Top: The new Shafter-Wasco Composting Facility is designed to process 100,000 tons/year of source separated organics (SSO). Photos courtesy of Kern County Public Works
Kern County Public Works held a grand opening of its Shafter-Wasco Composting Facility in Shafter, California in October 2025, providing the County with its own composting capacity versus using merchant facilities in the region. “We’ve been collecting curbside and self-haul green waste and brush trimmings since the 1990s, along with dimensional lumber and other wood waste at our solid waste facilities,” notes Dave Lee, Kern County Public Works Manager. “The County has done the chipping and grinding, and then takes the green materials to one of four or five composting facilities in the area. Tipping fees at those facilities, along with transportation costs, continued rising over the years, prompting the Public Works department — about 10 years ago — to put together a proposal for our own composting site and present it to the Kern County Board of Supervisors.”
The Board approved the proposal, and facility planning got underway in 2016. The county owns 20 acres to the north of its landfill; about half is used as a diversion area for materials self-hauled to the landfill. “About 10 acres of that property was vacant, and it wasn’t needed for landfill drainage or development, so it was a very easy location to choose,” adds Lee. The process of raising the funds, zoning and going through the permitting and environmental reviews took a number of years. When seeking a composting equipment provider, one of the main criteria was having a facility that could operate with a limited number of employees. The County couldn’t support or retain a large staff, and was willing to spend more on capital costs for a system that could be managed with six to eight people.
“In addition, Kern County is in the San Joaquin Valley Air Pollution Control District, which has very strict emissions regulations for volatile organic compounds (VOC),” he explains. “We selected Sustainable Generation’s Covered Aerated Static Pile (CASP) technology with GORE® covers to meet the VOC emissions limits. At the same time, the system falls within the confines and barriers we have in terms of labor requirements.” The site had an existing concrete pad where materials can be received and blended. That pad was connected to a newly constructed area that houses 32 concrete bunkers with capacity to process 100,000 tons/year of source separated organics. Materials received include green waste, agricultural residuals, manure, food waste and food-soiled paper. “Each bunker holds about 500 to 600 tons of feedstocks, and our goal is to process about 25,000 tons each quarter, yielding about 40,000 to 45,000 tons/year of compost,” says Lee.
Capital costs for the facility were $21.5 million, with concrete representing much of the expense. Kern County Public Works was awarded a $10 million grant in 2024 from CalRecycle’s Organics Grant Program to offset the construction of the composting facility. The remaining amount was covered by the County’s solid waste enterprise fund. Construction began in April 2024 and was completed in September 2025. The composting process is managed in three phases — active composting under the covers for three to four weeks, curing in another set of covered bunkers for two to three weeks, and then a finishing phase in uncovered bunkers for about two weeks. Sustainable Generation held four training days for the facility staff and provides continued support of the system. The site superintendent is a certified compost operator.
Kern County is heavily agricultural, therefore farmers, ranchers and land managers are key end users for the compost. “Groundwater usage is a big issue in this region, and compost utilization on ag land helps reduce demand,” notes Lee. In addition, local jurisdictions can utilize the compost to meet their compost procurement requirements established under SB 1383. Kern County has 11 incorporated cities that need to procure recovered organics to meet their annual targets.
