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1117 Lone Palm Avenue, Suite B <br /> Modesto, CA 95351 <br /> www.atcassociates.com <br /> *(YA 209-579-2221 <br /> AS SOCIATE s i N c . Fax 209-579-2225 <br /> Environmental,Geotechnical and Materials Engineers <br /> CONCLUSIONS <br /> The laboratory analytical results of the groundwater samples collected from all the monitoring wells <br /> in December 2005 are generally consistent with recent historical analytical results of groundwater <br /> samples collected from these wells. MW1 and MW8 located in the central portion of the site are the <br /> most impacted wells. The concentrations of benzene, ethyl benzene, and xylenes detected in the <br /> groundwater sample collected from MW1 increased slightly with respect to the previous sampling <br /> event. The TPHg concentration in this sample decreased with respect to the previous sampling event. <br /> The concentrations of petroleum hydrocarbons detected in the groundwater sample collected from <br /> MWS increased with respect to the previous sampling event. The concentrations of petroleum <br /> hydrocarbons detected in the groundwater sample collected from deep well MW7 increased slightly <br /> but insignificantly with respect to the previous sampling event and suggest that the vertical extent of <br /> impacted groundwater in the vicinity of this well is close to 120 feet bgs. <br /> The shallow groundwater plume appears to be adequately defined to the west and north in the <br /> vicinities of MW 10 and MW 11R, but is not defined to the east and south. The intermediate <br /> groundwater plume appears to be generally defined to the northwest in the vicinity of MW12,but not <br /> well defined in other directions. Groundwater flow in the shallow zone was variable with eastward <br /> and northward components flowing toward the center of the site. Groundwater flow in the <br /> intermediate zone was towards the south. <br /> �r Additional investigation to the east and south is necessary to evaluate the extent of petroleum <br /> hydrocarbon impact. ATC is in the process of addressing comments from the San Joaquin County <br /> Environmental Health Department regarding the Subsurface Investigation Workplan, dated October <br /> 31, 2005. <br /> Please contact our office at(209) 579-2221 if you have any questions or comments. <br /> Respectfully submitted, <br /> ATC Associates Inc. <br /> Todd Ha' er, P.G. <br /> Professional Geologists <br /> Jeanne Hornsey, P.E. `�,r •�� n.e�� t~ <br /> CA Registered Civil Engineer No. 47410 <br /> • cc: Mr. &Mrs. Ernest Foppiano <br /> Mr. Jim Barton, CRWQCB <br /> s:\enviromental\283491reports12005 4QMR.doc 4 ATC Associates Inc. <br />