El Portal Wastewater Treatment Plant
Yosemite National Park, California

The El Portal wastewater treatment facility handles up to a million gallons a day from Yosemite National Park and the town of El Portal. Originally constructed in 1977, the plant needed improvements to meet discharge standards, increase capacity, and provide a more economical and environmentally conscious method of handling sludge disposal.

JFSA provided structural engineering design and construction services for the project. A major part of the work was design of a new 230,000-gallon anaerobic digester tank. Because the site is located in a high seismic activity region (zone 4), analysis was performed to evaluate seismically-driven hydrostatic "sloshing" loads, and to ensure enough freeboard in the tank to prevent wave damage to the tank roof.

Other design services included converting the gravity flow thickener to a sludge storage basin, modifying the primary clarifiers, and expanding the digester building. Existing structures were also evaluated to assess their structural capacity for installation of new equipment. All design elements gave special consideration to crack control, durability, and resistance to chemical attack.

Client: National Park Service