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Geological reclutidInc. Page 2 { Groundwater Monitoring Report Project No. 750.2 \ July 22,2003 A vertical groundwater gradient calculation was made for the June 2003 groundwater- monitoring event. The vertical gradient was found to be in an upward direction with a slope that is less than the water table horizontal gradient. r 1.0 GROUNDWATER MONITORING 1.1 Hydrogeology of Site � The dominant soil type in the upper 75-feet of subsurface geologic soils investigated is sand with fine to coarse-grained texture. Varying amounts of silt, silty sand and laterally discontinuous clay lenses were encountered from borehole to borehole. A thick clay layer was encountered starting at 95-feet in SB-101/MW-101 and continues to at least 115-feet. The average groundwater elevation measured during the June 5, 2003, event was 56.96 feet above mean sea level, which is consistent with previously measured average elevations at r the site. The groundwater elevation represents a decrease of approximately 0.42 feet since the monitoring event of March 6, 2003. r j Groundwater gradients were calculated for the June 2003 event. Groundwater was flowing N74°W at 0.0026 ft/ft. The gradient was calculated from the groundwater contours that were generated using the contouring program, Surfer 7. The elevation, gradient and bearing data are summarized in Table 1, Appendix A. The groundwater gradient contour is illustrated on Figure 3: Groundwater Gradient Map. Historical groundwater directions and gradients are presented in Figure 4: Rose Diagram, which shows a consistent westerly flow direction. 7 Vertical Groundwater Gradients � Under vertical groundwater _flow conditions, the water level in a monitoring well is a function of the length of the well screen and its depth or vertical position in the aquifer. As with horizontal flow conditions,.the diameter of the well or piezometer is immaterial. The following procedure is used to calculate vertical groundwater gradient: Determine vertical distance between the two measuring devices by the distance from the mid-point between the top and bottom seal of the deep well (MW-101) and the mid- point between the groundwater elevation and the bottom seal in the shallow well (MW- Measure the head in both wells used in the calculations. • If the lateral distance between the well pair is greater than a few feet, then calculations must be made to correct the down-gradient piezometric head to account for the sloping water table between the wells. The calculation considers the slope of the water table and the distance in a down-gradient direction between the two wells used in the calculations. i i