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Water-Quality Engineering in Natural Systems E-Book

David A. Chin

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Herausgeber: John Wiley & Sons
Kategorie: Wissenschaft und neue Technologien
Sprache: Englisch

Beschreibung

This textbook describes in detail the fundamental equations that govern the fate and transport of contaminants in the environment, and covers the application of these equations to engineering design and environmental impact analysis relating to contaminant discharges into rivers, lakes, wetlands, groundwater, and oceans. The third edition provides numerous end-of-chapter problems and an expanded solutions manual. Also introduced in this edition are PowerPoints slides for all chapters so that instructors have a ready-made course.

Key distinguishing features of this book include: detailed coverage of the science behind water-quality regulations, state-of-the-art methods for calculating total maximum daily loads (TMDLs) for the remediation of impaired waters, modeling and control of nutrient levels in lakes and reservoirs, design of constructed treatment wetlands, design of groundwater remediation systems, design of ocean outfalls, control of oil spills in the ocean, and the design of systems to control the quality of surface runoff from watersheds into their receiving waters. In addition, the entire book is updated to provide the latest advances in the field of water-quality control. For example, concepts such as mixing zones are expanded to include physical nature and regulatory importance of mixing zones, practical aspects of outfall and diffuser design are also included, specific details of water-quality modeling are updated to reflect the latest developments on this topic, and new findings relating to priority and emerging pollutants are added.

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Leseprobe

COVER

TITLE PAGE

DEDICATION

PREFACE

1 INTRODUCTION

1.1 BACKGROUND

1.2 SOURCES OF WATER POLLUTION

1.3 CONTROL OF WATER POLLUTION

2 WATER QUALITY

2.1 INTRODUCTION

2.2 PHYSICAL MEASURES

2.3 CHEMICAL MEASURES

2.4 BIOLOGICAL MEASURES

PROBLEMS

NOTES

3 FUNDAMENTALS OF FATE AND TRANSPORT

3.1 INTRODUCTION

3.2 THE ADVECTION–DIFFUSION EQUATION

3.3 FUNDAMENTAL SOLUTIONS OF THE ADVECTION–DIFFUSION EQUATION

3.4 ADVECTION AND DIFFUSION OF HEAT

3.5 TRANSPORT OF SUSPENDED PARTICLES

3.6 FATE AND TRANSPORT OF MICROORGANISMS IN NATURAL WATERS

3.7 TURBULENT DIFFUSION*

3.8 DISPERSION

PROBLEMS

NOTES

4 RIVERS AND STREAMS

4.1 INTRODUCTION

4.2 TRANSPORT PROCESSES

4.3 MODELS OF SPILLS

4.4 MODELS OF DISSOLVED OXYGEN

4.5 MODELS OF NUTRIENTS

4.6 MODELS OF PATHOGENS

4.7 CONTAMINANT LOADS

4.8 MANAGEMENT AND RESTORATION

PROBLEMS

NOTE

5 GROUNDWATER

5.1 INTRODUCTION

5.2 CONTAMINANT SOURCES

5.3 FATE AND TRANSPORT MODELS

5.4 TRANSPORT PROCESSES

5.5 FATE PROCESSES

5.6 NONAQUEOUS PHASE LIQUIDS

5.7 MONITORING WELLS

5.8 REMEDIATION OF SUBSURFACE CONTAMINATION

PROBLEMS

NOTES

6 WATERSHEDS

6.1 INTRODUCTION

6.2 URBAN WATERSHEDS

6.3 AGRICULTURAL WATERSHEDS

6.4 AIRSHEDS

PROBLEMS

NOTES

7 LAKES AND RESERVOIRS

7.1 INTRODUCTION

7.2 PHYSICAL PROCESSES

7.3 EUTROPHICATION

7.4 THERMAL STRATIFICATION

7.5 WATER‐QUALITY MODELS

7.6 MANAGEMENT AND RESTORATION

PROBLEMS

NOTES

8 WETLANDS

8.1 INTRODUCTION

8.2 NATURAL WETLANDS

8.3 CONSTRUCTED TREATMENT WETLANDS

PROBLEMS

9 OCEANS AND ESTUARIES

9.1 INTRODUCTION

9.2 OCEAN OUTFALLS

9.3 MULTIPORT DIFFUSERS FOR DENSE DISCHARGES

9.4 OIL SPILLS

9.5 CHEMICAL SPILLS

9.6 ESTUARIES

PROBLEMS

10 ANALYSIS OF WATER‐QUALITY MEASUREMENTS

10.1 INTRODUCTION

10.2 PROBABILITY DISTRIBUTIONS

10.3 FUNDAMENTAL PROBABILITY DISTRIBUTIONS

10.4 DERIVED PROBABILITY DISTRIBUTIONS

10.5 ESTIMATION OF A POPULATION DISTRIBUTION FROM SAMPLE DATA

10.6 ESTIMATION OF PARAMETERS OF POPULATION DISTRIBUTION

10.7 PROBABILITY DISTRIBUTIONS OF SAMPLE STATISTICS

10.8 CONFIDENCE INTERVALS

10.9 HYPOTHESIS TESTING

10.10 RELATIONSHIPS BETWEEN VARIABLES

10.11 FUNCTIONS OF RANDOM VARIABLES

10.12 KRIGING

PROBLEMS

NOTES

11 MODELING

11.1 INTRODUCTION

11.2 CODE SELECTION

11.3 CALIBRATION

11.4 VALIDATION

11.5 SIMULATION

11.6 UNCERTAINTY ANALYSIS

NOTE

Appendix A: UNITS AND CONVERSION FACTORS

A.1 UNITS

A.2 CONVERSION FACTORS

NOTE

Appendix B: FLUID PROPERTIES

B.1 WATER

B.2 ORGANIC COMPOUNDS FOUND IN WATER

B.3 AIR AT STANDARD ATMOSPHERIC PRESSURE

Appendix C: STATISTICAL TABLES

C.1 AREAS UNDER STANDARD NORMAL CURVE

C.2 CRITICAL VALUES OF THE

DISTRIBUTION

C.3 CRITICAL VALUES OF THE CHI‐SQUARE DISTRIBUTION

C.4 CRITICAL VALUES OF THE F DISTRIBUTION ()

C.5 CRITICAL VALUES FOR THE KOLMOGOROV–SMIRNOV TEST STATISTIC

Appendix D: SPECIAL FUNCTIONS

D.1 ERROR FUNCTION

D.2 BESSEL FUNCTIONS

D.3 GAMMA FUNCTION

D.4 EXPONENTIAL INTEGRAL

BIBLIOGRAPHY

INDEX

END USER LICENSE AGREEMENT

List of Tables

Chapter 1

TABLE 1.1 Strengths of Various Point and Nonpoint Sources

Chapter 2

TABLE 2.1 Flow Velocity Versus Type of Substrate

TABLE 2.2 Saturation of Dissolved Oxygen in Water

TABLE 2.3 Pathogenic Microorganisms Commonly Found in Surface Waters

TABLE 2.4 Limiting Biological Indicator Criteria for Primary‐Contact Waters R...

