v>EPA
United States
Environmental Protection
Agency
2014 GREEN INFRASTRUCTURE TECHNICAL ASSISTANCE PROGRAM
City of Santa Monica
Santa Monica, CA
Building Resilience to Drought in Ozone Park
Conceptual Design for Potable Water Offset Using Treated Urban Runoff
Photo: Ozone Park, Santa Monica, CA
June 2015
EPA 832-R-15-010
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About the Green Infrastructure Technical Assistance Program
Stormwater runoff is a major cause of water pollution in urban areas. When rain falls in undeveloped
areas, soil and plants absorb and filter the water. When rain falls on our roofs, streets, and parking lots,
however, the water cannot soak into the ground. In most urban areas, stormwater is drained through
engineered collection systems (storm sewers) and discharged into nearby water bodies. The stormwater
carries trash, bacteria, heavy metals, and other pollutants from the urban landscape, polluting the
receiving waters. Higher flows also can cause erosion and flooding in urban streams, damaging habitat,
property, and infrastructure.
Green infrastructure uses vegetation, soils, and natural processes to manage water and create healthier
urban environments. At the scale of a city or county, green infrastructure refers to the patchwork of
natural areas that provides habitat, flood protection, cleaner air, and cleaner water. At the scale of a
neighborhood or site, green infrastructure refers to stormwater management systems that mimic
nature by soaking up and storing water. Green infrastructure can be a cost-effective approach for
improving water quality and helping communities stretch their infrastructure investments further by
providing multiple environmental, economic, and community benefits. This multi-benefit approach
creates sustainable and resilient water infrastructure that supports and revitalizes urban communities.
The U.S. Environmental Protection Agency (EPA) encourages communities to use green infrastructure to
help manage stormwater runoff, reduce sewer overflows, and improve water quality. EPA recognizes
the value of working collaboratively with communities to support broader adoption of green
infrastructure approaches. Technical assistance is a key component to accelerating the implementation
of green infrastructure across the nation and aligns with EPA's commitment to provide community
focused outreach and support in the President's Priority Agenda Enhancing the Climate Resilience of
America's Natural Resources. Creating more resilient systems will become increasingly important in the
face of climate change. As more intense weather events or dwindling water supplies stress the
performance of the nation's water infrastructure, green infrastructure offers an approach to
increase resiliency and adaptability.
For more information, visit http://www.ei3a.aov/areeninfrastructure.
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Acknowledgements
Principal USEPA Team
Christopher Kloss, USEPA
Jamie Piziali, USEPA
Tamara Mittman, USEPA
Eva Birk, ORISE Participant
John Kemmerer, USEPA Region 9
Community Team
Neal Shapiro, City of Santa Monica
Rick Valte, City of Santa Monica
Selim Eren, City of Santa Monica
Consultant Team
Merrill Taylor, Tetra Tech
Jason Wright, Tetra Tech
Martina Frey, Tetra Tech
John Kosco, Tetra Tech
Scott Dellinger, Tetra Tech
Photos and graphics are credited to Tetra Tech, Inc., unless otherwise noted.
This report was developed under EPA Contract No. EP-C-11-009 as part of the 2014 EPA Green
Infrastructure Technical Assistance Program.
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1. Executive Summary 1
2. Introduction 1
2.1. Water Quality Issues/Vision 2
2.2. Project Overview and Goals and Scope 2
2.3. Project Benefits 5
3. Design Approach 5
3.1. Cisterns 5
3.1.1. Hydrology 6
3.1.2. Water Quality 6
3.1.3. Applications 7
3.2. Infiltration Galleries 10
3.2.1. Hydrology 11
3.2.2. Water Quality 11
3.2.3. Applications 11
4. Conceptual Design 12
4.1. Water Source & Demand Strategy 13
4.1.1. Dry-weather Flow 13
4.1.2. Wet-weather Flow 14
4.1.3. Irrigation Demand 16
4.2. Diversion of Pipe Flows 16
4.2.1. Diversion Structure 16
4.2.2. Pre-treatment/Equalization Basin 17
4.3. Storage, Overflow, Treatment and Irrigation 17
4.3.1. Subsurface Cistern 18
4.3.2. Overflow Infiltration Gallery 19
4.3.3. Stormwater Pump Station 27
4.3.4. Water Treatment System 27
4.3.5. Irrigation System 28
4.4. Cost Estimates 29
4.5. Operation and Maintenance 32
4.5.1. Subsurface Cistern 32
4.5.2. Subsurface Infiltration Gallery 33
5. Policy Approach/Permits 33
6. Conclusion 34
7. References 35
iv
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Appendix A: Site Plan and Details A-l
Appendix B: Rainwater Harvesting Model Data B-l
Figure 2-1. Location and existing condition of the Ozone Park site 4
Figure 3-1. Cistern at Grand Canyon Visitor Center, Grand Canyon National Park, Arizona 5
Figure 3-2. Typical plastic cistern 7
Figure 3-3. Wood wrapped cistern 8
Figure 3-4. Decorative cistern 8
Figure 3-5. Below-ground cistern 9
Figure 3-6. Residential rain barrel 9
Figure 3-7. Rain barrels adequately sized for contributing roof area 10
Figure 3-8. Subsurface infiltration gallery 10
Figure 3-9. Example of a surface infiltration gallery in a park 12
Figure 3-10. Example of a subsurface infiltration gallery below a park 12
Figure 4-1. Flow diagram for water use strategy at Ozone Park 13
Figure 4-2. Typical dry-weather flow 24-hour distribution for Ozone Park 14
Figure 4-3. Continuous simulation runoff volume at Ozone Park from Oct 2001 to Sept 2011 15
Figure 4-4. Typical diversion structure 17
Figure 4-5. Wet-weather cistern sizing versus potable supply offset for Ozone Park 19
Figure 4-6. Infiltration gallery sizing optimization curve for Ozone Park (Scenario 1) 22
Figure 4-7. Infiltration gallery sizing optimization curve for Ozone Park (Scenario 2) 22
Figure 4-8. Infiltration gallery sizing optimization curve for Ozone Park (Scenario 3) 23
Figure 4-9. Scenario 1 (10,000 gallon) site layout at Ozone Park site 24
Figure 4-10. Scenario 2 (100,000 gallon) site layout at Ozone Park site 25
Figure 4-11. Scenario 3 (180,000 gallon) site layout at Ozone Park site 26
Table 1-1. Scenario results summary at Ozone Park 1
Table 4-1. Average monthly wet-weather volumes at Ozone Park 15
Table 4-2. Average daily irrigation demands observed for each month at Ozone Park 16
Table 4-3. Scenario cistern size results at Ozone Park 19
Table 4-4. Infiltration gallery results at Ozone Park (maximum available footprint & full diversion) 21
Table 4-5. Infiltration gallery results at Ozone Park (maximum available footprint & 20 cfs diversion). .. 21
Table 4-6. Infiltration gallery optimal size (point of diminishing returns) analysis at Ozone Park 21
Table 4-7. Infiltration gallery size 85th percentile analysis results at Ozone Park 21
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Table 4-8. 10,000 gallon cistern treatment cost (Scenario 1) 29
Table 4-9. 100,000 gallon cistern treatment cost (Scenario 2) 30
Table 4-10. 180,000 gallon cistern treatment cost (Scenario 3) 31
Table 4-12. Potable water savings through rainwater harvesting at Ozone Park 32
Table 4-13. Cost efficiency at Ozone Park 32
Table 4-14. Inspection and maintenance tasks for cisterns 33
Table 4-15. Inspection and maintenance tasks for subsurface infiltration galleries 33
VI
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I. Executive Summary
Regional droughts and increasingly stringent water quality requirements make stormwater management
more important than ever for the City of Santa Monica, California. In response, the City is implementing
best management practices (BMPs) on public parcels and rights-of-way to augment the local water
supply and improve water quality before storm flows discharge into the ocean. Santa Monica identified
Ozone Park as a potential location to implement water harvesting practices that will both reduce its
dependence on imported water and increase the City's resiliency to future droughts.
The purpose of the project is threefold:
1) Reduce City reliance on imported water by harvesting, treating, and using urban runoff for non-
potable uses.
2) Reduce urban runoff and improve water quality to meet the waste load allocations specified in
local Total Maximum Daily Load (TMDL) requirements for metals, trash, and bacteria.
3) Demonstrate the feasibility of implementing a runoff-use system at Ozone Park and compare to
other possible harvesting and use project locations.
Three scenarios were identified as feasible within the park footprint: a 10,000 gallon cistern, a 100,000
gallon cistern, and a 180,000 gallon cistern, each with an associated 0.5 acre-foot overflow infiltration
gallery. The water use and potential water quality impacts modeled in this report are summarized below
in Table 1-1. Annually, this project has the potential to harvest enough runoff to provide up to 100
percent of the 450,900 gallon irrigation demand at the Ozone Park site. This estimate is based on an
annual rainfall of 12 inches.
Table l-l. Scenario results summary at Ozone Park.
Model Cistern Annual Cistern Park Infiltration Annual Zinc Annual Zinc Annual Runoff Annual Runoff
Scenario Size, Usage, Gallons Irrigation Gallery Size, Reduction, Percent Volume Volume
Gallons Offset ac-ft Ibs Reduction1 Reduction, Percent
ac-ft Reduction1
Scenario 1
Scenario 2
Scenario 3
10,000
100,000
180,000
286,968
386,324
448,504
64.0%
86.1%
100.0%
0.5
0.5
0.5
12.
