HYDROLOGY OF MELTON VALLEY AT OAK RIDGE NATIONAL LABORATORY, TENNESSEE By Patrick Tucci U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 92-4131 Prepared in cooperation with the U.S. DEPARTMENT OF ENERGY Nashville, Tennessee 1992 U.S. DEPARTMENT OF THE INTERIOR MANUEL LUJAN, Jr., Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director For additional information write to: Copies of this report can be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Books and Open-File Reports Section 810 Broadway, Suite 500 Federal Center Nashville, Tennessee 37203 Box 25425 Denver, Colorado 80225 CONTENTS Abstract 1 Introduction 2 Purpose and scope 2 Description of study area 2 History 2 Topography and climate 4 Previous studies 5 Acknowledgments 7 Methods of investigation 7 Well construction and well identification 7 Aquifer tests 9 Geologic setting 10 Bedrock 10 Regolith 12 Alluvium 12 Structure 12 Hydrology of Melton Valley 13 Surface water 13 Stream discharge 15 Base flow 20 Ground water 26 Regolith 26 Hydraulic conductivity 26 Ground-water flow 29 Recharge and discharge 34 Bedrock 37 Hydraulic conductivity 37 Ground-water flow 38 Recharge and discharge 38 Simulation of ground-water flow 38 Cross-sectional model 40 Model construction, assumptions, and boundary conditions 40 Results of simulations 41 Area! model 45 Model construction, assumptions, and boundary conditions 45 Results of simulations 49 Sensitivity analysis 56 Model limitations 58 Water chemistry and radionuclides 62 Surface-water quality 64 Major-ion chemistry in surface water 64 Radionuclides in surface water 64 Ground-water quality 65 pH 66 Major-ion chemistry of ground water 68 Radionuclides in ground water 69 Summary and conclusions 72 Selected references 75 Contents III FIGURES 1. Map showing location of study area and waste burial grounds 3 2. Graph showing annual precipitation at Oak Ridge and Oak Ridge National Laboratory 4 3. Graph showing cumulative departure from normal monthly precipitation at Oak Ridge and at Oak Ridge National Laboratory 6 4-6. Maps showing: 4. Location of wells 8 5. Generalized geology of Melton Valley 11 6. Location of streamgaging stations on Whiteoak Creek and Melton Branch 14 7. Duration curves of daily-mean discharge at three stations on Whiteoak Creek at Oak Ridge National Laboratory, water year 1988 17 8. Hydrographs of daily-mean discharge at three stations on Whiteoak Creek at Oak Ridge National Laboratory, water year 1988, with estimated average effluent discharge 18 9. Duration curves of daily-mean discharge at stations on Whiteoak Creek and Melton Branch at Oak Ridge National Laboratory, water year 1988, and Poplar Creek near Oak Ridge, water years 1961 through 1988 19 10. Stream-discharge hydrograph and base-flow component at station Ml, Melton Branch near Melton Hill 22 11. Adjusted and unadjusted stream-discharge hydrographs of Whiteoak Creek below Melton Valley Drive and unadjusted stream-discharge hydrograph of Whiteoak Creek near Melton Hill 24 12-14. Graphs showing: 12. Relation between annual precipitation and adjusted annual base flow at stations on Whiteoak Creek and Melton Branch at Oak Ridge National Laboratory 27 13. Relation between adjusted annual stream discharge and adjusted annual base flow at stations on Whiteoak Creek and Melton Branch at Oak Ridge National Laboratory 28 14. Hydraulic-conductivity variation with depth 29 15. Boxplots showing ranges of hydraulic-conductivity values for selected depth intervals 30 16. Boxplots showing ranges of hydraulic-conductivity values for regolith developed over selected geologic units 31 17. Map showing location of wells in which water-table depth was measured on June 28,1988 32 18. Map showing water-table configuration and general directions of ground-water flow, June 28,1988 33 19. Hydrographs for north well cluster and south well cluster, burial ground 5 35 20. Hydrographs of wells U19 and U35, January 1986 through September 1988 36 21. Map showing potentiometric surface of the shallow bedrock zone, June 28,1988 39 22. Cross-sectional model grid and boundaries 40 23. Hydraulic-conductivity distributions, unadjusted for horizontal anisotropy, for cross-sectional model simulations 1 and 2 42 24. Hydrograph of well 474 showing water-level fluctuations from April 1983 through September 1988 43 25. Simulated water levels and general directions of ground-water flow for cross-sectional model simulations 1 and 2 44 26-32. Maps showing: 26. Areal model grid and boundary conditions 47 27. Areal distribution of simulated recharge 48 28. Saturated thickness of layer 1, June 28,1988 50 29. Simulated water levels for layer 1 51 iv Hydrology of Melton Valley at Oak Ridge National Laboratory, Tennessee 30. Simulated water levels for layer 2 52 31. Simulated