MOUAT INDUSTRIES

As of September 2026, the Mouat Superfund site (Site) is considered Insufficient Data to make a Human Exposure evaluation (HEID) because of a newly identified exposure pathway and/or contaminant(s). From 1957 to 1962, Mouat Industries processed chromite ore mined from the Stillwater Mining Complex in south-central Montana. The process generated wastes containing sodium chromate and sodium dichromate. Waste piles leached contamination into the soil and groundwater. Further contamination resulted from sodium dichromate spills during normal facility operations. Partial cleanup of soils and groundwater contaminated with the only site-related contaminant of concern, chromium (hexavalent and trivalent), was completed between 1990 and 2008. A non-time-critical removal action was conducted and included 1) for soil: the remedy is a combination of on-site containment of stabilized contaminated soil and off-site disposal of contaminated soil and 2) for groundwater: the remedy is monitored natural attenuation to restore the contaminated groundwater outside the on-site containment area to its beneficial use as drinking water. A partial deletion of the site for surface and subsurface soils was completed in 2009.

A Remedial Investigation (RI) was begun in Fall 2025 to determine data gaps associated with groundwater concentrations and delineation. During a site visit on November 3, 2025, salt pans were observed on the adjacent southeast golf course. The crystals in the salt pans were yellowish in color leading EPA to suspect hexavalent chromium impacts. A soil sampling event occurred in March 2026, where it was determined the hexavalent chromium was present in surface soils in exceedance of residential Regional Screening Levels. Preliminary Remediation Goals (PRGs) were developed for the recreational golfer and golf course worker scenario and the limited sampling results are below those numbers; however, only a limited area of the golf course was sampled. The scope of contaminated surface soils and migrating hexavalent chromium in the groundwater is unknown until more data is collected.

The EPA uses the HEID status when there is a lack of evidence to suggest that actual or reasonably anticipated human exposures are occurring, and that those exposures are above acceptable risk-based levels. The planned activities to collect sufficient information to evaluate this new exposure pathway and⁄or contaminants(s) are 1) a remedial investigation (RI) to define the extent and magnitude of trivalent and hexavalent chromium in soil and ground water at the Site, and 2) risk evaluations for exposures to hexavalent chromium at the Site. In the meantime, EPA has been in contact with the City of Columbus and the Stillwater Golf Course regarding the potential risks of exposure at and near the Site. Likelihood of exposures to community members is low due to the recreational scenario and known concentrations below PRGs; however more data should be collected in order to determine the scope of impacts. EPA currently anticipates that there will be sufficient data to make a Human Exposure evaluation by December 2030.