Monroe County officials are considering remediation options to address groundwater contamination near two closed landfills that has affected the drinking water of six homes on Sparta’s south side.
At a special county board meeting held Aug. 19, Ayres Associates presented findings on the source of the contamination near the city’s Sand Creek Landfill and Monroe County’s interim landfill and outlined possible solutions to treat the affected area. The firm is serving as the county’s engineering consultant on the project.
No action was taken at the meeting, which came one month after Sparta’s Common Council unanimously approved to start asking residents for easements to begin the bidding process for a project to extend a city water line to Idol Avenue. That project aims to provide safe drinking water to residents who have dealt with contamination issues for nearly three years.
Ayres Associates Project Manager and Geologist Bill Honea told supervisors the contamination dates back decades, when chlorinated solvents, chemicals once widely used in industrial degreasers, dry-cleaning fluids and household products, were disposed of at the landfill. Over time, those chemicals migrated into the groundwater.
Groundwater contamination was first detected outside Sand Creek Landfill in 1996, 16 years after it closed. To address the issue, the city and county installed a shared well to supply the residents with a safe water source. In 2001, the county removed the landfill waste, which Honea said caused a sharp drop in pollution levels. Since then, the county has monitored the site twice a year.
In December 2022, testing revealed elevated levels of contaminants near the landfills. Since then, affected residents have relied on bottled water and in-home filtration systems provided by the city and county to mitigate their exposure to the contaminants. Officials plan to seal the shared well once the city water line is extended and those residents are connected to city water.
Honea said testing shows the site is no longer actively leaking contaminants and that concentrations are about 10% of what they were in 2001. However, testing in recent years revealed contamination drifting southwest of the landfill.
“The data shows that even though nature is taking its course, the continuation that’s occurring naturally alone likely isn’t enough to halt the plume,” Honea said. “That’s the main issue right now is that it is moving but not breaking down fast enough. We need to try to do something to slow the plume down, so it has time to break down before it gets much further.”
Honea said the recommended treatment method includes injections of activated carbon to create underground barriers that would trap contaminants as groundwater passes through. Natural processes would then break down the chemicals over time. Monitoring wells would be added outside the barrier to track progress and adjust treatment if necessary.
He emphasized the plan is still in the concept stage and would require approval from the Wisconsin DNR. The county board would also need to approve a treatment plan after the state’s review. Honea estimated initial work could begin in fall 2026, depending on approvals.
County Board Supervisor Zach Zebell questioned whether the carbon barriers could handle contamination long term. Ayres Associates Senior Environmental Specialist Steve Lombardo said safety margins and contingency measures would be built into the design.
Other options, such as pump-and-treat systems, were also considered. But Honea said those approaches would be costly and difficult to maintain across such a large area. The activated carbon approach, he said, would take longer but ultimately be more effective with similar results.
“You’re eventually going to reach those levels through natural processes, but it is going to take longer than something like a pump-and-treat system,” Honea said.
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