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r YF <br /> A S S d C I A T E S I N C <br /> average decrease in the water table elevation of approximately 0 34 feet since October 1998 The <br /> water level data were used to develop the groundwater elevation contour map (Figure 3) <br /> Assuming that horizontal isotropic conditions prevail, groundwater in the uppermost aquifer <br /> beneath the site flowed generally towards the east-northeast The average hydraulic gradient on <br /> January 11, 1999 was calculated to be 0 0007 ft/ft or approximately 3 7 ft/nule A summary of <br /> groundwater monitoring data is presented in Table 1 <br /> CONCLUSIONS <br /> Concentrations of petroleum hydrocarbon constituents remained approximately the same in well <br /> MW-3 and remained at nondetectable concentrations in well and MW-6 It appears as though <br /> there is residual petroleum hydrocarbon contamination remaining in the soil <br /> The direction of groundwater flow and the magnitude of hydraulic gradient are generally <br /> consistent with previous quarters <br /> RECOMMENDATIONS <br /> Based on the results of the first quarter 1999 monitoring episode, we recommend the following <br /> o Conduct the Second Quarter 1999 groundwater monitoring and sampling of wells MW-3 <br /> and MW-6 <br /> o Continue to analyze the groundwater samples from all wells for TPHg, BTEX, and MTBE <br /> by EPA Method 8015/8020 <br /> Please contact our office at (209) 579-2221 if you have any questions or comments <br /> Respectfully Submitted, <br /> ATC Associates Inc <br /> Drew Van Allen _! <br /> Staff Scientist <br /> �i <br /> Jea a Homsey, <br /> CA Registered Civil Engineer No 47410 Exp <br /> civ <br /> cc Gerald Thiemann <br /> Mark List, RWQCB Q7 `� <br /> w 162605VW1y\1gr 1999 doc 3 <br />