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C A M B R I A hydrocarbons reported as TPHg did not match the laboratory's gasoline standard and were due to the presence of aged gasoline Benzene was detected in groundwater samples from borings CPT-4 and CPT-6 at concentrations ranging from 16 to 21 ppb 1,2-DCA was detected in the sample collected in boring CPT-6 at 85 fbg at 0 64 ppb Groundwater chemical analytical data are summarized in Table 3 and TPHd, TPHg, and benzene concentrations are presented on Figure 2 Laboratory analytical data are presented in Appendix D i CONCLUSIONS r In unsaturated soil, the lateral extent of TPHd in soil is defined to the north by results from bonng CPT-6 and to the west by borings B-8 and CPT-5 The TPHd reported in the five fbg samples in borings CPT-3, CPT-4, and CPT-7 do not match the diesel standard and are unidentifiable Therefore, these do not indicate the presence of TPHd in sail, and TPHd is defined onsite in soil The lateral extents of TPHg and benzene have been delineated onsite in unsaturated soil by previous investigations • Groundwater analytical results from the CPT borings indicate that groundwater beneath the site is impacted by petroleum hydrocarbons in each water bearing zone sampled, to the total explored depth of approximately 92 to 97 fbg However, the similarity in the TPHd, TPHg, and benzene concentrations reported at different depths suggests that cross-contamination dunng drilling or sampling may have occurred RECOMMENDATIONS Cambria recommends installing a deep well to further assess the vertical extent of petroleum hydrocarbons in groundwater beneath the site and whether cross-contamination did occur in the CPT samples We recommend monitoring the sandy zone identified in all the CPT borings, except CPT-7, at approximate depths of 40 to 45 fbg The proposed deep well would be placed near CPT-4, where the highest benzene concentration was reported (Figure 2) If SJCEHD concurs with this recommendation, Cambria will submit a work plan detailing these activities In addition, Cambria recommends continued groundwater monitoring to assess concentration trends in the shallow and deeper water bearing zones 0943 6