Hydrology and Quality of Ground Water in Northern Thurston County, Washington
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Hydrology and Quality of Ground Water in Northern Thurston County, Washington By B.W. Drost, G.L. Turney, N.P. Dion, and M.A. Jones U.S. Geological Survey Water-Resources Investigations Report 92-4109 [Revised] Prepared in cooperation with THURSTON COUNTY DEPARTMENT OF HEALTH Tacoma, Washington 1998 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Thomas J. Casadevall Acting Director Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. For additional information write to: Copies of this report may be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Branch of Information Services 1201 Pacific Avenue - Suite 600 Box 25286 Tacoma, Washington 98402 Denver. Colorado 80225-0286 CONTENTS Abstract - 1 Revision note 1 Introduction - 2 Purpose and scope - 2 Description of the study area 2 Site-numbering system 6 Acknowledgments 7 Geologic framework 7 Ground-water hydrology 10 Conceptual model of the ground-water system 10 Geohydrologic units 12 Hydraulic conductivity 14 Recharge 17 Movement 17 Discharge - - 18 Water-level fluctuations and trends 20 Water use 24 Water budget of the Ground Water Management Area - 28 Ground-water quality 29 Water-quality methods 29 General chemistry 32 pH, dissolved oxygen, and specific conductance 32 Dissolved solids 33 Major ions 34 Chloride 35 Nitrate 36 Water types 36 Iron and manganese 37 Trace elements - 38 Volatile organic compounds 39 Septage-related compounds 39 Bacteria 42 Drinking water regulations 44 Variations of water quality at times of high and low water levels 47 Water-quality problems 48 Seawater intrusion 48 Agricultural activities 51 Septic systems 52 Commercial and industrial activities 53 Natural conditions 53 Benefits of monitoring and possible additional studies 53 Summary and conclusions 54 Selected references 55 Appendix A. Physical and hydrologic data for the well and springs used in this study 60- Appendix B. Quality-assurance assessment of water-quality data - 153 Appendix C. Water-quality data tables 161 in PLATES (Plates are located in the pocket at the end of the report) 1-6. Maps showing: 1. Well and spring locations, surficial geohydrology, and geohydrologic sections. 2. Extent and thickness of geohydrologic units Qvr, Qvt, Qva, and Qf. 3. Altitude of tops of geohydrologic units Qva and Qc, and recharge from precipitation. 4. Water levels, water-level differences, and flow directions in geohydrologic units Qva and Qc, 1988. 5. Concentrations of dissolved solids in ground water and trilinear diagrams. 6. Concentrations of chloride, nitrate, iron, and methylene blue active substances (MBAS) in ground water. FIGURES 1. Map showing location of the study area 3 2. Graphs of long-term mean monthly and project-observed climatic conditions at Olympia. Washington, and areal distribution of mean annual precipitation in the study area 5 3. Graph of population trends for Olympia and Thurston County 6 4-7. Sketches showing: 4. Site-numbering system in Washington 7 5. Conceptual model of the ground-water system beneath northern Thurston County 11 6. Graphs of frequency distributions of well depths and of geohydrologic units tapped by wells 15 7. Precipitation-recharge relations used to estimate recharge in northern Thurston County 19 8-9. Hydrographs of: 8. McAllister Springs discharge, July 1988-July 1990, and long-term average monthly discharge 19 9. Water levels in selected wells in the Ground Water Management Area 22 10. Graphs of long-term water-level trend in well 18N/02W-07R01 and annual precipitation at Olympia 23 11. Graphs of ground-water use in 1988 in the Ground Water Management Area, categorized by types of use and geohydrologic unit 25 12. Maps showing ground-water use in 1988, and area served by public supply in the Ground Water Management Area 26 13. Sketch showing water-sampling apparatus and locations of sampling points 31 14. Graph of comparison of nitrate and methylene blue active substances (MBAS) 44 15. Sketches of hypothetical hydrologic conditions before and after seawater intrusion 50 TABLES 1. Lithologic and hydrologic characteristics of geohydrologic units in Thurston County 9 2. Summary of horizontal hydraulic conductivity values estimated from specific-capacity data, by geohydrologic unit 16 3. Principal springs in northern Thurston County 20 4. Summary of ground-water use in 1988 by water-use category, source, and geohydrologic unit 21 5. Summary of concentrations of common constituents 33 IV TABLES-Continued 6. Median concentrations of common constituents by geohydrologic unit 34 7. Summary of concentrations of selected trace elements 38 8. Summary of concentrations of volatile organic compounds 40 9. Concentrations of volatile organic compounds in samples where they were detected 41 10. Summary of concentrations of septage-related compounds 42 11. Analyses of samples containing elevated concentrations of septage-related compounds 43 12. Summary of