Falmouth health agent outlines how new DEP watershed permitting could require denitrifying septic systems for thousands of homes

Scott, the Town of Falmouth’s health agent, briefed the Board of Health and members of the public on the implications of a July 2023 Massachusetts Department of Environmental Protection (DEP) regulation that gives municipalities two paths to meet total maximum daily load (TMDL) nitrogen limits for impaired coastal ponds.

Scott said the regulation allows towns either to require denitrifying septic systems at each property within seven years or to pursue watershed permitting, the approach Falmouth selected. "Option 2...gives us more time, more flexibility, allows shellfish beds, widening of inlets, and a bunch of different mechanisms to get DEP to agree that we are meeting that TMDL," he said.

He summarized the technical difference between traditional Title 5 septic systems and enhanced nitrogen removal systems (often called I/A or IA). Under older design assumptions the industry used a target of about 19 milligrams per liter of nitrogen; the Board of Health’s local regulation sets a tougher local threshold of 12 mg/L. Scott warned that "there's really once there's two systems that can achieve 12...right now we have one promising technology that runs consistently under 12 per liter," creating potential supply and scale problems if many homes must retrofit.

Scott described the draft watershed maps Water Quality Management is preparing for Falmouth’s 14 coastal watersheds; those geo-boundaries will be vetted and—if adopted—enforced by the Board of Health. "When they're finalized, the board of health will have to adopt them," he said, adding the maps are not set in stone and could change as plans for outfalls or sewer purchases evolve.

He explained why sewer expansion is not a silver bullet: even high-performing treatment plants remove a high percentage of nitrogen but large volumes of wastewater still represent a significant total nitrogen load. "Even if we have one of the best performing nitrogen reducing plants in the state, it's still a lot of...if you put a million gallons and you take out 97%, that's still a boatload of nitrogen," Scott said, underscoring permitting and capacity constraints for sewer expansion.

Board members pressed Scott on practical details including which areas currently require IA systems, the footprint for retrofits, and alternatives like urine-diversion systems. Scott said Title 5 already triggers denitrifying technology in some cases (for example, when a property increases bedrooms in a zone with a town well), but there are no finalized, townwide environmental-designated IA zones yet: "There is nothing currently that says you're in a denitrifying septic system area." He described an "I/A reserve area" the Board uses on plans to reserve space for future installation and estimated equipment footprints at roughly the size of a 2,000-gallon tank for some technologies.

On costs and technology availability, Scott said older low-performance IA units are cheaper (he estimated roughly $12,000–$15,000) while higher-performing systems can run into the $30,000s, and that many homeowners might opt for less-expensive options. He also said urine-diversion shows strong nitrogen removal in some designs but remains less established and would require home plumbing changes.

Board members raised equity concerns for subsidized housing built under Chapter 40B and other affordable-unit programs. A board member warned that requiring retrofits in five years could impose significant burdens on owners and tenants of affordable units. Scott said the regulation and the watershed plans will need to account for such housing but cautioned that credit for nitrogen reductions must come from somewhere in the plan.

Resident Robert Pina asked whether a specific property under a pending 40B application was currently in a nitrogen-sensitive area; Scott said that under current draft maps the parcel was not in a nitrogen-sensitive overlay but emphasized that maps could change.

Scott recommended the Board consider watershed planning piecemeal—tackling one watershed at a time—so the town can balance sewer expansion, retrofit feasibility, financing and technology supply. He noted the Buzzards Bay Coalition and other nonprofits have been active in urging adoption of local regulations and that the board may need to open hearings to change local rules.

No formal motions or votes were recorded during the exchange; the session was a technical briefing and question-and-answer period. The next procedural steps are completion of Water Quality Management’s watershed maps, Board of Health consideration of the maps and any proposed local regulation, and additional outreach about potential costs and financing for homeowners.