In 1989, the Consolidated Aluminum Corp. (Conalco) and Dow Chemical Co. began to quietly clean up a 40-acre site adjacent to a foundry in Madison, Ill., that the two companies formerly owned. The plant and dump site are both located on the boundary between the Metro East cities of Madison and Venice.

The clean-up entailed dividing the area into a massive grid made up of hundreds of squares and then using a complicated formula to measure the contamination levels in each of them. To carry out the job, contractors constructed a laboratory, rail spur and loading station.

By the time the project ended in December 1992 more than 105,000 tons of thorium-contaminated slag had been loaded into 978 rail cars and shipped to a low-level radioactive waste facility in Utah, according to a final report prepared for the Illinois Department of Nuclear Safety (IDNS), the state agency responsible for overseeing the clean-up.

The 1992 report states: “Because of the proximity of the contaminated area to a residential neighborhood, and the inconvenience that the construction activity imposed upon the neighborhood, the construction was done in a manner such that all contaminated material above natural background was removed and the area was backfilled immediately. ” …

The history of radioactive contamination at the foundry dates back to 1957, when Dow began processing uranium for fuel rods under a subcontract with St. Louis-based Mallinckdrodt Chemical Co., which was working for the U.S. Atomic Energy Commission. The plant was one of hundreds of low-priority radioactive sites nationwide identified by the federal government’s Formerly Utilized Sites Remedial Action Program in the 1990s. The subsequent government-mandated clean-up, which was overseen by the U.S. Army Corps of Engineers in 2000, focused mainly on uranium contamination inside facility and did not include additional monitoring or remediation at the adjacent 40-acre site.

The thorium waste was the byproduct of another facet of the foundry’s operations — production of lightweight alloys used for military and aerospace applications. Between 1960 and 1973 Dow dumped millions of pounds of sludge containing 4 to 8 percent thorium behind the plant on the adjacent property. After Conalco took over the operation, the dumping continued for years, including monthly shipments of thorium waste produced at Dow facilities in Bay City and Midland, Mich.