HomeMy WebLinkAboutCT 02-22; LA COSTA GREENS NGBHD 1.09; PRELIMINARY STORM WATER MANAGEMENT PLAN; 2003-08-17I
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PLANNING
ENGINEERING
SURVEYING
IRVINE
LOS ANGELES
RIVERSIDE
SAN DIEGO
DAVE HAMMAR
LEX WILLIMAN
ALiSA VIALPANDO
10179 Huennekens 51.
San Diego, CA 92121
(858) 558-4500 PH
(858) 558-1414 FX
www.HunsakerSD.com
Info@HunsakerSD.com
HUNSAKER
&ASSOCIATES
5 AND lEG 0, INC.
PRELIMINARY STORM WATER
MANAGEMENT PLAN 1-
for 60~-'L
LA COSTA GREENS
NEIGHBORHOOD 1.09
City of Carlsbad, California
City of Carlsbad Project # CT 02-22
Prepared for:
Real Estate Collateral Management Company
clo Morrow Development
1903 Wright Place, Suite 180
Carlsbad, CA 92008
W.O. 2352-68
August 17, 2003
Eric Mosolgo, R. .E.
Water Resources Department Manager
Hunsaker & Associates San Diego, Inc.
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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
Executive Summary
Introduction
Vicinity Map
TABLE OF CONTENTS
Post Construction BMP Location Exhibit
Summary of Results
Storm Water Treatment Criteria and Methodology
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
-Vor,;technics 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
SECTION
II .
III
IV
(Pocket)
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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
SECTION I
EXECUTIVE SUMMARY
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La Costa Greens -Neighborhood 1.09
Preliminary 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 t 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 1.09 is located roughly in the center of the development, east of Alicante
Road, north of Neighborhood 1.12 and south of Neighborhood 1.08. Neighborhood
1.09 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.
VICINITY MAP
NTS
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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
All runoff from Neighborhood 1.09 will eventually drain to a proposed storm drain outlet
located at the southwest corner of Neighborhood 1 ;10 (at the Street KK cul-de-sac). In
, addition to the flow contributE}d by Neighborhood 1.09, Neighborhood 1.10, the
northern' portion of Neighborhood 1.12, and offsite area from adjacent residential .
developed areas east of La Costa Greens Phase 1 (totaling 98 acres) will also drain to
this storm drain outlet location. This runoff discharges from the storm drain to the
'unnamed tributary of San Marcos Creek, which flows in a southerly direction qlong the
west side of Neighborhood 1.10. 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; "Hydrolo,gy &
Hydraulic Study -La Costa Greens Phase 1 ", prepared by O'Day Consultants
May 25, 2002, and "Tentative Map Drainage Study for La Costa Greens -Phase1
Neighborhoods 1.08 through 1.14," prepared by Hunsaker & Associates San Diego,
Inc. April 17, 2003. The O'Day report identifi~d 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
offsite run on at the southeast corner of Neighborhood 1.09 will be collected and piped
through Neighborhood 1.09 and 1.10 to the outlet. 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 1.09 project will include construction of two (2)
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 75 residential lots and 2 open space lots, for a total
area of 21.04 acres (14.83 acres and 6.21 acres respectively). Approximately 30% will
remain undeveloped.
Summary of Results
Prior to discharge into the open channel, all storm water will pass though a proposed
diversion structure that will divert the entire 85th percentile flow to a proposed storm
water treatment unit. Flows in excess of the treatment flow will bypass the treatment
unit. This analYsis performed in this report indicates that a Vortechs Model PC16x24
will be required to meet the water quality treatment requirements. The proposed
Vortechs Model PC16x24 will be located offline from the main sto.rm drain system and
is proposed to be located in the vicinity of the Street KK cul-de-sac.
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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
In addition to the primary treatment facilitated by the proposed Vortechs Model
PC16x24, 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
treatment for the 85th percentile runoff (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. Maintenar:tce 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 b,e
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 for the project
site are based on 85th percentile de,sign 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" also presents a listing of recommended non-structural source c,ontrol BMPs,
which,include landscaping, urban housekeeping, etc.
