Publication Summary

A Class II Inspection was conducted at the Port of Benton wastewater treatment plant in Prosser, Washington on May 1 2, 1990. The wastewater generated at the plant was treated by a system consisting of settling lagoons, an aerated lagoon, and land application of the effluent on three sprayfields. This discharge is regulated under a state waste discharge permit. Non contact cooling water discharges separately into the Yakima River and is regulated under a NPDES permit.

A Class II Inspection was conducted at the Port of Benton wastewater treatment plant in Prosser, Washington on May 1 2, 1990. The wastewater generated at the plant was treated by a system consisting of settling lagoons, an aerated lagoon, and land application of the effluent on three sprayfields. This discharge is regulated under a state waste discharge permit. Non contact cooling water discharges separately into the Yakima River and is regulated under a NPDES permit.

The aerated lagoon was not adequately pretreating the wastewater prior to slow rate land application. Turbidity, total suspended solids, total nonvolatile suspended solids, and alkalinity were all present in greater concentrations in the effluent stream than in the influent to the aerated lagoon, indicating that minimal treatment was occurring. The effluent stream from the aerated lagoon was characterized as having elevated concentrations of arsenic, lead, zinc, acetone, methyl ethyl ketone, and toluene. The effluent also exhibited high toxicity.

The impact of the waste treatment system was apparent from an inspection of the analytical results obtained from ground water samples collected from two monitoring wells adjacent to the sprayfield area. The downgradient monitoring well typically contained a higher level of solids, some nutrients, and some metals compared to the upgradient monitoring well. Ground water is anaerobic as illustrated by the presence of ferrous iron and the accompanying absence of nitrate. The lagoons are unlined and apparently losing as much as 60% of the wastewater to evaporation and seepage. This may contribute to the observed results.

A second round of sampling was conducted on January 10, 1991, to see if the aerated lagoon sludge and a nearby occurrence of an orange slime (iron bacteria) were hazardous. Another objective was to compare the results of analyzing the metals content of iron bacteria samples from the Seneca facility and a control site. TCLP analysis on these samples showed that although both samples contained some metals in varying concentrations, these were not hazardous. These findings suggest that iron bacteria and the associated metals are not unique to the Seneca facility. Metals associated with the iron bacteria were also not readily available to higher trophic levels.

Installation of additional monitoring wells, dredging of the settling lagoons and aerated lagoon, installation of a lining in the aerated lagoon, and separating the wastewater from two other dischargers (Hogue and Holtzinger) are recommended to provide better treatment of the Seneca effluent generated at this site.