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Geological nclmics Inc. Page 3 Groundwater Monitoring Report Project No. 425.2 November 17,2003 1.1.2 Vertical Groundwater Gradients Vertical groundwater gradients were calculated using groundwater-monitoring wells: MW- 2/MW-102 (shallow/intermediate well pair) and groundwater monitoring wells: MW- 102/MW-202 (intermediate/deep well pair). During the September 5, 2003 groundwater- monitoring event, the vertical groundwater gradient in the shallow/intermediate well pair was in a downward, negative, direction with a magnitude of 6 times that of the water table horizontal gradient. Negative vertical gradients do not occur often at the site and tend to be in the early fall. Negative vertical gradients have occurred in September of 1997, 1999, 2000, 2001 and 2003. V The vertical gradient in the intermediate/deep well pair was upward, positive, at a �. magnitude of approximately 13.8 times that of the intermediate horizontal gradient. This site has experienced both negative (downward) vertical gradients and positive �. (upward) vertical gradients. Typically, the negative vertical gradients are 1.75 to 2 times greater than gradients in a horizontal direction and the positive vertical gradients are an order of magnitude greater than horizontal. Positive vertical gradient dominates and may be the main reason for preventing these contaminants from impacting the deeper aquifer. 40 Refer to Table 3 of Appendix A for a summary of the vertical gradient calculations. 1.2 Groundwater Sampling Procedure On September 5, 2003, Del-Tech Geotechnical Support (Del-Tech) 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 was suspected, a clear disposable bailer was used to gauge the interface. Del-Tech noted floating sheen product in monitoring well MW-2. Stagnant water in the well casing was purged using a Honda® centrifugal pump as recorded in the field logs (Appendix C). The rate of well purging was monitored. The wells were purged of at least three casing volumes or until the groundwater parameters (temperature, conductivity, and pH) had stabilized (Appendix C) indicating that water representative of actual aquifer conditions was entering the well. Groundwater parameter stabilization was characterized by three successive readings within 10%. Before a sample was collected, the well's water level was allowed to recharge to at least 80% of its initial level. MW-7 and MW-8 exhibited very poor recharge and recharged to 65% of their initial level before sampling. All water removed from the monitoring wells ..f L.