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Gedogccit TeChAtcs l/ec Page 3 Groundwater Monitoring Report Project No 724 2 February 3,2004 Vertical Groundwater Gradients ' Under vertical groundwater flow conditions, the water level in a monitoring well is a fiinction 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 ' Figure 2 shows 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 show 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] For the November 2003 event, the vertical gradient for the MW-4/MW-104 pair was negative (downward) In well pair MW-6/MW-106 the vertical gradient was positive (upward) while for well pair MW-7/MW-107 the vertical gradient was negative ' (downward) This is the first time these well pairs had opposite directions recorded or a downward gradient The trend of a negative gradient in MW-4/MW-104 and a positive or no gradient in the other 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 the distance of the other two well pairs, which may contribute to the apparent opposite flow direction 1.2 Groundwater Sampling Procedure P g ' On November 28, 2003, Del-Tech Geotechnical Support personnel arrived on-site, opened the wells and measured the depth to water with an electrically actuated sounding tape The