85th percentile calculations included in this report were generated using the Rational
Method. This method calculates the resultant 85th 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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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
SECTION II
STORM WATER TREATMENT CRITERIA
&
METHODOLOGY
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La Costa Greens -Neighborhood 1.09
Preliminary 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 con.centration of
pollutant discharge into waterways and bodies of water. Treatment BMPs
recommended for the proposed project site are based on 85th percehtile 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. The La Costa Greens Village 1.09 proposed project
" site is located in the Batiquitos watershed. After development, 85th 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 Quality 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 prior to
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 Tefer to specific storm water management
techniques that are applied to manage construction 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 gf automobile use. Runoff from paved surfaces can contain both sediment
(in the "form" oFsilt 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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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
All structural BMPs shall be located to infiltrate, filter, or treat the required runoff
volume or flow (based on the 85th 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 85th percentile design flow from
the proposed development. All grading operations for which a permit is required are
subject to periodic inspection and monitoring.
Flow-based BMPs shall be designed to mitigate the maximum f10wrate 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 receivin~ waters. Treatment BMPs recommended
for the proposed project site are based on 85t 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 #:re 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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La Costa Greens -Neighborhood 1.09
Preliminary 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 fn a water body and possibly the development of septic conditions.
Oil and Grease are characterized as high high-molecular weight organic compounds.
Prim~ry 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 1.09
Preliminary 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 1.09 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.
Priority
Project
Categories
1/1 -c Q)
E :c Q) tn
Development p(1)
>100 ft2
Automotive
Repair Shops
Restaurants
Hillside
Development X
>5 ft2
Parking Lots p(1)
Highways &
Retail Gas
Outl~ts
X = anticipated
p = potential
X
.l!! c Q) .;:: -::l Z
X
p(1)
p(1)
x
X
X
X
TABLE 1
1/1 "C C .~ S ~_I/I
C Co .c .-
C'CI E I/I.a ~ 0 e Q) 00 1-0
p(2) x
X(4)(5) x
x
X
X
X
X
(1) A potential pollutant if landscaping exists on-site.
p(5)
x
X
p(1)
p(5)
(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.
x
x
x x
X x
X p(1)
X
X
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La Costa Greens -Neighborhood 1.09
Preliminary 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 flow rate 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 storm drain system design incorporates the use of
Vortechnics' Vortechs stormwater treatment units. The table on the following page
compares the removal efficiencies of comparable hydrodynamic separation devices to
the removal efficiencies of Vortechs stormwater treatment units.
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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
Treatment Control BMP Removal Efficiencies(1)
Pollutant of Concern BMP Categories
Hydrodynamic
Separation
Devices(2)
(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 ftom 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 u'p to 25
cfs with the use of their precast treatment units. Vortechnics also provides design ana
system components that are cast-in-place (CIP). These CIP treatment units have the
ability to treat much greater flows.
Other featu.res 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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La Costa Greens -Neighborhood 1.09
Preliminary 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 85th per~entile flow.
Maintenance of Treatment Control BMPs
Maintenance of the project site BMPs will be the responsibility ofthe 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 org~nic 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.
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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
Maintenance of Flow-Based Treatment Units
Flow-based storm water treatment devices should be inspected periodically to assure
their cqndition 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 eff~ctiveness.
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 leaning other chambers, it is
imperative that the grit chamber be drained first.
The estimated annual maintenance cost associated with the Vortechs treatment 'unit
proposed for Neighborhood 1.09, 1 .. 10 and the northern portion of 1.12 is
approximat~ly $4,000. These costs will vary depending on site conditions and the
frequency of runoff producing rainfall events. During the life span of the treatment unit,
a record of maintenance should be kept current. This will aid in determining the
frequency of maintenance activities, and therefore provide a more -accurate
approximation of the annual maintenance costs required to keep the unit functiorJing
properly.
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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
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.
•
In the event that landscaping work requires materials such as fill,
gravel, dirt, loam, mulch, etc. to be piled for more than a single 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.
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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
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 Use -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:
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.
Disch~rges 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 75 residential lots and 2 open space lots, for a
total area of 21.04 acres (14.83 acres and 6.21 acres respectively). Approximately
30% of the project site, 6.21 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 m~I5hanism. .
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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
SECTION III
STORM WATER QUALITY TREATMENT
BEST MANAGEMENT PRACTICE
.. '''~,
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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
Structural Treatment BMPs
The 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 85th percentile flow for the La Costa Greens
Neighborhood 1.09 proposed project site. The storm water quality treatment unit has
been. sized to treat the 85th 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 85th 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 s'ite'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
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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
• 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 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.
Watershed Area (A) -Project Area totaling an area of 196.05 acres.
