PUBLIC HEALTH ASSESSMENT
MIDDLETON, DANE COUNTY, WISCONSIN
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.
|Chemical|| Maximum |
| USEPAa |
| Unit |
|Upper Level |
|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: 
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, accordingto the weight of evidence from epidemiological studies and animal studies. The following listexplains 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 animalsand 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.|
The EPA estimates the level of cancer risk posed by exposure to relatively low doses ofcarcinogens. The EPA uses the available data and a theoretical "model" of how chemicals causecancer to estimate the carcinogenic potency of a chemical. This potency is an "upper-boundestimate." In other words, the true risk is not likely to be higher and may be lower. Theestimated lifetime cancer risk is the upper bound estimate of the increase in one's probability ofcontracting 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 thechemical per liter of drinking water for a lifetime. The higher the unit risk, the greater is theestimated carcinogenic potency of the chemical .
The "upper level estimated lifetime cancer risk" is the product of the maximum concentration ofthe chemical in ground water at the Refuse Hideaway Landfill site and the unit cancer risk. Theestimated risk is rounded to one significant digit because of the great uncertainty involved inestimating the risk. At best the order of magnitude of the risk reflects the relative carcinogenichazard that a chemical poses. The table does not include risks associated with breathing VOC'sreleased from residential water or from dermally absorbing carcinogens in the water. As ageneral rule of thumb, combined inhalation and dermal exposures to VOC's would be roughlyequivalent to twice that from drinking contaminated water .
- The Agency for Toxic Substance and Disease Registry, a federal agency.
- Cancer Risk Evaluation Guide (CREG):
- An estimate of the excess upper-bound lifetime probability (at or less than 1 in1,000,000) of an individual developing cancer from an exposure to aconcentration of a specific chemical or substance.
- Cancer Slope Factor (CSF):
- The upper limit on the lifetime probability (at or less than 1 in 1,000,000) that a cancer causing chemical will cause cancer at a dose of 1.0 mg/kg/day.
- A substance which has been proven to cause cancer in humans or animals.
- The Comprehensive Environmental Response, Compensation, andEnvironmental Liability Act. Also known as "Superfund", this program isadministered by the U.S. Environmental Protection Agency.
- Wisconsin Department of Natural Resources.
- Division of Health, Wisconsin Department of Health & Social Services.
- Drinking Water Lifetime Health Advisory (LTHA):
- That portion of an individual's total exposure to a chemical that is attributed todrinking water, and is considered protective of noncarcinogenic health effectsduring a lifetime exposure, as established by the U.S. EPA.
- Environmental Media Evaluation Guideline (EMEG):
- Expressed in either µg/L or g/m3. Derived from ATSDR's Minimal Risk Level (expressed in mg/kg/day), whichis an estimate of the daily human exposure to or dose of a chemical that islikely to be without an appreciable risk of deleterious, noncancerous effectsover a specified duration of exposure. EMEGs are categorized by timeframesof exposure: acute ( 14 days); intermediate (15 - 365 days); and chronic( 365 days).
- Lower Explosive Limit (LEL):
- The minimum concentration of a chemical or substance in air which willcreate an explosive reaction on contact with an ignition source.
- Maximum Contaminant Level (MCL):
- Drinking water health goals set by the U.S. EPA at which "no known oranticipated adverse effect on the health of persons occur and which allows anadequate margin of safety".
- Milligrams per Liter, or PPM (water).
- Milligrams per Kilograms per Day.
- National Priorities List (NPL):
- U.S. EPA's list of top priority hazardous waste sites that are eligible forinvestigation and cleanup under Superfund.
- Pertaining to locations OUTSIDE of the boundaries of the Superfund site(Figure 2). It is possible for a location to be off-site and still be on theLandfill Property.
- Pertaining to locations WITHIN the boundary of Superfund site (Figure 2).
- Parts Per Billion - in water Micrograms per Liter (µg/L), or in air Microgramsper Cubic Meter (µg/m3).
- Parts Per Million - in water Milligrams per Liter (mg/L), or in air Milligramsper Cubic Meter (mg/m3).
- Tetrachloroethylene or Perchloroethylene
- Reference Dose (RfD):
- An estimate of a daily exposure level to a substance for the human populationthat is likely to be without an apparent risk of causing damaging health effectsduring a lifetime of exposure.
- Remedial Investigation and Feasibility Study (RI/FS):
- Two parts of the Superfund process. The Remedial Investigation includes thecollection and evaluation of data to define site conditions, including the natureof hazardous substances found at a site and the extent that those hazardoussubstances were released from the site. These releases are evaluated to assessthe effect on public health and the environment. The Feasibility Study definesa range of likely alternatives for cleaning up a site.
- Semi-Volatile Organic Compounds.
- Target Compound List / Target Analyte List.
- U.S. EPA:
- United States Environmental Protection Agency
- Micrograms per Liter or Parts Per Billion (water).
- Micrograms per Cubic Meter or Parts Per Billion (air).
- Micrograms per Kilogram.
- Milligrams per Kilogram.
- Volatile Organic Compounds.
Pathways are evaluated to determine whether nearby residents have been exposed tocontaminants originating from the site. A pathway is a route along which contaminants canmove away from a site and enter the bodies of people living nearby. There are five elements in acompleted pathway:
- Contaminant Source: The place where contaminants entering the environment arecoming from.
- Media: a media that the contamination is found in (soil, sediment, groundwater, air,surface water, fish, and game animals).
- Exposure Point: the location at which human contact is made with thecontamination. The Exposure Point is specific to each type of media (e.g. -groundwater, surface water, soil, etc.)
- Exposure Route: the process by which the contaminated media gets inside of people(eating/drinking, skin/dermal contact, or inhaling).
- Receptor Population: groups of people who are or may be exposed.
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).
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).
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).
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).
Comments on the Public Comment Draft of the Refuse Hideaway Landfill Public HealthAssessment were solicited for the period from November 10 to December 10, 1993. Publiccomments were received from one source. These comments pointed out minor inconsistencies,addressed items about grammar, and indicated areas needing additional clarification. Whereappropriate, this information was incorporated into the public health assessment, however thesecomments did not alter the conclusions and recommendations of the report.