A stormwater project is being planned for the Westchester area that would intercept stormwater and remove harmful pollutants such as litter and bacteria from a 2,400-acre drainage area that now empties directly into the ocean at Dockweiler Beach in Playa del Rey.
The Westchester Stormwater Best Management Practices (BMP) Project was presented by Ken Susilo, associate and manager of Los Angeles Operations for Geosyntec Consultants at an afternoon and an evening meeting Tuesday, September 30th, at Los Angeles City Councilman Bill Rosendahl’s office in the Community Building at Westchester Park.
Rosendahl represents the 11th Council District, which includes Westchester and Los Angeles International Airport (LAX).
The project principals are Los Angeles World Airports and the Federal Aviation Administration, with Geosyntec engineering consultants administering the project in conjunction with Salem Garawi, a civil engineer and project manager from the Bureau of Engineering of the City of Los Angeles Department of Public Works.
The project is on LAX property near the intersection of Pershing Drive and Westchester Parkway at Falmouth Avenue (near the Jet Pets gate).
Project documentation states that the project will assist in complying with the Santa Monica Bay Beaches Wet Weather Bacteria Total Maximum Daily Load (TMDL).
The project cost, estimated at $32.7 million, is being funded from $500 million in general obligation funds approved by city voters in 2004 under Proposition O, and is geared to help meet the Environmental Protection Agency (EPA) and federal Clean Water Act requirements in the Westchester-Playa del Rey area.
The following project information and description are from documentation available at www .lapropo.org/.
Approximately 2,400 acres of urbanized land (originating from both the Westchester residential neighborhood and the LAX airfield) drain directly into Santa Monica Bay and discharge at Dockweiler Beach. Urban runoff from this tributary area contains numerous pollutants that degrade water quality and contribute to frequent exceedances of beach water quality standards, resulting in significant numbers of beach closure days, with the pollutants of primary concern being fecal indicator bacteria, which are believed to be an indicator for pathogens and potential human health risks.
The project will divert water from the existing storm drain system, provide water quality treatment and restore some of the hydrologic balance (via infiltration) that has been limited as a result of urbanization and increases in impervious area (man-made surfaces that can’t be easily penetrated by water).
The project will direct stormwater that would have flowed to the ocean through storm drains near the northern border of LAX to be intercepted and directed to a water quality “treatment train.”
The interception of stormwater flows will occur both from the Argo Drain (the airport perimeter ditch that parallels Westchester Parkway) and from a major storm drain labeled by Los Angeles County as Project 647.
Stormwater flows will then pass through a gross solids removal device (such as a hydrodynamic separator, trash netting system or series of screens) which will separate trash, debris and larger particulate pollutants from the water.
Flows will then enter a detention basin that will serve two purposes — allowance for settlement of finer particulate pollutants and equalization of flows to maximize efficiency. Debris will be captured in nets and then removed and hauled away, said Susilo.
A pumping facility will extract water from the detention basin and direct flows to the infiltration facilities (basins, galleries and dry wells). Pumped stormwater will be metered into the infiltration facilities, which will be sited, sized and designed to optimize efficiency without causing engineering impacts to any adjacent facilities or structures.
Natural filtration and degradation processes within the soil will further clean the stormwater and groundwater will be supplemented and recharged.
The effect on the landscape will be minimal, said Susilo, with limited grading and the topsoil removed and stored, to be replaced after the work has been completed. There will be no asphalt or concrete on the ground surface.
The only apparent traces of the project will be air vents and hatches to access the underground facility for maintenance purposes. The basic elevation of the ground will slightly change four or five feet on average. Once the topsoil has been replaced, any vegetation present prior to the project will grow again, he said.
After the final design phase and requirements of CEQA (California Environmental Quality Act) and NEPA (National Environmental Policy Act) are met and bids awarded in the spring and fall next year, the post-construction phase is expected to run from fall 2010 to spring 2011.