The Onalaska Municipal Landfill sits on an 11-acre parcel next to the Black River in Onalaska, Wisconsin. The landfill operated from 1969 to 1980, accepting both municipal and industrial wastes. It was added to the EPA's National Priorities List (NPL) in September 1984. The site remains on the NPL today.
EPA identified 26 contaminants of concern at the site. These include volatile organic compounds (VOCs) such as benzene, toluene, trichloroethene, and xylene in both soil and groundwater. Heavy metals including arsenic, barium, lead, iron, and manganese are also present. Additional contaminants include chlorinated compounds like 1,1,1-trichloroethane and 1,1-dichloroethene, along with naphthalene, ethylbenzene, and trimethylbenzene found in groundwater.
The original cleanup, finished in 1994, used a landfill cover, a groundwater pump and treat system, and a bioremediation system. The bioremediation system shut down in 1998 and the groundwater system stopped in 2001. The Wisconsin Department of Natural Resources (DNR) took over site control in 2002. In September 2012, EPA and Wisconsin DNR approved an amendment to the cleanup plan that allowed the pump and treat system to be permanently shut down. The amended plan relies on monitored natural attenuation, meaning contamination is tracked over time rather than actively treated. Two private water supply wells near the landfill that had high manganese levels were replaced under this plan. Institutional controls, including zoning restrictions, are in place to prevent residential and other incompatible land uses.
EPA completed its sixth five-year review in July 2023 and confirmed the cleanup continues to protect people and the environment. Human exposure is currently under control, and contaminated groundwater movement has been stabilized with no unacceptable discharge to surface water. Physical construction of the cleanup is complete across the entire site. However, the site has not yet achieved sitewide readiness for anticipated reuse, meaning some cleanup goals or required land-use restrictions are not fully in place. The next five-year review is estimated between July and September 2028.
Community members with questions can contact the EPA Community Involvement Coordinator or Remedial Project Manager. State-level questions can be directed to the Wisconsin DNR. Site records are available at the Onalaska Public Library at 741 Oak Ave. S and the Holmen Area Library at 103 State St.
