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DISCUSSION As discussed in the Site Conceptual Model (SCM), review of the subsurface geology and groundwater well elevation data indicate that although different transmissive (i a sandy) zones have been identified at various depths at this site, these zones are hydraulically connected and form one continuous water- bearing zone The monitoring well network, as currently installed, was intended to target these sandy, more transmissive zones and potential migration pathways Groundwater monitoring wells 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 below ground surface (bgs), to monitor petroleum hydrocarbon impact to the uppermost 15 to 20 feet of the water-bearing zone 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 At the time of the second quarter 2003 monitoring event, groundwater was encountered in the monitonng wells screened within the upper zone at depths ranging from 47 76 to 49 88 feet bgs Well MW-3 is obstructed Groundwater was encountered in the monitoring wells screened within the lower zone at depths ranging from 48 09 to 51 98 feet bgs Groundwater elevations increased approximately 1 25 to 2 16 feet in upper zone wells since the February 5, 2003, monitoring event except for well MW-4 where groundwater elevation decreased by 1 07 feet In the lower zone wells, groundwater elevations increased 1 33 to 3 22 feet in wells MW-9 and MW-11 and decreased 0 38 to 1 10 feet in wells MW-10 and MW-12 The groundwater flow direction on May 28, 2003, was calculated to be to the southeast at a gradient of 0 012 ft/ft in the upper zone Since 1995, groundwater flow in the upper zone has consistently been • toward the east and southeast A groundwater contour elevation map for the upper zone is shown on Figure 2 In the lower zone, groundwater flow during the second quarter 2003 was toward the southeast at an average gradient of 0 014 ft/ft Groundwater flow in the lower zone has historically been toward the south and east A groundwater contour elevation map for the lower zone is shown on Figure 3 In the upper zone wells, THPG and BTEX were detected in wells VEW-1 and VEW-2 The highest TPHG concentration (120,000 µg/L) was detected in VEW-2, and the highest benzene concentration (2,500 µg/L) was detected in well VEW-1 TPHG or benzene were not detected in the samples collected from upper zone wells MW-2, MW-4, MW-5, or MW-7 MTBE was not detected in any of the upper or lower zone wells In the lower zone wells, TPHG and benzene were detected in well MW-9 at concentrations of 2,200 µg/L and 140 µg/L, respectively TBA and 1,2-DCA were detected in wells MW- 9 and MW-12 with the highest concentrations of TBA (170 µg&) and 1,2-DCA (21 µg/L) detected in well MW-9 Concentration and reporting limits for well MW-9 dropped two orders of magnitude from the first to the second quarter 2003 TPHG, benzene, and MTBE concentrations for samples collected and analyzed during the second quarter 2003 are included on Figure 4 PHS/EHD has requested that all peaks detected in the analyses be reported A copy of the laboratory tentatively identified compounds (TIC) report is attached Tentatively identified compounds were reported for wells MW-9, MW-12, VEW-1, and VEW-2 Results of the TIC analysis are summarized in Table 3 P\Apache Plastics%Quarterly reporls120031Apache_2Q03 DOC 57-KATU5