LISBON — The Maine Center for Disease Control and Prevention has issued a violation notice to the Lisbon Water Department following a crisis last week that left residents without safe drinking water for an entire day. 

The agency on Friday provided to the Lisbon Water Department the results of arsenic testing of the sludge sample taken from a separate part of the water treatment tank — known as the decant tank — following last Wednesday’s accidental release into the water system. 

“Laboratory testing of the sludge sample identified arsenic at 35.4 milligrams per liter (mg/L) or 35,400 parts per billion,” according to a the news release. “Although the arsenic levels in the undiluted sludge sample results are high, they do not represent the arsenic levels in the water of those served by the Lisbon Water Department on the day of the release last week. 

Last Wednesday’s accidental release of sludge mixed with clean, treated water and was diluted before entering the Lisbon Water Department’s distribution system, the release said. “This sludge sample taken from the water treatment decant tank reflects what was present in the treatment system — prior to filtration which is designed to remove arsenic before the water is distributed.” 

On Thursday, upon learning of the accidental release, the Maine CDC Drinking Water Program directed the Lisbon Water Department to issue a do-not-drink order for customers of the water department, which includes Lisbon, Lisbon Falls and Lisbon Village.  

Following that order, the Maine CDC’s Drinking Water Program worked with the Lisbon Water Department to take samples of drinking water to test for potential arsenic contamination in the town’s public drinking water system, according to the release.  

The State’s Drinking Water Program received those test results Aug. 30, which showed the presence of arsenic at 1-3 parts per billion, well below the U.S. Environmental Protection Agency’s requirement of no more than 10 parts per billion for public drinking water systems. 

The Maine CDC advised the Lisbon Water Department to lift the do-not-drink order that same day as the public drinking water was deemed safe to consume. 

“Following the release of the sludge and subsequent testing, the Maine CDC also conducted syndromic surveillance,” according to the release. “No apparent cases of acute arsenic poisoning were identified and there were no indications of an increase in the number or frequency of visits to hospitals involving relevant symptoms from residents served by the Lisbon Water Department during or following the accidental release. This data indicates that any potentially elevated levels of arsenic levels in the public drinking water supply shortly after the release were not high enough to result in obvious acute poisoning cases.” 

The Maine CDC is now requiring Lisbon water officials to work with an engineering firm to evaluate the existing treatment system and improve process controls to prevent a similar event from occurring in the future. Additional arsenic testing of Lisbon’s public drinking water supply will take place on a more frequent basis through at least the end of this year, according to the release. 

As a result of the accidental release and the lack of notification by the Lisbon Water Department to the Maine CDC’s Drinking Water Program, the Maine CDC has issued a violation notice to the Lisbon Water Department. 

It was not immediately clear what the violation notice will entail. 

The Maine CDC’s Drinking Water Program and the Maine Rural Water Association have been onsite in Lisbon, according to the release, and are providing technical assistance to the Lisbon Water Department to ensure the safety of the public drinking water supply.