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Cie 0gkat remxks I= Page 2 Groundwater Momtormg Report Project No 770 2 August 27,2004 1.0 GROUNDWATER MONITORING 1.1 Hydrogeology of Site The site exhibits a primarily silty/clayey geology with minor sand layers/lenses, pebbles, black organics and iron staining occasionally present The groundwater monitoring schedule was modified to include monthly depth to groundwater measurements in 2002 This was necessary to better define the gradients that have vaned greatly in the past On March 15, 2004, the water table well groundwater elevation averaged --39 45 feet mean sea level (MSL) For the June 7, 2004, event the water table well groundwater elevation averaged — 40 84 feet MSL A net decrease of 139 feet MSL was recorded between the March 2004 and June 2004 sounding events. Groundwater gradient calculations indicate that the flow in the water table wells was S350E with a slope of 0 002 ft/ft on June 7, 2004 while ' the deeper aquifer gradient was S59°E with a slope of 0 002 ft/ft Groundwater elevation and gradient data are summarized in Tables 1 and 2, Appendix A The water table and deep well gradient directions are shown in Figure 2 and Figure 3, respectively, for the June 2004 event The historical water table gradients are illustrated in Figure 4 & 5 Groundwater Gradient Rose Diagrams for Water Table and Deep Wells, respectively The site's shallow aquifer displays highly variable shifts in groundwater direction It is noted that groundwater direction has been predominantly to the southeast since additional wells were installed in May 2002 The deeper aquifer flow had been consistently to the east for the previous seven ' sounding events But on April 28 and May 23, 2003, the gradient reversed 180° from an easterly direction to a westerly direction The direction reversed again to the east for the remainder of the sounding events 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-105) and the mid-point ' between the groundwater elevation and the bottom seal in the shallow well (MW-5) • Measure the head in both wells used in the calculations • If the lateral distance between the well pair 1s 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