Greens Lot 2.
A separate drainage report (Master Drainage Report for La Costa Greens Project) has been prepared to support the design of the existing storm drain system. This study
assumed future development within the watershed when determining pipe sizes and
impacts to downstream facilities. Since runoff from the project discharges into new and
existing drainage facilities that are verified to accommodate peak runoff flow rates from a
100-year storm event, there are no conditions of concern associated with the project.
The Federal Insurance Rate Map (FIRM) for-this area shows that the projeôt's location is
out of the 100-year floodplain.
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4 POST-CONSTRUCTION BEST MANAGEMENT
PRACTICE PLAN
The project site 'incorporates four major types of post-construction best management
practices (BMPs).' These types are (1) site design BMPs; (2) source control BMPs; (3)
site design and source control BMPs for individual priority project categories; and (4)
treatment control BMPs. In general, site design BMPs and source control BMPs reduce
the amount of storm water and potential pollutants emanating from a site and focus on
pollution prevention. Treatment-control BMPs target anticipated potential storm water
pollutants. The project will apply these BMPs to the maximum extent practicable.
4.1 Site Design BMPs
Site design BMPs aim to conserve natural areas and minimize impervious cover,
especially impervious areas 'directly connected' to receiving waters, in order to maintain
or reduce increases in peak flow velocities from the project site. The U.S. EPA (2002)
has listed several site design BMPs that can be implemented in development projects.
The project has incorporated site design BMPs to the maximum extent praàticable.
Table 4-1 lists site-design BMP alternatives and indicates the practices that have been
applied to the project site.
Table 4-1 Site design BMPs alternatives.
Buffer Zones 0 Open Space-Design
Narrower Residential Streets 0 "Green" Parking
- 0 Alternative Turnarounds 0 Alternative Payers
El Urban Forestry D Conservation Easements
Eliminating Curbs And Gutters 0 Landscape Design
Other (Explained Below)
4.1.1 Minimize Impervious Footprint and Directly
Connected Impervious Areas
The project will minimize the use of impervious surfaces in landscape design, such as
decorative concrete, in order to minimize impervious footprint on the site and the amount
of directly connected impervious surface. Building roof drains, parking lots, and
sidewalks will discharge to vegetated swales and depressed areas, instead of directly to
the storm drain collection system, to reduce the amount of directly connected impervious
surface. Parking lots will be constructed to minimum widths and will drain to vegetated
areas. Curbs have been eliminated in various areas to allow sheet flow into Bio-
Retention Areas.
4.1.2 Protect Slopes and Channels
Site runoff will be directed away from the tops of slopes, and all slopes will be vegetated
to provide permanent stabilization.
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4.2 Source Control BMPs
Source-control BMPs are activities, practices, and procedures (primarily non-structural)
that are designed to prevent urban runoff pollution. These measures either reduce the
amount of runoff from the site or prevent contact between potential pollutants and storm
water. In addition, source-control BMPs are often the best method to address non-storm
(dry-weather) flows. Table 4-2 lists source-control BMP alternatives and indicates the
practices that will be applied at the project site.
'•T
Table 4-2 Source-control BMP alternatives.
Storm Drain Stenciling and Signage . 0 Homeowner Outreach
Material and Trash Storage Area Design 0 Lawn and Gardening Practices
Efficient Irrigation Systems 0 Water Conservation
Low-Irrigation Landscape Design 0 Hazardous Waste Management
0 On-Lot Treatment Measures - 0 Trash Management
0 Riprop or Other Flow Energy Dissipation 0 Outreach for Commercial Activities
o Other (Explained Below)
.....
4.2.1 Efficient Landscape Design and Irrigation Practices
Efficient landscape design and irrigation practices can be an effective source-control to
prevent pollution in storm water and dry-weather flows. The completed project will
implement principles of common-area efficient irrigation, runoff-minimizing landscape
design, and an effective landscape maintenance plan to the maximum extent
practicable.
4.2.1.1 Common-Area Efficient Irrigation
Automatic irrigation systems should include water sensors, programmable irrigation
timers, automatic valves to shut-off water in case of rapid pressure drop (indicating
possible water leaks), or other measures to ensure the efficient application of water to
the landscape and prevent unnecessary runoff from irrigation. Drip irrigation and other
low-water irrigation methods should be considered where feasible. Common elements
of efficient irrigation programs include:
Reset irrigation controllers according to seasonal needs.
