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). A sample tested in June of 2015 had a TTHM level of 84.3 ppb. As a result, the Town of Hanover had 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.

Correcting the Problem

The Town meeting authorized funding to make treatment improvements including 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 were completed in the winter of 2020 and went on-line in the spring of 2020.  We are pleased to report that as expected the improvements have reduced the total trihalomethanes to acceptable levels.

The table below lists the total trihalomthane (TTHM) test results.  

 HFD #3 - 925 Circuit St70 Ponderosa Drive2060 Washington St24 Rockland St, unit 8
1st Quarter 201840515621
2nd Quarter 2018989310372
3rd Quater 2018103102104103
4th Quarter 20181071177313
1st Quarter 201937522225
2nd Quarter 201953507227
3rd Quarter 2019921189583
4th Quarter 201965814352
1st Quarter 202063564532
2nd Quarter 202036412613
3rd Quarter 202024432832
4th Quarter 202042463237
1st Quarter 202118191714
2nd Quarter 20214039508

Compliance with the Federal Safe Drinking Water Act is based on a locational annual running average at a particular test site.  This means that the average of the past four values at any particular site must be below 80 ppb  (parts per billion).  The table below lists the locational running averages for each of the town's four sites.  The numbers in red show the periods in which the locational running average exceeded the federal action level.  Note that all numbers are now well below the action level.

 HFD #3 - 925 Circuit St70 Ponderosa Drive2060 Washington St24 Rockland St, unit 8
1st Quarter 201853733617
2nd Quarter 201859735933
3rd Quarter 201872768355
4th Quarter 201887918452
1st Quarter 201986917653
2nd Quarter 201975886842
3rd Quarter 201972926637
4th Quarter 201962835847
1st Quarter 202068846449
2nd Quarter 202064745245
3rd Quarter 202047553632
4th Quarter 202041473339
1st Quarter 202130372624
2nd Quarter 202131373223

We will continue to monitor the TTHM values from our four test sites on a quarterly basis and will report the results here as they become available.

In addition, whenever water chemistry changes, there is the risk of unintended consequences.  We are monitoring the distribution system for lead and copper as well as nitrates and will report the results here as they become available.  So far all systems are operating as expected. 

Click here for frequently asked questions and answers regarding chloramines


Disinfection Byproducts Test Data