HomeMy WebLinkAboutCT 02-20; LA COSTA GREENS NEIGHBORHOOD 1.10; STORM WATER MANAGEMENT PLAN; 2005-08-18HUNSAKER
^ASSOCIATES
SAN DIEGO, INC.
PLANNING
ENGINEERING
SURVEYING
IRVINE
LOS ANGELES
RIVERSIDE
SAN DIEGO
STORM WATER
MANAGEMENT PLAN
for
LA COSTA GREENS
NEIGHBORHOOD 1.10
RECEI\^D
APR 2 7 ZOO'.
ENGINEERING
DEPARTRAENT
City of Carlsbad, California
City of Carlsbad Project # CT02-20
Prepared for:
Real Estate Collateral Management Company
c/o IVIorrow Development
1903 Wright Place, Suite 180
Carlsbad, CA 92008
W.O. 2352-69
August 18, 2003
DAVE HAMMAR
LEX WILLIMAN
ALISAVIALPANDO
DAN SMITH
RAY MARTIN
10179 Huennekens St.
San Diego, CA 92121
(858) 558-4500 PH
(858) 558-1414 FX
www.HunsakerSD.com
lnfo@HunsakerSD.com
Eric Mosolgo, R.Gf.E.
Water Resources Department Manager
Hunsaker & Associates San Diego, Inc.
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La Costa Greens - Neighborhood 1.10
Stormwater Management Plan
TABLE OF CONTENTS
SECTION
Executive Summary
Introduction
Vicinity Map
Post Construction BMP Location Exhibit
Summary of Results
Storm Water Treatment Criteria and Methodology 11
Introduction
Regional Water Quality Control Board Criteria
Identification of Typical Pollutants
Conditions of Concern
Design Criteria and Examples of Treatment Control BMPs
Maintenance of Treatment Control BMPs
Source Control BMPs
Site Design BMPs
Storm Water Quality Treatment Best Management Practice
Structural Treatment BMPs
Determination of Design Treatment Flow
Rational Method Treatment Flow Determination Methodology
Treatment Unit Selection
Attachments
- Design Flow Determination Spreadsheets
- Vortechnics Treatment Flow and Treatment Area Spreadsheet
- Flow Calculations provided by Vortechnics
- Vortechnics Specification, Features and Operation
- San Diego County 85th Percentile, 24-Hour Rainfall
Map Land Development Manual
- Quadrangle Map Watershed exhibit for La Costa Greens
Developed Condition Site Map (Pocket)
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La Costa Greens - Neighborhood 1.10
Stormwater Management Plan
SECTION I
EXECUTIVE SUMMARY
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Stormwater Management Plan
EXECUTIVE SUMMARY
Introduction
This Water Quality Technical Report has been prepared to show the methodology
and calculations used to determine the sizing of the required storm water treatment
unit. All calculations are consistent with criteria set forth by the Regional Water
Quality Control Board's Order No. 2001-01, and the City of Carlsbad "Standard
Urban Storm Water Mitigation Plan."
Phase 1 of the La Costa Greens project site is located north of Alga Road, south of
the proposed extension of Poinsettia Lane, and east of the La Costa Golf Course.
Neighborhood 1.10 is located roughly in the center of the development, west of
Alicante Road, east of the golf course, north of Neighborhood 1.11 and south of
Neighborhood 1.08. Neighborhood 1.10 is one of seven subdivisions within the La
Costa Greens Phase I development. An exhibit showing the location of each
treatment unit and the breakdown of the areas tributary to each treatment unit is
included on the following page.
CITY OF SAN MARCOS
THE GREENS 1.W
VICINITY MAP
NTS
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LEGEND
WATERSHED TRIBUTARY
TO TREATMENT UNIT •
TREATMENT UNIT
LA COSTA GREENS
POST-CONSTRUCTION
BMP LOCATION EXHIBIT
FLOW-BASED BMP FOR
NEIGHBORHOOD 1.08, OFFSITE DEVELOPMENT
AND ALICANTE ROAD
/
FLOW-BASBD BMP FOR
NEIGHBORHOOD 1.09,
1.10, A PORTION OF 1.12,
AND OFFSfTE DEVELOPMENT
/
/
1
I 1
I
(
FLOvlf-BASED BMP FOR
NEIGHBORHOOD 1.11
\
\
)
FLOW-BASED BMP FOR
NEIGHBORHOOD 1.13, 1.14
PORTION OF 1.12,
ALICANTE ROAD, AND
OFFSITE DEVELOPMENT
Ri\0328\8,Hyd\Site Location Mop 8,5xll,clwg[ 1275]Apr-16-2004il2:26
La Costa Greens - Neighborhood 1.10
Stormwater Management Plan
All runoff from Neighborhood 1.10 will drain to a proposed storm drain outlet located
at the southwest corner of Neighborhood 1.10 (at the Street KK cul-de-sac). Storm
drain runoff discharges from this location to the unnamed tributary of San Marcos
Creek, which flows in a southerly direction along the west side of Neighborhood 1.10.
Runoff from Neighborhood 1.09, the northern portion of Neighborhood 1.12, and the
adjacent residential development east of La Costa Greens Phase 1 will also drain to
this storm drain outlet location. All stormwater draining to this location will be treated
in one treatment unit prior to discharge.