Chapter 3

TABLE 3.1 Centerline Concentrations for Various Diffusion Coefficient Formula...

TABLE 3.2 Typical Settling Velocities in Natural Waters.

TABLE 3.3 Measured Concentrations in mg/L.

Chapter 4

TABLE 4.1 Typical Characteristics of Streams and Rivers

TABLE 4.2 Estimates of Longitudinal Dispersion Coefficient in Rivers

TABLE 4.3 Parameters Used to Estimate Volatilization Coefficient,

TABLE 4.4 Typical Deoxygenation Rate Coefficients

TABLE 4.5 Typical Values of

TABLE 4.6 Empirical Formulas for Estimating Reaeration Constant,

, at

TABLE 4.7 Typical Benthic Oxygen Demand Rates,

, at

Chapter 5

TABLE 5.1 Leachate Characteristics from Municipal Solid Waste Disposal Sites.

TABLE 5.2 Well Function for Leaky Aquifer,

TABLE 5.3 Hydraulic Conductivity Statistics.

TABLE 5.4 Variances and Correlation Length Scales of Hydraulic Conductivity.

TABLE 5.5 Typical Longitudinal Dispersivities for Various Length Scales.

TABLE 5.6 Typical Carbon Content in Soils.

TABLE 5.7 Empirical Relations Between

and

TABLE 5.8 Values of

for Selected Organic Compounds.

TABLE 5.9 Typical Values of Bulk Density and Porosity in Porous Media.

TABLE 5.10 Values of

(cm

/g) for Selected Elements.

TABLE 5.11 First‐Order Decay Rates of Selected Organic Compounds in Soil.

TABLE 5.12 Densities and Solubilities of NAPLs.

TABLE 5.13 Residual Saturation of Petroleum Fuels.

TABLE 5.14 Major Organic Compounds in a Typical Gasoline Blend.

TABLE 5.15 Toxic Effects of BTEX Compounds.

TABLE 5.16 Groundwater Remediation Strategies.

TABLE 5.17 Capillary Rise in Unconsolidated Materials.

TABLE 5.18 Parameters

Chapter 6

TABLE 6.1 Sources of Toxic and Hazardous Substances in Urban Runoff.

TABLE 6.2 Average Water Quality of Combined Sewer Overflows.

TABLE 6.3 Event Mean Concentrations for Urban Land Uses Derived from NURP.

TABLE 6.4 Event Mean Concentrations for Urban Land Uses Derived from NSQD.

TABLE 6.5 Event Mean Concentrations Reported in Literature.

TABLE 6.6 Agricultural Land Use Versus Type of Pollution.

TABLE 6.7 Pollutant Concentration from Animal Operations.

TABLE 6.8 Magnitude of Soil Erodibility Factor,

TABLE 6.9 Exponent Parameter in Estimating Slope Length Factor.

TABLE 6.10 Values of

for Cropland, Pasture, and Woodland.

TABLE 6.11 Values of

for Agricultural Land Uses.

TABLE 6.12 USDA Soil Separates.

TABLE 6.13 USDA Slope Classifications.

TABLE 6.14 Half‐Lives of Insecticides in Soil.

TABLE 6.15 Guidelines for Effective Buffer Widths.

Chapter 7

TABLE 7.1 Empirical Relations Between Algal Biomass and TP Concentrations

TABLE 7.2 Limiting Nutrients for Various Water Bodies

TABLE 7.3 Trophic State of Lakes

Chapter 8

TABLE 8.1 Plant Categories Used in Wetland Delineation.

TABLE 8.2 Hydrologic Zones for Nontidal Areas.

TABLE 8.3 Resistance Factor in Estimating Manning's

TABLE 8.4 Typical Values of Background Concentration,

, in FWS Wetlands.

TABLE 8.5 Areal Rate Coefficient,

, and Temperature Factor,

, in FWS Wetland...

Chapter 9

TABLE 9.1 Characteristics of Several Ocean Outfalls

TABLE 9.2 Dilution Coefficients for Single Plumes

TABLE 9.3 Dilution Coefficients for Single Plumes in Stratified Environments

TABLE 9.4 Measures of Single Plumes in Stratified Environments

TABLE 9.5 Criteria for Using Single‐Plume and Line‐Plume Equations

TABLE 9.6 Dilution Coefficients for Line Plumes in Unstratified Environments

TABLE 9.7 Dilution Coefficients for Line Plumes in Stratified Environments

TABLE 9.8 Measures of Line Plumes in Stratified Environments

TABLE 9.9 Dense Discharges into Stagnant Receiving Water (for

)

TABLE 9.10 Dense Discharges into Flowing Receiving Water (for

)

TABLE 9.11 Properties of a Particular Crude Oil

TABLE 9.12 Relationship Between Oil Viscosity and Terminal Thickness

TABLE 9.13 Relationship Between Distillation Cuts and Chemical Characteristic...

TABLE 9.14 Aqueous Solubilities of Aromatic Hydrocarbons Commonly Found in Cr...

TABLE 9.15 Relationship Between Distillation Cuts and Fate Constants

TABLE 9.16 Habitat Recovery Times

TABLE 9.17 Minimum Toxicity Concentrations

TABLE 9.18 Standard European Behavior Classifications

TABLE 9.19 Major Estuaries in the United States

TABLE 9.20 Stratification Classification of Estuaries

TABLE 9.21 Longitudinal Dispersion Coefficients in Select Estuaries

Chapter 10

TABLE 10.1 Plotting Position Parameter

TABLE 10.2 Moments and L‐Moments of Common Probability Distributions

TABLE 10.3 Values of Shapiro–Wilk Statistic,

TABLE 10.4 Values of Shapiro–Francia Statistic,

TABLE 10.5 Data Transformations

TABLE 10.6 Values of

for Zero Correlation at

TABLE 10.7 Variances of Random Functions

TABLE 10.8 Commonly Used Stationary Covariance Functions

TABLE 10.9 Commonly Used Analytic Intrinsic Semivariograms

TABLE A.1 SI Derived Units

TABLE A.2 Multiplicative Factors for Unit Conversion

TABLE B.1 Properties of Water

TABLE B.2 Properties of Organic Compounds Commonly Found in Water at

TABLE B.3 Properties of Air at Standard Atmospheric Pressure (Chin, 2016)

TABLE C.1 Areas Under Standard Normal Curve

TABLE C.2 Critical Values of the

Distribution

TABLE C.3 Critical Values of the Chi‐Square Distribution

TABLE C.4 Critical Values of the

Distribution (

)

TABLE C.5 Critical Values for the Kolmogorov–Smirnov Test Statistic

TABLE D.1 Error Function

TABLE D.2 Useful Bessel Functions

TABLE D.3 Gamma Function

List of Illustrations

Chapter 1

Figure 1.1 River with floating trash.

