HomeMy WebLinkAboutSDP 02-19; LA COSTA CANYON HOMES; STORMWATER MANAGEMENT PLAN; 2006-03-31I
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TABLE OF CONTENTS
VICINITY MAP ................................................................................................................ Iii
INTRODUCTION ............................................................................................................. 1
1. PROJECT DESCRIPTION ......................................................................................... 1
1 .1 Topography and Land Use ................................................................................. 1
1.2 Hydrologic Unit Contribution ............................................................................... 1
2. WATER QUALITY ENVIRONMENT ........................................................................... 2
2.1 Beneficial Uses ................................................................................................... 2
2.1.1 Inland Surface Waters ............................................................................. 3
2.1.2 Groundwater ............................................................................................ 3
2.2 303(d) Status ...................................................................................................... 3
3. CHARACTERIZATION OF PROJECT RUNOFF ........................................................ .4
3.1 Existing and Post-Construction Drainage .......................................................... .4
3.2 Post-Construction Expected Discharges ........................................................... .4
3.3 Soil Characteristics ............................................................................................. 5
4. MITIGATION MEASURES TO PROTECT WATER QUALITY ................................... 5
4.1 Construction BM P's ............................................................................................ 5
4.2 Post-construction BMP's ·····························································•·.·····················5
4.2.1 Site Design BM P's ................................................................................... 5
4.2.2 Source Control BMP's ............................................................................. 6
4.2.3 Treatment Control BM P's ........................................................................ 7
4.2.3.1 Stormceptor ................................................................................... 7
4.2.3.2 Stormceptor Applications ........................................................... 7
5. OPERATION AND MAINTENANCE PROGRAM ................................................... ,.10
5.1 Stormceptor ..................................................................................................... 1 O
5.1.1 Stormceptor Maintenance Guidlines ...................................................... 10
5.1.2 Inspection Frequency ............................................................................ 11
5.1 .3 Debris and Sediment Disposal .............................................................. 11
5 .1.4 Hazardous Wastes ................................................................................ 11
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6. FISCAL RESOURCES
6.1 Mechanisms to Assure Maintenance ................................................................ 11
6.2 Maintenance Costs ........................................................................................... 11
7. SUMMARY AND CONCLUSIONS ........................................................................... 11
APPENDICES
Appendix A -Water Quality Flow Calculations
EXHIBITS
Exhibit A -BMP Exhibit
Exhibit B -Post-Construction Exhibit
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INTRODUCTION
The Stormwater Management Plan (SWMP) is required under the County of San Diego
Watershed Protection, Stormwater Management, and Discharge Control Ordinance
(section 67.817). The purpose of this SWMP is to address the water quality impacts
from the proposed improvements for APN 216-300-17, 18. Best Management Practices
(BMP's) will be utilized to provide a long-term solution to water quality. This SWMP is
also intended to ensure the effectiveness of the BMP's through proper maintenance that
is based on long-term fiscal planning. The SWMP is subject to revisions as needed by
the engineer.
1.0 PROJECT DESCRIPTION
The proposed project is located at 9240 La Costa Avenue, Carlsbad, California. The
project consists of 1 O condominium units and parking lots. The site is accessible both
La Costa Avenue. The entire site is approximately 0.77 Ac. The site currently drains
towards La Costa Avenue.
1.1 Topography and Land Use
The property is a graded area covered with grass and dirt mildly sloping south easterly
towards La Costa Avenue.
1.2 Hydrologic Unit Contribution
The project is within the Batiquitos Hydrologic Sub-Area, 904.51 of the Carlsbad
Hydrologic Unit, 904.00) as described by the Water Quality Control Plan for San Diego
Basin ("Basin Plan), adopted by the California Regional Water Quality Control Board,
San Diego Region, dated September 8, 1994 and amended May 5, 1998. The receiving
water of the project site is Batiquitos Lagoon. This project is approximately 0.0000432
percent (0. 77 acre /178, 13 acres) of the watershed.
Stormwater Management Plan
408-409-BMP
December 8, 2005
Masson & Associates, Inc.
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2.0 WATER QUALITY ENVIRONMENT
2.1 Beneficial Uses
The beneficial uses for the hydrologic unit are included in Tables 2.1 and 2.2. These
tables have been extracted from the Water Quality Control Plan for the San Diego
Basin.
Contact Water Recreation (REC-1) -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.
