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City staff outline biosolids operations, sampling and PFAS testing in public briefing
Summary
A city presentation explained how Spokane produces and land-applies Class B biosolids, described sampling and buffering protocols, noted no recorded illnesses associated with the program, and said early PFAS sampling has measured about 50 parts per billion in plant biosolids; staff said they are pursuing additional source-control and grant-funded testing.
City wastewater staff gave a technical presentation to the board on April 1 explaining the city's biosolids program and the safeguards used in land application.
The presenter described biosolids as an organic, processed product of wastewater treatment — not raw human waste — and walked the board through the treatment chain from headworks through primary and secondary clarifiers to membrane filtration and anaerobic digesters. The presenter said Spokane produces Class B biosolids and explained the Class A/Class B distinction: Class A processes kill pathogens to a higher standard, while Class B reduces but does not eliminate them.
Staff described operational practices: sample crews take multi-depth soil samples and biosolids samples before each field application; the city maintains buffer zones around wells and homes, prohibits grazing on application fields, coordinates closely with farmers who typically till in biosolids within six hours after application, and operates dryland application in regions such as Deer Park and the West Plains. The presenter said agronomic application rates have declined over time (from roughly 3.5–6 dry tons per acre in earlier years to 2.5–3.5 dry tons per acre now) based on research and agronomic needs.
On emerging contaminants, staff said the city has been participating with the Washington Department of Ecology in early PFAS sampling guidance. The presenter said their biosolids tested "right about the middle of the road, so 50 parts per billion," and that the city plans further source-control work and has grant applications to fund additional testing and reductions. The presenter stressed that determining the origin of PFAS at farm fields is complex because PFAS can come from historic sources, the collection system, or other inputs; staff recommended measuring the entire collection chain to create a baseline before any large-scale treatment spending.
Board members asked about polymers used in dewatering, anaerobic digestion processes, storage capacity for biosolids, public perception challenges, and whether the city has done field sampling to track contaminants. Staff said they have done farm-field sampling and quarterly biosolids sampling, and that further research and grant-funded projects are underway.