Figure 1.2 Point source of pollution.

Source

: South Florida Water Management...

Figure 1.3 Stormwater outlets into drainageway.

Figure 1.4 Livestock in a stream.

Source

: State of Arkansas (2005).

Figure 1.5 Directly connected impervious area.

Chapter 2

Figure 2.1 Longitudinal profile of a pool/riffle system in a piedmont stream...

Figure 2.2 Typical (a) pool and (b) riffle.

Figure 2.3 Effect of channel erosion on in‐stream habitat.

Figure 2.4 Riparian habitat.

Figure 2.5 (a) Typical BOD curve. (b) CBOD remaining versus time.

Figure 2.6 Apparatus for measuring BOD.

Figure 2.7

Escherichia coli

(

E.coli

) bacteria.

Figure 2.8(a) Cryptosporidium parvum and (b) Giardia lamblia.

Figure 2.9Pair of Schistosoma mansoni.

Figure 2.10Algae Anabaena flos‐aquae.

Figure 2.11Membrane filter test for coliforms.

Chapter 3

Figure 3.1 Advection and diffusion. (a) Uniform advection + molecular diffus...

Figure 3.2 Control volume in a fluid transporting tracer.

Figure 3.3 Change of coordinate system.

Figure 3.4 One‐dimensional diffusion.

Figure 3.5 Dirac delta function.

Figure 3.6 One‐dimensional diffusion.

Figure 3.7 Solution to the one‐dimensional advection–diffusion equation.

Figure 3.8 Initial concentration distribution.

Figure 3.9 Step‐function initial condition.

Figure 3.10 Diffusion from a step‐function initial condition.

Figure 3.11 Impermeable boundary condition.

Figure 3.12 Two impermeable boundaries.

Figure 3.13 Lake.

Figure 3.14 Temporal concentration distribution for continuous source. (a) I...

Figure 3.15 Waste discharge into river.

Figure 3.16 Concentration at 1 km downstream of mixing zone

Figure 3.17 Two‐dimensional diffusion.

Figure 3.18 Two‐dimensional diffusion from a finite source.

Figure 3.19 Plane sources with two‐dimensional diffusion. (a) Semi‐infinite ...

Figure 3.20 Confluence of two streams.

Figure 3.21 Steady continuous source.

Figure 3.22 Typical Lagrangian covariance function.

Figure 3.23 Relationship between Lagrangian time scale and velocity autocorr...

Figure 3.24 Dispersion processes.

Figure 3.25 Longitudinal dispersion.

Figure 3.26 Discretization of channel cross section

Figure 3.27 Concentration measurements.

Figure 3.28 Sources of contaminant to a narrow channel.

Chapter 4

Figure 4.1 Contaminant discharge into the Alpenrhein River (Germany).

Source

Figure 4.2 Initial mixing of stream discharge.

Figure 4.3 Concentration distribution resulting from an instantaneous spill....

Figure 4.4 Concentration 2 km downstream of spill.

Figure 4.5 Discharge of treated domestic wastewater into a river.

Source

: Ci...

Figure 4.6 Streeter–Phelps oxygen sag curve.

Figure 4.7 Variation of dissolved oxygen downstream of source.

Figure 4.8 Variation of dissolved oxygen due to nitrification.

Figure 4.9 Nitrogen species downstream of wastewater discharge.

Figure 4.10 Dissolved oxygen versus time for a time‐varying production rate....

Figure 4.11 Dissolved oxygen versus time in the Grand River, Michigan.

Figure 4.12 Flow duration curve.

Figure 4.13 Load duration curve.

Figure 4.14 Load duration curve for fecal coliform bacteria.

Figure 4.15 Contaminant loads on stream segment.

Figure 4.16 Allocation of contaminant loads.

Figure 4.17 Fecal coliform TMDL.

Figure 4.18 Load measurements plotted on load duration curve.

Figure 4.19 Comparison of measurements with TMDL.

Figure 4.20 Concentration reduction for given flow condition.

Figure 4.21 Silt fence.

Figure 4.22 Fish hatchery on the Columbia River.

Source

: U.S. Army Corps of ...

Figure 4.23 Riprap stabilization of a stream bank.

Figure 4.24 Fish ladder at the Bonneville dam on the Columbia River (Oregon)...

Figure 4.25 Removal of the Brownsville dam (Oregon).

Source

: National Oceani...

Figure 4.26 Slug of contaminated water in a channel.

Chapter 5

Figure 5.1 Contaminant dispersion in groundwater.

Figure 5.2 Treatment and disposal of wastewater via septic tank. (a) Septic ...

Figure 5.3 Gas station storage tank.

Figure 5.4 Irrigation system using pumped groundwater.

Figure 5.5 Landfill.

Source

: Energy Information Administration (2005)

Figure 5.6 Injection well.

Source

: U.S. Department of Energy (2012).

Figure 5.7 Control volume in a porous medium.

Figure 5.8 Dispersion from a continuous plane source.

Figure 5.9 Longitudinal dispersivity versus length scale in groundwater.

Figure 5.10 Longitudinal dispersivity versus length scale.

Figure 5.11 Typical (a) LNAPL and (b) DNAPL spills.

Figure 5.12 Residual saturation in porous media.

Figure 5.13 BTEX compounds.

Figure 5.14 Typical monitoring well.

Figure 5.15 Hollow‐stem auger. (a) Schematic and (b) actual.

Sources

: Scalf ...

Figure 5.16 Installation of a well casing. (a) Drill rig and (b) casing inst...

Figure 5.17 Well screen.

Source

: Browns Drilling (2005).

Figure 5.18 Gravel pack.

Figure 5.19 Dual‐recovery pump system.

Figure 5.20 Soil excavation at a Superfund site.

Source

: U.S. Army Corps of ...

Figure 5.21 Soil vapor extraction system. (a) Schematic and (b) actual.

Sour

...

Figure 5.22 Air sparging system.

Figure 5.23 Single extraction well in regional flow.

Figure 5.24 Multiple extraction wells in uniform flow. (a) Two extraction we...

Figure 5.25 Contaminated groundwater on industrial property.

Figure 5.28 (a) Pump‐and‐treat system and (b) disposal.

Source

: U.S. Environ...

Figure 5.27 Pump‐and‐treat system.

Figure 5.29 Bioremediation system.

