Appendices I - Preliminary Water Quality Technical Report
Espola Road Improvement Project
Appendix I
Preliminary Water Quality Technical Report
Prepared for:
City of Poway
March 2013
CITY OF POWAY
PRELIMINARY WATER QUALITY TECHNICAL
REPORT (WQTR)
ESPOLA ROAD WIDENING PROJECT
(Titan Way/Eden Lane to Twin Peaks Road)
November 14, 2011
Prepared for:
City of Poway
13325 Civic Center Drive
Poway, CA 92064
Prepared by:
Bureau Veritas North America Inc.
11590 West Bernardo Court, Suite 100
San Diego, CA 92127-1624
PRELIMINARY WATER QUALITY
TECHNICAL REPORT (WQTR)
FOR
ESPOLA ROAD WIDENING PROJECT
TITAN WAY/EDEN LANE TO TWIN PEAKS ROAD
November 14, 2011
Prepared For:
City of Poway
13325 Civic Center Drive
Poway, CA 92064
(858) 668-4400
Prepared By:
Bureau Veritas North America, Inc.
11590 West Bernardo Ct.
Suite 100
San Diego, CA 92127
(858) 451-6100
Owner:
City of Poway
13325 Civic center Drive
Poway, CA 92064
(858) 668-4400
BVNA Job No. 16000
City of Poway Project No. _______
Espola Road Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
ENGINEER’S CERTIFICATION
This Water Quality Technical Report has been prepared under the direction of Tracy Beach, a
Registered Civil Engineer in the State of California. The Registered Civil Engineer attests to the
technical information contained herein and the engineering data upon which recommendations,
conclusions, and decisions are based.
DATE
TRACY BEACH, PE
REGISTERED CIVIL ENGINEER
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
i
TABLE OF CONTENTS
APPENDICES ...................................................................................................................... ii
LIST OF TABLES ................................................................................................................. ii
ABBREVIATIONS ............................................................................................................... 3
ACRONYMS ....................................................................................................................... 3
INTRODUCTION ....................................................................................................................... 4
1.0 PROJECT DESCRIPTION ................................................................................................ 4
1.1 TOPOGRAPHY AND LAND USE .............................................................................. 4
1.2 HYDROLOGIC UNIT CONTRIBUTION ..................................................................... 4
2.0 WATER QUALITY ENVIRONMENT ................................................................................. 5
2.1 BENEFICIAL USES .................................................................................................. 5
2.1.1 INLAND SURFACE WATERS .............................................................................. 7
2.1.2 COASTAL WATERS ............................................................................................. 7
2.1.3 GROUND WATER ................................................................................................ 7
2.2 303(D) STATUS ........................................................................................................ 8
3.0 CHARACTERIZATION OF PROJECT RUNOFF .............................................................. 8
3.1 EXISTING AND POST-CONSTRUCTION DRAINAGE .................................................. 8
3.2 POST-CONSTRUCTION EXPECTED DISCHARGES ................................................... 9
3.3 HYDROLOGIC CONDITIONS OF CONCERN ........................................................... 11
4.0 MITIGATION MEASURES TO PROTECT WATER QUALITY .........................................12
4.1 CONSTRUCTION BMPS .........................................................................................13
4.2 POST-CONSTRUCTION BMPS ..............................................................................13
4.2.1 LID SITE DESIGN BMPs .....................................................................................13
4.2.2 SOURCE CONTROL BMPs .................................................................................15
4.2.3 TREATMENT CONTROL BMPs ..........................................................................16
4.3 LOW IMPACT DEVELOPMENT...............................................................................18
4.4 OPERATION AND MAINTENANCE PLAN ...............................................................18
6.0 FISCAL RESOURCES .....................................................................................................22
7.0 CONCLUSIONS ...............................................................................................................22
8.0 REFERENCES .................................................................................................................23
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
ii
APPENDICES
APPENDIX A: VICINITY MAP
APPENDIX B: BMP LOCATION EXHIBIT
APPENDIX C: CALCULATIONS
APPENDIX D: BIORETENTION SWALE DETAIL AND INFORMATION SHEETS
LIST OF TABLES
Table 1. Hydrologic Unit in Project Vicinity ..................................................................... 4
Table 2. Project Contributions to Watershed .................................................................. 5
Table 3. Description of Beneficial Uses .......................................................................... 5
Table 4. Beneficial Uses of Inland Surface Waters ......................................................... 7
Table 5. Beneficial Uses of Coastal Waters ................................................................... 7
Table 6. Beneficial Uses of Inland Ground Waters ......................................................... 7
Table 7. 303 (d) Water Bodies Listed with Constituents of Concern ............................... 8
Table 8. Anticipated and Potential Pollutants Generated By Land Use Type .................. 9
Table 9. General Pollutant Categories and Descriptions .............................................. 10
Table 10. Summary of 100-Year Hydrologic Results .................................................... 12
Table 11. BMPs Applicable to Priority Projects............................................................. 12
Table 12. BMP Categories and Descriptions ................................................................. 13
Table 13. Structural Treatment Control BMP Selection Matrix ....................................... 16
Table 14. Preliminary Bioretention Swale Design Calculations ..................................... 17
Table 15. Shear Pressure Determination within Bioretention Swales ........................... 18
Table 16. Permanent BMP Operation and Maintenance Requirements ........................ 19
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
iii
ABBREVIATIONS
ac Acre
ft Feet
hr Hour
in/hr Inch / Hour
mi Miles
min Minute
s Second
ACRONYMS
BMP Best Management Practice
CASQA California Stormwater Quality Association
CIP Capital Improvement Project
CWA Clean Water Act
DCIA Directly Connected Impervious Area
EPA United States Environmental Protection Agency
HA Hydrologic Area
HSA Hydrologic Subarea
HU Hydrologic Unit
IHC Interim Hydromodification Criteria
JURMP Jurisdictional Urban Runoff Management Plan
LID Low Impact Development
MEP Maximum Extent Possible
MS4 Municipal Separate Storm Sewer System
NPDES National Pollutant Discharge Elimination System
PMC Poway Municipal Code
ROW Right-of-Way
RWQCB California Regional Water Quality Control Board
SD San Diego
SUSMP Standard Urban Stormwater Mitigation Plan
SWMP Storm Water Management Plan
SWPPP Storm Water Pollution Prevention Plan
SWRCB California State Water Resources Control Board
WPCD Water Pollution Control Drawing
WQTR Water Quality Technical Report
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
4
INTRODUCTION
This Water Quality Technical Report (WQTR) is required under the City of Poway’s (City) local
Standard Urban Stormwater Mitigation Plan (SUSMP) dated September 23, 2008. The purpose
of this report is to document the process that was used to select and design the low impact
development (LID) site design, source control, and treatment control storm water best
management practices (BMPs) that will be incorporated within the project to mitigate the
impacts of urban runoff after construction. This WQTR is also intended to ensure the
effectiveness of the BMPs through proper long-term maintenance.
