Continued Use of Drinking Water Wells Contaminated with Hazardous Chemical Substances -- Virgin Islands and Minnesota, 1981-1993

Improperly disposed hazardous chemical substances are a common source for contamination of drinking water wells (1). The Agency for Toxic Substances and Disease Registry (ATSDR) and other environmental and public health agencies have recommended that exposure-reduction procedures (i.e., provision of alternative water supplies and construction of new water supplies) be implemented when drinking water wells are contaminated with hazardous substances in concentrations that approach or exceed levels potentially associated with adverse health outcomes in humans (2). Once these procedures are implemented, the original wells should not be used as sources for drinking water. This report summarizes two cases in which contaminated drinking water wells were being used even though health advisories had been issued to discontinue use of the wells. Tutu Well Field, St. Thomas, Virgin Islands

In 1987, the Virgin Islands Department of Planning and Natural Resources (VIDPNR) and the U.S. Environmental Protection Agency (EPA) determined that 22 commercial, residential, and public wells in the Tutu Well Field were contaminated with petrochemical and volatile organic compounds (e.g., benzene; trans-1,2-dichloroethylene; trichloroethylene; and tetrachloroethylene) that originated from several sources. This well field provided drinking water to persons throughout the island, either directly or by water trucked to different parts of the island. An estimated 11,000 persons may have been exposed for approximately 20 years to the volatile organic compounds, which may increase the risk for cancer for those persons.

After all households were disconnected from the contaminated wells, they were provided uncontaminated water (i.e., water trucked in and stored in cisterns) by EPA. During 1987-1988, the contaminated wells were condemned and capped (i.e., the top of the well was secured, but the shaft was left open) by VIDPNR. However, during a 1992 site visit, ATSDR and VIDPNR learned that contaminated wells had been reactivated because of water shortages (e.g., the desalinization drinking water plant had operational difficulties) or for economic reasons (3). In 1993, the reactivated wells were connected to a treatment system that removes contaminants before residents drink the water. VIDPNR and EPA are conducting investigations to determine how to clean up the contamination. Arden Hills, Minnesota

During 1981-1982, the Minnesota Department of Health (MDH) and the Minnesota Pollution Control Agency learned that 41 of 137 private and commercial wells downgradient of an industrial facility were contaminated with trichloroethylene and trichloroethane. In two mobile home park wells (serving approximately 750 residents) and seven residential wells, the contamination was at levels at which persons who relied on those wells for drinking water may be at increased risk for cancer. MDH issued a drinking water advisory requiring that the contaminated wells be closed and that residents be connected to alternative water supplies. The groundwater contamination is being remedied by a series of pumping and treatment systems at and near the industrial facility (4).

In 1983, a new well and distribution line were constructed to replace the two contaminated wells at the mobile home park; the new well tapped a deeper uncontaminated aquifer. After the new well was constructed, the old contaminated wells were capped. However, without notifying state or county health officials, the owner had continued to maintain one of the contaminated wells as an emergency backup well; this well was used intermittently when the newer, uncontaminated well was undergoing maintenance or repair. In 1993, MDH learned that the contaminated well was being used and requested that the well be abandoned according to the requirements of MDH well codes (4). MDH is continuing to monitor this situation.

Reported by: C Crooke, Dept of Planning and Natural Resources, Virgin Islands. Div of Health Assessment and Consultation, Agency for Toxic Substances and Disease Registry.

Editorial Note

Editorial Note: Contaminated wells and wells that have been inactivated for other reasons should be properly sealed (i.e., by filling the well completely with concrete, cement grout, neat cement, or clays) and abandoned (5) after an alternative water supply has been substituted. ATSDR does not recommend maintaining inactive residential wells for a long-term (i.e., more than 2 years) groundwater monitoring program because 1) detailed information about the wells (e.g., depth of well and depth and thickness of the well screen) needed to monitor groundwater usually is not available and 2) the monitoring wells could be reactivated as a drinking water supply before the contamination is remedied. Proper abandonment precludes potential future human exposure to groundwater contaminants from reuse of the contaminated wells. Plugging inactive bored or augured wells also may eliminate a physical hazard for children and prevent the use of such wells for improper disposal of liquid wastes.

Because exposure (inhalation, ingestion, and dermal contact) to concentrations of contaminants can increase the risk of cancer for persons who rely on the wells, in both cases in this report owners of contaminated wells were advised not to use the wells for drinking water. Human exposures to high concentrations of contaminants can occur before such situations are detected by public health officials because residential wells are not routinely monitored. Public health and environmental officials should require the proper closure of contaminated drinking water wells after uncontaminated water supplies have been provided; closure orders should include requirements for properly closing contaminated drinking water wells.

Before old residential wells are used as sources for nonpotable water, users should be informed of the potential for future contamination and the possible public health consequences. To protect potable water systems from cross contamination, ATSDR recommends severing the connections between nonpotable wells and associated residences (i.e., removing the water line from the well to the residence).

References

1. Agency for Toxic Substances and Disease Registry. Biennial report, 1989 and 1990. Atlanta: US Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, 1991.

2. Agency for Toxic Substances and Disease Registry. Public health assessment guidance manual. Atlanta: US Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, 1992.

3. Agency for Toxic Substances and Disease Registry. Preliminary public health assessment for Tutu Well Field, St. Thomas, Virgin Islands. Atlanta: US Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, 1993.

4. Agency for Toxic Substances and Disease Registry. Public health assessment for New Brighton/Arden Hills, Minnesota. Atlanta: US Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, 1993.

5. Driscoll FG. Ground water and wells. 2nd ed. St. Paul: Johnson Filtration Systems, Inc, 1986.

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