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• P,#s Engineering Science, Inc. SECTION 2 FINDINGS OF PREVIOUS INVESTIGATIONS BACKGROUND This work plan follows several previous site environmental characterization reports by other consultants in 1995 and 1996 and two phases of investigation by Parsons Engineering Science, Inc. (Parsons ES) in November 1996 and May 1997. The Phase I RI established a site subsurface stratigraphic model, determined groundwater depth and gradient, and assessed the extent of soil and groundwater contamination. Site characterization activities completed in September 1996 included 1) drilling six exploratory soil borings in the vicinity of the former hazardous materials/waste storage area(source zone) and two soil borings in the vicinity of the Building 3 drain line, 2) installation of four groundwater monitoring wells at the northern and western margins of the property, 3) observation of water levels, sampling and field and laboratory analysis of groundwater, 4)preliminary evaluation of natural attenuation of chlorinated compounds in the groundwater, 5) installation of two vapor monitoring points (VMPs) and sampling and laboratory analysis of vapor extracted from them, and 6) preparation of a remedial investigation report (Parsons ES 1996a). The Phase II RI was carried out in March and April 1997 to clarify the extent of ' contamination associated with the source zone and to provide essential parameters needed for site remediation. Investigation tasks consisted of 1) advancing 10 cone penetration test (CPT) probes in the vicinity of and downgradient of the source zone, 2) construction of three 2-inch diameter monitoring wells, two shallow and one deeper, positioned based on results of the CPT investigation, 3) installation of dedicated bladder pumps for groundwater sampling by micropurging technique, 4) hydraulic testing of wells by slug test method, 5) installation of a 4-inch vapor extraction well (VEW) and conducting a soil vapor extraction (SVE) pilot test in the former hazardous materials/waste storage area, and 6) preparation of a Phase II RI report (Parsons ES 1997a). The Phase II RI report focused on the former hazardous materials/waste storage area and recommended 1) continuation of quarterly groundwater monitoring with natural attenuation assessment as needed, 2) development of a conceptual design for SVE remediation at the source zone, 3) development of a remedial work plan for limited extraction of groundwater from the plume beneath the source zone, and 4) further hydrogeologic investigation at the northeast corner of the AASC property. The present scope of work addresses the last of these recommendations. Items 2) and 3) are planned for later in 1998. We have concluded that the 0997\09072\wks2add 12-18-97 2-1