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Groundwater monitoring wells at the site have been screened at two distinct intervals. Upper zone wells, MW-1 through MW-7, are screened in sandy zones between 46.5 and 70 feet bgs, to monitor petroleum hydrocarbon impact to the uppermost 15 to 20 feet of the water-bearing zone. Based on available historical potentiometric maps (Appendix B), groundwater flow in the upper zone was initially toward the south (third quarter 1989), with some later flow toward the west and southwest (fourth quarter 1994 and first quarter 1995). During the June 1991 monitoring event, wells MW-1 through MW-7 were dry, indicating water levels had dropped below 70 feet bgs. Since the fourth quarter of 1995, all flow in this zone appears to have been generally toward the east and southeast. Lower zone wells, MW-8 through MW-12, are screened between 94 and 115 feet bgs, within the laterally continuous sandy unit first encountered at approximately 95 to 105 feet bgs. Available monitoring data for these wells indicate that water levels have dropped between 3 and 5 feet since the second quarter of 2001. The static water levels measured in these wells are similar to those measured in the upper zone wells, except in wells MW-10 and MW-12, which occasionally have exhibited water levels between 4 and 9 feet below the static levels in the upper zone and in the other lower zone wells during the same monitoring period. Flow in the lower zone has generally been toward the south and east. 41 4.3 Extent of Petroleum Hydrocarbon Impact Soil and groundwater beneath the former Apache Plastics and the former Sunland service station sites have been impacted with petroleum hydrocarbons. Analytical data indicate the presence of TPHG and BTEX compounds, methyl tert-butyl ether (MTBE), tert-butyl alcohol (TBA), and 1,2-dichl oro ethane (1,2-DCA). Analytical data for soil samples collected during site assessment activities at both the former Apache Plastics and former Sunland service station sites are presented in Appendix C. Groundwater analytical data collected during site assessment i activities, and historical groundwater monitoring and analytical data and are presented in Appendix B. Figure 5 presents soil analytical data collected during site investigation activities. As discussed below, groundwater beneath the former Apache Plastics and former Sunland service station sites is impacted with TPHG, BTEX compounds, MTBE, TBA, and 1,2-DCA. Dissolved concentrations exceed the current State of California Maximum Contaminant Levels (MCLs) for benzene (1 microgram/liter, or p.g/L), and 1,2-DCA (0.5 µg/L). Based on the current MCLs and dissolved hydrocarbon concentrations identified beneath these sites, the chemicals of concern (COCs) identified at this site include TPHG, benzene, MTBE, and 1,2-DCA. Extent of Petroleum H drocarbon Im act in Soil Former Ache Plastics Facility TPHG and BTEX concentrations generally decrease with depth in the soil samples collected in the vicinity of the former UST (Figure 5). TPHG and benzene were detected in soil samples p;\Apache Plastics\Reports\Apache SCM.doc Page 7 Stratus