Publication Summary

An announced Class II inspection was conducted June 3-5, 1996 at the Clark County Salmon Creek Wastewater Treatment Plant (Salmon Creek) north of Vancouver, Washington.

An announced Class II inspection was conducted June 3-5, 1996 at the Clark County Salmon Creek Wastewater Treatment Plant (Salmon Creek) north of Vancouver, Washington.

Influent characteristics were generally similar to other typical treatment plants. Good reductions in BOD5, TOC, and TSS occurred across the Salmon Creek treatment plant. Ammonia nitrogen removal was less effective and its effluent concentration was relatively high. Verification of permitted dilution factors previously modeled for the outfall using UDKHDEN was not possible, and new estimates of dilution factors were derived using estuary regulatory boundaries and the 3PLUMES dilution zone model. The whole effluent ammonia nitrogen concentration was expected to be reduced to below water quality criteria using the new dilution factors derived for the three-riser diffuser configuration in place during the inspection. Dilution factors derived for the current five-riser diffuser configuration suggest that the maximum allowable chronic whole effluent ammonia nitrogen concentration would be exceeded by the effluent ammonia nitrogen results found during the inspection.

The 24-hour composite BOD5 and TSS concentrations were well within the NPDES weekly and monthly permit limits. All other inspection results were also within applicable effluent limits and influent overloading limits. Detected whole effluent priority pollutant organics and metals concentrations were generally within water quality criteria, with the exception of gamma-BHC, copper, and lead which all exceeded the chronic criteria. Dilution at the edge of the chronic boundary is expected to reduce these concentrations to within the criteria. The Salmon Creek effluent chronic fathead minnow bioassay indicated toxicity at low concentrations, and a reasonable potential exists for chronic conditions in the receiving water. Additional bioassays are recommended. Effluent TSS and BOD5 results were very similar for split sample results. Fecal coliform concentrations in Salmon Creek sludge exceeded the pathogen limits of Class A land application requirements, and it is recommended that these concentrations be reduced for this level of use. Organic and metal concentrations were well within both EPA land application concentration limits and state dangerous waste regulation designation criteria.