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California24 2000 iiia Department of Transportation February , Stockton Maintenance Station, Stockton, California Project No 103872-02 t4.3. Laboratory Analysis The groundwater samples were submitted for analysis to AL, a State of Califorma-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 (D1PE), 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 fourteen wells at the site on Janu- ary 5 and 6, 1999 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 September 1999 indicate a similar flow direction and gradient rate Groundwater elevation has increased in all of the on-site wells since the last monitoring event Depth to groundwater level increases are as follows MW-1, 1 22 ' ft , MW-2, 1 24 ft , MW-3, 121 ft , MW-4, 1 24 ft , MW-5, 1 27 ft , MW-6, 1 21 ft , MW-7, 1 18 ft , MW-8, 1 21 ft , MW-9, 1 19 ft , MW-10, 1 27 ft , MW-11, 1 2 ft , MW-12, 2 12 ft , VW-1, 1 19 ft , and VW-2, 1 2 ft 1 Laboratory data has indicated changes in many of the compounds analyzed for samples taken from various wells on site since the September 1999 monitoring event Highlights of the analyti- cal data follows TPH-D could not be analyzed for sample MWA due to broken containers upon lab arrival of 1 samples Benzene concentrations decreased in well MW-2 from 15 ug/l to 7 5 ligA and total xylene in- creased from non-detect to 7 8 µg11 .-kton doc4 V QU V g%�LlUry/ '&U�"/ 'mrs