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Geological recknccs Inc Page 2 <br /> ' 4"'Quarter 2002 Groundwater Monitoring Report <br /> Project No 507 2 <br /> March 7,2003 <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 —11 05 feet below msl on December 20, <br /> 2002, which corresponds to approximately 16 feet below grade surface (bgs) This <br /> ' elevation represents an increase of 0 69 feet since the September 2002 monitoring event A <br /> groundwater gradient was calculated for the event and found to be flowing N28°E at 0 004 <br /> ft/ft <br /> The gradient direction for the December 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 />' The groundwater gradient is relatively flat and the direction of groundwater flow has varied <br /> during the course of the investigation As evident in Figure 3, groundwater exhibited a <br /> strong bifurcated flow regime in 2000, trending predominantly to the southwest or north- <br /> northeast at approximately 180-degree direction reversal Since the installation of wells <br /> MW-7 and MW-10 in May 2001, the direction had been to the east-northeast in seven of <br /> eight quarterly events The site is quite close to the San Joaquin River and tidal fluctuations <br /> may contribute 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-109) 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 /> • 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 piezoinetric 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 /> I <br />