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16W C,eologicalTeckjucsl�c. N.O� Page 7 Sinclair&Thompson Property Soil Gas Survey Report r.. January 29,2007 © The purge test was performed in SG-4 (Figure 2). This sampling point was chosen because it is the closest to MW-1R and MW-4 and thus the most likely to produce the contaminants of concern. ❑ The purge volume of the sampling system included the internal volume of the tubing and the anular space around the probe tip. ❑ A step purge test of one, three, and seven purge volumes was performed on SG-4. The L. appropriate purge volume for sampling was selected based on the highest concentration for BTEX constituents detected during the purge volume tests. Benzene was not detected at any of the purge volume tests. The highest levels were detected during one purge volume and this was set as the default for the remaining soil gas sample points. Leak Test v A two-part leak test was performed on each of the borings: ❑ First, at each sample point an equipment vacuum test was performed after the drive rod has been driven to the desired sample depth. A vacuum was applied to the tubing before t„ the probe is opened and let stand for 30 seconds to confirm a tight seal. This test was successful at each location. The probe was opened and a 20-minute equilibrium period was performed at each boring. After equilibrium was reached each sample point was purged as described below. a Second, prior to collecting the sample, 1,1-Diflouroethane (1,1-DFA), a tracer, was applied to the ground surface around the drive rod, above the hydrated bentonite, and LO around the connection of the tubing to the syringe of each boring. Pur a/Sample Flow Rate LN The purge and sampling flow rate was between 20 to 150 ml/min. Thus avoiding or reducing the potential problem of stripping or ambient air dilution from occurring. A new plastic syringe was used at each borehole. L. Sample Tubing ' The polyethylene tubing was approximately 1/-inch diameter and new tubing was dedicated LO to each sample point. ' 3.2.3 Sample Handling Procedures A new syringe and polyethylene tubing were used on each of the soil gas samples collected during the soil gas investigation. The laboratory technician wore disposable gloves while i collecting syringe from the boring. The laboratory technician wore disposable gloves while LN analyzing the collected vapor samples. Gloves were changed with each sample collection. ' 3.2.4 Soil Gas Analytical Procedures +O TEG mobile laboratory and direct push service was selected for the soil gas investigation at the Site. TEG offers state-of-the-art active, passive, and flux chamber soil vapor surveys using EPA endorsed methods. MEG has completed more than 100,000 soil vapor locations at a variety of industrial and military sites across the United States and the world. TEG has designed and developed proprietary methods for Tier H landfill gas sampling, automated vapor monitoring at remediation sites, and tracer gas injection and testing.