Voters in Oak Bluffs and Tisbury this year will be asked to move forward on ambitious plans to expand each town’s sewer district, with a common goal of benefitting both local business and coastal ponds.

The towns have been collaborating for some time on efforts to protect Lagoon Pond, which they share almost equally, and which has suffered from an overabundance of nitrogen, mostly from outdated septic systems in the watershed. Sewers are seen as one solution to the problem, especially in the more heavily developed down-Island towns, since they remove almost all of the nitrogen in wastewater. But the sewer initiatives in Oak Bluffs and Tisbury are mostly independent of each other.

Spending articles related to sewering in Oak Bluffs total $1.7 million this year, marking the start of a five-year plan to expand capacity at the town wastewater treatment facility on Pennsylvania avenue and extend the town’s sewer lines. In Tisbury, which is further along in its own efforts, voters will be asked to allocate $50,000 for the engineering and design of a new sewer district along State Road, where many town businesses are located. In both cases, the boundaries of the proposed districts are yet to be determined, but the spending requests this year would help set the stage for more detailed plans.

In Oak Bluffs, $400,000 would pay for planning and design aimed at improving the wastewater treatment plant, while $350,000 would pay for a comprehensive wastewater management plan. The plan could help determine the boundaries of a new sewer district and identify alternatives such as increased aquaculture and the use of denitrifying septic systems. An additional $100,000 would fund a study to determine whether water is infiltrating the town’s wastewater collection system, and $20,000 would pay for repairs of the wastewater infiltration system in Ocean Park.

The spending requests in Oak Bluffs this year represent only a small fraction of the total cost of increasing plant capacity and extending the sewer lines, which the town’s five-year Capital Improvement Plan sets at around $38 million. The biggest cost would be $20 million for plant improvements in fiscal year 2019, followed by $5 million in each of the following two years for the laying of new pipes.

Funding for the project is still unclear, although it would likely involve some level of borrowing. The Capital Improvement Plan recommends a reduction in overall debt levels to accommodate the project. Other funding would come from the town’s wastewater enterprise fund and tax base. Selectman Gail Barmakian said this year’s requests would likely require a debt exclusion.

It was too soon to say where the new sewer lines would go, but Ms. Barmakian said the priorities have been the Lagoon and Sengekontacket Pond watersheds, both of which are severely impaired by nitrogen and the resulting algal blooms each year.

A 2011 study by the Massachusetts Estuaries Project (MEP) found that sewering an area between the head of Lagoon Pond and Barnes Road could cut the pond’s nitrogen load by 18 per cent each year. The study also points to Oklahoma avenue in Tisbury as a candidate for sewering.

“Water quality was some of the impetus, as well as expanding user capacity,” Ms. Barmakian said of the expansion project. “When the plant went in, it was never contemplated that we would hook up the school, the hospital and community services, so that took up a lot of capacity.” She said the project as proposed by the town capital program committee could increase plant capacity by 60 or 70 per cent while bringing the plant up to code, keeping additional nitrogen out of the groundwater, and allowing for more economic growth in town.

To some degree, the sewering efforts have gained steam from the MEP, which has set specific nitrogen reduction goals for most coastal ponds on the Island. When the MEP report for the Lagoon came out in 2010, Oak Bluffs was already working to expand its effluent beds in Ocean Park, which in turn laid the groundwork for the larger wastewater expansion project.

“The big thing at this point is the treatment capacity,” Ms. Barmakian said, noting that the plant is nearing the end of its 20-year lifespan.

Tisbury’s efforts also have resulted from years of planning and a need to stay ahead of the game in terms of plant capacity. In addition to the $50,000 request on the annual town meeting warrant this year, voters will decide whether to allocate $60,000 for design services related to a new wick system, which acts like a vertical leaching field for the town’s wastewater treatment facility. The system will save space and almost double the capacity of the plant.

Ray Tattersall, director of the Tisbury department of public works and a member of the town sewer advisory board, which reports to the selectmen, said installation has already begun for the wick system, but he highlighted the importance of the new State Road district as well.

“The whole idea is to get that designated so that when the plant is upgraded and the wicks come online, it will all come together,” he said.

The town has already approved a number of future sewer connections, including for the Martha’s Vineyard Museum, which plans to relocate to the former Marine Hospital overlooking Vineyard Haven Harbor, and the Cape Cod Five Cent Savings Bank, which plans to replace its modular building on State Road with a more permanent structure, but only after it can connect to the sewer. Mr. Tattersall said the museum connection may open the door to more connections on Skiff avenue and Hines Point Road.

Tisbury selectman and wastewater commissioner Melinda Loberg, who has helped lead the expansion efforts in her town, said the new district would extend as far as High Point Lane, off State Road, although it was too soon to know the precise boundaries.

As in Oak Bluffs, the goal in Tisbury is largely to benefit local business. As one benefit, the new district would make it easier for businesses to expand, since the Martha’s Vineyard Commission would likely require additional wastewater treatment in those cases. The new districts could also help distribute maintenance costs more broadly.

Joshua Goldstein, general manager the Mansion House on the corner of State Road and Main street, part of the current sewer district, said expanding the system was vital for continued economic growth in Tisbury. Mr. Goldstein also serves on the town sewer advisory board and the Martha’s Vineyard Commission.

“There are 124 users paying an exorbitant amount of money for the system,” he said of the current district, which extends down Beach and Lagoon Pond roads and includes most of the businesses on Main Street. “It’s not hooked up all the way down to the Woodland Business Park, it doesn’t go where it needs to go. It protects the harbor but it doesn’t protect the ponds.”

He added that his own business pays hundreds of thousands of dollars in sewer bills, and that new businesses in the district can’t afford to open, given the high costs. “I think expansion really is a great thing that needs to happen — for both the business community and the environment of Tisbury,” he said.