1.0 PROJECT DESCRIPTION
The proposed project will provide improvements to Espola Road, a key access road for the City
of Poway, between approximately 1000-ft south of the intersection of Espola Road and Titan
Way/Eden Lane to approximately 200-ft south of the crossing of Espola Road by Rattlesnake
Creek. Improvements will consist of widening the two-lane road to a three-lane major facility
between the northern project terminus south of Titan Way/Eden Lane to the intersection of
Espola Road and Twin Peaks Road, as well as necessary traffic safety, drainage, pedestrian,
and landscaping improvements.
A Vicinity Map, which identifies the project’s location, has been included in Appendix A and a
BMP Location Map, included in Appendix B, indicates drainage areas, direction of flow,
proposed storm water conveyance systems, proposed source control BMPs, proposed
treatment control BMPs and their respective treatment areas, and pervious and impervious
areas.
1.1 TOPOGRAPHY AND LAND USE
The project occurs along an area with elevations ranging from approximately 585-ft to 811-ft
above mean sea level. The onsite drainage tributary area consists solely of the roadway
sections while the offsite drainage tributary area is primarily residential and natural open space.
1.2 HYDROLOGIC UNIT CONTRIBUTION
Table 1 identifies the hydrologic unit within the project limits. The hydrologic unit and area
numbers were taken from the Water Quality Control Plan for the San Diego Basin.
Table 1. Hydrologic Unit in Project Vicinity
Hydrologic Unit Hydrologic Area Name Basin Number
Peñasquitos HU 906
Poway HA 906.20
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
5
A comparison of the acreage of the hydrologic area versus the contributing project area is
shown in Table 2. The project constitutes less than 0.0092 % of the area within the affected
watershed.
Table 2. Project Contributions to Watershed
Hydrologic
Area
Watershed Area, WA
(Acres)
Approximate Project
Area (Acres)
Estimated Project
Contribution (%)
904 108,800 10.0 0.0092
2.0 WATER QUALITY ENVIRONMENT
2.1 BENEFICIAL USES
The descriptions of beneficial uses that are within the project limits or that the project discharges
directly to are contained in Table 3. Beneficial uses of inland surface waters, coastal waters,
and inland ground waters are contained in Tables 4, 5 and 6, respectively. The beneficial uses
for inland surface waters, coastal waters, and ground waters must be protected as required by
the Water Quality Control Plan for the San Diego Basin and the Municipal Permit. Beneficial
uses were adopted and are to be used by the SD RWQCB and the nine RWQCBs uniformly
throughout all basins of the State. There are 23 beneficial uses within the San Diego Region, of
which 14 beneficial uses are within the project limits.
Table 3. Description of Beneficial Uses
Beneficial Use
Designation Beneficial Use Description
MUN
Municipal and
Domestic
Supply
Includes uses of water for community, military, or individual water supply
systems including, but not limited to, drinking water supply.
AGR Agricultural
Supply
Includes uses of water for farming, horticulture, or ranching including, but not
limited to, irrigation, stock watering, or support of vegetation for range
grazing.
IND
Industrial
Services
Supply
Includes uses of water for industrial activities that do not depend primarily on
water quality including, but not limited to, mining, cooling water supply,
hydraulic conveyance, gravel washing, fire protection, or oil well re-
pressurization.
REC1 Contact
Recreation
Includes uses of water for recreational activities involving body contact with
water, where ingestion of water is reasonably possible. These uses include,
but are not limited to, swimming, wading, water-skiing, skin and SCUBA
diving, surfing, white water activities, fishing, or use of natural hot springs.
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
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Table 3. Description of Beneficial Uses
Beneficial Use
Designation Beneficial Use Description
REC2 Non-Contact
Recreation
Includes the uses of water for recreational 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, camping, boating, tide pool and marine life study,
hunting, sightseeing, or aesthetic enjoyment in conjunction with the above
activities.
WARM
Warm
Freshwater
Habitat
Includes uses of water that support warm water ecosystems including, but
not limited to, preservation or enhancement of aquatic habitats, vegetation,
fish or wildlife, including invertebrates.
