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' U eolo iutTechmaIna Page 2� g <br /> 2°d Quarter 2003 Groundwater Monitor ng Report <br /> Project No 507 2 <br /> September 24,2003 <br /> 1.0 GROUNDWATER MONITORING <br /> 1.1 Hydrogeology of Site <br /> The geology of the site is predominately clays and sandy clays with lesser amounts of silts <br /> ' and sands The average groundwater elevation was —10 87 feet below msl on June 24, <br /> 2003, which corresponds to approximately 16 feet below grade surface (bgs) This <br /> elevation represents a decrease of 0 57 feet since the March 18, 2003 monitoring event A <br /> ' specific groundwater gradient could not be calculated due to anomalous elevations in wells <br /> MW-5, 7, & 10 This site consistently exhibits a flat groundwater gradient <br /> The gradient direction for the June 2003 monitoring event is shown in Figure 2, and the <br /> historical groundwater directions and gradients are shown in Figure 3, Groundwater <br /> ' Gradient Rose Diagram The groundwater elevation data are summarized in Table 1, <br /> Appendix A Table 5 provides a summary of monitoring well construction <br /> An anomalous low is present in the vicinity of well MW-5 as shown in Figure 2 This is <br /> accompanied by an anomalous "low" in well MW-7 and "high" in well MW-10 that results <br /> in variable gradients for the event As evident in Figure 3, groundwater exhibited a strong <br /> bifurcated flow regime in 2000, trending predominantly to the southwest or north-northeast <br /> at approximately 180-degree direction reversal Since the installation of wells MW-7 and <br /> MW-10 in May 2001, the direction had been to the east-northeast in eight of ten quarterly <br /> ' events The site is quite close to the San Joaquin River and tidal fluctuations may contribute <br /> to some of the observed changes in groundwater direction <br /> ' Vertical Groundwater Gradients <br /> Under vertical groundwater flow conditions, the water level in a monitoring well is a <br /> ' function of the length of the well screen and its depth or vertical position in the aquifer As <br /> with horizontal flow conditions, the diameter of the well or piezometer is immaterial <br /> ' The following procedure is used to calculate vertical groundwater gradient <br /> • Determine the vertical distance between the two measuring devices by the distance from <br /> the mid-point between the top and bottom seal of the deep well (MW-1 09) and the mid- _ <br /> point between the groundwater elevation and the bottom seal in the shallow well (MW- <br /> 9) <br /> • Measure the head in both wells used in the calculations <br /> ' 0 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 piezometnc head to account for the sloping <br /> water table between the wells The calculation considers the slope of the water table and <br /> the distance in a down-gradient direction between the two wells used in the calculations <br />