There are groundwater plumes of TCE around air force bases because they used to just dump extra TCE into open pits thinking it would evaporate. Maybe those plumes reached enough city wells to cause problems over the last few decades.
Example: https://www.library.pima.gov/blogs/post/trichlorethylene-tce...
Hughes is now Raytheon
Trichlorethylene (TCE), an industrial solvent, was routinely dumped in areas of South Tucson during the 1950s. The Tucsonans who lived in these areas have had various cancers as a result of this pollution.
The boundary of the area contaminated by TCE is roughly south of 22nd street, north of Los Reales Road, east of Interstate 19 and west of Del Moral Boulevard.
Hughes Aircraft and the city of Tucson were accused of dumping TCE in the water table for 29 years, beginning in 1952. A lawsuit against the city was settled in 1981 for $31 million, and in 1991 a suit against Hughes Aircraft was settled for $84.5 million. In 1981 the Environmental Protection Agency (EPA) tested water wells on the south side of Tucson and found TCE levels were beyond the EPA limits.
In 1983, the EPA set a large southside area of Tucson on its Superfund cleanup list. In March 2000, a $35 million plan was secured for cleanup of the contaminated areas. Other government supervised cleanups started about 20 years ago. The last settlements involving TCE lawsuits occurred in June 2006.
