Publication Summary

An announced Class II Inspection was conducted October 3 - 6, 1994 at the Colville City Wastewater Treatment Plant (Colville) in Stevens County, Washington. Large to moderate reductions in BOD5, TSS, TOC, NH3-N, and NO2&NO3-N occurred across the plant. The effluent ammonia nitrogen and chloride concentrations found at mixing zone boundaries, derived from ambient conditions found during the inspection, exceeded state acute and chronic freshwater quality standards. Several problems with plant design and operation were identified, and corrective strategies are suggested.

An announced Class II Inspection was conducted October 3 - 6, 1994 at the Colville City Wastewater Treatment Plant (Colville) in Stevens County, Washington. Large to moderate reductions in BOD5, TSS, TOC, NH3-N, and NO2&NO3-N occurred across the plant. The effluent ammonia nitrogen and chloride concentrations found at mixing zone boundaries, derived from ambient conditions found during the inspection, exceeded state acute and chronic freshwater quality standards. Several problems with plant design and operation were identified, and corrective strategies are suggested.

Effluent concentrations and loads of all permitted parameters were below NPDES permit monthly and weekly average limits. The influent BOD5 load for the October 5 24-hour composite sample exceeded the permit design limit. All whole effluent organic concentrations were within state water quality standards, with the exception of gamma-BHC (Lindane). All metals concentrations were within criteria, with the exception of mercury. Based on inspection conditions lindane and mercury were reduced to below criteria by dilution, but based on projected critical conditions dilution at the chronic boundary would be unlikely to reduce mercury below its water quality criterion. Influent metal concentrations were elevated, and Colville should determine their sources and reduce their discharge to the collection system.