CONTENTS Abstract 1 Introduction 1 Purpose and scope 3 Description of the study area 3 Well-numbering system 4 Acknowledgments 4 Study methods 6 Hydrogeologic methods 7 Water-use methods 10 Water-quality methods 11 Hydrogeologic framework 20 Ground-water system 34 Ground-water recharge 35 Ground-water movement 37 Water-level fluctuations 40 Ground-water discharge 58 Natural discharge 58 Water use 59 Ground-water budget 63 Ground-water quality 64 Conceptual model of factors affecting water quality 70 Effects of land-use activities on water quality 70 Nitrate 70 Pesticides and volatile organic compounds 73 Bacteria 79 Other factors affecting water quality 79 Quality assurance of water-quality data 83 Standard reference samples 83 Duplicate and replicate samples 86 Blanks 86 Cation-anion balance 86 Checks on field values 90 Summary and conclusions 90 Selected references 91 Appendix 1. Physical and hydrologic data for the wells and springs in the Tacoma-Puyallup area, Wash. 109 Appendix 2. Drillers' lithologic logs of wells used in construction of hydrogeologic sections, in the Tacoma-Puyallup area, Wash. 120 Appendix 3. Water-quality data, in the Tacoma-Puyallup area, Wash. 150 FIGURES 1. Map showing location of the study area 2 2. Map showing well- and spring-numbering system used in Washington 5 3. Map showing locations of wells and springs inventoried in the Tacoma-Puyallup area, Wash. 8 4. Diagram of ground-water sampling system and equipment precision 19 5. Map showing thickness of unconsolidated deposits in the Tacoma-Puyallup area, Wash. 21 6. Map showing distribution of hydrogeologic units at land surface, inventoried wells, and traces of the hydrogeologic sections A-A' to E-E' in the Tacoma-Puyallup area, Wash. 22 7. Hydrogeologic sections A-A' to E-E', showing locations of hydrogeologic units in the Tacoma-Puyallup area, Wash. 25 8-12. Maps showing altitude of the top and extent of hydrogeologic units in the Tacoma-Puyallup area, Wash.: 8. Qvr 28 9. Qvt 29 10. Qc1 31 11. Qf1 32 12. Qc2 33 13. Map showing distribution of estimated ground-water recharge in the study area, in inches per year in the Tacoma-Puyallup area, Wash. 36 14. Map showing water-level altitude in aquifer Qc1. Water levels were compiled from current and historical data in the Tacoma-Puyallup area, Wash. 38 15. Map showing water-level altitude in aquifer Qc2. Water levels were compiled from current and historical data in the Tacoma-Puyallup area, Wash. 39 16. Map showing locations of bimonthly water-level observation wells in the Tacoma-Puyallup area, Wash. 41 17a-e. Graphs showing water levels and where available, specific conductance measurements for the bimonthly observation wells 0 - 100 feet deep in the Tacoma-Puyallup area, Wash. 42 18. Map showing locations of wells and springs sampled for water quality in 1996 in the Tacoma-Puyallup area, Wash. 65 19. Graphs showing relation between hydrogeologic unit and depth to first opening, specific conductance, and percent sodium plus potassium in the Tacoma-Puyallup area, Wash. 69 20. Schematic diagram showing overview of ground-water quality and factors affecting it 71 21. Map showing concentrations of nitrite plus nitrate in water sampled from wells and springs, 1996 in the Tacoma-Puyallup area, Wash. 72 22. Graph showing trends in concentrations of nitrate and chloride in water from Maplewood Spring, 1936-96 in the Tacoma-Puyallup area, Wash. 74 23. Graph showing trend in concentration of nitrate in water from Maplewood Spring, 1988-94 in the Tacoma-Puyallup area, Wash. 77 24. Map showing locations of wells and springs sampled for pesticides and where pesticides were detected, 1996 in the Tacoma-Puyallup area, Wash. 78 25. Map showing locations of wells and springs sampled for volatile organic compounds (VOCs) and where VOCs were detected, 1996 in the Tacoma-Puyallup area, Wash. 80 26. Map showing locations of wells and springs sampled for bacteria and where bacteria were detected, 1996 in the Tacoma-Puyallup area, Wash. 81 27. Graphs showing relation between hydrogeologic unit and depth to the first opening, concentrations of nitrate, and dissolved oxygen in the Tacoma-Puyallup area, Wash. 82 28. Graph showing cation and anion percent difference 90 TABLES 1. Chemical Abstract Services registry number and minimum reporting level for selected major ions, trace elements, and other constituents 12 2. Volatile organic compound analyzed for, Chemical Abstract Services registry number, and minimum reporting level 13 3. Pesticide target analytes, Chemical Abstract Services registry number, method detection limits, and drinking water standards 15 4. Summary of hydraulic conductivity values estimated from specific capacity of wells, by hydrogeologic unit in the Tacoma-Puyallup area, Washington 24 5. Summary of water-level and specific conductance data for the 1996 water year in the Tacoma-Puyallup area, Washington 57 6. Records of springs inventoried for this study during 1995 and 1996 in the Tacoma-Puyallup, area, Washington 60 7. Summary of estimated water use during 1996 by water-use category, source, and hydrogeologic unit in the Tacoma- Puyallup area, Washington 62 8. Matrix indicating analyses performed on sample from well or spring and hydrogeologic unit tapped by well or spring in the Tacoma-Puyallup area, Washington 66 9. Summary of concentrations of inorganic constituents, trace elements, and bacteria, values of other properties, concentrations of pesticides and volatile organic compounds detected, and associated drinking water standards or guidelines, in the Tacoma-Puyallup area, Washington 67 10. Concentrations of nitrate and chloride in water from Maplewood Spring, in the Tacoma-Puyallup area, Washington 75 11. Estimated error in analysis of inorganic constituents 85 12. Constituent concentrations in duplicate samples 87 13. Replicate sample results for bacteria determinations 88 14. Summary of constituent concentrations reported for blank samples 89 15. Altitude of top of hydrogeologic units in wells in the Tacoma-Puyallup area, Washington 100