While Connecticut State Water Quality Standards (WQS) set limits for the total concentration (ppb) of certain industrial compounds in surface waters, the vast majority of chemicals do not have established limits to prevent acute or chronic impacts on aquatic organisms. The National Pollutant Discharge Elimination System (NPDES) program regulates the concentration of individual compounds released by each industrial facility, however the cumulative impact of compounds sharing similar properties (structure-activity relationships) cannot be evaluated without an estimate of total chemical concentration within a given body of water. Using municipal Daily Monitoring Reports (DMR) and industrial Toxic Release Inventory (TRI) data from 1987-1997, a conservative model of annual releases of heavy metals, inorganic nitrogen, acid/bases, aromatics, chlorinted aromatics, chlorinated solvents, and miscellaneous industrial compounds (MIC) was used to estimate cumulative chemical concentrations within the Quinnipiac River.

Model Estimates suggest that the concentration of MICs exceed 0.01 mg/L (10 ppb) in 1987, while the concentration of acrylonitrile - a compound with relatively high toxicity within its class of chemicals - approached the State WQS for safe human consumption of aquatic organisms. The five Publicly Owned Treatment Works - which recieve pretreated wastewater from approximately 35 industrial facilities - are shown to discharge high quantities of heavy metals (Zn and Cu) to the Quinnipiac River, relative to direct industrial dischargers.