AWWA WQTC60736

In 2002, the Disinfectants/Disinfection Byproducts (D/DBP) Rule affected surface water treatment plants serving at least 10,000 people. The rule required staff at conventional treatment plants to begin monitoring for total organic carbon (TOC). Staff at smaller plants also started monitoring for disinfection byproducts, TOC and other parameters in the first quarter of 2004. Additionally, the D/DBP Rule contains provisions for TOC removal through the conventional treatment processes. Because these monitoring and removal requirements are a vital part of regulations affecting numerous water suppliers across the nation, TOC is now used as the primary surrogate for the determination of precursors to disinfection byproduct formation. These same water suppliers must comply with maximum contaminant levels for total trihalomethanes (TTHM) and haloacetic acids (HAA5), both of which are implicated as having long-term, adverse health consequences. Up until now, few large-scale studies have analyzed the data collected during the first two years of the D/DBP Rule, and fewer still have compared treatment plant TOC data to TTHM and HAA5 data collected from the distribution system. In Pennsylvania, compliance data for TOC, TTHM and HAA5 is available from 73 surface water systems using a total of 85 conventional filtration plants, covering the first two years of monitoring under the D/DBP Rule. The data was gathered from a regulatory reporting database housed at the Pennsylvania Department of Environmental Protection. This compliance data was then compiled and analyzed to examine the relationships between TOC concentrations at the plants and TTHM/HAA5 formation in the distribution system. In addition, an analysis was completed on 8 plants with the highest and lowest finished water TOC concentrations out of the 73 systems in Pennsylvania. Finally, three plants in southeastern Pennsylvania were examined more closely to study the effects of enhanced coagulation on the levels of TTHM and HAA5 in the finished water. When comparing data from the 73 water systems, the authors observed no apparent correlation between either raw or finished water TOC and TTHM concentrations over much of the range of TOC values examined in this study. In addition, they found no apparent correlation between TOC and HAA5 over the entire range of TOC values. Examining data from the 8 plants with the highest and lowest average TOC concentrations in the finished water showed no group relationship with TTHM or HAA5 levels in the distribution system. Of the three treatment plants studied in detail, all were able to improve TOC removal through the plant as a result of enhanced coagulation. Enhanced coagulation processes reduced TTHM levels but not HAA5 levels. Overall, this study found no universal relationship that can be used to predict disinfection byproduct formation in the distribution system based on TOC values in the source water or finished water. While such a relationship may be possible at an individual water system, the relationship would have to be established empirically on a system-by-system basis. Includes tables, figures.