Risk Communication: Health Risks Associated with Environmentally Contaminated Private Wells versus Chloroform in a Public Water Supply

Article excerpt


During March 1988, 16 private residential shallow wells near a radar base in Sault Ste. Marie, Chippewa County, Michigan, were found to be contaminated with one or more environmental contaminants. The carcinogens in the groundwater were benzene, CAS 71-43-2; 1,2-dichloroethane, CAS 107-06-2; dichloromethane, CAS 75-09-2; trichloroethylene, CAS 79-01-6; and tetrachloroethylene, CAS 127-18-4. Traces of 1,1,1-trichloroethane, CAS 71-55-6, a non-carcinogen, were also detected. The source of the contamination was indeterminate at the time. In accordance with the Michigan Environmental Response Act (1), the state provided the residents, on an interim basis, with bottled water for drinking purposes.

Concurrently, the Michigan Department of Public Health (MDPH), in collaboration with the Michigan Department of Natural Resources (MDNR), began to develop a response action that would result in either site remediation or a permanent alternate source of potable water.

The public water treatment facility at Sault Ste. Marie used raw water from the St. Mary's River. The maximum concentration of chloroform, a carcinogen, in this drinking water source was 26 [[micro]grams]/L due to chlorination to meet drinking water quality standards. The system was not equipped to filter the surface water prior to treatment.

The relative health risks for the two water sources (groundwater versus public water supply) were computed. We also assisted the Division of Water Supply and the Division of Upper Peninsula (MDPH) in the communication of the relative health risks attributable to the different possible solutions to the problem. The citizens' views were fully ascertained and incorporated in the final decision for the management of the risk.

The objective of this paper is to report the relative health risks, risk communication activities, and the events that led to the final decision. An abstract of this work appeared in the Society for Risk Analysis Abstract Supplement (2).

Materials and Methods

The data on the analyses of water samples from the residential wells and the public water supply were provided by the Division of Water Supply (MDPH). The chemical analyses were conducted by the department's water laboratory.

The cancer risk assessment formulations for benzene, 1,2-dichloroethane, dichloromethane, trichloroethylene, tetrachloroethylene, and chloroform were formulated by using the United States Environmental Protection Agency (EPA) guidelines and procedures (3-7). The EPA oral slope factors (potency factors) for carcinogen contaminants were applied to compute the cancer risk assessments (8). The cancer slope factors for benzene and chloroform have since been revised (9-11). The carcinogenicity assessments for trichloroethylene and tetrachloroethylene were withdrawn by the EPA in 1992 for further review and evaluation (12-13). However, risk assessment formulations for carcinogens reported herein were made by using the scientific information available in 1988 at the time of the decision for the management of the risk (8). The standard EPA assumptions were used in formulating the risk assessments (5,7,14,15). These assumptions were: average human lifetime, 70 years; average human body weight, 70 kg; average daily water consumption, 2 L; and an acceptable risk level, 1 in [10.sup.6].

Table 1. Maximum concentration of contaminants in private wells.(*)

Contaminant                     Maximum            Comparison
                              Concentration         Value(**)
                            ([[micro]gram]/L)   ([[micro]gram]/L)


Benzene                             2                  5
1,2-Dichloroethane                  2                  5
Dichloromethane                     1                  5
Trichloroethylene                   8                  5
Tetrachloroethylene                 2                  5


1,1,1 -Trichloroethane              8                 200

* The chemical analyses were provided by the Division of Water Supply,
Michigan Department of Public Health, Lansing, Michigan. …