The Hopkinton transfer station is facing a $3.6 million cleanup after sludge that accumulated over the years in its septic lagoons was found to contain harmful “forever” chemicals.

Capping the contaminated site to prevent further environmental damage is now a costly but necessary project for the town.

Since both Hopkinton and Webster use the transfer station, the two towns will split the costs, with Hopkinton covering 75% and Webster contributing 25%.David Hemenway, Webster’s select board chair, expressed concern about Webster’s portion of the project funding.

“Obviously you want to make it better for Hopkinton residents to do this than to have to ship that out,” said Hemenway.

At the same time, Hemenway said Webster residents don’t want to end up covering additional costs for this project simply because they use the transfer station.

Over the years, the 52,000 tons of sludge containing “forever” chemicals at the transfer station lagoons have accumulated from residential and commercial waste pumped from septic tanks, primarily from Hopkinton and Webster.

Neal Cass, Hopkinton’s town administrator said that sludge removal would typically involve preparing and spreading it on fields, but the presence of forever chemicals, or PFAS, has altered that approach.

A 10% contingency has been added to the total project cost, bringing the total bond amount to $4.15 million, which will be voted on in the upcoming town meeting. Additionally, the town has been awarded a grant that enables it to borrow this amount from the state’s Clean Water Revolving Fund.

Instead of shipping the waste elsewhere, which would cost around $13 million, a proposed plan presented to the New Hampshire Department of Environmental Services focuses on a more economical approach.

This plan involves relocating the contaminated material from one lagoon to stockpile it on site. The dug-out area will be filled with stone, sand and a separation layer to ensure the sludge remains six feet above the groundwater level. Following this, the excavated sludge will be placed back in the lagoon, covered and finally capped with another separation layer and a few inches of topsoil.

“The plan is really designed to protect the towns in the future, too,” said Cass. “It follows all the solid waste regulations.”

Sruthi Gopalakrishnan can be reached at sgopalakrishnan@cmonitor.com.