WELLFLEET — Town officials are working to finalize a targeted watershed management plan aimed at reducing the nitrogen load in the harbor and bringing Wellfleet into compliance with state and federal clean water acts.

Thirty watersheds on Cape Cod are designated “impaired water bodies”; Wellfleet Harbor is the only one on the Outer Cape.

The town is now on track to submit its plan before new regulations that would require homeowners to upgrade septic systems kick in next summer, according to Town Administrator Rich Waldo.

Wellfleet has been updating its plan to respond to Mass. Department of Environmental Protection (DEP) comments since the agency approved a draft in June 2022. The town must submit a notice of intent to apply for a watershed permit before July 8, Waldo said. After that, he said, the town has until 2030 to apply for the actual permit.

The watershed management plans required by the DEP allow Cape municipalities with “designated nitrogen sensitive areas” to develop 20-year plans to address water quality impairment as a community. New regulations released last summer offered that reprieve in lieu of requiring homeowners to upgrade their septic systems within five years.

Wellfleet’s $106.6-million hybrid plan includes a downtown sewer district and an update to regulations that would trigger septic system upgrades to a new generation called enhanced Innovative and Alternative systems, known as “I/A” systems. The latest version of the plan was presented at a Wellfleet Community Forum on Dec. 18.

The town’s water resources consultant, Scott Horsley, and Anastasia Rudenko of GHD, an environmental consulting company, said at the forum that an updated plan based on comments from the DEP includes a larger sewer district and the development of a cluster wastewater treatment facility at Maurice’s Campground for planned housing there.

A cluster approach at Maurice’s would include abutting subdivisions as well as two motels to the north and the movie theater across the street.

According to Horsley, a treatment facility serving a housing development with 200 units could cut 771 kg per year of nitrogen loading — about 70 percent of current levels.

Because of the 35 cesspools currently on the property and a wastewater volume of over 10,000 gallons a day in the summer, DEP had asked the town to include Maurice’s Campground in its watershed plan. According to Horsley, a treatment facility for the housing development could constitute 20 percent of the total required nitrogen reduction to bring Wellfleet into compliance.

Along with another treatment facility planned for housing at 95 Lawrence Road, Horsley said, the watershed plan puts Wellfleet in a “unique” position — “the town adds badly needed affordable housing, but at the same time generates a net reduction in nitrogen loading.”

According to Rudenko, the planned sewer district has grown by 10 percent per DEP recommendations, stretching from East Commercial and Commercial Streets to Holbrook Avenue and Main Street. A treatment plant would be built at the transfer station, and homes along West Main Street and Pole Dike Road would be able to hook up.

Waldo said that construction of the downtown sewer system is anticipated for June 2029 to 2031; properties would be able to connect in June 2031.

For homes that do not fall within sewerage zones, updated board of health regulations would require upgrading septic systems to enhanced I/A systems. According to Waldo, a proposed regulation change provided to the board of health would require upgrades for new construction, expansions, repairs, and real estate transfers. The aim, Waldo said, is that the regulations will achieve required nitrogen reduction over 20 years as Title 5 septic systems are gradually replaced.

Enhanced I/A systems include two additional chambers between the septic tank and the leach field. The result is 90 percent removal of nitrogen, Horsley said. Standard Title 5 systems remove only about 20 percent.

There are currently only 60 enhanced I/A systems in operation on the Cape and Islands, Horsley said. They cost between $25,000 and $50,000, depending on whether existing septic tanks and leach fields can be maintained.

Funding options will be available for homeowners looking to upgrade. According to Waldo, the town is seeking a $450,000 grant through the Cape and Islands Water Protection Fund to match the town’s appropriations, which would fund 20 systems during the first two to three years of the watershed plan.

A newly tripled tax credit worth up to $18,000 as part of a tax package announced by Gov. Maura Healey on Oct. 4 would also help homeowners defray the cost of upgrading a failed septic to an enhanced I/A system, according to an Oct. 13 report in the Falmouth Enterprise. That credit applies only to a primary residence.

The town is still working out the kinks on a model for sharing the cost of upgrades with homeowners, Waldo said. A betterment agreement between the town and taxpayers could mitigate the high cost of treating Wellfleet’s nitrogen problem.

“We are going to start that next step fairly soon to find a system that is fair and equitable for all,” he said.