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I Subsurface Investigation Report ' Installation of Wells MWS,MW6,and MW7 640 N El Dorado Street, Stockton, CA ' Well MW2 contained PCE at concentrations exceeding the MCL of 5 ppb in September (8 7 ppb) and December(9 4 ppb) Well MW2 also contained chloroform, cis-1,2-DCE, and TCE at levels below their ' respective MCLs Well MW3 did not contain PCE at concentrations exceeding the detection limit of 2 0 ppb in either September or December However, MW3 contained benzene, cis-1,2-DCE, and TCE at levels exceeding ' their respective MCLS, and several other compounds at lower levels Well MW4 contained PCE at concentrations exceeding the MCL of 5 ppb in September (8 1 ppb) and ' December(7 4 ppb) Well MW4 also contained chloroform and cis-1,2-DCE at lower levels Well MW5 contained PCE at concentrations equal to or exceeding the MCL of 5 ppb in September(6 3 ' ppb) and December(5 0 ppb) Well MW5 also contained chloroform at lower levels Well MW6 contained PCE at concentrations exceeding the MCL of 5 ppb in September (48 ppb) and ' December(34 ppb) Well MW6 also contained chloroform, cis-1,2-DCE, and TCE at lower levels Well MW7 contained PCE at concentrations exceeding the MCL of 5 ppb in September (120 ppb) and ' December (77 ppb), and TCE at concentrations exceeding its MCL of 5 ppb in September (6 5 ppb) Well MW7 also contained chloroform and cis-1,2-DCE at lower levels No 1,1,2,2-TCA was detected in groundwater sampled from well MW7 Groundwater analytical results from June through December 2003 are summarized in Table 7 Laboratory reports and chain of custody documentation are included in Appendix 4 ' 4.0 SUMMARY ' Three soil borings (SB9 through SB 11) were advanced and three groundwater monitoring wells (MW5- MW7) were installed at the site to further investigate the extent of soil and groundwater contamination at ' the site The first water-bearing zone encountered during drilling was a well graded sand from approximately 29- 30 feet bsg in upgrad►ent boring S139 (MW5), from approximately 25-27 feet bsg in downgradient boring ' SB 10 (MW6), and from approximately 25-30 feet bsg in cross-gradient boring SB 11 (MW7) Groundwater was initially encountered at depths corresponding to these upper sand units, but eventually rose within the well bore In addition, deeper sandy zones were encountered in boring SB9/MW5, from approximately 40-43 bsg, and in boring SB 10/MW6, from approximately 48-51 feet bsg No petroleum hydrocarbons or VOCs were detected in soil samples collected during drilling Discrete groundwater samples collected from the upper sand zone in borings SB9 and SB10 contained PCE at 5 5 ppb and 7 9 ppb, respectively No PCE was detected in the shallow water sample collected from boring SB11 PCE was also detected in a discrete water sample collected from the deeper sandy zone in boring ' SB 10, at 25 ppb No deeper water samples could be collected from borings SB9 or SB 11 because the deeper formations in these borings did not yield sufficient water to the sampler Several other VOCs iwere also detected in the discrete groundwater samples (Table 6) 1 -6-