The Tisbury board of health is putting the final touches on a strict new nitrogen policy that aims to protect the health of Lake Tashmoo and the Lagoon Pond while satisfying the concerns of property owners in the watersheds.

At least 40 people attended a public hearing Tuesday to weigh in on the proposal, revised from an earlier version that would have required a fee based on the type of wastewater system installed. The first version came under fire from residents at public hearings this spring and summer.

Doug Reece heads Lagoon Pond Association, which backs new board of health policy. — Alex Elvin

Under the proposed new regulation, property owners in the watersheds would need to install septic systems that discharge no more than 19 milligrams of nitrogen per liter — far less than conventional Title 5 systems as regulated by the state. The so-called innovative/alternative or I/A systems would be required for all new construction, along with some new additions and property transfers in the Tisbury portion of the watersheds.

Tuesday’s hearing marked a shift in tone, with discussion focused more on details of the new proposal and a desire for more data, rather than the legitimacy of the data itself and questions of fairness, although those issues remained.

Board of health member Michael Loberg, who spearheaded the proposal this year, acknowledged some controversy surrounding the findings of the Massachusetts Estuaries Project, which has studied most of the coastal ponds in Massachusetts and recommended nitrogen thresholds to restore the ponds. Much of the controversy has focused on a lack of groundwater measurements that could support the MEP findings. Mr. Loberg opened the hearing by citing measurements at the former lobster hatchery on Lagoon Pond, and government reports related to Florida estuaries and the Chesapeake Bay that reveal elevated nitrogen levels in groundwater.

According to the MEP, about two thirds of the nitrogen flowing into Lake Tashmoo and Lagoon Pond comes from Title 5 septic systems that were designed to remove bacteria but not nitrogen, with the rest coming from runoff and other sources.

Mr. Loberg defended the proposal as a matter of both human and environmental health, since too much nitrogen causes algal blooms that are known to cause illness and may eventually put a dent in Island tourism. Too much nitrogen starves the ponds of oxygen, he said, and may lead to “a present danger to aquatic life, and an emergent danger to human health and our way of life.”

The board of health estimates that each new system would cost between $8,000 and $12,000 more than a conventional system, but it has not studied what each individual system would cost in Tisbury. And it was unclear Tuesday how many properties would be affected, with estimates ranging from around 500 to more than 1,000. The two watershed districts combined include 1,697 buildings with a rooftop footprint greater than 400 square feet, according to the Martha’s Vineyard Commission.

Homeowner George Balco raised questions of fairness around proposed new policy. — Alex Elvin

Island realtor Doug Reece, who is also president of the Lagoon Pond Association, took another approach to cost, noting up to a 15 per cent decline in property values in some areas as a result of pond pollution.

“It is part of the responsibility of a homeowner to bear the cost of helping protect the ponds,” he said, adding that he believed the policy would open the door for other towns to follow suit. “They’ll see that it’s working and that people accept it.”

On Monday this week the Lagoon Pond Association voted to support the board of health policy.

But some residents still challenged the proposal as unrefined.

Doug Dowling, a surveyor who has represented real estate developers in the past, questioned the need for property owners to conduct testing beyond what the state requires for Title 5 systems. The proposal allows for pilot projects as well as systems approved for general and provisional use by the state, but Mr. Dowling doubted whether anyone would risk installing a system not approved for general use. “I’m going to build a system that works,” he said. “So why continue with testing?”

Melinda Loberg, a selectman, town wastewater commissioner and member of the Tisbury-Oak Bluffs watershed planning committee, said the testing would provide valuable data as the efforts move forward. Health agent Maura Valley said the board is working with Barnstable County on ways to track and monitor the systems. The policy itself aims partly to help build a market for new technologies.

Board members have acknowledged that the policy alone would fall short of meeting the MEP thresholds for the ponds. And concerns about weighing the alternatives emerged at the hearing.

“The analysis of one tool versus another, that’s critical,” said Victor Capoccia, a member of the Tisbury community preservation committee who said he supported efforts to reduce nitrogen in the ponds but wondered about other solutions, such as expanded sewering. The town is considering expanding its sewer lines near the wastewater treatment plant on High Point Lane, but Mrs. Loberg said onsite systems would be far more cost-effective in areas farther from the plant.

The policy as drafted excludes official sewer districts in the watersheds.

No date has been set yet for a vote by the board of health. — Alex Elvin

Harriet Barrow, a board member for Tisbury Waterways Inc., urged the board to consider smaller steps first — including increased aquaculture to remove nitrogen already in the ponds, and the possibility of aeration to restore oxygen to the water. “I’m not about to say they would save the world and the ponds, but they are smaller, manageable steps that each and every one of us can contribute to,” she said.

George Balco, who argued that his property near the edge of the Tashmoo watershed actually drains to Mink Meadow Pond, touched again on the issue of fairness. “We don’t need to hassle an unknown number of people,” he said of the proposal. He suggested relying more on sewering “and not leaving my grandchildren under a financial guillotine.”

Mr. Capoccia again highlighted the uncertainty related to systems approved only for provisional or piloting use. “You don’t know the long-term impact,” he said. He recommended omitting reference to the cost of the systems, and leaving more flexibility in terms of areas that may be sewered.

Board chairman Jeffrey Pratt welcomed the concerns, but appeared ready to move forward with the policy as written, alluding to the four public hearings and substantial revisions this year. “When does this circle stop and the actual process of lowering the nitrogen load begin,” he said.

The board took no action and the hearing eventually dissolved into smaller discussions. Mr. Loberg said if the board votes to adopt the policy, it will go into effect immediately.

The timeframe for a vote remained unclear.