WILD Wildlife Habitat
Includes uses of water that support terrestrial ecosystems including, but not
limited to, preservation and enhancement of terrestrial habitats, vegetation,
wildlife, (e.g., mammals, birds, reptiles, amphibians, invertebrates), or
wildlife water and food sources.
BIOL
Preservation of
Biological
Habitats of
Special
Significance
Includes uses of water that support designated areas or habitats, such as
established refuges, parks, sanctuaries, ecological reserves, or Areas of
Special Biological Significance (ASBS), where the preservation or
enhancement of natural resources requires special protection.
EST Estuarine
Habitat
Includes uses of water that support inland saline water ecosystems
including, but not limited to, preservation or enhancement of estuarine
habitats, vegetation, fish, shellfish, or wildlife (e.g., estuarine mammals,
waterfowl, shorebirds).
RARE
Rare,
Threatened, or
Endangered
Species
Includes uses of water that support habitats necessary, at least in part, for
the survival and successful maintenance of plant or animal species
established under state or federal law as rare, threatened or endangered.
MAR Marine Habitat
Includes uses of water that support marine ecosystems including, but not
limited to, preservation and enhancement of terrestrial habitats, vegetation
such as kelp, fish, shellfish, of wildlife (e.g., marine mammals, shorebirds).
MIGR
Migration of
Aquatic
Organisms
Includes the uses of water that support habitats necessary for migration,
acclimatization between fresh and salt water, or other temporary activities by
aquatic organisms, such as anadromous fish.
SPWN
Spawning,
Reproduction,
and/or Early
Development
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.
SHELL Shellfish
Harvesting
Includes uses of water that support habitats suitable for the collection of
filter-feeding shellfish (e.g., clams, oysters and mussels) for human
consumption, commercial, or sport purposes.
Excerpt from Water Quality Control Plan for the San Diego Basin.
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
7
2.1.1 INLAND SURFACE WATERS
Table 4. Beneficial Uses of Inland Surface Waters
Hydrologic Area Basin
Number
M
U
N
A
G
R
I
N
D
R
E
C
1
R
E
C
2
W
A
R
M
C
O
L
D
W
I
L
D
Inland Surface Waters
Rattlesnake Creek 906.20 + • o • • • • •
Los Peñasquitos Creek 906.20
• Existing Beneficial Use
o Potential beneficial use
+ Excepted from MUN
2.1.2 COASTAL WATERS
Table 5. Beneficial Uses of Coastal Waters
Hydrologic Area Basin
Number
R
E
C
1
R
E
C
2
B
I
O
L
E
S
T
W
I
L
D
R
A
R
E
M
A
R
M
I
G
R
S
P
W
N
S
H
E
L
L
Coastal Waters
Peñasquitos Lagoon 906.10 • • • • • • • • • •
• Existing Beneficial Use
2.1.3 GROUND WATER
Table 6. Beneficial Uses of Inland Ground Waters
Hydrologic Area Basin
Number
M
U
N
A
G
R
I
N
D
Ground Waters
Poway HA 906.20 • • o
• Existing Beneficial Use
o Potential beneficial use
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
8
2.2 303(d) STATUS
The nearest downstream impaired water bodies are listed below.
Table 7. 303 (d) Water Bodies Listed with Constituents of Concern
Hydrologic Descriptor Waterbody Pollutant / Stressor Extent of
Impairment
Los Peñasquitos Creek
(HA 906.10)
Los Peñasquitos
Creek
Phosphate (Nutrients)
TDS (Nutrients)
12-mi
12-mi
Los Peñasquitos Lagoon
(HA 906.10)
Los Peñasquitos
Lagoon Sedimentation/Siltation 469-ac
Excerpt from 2006 CWA 303(d) List
TDS = Total Dissolved Solids
3.0 CHARACTERIZATION OF PROJECT RUNOFF
3.1 Existing and Post-Construction Drainage
In general, the site’s onsite runoff currently (in existing conditions) drains in a southerly direction
along Espola Road and eventually flows into an existing 7-ft storm drain commencing just north
of Twin Peaks Road and running south along the eastern right-of-way (ROW) of Espola Road.
The storm drain then outlets into Rattlesnake Creek, which is located immediately southwest of
Twin Peaks Road, enroute to Peñasquitos Creek, Peñasquitos Lagoon, and the Pacific Ocean.
More specifically, offsite runoff from the area east of Espola Road and north of High Valley
Road drains in an easterly direction towards Espola Road where various CMP culverts drain the
stormwater across the roadway into a natural drainage stream that flows into a sump area
located on the northwest corner of the Espola Road-Del Poniente Road intersection. Offsite
runoff from the area west of Espola Road and north of Del Poniente Road also drains towards
this sump area via the same natural drainage stream. From the sump area, the offsite
discharge is conveyed across Del Poniente Road via a 48-in culvert where it then flows
southerly along a natural drainage stream until it reaches a culvert headwall situated along the
western boundary of Espola Road across the street from Mountain Road. Said culvert conveys
the offsite flows across Espola Road towards a trapezoidal concrete channel. A confluence of
stormwater, from a large offsite area east of Espola Road and north of Mountain Road, occurs
at the upstream end of the trapezoidal concrete channel. Said channel then drains the runoff in
a southerly direction along Espola Road’s eastern ROW conveying additional offsite discharge
from the offsite area east of Twin Peaks Road until it eventually reaches the aforementioned 7-ft
storm drain enroute to Rattlesnake Creek, Peñasquitos Creek, Peñasquitos Lagoon, and finally
the Pacific Ocean.