Source

: Pacific Northwest National Labor...

Figure 5.30 Construction of a slurry wall.

Source

: Permeable Reactive Barrie...

Figure 5.31 Natural attenuation processes.

Source

: U.S. Geological Survey (2...

Figure 5.32 Benzene concentrations in gasoline spill.

Figure 5.33 Contaminated soil. (a) Plan view and (b) elevation view.

Chapter 6

Figure 6.1 Typical watershed.

Figure 6.2 Impact of imperviousness on stream water quality.

Figure 6.3 Runoff coefficients derived from NURP studies.

Figure 6.4 Porous pavement.

Figure 6.5Rain‐barrel cistern.

Figure 6.6 Direct connection between roadway and a stormwater inlet.

Figure 6.7 Infiltration basin.

Figure 6.8 Infiltration trench. (a) During construction. (b) After construct...

Figure 6.9 Filter strip.

Figure 6.10Riparian buffer strip.

Figure 6.11 Silt fence.

Figure 6.12 Typical grassed roadside swale.

Figure 6.13 (a) Riprap. (b) Gabions.

Figure 6.14 Catch basin and drainage‐system connection. (a) Schematic. (b) A...

Figure 6.15 Detention pond.

Figure 6.16 Dry detention basin. (a) Inflow structure. (b) Outflow structure...

Figure 6.17 Sequential relation between sheet, rill, and gully erosion. (a) ...

Figure 6.18 Gully.

Figure 6.19 Annual rainfall-runoff erosivity factor,

(

mm/ha

h).

Figure 6.20 (a) Soil horizons and (b) typical soil profile.

Figure 6.21 USDA Soil texture triangle.

Figure 6.22 Cropping practices: (a) cover cropping and (b) conservation till...

Figure 6.23 Integrated pest management.

Figure 6.24 Nutrient management.

Figure 6.25 Terraces.

Figure 6.26 Drop structure.

Figure 6.27 Animal waste treatment lagoon.

Figure 6.28 Filter strip adjacent to Bear Creek.

Figure 6.29 Range and pasture management. (a) Rangeland. (b) Grass drill in ...

Chapter 7

Figure 7.1 Typical lake view.

Figure 7.2 Wind‐induced circulation in lakes. (a) Shallow lake. (b) Deep lak...

Figure 7.3 Suspended solids distribution in water column.

Figure 7.4 Algae mat.

Figure 7.5 Components of total phosphorus.

Figure 7.6 Components of total nitrogen.

Figure 7.7 Secchi disk.

Figure 7.8 Lake stratification cycle.

Figure 7.9 Response of a well‐mixed lake to a constant contaminant inflow. (...

Figure 7.10 Response of a well‐mixed lake to a variable contaminant inflow: ...

Figure 7.11 One‐dimensional conservation of mass in lake.

Figure 7.12 Temperature profile in a stratified lake.

Figure 7.13 Temperature profile in lake.

Figure 7.14 Contaminant discharge into a lake.

Figure 7.15 Pollutant source on the side of a lake.

Figure 7.16 Diffused‐air circulation system. (a) Diffusers. (b) Support equi...

Figure 7.17 Water fountains.

Figure 7.18Lake dredging.

Figure 7.19Grass carp.

Figure 7.20Mechanical harvester.

Figure 7.21 Two reservoirs discharging into a common stream.

Chapter 8

Figure 8.1 Typical marsh.

Figure 8.2 Typical forested swamp.

Figure 8.3 Mangrove swamp. (a) Far view. (b) Near view.

Figure 8.4 Aerial view of a bog wetland.

Figure 8.5 Typical fens.

Figure 8.6 Wetland plants. (a) Marsh grass (

Spartina alterniflora

). (b) Bald...

Figure 8.7 Canada geese.

Figure 8.8 Types of constructed treatment wetlands. (a) Free water surface w...

Figure 8.9 Plant unit in a floating treatment wetland.

Figure 8.10 Constructed surface flow wetland.

Figure 8.11 Constructed subsurface flow wetland.

Figure 8.12 Wetland outlet weir.

Figure 8.13 Flow through a wetland.

Figure 8.14 Flow over a weir.

Figure 8.15 Wetland mixing model.

Figure 8.16 Typical wetland design.

Figure 8.17 Cattails (

Typha

spp.)

Figure 8.18 Fence for wildlife exclusion.

Chapter 9

Figure 9.1 Mawddach estuary, UK.

Source

: Newbould (2005).

Figure 9.2 (a) Discharge port and (b) plume rising in a stratified environme...

Figure 9.3 Wastewater discharge from an ocean outfall diffuser.

Figure 9.4 Installation of a diffuser.

Figure 9.5 Plume in unstratified ocean.

Figure 9.6 Single plume with ambient flow.

Source

: Wright (1977b).

Figure 9.7 Plume in stratified ocean.

Figure 9.8 Plan view of a line plume.

Source

: Philip J.W. Roberts.

Figure 9.9 Line‐plume dilution characteristics.

Source

: Roberts et al. (2010...

Figure 9.10 Diffuser ports.

Source

: Red Valve Co., Inc.

Figure 9.11 Transition from near‐ to far‐field mixing.

Source

: Wood (2005)....

Figure 9.12 Apparent diffusion coefficient versus length scale in coastal wa...

Figure 9.13 Interface between near‐ and far‐field models.

Figure 9.14 Dense discharge.

Figure 9.15 Evaporation characteristics of various oils.

Source

: NRC (2003)....

Figure 9.16 Fingas evaporation models.

Figure 9.17 Comparison of exponential model with typical crude oil model

Figure 9.18 Typical estuary system.

Figure 9.19 Salinity gradient in an estuary.

Figure 9.20 Typical pattern of water movement in an estuary.

Figure 9.21 Cycling of nutrients in an estuary.

Source

: Laws (2000).

Chapter 10

Figure 10.1 Normal probability distribution.

Figure 10.2 Lognormal probability distribution.

Figure 10.3 Uniform probability distribution.

Figure 10.4 Chi‐square probability distribution.

Figure 10.5 Student's

probability distribution.

Figure 10.6

probability distribution.

Figure 10.7 Comparison of sample and lognormal distribution.

Figure 10.8 Semivariogram properties.

Guide

Cover

Table of Contents

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Water‐Quality Engineering in Natural Systems

Fate and Transport Processes in the Water Environment

Third Edition

David A. Chin

This edition first published 2021

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Names: Chin, David A., author.

Title: Water-quality engineering in natural systems : fate and transport

processes in the water environment / David A. Chin.

Description: Third edition. | Hoboken, NJ : Wiley, 2021. | Includes

bibliographical references and index.