Do not over-water landscape plants or lawns.
:. Keep irrigation equipment in good working condition.
Promptly repair all water leaks.
4.2.1.2 Runoff-Minimizing Landscape Design
Landscape designs that group plants with similar water requirements can reduce excess
irrigation runoff and promote surface infiltration. Landscape designs should utilize non-
invasive native plant species and plants with low water requirements when possible.
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4.2.1.3 Landscape Maintenance
The landscape maintenance plan should include a regular sweeping program of
impervious surfaces, litter pick-up, and proper equipment maintenance (preferably off-
site), and proper use of chemicals to help eliminate sources of storm water pollutants.
Common elements of an effective landscape maintenance plan include:
+ Implementing a regular program of sweeping sidewalks, driveways, and gutters as
part of the landscape maintenance plan.'Pick-up litter frequently. Provide
convenient trash receptacles,for public use if necessary.
:• Avoid using water to clean sidewalks, driveways, and other areas.
:. Discourage washing of landscape maintenance equipment on-site. Minimize water
use and do not use soaps or chemicals. Use a commercial wash-rack facility
whenever possible.
:• Keep landscape maintenance' equipment' in good working order. Fix all leaks
promptly, and use drip pans/drip cloths when draining and replacing fluids. Collect
all spent fluids and dispose of them properly. Designate equipment maintenance
areas that are away from storm water inlets. Perform major maintenance, and repairs
off-site if feasible.
+ Materials with the potential to pollute runoff (soil, pesticides, herbicides, fertilizers,
detergents, petroleum products, and other materials) should be handled, delivered,
applied, and disposed of with care following manufacturer's labeled directions and in
accordance with all applicable Federal, state, and local regulations. Materials will be
stored under cover or otherwise protected when rain is forecast or during wet
weather.
;. Pesticides and fertilizers, if used, will be applied according to manufacturer's
directions and will not be applied prior to a forecast rain event. Any material
broadcast onto paved surfaces (e.g. parking areas or sidewalks) will be promptly
swept up and properly disposed.
4.2.2 Material and Trash Storage Area Design
There are no outdoor material storage areas associated with the proposed project. The
trash storage area will be designed to contain stored material to prevent debris from
being distributed into storm water collection areas. For example, dumpsters with lids will
be kept in a separate enclosed area to prevent debris from being scattered by wind or
animals. The trash storage area will be paved with an impervious surface such as
concrete or asphalt concrete. In addition, the trash storage area will be graded to
prevent run-on from adjoining areas.
4.2.3 Pollution Prevention Outreach for Businesses
One source-control best management practice for commercial sites is pollution
prevention outreach. For instance, at the lease signing or as part of the lease, the tenant
can be presented with a brochure to encourage them to develop and implement a
pollution prevention program. The pollution prevention program would emphasize
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source reduction, reuse and recycling, and energy recovery. The following offer
.. suggestions for measures to be included in these areas of pollution prevention. The
pollution prevention outreach should choose the measures most applicable to the project
site for the project site. .
4.23.1 Source Reduction
• Incorporating environmental considerations into the designing of products, buildings,
and manufacturing systems enables them to be-more resource efficient.
:• Rethinking daily operations and maintenance activities can help indütries eliminate
wasteful management practices that increase costs and cause pollution.
. •. Controlling the amount of water used in cleaning or manufacturing can produce. less
wastewater.
Re-engineering and redesigning a facility or certain operation can take advantage .of
newer, cleaner and more efficient process equipment.
:. Buying the correct amount of raw material will decrease the amount of excess
materials that are discarded (for example, paints that have a specified shelf life)..
4.2.3.2 Reuse/Recycling
]
Using alternative materials for cleaning, coating, lubrication, and other production
processes can provide equivalent results while preventing costly hazardous waste
generation, air emissions, and worker health risks.
1 • Using "green" products decreases the use of harmful or toxic chemicals (and are
I . more energy efficient than other products).
One company's waste may be another company's raw materials. Finding markets for
waste can reduce solid waste, lessen consumption of virgin resources, increase
income for sellers, and provide an economical resource supply for the buyers.
4.2.3.3 Energy Recovery •.
I ' •:• Using energy, water, and other production inputs more efficiently keeps air and water
clean, reduces emissions of greenhouse gases, cuts operating costs, and improves
productivity.
