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Figure C-1: Example Apparatus for Field Screening and Sampling using Helium Tracer APPENDIX D SOIL GAS SAMPLING IN LOW-PERMEABILITY SOIL(EXAMPLE) Shroud Flow Controller and Soil-Gas Probe Design and Construction:The following is an example of the probe 5 Micron Filter construction and design,which may be used for collection of soil gas from a low- ---- -- - permeability soil. Alternative designs may be acceptable;however any probe in low permeability material should meet the following conditions: Summa canister Pump 1. Probes installed in a cored borehole(e.g.,Geoprobe Dual Tube 3.25-inch Helium meter diameter core barrel system(DT325),or similar); monitoring port ` 2. Probes constructed of clean inert materials(i.e.,Teflon, PEEK,nylon); 3. Probes having a sand filter pack around the probe tip with a pore volume of Lung Box about 1 L 4. Probes having an annular seal of well-hydrated bentonite and 5. Probes having a ball valve with compression fitting(e.g.,SwagelokTM'),or -Tedlarr Bag Teflon's-taped threaded fittings on the top. t Soil Gas/—,--,*' as/ If lithology with low permeability is anticipated,a continuous core should be collected Sub-Slab Probe and visual inspection of the core should be performed to assess the moisture profile and the probe screen should be installed at a depth above the capillary fringe. Laboratory Helium Addition Point analysis of the grain size distribution(sieves and hydrometer)and moisture content in selected samples from the soil core is also recommended. Soil Vapor Well Emplacement Method: In this example,a screened tip(e.g., - Geoprobe®6-inch permanent implant screen with conical stainless steel tip)is used References: attached via compression fittings to the'/4-inch tubing. As a precaution,the implant screens are soaked in isopropyl alcohol and oven-dried to remove any cutting oils. An McAlary,T.A.,P.Nicholson,H,Groenebelt,D. Bertrand.2009.A Case Study of Soil- equipment blank sample(i.e.,blank air sample)is collected from a fully assembled pp.144. probe prior to subsurface installation to identify any target analytes that may be &Remediation,29,no:1, p.14 Gas Sampling in Silt and Clay-Rich(Low-Permeability)Soils,Ground Water Monitoring attributable to contaminant from the equipment. USEPA. 1996:United States Environmental Protection Agency, EPA Publication SW- The well design described below is a modification of the design in main text. In this 846,Test Methods for Evaluating Solid Waste,Physical/Chemical Methods 0040, example,filter sand is installed in the bottom of the borehole before the probe is Sam � o Principle Organic Hazardous Constituents from Combustion Sources Using inserted,then sand is added to surround and extend above the screen. The total Tedlar Bags:National Technical Information Services,U.S. Department of Commerce. volume of sand should be sufficient to provide a pore volume of at least 1 L,assuming Springfield,VA, December,Technical Section on S Figure 1 40%porosity. For a 3.25-inch diameter borehole,this corresponds to a filter sand Spri gwww.VA, December, r,199 azwa tion .1.2, Figure df) interval of about 18 inches. Above the filter sand,3 to 6 inches of dry granular bentonite (httiis placed to trap any liquid that might separate from the overlaying bentonite slurry or the water used to seal the borehole annulus. The bentonite seal should preferably be mixed as slurry. The actual volume of slurry added to the borehole should be verified to be equal to the calculated volume of the annular space between the probe tubing and borehole wall. Alternatively,the seal may be placed using alternating lifts of water and granular bentonite,provided that a tamping rod is used to facilitate mixing of the two components in-situ. A bolt-down flush-mounted casing or a well box should be installed as a ground surface completion. 12/10/2009 _59- 12/10/2009 -60-