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GeclogicalTeclucccsl�ct Page 3 ' Groundwater Momtoring Report Project No 724 2 March 29,2005 ' Figure 5C shows that the deep aquiferadient was to the east for the five events following g 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 1 The following procedure is used to calculate the vertical groundwater gradient • Determine vertical distance between the two measuring devices by the distance from the ' nud-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) W vertical head] ' • vertical gradient [(vertical head) / (vertical distance) = vertical gradient] For the January 2005 event, the vertical gradient for the MW-4/MW-104 pair was negative ' (downward) In well pair MW-6/MW-106 & MW-7/MW-107 the vertical gradient was positive (upward) The trend of a negative gradient in MW-4/MW-104 and a positive 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 that observed in the other two well pairs, which may have an influence over the vertical gradient direction 1.2 Groundwater Sampling Procedure On January 12 & 13, 2005, 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 Ievel reading was recorded to an accuracy of 0 01 foot In wells where free-floating product is suspected, a clear disposable bailer is used to gauge the interface No free-floating