About 25 to 30% of all United States (U.S.) publicly owned treatment works (POTW) discharges enter estuaries and coastal waters. An expert system has been developed to model the fate and transport of chemicals discharged from POTWs into estuaries. Each POTW has been classified as one of four groups: primary, trickling filter, lagoon and activated sludge in terms of treatment level. The system is designed to calculate concentrations under 7‐d 10‐year low flow, summer low flow and annual mean flow conditions. To account for varying mixing characteristics and salinity distributions observed in a given estuary, the system includes one‐dimensional and two‐dimensional (longitudinal and vertical) mass transport algorithms. To date, the modeling framework has been applied to nine estuaries. For validation purposes, biochemical oxygen demand (BOD) concentrations are also predicted based on industrial as well as municipal organic carbon loads. In several estuaries, predicted in‐stream BOD levels have been compared to measured BOD data resulting in successful model validation. The validated models are then used to predict linear alkylbenzene sulfonate (LAS) concentrations in estuaries. These LAS concentrations are found to be less than 20 μg/L in these estuaries under the three flow conditions.

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