PUBLIC HEALTH ASSESSMENT
REFUSE HIDEAWAY
MIDDLETON, DANE COUNTY, WISCONSIN
Figure 1. Refuse Hideaway Landfill, Dane County, Wisconsin
Figure 2. Refuse Hideaway Landfill and immediate vicinity. Off-site groundwater monitoring wells.
APPENDIX B: 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 and off-site groundwater currently do not
pose a cancer risk because people are not exposed to contaminated groundwater.
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 in on-site and adjacent off-site
monitoring wells are at concentrations which are not likely to reach private
wells due to natural attenuation and biodegradation of the contaminants between
the site and private wells. The estimates below are only a relative
index of the potential lifetime cancer risks that the chemicals pose.
A more detailed discussion of the potential toxic effects of each chemical begins
on page 23.
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| Chemical | Maximum Level Detected (µg/L) |
USEPAa Carcinogen Group |
Unit Cancer Risk (µg/L)-1 |
Upper Level Estimated Lifetime Cancer Risk (x 10-6) |
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| Tetrachloroethyleneb | 530 | B2 | 1.5 x 10-6 | 795 |
| Trichloroethyleneb | 180 | B2 | 3.1 x 10-7 | 60 |
| Vinyl Chloride | 525 | A | 5.4 x 10-5 | 28,500 |
a Source: [60]
b Carcinogen classification group is 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 [60].
The "upper level estimated lifetime cancer risk" is the product of the maximum concentration of the chemical in ground water at the Refuse Hideaway 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, combined inhalation and dermal exposures to VOC's would be roughly equivalent to twice that from drinking contaminated water [51].
APPENDIX D: Pathways Evaluation
Pathways are evaluated to determine whether nearby residents have been exposed to contaminants originating from the site. A pathway is a route along which contaminants can move away from a site and enter the bodies of people living nearby. There are five elements in a completed pathway:
APPENDIX E: Supporting Calculations - Toxicological Evaluation
cis-1,2-Dichloroethylene
Past exposure not expected to affect resident's health (page 23): Assuming the combined exposure of all three routes (dermal, ingestion, and inhalation) is three times that expected from drinking water alone, this combines to create a total DCE exposure of 108 µg/L, and converts to 11 g/kg/day or 0.011 mg/kg/day (10 kg child drinking 1 liter of water per day). The USEPA Lifetime Health Advisory (LTHA) and the MCL is 70 µg/L, which is based on 20 percent drinking water contribution of the DWEL of 400 µg/L. The intermediate Oral MRL is 300 g/kg/day, which would convert to a 3,000 µg/L intermediate EMEG (for a 10 kg child).
Tetrachloroethylene
No apparent increased risk of cancer from highest PCE levels found in private wells (page 24): Assuming that tetrachloroethylene (PCE) is a carcinogen, as previously determined by the U.S. EPA, and the cancer screening value is used (Cancer Slope Factor [5.1E-02] is 0.69 µg/l), this 1:1,000,000 excess cancer risk level was exceeded by all the levels detected in private wells. Assuming the combined exposure of all three routes (dermal, ingestion, and inhalation) is three times that expected from drinking water alone, this combines to create a total PCE exposure equivalent to 78 µg/L, and converts to 2 g/kg/day or 0.002 mg/kg/day (70 kg adult drinking 2 liters of water per day). Using the U.S. EPA's former cancer slope factor it is estimated that a person exposed to drinking water contaminated at 26 µg/l for four years would have no apparent increased risk of cancer ([0.002 x 5.1E-02 x 4/70] = [1.02E-04 x 4/70] = 5.8E-06). There are no other known health effects from ingesting the highest level of PCE found in private wells.
Moderate increased risk of cancer potentially resulting from PCE exposure caused by failure to clean-up the site (page 24): Assuming ingestion, inhalation and dermal exposure from drinking water contaminated with 265 µg/L would combine to create a total PCE exposure of 22.7 g/kg/day or 0.0227 mg/kg/day (70 kg adult drinking 2 liters of water per day) and using U.S. EPA's former cancer slope factor, there would be a moderately increased cancer risk ([0.0227 x 5.1E-02 x 30/70] = 5.0E-04).
Trichloroethylene
No apparent increased risk of cancer at highest TCE levels found in private wells (page 25): Assuming trichloroethylene (TCE) is a carcinogen, as previously defined by the U.S. EPA, and a Cancer Slope Factor of 1.1E-02, this value was exceeded by all levels detected in one private well (PW-1), and in the levels detected in the other well before March 1989. Combined ingestion, inhalation and dermal exposures would then total an equivalent TCE exposure of 30 µg/L. This converts to 8.6 g/kg/day or 0.0086 mg/kg/day (70 kg adult drinking 2 liters of water per day). Using the slope factor it is estimated a person drinking water contaminated at 10 µg/l for four years would have a no apparent increased risk of cancer ([0.0086 x 1.1E-02 x 4/70] = [9.5E-05 x 4/70] = 5.4E-06).
Low increased risk of cancer potentially resulting from TCE exposure caused by failure to clean-up the site (page 25): Assuming ingestion, inhalation and dermal exposure would combine to create a total TCE exposure of 540 µg/L, this converts to 15.4 g/kg/day or 0.0154 mg/kg/day (70 kg adult drinking 2 liters of water per day). If TCE maintains a carcinogen classification from the U.S. EPA and the cancer slope factor is used, there would be a low increased cancer risk ([0.0154 x 1.1E-02 x 30/70] = 7.3E-05).
Vinyl Chloride
No apparent increased risk of cancer at highest Vinyl Chloride levels found in private wells (page 26): Vinyl chloride is a known human carcinogen and has a Cancer Slope Factor of 1.9E-00, which converts to 0.015 µg/L. This 1:1,000,000 risk level was exceeded when vinyl chloride was detected in two private wells (PW-1 & PW-2) early in 1988. The highest concentration detected in these well was 6 µg/L. A combined ingestion, inhalation and dermal exposure to vinyl chloride is equivalent to an oral exposure of 18 µg/L. This converts to 0.52 g/kg/day or 0.00052 mg/kg/day (70 kg adult drinking 2 liters of water per day). Using the slope factor it is estimated a person drinking water contaminated at 6 µg/L for two years would have a no apparent increased risk of cancer ([0.00052 x 1.9E-00 x 2/70] = [9.9E-04 x 2/70] = 2.8E-05).
High increased risk of cancer potentially resulting from PCE exposure caused by failure to clean-up the site (page 26): Assuming ingestion, inhalation and dermal exposure to 263 µg/L would combine to create a total vinyl chloride exposure of 22.5 g/kg/day or 0.0225 mg/kg/day (70 kg adult drinking 2 liters of water per day) and using U.S. EPA's cancer slope factor, there would be a high increased cancer risk ([0.0225 x 1.9E-00 x 30/70] = 1.8E-02).
APPENDIX F: Response to Public Comments
Comments on the Public Comment Draft of the Refuse Hideaway Landfill Public Health Assessment were solicited for the period from November 10 to December 10, 1993. Public comments were received from one source. These comments pointed out minor inconsistencies, addressed items about grammar, and indicated areas needing additional clarification. Where appropriate, this information was incorporated into the public health assessment, however these comments did not alter the conclusions and recommendations of the report.
