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to validate the results first before any conclusions are made. Validation would involve reviewing the sampling procedures,collection containers,sample introduction technique (i.e.,purge-and-trap or mass Flow controller,etc.),QA/QC,etc. Any differences noted F-11 LABORATORY CERTIFICATION should be scrutinized to explain the differences in results. All QA/QC results should be reviewed to make sure the parameters are within the established control limits. More All laboratories performing soil gas testing should be certified.According to the importantly,the calculations should be checked. Results from modified 8260B/C should California Health and Safety Code Section 25356.1.5(e)[Response action criteria, risk be reviewed to make sure the proper units are used and properly calculated for soil gas assessment],exposure assessments shall include the development of reasonable (see section above on reporting units). maximum estimates or exposure to VOCs that may enter existing or future structures on a site.Section 25358.4 requires that analysis of any material that is required to show Finally,the characteristics of the specific compounds should be checked where the compliance with Chapter 6.8 of the Health and Safety Code shall be performed by a • results do not agree. For example,Naphthalene is known to have poor recovery if laboratory accredited by the Department of Public Health pursuant to Article 3 of vapor samples are collected,transferred or stored in glass vessels such as glass bulbs Chapter 4 of Part 1 of Division 101. or air-tight syringes. Naphthalene purges well if liquid standard is used in the purge- and-trap. However,vapor phase naphthalene standard will purge poorly due to Soil gas testing laboratories can obtain certification from the California Department of adsorption onto the glass syringe used to transfer into the purge-and-trap. Highly Public Health's Environmental Laboratory Accreditation Program(ELAP)for all volatile VOCs such as the Freons are well-recovered with modified 8260B/C compared analytical methods they are using for sail gas testing. Certification assures that the to TO-15. Some compounds are better analyzed by one method than the other. If the laboratories have the requisite facilities,equipment and personnel to perform the testing discrepancies cannot be explained after validation,then it maybe necessary to and have demonstrated competence and compliance with the methods being certified. resample and reanalyze. In addition,certification entails the validation of the analytical method as well as periodic To avoid discrepancies,sites can be initially evaluated for soil gas with any one of the checks with performance evaluation(PE)or blind samples(where available)to assess available analytical methods described above. If soil gas is detected at a site,and It is laboratory continued competence with the method. determined that further characterization is needed,the analytical method used should take into consideration the factors previously discussed. Consultants,regulators or Soil gas certification for EPA Methods 8015, 8021,8260,TO-13A,TO-15 and TO-17 is other parties involved in the process need to decide which method(s)to use based on available from ELAP. many considerations including: sampling method,sampling containers,target compounds list laboratory equipment available(e.g.,the limited number of mobile labs National Environmental Laboratory Accreditation Program(NELAP)accreditation for have the capability for TO.15)and most importantly data quality objectives. However, EPA Methods TO-13A,TQ-15 and TO-17 should be accepted in lieu of California ELAP all final risk assessment and risk management decisions should be based on the results certification for soil gas testing. from analyses using a GC/MS method. Laboratories that have either certification from ELAP or NELAP for EPA Methods 8015, All soil gas samples for decision-making purposes should be of the highest quality,even 8021 or 82608(For either soil or water matrices)should obtain separate certification those samples used to"screen"sites initially. If the initial sampling shows"clean" from ELAP for soil gas work with those methods. • results but the samples are biased low due to inappropriate DQOs,then potential , contamination might be overlooked. Laboratories seeking certification for modifications of methods not discussed in this guidance document need to obtain written approval for the alternate test method to be used from the California Environmental Protection Agency,Environmental Chemistry F-10 METHOD REFERENCES IN ANALYTICAL REPORTS Laboratory pursuant to ELAP regulations. The analytical method used to test soil gas samples should be clearly identified in the laboratory reports. Since soil gas samples are analyzed by modifying existing air,water or water methods, analytical laboratories should reference the analytical methods as"modified"versions of the methods in laboratory reports. For example,"Modified EPA 8260B"should be used as the method reference instead of"EPA 8260B"for soil gas results. 12/10/2009 -87- 12/10/2009 -88-