Treatment Unit Selection
Per the special design prepared by Scott Gorneau of Vortechnics, (excerpts attached
dated August 15, 2003) the Vortechs Model PC16x24 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 structure, while flows in excess of the
design flow rate pass over an in line 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 PC16x24, 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.
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La Costa Greens -Neighborhood 1.09
Preliminary Stormwater Management Plan
SECTION IV
ATTACHMENTS
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VILLAGES OF LA COSTA
NEIGHBORHOOD 1.09, 1.10 AND PORTION OF 1.12 (NORTH)
TREATMENT FLOW DETERMINATION:
Q=C*I*A
TREATMENT AREA
RAINFALL INTENSITY
WEIGHTED CURVE NUMBER
Q= 20.78 CFS
10:45 AM8/18/2003
196.05 ACRES
0.201N/HR
0.53
Sheet1 RM-TREATMENT FLOW.xls
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T FLOW CALCULATIONS ,brteclmics La Costa Greens Village Neighborhood .,..-,.
Carlsbad, CA V PC16X26
System 1.10
VgiEchs Qrifl~g ~olEchli Weir
Cd= 0.66 Cd=O
A (ft~ = 6.31 Weir Crest Length (tt) = a
Crest Elevation (ft) = 100.00 Crest Elevation (ft) = 104.00
Head Elevation
(ft) (ft)
0.00 100.00
0.25 100.25
0.50 100.50
0.75 100.75
1.00 101.00
1.25 101.25
1.50 101.50
1.75 101.75
2.00 102.00
2.25 102.25
2.50 102.50
2.75 102.75
3.00 103.00
3.25 103.25
3.50 103.50
4.34 104.34
Calculated bv: WSG
105.0
104.5
Orifice Flow Weir Flow
(efs) (efs)
0.00 0.00
1.34 0.00
3.78 0.00
6.94 0.00
10.68 0.00.
14.93 0.00
19.63 0.00
24.73 0.00
30.08 0.00
33.26 0.00
36.15 0.00
38.84 0.00
41.34 0.00
43.71 0.00
45.95 0.00
52.82 0.00
5120l2OO3 IIChecked by:
VortechslM System
Stage Discharge Curve
B~assWelr
Cd=3.3
Weir Crest Length (It) = 16
Crest Elevation on = 101.5
BvpassFlow Total Flow
{efs) (efs)
0.00 0.00
0.00 1.34
0.00 3.78
0.00 6.94
0.00 10.68
0.00 14.93
0.00 19.63
6.60 31.33
18.67 48.75
34.29 67.55
52.80 88.95
73.79 112.63
97.00 138.34
122.23 165.94
149.34 195.29
253.18 306.00
----f-
104.0
103.5 ------€ 103.0
:5 102.5
11 102.0 } 101.5 w
101.0
10o.s
l..----
~
-----,.,.,.-
·f
/
100.0
99.5
0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0
DlsChsrge(cf$)
-----------------,--
APPROXIMATE VORTECHNICS TREATMENT
AREAS
2.8 ~ 17 24 26 31 I 39
Model 3000 4.5 27 38 41 49 I 62
Model 4000 6.0 37 51 55 66
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
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Plan View
. .~. ."
.. : .•... ~ ~
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 aver. ...... ..' . '1
'. . • " ••• ' '. v' ".: .'. I Oil Chainber &: Bcdfle Wall . :'. ;
'The center baffle traps floatables in : 'j
. ,',' :the oil chamber, 'even during clean:.. ,';,.;.1
.:.out. Highly resistaf)t to flow.surgl?s. "3
. : '". ':::," ............ ~": .'··\·f·:~:":. ',. '::~' ... !
.. ~..;. ; ..... .,. Flow Control Chamber :'~;',:.~ ~~:.\;.r·1
.' : ..... The weir and orifice flaw conliols~·::'·." i
'.. . ~ ... ":.~ .: :.1) Rai~e 'Ievel and V?lume i~. ~~ .. {:~ ' .. :,!.] . . .. ''' .. :' : system as flow rate Increases; arid : ~.'!
: " ' ..... ~.... . '. . ..... . ',. . 2). gradually drain the:system: as"',·:;;·: "::':.J
"7':':.: ··:.:·Elevation View: Dry-Weather. .. . ..,.. flow rate subsides: :: .. ; .. ': :.,,::::.:';':~:.! .:.~~~:~~.u:::~._ :'~ ... ~ ':. '. ".:': !~:. ~.~:" ',. ,',. : . _ '. ~ ..... _ .. ': .:~.\' ~:.:: .~;: ~.~ . .:~::~~~;~~, "~'!~;:~;~~:~~.:' ... ~
1) Initial Wet Weather Phase 2) Transition Phase
During a two-rnonth storm event the water level begins to .
