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Water Chemistry Reconnaissance 7 and Geochemical Modeling in the Meadow Valley Wash Area, Southern Nevada

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Water Chemistry Reconnaissance 7 and Geochemical Modeling in the Meadow Valley Wash Area, Southern Nevada Water Chemistry Reconnaissance 7 And Geochemical Modeling In The Meadow Valley Wash Area, Southern Nevada Brian K . Schroth In requirement for the degree of Master of Science in Hydrology/Hydrogeology University of Nevada Reno 20 April, 1987 n ,|NE3 LIBRARY i k s i s The thesis of Brian Schroth is approved: s < Z I University of Nevada Reno April 1987 i ACKNOWLEDGEMENTS This study would not be possible without the input of Nevada Power Com­ pany of Las Vegas, Nevada, and the State of Nevada. Nevada Power Company provided financial support and access to their data in preparation for this study. The State of Nevada provided financial support as part of the Nevada Carbonate-Aquifer Studies Program. The author wishes to thank Roger Jacobson for his advisement and countless ideas. A very special thanks goes to Alan McKay, who was always there with opin­ ions, thoughts and general good cheer. The task would be much longer and more painful if not for his support. And of course, immeasurable thanks to Leslie for making it easy. ABSTRACT The study area groundwater system encompasses Coyote Springs, Kane Springs, Moapa and Meadow Valleys. The geology is dominated by Paleozoic carbonates to the north, and younger alluvium and lacustrine deposits to the south. Underflow from Pahranagat Valley mixes with groundwater from Kane Springs Wash and recharge from the Sheep Range to produce the final discharge of Muddy Springs at the head of Moapa Valley. It is possible that at least 4,000 acre- ft/y r of underflow from Meadow Valley Wash contributes to Muddy Spring discharge. The use of BALANCE, WATEQ, and PHREEQE chemically verifies these proposed flowpaths. Volcanic rocks are the probable explanation of sodium-dominated waters in the south. In lower Moapa Valley and Meadow Valley Wash, the Muddy Creek Formation produces saline, generally sodium-sulfate waters (up to 4500 mg/1 TDS) by dissolution of evaporite minerals, primarily gypsum and thenar- dite. Flow is complex due to local geology and thus geochemical simulation was limited. Table of Contents signature page ..................................................................................................................... i ACKNOWLEDGEMENTS ................................................................................................ ii ABSTRACT ....................................................................................................................... iii List of Figures .................................................................................................................... v List of Tables ..................................................................................................................... vi INTRODUCTION.............................................................................................................. 1 Purpose ......................................................................................................................... 3 Geology.......................................................................................................................... 3 HYDROGEOLOGY ........................................................................................................... 5 The White River Drainage System ............................................................................... 5 Moapa Valley and Meadow Valley Wash ................................................................... 14 Water Chemistry Overview......................................................................................... 16 SOURCES OF DATA ....................................................................................................... 19 MODELS USED ................................................................................................................. 22 SOURCES OF DISSOLVED SALTS ................................................................................ 24 The Muddy Creek Formation ...................................................................................... 24 Sodium Sources....................................................................................................... 25 Magnesium Sources ................................................................................................ 31 Carbonate and Volcanic Source Rocks ....................................................................... 32 MUDDY CREEK FORMATION WATER CHEMISTRY VARIATION ...................... 35 Time Series Analysis .................................................................................................... 39 Chemical Groupings..................................................................................................... 41 DRI EXPLORATION HOLES AND ISOTOPES ............................................................. 55 COMPUTER SIMULATIONS........................................................................................... 66 SUMMARY AND CONCLUSIONS .................................................................................. 75 REFERENCES .................................................................................................................. 78 APPENDIX ........................................................................................................................ 80 iv List of Figures Figure 1. Study area and surrounding region................................................................. 2 Figure 2. Locations of previous work data points.......................................................... 6 Figure 3. Study area data points.................................................................................... 7 Figure 4. Moapa Valley data points................................................................................ 8 Figure 5. Meadow Valley Wash data points................................................................... 9 Figure 6. The White River Drainage System.................................................................. 11 Figure 7. Study area water levels.................................................................................... 13 Figure 8. Meadow Valley Wash water levels.................................................................. 17 Figure 9. General water quality of thesis area................................................................ 18 Figure 10. Moapa Valley water quality........................................................................... 20 Figure 11. Silica vs. sodium/sulfate in Meadow Valley Wash....................................... 28 Figure 12. Simplified surface geology map of the junction between Pahranagat and Coyote Springs Valleys....................................................... 34 Figure 13. Well depth vs. conductivity in Meadow Valley Wash.................................. 37 Figure 14. Withdrawl vs. conductivity in Meadow Valley Wash.................................. 38 Figure 15. TDS vs. time: Moapa Valley and Meadow Valley Wash............................. 40 Figure 16. Piper representation of thesis area waters..................................................... 42 Figure 17. Location of chemical groups 1-7..................................................................... 43 Figure 18 (a-g). Stiff representation of chemical groups 1-7...........................................44-50 Figure 19 (a-g). Lithologic logs and chemical profiles of EHl-8.....................................56-62 Figure 20. Deuterium vs. oxygen-18: EHl-8.................................................................... 64 Figure 21. Deuterium vs. oxygen-18: EHl-8 and regional waters.................................. 65 Figure 22. Map view of oxygen-18 and deuterium.......................................................... 67 Figure 23. Map view of flowpath simulations................................................................. 68 Figure A-l (a-b). XRD output: salt crust ;#3...................................................... 93-94 Figure A-2 (a-b). XRD output: EH6 well cuttings..........................................................95-96 v List of Tables Table 1. Results of cation exchange experiment............................................................ 30 Table 2. Comparison of gypsum saturation indeces and TDS in groups 1-7............... 54 Table 3 (a-b). PHREEQE simulation results................................................................ .70-71 Table A -l. Chemical data from data points shown in Figure 3................................... 81 Table A-2 (a-b). Chemical data from data points shown in Figure 4....................... .82-83 Table A-3 (a-c). Chemical data from data points shown in Figure 5........................ 84-86 Table A-4. Supplemental chemical data......................................................................... 87 Table A-5. Sources of data in previous work................................................................. 88 Table A-6 (a-d). XRD peaks for SCI, SC2, SC3, and EH6...........................................89-92 Table A-7. PHREEQE sensitivity analysis..................................................................... 97 vi INTRODUCTION The region under study consists of the southern ends of the Meadow Valley Wash and White River drainage system (see Figure l). The latter may be broken down into three drainage areas: (l) Kane Springs Valley, (2) Coyote Springs Val­ ley, and (3) Moapa Valley. The Muddy River flows through Moapa Valley and intersects the Meadow Valley Wash at Glendale. It continues flowing to the Over- ton arm of Lake Mead, about
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