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Preface
Basic Environmental Technology offers a practical introduction to the topics of municipal water supply, waste management, and pollution control. The book is designed primarily for students in civil/construction technology programs and related disciplines in community colleges and technical institutes. It can also be useful in baccalaureate engineering and technology programs when a broad but elementary course of study is desired, or for independent learning by individuals who want to explore the rudiments of environmental quality control and public health protection. Experienced technicians, engineers, scientists, and others in different disciplines who may become involved in environmental work for the first time will also find this book of value as an initial reference.
The qualities that continue to distinguish this book in its sixth edition are its clear, easy-to-read style and its logical and systematic treatment of the subject. Because the field of environmental technology is multidisciplinary and extensive in scope, review or primer sections are included so readers with little or no experience in biology, chemistry, geology, and hydraulics can comprehend and use the book. Mathematical topics are presented at a relatively basic level; to understand the numerical examples in the book, some knowledge of algebra and geometry will be useful.
Example problems, diagrams, and photographs are used throughout to illustrate and clarify important topics. Numerous review questions and practice problems follow each chapter; answers to the practice problems are presented in Appendix F. Both SI metric and U.S. Customary units are used because students and practitioners in the United States must be familiar with these two systems. Online Instructor’s Resources are available that include downloadable resources for lecture, modified classroom, and distance education. Chapter 1 provides an overview of environmental technology, including elements of public health, ecology, geology, and soils. The next nine chapters, that is, Chapters 2 to 10, focus on water and wastewater topics, including hydraulics and hydrology, water quality and water pollution, drinking
water treatment and distribution, sewage collection, sewage treatment and disposal, and stormwater management. Municipal solid waste, hazardous waste, air pollution, and noise pollution are covered in Chapters 11 through 14. Finally, appendixes regarding environmental impact statements and audits; the education and employment of technicians, technologists, and engineers; green building project certification; basic mathematics; units and conversions; and an extensive glossary are included.
There is more than ample material in this book for a typical one-semester course. Chapters 1 through 10 should suffice for introductory courses that focus mostly on water and wastewater topics. In courses where air quality, solid and hazardous waste, and noise pollution are also part of the syllabus, the instructor may find it necessary to be selective in coverage of topics from the first 10 chapters to allow time for discussion and study of the last four chapters. In such circumstances, less time could be spent on the quantitative parts of the text (e.g., hydraulics) and more time spent on the descriptive and qualitative aspects of environmental technology. Another option is to focus lectures on the first 10 chapters for most of the semester, and allow students to select topics of special interest from the last 4 chapters for a term paper and/or oral presentation to the whole class. In this way, students get some exposure to those topics, as well as practice in communication skills.
The original sequence of the chapters remains the same as in previous editions (although some instructors have suggested changes in this regard). It is not possible, however, to satisfy the different preferences of all instructors. Naturally, a course syllabus can readily designate a sequence of reading assignments that will meet particular course needs. In fact, one of the purposes of the extensive glossary in Appendix E is to provide brief definitions of terms that students may need to know and encounter for the first time, particularly if they read the chapters in a different sequence than that presented in the book.
This introductory textbook addresses a wide range of environmental topics, each of which is covered in greater
depth and detail in other, more narrowly specialized and advanced texts. They are presented here in a form and at a level that is more readily accessible to students and others who are studying the subject for the first time. In writing and revising the book over six editions, decisions had to be made to include or exclude certain facts, details, examples, and illustrations, and some compromises were inevitable. Every effort has been made to maintain a balance between thoroughness and practicality in covering the material to ensure that the book will continue to be a user-friendly and useful learning tool for all readers.
An important factor in deciding what to include is the prescribed limit to the total size of the book, and we have necessarily resisted the temptation (and requests by some instructors) to add even more topics and details. From our experience, a good textbook is one that provides a broad, solid foundation on which experienced instructors can (and should) build and provide additional information and explication to satisfy the needs of their students. We hope this updated textbook provides that basic foundation for student learning, and that it helps motivate and prepare readers to study environmental technology or engineering at a more advanced level.
