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GEGMATRIX No benzene,toluene,ethylbenzene,xylenes,or MTBE were detected in the groundwater sample collected from boring GMX-6. Fluorene and phenanthrene were the only PAHs detected in the groundwater sample;these were detected at concentrations of 0.2 and 0.3 micrograms per liter(µg/1), respectively. Analytical laboratory reports for the soil and groundwater samples are presented in Appendix B. 5.0 HUMAN HEALTH SCREENING EVALUATION A health risk screening evaluation was conducted to assess the potential human health risks associated with residual petroleum constituents detected in soil and groundwater. This evaluation was conducted based on the methodology presented in the Human Health Screening Evaluation section of the Preliminary Endangerment Assessment Guidance Manual(PEA;Cal-EPA, 1994). The PEA evaluation consists of a compilation of methods,models,and assumptions commonly used by California and United States Environmental Protection Agencies(Cal-EPA and U.S.EPA)to quantify human health risk and hazard at a site. The PEA evaluation is intended to provide conservative estimates of the theoretical lifetime excess cancer risk and noncancer hazard index based on reasonable maximum exposure in a residential setting. It should be noted,however,that the site is currently vacant and it is anticipated that the future use of the property will be commercial. Potential likely receptors at the site include future on-site commercial workers and construction workers. Nonetheless,to avoid restricting land use,the PEA methodology was used to evaluate a hypothetical future residential receptor as a conservative measure. Exposure pathways considered in this evaluation include inhalation of volatile organic chemicals from soil and household water, inhalation of airborne dust from soil;ingestion of soil,surface water,and groundwater; and dermal contact with soil,surface water,and groundwater. For purposes of this evaluation,all equations and default input assumptions provided in the PEA were used. As discussed in Section 4.0,TPHd,TPHc,TPH&toluene,xylene,ethylbenzene,and some PAHs have been detected in soil at the site;two PAHs have been detected in shallow groundwater. For purposes of this evaluation,all detected constituents in soil and groundwater were quantitatively evaluated;the maximum detected concentration for each constituent was conservatively used as the representative concentration. It should be noted,however,that TPH measurements were not directly included in this evaluation,as prescribed in the PEA. The toxicity of these petroleum mixtures is best described by the aggregated toxicity of key individual constituents in the mixture,such as BTEX and PAHs(Cal-EPA, 1994). \\SF3\DEPTDATA\DDC SAFE9000S\5650\POMaOWOM-SOIL- W.TX .DOC 4