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…