Non-contact Water Recreation (REC-2) -Includes the uses of water for recreational
activities involving proximity to water, but not normally involving body contact with water,
where ingestion of water is reasonably possible. These uses include, but are not limited
to, picnicking, sunbathing, hiking, beachcombing, camping, boating, tidepool and marine
life study, hunting, sightseeing, or aesthetic enjoyment in conjunction with the above
activities.
Preservation of Biological Habitats of Special Signification (BIOL) -Includes use of water
that support designated areas or habitats, such as established refuges, parks,
sanctuaries, ecological reserves, or Area of Special Biological Significance of (ASBS),
where the preservation or enhancement of natural resources special protection.
Estuarine Habitat (EST) -Includes uses of water that support estuarine ecosystems
including, but not limited to, preservation or enhancements of estuarine habitats,
vegetation, fish, shellfish, or wildlife (e.g., estuarine mammals, waterfowl, shorebirds).
Wildlife Habitat (WILD) -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 and food sources.
Rare. Threatened. or Endangered Species (RARE) -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.
Marine Habitat (MAR)-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).
Migration of Aquatic Organisms (MIGR) -Includes uses of water that support habitats
necessary for migration, acclimatization between fresh and slat water, or other temporary
activities by aquatic organisms, such as anadromous fish.
Stormwater Management Plan
408-409-BMP
2 December 8, 2005
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Spawning, Reproduction, and/or Early Development (SPWN) -Includes uses of water
that support high quality aquatic habitats suitable for reproduction and early development
of fish. This use is applicable only for the protection of anadromous fish.
2.1.1 Inland Surface Waters
Inland surface waters have the following beneficial uses as shown in Table 2.1.
Table 2.1 Beneficial Uses for Inland Surface Waters
Hydrologic
Unit Number
-ct! ,.... C\I -:.a C C ct! 0 0 I :.::; :.::;
ct! ct! Q) w z Q) Q) !!:: a: .... .... ...J :§ a: a: s 0 0 0 I-C) Q) Q) (J) ~ <( <( fl. a: a: in w a: ~ ~ (J)
904.51 X X X X X X X X X
2.1.2 Ground Waters
Ground waters have the following beneficial uses as shown in Table 2.2.
Table 2.2 Beneficial Uses for Ground Waters
Hydro logic
ci:l Unit Number 0..
:2
C ~
~
904.51 X
904.51 0
x Existing Beneficial Use
0 Potential Beneficial Use
+ Excepted from Municipal
2.2 303(d) Status
Q) .... ci:l :E ·;:::
~ ti,
0 ~ ·;::: "O C) .!: <(
X X
0 0
According to the California 2002 303(d) list published by the San Diego Regional Water
Quality Control Board, the nearest impaired water body is Pacific Ocean Shoreline, San
Marcos HA which is listed as being sensitive to Bacterial Indicators. The site is
approximately 1 .1 miles from Pacific Ocean Shoreline.
Stormwater Management Plan
408-409-BMP
3 December 8, 2005
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3.0 CHARACTERIZATION OF PROJECT RUNOFF
3.1 Existing and Post-Construction Drainage
The existing site is grass and dirt which currently allows storm runoff to sheet flow
across the surface and into concrete gutters located in La Costa Avenue.
. The proposed development is adding impervious surfaces to the site. The proposed
project is bounded with high retaining wall on the southwesterly and portion of
southeastern of the project site. The runoff from basin (B-1) flows via landscape and
valley gutter to proposed inlet/stormceptor located on eastern portion of the project site.
The runoff from basir. {B-2) flows northeasterly via proposed storm drsin systems to
proposed inlet/stormceptor located on project. This runoff confluences with runoff from
basin (B-1) and the total runoff will discharge via a pipe to the proposed curb outlet in La
Costa Avenue.
A Stormceptor (STC) {450i model) is proposed at this inlet where basin B-1 and B-2
confluence. The STC is designed to capture and treat 1.4 cfs runoff, during a 100-year
event.
A summary of the post-construction water quality flows is included in Table 3.1. See
Appendix A for calculations.
Table 3.1 Post-Construction Water Quality Flows
Basin/Node C Coeffecient Area (ac) 0100 (cfs) Owo (cfs)
B-1 0.71 0.39 1.0 0.06
B-2 0.71 0.15 0.4 0.02
CP#1 0.71 0.53 1.4 0.08
3.2 Post-Construction Expected Discharges
There are no sampling data available for the existing site condition. In addition, the
project is not expected to generate significant amounts of non-visible pollutants.
