Disinfection Byproducts

When chlorine is added to the water to kill bacteria and other microorganisms, the chlorine reacts with organic material naturally found in all rivers, lakes, and ground water. These reactions can produce disinfection byproducts, some of which may lead to increased health risks if exposed to over many years. EPA set maximum contaminant levels (MCLs) of 80 parts per billion (ppb) for total trihalomethans (TTHMs) and 60 ppb for five haloacetic acids (HAA5). These MCLs are based on an annual average. EPA determined the health-risk is more related to long-term exposure and, therefore, uses annual averages for the MCLs.

In November 2000, DCWASA began delivering water with chloramines, instead of chlorine, to reduce the amount of disinfection byproducts in the water. The treatment change caused a significant drop in the TTHM and HAA5 concentrations.

EPA requires testing every 3 months, or quarterly. The graph below displays the annual averages reported to EPA for the last five monitoring periods. The annual average is calculated using the data from the given quarter and the three previous quarters.

TOP