Publication Summary

Un-ionized ammonia concentrations in the South Fork Palouse River (SFPR) at Pullman often exceed state water quality standards. Effluent from publicly-owned treatment works (POTWs) from the cities of Moscow and Pullman comprises most of the river flow during July-November of a typical year, and during any month of the year for design low flows. The Albion POTW makes up a relatively small fraction of the total river flow.

Un-ionized ammonia concentrations in the South Fork Palouse River (SFPR) at Pullman often exceed state water quality standards. Effluent from publicly-owned treatment works (POTWs) from the cities of Moscow and Pullman comprises most of the river flow during July-November of a typical year, and during any month of the year for design low flows. The Albion POTW makes up a relatively small fraction of the total river flow.

Ecology ambient monitoring Station 34B110 was recommended for developing design conditions for temperature and pH in combination with data collected by Pullman POTW upstream and downstream from the POTW outfall, and by Ecology during wateryear 1992 in Paradise Creek at the state line. Semi-annual total ammonia criteria for Paradise Creek at the state line were proposed based on design conditions for temperature and pH, and regressions with Ecology Station 34B110.

Total maximum daily loads (TMDLs) for ammonia were established for critical points in the SFPR. Waste load allocations for POTWs, load allocations for nonpoint sources, and a margin of safety were factored into the analysis. Semi-annual and monthly periods for permitting were evaluated. Exemptions from mixing zone size limits were also considered. Four alternatives were considered for evaluating TMDLs: monthly and semi-annual limits, each with and without mixing zone size restrictions. Semi-annual limits were recommended instead of monthly limits for administrative simplicity. An engineering analysis of the treatment process is recommended to determine feasibility of operational changes or improvements required to meet the proposed ammonia limits. Comparison of proposed limits with 1991 data from Pullman POTW suggests that the proposed limits could be achieved. Permit limits for effluent ammonia for the Albion POTW may be unnecessary during February and March, but may be required during April and May.