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Disinfection Byproducts

This is part of our series where we are taking a closer look at the 2015 Water Quality Report. Today we are talking about disinfection byproducts (DBP) and how they are formed. There are many types of DBP including TTHM (trihalomethane), HAA5 (haloacetic acid), bromate and chlorite.  In all there are 9 types of DBP and 5 are regulated by the North Carolina Department of Environment and Natural Resources (DENR) through rules prescribed by the U.S. Environmental Protection Agency (EPA) under the federal Safe Drinking Water Act.

According to public health officials, the regulations were established because laboratory animal testing indicates high consumption of some DBPs over an extended period of time (equivalent to 20 – 30 years in humans) seems to be associated with a higher risk of some types of liver and kidney cancers in those animals.  However, continued research has shown inconsistent results.  The International Agency for Cancer Research and the World Health Organization have concluded there is not enough evidence to prove that DBPs pose a health risk to humans.  Nonetheless, U.S. EPA has made DBP regulations more stringent several times, most recently in 2012/2013.

Since we use chlorine to disinfect our water, TTHMs and HAA5s may be present. DBPs form when chlorine reacts with natural organic matter present in water. THM levels increase over time if the water is not used and also increase as temperatures rise. So, the highest THM levels are generally found during the hottest summer months in the parts of the water distribution system that are the farthest distance from the treatment plants where the water has been in the pipes for the longest amount of time.

It is a constant challenge our staff face. State certified operators continuously monitor water quality to determine the amount of chlorine necessary to inhibit bacteria growth, while limiting the formation of DBPs.   Staff uses various methods to ensure that your water is disinfected and THM/HAA5 levels are tested throughout the distribution system. To reduce water age we flush so that fresh water gets to your door.

During the summer of 2015, there were elevated levels of bromide in our source water (Mt. Island Lake and Lake Norman). Those elevated levels of bromide caused elevated levels of THMs in our distribution system. Though we never violated state or EPA water quality standards, we made the test results public via a press conference. Bromide levels have decreased and DBP has returned to normal levels in 2016.

THM

2015 Data