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' Stockton Meat Plant - Case Closure Page 9 March, 1996 According to Soil Survey maps published by the Soil Conservation Service (SCS), the soils at the subject site consist predominantly of the Jacktone Clay. This urut is slowly permeable and contains a hardpan at depths of 20 to 40 inches Previous subsurface borehole data at the site show the upper soil profile (to approximately 26 feet bgs) to be dominated by low permeability silty and clayey units More permeable clean to silty sands interbedded with low permeability units were noted below a depth of 26 feet bgs " The above geologic description matches the subject site well However, other investigators have identified the interface between the low permeability upper zone with the high permeability sandy unit from between 17 to 25 feet bgs Site Hydrogeology The following excerpt is taken from the Krazen Report, reference Attachment G "Review of the San Joaquin County Flood Control and Water Conservation District map entitled "Ground Water Elevations, Spring 1993" shows a groundwater elevation contour of -20 feet in the vicinity of the subject property Review of the 7 5 minute Stockton West, California topographic quadrangle map, photo-revised 1987, indicates an elevation of 7 feet above mean sea level (amsl) near the subject property Comparison of the two elevations indicates that groundwater in the vicinity of the project site would approximately 27 feet below existing grade On site monitoring well MW-5 was sounded at the start of field activities (September 21, 1995), the depth to groundwater was noted to be approximately 24 5 feet below ground surface at the time The WCD map also indicates that the lateral component of groundwater flow is generally in a east-northeast direction in the vicinity of the site. Review of the WCD maps from previous years indicate that groundwater flow direction has remained essentially unchanged during recent years The most recent groundwater elevation data from on-site monitoring wells also suggests an easterly flow direction . " Table 1 summarizes the known depths to groundwater and the flow direction As indicated the flow direction in the last six sampling events has been primarily in an easterly direction, matching the regional flow direction noted in the WCD maps Figures 3 and 4 are graphical representations of changes over the last 6 sampling events in groundwater elevation and the diesel concentrations, respectively, for each monitoring well MW-4, -5, and -6 As indicated in