13.
14.
3
7
8
10.
11.
12.
2%
3%
3%
7.4
7.6
7.9
4,
4,
4,
.1%
.3%
.4%
1. Percent reduction is the anticipated reduction from the current conditions.
2. Introduction
Santa Monica, California, is situated on the west side of Los Angeles County, about 16 miles west from
downtown Los Angeles, where the Pacific Coast Highway and interstate Highway 10 meet. It is 8.3
square miles and bordered by the City of Los Angeles on three sides and the Pacific Ocean to the west.
Its population is approximately 90,000 residents.
The City of Santa Monica depends on imported water from distant watersheds to supplement its local
water supply. Currently, imported water accounts for 28 percent of the City's water supply, while the
other 72 percent is provided by wells, along with treated stormwater and dry-weather runoff. This
reliance leaves the City in a precarious position. In the future, imported water prices will undoubtedly
rise, less imported water will be available as the City competes with other growing communities, and
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ecosystem requirements to protect endangered and threatened species and aquatic habitat will
increase. In addition, supply disruptions due to natural disasters could further strain statewide water
transportation systems. These factors contribute to an unreliable water supply and the need to improve
the resiliency of Santa Monica's local water supply.
Where water supplies are limited, stormwater and dry-weather runoff harvesting provides a sustainable,
alternative source of water for non-potable irrigation purposes, and can also significantly reduce
demand on higher quality potable water sources. Stormwater and dry-weather runoff harvesting allows
the conservation of potable water supplies by providing an alternative water source for irrigation of
residential and commercial landscaping, agriculture, public parks, and golf courses. According to the
City's Office of Sustainability and the Environment (2015), to meet the City's self-sufficiency goal to stop
importing water by 2020 residents would need to reduce their water use to 123 gallons a day - a savings
of 4,000 gallons, per person, per year.
2.1. Water Quality Issues/Vision
Santa Monica is a NPDES Phase I municipal separate storm sewer system (MS4) permittee and has a
history of bacterial exceedances in stormwater and dry-weather runoff.
The City's Sustainable Water Master Plan was finalized in the summer of 2014 and has two major
strategy portfolios: Supply Management and Demand Management. Supply management strategies
include increasing groundwater pumping and maximizing local, non-traditional water supplies: gray
water and stormwater (rain harvesting). This project is one critically important step to demonstrate the
feasibility of harvesting local urban runoff (mainly stormwater) from the stormwater drainage network,
treating and using the water to replace imported water, and helping the City to reach its 2020 goal of
being self-reliant for water. Unlike traditional supply side projects, which build surface structures to
divert surface waters from their natural flows, the City's strategy is to promote green infrastructure in
its capital improvement water projects. Other community priorities that a green infrastructure approach
would address include the City's Watershed Management Plan (2006), which promotes the use of green
infrastructure to help meet water quality standards for its impaired water body, Santa Monica Bay.
The City also has an urban runoff pollution mitigation ordinance (SMMC 7.10) that promotes post-
construction structural green infrastructure BMPs. While traditional watershed management often
focuses on treating and releasing runoff to the receiving water body, the City's comprehensive
watershed management strategy emphasizes stormwater harvesting, and indirect and direct onsite
uses. This project is another example of a green infrastructure investment that, in keeping with the
City's vision, harvests runoff for onsite beneficial uses and keeps water pollution sources out of receiving
water bodies.
2.2. Project Overview and Goals and Scope
Ozone Park is a linear park located on the southern border of the City where Santa Monica meets Los
Angeles. It has playgrounds on the eastern and western ends and a grassy lawn in between. Figure 2-1
shows the existing condition and location of the park.
This project aims to offset imported water demand by harvesting local stormwater and dry-weather
runoff and applying it for park irrigation. Through this project, the City hopes to integrate the concept of
green infrastructure water use systems for future landscaping, and to educate developers, engineers,
and architects on green infrastructure design principles. The project identified three specific goals during
the application process:
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1) Reduce City reliance on imported water by harvesting, treating, and using urban runoff for non-
potable uses.
2) Reduce urban runoff and improve water quality to meet the waste load allocations specified in
local TMDLs.
3) Demonstrate the feasibility of implementing a runoff-use system at Ozone Park and compare to
other possible project locations.
This project demonstrates an innovative water collection system that uses available dry- and wet-
weather runoff to irrigate the turf within a park. This report includes recommended conceptual designs
and planning level cost estimates. Also included are the anticipated permits required for project
implementation. This project builds on the City's efforts to install similar green infrastructure on both
private and public parcels, and to achieve its water self-sufficiency goal by 2020.
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Legend
* Maintenance Access
awm Drain Gravity Mam
Ozone Park: Santa Monica, CA
Figure 2-1. Location and existing condition of the Ozone Park site.
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2.3. Project Benefits
Annually, this project has the potential to harvest enough runoff to provide up to 100 percent of the
450,900 gallon irrigation demand at the Ozone Park site. This estimate is based on an annual rainfall of
12 inches.
By removing polluted urban runoff from the storm drain system, this project will help improve water
quality in Santa Monica Bay and help the City comply with requirements of its new green infrastructure-
focused NDPES permit and meet TMDL requirements for marine debris, bacteria, and organic chemicals.
Since the project prevents polluted water from entering the Bay, endangered and threatened species
found in the Bay will also be better protected.
As the City begins to implement its 2020 water self-sufficiency plan, eliminating the need for imported
water on this site will help the City reach this goal. This project will also help the City become more
resilient to drought conditions and be better prepared for a time when water supplied from other
sources is no longer reliable, as has been the case in past drought years.
Where runoff is harvested locally and used to replace imported water, energy is saved by not having to
pump water into the local area. Based upon data from the Metropolitan Water District of Southern
California, 11,111 kWh of energy is required per million gallons of water pumped or diverted into
Southern California from other sources. Based upon the amount of water replaced from this project, the
energy saved is estimated to be up to 3,189 kWh, 4,292 kWh, and 4,983 kWh on an annual basis for
Scenarios 1, 2, and 3, respectively. Additionally, if the energy saved would have been produced by fossil
fuels, there will be benefits associated with a reduction in greenhouse gas production (City of Santa
Monica 2014).
3. Design Approach
The Ozone Park project is intended to harvest and use stormwater and dry-weather runoff for irrigation,
and reduce downstream pollutant loading. Based on the park properties and project goals, below-
ground cisterns and a subsurface infiltration gallery were proposed. These two strategies are described
below.
3.1. Cisterns
A cistern is an above-ground or below-ground
storage vessel with either a manually operated
valve or a permanently open outlet (Figure 3-1).
If the cistern has an operable valve, the valve can
be closed to store stormwater and dry-weather
runoff for irrigation or infiltration. This system
requires continual monitoring by the grounds
crews, but provides greater flexibility in water
storage and metering. If a cistern is provided with
an operable valve and water is stored inside for
long periods, the cistern system openings must
be covered to prevent mosquitoes from
breeding. A cistern system with a permanently
open outlet can also passively regulate the
outflow of stormwater runoff. If the cistern
Figure 3-1. Cistern at Grand Canyon Visitor
Center, Grand Canyon National Park, Arizona.
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outlet is significantly smaller than the size of the inlet (e.g., %- to ^-inch diameter), runoff will build up
inside the cistern during storms, and will empty out slowly after peak intensities subside. The cistern
must be designed and maintained to minimize clogging by leaves and other debris.
3.1.1. Hydrology
Cisterns have been used for millennia to harvest and store water. Droughts in recent years have
prompted a resurgence of rain harvesting technologies such as cisterns as a means of offsetting potable
water use. Studies have shown that adequately designed and used systems reduce the demand for
potable water and can provide important hydrologic benefits (Vialle et al. 2012; DeBusk et al. 2012).
Hydrologic performance of rain harvesting practices varies with design and use; systems must be
drained between rain events to reduce the frequency of overflow (Jones and Hunt 2010). When a
passive drawdown system is included (e.g., an orifice that slowly bleeds water from the tank into an
adjacent vegetation bed or infiltrating practice), significant runoff reduction can be achieved (DeBusk et
al. 2012).
Cisterns are typically placed near a concentrated source of runoff (such as a roof downspout or existing
drainage pipes) so that flows from existing downspouts or drainage networks can be easily diverted into
the cistern. Pre-treated runoff (after large sediment and debris is removed) enters the cistern near the
top and is stored for later use or infiltration. Collected water exits the cistern from near the bottom (4 to
6 inches above the bottom) or can be pumped. Water can be used to offset potable supply or piped to
areas more conducive for infiltration. Cisterns can be used either as a reservoir for temporary storage or
as a flow-through system for peak flow control. Cisterns are fitted with a valve that holds the
stormwater for later use or slowly releases the stormwater from the cistern at a rate below the design
storm rate. Regardless of the intent of the storage, an overflow must be provided for times when the
capacity of the cistern is exceeded. The overflow system should route the runoff to a green
infrastructure practice for treatment or safely pass the flow into the stormwater drainage system. The
overflow should be conveyed away from structures.
3.1.2. Water Quality
Because most harvesting systems collect rooftop rainwater runoff, the water quality of runoff harvested
in cisterns is largely determined by surrounding environmental conditions (e.g., overhanging vegetation,
bird and wildlife activity, atmospheric deposition), roof material, and cistern material (Despins et al.
