JAR-TEST EVALUATIONS OF ENHANCED COAGULATION

The proposed Disinfectants/Disinfection By-Products (D/DBP) Rule inclu des a requirement that surface water systems using conventional treatm ent must remove DBP precursors-as measured by total organic carbon (TO C)-in addition to meeting standards for the D/DBPs themselves. TOC rem oval criteria are based on influent TOC and alkalinity (referred to as step 1); however, systems can demonstrate the need for alternative TO C removal performance criteria based on jar-testing (referred to as st ep 2). Tests based on various source waters throughout the United Stat es show that some waters will be able to meet step 1 TOC removal crite ria and that although step 2 analysis is not required, jar testing can be used to determine means of complying with the DBP precursor remova l criteria. In other waters, however, jar tests will be needed to dete rmine a point of diminishing returns (i.e., <0.3 mg/L TOC removal for an incremental dose of 10 mg/L alum) that can be employed in requestin g alternative TOC removal performance criteria.