After development, all onsite surface flows along the proposed roadway will be carried southerly
along the curb-and-gutter and captured by several proposed curb inlets located on both sides of
the road. The existing trapezoidal concrete channel that runs southerly along Espola Road,
from Mountain Road towards the existing 7-ft pipe, is proposed to be replaced by an
underground storm drain pipe since the widening of the road forces the elimination of said
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
9
channel. The discharge will still follow the same general drainage pattern as in existing
conditions, ultimately flowing into the previously mentioned 7-ft storm drain and discharging into
Rattlesnake Creek, Peñasquitos Creek, Peñasquitos Lagoon, and finally the Pacific Ocean
(refer to the hydrology maps located in the Preliminary Drainage Study for Espola Road
Widening Project prepared by Bureau Veritas North America, Inc. and dated November 21,
2008).
First-flush flows will be filtered through several proposed bioretention swales, located adjacent
to both sides of the roadway, prior to being rerouted via proposed catch basins onto the main
storm drain systems and finally discharging into Rattlesnake Creek. The proposed catch
basins, located at the downstream end of the bioretention swales, will be connected to the back
of the proposed inlets along Espola Road by a low-flow pipe. In addition, curb openings are
proposed at the upstream end of every swale in order to route the required first-flush runoff into
the bioretention swales. Underdrain pipes are also proposed under driveways in order to
maintain a consistent flowpath between bioretention swales throughout the majority of Espola
Road’s length. Maintenance of the proposed bioretention swales must be part of the City’s
Operation and Maintenance Plans (refer to Section 4.4).
3.2 Post-Construction Expected Discharges
Development of the proposed project will not significantly alter drainage patterns on the site.
Currently, Espola Road consists of a two-lane street (one northbound lane and one southbound
lane). As such, the pollutants of concern before commencement of construction activities
include those listed in Table 8 for the “Streets, Highways, and Freeways” project category.
Table 8 also lists potential pollutants of concern from the proposed project based on the
applicable project category of “Streets, Highways and Freeways”, since the proposed project
consists of the widening of the street to a three-lane street. These pollutants are the same
pollutants generated prior to construction. Table 9 describes these pollutants and their possible
sources.
Table 8. Anticipated and Potential Pollutants Generated By Land Use Type
General Pollutant Categories
Priority
Project
Categories
Sediment* Nutrients* Heavy
Metals
Organic
Compounds
Trash &
Debris
Oxygen
Demanding
Substances
Oil &
Grease
Bacteria &
Virus Pesticides
Streets,
Highways,
and
Freeways
X P(1) X X(4) X P(5) X
X = anticipated
P = potential
(1) A potential pollutant if landscape exists on-site.
(4) Including petroleum hydrocarbons.
(5) Including solvents.
Excerpt from Table 1 of City of Poway SUSMP
* Sediment and Nutrients are the primary pollutants of concern since they are also impairments in the receiving waters (refer to
Section 2.2).
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
10
Table 9. General Pollutant Categories and Descriptions
Sediments
Sediments are soils or other surficial 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, lower young aquatic organisms
survival rates, smother bottom dwelling organisms, and suppress aquatic
vegetation growth.
Nutrients
Nutrients are inorganic substances, such as nitrogen and phosphorus. 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.
Heavy
Metals
Metals are raw material components in non-metal products such as fuels,
adhesives, paints, and other coatings. Primary source of metal pollution in storm
water are typically commercially available metals and metal products. Metals of
concern include cadmium, chromium, copper, lead, mercury, and zinc. Lead and
chromium have been used as corrosion inhibitors in primer coatings and cooling
tower systems. At low concentrations naturally occurring in soil, metals are not
toxic. However, at higher concentrations, certain metals can be toxic to aquatic
life. Humans can be impacted from contaminated groundwater resources, and
bioaccumulation of metals in fish and shellfish. Environmental concerns,
regarding the potential for release of metals to the environment, have already led
to restricted metal usage in certain applications.
Organic
Compounds
Organic compounds are carbon-based. Commercially available or naturally
occurring organic compounds are found in pesticides, solvents, and
hydrocarbons. Organic compounds can, at certain concentrations, indirectly or
directly constitute a hazard to life or health. When rinsing off objects, toxic levels
of solvents and cleaning compounds can be discharged to storm drains. Dirt,
grease, and grime retained in the cleaning fluid or rinse water may also adsorb
levels of organic compounds that are harmful or hazardous to aquatic life.
Trash &
Debris
Trash (such as paper, plastic, polystyrene packing foam, and aluminum
materials) and biodegradable organic matter (such as leaves, grass cuttings, and
food waste) are general waste products on the landscape. The presence of trash
& debris may have a significant impact on the recreational value of a water body
and aquatic habitat. Excess organic matter can create a high biochemical
oxygen demand in a stream and thereby lower its water quality. Also, in areas
where stagnant water exists, the presence of 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.
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
11
Table 9. General Pollutant Categories and Descriptions
Oxygen-
Demanding
Substances
This category includes biodegradable organic material as well as chemicals that
react with dissolved oxygen in water to form other compounds. Proteins,
carbohydrates, and fats are examples of biodegradable organic compounds.
Compounds such as ammonia and hydrogen sulfide are examples of oxygen-
demanding compounds. The oxygen demand of a substance can lead to
depletion of dissolved oxygen in a water body and possibly the development of
septic conditions.