. rise ab~ve 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, SIlJnn
drains are flawing at peak capacil11. The Vortschs System is
designed to match your design storm flow and provide treat~
ment throughout the range of storm events withcut bypass~
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) Stonn Subsidence Phase/Cleaning
Treated runoff is decanted at a controlled rate, restoring the
water level to a low dry-weather volume and revealing a conical
pile of sediment. The low water level facilitates inspection and
cleaning, and significantly reduces maintenance casts. The
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the Stormwater Treatment
-..-----0 Plus 6' Typical-----~I
1'.10' 1'.9 '.9" ---1 .. -.,\
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Plan 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. Th~m 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.
. ~. rtf!
~to5'
IN\/. ~ -t-
S'to4'
•
Typical
j
Bevation View
2.8
4.5
6.0
.,'.' •• f · '.' il ~o~' I~I~~ V~r~e~~' ~~.~~ :w~~~~ ~ byP!!,!s,. sizing cntaria is·tia~ed ~~ :;~i~i~~:'~n~ SqU~~ ;oot '~f'9~~:'
.chamber-surface area for each 100 gpm of:pes~ design storm flqw rate (e.g .. 1Q.year storm). Fm: more ".:. ,
· " detaija about Vcrtechnics sizing·criteria refer to VortachnicS Technical Buifetin'3: '. .' . . '. ' .• :. '.' : .'
. ;BrSedimentstUragevoliJ/·iiaassurn~a,3fu~t,sump •. :·:· . .::-,..: .. :' ; •.. ,.'. .. ',:.. ". ":" · .... 6, ConS:rUct!c~ details' 'm~'veN dep'eod'ing cn~the ~peCifio ~ppllcation. Arri elteratlons to the sfzlng chart specifi· .
· :'. c~tions will appeer' cn ~~chnics_di~.elJ~onel .~nd ~hop. dfawings. PI~a~e' call, Vcrtechn.!cs for the w;igt'!t ~! ,sP,e-·, ,
.-:,cUic:Vertechs.system;slfnesdsd •. · ... : ...... ~:: .. :" ".: ':: , .. , .. " : ... :., . '. '. . .i .. ·.' ' ..
: Special N~~ all storage ca'pacity,.wh!ll) it is. needed to,.illest·s speciflc:requirSment for spill ccntainmBn~, can be ,
.. sized to meet the storage requir'emen~·with· tl)e selected medel. Vortachnics taqhnical staff will ep.timiza sy'sten:t,' .
. , geometry to ,meet containment raquirements within a correctiy sized Vortechs System;· .' •. : : ;·:r'M~:;;ia ;P~~ifi~tiOr ~~rt l!v8i;a~i~, by i:S/~~~. ib:~cfm;cs ~t '(~J 87~.:3BB2: . ~ .. : . '
•• :., • #~ :'., • !': • ,10 ... ,' • .: ••••• ' ••• 1) : ••• '':'. I.... .' • ••• •
Vortechs System Inlet/Outlet Comigurations 1)11 L 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
-
To
Polish
To
Outfall
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- - ---'" o J> r f'l ... • II ro o o o , o ro o o o ~ o o o (J\ o o o ------ - -----~-,.-
.' .
, , ,
•
2: 1 SLOPE P£R fj
DRAWING NO. J97-2Ai
I, \ ' II '
19 ACRES OF
OFFslTE
DEVELOPMENT
79 ACRES OF
OFFslTE
DEVELOPMENT
LEGEND
WATERSHED BOUNDARY
OFFSITE WATERSHED
BOUNDARY
BROW DITCH
o 120 240 ~~~I 360
SCALE 1'-120'
--------
3> 3> 3> 3> 3> OR"'·o '0
SITE DEVELOPMENT MAP FOR SHEET
HUNSAKER
& ASSOCIATES
SAN DIEGO. INC.
PLANNING 10179 Huennekms Street
ENQNrrRING San Diego, Ca 92121
SURVEYING PH(858)55B-4500· FX(858)55S-1414
LA COSTA GREENS
NEIGHBORHOOD 1.09
1
OF
CITY OF CARLSBAD, CALIFORNIA 1
R'\0327\&Hyd\327$H06-UL T SITEMAP 109,dwg[ 2030JAug-18-2003'12'49
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