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' C4010g&01 TeckAk$11C Page 3 g g Groundwater Monitoring Report Project No 723 2 February 28,2005 ' 1,1 Hydrogeology of Site A site-specific groundwater gradient and bearing were calculated from computer-generated contours for the October 21, 2004 event The groundwater was flowing N63°E at a gradient of 0 0070 ft/ft The average elevation of groundwater at the site was 29.49 feet below mean sea level or approximately 40 feet below grade surface (bgs) This represents a decrease of 2 06 feet since the August 8 monitoring event and a cumulative decrease of 5 83 feet since March 2004 ' Figure 2 is a groundwater gradient map for the October 2004 event Figure 3, Groundwater Gradient Rose Diagram, includes the historical groundwater directions and gradients ' Table 1 in Appendix A contains 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 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 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, then calculations must be made to correct the down-gradient piezometne head to account for the sloping 1 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 Table 1 shows a Summary of Water Level and Gradients Slope 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 head] ' ❑ Vertical gradient [(vertical head)/(vertical distance) =vertical gradient] 1