ARCHIVED REPORTS_REPORT OF ADDITIONAL SOIL AND GROUNDWATER INVESTIGATION

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• sample. Acenaphthene and fluorene were the only PAHs detected at concentrations of 0.1 and 0.3 ' micrograms per liter(µg/1),respectively. ' Geomatrix performed a human health screening evaluation(Geomatrix,2000)based on the data collected by Earth Systems and Geomatrix in 1999;the evaluation was submitted to Department of Toxic Substances Control(DTSC). The potential health risk posed by the residual petroleum constituents detected in on-site soil and groundwater was evaluated based on the methodology presented in the Human Health Screening Evaluation section of the Preliminary Endangerment 1 Assessment Guidance manual(PEA)used by California Environmental Protection Agency(Cal- EPA, 1994). In the evaluation,the maximum detected concentration for each constituent detected in soil and groundwater was conservatively used as the representative concentration. This evaluation indicates that exposure to residual petroleum constituents present in soil and groundwater should not pose an unacceptable health risk to hypothetical future on-site residents under the conditions evaluated. The theoretical excess lifetime cancer risk for an adult and child resident is 1x10,which is at the lower end of the acceptable risk range of 1x10 to 1x10 used by Cal-EPA and United ' States Environmental Protection Agency(U.S. EPA)at sites where remediation is considered(CCR Division 4.5,Title 22,Section 67500.15 and U.S.EPA, 1990). The non-cancer hazard index for an 1• adult and child resident is 0.65; this value is less than 1,indicating that the predicted exposure to petroleum at the site should not result in an adverse non-carcinogenic health effect(U.S.EPA, 1989). ' In addition,based on the conservative nature of the PEA evaluation,the presence of residual petroleum constituents in soil and groundwater should also not pose an unacceptable human health risk to future commercial and construction workers at the site. On March 8,2000 DTSC issued a memorandum with comments on Geomatrix's assessment. The ' memorandum concluded that the residual petroleum at the site meets the criteria for a"no further action"determination as outlined in the PEA. Geomatrix responded to DTSC's comments in a March 29,2000 letter to CEMC. On April 27,2000 DTSC issued a letter stating that the analytical data at the site were adequate in both quantity and quality and the residual levels of petroleum-related hydrocarbons in soils are below levels that would constitute an unacceptable risk to human health and the environment. The DTSC letters and Geomatrix's response to DTSC comments are presented in Appendix A. 3.0 INVESTIGATION OBJECTIVES ' On May 16,2000,Geomatrix drilled two borings(GMX-23 and GMX-24)to assess the lateral extent • of affected soil north of the site and to assess groundwater conditions in this area,which is \\SF3\DEPTDATA\DOC_SAFE\6000S\6115.007\DEC2000REPORT\BURNS SOILGW RPTNOV00_1.DOC 3