2009; Lee et al. 2012; Thomas and Greene 1993). Rooftop runoff tends to have relatively low levels of
physical and chemical pollutants, but elevated microbial counts are typical (Gikas and Tsihrintzis 2012;
Lee et al. 2012; Lye 2009; Thomas and Greene 1993). Physicochemical contaminants can be further
reduced by implementing a first-flush diverter or similar pre-treatment device, depending upon runoff
flow volume (see below for additional discussion); however, first-flush diverters and hydrodynamic pre-
treatment devices generally have little impact on reducing microbial counts (Lee et al. 2012; Gikas and
Tsihrintzis 2012).
Despite limited data describing reduction in stormwater contaminant concentrations in cisterns, urban
runoff harvesting can greatly reduce pollutant loads to waterways if stored rainwater is infiltrated into
surrounding soils using a low-flow drawdown configuration or when it is used for alternative purposes
such as toilet flushing or vehicle washing. Urban runoff harvesting systems can also be equipped with
filters and disinfection to further improve water quality.
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3.1.3. Applications
A cistern typically holds several hundred to several thousand gallons of rainwater and can come in a
variety of sizes and configurations. Figure 3-2 shows a typical above-ground plastic cistern and Figure
3-3 shows the same cistern with a wooden wrap. Cisterns can also be decorative, such as the one shown
in Figure 3-4 at the Children's Museum in Santa Fe, New Mexico, or be placed below ground as shown in
Figure 3-5. Cisterns can also be used in more innovative ways, such as part of the Oncenter War
Memorial Arena Rainwater Reuse System Project in Syracuse, New York. The project captures rainwater
and snow melt runoff from the War Memorial Arena roof, and uses the water for ice production and ice
maintenance for sporting events and recreational activities at the arena (Onondaga County 2015).
Smaller cisterns (fewer than 100 gallons), or rain barrels, can be used on a residential scale (Figure 3-6).
Collected water can be used to supplement municipal water for non-potable uses, primarily irrigation.
Although useful for raising public awareness and for meeting basic irrigation needs, rain barrels do not
typically provide substantial hydrologic benefits because they tend to be undersized relative to their
contributing drainage area. Figure 3-7 shows rain barrels adequately sized for the contributing roof area.
Figure 3-2. Typical plastic cistern.
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Figure 3-3. Wood wrapped cistern.
Source: Santa Fe, New Mexico Children's Museum
Figure 3-4. Decorative cistern.
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Figure 3-5. Below-ground cistern.
Figure 3-6. Residential rain barrel.
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Figure 3-7. Rain barrels adequately sized for contributing roof area.
3.2. Infiltration Galleries
An infiltration gallery is typically an excavated area
containing voided space filled with plastic, concrete
or metal structures with 95% void space, unlike rock
or soil. It functions like a media filter but is
implemented at a larger scale (Figure 3-8). Infiltration
galleries can be designed as surface or subsurface
units allowing for implementation adjacent to or
below paved streets, parking lots, and buildings to
provide initial stormwater detention or retention,
and treatment of runoff. Such applications offer an
ideal opportunity to minimize directly connected
impervious areas in highly urbanized areas. In
addition to stormwater management benefits,
surface infiltration galleries provide green space and
improve natural aesthetics in urban environments.
Figure 3-8. Subsurface infiltration gallery.
10
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3.2.1. Hydrology
Subsurface infiltration galleries are underground storage areas that harvest and temporarily store
stormwater runoff. The harvested runoff percolates through the bottom of the gallery and an
approximately 1-foot amended, tilled native soil layer, which has an infiltration rate capable of draining
the infiltration gallery within a specified design drawdown time (usually up to 72 hours). After the
stormwater infiltrates through the amended surface, it percolates into the subsoil if site conditions
allow for adequate infiltration and slope protection. If site conditions do not allow for adequate
infiltration or slope protection, filtered water is directed toward a stormwater conveyance system or
other stormwater runoff BMP via underdrain pipes. Infiltration galleries can be designed to help meet
hydromodification criteria and also for conveyance of higher flows.
Infiltration galleries are designed to harvest a specified design volume and can be configured as online
or offline systems. Online BMPs require an overflow system for managing extra volume created by
larger storms. Offline BMPs do not require an overflow system but do require some freeboard (the
distance from the overflow device and the point where stormwater would overflow the system) and a
diversion structure.
If an underdrain is not needed because infiltration rates are adequate and slope is not a concern, the
remaining stormwater passes through the soil media and infiltrates into the subsoil. Partial infiltration
(approximately 20 to 50 percent, depending on soil conditions) can still occur when underdrains are
present as long as an impermeable barrier is not between the soil media and subsoil. Partial infiltration
occurs in such cases because some of the stormwater bypasses the underdrain and percolates into the
subsoil (Hunt et al. 2006; Strecker et al. 2004).
3.2.2. Water Quality
Infiltration galleries are volume-based BMPs intended primarily for harvesting and infiltrating the design
water quality treatment volume. These practices perform water quality functions through infiltration
and runoff contact with soil media. Water quality improvement is accomplished through sedimentation,
filtration, and adsorption associated with percolation of runoff through aggregate and underlying soil.
Where site conditions allow, the volume-reduction and pollutant-removal capability of an infiltration
gallery can be enhanced to achieve additional credit toward meeting any volume-reduction
requirements by omitting underdrains and providing a gravel drainage layer beneath the soil media.
3.2.3. Applications
Infiltration galleries can be adapted and incorporated into many landscaped and paved settings.
Common applications of surface infiltration galleries include parks, spreading grounds, groundwater
recharge basins, and other open space areas. Common applications of subsurface infiltration galleries
include parking lots, roadways, and park playing surfaces. Figure 3-9 shows an example of a surface
infiltration gallery integrated into a park, and Figure 3-10 shows an example of a subsurface infiltration
gallery using the StormTrap system.
11
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Figure 3-9. Example of a surface infiltration gallery in a park.
Source: County of Los Angeles
Figure 3-10. Example of a subsurface infiltration gallery below a park.
4. Conceptual Design
Currently, approximately 300 acres drain through a 78-inch storm drain line that passes directly below
the park and conveys upstream runoff out of the City and to the ocean. This conceptual design proposes
alternative scenarios that harvest and utilize both the dry-weather and wet-weather flows found within
the pipe network in an attempt to reduce the demand on potable water. These water sources will act as
12
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an offset to the irrigation potable demand of the park. The project proposes to install a pre-treatment
device, storage tank, post-storage treatment train, and overflow infiltration gallery within the existing
park footprint. The details of the proposed system, including the water quantity of the supply and
demand, are outlined below.
The Santa Monica project partner American Rainwater Catchment Systems Association (ARCSA) provides
technical guidance on finalizing rain harvesting systems including the pre-treatment, storage, final
treatment, overflow and backup water supply components. Additional information on each of these
components described in the subsequent sections can be found on the ARCSA website.1
4.1. Water Source & Demand Strategy
The schematic shown in Figure 4-1 summarizes the potential sources of water, potential diversion
process, and potential end use elements. The primary sources of water are dry-weather and wet-
weather runoff from upstream that is conveyed through the 78-inch storm drain pipe that travels
underneath the park. The proposed layout of each element is found in Appendix A.
BYPASS
HIGH
FLC
Storm Drain
Network
Santa
Monica
Bay
Pretreatment/
Equalization
Basin
GRAVITY Of
Treatment
Svstem
PUMPED
IRRIGATION
OZONE
are
OVERFLOW
Subsurface Infiltration Gallery
I
Ground
Figure 4-1. Flow diagram for water use strategy at Ozone Park.
4.1.1. Dry-weather Flow
Dry-weather flow results from excess irrigation, spills, construction sites, pool draining, car washing, and
other outdoor water applications during dry periods of time, and then enters the storm drain network.
This flow is typically observed on a daily basis and provides a baseline condition that can supply a
1 http://www. arcsa.org
13
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constant inflow of water into the proposed system. A 24-hour dry-weather distribution was desired to
determine the typical daily total flow that is available for harvesting at this site. Continuous monitoring
data was not available for the pipe beneath Ozone Park but a total of three dry-weather grab samples
were taken at three different times over the course of several days. These samples allowed for scaling of
typical dry-weather patterns that are observed within the Los Angeles County region. Continuous dry-
weather monitoring for a watershed of nearly the same size and similar land use was performed in the
City of Los Angeles and acts as the baseline dry-weather pattern (Tetra Tech 2015). The baseline was
shifted and scaled to match the observed grab samples. The final 24-hour dry-weather distribution is
shown below in Figure 4-2. The total daily dry-weather flow available was calculated to be 730 gallons
per day.
The dry-weather pattern is likely to vary based on the seasons and the amount of rainfall received. For
the purposes of this analysis, it was assumed that the daily dry-weather pattern observed would be
consistent throughout the year due to limited monitoring data. Further dry-weather sampling can be
performed during the full design process to determine the temporal distribution of the dry-weather
flows through the multiple seasons of the year.
Average Dry Weather Flow
9:00 PM
Figure 4-2. Typical dry-weather flow 24-hour distribution for Ozone Park.
