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1 Geological Tecluc a Inc Page 4 Groundwater Monitoring Report Project No 723 2 October 25, 2005 Tables 1 —4 in Appendix A contain the groundwater elevations and gradients for the site ' 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 A vertical gradient was calculated for the well pairs MW-3/MW-201, MW-8/MW-108 and MW- 108/MW-208 ' 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-201) and the mid-point between the groundwater elevation and the bottom seal in the shallow well (MW-3) ' ❑ Measure the head in both wells used in the calculations ❑ If the lateral distance between the well pair is greater than a few feet, there 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 Figure 2 shows the location of the well pairs used for calculating vertical groundwater gradient in this report MW-3/MW-201, MW-8/MW-108 and MW-108/MW-208 Tables 1 - 4 show Summaries of Water Level and Gradients Slope and Bearing and Table 6 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 head] ❑ Vertical gradient [(vertical head) /(vertical distance) - vertical gradient] For the 3rd Quarter 2005 event o The vertical gradient for the MW-3/MW-201 pair was negative (or downward) at - t0 01 ft/ft o The vertical gradient for the MW-8/MW-108 pair was negative (or downward) at - 0 001 ft/ft ' o The vertical gradient for the MW-108/MW-208 pair was neutral (or no vertical gradient) at 0 0 ft/ft ' o Previous calculations have revealed both positive and negative gradients at the site but additional monitoring is needed to determine long-term trends especially in the CMTTm well sets 1