Identifiers: LCCN 2020025490 (print) | LCCN 2020025491 (ebook) | ISBN

9781119532026 (hardback) | ISBN 9781119532064 (adobe pdf) | ISBN

9781119532088 (epub)

Subjects: LCSH: Water quality management. | Water quality – Measurement. |

Water – Pollution – Measurement.

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627 – dc23

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Cover Design: Wiley

To Andrew and Stephanie

Trust in the Lord with all your heart and lean not on your own understanding; in all your ways acknowledge him, and he will make your paths straight.

Proverbs 3: 5‐6

PREFACE

This book is primarily intended to be used as a core textbook by undergraduate and graduate students in environmental engineering, and as a technical reference for practicing environmental engineers. The book focuses on water‐quality engineering in natural systems, which is the broadest of the water‐quality specialty areas in environmental engineering, which includes water treatment, wastewater treatment, and water‐quality control in natural systems. In practical applications, water‐quality engineering in natural systems is concerned with protecting humans, aquatic life, and other users of water bodies from the harmful effects of pollutants. In this context, water‐quality engineers and managers must understand the types and characteristics of pollutants discharged into water bodies, the manner in which they affect water‐quality, and the fate and transport of these pollutants within a water body.

Motivation. The need for competent water‐quality engineers is apparent when one realizes that, in the United States, over 50% of natural surface waters do not meet their designated uses and statutory water‐quality standards. In addition, many shallow aquifers are contaminated by anthropogenic contaminants such as nitrates and toxic organic chemicals, primarily pesticides and organic solvents. It is apparent that water‐quality engineering in natural systems is and will be an important practice area for the foreseeable future.

Water‐quality engineering. The practice of water‐quality engineering is significantly influenced by laws and regulations, and it is essential that practitioners be aware of all applicable statutory requirements relating to water‐quality. The phenomenological fundamentals of water‐quality engineering in natural systems are the relationships between contaminant concentrations in the aqueous phase and other phases (solid, vapor), the biochemical reactions of contaminants in the environment, and the flow fields that transport and disperse contaminants in the environment. These fundamental processes are typically represented by fate and transport equations, which include process equations that describe the chemical and biochemical transformation processes in the aqueous environment. Although the generic fate and transport equations can be applied in most natural waters, the physical, chemical, and biological differences between various types of water bodies dictate that these water bodies be considered separately to more closely focus on the dominant processes in particular types of water bodies. For example, nutrient enrichment (eutrophication) is a primary concern in lakes and reservoirs, while toxic substances released from spills or leaking storage facilities is a primary concern in groundwaters. The major categories of natural waters are rivers and streams, lakes and reservoirs, wetlands, groundwater, and oceans and estuaries. Aside from assessing the fate and transport of contaminants purposely discharged into natural waters, remediation of contaminated waters also requires an understanding of fate and transport processes in the water environment.

Water‐quality data analysis. An important aspect of water‐quality engineering is the analysis of water‐quality and related data that are used to assess the state of a water body. Water‐quality data are samples of stochastic variables, and therefore these data must be analyzed using appropriate probabilistic and statistical methods in order to properly evaluate the state of a water body relative to benchmark conditions, such as water‐quality standards or permit requirements. The appropriate analytical techniques must generally be tailored to specific conditions, such as limited amounts of data, and the types of questions that are posed, such as the likelihood of exceeding a standard or the identification of any trends in the data.

Water‐quality modeling. In water environments that cannot be adequately described by simple analytical models, numerical water‐quality models are sometimes used to simulate the fate and transport of contaminants. In developing and using these models, a basic understanding of calibration, validation, and estimation of predictive uncertainty are essential for the proper use of these models and the interpretation of model results.

Contents of this book. The book begins with an introduction to the principles of water‐quality control, and is followed in Chapter 2 by an exposition of the various measures of water‐quality, including physical, chemical, and biological measures. Chapter 3 covers the mathematical formulation of fate and transport processes in aquatic systems. The generic fate and transport equation (FTE) is derived from first principles, and the fundamental solutions of the FTE for a variety of boundary and initial conditions are presented. The FTE is applicable to all natural waters, with the principal differences being the relative importance and nature of the fate and transport processes represented in the FTE. Chapter 4 covers fate and transport processes in rivers and streams, including the dispersion of contaminants originating from instantaneous spills and continuous discharges, the fate of volatile organic compounds, the depletion of dissolved oxygen resulting from the discharge and accumulation of biodegradable organics, and the determination of allowable loadings of various contaminants in impaired streams. Chapter 5 covers water‐quality‐related processes in groundwater, including the natural quality of groundwater, quantification of sources of groundwater contamination, advection, dispersion, sorption onto aquifer materials, biochemical decay, and the fate and transport of nonaqueous phase liquids in groundwater. Detailed coverage is provided on the application of fate and transport principles to the remediation of contaminated groundwater. Chapter 6 covers water‐quality‐based watershed management, where the primary focus is on estimating the contaminant loading on receiving waters from activities within the watershed. Detailed attention is given to sources of pollution and fate and transport processes associated with urban and agricultural watersheds. Chapter 7 describes water‐quality processes in lakes and reservoirs, with particular emphasis on quantitative relationships describing flow and dispersion, sedimentation, eutrophication, nutrient recycling, and thermal stratification. Techniques to control eutrophication, dissolved oxygen levels, toxic contaminants, acidity, and aquatic plants are all covered. Chapter 8 describes the occurrence, function, and hydrology of wetlands; the delineation of jurisdictional wetlands; and the design, construction, and operation of constructed wetlands. Particular attention is given to factors controlling the contaminant removal efficiencies in constructed wetlands. Chapter 9 covers water‐quality processes in oceans and estuaries, with particular attention to the design and operation of domestic wastewater outfalls, the fate and transport of oil and chemical spills, and water‐quality control in estuaries as they relate to the physical, chemical, and biological conditions in an estuary. Analysis of water‐quality data is covered in Chapter 10, which includes a concise review of the relevant basics of probability and statistics, and an exposition of statistical methods commonly used in analyzing water‐quality data. The fundamentals of numerical modeling are covered in Chapter 11, with particular emphasis on calibration, validation, and estimation of predictive uncertainty when using numerical models.

Target audience. The material covered in this book is most appropriate for seniors and graduate students in environmental and civil engineering programs. Practicing environmental engineers and others with backgrounds in environmental science, will also find the contents of this book comprehensible and useful.

About the Companion Website. This book is accompanied by a companion website www.wiley.com/go/chin/waterquality3e

The website features: Solution Manual

Final comments. The fate and transport of anthropogenic contaminants introduced into natural waters must be understood and manipulated to minimize the negative impacts of contaminant discharges into these waters. By controlling contaminant discharges into the water environment, the effects of human activities on human and aquatic ecosystems that depend on natural waters can be controlled and/or predicted. For contaminated waters, the design of effective remediation measures is based on these same principles, with additional technological considerations relating to the efficacy of various remediation systems. The essential background for all these practices is contained in this book.

