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Geo(cyca(Techmes 2nc Page 2 Groundwater Monitoring Report Project No 4212 March 24, 1998 1.0 GROUNDWATER MONITORING 1.1 Hydrology of Site Horizontal Groundwater Gradient The average groundwater elevation at the site was 76 03 feet above mean sea level The large change in the average groundwater elevation since the last monitoring event is due to the well tops being surveyed into an actual USGS benchmark Table 1 of Appendix A summarizes the groundwater level measurements to date Groundwater gradient calculations show that the dominant groundwater flow is in a northern direction with the slope ranging from 0 0012 up to 0 0289 ft/ft Vertical groundwater gradients were not calculated using MW-2 and MW-102 because the floating product in MW-2 prevented an accurate depth to water measurement However, past events has shown the vertical gradient to be 175 to 2 times greater then horizontal See Table 2 of Appendix A 1.2 Groundwater Sampling Pa-ocedui-e lei On February 24, 1998, 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 is used to gauge the interface Stagnant water in the well casing was purged using either a Grundfos pump or electronic bailer as recorded in the field logs (Appendix Q The rate of well purging was monitored The wells were purged of at least three casing volumes and until the groundwater parameters (temperature, conductivity, and pH) had stabilized (Appendix Q indicating that water, representative of actual aquifer conditions, was entering the well Groundwater parameter stabilization was characterized by three successive readings within 10% In this case the instrument was not calibrating properly, and pH measurements were not considered reliable Before a sample was collected, the well's water level was allowed to recharge to at least 80% of it's 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 temporally stored on-site I A 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 vial) prior to collecting the analytical sample