Prepared in cooperation with the California State Water Resources Control Board A product of the California Groundwater Ambient Monitoring and Assessment (GAMA) Program Evaluation of Volatile Organic Compound (VOC) Blank Data and Application of Study Reporting Levels to Groundwater Data Collected for the California GAMA Priority Basin Project, May 2004 through September 2010 Scientific Investigations Report 2012–5139 U.S. Department of the Interior U.S. Geological Survey Cover: Left: Field crew member collecting VOC samples inside a mobile laboratory using long sampling lines. (Photograph by Cathy M. Munday, U.S. Geological Survey.) Right: Field crew members collecting VOC samples at a well site using short sampling lines. (Photograph by Michael T. Land, U.S. Geological Survey.) Evaluation of Volatile Organic Compound (VOC) Blank Data and Application of Study Reporting Levels to Groundwater Data Collected for the California GAMA Priority Basin Project, May 2004 through September 2010 By Miranda S. Fram, Lisa D. Olsen, and Kenneth Belitz A product of the California Groundwater Ambient Monitoring and Assessment (GAMA) Program Prepared in cooperation with the California State Water Resources Control Board Scientific Investigations Report 2012–5139 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2012 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS. 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Suggested citation: Fram, M.S., Olsen, L.D., and Belitz, Kenneth, 2012, Evaluation of volatile organic compound (VOC) blank data and application of study reporting levels to groundwater data collected for the California GAMA Priority Basin Project, May 2004 through September 2010: U.S. Geological Survey Scientific Investigations Report 2012–5139, 94 p. iii Contents Abstract ...........................................................................................................................................................1 Introduction ....................................................................................................................................................2 Use of Study Reporting Levels ............................................................................................................4 Philosophy of Quality-Control Evaluation of Blanks ........................................................................5 Purpose and Scope .............................................................................................................................6 Methods Used to Collect and Evaluate VOC Data ....................................................................................7 Field Methods ........................................................................................................................................7 Groundwater Samples ................................................................................................................7 Blanks .........................................................................................................................................10 Laboratory Methods ...........................................................................................................................11 Data Analysis Methods ......................................................................................................................14 Identification of Representative Field Blanks .......................................................................15 Definition of Study Reporting Levels (SRLs) ..........................................................................16 Binomial Probability Approach .......................................................................................16 Maximum Concentration Approach ..............................................................................18 Maximum LT-MDL Approach ..........................................................................................18 Evaluation of Potential Sources of Contamination to Blanks and Groundwater Samples and Selection of Appropriate SRLs ....................................................................18 Statistical Tests Used in Identification of Representative Field Blanks and Evaluation to Infer Potential Sources of Contamination ....................................................................19 Quality-Control Assessment Results ........................................................................................................20 Identification of VOCs for Which the SRL Approach Can be Applied and of Representative Quality-Control Field Blanks (QCFBs) for Use in Calculation of SRLs ....................................................................................................................................20 Minimal Contamination from the Certified Blank Water .....................................................20 Acetone, 2-Butanone, and Tetrahydrofuran Contamination Associated with Methanol ........................................................................................................................20 Inadvertent Field Test of Contamination by Methanol ................................................20 Acetone, 2-Butanone, and Tetrahydrofuran Contamination in Field Blanks...........26 Acetone, 2-Butanone, and Tetrahydrofuran Contamination in Groundwater Samples ................................................................................................................26 SRLs for Acetone, 2-Butanone, and Tetrahydrofuran.................................................31 Differences Between Sample-Collection Equipment Configurations ...............................31 Quality-Control Field Blanks (QCFBs) .....................................................................................32 iv Contents—Continued Quality-Control Assessment Results—Continued Evaluation of Potential Sources of Contamination, Selection of SRLs, and Application of SRLs to Groundwater Data for VOCs Detected in Blanks ..........................................32 Hydrocarbons .............................................................................................................................32 Ethylbenzene, m- and p-Xylenes, o-Xylene, Benzene, and Styrene ........................32 Inferred Mechanisms of Contamination .............................................................38 SRLs for Ethylbenzene, m- and p-Xylenes, o-Xylene, Benzene, and Styrene .........................................................................................................40 Toluene ...............................................................................................................................45 Inferred Mechanisms of Contamination ..............................................................45 SRL for Toluene ........................................................................................................48 1,2,4-Trimethylbenzene ....................................................................................................48 Inferred Mechanisms of Contamination ..............................................................50 SRL for 1,2,4-Trimethylbenzene .............................................................................53 Chlorinated Organic Solvents ..................................................................................................54 Dichloromethane, 1,1-Dichloroethene, and Trichloroethene ....................................54 Tetrachloroethene ............................................................................................................54 Other VOCs ..................................................................................................................................54 Bromodichloromethane and Trichlorofluoromethane ................................................54 Carbon Disulfide ................................................................................................................61 Inferred Source of Contamination ........................................................................61 SRL for Carbon Disulfide .........................................................................................61 Chloroform .........................................................................................................................63 Inferred Source of Contamination ........................................................................63 SRL for Chloroform ..................................................................................................63 Application of SRLs and Maximum LT-MDLS ..........................................................................................65 Effect of LT-MDL Changes on VOC Detection Frequencies .........................................................65