The number one cause of coastal water pollution in Southern California is urban stormwater runoff. The City of Redondo Beach is taking steps to protect their coastal waters south of the Redondo Beach Municipal Pier in Santa Monica Bay by collecting the stormwater runoff that would have been harmful to the beach, treating the runoff to clean out the debris and then using it to irrigate Alta Vista Park. Water that is not needed for irrigation will be infiltrated into the ground, thus reducing discharge to the ocean.
According to a statement by the EPA’s Pacific Southwest Region, with this innovative project, the City of Redondo Beach is taking a positive step to protect beach users and at the same time conserve Southern California’s scarce water supply.
The Alta Vista Park Diversion and Reuse Project is a $2.2 million venture designed to help the city comply with Regional Water Quality Control Board requirements to reduce stormwater pollution. This system will store runoff from dry weather and first flush flows as well as larger rain events.
The project funded by the American Recovery and Reinvestment Act (ARRA) and administered through the State Water Resources Control Board’s Clean Water State Revolving Fund (CWSRF). Under the Recovery Act, California received $280 million from the U.S. Environmental Protection Agency (EPA) for water quality protection projects and at least 20% of these funds must be provided to “Green Projects” that support sustainable practices, such as the Alta Vista Park project.
“The City Council has been very proactive regarding water quality and “Green” development. Their support has given the staff the incentive to think outside the box and to come up with innovative projects that protect the bay and our valuable resources,” said Mike Shay, Principal Civil Engineer, City of Redondo Beach.
Capturing and reusing stormwater – also known as rainwater harvesting – helps maintain a site’s predevelopment hydrology. The City of Redondo Beach needed a rainwater harvesting system installed below ground to accommodate the small site constraints of Alta Vista Park. Several alternatives were considered for the underground storage component, including modular tank systems and slip joint piping systems. Ultimately, a four phase rainwater harvesting system from Contech was utilized for Alta Vista Park. This includes two treatment systems and two storage cisterns.
Mehta Mechanical Company (MMC Inc.) installed a CDS system as phase one of the project to collect and pretreat the stormwater runoff. The CDS system uses patented continuous deflective separation technology to screen, separate and trap the debris, sediment and oil from the stormwater runoff. The indirect screening capability of the system allows for 100% removal of floatables and neutrally buoyant material, without blinding and allowing consistency for maintenance within the City.
Stormwater runoff then flows to a DuroMaxx steel reinforced polyethylene (SRPE) storage system consisting of two 60-in. diameter cisterns designed to contain the water for re-use in irrigation. The system consists of a North Buffer (Surge) Tank and a South Cistern Storage Tank. The North Buffer Tank is a 29-ft. wide by 40-ft. long double header system responsible for 20,714 gallons of storage and will regulate the stormwater flow through the main pipelines by acting as a buffer during peak loads.
DuroMaxx was chosen because of its superior joint quality. DuroMaxx uses welded couplers that are manufactured using high density polyethylene pressure rated resins and flat steel band couplers. The frequency of rain events can be very sporadic in Southern California, and the reduction of water loss makes the joint integrity of the welded coupler joints very important.
Water flow is refined in the third phase with a Stormwater Management StormFilter before it is utilized for watering the landscape. Two 8-in. x 16-in. Stormwater Management StormFilter precast vault systems – each consisting of 33 cartridges – were installed upstream of the South Cistern Storage Tank and utilize a filtration media to remove the remaining pollutants.
The City used two StormFilter systems instead of one as a precautionary measure in case maintenance on one system is needed. The StormFilter was chosen because its patented, surface-cleaning system prevents surface blinding, extending the cartridge life cycle, thus reducing maintenance.
The South Cistern is a 97-ft. wide x 95-ft. long single header system responsible for 123,339 gallons of storage and will act as the main storage before irrigation re-use. The irrigation water supply system included two vertical turbine pumps and a hydropneumatic tank to maintain the water pressure and flow rates equivalent to current irrigation demands. If the South Cistern is dry, the structure will isolate itself and water will be provided by the municipal water system. A reduced pressure double check backflow preventer has also been installed to prevent cross-contamination.
The project was completed in 2010 and is being monitored through an SCADA (Supervisory-Control and Data Acquisition) system allowing for remote real time observation.