4.1.2. Wet-weather Flow
The wet-weather flow varies significantly from storm to storm and from year to year. To analyze the
proposed system and determine the potential inflow during wet weather, a continuous simulation
period from October 1, 2001 to September 30, 2011 was used. The wet-weather information was
obtained from the calibrated Los Angeles County Watershed Management Modeling System (WMMS)
model (Tetra Tech 2010a; Tetra Tech 2010b). The runoff time series information from the WMMS model
was multiplied by the associated land use and aggregated to determine the total anticipated flow rate
14
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within the pipe for every hour over the 10-year period. The runoff total for each month is displayed in
Figure 4-3, while the average monthly runoff total is found in Table 4-1.
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4.1.3. Irrigation Demand
The current average daily irrigation demand for each month at Ozone Park was calculated using the
water bill information from January 1, 2001 to December 31, 2013. The calculated daily and monthly
demands by each month are shown in Table 4-2. Using these daily and monthly rates, the average
annual irrigation demand was calculated to be 450,900 gallons.
Table 4-2. Average daily irrigation demands observed for each month at Ozone Park.
Month Daily Irrigation Monthly Irrigation
Demand, Gallons Demand, Gallons
January
February
March
April
May
June
July
August
September
October
November
December
624
648
799
1,160
1,444
1,757
1,977
1,889
1,761
1,276
835
616
19,339
18,147
24,780
34,792
44,762
52,711
61,290
58,565
52,824
39,559
25,051
19,080
4.2. Diversion of Pipe Flows
To harvest the dry- and wet-weather flows within the storm drain, the runoff must be diverted out of
the pipe, while still allowing for flood control during large storm events. Flows from the drainage pipe
below the park would be routed through a pre-treatment system installed adjacent to the drainage pipe
below the park. The flows would be routed through a primary treatment and effluent distribution
system providing treatment, as well as a consistent irrigation source for the park.
4.2.1. Diversion Structure
A diversion structure is needed to divert stormwater from the existing 78-inch storm drain under the
park to the cistern and pump station for irrigation. The diversion structure would be located at the
existing maintenance hole found on the east end of the park. The invert elevation of the existing pipe is
approximately 28.38 feet and is around 13 feet deep as measured from the surface per the City as-
builts.
To divert the water from the drainage pipe, the existing maintenance hole would be upgraded with a
passive low-flow diversion system consisting of a weir and a diversion pipe similar to the schematic
shown in Figure 4-4. The floor of the junction box would be lowered in elevation to divert the water
away from the main pipe and into the smaller diversion pipe. The existing pipe would remain at the
current elevation for the incoming and outgoing pipe to ensure flood control. It is recommended to
divert the flow from the side of the pipe, rather than the floor of the pipe, to ensure that sediment and
trash build up will not block the diversion.
16
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PLAN VIEW
INFLOW
t
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WEIR PLATE /
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B
-------
daily or hourly rainfall input files, daily constant supplies, customized water demand inputs, and various
hydrologic performance output metrics.
Several input scenarios were modeled to evaluate the performance of the Ozone Park runoff harvesting
system for offsetting the turf grass irrigation demand. Scenario 1 investigates harvesting only the dry-
weather flows and then adds the wet-weather flows for the minimum tank size of 10,000 gallons.
Scenario 2 increases the cistern size to investigate intermediate options. Scenario 3 determines the
minimum tank size needed to harvest wet-weather flows for 100 percent potable offset.
4.3.1. Subsurface Cistern
To provide different sizing options, three alternative scenarios were developed to evaluate the impact of
different cistern sizes.
Scenario 1 -10.000 Gallon Cistern. Dry-weather flows only
Dry-weather flow acts as the primary water source for potable water offset. The dry-weather
information calculated in Section 4.1.1 was used in the RH model to determine the maximum tank size
required to meet the irrigation demand. It was determined that a cistern of 10,000 gallons will harvest
all of the dry-weather flow and reduce the potable water demand by 60 percent. This tank size ensures
that storage will be available for months where the dry-weather flow exceeds the irrigation demand
(December, January, and February) and will carry it over to later months for use.
The wet-weather flows will also be partially diverted to the 10,000 gallon cistern when there is available
capacity. The wet-weather flows will provide additional water supply when dry-weather flows do not fill
the cistern. The model results show that when wet-weather is added to the 10,000 gallon cistern that
total potable water offset of 64 percent could be achieved. See Figure 4-9 for a general site layout for
Scenario 1.
Scenario 2 -100,000 Gallon Cistern
For Scenario 2, the cistern size was dramatically increased to determine if a point of diminishing returns
was easily identified where potable offset versus tank size began to shrink significantly. The cistern size
compared to the potable water offset displayed a linear relationship and the point of diminishing
returns was identified as the 100 percent offset tank size. The point of diminishing returns is defined as
the point at which the potable offset benefit decreases relative to the tank size. Because the diminishing
point was not significant due to the linear nature, an intermediate tank size was selected for analysis.
Interest was expressed in a 100,000 gallon tank and the model results show that a cistern of this
capacity can provide a potable water offset of 86 percent. See Figure 4-10 for the site layout for the
100,000 gallon scenario.
Scenario 3 -180,000 Gallon Cistern
To meet the goal of maximum potable water offset, Scenario 3 was used to determine the minimum
cistern size required to offset 100 percent of the potable water demand. This tank size will maintain
enough water through the summer by capturing significant storm volumes during the wet winter
months (Figure 4-3). The minimum tank size to offset the potable water demand by 100 percent was
identified as 180,000 gallons. Figure 4-5 shows the multiple cistern size options that were compared in
the model. The maximum potable water offset size was identified as the significant point of diminishing
returns due to the linear nature of the relationship but sizing selection should be determined by the
desired potable water offset. See Figure 4-11 for the site layout for the 180,000 gallon scenario.
18
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100%
90%
: ;
Point of
Returns
50,000 100,000 150,000
Storage Tank Size (gallons)
200,000
Figure 4-5. Wet-weather cistern sizing versus potable supply offset for Ozone Park.
The results of the three scenarios are summarized in Table 4-3. Model inputs and outputs are shown in
Appendix B.
Table 4-3. Scenario cistern size results at Ozone Park.
Model Scenario Cistern Size,
Gallons
Scenario 1 - Dry
Scenario 1 -Wet
Scenario 2
Scenario 3
10,000
10,000
100,000
180,000
Annual Cistern
Usage, Gallons
267,115
286,968
386,324
448,504
Irrigation
Offset
60%
64%
86%
100%
Dry
Frequency
62%
48%
20%
0%
4.3.2. Overflow Infiltration Gallery
During dry- and wet-weather events, if the cistern system is full, excess flows will be diverted to an
underground infiltration gallery. The gallery will provide groundwater recharge3 and additional water
quality benefits to meet regional water quality standards. It is anticipated that during abnormally high
dry-weather flows and small storms that the overflow will be utilized. Once the underground infiltration
gallery is full during high-flow events, runoff will continue through the existing 78-inch pipe to provide
flood management and will not overwhelm the diversion system.
To optimize the size of the infiltration gallery, different size basins for each of the cistern scenarios were
modeled in the EPA System for Urban Stormwater Treatment and Analysis IntegratioN (SUSTAIN)
3 Infiltrated water will enter the Coastal portion of the Santa Monica Basin. The groundwater is greater than 10 feet below the
surface and sufficient filtration will occur to prevent the migration of pollutants (USEPA 2013). The basin is not actively used for
drinking water but feasibility studies have been performed to identify potential locations for pumping. The infiltrated water will
also act to supplement the water table in preventing seawater intrusion from occurring (MWD 2007; LADWP 2011).
19
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model4 using the 10-year, continuous simulation data to measure the overall impact on the water
quality. For this particular region, zinc has been identified as a pollutant of concern and was used as the
basis for removal comparison.
To limit the excavation depths to 20 feet, a total maximum depth of 4 feet was assumed possible for the
infiltration gallery. Using this depth, the maximum footprint and volume were found to be 5,400 square
feet and 21,600 cubic feet (0.5 acre feet) respectively. Due to the small park footprint and the large
drainage area runoff volumes, pollutant removal is limited. It is recommended to make the infiltration
gallery as large as feasibly possible to have the greatest water quality impact, as it may still be cost-
effective even at the maximum footprint identified. Results are shown in Table 4-4.
The next analysis looks at the impact of the diversion structure on the overall water quality. The first
analysis assumes that all of the runoff can be diverted to the BMP (an online system - all pipe flow will
enter the BMP) when in reality, the system will be designed and implemented as an offline system with
a design flow rate diverted towards the BMP. For Ozone Park, the peak flow rate from the online model
was found to be 395.6 cfs and is likely not able to be harvested. As the diversion flow rate is decreased
from the peak flow rate of the online system, the overall water-quality impact of the BMP is reduced,
even when the infiltration gallery is the same size. This is due to the fact that access to the higher flow
and more pollutant-laden storms is not possible thus decreasing the total load reduction and increasing
bypass flows. Based on past project experience, a design diversion rate of 20 cfs was assumed feasible,
and the results comparing the online versus offline zinc reductions for the maximum footprint available
are shown in Table 4-5.
The next analysis performed allows for nearly unlimited infiltration gallery sizes to determine the point
at which the cost begins to outweigh the benefit (the point of diminishing returns). These sizes far
exceed the identified maximum available footprint and volume. However, the infiltration gallery volume
can be increased through greater excavation or an increase in footprint size. The point of diminishing
returns varies based on the diversion rate analysis that was performed prior to this analysis. As the
diversion rate is decreased, the point of diminishing returns identifies smaller BMP volumes. Results are
shown in Table 4-6 comparing the identified point of diminishing return for the online, full diversion
system and the offline, 20 cfs design flow diversion system.
