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APPENDIX B Justification CANISTER HOLDING TIME,USE OF TEDLAR''BAGS,AND TUBING TYPES USEPA(2003)notes that samples collected in Tedlar bags must be analyzed within 72 hours,otherwise the compounds sampled may escape or become altered. The Method TO-15 summary document refers to holding times for Tedlar bags and outlines the Holding Times for SUMMA®s holding times as technical and contract.The technical holding time is stated as 72 hours from collection and 36 hours from the receipt at laboratory(USEPA 2003). Studies Soil gas samples collected in SUMMA®canisters may be analyzed with 14 days from conducted by Wang,Raihala,and John(1996)examined the issue of VOC losses.The collection(see Section 3.6). paper cites numerous studies to quantify sample loss.One study noted a 21 percent loss of toluene within 12 hours,with an additional 4 percent loss during the next 12 Justification hours.Similarly,a 15 percent loss of toluene was noted in the first 12 hours while additional 2.9 percent was lost in next 12 hours.Other VOCs showed similar losses. The Compendium of Methods for the Determination of Toxic Organic Compounds in The study clearly indicated that there were significant losses in the commercial Tedlar Ambient Air,Second Edition,states that storage times of up to 30 days have been bags.The losses are generally shown to be associated with hose valve assemblies demonstrated.The EPA Method TO-15 summary documentrefers to holding times as supplied with the commercial bags.Commercial Tedlar bags and the hose valves technical and contract.The technical holding time is stated as 14 days from collection replaced with septa and homemade Tedlar bags with Teflon valves both showed much and 10 days from the receipt at laboratory(USEPA, 1999). It is unclear whether total lower losses than the commercial Tedlar bags. holding time can be interpreted as 24 days. Use of Tubing Types Several studies have been conducted to demonstrate stability of VOCs in SUMMA® canisters.A study conducted by Sin et al(2001)indicated stability of 143 VOCs up to 4 Nylaflow,polyetheretherketone(PEEK),and Teflon*are recommended for use in the months assuming consistent environmental conditions.However,eight VOCs showed soil vapor sampling train. Use of low-density polyethylene(L-D PE)is discouraged due significant loss beginning at approximately 25 days.The average loss was less than 15 to decreased performance relative to other tubing types in both introduction of percent during the entire study period of four months.Brymer et al(1996)demonstrated background analytes and sample recovery. Reduced recovery of naphthalene has that certain VOCs(mercaptans,dimethyl acetal and bis-[chloromomethyl]ether)are not been observed when using Nylaflow tubing with small sample sizes(see Sample Tube, suitable for collecting samples in a SUMMA'canister at lower concentrations.The study Section 2.3 of main text). indicates that storage pressure and humidity in a canister are also important factors that determine recoveries.Oliver and Pliei(1985)also showed stability of 15 VOCs for 7 and Justification 30 days storage and periods.Of all of these compounds tested,none showed significant loss or gain in concentration during the test period.The study stated that There is very little information available in the literature regarding the effects on various holding period between collection and analysis should be minimized to improve tubing tyees on sample duality. Hayes et al(2006)evaluated four different tubing types, recovery of VOC mixtures, Bontempo(2004)tested 44 VOCs on days 0,7,15,and 33 Nylaflow ,PEEK,Teflon ,and L-D PE for contribution to background(off-gassing of and indicated that analysis by TO-15 at parts per trillion by volume should be performed VOCs inherent in the tubing structure)and for reactivity(decreased recovery)using within 14 days to minimize high or low biased data.Kelly and Holdren(1995)concluded zero-air drawn from a 6 L SUMMA®canister, that most volatile organics show sufficient stability during storage in a SUMMA® canister. US EPA Region 9 SOP 310 specifies a holding time of 30 days,which is Some off-gassing of toluene,and to a lesser extent benzene,propylbenzene,and based on studies referenced in Method TO-15 that indicate stable storage of up to 30 methanol were noted with the Nylaflow tubing,though the reported concentrations days for most VOCs(USEPA,2003). were less than typical risk-based screening levels. There was low initial recovery of 1,2,4-trimethylbenzene and naphthalene(22 and 12 percent,respectively). Recovery Use of Tedlar®Bags increased with subsequent aliquots,suggesting that the humidified air deactivated reactive binding sites or they became saturated with the increasing sample size. These While the use of Tedlar bags is discouraged,samples collected using Tedlar bags data suggest the sample loss of 1,2,4-trimethylbenzene and naphthalene would not should be analyzed as soon as possible,and within six hours of sample collection(see likely be significant with a 6 L sample. Nicholson et al(2007)noted low recovery of Section 2.7). aromatic and cyclic aliphatic hydrocarbons in a 24-hr absorption study of Vafow tubing. PEEK tubing exhibited less background contribution than Nylaflow ,and overall 12/10/2009 -53- 12/10/2009 -54-