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• Significant levels of impact have been detected beneath the former USTs to at least 50 feet bgs, and this impacted soil has been submerged by rising groundwater levels. Extent of Petroleum Hydrocarbon Impact in Groundwater Anecdotal reports indicate that groundwater in the site vicinity was as deep as 110 feet bgs in 1979. Groundwater beneath the site has risen from approximately 68 to 44 feet bgs since initiation of the groundwater monitoring program. Gasoline from the USTs appears to have impacted vadose zone (unsaturated) soil to depths as deep as 66 feet bgs. A subsequent rise in groundwater elevation then submerged hydrocarbon-impacted soil. Former Apache Plastics FacilitX Groundwater Grab Samples: TPHG and BTEX were detected in the HydropunchTM groundwater samples collected between 62 and 120 feet bgs from borings CPT-1 and B-1/MW-9 at concentrations that generally decrease with depth. TPHG and BTEX were detected at 152 feet bgs at boring CPT-8. The vertical extent of petroleum hydrocarbon impact to groundwater was not completely characterized. The distribution of COCs at various depths based on the HydropunchTM data are shown on Figures 6 through 10. TPHG or benzene were not detected in any of the HydropunchTM groundwater samples collected above 86 feet bgs at any of the CPT borings advanced outside of the former UST complex area. The highest concentration of benzene (23,000 µg11) in groundwater was detected at 88 feet bgs at boring CPT-10. TPHG was detected in groundwater at 150 mg/1 at 88 feet bgs in CPT-10 and 87 feet bgs in CPT-11. As discussed above in reference to COC distribution in soil, this apparent COC distribution in the groundwater may be a function of the sampling intervals. TBA and 1,2-DCA were detected in groundwater samples collected at borings CPT-1, CPT-4, CPT-8, and CPT-13. 1,2-DCA was also detected in samples collected at borings CPT-5, CPT-7, CPT-10, and CPT-11. MTBE, ETBE, TAME, or DIPE were not detected in any of the groundwater samples. As shown on Figures 6 through 10, the Hydropunch"M data suggest a co- mingling of the Sunland and Apache plumes. Monitoring Well Network: Groundwater monitoring wells at the Apache site are screened in two zones: an upper zone between 46.5 and 70 feet bgs, and a lower zone between 94 and 115 feet bgs. Figures 11 and 12 depict the distribution of CDCs in the upper and lower water-bearing zones, respectively. TPHG, benzene, TBA, and 1,2-DCA concentrations in groundwater are included on Figures 3 and 4. During the most recent sampling event (second quarter 2002), TPHG and benzene in the upper water-bearing zone were detected in wells VEW-1 (19,000 and 1,600 µg/L, respectively), and VEW-2 (120,000 and 1,500 µg/L, respectively), situated near the former UST. The lateral extent of TPHG and benzene appear to be adequately delineated. In the lower zone during the second quarter 2002, TPHG and benzene were reported 160,000 and 20,000 µg/1, respectively, in the p:\ppache Plastics\Reports\Apache SCM.doc Page 9 Stratus