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1 Extended Plume Definition:-7500 W 111h St., Tracy,CA. Page 15 depths to groundwater in all wells were available for the same date, the depth to groundwater in all wells -both pre-existing and newly-installed -was measured on April 30. By managing the sampling round in that way, it was possible for all the requisite work to be completed by April 30, as required by the SJCEHD-directed schedule. The procedures used to measure the depth to groundwater and to sample and analyze the groundwater in the monitoring wells are described below. i 4.10.1 Determination of Groundwater Elevations The depth from the top of the casing to the water table was measured using a conductivity meter. That data, together with the floating product monitoring well data (see Section 5A), was used to compute the groundwater table elevations relative to MSL that are shown in Table 3. The computed groundwater table elevations were used to produce Figure 9, a contour map of the groundwater table and to determine the direction and magnitude of the groundwater flow gradient. The groundwater in the area of the Navarra wells flows to the north-northeast.at a gradient of 0.003 fl/ft. As was discussed in Section 4.8 above, while the general direction and the gradient of the groundwater flow at the 7500 West Eleventh Street site as computed from the data gathered during the April 2004 sampling round is consistent with those found throughout the history , of monitoring at the site, the additional wells that were installed at that time have permitted the detail of the contour pattern to be enhanced. As is shown on Figure 9, that detail confirms the presence of a relatively high permeability zone in the subsurface that extends north- northeast from the area where the fuel hydrocarbons were released to the subsurface down- gradient along the primary plume of affected groundwater. 4.10.2 Well Purging After the depths to groundwater were measured, a small-diameter, submersible pump was used to purge each groundwater-quality monitoring well to be sampled of stagnant water. The pumped water was discharged into 5-gal. pails, each of which was, in turn, discharged into an open-topped, 55-gallon drum. Periodically during the well purging operation, the drum was decanted into the 1,100 gallon, polyethylene holding tank on the 7500 West Eleventh Street property. During the purging procedure, the temperature, electrical conductivity and pH of the stream of purge water were monitored by periodically checking those parameters using a multi- function electronic meter. Purging continued until all three parameters stabilized, i.e., variations between measurements are less than 10%. The array of parametric results for each well is recorded in the field notes found in Appendix B. 4.10.3 Groundwater Sampling Procedure After purging, samples were recovered from each monitoring well to be sampled using a disposable bailer. Water brought to the surface in the bailers was decanted via a discharge spigot valve placed in the bottom of the bailer so as to completely fill clean glassware sic