However, the following constituents are commonly found on similar developments and
could affect water quality:
• Sediment discharge due to construction activities
• Sediments due to post-construction areas left bare.
• Nutrients from fertilizers
• Heavy Metals
• Oxygen Demanding Substances
• Hydrocarbons from paved areas
• Pesticides from landscaping and use in buildings
• Trash and debris deposited in gutters.
• Oil and grease from paved areas
Stormwater Management Plan
408-409-BMP
4 December 8, 2005
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3.3 Soil Characteristics
The project area consists of soil group D. The project will not have slopes steeper than
1.5:1. All slopes will include slope protection for construction and post-construction
conditions.
4.0 MITIGATION MEASURES TO PROTECT WATER QUALITY
To address water quality for the project, BMP's will be implemented during construction
and post-construction. Placements of the BMP's are as noted on Exhibit A.
4.1 Construction BMP's
A detailed description of the construction BMP's will be shown on the Grading Plans
and Improvement Plans. Typical BMP's include the following:
• Silt Fence
• Fiber Rolls
• Sandbag Barrier
• Material Delivery and Storage
• Stockpile Management
• Solid Waste Management
• Stabilized Construction Entrance/Exit
• Desalting Basin
• Gravel Bag Berm
• Spill Prevention and Control
• Water Conservation Practices
• Erosion Control Mats and Spray-on Applications
• Vehicle and Equipment Maintenance
Construction BMP's for this project have been selected and will be placed and
maintained so as to comply with all applicable ordinances and guidance documents.
4.2 Post-Construction BMP's
Pollutants of concern as noted in Section 3 will be addressed through three types of
BMP's. These types of BMP's are site design, source control and treatment control.
4.2.1 Site Design BMP's
The project is designed to minimize, to the maximum extent practicable, the introduction
of pollutants and conditions of concern that may results in significant impacts, generated
from site run off to the storm water conveyance system. This development is a medium
priority project, because of the additional parking being constructed. The potential for
erosion on this site is reduced by asphalt covering the bare ground. No manufactured
slopes will be created. There is a minimal amount of grading being proposed. The
graded areas are to be landscaped, and the runoff conveyed through the on-site gutter
system. There is no planned widening of the existing streets.
Stormwater Management Plan
408-409-BMP
5 December 8, 2005
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Observing Principal Number one
There will be increase in peak runoff from the site. Therefore, post-development peak
runoff flow rates and velocities from the project site will increase.
4.2.2 Source Control BMP's
Source control BMP's will consist of measures to prevent polluted runoff. This program
will include an educational component directed at homeowner. The homeowner will
receive a set of brochures developed by the city of Carlsbad Environmental Health
Department. These wiil include the following:
• Storm Water Runoff Pollution Fact Sheet
• Storm Water Runoff Pollution Prevention Tips for homeowners
• Storm Water Pollution Prevention Yard Work (Landscaping,
Gardening, Pest Control)
• Stormwater Pollution Prevention Pet Waste
• Stormwater BMP Swimming Pool and Spa Cleaning
Observing Principal Number Two
In addition; any storm drain inlets located on and near the site will be stenciled with a
message warning citizens not to dump pollutants into the drains.
Also, the new impervious surfaces are designed to drain toward landscaping prior to
discharging into the Stormseptor.
Observing Principal Number Tree
The out door trash bin (Dumpsters) shall meet the requirements set forth in the current
San Diego SUSMP. The storage location shall be paved with an impervious surface,
designed not to accept any run-on from adjoining areas.( Concrete Curb or AC Berm) It
should be screen or wall to prevent off site transfer of trash by wind. The dumpsters
shall have lids on all containers that exclude rain. If no lids are to be used then the
storage shall be roofed or an awning that will exclude rain. Additionally there should be
a drain and a method to treat the small amount of water that may become trapped in the
storage area. There should be a message warning citizens to deposit all trash inside the
container and to close the lids.
Parking areas
The requirements in this section shall be considered and incorporated and apply to the
parking of any motorized vehicles in any location on site within the County. Parked
vehicles present a problem in urbanized areas due to their potential cumulative effects
on water quality. Poorly maintained vehicles leak oil antifreeze, and other fluids when
parked. As a result, parking areas can contain heavy deposits of many automotive
pollutants. These pollutants accumulate on driveway streets, parking lot surfaces, etc.
and are directly transported to local Receiving Waters. The following source control
BMP's should be implemented by the project proponent or equivalent measures,
methods, or practices for all vehicles parking on site:
Stormwater Management Plan
408-409-BMP
6 December 8, 2005
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Vehicles that use this facility should not have excessive accumulations of oil and grease
so that deposits do not end up on the site. Any deposits that do end up in the park lot
should be cleaned by using "dry cleaning" methods (e.g., absorbents, scraping,
vacuuming, or sweeping).
