Maine CDC Announces Results of Lisbon Water Department Sludge Sampling

AUGUSTA- The Maine Center for Disease Control and Prevention (Maine CDC) today provided to the Lisbon Water Department the results of arsenic testing of the sludge sample taken from a separate portion 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. 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 to was diluted before entering the Lisbon Water Department's distribution system. 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 issuance, 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. The State's Drinking Water Program received those test results on August 30, 2024, 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. 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 requiring the Lisbon Water Department 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.

As a result of this 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.

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