The offsite developed areas, which will drain to the storm drain outlet located in
Neighborhood 1.10 have been quantified in two hydrology studies; "Hydrology &
Hydraulic Study-La Costa Greens Phase 1", prepared by O'Day Consultants May
25, 2002, and 'Tentative Map Drainage Study for La Costa Greens - Phasel
Neighborhoods 1.08 through 1.14," prepared by Hunsaker & Associates San Diego,
Inc. April 17, 2003. The O'Day report identified a total of 98 acres of offsite
developed area that contribute flow to the La Costa development in the vicinity of the
1.09 and 1.12 Neighborhood. The Hunsaker & Associates report identified two run
on locations: one at the southeast corner of Neighborhood 1.09 consisting of 19
acres of area; and one at the northeast corner of Neighborhood 1.12 consisting of 79
acres of area. The Quadrangle Map Watershed Exhibit for La Costa Greens
illustrates the extent of offsite areas draining to the La Costa Greens Phase I
proposed development and has been included in the Attachment section of this
report.
The La Costa Greens Neighborhood 1.10 project will include construction of four (4)
proposed roads, grading of the proposed site to make it suitable for construction of
single-family residential dwellings, construction of underground utilities typically
associated with residential developments, and the construction of 64 residences.
The proposed project site consists of 64 residential lots and 5 open space lots, for a
total area of 29.64 acres (20.33 acres and 9.31 acres respectively). Approximately
31% of Neighborhood 1.10 will remain undeveloped.
Summary of Results
Priorto discharge into the open channel all storm water will pass though a proposed
diversion structure that will divert the entire 85"^ percentile flow to a proposed storm
water treatment unit. Flows in excess of the treatment flow will bypass the treatment
unit. This analysis indicates that a Vortechs Model PC16x24 will be required to meet
the water quality treatment requirements. The proposed Vortechs Model PCI 6x24
will be located offline from the main storm drain system and is proposed in the vicinity
of the Street KK cul-de-sac.
In addition to the primary treatment facilitated by the proposed Vortechs Model
PCI 6x24, storm water treatment in excess of the Regional Water Quality Control
Board requirements will be provided downstream of the storm drain outfall. After
discharge storm water will drain through an existing vegetated constructed channel
en route to the Alga Road culverts. This vegetated channel will provide additional
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Stormwater Management Plan
treatment for the 85"^ percentile flow (by reducing the flow velocities in the channel
and in turn settling out pollutants).
Since primary and additional treatment will be provided, a volume-based BMP will not
be required. Maintenance of the proposed Vortechs units, which will be the
responsibility of the Master Homeowners Association, is addressed in Section II of
this report.
This report replaces any post-construction BMP text included in the Preliminary
SWPPP prepared along with the Master Tentative Map. SWPPP reports are typically
required for storm water pollution prevention during interim construction activities.
Desiltation basins previously designed for this project were intended only to collect
sediment during the construction phase of the project and were not intended to be
permanent facilities. This report specifies post-construction condition BMP treatment
controls.
Anticipated pollutants of concern are included in Section II of this report. Tables
included in Section II show that the proposed Vortechs system adequately treats the
anticipated pollutants of concern to a degree previously determined acceptable by
the Regional Water Quality Control Board. Treatment BMPs recommended forthe
project site are based on 85th percentile flow calculations and are not based on
quantitative pollutant loading analysis. Previous attempts to apply quantitative
methods for estimating pollutant loading and removal efficiencies, such as in the
1993 Municipal Handbook, are no longer considered accurate for southern California.
Section 11 also presents a listing of recommended non-structural source control
BMPs, which include landscaping, urban housekeeping, etc.
85*^^ percentile calculations included in this report were generated using the Rational
Method. This method calculates the resultant 85"^ percentile flow rate based upon a
peak rainfall intensity of 0.2 inches per hour. This is consistent with criteria set forth in
the City of Carlsbad "Standard Urban Storm Water Management Plan."
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Stormwater Management Plan
SECTION II
STORM WATER TREATMENT CRITERIA
&
METHODOLOGY
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Stormwater Management Plan
STORM WATER TREATMENT CRITERIA & METHODOLOGY
The purpose of this report is to address pollutants associated with residential
developments, and to recommend techniques used to reduce the concentration of
pollutant discharge into watenways and bodies of water. Treatment BMPs
recommended for the proposed project site are based on 85'^ percentile design flow
calculations and are not based on quantitative pollutant loading analysis. Previous
attempts to apply quantitative methods for estimating pollutant loading and removal
efficiencies, sucii as in the 1993 Municipal Handbook, are no longer considered
accurate for southern California. The La Costa Greens Village 1.10 proposed project
site is located in the Batiquitos watershed. After development, 85"^ percentile flow
from the proposed project site will be collected in catch basins, curb inlets, and brow
ditches and conveyed to the proposed Vortechnics treatment unit through a proposed
storm drain system. After treatment, storm water will be discharged into an unnamed
tributary of San Marcos Creek and ultimately into San Marcos Creek. San Marcos
Creek is not listed as an impaired water body on the 2002 CWA Section 303(d) List
of Water Quality Limited Segment
Regional Water Qualitv Control Board Criteria
All runoff conveyed in the proposed storm drain systems will be treated in compliance
with Regional Water Quality Control Board regulations and NPDES criteria priorto
discharging to natural watercourses. California Regional Water Quality Control Board
Order No. 2001-01, dated February 21, 2001, sets waste discharge requirements for
discharges of urban runoff from municipal storm separate drainage systems draining
the watersheds of San Diego County.
