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' California Department of Transportation p September 6, 2001 Stockton Maintenance Station, Stockton, California Project No 400296001 ' 4.3. ]Laboratory Analysis The groundwater samples were submitted for analysis to AL, a State of California-certified hazardous waste analytical laboratory Samples were analyzed for TPH-G and TPH-D, using EPA method 8015 (modified), and volatile organic compound (VOCs), including methyl ' tertiary butyl ether (MTBE), tertiary-amyl-methyl ether (TAME), isopropyl ether (DIPE), tertiary butyl alcohol (TBA), and ethyl-tertiary-butyl ether (ETBE) using EPA method 8260B Samples were also analyzed for BTEX using EPA method 8021 B A summary of the past and present laboratory results for the groundwater samples is presented in Table 1 Copies of laboratory results and chain-of-custody documents are included in Appendix B 5. SUMMARY AND CONCLUSIONS Ninyo & Moore measured depth-to-groundwater and sampled fourteen wells at the site on June 4 and 5, 2001 Groundwater elevation data indicates that the groundwater flows to the east beneath the site with a hydraulic gradient of 0 13 ft/ft Comparatively, groundwater levels taken during the last monitoring event in March indicate the flow direction towards the southeast and a hy- draulic gradient of 0 003 ft/ft Groundwater elevation has decreased in all of the on-sate wells since the last monitoring event Groundwater elevations have decreased in momtonng well MW- I by086ft , MW-2by072ft , MW-3by09fl , MW-4by088ft , MW-5by088ft, MW-6 by 0 84 ft , MW-7 by 0 93 fl , MW-8 by 0 08 ft , MW-9 by 0 8 ft , MW-10 by 0 86 fl , MW-11 by 0 62 ft , MW-12 by 0 88 fl , VW-I by 0 85 ft and VW-2 by 0 85 ft Laboratory analytical data has indicated changes in many of the compounds analyzed in samples taken from various wells on site since the March 2001 monitoring event In well MW-1, benzene concentration increased from non-detectable levels to 1 0 micrograms per liter(µg/1) Total xylenes concentration increased from non-detectable le%els to 10 µg/1 In well MW-2, TPH-G concentration increased from 200 [ig/1 to 660 µg/] Benzene concentra- tion increased from 49 pg/l to 1,130 µg/t Toluene concentration increased from non-detectable . levels to 163 µg/1 Total xylene concentration increased from 30 µg/1 to 778 µg/1 Ethylbenzene 0296 01 stockton 2Q01 doc Mftt(y!