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La GeO&g&OI Technics Inc. Page 6 Sinclair&Thompson Property Soil Gas Survey Report LM January 29,2007 &W The sample locations were chosen at points as close as possible to the residence and the shop. These locations were between the buildings and the extents of excavation. The first location (SG-4) is located along the southeastern portion of the property that is closest to MW-1R and L, MW-4. MW-1R and MW-4 show the highest levels of contamination and the location of SG-4 was the most likely location to find vapor phase constituents. v 3.2.2 Sample Collection Procedures The active soil gas investigation (ASGI) was performed in accordance to the DTSC guidance document titled Advisory -Active Soil Gas Investigations, dated January 28, 2003. Field Conditions ° • Soil gas sampling was conducted during a period of dry weather, three days after a rain s. event. • The soil was dry and there was no moisture noted in the upper 9-feet of the subsurface. +O Soil Gas Borehole Sam le Depths • All borings were advanced to a depth of 9.0-feet bgs. The rods were pulled back, exposing the screened interval, until flow was measurable in the syringe. The recorded R- sampling depth indicates the top of the exposed screen interval. o SG-1 and the duplicate SG-1 were sampled at 8.5-feet bgs o SG-2, -4, and -5 were sampled at 9A-feet bgs (the rods were pulled back no more i. than 3-inches) o SG-3 was sampled at 8.0-feet bgs o SG-6 was sampled at 7.0-feet bgs Drilling Method A 9600 Series Power Probe, direct push drill rig, was used to advance rods to the selected sampling depth using a 135-foot pound hammer. The drive rod was driven to a depth of approximately 9-feet bgs and then pulled back L' approximately 2- to 24-inches to expose the inlets of the gas probe. A hydrated bentonite seal was placed around the drive rod at ground surface to prevent ambient air intrusion into the annual space of the borehole. Silicon tape was wrapped around the junction where the tubing entered the drive rod. A lag time of 20 minutes, or more, was allowed for equilibration of subsurface conditions after probe insertion to the sample depth. A sampling tube was attached to the probe tip to prevent infiltration. Silicon tape was wrapped around the junction where the tubing entered the drive rod. After sample collection, both the drive rod and the tubing were removed. Each #' boring used independent tubing and rods, eliminating the need to decors between sampling boreholes. Purge Volume Test To ensure that stagnant or ambient air is removed from the sampling system, a purge volume vs. contaminant concentration test was performed as described below: