ProjectCity of Beverly Hills - La Cienega Park and Frank Fenton Field
As a co-permittee of the 2012 Municipal Separate Stormwater Sewer System (MS4) for the Los Angeles County, the City of Beverly Hills (BH) and other agencies within the Ballona Creek Watershed Management Group developed an Enhanced Watershed Management Program (EWMP) to serve as a planning and implementation document in meeting water quality standards for the MS4 permit. The concept for the La Cienega Park and Frank Fenton Field project was developed through collaboration with the Ballona Creek Watershed Management Group and staff from the cities of Beverly Hills, Los Angeles, and West Hollywood.
The EWMP identified the La Cienega Park and Frank Fenton Field project site as a location for a signature regional project to capture and infiltrate a large volume of runoff through subsurface retention and infiltration. The EWMP determined that a below-ground retention and infiltration Best Management Practice (BMP) facility sized to accommodate the 85th percentile, 24-hour storm event runoff from a drainage area of approximately 578 acres is best suited for this project—resulting in an active BMP design volume of 24 acre-feet. BH was interested in evaluating the potential development of a groundwater recharge system and/or project alternatives that would achieve similar goals for MS4 compliance. The feasibility assessment addressed the opportunities and constraints at La Cienega Park and Frank Fenton Field.
Municipal Separate Storm Sewer System (MS4) are publicly owned storm drains, gutters, roadside ditches, grassy swales, sediment ponds, and similar features that function collectively to manage stormwater and non-storm water. Stormwater and non-storm water discharges consist of surface runoff generated from various land uses, which are conveyed via the MS4 and ultimately discharged into surface waters throughout the region including the Ballona Creek Watershed. Pollutants in stormwater and non-storm water have damaging effects on both human health and aquatic ecosystems. MS4 permits authorize public entities to discharge pollutants from public stormwater systems. On November 8, 2012, the Regional Water Board adopted Order No. R4-2012-0175, Waste Discharge Requirements for MS4 Discharges within the Coastal Watersheds of Los Angeles County (LA County), except those discharges originating from the City of Long Beach MS4 (hereinafter LA County MS4 Permit). The LA County MS4 Permit was amended on June 16, 2015 by Order WQ 2015-0075.
EWC provided meeting, workshop and data collection coordination between the Beverly Hills, LA County Public Works, and the Consulting team as well as provided technical support. EWC reviewed EWMP compliance requirements and evaluated technical memorandums and reports and provide recommendations to both BH and B&V. The technical support provided included the following activities:
- Feasibility Assessment
- As-built collection; Site Characterization and Construction Constraints
- Review of geotechnical Investigations
- Review Ongoing Sampling and Monitoring Programs
- Review and Develop Stormwater Capital Improvement Program and Project Concepts for EWMP Compliance
- Evaluate Other EWMP Compliance Strategies
- Permeable Surface Alleys/Street Gutters/Intersections
- Identify Miniature Parkway/Sidewalk Biofilters
To evaluate the feasibility of the LCP/FFF Project, the design parameters provided in the EWMP were reviewed for accuracy and applicability. An updated analysis of the watershed and subsurface drainage infrastructure estimated that the project goals be reduced to 21 AF of BMP volume based on the feasible drainage area of 468 acres. This reduction in drainage area from the 578 acres was realized when a closer evaluation of the drainage boundaries was performed using surface contours. Also, the LA County stormwater infrastructure as-built drawings showed that drainage pipelines around the park include diversions which direct stormwater away from the project site.
In addition, the EWMP predicted that a stormwater retention/infiltration basin would be a feasible BMP for the LCP/FFF Project based on reviewing the LAC provided soil type maps and estimating infiltration rate based on soil type. To verify subsurface conditions and in-situ infiltration rates, geological and hydrogeological investigations were performed at LCP/FFF. The results of these investigations show that the soils at LCP/FFF do not meet LA County standards for infiltration, therefore the EWMP proposed belowground retention/infiltration basin is not a viable BMP.
With retention/infiltration no longer a viable BMP, the City evaluated the following alternative regional project configurations to meet the goals outlined in the EWMP:
- Stormwater diversion, storage, and harvesting for direct use at the LCP/FFF sites
- Stormwater diversion, treatment, and discharge back into the LA County MS4
- Stormwater diversion, detention, and discharge to the City of LA Department of Sanitation’s (LASAN) sanitary sewer system to be treated downstream at the Hyperion Water Reclamation Plant (HWRP)
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