Oil &
Grease
Oil and grease are characterized as high-molecular weight organic compounds.
Primary sources of oil and grease are petroleum hydrocarbon products, motor
products from leaking vehicles, esters, oils, fats, waxes, and high molecular-
weight fatty acids. Introduction of these pollutants to the water bodies are very
possible due to the wide uses and applications of some of these products in
municipal, residential, commercial, industrial, and construction areas. Elevated oil
and grease content can decrease the aesthetic value of the water body, as well
as the water quality.
Bacteria
& Virus
Bacteria and viruses are ubiquitous microorganisms that thrive under certain
environmental conditions. Their proliferation is typically caused by the transport
of animal or human fecal wastes from the watershed. Water containing
excessive bacteria and viruses can alter the aquatic habitat and create a harmful
environment for humans and aquatic life. Also, the decomposition of excess
organic wastes causes increased growth of undesirable organisms in the water.
Pesticides
Pesticides (including herbicides) are chemical compounds commonly used to
control nuisance growth or prevalence of organisms. Excessive application of a
pesticide may result in runoff containing toxic levels of its active component.
3.3 Hydrologic Conditions of Concern
An Interim Hydromodification Criteria (IHC) analysis is not required since the project does not
disturb 50-ac or more. However, per the City’s SUSMP, a drainage study must be prepared for
the proposed project (refer to the Drainage Study for Espola Road Widening prepared by
Bureau Veritas North America, Inc. and dated November 21, 2008). Development of the
proposed project yielded a 100-year peak flowrate increment of a mere 4.7-cfs, or 0.35%, as
shown in Table 10 on the next page. Said increase is considered negligible given the
contributing watershed’s size.
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
12
Table 10. Summary of 100-Year Hydrologic Results
Node ID
Existing Conditions Proposed Conditions
Drainage
Area
A
(ac)
Time of
Conc.
Tc
(min)
Peak
Flowrate
Q100
(cfs)
Drainage
Area
A
(ac)
Time of
Conc.
Tc
(min)
Peak
Flowrate
Q100
(cfs)
120
(U/S of Twin Peaks Road) 569.3 16.3 1,044.2 568.5 16.3 1,048.1
120
(D/S of Twin Peaks Road
at Rattlesnake Creek Outfall)
673.8 16.3 1,239.1 673.0 16.3 1,243.4
4.0 MITIGATION MEASURES TO PROTECT WATER QUALITY
To address the water quality concerns identified above, BMPs will be implemented during
construction and post-construction. According to Table 2 of the City of Poway’s SUSMP, which
has been excerpted in Table 11 below, post-construction LID site design and source control
BMPs will be required for the project.
Table 11. BMPs Applicable to Priority Projects
Priority
Project
Category
LID Site
Design
BMPs(1)
Source
Control
BMPs(2)
Requirements Applicable to Individual Priority Project
Categories(3)
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Highways &
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R R
R
R = Required; selected BMPs as required from the applicable steps in Chapter 16.105 or 16.106 Poway
Municipal Code (PMC).
(1) Refer to Chapter 16.105 PMC.
(2) Refer to Chapter 16.406 PMC.
(3) Priority project categories must apply specific stormwater BMP requirements, where applicable.
Projects are subject to the requirements for all priority project categories that apply.
Excerpt from Table 2 of City of Poway SUSMP
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
13
4.1 CONSTRUCTION BMPS
The proposed project will be covered under the General Construction Storm Water Permit,
NPDES Order 2009-2009-DWQ. The project plans will cover construction site BMPs; more
descriptive information on these BMPs can be found in the project’s SWPPP. The SWPPP may
include a Sampling and Monitoring Program that addresses both direct discharges from the
project into a Section 303(d) water body and discharges that have been discovered through
visual monitoring to be potentially contaminated by pollutants not visually detectable in the
runoff.
Additionally, Erosion Control Plans will be developed and will be included in the contract plans
in order to address temporary BMPs during the construction phase.
4.2 POST-CONSTRUCTION BMPS
Post-construction BMPs will be implemented to address water quality impacts during the
planning, design, and operational stages of this project. The general categories of these BMPs
are shown in Table 12. Specific BMP descriptions for LID site design, source control, and
treatment control BMPs are presented in Sections 4.2.1 through 4.2.3 of this report,
respectively.
Table 12. BMP Categories and Descriptions
Category Description
LID Site Design BMPs
Any project design feature that reduces the creation or severity of potential
pollutant sources or reduces the alteration of the project site’s natural flow
regime.
Source Control BMPs
Land use or site planning practices or structures that aim to prevent urban
runoff pollution by reducing the potential for contamination at the source of
pollution. Source control BMPs minimize contact between pollutants and site
runoff (covers over trash bins, berms around fuel dispensers)
Treatment Control BMPs
An engineered system designed and constructed to remove pollutants from
urban runoff. Pollutant removal is achieved by simple gravity settling of
particulate pollutants, filtration, biological uptake, media absorption or any
other physical, biological, or chemical process.
4.2.1 LID SITE DESIGN BMPs
The following LID site design BMPs, from the City’s SUSMP, have been incorporated into the
project design and are standard technology-based, non-treatment controls selected to reduce
pollutant discharges to the maximum extent possible (MEP) requirements.
