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1 Groundwater Investigation Report Country Club Dram System Project City of Stockton Municipal Utilities Department October 2 2003 Page 7 1 vicinity of the Shell Oil site BTEX constituents were not detected at or above the laboratory reported detection limit in any of the groundwater samples TAME was detected in one sample (GP4) west of the Shell Oil site at a concentration of 34 µg/L MTBE was detected in 11 of the 15 samples at ' concentrations ranging from 1 1 to 3,400 µg1L The highest concentrations of MTBE were detected in samples collected in the vicinity of the Shell Oil site Groundwater sample analytical results are presented in Table 3, below Copies of the laboratory analytical reports and chain-of-custody forms are Ilocated in Appendix B Table 3—Groundwater Analytical Results 1 TBA MTBE TAME Benzene Toluene Total Ethyl Comments Xylenes Benzene Sample Number pg/L µglL Ng/L pg/L µg/L pg/L lig/L I 4176A-GP-1-09/17/03 <5 0 <0 5 <0 5 <0 5 <0 5 <l 0 <0 5 Upgradient of Shell Oil Site 4176A-GP-2-09117103 <5 0 48 <0 5 <0 5 <0 5 <1 0 <0 5 Crossgradient of Shell Oil Site 4176A-GP-3-09/17103 <5 0 <0 5 <0 5 <0 5 <0 5 <1 0 <0 5 Crossgradient of Shell Oil Site 4176A-GP-4-09117103 <5 0 3,400 34 <0 5 <0 5 <1 0 <0 5 Downgradient of Shell Oil Site I 4176A-GP-5-09117103 <5 0 5 5 <0 5 <0 5 <0 5 <1 0 <0 5 Downgradient of Shell Oil Site 4176A-GP-6-09117103 <5 0 26 <0 5 <0 5 <0 5 <1 0 <0 5 Downgradient of Shell Oil Site 4176A GP-7-09/17103 <5 0 1 1 <0 5 <0 5 <0 5 <1 0 <0 5 South end of Plymouth Road 4176A-GP-8-09/17103 <5 0 5 7 <0 5 <0 5 <0 5 <l 0 <0 5 South end of Plymouth Road 4176A GP-9-09124103 <5 0 11 <05 <0 5 <0 5 <l 0 <0 5 Downgradient of Shell Oil Site 4176A-GP-10-09124103 600 2 2 <0 5 <0 5 <0 5 <l 0 <0 5 Crossgradient of Shell Oil Site 4176A-GP-I1-09124103 52 21 <0 5 <0 5 <0 5 <1 0 <0 5 Down radient of Shell Oil Site 4176A-GP-12-09/24103 <5 0 <0 5 <0 5 <0 5 <0 5 <1 0 <0 5 Downgradient of Exxon Site ' 4176A-GP-13-09124103 <5 0 16 <0 5 <0 5 <0 5 <1 0 <0 5 Downgradient of Exxon Site 4176A-GP-14-09124/03 <5 0 <0 5 <0 5 <0 5 <0 5 <l 0 <0 5 Downgradient of Exxon Site 4176A-GP-15-09/24103 <5 0 3 6 <0 5 1 <05 <0 5 1 <10 I <0 5 Downgradient of Exxon Site ' hg/L nucrogram per liter,parts per billion TBA tertiary butanol MTBE methyl tertiary-butyl ether TAME tertiary-amyl methyl ether I 5 0 DISCUSSION OF GEOPROBE RESULTS Condor observed the advancement of 15 borings in the vicinity of Country Club Blvd and Plymouth Road to identify potential sources of contamination (primarily additives/oxygenates) that have impacted the City of Stockton MUD storm drain system The results show that MTBE was detected in 11 of the 15 samples collected, TBA was detected in two samples, and TAME was detected in one sample There were two detections of MTBE downgradient of the Exxon Mobil site, with the remaining detections crossgradient or downgradient of the Shell Oil site TAME and TBA were detected at locations ' crossgradient and downgradient of the Shell Oil site The highest concentration of MTBE and the only detection of TAME were detected in GP-4, downgradient of the Shell Oil site The highest concentration of TBA was detected in GP-10,crossgradient of the Shell Oil site ' 6.0 STORM DRAIN VIDEO SURVEILLANCE RESULTS On October 2, 2003, Cal Sierra Construction conducted a video surveillance of the storm drain along Plymouth Road A total of 206 3 feet of the storm drain was surveyed with a specially-equipped video camera The storm drains were surveyed by plugging sections of the drain, pumping out the existing water, and then conducting a video surveillance of the drain Based on visual inspection, the storm drains that run west of GP-1 and west of Plymouth Road, along Country Club Blvd , are above the water table, and thus the drains were dry What appeared to be open or offset points were observed at several places . along the drain Staining was observed at the locations identified as having offset joints, indicating ' �� CONDOR