concentrations of bacteria 43 13. Concentrations of bacteria in samples where they were present 45 14. Drinking-water regulations and the number of samples not meeting them 46 15. Wells with samples that had large differences in nitrate concentrations between 1988 and 1989----------- 48 16. Summary of comparison of chloride concentrations for samples collected in 1978 and 1989 form 112 coastal wells 51 CONVERSION FACTORS AND VERTICAL DATUM Multiply By To obtain inch (in.) 25.4 millimeter foot (ft) 0.3048 meter foot per day (ft/d) 0.0000035 meter per second mile (mi) 1.609 kilometer square mile (mi2) 2.590 square kilometer gallon (gal) 3.785 liter acre 4,047 square meter acre-foot (acre-ft) 1,233 cubic meter cubic foot per second (ft3/s) 0.02832 cubic meter per second ounce 28.35 grams Temperature: Air temperatures are given in degrees Fahrenheit (°F), which can be converted to degrees Celsius (°C) by the following equation: °C = 5/9(°F-32). Following convention, water temperatures are given in degrees Celsius, which can be converted to degrees Fahrenheit by the following equation: °F = 1.8(°C) + 32. Sea Level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD 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. HYDROLOGY AND QUALITY OF GROUND WATER IN NORTHERN THURSTON COUNTY, WASHINGTON By B.W. Drost, G.L. Turney, N.P. Dion, and M.A. Jones ABSTRACT The close correlation of nitrate concentrations with deter gent concentrations supports the theory that the nitrate Northern Thurston County is underlain by as much as originates in septic systems, the only likely source of the 1,800 feet of unconsolidated deposits of Pleistocene Age detergents. that are of glacial and nonglacial origin. Iterpretation of approximately 1,140 drillers' logs led to the delineation of seven major geohydrologic units, four of which are signif Most water-quality problems in the study area, how icant aquifers. ever, are due to natural causes. Iron concentrations are as large as 21,000 micrograms per liter, manganese concen Precipitation ranges from about 35 to 65 inches trations are as large as 3,400 micrograms per liter, and per year across the study area. Estimates of recharge indi connate seawater is present in ground water in the south cate that the ground-water system of the Ground Water ern part of the study area. Management Area (GWMA), a subset of the study area, receives an average of about 28 inches per year. Ground water generally moves toward marine water bodies and to major surface drainage channels. REVISION NOTE At least 33,000 acre-feet per year of ground water dis The original version of the report was published in charges as springs from the GWMA. Approximately 1994. During a subsequent phase of study, while applying 21,000 acre-feet of water was withdrawn from the a numerical model to simulate the ground-water flow sys ground-water system of the GWMA through wells in tem, errors were discovered in the original report. These 1988. Total ground-water use in the GWMA in 1988 was approximately 37,000 acre-feet. About 16,000 acre-feet errors resulted from the method used to assign geohydro of water that discharges naturally through springs was logic units to wells. used together with water withdrawn by wells for domestic supply, agricultural, commercial, industrial, institutional, Geohydrologic unit assignments have been reevalu- and aquaculture and livestock uses. ated for all wells. This has resulted in changes to the surf- icial geologic map, unit top and thickness maps, geo Generally, the chemical quality of the ground water hydrologic sections, and water-level maps, as well as was good and 94 percent of the water samples were classi fied as soft or moderately hard. Of the few water-quality revised statistics for hydraulic conductivity, water use, problems encountered, the most widespread anthropo common constituents by geohydrologic unit, and trilinear genic problem appeared to be seawater intrusion. How diagrams. ever, a comparison with data from 1978 indicated that the degree and extent of intrusion had not changed signifi Most of the data presented in this report were col cantly since that time. Agricultural activities may be lected in 1988 and 1989. The discussions and conclusions responsible for the presence of nitrate in ground waters at some individual wells, but septic tanks in areas of high in this report are based on the original field data and repre housing density are likely responsible for elevated nitrate sent our knowledge of the hydrology and quality of the concentrations near the Cities of Lacey and Tumwater. ground water at that time. INTRODUCTION Describe the general chemical characteristics of waters in the major aquifers and the areal patterns of any ground-water contamination; Demand for water in the northern part of Thurston County, Wash., has increased steadily in recent years Provide guidelines for the establishment of networks because of rapid growth in population and residential to monitor ground-water levels and ground-water development.