Maintaining Pre-Development Rainfall Runoff Characteristics
The post-development peak storm water runoff discharge rates are controlled; and maintain, if
not reduce, pre-development downstream erosion through the application of the following
design concepts:
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
14
1) Design Concept 1 – Minimize Project’s Impervious Footprint and Conserve Natural Areas
• Minimize and disconnect impervious footprint:
- Streets and sidewalks will be designed and built to the minimum widths necessary while
maintaining public safety and a walkable environment for pedestrians.
- Impervious surfaces, such as decorative concrete, will not be used within the proposed
landscaping designs.
- Approximately 70% of the roadway drainage (including all newly impervious street
areas) will drain towards proposed bioretention swales adjacent to the street.
• Construct streets, sidewalks, and parking lot aisles to the minimum widths necessary while
maintaining public safety and a walkable environment for pedestrians:
- As previously mentioned, streets and sidewalks will follow this LID site design concept.
• Maximize canopy interception and water conservation by preserving existing native trees
and shrubs, and planting additional native or drought-tolerant tress and large shrubs:
- Where possible, existing native trees and shrubs will be preserved.
- Additional native and/or drought-tolerant vegetation will be planted along the proposed
landscaped areas.
- At least a portion of the proposed bioretention areas will also be landscaped with native
and/or drought-tolerant vegetation.
• Minimize the use of impervious surfaces, such as decorative concrete, in the landscape
design:
- As previously mentioned, impervious surfaces will not be used within the proposed
vegetated areas.
• Use natural drainage systems to the MEP:
- The proposed bioretention swales act as natural drainage systems for the first-flush
runoff.
2) Design Concept 2 – Minimize Directly Connected Impervious Areas (DCIAs)
• Where landscaping is proposed, drain impervious sidewalks, walkways, trails, and patios
into adjacent landscaping:
- Approximately 70% of the roadway drainage (including all newly impervious street
areas) will drain towards proposed bioretention swales adjacent to the street.
Protection of Slopes and Channels
The potential for erosion of slopes and/or channels will be decreased through the
implementation of the following:
• Minimize disturbances to natural drainages: Disturbances to natural channels will be
minimized to the MEP and will only occur if the headwalls of the existing culverts are in need
of replacement (including energy dissipation devices) in order to control erosive velocities
outfalling from them.
• Convey runoff safely from the top of slopes: Proposed drainage ditches and other similar
drainage structures will ensure that runoff at the top of slopes is safely conveyed. In
addition, all proposed slopes will be vegetated.
• Vegetate slopes with native or drought-tolerant vegetation: All slopes within the proposed
project will be vegetated with native and/or drought tolerant vegetation in order to minimize
erosion. During the construction phase of the project, all these slopes will be hydroseeded.
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
15
• Control and treat flows in landscaping and/or other control prior to reaching existing natural
drainage systems: Approximately 70% of the roadway drainage (including all newly
impervious street areas) will drain towards proposed bioretention swales adjacent to the
street prior to outfalling into Rattlesnake Creek.
• Install energy dissipators, such as riprap, at the outlets of new storm drains, culverts,
conduits, or channels that enter unlined channels: Energy dissipators will be installed at the
outlets of the existing culverts only if it has been determined that the existing facilities do not
control erosion due to high velocities.
4.2.2 SOURCE CONTROL BMPs
The following source control BMPs, from the City’s SUSMP, have been incorporated into the
project design and are control measures used on disturbed areas to reduce the potential for
discharge of sediment or other pollutants into storm water runoff. Source controls prevent or
limit the exposure of materials to storm water at the source.
Providing Storm Drain System Stenciling and Signage
Concrete stamping, porcelain tile, inset permanent marking, or equivalent will be provided at all
existing and proposed storm water conveyance system inlets and catch basins within the project
area with prohibitive language (i.e., “No Dumping – I Live Downstream”), satisfactory to the
Director of Development Services. If necessary, the stamping will also be in Spanish.
Using Efficient Irrigation Systems and Landscape Design
The following methods to reduce excessive irrigation runoff will be implemented on this project:
• Rain shutoff devices will be employed to prevent irrigation during precipitation.
• Irrigation systems will be designed to each landscape areas’ specific water requirements.
• Flow reducers or shutoff valves will be employed so that in the event of a broken sprinkler
head or line they can be triggered by a pressure drop and; thus, control water loss.
Incorporating Requirements Applicable to Individual Priority Project Categories - Roadways
Per the City’s SUSMP, priority roadway projects must incorporate treatment control BMPs
following the selection procedure identified in the SUSMP. As such, bioretention swales have
been selected to treat stormwater runoff.
Other source control BMPs that will be implemented within the project site, but are not
specifically mentioned in the City’s SUSMP include the following:
Inlet and Catch Basin Inspection
The site’s proposed drainage is picked up in inlets and catch basins at various places and is
transported underground to the storm drain system. The City will ensure that all catchment
structures are clean and functioning properly and will also check for illegal discharges into said
catchment structures.
Landscape Maintenance
The City will ensure that all landscaped areas are inspected for damage to vegetation,
trash/debris accumulation, and standing water. Landscaped areas will be trimmed, all weeds
will be removed, and regrading will be performed as necessary.
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
16
Street Sweeping
The City sweeps Espola Road every other week; therefore, street sweeping will be directly
applied to the proposed project. Street sweeping helps reduce the amount of sediment, trash,
and debris entering the storm drain systems.