David A. Chin

Professor of Civil and Environmental Engineering

University of Miami

1INTRODUCTION

1.1 BACKGROUND

Natural waters can be broadly grouped into surface waters, groundwaters, and ocean waters, with each having their unique characteristics and dynamics, and yet all are connected. Water above land surface (in liquid form) is called surface water, and water below land surface is called groundwater. Although surface water and groundwater are directly connected, these waters are typically considered as separate water bodies and are usually managed under different rules and regulations. Surface waters and groundwaters are sources of drinking water for humans and, along with ocean waters, are habitats for aquatic life. However, these waters are also depositories of discharges of human and industrial wastes. As a consequence, the relationship between waste discharges into natural waters and the resulting quality of these receiving waters is at the core of water‐quality management.

Scientific and engineering foundations

Hydrology, chemistry, biology, and ecology are the scientific foundations of water‐quality management. Hydrology is concerned with the occurrence and movement of water, chemistry is concerned with the properties of matter and their reactions, biology is concerned with the structure and function of living organisms, and ecology is concerned with interactions between living things and their nonliving (abiotic) environment or habitat. The discipline of ecohydrology covers the intersection of ecology and hydrology; however, ecohydrology is sometimes more narrowly understood to mean the interaction of plants and water. Civil and environmental engineering are the professional disciplines that are commonly associated with designing systems for water‐quality control, with particular concerns regarding the interrelationship between surface water, groundwater, chemical pollutants, nonchemical stressors, water‐quantity, and land management.

Anthropogenic impacts

Changing land uses, the addition of new pollutant sources, the establishment of new hydrologic connections, and modification of natural connectivity in landscapes can have significant ecosystem impacts. For example, the modification of free‐flowing rivers for energy or water supply and the drainage of wetlands can have a variety of deleterious effects on aquatic ecosystems, including losses in species diversity, floodplain fertility, and biofiltration capability. Specific environmental issues that are of global concern include regional declines in the numbers of migratory birds and wildlife caused by wetland drainage, bioaccumulation of methylmercury in fish and wildlife in newly created reservoirs, and deterioration of estuarine and coastal ecosystems that receive the discharge of highly regulated silicon‐depleted and nutrient‐rich rivers.

Figure 1.1 River with floating trash.

Watersheds and airsheds

A key feature of any surface water body is its watershed, which is delineated by topographic high points surrounding the water body. Surface water bodies are the potential recipients of all contamination contained in surface runoff from all locations within the watershed. In the case of rivers, the contributing watershed area increases as one moves downstream. Since most river pollutants originate from terrestrial sources, surface waters are best managed at the watershed scale. This is the watershed approach to water‐quality management. The main limitations to implementing the watershed approach are rooted in our inability to quantify most of the watershed‐scale contaminant‐transport processes that are fundamental to implementing watershed controls. Contaminant inputs into surface waters from the atmosphere are also considered in water‐quality management plans, and in these cases, the contributing region is called the airshed. In contrast to surface waters, the quality of groundwater is influenced primarily by activities on and below the ground surface, and the potential sources of groundwater contamination are influenced by overlying land uses and subsurface geology. The concept of a watershed is not applicable to groundwater; however, the management of land overlying groundwater that serves as a source of drinking water for humans and animals is an essential endeavor.

Recognizing polluted waters

In many cases, identification of polluted water bodies is obvious to the casual observer, such as a stream with floating trash as shown in Figure 1.1. However, some polluted water bodies are not so obvious, such as an apparently pristine lake that is so contaminated with acid rain that the existence of aquatic life is extremely limited.

1.2 SOURCES OF WATER POLLUTION

Sources of water pollution can be broadly grouped into point sources and nonpoint sources. Point sources are localized discharges of contaminants that include industrial and municipal wastewater outfalls, septic tank discharges, and hazardous waste spills. Nonpoint sources of pollution include contaminant sources that are distributed over large areas or are a composite of many point sources. Nonpoint sources include runoff from agricultural operations, fallout from the atmosphere, and urban runoff. Surface runoff that collects in storm sewers and is discharged through a pipe into a receiving water is still considered nonpoint source pollution, since it originates as diffuse runoff from the land surface. Pollution loads from nonpoint sources are sometimes called diffuse loads. Much of the pollution in waterways is caused by nonpoint source pollution, as opposed to point source pollution. Although most pollutant sources can be classified as point or nonpoint sources, other less common classifications of pollution sources have also been identified, such as mobile pollution, which is primarily associated with the marine environment and in particular is associated with such ship‐ and boat‐related sources, such as bilge water, ballast water, and marine accidents.

Wet weather discharges

Wet weather discharges refer to discharges that result from precipitation events, such as rainfall and snowmelt. Wet weather discharges include stormwater runoff, combined sewer overflows (CSOs), and wet weather sanitary sewer overflows (SSOs). Stormwater runoff collects pollutants such as oil and grease, nutrients, metals, bacteria, and other toxic substances as it travels across land. CSOs and wet weather SSOs contain a mixture of raw sewage, industrial wastewater, and stormwater, and can result in beach closings, shellfish bed closings, and aesthetic problems.

Figure 1.2 Point source of pollution. Source: South Florida Water Management District.

1.2.1 Point Sources

The identifying characteristic of point sources is that they discharge pollutants into receiving waters at identifiable single‐ or multiple‐point locations. A typical point source of contamination is shown in Figure 1.2, where wastewater is being pumped directly into a drainage channel. In most countries, these (point) sources are regulated, and a permit is required to operate waste-discharge systems. Point sources of contamination that are of concern in managing surface waters include domestic wastewater discharges and industrial discharges.

1.2.1.1 Domestic Wastewater Discharges

Most domestic wastewater treatment plants discharge their effluent into rivers, lakes, or oceans. For river discharges of treated domestic wastewater, the effect on the dissolved oxygen, pathogen, and nutrient concentrations in the river is usually of most concern. Decreased oxygen concentrations in rivers can cause harm to the aquatic life, pathogens can cause illness in humans, and increased nutrient concentrations stimulate the growth of algae, which consume oxygen (during nighttime and in the decay process) and make the water undesirable for recreational use and as a source of drinking water. For ocean discharges of treated domestic wastewater, pathogen and heavy metal concentrations are usually of most concern. In particular, pathogenic microorganisms discharged into the ocean can infect humans who come in contact with the ocean water in recreational areas, such as beaches. Domestic wastewater discharged below ground from septic tanks contains large numbers of pathogenic microorganisms, with viruses of particular concern because of their ability to move considerable distances in groundwater.

