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ul—u4-34 IL:LOrz KUM ul6whL] lu 81Lu9404uljb ruun/uu <br /> Mr. Derrick Adace • <br /> December 17, 1993 <br /> Page 5 <br /> tank will not he known until deep si.dewdll samples are taken or <br /> the tank is removed allowing for complete access for <br /> confirmation sampling. Currently, confirmation sampling is <br /> planed for the sidewalls and excavation floor. It is not clear <br /> if sidewall sampling is planed for material beneath the tank. <br /> Present contaminant distribution is based mostly on boreholes T- <br /> 1 and T-2, at the northwest corner and eastern edge of the tank <br /> respectively. <br /> Recommendation: <br /> GSU recommends removing the concrete tank, confirming the <br /> extent of hydrocarbon contaminated soil beneath the tank and <br /> south of the tank, and removing soil for screening and treatment <br /> or disposal. Further, the RWQCB may interpret that the concrete <br /> tank be considered an underground tank requiring removal. <br /> General Comment 2: Use of Pea-Gravel for Fill <br /> WZZ proposes using pea-gravel compacted to approximately go% <br /> of the former field density as backfill for the soil <br /> excavations. It is essential that the backfill exhibit equal or <br /> lower hydraulic properties than the original field conditions. <br /> Merely compacting the material to former field density does not <br /> address the permeability issue. Additionally, Gsu questions the <br /> concept of compacting pea-gravel. <br /> Recommendation: <br /> A suitable backfill material with sufficient fines should be <br /> selected which when compacted in small lifts will generate <br /> vertical hydraulic conductivities equal to or less than <br /> original field conditions. <br /> General Comment 3: Resurfacing The Excavation surface <br /> The RAP discusses resurfacing the site with asphalt. It is <br /> assumed that asphalt paving is intended to represent an <br /> impermeable barrier or cap. The RAP does not discuss in <br /> sufficient detail the construction of the asphalt cap so that <br /> cap efficiency and maintenance schedules can be evaluated. <br /> Recommendation: <br /> Construction of the asphalt cap should be discussed in more <br /> detail. Type of asphalt (standard grade, fine grade, rubber <br /> amended, etc.) should be addressed as well as type of foundation <br /> layer. Discussions on the areal extent of the cap and relation <br /> to potential remediations for the chlorinated hydrocarbons <br /> should also be addressed in the RAP. Inspection, maintenance, <br /> repair and resurfacing schedules should be addressed. <br />