The Environmental Protection Agency has fined Groton and Norwich public utilities $7,000 and $8,330 respectively for violating federal clean air laws pertaining to the chlorine gas used in disinfecting public water supplies.

In an announcement Tuesday, the EPA said both utilities will eliminate the use of chlorine gas, make significant upgrades to their water treatment plants and prevent chemical accidents. Both utilities are replacing the chlorine gas with sodium hypochlorite, a safer chemical for water disinfection, the EPA said. Groton Utilities is paying about $449,000 for the upgrade, while Norwich is paying more than $150,000, the EPA said.

Tom Bachey, director of utilities for Groton, said there was no release of chlorine gas there. Rather, the EPA fined the utility after it applied for permits to switch from chlorine gas to sodium hypochlorite. The EPA faulted the utility for having incomplete documentation, among other issues, he said.

The new disinfection system went into service this week, he said.

At Norwich Public Utilities, spokesman Chris Riley said that the violations stemmed from an inspection at the water purification plant in 2012, and that the utility was notified last July. The EPA said the Groton violations also came out of a 2012 inspection.

“The concerns identified by the EPA were largely related to administrative issues, labeling of piping at the plant and record keeping,” Riley said. “At no time was the health or safety of NPU customers in question.”

He said the conversion from chlorine gas to sodium hypochlorite is underway and will “significantly reduce any potential risks” associated with the older process.

The EPA said removing chlorine gas from these utilities “will eliminate the chance of an accidental release ... without compromising water treatment.” Sodium hypochlorite is easier to handle and less hazardous, the EPA said.

Exposure to chlorine gas can be harmful to the eyes, skin and lungs, the EPA said, and high concentrations can be fatal. Inhalation of chlorine at lower concentrations can cause lung inflammation, fluid in the lungs, chest pain and vomiting, according to the EPA.

At the Groton treatment plant, the EPA said it found violations of the risk management regulations related to the storage and handling of chlorine gas. At the Norwich plant, the EPA said it identified a number of violations of the risk management requirement.

As part of their settlements, the Groton and Norwich plants have certified that they have corrected the alleged violations and are now operating the facilities in compliance with Clean Air Act requirements, the EPA said.

j.benson@theday.com

Twitter: @BensonJudy