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Report:Groundwater-quality Monitoring—October 20-21,2005, 7500 West Eleventh Street, Tracy, CA. Page 11 spring of each year and typically continues through the summer, after which it declines and groundwater levels in shallow aquifers begin to fall. Groundwater elevations usually continue to fall until some time in February or March. Inspection of Table 1 shows that the rise and fall in the groundwater table elevation beneath the 7500 West Eleventh Street site usually occurs with little or no relationship to seasonal precipitation in the San Joaquin Valley where little rain falls between May and September of each year. "1 The groundwater elevations presented in Table 1 were used to generate the groundwater contours shown on Figure 2. The groundwater elevations in monitoring wells MW-3A, MW-313 and MW-12A were not considered when the groundwater contours were drawn because the differences between the elevations of the groundwater in Wells MW-3, MW-3A and MW-313 and in MW-12 and MW-12A are sufficiently great to indicate that the groundwater monitored by the shallow well at the locations of each of those well clusters has a different piezometric pressure from that of the deeper wells in the same cluster. It must therefore be assumed that, at least locally, the shallow wells monitor aquifers different from those monitored by the deeper wells. 2.1.1 Groundwater Mound A significant feature of the groundwater contours shown on Figure 2 is the groundwater mound centered near Monitoring Well MW-16. The existence of that mound was first = -' observed in the groundwater measurements made on February 24, 2005 (The San Joaquin Company 2006). As was noted at that time, SJC believes that it can 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 depth to groundwater in Monitoring Well MW-16 was measured at 6.65 ft. BGS, which is 3.15 ft. lower than the depth to groundwater last measured in that well on June 23, 2005. The groundwater mound has not fully dissipated and its continued existence -:j produced the highly complex pattern of groundwater contours that are shown on Figure 2. However, despite the continuing presence of the mound of groundwater, 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 fl/ft, as generally has been the case throughout the six-year period that groundwater depths have been monitored at the site. :j 2.2 Purging of Groundwater-quality Monitoring Wells 1 After the depths to groundwater in the seventeen groundwater-quality monitoring wells to be sampled were measured, a small-diameter, submersible pump was used to purge each 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 SJC