Per the RWQCB Order, post-development runoff from a site shall not contain
pollutant loads which cause or contribute to an exceedance of receiving water quality
objectives or which have not been reduced to the maximum extent practicable. Post-
construction Best Management Practices (BMPs), which refer to specific storm water
management techniques that are applied to manage constmction and post-
construction site runoff and minimize erosion, include source control - aimed at
reducing the amount of sediment and other pollutants - and treatment controls that
keep soil and other pollutants onsite once they have been loosened by storm water
erosion.
Post construction pollutants are a result of the urban development of the property
and the effects of automobile use. Runoff from paved surfaces can contain both
sediment (in the form of silt and sand) as well as a variety of pollutants transported by
the sediment. Landscape activities by homeowners are an additional source of
sediment
Most harmful pollutants accumulate within three feet of the curb. Many of these
pollutants adhere to fine materials, thus avoiding removal by old-time street-
sweepers. Harmful pollutants are also present in high concentrations in urban "hot
spots" such as automotive, cleaning, or servicing shops.
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Stormwater Management Plan
All structural BMPs shall be located to infiltrate, filter, or treat the required runoff
volume or flow (based on the 85'^ percentile rainfall) prior to its discharge to any
receiving watercourse supporting beneficial uses. The BMPs will be designed to
reduce toxin, nutrient and/or sediment loading of the 85'*^ percentile design flow from
the proposed development.
Flow-based BMPs shall be designed to mitigate the maximum flowrate of runoff
produced from a rainfall intensity of 0.2 inch per hour. These BMPs utilize either
mechanical devices (such as vaults that produce vortex effects) or non-mechanical
devices (based on weir hydraulics and specially designed filters) to promote settling
and removal of pollutants from the runoff.
Identification of Typical Pollutants
Urban runoff from a developed site has the potential to contribute pollutants,
including oil and grease, suspended solids, metals, gasoline, pesticides, and
pathogens to the storm water conveyance system and receiving waters. Treatment
BMPs recommended forthe proposed project site are based on 85'^ percentile
design flow calculations and are not based on quantitative pollutant loading analysis.
Previous attempts to apply quantitative methods for estimating pollutant loading and
removal efficiencies, such as in the 1993 Municipal Handbook, are no longer
considered accurate for southern California. Per the model SUSMP, this report
identifies the removal efficiencies of the following pollutants using Vortechs
Stormwater Treatment unit in terms of low, medium and high removal. For the
purposes of identifying pollutants of concern and associated storm water BMPs,
pollutants are grouped in the following general categories:
Sediments are soils or other surface materials eroded and then transported or
deposited by the action of wind, water, ice, or gravity. Sediments can increase
turbidity, clog fish gills, reduce spawning habitat, smother bottom dwelling organisms,
and suppress aquatic vegetative growth.
Nutrients are inorganic substances, such as nitrogen and phosphorous. They
commonly exist in the form of mineral salts that are either dissolved or suspended in
water. Primary sources of nutrients in urban runoff are fertilizers and eroded soils.
Excessive discharge of nutrients to water bodies and streams can cause excessive
aquatic algae and plant growth. Such excessive production, referred to as cultural
eutrophication, may lead to excessive decay of organic matter in the water body, loss
of oxygen in the water, release of toxins in sediment, and the eventual death of
aquatic organisms.
Metals are raw material components in non-metal products such as fuels, adhesives,
paints and other coatings. Metals of concern include cadmium, chromium, copper,
lead, mercury, and zinc. At high concentrations, metals can be toxic to aquatic life.
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Stormwater Management Plan
Organic Compounds are carbon-based and commonly found in pesticides,
solvents, and hydrocarbons. Organic compounds can, at certain concentrations,
constitute a health hazard. Dirt, grease, and grime retained in cleaning fluid or rinse
water may also adsorb levels of organic compounds that are harmful or hazardous to
aquatic life.
Trash & Debris, such as paper, plastic, leaves, grass cuttings, and food waste, 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. In areas where stagnant water is present,
the presence of excess organic matter can promote septic conditions resulting in the
growth of undesirable organisms and the release of odorous and hazardous
compounds such as hydrogen sulfide.
Oxygen-Demanding Substances include biodegradable organic material as well as
chemicals that react with dissolved oxygen in water to form other 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.
Oil and Grease are characterized as high high-molecular weight organic
compounds. Primary sources of oil and grease are petroleum hydrocarbon products,
motor products from leaking vehicles, oils, waxes, and high-molecular weight fatty
acids. Elevated oil and grease content can decrease the aesthetic value of the water
body, as well as the water quality.
