Total organic carbon (TOC) analysis is an important indicator of water quality throughout the drinking water treatment process. Raw source water is progressively treated in chemical coagulation, flocculation, sedimentation, and filtration steps to remove particulate matter and natural organic matter (NOM). Humic acid and fulvic acids contained in the residual NOM of water undergoing disinfection by chlorination react with chlorine to form disinfection by-product compounds such as trihalomethanes (THMs) and haloacetic acids (HAAs), which have been linked to cancer. THMs continue to form during drinking water distribution due to excess chlorine levels required to maintain microbial disinfection.
Disinfectants and Disinfection Byproducts Rule
The U.S. EPA has issued two rules regulating levels of disinfectants and disinfection by-products in drinking water. The Stage 1 Disinfectants and Disinfection Byproducts Rule (D/DBPR) was promulgated in 1998 and took effect on January 1, 2002. This rule lowered permissible levels of trihalomethanes (THMS) to 80 μg/L and regulated levels for five haloacetic acids (HAAs), bromate and chlorite in drinking water for the first time.
The USEPA Stage 2 D/DBPR was promulgated in 2006. Compliance dates for the Stage 2 D/DBPR are phased in over time based upon the number of people served by a water system. The compliance date for systems serving over 100,000 people was April 1, 2012. Systems serving 10,000-49,000 people and less than 10,000 people must be in compliance by October 1, 2013. TOC analysis is an indicator of NOM and THM levels in source water and finished drinking water.