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1 28 May 1991 GeoAudit CV 43C4 . 1. 1 - Work Plan for Vacuum Extraction ' Page 8 of 10 The data presented here are based upon the operation of the Vaclean 1000 using propane as supplementary fuel. The use of natural gas for this purpose has several additional advantages. Natural gas, is less expensive than propane and is readily available at the site. ' Natural gas promotes not only a more complete combustion of the hydrocarbon contaminants, it is also proven to burn very cleanly, leaving practically no by-products. 8 . MONITORING PROGRAM To maximize the degradation of hydrocarbons, vapor from the extraction wells is monitored for the presence of volatile organics. A weekly-monthly monitoring is scheduled for this purpose. A decrease of the organic vapor content is anticipated to occur within the first weeks. Upon reaching a constant level of typically between 500 to 1, 000 ppm as hexane, a confirmatory sampling is scheduled (see Section 9 6) . A treatment period between 6 to 18 months is estimated. 9 . DETAILED WORK PLAN 9 . 1. INSTALLATION OF VACUUM EXTRACTION SYSTEM 1) Construct a lockable station in the northern portion of the storage structure. 2) Affix noise insulator at the inside of the structure. ' Provide openings for natural gas and extraction lines. 3) Extend the existing natural gas line and provide a proper ' connection to the vacuum extraction unit. This item is conducted by PG&E personnel. ' 9 . 2 . INSTALLATION OF EXTRACTION WELL The items for this plan are detailed in a separate work plan, which was submitted to the SJEHD on 21 March 1991. 9. 3 . INSTALLATION OF VAPOR EXTRACTION LINES ' 4) Connect a 2-inch diameter PVC (Schedule 40) line to the extraction wells. Install. ball valve at each line for individual and manifold extraction selection.