4.2.3 Storm Drain Stenciling and Signage
All new storm drain grate inlets constructed as part of this project will be signed with the
message "No Dumping - Drains to Oceans" or equivalent message as directed by the
City.
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4.3 BMPs for Individual Project Categories
The City of Cthr1bad SUSMP Iitteri individual project categories for which BMPs must
be provided. .Table 4-3 below lists these individul project categories and indicates that
the individual category of parking areas is applicable to.the proposed project. Inlets
equipped with filter inserts treat any runoff generated and additional treatment is
provided-as discussed in Section 4.4. Most parking areas will discharge to depressed
vegetated areas, instead of directly to the storm drain collection system. Slopes will be
vegetated to provide permanent stabilization and to prevent erosion.
Table 4-3 Carlsbad SUSMP Individual Project Categories
0 Private Roads
Residential Driveways & Guest Parking
El Dock Areas
Maintenance Bays
Vehicle Wash Areas :
0 Outdoor Processing Areas
D Equipment Wash Areas :
Parking Areas
0 Fueling Area
Hillside Landscaping
4.4 Treatment Control BMPs
-. Pest-construction "treatment control" storm water management .BMPs provide treatment
for storm water emanating from the project site. Structural BMPS are an integral element
of post-construction storm water management and may include storage, filtration, and
infiltration practices. BMPs have varying degrees of effectiveness versus different pollutants of concern. Table 4- below summarizes whibh treatment iontrol BMPs and
removal effectiveness for certain constituents.
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Of the treatment control options available for this project, infiltration practices are not
feasible- due to the preponderance of hydrologic soil type D throughout the site, which
has poor infiltration:properties. Wet ponds and constructed wetlands rely On a perennial
water source, which is generally difficult to sustain in. .the projects arid environment.
While filtration devices, such as sand filters and media filters, typically have medium to
high removal efficiencies for the project's pollutants of concern, they are aesthetically
unsuitable for use in developments such as this project. An underground sand/media
filter -might improve aesthetics, but these are not recommended for drainage, areas
greater than 2 acres (2003 California New Development BMP Handbook, : Fact Sheet
TC-40), and the proposed project covers 7.7 acres. Since the proposed project site
consists of a generally flat graded pad, implementing several filters for smaller drainage
areas is not feasible due to the lack of required head needed to ensure that water
passes through the filter.
The treatment controls which are both effective at removing the project pollutants of
concern and, suitable for incorporation into the prqposed project include bio-retention
area, and &ainage inlet inserts as described in the following sections. The combination
of -vegetated-- strips, bio-retention areas, and drainage inserts in all drainage areas
provides a multiple BMP approach to water quality treatment for runoff.
4.4.1.1. Drainage Filter Inserts.
To provide additional treatment and removal of potential pollutants, drainage inlet inserts
will be installed in all storm drain inlets capturing runoff from the parking lots. Kristar
Floguard Plus® inserts or equivalent will be specified to treat runoff for hydrocarbons and
trash/debris. The Kristar Floguard Plus® inlet insert is shown in Figure 4-1, and is
similar in design and function to other proprietary inlet inserts. Surface runoff enters the
inlet and passes over/through and adsorbent material to remove hydrocarbons, while
sediments and trash/debris are collected in the hanging basket. Recommended
maintenance consists of three inspections per year (once before the wet season and two
during, or more as may be needed) plus replacement of the adsorbent when it is more
than 50% coated with pollutants and removal of excessive sediment/debris. Each inlet
insert costs about $570 and is available locally through Downstream Services (760-746-
2544 or 760-746-2667). The inserts can be installed by Downstream Services for
additional cost or by the project construction contractor. Màintenänce costs are
estimated at about $400 per year: (Refer to Appendix B fOr design calculations).
4.4.1.2 Bio-Retention Areas
The bio-retention areas function 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. Cost ranges between $10 and $40 per
square foot depending on other drainage facilities associated with the bio-retention
areas, such as drain piping. The areas function to reduced the velocity of runoff by
passing, over or through buffer strip and subsequently distributed evenly along a 'ponding
area. Exfiltration of the stored water in the bio-retention area planting soil into the
underlying soils occurs over a period of days. (Refer to TC-32 in Appendix B).
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5 MAINTENANCE
To ensure lon-term. maintenance of project BMPs, the projet proponent will enter into
a contract with the City of Carlsbad to obligate the project proponent to maintain, repair
and replace the storm water BMP as necessary into perpetuity. Scurity will be required
in the form of a Letter of Credit.