An additional analysis was performed to identify the size required to harvest and treat the 85th
percentile, 24-hour design storm. Per the MS4 permit, the 85th percentile event is identified as the
starting point for water quality BMP sizing. The design storm analysis distributes a hypothetical, typical
storm over a 24-hour period, and the BMP is sized just large enough to ensure full harvesting with no
overflow. The 10-year continuous time period is then modeled through the identified BMP size to
measure the overall, long-term expected water quality impacts. Results are shown in Table 4-7. The
required footprints are not possible at this location, and the required volume will be difficult to achieve
even with significant excavation efforts due to the lack of available space. Creative measures to utilize
greater depths or areas within the right-of-way can be further explored to discover feasible options if
harvesting of the 85th percentile storm is desired.
Figure 4-6, Figure 4-7, and Figure 4-8 graphically display the total infiltration gallery BMP volume versus
the percent load reduction results of the four wet-weather analyses for each of the three identified
scenarios. Two curves relating the BMP volume to the average annual zinc reduction for each scenario
are presented; one for the online, full diversion situation (orange line) and the other for the offline,
' http://www2.eDa. aov/water-research/svstem-urban-stormwater-treatment-and-analvsis-inteamtion-sustain
20
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design diversion situation (blue x). These cost-effectiveness curves can be used to approximate the
anticipated water quality impact for any BMP volume ranging from 0 to 20 acre-feet. The assumed
maximum BMP volume (0.5 acre-feet) is represented as a vertical line showing the maximum feasible
BMP volume that can be constructed at the site. The cost-effectiveness curves also illustrate the optimal
points (point of diminishing returns) found for both diversion situations. The final point shown on the
curves is the BMP size required to harvest the 85th percentile storm. The optimal points and the 85th
percentile volume far exceed the maximum feasible volumes for the site and are not likely to be
achievable.
Table 4-4. Infiltration gallery results at Ozone Park (maximum available footprint & full diversion).
Model Scenario
Scenario 1
Scenario 2
Scenario 3
Cistern
Size,
Gallons
10,000
100,000
180,000
Maximum
BMP Volume,
ac-ft
0.5
0.5
0.5
Maximum BMP
Load, Ibs
35.2
36.7
38.0
Zinc Reduction
Percent
29.2%
30.4%
31.5%
Maximum
Volume,
7.3
7.6
7.8
BMP Volume Reduction
ac-ft Percent
4.2%
4.3%
4.4%
Table 4-5. Infiltration gallery results at Ozone Park (maximum available footprint & 20 cfs diversion).
Model Scenario
Scenario 1
Scenario 2
Scenario 3
Cistern
Size,
Gallons
10,000
100,000
180,000
Maximum
BMP Volume,
ac-ft
0.5
0.5
0.5
Maximum BMP
Load, Ibs
12.3
13.7
14.8
Zinc Reduction
Percent
10.2%
11.3%
12.3%
Maximum
Volume,
7.4
7.6
7.9
BMP Volume Reduction
ac-ft Percent
4.1%
4.3%
4.4%
Table 4-6. Infiltration gallery optimal size (point of diminishing returns) analysis at Ozone Park.
Model Scenario
Scenario 1
Scenario 2
Scenario 3
Cistern
Size,
Gallons
10,000
100,000
180,000
Optimal BMP Optimal BMP
Volume, Annual Zinc
ac-ft Reduction
Full Diversion (395.6 cfs)
12.53 79%
12.53 79%
12.69 79%
Optimal BMP
Volume,
ac-ft
Optimal BMP
Annual Zinc
Reduction
Design Diversion (20 cfs)
9.02
8.46
8.26
34%
34%
34%
Table 4-7. Infiltration gallery size 85th percentile analysis results at Ozone Park.
Model Scenario
Scenario 1
Scenario 2
Scenario 3
Cistern
Size,
Gallons
10,000
100,000
180,000
85th Percentile
BMP Area,
ac
2.72
2.65
2.64
85th Percentile
BMP Volume,
ac-ft
10.9
10.6
10.6
21
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Santa Monica - Ozone Park (10,000 gal Cistern)
100%
E
I
60%
I
40'.'.
20% e
/
x*x
aaocx
Full Diversion [Online!
X Off line Diversion (20 cfs)
Point of Diminishini Returns
A S5th Percentile
Maximum Available Volume
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
BMP Volume (ac-ft)
Figure 4-6. Infiltration gallery sizing optimization curve for Ozone Park (Scenario I).
Santa Monica - Ozone Park (100,000 gal Cistern)
100%
so%
1
1
e
60%
I
To
40',,
20%
X**
.:
MI* «xx*
Full Diversion (Online)
x Offline Diversion (20 cfs)
Point of Diminishing Returns
A SSth Percentile
- Maximum Available Volume
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
BMP Volume (ac-ft)
Figure 4-7. Infiltration gallery sizing optimization curve for Ozone Park (Scenario 2).
22
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Santa Monica - Ozone Park (180,000 gal Cistern)
100%
E
I
60%
I
40'.'.
Iff.:,
» Full Diversion (Online)
X Offline Diversion (20 cfs)
Point of Diminishini Returns
A 85th Percentile
Maximum Available Volume
0.0 2.0 4.0 6.0
8.0
10.0 12.0 14.0 16.0 18.0 20.0
BMP Volume (ac-ft)
Figure 4-8. Infiltration gallery sizing optimization curve for Ozone Park (Scenario 3).
23
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InExistinqEnSintenanceiaccess)
Legend
* Maintenance Access
Storm Drain Gravity Main
^ Cistern (450 square feet)
Pretreatment/Equalization Basin
Infiltration Basin
] Treatment System
Ozone Park -Scenario 1: Santa Monica, CA
Figure 4-9. Scenario I (10,000 gallon) site layout at Ozone Park site.
24
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Ozone Park - Scenario 2: Santa Monica, CA
NAD_1833_StatePhme_Ca»ms_VJ!IPS_04(l5_F(l«l
Map Produced 11-03-2014 - A Porteous
Legend
* Maintenance Access
^^ Storm Drain Gravity Mam
}> Cistern (4,500 square feet)
Pretreatment/Equalization Basin
Infiltration Basin
Treatment System
140
3 Feet
TETRA TECH
Figure 4-10. Scenario 2 (100,000 gallon) site layout at Ozone Park site.
25
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Ozone Park - Scenario 3: Santa Monica, CA
aintenance Access
Storm Drain Gravity Mam
Cistern (8,000 square feet)
Pretreatmentr'Equalizatian Basin
Infiltration Basin
Treatment System
HAD_1933_SlaLePlane_C3^ornia_V FIPSJJ405
Map Produced fl -03-20T 4~ A~ ParteoiiE
TETRA TECH
Figure 4-1 I. Scenario 3 (180,000 gallon) site layout at Ozone Park site.
26
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4.3.3. Stormwater Pump Station
A pump station is required to lift the stormwater from the cistern to the treatment system and
subsequent use. To size and recommend a pump, the flows were assumed to peak at 200 gallons per
minute and a need for 200 feet of total dynamic head to provide 75 to 90 psi of working pressure. The
pump will need to be approximately 40 horsepower.
A non-clogging submersible pump is recommended for this application. These pumps provide reliability
while functioning under adverse/harsh conditions such as that expected to be encountered from non-
potable water applications. They also are designed to pass solids such as dirt, grit, sand, trash, and
debris that would be expected to pass through the diversion bar screens. Finally, they can easily be
removed for maintenance purposes. These pumps can operate across a multitude of head and flow
conditions to ensure operational efficiencies. These pumps can also be installed with variable-drives to
allow for pumping under different flow conditions.
4.3.4. Water Treatment System
The Los Angeles County Department of Public Health (CDPH) prepared a guidance document titled the
Guidelines for Harvesting Rainwater, Stormwater, & Urban Runoff for Outdoor Non-Potable Use (2011).
These guidelines are based on public health risks, with Tier I being low risk and Tier IV being higher risk.
Based on the upstream land use and the scale of the collection system, Ozone Park falls under the Tier
IV requirements and standards (runoff that includes agricultural, industrial, manufacturing, and
transportation sources). The non-potable use guidelines applicable to the BMPs used in this project are
as follows:
Requirements
o Install using manufacturer's instructions and local agency requirements.
o Include an overflow and screened inlets to prevent vector intrusion.
o Require prior plan review by the CDPH and local Building & Safety Department.
o Spray irrigation allowed only when negligible human exposure (i.e., at night).
o Offsite source waters generally result in the need for a storm drain diversion, stored
water recirculation/disinfection, pump station, supplemental domestic water, and
dedicated backflow preventer.
o Implement stormwater monitoring plan
Sample three storms annually, analyze for metals, volatiles, and semi-volatiles.
Prepare and maintain onsite an annual water quality summary.
After nine sampling events, CDPH will assess and notify if sampling required.
If Tier IV water is present, test quarterly and compare to California Maximum
Contaminant Levels (MCL) and California Toxics Rule (CTR).
If CTR human health standards are exceeded, cease distribution and
notify enforcement agency.
