The MWRA's Deer Island Waste Water Treatment Plant. Photo by Daderot | CC0 1.0

Pledging to file a federal lawsuit if its calls for change are not met, the Conservation Law Foundation on Wednesday alleged that the Boston region’s water and sewer authority has repeatedly failed to enforce pre-treatment standards and allowed its users to pump water with excessive pollutants.

CLF alerted the Massachusetts Water Resources Authority it plans to sue, contending that the independent agency for years has fallen short of requirements outlined in the Clean Water Act to rein in discharges from industrial and municipal water users that could threaten water quality, local ecosystems and aquatic life.

In a letter CLF made public, the foundation contended that MWRA on dozens of occasions took insufficient action to enforce existing clean water regulations and escalate consequences in response to repeated violations.

“Boston’s coastal waters are at risk of dangerous, toxic pollution,” said Heather Govern, vice president of clean air and water at CLF. “The public spent millions to clean up Boston Harbor decades ago, and sustaining that incredible progress requires MWRA get serious about doing its job properly.”

A spokesperson for MWRA, which provides wholesale water and sewer services to about 3.1 million people and more than 5,500 large industrial users in eastern and southern Massachusetts, did not respond to multiple requests for comment Wednesday.

As part of the federal Clean Water Act, the U.S. Environmental Protection Agency launched a National Pretreatment Program that requires publicly owned wastewater treatment works to ensure their industrial users pre-treat wastewater to minimize pollutants before they pass to the next step in the process.

MWRA has had a plan on the books since 1992, according to CLF, to enforce its users pre-treating wastewater before it is pumped to the agency’s facility on Deer Island and then discharged through an outfall pipe into Massachusetts Bay.

But CLF alleged that in recent years, the independent agency has failed to respond properly to many instances of its users pumping water with mercury, zinc, pH pollution and other contaminants above limits that “harm water quality and endanger wildlife and human health.”

Govern wrote in her letter to MWRA Executive Director Frederick Laskey that since January 2017, “MWRA has not responded with any enforcement action to at least 70 instances of noncompliance” by significant industrial users, or SIUs.

She added that in fiscal years 2017 through 2021, MWRA’s significant industrial users were in “significant noncompliance” with discharge limits on at least 123 occasions. In at least 83 of those, Govern alleged, the authority failed to issue a notice of noncompliance and in many cases only issued a less severe notice of violation.

“MWRA has regularly failed to escalate its enforcement responses for repeated discharge violations of the same parameter and/or in a consecutive year,” Govern wrote. “Publicly available information shows that since 2017, MWRA has failed to escalate its enforcement for repeated violations by SIUs in at least 46 instances.”

CLF additionally alleged that MWRA has fallen short of imposing financial penalties on those in violation of pre-treatment standards. Between fiscal years 2017 and 2021, MWRA issued 23 penalty assessment notices, only five of which came after 2017, according to CLF.

The threatened lawsuit could spur another round of action to address water pollution in the area.

CLF said it would provide the MWRA 60 days to respond before it files its lawsuit, and Govern said the organization is willing to meet during that period and “discuss effective remedies for the violations noted in this letter that may avoid the necessity of further litigation.”

MWRA serves dozens of cities and towns in the area, and its wastewater system features 65 facilities.

Joseph Favaloro, executive director of the independent MWRA Advisory Board that represents communities and ratepayers served by the authority, declined to comment on the threatened lawsuit Wednesday.