SITE INFORMATION AND CORRESPONDENCE

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water extraction, soil vapor extraction and Since June 1991, LLNL has operated a treatment was initiated in July 1994. Soil va- ground water extraction and treatment system por extraction is needed in the central GSA to in the vicinity of the eastern GSA debris burial 1)reduce soil VOC concentrations, 2) address trench area. With this system, LLNL has sig- the possible presence of residual adsorbed con- nificantly reduced VOC concentrations in taminants in the dewatered zone,and 3)reduce ground water in this area. Over 50 million gal- VOC concentrations in soil vapor to mitigate Ions of ground water have been extracted and inhalation risk inside Building 875. Analytic treated with approximately 5 pounds of VOCs data from vapor extraction wells in the vicin- removed from ground water. In addition, the ity of Building 875 indicate that VOC concen- length of the eastern GSA ground water plume trations in soil vapor are decreasing signifi- with TCE concentrations above drinking wa- cantly over time. The total mass of VOCs re- ter standards (5 ppb) has been decreased by moved from ground water and soil through over 4,000 feet since the initiation of remedia- third quarter 1994 is approximately 20 pounds. tion (Fig. 7). Summary of Site Risks As part of the Remedial Investigation, a stances Pollution Contingency Plan(NCP). An baseline risk assessment was conducted to excess cancer risk between 10-4(one in ten thou- evaluate the potential risk and hazard to people, sand)and 101 may be acceptable provided risk and plants and animals that may be exposed to is sufficiently managed. VOCs in soil, air and/or ground water. An ecological assessment evaluates the po- tential for adverse impact to plants and animals What Is a Baseline Risk from long-term exposure to chemicals. The Assessment? ecological assessment focuses on potential re- Risk assessments evaluate toxicological productive damage and reductions in reproduc- and environmental data, and use those data to tive life span rather than the risk of developing predict the extent, if any, of adverse health ef- cancer. fects on people and plant and animal species Baseline risk assessments typically use con- under given exposure conditions. servative assumptions that favor protecting pub- Risk for humans is expressed as the prob- lic health and the environment. Therefore, ac- ability of developing cancer over a lifetime and tual human or nonhuman exposures and risks as the potential for noncancer adverse health are likely to be much less than those calculated effects (e.g.,effects to central nervous system, for the risk assessments. liver, kidney) to occur due to long-term expo- General Service Area Baseline Risk sures. For example, an excess cancer risk of Assessment one in one million means that a person exposed to a chemical over the course of a lifetime could The General Services Area baseline risk potentially increase his or her cancer risk by assessment determined that two exposure routes one in one million above the cancer risk of one could potentially result in unacceptable risk to in three for Californians(American Cancer So- the community and workers on site. For ground ciety, 1994). An excess cancer risk of 10-6(one water ingestion and inhalation of TCE vapor in one million) is an acceptable level accord- inside Building 875, the baseline risk assess- ing to the National Oil and Hazardous Sub- 7