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i S .r • • pressure;or,well identification number and depth interval of screen. Typical sampling ports consist of a 1/4—inch ball valve fitted With a 3/16-inch hose barb to forth a slip stream from the sample source. The sampling procedure requires one end of the tubing be slipped over the sample port hose barb and the other end over the diaphragm pump inlet hose barb to form an air-tight connection. The sampling pump is then started and the pump is purged for 1 minute with the vapor to be sampled. Following purging,the discharge of the pump is then connected to the'Tedlar"bag using a section of 3116-inch tubing.The pump is restarted and the bag is opened and allowed to fill to approximately 314 of its capacity. Caution should be taken not to overfill the sampling bag. The sample is placed in a non-refrigerated dry cooler with sufficient packing to prevent damage during transport. Cooling samples will cause condensation of moisture within the sample,thereby distorting the laboratory analysis. For quality control purposes,a duplicate vapor sample should be collected from each sampling port. This sample is then put on hold at the laboratory pending initial analysis. To ensure quality control and minimize the potential for cross- contamination prior to and during sampling,the diaphragm pump is thoroughly purged for approximately 5 minutes with nitrogen or clean air(i.e.,compressed clean air). A"blank" sample of the discharged air is raptured in a"Tedlar"bag at the end of the purging procedure and may be analyzed to ensure the purging was effective. To minimize the potential for cross-contamination between air samples,the polyethylene tubing,if not sample dedicated, is thoroughly cleaned and rinsed. Vapor samples are subject to very limited holding times, typically 48 hours. Thus,care must taken to avoid delays in submittal of vapor samples to the laboratory. In the event the vapor samples cannot be submitted to the analytical laboratory on the same day they are collected,they are to be temporarily stored in the dry,non-refrigerated,packed cooler until the very first opportunity for submittal well within the required holding time,taking into account the time needed for shipment to and receipt by the laboratory.