Water-quality assessment and wastewater-management alternatives for Dardenne Creek in St. Charles County, Missouri

The quality of water in the 15 mile downstream reach of Dardenne Creek in St. Charles County, Missouri, was assessed to determine if it met the Missouri water quality standards. Concentrations of dissolved oxygen and total ammonia failed to meet water quality standards downstream from the Harvester-Dardenne and St. Peters Wastewater-Treatment Plants. The QUAL-II SEMCOG water quality model was calibrated and verified using two independent data sets from Dardenne Creek. Management alternatives using current, design capacity, and future expansion wastewater discharges from the St. Peters Wastewater-Treatment Plant were evaluated. Results of the computer simulation indicate that a nitrification-type advanced-treatment facility installed at the plant would produce a 5-day carbonaceous biochemical oxygen demand of 10 mg/L. An effluent limit of 5.0 mg/L of 5-day carbonaceous biochemical oxygen demand would further improve the water quality of Dardenne Creek; however, an additional treatment process, such as sand filtration, would be needed to meet this criterion.