Because regional-scale atmospheric deposition data in the Rocky Mountains are sparse, a program was designed by the U.S. Geological Survey to more thoroughly determine the quality of precipitation and to identify sources of atmospherically deposited pollution in a network of high-elevation sites. Depth-integrated samples of seasonal snowpacks at 52 sampling sites, in a network from New Mexico to Montana, were collected and analyzed each year since 1993.The results of the first 5 years (1993ñ97) of the program are discussed in this report. Spatial patterns in regional data have emerged from the geographically distributed chemical concentrations of ammonium, nitrate, and sulfate that clearly indicate that concentrations of these acid precursors in less developed areas of the region are lower than concentrations in the heavily developed areas. Snowpacks in northern Colorado that lie adjacent to both the highly developed Denver metropolitan area to the east and coal-fired powerplants to the west had the highest overall concentrations of nitrate and sulfate in the network. Ammonium concentrations were highest in northwestern Wyoming and southern Montana. BACKGROUND AND PROGRAM HISTORY

Introduction 2 Purpose and scope 2 Approach 2 Previous investigations 4 Description of study area 5 Geography and climate 5 Drainage features 5 Geology 8 Bedrock 8 Regolith 8 Hydrogeology 8 Hydraulic characteristics of regolith and bedrock 8 Ground-and surface-water interaction 9 Recharge 11 Water-level fluctuations 16 Groundwater flow and potential contaminant pathways 19 Geochemistry of ground water 23 Database 23 Geochemical methods 25 Chemically distinct zones 25 Shallow water-bearing zone 25 Deep water-bearing zone 29 Geochemical evolution of ground water 31 Rome Formation 35 Maynardville Limestone 37 Copper Ridge Dolomite 39 Simulation of groundwater flow 44 Model assumptions 44 Conceptual model 44 Model boundaries 46 Model construction 46 Model calibration 49 Sensitivity analysis 56 Conclusions 62 References cited 65 Appendix A 68 Appendix B 72 iii ILLUSTRATIONS Figure 1. Map showing location of study area 3 2. Hydrograph of mean daily discharge of Bearl Creek at Highway 95,1984-86 7 3. Map showing bedrock geology 10 4. Duration curves showing flow duration for B ear Creek, East Fork Poplar Creek, and Poplar Creek 12 5-7. Graphs showing: 5. Groundwater gains and losses and cumulative groundwater discharge along Scarboro Creek, Marcfi 10,1984 13 6. Groundwater gains and losses and cumulative groundwater discharge along Bear Creek 14 7. Water levels in observation wells representing Groups A, B, and C, and precipitation at Oak Ridgej Tenn. 17 8. Map showing water-table configuration for a segment of Bear Creek Valley, October 1986 20 9. Hydrogeologic section showing model-simulated water levels and direction of groundwater flow along section A-A' 22 10. Hydrogeologic section showing direction of groundwater flow in the Maynardville Limestone and Nolichucky Shale along section B-B', September 1986 24 11. Graph showing relation between concentration of dissolved solids and depth of ground water 26 12. Piper diagram showing chemical compositioki of water from wells shallower than 50 feet 27 13. Piper diagram showing chemical composition of water from Bear Creek, September 1984 28 14. Map showing concentration of dissolved solids in water from wells less than 50 feet deep 30 15. Map showing concentration of dissolved calcium in water from wells less than 50 feet deep 32 16. Piper diagram showing chemical composition of water from wells deeper than 50 feet 34 17. Map showing concentration of dissolved solids in water from wells deeper than 50 feet 36 18. Map showing concentration of dissolved calcium in water from wells deeper than 50 feet 38 19. Generalized geologic section showing distribution of dissolved solids in the water-bearing zone shallower than 50 feet and the zone deeper than 50 feet 40 20-22. Graphs showing: 20. Mineral saturation states of ground water from wells in the Rome 21. Formation, Nolichucky Shale, and the Chemical evolution of water in the Rome Formation from the PHREEQE model and chemical analyses of water from selected wells 42 Maynardville Limestone 41 iv 20-22. Graphs showing Continued...

Introduction 1 Geologic setting 3 Acknowledgments 3 Well construction 3 Well locations and general lithology 7 Lithology 7 Boreholes at the base of Chestnut Ridge 13 Boreholes along Pine Ridge 14 Geophysical logs 14 Boreholes at the base of Chestnut Ridge 16 Boreholes along Pine Ridge 19 Summary 20 References cited 21

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A preliminary interpretation of the lithology, thickness of regolith, and configuration of the bedrock surface underlying Bear Creek and Union Valleys near Oak Ridge, Tennessee, was made based on geologic and geophysical data from boreholes and cores in Bear Creek Valley and on the related work of other investigators. Analysis of drillers' logs and lithologic logs and comparison of these data with a topographic map indicated that topography and depth of weathering are interdependent and are ultimately controlled by lithology. Topographic patterns were, therefore, used to extend localized geologic data to a larger scale. Maps of the surficial geology, thickness of regolith, and configuration of the bedrock surface are presented.