The.site thall be kept in a neat and orderly fashion with a regularly scheduled landscape
maintenance -crew in charge of keeping gutters and inlets free of litter and debris. The
landscape crew will also maintain the landscaping to prevent soil erosion and minimize
sediment transport.
The project consists of a series o Brooks boxes, which will include Kristar Floguard
PFus' inlet inserts.. It. is recommended that the hydrocarbon absorption booms be
. replaced four times per year. Currently the approximate cost to replace each boom is
$100.00. This amounts to a maintenance cost of $400.0.0 per year, per inlet.
. The project also includes several bio-retention .areas. These áreàs will require nothing
more than the routine periodic maintenance that is required of any landscaped area.
This includes regular pruning and weeding. Mulch should be replaced as erosion occurs
or, at the very least, every 2-3 years prior to the wet season.
Maintenance records shall be retained for at least 5-years. These records shall be made
available to the City of Carlsbad for inspection Upon request.
I
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I APPENDIX A
Storm Water Standards
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APPENDIX A
STORM WATER REQUJREMENTS APPLICABILITY CHECKLIST
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," "Standard Permanent Storm
Water BMP Requirements" in Seption 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?* Yes No
Detached residential development of 10 or more units .2L Attached residential development of 10 or more units
- Commercial development greater than 100,000 square feet X - Automotive repair shop
- --... Restaurant
Steep hillside development greater than 5,000 square. feet
- X Project discharging to receiving waters within Environmentally Sensitive Areas
- Parking lots greater than or equal to 5,000 fV or with at least 15 parking spaces, and
potentially exposed to urban runoff
9. Streets, roads, highways, and freeways which would create a new paved surface that is
5,000 square feet or greater I - * Refer to the definitions section in the Storm Water Standards for expanded definitions of the priority project categories.
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.
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Part B: Determine Standard Permanent Storm Water Renuirements.
Does the project propose: Yes No
New impervious areas, such as rooftops, roads, parking lots, driveways, paths and
sidewalks? -
2_..
-
- New pervious landscape areas and irrigation systems?
- Permanent structures within 100 feet of any natural water body?
- X Trash storage areas? X - Liquid or solid material loading and unloading areas? X Vehicle or equipment fueling, washing, or maintenance areas?
- _ Require a General NPDES Permit for Storm Water Discharges Associated with
Industrial Activities (Except construction)?*
- Commercial or industrial waste handling or storage, excluding typical office or
household waste?
Any grading or ground disturbance during construction?
Any new storm drains, or alteration to existing storm drains? X 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
t, www.swrcb.ca.gov/stormwtr/industniaihtml
Section 2. Construction Storm Water BMP Requirements:
If the answer to question I 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 I is "No,"
but the answer to any of the remaining questions is "Yes," your project is subject to Section IV, "Construction Storm 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 Reauirements.
Would the project meet any of these criteria during construction? Yes No
Is the project subject to California's statewide General NPDES Permit for Storm Water-
Discharges Associated With Construction Activities?
- Does the project propose grading or soil disturbance?
- Would storm water or urban runoff have the potential to contact any portion of the x construction area, including washing and staging areas?
- - 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)?
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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 projecVs 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
Projects where the site is 50 acres or more and grading will occur during the
rainy season
Projects 5 acres or more. 3) Projects 5 acres or more within or directly
adjacent to or discharging directly to a coastal lagoon or other receiving water
within an environmentally sensitive area
Projects, active or inactive, adjacent or tributary to sensitive water bodies
B) Medium Priority
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.)
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.
Permit projects on private property .where grading permits are required,
however, Notice Of Intents (NOls) and SWPPPs are not required.
0 C) Low Priority
Capital Projects where minimal to no grading occurs, such as signal light and
loop installations, street light installations, etc.
Permit projects in the public right-of-way where minimal to no grading occurs,
such as pedestrian ramps, driveway additions, small retaining walls, etc.
) Permit projects on private property where grading permits are not required,
such as small retaining walls, single-family homes, small tenant
improvements, etc.
32
APPENDIX B
Targeted Constituents
El Sediment I
El Nutrients A
El Trash I
El Metals U
El Bacteria
El Oil and Grease I
El Organics I
Legend (Removal Effectiveness)
Low I High
A Medium
Bioretention TC-32
Design Considerations
Soil for Infiltration
TributaryArea
a Slope
Aesthetics
a Environmental Side-effects
Description
The 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 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. Exflltration 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
N 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 windbreaks, absorbs
noise, and improves an area's landscape.