A plethora of information related to environmental topics is, of course, now available on the World Wide Web. There is so much information and so many links among the profusion of Web pages that it is easy for beginners to be quickly overwhelmed. It is best to start exploring environmental topics on the Web gradually, after using a textbook such as this, in which the information is organized and presented so that students can understand the underlying concepts before delving online into the details of specific environmental technology subjects.
As the topics in this book are studied and mastered, students will be much better prepared to mine the wealth of environmental information in cyberspace. Lists of relevant website URLs are intentionally not presented because they are so numerous and, in many cases, transitory. Users of this book can, at their convenience, quickly search the World Wide Web for more specific online information using appropriate keywords and topic headings.
New to the sixth editioN
● Discussions related to environmental sustainability, integrated water management, low impact development, and green building design are included throughout the relevant sections of the text.
● A section on water resources augmentation using advanced wastewater treatment and recycling, including expanded description of membrane filtration technology for advanced water purification.
● Discussions of new topics, including dual water systems, new pipeline materials, environmental impacts of hydraulic fracturing (fracking), constructed wetlands, single stream municipal solid waste recycling, and plasma gasification of solid and hazardous waste.
● Updated water and air quality standards and regulations, including the recent acknowledgment by the EPA that carbon dioxide is an air pollutant that can harm public health and welfare by causing global warming and climate change.
● Expanded glossary and list of acronyms; expanded discussion of environmental education, certification, and employment; new section introducing LEED green building project certification.
● Expanded online Instructor’s Resources materials, including worked-out solutions to all practice problems and text-page references for answers to review questions; supplemental problems, 100 + multiple-choice test questions (and answers), and additional test problems and student project assignments; photos; descriptions of selected URLs of environmental websites for each chapter; suggested references and video materials; and so on.
supplemeNts
To access supplementary materials online, instructors need to request an instructor access code. Go to www.pearsonhighered .com/irc to register for an instructor access code. Within 48 hours of registering, you will receive a confirming e-mail including an instructor access code. Once you have received your code, locate your text in the online catalog and click on the Instructor Resources button on the left side of the catalog product page. Select a supplement, and a login page will appear. Once you have logged in, you can access instructor material for all Pearson textbooks. If you have any difficulties accessing the site or downloading a supplement, please contact Customer Service at http://247pearsoned.custhelp.com/.
AckNowledgmeNts
The helpful comments, suggestions, and contributions from the many people (too numerous to list here) who used and reviewed the book as it developed over the first five editions are gratefully acknowledged. We would also like to thank Kenneth R. Leitch, PhD, PE, West Texas A&M University; Dr. Brian Matthews, NC State University, Raleigh, NC; and Tom Spendlove, Baker College of Flint, who took the time to review the previous edition of this book and offer useful suggestions. And last, but certainly not least, we thank the exemplary editorial, design, production, and marketing team who, at Pearson Education, continue to make this book a reality.
We have made every attempt to keep errors and inaccuracies in this textbook to a minimum. Nevertheless, we remain fully responsible for any mistakes that may be found herein, and welcome constructive comments and suggestions for the book’s improvement from those who use it.
