Pullman wastewater plant hauled compostable biosolids after land-application options fell through

Pullman public works staff updated the City Council on Feb. 11 about 2024 biosolids management at the city’s wastewater treatment plant and the ongoing special assessment fee intended to cover unplanned hauling costs.

Public Works Director Sean Wells and Wastewater Treatment Plant Supervisor Trevor Cook told the council the plant produced 467 dry tons of Class B biosolids in 2024. Because previously contracted local land-application partners withdrew their participation, the city hauled 247 dry tons — about 53% of the year’s total — to regional composters during an August–November hauling window. “Last year in 2024, the wastewater treatment plant produced 467 dry tons of biosolids,” Trevor Cook reported. “We were able to haul off 247 dry tons to the composters, which is roughly 53% of the total amount produced for the year.”

Staff explained the Department of Ecology’s statewide general biosolids permit was appealed and reissued during 2023–25, which affected permit processing timelines. Ecology issued a new statewide general permit effective at the start of the month, and Pullman is preparing an application under that reissued coverage. Wells said the city met Class B sampling and pathogen-reduction requirements and had zero exceedances for metals in required quarterly lab tests.

Because land-application sites were unavailable after late 2023 and again in late 2024, Pullman contracted to haul biosolids to facilities in other jurisdictions, incurring higher-than-expected costs. In July 2024 the council approved a special assessment to begin in August to cover those hauling costs; staff said the surcharge needs to remain in place while the city seeks permanent land-application partners.

Wells said the department built a temporary loading ramp to enable truck loading for hauling, and operations changed after leaf pickup and colder weather limited hauling in November. Staff reported that the digesters well exceeded pathogen-reduction time‑and‑temperature requirements (an average of about 36 days detention at roughly 100°F) and achieved a volatile solids reduction of about 57% (above the 38% minimum used to reduce vector attraction).

Staff outlined next steps: finalize and submit the application for basic coverage under the reissued Ecology general biosolids permit (which would allow hauling to composters now and add land-application sites later), continue to seek land-application sites, and maintain the special assessment surcharge until land application resumes.

Council members asked whether a successful permit application and new land-application agreements could allow the city to remove the special assessment surcharge. Wells said yes: “The intent is that we ultimately would have the ability to remove the biosolid special assessment fee at some point in time when we start land applying again,” he said.

The presentation included a plant tour invitation; staff said they will return with permit application updates and any cost-recovery recommendations.