Trihalomethanes in Chlorinated Sacramento-San Joaquin Delta Drinking Water Simulated with the EPA WTP-THM Model

by Russ T. Brown, (A.M.ASCE), Jones & Stokes Associates Inc, Street Sacramento, United States,
Doug Brewer, Jones & Stokes Associates Inc, Street Sacramento, United States,
Doug Owen, Jones & Stokes Associates Inc, Street Sacramento, United States,
Zaid Chowdhury, Jones & Stokes Associates Inc, Street Sacramento, United States,



Document Type: Proceeding Paper

Part of: Critical Issues in Water and Wastewater Treatment

Abstract: Trihalomethane (THM) concentrations at a representative water treatment plant simulated with the EPA Water Treatment Plant THM (WTP-THM) model were used to assess potential drinking water quality impacts of a proposed water storage project in the Sacramento-San Joaquin Delta. Bromide and dissolved organic carbon (DOC) are the most important precursor water quality parameters. Bromide and DOC concentrations were estimated from a mass balance transport model of Delta inflows and agricultural drainage sources. The EPA WTP-THM simulation model results were compared with data from a conventional water treatment plant using Delta water as its source. The raw water quality data were used in combination with unit process operating data to evaluate the accuracy of model predictions of THM concentrations. The EPA WTP-THM model was modified to accept 25 years of monthly raw water quality and to automatically estimate the chlorine doses necessary to satisfy requirements for disinfection and predict THM concentrations for each set of raw water quality conditions with the specified treatment process parameters (Jones & Stokes 1992). The impact assessment strategy determined the incremental THM concentrations at a representative water treatment plant resulting from bromide and DOC concentrations changes attributable to the proposed water storage project. The risk of increasing the frequency, magnitude or duration of exceedances of the current EPA THM maximum contaminant level (MCL) standard of 100 μg/1 (and the proposed 80 μg/1 MCL) were determined for each project alternative.

Subject Headings: Water treatment plants | Water quality | Hydrologic models | Trihalomethanes | Water storage | Simulation models | Data processing

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