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100488 IS!31 $2094'351 <br /> 01003 <br /> September 21 , 1988 Page 2 <br /> Chevron U . S . A. <br /> PHASE 1 : <br /> The first phase will address contamination of subsoi is <br /> in the tank backfill , waste oil tank removal and product line <br /> areas of the subject peopert.v which were observed to exhibit <br /> subsoils contamination, and are currently accessi.hle fof' <br /> system h. rdware installation . The accessibility component of <br /> the first phase represents the ability to install 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.mate.ly 12 ft , <br /> deep and within about 15 ft , of the existing building . In <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 ex.i,sLi.ng excavation as a remedial alternative . <br /> In our opinion , an air venting system should be considered as <br /> a remedial system for the contaminated soil. . The attached <br /> drawing presents €a. preliminary design of such a system , This <br /> design concept: has been shown to take advantage of the <br /> gasoline ' s volatilizing vapors density being heavier than <br /> air . The volatiles will therefore have a tendency to collect, <br /> near the Bottom of the pea gravel backfill , therefor the <br /> perfortaLed pipe collection system is proposed around the <br /> bottom of.excavation . Perforated piping will also be placed <br /> in the boUom arca of the previous product line entering the <br /> tank backfill , and waste oil tank removal location. A small <br /> vacuum pump placed along line will draw the gasoline <br /> volatiles from the: tank excavation. A condensate c0lection <br /> system will. be collected in lime with the system to <br /> accomodate vapor--to-liquid condensation. <br /> MAE <br /> The second phase of the remedial effort addresses the <br /> possible lateral movement of cor►ta.mination from the tank <br /> excavation . The second phase system will include the <br /> installation of five: battered soil- borings at the p�,,r9meter <br /> of the tank removal excavation, in which vapor extra t ' n � <br /> ells would be installed . These second phase vapor wells <br /> would addrt-ss ( eepe.r contamination as well as lateral <br /> migration of contamination , as well as enhancing the <br /> performance of the Phase I system. The Phase IT system would <br /> share the vacuum and manifolding system with the ['horse I <br /> system. <br /> It is anticipated that the Phase II 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 diameter 0 . 020 inch <br /> screened PVC well pipe . A parous media comprised of a cWrse <br />