Waste-Assimilation Capacity of the Arkansas River in Pueblo County, Colorado, as it Relates to Water-Quality Guidelines and Stream Classification

摘要

Waste-assimilation capacity of a 42-mile reach of the Arkansas River in Pueblo County was evaluated using a one-dimensional steady-state water-quality model calibrated and verified using hydraulic and water-quality data collected in 1976 and 1979. The water-quality constituents modeled were 5-day carbonaceous biochemical oxygen demand, total organic nitrogen, total ammonia, total nitrite, total nitrate, and dissolved oxygen. The model was used to simulate water-quality effects of 63 combinations of wastewater treatment, based on a 7-day low flow with a 10-year recurrence interval that occurs between August 15 and October 15 and on a winter low-flow period that occurs as a result of upstream storage of water. Evaluation of the mixing zone downstream from the Pueblo Wastewater Treatment Plant determined that complete lateral mixing of the effluent occurred 2.7 river miles downstream. Model simulations indicated some guidelines of constituents would be exceeded with projected effluent discharges and projected wastewater-treatment possibilities.