Disinfection Byproducts

Total Trihalomethane (TTHM) MCL Violation

In the past 30 years, the Safe Drinking Water Act (SDWA) has been highly effective in protecting public health and has also evolved to respond to new and emerging threats to safe drinking water. Disinfection of drinking water is one of the major public health advances in the 20th century. One hundred years ago, typhoid and cholera epidemics were common through American cities; disinfection was a major factor in reducing these epidemics.

However, the disinfectants themselves can react with naturally-occurring materials in the water to form byproducts, which may pose health risks. One of these by-products is total trihalomethanes (TTHMs). In June of 2015, the Hanover Water Department exceeded the drinking water standard for TTHMs as established by the Environmental Protection Agency (EPA). That standard is set at 80 parts per billion (ppb). TI1e sample tested in June of 2015 had a TTHM level of 84.3 ppb. As a result, the Town of Hanover has issued a public notice regarding this violation of the EPA standard for TTHMs in our drinking water. Some people who drink water containing TTHMs in excess of the Maximum Contaminant Level (MCL) over many years could experience liver, kidney, or central nervous system problems and increased risk of cancer.

Amendments to the SDWA in 1996 required the EPA to develop rules to balance the risks between microbial pathogens and disinfection byproducts (DBPs). These rules will reduce potential cancer and reproductive and developmental health risks from disinfection byproducts (DBPs) in drinking water. Over 260 million individuals within the United States are exposed to DBPs. The EPA has projected that current SDWA regulations will prevent approximately 280 bladder cancer cases per year. To protect public health, EPA continues to strongly support both the disinfection of drinking water to reduce the risk of waterborne disease and the reduction of disinfection byproducts. EPA has regulated DBPs since 1979 to address health risks posed by a potential association between chlorinated drinking water and cancer, particularly bladder cancer. Current reproductive and developmental health effects data do not support a conclusion at this time as to whether exposure to chlorinated drinking water or disinfection byproducts causes adverse developmental or reproductive health effects, but do support a potential health concern.

The most important thing to know is that this situation is not a public health emergency. The Massachusetts Department of Environmental Protection (DEP) and the Massachusetts Department of Public Health (DPH) have advised us that there is not a need for our residents to use an alternate water supply. However, if you have specific health concerns, you should consult your doctor. The Hanover Health Department has notified health care providers in the community about this issue so they can be prepared to answer any questions you may have.

Correcting the Problem

We have been working to minimize the likelihood of disinfection byproducts in our water for several years.  Our efforts include optimizing our treatment processes to reduce the residual organics in the finished water and the reduction of chlorine in certain phases of our treatment processes.  However, as we stated above, continued chlorine use essential in controlling waterborn diseases.  These efforts have delayed violations of the regulations but have not been enough. Upon learning that one of our THM test sites exceeded EPA standards, we notified the Massachusetts Department of Environmental Protection.  Pursuant to State and Federal Drinking Water Regulations, the Town published the following public notices in the Patriot Ledger and mailed them to Hanover households.

Improvements are Coming

Improvements to all three of the Town's water treatment facilities are currently under construction to reduce disinfection byproducts to acceptable levels.  These improvements include conversion of older chlorination systems to safer liquid based systems, conversion of free chlorine to chloramines through the use of liquid ammonium sulfate, updates to chemical feed and chemical storage systems, upgrades to controls, and the installation of water storage tank mixing systems.  These improvements are expected to come on-line by the late  fall/early winter of 2019.  Please watch this page for further updates.

Click here for frequently asked questions and answers regarding chloramines


Disinfection Byproducts Test Data