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a i <br /> T <br /> �I Geo(ngica(Technirs Inc. <br /> Groundwater Monitoring Report Page 4 <br /> Project No. 750.2 <br /> June 15,2001 i <br /> s ' <br /> f1.3 Laboratory Analyses <br /> I' L <br /> The groundwater samples collected on May 15, 2001, were delivered to Sherwood Lab <br /> t (Department of Health Services Certification No. 1400), of Hilmar, California, for analysis. <br /> The groundwater samples were analyzed for: <br /> • Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX). <br /> • Total Petroleum Hydrocarbons as Gasoline (TPH-G) by EPA method 503018015(M). <br /> j <br /> tAdditional samples were sent to Entech Analytical Labs, Inc. from Sherwood Labs for the <br /> analysis of: <br /> • Fuel oxygenated compounds (MTBE, DIPE, ETBE, TAME & TBA) by EPA method <br /> 8260. ; <br /> i <br /> The detection limits for the above analyses are listed in Table 2 of Appendix A and the lab <br /> data is presented in Appendix B. <br /> 2.0 FINDINGS AND DISCUSSION <br /> fThe results of the groundwater sample analyses show the following: <br /> • Since monitoring was initiated in April 2000, well MW-1 has consistently contained <br /> F gasoline range petroleum hydrocarbons (TPH-G, BTEX, & MTBE). However, for this <br /> { <br /> event, MW-1 did not contain BTEX and TPH-G contaminants for the first time. This is <br /> indicative of a shrinking plume with leaching from the. residual soil contamination <br /> approaching negligible levels. <br /> • The discretely screened deep well MW- <br /> 101 did not contain contaminant concentrations <br /> 1 above the laboratory reporting limits. This suggests that the previously recorded <br /> contamination was a drilling artifact. <br /> • Cross gradient well MW-5 contained 354 ug/l TPH-G, suggesting that preferred <br /> migration pathways in the vadose zone might actually be channeling the contaminants to <br /> the north. <br /> • All other wells were found to be free of contaminants, which is consistent with other <br /> + events. <br /> • Vertical groundwater gradient was calculated and determined to be downward and <br /> greater than the horizontal gradient of the water table, suggesting that the contaminants <br /> in the water table may be transported to deeper depths in the subsurface. <br /> + Oxidation-Reduction Potential measurements (Table 4) are positive for all the wells, <br /> l suggesting that the volume of contaminants leaching into groundwater is minimal and <br />