1.2.1.2 Sanitary Sewer Overflows

Properly designed, operated, and maintained sanitary sewer systems collect and transport domestic sewage to publicly owned treatment works (POTWs). However, occasional unintentional discharges of raw sewage from municipal sanitary sewers occur in almost every system. These types of discharges, collectively called SSOs, have a variety of causes, including but not limited to extreme weather, improper system operation and maintenance, and vandalism. The untreated sewage from SSOs can contaminate receiving waters and cause serious water‐quality problems.

1.2.1.3 Combined Sewer Overflows

Combined sewer systems are designed to transport rainwater runoff, domestic sewage, and industrial wastewater in the same pipe. Most of the time, combined sewer systems transport all of their wastewater to a sewage treatment plant, where it is treated and safely discharged to a receiving water body. During periods of heavy rainfall or snowmelt, the wastewater volume in a combined sewer system can exceed the capacity of the sewer system or treatment plant. For this reason, combined sewer systems are designed to overflow occasionally and sometimes discharge excess wastewater directly to nearby streams, rivers, or other water bodies. These overflows, called CSOs, contain not only stormwater but also untreated human and industrial waste, toxic materials, and debris.

Figure 1.3 Stormwater outlets into drainageway.

1.2.1.4 Stormwater Discharges

Stormwater discharges are generated by runoff from both pervious and impervious areas. Pervious areas include lawns, and impervious areas include paved streets, parking lots, and building rooftops. Stormwater runoff often contains pollutants in quantities that can adversely affect the quality of the receiving water. A typical stormwater outlet into a drainageway (that leads to a receiving water) is shown in Figure 1.3. The stormwater outlet discharges runoff from the heavily traveled highway shown in the background. Although stormwater runoff is commonly discharged through a single outfall pipe, such discharges are more accurately classified as nonpoint pollutant sources, since they collect and transport contaminants from an entire catchment area.

1.2.1.5 Industrial Discharges

There is a wide variety in the types of industrial wastewaters, and elevated concentrations of nutrients, heavy metals, heat, and toxic organic chemicals are common in industrial wastewaters. Some industries provide pretreatment prior to discharging their wastewaters directly either into surface waters or into municipal sewer systems. In many countries outside the United States, industries are permitted to discharge their wastewater without adequate pretreatment, and the resulting human and environmental impacts are usually noticeable.

1.2.1.6 Spills

Spills and accidental or intentional releases can occur in a variety of ways. Transportation accidents on highways and rail freight lines can result in major chemical spills, and accidental releases at petroleum‐product storage installations are another common source of accidental spills. Leaks and spills from underground storage tanks into the groundwater are of special concern because these releases may remain undetected for long periods of time.

1.2.2 Nonpoint Sources

Nonpoint sources of contamination generally occur over large areas and, because of their diffuse nature, are more difficult to control than point sources. Nonpoint source pollution is a direct result of land use patterns and runoff controls, so many of the remedies to pollution by nonpoint sources lie in finding more effective ways to manage land and stormwater runoff. Much nonpoint source pollution occurs during rainstorms and snowmelts, resulting in sporadic large flow rates that make treatment even more difficult. Nonpoint sources of contamination that must generally be considered in managing water bodies include agricultural runoff and urban runoff; these are typically the primary sources of surface water pollution. Groundwater contamination originating from septic tanks, leaking underground storage tanks, and waste injection wells is quite common, and is of particular concern when groundwater is the source of domestic drinking water.

TABLE 1.1 Strengths of Various Point and Nonpoint Sources

Source

BOD

(mg/L)

Total Suspended Solids (mg/L)

Total Nitrogen (mg/L)

Total Phosphorus (mg/L)

Total Coliforms (MPN/dL)

Urban stormwater

10–250 (30)

3000–11,000 (650)

3–10

0.2–1.7 (0.6)

–10

Construction‐site runoff

10,000–40,000

Combined‐sewer overflows

60–200

100–1100

3–24

1–11

–10

Light industrial area

8–12

45–375

0.2–1.1

Roof runoff

3–8

12–216

0.5–4

Typical untreated sewage

190–500

210–300

40–50

7–16

–10

Typical POTW

effluent

(20)

(30)

(10)

–10

aNumber in brackets indicates mean.

bNA means not available or unreliable.

cPOTW means publicly owned treatment works with secondary (biological) treatment.

Strengths of pollutant sources

The strengths of various sources of water pollution are shown in Table 1.1. It is apparent from these data that pollutants at high concentrations can enter water bodies from a variety of sources, and control of these sources is central to effective water‐quality management.

1.2.2.1 Agricultural Runoff

Applications of pesticides, herbicides, and fertilizers are agricultural practices that influence the quality of surface and groundwaters that receive runoff or infiltration from these areas. The application of fertilizers is of major concern because dissolved nutrients in surface runoff can accelerate the growth of algae and the depletion of oxygen in surface waters. Nitrogen, in the form of nitrates, is a contaminant commonly found in groundwater underlying agricultural areas, and can be harmful to humans, particularly infants. Erosion caused by improper tilling techniques is another agricultural activity that can adversely affect water‐quality through increased sediment load, color, and turbidity.

1.2.2.2 Livestock

Feedlots have been shown to contribute nitrates to groundwater and pathogenic microorganisms to surface waters. Overgrazing eliminates the vegetative cover that prevents erosion, increasing the sediment loading on surface waters. In some extreme cases, livestock are allowed to wade in and cause direct contamination of streams, and such a circumstance is shown in Figure 1.4. This practice should be avoided as much as possible.

1.2.2.3 Urban Runoff

Figure 1.4 Livestock in a stream. Source: State of Arkansas (2005).

Figure 1.5 Directly connected impervious area.

Urban runoff contains contaminants that are washed from the land surface and carried to surface water bodies. Contaminants contained in urban runoff include petroleum products, heavy metals such as cadmium and lead from automobiles, and silt and sediment from land erosion. Bacterial contamination from human and animal sources is also often present. The initial “flushing” of contaminants during rainfall events typically creates an initial peak in contaminant concentration in the surface runoff, with diminishing concentration as pollutants are washed away.

Role of Impervious Area

A major factor associated with the impairment of receiving waters is the amount of impervious area that is directly connected to urban stormwater collection systems. An example of directly connected impervious area is shown in Figure 1.5, where the impervious area in the foreground also surrounds the stormwater inlet, and so runoff from the impervious area flows directly into the inlet, without flowing over any pervious area that might provide some pollutant attenuation. Stormwater inlets, such as the one shown in Figure 1.5, typically discharge collected stormwater directly into a receiving stream or other drainage pathway. A typical rule of thumb is that receiving‐stream degradation can occur when the contributing watershed is more than 10% impervious, and degradation is unavoidable when the contributing watershed is more than 30% impervious. It has also been reported that impacts on flows in receiving streams begin to become noticeable when the imperviousness of the contributing watershed exceeds 10% (Oudin et al., 2018).

