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Stonington finds large source of river water entering sewer system

Stonington — The Water Pollution Control Authority has identified and now blocked a pipe in Old Mystic that was allowing a large amount of Mystic River water to enter the sewer treatment system.

The authority has been grappling with increased flows into the Mystic sewer plant which have resulted in the town placing a moratorium on new sewer hookups in Mystic because the plant had reached the limit of sewage it is allowed to process set by its permit. 

The plant's permitted treatment capacity is 800,000 gallons per day but at times it has exceeded 900,000.

The authority has completed the initial phase of an inflow and infiltration study and is set to begin phase two, which is designed to determine the specific sources of the water entering the system.

Authority Director Douglas Nettleton said a few weeks ago the authority had a "positive turn of events" when it analyzed some metering data from 28 homes off Main Street in Old Mystic. That led the authority to discover an open 6-inch pipe that was allowing a "significant" amount of water to enter the sewer system during high tides and storms.

He said the authority blocked the pipe on Nov. 2  and is analyzing the current flows to help determine exactly how much water had been getting into the system from the pipe. He said that review could take a few months.

Nettleton estimated the outside flow could have been between 30,000 and 100,000 gallons per day. The identification and blocking of the excess flow eventually could allow the town to lift the moratorium and add sewer hookups for new homes and businesses.

While Nettleton said the authority is glad to have identified the source of the water in Old Mystic, he stressed there may be other leaks that have not yet been identified.

Among the possible sources of the additional flow into the plant are the increased number of people visiting Mystic, homes that illegally use sump pumps to discharge flood water into the sewer system and infiltration of ground water into existing pipes that then has to be treated at the plant.


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