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CONTENTS <br />Page <br />Foreword III <br />Abstract Al <br />Introduction 1 <br />Purpose and scope 2 <br />Basin environment 2 <br />Previous investigations 7 <br />Well-numbering system 7 <br />Hydrogeology 7 <br />Geologic setting 8 <br />Water-bearing characteristics of the aquifer system <br />(post-Eocene continental deposits) 12 <br />Storage coefficient 12 <br />Hydraulic conductivity 14 <br />Ground-water flow system 15 <br />Regional flow 15 <br />Ground water in storage 21 <br />Ground-water development 22 <br />History of development 22 <br />Depth and yield of wells 22 <br />Effects of ground-water withdrawal on the Central Valley <br />aquifer system 23 <br />Page <br />Ground-water development Continued <br />Effects of ground-water withdrawal on the Central Valley <br />aquifer system Continued <br />Changes to the ground-water flow system 23 <br />Changes in aquifer storage 26 <br />Land subsidence 27 <br />Mechanics of land subsidence 30 <br />Areal extent and effects 32 <br />Quality of ground water 34 <br />Base of freshwater 34 <br />Dissolved solids 36 <br />Hydrochemical facies 36 <br />Sacramento Valley 37 <br />San Joaquin Valley 37 <br />Problem compounds 39 <br />Chloride 39 <br />Boron 39 <br />Nitrate 40 <br />Effects of human activities 40 <br />Selected references 41 <br />ILLUSTRATIONS <br />FIGURE 1. Maps showing location of study area <br />2. Photograph of Sutter Buttes <br />3. Graphs showing precipitation in the Sierra Nevada and runoff in the Central Valley <br />4. Graphs showing mean annual precipitation and cumulative departure of precipitation from mean value, 1860 to 1980, at four <br />Central Valley stations <br />5. Diagram showing well-numbering system <br />6. Generalized oblique view of part of Central Valley structural trough <br />7. Map showing approximate areas of marine deposition during the Tertiary <br />8. Map showing thickness of Central Valley aquifer system <br />9. Geologic and hydrologic units and equivalent layers in digital flow model <br />10. Diagrams showing concepts of Central Valley aquifer system <br />A3 <br />5 <br />5 <br />6 <br /> 7 <br />9 <br />10 <br />11 <br />13 <br />16 <br />11. Map showing estimated predevelopment water table 18 <br />12. Representative hydrographs showing long-term changes in ground-water levels in the Central Valley 19 <br />13. Map showing water table in 1976 20 <br />14. Generalized sections showing predevelopment and current ground-water flow conditions in the San Joaquin Valley 21 <br />15. Maps showing ground-water pumpage in the Central Valley 24 <br />16. Diagrams showing change in regional ground-water flow system due to development 26 <br />17. Diagrams showing change in effective vertical conductance of Central Valley aquifer system due to development 26 <br />18. Map showing estimated change in hydraulic head in lower pumped zone from 1860 to 1961 28 <br />19. Map showing areal extent of land subsidence in the Central Valley 29 <br />20. Graph showing relation of ground-water storage to hydraulic head in a compacting aquifer system 30 <br />21. Diagrams showing influence of hydrogeology and well construction on potential for land subsidence 31 <br />22. Graphs showing changes in hydraulic head and compaction at two wells in subsiding areas of San Joaquin Valley, 1960-80 32 <br />23. Photograph showing magnitude of subsidence at a site 10 miles southwest of Mendota in the San Joaquin Valley 33 <br />24. Map showing distribution of dissolved-solids concentrations in ground water of the Central Valley 35 <br />25. Map showing chemical types of ground water in the Central Valley 38