If MCLs, but not CTR human health standards, are exceeded, then night
time spray irrigation with Tier IV water allowed.
Water Uses
o Drip, subsurface, or spray irrigation, non-interactive outdoor water feature, street
sweeping, dust control.
Water Quality Standards
o Not applicable for drip and subsurface irrigation.
o All other water uses (standard applied at point of use).
27
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Total coliforms: <10,000 MPN/100 ml.
Fecal coliforms: <400 MPN/100 ml.
Enterococcus: <104 MPN/100 ml.
Treatment Process
o Prescreening
o Water uses other than drip and subsurface irrigation.
Screening/sedimentation device pre-treatment for offsite sources.
Disinfection by chlorination or equivalent.
Street sweeping applications require retention/sedimentation.
The CDPH guidelines identify the treatment process components as prescreening, sedimentation, and
disinfection as the minimum allowable standard. Trash and other large solids are removed through a
trash screen on the equalization basin. The screen also acts to ensure the pumps will not be fouled. The
equalization basin also serves a pre-treatment function by removing gross solids and settling out some
sediment and other sediment-bound pollutants.
Three potential disinfectants are available to treat the collected flow prior to spray irrigation in the park:
chlorination, ultraviolet, and ozonation. All systems are required to treat at around 200 gallons per
minute to meet the irrigation demands at Ozone Park. Chlorine is a common disinfectant and is available
in a gaseous, solid (calcium hypochlorite), or liquid phase (sodium hypochlorite). Safety concerns favor
the use of liquid sodium hypochlorite or solid calcium hypochlorite.
Ultraviolet (UV) disinfection can be used to meet the CDPH standards. UV uses irradiation that
inactivates waterborne pathogens without the use of chemicals. The effectiveness of a UV disinfection
system depends on the characteristics of the water (e.g., turbidity), the intensity of UV radiation, the
amount of time the microorganisms are exposed to the radiation, and the reactor configuration.
Ozonation is another disinfection method used to meet the bacteriological standards. Ozone causes a
chemical reaction which inactivates waterborne pathogens. Ozone is a highly unstable molecule and is
required to be generated on-site, as it cannot be stored. The ozone generation systems require high
voltage electricity to pass through an oxygen source.
4.3.5. Irrigation System
The park has an existing spray irrigation system that will be disconnected from the potable water line
and re-connected to the cistern irrigation pumps. Water will be drawn from the cistern, pass through
the treatment system, and then be immediately irrigated. To ensure a sufficient water supply, potable
water will act as a supplement and will be connected post-final treatment through 3-way valves and a
reduced pressure zone device. This ensures that potable water is not double treated. This meets the Los
Angeles County Department of Public Health requirement to maintain a 2-inch air gap between a
potable and non-potable source.
An alternative to the existing spray irrigation system is a subsurface drip line that would directly deposit
water to the root systems of the plants. The subsurface irrigation system does not require the same
level of water treatment as spray irrigation and can be used with minimal treatment. Installation of the
subsurface irrigation system would require removal of the existing park surface and replacement. The
existing spray system currently in place requires only minor surface impacts.
28
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4.4. Cost Estimates
Planning level cost estimates for Scenarios 1, 2, and 3 are provided in Table 4-8, Table 4-9, and Table
4-10 respectively.
Table 4-8. 10,000 gallon cistern treatment cost (Scenario 1).
Item No.
Description
Quantity
Unit
Unit Cost
Total
Planning/Design
1
2
3
Planning (10% of subtotal)
Permits/Studies
Design (15% of construction total)
1
1
1
LS
LS
LS
-
-
-
$126,000
$15,000
$245,700
Construction
4
5
6
Temporary construction entrance
Temporary construction fence
Dewatering
1
400
1
EA
LF
LS
$2,500
$2.50
$368
$2,500
$1,000
$368
Cistern & Irrigation
7
8
9
10
11
12
13
14
15
16
Excavation
Diversion structure
Pre-treatment system
Hydraulic restriction layer (30 mil liner)
Cistern
Bedding
Stormwater lift station/wet well (200 gpm)
Water treatment system (UV)
Landscaping
Electrical/control integration
1,350
1
1
1,000
10,000
29
1
1
8,000
1
CY
EA
EA
SF
Gal
CY
EA
EA
SF
EA
$45
$100,000
$4,500
$0.50
$1.50
$50
$200,000
$300,000
$2
$3,000
$60,750
$100,000
$4,500
$500
$15,000
$1,450
$200,000
$300,000
$16,000
$3,000
Infiltration Gallery
17
18
19
20
21
22
Excavation
Structure
Bedding
Subtotal
Mobilization (10% of subtotal)
Bonds and Insurance (5% of subtotal)
Construction contingency (15% of subtotal)
Construction Total
Project Total
Total Estimate (Rounded)
6,725
161,568
200
CY
Gal
CY
$45
$1.50
$50
$302,625
$242,352
$10,000
$1,260,045
$126,000
$63,000
$189,010
$1,638,055
$2,024,755
$2,030,000
29
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Table 4-9. 100,000 gallon cistern treatment cost (Scenario 2).
Item No.
Description
Quantity
Unit
Unit Cost
Total
Planning/Design
1
2
3
Planning (10% of subtotal)
Permits/Studies
Design (15% of construction total)
1
1
1
LS
LS
LS
-
-
-
$161,000
$15,000
$314,200
Construction
4
5
6
Temporary construction entrance
Temporary construction fence
Dewatering
1
550
1
EA
LF
LS
$2,500
$2.50
$368
$2,500
$1,375
$368
Cistern & Irrigation
7
8
9
10
11
12
13
14
15
16
Excavation
Diversion structure
Pre-treatment system
Hydraulic restriction layer (30 mil liner)
Cistern
Bedding
Stormwater lift station/wet well (200 gpm)
Water treatment system (UV)
Landscaping
Electrical/control integration
5,520
1
1
5,350
100,000
200
1
1
16,650
1
CY
EA
EA
SF
Gal
CY
EA
EA
SF
EA
$45
$100,000
$4,500
$0.50
$1.50
$50
$200,000
$300,000
$2
$3,000
$248,400
$100,000
$4,500
$2,675
$150,000
$10,000
$200,000
$300,000
$33,300
$3,000
Infiltration Gallery
17
18
19
20
21
22
Excavation
Structure
Bedding
Subtotal
Mobilization (10% of subtotal)
Bonds and Insurance (5% of subtotal)
Construction contingency (15% of subtotal)
Construction Total
Project Total
Total Estimate (Rounded)
6,725
161,568
200
CY
Gal
CY
$45
$1.50
$50
$302,625
$242,352
$10,000
$1,611,095
$161,1100
$80,550
$241,660
$2,094,415
$2,584,715
$2,590,000
30
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Table 4-10. 180,000 gallon cistern treatment cost (Scenario 3).
Item No.
Description
Quantity
Unit
Unit Cost
Total
Planning/Design
1
2
3
Planning (10% of subtotal)
Permits/Studies
Design (15% of construction total)
1
1
1
LS
LS
LS
-
-
-
$189,400
$15,000
$369,400
Construction
4
5
6
Temporary construction entrance
Temporary construction fence
Dewatering
1
700
1
EA
LF
LS
$2,500
$2.50
$368
$2,500
$1,750
$368
Cistern & Irrigation
7
8
9
10
11
12
13
14
15
16
Excavation
Diversion structure
Pre-treatment system
Hydraulic restriction layer (30 mil liner)
Cistern
Bedding
Stormwater lift station/wet well (200 gpm)
Water treatment system (UV)
Landscaping
Electrical/control integration
8,650
1
1
9,250
180,000
341
1
1
23,110
1
CY
EA
EA
SF
Gal
CY
EA
EA
SF
EA
$45
$100,000
$4,500
$0.50
$1.50
$50
$200,000
$300,000
$2
$3,000
$389,250
$100,000
$4,500
$4,625
$270,000
$17,050
$200,000
$300,000
$46,220
$3,000
Infiltration Gallery
17
18
19
20
21
22
Excavation
Structure
Bedding
Subtotal
Mobilization (10% of subtotal)
Bonds and Insurance (5% of subtotal)
Construction contingency (15% of subtotal)
Construction Total
Project Total
Total Estimate (Rounded)
6,725
161,568
200
CY
Gal
CY
$45
$1.50
$50
$302,625
$242,352
$10,000
$1,894,240
$189,420
$94,710
$284,140
$2,462,510
$3,036,310
$3,040,000
31
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The cistern and subsequent use for irrigation will reduce demand for potable. This resulting cost savings
is calculated using the City of Santa Monica water rate of $3.57 per hundred cubic feet. The results are
shown in Table 4-12.
Table 4-11. Potable water savings through rainwater harvesting at Ozone Park.
Model Scenario Cistern Average Annual Average
Size, Irrigation Offset, Annual Cost
Gallons HCF Savings
Scenario 1
Scenario 2
Scenario 3
10,000
100,000
180,000
384
516
600
$1,375
$1,850
$2,150
To help compare the three scenarios, the cost efficiency for irrigation, infiltration, and zinc removal
were calculated. The total cost was divided by the annual totals for irrigation from the system, the
volume infiltrated, and the total zinc removal. The infiltration gallery remains constant through all three
scenarios, and the primary cost difference is the cistern size and associated excavation. The values in
Table 4-13 give a side-by-side comparison of the benefit received per each dollar spent.
