VIROQUA, Wis. – At the regular meeting of the the Viroqua City Council on Tuesday, May 27, the Council approved a request from City Engineer and Director of Public Works Sarah Grainger to skip the usual bidding process so she can meet a timeline from the Wisconsin DNR to address high levels of methane gas leaking from the closed City of Viroqua landfill site. Grainger and the City received notice from the Wisconsin Department of Natural Resources (DNR) on May 27 that the old city landfill is not in compliance with closure requirements because of high levels of methane gas discovered around the perimeter of the site.
The notice was not a surprise to Grainger since she was the one who informed the DNR of the potential problem of leaking gas. On March 5 Grainger notified the department about potential gas migration occurring at the landfill after a utility conducting work in the area (at the end of Sands RD) identified a high gas reading near the landfill.
On March 18 the DNR met with Grainger at the landfill to walk the site and discuss the potential of gas migration occurring at the landfill.
On May 6 the DNR had a meeting with Mike Amstadt of TRC (Consultant hired by the city) and Grainger to get an update on the gas migration investigation. A preliminary findings report was shared with the DNR, which contained results for monitoring of newly installed gas probes that had been conducted on April 30 and May 1. This report was later revised to add more gas probes and monitoring events.
On May 15 the DNR received a finalized report for the landfill’s gas migration investigation. The report included an access point measuring probe adjacent to a nearby church off the landfill property (On Sands RD) having monitoring results showing elevated gas readings between 1.2-20.5% methane by volume. State regulations say that at no time will the concentration of explosive gases in the soils outside of the limits of filling or air within 200 feet of or beyond the landfill property boundary exceed the lower explosive limits for such gases. The lower explosive limit of methane is 5% by volume.
Because of the high levels of gas being detected the DNR has ordered the city to develop a remediation plan June 6 and to begin work on that plan by June 30. Because of those tight time requirements the city council approved a resolution to allow Grainger to forego the normal bid process and work with their consultant, and a contractor to develop a work plan it can submit to the DNR by June 6.
Grainger said the old city landfill is what is often referred to as a “town dump”. It was not designed for holding waste and was essentially a hole in the ground where the city dumped its waste for years. The site was closed in the early 1990s when the state tightened regulations and the county built a landfill that met state standards.
Mike Amstad with TRC, the firm hired by the city to help investigate the issue and develop a mitigation plan, said their investigation up to this point indicates the vents that were installed on the site when it was closed are not working. Because those vents are not working the gas has found a path through layer of sand that it is following and venting around the outside of the site. Amstad’s recommendation to mitigate the gas is to install a passive venting system. That system would essentially involve digging a trench around the north and east side of the site that is filled with porous rock and a pipe that will collect the gas and allow it to vent up into the atmosphere, and not out the sides.
Amstad clarified that all landfills produce gas as part of the decaying process, but this site is not venting properly so it is building up and venting in areas that you don’t want it to.
“There’s biological activity happening within the landfill,” said Amstad. “Which is normal in that over time, I call them bugs, they’re eating waste that’s in the landfill and the byproduct of them breaking down the waste is methane gas. And then methane gas is supposed to be captured in the passive gas vents that are out there and vented to the atmosphere. However, it is not working as designed for whatever reason, so it’s taking a path of least resistance, which is going out horizontally and then coming out of the ground off of the landfill property.”
When asked how long it may take to mitigate the high levels of gas Amstad said it depends on the level of biological activity taking place in the landfill itself.
“If we give it a place to go I believe it’ll dissipate over time and will no longer be a issue at the site,” said Amstad. “Can I guarantee that it’ll be gone or two months? It may take some time. It depends on the biological activity that’s going on in the landfill.”
Grainger said after working Amstad, the DNR and a local contractor a very rough estimate of what that mitigation work could cost was in the range of $450,000 to $750,000. Grainger and Amstad said those numbers will be refined as the details of the work plan are finalized.
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