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PRCS - PRESENTATION: Receive Presentation of Syd Kronenthal Park Stormwater Project Feasibility Study
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Meeting Date: July 6, 2023
Contact Person/Dept: Sean Singletary/Public Works - Environmental Programs & Operations
Phone Number: (310) 253-6457
Fiscal Impact: Yes [X] No [] General Fund: Yes [] No [X]
Attachments: []
Public Notification: (E-mail) Meetings and Agendas - Parks, Recreation and Community Services Commission (06/29/2023); (E-mail) Parks, Recreation & Community Service Department Updates (06/29/2023)
Department Approval: Armando Abrego, PRCS Director (06/29/2023)
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BACKGROUND
The City of Culver City’s stormwater pollution efforts are driven by the Los Angeles County Municipal Separate Storm Sewer System Permit (MS4 Permit), which became effective on December 28, 2012, in accordance with the Clean Water Act. In 2021, the permit was updated to include 85 cities of Los Angeles County, Ventura County Watershed Protection District, the County of Ventura, and 10 cities within Ventura County. Culver City takes a regional approach at compliance by partnering with other agencies within the watershed for annual reporting, water quality monitoring, project implementation and other tasks. The Ballona Creek Watershed Management Group (WMG) is comprised of Culver City, County of Los Angeles, the Los Angeles County Flood Control District (LACFCD), and the Cities of Los Angeles, Beverly Hills, West Hollywood, Santa Monica, and Inglewood. In addition to regional compliance efforts, Culver City also addresses stormwater pollution through the construction of capital projects; enhanced street sweeping and catch basin cleaning efforts; hazardous waste, electronic waste and used oil events; inspections of businesses and construction sites to confirm no pollutants are entering the storm drain system; sanitary sewer overflow prevention efforts; and other programs intended to ensure the quality of the waterways that City streets drain into.
In order to focus the City’s efforts in the prioritization and construction of capital stormwater projects, the Department of Public Works began compiling a Stormwater Quality Master Plan (SWQMP) in 2019. The objective of the SWQMP is to provide a planning tool to identify potential regional, green streets, and Low Impact Development (LID) projects to collectively meet the City’s water quality compliance goals.
Culver City’s planned projects, GIS data, and the Los Angeles Region Imagery Acquisition Consortium (LARIAC) were used to generate planimetric data, land use, hydrology, historical high groundwater levels, storm drain and sanitary sewer systems to determine project opportunities. Based on the data collected, over 400 potential project opportunities were identified to help manage runoff volumes in the SWQMP. Based on these metrics, the City prepared compliance strategies that included concept plans for top ranked multi-benefit priority projects. Projects were prioritized based on budget, cost-effectiveness, and multi-benefit metrics. Syd Kronenthal Park was identified as a top priority project in concept design due to its location and environmental features. Syd Kronenthal Park is ideally situated to combine Culver City Capital Improvement Projects, multi-jurisdictional coordinated projects, and multi-benefit water quality projects. The SWQMP was open for public comment in June 2021 and was approved by Council on August 23, 2021. The Syd Kronenthal Park Stormwater Project was added to the City’s Capital Improvement Program (CIP) in FY 2022, and the City applied for and received regional Measure W funding for a feasibility study for the project, overseen by the County of Los Angeles.
FEASIBILITY STUDY DISCUSSION
Given its ideal location next to Ballona Creek just downstream of Adams Channel tributary, as well as the available public open space at the park to accommodate a regional BMP footprint, the Syd Kronenthal Park Stormwater Project is a potential valuable water quality asset for water storage during wet weather and year-round irrigation. For this Feasibility Study, additional desktop analyses, field visit, geotechnical survey, and storm water modeling were conducted to refine Project details in the original concept and explore the potential of a second alternative which includes a dry- and partial wet-weather flow diversion from Adams Channel. The potential stormwater capture area of the original concept drainage area and the Adams Channel concept drainage area were determined to be approximately 77 acres and 6,785 acres, respectively. The Project aims to improve recreation and greenspace, increase public awareness of stormwater impacts, and supply other benefits while addressing regulatory requirements and reducing pollutant discharges in stormwater runoff.
Due to infiltration rates determined through the geotechnical analysis, the original infiltration alternative was determined to be likely infeasible. Using the Los Angeles County Watershed Management Modeling System (WMMS), stormwater capture benefits were simulated over a 10-year period using historical rainfall data. The model incorporated assumptions developed from the diversion, storage, and irrigation demand details to assess the feasibility of treatment options. From this analysis, it is estimated that stormwater captured by the Project will meet 99.6% of the Park’s irrigation needs.
Modeling determined that approximately 3.3 acre-feet of runoff will be generated from the Syd Kronenthal Park drainage area and 358 acre-feet of runoff from the Adams Channel drainage area during the 85th percentile, 24-hour storm event that is used to determine the treatment capacity of wet-weather projects. While the Project aims to achieve 100% capture of 85th percentile, 24-hour storm runoff from Syd Kronenthal Park drainage area, the City hopes to divert some runoff from Adams Channel to utilize excess capacity at the site. After reserving 3.3 acre-feet of the available 10.3 acre-feet of storage capacity, 7 acre-feet of excess capacity would be available to capture and store runoff from Adams Channel.
From the geotechnical evaluation and infiltration tests, it was determined that the on-site soils and infiltration rates are highly variable, with infiltration rates of the on-site soils ranging between 4.0 and 0.03 inches per hour. An infiltration rate of 0.03 inch per hour will not meet the County of Los Angeles minimum rate for infiltration (0.3 inch per hour). The soils in the upper 20 feet of the borings generally consisted of lean clay and clayey sand. Due to presence of clayey soils and the low infiltration rate of percolation tests, large-scale infiltration at the site was generally not considered feasible. Performing additional infiltration testing at different locations and depths at the subject site in a future design phase will be appropriate to evaluate the overall infiltration rate of the on-site soils and the feasibility of infiltration, or if smaller-scale infiltration in selected areas is feasible.
The project will consist of a large subsurface stormwater storage gallery beneath the existing ballfields at the Park. Diversions from three local storm drains will be captured to feed into the chamber, controlled by gravity and outfitted with a pretreatment unit (hydrodynamic separator or similar device) to screen trash and remove grease, solids, and sediment-associated pollutants. A Permavoid passive irrigation system is proposed as the primary mechanism for use of captured stormwater. The Permavoid layer would be a shallow storage layer above the primary storage gallery that would passively irrigate the ballfield turf grass via capillary action. A small pump would control movement of stormwater from the primary storage gallery to the Permavoid system. Permavoid is completely subsurface and, since there is no risk of stormwater coming in contact with park users, advanced treatment of stormwater is not required prior to irrigation. Water will be treated by one of the following or combination thereof: diversion to sanitary sewer; localized infiltration; and biofiltration/wetland treatment (nature-based solution).
The project has been presented to the City’s Sustainability Committee and to Ballona Creek Renaissance, while initial outreach to stakeholders has begun at City events such as La Fiesta Ballona and Envirofest.
NEXT STEPS
Staff intends to hold public meetings with the neighborhood and other stakeholders to determine what park improvements are desired that fall within the scope of the project. A survey is currently available on the City’s website at <https://www.culvercity.org/City-Projects/PW-Project-Syd-Kronenthal-Park-Stormwater-Project>. Design and construction funds will be sought through the County’s Measure W program, as well as a partnership with Caltrans, a drainage contributor to the Adams Channel watershed. Design will begin toward the end of FY 2024, with a proposed construction date of January 2027.