water levels for layer 3 53 32. Simulated water levels for layer 4 55 33-36. Graphs showing: 33. Changes in root mean square error of simulated water levels with respect to changes in recharge rate and layer 1 hydraulic conductivity 57 34. Changes in root mean square error of simulated water levels with respect to simultaneous changes in recharge and hydraulic conductivity 59 35. Changes in root mean square error of simulated water levels with respect to changes in layer 1 row-to-column anisotropy and layer 2 transmissivity 60 36. Changes in root mean square error of simulated water levels with respect to changes in river and drain conductance values and vertical leakance between layers 1 and 2 61 37. Map showing location of water-quality sampling sites and burial grounds 63 38. Trilinear diagram of principal-ion data of water from 31 wells in Melton Valley 69 39. Graph showing concentrations of dissolved gross beta and tritium in ground- water samples collected at Oak Ridge National Laboratory in August and September 1987 71 TABLES 1. Monthly and annual precipitation at Oak Ridge National Laboratory and normal monthly and annual precipitation at Oak Ridge, Tennessee 5 2. Results of slug tests in wells at Oak Ridge National Laboratory 9 3. Streamgaging stations on Whiteoak Creek and Melton Branch, and periods of record and drainage areas above the stations 15 4. Summary of discharge data for stations on Whiteoak Creek and Melton Branch, water year 1988, and Poplar Creek, water years 1988 and 1961 through 1988 20 5. Summary of annual discharge data, including effluent part, in cubic feet per second, for all complete years of record at stations on Whiteoak Creek and Melton Branch 21 6. Annual base flow at stations on Whiteoak Creek and Melton Branch that are not affected by effluent discharge 23 7. Estimates of annual base flow at stations on Whiteoak Creek and Melton Branch that are affected by effluent discharge 25 8. Model-calculated water-budget components for cross-sectional model simulations 45 9. Adjustments to June 28,1988, water levels used to estimate average-annual water levels 49 10. Percentage of simulated water levels within 20,10, and 5 feet of estimated average- annual water level 54 11. Model-calculated water-budget components for areal model simulations 56 12. Concentrations of major ions in water from streamflow stations in the vicinity of burial grounds 4, 5, and 6 64 13. Activities of radiochemical constituents in water from streamflow stations and wells distant from trenches 65 14. Concentrations of major ions in water from wells in the vicinity of burial grounds 5 and 6 67 15. Activities of radiochemical constituents in water from wells in the vicinity of burial grounds 5 and 6 70 Contents CONVERSION FACTORS AND VERTICAL DATUM Multiply By To obtain inch (in.) 25.4 millimeter inch per year (in/yr) 25.4 millimeter per year foot (ft) 0.3048 meter foot per day (ft/d) 0.3048 meter per day mile (mi) 1.609 kilometer square foot (ft2) 0.0929 square meter square mile (mi ) 2.590 square kilometer gallon (gal) 3.785 liter gallon (gal) 0.003785 cubic meter cubic foot (ft3) 0.02832 cubic meter foot per day (ft/day) 0.3048 meter per day cubic foot per second (ft3/s) 0.02832 cubic meter per second cubic foot per second-day (ft3/s-d) 0.02832 cubic meter per second-day cubic foot per second per square mile 0.01093 cubic meter per second [(ft3/s)/mi2] per square kilometer foot squared per day (ft2/d) 0.0929 meter squared per day picocurie (pCi) 0.037 becquerel Sea Level: In this report "sea level" refers to the National Geodetic Vertical datum of 1929 a geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929. vi Hydrology of Melton Valley at Oak Ridge National Laboratory, Tennessee HYDROLOGY OF MELTON VALLEY AT OAK RIDGE NATIONAL LABORATORY, TENNESSEE By Patrick Tucci Abstract range from about 1 x 10"5 to 2.4 feet per day, and the values generally decrease with increasing depth. A hydrologic investigation of Melton Valley, Recharge to the ground-water system is primarily by the site of three low-level, radioactive solid-waste precipitation on the ridges and hills. Average annual- burial grounds, was initiated by the U.S. Geological recharge rates are estimated to range from about 1 to Survey, U.S. Department of the Interior, in 1975. The 8 inches per year. Discharge from the ground-water investigation included description and analysis of the system is primarily to streams within, or bordering, the geology, surface water, ground water, and water qual­ valley and to springs. ity of the valley. This report focuses on information Cross-sectional and areal ground-water-flow obtained since 1983. models were used to provide an understanding of the Melton Valley normally receives abundant flow system of Melton Valley.