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La Costa Greens - Neighborhood 1.10
Stormwater Management Plan
Table 1 below, details the typical anticipated and potential pollutants generated by
various land use types, based on the draft model SUSMP prepared by the
copermittees. The La Costa Greens Neighborhood 1.10 development will consist of
detached single-family residences, and the Detached Residential Development
category has been highlighted to clearly illustrate which general pollutant categories
are anticipated from the project area.
TABLE 1
General Pollutant Categories
Priority
Project
Categories Sediments Nutrients Heavy Metals Organic Compounds Trash & Debris Oxygen Demanding Substances Oil & Grease Bacteria & Viruses Pesticides Detached
Residential
Development
X X x X X X X
Attached
Residential
Development
x x x p(i) p(2) P X
Commercial
Development
>100,000 ft^
p(i) p(1) p(2) x p(5) X p(3) p(5)
Automotive
Repair
Shops
x X(4)(5) x X
Restaurants x X X X
Hillside
Development
>5,000 ft^
x x x X X X
Parking Lots p(1) p(1) x X p(1) X p(1)
Streets,
Highways &
Freeways
x p(1) x X(4) X p(5) X
Retail Gas
Outlets x X(4) X X
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.
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La Costa Greens - Neighborhood 1.10
Stormwater Management Plan
Conditions of Concern
The Master Drainage Study for La Costa Greens addresses the City of Carlsbad
Standard Urban Storm Water Mitigation Plan requirements per Section III -1 C for
identifying the conditions of concern. After treatment, storm water will be discharged
into an unnamed tributary of San Marcos Creek and ultimately into San Marcos
Creek. San Marcos Creek is not listed as an impaired water body on the 2002 CWA
Section 303(d) List of Water Quality Limited Segment. In order to meet water quality
objectives, the pollutants that will be treated and addressed in this report are
sediment, nutrients, trash and debris, oxygen demanding substances, oil and grease,
bacteria and viruses, and pesticides.
Design Criteria and Examples of Treatment Control BMPs
Storm water quality treatment (pollutant removal) will be attained by flow-based
methods. Treatment control (structural) BMPs are engineered system designs
constructed to remove pollutants from urban runoff by simple gravity settling of
particulate pollutants, filtration, biological uptake, media absorption, or any other
physical, biological, or chemical process.
Flow-based BMPs shall be designed to mitigate the maximum flowrate of runoff
produced from a rainfall intensity of 0.2 inch per hour. Such basins utilize either
mechanical devices (such as vaults that produce vortex effects) or non-mechanical
devices (based on weir hydraulics and specially designed filters) to promote settling
and removal of pollutants from the runoff.
Examples of flow-based BMPs include hydrodynamic separation devices, such as
those designed by CDS Technologies, Vortechnics, HIL Technologies, etc.. For the
La Costa Greens development, the proposed storm drain system design incorporates
the use of Vortechnics' Vortechs stormwater treatment units into its design. The
table on the following page compares the typical ranges of removal efficiencies of
comparable hydrodynamic separation devices to the removal efficiencies of Vortechs
stormwater treatment units.
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La Costa Greens - Neighborhood 1.10
Stormwater Management Plan
Treatment Control BMP Removal Efficiencies (1)
Pollutant of Concern BMP Categories
Hydrodynamic
Separation
Devices*^'
Vortechs™
Stormwater
Treatment System
Sediment M-H H
Nutrients L-M L-M
Heavy Metals L-M L-M
Organic Compounds L-M L-M
Trash & Debris M-H H
Oxygen Demanding Substances L L
Bacteria L L
Oil & Grease L-H H
Pesticides L .L.
(1) The County will periodically assess the performance characteristics of these BMPs to
update this table.
(2) Proprietary Structural BMPs. Not all serve the same function.
L (Low): Low removal efficiency (roughly 0-25%)
M (Medium): Medium removal efficiency (roughly 25-75%)
H (High): High removal efficiency (roughly 75-100%)
U: Unknown removal efficiency, applicant must provide evidence supporting use
Sources: Guidance Specifying Management Measures for Sources of Nonpoint Pollution in
Coastal Waters (1993), National Stormwater Best Management Practices Database (2001),
and Guide for BMP Selection in Urban Developed Areas (2001).
The Vortechs Storm Water Treatment System is designed to efficiently remove grit,
contaminated sediments, metals, hydrocarbons and floating contaminants from
surface runoff. Combining swirl-concentrator and flow-control technologies to
eliminate turbulence within the system, the Vortechs System ensures the effective
capture of sediment and oils and prevents resuspension of trapped pollutants for
flows up to 25 cfs with the use of their precast treatment units. Vortechnics also
provides design and system components that are cast-in-place (CIP). These CIP
treatment units have the ability to treat much greater flows.
Other features of the Vortechs Systems include the following:
• Large capacity system provides an 80 percent net annual Total Suspended
Solids (TSS) removal rate
• Unit is installed below grade
• Low pump-out volume and one-point access reduce maintenance costs
• Design prevents oils and other floatables from escaping the system during
cleanout
• Enhanced removal efficiencies of nutrients and heavy metals with offline
configuration
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Stormwater Management Plan
The tangential inlet to the system creates a swirling motion that directs settleable
solids into a pile towards the center of the grit chamber. Sediment is caught in the
swirling flow path and settles back onto the pile after the storm event is over.
