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2.8 Sample Container Cleanliness and Decontamination column. A low-flow or low-permeability probe is defined as a condition where the minimum flow rate(100 mUmin)could not be sustained at the maximum 1. New containers should be shown to be free of contaminants by providing data applied vacuum level(100 inches water). See Appendix D for sampling from either the supplier or the analytical laboratory. protocols for low-permeability soils. 2. After each use,reusable sample containers should be decontaminated as 3. Soil Gas Sample Collection using Sorbents for Method TO-17:Soil gas follows: sampling for analysis by Method TO-17 is described in Appendix E and F. Low permeability materials may result in a lower flow rate. Use of vacuum A. Glass syringes or bulbs should be disassembled and baked at 240°C for gage is recommended between the sorbent and extraction device. a minimum of 15 minutes or at 120°C for a minimum of 30 minutes,or be Permeability testing of soil is recommended to determine the optimal flow rate decontaminated by an equivalent method. If a syringe is re-used,it should at a vacuum of less than 100-inches of water(McAlary et al,2009). TO-17 is be blank tested,and tested for adsorptive losses via spike testing. Blank currently recommended only for naphthalene analysis;however,TO-17 may testing frequency(or certification frequency)of syringes should also be also be used for other volatile constituents depending on the DQOs for the included in the workplan. project. The regulatory agency should be notified and concurrence is required prior to implementation of sorbent/TO-17 for other volatile B. SUMMA®canisters should be properly decontaminated as specified in US constituents other than naphthalene. EPA Method TO-15,and/or should be certified according to project DQOs, either be batch or individually certified. 3.0 Field Conditions C. Tedlar bags may be reused if data are provided to show the bags are Field conditions,such as rainfall,irrigation,fine;-grained sediments,or drilling free of contaminants. conditions may affect the ability to collect soil gas samples. D. Equipment blanks should be analyzed to verify and evaluate the 1. Rainfall and Barometric Pressure(see Appendix G):Rainfall decreases effectiveness of decontamination procedures for recycled or reused the air-filled porosity of the shallow soil,thereby limiting diffusion transport of containers. At a minimum,one equipment blank should be run per 20 volatile contaminants and potentially biasing soil gas sampling results, sample containers cleaned;of at least one per day. Hence,do not conduct soil gas sampling during or within five days of a significant rain event(1/2 inch or greater). Stop irrigation or watering of soil at least five days prior to the soil gas sampling event. Likewise,areas subject to 2.9 Sample Collection soil gas sampling should be free of standing or ponded water for at least five days prior to sampling. Do not perform soil gas sampling in swales or 1. Vacuum Pump:When a vacuum pump is used,collect samples on the intake depressions where large volumes of water can potentially accumulate. side to prevent potential contamination from the pump. Use a lung box when collecting samples using Tedlar bag(see Appendix C,Figure C-1). Record Barometric pressure fluctuations associated with the passage of frontal vacuum readings and corresponding flow rates on field data sheets for each systems can introduce atmospheric air into the shallow vadose zone. sample.If the pump is battery operated,the batteries should be checked Therefore,soil gas sampling should be delayed until frontal systems have before and during operation to insure a proper charge is maintained. passed the area.Alternatively,soil gas sampling times and depths may be chosen to minimize the effects of changes in barometric pressure. 2.. Soil Gas Sampling in Low-Permeability Soil:Soil gas sampling from low permeability material(i.e.,silt and clay-rich soils)is feasible and high quality 2. Wet Conditions:If no-flow or low-flow conditions are caused by wet soils due data can be produced with:(1)good annular seals;(2)careful monitoring of to a rain event or irrigation or water is drawn into a probe,cease the soil gas flow and vacuum during purging and sample collection;and(3)using tracer sampling. Low or no-flow condition corresponds to cases where the minimum gas(i.e.,helium)for leak-testing. If the soil gas permeability is too low to flow rate of 100 mUmin cannot be sustained at the maximum applied vacuum allow sustainable purging at appreciable flow rates without applying excessive of 100 inches of water(McAlary at al.,2009). If the low-flow condition is due vacuum,follow the protocols as described in Appendix D. An"appreciable to wet conditions or shallow groundwater,then passive samplers may be flow rate"is defined as flow of 100 mUmin or greater,and an"excessive deployed to detect VOCs. vacuum"is defined as any vacuum greater than about 100 inches of water 3/3/2010 -29- 3/3/2010 -30-