Water disinfectant switch will be ready by the spring

Jan 7, 2020

A switch in how Dartmouth treats its municipal water supply is on its way this spring, which town officials hope will solve a series of drinking water standard violations issued by the state over the past few years. 

Work is currently underway to switch the chemical the town uses to disinfect municipal water from chlorine to chloramine. The conversion process began in June, but with three water treatment plants and several different sources of municipal water, the process is taking longer than expected. 

The goal of the switch is to eliminate the presence of trihalomethanes (TTHMs) and haloacetic acids (HAAs) in the town’s water supply. The town was issued drinking water standard violations in in 2013, 2016, and 2019 after levels above the state standards were discovered.

According to the Massachusetts Department of Environmental Protection, these two chemicals, when consumed over a long period of time at levels well above state drinking water standards, may increase a person’s risk of certain types of cancers. However these links are not certain and still being researched.

Both chemicals are referred to as “disinfection byproducts,” which are formed when the chlorine used to disinfect the town’s water reacts to naturally occurring organic materials within the water supply. 

According to Director of Public Works David Hickox, nothing about Dartmouth’s water quality changed, but rather testing standards. He stressed that as of right now the water is safe to drink. Residents do not need to boil their water, or seek expensive water purification methods. When the town violated the drinking water standards, the department was required by law to issue notifications informing residents about it. 

“The intent of these notifications is to let residents know we’re aware of the violations, and we’re addressing it,” Hickox said. 

The change in drinking water standards which prompted the first letters came in 2012, when the town became subject to new regulations governing maximum containment levels of TTHMs and HAAs. 

In 2013, shortly after the new regulations took effect, the town was issued a violation of the TTHM standard, after testing at a 16” water main on Reed Road revealed levels at 86 parts per billion. The new state standard is 80 parts per billion. 

The water main affected ran below Reed Road and ended near Harvey Building Products. With few users, it is one of what Hickox calls “dead ends” in the system: Low-use and large-volume water mains with water flows which may slow, increasing the risk of TTHMs accumulating. 

“It is a large main with low demand, making it a perfect setting for TTHMs,” Hickox said.

In response, the town implemented a number of changes to fix the issue. The most expensive was a $1.4 million project to eliminate the “dead end” on the Reed Road water main. 

Despite that work, the town again received a violation, this time for testing done at the end of Allen Street which revealed TTHM levels at 82 parts per billion. The town responded by monitoring TTHMs monthly, and after testing, decided to add new technology to the town’s water tanks. 

In 2019, the town began the process of switching the town’s water supply to chloramine.

“Chloramine is essentially chlorine with added ammonia,” Hickox said. “It’s a disinfectant too and it appears to be the direction many communities throughout the country are going to. The important thing is it does not generate disinfection byproducts.” 

Preparations for the switch are ongoing at three of the town’s water treatment plants, with an anticipated springtime deadline to make the switch official.

Before making the switch, Hickox said a priority for the department and the town is ensuring everyone is kept in the loop about what is going on. Informational packages and updates about the process will be distributed. 

“We’ll be getting out public information about the conversion before it occurs,” Hickox said. 

The most recent drinking water standard violation was in 2019, after the decision was made to switch the town’s water supply to chloramine treatment.