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RESULTS OF CERTIFIED ANALYSIS OF GROUNDWATER SAMPLES <br /> MONITOR WELLS <br /> Monitor wells MWI, 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 I 1 ug/L) <br /> Figure 5B represents the hydrocarbon groundwater plume in the B zone and shows a <br /> similar elongated plume extending west from MW2 out to "Geoprobe" hole P9 were <br /> degradation has left only minor amounts of Toluene (0 81 ug/L), Xylenes (0 83 ug/L) <br /> and MTBE (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 RIA expands to the west past Cluster well MW6A and to the north past MWI The <br /> second MTBE plume seems to originate east of MW5 and expands to the north towards <br /> MW3 and and to the west near cluster well MW7A <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 MWI The second MTBE plume also seems to originate east of MW5 and expands <br /> to the north 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 <br /> 2) Over-excavate former UST - piping and dispenser areas to approximately 24 feet <br /> bgs, see Figures 10 and 11 Backfill excavation with piping and pea gravel for use in <br /> future vapor extraction/air spargmg and groundwater recovery <br /> 3) Conduct airspargmg/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 /> 6 Sanchez 3rd QM 2001 <br />