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3.2 AIR SPARGING WELLS ' Air-sparging wells SWI and SW2 were installed as shown in Figure 2 Boreholes for the wells were drilled using a truck-mounted rotary drill and S 5-inch outside-diameter hollow-augers The boreholes were drilled down to 45 feet (SWI) and 50 feet (SW2) below ground surface Soil samples were collected at 5-foot intervals in the saturated zone in order to define entrapped petroleum hydrocarbons and so that the well screen could be placed beneath them For quantitative confirmation of hydrocarbon concentrations in the soils, two ' soil samples from these selected zones were retained, labeled, placed in an ice-filled cooler, and shipped to Pace Incorporated, where they were analyzed for TPH-g and BTEX On the basis of OVA readings and soil appearance, screened well casing (0 010-inch slot, nominal 2-inch diameter) was placed in each well from 40 to 45 feet below ground surface The annular space around and above the screen (2 feet in SWI and 5 feet in SW2) was filled with ' sand, which was sealed with bentonite pellets one-foot thick, and the remaining annular space was filled with cement-bentonite grout to ground surface Each air-sparging well was completed and secured at the surface in a watertight monitoring well cover Boring logs and ' completion details for SWI and SW2 are included in Appendix A. 3.3 QUARTERLY GROUNDWATER SAMPLING ' On 18 May 1993, MW 13 was developed and groundwater samples were collected from 11 wells, including MW13 The wells were monitored for the presence of liquid-phase hydrocarbons and depths to water were measured with an optical interface probe. Selected wells were purged with a vacuum truck and dedicated PVC piping that had been steam-cleaned before being used in the well At least four casing volumes of water were ' removed before samples were collected. Groundwater samples were collected with disposable polyethylene bailers that had been cleaned at the factory and that had been rinsed three times with deionized water before being used in a well The water was poured from the bailer into 40-m1 VOA vials, which were then labeled properly and placed in an ice-filled cooler for storage and transport The samples were collected, stored, and transported under chain-of-custody procedures. Copies of purge and sample forms are included as Appendix B 1 4. RESULTS OF THE CURRENT INVESTIGATION ' 4.1 SOIL ANALYTICAL RESULTS ' Table 1 presents the analytical results for soil samples collected from the boreholes of MW 13, SWI, and SW2 Copies of the laboratory analytical reports are included in Appendix C. tTwo soil samples from the borehole for MW 13, collected 7 feet above the water table (25 5 feet below ground surface) and immediately above groundwater (32 5 feet below ground surface) were analyzed for TPH-g and BTEX No petroleum hydrocarbons were detected in these samples at concentrations equal to or greater than the method detection limits, which are 1 mg/kg for TPH-g and 0 005 mg/kg for BTEX 6373942(2yRoI69_vrx 3 3