High levels of a contaminant known to increase the risk of cancer were found in the town’s water supply last month, violating drinking water standards in an area of North Dartmouth around Reed and State Roads.

According to a letter sent to area residents by the Department of Public Works Water Division, test results at a Reed Road location in August revealed Haloacetic Acid 5 (HAA5) levels of 62 parts per billion, just over the safety standard of 60 parts per billion for that contaminant.

The letter emphasized that the presence of higher levels of HAA5 does not constitute an emergency and residents currently do not need to take any action, although those with compromised immune systems, those with infants, the pregnant or the elderly should speak to a doctor about drinking the water.

“If a situation arises where the water is no longer safe to drink, you will be notified within 24 hours,” the letter reads.

Haloacetic acids are a group of compounds that form as byproducts of disinfection when chlorine reacts with natural chemicals in water. 

HAA5 are five such compounds considered possibly carcinogenic to humans by the US EPA, and may increase the risk of certain types of cancer if consumed over the long term.

According to the Massachusetts Department of Environmental Protection, high levels of exposure to some of the chemicals in HAA5 have also been known to cause adverse developmental and reproductive effects, including toxicity to the liver, kidneys, neurological and reproductive systems.

State law requires drinking water to be tested for HAA5 every three months.

The Water Division noted in the letter sent to residents that the Town of Dartmouth is “working on a comprehensive plan to address HAA5 concerns for several years,” a plan that is expected to be put in place over the next year.