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i HorizSW Field Methods and Proce res A dedicated 50 cubic centimeter (cc) syringe will be connected to the 118 inch Nylaflow tubing at the surface via an on/off valve. Prior to opening the vapor sampling port, a 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 back pressure via the syringe, the probe rod will be retracted to open the vapor sampling port. The probe rod will be retracted until the backpressure is released indicating the presence of in-situ soil vapor. The target depth and the actual depth of the rod will be recorded. The probe rod will be sealed at the surface with granular and hydratedbentonite and vapor pressure inside the Nylaflow tubing allowed to equilibrate for a minimum 20 minutes before sampling. A tracer compound, typically difluoroet a_ne, isopropanol, or butane, will be used for leak testing around the prob re od to the ground surface and along the sampling tubing above ground. The tracer will.be dispensed around the base and top of the probe rod and along the tubing train during sample collection. If the tracer compound is detected in air sample,;.ariother sample will be collected,--.;a Soil vapor will be withdrawn from the end of the inert Nylaflow tubing that runs from the sampling tip to the surface using a dedicated 50 Scc glass syringe or a gas-tight canister (Summa) under vacuum connected via an onloff valve. The probe tip and sampling tubing will be nominally purged by a purge volume test as described below. A sample of in-situ soil 'vapor will be withdrawn and immediately transferred to the mobile lab for analysis within minutes of collection. For off-site analysis, sample collected will'be collected in §6mma or in Tedlar bags when allow 4.0 PURGE VOLUME TEST A site specific purge volume test will be conducted at the beginning of the soil gas investigation to purge ambient air from the sampling system. Three different volumes will be purged and sampled (nominally 1, 3 and 7 purge volumes) and analyzed immediately to determine the volume amount with the highest concentration. Therefore, the optimum purge volume will be achieved and utilized during the entire soil gas investigation. 5.0 SAMPLE FLOW RATE Sample collection will be timed so that the soil gas flow rate does not exceed 200., milliliters per minute (mUmin). This will be accomplished by withdrawing the plunger on the syringe at a constant rate of 3;milliliters per'second (mVsec).The sample collector will record collection time and any resistance to sample flow felt on the syringe during collection. If soil gas is contained in Summa canisters, a flow controller pre-calibrated to a flow rate of maximum 200 mUmin will be utilized at the end of 118 inch OD polyethylene conveyance tubing and tight-fitted to the canister. Th c Ilector.will record the initial and final collection time and vacuum readings`` ' Project No. 7076.15 B -2 HORIZON ENVIRONMENTAL INC.