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TO E RO E K SOP No.021,REV.1 „ SOIL GAS SAMPLING METHODS ASSomns,iNc. PAGE 7 packs to the laboratory 2.7 DUPLICATE AND EQUIPMENT BLANK COLLECTION Duplicate soil gas samples will be collected at each site as required in the site-specific quality assurance project plan and field sampling plan. Generally, one duplicate sample will be collected for every ten samples collected. Each duplicate is collected in conjunction with a corresponding environmental sample. To collect duplicate samples in Tedlar® bags, a Y-branched sampling hose will be connected to the vacuum chamber or pump. Two Tedlar® bags are then attached, one to each end of the Y-branched hose. Syringe duplicate sampling is performed by collecting and analyzing a subsequent sample. To collect duplicate samples in canisters, a Swagelok "T"will be connected to two canisters. Purging and sample collection will proceed as described above. After collection, one sample will be labeled as the environmental sample and one as the duplicate. Equipment blanks also will be collected at each site as required in the site-specific quality assurance project plan and field sampling plan. Generally, one blank will be collected for every ten samples collected. Blanks will be collected by running ambient air through the sampling system immediately after it has been decontaminated,and by collecting the ambient air in a Tedlar® bag, Summa canister, or sorbent tube using the same procedures used to collect environmental samples. Blank sample collection is conducted upwind of any observed interference, and the location of the sampling must be recorded in a field logbook. Equipment blanks are collected to ensure that field equipment decontamination procedures are adequate. 2.8 LEAK CHECK PROCEDURES Leakage during soil gas sampling may dilute samples with ambient air and produce results that underestimate the actual site concentrations, or may contaminate the sample with external contaminants. Leak tests should be conducted to determine whether leakage is occurring. Leak detection is performed using the following procedures: 1. Leak tests should be conducted at every soil gas probe. 2. Tracer compounds such as isopropanol, butane, helium, or 1,1-difluoroethane may be used as leak check compounds. These compounds may be contained in common products such as Dust-Off and rubbing alcohol. Be sure the tracer compound used does not contain chemicals or impurities that may be present as a site contaminant.