AWWA WQTC63961

This paper presents an analysis of nine years of Total Trihalomethane (TTHM) and haloacetic acids (HAA5) data for 76-88 utilities in the state of Missouri for the years 1997-2005. Although these results show that since 2001, TTHM and HAA5 concentrations have decreased significantly, many plants are still in violation of the maximum contaminant levels. The month in which the maximum concentration of these disinfection byproducts occurred in the samples varied widely throughout the year, and from year to year, for most utilities. Small systems continue to have greater TTHM and HAA5 concentrations, and to have greater difficulty in achieving regulatory compliance. A majority of both TTHM and HAA5 appear to be formed within the treatment plant, even though significant increases in both concentrations are observed in distribution systems. Use of monochloramine in distribution systems was correlated with significantly lower TTHM and HAA5 concentrations in large systems, but not for small systems. Higher raw and finished total organic carbon concentration both correlated with significantly higher TTHM and HAA5 concentrations. Compliance with the enhanced coagulation requirements was observed to be better for large systems (>10k) than for small systems (<10k). For small systems, the utilities in compliance with enhanced coagulation requirements had lower TTHM and HAA5 concentrations than the utilities out of compliance, though a similar trend was not observed for large systems. Includes 14 references, table, figures.