Since the late 1950's more than 750 million tons of toxic chemical wastes have been discarded in an estimated 30,000 to 50,000 hazardous waste sites (HWS). The uncontrolled discarding of chemical wastes creates the potential for risks to human health. Utilizing the National Priorities Listing (NPL) of hazardous waste sites developed by the U.S. Environmental Protection Agency (EPA), the study identified 593 waste sites in 339 U.S. counties in 49 states with analytical evidence of contaminated ground drinking water providing a sole source water supply to an estimated 'at risk' population. For each of the 339 identified counties the authors extracted age-adjusted, site-specific cancer mortality rates for 12 major sites for the decade 1970-1979, for white males and females, from U.S. Cancer Mortality and Trends 1950-1979. Each county in the U.S. was also coded as to whether it had an excessively high number of deaths and the total number of non-HWS and HWS counties showing excess numbers of deaths were enumerated for each selected cancer. Significant associations (p < 0.002) between excess deaths and all HWS counties were shown for cancers of the lung, bladder, esophagus, stomach, large intestine, and rectum for white males; and for cancers of the lung, breast, bladder, stomach, large intestine, and rectum for white females when compared to all non-HWS counties.