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California Department of Transportation April 24 2000 Shop 10 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 I 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 eleven wells at the site on March 27 and 28, 2000 Groundwater elevation data indicates that the groundwater flow is to the north- east beneath the site with a hydraulic gradient of 0 003 feet per foot Comparatively, groundwater measurements recorded during the last monitoring event in January 2000 indicated groundwater movement beneath the site was similar The groundwater elevation has increased in all wells since the last sampling event Increases in groundwater elevations were recorded in wells MW-9 by 2 63 ft , MW-11 by 2 5 ft , MW-12 by 2 75 ft , MW-13 by 2 59 ft , MW-14 by 2 69 ft , MW- 16 by 2 6 ft , MW-19 by 2 68 ft , MW-20 by 2 45 ft , MW-24 by 2 71 ft , MW-25 by 2 3 ft and VM-1 by 2 68 ft Laboratory data indicates changes in concentrations in many of the compounds analyzed for in samples taken from various wells on site since the last monitoring event In well MW-13, TPH-G concentrations remained at 300 pg/l and benzene increased from 7 3 pg/l to 33 pg/l In well MW-16, TPH-G concentrations decreased form 150 pg/l to non detect • shop 10 DEL d" 4