Publication Summary

An announced Class II wastewater inspection of the Moses Lake (Dunes) wastewater treatment plant (WWTP) was conducted April 27-29, 1998. The inspection was conducted in conjunction with a Class II groundwater inspection of the WWTP and in conjunction with Class II wastewater and groundwater inspections of the nearby Basic American Foods facility.

An announced Class II wastewater inspection of the Moses Lake (Dunes) wastewater treatment plant (WWTP) was conducted April 27-29, 1998. The inspection was conducted in conjunction with a Class II groundwater inspection of the WWTP and in conjunction with Class II wastewater and groundwater inspections of the nearby Basic American Foods facility.

The Moses Lake WWTP was performing well during the inspection. Effluent quality was good as measured by conventional parameters of 5-day biochemical oxygen demand (BOD5) and total suspended solids (TSS). The effluent met the permit limit for flow and the design criteria for BOD5 and TSS loading. A recommendation to seek an independent calibration of the flow meter was made.

Ecology Manchester Laboratory analyses of samples collected by Ecology and Moses Lake gave close results for both influent and effluent composite samples, indicating that the collection techniques were comparable. Some discrepancies between Ecology and Moses Lake laboratory analytical results were found. It is recommended that Moses Lake investigate possible causes of low BOD5 results.

Volatile organic analysis compounds were found in low concentrations in the WWTP influent. Of the base-neutral acid extractables (semivolatile organics) (BNA) found in the influent, benzoic acid (143 µg/L est.) was found in the highest concentration. Other than acetone, a probable sampling equipment residue, toluene (0.13 µg/L est.) was the only volatile organic analysis (VOA), found in the influent. Four BNAs were found in the effluent sample. Benzoic acid (3.1 µg/L est.) was the BNA found in the highest concentration. All VOAs and BNAs found in the effluent sample were in concentrations below applicable state groundwater quality criteria. Bis(2-ethylhexy)phthalate in the effluent sample (2.1 µg/L) was found at a concentration 35% of groundwater quality criteria. A recommendation is made to initiate organic analyses of Moses Lake groundwater monitoring well samples and to continue monitoring organic compounds in the Moses Lake WWTP effluent.

Arsenic, copper, lead, silver, and zinc were detected in the effluent composite sample. Because lead and zinc were found in the transfer blank in concentrations close to those found in the effluent sample, the finding of lead and zinc in the effluent may be false. All metals detected in the effluent were found in concentrations below Washington state water quality criteria for groundwaters.