Floatables entrapment is achieved by sizing the low flow control to create a rise in the
water level of the vault that is sufficient to just submerge the inlet pipe with the 85"^
percentile flow.
Maintenance of Treatment Control BMPs
Maintenance of the project site BMPs will be the responsibility of the Master
Development Homeowners Association. Per this report, a maintenance plan will be
developed which will include but is not limited to the following information:
• Specification of routine and non-routine maintenance activities to be
performed
• A schedule for maintenance activities
• Name, qualifications, and contact information for the parties responsible
for maintaining the BMPs
For proper maintenance to be performed, the storm water treatment facility must be
accessible to both maintenance personnel and their equipment and materials.
Amenities such as depressed curbs, hand and safety rails, gates, access roads and
manholes expedite both inspection and maintenance efforts and help to reduce costs
and improve efficiency.
The use of strong, durable and non-corroding materials can greatly expedite
maintenance efforts. These include strong, lightweight metals (orifice and weir
plates), reinforced concrete for outlet structures and headwalls, disease resistant
vegetation for channel bottoms and side slopes, and durable rock for gabions and
riprap lining.
A variety of contaminants that may be classified as hazardous or toxic may enter
storm water management systems. These contaminants include heavy metals,
petroleum hydrocarbons, pesticides, and a variety of organic chemicals. Federal and
state laws may apply to the disposal of sediments that are captured in these storm
water systems.
Inlet cleaning, ditch clearing, and street sweeping are examples of other commonly
used maintenance practices and are typically part of the individual municipality's or
City's maintenance plans.
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Stormwater Management Plan
Maintenance of Flow-Based Treatment Units
Flow-based storm water treatment devices should be inspected periodically to assure
their condition to treat anticipated runoff. Maintenance of the proposed Vortechnics
unit includes inspection and maintenance 1 to 4 times per year, and maintenance
involves the use of a "vactor truck" which clears the grit chamber of the treatment unit
by vacuuming all the grit, oil and grease, and water from the sump. Typically a 3-
man crew is required to perform the maintenance of the treatment unit. After
installation, the condition of the unit should be checked after every runoff event for
the first 30 days. Proper inspection includes a visual observation to ascertain whether
the unit is functioning properly and measuring the amount of deposition in the unit.
During the wet season, units should be inspected at least once every 30 days.
Floatables should be removed and sumps cleaned when the sump storage exceeds
85 percent of capacity.
The Vortechs System should be inspected at regular intervals and cleaned when
necessary to ensure optimum performance. The rate at which the system collects
pollutants will depend more heavily on site activities than the size of the unit. During
the wet season, units should be inspected at least once every 30 days. During
construction, BMP inspections shall be performed before and after storm events and
once each 24-hour period during extended storm events to identify BMP
effectiveness.
Inspection is the key to effective maintenance. Vortechnics recommends ongoing
quarterly inspections of the accumulated sediment. According to Vortechnics
literature, the systems needs only to be cleaned when the inspection reveals that the
system is nearly full - specifically, when the sediment depth has accumulated within
6 inches of the dry-weather water level.
Cleanout of the Vortechs System with a "vactor truck" is generally the most effective
and convenient method. Properly maintained Vortechs Systems will only require
evacuation of the grit chamber portion of the system. In some cases, it may be
necessary to pump out all chambers. In the event of cleaning other chambers, it is
imperative that the grit chamber be drained first.
Source Control BMPs
Source controls, which are implemented to prevent or reduce the presence of
pollutants and minimize the contact between pollutants and urban runoff, include the
following:
• Landscaping - Manufactured slopes shall be landscaped with
suitable ground cover or installed with an erosion control system.
Homeowners should be educated as to the proper routine
maintenance to landscaped areas including trimming, pruning,
weeding, mowing, replacement or substitution of vegetation in
ornamental and required landscapes.
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La Costa Greens - Neighborhood 1.10
Stormwater Management Plan
In the event that landscaping work requires materials such as fill,
gravel, dirt, loam, mulch, etc. to be piled for more than a sinqle day.
the pile(s) should be securely covered in order to prevent suspension
of the loose material in runoff from any storm event.
Per the RWQCB Order, the following landscaping activities are
deemed unlawful and are thus prohibited:
- Discharges of sediment, pet waste, vegetative clippings, or other
landscaping or construction-related wastes.
Urban Housekeeping - Fertilizer applied by homeowners, in addition
to organic matter such as leaves and lawn clippings, all result in
nutrients in storm water runoff. Consumer use of excessive herbicide
or pesticide contributes toxic chemicals to runoff. Homeowners should
be educated as to the proper application of fertilizers and herbicides
to lawns and gardens.
The average household contains a wide variety of toxins such as
oil/grease, antifreeze, paint, household cleaners and solvents.
Homeowners should be educated as to the proper use, storage, and
disposal of these potential storm water runoff contaminants.
