Maine’s largest composting facility has decided to close its doors after state regulators linked it to elevated levels of so-called forever chemicals in nearby rivers, streams and fish, saying the current regulatory environment makes its recycling operation unsustainable.

“The current regulatory environment no longer supports (our) efforts and Casella has deemed that the continued operation of the Hawk Ridge Facility is not sustainable,” Samuel Nicolai, a vice president at Vermont-based Casella Waste Systems, said in a June 30 letter to the state.

Casella stopped accepting the treated sewage sludge it mixes with wood shavings, sawdust and wood chips to make its commercial compost product at Hawk Ridge on Monday, according to a closure plan submitted to the Maine Department of Environmental Protection.

The company, which also manages the state-owned Juniper Ridge Landfill in Old Town, plans to sell the last of the compost it will make to commercial customers, then start draining its retention ponds and cleaning off the buildings. The site should be closed by next summer.

Casella told the DEP that it plans to retain ownership of the 15-acre site and doesn’t plan to tear down the buildings. It may use the facility to store equipment. The state will require Casella to continue long-term environmental monitoring of the groundwater.

DEP groundwater testing found Hawk Ridge to be “significantly contaminated” with most wells testing at a total PFAS concentration of greater than 10,000 parts per trillion, or PPT. Some wells tested above 100,000 PPT. A well on the downhill property boundary tested at 150,000 PPT.

Maine’s drinking water standards limit the sum of six different PFAS to no more than 20 PPT.

Additional testing showed the PFAS was traveling off the property and could be found in Fowler Brook and Fifteenmile Stream, more than 2 miles away. Tests found a PFAS signature tracking at least some of that pollution back to Hawk Ridge, according to a February 2024 DEP memo.

Tissue samples from smallmouth bass landed near the confluence of Fifteenmile Stream and the Sebasticook River in 2024 found levels of PFOS, a forever chemical deemed especially toxic, of 18 and 32 parts per billion. Maine’s fish action level for PFOS is 3.5 parts per billion.

Located a few miles from downtown Unity, Hawk Ridge has turned about 1.5 million cubic yards of sewage sludge into 2 million cubic yards of compost since it began in 1989, Casella says. Most customers of Casella’s compost are contractors, landscapers or bulk buyers.

The state outlawed the spreading of sewage sludge as an agricultural fertilizer in 2022 after farm products began testing high for so-called forever chemicals, a class of manmade chemicals found in many common household and industrial products, from nonstick pots to waterproof coats.

Per and poly-fluoroalkyl substances, or PFAS, are called forever chemicals because they can linger in the environment for decades. Even trace amounts of these chemicals can be linked to compromised immune systems, low birth weights and several types of cancer.

The state investigation into the widespread sludge spreading operation has taken several years to identify the more than 1,000 sites where the state-sanctioned spreading occurred and the testing required to determine if the chemicals were still present in the water, soil, crops or livestock.

High levels of forever chemicals have also been found leaking from many Maine landfills in the form of pollutant-laden leachate that winds up sprayed on fields, hauled to wastewater treatment plants around the state, and discharged into rivers and streams.