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California Department of Transportation August 17, 1999 Shop 10 Maintenance Station, Stockton, California Project No 103872-02 I4.3 Laboratory Analysis The groundwater samples were submitted for analysts 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 kkere 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 5 SUMMARY AND CONCLUSIONS Ninyo & Moore measured depth-to-groundwater and sampled twelve wells at the site between June 24 and June 29, 1999 Groundwater elevation data indicates that the groundwater flow is to the southeast beneath the site with a hydraulic gradient of 0 0015 feet per foot Comparatively, groundwater measurements recorded during the last monitoring event in April 1999 indicated groundwater movement beneath the site was toward the southeast under a h}draulic gradient of 0 0026 feet per foot The depth to groundwater has increased in all wells except MW-19 where ' groundwater depth has decreased in depth since the last sampling event Increases in depth to groundwater were recorded in wells MW-9 by 0 37 ft ,MW-11 by 0 17 ft , MW-12 by 0 39 ft , IMW-13 by 0 20 ft , MW-14 by 0 38 ft , MW-16 by 0 37 ft , MW-20 by 0 35 ft , MW-24 by 0 45 ft , MW-25 by 0 40 ft , VM-1 by 0 25 ft , and VM-2 by 0 18 ft , respectively A decrease in depth to groundwater was recorded in well MW-19 by 3 48 ft Laboratory data has indicated increases and decreases in many of the compounds analyzed for in 1 samples taken from various wells on site In well MW-13, TPH-G increased in concentration from non detect to 500 microgram per liter (ug/1), and TPH-D decreased from 400 ug/1 to non detect Benzene decreased from 950 ug/l to 471 ug/l, toluene, ethylbenzene, and total xylenes also decreased from 4 3 ug/l to non detect, from 75 ug/l to non detect, and from 35 ug/1 to 8 6 ' ,u Ilrespectively, since April 1999 g shop]0 doc 4