Per the RWQCB Order, the following housekeeping activities are
deemed unlawful and are thus prohibited:
- Discharges of wash water from the cleaning or hosing of
impervious surfaces including parking lots, streets, sidewalks,
driveways, patios, plazas, and outdoor eating and drinking areas.
Landscape irrigation and lawn watering, as well as non-
commercial washing of vehicles in residential zones, is exempt
from this restriction.
Discharges of pool or fountain water containing chloride, biocides,
or other chemicals.
Discharges or runoff from material storage areas containing
chemicals, fuels, grease, oil, or other hazardous materials.
Discharges of food-related wastes (grease, food processing, trash
bin wash water, etc.).
Automobile (/se - Urban pollutants resulting from automobile use
include oil, grease, antifreeze, hydraulic fluids, copper from brakes,
and various fuels. Homeowners should be educated as to the proper
use, storage, and disposal of these potential storm water
contaminants.
Per the RWQCB Order, the following automobile use activities are
deemed unlawful and are thus prohibited:
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Discharges of wash water from the hosing or cleaning of gas
stations, auto repair garages, or other types of automotive service
facilities.
- Discharges resulting from the cleaning, repair, or maintenance of
any type of equipment, machinery, or facility including motor
vehicles, cement-related equipment, port-a-potty servicing, etc.
- Discharges of wash water from mobile operations such as mobile
automobile washing, steam cleaning, power washing, and carpet
cleaning.
The Homeowners Association should make all homeowners aware of the
aforementioned RWQCB regulations through a homeowners' education program. A
monitoring program should also be implemented to insure compliance.
Site Design BMPs
The proposed project site consists of 64 residential lots and 5 open space lots, for a
total area of 29.64 acres (20.33 acres and 9.31 acres respectively). Approximately
31% of the project site, 9.31 acres, will not be developed and will be preserved as
open space. This will minimize the pollutant loads generated and potentially
discharged from the site. Furthermore, while the project does not depend on this
open space to provide treatment of potential pollutants, there will be a natural benefit
derived from its existence, both as a natural buffer between the site and water bodies
and as a cleansing mechanism as a result of the natural existing vegetation present
in these open spaces.
JC:TK h:\sw quallty\2352\69\wqtr-06.doc
W.O. 2352-69 4/16/04 9:25 AM
La Costa Greens - Neighborhood 1.10
Stormwater Management Plan
SECTION III
STORM WATER QUALITY TREATMENT
BEST MANAGEMENT PRACTICE
I
I JC:TK h:\sw quality\2352\69\wqtr-06.doc
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La Costa Greens - Neighborhood 1.10
Stormwater Management Plan
Structural Treatment BMPs
The proposed improvement design for the project site incorporates the construction
of a Vortechs Model PC16x24 storm water quality unit. One Vortechnics storm
water treatment unit is being proposed to treat the 85*^ percentile flow for the La
Costa Greens Neighborhood 1.10 proposed project site. The storm water quality
treatment unit has been sized to treat the 85*^ percentile runoff flow from
Neighborhood 1.09,1.10, a portion of Neighborhood 1.12, and offsite areas to the
east, all which drain through Neighborhood 1.10.
Determination of Design Treatment Flow
The 85"^ percentile flow rate has been calculated using the Rational Method.
Required data for the Rational Method Treatment flow determination is as follows:
- Drainage Area (A) = 196.05 acres (Neighborhoods 1.09,1.10, a portion of
1.12 North and offsite areas to the east)
Rainfall Intensity (I) = 0.20 inches per hour
- Runoff Coefficient (C) = 0.53
The site's overall runoff coefficient was derived based upon a weighted average of
each area tributary to the treatment unit and the associated runoff coefficient. Using
this method, the site's runoff coefficient was estimated to be 0.53. Bases on this data
the treatment flow for the storm water treatment unit was determined to be 20.78 cfs.
Rational Method Treatment Flow Determination Methodology
As stated in the Introduction of Section II, Regional Water Quality Control Board
regulations and NPDES criteria have established that flow-based BMPs shall be
designed to mitigate a rainfall intensity of 0.2 inch per hour.
The basic Rational Method runoff procedure is as follows:
Design flow (Q) = (C) * (I) * (A)
Runoff Coefficient (C) - In accordance with the County of San Diego standards, the
weighted runoff coefficient for all the areas tributary to the treatment unit was
determined using the areas analyzed in the hydrology report. A runoff coefficient of
0.53 was used for this analysis. The runoff coefficient is based on the following
characteristics of the watershed:
• Land Use - Single Family Residential in Developed Areas
• Soil Type - Hydrologic soil group D was assumed for all areas. Group D
soils have very slow infiltration rates when thoroughly wetted.
Consisting chiefly of clay soils with a high swelling potential, soils with a
high permanent water table, soils with clay pan or clay layer at or near
JC:TK h:\sw quality\2352\69\wqtr-06.doc
W.O. 2352-69 4/16/04 9:25 AM
La Costa Greens - Neighborhood 1.10
Stormwater Management Plan
the surface, and shallow soils over nearly impervious materials. Group
D soils have a very slow rate of water transmission.
Rainfall Intensity (I) - Regional Water Quality Control Board regulations and NPDES
criteria have established that flow-based BMPs shall be designed to mitigate a rainfall
intensity of 0.2 inch per hour.
