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• MONITOR WELLS <br /> Monitor wells MW1, MW2, MW3, MW4, and MW5 transverse both the A and B zones <br /> Contaminants found in these wells would mix with the groundwater of both zones <br /> Figure 5A represents the hydrocarbon groundwater plume in the A zone and shows an <br /> elongated plume extending west of MW2 out to "Geoprobe" hole P9 were degradation <br /> has left only minor TPHg (470 ug/L), Toluene (0 65 ug/L) and the degradation byproduct <br /> of MTBE (tert-Butanol at 11 ug/L) <br /> Figure 5B represents the hydrocarbon groundwater plume in the B zone and show a <br /> similar elongated plume extending west from MW2 out to "Geoprobe" hole P9 were <br /> degradation has left only minor Toluene (0 81 ug/L), Xylenes (0 83 ug/L) and MTBE <br /> (1 6 ug/L) <br /> Figure 6A represents the MTBE groundwater plume in the A zone and indicates that a <br /> possibility of two plumes exist One plume originating from the UST area near cluster <br /> well RI A expands to the west past Cluster well MW6A, to the north past MW 1 and to the <br /> south towards MW3 The second MTBE plume originates east of MWS and expands to <br /> the north towards MW2 and MW3 and to the west near cluster well MW7A <br /> 14 <br /> Figure 6B represents the MTBE groundwater plume in the B zone and shows similar <br /> plumes as indicated in Figure 6A One plume originating from the UST area near cluster <br /> well RIB expands to the west past "Geoprobe" P9, to the south MW3 and to the north <br /> past MW1 The second MTBE plume originates east of MW5 and expands to the north <br /> towards MW2 and MW3 and to the west near cluster well MW7A <br /> RECOMMENDATIONS <br /> 1) Conduct pump test to determine feasibility of dewatering during overexcavation of <br /> former UST area and/or dewatering in conjunction with vapor extraction At the end <br /> of the dewatering pump test, test the cluster wells for aquifer parameters and <br /> leakeage between the A and B zone, see Appendix J - Pump Test Procedures <br /> 2) Over-excavate former UST - piping and dispenser areas to approximately 24 feet <br /> bgs, see Figures 10 and I 1 Backfill excavation with piping and pea gravel to utilize <br /> as vapor extraction/air sparging area and groundwater recovery area <br /> 3) Conduct airsparging/vapor extraction pilot test using air sparging in conjunction with <br /> the installation of horizontal vapor collection piping within a backfilled over- <br /> excavation area that traverses the former UST - dispenser areas <br /> • <br /> 14 Sanchez 2nd QM 2001 <br />