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Decontamination may consist of steam cleaning or a three-stage wash and rinse tracer compounds are applied to towels or clean rags and placed around ail
<br /> consisting of a wash with a non-phosphate detergent,a rinse with tap water,and connections in the sampling train in order to evaluate potential leaks of ambient
<br /> a final rinse with distilled water. Collect one equipment blank at the beginning of air into the sampling train.The leak check compound selected should not be a
<br /> sampling,and at least one each day after decontamination. Air dry equipment suspected site-specific contaminant.
<br /> prior to re-use. Use new or unused sample tubing for each probe location.
<br /> Reuse of tubing is not recommended. Seal integrity is confirmed by analyzing subsequent soil gas samples for the
<br /> tracer compound. Alternatively,gaseous tracer compounds,such as helium,
<br /> isobutene,propane,and butane,can be used along with a shroud or tent over
<br /> Sub-Slab Investigation Methods the sampling equipment.Procedures for conducting a quantitative leak test using
<br /> helium as a tracer compound are described in Appendix C.
<br /> The procedure for collecting sub-slab soil gas samples are the same as for
<br /> collecting sub-surface soil gas samples except that a slower flow rate and lower Leak check compounds(i.e.,liquid tracer compounds)should be included in the
<br /> vacuum should be utilized.Using a flow rate of less than or equal to 50 milliliters method analyte list. The laboratory reports should quantify and annotate all
<br /> per minute(mUmin)and maintaining a low vacuum of less than 100 inches of detections of the leak check compound at the reporting limit of the target
<br /> water should prevent ambient air breakthrough into samples(McAlary et al., analytes. If the concentration of the leak check compound is greater than or
<br /> 2009).Methods and procedures for installing sub-slab vapor wells are described equal to ten times the reporting limit for the target analyte(s),then corrective
<br /> in the DTSC Vapor Intrusion Guidance(Cal/EPA,2005, Page G-1) action is necessary as discussed below.
<br /> 2.4 Soil Gas Sampling e If a leak check compound(i.e.,liquid tracer compounds)is detected in the
<br /> sample,the cause of the leak should be determined,evaluated,and corrected
<br /> Before obtaining soil gas samples,leak and purge volume tests are necessary. through retesting. If a leak is confirmed and the problem cannot be corrected,
<br /> ter,
<br /> the ambient air leak may be quantified using a gaseous tracer with a shroud,as
<br /> Leak Test - described in Appendix C. An ambient air leak up to five(5)percent is acceptable
<br /> w if quantitative tracer testing is performed by shrouding. Otherwise,the soil gas
<br /> A leak test is used to evaluate whether a good seal was established in the vapor well should be decommissioned if the leak cannot be corrected.
<br /> sampling train,ground surface,and probe interface. A leak test should be Replacement vapor wells should be installed at least five(5)feet from location
<br /> conducted at every vapor monitoring well each time a soil gas sample is where the original vapor well was decommissioned due to a confirmed leak.
<br /> collected because a poor seal may result in soil gas samples that are diluted by Include the leak check compound concentrations detected in the soil gas
<br /> ambient air.This may result in an underestimation of actual site contaminant samples in the laboratory report and discussed in the site characterization report.
<br /> concentrations or, alternatively,introduce external contaminant into samples from
<br /> ambient air. Note that if sampling is done exclusively from a SUMMA®canister at a stationary
<br /> laboratory and there is a significant leak,it will not be identified until after the
<br /> Shut-In Test:Prior to purging or sampling soil gas,a shut-in test should be sample has been collected and analyzed. Therefore,field screening prior to
<br /> conducted to check for leaks in the above ground fittings. The shut-in test laboratory confirmation is recommended.
<br /> consist of assembling the above-ground apparatus(e.g.,valves,lines and fittings
<br /> downstream from the top of the probe),and evacuating the lines to a measured
<br /> vacuum of about 100 inches of water column(in-1-12O),then shutting the vacuum 2.5 Purge Volume Test
<br /> in with closed valves on opposite ends of the sampling train. The vacuum gauge
<br /> connected to the line via"T'-fitting is observed for at least one minute,and if The purpose of a purge volume test is to ensure stagnant or ambient air is
<br /> there is any observable loss of vacuum,the fittings are adjusted as needed until removed from the sampling system and to ensure samples collected are
<br /> the vacuum in the above-ground portion of the sample train does not noticeably representative of subsurface conditions. The purge volume test should be the
<br /> dissipate(McAlary et al.,2009). first soil gas sampling activity at the selected purge volume test point,and should
<br /> be located as near as possible to the anticipated or confirmed contaminant
<br /> Leak Check Compounds:Liquid tracer compounds,such as hexane,pentane, source,and in an area where soil gas concentrations are expected to be
<br /> and n-propanol,can be used to evaluate the sample integrity. Typically,liquid elevated,based on lithology.The purge volume test is conducted by collecting
<br /> and analyzing a sample for target compounds after removing one,three,and ten
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