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Background
Early History
Charles R. Lindsay Jr. founded the company bearing his name in 1902. Until the mid-1930s, the Lindsay Light Company manufactured incandescent gaslight mantles at several addresses in Chicago's downtown Streeterville neighborhood. A gaslight mantle is actually a fabric pouch that fits over the gas source. Gas mixes with air and burns at the exterior of the mantle, making the mantle glow brightly. The Lindsay Light Company used the radioactive chemical thorium nitrate to manufacture their gaslight mantles. Lindsay obtained thorium containing ore, typically monazite, to refine and extract the thorium. The refining process produced a sand-like waste known as thorium mill tailings, which were used for fill in the low lying Streeterville area of Chicago.
Lindsay Light's first location was at 22 W Hubbard. The company later expanded its operations to 161 E. Grand Ave. and 316 E. Illinois St. Ore containing radioactive thorium was processed at the Illinois St. site and the mantles were manufactured at the Grand Ave. location. In 1932, the company began moving its operations to West Chicago, Ill. (see Kerr-McGee Superfund site.) The company closed the last of its Chicago facilities in 1936.
Thorium contamination
US EPA first discovered thorium contamination at Lindsay Light's Illinois St. location in 1993. Since then, further investigations have discovered thorium in the soil at more than a dozen locations in the Streeterville neighborhood and at another downtown location to the south. Thorium contaminated soil is not considered to be a threat to human health and the environment if it is covered by an intact hard surface of sufficient thickness such as concrete or asphalt. Fortunately, almost all locations in the Streeterville neighborhood were covered by hard surfaces.
To protect human health and the environment, EPA and the City of Chicago developed a system requiring anyone planning to remove hard surfaces in the area to test the soil if EPA suspected the property might have thorium contamination. [ see Chicago Department of Environment Streeterville Thorium web page 
] To date, cleanups have been conducted at more than a half-dozen properties and about 55,000 cubic yards of contaminated soil have been removed. Because the soil was radioactive, it had to be shipped to a special disposal site in Utah permitted to accept such waste.
There are several properties known to have contamination and that remain to be cleaned, including the proposed DuSable Park location . There are also at least five locations that EPA has determined should be investigated before those properties can be developed. The City has not made any determination.
Working in the rights-of-way within the areas that possibly might have thorium contamination in the soil
EPA and the City of Chicago have tried to protect the public and those who work on construction projects and underground utilities from possible exposure to thorium contaminated soil by requiring radiation monitoring of areas that may be thorium contaminated. Anyone requesting permission to work in these areas is required to test for thorium.
Because of the long-lived nature of thorium contamination (some radiation contamination is very short lived) , the need to know that these areas are safe for workers will continue far into the future. Therefore EPA has agreed to host a web-based repository of radiation testing reports and other technical documents for the benefit of those conducting work within the rights-of way . The reports in the web-based repository allow private utilities companies and city departments to easily check to see if an area has already been tested and determined to be clear of contamination, or if the area has never been investigated and still needs to be tested. The repository should save utilities and construction companies time and money by avoiding the duplication of radiation testing.