4.2.3 TREATMENT CONTROL BMPs
This proposed project falls under the “Priority Project” category and as such, requires treatment
control BMPs. A total of six (6) bioretention swales are adjacent to the roadway (refer to
Appendix B for the BMP Location Map). The proposed bioretention swales will provide at least
medium efficiency treatment against sediment, nutrients, heavy metals, bacteria, and oil and
grease. The primary pollutants of concern, those generated by the project site and also causing
impairments in the receiving waters, are sediment and nutrients, which the bioretention swales
remove efficiently (assuming an ongoing long-term Operation & Maintenance Plan is followed;
refer to Section 4.4).
Table 13 was developed as part of the SUSMP to aid in selecting the appropriate BMPs based
on pollutants associated with the project category and depicts the targeted pollutants for
bioretention BMPs.
Table 13. Structural Treatment Control BMP Selection Matrix1
Pollutant of
Concern
Treatment Control BMP Categories
Bioretention
Facilities
(LID)
Settling
Basins
(Dry
Ponds)
Wet
Ponds
and
Wetlands
Infiltration
Facilities
and
Practices
(LID)
Media
Filters
High-rate
Biofilters
High-rate
Media
Filters
Trash
Racks &
Hydro-
dynamic
Devices
Coarse
Sediment &
Trash1
H H H H H H H H
Pollutants
that tend to
associate
with fine
particles
during
treatment2
H H H H H M M L
Pollutants
that tend to
be dissolved
following
treatment3
M L M H L L L L
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
17
Table 13. Structural Treatment Control BMP Selection Matrix1
Pollutant of
Concern
Treatment Control BMP Categories
Bioretention
Facilities
(LID)
Settling
Basins
(Dry
Ponds)
Wet
Ponds
and
Wetlands
Infiltration
Facilities
and
Practices
(LID)
Media
Filters
High-rate
Biofilters
High-rate
Media
Filters
Trash
Racks &
Hydro-
dynamic
Devices
(1) Includes sediment and trash & debris.
(2) Includes sediment, nutrients, heavy metals, organic compounds, oxygen demanding substances,
bacteria, oil &grease, and pesticides.
(3) Includes nutrients.
L: Low removal efficiency
M: Medium removal efficiency
H: High removal efficiency
Excerpt from Table 3 and Table 4 of the City of Poway SUSMP
The typical treatment flow calculation for the bioretention swale has been determined based on
the rational method and the flow-based numeric sizing treatment standards identified in the
City’s SUSMP. The runoff coefficient value used for 100% impervious areas is 0.90, based on
the San Diego County Hydrology Manual, as follows:
C = [0.90 x (% Impervious)] + [Cp x (1 - % Impervious)]
C = (0.90 x 1) + [0 x (1 – 1)]
C = 0.90
However, since this is a preliminary design, a more conservative coefficient of 0.95 has been
used. A runoff coefficient of 0.35 was used for natural and/or landscaped areas; and a runoff
coefficient of 0.55 as used for manufactured slopes. The intensity for the subbasins is 0.2-in/hr
based on the City of Poway SUSMP. Areas were measured using the AutoCAD software.
Appendix C contains the swale design calculations and Table 14 summarizes the results.
Table 14. Preliminary Bioretention Swale Design Calculations
Swale
ID
Runoff
Coeff.
C
Inten-
sity
I
(in/hr)
Drain-
age
Area
A
(ac)
Treat-
ment
Flow
Qt
(cfs)
Swale
Long.
Slope
s
(%)
Flow
Depth
d
(ft)
Flow
Velo-
city
v
(ft/s)
Min.
Req'd
Time
tmin
(min)
Min.
Req'd
Swale
Length
Lmin
(ft)
Available
Swale
Length
L
(ft)
A 0.95 0.2 1.22 0.23 3.00 0.32 0.36 10.0 216 232
B 0.95 0.2 1.08 0.21 3.00 0.31 0.35 10.0 210 225
C 0.95 0.2 0.98 0.19 4.30 0.27 0.39 10.0 234 248
D 0.95 0.2 1.50 0.29 2.80 0.37 0.38 10.0 228 245
E 0.95 0.2 1.71 0.32 1.90 0.42 0.33 10.0 198 290
F 0.95 0.2 0.95 0.18 2.85 0.29 0.33 10.0 198 300
Refer to the Bioretention Swale Detail in Appendix D
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
18
A root reinforcement matrix, such as Enkamat®, is a viable option within the proposed
bioretention swales. Said matrixes are recommended when the shear pressure of the runoff
within the bioretention swales exceeds 1.0-lb/ft2. As depicted in Table 15, the shear pressure
for the six bioretention swales does not exceed 1.0-lb/ft2; thus, root reinforcement matrixes are
not required. The Enkamat® product can also be used in conjuction with a 90% silica and 10%
organic subgrade to achieve a mechanical filtration of fines.
Table 15. Shear Pressure Determination within Bioretention Swales
Swale
ID
Treatment
Flow
Qt , cfs
Swale
Longitudinal
Slope, %
Shear
Pressure
P, lb/ft2
A 0.23 3.00 0.60
B 0.21 3.00 0.58
C 0.19 4.30 0.72
D 0.29 2.80 0.65
E 0.32 1.90 0.49
F 0.18 2.85 0.51
Data provided by the Enkamat® manufacturer, Colbond Geosynthetics
4.3 LOW IMPACT DEVELOPMENT
Per the new Municipal Permit, Order No. R9-2007-0001, Low Impact Development (LID)
measures must be incorporated on all projects. The following LID features for public roads,
from the County of San Diego LID Handbook, have been incorporated into the project design:
• Sidewalk widths have been reduced while meeting ADA requirements
• Landscape areas, in the form of bioretention swales, have been added in order to reduce
impervious cover as well as treat stormwater runoff.
