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1 Geological r"halcs Inc Page 3 Groundwater Monitoring Report Project No 723 2 August 31,2004 ' 0 0051 ft/ft The average elevation of groundwater at the site was 23 72 feet below mean sea level or approximately 34 feet below grade surface (bgs) This represents a decrease of 0 06 ' feet since the March 21, 2004 monitoring event Figure 2 is a groundwater gradient map for the May 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-paint 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 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 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 v 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] r For the May 6, 2004 event, the vertical gradient for the MW-3/MW-201 pair was negative (or downward) at -0 008 ft/ft Previous calculations have revealed both positive and negative gradients but additional monitoring is needed to determine long-term trends 1 r r