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Coo 4(gteaI Teduuts W Page 3 Groundwater Monitoring Report Project No 724 2 February 7,2005 Figure 5C shows that the deep aquifer gradient was to the east for the three 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 headl • vertical gradient [(vertical bead) / (vertical distance) = vertical gradient] For the November 2004 event, the vertical gradient for the MW-4/MW-104 and MW-7/MW- 107 pairs was negative (downward) In well pair MW-6/MW-106 the vertical gradient was positive (upward) 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 However, the negative gradient in MW-7/MW-107 pair is only the third time for this situation 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 ' 1.2 Groundwater Sampling Procedure ' On November 5, 2004, Del-Tech Geotechnical Support personnel arrived on-site, opened the wells and measured the depth to water with an electrically actuated sounding tape The water level reading was recorded to an accuracy of 0 01 foot In wells where free-floating product