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California Department of Transportation April 24 2000 Stockton Maintenance Station, Stockton, California Project No 400296-01 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 method EPA 8015 (modified) Samples were analyzed for BTEX, methyl tertiary-butyl ether (MTBE), tertiary-amyl-methyl ether (TAME), isopropyl ether (DIPE), tertiary butyl (TBA), ethyl-tertiary-butyl ether (ETBE), and volatile organic compounds (VOCs) using method EPA 8260B A summary of the past and present laboratory results for the groundwater sam- ples is presented in Table 1 Copies of laboratory results and chain-of-custody documents are included in Appendix B 1 5 SUMMARY AND C®NCLUSI®NS Ninyo & Moore measured depth-to-groundwater and sampled fourteen wells at the site on March 27 through March 29, 2000 Groundwater elevation data indicates that the groundwater flows to • the southeast beneath the site with a hydraulic gradient of 0 002 feet per foot Comparatively, groundwater levels taken during the last monitoring event in January 2000 indicate flow direc- tion southeast beneath the site with a similar hydraulic gradient of 0 002 feet per foot Groundwater elevation has increased in all of the on-site wells since the last monitoring event Ggroundwater elevations have increased in monitoring well MW-1 by 2 7 ft , MW-2 by 2 53 ft , MW-3 by 2 56 ft , MW-4 by 2 52 ft , MW-5 by 2 51 ft, MW-6 by 2 55 ft , MW-7 by 2 57 ft , MW-8 by 2 56 ft , MW-9 by 2 57 ft , MW-10 by 2 5 ft , MW-11 by 2 54 ft , MW-12 by 1 64 ft , VW-1 by 2 57 ft and VW-2 by 2 56 ft , respectively Laboratory data has indicated changes in many of the compounds analyzed for in samples taken from various wells on site since the January 2000 monitoring event Highlights of the analytical data follows Benzene concentrations decreased in well MW-2 from 7 5 ug/l to non detect levels and total xy- lene decreased from 7 8 µg11 to non-detect levels • TPH-G concentrations increased in well MW-6 from 36 µg/1 to 380 gg/l stockton AR ax 4