Do Natural Chloride Gradients Affect the Formation of Disinfection By-Products in Public Water Supplies?

Abstract:
Disinfection by-products (DBP) are chlorinated or brominated compounds representing the reaction of the halogens with natural organic matter (NOM) in the water. These compounds in drinking water are themselves a health concern. We have preliminary evidence that the formation of DBPs is associated with environmental gradients, such as chloride, in source waters. The hypothesis is that natural chloride (and other marine halides) predisposes NOM in the source water to become a particular type of DBP in the finished water. We propose to test this hypothesis by analyzing the chemical associations between NOM, halides (Cl and Br), and DBP along a 350 km long gradient from coastal to interior drinking water
supplies. Our hypothesis, if supported, would affect the management of water supplies, and potentially alter how source water is processed. The understanding and control of DBPs is the single biggest compliance challenge facing small to medium-sized water utilities in the near future (USEPA, 2001).

Critical Regional Need
Water is disinfected to control pathogens and protect public health, but the disinfection process can form other compounds that are themselves a health concern. Disinfection by-products (DBPs) are chlorinated or brominated compounds, tri-halomethanes (THM) and halo-acetic acids (HAA) that are formed by disinfection chemicals reacting with natural organic matter (NOM) in the water. The EPA has set maximum contaminant levels for specific compounds (USEPA, 2001). The detection of DBPs in public water supplies is nearly universal (USEPA, ICR database, http://www.epa.gov/enviro/html/icr/index.html).

January 2004 marked the start of the compliance cycle for small drinking water systems serving <10,000 customers (40 CFR Parts 9, 141, 142). The majority of 2,200 water systems in Maine, and in many other states, fall in this size range. During 2004, these small systems will start monitoring for disinfection by-products and in 2005 they will need to have instituted control measures. However, there are numerous variables that contribute to the formation of DBPs, and not all are well understood (USEPA, 2001). The presence of natural factors that affect the formation and type of DBPs will have a significant effect on the types of management techniques employed. The understanding and control of DBPs is the single biggest compliance challenge facing water utilities in the near future. Public water utility managers in Maine have requested help to understand how DBPs are forming in their systems so that they can best manage their risks.