4.2.3 Treatment Control BMP's
The following treatment control BMP's will be implemented to address water quality:
4.2.3.1 Stromceptor
The Stormceptor (STC 450i) consists of a lower treatment chamber, which is always full
of water, and a by-pass chamber. Stormwater flows into the by-pass chamber via the
storm drain or grated inlet (Inlet Stormceptor). Normal flows are diverted by a weir and
drop pipe arrangement into a treatment chamber. Clean water flows up through the
submerged outlet pipe based on the head at the inlet weir and is discharged back into
the by-pass chamber downstream of the weir. The downstream section of the pipe is
connected to the outlet storm drain pipe.
Oil and other liquids with a specific gravity less than water will rise in the treatment
chamber and become trapped under the fiberglass weir, since the outlet pipe is
submerged. Sediment will settle to the bottom of the chamber by gravity. The circular
design of the treatment chamber helps to prevent turbulent eddy currents and to
promote settling.
During infrequent high flow conditions, stormwater in the by-pass chamber will by-pass
the weir and be conveyed to the outlet storm drain directly (Figure 2). Water, which
overflows the weir, creates a backwater effect on the outlet pipe (head stabilization
between the inlet drop pipe and outlet riser pipe) ensuring that excessive flow will not be
forced into the treatment chamber which could scour or resuspend the settled material.
The by-pass is an integral part of the Stormceptor since other oil/grit separators have
been noted to scour during high flow conditions (Schueler and Shepp, 1993).
Stormceptor comes complete to the job site with its own frame and cover. The cover
(excluding the inlet design) has the name STORMCEPTOR clearly embossed on it to
allow easy identification of the unit in the field for maintenance.
4.2.3.2 Stormceptor Applications
Stormceptor is applicable in a variety of development situations including:
• stormwater quality retrofits for existing developments
• industrial and commercial parking lots
• automobile service stations
• airports and military installations
• vehicle loading and unloading areas
Stormwater Management Plan
408-409-BMP
7 December 8, 2005
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• areas susceptible to spills of material lighter than water (bus depots, transfer
stations, etc.)
• new residential developments (as part of a treatment train)
• re-development in the urban core
Figure 1. Stormceptor Operation During Normal
Flow Conditions
Stormwater Management Plan
408-409-BMP
8 December 8, 2005
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5.0 OPERATION AND MAINTENANCE PROGRAM
5.1. Stormceptor
Stormceptor is a patented water quality structure for storm drain systems. Stormceptor
removes free oil and suspended solids from stormwater preventing spills and non-point
source pollution from entering downstream lakes and rivers. The key benefits of
implementing Stormceptor include:
• Capable of removing more than 80% of the annual sediment load when properly
applied as a source control for small areas
• Captures free oil from stormwater during normal flow conditions
• Prevents scouring or re-suspension of trapped pollutants
• Can be implemented as part of a treatment train (ex. prevents groundwater
contamination in recharge measures, extends the maintenance period for other
stormwater quality measures)
• Excellent hydrocarbon spills control device for commercial and industrial
developments
• Simple to design and specify
• Easy to install in new or retrofit situations
• Easy to maintain (vacuum truck)
• Can be used as a bend structure
• Engineered for traffic loading
• Does not require a large drop in storm drain elevation for implementation (1" for
single inlet, 3" for multiple inlet)
• STORMCEPTOR clearly marked on the cover (excluding inlet designs)
5.1.1 Stormceptor Maintenance Guidelines
The operational and maintenance needs of a Stormceptor:
The performance of all stormwater quality measures decrease as they fill with sediment.
Maintenance of a Stormceptor should be performed when the sediment volume in the
unit reaches 15% of the total storage. Although the maintenance frequency will be site
specific, maintenance is typically performed annually. This recommendation is based on
several factors:
• Minimal performance degradation due to sediment build-up.
• Sediment removal is easier when removed on a regular basis (as sediment
builds up it compacts and solidifies making maintenance more difficult).
• Development of a routine maintenance interval helps ensure a regular
maintenance schedule is followed. Although the frequency of maintenance will
depend on site conditions, it is estimated that annual maintenance will be
required for most applications; annual maintenance is a routine occurrence which
is easy to plan for and remember.