Limitations
a The bioretention BMP is not recommended for areas with
slopes greater than 20% or where mature tree removal would
January 2003 Californi a Stormwater BMP Handbook 1 of 8
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TC-'32 Bioretention
be required since clogging may result, particularly if the BMP receives runoff with high sediment loads (EPA, 1999).
Bioretentionis not a suitable BMP at locations where the water table is within 6 feet of the
m 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.
I • 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 tree or shrub per 50 ft2 ofbioretention area should be included.
• Cover area with about 3 inches of mulch.
Construction/Inspection Considerations
Bioreterition area should not be established until contributing watershed is stabilized.
Performance
Bio retention 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 ibr 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 stonnwater 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
require oxygen and can, result in depleted oxygen levels if the bioretention area is not adequately
2 of 8 CaIifoma StormwatEr BMP Handbook January 2003
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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 a], 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 I Removal Bate
Total Phosphorus 70-83%
Metals (Cu,Zn, Pb) 93-98%
TKN 68-80%
Total Suspended Solids 90%
Organics 90%
Bacteria 90%
Results for both the laboratory and field experiments were simi1r for each of the pollutants
analyzed. Doubling or halving the influent pollutant levels had little effect on the effluent
pollutants concentrations (Davis et a], 1998).
The microbial activity and plant uptake occurring in the bioretention area will likely result in higher removal rates than those determined for infiltration BMPs.
SitiAg Criteria
Bio retention BMPs are generally used In treat stormwater from impervious surfaces at
commercial, residential, and industrial areas (EPA, i). 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 away that minimizes erosive conditions as sheet flow is conveyed to the treatment area Locations where a bióretention 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.
January 2003 Calilbmla Stormwater BMP Handbook 3 of 8
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TC32 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, thus 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 2.5 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 fbr a bioretention area should be between 0.1 and 0.4 hectares (0.25
and 1.0 acres). Larger drainage areas may require multiple bioretention areas. Furthermore,
the maximum drainage area for a bioretention area is determined by the expected rainIll 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 fu.uetion of the drainage area and the runoff
generated from the area is sized to capture the water quality volume.
The 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 landscapd
areas in urban settings typically are unable to tolerate. The preferred width i525 feet (7.6
meters), with a length oftwice 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 barns, loamy sands, or barns. 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 a1-5 to 3 percent organic content and a maximum 500 ppm concentration of soluble
salts.
4of 8 California StormwaIr BMP Handbook January 2003
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Pli
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 (lo.:. centimeters) deeper than
the bottom of the largest root ball aud. 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 i8 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 ofbothtrees and shrubs are recommended to be planted at a rate of 2500 trees and shrubs
per hectare (i000 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 IbiJowing 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 bardwoodmu]chor 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 areas 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 hpuld blend over
time through plant and root growth, organic decomposition, and the development of natural
January 2003 California StDrmwathr BMP Handbook 5 o 8
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TC-32 Bioretention
soil horizon. These 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
'9 because of highly organic, often heavily vegetated areas mixed with shallow water. Routine inspections for areas of standing water within the BUT and corrective measures to restore proper infiltration rates are necessary to prevent creating mosquito and other vector habitat. In
-ì 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,
unclogging 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 abioretention area are slightly greater than those for the required laiadsaping for a new development (EPA, 1999). A general rule of thumb (COfflnan, 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 $io 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 with plrniting soil The costs of retrofitting a commercial site in Maryland, Kettering Development, with 15 bioretention areas were estimated at $in,6ôo.
In any bioretention 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, backfillmaterial, use ofunderdrains etc.), those landscaping expenses that would be required regardless of the bioretention i12sta11at1on should be subtracted when determining the net cost.
6 of 8 California StormwaIr BMP Handbook January 2003 New Developmentand Redevelopment
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Bioretention TC-32
Perhaps of most importance, however, the cost savings compared to the use of traditional structural stormwater conveyance systems makes bioretention areas quite attractive firnrncislly. For example, the use of bioretention 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 $ioo,000
using bioretention cells on each lot instead of nearly $400,000 for the traditional stormwater ponds that were originally planned (Rapphrninclg). 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
Coffinan, LS., R. Goo and R. Frederick, 1999: Low impact development an innovative
alternative approach to stormwater management. Proceedings of the 26th Annual Water Resources Pbnming and Management Conference ASCE, June 6-9, Tempe, Arizona-
Davis, AP., Shokouhiri, M., Shanna, H. and Minami, C., "Laboratoiy Study of Biological
Retention (Bioretention) for Urban Stoimwater.Management," Water Enu iron. Res., 73(l),5-14 (2001).
