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mobile laboratory for Total Volatile Hydrocarbon concentrations 2.2.2 Preliminary Soil Assessment Neumiller & Beardslee retained Geological Audit Services (GeoAudrt) in 1992 to perform the second step in the investigation GeoAudrt drilled six borings and collected 38 soil samples, 22 of which were submitted for laboratory analysis (Figure 4) The bonngs ranged Two samples from boring in depth from 29 5 to 36 5 feet p g B-3 emitted faint odors of degraded"old" gasoline, and xylene and/or ethylbenzene were detected in both samples No other hydrocarbons were detected in any other samples, and in its Preliminary Investigation and Evaluation Report (PIER) GeoAudrt concluded that the residual contamination posed no threat to public health 2.2.3 Soil and Groundwater Assessment The detection of low concentrations of ethylbenzene and xylene in the capillary fringe prompted PHS/EHD to request the installation of monitoring wells to gauge the impact of the contamination to groundwater In late 1993, GeoAudrt installed monitor wells MW-1 through MW-3 and began quarterly groundwater monitoring Low concentrations of gasoline hydrocarbons were detected at and below the groundwater interface in MW-1 and MW-2,but no hydrocarbons were detected within the vadose zone Clearwater Group continued the assessment by installing monitor wells MW-4 and MW-5 in 1994 and MW-6 in 1996 (Figure 5) Clearwater also drilled a cone-penetrometer-testing • boring (CPTB-7) to a depth of 81 feet in order to examine the vertical extent of soil contamination None of the wells encountered contarmnated soil, but very low TPH-g and BTEX concentrations were detected at the base of the shallow aquifer (40-50 feet) and below in CPTB-7 Benzene and ethylbenzene were detected in the water sample from MW- 5, and all three wells were added to the quarterly monitoring program Clearwater reported the results in its 1995 Report on Site Assessment Activities, Pilot Test, and Quarterly Groundwater Monitoring and concluded that the extent of soil and groundwater contamination had been fully delineated PHS/EHD concurred with this conclusion 2.2.4 Feasibihty Testing The third step in the investigation was to conduct feasibility tests of potential remedial methods Clearwater began this phase by installing air spargmg wells SW-1 and SW-2 and soil vapor extraction wells VW-1 and VW-2 in 1995 (Figure 6) The vapor extraction wells were dialled to 25 feet and completed with 10 feet of 4-inch-diameter PVC screened casing, and the sparging wells were drilled to 32 feet and completed with 2 feet of 2-ouch-diameter PVC casing Soil samples were collected at 5-foot intervals, but no water samples were collected Clearwater performed a three-hour SVE test on each vapor extraction well and a 2-1/4 hour sparginng test in each sparge well in November 1995 Vacuum pressures, flow rates, dissolved oxygen concentrations, vapor concentrations, and water levels were measured 2