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0 <br /> CrNMR.. SACF�AME�fTO REVIEW DRAFT <br /> Addendum Letter to Mr. Harlan Knoll <br /> August 31, 1990 <br /> Page 2 <br /> Based upon the finding of the site assessment, Versar developed a <br /> remediation plan for the facility. The plan was presented in the report <br /> entitled "Remediation Plan for the Pacific Bell Ashley Road Facility <br /> (UE-132)" dated March 8, 1989. The remediation plan recommended the <br /> excavation and bioremediation of contaminated soil from beneath the <br /> former UST site. <br /> REVISED REMEDIATION PLAN <br /> i <br /> Since the submission of the remediation plan, the feasibility of <br /> excavation at the site has been re-evaluated. The former UST site is <br /> located directly adjacent to the front of the Pacific Bell Facility <br /> building. Because of the sensitive nature of the facility, it is <br /> constructed to withstand large magnitude earth tremors. As a result, <br /> the weight bearing load upon the structure's foundation is significant; <br /> however, the footings for this structure are shallow due its location in <br /> a broad flat alluvial plain. Furthermore, the extreme cost of shoring <br /> for the execavation of the contaminant plume presents a cost/benefit <br /> feasibility problem. It is therefore necessary to determine if <br /> site remediation can be accomplished without excavation and the <br /> accompanying risk to the integrity of the facility. <br /> Alternate Method of Remediation <br /> The alternate method of remediation proposed for the site is soil <br /> vapor extraction and enhanced natural biodegradation of the <br /> contaminants. In order to determine if the proposed methodology is <br /> suitable for the site, a pilot study will be undertaken at the facility. <br /> The goals of the pilot study will be to: <br /> 1) More fully define the vertical and lateral extent of soil <br /> contamination at the site. <br /> 2) Determine the suitability of the site for in situ vapor extraction <br /> as a remediation method. <br /> 3) Determine the effectiveness of naturally occurring in situ <br /> biodegradation under conditions of enhanced air flow. <br /> 4) Calculate the vapor extraction well placement, spacing, and <br /> system needs for projects duration and cost in the event of full <br /> scale remediation using the proposed methodology. <br />