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Study and Interpretation of the Chemical Characteristics of Natural Water Second Edition GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1473 Study and Interpretation of the Chemical Characteristics of Natural Water Second Edition By JOHN D. HEM GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1473 A review of chemical, geologic, and hydrologic principles and processes that control the composition of natural water, with methods for studying and interpreting chemical analyses UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 73-606921 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.G. 20402 - Price $2.25 (paper cover) PREFACE Most of the text of the first edition of this publication, U.S. Geologi­ cal Survey Water-Supply Paper 1473, was written in 1955 and 1956. When the plans were being made for the report a few years earlier, the expectation was that it would be used within the U.S. Geological Survey for the most part as a guide for field investigators to help in determining and interpreting the chemical quality of water resources. At the same time, however, a substantial increase of interest and activity in the fields of natural-water chemistry and waterrpollution control was beginning to be noticeable, and, as a result, when the report was published in 1959, it soon attained a considerably wider circulation than had originally been anticipated. A series of reprintings was necessary. This revision of the earlier book has been prepared because of the continued and still-growing interest in the subject matter. The first edition is now seriously out of date. It no longer gives a satisfactory indication of present-day techniques of water-analysis interpretation or of the state of development of the field of water chemistry. This revision has two principal objectives: (1) to outline more completely the principles and processes, chemical and environmental, which shape and control the chemical composition of natural water and (2) to bring the discussions of chemistry of individual constituents, methods of data interpretation, and associated bibliographic references up to date. It is to be expected that most potential users of this book will have some chemical training. In any event, it seems inappropriate for anyone without such training to specialize in the interpretation of chemical data. Accordingly, a somewhat more extensive use of theoretical chemistry has been introduced here as compared to the earlier edition. The book should still be useful to the nonchemist, however, and it is nowhere very demanding in either a chemical or a mathematical sense. The interdisciplinary nature of the field requires the introduction of much material which can be discussed only briefly. Many of the concepts which are introduced will be familiar to the reader, and supplementary material referred to in the bibliography should enable him to obtain more information on various topics. The state of knowledge of the field covered here is rapidly improving, but broad areas remain where little serious research has been done. IV PREFACE The reader will note occasional comments to this effect, and hopefully he will be able to draw some conclusions of his own both from what is contained here and from what has been left out, as to what subjects need more careful study. Discussions and correspondence with many of my friends and colleagues within the U.S. Geological Survey and elsewhere have probably had even more influence on my thoughts and their expression here than I realize, but certainly I owe much to the aid of others which cannot be fully acknowledged. Colleagues who helped review the manuscript include D. C. Culbertson, Eugene Brown, J. H. Feth, B. B. Hanshaw, R. O. Fournier, V. C. Kennedy, M. W. Skougstad, and T. D. Steele, all of the U.S. Geological Survey. The tireless labor of Mrs. Mary E. Grisak in preparing the manuscript, reviewing, and repairing it where necessary also is gratefully acknowledged. CONTENTS Page Preface.________________________________________________________ m Abstract ___ __ ___________________________________________________ 1 Scope and purpose_______________________________________________ 2 Arrangement of topics______________________________________________ 3 Properties and structure of water______-________-______--__--________ 4 Composition of the earth's crust-__-_-______--------_------_-_____-__ 5 The hydrosphere_______________________________________________ 10 The atmosphere.---___---____---___________--___--___--_-_________ 10 Principles and processes controlling composition of natural water________ 12 Atomic and nuclear alterations.____________--_-___---_-_________ 14 Induced radioactivity._________________________________________ 14 Chemical reactions.__________________________________________ 15 Types of reactions in water chemistry_________-_-_______-____ 16 Chemical equilibrium..___________________________________ 18 Temperature and pressure effects._______________________ 22 Solution of calcite.____________________________________ 22 Application of chemical thermodynamics.____________________ 24 Electrochemical equilibrium.______________________________ 28 Chemical reaction rates.___________________________________ 30 Reaction order._______________________________________ 30 Effect of temperature on reaction rate__________________ 33 Solubility concepts._______________________________________ 34 Solubility product____________________________________ 34 Reactions at interfaces.____________________________________ 35 Gas-liquid interfaces.__________________________________ 35 Liquid-solid interfaces________________________________ 36 Adsorption and ion-exchange calculations.________________ 38 Membrane effects____________________________________ 39 Clays as semipermeable membranes._____________________ 40 Environmental influences.______________________________________ 40 Climate __________________________________________________ 41 Geologic effects.__________________________________________ 41 Biochemical factors._-__-______-____-_______-_-_-_--__---_- 42 Ecology applied to natural water._______________________ 43 Influence of soil and soil-forming processes._______________ 44 Aquatic biota___-_-____-_______-___------_---_---___-_ 45 The hydrologic cycle.-________________________-_---___-_-_- 47 Sources of solutes in the atmosphere.________________________ 47 Composition of atmospheric precipitation______-__-_--__---__- 48 Influence of man__ ________________________________________ 50 A systems approach to study of water chemistry __________________ 51 Open versus closed systems_____-_-___-___________--___-_-__ 51 The phase rule.___________________________________________ 52 Influence of water movement.__________________________________ 54 Some characteristics of ground-water systems.____________________ 54 v VI CONTENTS Principles and processes controlling composition Page of natural water Continued Surface water systems rivers_____.--_.________-__--_-________ 55 Lakes and reservoirs.__________________________________________ 56 Geochemical cycles____________________________________________ 56 Buffer capacity.________________________________________________ 59 Evaluation of water composition______-_---_--_---__-__--_------_-__ 60 Collection of water samples_________-____--___-__--_______-_____ 60 Sampling of river water._______________________________________ 61 Lake and reservoir samples____-_-__-_-_-_-____-_-__-_-_-------- 68 Ground-water samples _________________________________________ 68 Completeness of sample coverage__--_--_---_----__________------ 71 Analysis of water samples._________________________________________ 74 Field testing of water._________________________________________ 74 Electric logs as indicators of ground-water quality _________________ 75 Laboratory procedures.________________________________________ 76 Expression of water analyses.___________________________________ 77 Hypothetical combinations_____-_____________-_--__-_--_--_ 77 Analyses reported in terms of ions___________________________ 77 Determinations included in analyses_____________________________ 78 Units used in reporting analyses_______________________________ 79 Weight-per-weigh't units_______________-_____--_______-___-_ 79 Weight-per-volume units.__________________________________ 79 Equivalent-weight units___-______________ _________________ 81 Composition of anydrous residue.___________________________ 82 Concentration in terms of caleium carbonate..________________ 84 Comparison of units of expression.__________________________ 85 Significance of properties and constituents reported in water analyses.... 86 Nature of the dissolved state__________________________________ 86 Hydrogen-ion activity (pH)___________________________________ 88 Buffered solutions____________________________--_--________ 92 Range of pH of natural water______________________________ 93 Measurement and interpretation ofpH_______________________ 95 Specific electrical conductance_________________________________ 96 Units for reporting conductance--.---------------------.---- 96 Physical basis of conductance...........-------------------- 96 Range of conductance values_____________________________ 102 Accuracy and reproducibility______-_-__-_-_-----------_-.._ 103 Silica----..._-________________________.___..___ 103 Forms of dissolved silica__________________________________
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