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Geologicalnchwcslac Page 3 Groundwater Monitoring Report Project No 770 2 February 7,2005 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 mrd-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 is greater than a few feet, then calculations ' must be made to correct the down-gradient piezometrrc 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 Figures 2 & 3 show the location of the well clusters, MW-5/105 and MW-6/106, used for calculating vertical groundwater gradient in this report Table 1 includes Summary of Water Level and Gradients Water Table Wells, Table 2 includes Summary of Water Level and Gradients Deep Wells, Table 3 shows the calculated vertical gradients, and Table 6 contains the well construction details 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] Y Vertical head [(head of deep well) - (head of shallow + correction) = vertical head] • Vertical gradient [(vertical head) /vertical distance) = vertical gradient] ' Vertical gradients were calculated for the MW-5/105 & MW-61106 well pairs for the 4h quarter 2004 monitoring events The vertical gradient was negative (a downward direction) ' for the MW-5/105 well pair for all six sounding events completed in 2004 The MW-6/106 well pair vertical gradient was positive (an upward direction) on January 22 and February 26, and negative (a downward direction) on March 15, June 7, August 19 and December 09, ' 2004 Both positive and negative vertical gradients- have been calculated-for previous events Similar to the historical lateral directions, the direction of groundwater in the vertical plane also fluctuates at the site The magnitude of vertical groundwater flow direction ranged from —0 02 to 0 0097 for the site investigation 1.2 Groundwater Sampling Procedure ' On December 9, 2004, Del-Tech Geotechnical Support Services staff mobilized to the site to complete the quarterly groundwater monitoring and sampling of the site's monitoring wells 1