Table 4-12. Cost efficiency at Ozone Park.
Model Scenario
Scenario 1
Scenario 2
Scenario 3
Cistern
Size,
Gallons
10,000
100,000
180,000
Cost per Gallon
of Irrigation
$7.07
$6.70
$6.78
Cost per
Gallon of
Infiltration
$0.85
$1.04
$1.19
Cost per
Pound Zinc
Removed
$164,568
$189,787
$205,389
4.5. Operation and Maintenance
Routine operation and maintenance is critical for the long-term performance of any green infrastructure
practice. Specific recommendations for scheduling inspection and maintenance for cisterns and
subsurface infiltration galleries are presented in the following sections.
4.5.1. Subsurface Cistern
General maintenance activities for subsurface cisterns are similar to the routine periodic maintenance
for on-site drinking water wells. The primary maintenance requirement is to inspect the tank and
distribution system and test any backflow-prevention devices. Cisterns also require inspections for
clogging and structural soundness twice a year, including inspection of all debris and vector control
screens. If a pre-treatment device is used, it should be dewatered and cleaned between each significant
storm event. Self-cleaning filters and screens can help prevent debris from entering the cistern and
reduce maintenance. Accumulated sediment in the tank must be removed at least once a year.
32
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Table 4-1 3. Inspection and maintenance tasks for cisterns.
Task
Frequency
Maintenance Notes
Dry season inspection One time per year
Inspect once during the dry season to
ensure volume capacity. Clean if
required.
Wet season inspection
Monthly during wet
season
Monthly during the wet season to
ensure volume capacity
Trash well cleaning
Dry season - 1 time
Wet season - 3 times
Dry season cleaning to happen just
before the start of the wet season
Pump well cleaning
Dry season - 1 time
Wet season - 3 times
Dry season cleaning to happen just
before the start of the wet season.
Pump maintenance
As needed
Valve maintenance
As needed
Control panel
maintenance
As needed
4.5.2. Subsurface Infiltration Gallery
General maintenance activities for subsurface infiltration galleries are similar to the routine
maintenance for cisterns. The primary maintenance requirement is to inspect the facility for clogging
and structural soundness. Accumulated sediment removal might be required on an annual basis to
ensure proper infiltration function.
Table 4-14. Inspection and maintenance tasks for subsurface infiltration galleries.
Task
Frequency
Maintenance Notes
Dry season inspection One time per year
Inspect once during the dry season to
ensure volume capacity. Clean if
required.
Wet season inspection Monthly during wet
season
Monthly during the wet season to
ensure volume capacity.
Vault cleaning
Dry season - 1 time
Wet season - 3 times
Dry season cleaning to happen just
before the start of the wet season.
Valve maintenance
As needed
5. Policy Approach/Permits
Consultation with regulatory agencies and acquisition of permits is required before the project
components can be constructed. The following summarizes the local regulatory permits and approvals
relevant to the Ozone Park project.
California Environmental Quality Act (CEQA)
A Mitigated Negative Declaration may be required due to the potential for impacts that will occur during
construction and operation.
State Water Resources Control Board - Construction General Permit
The State Water Resources Control Board adopted the National Pollutant Discharge Elimination System
(NPDES) Construction General Permit (CGP). The goal of the CGP is to prevent polluted discharges from
33
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entering the storm drain system and receiving waters during construction activities. The CGP requires
the development and implementation of a Storm Water Pollution Prevention Plan (SWPPP) which
specifies BMPs that will prevent construction pollutants from contacting stormwater and with the intent
of keeping products of erosion from moving offsite into receiving waters, eliminating or reducing non-
stormwater discharges to storm sewer systems, and performing inspections of all BMPs.
Regional Water Quality Control Board. Los Angeles Region
The Regional Water Quality Control Board issues discharge permits to surface waters in compliance with
the Clean Water Act and NPDES program.
In October 2012, the Los Angeles Regional Water Quality Control Board adopted the Los Angeles County
Municipal Separate Storm Sewer System (MS4) Permit. The MS4 Permit includes extensive planning and
construction requirements to manage the post-construction site runoff. The final plans require
assurances that the appropriate BMPs are incorporated to address stormwater pollution prevention
goals. For Ozone Park, the project retrofit itself includes implementation of stormwater BMPs.
South Coast Air Quality Management District
Construction activities in the South Coast Air Basin are subject to the South Coast Air Quality
Management District's Rule 403, which requires applicable operations to prevent, reduce, or mitigate
fugitive dust emissions. All construction must incorporate best available control measures included in
Table 1 of Rule 403. During the active construction phase, the contractor would be required to
implement dust control measures to ensure compliance with Rule 403.
County of Los Angeles
Structures that have the potential to alter storm drain conveyance capacities or change the timing of
accumulated flows are required to be reviewed and approved by the Los Angeles County Flood Control
District (LACFCD) Design Division. An Encroachment Permit to disturb the storm drain is also required by
the Los Angeles County Department of Public Works Construction Division. It is anticipated that this
project would require the LACFCD review and the Encroachment Permit.
City of Santa Monica (building permit, tree removal/relocation, grading, storm drain)
Various City of Santa Monica departments are likely to require some or all of the following permits:
building permit, tree removal/relocation, grading, and storm drain permit. Collaboration with other City
departments should be conducted before construction begins.
With Southern California facing water supply challenges, innovative solutions are necessary to reduce
and replace potable water demand. Rain harvesting and use is one approach to help the City of Santa
Monica achieve its water independence goals and build resiliency to drought. The proposed Ozone Park
stormwater and dry-weather runoff harvesting project would provide sufficient on-site irrigation supply
and help contribute to the City's regional requirement to improve outfall water quality. The project
builds on the City's efforts to install similar green infrastructure on both private and public parcels, and
to achieve its water self-sufficiency goal by 2020.
34
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7. References
City of Santa Monica. 2014. Applying for: U.S. E.P.A.'s Green Infrastructure Technical Assistance Program
-2014 Request for Letters of Interest. Santa Monica, CA.
City of Santa Monica - Office of Sustainability and the Environment. 2015. Use 20% Less Water to Reach
Our Goal. Accessed on April 6, 2015.
htt[)://www.smaov.net/De[)artments/OSE/cateaories/water.as[)x
DeBusk, K.M., W.F. Hunt, M. Quigley, J. Jeray, and A. Bedig. 2012. Rainwater harvesting: Integrating
water conservation and stormwater management through innovative technologies. World
Environmental and Water Resources Congress 2012: Crossing Boundaries, Proceedings of the
2012 Congress, pp. 3703-3710.
Despins, C., K. Farahbakhsh, and C. Leidl. 2009. Assessment of rainwater quality from rainwater
harvesting systems in Ontario, Canada. Journal of Water Supply: Research and Technology
AQUA58(2):117-134.
Gikas, G.D., and V.A. Tsihrintzis. 2012. Assessment of water quality of first-flush roof runoff and
harvested rainwater. Journal of Hydrology 466-467:115-126.
Hunt, W.F., A.R. Jarrett, J.T. Smith, and LJ. Sharkey. 2006. Evaluating bioretention hydrology and
nutrient removal at three field sites in North Carolina. Journal of Irrigation and Drainage
Engineering 132(6):600-608.
Jones, M.P. and W.F. Hunt. 2010. Performance of Rainwater Harvesting Systems in the Southeastern
United States. Resources, Conservation & Recycling, 54:623-629.
Carolina Cooperative Extension, Raleigh, NC.Lee, J.Y., G. Bak, and M. Han. 2012. Quality of roof-
harvested rainwater - Comparison of different roofing materials. Journal of Environmental
Pollutation. 162(2012)422-429.
LACDPH (Los Angeles County Department of Public Health). 2011. Guidelines for Harvesting Rainwater,
Stormwater, & Urban Runoff for Outdoor Non-Potable Use. September 2011.
LADWP (Los Angeles Department of Water and Power). 2011. Feasibility Report for Development of
Groundwater Resources in the Santa Monica and Hollywood Basins. Los Angeles, CA. December
2011.
Lye, D.J. 2009. Rooftop runoff as a source of contamination: A review. Science of the Total Environment
407:5429-5434.
MWD (Metropolitan Water District) of Southern California. 2007. Groundwater Assessment Study.
Chapter IV - Groundwater Basin Reports - Los Angeles County Coastal Plain Basins - Santa
Monica Basin. Report Number 1308. September 2007.
Onondaga County. 2015. Save the Rain - War Memorial Cistern System. Accessed on April 6, 2015.
h ttp://savetherain. us/str project/war-memorial/
Strecker, E.W., M.M. Quigley, B. Urbonas, and J. Jones. 2004. Analyses of the expanded EPA/ASCE
International BMP Database and potential implications for BMP design. In Proceedings of the
World Water and Environmental Resources Congress, American Society of Civil Engineers, Salt
Lake City, UT, June 27-July 1, 2004.
35
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Tetra Tech 2010a. Los Angeles County Watershed Model Configuration and Calibration - Part I:
Hydrology. Prepared for County of Los Angeles Department of Public Works, Watershed
Management Division. Los Angeles County, CA by Tetra Tech, Pasadena, CA.
Tetra Tech 2010b. Los Angeles County Watershed Model Configuration and Calibration - Part II: Water
Quality. Prepared for County of Los Angeles Department of Public Works, Watershed
Management Division. Los Angeles County, CA by Tetra Tech, Pasadena, CA.
