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JA14-16-'91 WED 12:073 - l.IAX TECHNOLOGIES TEL N0:4.58 7 -•i #4138 P06 SITE INVESTIGATION REMEDIAL INVESTIGATION Procedures A Soil Gas Survey was conducted to screen for the presence of hydrocarbon vapors in the soil and, if found, delineate the lateral and vertical boundaries of hydrocarbon vapors, The Soil Gas Survey was initiated on 12 March 1990 and was completed the following day at this site. Soil gases were extracted from 13 temporary vapor probes installed for the investigation and five existing groundwater monitoring wells. Placement of the temporary vapor probes was determined in the field by the site investigator as the survey progressed (Figure 1) . Soil gases extracted from the temporary vapor probes and existing groundwater monitoring wells were analyzed for total hydrocarbon concentration as vapor (TVH) during the Soil Gas Survey. temporary The tem vapor� F Y p or probes installed for the investigation were constructed of 1/2-inch diameter Schedule 40 steel pipe. A point was forged on one end of each probe. A 24-inch range of 3/16-inch perforations were drilled into each probe beginning at 3 inches from the point. The vapor probes were driven pneumatically into the soil to various depths . The perforated depth intervals tested include 8 to 10 feet, 14 to 16 feet, 19 to 21 feet, 28 to 30 feet, and 32 to 34 feet below grade. In locations where the soil was covered by concrete or asphalt, a 1 -inch diameter hole was drilled through the surface material with an electric roto-hammer to facilitate probe installation. The existing groundwater monitoring wells were screened at a depth interval of 28 to 58 feet below grade. A vacuum was applied to each probe to extract soil gas during the survey. One pound per square inch (psi ) sample pressure was maintained during the analysis . Sample flow rate and instrument pressures were checked before each test. The sail gas was sampled through a 1/4-inch Teflon sample line that was connected to a stainless steel well head fitting , Use of Teflon tubing minimizes sample loss through adsorption and the possibility of distorted results from a sample line contaminated by a previous analysis . Leak checks were performed on the sample line before and during the analysis. Filters were used extensively throughout the system to remove foreign material from the sample pathway. The sample line was connected to a diaphragm pump located in a mobile laboratory. The extracted soil gas was analyzed using a Beckman Model 400 Total Hydrocarbon Analyzer equipped with a Flame Ionization Detector (FID) . - 2 -