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residual vacuum in the SUMMA®canister of less than 10 inches HP which APPENDIX E corresponded to a sample volume of about 0.6 Lin a 1-L SUMMA canister(i.e.,two aliquots of sample would be required).For a low-flow probe the volume of soil gas NAPHTHALENE SOIL GAS COLLECTION extracted from the formation is known from the permeability testing and from the volume expected to be collected based on the Ideal Gas Law(i.e.,0.33 L,excluding the dead volume of above ground tubing). Therefore,sample collection into canisters that do not Soil gas sampling for naphthalene is more complex than traditional soil gas investigation exceed the maximum applied vacuum(100 inches of water)can be collected if the procedures. The appropriate sample collection approach for naphthalene is USEPA sample collection time(3 minutes)is not exceeded with a calibrated flow of 100 ml/min. Method TO-17,requires the use of sorbent tubes(USEPA,1999). Soil gas investigators should select an appropriate sorbent material pursuant to the physical Additional Testing Prior to Soil Gas Sampling:Passive soil gas survey can be"a, properties of the subsurface contaminant along with the appropriate applied vacuum, performed to determine whether active soil gas samples are required at specific'; sampling flow rate,and sampling volume. Soil gas workplans should describe how the location(s)or throughout the site with low-permeability soil. The passive soil gas field investigation will meet all the requirements within this advisory as weil as those sampling method is described in Appendix A. Other guidance documents recommend noted in Method TO-17. passive sampling method in low-permeability soil for site characterization purpose (USEPA 2008,Page 13). rh Both passive and active soil gas samples may need to be collected in order to provide multiple lines of evidence to evaluate vapor intrusion exposure to naphthalene. The trademarks and brand names mentioned in this appendix is not an endorsement of Quantification of the contaminant source term is critical for risk-based decision making. a specific product but is provided as an example to the reader as a reference to what Repetitive soil gas sampling from permanent points may be warranted as soil gas grab instrument or material was successfully used in the past. Other products,which meet samples approach risk-based concentrations. Long-term monitoring may be needed,in the similar standards and quality as the above mention products may be acceptable. a fashion similar to groundwater,to ascertain representative subsurface concentrations and to document contaminant plume stability. References: 1 Sampling System Materials API,2005:American Petroleum Institute.Collecting and interpreting soil-gas samples from the vadose zone:A practical strategy for assessing the subsurface vapor-to-indoor Sorbent/Method TO-17 is recommended for confirmation sampling and analysis for air migration pathway at petroleum hydrocarbon sites. Publication#4741.Washington, naphthalene in soil gas at probe locations where this chemical was previously detected D.C.:API. by another soil gas method such as EPA Methods 5030/8260B or TO-15 or in the soil Johnson,P.C.,M.W.Kemblowski,and J.D.Colthart. 1990. Quantitative Analysis for matrix samples. Naphthalene analysis by EPA MethodTO-15 presents several the Cleanup of Hydrocarbon-Contaminated Soils by In-situ Soil Venting. Ground Water, challenges,such as contaminant carryover and variability in recovery(Hayes et al., 28(3):413-429. 2005). EPA Method TO-15 defines target analytes as having a vapor pressure greater than 0.1 mm Hg at 25°C at 1 atmosphere,and is suitable for organic compounds with McAlary,T.A.,P.Nicholson,H.Groenevelt,D.Bertrand.2009."A Case Study of Soil- carbon content ranging from C3 to C10. However,naphthalene with vapor pressure of Gas Sampling in Silt and Clay-Rich(Low-Permeability)Soils",Ground Water Monitoring 0.087 mmHg falls just below this threshold for TO-15. USEPA Method TO-17 allows &Remediation,29, No.1,Winter 2009,pp.144. greater flexibility in targeting lower vapor pressure compounds,and hydrophobic sorbents,such as Tenax TA or GR which traps organic compounds ranging from C7 to USEPA,2008:United State Environmental Protection Agency,Brownfields Technology C20 have been demonstrated to perform well when sampling heavier molecular weight Primer Vapor Intrusion Considerations for Development.EPA 542-R-08-001. VOCs(or SVOCs)such as naphthalene(Fortune,A.et al,2008). Data from samples htto://www.brownfiieldstsc.orci collected in sorbent and analyzed using TO-17 for naphthalene are reliable,provided that the requisite volume of soil gas passes through the sorbent tube. A maximum applied vacuum of 100 inches of water or less with an appropriate flow rate(e.g., s 50 ml/min)derived from the soil gas permeability testing(McAlary,T.et al,2009)should allow the sampler to collect the requisite soil gas volume. Some stationary laboratories are capable of obtaining data of acceptable quality using SUMMA®/EPA Method TO-15. If EPA Method TO-15 is used for sampling and analysis 12/10/2009 -63- 12/10/2009 -64-