PUBLIC HEALTH ASSESSMENT
MUSKEGO SANITARY LANDFILL
MUSKEGO, WAUKESHA COUNTY, WISCONSIN
APPENDIX A: Cancer Risk Estimation
UPPER LEVEL ESTIMATES OF LIFETIME CANCER
RISKS ASSOCIATED WITH POTENTIAL FUTURE
CONSUMPTION OF CONTAMINANTS IN GROUND WATER
Chemical contaminants in on-site ground water currently do not pose a cancer risk because people are not exposed to this water. The upper level estimates of lifetime cancer risks listed in the table below offer a perspective on the relative cancer risks the contaminants in on-site ground water would pose if that water were used for drinking water. In general, the chemicals with the highest estimated risk pose the greatest threat to downgradient wells. Obviously, the maximum concentrations found on site are not the concentrations likely to reach off-site wells. The estimates below are only a relative index of the potential cancer risks that the chemicals pose. A more detailed discussion of the potential toxic effects of each chemical begins on page 25
43.
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| Chemical | Maximum Level Detected (µg/L) |
USEPA Carcinogen Group* |
Unit Cancer Risk* (µg/L)-1 |
Upper Level Estimated Lifetime Cancer Risk (x 10-6) |
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| Benzene | 21 | A | 8.3 x 10-7 | 17 |
| Vinyl chloride+ | 7 | A | 5.4 x 10-5 | 380 |
| 1,2-Dichloropropane+ | 5 | B2 | 1.9 x 10-6 | 10 |
| Methylene chloride | 2 | B2 | 2.1 x 10-7 | < 0 |
| Tetrachloroethylene+ | 1 | B2 | 1.5 x 10-6 | 2 |
| 1,2-Dichloroethylene | 12 | C | 1.7 x 10-5 | 26 |
| Trichloroethylene+ | 7 | B2 | 3.2 x 10-7 | 16 |
| 1,2-Dichloroethane | 9 | B2 | 2.6 x 10-6 | 23 |
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* Source: [29]
+ chemicals marked "+"
are under review by the U.S. EPA.
EPA Carcinogen Group
The EPA uses one of five groups to classify the carcinogenic potential of a chemical, according to the weight of evidence from epidemiological studies and animal studies. The following list explains categories listed on the above table:
Group A - Human Carcinogen (sufficient evidence of carcinogenicity in humans);
Group B2 - Probable Human Carcinogen (sufficient evidence of carcinogenicity in animals and inadequate or no evidence of carcinogenicity in humans);
Group C - Probable Human Carcinogen (limited evidence of carcinogenicity in animals and inadequate or no evidence of carcinogenicity in humans).
NA - This is not an EPA category. This notation indicates that information is "not available" because the EPA has not evaluated this chemical.
Cancer Risk
The EPA estimates the level of cancer risk posed by exposure to relatively low doses of carcinogens. The EPA uses the available data and a theoretical "model" of how chemicals cause cancer to estimate the carcinogenic potency of a chemical. This potency is an "upper-bound estimate." In other words, the true risk is not likely to be higher and may be lower. The estimated lifetime cancer risk is the upper bound estimate of the increase in one's probability of contracting cancer as a result of ingesting the chemical in drinking water for a lifetime. The "unit cancer risk" is the EPA's estimate of one's increased risk from drinking 1 µg of the chemical per liter of drinking water for a lifetime. The higher the unit risk, the greater is the estimated carcinogenic potency of the chemical [29].
The "upper level estimated lifetime cancer risk" is the product of the maximum concentration of the chemical in ground water at the Muskego Sanitary Landfill site and the unit cancer risk. The estimated risk is rounded to one significant digit because of the great uncertainty involved in estimating the risk. At best the order of magnitude of the risk reflects the relative carcinogenic hazard that a chemical poses. The table does not include risks associated with breathing VOC's released from residential water or from dermally absorbing carcinogens in the water. As a general rule of thumb, exposure to VOC's would be roughly twice that from drinking the contaminated water [24].
