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I <br /> 2 . 3 Soil Excavation <br />' In January 1990, further excavation of the former tank cavity took <br /> place. Soil was excavated to a depth of 14 feet. Groundwater was <br /> encountered and the tank pit was dewatered. The water was placed in <br />! an 8 , 000-gallon above ground tank and stored on-site. Between March <br /> and May 1990 , all of the previously excavated soil was returned to <br /> the excavation, bringing the surface of the excavation to 7 feet <br />' below grade. Subsequently, additional soil was imported and used to <br /> backfill the excavation to surface grade. The water stored on-site <br /> in the above ground tank was released to the area of the former <br />' excavation. The backfilling and discharge of purged groundwater <br /> were done without notification of the San Joaquin County Public <br /> Health Services - Environmental Health Division (PHS/EHD) and, <br /> therefore, no official documentation was available. <br /> 1 2 . 4 Groundwater Monitoring <br />' Between 1988 and 1993 , no regularly scheduled groundwater <br /> monitoring program was in place It appears that the first <br /> monitoring event after the initial (June 1988) event occurred in <br /> January 1990 . Hydrocarbon contamination was again detected in <br /> monitoring well #1, north of the tank cavity. We are unaware of any <br /> additional field work between January 1990 and February 1993 . <br />' 2 .4 . 1 Quarterly Monitoring Program <br /> A quarterly monitoring program was initiated by GeoAudit in early <br />' 1993 . The first event took place on February 24 , 1993 . The depth to <br /> groundwater in each well was measured and recorded. An oily <br /> substance was observed in monitoring well MW-1 during subsequent <br /> bailing, and GeoAudit elected to suspend sampling until an <br />' interface meter could be obtained to determine the thickness of <br /> this layer, <br />' On March 5, 1993 , GeoAudit returned to the site with an interface <br /> meter. The oily substance was determined to be a film, and not <br /> significant for depth-to-groundwater measurements. The depth to <br /> groundwater was then measured in each well, the wells were purged, <br /> and samples were collected. The results of this sampling event were <br /> presented in the April 1993 Quarterly Groundwater Monitoring <br /> Report, and are summarized below. <br /> 2 . 4 . 2 Groundwater Depth and Gradient <br /> 1 The depth to groundwater in the first quarter of 1993 ranged from <br /> 8 . 5 to 10 feet. The groundwater gradient was determined to be <br /> 0 . 0050 ft/ft, with groundwater flow oriented N 16' W on February <br /> 241 1993 and 0. 0022 ft/ft oriented N 80 W on March 5, 1993 . This <br /> was consistent with previous groundwater determinations and <br /> regional trends. <br />' 4 <br />