Tisbury and Oak Bluffs are gearing up for expansions to their aging wastewater facilities, as officials root out illegal sewer hookups and seek nitrogen mitigation methods in anticipation of the state’s crackdown on pollution.

Down-Island wastewater officials are in various stages of their Comprehensive Wastewater Management Plans (CWMPs) — a complex, locally-managed but state-guided process that towns in southeastern Massachusetts can initiate to help establish a “total maximum daily load” (TMDL) of nitrogen in their at-risk watersheds. The CWMP process can be expensive and time consuming, forcing towns to weigh future development with the size of their sewer plants and the ecological health of their ponds and estuaries.

Excess nitrogen can damage sensitive watersheds, and a study released this summer revealed septic systems to be the largest nitrogen polluter for the Island’s great ponds.

Wastewater facility expansions in both Vineyard Haven and Oak Bluffs are ramping up at just the right time, officials said, as new state Title Five regulations would require towns with sensitive watersheds to develop a plan to meet their total maximum daily nitrogen loads, as set by the state DEP. If they don’t, the regulations will force the upgrade of thousands of private septic systems. Both are costly propositions.

Five down-Island watersheds have established total maximum daily loads, including Edgartown Great Pond, Sengekontacket, Farm Pond, Lagoon Pond and Lake Tashmoo, with others are still under study. For the down-Island towns, the CWMP process represents a critical step in meeting the state’s new requirements.

“I want to crush it. I want to crush this TMDL,” said Tisbury wastewater superintendent Jared Meader about his goal of coming in under the total maximum daily load. He said his town recently completed the needs assessment portion of the CWMP process.

The Tisbury wastewater facility will expand capacity to about 140,000 gallons of flow per day. — Mark Alan Lovewell

Luckily for Vineyard Haven and Oak Bluffs, which share the Lagoon Pond watershed, recent wastewater developments have helped alleviate some of the capacity issues that have long plagued their plants.

In Tisbury — which has a small wastewater treatment facility that mainly services the downtown commercial district — the disconnection of several illegal sewer hookups in town has revealed significant excess capacity, town wastewater officials said. In Oak Bluffs, a $26 million plan to expand capacity at their sewer plant will provide needed upgrades. as well as the opportunity for state grant money.

Mr. Meader was hired in Tisbury in October 2020, inheriting a town wastewater facility stretched to capacity. The facility, built in 2004 to address septic pollution, was designed to be intentionally small, with an eye toward curtailing rampant growth in the town. The Tisbury plant was originally permitted by the state to process 104,000 gallons of flow per day. The Edgartown plant, in comparison, was permitted for 750,000 gallons per day in 1995. By Mr. Meader’s estimation, the efforts were misdirected.

“People think, if you have sewers, you’ll have strip malls all over the place, and skyscrapers. But that’s a zoning issue,” he said.

Already strapped for capacity, the Tisbury plant was further stressed by a series of illegal hookups discovered in 2020, including a 15,000 gallon-per day groundwater pump at the Mansion House hotel. Following the removal of that hookup, and two others found on Beach Road, including at the Citgo station, Mr. Meader said the town has now freed up over 20,000 gallons of daily flow at their plant, making the situation far less dire.

That capacity, Mr. Meader said, has allowed the town more flexibility to act on nitrogen reduction. With a lower level of wintertime flow, the town has been able to redirect their off-season sewer plant outflow to a leeching field outside of the watershed.

Tisbury’s planned sewer expansion upgrade, which will hook up 50 new parcels on State Road and increase total capacity to 140,000 gallons per day, is also in progress, with construction set to begin next fall.

But the additional capacity will force the town to make difficult decision about its development priorities, officials said.

“Right now, we are trying to give some direction on what to do with the remaining flow,” Mr. Meader said, though he said part of the flow will be allocated to the harbormaster’s office, to install a hookup for boat outflow. “We don’t want, six months from now, to be like ‘hey, we don’t have flow anymore.’”

But with the impetus to remove watershed pollutants higher than ever, towns are looking beyond infrastructure projects to meet the requirements.

“Our answer is not just sewering. It’s the most expensive option,” said Gail Barmakian, Oak Bluffs select board member and wastewater commissioner.

Oak Bluffs completed their CWMP needs assessment back in 2018, and Ms. Barmakian said the recently-approved $26 million plan to expand town sewer capacity will help unlock state grants and reimbursement funds.

“I am really proud of our town,” said Ms. Barmakian of the process so far. “It is a time consuming and very expensive process… Oak Bluffs has done it incrementally.”

The Oak Bluffs wastewater facility plans are focused on upgrading and retrofitting existing equipment, rather than installing new systems. Because of that, the town has already begun work on non-sewer solutions to the nitrogen issue, including a new culvert on Farm Pond to allow for water to flush in and out of the pond, and the installation of a “Permeable Reactive Barrier” to filter out water before it enters Lagoon Pond – a project stemming from a collaboration between Vineyard Haven, Oak Bluffs and the Martha’s Vineyard Commission. Ms. Barmakian said the town is now planning the installation of another barrier at Sailing Camp Park.

She expressed some skepticism, however, at another oft-cited solution: miniaturized “package plant” systems. Often installed underground, the plants operate a bit like small wastewater facilities, able to serve dense areas too distant from a town plant to sewer cost-effectively. They have the potential, Mr. Meader said, to remove nitrogen more effectively than enhanced septic systems, and at a lower overall cost.

The problem with them, Ms. Barmakian noted, is that they would primarily serve private developments. “Where are you gonna put it? On whose land are you gonna put it?” she said.

Still, Mr. Meader believes the miniaturized plants could have applications in Vineyard Haven, and he is eagerly watching the installation of the first Amphidrome package system at the Lagoon Ridge development. “Those are areas I eyeball all the time,” he said. While the systems have a considerable footprint underground, he said that the above-ground component could be contained in a small, 10-by-12 shed.

And with the town finally embarking on its lengthy CWMP process, town officials in Tisbury are considering all options for how to handle nitrogen runoff, however big or small.

“It’s an all hands on deck kind of approach,” Mr. Meader said. “You gotta go in there with an open mind.”