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California Department of Transportation February ry24, 2000 Shop 10 Maintenance Station, Stockton, California Project No 103872-02 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 rincluded in Appendix B 5. SUMMARY ANIS CONCLUSIONS Ninyo & Moore measured depth-to-groundwater and sampled eleven wells at the site on January 4 and 5, 2000 Groundwater elevation data indicates that the groundwater flow is to the northeast beneath the site with a hydraulic gradient of 0 003 feet per foot Comparatively, groundwater measurements recorded during the last monitoring event in September 1999 indicated ground- water movement beneath the site was toward the southeast under a hydraulic gradient of 0 002 feet per foot The depth to groundwater has increased in wells MW-12, MW-13, MW-14, MW- 19, MW-24, MW-25, and VM-1 since the last sampling event Monitoring wells MW-9, MW-11, MW-16, and MW-20 were not compared because the last groundwater measurements taken were during the Second Quarter Groundwater Monitoring Event in June, 1999 Increases in ground- water elevations were recorded in wells MW-12 by 1 07 ft , MW-13 by 0 31 ft , MW-14 by 0 99 tft , MW-19 by 1 02 ft , MW-24 by 0 69 ft , MW-25 by 1 2 ft , and VM-1 by 0 98 ft , respectively Laboratory data indicates changes in concentrations in many of the compounds analyzed for in samples taken from various wells on site In well MW-12, Total xylenes decreased in concentration from 7 5 microgram per liter (µg/1) to non-detect levels ahoplO doc 4