• An urban curb/swale system is proposed, in which the street slopes to the curb and periodic
curb openings along the street’s curb-and-gutter drain the first-flush into proposed
bioretention swales.
4.4 OPERATION AND MAINTENANCE PLAN
The proposed BMPs will be located within the public ROW, thus, the City will implement all
maintenance operations of said permanent BMPs. The Contractor is responsible for the
maintenance of all the construction BMPs.
Operation and Maintenance guidelines for the proposed permanent BMPs are provided in Table
16 on the next pages.
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r
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Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
22
6.0 FISCAL RESOURCES
The City of Poway will be responsible for all the maintenance of all the permanent post-
construction BMPs as specified in Table 16 of this report. Funding for said operations will be
provided by the City of Poway.
7.0 CONCLUSIONS
It is our conclusion that the project design measures and proposed BMPs will provide
conformance with applicable requirements under the current NPDES Municipal Permit and the
related City of Poway SUSMP requirements.
Espola Widening Project
City of Poway – WQTR
Preliminary Report 11/14/2011
23
8.0 REFERENCES
Drainage Study for Espola Road Widening Project, Bureau Veritas North America Inc.,
11/21/2008
Standard Urban Storm Water Mitigation Plan, Division VI of the Poway Municipal Code, City of
Poway, 09/23/2008
Low Impact Development Manual – Stormwater Management Strategies, County of San Diego,
02/31/2007
California Stormwater Quality Association Stormwater Best Management Practice Handbook -
Construction Handbook, 01/2003
Water Quality Control Plan for the San Diego Basin – Region 9, San Diego RWQCB,
09/08/1994
NPDES General Permit for Discharges of Storm Water Associated with Construction Activity,
Construction General Permit 2009-2009-DWQ, State of California SWRCB, 2009
Waste Discharge Requirements for Discharges of Urban Runoff from the Municipal Separate
Storm Sewer Systems (MS4s) Draining the Watershed of the County of San Diego, the
Incorporated Cities of San Diego County, the San Diego Unified Port District, and the San Diego
County Regional Airport Authority, Order No. R9-2007-0001, NPDES No. CAS0108758, San
Diego RWQCB, 01/24/2007
Enkamat®, www.colbond-geosynthetics.com
APPENDIX A
VICINITY MAP
Vicinity Map – Street View
Vicinity Map – Aerial View
APPENDIX B
BMP LOCATION MAP
APPENDIX C
CALCULATIONS
PRELIMINARY TREATMENT FLOW
& SWALE DESIGN CALCULATIONS
PRELIMINARY SWALE CURB OPENING DESIGN
ES
P
O
L
A
R
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gthLength
s
d
v
t
m
i
n
L
m
i
n
L
(%
)
(
f
t
)
(
f
t
/
s
)
(
m
i
n
)
(
f
t
)
(
f
t
)
A
0
.
9
5
0
.
2
1
.
2
2
0
.
2
3
3
.
0
0
0
.
3
2
0
.
3
6
1
0
.
0
2
1
6
2
3
2
B
0
.
9
5
0
.
2
1
.
0
8
0
.
2
1
3
.
0
0
0
.
3
1
0
.
3
5
1
0
.
0
2
1
0
2
2
5
C
0
.
9
5
0
.
2
0
.
9
8
0
.
1
9
4
.
3
0
0
.
2
7
0
.
3
9
1
0
.
0
2
3
4
2
4
8
D
0
.
9
5
0
.
2
1
.
5
0
0
.
2
9
2
.
8
0
0
.
3
7
0
.
3
8
1
0
.
0
2
2
8
2
4
5
E
0
.
9
5
0
.
2
1
.
7
1
0
.
3
2
1
.
9
0
0
.
4
2
0
.
3
3
1
0
.
0
1
9
8
2
9
0
F
0
.
9
5
0
.
2
0
.
9
5
0
.
1
8
2
.
8
5
0
.
2
9
0
.
3
3
1
0
.
0
1
9
8
3
0
0
*
N
O
T
E
:
B
a
s
e
d
o
n
a
t
r
a
p
e
z
o
i
d
a
l
s
w
a
l
e
c
r
o
s
s
-
s
e
c
t
i
o
n
w
i
t
h
1
.
0
-
f
t
b
o
t
t
o
m
w
i
d
t
h
,
3
:
1
s
i
d
e
s
l
o
p
e
s
,
a
n
d
a
m
a
x
i
m
u
m
d
e
p
t
h
o
f
0
.
5
8
-
f
t
(
r
e
f
e
r
t
o
A
p
p
e
n
d
i
x
D
f
o
r
a
d
e
t
a
i
l
)
.
PR
E
L
I
M
I
N
A
R
Y
S
W
A
L
E
D
E
S
I
G
N
C
A
L
C
U
L
A
T
I
O
N
S
Sw
a
l
e
ID
Ru
n
o
f
f
Co
e
f
f
.
C
In
t
e
n
s
i
t
y
I
(i
n
/
h
r
)
Dr
a
i
n
a
g
e
Are
a
A
(a
c
)
Tr
e
a
t
m
e
n
t
Fl
o
w
Qt
(c
f
s
)
P:
\
1
6
0
0
0
\
N
P
D
E
S
\
W
Q
T
R
\
Q
f
f
P
r
e
l
i
m
1
1
-
2
1
-
2
0
0
8
1 of 1
APPENDIX D
BIORETENTION SWALE DETAIL
AND INFORMATION SHEETS