Hopewell Precision Area Contamination

Attachment I: Method Use to Estimate Cancer Risk For Exposure to TCE in Drinking Water

The purpose of the public health assessment is to estimate and characterize the potential health risks resulting from the contamination. The public drinking water standard was used as one of several comparison values to select chemicals for further evaluation. Since several private wells had TCE levels that exceeded the standard, TCE was selected as one of the chemicals for which the health risks would be characterized. To characterize the health risks, we assumed a person drinks 2 liters of water every day containing the highest measured level of TCE found in a private well (250 mcg/L) for 29 years, averaged over a 70 year lifetime. We also assumed that a person receives additional exposure to TCE through non-ingestion exposure pathways such as cooking, showering and bathing. We assumed that this exposure was equal to the exposure from ingestion pathways, and doubled the drinking water concentration to account for it. The estimated increase in cancer risk is calculated from the exposure in drinking water (expressed as a TCE dose in milligrams per kilogram body weight per day (mg/kg/day)) and the cancer potency factor (0.00572 per mg/kg/day (NYS DEC, 1997)). A cancer potency factor is a number (usually derived by health agencies) that is based on toxicological studies of the chemical, and represents a measure of the chemical's ability to cause cancer. The calculation for the estimated increased cancer risk for someone exposed to 250 mcg/L TCE in drinking water is as follows:

Calculation of Contaminant Dose from Drinking Water:

250 mcg/L x 2 x 2 L/day x 1/70 kg x 1 mg/1000 mcg x 29 years/70 years = 0.0059 mg/kg/day


250 mcg/L = highest detected level of TCE

2 = factor to account for non-ingestion exposure to TCE

2 L/day = drinking water ingestion rate (US EPA, 1989)

70 kg = body weight (US EPA, 1989)

1 mg/1000 mcg = conversion factor to convert micrograms to milligrams

29 years/70 years = fraction of lifetime exposure

Calculation of Increased Lifetime Cancer Risk from Contaminant Dose:

0.0059 mg/kg/day x 0.00572/mg/kg/day = 0.000034 or 3.4 per 100,000


0.0059 mg/kg/day = estimated contaminant dose for TCE

0.00572/mg/kg/day = cancer potency factor for TCE (NYS DEC, 1997)