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Subsurface Investigation Report
<br /> Installation of Wells MWS,MW6,and MW7
<br /> 640 N El Dorado Street, Stockton, CA
<br /> I3.3 Groundwater Analytical Results
<br /> I3 3 1_ Discrete Groundwater Samples
<br /> Discrete groundwater samples were collected from boring SB9 at a depth of approximately 25 feet bsg,
<br /> from boring SB10 at depths of approximately 25 and 49 feet bsg, and from boring SBI 1 at a depth of
<br /> approximately 25 feet bsg Attempts to collect discrete water samples from SB9 a feet bsg and from
<br /> SB 11 at 50 feet fbsg were unsuccessful because the formation would not yield sufficient water
<br /> I No petroleum hydrocarbon constituents were detected in any groundwater samples collected from
<br /> borings SB9, SB 10 or SB 11 Several chlorinated hydrocarbons were present, however The groundwater
<br /> sample collected from SB9 at 30 feet contained chloroform at 1 7 parts per billion (ppb) and
<br /> I tetrachloroetbene (PCE) at 5 5 ppb The sample collected from SB 10 at 25 feet contained chloroform,
<br /> cis-l,2-dichloroethene (cis-1,2-DCE), and PCE at 2 0 ppb, 0 6 ppb, and 7 9 ppb, respectively The
<br /> sample collected from SB10 at 49 feet contained cis-1,2-DCE, PCE, and trichloroethene (TCE) at 5 5
<br /> ppb, 25 ppb, and 2 0 ppb, respectively The sample collected from SB 11 at 25 feet contained only
<br /> 1,1,2,2-tetrachloroethane (1,1,2,2-TCA) at 1 9 ppb Of the chlorinated hydrocarbons detected only PCE
<br /> and 1,1,2,2-TCA were detected at levels exceeding their primary Maximum Contamamant Levels
<br /> (MCLs)of 5 ppb and 1 ppb, respectively
<br /> Discrete groundwater analytical results from borings SB9, SB10, and SBI1 are summarized in Table 6
<br /> Laboratory reports and chain of custody documentation are included in Appendix 4
<br /> 3 3 2 Monitoring Wells
<br /> No petroleum hydrocarbon constituents were detected in any site wells sampled in June 2003 Well
<br /> MW3 was not sampled due to the presence of free product in the well VOCs were detected at relatively
<br /> low concentrations in each well, however
<br /> Chloroform and cis-1,2-DCE were detected in each well, but at levels below their respective MCLs of 80
<br /> ppb and 6 ppb PCE was detected at concentrations exceeding its MCL of 5 0 ppb in each site well
<br /> (except MW3 which was not sampled), ranging from 7 9 ppb in well MW5 to 110 ppb in well MW7
<br /> TCE was detected in wells MW1, MW6, and MW7, but its MCL of 5 ppb was exceeded only in well
<br /> MW7, which contained 5 1 ppb TCE No 1,1,2,2-TCA was detected in groundwater sampled from well
<br /> I MW7 or any other site well Analytical results are summarized in Table 7 Laboratory reports are
<br /> included in Appendix 4
<br />' Monitoring wells were also sampled in September and December 2003 as part of the quarterly sampling
<br /> program The groundwater gradient in September 2003 (Figure 7) and December 2003 (Figure 8) was
<br /> toward the northeast, consistent with previous data (Table 8) Petroleum hydrocarbon constituents were
<br />' detected only in well MW3, but each site well contained one or more VOC constituents, as follows
<br /> Well MW I contained PCE at concentrations exceeding the MCL of 5 ppb in September (15 ppb) and
<br /> I
<br /> December(12 ppb) Well MW1 also contained chloroform, cis-1,2-DCE, and TCE at levels below their
<br /> le respective MCLs
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