Water Shed Area (A) - Project Area totaling an area of 195.05 acres.
Treatment Unit Selection
Per the special design prepared by Scott Gorneau of Vortechnics, (excerpts attached
dated August 15, 2003) the Vortechs Model PCI 6x24 has been designed to treat a
flow rate of 52.82 cfs. This unit (details attached), as proposed on the improvement
plans, is an offline precast treatment unit, meaning that the design flow rate is forced
into the treatment area through a diversion stmcture, while flows in excess of the
design flow rate pass over an inline weir and proceed downstream.
The weir in the diversion structure will create a restriction, which will raise the HGL
upstream of the weir. These losses will be analyzed in the Hydrology study to ensure
that the potential for flooding occurrences during high return rainfall events is
minimized to an acceptable level.
As discussed in the Structural Treatment BMP section the design flow using the
Rational Method was calculated to be 20.78 cfs. The Vortechs Model PCI 6x24, with
a designed peak treatment flow capacity of 52.82 cfs, was selected because of the
results of the Flow Calculation spreadsheet, provided by Vortechnics and included in
the Attachments section of this report, show that during the 100-yr storm the
diversion weir would divert 52.82 cfs through the treatment unit. Therefore the unit
has been sized to handle the flow of 52.82 cfs.
JC:TK h:\sw quality\2352\69\wqtr-06.doc
W.O. 2352-69 4/16/04 9:25 AM
La Costa Greens - Neighborhood 1.10
Stormwater Management Plan
SECTION IV
ATTACHMENTS
JC:TK h:\sw quallty\2352\69\wqtr-06.doc
W.O. 2352-69 4/16/04 9:25 AM
VILLAGES OF LA COSTA
NEIGHBORHOOD 1.09, 1.10 AND PORTION OF 1.12 (NORTH)
I KtA I IVItN I t-LUVV Ut I tKMINA I lUN:
Q=C*I*A
TREATMENT AREA
RAINFALL INTENSITY
WEIGHTED CURVE NUMBER
196.05 ACRES
0.20 IN/HR
0.53
Q = 20.78 CFS
12:28 PM4/16/2004 Sheetl RM-TREATMENT FLOW-02.xls
APPROXIMATE VORTECHNICS TREATMENT
AREAS
MODEL Q treatment
(CFS)
AREA (ACRES) MODEL Q treatment
(CFS) COMML. CONDO. 8-10 DU 5-8 DU 3-5 DU
Q treatment
(CFS) 8-10 DU 5-8 DU 3-5 DU
Model 1000 1.6 10 14 15 18 23
Model 2000 2.8 17 24 26 31 39
Model 3000 4.5 27 38 41 49 62
Model 4000 6.0 37 51 55 66 83
Model 5000 8.5 52 72 78 94 117
Model 7000 11.0 73 102 110 132 165
Model 9000 14.0 93 129 140 168 210
Model 11,000 17.5 117 162 175 210 263
Model 16,000 25.0 167 231 250 300 375
05/20/2003 15:55 2078859825 VORTECHNICS INC PAGE 04/
lirtedmics
FLOW CALCULATIONS
I Cgsfg CrTssiis V}!!s^s '1.G9,1.10 srmi 1<i3
A 4,94
Crest Elevation (R) 0.03
PC15X25
Svitgm 1 i-Jti
Weir Crrot Length (II) = 0
CreaEleyatio»iffl)" 4.130
W«if Crwi Leregth ^Jl) = 26
Crest Elevation ffl)« 1.86
4.S
4.0
3.S
o 3.0
2J0
1.5
1.0
0.S
D.0
I
i
He«ii OffflC« Flow BVPWMI Flow
W
0.00 O.DB 0.00 0,00 OiOO D,GO
0.25 0,33 1,23 0.00 0.00 1,23
0.60 O.SB 3.46 0.00 0,00 3.48
0.75 0.63 8.39 0.00 aoo 6.39
1.00 1.08 9.64 0.00 o:oo 9.64
1.25 1.33 13.75 0.00 0.00 • 13.75
1.50 1.68 18.08 0,00 0.00 10.08
1.75 1.83 22,20 Q.oa aoo
2.00 2.08 24.63 0.00 aes i4.48
2.33 27.19 0,00 28.80 56.00
2.60 2.SB 29.37 0.00 S3B4 93.22
2.75 2.83 31,40 0.00 83.82 115.02
3.00 3.0B 33,31 0,00 117,47 150.78
3.25 3.33 35.11 0.00 154,95 190.08
3.50 3.53 36,82 0.00 195.74
3.92 4,00 39.52 0.00 270,49 310.00
CalCUlatdd bv: WSG 5ii2DiQ003 IChdckedby:
Vortechs^ System
Stage Discharge Curve
'"'t • /
/
Ortflnni>p)it
0.O 5DJ) lOOJO ISOJO 200,0 2S0,0 300.0 35D.0
Dttchargetcts)
Plan View
Grit Chamber °'l S'iSf"'??r< Row Control Baffle Wall . Chamber
. Elevation View: Dry-Weather
Grit Chamber
The swirling motion created by the
tangential inlet directs settleable
solids toward the center of this
chamber. Sediment is caught in.. .
the swirling flow path and settles
back onto the pile after the storm
•event is over.
