Publication Summary

A Class II Inspection was conducted in July 1992, at the city of Chelan Sewage Treatment Plant in Chelan County, Washington. The Chelan facility is a rotating biological contractor secondary treatment plant with both anaerobic and aerobic digestion of sludge. The plant is unusual in that the primary treatment plant is separated from the secondary treatment plant by several miles. Inspection data found that Chelan was producing a fairly good effluent quality.

A Class II Inspection was conducted in July 1992, at the city of Chelan Sewage Treatment Plant in Chelan County, Washington. The Chelan facility is a rotating biological contractor secondary treatment plant with both anaerobic and aerobic digestion of sludge. The plant is unusual in that the primary treatment plant is separated from the secondary treatment plant by several miles. Inspection data found that Chelan was producing a fairly good effluent quality.

Split samples comparison found relatively small differences between Ecology's and Chelan's analyses. Effluent concentrations were within NPDES permit limits with the exception of fecal coliform and chlorine residual. The facility did not meet the NPDES standard for 85% removal of BOD5. Fecal coliform concentrations were greatly in excess of permit limits. Plant effluent flow exceeded permit limits and influent flow exceeded 85% of the permit loading criteria. Most organic compounds in the effluent were well within both the EPA chronic and acute water quality criteria. Copper and silver exceeded both the acute and chronic EPA water quality criteria for receiving waters, and several other metals exceeded the chronic criteria. Bioassays found no acute toxicity, but the fathead minnow test did indicate slight chronic toxicity. Several recommendations for improved plant performance were made.