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sample is not necessary since the"clean"matrix is humidified laboratory grade ultra with each batch of samples)by spiking a blank sample at the RL level. There is no pure air. When prepared as such,this is equivalent to the daily calibration limit on the number of samples per batch for RL verification. Once per day is (continuing calibration)sample. Therefore,it would be redundant to analyze this sufficient. QA/QC sample. This QA/QC sample is optional depending on the requirement of the project CAPP and the project manager. Methods TO-13,TO-15 and TO-17 do not Acceptance Limits:Laboratories should establish their own acceptance levels(limits) have any requirements for LCS sample analysis. for their QA/QC parameters(i.e.,percent recoveries for surrogates,matrix spikes, laboratory control samples and percent relative difference for duplicates,etc.)based • Surrogates:The use of surrogates in soil gas analysis is discretionary. EPA Method on laboratory performance. The limits should be evaluated and updated periodically. 82608/C requires surrogates whereas Method TO-15 does not. The introduction of For guidance on establishing acceptance limits,consult EPA Method 80008 surrogates into soil gas samples can present some logistical challenge. Surrogates (December 1996),Section 8.0(SW-846,1996). • are designed to monitor recoveries of target analytes. Therefore,they should be introduced at the point of sample collection in order to fully assess the recovery • Standard Operating Procedures:Laboratories should have detailed written Standard process. Depending on the type of containers being used to collect soil gas samples, Operating Procedures(SOP)for their soil gas sampling and testing procedures. the introduction of surrogates can be problematic. Copies of the SOP should be available in the laboratory for review and reference. The SOP should be reviewed on annual basis and updated as needed. Field For most laboratories that use modified EPA Method 8260B/C,the surrogates are procedures,including sampling procedures,can be written as a'separate SOP from usually added to the water in the sparger either before or after the soil gas sample the laboratory analytical procedures. has been forced into the water. Vapor-phase surrogates(which are available for air analysis)can be theoretically added into soil gas sample aliquot in a gas-tight syringe just before injecting into the sparger. However,few if any laboratories are using this F-6 DETECTION LIMITS ve REPORTING LIMITS practice for various reasons. For laboratories using EPA Method TO-15,the surrogates are added to the sample loop at the same time the soil gas sample is For the purpose of this Advisory,Detection Limit(DL)is defined as the"the minimum being loaded onto the concentrator. In both instances,the surrogates are added concentration of a substance that can be measured and reported with 99%confidence after the sample has already been collected. There is a gap between when the that the analyte concentration is greater than zero and is determined from analysis of sample is collected and when the sample:is analyzed where there are no surrogates sample in a given matrix type containing the analyte"(SW-846,Chapter One,Quality to monitor the process. Control,Revision 1,July 1992). Reporting Limit(RL)is defined as the lowest concentration of an analyteahat can be detected in a sample by the given analytical Some laboratories add"vapor surrogates"immediately after sampling to samples procedure taking into account sample matrix,interferences,dilution factor and the collected in glass bulbs.The"vapor surrogates"are liquid surrogates that have been lowest point of the calibration curve. Laboratories should use RL in their analytical injected into a glass bulb,allowed to expand,and aliquots of the"vapor surrogates' reports since it is a more reliable indicator of the limit of detection. are injected into the glass bulb with the soil gas sample. Cautions should be . exercised when preparing"vapor"internal standards or surrogates with liquid standards in either Tedlar bags or glass bulbs. Make sure the internal standards or F-7 REPORTING LIMITS • surrogates.have completely vaporized before aliquots are taken. Droplets of liquid standards or surrogates can adhere to the internal surface of the bags or bulbs. This The appropriate RLs to be used on a specific project should be based on the project practice is not recommended because of the inherent difficulty in preparing the data quality objectives(DQOs)taking into consideration various factors. The project surrogates or standards. Commercially prepared surrogates or standards should be manager and the parties involved with the project should consider factors such as: used. Due to variations with where and when the surrogates are added to the soil sampling protocols,analytical method(s)to be used list of target compounds and other gas samples,laboratories are advised to note in their final analytical reports the exact DQO need for risk assessment. step in the process where the surrogates(if used)are added so the results can be evaluated accordingly. Table F-4 delineates the reporting limits of the common soil gas analytical techniques. The ranges in this table are based on the survey of analytical laboratories conducted by • Reporting Limit Verification:The Reporting Limit(RL)is defined as the limit of the Soil Gas Advisory Workgroup. For the reporting limits of other methods/techniques, quantification reported by the analyzing laboratory. The RL should not be lower than consult with the analytical laboratory. the lowest calibration point. The RL should be validated periodically(recommended 12/10/2009 -83- 12/10/2009 -84-