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' CMIO fCal Txk4 c 11M Page 3 Groundwater Monitoring Report Project No 724 2 May 16,2005 ' measurements made after November 2000 Since additional wells were installed in November 2000, the groundwater direction has had a more southerly component suggesting ' that the earlier measurements were biased due to the spatial orientation of fewer wells The rose diagram included in Figure 5B shows that the intermediate aquifer gradients at this site have been consistently to the east for the last 15 events The rose diagram included in Figure ' 5C shows that the deep aquifer gradient was to the east for the 6 events following the installation of four additional deep wells in December 2003 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 the 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-104, MW-106, MW- 107) and the mid-point between the groundwater elevation and the bottom seal in the ' shallow well (MW-4, MW-6, MW-7) • 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 Figures 2 — 4 show the location of the well pairs used for calculating vertical groundwater ' gradient in this report MW-4/MW-104, MW-6/MW-106, and MW-7/MW-107 Tables 1, 2 & 3 show a Summary of Water Level and Gradients Slope and Bearing and Table 4 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 April 2005 event, the vertical gradient for the MW-4/MW-104 and MW-7/MW-107 well pairs was negative (downward) In well pair MW-6/MW-106 the vertical gradient was ' positive (upward) The trend of negative and positive gradients in these well pairs is consistent with the historical data It is noted that the vertical distance to the deep well screen in the MW-4/MW-104 well pair is double that observed in the other two well pairs, which ' may have an influence over the vertical gradient direction. I 1