Publication Summary

Located in northeastern Washington State, the Colville River watershed lies within the Selkirk Mountains between the Pend Oreille and Columbia rivers. The Colville watershed is about 50 miles long and 25 miles wide, with a north to south orientation. The Colville River begins at the confluence of Sheep Creek and Deer Creek in southern Stevens County. Along its course the river passes through the cities of Chewelah and Colville, eventually discharging near the town of Kettle Falls to Franklin D. Roosevelt Lake, an impoundment of the Columbia River behind Grand Coulee Dam.

Colville River discharge is driven by a snow-melt regime. The high-flow period is in the spring as a result of melting of the previous winter snow pack, in combination with spring rainfall. April is the highest month for discharge, while August is the lowest. Although the major focus of the TMDL study is on point sources of pollution, nonpoint sources are considered, but only as loads from the headwaters and tributaries entering the Colville River. Ammonia concentrations in the river are highest immediately downstream from the Chewelah and Colville WWTP discharges. Modeled concentrations at the Colville WWTP mixing zone exceeded the acute water quality standards for ammonia and chlorine (Hoyle-Dodson, 1994). Ammonia concentrations decrease proceeding downstream from the WWTPs due to algal uptake and nitrification.