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Geologual reckwes kc Page 3 ' Groundwater Monitoring Report Project No 770 2 . March 16,2006 ' Vertical Groundwater Gradients Under vertical groundwater flow conditions, the water level in a monitonng 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 mid-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 piezometnc 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-51105 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 contains the well construction details The information used in the calculations is shown below M4f sshet0_ Vertical gradient calculation formulas are as follows R tlZ 4-. • 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] Vertical gradients were calculated for the MW-51105 & MW-6/106 well pairs for the 4t' quarter 2005 monitoring event The vertical gradient was positive (or upward direction) for ' the MW-5/105 well pair The vertical gradient was negative (a downward direction) for the MW-6/106 well pair The calculated gradients were 0 0019 ft/ft and -0 0011 ft/ft for the ' MW-5/105 and MW-6/106 well pairs, respectively, for the December 2005 monitoring event The well pairs displayed predominantly downward gradients for all four 2005 events 1..2 Groundwater Sampling Procedure On December 9, 2005, Del-Tech Geotechnical Support Services staff mobilized to the site to complete the quarterly groundwater monitoring and sampling of the site's monitoring wells Before sampling was attempted the wells were sounded for depth to water and then a clear disposable bailer was used to determine if floating product was present No free product was noted but a slight petroleum sheen was present in well MW-4 & MW-5 The wells were purged using a dedicated Waterra check-ball assembly and Yz inch tubing Purging continued until the temperature, conductivity and pH of the groundwater stabilized (<100lo variation