Hi-Mill Manufacturing Co. sits on 4.5 acres in Highland Township, Michigan. The company made aluminum and brass parts from 1946 to the 1980s, using chemicals such as trichloroethylene (TCE) for degreasing. EPA placed the site on the National Priorities List (NPL) in February 1990, and it remains listed today. The site is divided into three operable units covering sitewide work, groundwater monitoring, and a vapor intrusion remedy.
The contaminants of concern are all found in groundwater. They are trichloroethene (TCE), 1,2-dichloroethene (in cis and trans forms), and chloroethene, also called vinyl chloride. EPA determined these chemicals pose unacceptable risks to human health through ingestion and contact with contaminated groundwater.
Cleanup work started in 1983 when Michigan regulators ordered removal of a contaminated lagoon. Workers removed over 140 cubic yards of soil, thousands of gallons of sludge, and wastewater. EPA issued its first cleanup decision in 1993, calling for long-term groundwater monitoring and institutional controls to prevent residential use. A chemical oxidation treatment tried in 2000 did not work. In 2014, the property owner installed a vapor intrusion mitigation system in the office and warehouse. EPA replaced five old monitoring wells with two new ones in 2020. Construction of the initial cleanup is listed as complete, but there is not enough data yet to confirm that human exposure is under control or that groundwater contamination has stopped spreading.
A second investigation began in September 2023 to determine the full extent of contamination. New remedial design and action phases for groundwater are estimated for 2027 to 2028. The vapor intrusion remedy is also on that timeline, with a record of decision planned for August to October 2027, remedial design running through February 2028, and remedial action finishing by August 2028. The most recent five-year review was completed in September 2025. The site has not been deleted from the NPL. Two businesses currently operate on the property, employing six people and generating about $2.4 million in annual sales. Institutional controls, including zoning restrictions against residential development, remain in place.
Community members who want to follow cleanup progress or ask questions can contact the EPA staff assigned to the site. Administrative records are also open to public review at the Highland Township Library, 205 W. Livingston St., Highland, Michigan.
