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1 <br /> ' 4.2 Field Observations <br /> Due to their close proximity, borings B4A and B5A penetrated identical materials, as did <br /> B4 and B5 (Figure 5). The upper several feet of material consists of loose fill, and only 2 <br /> to 5 blows were required to advance the sampler 0 5 feet in this unconsolidated material <br /> A layer of black, granular, coal-like material is present to a depth of 5 feet; this layer was <br /> ' visible in the walls of the tank excavation at depths of between 1 and 3 feet (see PIER <br /> Report, dated July 17, 1992) Beneath this layer is a thin lens of very-fine-grained sand, <br /> which is present from 5 to 6 5 feet in depth in B4A but thins to 0 5 feet in thickness in <br /> ' B5A <br /> In 134A, this layer was dark gray in color, wet, and emitted a strong petroleum odor. In <br /> ' BSA, this layer was yellow-gray to brownish gray, slightly damp, and emitted no odor <br /> The fill material is underlain by orange-brown to blue-gray or dark-gray silty clay This <br /> material was more consolidated, requiring 10 to 15 blows to advance the sampler No <br /> ' hydrocarbon odors were detected in samples collected at 7 5 and 10 feet in boring B4 <br /> The silty clay layer continues downward to a depth of between 14 and 15 feet in both B4 <br /> and B5 In MW-2, this layer was present to 15 5 feet It is slightly damp, and locally <br /> oxidized to reddish or orangeish colors No odors were detected <br /> ' From 15 to 20 feet, MW-2, B4, and B5 penetrated saturated, partially oxidized orange- <br /> brown to gray or brown moderately well-sorted silty very-fine-grained sand No odors <br /> were detected <br /> 4.3 Laboratory Results <br /> No petroleum hydrocarbons were detected in any of the groundwater samples <br /> B and Table 2) No groundwater contamination has been detected at this ite (Appendix <br /> four <br />' consecutive quarters <br /> No hydrocarbons were detected in any of the soil samples from B4, 134A, B5, or BSA <br />' above method detection limits The very minor soil contamination that was previously <br /> detected in MW-2 was extremely limited in lateral extent and has probably remediated <br /> naturally <br /> 1 <br /> 5.0 CONCLUSIONS AND RECOMMENDATIONS <br /> In accordance with written communication from PHS/EHD in November and December <br /> 1993, the Bank of Stockton has completed additional investigations at the site for closure <br /> certification No groundwater contamination has been detected for four consecutive <br /> quarters This confirms that groundwater is no longer contaminated The low <br /> concentrations of hydrocarbons that were detected in the first two monitoring events <br /> have apparently been diluted to below detection limits <br /> 12 <br />