As a tectonic shift in state wastewater regulations is under consideration by state officials, Island homeowners and towns are bracing for what could be millions of dollars in mandatory upgrades in the coming years.

The state Department of Environmental Protection released plans to update its septic code, known as Title 5, last year. If implemented as proposed, the update could require thousands of septic systems on the islands, Cape Cod and the South Shore to be overhauled or replaced. 

Homeowners are raising questions about what their financial burden might be under the new regulations. State and local officials have, in turn, begun work on plans to ease that burden, either through direct subsidies or by finding ways to manage on-site wastewater systems at the municipal level.

Reached by phone on Wednesday, DEP spokesman Edmund Colletta said the agency is still weighing public reaction to the proposed updates, and they would only immediately go into effect on the Cape.

But Vineyard officials are already grappling with the potential costs, exploring ways to fund initiatives and re-imagining municipal wastewater in the process.

“We could be spending, easily, in just the three down-Island towns, half a billion dollars on wastewater over the next 20 years,” said Ben Robinson, the Tisbury representative on the Martha’s Vineyard Commission.

The DEP amendments would create new designations for coastal communities that have been polluted by nitrogen runoff. Areas that fall under the “nitrogen sensitive area” category would need to install enhanced septic systems on all new and existing properties within five years. Communities may be exempted from the five-year deadline if they apply for a watershed permit, giving them more flexibility in developing a 20-year plan to address nitrogen pollution.

For officials, the latter option is a no-brainer.

“Obviously, towns are going to choose the 20-year plan,” said Mr. Robinson.

The proposed revisions were unveiled last year after DEP was sued by the Conservation Law Foundation for allegedly failing for decades to enforce regulations, causing environmental degradation on Cape Cod. According to CLF lawyer Maggie Nivision, that suit is currently stayed, with a stipulation that DEP publish the regulations by May 31.

“We are cautiously optimistic that DEP still intends to pass strong regulations,” Ms. Nivision said, noting the high volume of public comment DEP is sorting through. “We, like everyone, are waiting.”

If the changes go into effect, Oak Bluffs, West Tisbury, Edgartown, Tisbury and Chilmark could all be considered nitrogen sensitive areas after the regulations go into effect on the Cape.

Critics have pointed to the high cost of upgrades, accusing DEP of passing the buck to towns and homeowners to pay for decades of regulatory neglect.  

“Title 5 doesn’t do anything for nitrogen, and the state wasn’t moving fast enough,” said Oak Bluffs select board member Gail Barmakian, who has been involved in wastewater planning for the last 15 years.

However, Ms. Barmakian, said the Vineyard is “ahead of the curve” compared to the Cape in anticipating the new regulations. All three down-Island towns are already developing Comprehensive Wastewater Management Plans (CWMPs), needed to secure the 20-year permit, and the MVC is working on a combined down-Island plan.

Oak Bluff’s wastewater plan is up for state review this summer. It involves sewer upgrades and a program to replace septic systems, along with less conventional technologies like the permeable reactive barrier installed at the base of Lagoon Pond in Vineyard Haven. Currently, the estimated cost for the plan is $136 million.

If all goes according to plan, Ms. Barmakian said, the CWMP will lower the town’s nitrogen pollution to a level acceptable by the state over a 20-year timeframe, while also factoring in town growth.

But nearly as complex as the plan itself, Ms. Barmakian said, is the process of funding it.

“It’s a big puzzle, and there are a lot of pieces to it,” she said.

Part of that puzzle will be the State Revolving Fund (SRF), which gives low-interest and zero interest loans, along with principal forgiveness for town water projects.

As of March, a $26 million project in Oak Bluffs to upgrade sewer equipment was accepted into the fund, making the town eligible for such loans. Only about half of the municipalities that apply make it into the program, she said.

Now that Oak Bluffs has been accepted, Ms. Barmakian said, the town will be able to secure loans, with an interest rate between zero and two per cent. There is also potential for some level of loan forgiveness.

For larger communities with centralized downtowns, sewering is an option. But many neighborhoods on-Island are too sparsely populated to support a central sewer, prompting them to look at innovative septic systems designed to minimize nitrogen.

Installing those can cost between $30,000 and $50,000 per system, with several thousand systems on-Island due to be updated in the new regulation.

“We’re looking at upwards of 1,200 for just Tisbury,” said Mr. Robinson.

The challenge of funding such an infrastructure overhaul is compounded, officials said, by the problem of managing projects on thousands of private properties.

“That’s what the hard part is,” said Tisbury wastewater superintendent Jared Meader.

Recently, Mr. Meader has been brainstorming ideas for how to manage his town’s decentralized wastewater system, as they develop a Tashmoo-focused watershed plan meant to move faster than a full CWMP.

Since the area cannot feasibly be hooked up to the sewer, Mr. Meader said they are looking to bankroll the upgrade of the private systems through the revolving fund. When completed, he said, the town might be able to take over monitoring, charging individuals like they do for the sewer.

Centralizing management could also help with the shortage of local engineers and inspectors, said Mr. Meader, who once served as a private inspector himself.

Without that centralized testing, Mr. Meader worried that it may be difficult to guarantee the efficacy of the systems over time, and to enforce noncompliance.

Gov. Maura Healey has also proposed increasing the septic upgrade state tax credit from $6,000 to $12,000.

Another funding source yet to be tapped by Vineyard towns would be opting into the Cape Cod and Islands Water Protection Fund, which would allow Vineyard towns to collect a 2.75 per cent tax on lodging and short-term rentals to help pay for wastewater projects, Mr. Robinson said. Towns are required to have a completed CWMP before enrolling, and Ms. Barmakian says she plans to initiate that process for Oak Bluffs.

Whatever emerges from the Title 5 revisions, the issues around wastewater are not likely to stay static, Mr. Robinson added, as planners consider how water resources will be affected by climate change.

“We’re going to have to be thinking about...what does this mean for 50 years? What does this mean for 70 years? What does this mean for 10 years?” he said. “The alternative is you give up your pond or watershed.”