OXFORD — The Aquarion Water Company is facing a $13,500 fine from the Massachusetts Department of Environmental Protection for violating drinking water regulations at its water treatment plant in Oxford.

The company investigated after a customer complained of a rash that broke out after a shower, the DEP said in a news release. The investigation determined that an equipment malfunction had caused eight gallons of undiluted potassium hydroxide to flow into a pipe at the North Main Street water treatment plant. 

"Providing safe, high-quality water to our customers is our highest priority. When this incident occurred in June 2021, our operations staff took immediate action to resolve the issue within hours," said John Walsh, vice president of operations at Aquarion. "We’ve also replaced equipment and enhanced procedures to ensure safe, reliable operation of the water treatment facility."

Potassium hydroxide is added to drinking water at the treatment plant to increase the water's pH, for corrosion control purposes. In Oxford, the pH level of drinking water is typically between 7 and 7.5.

The pH level was 10 at the customer's home and as high as 11 at another location in the distribution system. A pH value at or above 11 can cause skin and eye irritation, or possible "exacerbation of skin disorders," the DEP said. 

The potassium hydroxide overfeed, the DEP said, was due to a malfunction of a valve. The water treatment plant then failed to detect the elevated pH levels in the water. 

The valve and pH probe have been since been replaced, the DEP said. 

According to the DEP release, the company also took "corrective measures" immediately after discovering the elevated pH levels by calling affected customers, as well as flushing the distribution lines.

As part of a consent order signed with MassDEP, Aquarion must pay the penalty and hire a company to conduct an evaluation of all existing critical chemical feed systems at its plants in Oxford and Millbury.

Aquarion must also hire a company to review and update its standard operating procedures for its existing critical chemical feed systems to, "ensure its pH analyzers are properly managed and calibrated to measure a minimum pH of 10." It must also maintain a log documenting all alarm tests and equipment maintenance. 

“Proper operations and maintenance of components to critical chemical feed systems such as a pH analyzer at water treatment facilities are essential to ensure the delivery of safe drinking water to its users,” said DEP Central Regional Office Director Mary Jude Pigsley in the release. “It is important to test the components routinely and document those test results to ensure the safety system works as intended.”