The Tisbury board of health last week approved changes to town wastewater regulations, widening the scope of conditions under which property owners must install advanced denitrification septic systems.

The new rules, which go into effect Jan. 1, 2024, apply only to properties in the Lagoon Pond and Lake Tashmoo watersheds, Tisbury health agent Maura Valley said at a public hearing Sept. 26.

Under past town regulations, advanced denitrification systems in the watersheds are required under four circumstances: for new construction; when an existing wastewater treatment system fails; in the case of additional development or intensified use of a property and when the health board deems a new system necessary after a property changes hands.

The updated rules for Tisbury watershed properties will require the advanced systems to replace any existing septic systems that need to be upgraded, repaired or replaced, whether or not they have failed.

Watershed properties that change hands after Jan. 1 will also be required to have or install advanced denitrification, without the board of health becoming involved.

Tisbury’s new regulations will help it meet stricter target nitrogen concentrations for sensitive watersheds identified by the state of Massachusetts, said water resources biologist Scott Horsley, who consulted with the town on its recently-completed wastewater plan for Lake Tashmoo.

“Tisbury is really out front on this, and you have been out front and I think that’s a real credit to the town,” Mr. Horsely said.

Cape Cod towns are already grappling with the new state requirements, which had once been also considered for Vineyard watersheds before they were rolled back earlier this year.

A grant program funded by the Covid-era American Rescue Plan Act (ARPA) allows homeowners to apply for up to $35,000 to switch to advanced denitrification.

The Dukes County website has more information about the grants on its ARPA page at