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Geo(ogtcaf?echnws 2nc Page 3 Groundwater Monitoring Report Project No 425 2 January 12,2001 1.1.2 Vertical Groundwater Gradients Vertical groundwater gradients were calculated using MW-2 / 102 (shallow/intermediate well pair) and MW-102 / 202 (intermediate/deep well pair) During the September 2000 event the vertical groundwater gradient in the shallow/intermediate well pair was in a ' downward direction with a magnitude of five times that of the horizontal gradient The vertical gradient in the intermediate/deep well pair was upward at a magnitude ' approximately 1 5 times that of the 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 ' Refer to Table 3 of Appendix A for a summary of the vertical gradient calculations ' 1.2 Groundwater Sampling Procedure On September 20, 2000 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 was suspected, a clear disposable bailer was used to gauge the interface Free product was not evident in any well for the event Stagnant water in the well casing was purged using a 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, were entering the well Groundwater parameter stabilization was characterized by three successive readings within 10% iBefore a sample was collected, the well's water level was allowed to recharge to at least 80% of its initial level All water removed from the monitoring wells and not used as a ' sample, was placed in a 55 gallon DOT (Department of Transportation 17-H) approved container that is properly labeled and temporarily stored on-site ' A stainless steel bailer was used to collect each sample Bailer cleanliness was assured by collecting a bailer blank (pouring distilled water- through the bailer and collecting it in a VOA via]) prior to collecting the analytical sample Extreme care was exercised while collecting samples to prevent agitation of the water contained in the bailer Water samples were transferred from the bailer into 40-m1 VOA