Source, Occurrence, and Extent of Arsenic in the Grass Mountain Area of the Rosebud Indian Reservation, South Dakota
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U.S. Department of the Interior U.S. Geological Survey Source, Occurrence, and Extent of Arsenic in the Grass Mountain Area of the Rosebud Indian Reservation, South Dakota By Janet M. Carter, Steven K. Sando, and Timothy S. Hayes, U.S. Geological Survey, and Richard H. Hammond, South Dakota Geological Survey Water-Resources Investigations Report 97-4286 Prepared in cooperation with the Rosebud Sioux Tribe and the South Dakota Geological Survey U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Thomas J. Casadevall, Acting Director The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey. United States Government Printing Office: 1998 For addtional information write to: Copies of this report can be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Branch of Information Services 1608 Mt. View Rd. Box 25286 Rapid City, SD 57702 Denver, CO 80225-0046 CONTENTS Abstract..............................................................................................................^ 1 Introduction ........................................................................................................................................................................... 2 Purpose and scope ....................................................................................................................................................... 4 Description of study area and general geology and hydrology ................................................................................... 4 Acknowledgments....................................................................................................................................................... 6 Sampling sites................................................................... 6 Water-quality, bed-sediment, and drill-hole-cuttings data..................................................................................................... 9 Methods of collection.................................................................................................................................................. 9 Ground-water and spring-water samples........................................................................................................... 9 Surface-water samples....................................................................................................................................... 14 Bed-sediment samples....................................................................................................................................... 14 Drill-hole-cuttings samples................................................................................................................................ 14 Quality-assurance data................................................................................................................................................. 15 Sources of arsenic..................................................................~^ 16 Occurrence of arsenic and geochemical processes................................................................................................................ 22 Extent of arsenic........................................................................^ 32 Summary and conclusions..................................................................................................................................................... 33 References ............................................................................................................................................................... 34 ILLUSTRATIONS 1. Map showing location of study area........................................................................................................................... 3 2. Potentiometric surface of the Arikaree aquifer in the vicinity of Grass Mountain Community, 1996....................... 5 3. Well-location diagram................................................................................................................................................. 6 4. Map showing locations of ground-water, drill-hole-cuttings, and spring-water sampling sites................................. 8 5. Map showing locations of surface-water and bed-sediment sampling sites............................................................... 10 6. Probability plots for concentrations of arsenic and associated elements in ground water in Todd County and neighboring counties...................................................................................................................... 17 7. Map showing arsenic concentrations in ground water and spring water, 1995.......................................................... 19 8. Boxplots of dissolved arsenic concentrations in aquifers in south-central South Dakota.......................................... 20 9. Plots showing selected relations between arsenic, pH, oxidation-reduction potential, and arsenite.......................... 24 10. Map showing oxidation-reduction potential of ground-water samples calculated using arsenic speciation data, 1995................................................................................................................................................... 25 11. Arsenic concentrations and pH in water samples collected from wells completed in the Arikaree aquifer in south-central South Dakota........................................................................................................................ 26 12. Trilinear diagram showing proportional concentrations of major ions in ground-water samples, 1955.................... 27 13. Selected mineral saturation indices and proportions of major ions in water samples collected from observation wells 3,5,4, and 8, ordered from most upgradient to most downgradient well..................................... 29 14. Map showing arsenic concentrations in surface water and bed sediments, 1995....................................................... 31 Contents III TABLES 1. Site information and well-construction data for ground-water sampling locations ............................................... 7 2. Properties and constituents analyzed in samples of ground water, surface water, spring water, bed sediment, and drill-hole cuttings............................................................................................................................. 11 3. Processing and analytical methods for properties and constituents analyzed in samples of ground water, surface water, springs, bed sediment, and drill-hole cuttings...................................................................... 12 4. Properties and constituent concentrations for ground-water samples .................................................................... 39 5. Properties and arsenic concentrations for spring-water samples............................................................................ 45 6. Properties and constituent concentrations for surface-water samples.................................................................... 46 7. Constituent concentrations for bed-sediment samples ........................................................................................... 51 8. Constituent concentrations for drill-hole-cuttings samples.................................................................................... 55 9. Constituent concentrations for quality-assurance equipment blanks...................................................................... 67 10. Precision statistics for duplicate drill-hole-cuttings samples.................................................................................. 68 11. Significant (a less than or equal 0.10) positive Spearman rank correlations between arsenic and selected constituents for drill-hole-cuttings samples.............................................................................................. 69 12. Oxidation-reduction potential (Eh) values calculated using the PHREEQC program for the ground-water samples............................................................................................................................................. 70 13. Mineral saturation indices calculated using PHREEQC ........................................................................................ 71 14. Significant (a equal 0.10) Spearman rank correlations between arsenic constituents and selected properties, constituents, and mineral saturation indices for ground-water, surface-water, and bed-sediment samples............................................................................................................................................. 87 IV Contents Source, Occurrence, and Extent of Arsenic in the Grass Mountain Area of the Rosebud Indian Reservation, South Dakota By Janet M. Carter, Steven K. Sando, Timothy S. Hayes, and Richard H. Hammond ABSTRACT commonly associated with naturally occurring arsenic in rocks. Additionally, elevated uranium Elevated concentrations of dissolved concentrations were detected in two of the ground- arsenic in ground water have been reported in the water samples that had high arsenic concentra Grass Mountain area of the Rosebud Indian tions. Because the only probable local source of Reservation, South Dakota. The two possible vanadium, molybdenum, and uranium is natural sources of the arsenic are a naturally occurring and because of these elements' association