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Water Flow in the Silurian-Devonian Aquifer System, Johnson County, Iowa

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Water Flow in the Silurian-Devonian Aquifer System, Johnson County, Iowa Hydrogeology and Simulation of Ground- Water Flow in the Silurian-Devonian Aquifer System, Johnson County, Iowa By Patrick Tucci (U.S. Geological Survey) and Robert M. McKay (Iowa Department of Natural Resources, Iowa Geological Survey) Prepared in cooperation with The Iowa Department of Natural Resources – Water Supply Bureau City of Iowa City Johnson County Board of Supervisors City of Coralville The University of Iowa City of North Liberty City of Solon Scientific Investigations Report 2005–5266 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior Gale A. Norton, Secretary U.S. Geological Survey P. Patrick Leahy, Acting Director U.S. Geological Survey, Reston, Virginia: 2006 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS--the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Tucci, Patrick and McKay, Robert, 2006, Hydrogeology and simulation of ground-water flow in the Silurian-Devonian aquifer system, Johnson County, Iowa: U.S. Geological Survey, Scientific Investigations Report 2005–5266, 73 p. iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................2 Previous Studies ...................................................................................................................................5 Physical Setting and Climate ..............................................................................................................5 Water Use ..............................................................................................................................................8 Acknowledgments ................................................................................................................................8 Hydrogeologic Setting...................................................................................................................................8 Hydrogeologic Units .............................................................................................................................8 Quaternary Deposits ...................................................................................................................8 Bedrock Topography ...................................................................................................................8 Bedrock Hydrogeologic Units ..................................................................................................10 Maquoketa Confining Unit ...............................................................................................10 Silurian Aquifer .................................................................................................................15 Wapsipinicon Group .........................................................................................................15 Cedar Valley Aquifer .........................................................................................................18 Upper Devonian Shale Confining Unit ...........................................................................18 Cherokee Confining Unit ..................................................................................................18 Geologic Structure..............................................................................................................................18 Hydraulic Characteristics ..................................................................................................................21 Recharge and Discharge ...................................................................................................................21 Ground-Water Occurrence and Movement ...................................................................................24 Simulation of Ground-Water Flow .............................................................................................................24 Model Construction and Boundary Conditions ..............................................................................27 1996 Steady-State Calibration and Simulation ...............................................................................30 Model Calibration ......................................................................................................................30 Simulation Results .....................................................................................................................34 Model Sensitivity.................................................................................................................................37 Simulation of Potential Future Withdrawals ..................................................................................38 Simulation of 2004 Conditions ..................................................................................................39 Simulation of Potential 2025 Steady-State Pumping ............................................................39 Simulation of Potential Future Drought Conditions ..............................................................41 Model Limitations and Additional Data Needs ..............................................................................44 Summary........................................................................................................................................................45 References Cited..........................................................................................................................................48 Appendix........................................................................................................................................................51 iv Figures 1. Map showing location of study area and the North Corridor area of Johnson County ......3 2. Map showing observation wells used for comparison to model results ...............................4 3. Graph showing altitude of the surface of Coralville Reservoir, 1958–2003 ............................6 4. Graphs showing annual precipitation for Iowa City, 1931–2004 ..............................................7 5. Map showing pumping wells used in the 1996 steady-state simulation ...............................9 6. Map showing bedrock topography ............................................................................................11 7. Southwest-northeast hydrogeologic section of Johnson County, Iowa .............................12 8–12. Maps showing: 8. Generalized bedrock hydrogeology of Johnson County, Iowa ......................................13 9. Top of the Maquoketa confining unit .................................................................................14 10. Top of the Silurian aquifer ....................................................................................................16 11. Top of the Wapsipinicon Group ...........................................................................................17 12. Top of the Cedar Valley aquifer ...........................................................................................19 13. Photograph of solution features in Devonian-age limestone near Coralville Dam ............20 14. Map showing wells completed in Silurian- and Devonian-age rocks that have specific-capacity test data ..............................................................................................22 15. Map showing the potentiometric surface of the Silurian-Devonian aquifer system, Johnson County, Iowa, for average 1996 conditions .............................................25 16. Graph showing ground-water levels in glacial deposits and Silurian- and Devonian-age rocks near Coralville, Iowa, April 1990 through February 2003 .................26 17–20. Maps of Johnson County and model grid showing: 17. Boundary conditions.............................................................................................................28 18. Final distribution of recharge for the 1996 steady–state simulation ............................29 19. Final distribution of hydraulic conductivity for the 1996 steady-state simulation ............................................................................................................................32 20. Simulated potentiometric surface for 1996 steady-state conditions ...........................33 21. Map showing the difference between measured and simulated 1996 water levels .........35 22. Graph showing the distribution of 1996 water-level residuals ..............................................36 23. Graph showing composite scaled sensitivities of estimated model parameters ..............38 24. Map showing the simulated potentiometric surface for 2004 steady-state conditions ....40 25. Map showing the changes in simulated water levels between 2004 and potential future steady-state
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