A one-dimensional, steady-state, dissolved-oxygen model and waste-load assimilation study for Clear Creek, Monroe County, Indiana

Abstract

The Indiana State Board of Health is developing a State water-quality management plan that includes establishing limits for wastewater effluents discharged into Indiana streams. A digital model calibrated to conditions in Clear Creek was used to develop alternatives for future waste loadings that would be compatible with Indiana stream water-quality standards defined for two critical hydrologic conditions, summer and winter low flows. The Winston Thomas wastewater-treatment facility is the only point-source waste load affecting the modeled segment of Clear Creek. A new wastewater-treatment facility under construction at Dillman Road (river mile 23.78) will replace the Winston Thomas wastewater-treatment facility (river mile 16.96) in 1980. Natural streamflow during the summer and annual 7-day, 10-year low flows are zero, so no benefit from dilution is provided. The model indicates that ammonia-nitrogen toxicity is the most significant factor affecting the stream water quality during summer and winter low flows. The ammonia-nitrogen concentration of the wastewater effluent exceeds the maximum total ammonia-nitrogen concentrations of 2.5 milligrams per liter for summer months (June through August) and 4.0 milligrams per liter for winter months (November through March) required for Indiana streams. Nitrification, benthic-oxygen demand, and algal respiration were the most significant factors affecting the dissolved-oxygen concentration in Clear Creek during the model calibration. Nitrification should not significantly affect the dissolved-oxygen concentration in Clear Creek during summer low flows when the ammonia-nitrogen toxicity standards are met. Carbonaceous biochemical-oxygen demand is probably not a significant factor in the dissolved-oxygen dynamics of Clear Creek because most of the carbonaceous biochemical-oxygen demand was estimated to be removed through settling or some other process. The 5-day biochemical-oxygen demand of the effluent from the new wastewater-treatment facility at Dillman Road will be limited to 5 milligrams per liter after the implementation of advanced-waste treatment in 1980.