Norwich ― Norwich Public Utilities hopes to stop millions of gallons of rainwater-created sewage discharges from flowing into the Shetucket River after receiving a $4.4 million grant and loan.

The state Department of Energy and Environmental Protection announced the funding Tuesday, listing Norwich’s ongoing $200 million sewage treatment plant upgrade among the top priorities for its $500 million allocation from the federal Clean Water Fund.

NPU will receive $4.4 million ― 50% in the form of a grant and 50% as a 2% loan ― to insert liners into some of the city’s oldest sewer pipes. NPU hopes to line about 28,000 feet of sewer pipes that date from 1885 to 1950.

The old clay, brick or concrete pipes have deteriorated or become clogged with sediment over the decades, said Larry Sullivan, NPU’s water division integrity manager. The pipes have become porous, allowing rainwater and groundwater to infiltrate them. In some cases, the pipe bottoms have worn away completely.

When the city is inundated with rain, millions of gallons of combined rainwater and untreated wastewater dump into the Shetucket River, which flows into the Thames River and eventually to Long Island Sound. About 99% of the discharge is rainwater and 1% untreated sewage, according to information provided by NPU.

The success of a new pipe liners that keep out rainwater and groundwater is evident in Greeneville, NPU officials said. NPU lined 6,000 feet of pipes in the urban neighborhoods in 2018.

In 2018, 66 inches of rain resulted in 31.2 million gallons of overflow discharged to Shetucket River. In 2023, 63 inches of rain resulted in 9.5 million gallons of overflow discharged to Shetucket River, NPU spokesman Chris Riley said.

NPU General Manager Chris LaRose said NPU hopes the $4.4 millon will be enough to line the remaining 28,000 linear feet of aging pipes in Greeneville. The project is expected to be put out to bid in late 2025, with construction starting in early 2026.

Another benefit of the new technology is in its name: “trenchless technology,” which requires very little digging and much less traffic disruption, LaRose said.

A heated plastic, coated with an exterior of felt and fiberglass, is blown into the pipe, like a balloon, until it completely lines the pipe. The felt and fiberglass layer hardens, forming a new pipe within the old structures.

The project area will run from the streets surrounding St. Joseph Cemetery, down Golden Street, Central Avenue, North Main Street and many connecting side streets.

Riley said NPU will continue to seek funding to eliminate additional overflows into the Shetucket and Thames rivers.

LaRose said after Greeneville, the next priority areas will be Laurel Hill-Route 12 and Thamesville-Route 32 areas and side streets.

Without the federal Clean Water Fund grants and loans, NPU was pursuing the upgrades slowly, budgeting $500,000 per year for the work.

“The projects on the Priority List will reduce the frequency and severity of sewage overflows,” DEEP Commissioner Katie Dykes said in a news release announcing the funding awards, “and provide more enhanced treatment of excess nutrients that will improve the water quality of our rivers and the Long Island Sound.”

c.bessette@theday.com