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N Treadwell& lolo <br /> 6.0 WELL DESTRUCTION <br /> During January. 2005 Treadwell & Rollo submitted a well destruction work plan to the SJCEHD (Treadwell <br /> -_ & Rollo 2005b), which was accepted on _li January 2005 (SJCEHD, 2005). On 3 and 8 February 2005, all <br /> four monitoring wells, MW- 1 through MW-4, were destroyed according to the procedures described in the <br /> work plan and permit. <br /> Wells were destroyed using 110-inch hollow stem augers. Well casings and filter packs were drilled out <br /> and then the open bore hole was grouted using a tremie pipe system . <br /> r � 7.0 FINDINGS AND CONCLUSIONS FROM SUBSURFACE INVESTIGATION <br /> 1 <br /> _- Subsurface investigations have identified the presence of significant concentrations of gasoline in shallow <br /> t 1 <br /> and deep soil and groundwater, specifically TPHg and BTEX compounds. The releases appear to have <br /> _= come from the two gasoline USTs formerly located in the sidewalk along Hunter Street (Figure 2). <br /> _- i <br /> Two groundwater zones have been defined at the site. The shallow zone exists approximately between <br /> r � <br /> 25 and 35 feet. The deep zone exists approximately between 55 and 60 feet. The presence of high <br /> TPHg and BTEX concentrations up to 60-feet bgs indicates that the release began prior to the 1990s <br /> when groundwater was significantly deeper than it is currently. <br /> i <br /> The following sections identify the contaminants of concern at the Site, and summarize the extent of <br /> groundwater impacts. <br /> 7.1 Site Contaminants of Concern <br /> Subsurface investigations have identified the presence of significant concentrations of petroleum <br /> hydrocarbon in shallow and deep soil and groundwater, specifically TPHg and BTEX compounds. <br /> The groundwater analytical results show that for 81 % of the TPH-kerosene detections, the laboratory <br /> reported that the sample chromatogram did not match the laboratory standard for TPH-kerosene (25 out <br /> - , of 31 samples, Table 2) and appeared to be identified due to lighter end petroleum hydrocarbons (such <br /> as TPHg). In contrast, none of the TPH-gasoline detections produced a similar notation, indicating that <br /> the TPH-gasoline groundwater detections had similar chromatograms to the laboratory standard (41 out <br /> 25971201 . DGD 6 February 2008 <br /> j <br />