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. . . . ... .. . . .. ....... Extended Site Characterization Report,- 7500 West Eleventh Street, Tracy, CA. Page 24 must therefore, at least locally, be assumed to monitor different aquifers than that monitored by the shallow wells. On April 11, 2002, the mean groundwater gradient in the shallow, near-surface aquifer beneath the site was approximately 0.004 ft/ft. However, as indicated by the groundwater table contours shown on Figure 8, the gradient in the area north of the subject property's frontage onto West Eleventh Street is somewhat steeper than that beneath the subject property itself. The northeasterly trend of the groundwater flow direction derived from the measurement - of depths to the water level in the monitoring wells is compatible with the general flow of groundwater in the region and follows the general slope of the topography in the area (U.S. Department of the Interior, Geological Survey 1978, 1981). However, on first inspection, it appears that the groundwater flow direction derived from measurements in the wells drilled for the 7500 West Eleventh Street property might conflict with the direction of groundwater flow computed at several nearby sites, the records of which are available in the SJCEHD archives. >� Geological Technics Inc. of Modesto, California (GTI) performed a site characterization program at C&B Equipment (now occupied by Troy's Body and Paint) at 7474 West Eleventh Street. As shown on Figure 2, that site is located to the east of the subject property across Chrisman Road. Groundwater-quality monitoring wells were installed at C&B Equipment in 1995 at the direction of the SJCEHD to investigate the extent to which the subsurface beneath that property was affected by a release of fuel hydrocarbons from underground storage tanks previously located there. SJC reviewed a groundwater-quality monitoring report prepared by GTT, which based on measurements of depths to groundwater made by that company on March 18, 1998, indicated groundwater flow to be approximately 10 degrees west of north beneath the 7474 West Eleventh Street property (Geological Technics Inc. 1998). During the course of the initial site characterization, SJC checked the depth to groundwater and well casing elevation data presented in GTI's report and computed the same apparent direction of groundwater flow beneath the C&B Equipment property that was calculated by that consultant. To ensure that the apparent discrepancy between the direction of groundwater flow beneath the 7500 West Eleventh Street property and adjacent areas computed by SJC and the direction of groundwater flow beneath the C&B Equipment property computed by SGI was not due to a surveying error or an error in field measurement made in Wells J MW-1 through MW-7, SJC re-surveyed the elevations of the well casings and re- measured the depths to groundwater in those wells on August 22, 2000. The casing elevations were found to be correct. The measured depths to groundwater are shown in Table 2. In addition to the data from the 7474 and 7500 West Eleventh Street properties, groundwater flow direction information is available for three other sites in the SJC � 3