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t , <br /> Geological Technics inc. Page 2 <br /> Groundwater Monitoring Report <br /> Project No.750.2 <br /> May;15,2003 <br /> from the site due.to mechanical failure. The IC was rebuilt again and returned to the site on <br /> June 14. The IC ran continuously from June 14 to December 10, 2002, when it was <br /> shutdown for a spike test. The VETS was restarted on January 1, 2003 and ran until January <br /> 31, 2003 when it was shutdown due to the end of operation for both the air permit and cost <br /> pre-approval. The VETS removed approximately 700 gallons of gasoline from the <br /> subsurface during 256 days of operation. <br />! 1.0 GROUNDWATER MONITORING <br />{ <br /> 1.1 ✓ Hydrogeology of Site <br />+ The dominant soil type in the upper 75-feet of subsurface geologic soils investigated is sand <br /> with fine to coarse-grained texture. Varying amounts of silt, silty sand and laterally <br /> discontinuous clay lenses were encountered from borehole to borehole. A thick clay layer <br /> was'encountered starting at 95-feet in SB-101/MW-101 and continues to at least 115-feet. <br /> The average groundwater elevation on the December 30, 2002, event was 57.38 feet above <br /> mean sea level, which is consistent with previously measured average elevations at the site. <br /> + The' groundwater elevation represents an increase of approximately 0.4 feet since the <br /> monitoring event of December 30, 2002. <br /> Groundwater gradients were calculated for the March 2003 event. Groundwater was flowing <br /> N820W at 0.0012 ft/ft. The gradient was calculated from the groundwater contours that were <br /> generated using the contouring program, Surfer 7. The elevation, gradient and bearing data <br /> j are summarized in Table 1, Appendix A. The gradient direction is illustrated on Figure 2: <br /> Gradient Map. Historical groundwater directions and gradients are presented in Figure 3: <br /> Groundwater Gradient Rose Diagram, which shows a consistent westerly flow direction. <br /> Vertical Groundwater Gradients <br /> Under vertical groundwater flow conditions,the water level in a monitoring well is a function <br /> of the length of the well screen and its depth or vertical position in the aquifer. As with <br /> horizontal flow conditions,the diameter of the well or piezometer is immaterial. <br /> f <br /> Thefollowing procedure is used to calculate vertical groundwater gradient: <br /> • Determine vertical distance between the two measuring devices by the distance from the <br /> mid-point between the top and bottom seal of the deep well (MW-101) and the mid-point <br /> between the groundwater elevation and the bottom seal in the shallow well (MW-,1). <br /> • Measure the head in both wells used in the calculations. <br /> L` • If the lateral distance between the well pair is greater than a few feet, then calculations <br /> must be made to correct the down-gradient piezometric head to account for the sloping <br />