Tetra Tech. 2015. Albion Riverside Park Project - Predesign Report. Submitted to the City of Los Angeles
on March 30, 2015.
Thomas, P.R., and G.R. Greene. 1993. Rainwater quality from different roof catchments. Water Science
USEPA (U.S. Environmental Protection Agency). 2013. Evaluation of Dry Wells and Cisterns for
Stormwater Control: Millburn Township, NJ. EPA/600/R-12/600. U.S. Environmental Protection
Agency, Office of Research and Development, Edison, NJ. March 2013.
Vialle, C, C. Sablayrolles, M. Lovera, M.-C. Huau, S. Jacob, and M. Montrejaud-Vignoles. 2012. Water
quality monitoring and hydraulic evaluation of a household roof runoff harvesting system in
France. Water Resource Management 26:2233-2241.
36
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Appendix A: Site Plan and Details
A-l
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A-2
-------
Site Location
Watershed Characteristics
Retrofit Characteristics
AIN
Major
Watershed
4287033900 Latitude 34°0'5.71"N Drainage Area, acres 307
Santa Monica
Bay Watershed
Longitude 118°28'19.48"W LA County Soil Class 013
Street Address °Z°ne St & 7 Landowner Santa Monjca Total Impervious, %
St. CA, 90405
65
Estimated Cost $2,030,000
Potable Offset, % 60
Zinc Reduction, % 10
Existing Site Description: Ozone Park is a linear park with a total area of 0.7 acres located on
the southern border of the City of Santa Monica where Santa Monica meets Los Angeles. The
park has playgrounds on the eastern and western ends and a grassy lawn in between. It
currently has a sprinkler irrigation system that sprays water through the park.
Cistern Size, gal. 10,000
Infiltration Gallery footprint, ft2 5,400
Ponding Depth, ft 4
Diversion Rate, cfs 20
Proposed Retrofit Description: The proposed retrofit would involve installation of an
underground diversion structure, pre-treatment basin, cistern, post-treatment system and
overflow infiltration gallery within the existing park footprint. This conceptual design proposes
a 10,000-gallon cistern to harvest all of the dry-weather flow and use it through park irrigation.
The design would reduce the potable water demand by 60 percent.
o
^
CD
CO
O O
O CD
CO
o
CD
rV,^
X O
1C CD
tt>
E!cQ-
I =5
> 32
v co
Diversion
Structure
78" Storm
Drain
Current Park View
Cistern
Infiltration Gallery
m
Cross Section
-------
Site Location
Watershed Characteristics
Retrofit Characteristics
AIN
Major
Watershed
4287033900 Latitude 34°0'5.71"N Drainage Area, acres 307
Santa Monica
Bay Watershed
Longitude 118°28'19.48"W LA County Soil Class 013
Street Address °Z°ne St & 7 Landowner Santa Monjca Total Impervious, %
St. CA, 90405
65
Estimated Cost $2,590,000
Potable Offset, % 86
Zinc Reduction, % 11
Existing Site Description: Ozone Park is a linear park with a total area of 0.7 acres located on
the southern border of the City of Santa Monica where Santa Monica meets Los Angeles. The
park has playgrounds on the eastern and western ends and a grassy lawn in between. It
currently has a sprinkler irrigation system that sprays water through the park.
Cistern Size, gal. 100,000
Infiltration Gallery footprint, ft2 5,400
Ponding Depth, ft 4
Diversion Rate, cfs 20
Proposed Retrofit Description: The proposed retrofit would involve installation of an
underground diversion structure, pre-treatment basin, cistern, post-treatment system and
overflow infiltration gallery within the existing park footprint. This conceptual design proposes
a 100,000-gallon cistern to harvest dry and wet-weather flow and use it through park irrigation.
The design would provide a potable water offset of 86 percent.
o
^
CD
CO
O O
O CD
CO
o
CD
rV,^
X O
1C CD
tt>
E!cQ-
I =5
> ~D
Treatment
System
Diversion Pretreatment
Structure Basin
Maintenance
Access
Irrigation Water
Maintenance
Access
78" Storm
Drain
Cistern
Infiltration Gallery
m
3
Current Park View
Cross Section
-------
Site Location
Watershed Characteristics
Retrofit Characteristics
AIN
Major
Watershed
4287033900 Latitude 34°0'5.71"N Drainage Area, acres 307
Santa Monica
Bay Watershed
Longitude 118°28'19.48"W LA County Soil Class 013
Street Address °Z°ne St & 7 Landowner Santa Monjca Total Impervious, %
St. CA, 90405
65
Estimated Cost $3,040,000
Potable Offset, % 100
Zinc Reduction, % 12
Existing Site Description: Ozone Park is a linear park with a total area of 0.7 acres located on
the southern border of the City of Santa Monica where Santa Monica meets Los Angeles. The
park has playgrounds on the eastern and western ends and a grassy lawn in between. It
currently has a sprinkler irrigation system that sprays water through the park.
Cistern Size, gal. 180,000
Infiltration Gallery footprint, ft2 5,400
Ponding Depth, ft 4
Diversion Rate, cfs 20
Proposed Retrofit Description: The proposed retrofit would involve installation of an
underground diversion structure, pre-treatment basin, cistern, post-treatment system and
overflow infiltration gallery within the existing park footprint. This conceptual design proposes
a 180,000-gallon cistern to harvest all of the dry and wet-weather flow and use it through park
irrigation. The design would offset 100 percent of the potable water demand.
o
^
CD
CO
O O
O CD
CO
o
CD
rV,^
X O
1C CD
tt>
E!cQ-
I =5
> 32
GO M
^Sl
Diversion Pretreatment
Structure Basin
Maintenance
Access
Treatment
System
78" Storm
Drain
Irrigation Water
Maintenance
Access
Cistern
Submersible
Pump(s)
Infiltration Gallery
m
3
Current Park View
Cross Section
-------
Appendix B: Rainwater Harvesting Model Data
£ RainwaterHarvesterV3
[ = \m x
RAINWATER HARVESTER A
S)^tem Design Basic Usage Custom Usage Imgation Output
System Design
tonica\TimeSenes\RaraaterHarvesting_INPUTrai | Browse | Q Use Output File
Roof*rea 43560 sq.ft.
1 '_.' Lookup Capture Factor Slope [_
* Input Capture Factor SurfaceC
Vakje 1.0
City Other
Water Cost 0.00678 s/gd
SewerCost 0.00448 J/gd.
Discharge to Sewer 10Q
QsternCost 100000 5
D Use Backup
Start Tngger | | %
Stop Backup | | >/t
w
Nitrogen 1.56 mg/l
Phosphorus Q.D3 mg/l
Suspended Soilds 3.48 mg/l
D Use Passive Release
Detention Volume gg\
Volume 10DDO Gallons Drawdown Rate
Status:
Smuiate
B-l
-------
RainwaterHarvesterVB
-
n Design I Basic Usage [custom Usage | Imgaljon | Output
RAINWATER HARVESTER A
Basic Water Usage
People Rushing C
Gal per Hush B
Consistent Daly Usage D
Constant Water Supply
people / day
El Weekend Usage1)
gal. /day
Jan.
Feb. Mar. Apr. May Jun
Sep. Oct. HOY. Dec.
732.0 732.0 732.0 732.0 732.0 732.0 732.0 732.0 732.0 732.0 732.0 732.0 gal. /day
- dick the arrows to copy between months
Simulation Complete!
B-2
-------
RarnwaterHarvesterV3
1
System Design | Basic Usage 1 Custom Usage foigj
Custom Water Usage
Jan
tion | Output |
Feb. Mar. Apr Hay
RAINWATER HARVESTER £
Jun Jd. Ajg. Sep. Od. Mov. Dec
Sunday 623.8 648.1 799.4 1159.7 1443.9 1757.0 1977.1 1889.2 1760.8 1276.1 S35.0 6155 gal. /day
Honda, 623.8 648.1 799.4 1159.7 1443.9 1757.0 1977.1 1889.2 1760.8 1276.1 835.0 615.5 gal. /day
Tuesday 623S m -1 7994 11597 1443'9 1757° 19771 18892 17S0-8 127G1 335° G155 9al./day
Wednesday S23 8 648-1 799-4 1159-7 1443'9 1757° 19771 18892 1760'8 1276'1 S35'° 615'5 Sal-/day
-n,,,^,,^ 6238 6481 7994 1159.7 1443.9 1757.0 1977.1 1889.2 1760.8 1276.1 835.0 615.5 gal. /day
Friday K3-8 MS 1 7954 11597 1443-9 1757-° 1977'1 1889-2 1760'8 1276'1 835'° 615-5 9al-/dBV
Saturday ffi3
8 648.1 793.4 1159.7 1443.9 1757.0 1977.1 1889.2 1760.8 1276.1 835.0 615.5 gal. /day
Times of Usage
Mdnight I 6AM
DIAM O7AM
El 2AM , EAM
n 3AM : SAM
Q 4AM D 10AM
D 5AM D 11AM
Midrtght-5AM
6AM-11AM
U Noon
D 1PM
n 2PM
n 3PM
D 4PM
n 5PM
Noon -5PM
- dick the arrows to copy between months
D 6PM dear M Times ]
n 7PM
n BPM
n 9PM
r: 11PM
6PM -11PM ]
Slat°nC°"
0M
Simulate
B-3
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