Jensen Deflective Separator Pretreats Stormwater Runoff

Long Beach, California

The 17,771-acre Los Cerritos Channel Freshwater Watershed in Southern California showed exceedances of the total maximum daily load limits (TMDLs) established by the US Environmental Protection Agency (EPA) for total suspended solids (TSS) and several heavy metals. Seven cities in the watershed were accountable for resolving the EPA mandate to lower TSS and heavy metals below the TMDL levels. Bellflower, Cerritos, Downey, Lakewood, Long Beach, Paramount, and Signal Hill each needed a solution to manage and monitor water quality in their respective oversight areas.

“It represents the start of the remaking of water infrastructure in California,” says Sam Unger, Executive Director of the Los Angeles Regional Water Quality Control Board.

Installing multiple stormwater treatment systems to eliminate the pollutants would be more costly for the individual cities and perhaps not as efficient as a single large diversion, treatment, and infiltration infrastructure on the Los Cerritos Channel at the bottom of the entire watershed.

The seven cities impacted by the EPA mandate formed the Los Cerritos Channel Watershed Group to streamline a solution. Instead of each municipality addressing stormwater treatment individually, one large regional system was built to collectively remove the pollutants and curb costs. The Los Cerritos Channel Sub-Basin 4 Stormwater Capture Facility eliminates most polluted dry weather runoff while diverting, treating, and infiltrating first flush stormwater flows impacting the watershed.

Capture and Treatment

The solution was a single, large diversion, treatment, and infiltration infrastructure. Jensen Precast engineers designed, manufactured, and delivered a Jensen Deflective Separator system for the $20 million multi-city effort to capture and treat stormwater runoff in Los Angeles County.

“We built a system that takes in 166 cubic feet of stormwater per second through a precast concrete flow splitting structure into dual hydrodynamic separator units deployed inside two 16-foot diameter precast concrete structures,” says Walter Stein, Jensen Precast Stormwater Systems Manager. “The system efficiently pretreats diverted stormwater from the Los Cerritos Channel into a detention and infiltration gallery.”

Prior to installing the system, the contractor had to quickly react to a higher than expected water table. It meant getting control of the water seeping into the capture and treatment installation area.

“Mike Bubalo Construction brought Trench Shoring Company, a specialty watering company,” Stein says. “They got control of the water in three days to get above the water table. That’s the beauty of precast concrete. We can get into the bottom of the hole and stack out very, very rapidly, unlike a cast in place structure.”

The Los Cerritos Channel Sub-Basin 4 Stormwater Capture Facility pretreatment system was completed in May 2018. Jensen Precast provided build and installation expertise for the largest known hydrodynamic separator systems in the United States. The facility will provide higher water quality in the Los Cerritos Channel Freshwater Watershed.

“It’s a good product for us,” says Dave Sorem, Vice President, Mike Bubalo Construction. “It takes in 166 cubic feet per second through the transition structure, then into two hydrodynamic separators, then into an infiltration gallery. I don’t know of any other system that could do that. That’s a lot of flow. We selected Jensen Precast because of their reputation supplying vaults. Their proposal was  comprehensive. We enjoyed the staff interaction, their preconstruction video, and their sequencing. It all went correct.”

Jensen Precast provides stormwater solutions for engineers and contractors seeking large and small scale structures approved by agencies and ready to deploy. Contact us to go over your project and get the quote you need for your bid.

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