The West Falmouth Harbor watershed is the first estuary in Falmouth that is on the path to meeting the total maximum daily load, or TMDL, of nitrogen, Falmouth Water Quality Management Committee chairman Eric T. Turkington said Wednesday, June 19.
“This is a really significant effort,” Mr. Turkington said.
Brian L. Howes, a professor in University of Massachusetts Dartmouth’s school of marine science and technology and director of the coastal systems program, went even further, saying, “This is the first estuary on Cape Cod that is showing improvement in nitrogen removal.”
The committee unanimously approved a draft scenario for achieving TMDL compliance in the West Falmouth Harbor watershed.
The draft scenario is for the committee’s use and will not be part of the 2019 update to Falmouth’s comprehensive wastewater management plan for the Massachusetts Department of Environmental Protection, Mr. Turkington said.
“Falmouth is meeting the requirements of the discharge permit, which should result in meeting the target threshold total nitrogen concentration of 0.35 milligrams per liter at the Snug Harbor sentinel station once the plume has flushed out,” Kristin Rathjen, a water quality technical consultant with Science Wares Inc., told the committee.
Additional efforts to reduce the nitrogen concentration include state-approved fertilizer credits estimated to result in removal of 91 kilograms of nitrogen per year and stormwater credits resulting in removal of 285 kilograms of nitrogen per year.
Also, the West Falmouth Harbor Shoreline Septic Remediation Project, which installed 25 innovative/alternative septic systems at homes in the watershed, removes an estimated 114 kilograms of nitrogen per year, Ms. Rathjen said.
Sixty-five percent of the nitrogen inputs to the watershed have come from the plume at the Blacksmith Shop Road wastewater treatment facility.
Locally controllable sources include wastewater, lawn fertilizers and impervious surfaces.
In 2016, Dr. Howes’s program completed additional modeling for the watershed to reach the TMDL, Ms. Rathjen said.
“Under buildout scenarios, a maximum effluent concentration of 3 milligrams per liter at a maximum flow rate of 0.45 million gallons per day was calculated to allow the system to meet the TMDL once the plume has flushed out,” she said.
In 2005, the Town of Falmouth estimated seven to 10 years for the old plume to flush out. In 2011, the Buzzards Bay Coalition appealed the new discharge permit, limiting total flow to 1 million gallons per day. The next year, a settlement agreement limited flow to 800,000 gallons per day and an annual nitrogen load of 5,204 pounds per year.
In 2015, a new permit, new appeal and a new final decision limited flow to 710,000 gallons per day, of which 450,000 gallons per day is the maximum allowed in the West Falmouth watershed. The current permit limits discharge to 450,000 gallons per day. In 2017, the town constructed new sand filter beds outside the watershed to handle the flow of 260,000 gallons per day from the Little Pond Sewer Service Area.
In 2016, the US Environmental Protection Agency began to fund oyster reefs in the watershed through grants from the Southeast New England Program of the Buzzards Bay National Estuary Program.
“The goal is to achieve nitrogen reductions and evaluate whether oyster reefs could be self-sustaining. Visual inspection in 2018 indicated an established, thriving bed,” Ms. Rathjen said.
During the discussion, committee member Stephen B. Leighton suggested that the draft scenario specify the reasons why the expected plume flush-out of seven to 10 years is now four years overdue, at 14 years from the outset.
“Data showed early indications of improvement of the monitoring wells that were closer to the plant. It means the rate of groundwater travel is slower than originally projected and/or there’s also a tailing-off effect,” said Virginia Valiela, the committee’s vice chairman.
“The predictions ahead of time were very rough, and I don’t see a cause for concern that the overall model or concept is not valid,” Amy A. Lowell, Falmouth’s wastewater superintendent, said. “I think it’s just taking a little longer. We have seen declines in all the monitoring wells. It just hasn’t gotten as low down to the closest wells to the harbor as quickly as we might have hoped. We monitor those wells quarterly for nitrogen, and we will continue to do that, and I expect to continue to see declines.”