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Public Works Flood Control Section 1990 This depth was confirmed <br /> Department of ( ) <br /> during drilling in March 1993, when groundwater was first encountered at a depth of <br /> between 65 and 70 feet and subsequently stabilized at a depth of approximately 68 feet In <br /> an earlier Ietter to Mr. Ed Gotelh, dated December 11, 1992, the PHS/EHD reported that <br /> seasonal high groundwater (1986) at this site was estimated to be between 45 and 50 feet <br /> 2.4 Initial Assessment and Drilling, October 1992 <br /> On October 9, 1992, a soil boring was installed in the center of the gasoline tank cavity to <br /> a depth of 60 feet. Samples were collected at five-foot intervals and analyzed for total <br /> petroleum hydrocarbons (TPH as gasoline) and volatile aromatics (BTE&X) Analytical <br /> results are summarized in Table 1 GeoAudrt concluded in the Soil Bonng Installation <br /> Report dated November 16, 1992 that assessment of the extent of contamination could be <br /> achieved by further excavation <br /> TABLE 1 <br /> ANALYTICAL RESULTS FOR BORING B-1 IN FORMER TANK CAVITY <br /> mg/kg <br /> Sample TPH as Ethyl- Total <br /> ID Gas Benzene Toluene benzene Xylene Lead <br /> B1-20 93 05 15 35 14 11 <br /> B1-30 6100 31 520 170 520 NA <br /> B1-40 13 021 26 037 13 NA <br /> B1-50 ND 001 002-5 ND 0 007 NA <br /> B1-60 ND ND ND ND ND 93 <br /> ND=Not detested <br /> NA=Not Analyzed <br /> 2.5 Monitoring Well Installation and Sampling, March 1993 <br /> On March 9 - 10, 1993, three soil bonngs (B1 through B3) weie drilled to a depth of 77 <br /> feet Samples were collected at five-foot intervals and selected samples were analyzed for <br /> TPH as gasoline and BTE&X The borings were completed as groundwater monitoring wells <br /> (MW-1 through MW-3) A benzene concentration of 0 0079 mg/kg was detected at a depth <br /> of 45 feet in MW-2, lust south of the tank pit Analytical results for soil borings B-1 <br /> through B-3 are presented in Table 2 Based on these and pnor results, GeoAudrt <br /> recommended further excavation to remove the contaminated soil At the request of Mr <br /> Gotelli, GeoAudrt subsequently submitted an Intenm Remediation Plan for overexcavation <br /> Excavation activities and results are presented in section 2 6 <br /> I.6W%Md al OR 4 <br />