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Geological Technics Inc. Page ge 2 , <br /> Bank of Stockton-Western Lift <br /> Remedial Feasibility Study-Work Plan <br /> Project#358.3 <br /> September 28, 1995 <br /> Chronology <br /> This document presents a brief site history, and presents a work plan conduct a <br /> feasibility study to determine how best to address the remaining groundwater <br /> ' contamination. <br /> A brief project chronology is as follows: <br /> • 06/91 3 USTs removed <br /> • 09/91 1st phase over excavation <br /> • 10/91 2nd phase over excavation <br /> • 05/92 Backfilling with pea gravel completed <br /> • 06/92 MW-1 installed <br /> ' • <br /> 11/92 MW 2&3 installed <br /> • <br /> 06/93 MW 4 &5 installed <br /> ' + 06/93 Complete round of groundwater monitoring <br /> • 09/95 Request by PHS/EHD for feasibility study <br /> This feasibility study is intended to address the advisability of undertaking the <br /> following remedial actions: <br /> ' • Bioventing / Soil Vapor Extraction (Sec. 3) <br /> • Groundwater pumping (Sec. 4) <br /> • Additional Over-Excavation (Sec. 5) <br /> ' • Groundwater Monitoring Only(Sec. 6) <br /> 2.0 WELL INSTALLATION - PRIOR TO SYSTEM TEST <br /> A major goal of this feasibility study is to evaluate a bioventing / soil vapor <br /> extraction system (BV/SVES). The existing groundwater monitoring wells are not <br /> well positioned or designed to accomplish this goal. A significant offsite feature <br /> that will influence this study is the pea gravel which fills the excavation pit. The <br /> ' pea gravel is extremely porous and permeable in comparison with the native soil <br /> and will tend to thief any induced air flow in the immediate vicinity of the pit, thus <br /> seriously compromising any flow data that may be obtained from MW-1 or any <br /> ' other well which may be installed in the vicinity of the pit. Moreover, none of the <br /> existing wells are positioned directly down gradient of the tank pit. This means that <br /> the down-gradient extent of soil and groundwater contamination has not yet been <br /> fully determined. To simultaneously address both of these problems, the BV/SVES <br /> Pilot study discussed in Section 3.0 below will require the installation of two <br /> new,dual purpose wells to be used for vapor extraction and groundwater <br /> I <br />