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C\TL V( <br /> A S S O C I A T E S I N C <br /> GROUNDWATER FLOW DIRECTION <br /> Water level measurements were collected from wells MW1 through MW3 on September 8, 1999. <br /> Water levels ranged from 24.84 to 25.42 feet below the tops of the well casings elevation, <br /> representing an average decrease in the water table elevation of approximately 1.70 feet since <br /> June 1999. The water level data were used to develop the groundwater elevation contour map <br /> (Figure 2). Assuming that horizontal isotropic conditions prevail, groundwater in the uppermost <br /> aquifer beneath the site flowed towards the northeast. The average hydraulic gradient on <br /> September 8, 1999 was calculated to be 0.002 ft/ft or approximately 10 ft/mile. A summary of <br /> groundwater monitoring data is presented in Table 1. <br /> CONCLUSIONS <br /> Concentrations of petroleum hydrocarbons remained the same in wells MW1 and MW2 as the <br /> previous sampling event. Concentrations of TPHg and TPHss increased in well MW3 and the <br /> concentration of TPHd decreased in well MW3. The direction of groundwater flow has been <br /> consistently northeast since the groundwater wells were installed in September 1998. <br /> Groundwater elevations have decreased since June 1999. <br /> RECOMMENDATIONS <br /> Based on the results of the third quarter 1999 monitoring episode, we recommend the following: <br /> • Conduct the Fourth Quarter 1999 groundwater monitoring and sampling of wells MW 1 <br /> through MW3 and analyze samples for TPHg, TPHd, TPHss,and BTEX. <br /> • Groundwater concentrations and gradient have remained relatively consistent during four <br /> quarters of monitoring subsequent to the installation of the groundwater monitoring <br /> wells. ATC recommends installing one additional groundwater monitoring well <br /> southwest of well MW3 in the driveway of the muffler shop, to define lateral extent of <br /> impacted groundwater. This well will be located directly upgradient of well MW3. <br /> If PHSIEHD agrees with these recommendations, ATC will submit a workplan showing the <br /> proposed location of the additional monitoring well and permit application for the installation of <br /> the groundwater monitoring well. <br /> w;1172951quart1yl3gr-1999.doc 3 <br />