Oil Chconber & Baffle Wall
The center baffle traps floatables in
•the oil chamber, even during clean-
'out. Highly resistant to flow surges.
Flow Control Chamber j
•The weir and oriffce flow controls:- •
1) Raise level and volume in, the -: .;'
system as flow rate increases; arid' ^
2\ gradually drain the. system as' - v
flow rate subsides.' . .. ': .• ..
1) Initial Wet Weather Phase
During a two-month storm event the water level begins to
rise above the top of the inlet pipe. This influent control
feature reduces turbulence and avoids resuspension
of pollutants.
3) Full Capacity Phase
When the high-flow outlet approaches full discharge, storm
drains are flowing at peak capacits/i The Vortechs System is
designed to match your design storm flow and provide treat-
ment throughout the range of storm events without bypass-
ing. To accommodate very high flow rates, Vortechnics can
2) Transition Phase
As the inflow rate increases above the controlled outflow
rate, the tank fills and the floating contaminant layer accu-
mulated from past storms rises. Swirling action increases
at this stage, while sediment pile remains stable.
4) Storm Subsidence Phase/Cleaning
Treated runofl= is decanted at a controlled rate, restoring the
water level to a low dryweather volume and revealing a conical
pile of sediment. The low water level facilitates inspection and
cleaning, and significantly reduces maintenance costs. The
system's central baffle prevents transfer of floatables to the
^ ^ the \/6n:ech"s' Stormwater Treatment System
Perforated Covers
Plan View Elevation View
To begin the design of your
Vortechs System, refer to the
sizing chart below and com-
plete a Specifier's Worksheet to
provide details about your site
and design flows. Then simply
fax or mail the worksheet to
Vortechnics with your site plan,
and we'll produce detailed
Vortechs System scale draw-
ings free of charge.
''".-J:
«sgmMgg»Mji
\ •'•-ji.ljEI •'•"-V'"
\ ioqo 3/7 1.B .75 \
:?'^'v4/13 2.8 1.25 •^v^1Qx-4--;?-??p
; 3000 ;;.;;:.i:.;:;5/2Q " 4.5 .1.75. • -.11x5 |r:
. 6/28 6.0 2.5 . ;.
• ' „ ,.
:• ;i2 X e-'KS
IfgaDQO ^7/38 8.5 3.25 1.3, X.7..-V:iVg
,',J,;V.70Q0 , •: •;: : :> 8/50 11.0 •. 4.0\;: .,.
:v;;.i;-;:.;g/B4;,. ,. 14.0 • 4.75 „ '•••: —: : :—
' 15x3 ..|
•••;V: viO/79 ••• . 17.5 : '5,5 , -i-Bx-ia- • ll
^Si^ciQD:|v;. ;#:V.;12/il3 ::;. V,-,;• • 25.0:. • :->:• :::7.OV:-\:P;.^ ' 18x12' W
*„:.:-.;..::'j:,/u-riii'5r."": . -: ^mmssmmmmmmmmm ' ..• Engineering Notes
' A) For in-liha Vortechs Systems without a bypass, sizing criteria is based on providing one square foot of grit
chamber surface area for each 100 gpm of peak design storm flow rate (e.g.. lO-year storm). For more '
. details about Vortechnics sizing criteria refer to Vortechnics Technical Bulletin 3: .
. B) Sediment storage volume assumes a 3 foot sump. • . • . . .
• • C)- Construction details may vary depending on the specific application. Any alterations to the sizing chart specifi-
• cations will appear on Vortechnics dimensional and shop drawings. Please call Vortechnics for the weight of spe-.
. cific Vortechs systems if needed. •. '
• Special Note^ Oil storaga capacity,,when it is needed to. meet a specific requirement for spill containment, can be .
• sized to meet the storage requirement with the selected model. Vortechnics technical staff will optimize system
. . geometry to meet containment requirements within a correctly sized Vortechs System;
'•{.Metric Specilication Chart avBilabIa by calSng Vorteclinics ac ISO?] , '. . •
Vortechs System Inlet/Outlet Configurations
Vortechs Systems can be configured to accommo-
date various inlet and outlet pipe orientations.
The inlet pipe can enter the end or side of the
tank at right angles - outlet pipes can exit the end
or the side of system at most angles.
End Inlet
H Offline U la
Outfall
OCEANSiDE
Well
32%-
\\ Palo-^.v -
/:\.'^7|,caf COURSE:
aooo 4000
SCALE i'=aooo'
PREPARED FOR:
HUNSAKER
& ASSOCIATES
SAN DIECO. INC
PIANNINC 10179 Huemekec SnsM
ENCINEEIUNC Sm 0ie(O, d 92121
SlKVfYlNC Prt8S8)556^500. FX(e58)55».14«
QUADRANGLE MAP WATERSHED
EXHIBIT FOR
LA COSTA GREENS
CARLSBAD, CALIFORNIA 1
Ri\0165\8,Hyd\0165*H09-QUADMAPS.c(WQt 20B53Au9-15-2003.10e8