Hexavalent and Total Chromium at Low Reporting Concentrations in Source-Water Aquifers and Surface Waters Used for Public Supply in Illinois, 2013
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Prepared in cooperation with the Illinois Environmental Protection Agency Hexavalent and Total Chromium at Low Reporting Concentrations in Source-Water Aquifers and Surface Waters Used for Public Supply in Illinois, 2013 Scientific Investigations Report 2015–5020 U.S. Department of the Interior U.S. Geological Survey Front cover and other images: Front cover shows collection of groundwater samples, Union-York Water District (intake 00251). This and other photography by Patrick Mills, U.S. Geological Survey. Hexavalent and Total Chromium at Low Reporting Concentrations in Source-Water Aquifers and Surface Waters Used for Public Supply in Illinois, 2013 By Patrick C. Mills and Richard P. Cobb Prepared in cooperation with the Illinois Environmental Protection Agency Scientific Investigations Report 2015–5020 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette M. Kimball, Acting Director U.S. Geological Survey, Reston, Virginia: 2015 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. For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod/. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Mills, P.C., and Cobb, R.P, 2015, Hexavalent and total chromium at low reporting concentrations in source-water aqui- fers and surface waters used for public supply in Illinois, 2013: U.S. Geological Survey Scientific Investigations Report 2015–5020, 58 p., http://dx.doi.org/10.3133/sir20155020. ISSN 2328-0328 (online) iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................2 Purpose and Scope ..............................................................................................................................3 Previous Studies ...................................................................................................................................3 Chemistry of Hexavalent Chromium ...........................................................................................................4 Study Methods ...............................................................................................................................................7 Well, Intake, and Treated-Sample Site Selection ............................................................................7 Sample Collection and Laboratory Analyses .................................................................................12 Quality Assurance...............................................................................................................................14 Data Analysis .......................................................................................................................................16 Accuracy of Chromium Data ......................................................................................................................17 Occurrence and Distribution of Chromium ..............................................................................................19 Frequency of Detection and Concentration ...................................................................................19 Hexavalent Chromium ...............................................................................................................19 Total Chromium and Relation to Hexavalent Chromium ......................................................22 Comparison to Regulatory Standards and Results of Other Studies .........................................22 Geochemical and Physical Factors Associated with Occurrence of Chromium ..............................24 pH Conditions.......................................................................................................................................24 Land Use ...............................................................................................................................................25 Geohydrology and Well Construction ..............................................................................................28 Groundwater-Related Factors .................................................................................................28 Surface-Water-Related Factors ..............................................................................................35 Other Factors .......................................................................................................................................36 Effects of Treatment and Distribution on Sample Concentrations ......................................................37 Sampling Factors Associated with Analytical Results of Chromium ..................................................39 Sample Temperature and Holding Time ..........................................................................................39 Sample Tap Composition ...................................................................................................................40 Summary and Conclusions .........................................................................................................................41 References Cited..........................................................................................................................................42 Appendix 1. Table of well and surface-water intake information, field characteristics of water quality, and concentrations of hexavalent chromium and total chromium in samples from selected source-water aquifers and surface waters used for public supply in Illinois, 2013 ....................................................................................................................48 Appendix 2. Protocols for collecting representative samples of untreated source water and treated water. A, Hexavalent chromium. B, Total chromium ...........................................58 Appendix 3. Example Illinois Environmental Protection Agency field sampling record ..................60 Appendix 4. Example analytical result report and quality-assurance documentation provided by UL laboratory .............................................................................................................65 iv Figures 1. Map showing principal source-water aquifers and surface waters used for public supply, selected wells and intakes, and extent of episodic glaciation in Illinois ..............5 2. Diagram showing relation of chromium speciation in water to oxidation-reduction (redox) conditions and pH ...........................................................................................................6 3. Diagram showing general classification of lithostratigraphic and hydro- stratigraphic units that compose source-water aquifers in Illinois .....................................9 4. Map showing locations and designations of selected public-supply wells and intakes that tap source-water aquifers and surface waters in Illinois .............................10 5. Photos showing typical quality-assurance measures and collection of samples for chromium at selected public-water-supply facilities in Illinois, 2013 ......................... 13 6. Graph showing frequency of detection and maximum concentrations of hexavalent chromium and total chromium in public-supply source waters in Illinois, 2013 ..................................................................................................................................19 7. Map showing locations of selected wells and intakes that tap public-supply source-water aquifers and surface waters in Illinois, and the occurrence and relative concentrations of hexavalent chromium [Cr(VI)] in untreated water samples, 2013 ..............................................................................................................................20 8. Graphs showing frequency of detection and maximum concentrations of hexavalent chromium and total chromium in public-supply source-water aquifers and surface waters in Illinois, by source type, 2013 .............................................21 9. Graphs showing hexavalent chromium and total chromium in samples from public-supply source-water aquifers and surface waters in Illinois, by source type, 2013 ......................................................................................................................................23 10. Graphs showing relation of concentrations of hexavalent chromium to pH in source waters used for public supply in Illinois, 2013 ..........................................................26 11. Box-and-whisker plots of concentrations of hexavalent chromium in public- supply source waters in Illinois, by urban and rural land use, 2013 ..................................28 12. Box-and-whisker plots of concentrations of hexavalent chromium in public- supply