Davis, AY., Shokouhian, M., Sharma, H, Minami, C., and Winogradoif, D. "Water Quality
Improvement through Bioretention: Lead, Copper, and Zinc,' WaterEnviron. Res., accepted for publication, August 2002.
Kim, H., SeagTen, EA., and Davis, A.P. "Engineered Bioretention for Removal of Nitrate from Storrnwater Runoff" W.RF1'EC 2000 ConferenceProceedings on CDROMResearch
Symposium, Nitrogen Removal, Session 19, Anaheim CA, October 2000.
Hsieh, C.-h. and Davis, A.P. "Engineering Bioretention for Treatment of Urban Stonnwater
Runoff" Watersheds 2002, Proceedings on CDROMResearch Symposünn, 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. Landover, MD.
U.S. EPA Office of Water, 1999. Stormwater Technology Fact Sheet Bioretention. EPA 832-F-
99-012.
Weinstein, N. Davis, A.P. and Veeramachane.ni, R. "Low Impact Development (LID) Stonnwater Management Approach for the Control of Diffuse Pollution from UrbanRoadways," 5th International Conference Diffiise/NonpointPollution and Watershed Management Proceedings, C.S. Meiching and Ernie Alp, Eds. 2001 International Water Association.
January 2003 California stormwater BlIP Handbook 7 of 8
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TC-32 Bioretention
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801' 8 California Stormwathr BMP Handbook . January 2003
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Multiple System Fact Sheet TC-60
Design Considerations Description
A multiple treatment system uses two or more BMPs in series. • Area Required
Some examples of multiple systems include: settling basin • Slope
combined with a sand filter; settling basin or biofilter combined a Water Aiability with an infiltration basin or trench; extended detention zone on a
wet pond. • Hydraulic Head
a ErnAronmental Side-effects 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 iifiltration devices where the potential for
clogging exists.
a BMPs which target different constituents can be combined to Targeted Constituents provide treatment for all constituents of concern-
jj Sediment
a BMPs which use different removal processes (sedimentation, El
filtration, biological uptake) can be combined to improve the El Trash
overall removal efficiency for a given constituent. El Metals a
• El Bacteria A a BMPs in series can provide redundancy and reduce the El Oil and Grease likelihood of total system failure. El Organics a
Limitations Legend (RemovaiEffective'ie33)
a Capital costs of multiple systems are higher than for single Low 9 High
devices. A Medium
a Space requirements are greater than that required for a
single technology.
Design and Sizing Guidelines
Refer to individual treatment control BMP fact sheets.
- Performance
a 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 hrnd 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.
QALTrY 5SOC1AT3
January 2003 California StorrnwatEr BMP Handbook 1 of 2 New Development and Redevelopment
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TC-60 Multiple System Fact Sheet
When addressing multiple constituents though multiple BMPs, one BMP may optimize removal of particular constituent while another BMP optimizes removal of 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.
I Additional Design Guidelines
When using two or more BMPs in series, it maybe possible to reduce the size of BMPs.
1 • 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.
I Refer to individual treatment control BUT fact sheets.
2 of 2 California Stormwater BMP Handbook January 2003
New Development and Redevelopment
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PRELIMINARY HYDROLOGY STUDY
PRELIMINARY HYDROLOGY STUDY
TABLE OF CONTENTS
SECTION 1—INTRODUCTION
1.1 General Introduction ............................................ ................ .................... ........... 1
SECTION 2 -. PROJECT INFORMATION 0
2.1 Existing Conditions ......................................................... .................... ................. 1 .2.2 Proposed Conditions ........................................................................................... 1
- SECTION 3—ANALYSIS/CONCLUSION ....................................... ....... ........
-, APPENDIX - HYDROLOGY CALCULATIONS.......................................
.3
A
Al
La Costa Greens - Lot 1
Preliminary Hydrology Study
PRELIMINARY HYDROLOGY STUDY
1 INTRODUCTION
The purpose of this study is to identify and propose remedial action for storm water flows
generated- from the proposed improvement of La Costa Greens - Lot 1. This report is to
verify that the proposed drainage design will have no effect on the direction of runoff and.
a negligible diversion of flow. ,. . . .
