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10/0588 09725 $20940951 003 <br /> y 4+ <br /> September 21 , 1983 page 2 <br /> Chevron M . A . <br /> PHASE <br /> The first phase will address contamination of subsoils <br /> in the tank backfill , waste oil tank removal, and product line: <br /> areas of the subject property which were obwerve6 to exhibit <br /> subsoils contamination , and are currently accessible for <br /> system hardware installation. The accessibi Z i ny c omponQnt of <br /> the first phase represents the ability to i.nstal-1 a system <br /> which would otherwise require extensive excavation, and <br /> affords a considerable cost savings at this time . <br /> The current tank excavation is approxi.matcly 12 ft , <br /> deep and within about 15 ft . of the existing building . Ir) <br /> our opinion , any further excavation without shoring could , <br /> influence the foundation performance of the adjacent <br /> building . It. is therefore not advisable to excavate any <br /> deeper in the existing excavation as a remedial alternative , <br /> In our opinion , an air venting system should be considered ds <br /> a remedial system for the contaminated soil . The attached <br /> drawing presents a prcli-urinary design of such a system. T'hK, <br /> design concept- has been shown to take advantage of the <br /> gasoline ' s volatilizing; vapors density being Wavier Uan <br /> air . The volatil os will therefore have a tendency Uo collect, <br /> near the boL om of the pea grr"vel backfill , therefor the <br /> perforated pipe collection system is proposed around thc, <br /> bottom of excavation , Perforated pilling will also be placed <br /> in the bottom area of the previous product line entering the <br /> tank backfill , and waste oil tank removal location. r? small <br /> vacuum pump placed along line will draw the gasoline <br /> volatiles from the tank excavation . A condensate wol.lecti.on <br /> system will be collected in line with the system to <br /> accomodate vapor-to-liquid condensation. <br /> PHAlg 11 : <br /> The second phase of the: remedial effort addresses the <br /> Possible literal movement of contamination from the tank <br /> excavation. The second phase system will include the <br /> installation .of five battered soil borings at the perimeter <br /> of the think removal excavation, in which vapor ext;rta.c.tioN <br /> wells would by installed. These second phase vapor Wells <br /> would address deeper contamination as well as lateral <br /> migration of contamination , as well as enhancing the <br /> Performance of the Phase F system. The Pha c JI system would <br /> share the vacuum and manifoldi.ng system with the Phase l <br /> system . <br /> It is anticipated that the Pha5c 1I system would include <br /> a total of five soil borings advanced at an approximate angle <br /> of 45 degrees , with the insertion point located about 25 feet <br /> from the edges of the excavated area. The wells are <br /> anticipated to be constructed of 2 inch diamet-er 0 , 020 inch <br /> Screened PVC well pipe . A Porous media comprised of a coarso <br /> E <br />