1.2.2.4 Landfills

Leachate from landfills can be a source of contamination, particularly for groundwater. Water percolating through a landfill (leachate) contains many toxic constituents, and is typically controlled by capping the landfill with a low‐permeability cover and installing a low‐permeability lining and a leachate collection system underneath the landfill. Many older landfills do not have underlying low‐permeability linings or leachate collection systems, and these older landfills remain as continuous sources of groundwater pollution.

1.2.2.5 Recreational Activities

Recreational activities, such as swimming, boating, and camping, can have a significant impact on water‐quality. The impact of human activities has typically been reported in terms of increased levels of pathogenic microorganisms.

1.3 CONTROL OF WATER POLLUTION

Polluted water is defined as water that does not meet the water‐quality criteria or standards associated with its use. Control of water pollution ultimately requires that the level of pollutants introduced from point and nonpoint sources be controlled such that the receiving waters are able to meet their applicable water‐quality criteria or standards. Pollutants of concern vary depending on the type of water body, its designated use, and local circumstances. For rivers and streams, the most common water‐quality problems are high pathogen concentrations, siltation, habitat alteration, oxygen depletion caused by excessive levels of biodegradable organics or nutrients, and heavy metals that have the potential to bioaccumulate in fish and other aquatic life. In lakes and reservoirs, low oxygen levels exacerbated by high nutrient levels are the most common water‐quality problem. In groundwater, contamination by carcinogenic organic substances originating from aboveground spills and poor handling practices of hazardous substances, as well as pathogenic viruses originating from septic tanks, are common water‐quality problems.

Differences between types of water bodies

The types of water‐quality concerns expected in any particular situation usually depend on the type of water body, since the dominant fate and transport processes can vary substantially between types of water bodies. For example, rivers are fast moving and most commonly the recipients of uncontrolled surface runoff and wastewater discharges; lakes are slow moving, deep, and prone to retaining nutrients and other anthropogenic contaminants; and groundwater is typically a pristine, slow‐moving, and direct source of drinking water that is prone to contamination from surface spills of hazardous substances that interact with the subsurface solid matrix in unique ways. Given these differences between the dominant fate and transport of pollutants in different types of water bodies, the approach to pollution control is significantly influenced by the type of water body. As a consequence, the dominant fate and transport processes in rivers, groundwater, lakes and reservoirs, and ocean waters are covered separately in different chapters of this book.

Control of contaminant sources

Point sources are most easily controlled since they have identifiable discharge locations. The quality of these discharges can usually be monitored, and appropriate treatment can be performed prior to discharge. In contrast to point sources, nonpoint sources are not easily identifiable, and the discharges from these sources cannot be easily monitored. As a consequence, control of nonpoint sources of pollution is usually accomplished by instituting best management practices at the watershed level. Ideally, watershed‐scale fate and transport models can be used to simulate the movement and attenuation of pollutants from their terrestrial source to the receiving water body, and such modeling can be helpful in establishing the link between watershed controls and water‐quality in the receiving water body.

Remediation of polluted water bodies

Once a water body is polluted, then there is the added dimension of remediation. The design of an effective remediation scheme requires a fundamental understanding of the fate and transport of pollutants in the water body, and an understanding of how the pollutant will respond to various remediation approaches. Any effective remediation approach must be accompanied by pollutant source controls that are consistent with the water‐quality requirements being met.

Contribution of this book

This book presents the tools and concepts required for water‐quality control in natural waters. These include an understanding of water‐quality criteria, the fundamentals of fate and transport in natural waters, the design of water‐quality control systems, and the design of remediation systems.

2WATER QUALITY

2.1 INTRODUCTION

The acceptable water quality for a natural water body generally depends on its present and future most beneficial use. Commonly designated beneficial uses include public water supply, recreational use, fisheries and shellfish production, agricultural and industrial water supply, aquatic life, and navigation. Each of these designated uses has its own set of water‐quality criteria, which includes the physical, chemical, and biological attributes that are consistent with the designated use of the water body. Water‐quality criteria generally take into consideration both human health and aquatic life impacts. Human health‐based water‐quality criteria are derived from assumptions related to the degree of human contact, quantity of water ingested during human contact, and the amount of aquatic organisms (e.g., fish) consumed that are derived from the water body. Aquatic life water‐quality criteria are derived from mortality studies of selected organisms exposed to various levels of contamination in the water, as well as other factors that measure the health of aquatic ecosystems. Overall, water‐quality criteria are formulated to maintain the physical, chemical, and biological integrity of a water body, with alterations in the physical and/or chemical condition generally resulting in changes in biological condition.

Water‐quality criteria versus water‐quality standards

Water‐quality criteria are desirable water‐quality characteristics, while water‐quality standards are legally required water‐quality characteristics. By definition, water‐quality criteria are not legally binding or enforceable; however, when they are included as regulatory requirements, they are typically referred to as water‐quality standards. The quality of natural waters should generally be measured relative to either the water‐quality criteria or the water‐quality standards associated with their designated use.

2.2 PHYSICAL MEASURES

Physical measures that directly affect the quality of aquatic life habitat include flow conditions, substrate, in‐stream habitat, riparian habitat, and thermal condition. These measures are described below.

Figure 2.1 Longitudinal profile of a pool/riffle system in a piedmont stream.

Figure 2.2 Typical (a) pool and (b) riffle.

Source: Organization for the Assabet River. Photo by Suzanne Flint.

2.2.1 Flow Conditions

Slope and velocity divide streams into four categories: (1) mountain streams, (2) piedmont streams, (3) valley streams, and (4) plains and coastal streams. Mountain streams, which are sometimes called trout streams, have steep gradients and rapid currents and streambeds consisting of rock, boulders, and sometimes sand and gravel and are well aerated and cool, with temperatures rarely exceeding 20C (68F). Piedmont streams are larger than mountain streams, with depths up to 2 m (6 ft); have rapid currents with alternating riffles (shallow, fast‐moving waters) and pools (deep slow‐moving waters); and streambeds typically consist of gravel. The longitudinal profile of a pool/riffle system is shown in Figure 2.1, and a typical pool and riffle in Elizabeth Brook (Massachusetts) are shown in Figure 2.2. Valley streams have moderate gradient and current with alternating rapids and more extensive quiet waters than in piedmont streams. Plains and coastal streams are typically the lower elevation stretches of rivers and canals, have low currents, high temperatures and low dissolved oxygen (DO) in the summer, and are typically turbid.

Pool/riffle ratio and bend/run ratio

The pool/riffle ratio or bend/run ratio

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