No options. or exceptions have been taken for this study within the regulations of the' San
Diego County. .
No other hydrologic and hydraulic design criteria outside of the San Diego. County (June
2003) are referenced for this study.
2 PROJECT INFORMATION
2.1 Existing Conditions
The project is located within the City of Carlsbad in the La Costa Greens Development.
The project is adjacent to El Camino Real, just south of Town Garden Road (see Figure
2-1). The site will be rough graded per City Drawing No. 397-2Y and is currently
vacant.
Existing site conditions include one 7.7 acre graded pad with a vegetated parkway along•
El Camino Real. The project site contains side slopes of 2:1 of less. The project is not
located within the Coastal Zone. Its existing land use designation is Light Industrial, but
the designation is subject to change to Medical for the proposed project. There are no
water bodies, sanitary landfills, historical, archaeological or paleontological resources
located within a half-mile of the project site. A conservation easement (within La Costa
Greens Lot 20) borders the project area to the east. .
2.2 Proposed Conditions
The project will consist of two medical office buildings (42,500 sq. ft.) with adjacent
parking lots (152,150 sq. ft.). Landscaping will be incorporated into the planter medians
and parkway strips surrounding each lot. There are two private driveways proposed as
part of this project. The driveways will provide access to the site from El Camino Real
and from Metropolitan Street. Drainage from the project will be directed into a proposed:
storm drain system and connected to an existing piping system and will outlet to open
space located directly south of the project area on La Costa Greens Lot 2. Although the
site is to be rough graded, approximately 90% of the site will be re-graded as part of this
project.
La Costa Greens - Lot 1
Preliminary Hydrology Study
PRELIMINARY HYDROLOGY STUDY
3 ANALYSIS/CONCLUSION
Runoff within the project site will discharge into a proposed drain system to be located
onsite.. This storm drain system will connect into an existing storm drain system, which
discharges runoff into open space located south of the project site. A separate drainage
report (Mass -Graded Hydrology Study for *La Costa Greens Neighborhoods 1.1-1.3 & El
Camino Real Widening) has been prepared to support the design of the proposed storm
drain system. The approved master study anticipated and made allowance for 100 year
flows of 3097 cfs/acre (31.9 cfs overt 10.3 acres to Node 113). Given our development
watershed of 6.1 acres that drains to the Lot 1 pipe system, this equates to an initial
allowance of 18.9 acres. Final calculations show an actual 100 year flow of 20.7 cfs
(Q=0.85*4.0in/hr *6.lac), based upon anoverall "C" value of 0.85, an on-site Tc of 7:40
minutes, and use of the former County of San Diego IDF Standard Curve, 2003 (for
"apples to apples" comparison.) This increase represents about dditional flow
compared to that originally estimated in the master. study. This increase is negligible,
becausethe existing 30" to which Lot 1 discharges has more than adequate capacity to
handle the flow calculated. .
La Costa Greens - Lot 1 2
Preliminary Hydrology Study PF
PRELIMINARY HYDROLOGY STUDY
3 ANALYSIS/CONCLUSION
Runoff within the project site will discharge into a proposed drain system to be located
onsite. This storm drain system will connect into an existing storm drain system, which
discharges runoff into open space located south of the project site. A separate drainage
report (Mass-Graded Hydrology Study for La Costa Greens Neighborhoods 1.1-1.3 & El
Camino Real Widening) has been prepared to support the design of the proposed storm
drain system. The approved master study anticipated and made allowance for 100 year
flows of 3.097 cfs/acre (31.9 cfs over 10.3 acres to Node 113). Given our development
watershed of 6.1 acres that drains to the Lot 1 pipe system, this equates to an initial
allowance of 18.9 cfs. Final calculations show an actual 100 year flow of 20.7 cfs
(Q=0.85*4.oin/hr *6.lac), based upon an overall "C" value of 0.85, an on-site Tc of 7.20
minutes, and use of the former County of San Diego IDF Standard Curve, 1983 (for
"apples to apples" comparison.) This increase represents about 9% additional flow
compared to that originally estimated in the master study. This increase is negligible,
because the existing 30" to which Lot 1 discharges has capacity to handle this additional
flow (see calculations attached.)
La Costa Greens - Lot 1 2 PF Preliminary Hydrology Study
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