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� t��MA <br /> "fra Working To Restore Nature <br /> F: <br /> 5.0 SPECIFIC INFORMATION FOR CLOSURE REQUEST <br /> 5.1 Introduction <br /> This section provides information specifically required for closure review as per the October 7, <br /> F: <br /> t : 1993 Addendum to Appendix A to the Tri-Regional Recommendations. <br /> 5.2 Rationale for Closure with Residual Petroleum Hydrocarbon Impacted Soil <br /> Removal of the remaining petroleum hydrocarbon impacted soil is not physically possible due <br /> to the existence of a structure located above the impacted area. A majority of the impacted soil <br /> _... in the vicinity of the former diesel tank location was removed during excavation activities in <br /> October 1992. The estimated volume of affected material removed is approximately 375 cubic <br /> yards. Utilizing stockpile composite sample analytical results, it is calculated that this volume <br /> of soil contains approximately 10.6 pounds of diesel range hydrocarbons (possibly an <br /> underestimate). The residual volume of impacted soil is estimated to be approximately 102 <br /> cubic yards containing approximately 15.1 pounds of TPHd (Table 6). Figure 4 depicts the <br /> F . excavated area as well as the area of residual soil contamination. <br /> groundwater with detectable The residual soil contamination is not expected to impact P P <br /> concentrations of petroleum hydrocarbons. This expectation is based on the high adsorbancy of <br /> € the soil type (clay/silty clay with 1-2% organic matter, USDA, 1992), the minimization of <br /> infiltration due to the overlying concrete cap and site specific empirical observations, as below. <br /> �s <br /> Prior to excavation, with one exception, no significant impact to groundwater occurred as a <br /> result of contact with contaminated soil. Of primary importance are the results of groundwater <br /> _r <br /> analyses from monitoring well MW4. This well, destroyed during excavation activities, was <br /> _ installed within the area of soil impact. Excepting the initial sampling round, detectable analytes <br /> O W01951REPORTS%CLO 12594.FNL <br /> 1. 9 <br /> f!� i <br />