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1 <br /> 26 September 1996 <br /> AGE-NC Project No 95-0130 <br />' Page 3 of 4 <br />' concentrations of these aromatic compounds <br /> MTBE was detected in ground water samples from MW-2 and MW-3 at concentrations of 1 9 ppb <br />' and 15 ppb, respectively Analytical results of ground water samples are summarized in Table 2 - <br /> Analytical Results of G7 ound Water Samples The laboratory report (CAL Laboratory No 815) and <br /> chain-of-custody are included in Appendix B <br /> 1 <br /> 3 3 HISTORICAL RESEARCH OF SURROUNDING PROPERTIES <br />' A review of Sanborn Fire Insurance Maps for the surrounding area, especially for the former Wells <br /> p Y <br /> Fargo Bank property, located north of the site, was performed to identify possible additional sources <br /> of hydrocarbon contamination in the area <br /> The Sanborn map From 1950 indicated that one or possibly more USTs was present at the property <br /> (see Appendix C -Sanboi n Fire Insw ante Map) ]he PHS-EHD does not have any records on the <br /> presence nor removal of USTs on file for the property that was occupied by Wells Fargo Bank <br /> 4.0. CONCLUSIONS & RECOMMENDATIONS <br /> 4I CONCLUSIONS <br /> Ground water flow direction and gradient has remained relatively constant during the past monitoring <br /> year Monitoring well MW-5 is located up-gradient from the UST area, while monitoring well MW-4 <br /> is located down-gradient (Figure 3) Based on the consistently highest concentration in MW-5, it <br /> appears likely that the hydrocarbon compounds detected here could be attributed to the operation of <br /> USTs at the former Wells Fargo Bank property Furthermore, it is also possible that a portion of <br /> hydrocarbons in MW-3 could be attributed to the same source <br /> Since the ground water level was between 4 to 10 feet above the tops of the screen intervals in <br /> monitoring wells MW-I through MW-4 during the July 1996 monitoring, the analytical results may <br /> not be entirely indicative of the actual dissolved petroleum hydrocarbon concentration in the native <br /> ground water However, we believe that the results are adequately representative to obtain a <br /> generalized hydrocarbon distribution in the saturated zone <br /> 4 2 RECOMMENDATIONS <br /> Based on the likelihood that there is an off-site source of hydrocarbon release, further delineation of <br /> the plume should be performed in the up-gradient direction We recommend the installation of two <br /> 1 <br />