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1 Geological Technics W, Page 2 Groundwater Monitoring Report r ! Project No, 723.2 1' March 10, 2003 in the shallow wells ranged from 33.95 — 34.75 feet bgs. It is noted that the water table .,. exceeded the screened interval of all of the site's eight wells. Figure 2 is a groundwater gradient map for the December 17, 2002, event_ Figure 3, 1 Groundwater Gradient Rose Diagram, includes historical groundwater directions and gradients. t Table 1 in Appendix A contains the groundwater elevations and gradients for the site. ' Vertical Groundwater Gradients �'I Under vertical groundwater flow conditions, the water level in a monitoring well is a L� 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. A vertical gradient was calculated for well pair MW-3/MW-201. These wells are located approximately 5 feet apart. The following procedure is used to calculate vertical groundwater gradient: • Determine vertical distance between the two measuring devices by the distance from the r ---., mid-point between the top and bottom seal of the deep well (MW-201) and the mid- point between the groundwater elevation and the bottom seal in the shallow well (MW- C 3) �-+ . Measure the head in both wells used in the calculations. ' 0 if the lateral distance between the well pair is greater than a few feet, then calculations ' must be made to correct the down-gradient piezornetric 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 Figure 2 shows the location of the well pairs used for calculating vertical groundwater gradient in this report: MW-3/MW-201. Table 1 shows a Summary of Water Level and Gradients SIope and Bearing and Table 3 shows the calculated vertical gradients. The information used in the calculations is shown below. Vertical gradient calculation formulas are as follows: • Vertical correction for gradient: [(gw gradient slope) x (distance) =vertical correction] • Vertical head: [(head of deep well) - (head of shallow + correction) =vertical bead] t ' . Vertical gradient: [(vertical head) / (vertical distance) = vertical gradient] For the December 2002 event, the vertical gradient for the MW-3/M.W-201 pair was`000 ft/ft., or no vertical gradient. This is the fifth time that vertical gradients were calculated�or this well pair. Previous calculations have revealed both positive and negative gradients but additional monitoring is needed to determine long terin trends. II h