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Horizon Field Methods and Procedures - Soil Gas Investigations vacuum test of the tubing and PRT connection will be performed using the syringe to place a .vacuum on the system to check for integrity of the connections. While holding vacuum on the syringe, the probe rod will be retracted to open the vapor sampling port. The probe rod will be retracted until the vacuum is released, indicating the sampling port is open. The probe rod will be sealed in the auger boring to the surface with hydrated granular bentonite. The sampling apparatus will be allowed to equilibrate with formation soil gas for a minimum 20 minutes prior to sampling. Conduct leak testing at each sampling location. install shroud over the sampling apparatus where it protrudes above surface grade. Utilize a tracer compound (typically difluoroethane, iso -propanol, or butane) to detect leakage of ambient air into the sample point boring during sampling. If leak -test compound is detected in the sample, another soil gas sample will be collected. Soil gas will be withdrawn from the end of the inert Nylaflow tubing that runs from the sampling tip to the surface via an on/off valve using a dedicated 50 -cc glass syringe or a Summa canister. The sampling apparatus will be purge -volume tested as described below.. A soil gas sample will be withdrawn and immediately transferred to the mobile laboratory within 5 minutes of collection for analysis. For off-site analysis, soil gas samples will be collected in Summa canisters or in Tedlar bags. 4.0 PURGE VOLUME TEST A site-specific purge -volume test will be conducted at the initial soil gas sample location to evaluate the number of apparatus volumes to be purged prior to collection of soil gas samples. Three separate soil gas samples will be collected after purging 1, 3 and 7 apparatus volumes from the initial soil gas sample location. The number of apparatus volumes associated with the sample that contains the greatest analyte concentration will be used for collection of the remaining soil gas samples. 5.0 SAMPLE FLOW RATE Collection of soil gas samples into the syringes will be timed so that the soil gas flow rate does not exceed an average rate of 200 milliliters per minute (mL/min). This will be accomplished by withdrawing the plunger on the syringe to the desired volume over a period of time so that the sampling rate will not exceed 200 ml/min. If soil gas is collected into a Summa canister, a flow controller calibrated to a flow rate of maximum 200 mL/min will be utilized to control the sample flow rate. 6.0 BOREHOLE ABANDONMENT AND SURFACE RESTORATION After completion of sampling, the borehole shall be backfilled from total depth to the surface with cement grout. If located in pavement, the surface shall be finished utilizing quick -set cement tinted to match surrounding pavement. 2 HORIZON ENVIRONMENTAL INC.