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Chemical analysis <br /> . The groundwater samples collected were analyzed for Total Petroleum <br /> Hydrocarbons as Gasoline (TPHG) ; Benzene, Toluene, Ethylbenzene <br /> and Xylene (BTEX) and Methyl-tert-butyl ether (MTBE) . The <br /> groundwater samples were analyzed for TPHG by EPA Method 8015 <br /> modified with purge and trap preparation 5030 (GC/FID) with <br /> detection limits of 50ug/l. EPA Method 602 was utilized for BTEX <br /> with a detection limit of 0. 5ug/l as required by the SJCEHD. <br /> The results of the analysis of the groundwater samples in parts per <br /> billion (ppb) are shown in Table 3. The laboratory data sheets <br /> with detection limits and COC documentation are contained in <br /> Appendix B. <br /> TABLE 3 <br /> Sept. 13, 1996 Groundwater Sample Analysis Results in ppb. <br /> Sample TPHG MTBE B T E X <br /> MW-1 ND ND 0.98 3 . 3 0.74 2 .7 <br /> MW-2 1, 400 ND 360 31 11 16 <br /> MW-3 180 ND 5. 6 5. 1 3 . 5 4 .0 <br /> ND = <4 <br /> SUMMARY CONCLUSIONS AND RECOMMEN ATIONS <br /> The concentrations of TPHG and BTEX in the groundwater collected <br /> from the monitoring wells have decreased significantly over the <br /> last 15 months. <br /> The calculated gradient is to the south at approximately 0.005 <br /> ft/ft. The calculated gradient in the prior quarterly measurement <br /> had shifted from a southeasterly to a southerly direction with a <br /> slight slope. The irrigation ditches around the area have water <br /> in them. The local groundwater recharge conditions irrigation and <br /> slough depths are most likely the main influences on the gradient. <br /> The concentrations of TPHG and BTEX in the groundwater are less <br /> than the values initially reported in the prior environmental <br /> investigation at this site. <br /> This site is a likely candidate for the newly suggested Risk Based <br /> Corrective Action (RBCA)_ being developed by the California State <br /> Water Control Board for the following reasons. <br /> i <br />