and distribution of human exposure to releases from hazardous-waste sites is unknown. EPA now acknowledges that undiscovered sites could well present significant health risks, even though previously the agency had announced that most sites with serious potential for harm had been detected. Reviews in several states show that the current system of CERCLIS reporting misses potential health risks. In 1984 an evaluation of 93 sites on the California Department of Health State Superfund list showed that only 19 of the sites were on the federal NPL. Forty-six of the sites showed evidence of waste release into groundwater, and in 34 of these cases the groundwater was known to be used for drinking. Extensive or systematic sampling existed for only 22 of the sites where release into groundwater had occurred, despite the evidence of potential human exposure. Moreover, in all of the sites where there was known contamination of groundwater, more than 10,000 persons were potentially exposed.

PROBLEMS OF EXPOSURE ASSESSMENT

Exposure assessment provides critical information about potential human contact with relevant materials. Best estimates are that groundwater provides the major source of drinking water for about 50 percent of the U.S. population. In California, groundwater provides drinking water to nearly 70 percent of the population. Although current risks could be negligible, studies show that millions of tons of hazardous materials are slowly migrating into groundwater in areas where they could pose problems in the future. For instance, plumes of chemicals, including many nonconventional pollutants, are moving down the canyon from the Superfund site at Stringfellow Pits in California and could pose important problems in the future.

The public health component of the information base for decisions about site listing and remediation is inadequate, and there is no systematic tracking of deferred sites. The attendant cost has been confusion about the actual risks that hazardous-waste sites pose to human health. Clues to the potential scale of human exposure to toxic chemicals released from hazardous-waste sites are emerging, however. By mid-1990, ATSDR had completed 1151 health assessments at NPL sites. ATSDR determined that hazardous substances had been released at 85 percent of the sites and that about 15 percent of these sites merited further public health investigation.

The committee urgently recommends the development and validation of an adequate initial health assessment methodology for hazardous-waste sites. The committee recommends that initial site characterization include at least minimal information on potential exposure.



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