Publication Summary

A series of Class II Inspections was conducted at three municipal wastewater treatment plants (WTPs), one industrial WTP, and four fish farms in the Chehalis River basin over a period of one year beginning in August 1991.

A series of Class II Inspections was conducted at three municipal wastewater treatment plants (WTPs), one industrial WTP, and four fish farms in the Chehalis River basin over a period of one year beginning in August 1991. Centralia, Chehalis, and Darigold employ trickling filters, while Pe Ell uses an oxidation ditch. Each fish farm typically consists of rearing ponds and a settling basin. All facilities were operating reasonably well at the time of inspection, and met effluent discharge limitations with the following exceptions: 1) Centralia WTP did not meet the requirement of 85% removal for five-day biochemical oxygen demand (BOD5) and total suspended solids (TSS) on August 26-27, 1991; 2) Chehalis effluent had high levels of residual chlorine; 3) Pe Ell WTP's removal efficiency for BOD5 was marginally less than the 85% requirement, and the design flow was exceeded; and 4) Darigold WTP failed to meet permit limits for fecal coliform, residual chlorine, and TSS concentration, and BOD5 and TSS loadings in effluent were excessive. A mixing zone evaluation may be required to confirm that dilution is sufficient to prevent ammonia, chloride, and chlorine toxicity at Darigold WTP. Centralia, Chehalis, Pe Ell, and Darigold WTPs all had assorted problems with sampling and lab procedures. Other recommendations for these facilities are included in this report. Effluents collected from the four fish farms met NPDES permit limits for settleable solids and TSS.