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of naphthalene,then performance testing for naphthalene recovery and carryover from where soil permeability is not an issue,a vacuum of less than 100-inches of water each laboratory should be conducted. Acceptable recovery of naphthalene should be should be applied in conjunction with a Bow rate of less than or equal to 100 mUmin demonstrated by EPA Method TO-15 from a gas standard at a concentration of 32 (e.g.,50 mUmin for 30 min to collect a 1.5 L sample). Since naphthalene contamination ug/m or less prepared in a passivated canister of the same make and approximate age from industrial activities,such as those from manufactured gas plants,is frequently as those used for sampling. A blank sample should be processed and analyzed to encountered at shallow depths(e.g.5 it bgs or less),quantitative tracer testing using check for any carry over after the naphthalene gas standard is analyzed and after the helium is recommended to monitor potential ambient air breakthrough.An example highest naphthalene standard analyzed for the calibration curve is processed. Any sampling setup using Tenax GR for naphthalene can be found in the reference provided subsequent carryover concentration of naphthalene from the blank sample,which is below by Hayes at al.,2008. A field duplicate should be collected and a trip blank greater than the method detection limit(MDL),should be substantially lower than the should be used. When sample collection is complete,the sorbent tube is sealed with reporting limit(RL)to assure that the following analyses are not compromised. dedicated fittings or non-sorbing,non-reactive caps,and the tubes are shipped to the laboratory in a cooler chilled to<4'C. Standard chain-of-custody protocols should be . Naphthalene may also condense onto the surface of canisters;therefore,storage followed. Holding times for most EPA Method TO-17 samples is 30 days. stability tests for the prepared naphthalene vapor standards should be performed for the - duration of expected holding time. A calibration curve,which takes into account any Items to consider when soil gas sampling and analyses pursuant to Sorbent/Method expected carry over or condensation,should be used for quantification. Furthermore, TO-17 areas follows: naphthalene readily sorbs onto traditional soil gas sampling tubing such as polyethylene and nylaflow(Hayes et al.,2006;Ouellette,2004). Thus,the entire sampling system • Practitioner's Unfamiliarity,.The practitioner's unfamiliarity with sampling using a should be composed of Teflon,Polyetheretherketones.(PEEK).or other tubing types vacuum pump due to the recommendation of many guidance documents for use of with demonstrated inertness for naphthalene and with acceptable background criteria. fixed flow rate(generally 100 or 200 mUmin)rather than the applied vacuum for Using proper materials in the sampling system will ensure that soil gas samples are - collection of soil gas samples. The applied vacuum,which is the more important representative of subsurface conditions. component of soil gas permeability,is frequently overlooked in collecting soil gas Future recommendation for the naphthalene sample collection method may ultimately samples. depend on the capability of the stationary laboratory performing the analyses. As an Perceived Limitations with Sorb nt Tubes.Other concerns and perceived limitations example,some laboratories are now equipped with updated Thermal Desorption(TD) with use of the sorbent tube include:.(1)lack of repeat analysis for samples collected units capable of sample reruns as well as dilutions for EPA Method TO-17. The in sorbent;(2)breakthroughof target analytes during sampling;and(3)potential improved TO unit overcomes the perceived limitation of sorbent method being a"one- mass spectrometer overload from high VOCs concentrations. By practice,the shot deal"without repeat analysis and reduces concern for the potential mass trapped VOCs/SVOCs constituents are desorbed completely from the sorbent into spectrometer overload(Hayes, H.et al,2007). A new innovation for EPA Method TO- the mass spectrometer;therefore.the potential for instrument overload is still 15 analysis includes design to allow recovery of C2 to C25 compounds with extremely possible even with use of the updated TD instrumentation. Unlike the ambient air low carryover(<0.1%);therefore,extending EPA Method TO-15 analysis to include a and indoor air samples where the concentrations of VOCs and SVOCs are in the similar compound range as the Tenax/TO-17. The low carryover within the system lower,more predictable range,soil gas concentrations can be variable and are alleviates the potential for reported naphthalene concentrations to be biased low due to potentially much greater than 1000-fold above the ambient air concentration. losses within the internal hardware. Therefore;if the soil gas constituent concentrations from probes are not pre- screened using another active(or passive)method prior to sorbent sampling,there Sample Collection Method for Naphthalene is a potential for analytical instrumentation overload. In this regard,sorbent/EPA Method TO-17 as a"stand alone"method for naphthalene deserves caution. The Soil gas samples for analysis by EPA Method TO-17 should be collected with sampling reporting limit of handheld photo-ionization detectors(PID)are in the range of parts tubes packed with an appropriate sorbent material. For naphthalene,the sorbent per million(ppmv)and is too elevated for screening chemical constituents for vapor material is usually Tenax(e.g.,Tenax TA or GR). The analytical laboratory conducting intrusion purposes(except if a more sensitive PID such as ppbRAET"is used). the analysis typically supplies the sorbent tubes used for sampling. As an example,two 3.5-inch Tenax GR traps in series(i.e..front to back)with 200 mg sorbent in each Breakthrough Volumes The sampling volume should be calculated by taking two- column can be used to monitor breakthrough.Sampling should be based on both flow thirds of the estimated breakthrough volume. If breakthrough volumes cannot be rate and applied vacuum to address the gas permeability of the soil. Nested semi- determined,sorbent tubes should be arranged in series(as described above)and all permanent or permanent probes should be used for soil gas sampling,with hydrated tubes should be submitted to the laboratory for analysis. bentonite seals throughout the annulus with compression fittings. For a probe location 12/10/2009 -65- 12/10/2009 -66-