Stormwater Management Plan
408-409-BMP
10 December 8, 2005
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5.1.2 Inspection Frequency
Stormceptor should be inspected and serviced at least once a year.
5.1.3 Debris and Sediment Disposal
Disposal of sediment, debris, and trash will be contracted out in accordance with local,
county, state, and federal waste control programs.
5.1.4 Hazardous Wastes
Suspected hazardous wastes will be analyzed to determine disposal options.
Hazardous materials generated on site will be handled and disposed of according to
local, state, arid federal regulations. A solid or liquid waste is considered a hazardous
waste if it exceeds the criteria listed in the California Code of Federal Regulations, Title
22, Article 11 (State of California, 1985).
6.0 FISCAL RESOURCES
6.1 Mechanisms to Assure Maintenance
The project proponent shall enter an agreement with the City to maintain, repair and
replace permanent BMP's as necessary.
6.2 Maintenance Costs
Costs to clean a Stormceptor will vary based on the size of the unit and transportation
distances.
7.0 SUMMARY/CONCLUSIONS
This SWMP has been prepared in accordance with the Watershed Protection,
Stormwater Management, and Discharge Control Ordinance and the Stormwater
Standards Manual. This SWMP has evaluated and addressed the potential pollutants
associated with this project and their effects on water quality. A summary of the facts
and findings associated with this project and the measures addressed by this SWMP is
as follows:
• The beneficial uses for the receiving waters have been identified. None of
these beneficial uses will be impaired or diminish due to the construction and
operation of this project.
• Open areas and slopes will be landscaped to reduce or eliminate sediment
discharge.
• Stormceptor will be used to filter all parking lot runoff from the project.
• There will be increase in peak runoff from the site. Therefore, post-
development peak runoff flow rates and velocities from the project site will
increase. Likewise, sedimentation and erosion also will increase
Stormwater Management Plan
408-409-BMP
11 December 8, 2005
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• The proposed construction and post-construction BMP's address mitigation
measures to protect water quality and protection of water quality objectives
and beneficial uses to the maximum extent practicable
Stormwater Management Plan
408-409-BMP
12 December 8, 2005
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APPENDIX A
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WATER QUALITY PEAK FLOW
Modified Rational Method -Effective for Watersheds < 1.0 mi2
Masson & Associates -Escondido
Note: Only Enter Values in Boxes -Spreadsheet Will Calculate Remaining Values
Project Name La Costa Canyon Homes
Work Order oo-40 I
Jurisdiction I
BMP Location IBasin B-2
Developed Drainage Area = 0.1
Natural Drainage Area = 0.0 acres ~~~--:---=---~~----~---Tot a I Drainage Area to BMP = 0.1 acres
Dev. Area Runoff Coefficient=
Nat. Area Runoff Coefficient =
Runoff Coefficient =
RATIONAL METHOD RESULTS
0.71
0.71
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O=CIA where 0=
C=
I=
A=
Water Quality Peak Flow (cfs)
Runoff Coefficient
Using the Total Drainage Area:
C=
I=
P=
A=
Rainfall Intensity (0.2 inch/hour per RWQCB mandate)
Drainage Area (acres)
0.71
0.2 inch/hour
0.00 inches
0.1 acres
0.021 cfs
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WATER QUALITY PEAK FLOW
Modified Rational Method -Effective for Watersheds < 1.0 mi2
Masson & Associates -Escondido
Note: Only Enter Values in Boxes -Spreadsheet Will Calculate Remaining Values
Project Name La Costa Canyon Homes
Work Order 00-40 I
Jurisdiction I
BMP Location ICP#1
Developed Orainagq Area = 0.5
Natural Draina e Area = 0.0 acres -~----'-!~""""!""~~~----~ .. Total Drainage Area to BMP = 0.5 acres
Dev. Area Runoff Coefficient =
Nat. Area Runoff Coefficient =
Runoff Coefficient =
RATIONAL METHOD RESULTS
0.71
0.71
I
O=CIA where 0=
C=
I=
A=
Water Quality Peak Flow (cfs)
Runoff Coefficient
Using the Total Drainage Area:
C=
I=
P=
A=
Rainfall Intensity (0.2 inch/hour per RWQCB mandate)
Drainage Area (acres)
0-71
0.2 inch/hour
0.00 inches
0.5 acres
0.08 cfs