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i.. rjeafoBicaf7ecfrnics Znc. Page 2 Groundwater Monitoring Report Project No. 723.2 January 19,2000 1.0 GROUNDWATER MONITORING 1.1 Hydrogeology of Site A site-specific groundwater gradient and bearing was calculated from the depth to water measurements taken during the groundwater monitoring. The gradient was 0.0029 ft/ft �.. flowing N661E. This is the third event where a site specific groundwater gradient was calculated. The groundwater gradient was calculated by resolving a three-point problem using MW-4, MW-5 and MW-6. These wells were selected because they are constructed LW relatively similar in regards to depth of screen interval. The average elevation of groundwater under the site was —18.36 feet below mean sea level. Depths to water ranged from 28.4 to 29.2 feet bgs. Figure 2 is a groundwater gradient map for the December 16, 1999 event. This is the second event where the deep discretely screened well, MW-101, was monitored. A shallow well was not installed next to MW-101 so a vertical gradient cannot easily be calculated. The groundwater head in MW-101 is equal to the head in nearby MW-3 so it appears there is not a significant vertical gradient at this time. The previous event appeared to show a downward vertical gradient. r.✓ Table 1 in Appendix A contains the groundwater elevations and gradients for the site. �. 1.2 Groundwater Sampling Procedure On December 16, 1999, 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. During this '`'' monitoring no free product was noted. Stagnant water in the well casing was purged using a Waterra pump as recorded in the field logs (Appendix C). The rate of well purging was monitored. The wells were purged of approximately three casing volumes and 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 the initial level. All water removed from the monitoring well 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.