Trihalomethanes (THM)are formed as a by-product predominantly when chlorine is used to disinfect water for drinking. THMs are formed mainly in the distribution system or pipes bringing the water to your home and do not come from the wells or the treatment plant providing your drinking water. They represent one group of chemicals generally referred to as disinfection by-products. They result from the reaction of chlorine or bromine with organic matter present in the water being treated. The THMs produced have been associated through epidemiological studies with some adverse health effects. Many governments set limits on the amount permissible in drinking water. However, trihalomethanes are only one group of many hundreds of possible disinfection by-products—the vast majority of which are not monitored—and it has not yet been clearly demonstrated which of these are the most plausible candidate for causation of these health effects. In the United States, the EPA limits the total concentration of the four chief constituents (chloroform, bromoform, bromodichloromethane, and dibromochloromethane), referred to as total trihalomethanes (TTHM), to 80 parts per billion in treated water. The current amount was lowered in 2003 from 100 parts per billion.
Starting in the second quarter of 2012 ONWASA began sampling under a new protocol for THM as directed by the EPA and North Carolina Division of Environment and Natural Resources (DENR). This new protocol now looks at the running average of each individual site instead of all the sites averaged as a whole. This site located at the very end of White Oak River Road had a 4 quarter annual running average that exceeded the Maximum Contaminant Level (MCL). This means that 4 individual samples collected every 3 months when averaged together produce a number over the MCL. It was the August sample of 2013 when averaged with the preceding 2012 and 2013 samples that put ONWASA in violation. Previous 2012 samples indicated the site was not in exceedance at that time. ONWASA was notified January 17, 2014 of the violation. ONWASA takes every precaution to minimize the levels of Disinfection By-Products in the distribution system. Because there are many factors that affect the levels of THMs such as temperature, time the water is in the distribution system (age),and chlorine levels, the levels of THMs can change for one month or even from one day to the next. ONWASA has placed automatic flushing devices at strategic points in the distribution system to pull fresh water into the outer ends of the system where Trihalomethanes are most likely to occur. The site that exceeded the standard for THMs has several of these flushing devices and ONWASA continues to monitor their performance to ensure we are maintaining fresh water at this site. We also perform daily chlorine monitoring to maintain levels sufficient for disinfection and to minimize creation of Disinfection By-Products. State mandates chlorine levels be maintained between 4.00 mg/l to 0.20 mg/l and ONWASA's average for the system is 0.80 mg/l.
ONWASA reports the ranges of detection for THMs every year in the Consumer Confidence Report to better inform the customer of what these levels are in the system. If you do not receive these reports every year please notify our office or go on line to view the report at http://www.onwasa.com/143/Reports.
Some people who drink water containing total trihalomethanes in excess of the MCL over many years could experience liver, kidney, or central nervous system problems and increased risk of cancer. Contamination levels are measured using Maximum Contaminant Levels (MCL’s), which are set at very stringent levels. To understand the possible health effects described for many regulated constituents, a person would have to drink 2 liters of water every day at the MCL level for a lifetime to have a one-in-a-million chance of having the described health effect.
For more information on Trihalomethanes and other water quality issues please visit the EPA’s web site by clicking below.
