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' California Department of Transportation November 24, 1999
<br /> Stockton Maintenance Station, Stockton, California Project No 103872-02
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<br /> 4.3. Laboratory Analysis
<br /> The groundwater samples were submitted for analysis to AL, a State of California-certified
<br />' hazardous waste analytical laboratory Samples were analyzed for TPH-G and TPH-D, using
<br /> method EPA 8015 (modified) Samples were analyzed for BTEX, methyl tertiary-butyl ether
<br />' (MTBE), tertiary-amyl-methyl ether (TAME), isopropyl ether (DIPE), tertiary butyl (TBA),
<br /> ethyl-tertiary-butyl ether (ETBE), and volatile organic compounds (VOCs) using method
<br /> EPA 8260B A summary of the past and present laboratory results for the groundwater sam-
<br /> ples is presented in Table 1 Copies of laboratory results and chain-of-custody documents are
<br />' included in Appendix B
<br />' 5. SUMMARY AND CONCLUSIONS
<br />' Ninyo & Moore measured depth-to-groundwater and sampled fourteen wells at the site on Sep-
<br /> tember 22 and 23, 1999 Groundwater elevation data indicates that the groundwater flows to the
<br /> southeast beneath the site with a hydraulic gradient of 0 002 feet per foot Comparatively,
<br /> groundwater levels taken during the last monitoring event in June 1999 indicate groundwater
<br /> movement beneath the site towards the south under a hydraulic gradient of 0 002 feet per foot
<br /> Groundwater elevation has decreased in all of the on-site wells since the last monitoring event
<br /> Depth to groundwater level decreases are as follows MW-1, 2 86 ft , MW-2, 2 86 ft , MW-3,
<br /> 2 86 ft , MW-4, 2 85 ft , MW-5, 2 86 ft , MW-6, 2 87 ft , MW-7, 2 82 ft , MW-8, 2 87 ft , MW-
<br /> 9, 2 82 ft , MW-10, 2 96 ft , MW-11, 2 84 ft , MW-12, 2 8 ft , VW-1,
<br /> W-
<br /> 9, 282ft , MW-10, 296ft , MW-11, 284ft , MW-12, 28ft , VW-1, 282 ft , and VW-2, 285ft
<br /> Laboratory data has indicated changes in many of the compounds analyzed for in samples taken
<br /> from various wells on site since the June 1999 monitoring event Highlights of the analytical data
<br />' follows
<br /> According to laboratory data well MW-1 showed decreases in benzene concentrations from 2 26
<br />' microgram per liter (ug/1) to non detect and total xylenes concentrations from 16 ug/1 to non-
<br /> detect
<br /> Benzene concentrations increased in well MW-2 from non detect levels to 15 ugA
<br />' stocMon doc 4
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