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Creohgical Technics Inc Page 2 ' Groundwater Monitoring Report Project No, 1030.2 September 29,2003 1.0 GROUNDWATER MONITORING r1.1 Hydrogeology of Site ' On July 23, 2003, the depth to groundwater was measured in all of the monitoring wells prior to purging. Depths to groundwater, at the site, averaged 9.50 feet below the top of casing. The average groundwater elevation for the July 2003 event was 67.12 feet above mean sea level (MSL). Site-specific groundwater bearing and slope were calculated and found to be N65°E @ 0.0040 ft/ft. These results are consistent with historical groundwater bearing and slope for this site. ! Groundwater elevation increased 2.88 feet since the April 2003 monitoring event. This raise in groundwater elevation corresponds with seasonally high groundwater elevation ' measurements recorded at this site between June and August. There is flood irrigation north and east of the site, which may explain the seasonal increase. Vertical groundwater gradients were calculated for the site using the MW-1/MW-101 well pair and found to be negative. This is the first time a negative vertical gradient has been recorded at the site. The site-specific vertical groundwater gradient is -0.0274 ft/ft. MW-1 is screened from 5 to 20 feet bgs and MW-101 is screened from 29.5 to 34.5 feet bgs. Vertical groundwater gradient calculations have been performed at regular intervals since ' the installation of MW-101 on April 12, 2002. The vertical gradient calculated for the July 2003 monitoring event is one order of magnitude greater than the horizontal gradient. The historical vertical gradients have been approximately one order of magnitude less than the ' horizontal gradients. Groundwater elevation, bearing and slope were calculated using data gathered from MW-2, MW-3 and MW-4 during the July 23, 2003, monitoring event and the results are summarized in Table 1 of Appendix A. Table 2 of Appendix A summarizes the vertical groundwater gradient calculations. 1.2 Groundwater g Sam lin Procedure Sampling ' On July 23, 2003, Del-Tech Geotechnical Support Service 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. If free floating product had been suspected, a clear disposable bailer would have been used to gauge the interface. No floating product was observed during this sampling event. Stagnant water in the well casing was purged using a Waterra pump and dedicated tubing. The rate of well purging was monitored. The well was purged of at least three casing volumes until the groundwater parameters (temperature, conductivity and pH) had stabilized