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t between the depths of 25 and 35 feet in this area ranged from 10 to 50 ppm Therefore, it is our conclusion that the maximum depth of contamination north of sample JL-P-3 was 30 feet or Cess 9.2 Areal Extent of Contamination Samples JIrP-9 through JL-P-26 confirm that the lateral extent of contamination has been delineated on the north, east, and south If the location of sample JL-P-3 is taken as the former location of the southeastern dispenser(see Figure 2), then contamination extended 12 feet to the east of the dispenser prior to excavation Contamination extended 20-25 feet to the south of the dispenser and 45-50 feet to the north along the product lune Contamination also extended at least 25 feet west of the dispenser, however, due to the location of the service station building, not all of the contaminated soil could be removed in this direction The western limit of contamination is probably close to the foundation of the building If so, it is possible that an area measuring 15 ft x 30 ft x 10 ft may contain residual hydrocarbons 9.3 Potential for Groundwater Contamination According to the Fall 1993 "Lines of Equal Depth of Water Wells" map published by the Flood Control Section of the San Joaquin County Department of Public Works, the depth to groundwater in the site area was between 35 and 40 feet in the late 1993 Historically, 1993 was a relatively low water year Therefore, if the 1993 map is correct, it is probable that groundwater has been as shallow as 30 feet in wetter years As this depth is within 5 feet of the maximum depth of contaminated soul, it is possible that groundwater has been impacted Based on the probable minimum historic depth of groundwater, the site would not be eligible for closure under the LUFT Leaching Potential procedure 9.4 Groundwater Assessment Further investigation of the potential impact to groundwater may be warranted This could be achieved either by installing a groundwater monitoring well in the central portion of the spill area (between samples JL-P-3 and JL-P-13) or by drilling two or three borings and collecting water samples with a hydropunch-type device 9.5 Further Soil Remediation Although remediation of the remaining contaminated soil along the west wall of the excavation might be desirable, it cannot be achieved by excavation without demolishing the building Upgradnent Environmental recommends that this soil be left in place t The residual contamination on the west sidewall is contained within unit 4, a sand layer that ranges from absent to approximately 5 feet in thickness Grain size ranges from very coarse on the east sndewall to fine on the west sndewall The unit is underlain by a caliche-cemented clay bed that is relatively uniform in thickness and appears to have significantly slowed downward migration of gasoline These conditions are amenable to nn-situ remediation technologies that rely on permeability, 8