Critical Edgartown sewer main showing its age

A long and critical sewage main in Edgartown that is nearing the end of its life expectancy has broken twice in the past two years, prompting wastewater department officials to request nearly $5 million to replace the mile-long pipe.

Wastewater officials say the most recent break occurred about two weeks ago at the intersection of Chase Road and West Tisbury Road. The leak from a small hole in the pipe compromised the safety of the road above, and also led to some unpleasant odors, with raw sewage leaking out.

The funding request also arrives as the wastewater department is asking for about $3 million to start undergoing preliminary design work on the town’s 20-year wastewater plan, a massive infrastructure project intended to clean up nitrogen from the town’s watersheds.

Ian Catlow, a consultant for the town’s wastewater department and technical director at engineering firm Tighe and Bond, was before the Edgartown Select Board on Monday evening, presenting options for both the sewer main replacement project and the larger infrastructure plan.

The pipe of the compromised sewer line runs about a mile from the town’s treatment plant to a sewer pump at Chase Road. Catlow told the board that it was originally installed in 1971, and is made of cast iron. A cast iron pipe, while durable, has a life expectancy of 50 to 65 years. 

Compounding the issue, Catlow said, was that 90 percent of the town’s sewage flows through the main to get to the town’s treatment facility; he called it a “critical” piece of the town’s sewer system. 

Catlow said patching the pipe each time it breaks is difficult, because sections of the pipe are deep in the ground — up to 15 feet deep. And manhole covers accessing the pipes aren’t available, leading to a complicated repair.

While the wastewater department has been lucky that the breaks have occurred over the winter months, Catlow says it would be highly problematic in the summer, when the sewer main is in high demand, and when traffic on the roads would be disrupted by the construction work.

The wastewater department is proposing to borrow $4.9 million to replace the main with a more modern system during the upcoming spring town meeting. Included would be the construction of a series of manhole covers to make accessing possible breaks in the line easier. 

The funding request could allow construction to begin in the fall, after design and permitting work is completed.

In the meantime, the town’s wastewater department is gearing up for its larger wastewater management plan, referred to as a comprehensive wastewater management plan, or CWMP. The plan will include removing nitrogen — mostly from backyard septic systems — from the town’s watersheds.

The watersheds of most concern in Edgartown are Sengekontacket Pond and Edgartown Great Pond. The total maximum daily load (TMDL) — which is the calculated highest amount of nitrogen that a watershed can take in while maintaining a healthy system — for Sengekontacket is 16,757 kg of nitrogen per year, and 16,812 kg of nitrogen per year for Edgartown Great Pond. The maximum loads are based on the Massachusetts Estuaries Plan, a report from 2001 that chronicled nitrogen issues across the state.

The 2023 nitrogen loads for both watersheds are exceeding those targets. The load in Sengekontacket is 18,742 kg of nitrogen per year, and Edgartown Great Pond’s load is 19,424 kg of nitrogen per year. 

Edgartown also shares these watershed areas with other towns. Sixty-four percent of the Sengekontacket watershed is within Edgartown’s borders. The rest is from Oak Bluffs. That will require Edgartown to work with its neighbors to remediate nitrogen getting into the Sengekontacket watershed.

Catlow says that to be able to meet those nitrogen targets, the plan is to extend the town’s sewer line to homes and developments in those watersheds. Sewers will likely go to the more densely populated areas, like Ocean Heights. For homes with larger lots that are closer to the water, he said, it is less economical to extend the sewer line. They are still exploring alternatives like innovative-alternative septic systems that can remove nitrogen, or permeable reactive barriers that can intercept nitrogen before it gets into the watershed.

The town’s wastewater commission is requesting $3.1 million for the upcoming town meeting. The funding will help to evaluate soils and groundwater to identify where pipes could be laid, and to investigate a possible place where treated wastewater could be discharged back into the watershed.

Edgartown Town Meeting is planned for April 9.