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Report: Groundwater-quality Monitoring—July 14-I5,2006, 7500 West Eleventh Street, Tracy, CA. Page 10 ` 2.1.1 Groundwater Mound When the February 2005 groundwater-quality monitoring round was conducted, a groundwater mound with an amplitude of some 5.0 ft. relative to the unperturbed groundwater table that prevailed previously. As was noted at that time, SJC believes that it could be attributed to a failing septic tank leach field that is located in an area to the east of the Capitol Furniture building at 7501 West Eleventh Street (The San Joaquin Company 2006a). Although the amplitude of the groundwater mound waxed and waned, it continued to be present through late March 2006. By July 8, 2006 when the depth to groundwater was measured in Monitoring Well MW-16 as part of the work performed for the groundwater-quality monitoring round reported herein, the mound had almost entirely dissipated. However, as can be seen from the groundwater contours shown on Figure 2, the groundwater in the vicinity of Monitoring Well MW-16 continues to be somewhat perturbed. Despite the continuing minor perturbation of the groundwater in the vicinity of Monitoring Well MW-16, at the scale of the site as a whole, the general direction and gradient of groundwater flow remains to the north-northeast at approximately 0.003 ft/ft, as generally has been the case throughout the years that groundwater depths have been monitored at the site. 2.2 Purging of Groundwater-quality Monitoring Wells f After the depths to groundwater were measured, a small-diameter, submersible pump was used to purge Monitoring Wells MW-3, MW-4, MW-5, MW-7, MW-11, MW-12, MW- 13, MW-14, MW-17, MW-18, MW-19, MWFP-1, MWFP-2, and MWFP-5 of stagnant water. The pumped water was discharged into 5-gallon pails, each of which was, in turn, discharged into a 55-gallon drum. The water in the drum was periodically discharged into a 1,100-gallon holding tank on the 7500 West Eleventh Street property. During the purging procedure, the temperature and electrical conductivity of the stream of purge water were monitored by checking those parameters periodically using a multi- function electronic meter. Purging continued until both parameters stabilized (i.e., variations between measurements were less than 10%) or, in the case of wells screened above the water table, until a minimum of 15 gallons of groundwater had been removed, whichever was greater. The array of parametric results for each well is recorded in SJC's field notes (see Field Notes, Appendix A). 2.2.1 Disposal of Purge Water As noted above, purge water extracted from the monitoring wells was discharged periodically into in a 1,100-gallon storage tank located on the Navarra Site. For economy and efficiency, water will be held in that tank until it is full. It will then be pumped into a vacuum truck and transported to a recycling facility, where the petroleum hydrocarbons will be recycled into beneficial use before the cleaned water is discharged. SJC