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• <br /> A review of historical data using corrected wellhead elevations shows the groundwater flow <br /> direction at the site to generally be to the East-northeast not the southeast as previously reported <br /> The only exception was on April 1, 1997 when the groundwater flowed to the north-northwest <br /> Tins was likely the result of record rainfall totals and the groundwater elevation was at its highest <br /> elevation since monitoring began in August 1993 Copies of survey calculations and related data <br /> are included in Attachment 3 <br /> GROUNDWATER FLOW DIRECTION <br /> Water level measurements were collected from wells MW-1, MW-2, MW-3, MW-4, MW-5, and <br /> MW-6 on October 2, 1997 Water levels ranged from 25 58 to 26 36 feet below the tops of the <br /> well casing elevations, representing an average decrease in the water table elevation of <br /> approximately 3 50 feet since July 1997 The water level data were used to develop the <br /> groundwater elevation contour map (Figure 2) Assuming that horizontal isotropic conditions <br /> prevail, groundwater in the uppermost aquifer beneath the site flowed towards the northeast The <br /> average hydraulic gradient on October 1, 1997 was calculated to be 0 001 ft/ft or approximately 6 <br /> ft/mile A summary of groundwater monitoring data is presented in Table 1 <br /> CONCLUSIONS <br /> • Concentrations of petroleum hydrocarbon constituents increased in wells MW-3 and MW-6 It <br /> appears as though there is residual petroleum hydrocarbon contamination remaining in the soil <br /> The direction of groundwater flow and the magnitude of hydraulic gradient are consistent with the <br /> previous quarter Groundwater elevations have decreased since reaching their highest point in <br /> April 1997 since quarterly monitoring was started in August 1993 <br /> RECOMMENDATIONS <br /> Based on the results of the fourth quarter 1997 monitoring episode, we recommend the following <br /> o Conduct the First Quarter 1998 groundwater monitoring and sampling of wells MW-3 and <br /> MW-6 <br /> o Analyze the groundwater sample from well MW3 for MTBE to confirm the fourth quarter <br /> 1997 result, but discontinue analyzing groundwater samples from well MW3 for other <br /> oxygenate fuel additives <br /> o Discontinue analyzing the groundwater samples from well MW6 for oxygenate fuel <br /> additives <br /> • w 1943731quwt[yl4W-1997 doe 3 <br /> • <br /> SMTH <br />