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Department of Public Works, Flood Control Section (1990) This depth was confirmed <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 Gotelli, 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 GeoAudit concluded in the Soil Boring Installation <br />Report dated November 16, 1992 that assessment of the extent of contamination could be <br />achieved by further excavation f <br />TABLE 1, _ <br />ANALYTICAL RESULTS FOR BORING B-1 IN FORMER TANK CAVITY <br />mg/kg <br />a <br />Sample <br />ID <br />TPH as <br />Gas <br />Benzene <br />Toluene <br />Ethyl- <br />benzene <br />Xylene <br />Total <br />Lead <br />B1-20 <br />93 <br />05 <br />15 <br />35 <br />14 <br />11 <br />B1-30 <br />6100 <br />31 <br />520 <br />170 <br />520 <br />NA <br />B1-40 <br />13 <br />021 <br />26 <br />037 <br />13 <br />NA <br />B1-50 <br />ND <br />001 <br />0 025 <br />ND <br />0 007 <br />NA <br />Bl -60 <br />ND <br />ND_ <br />ND <br />ND <br />ND <br />93-, <br />ND = Not detected <br />NA = Not Anahzed <br />2.5 Monitoring Well Installation and Sampling, March 1993 <br />On March 9 and 10, 1993, three soil borings (131 through B3) were 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, dust south of the tank pat Analytical results for soil borings B-1 <br />through B-3 (MW -1 through MW -3) are presented in Table 2 Based on these and prior <br />results, GeoAudit recommended further excavation to remove the contaminated soil At the <br />request of Mr Gotelli, GeoAudit subsequently submitted an Interim Remediation Plan for <br />overexcavation Excavation activities and results are presented in section 2 7 <br />G—$.V.1 Audra s<,.,n. Inc 4 <br />6V'_9 Md{3] QR <br />