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Mr. Steve Ascher, P. E. GEOMATRIX <br /> Schwan's Sales Enterprises, Inc. <br /> 20 April 1994 <br /> Page 2 <br /> MONITORING WELL REHABILITATION <br /> Geomatrix mobilized to the Manteca Depot on 9 March 1994 and removed the existing security <br /> casings from the three wells. The damaged casing of MW-2 was repaired, and new surface-flush <br /> well vaults with locking security covers were installed on all three wells. The grading plan for the <br /> Manteca Depot called for a lowering of the surface in the vicinity of the monitoring wells by <br /> approximately one foot. The tops of the well vaults were set about one foot below ground surface <br /> to accommodate the grading plan. <br /> SURVEY <br /> The repaired monitoring wells were surveyed for location and elevation on 10 March 1994 by Yolo <br /> Engineers, of Woodland, California. The top of the well casing, top of security cover, top of well <br /> vault, and average ground surface elevation at the well were surveyed with reference to on-site <br /> benchmark elevations and USGS datum. Pertinent survey data are presented in Table 1. A copy <br /> of the survey notes is included in the appendix to this letter. <br /> MONITORING <br /> The depth to groundwater was measured by Geomatrix on 11 March and 13 April 1994 with <br /> reference to the surveyed top of the well casings. The groundwater elevation was calculated using <br /> the surveyed well casing elevations. These measurements are included in Table 1 and indicate that <br /> the horizontal groundwater flow direction is to the northwest at a gradient of approximately 0.002. <br /> Figure 2 presents groundwater elevation contours based on the 11 March 1994 data. This flow <br /> direction is consistent with the flow direction reported by Treadwell &Rollo, Inc. at the time the <br /> wells were installed. <br /> Field water quality parameters were also measured in samples collected from the Manteca Depot <br /> monitoring wells on 13 April 1994. A clear acrylic bailer was washed with a non-ionic detergent <br /> in water, rinsed with clean water, and rinsed with deionized water prior to use. The bailer was <br /> lowered slowly into each well and partially filled. The bailer was returned to the surface and the <br /> water was observed for evidence of floating hydrocarbons. No floating hydrocarbons (such as an <br /> oily sheen)were observed. There also was no detectable odor from the groundwater bailed from <br /> the three monitoring wells. The groundwater temperature was measured between 18.5 degrees <br />