Jerry A. Nathanson, MS, PE Union County College Cranford, New Jersey
Richard Schneider, MS, PE Madison Area Technical College Madison, Wisconsin
c on T en TS
BaSic concePTS 1
1-1 overview of environmental Technology 2
1-2 Public Health 5
1-3 ecology 8
1-4 geology and Soils 15
1-5 Historical Perspective 18
1-6 chapter Synopsis 21 review Questions 22 c hapter 2
HydraUlicS 24
2-1 Pressure 24
2-2 flow 29
2-3 flow in Pipes under Pressure 32
2-4 gravity flow in Pipes 36
2-5 nonuniform open channel flow 42
2-6 computer applications in Hydraulics 46
2-7 chapter Synopsis 46 review Questions 47 Practice Problems 48
Practice Problems 105 c hapter 1
c hapter 3
Hydrology 50
3-1 Water Use and availability 50
3-2 The Hydrologic cycle 52
3-3 rainfall 53
3-4 Surface Water 59
3-5 droughts 64
3-6 reservoirs 65
3-7 groundwater 69
3-8 chapter Synopsis 72 review Questions 73 Practice Problems 74 c hapter 4
WaTer QUaliTy 76
4-1 fundamental concepts in chemistry 77
4-2 Physical Parameters of Water Quality 86
4-3 chemical Parameters of Water Quality 88
4-4 Biological Parameters of Water Quality 95
4-5 Water Sampling 101
4-6 chapter Synopsis 102 review Questions 103
c hapter 5
WaTer PollUTion 106
5-1 classification of Water Pollutants 106
5-2 Thermal Pollution 108
5-3 Soil erosion and Sediment control 109
5-4 Stream Pollution 110
5-5 lake Pollution 114
5-6 groundwater Pollution 117
5-7 ocean Pollution 121
5-8 Water Quality Standards 124
5-9 chapter Synopsis 126 review Questions 128 Practice Problems 128
c hapter 6
drinking WaTer PUrificaTion 129
6-1 Safe drinking Water act 130
6-2 Sedimentation 136
6-3 coagulation and flocculation 140
6-4 filtration 141
6-5 disinfection 145
6-6 other Treatment Processes 149
6-7 chapter Synopsis 154 review Questions 155 Practice Problems 155
c hapter 7
WaTer diSTriBUTion SySTemS 157
7-1 design factors 158
7-2 Water mains 161
7-3 centrifugal Pumps 167
7-4 distribution Storage 175
7-5 flow in Pipe networks 179
7-6 computer applications 182
7-7 chapter Synopsis 184 review Questions 186 Practice Problems 187 c hapter 8
SaniTary SeWer SySTemS 189
8-1 Sanitary Sewer design 190
8-2 Sewage lift Stations 199
8-3 Sewer construction 201
8-4 infiltration and inflow 207
8-5 Sewer rehabilitation 208
8-6 alternative Wastewater collection Systems 211
8-7 computer applications and giS 213
8-8 chapter Synopsis 213 review Questions 215 Practice Problems 215 c hapter 9
STormWaTer managemenT 217
9-1 estimating Storm runoff 218
9-2 Storm Sewer Systems 225
9-3 Stormwater mitigation Techniques 229
9-4 floodplains 236
9-5 control of combined Sewer overflow 238
9-6 computer applications 241
9-7 chapter Synopsis 242 review Questions 243 Practice Problems 243 c hapter 10
WaSTeWaTer TreaTmenT and diSPoSal 245
10-1 legislation and Standards 246
10-2 Primary Treatment 248
10-3 Secondary Treatment 249
10-4 Tertiary Treatment 260
10-5 on-Site Wastewater Treatment and disposal 267
10-6 Sludge (Biosolids) management 278
10-7 operation and maintenance 285
10-8 chapter Synopsis 287 review Questions 288 Practice Problems 289
c hapter 11
mUniciPal Solid WaSTe 291
11-1 Historical Background 292
11-2 Solid Waste characteristics 292
11-3 Solid Waste collection 295
11-4 Solid Waste Processing 297
11-5 recycling 304
11-6 Sanitary landfills 309
11-7 chapter Synopsis 316 review Questions 317 Practice Problems 318
c hapter 12
HazardoUS WaSTe managemenT 319
12-1 characteristics and Quantities 321
12-2 Transportation of Hazardous Waste 323
12-3 Treatment, Storage, and disposal 325
12-4 Site remediation 331
12-5 Hazardous Waste minimization 341
12-6 chapter Synopsis 342 review Questions 343
air PollUTion and conTrol 345
13-1 Historical Background 345
13-2 atmospheric factors 346
13-3 Types, Sources, and effects 350
13-4 global air Pollution 355
13-5 indoor air Quality 362
13-6 air Sampling and measurement 367
13-7 air Pollution control 373
13-8 chapter Synopsis 385 review Questions 387
Practice Problems 388 c hapter 14
noiSe PollUTion and conTrol 389
14-1 Basic Physics of Sound 389
14-2 measurement of noise 391
14-3 effects of noise 396
14-4 noise mitigation 397
14-5 chapter Synopsis 401 review Questions 402 Practice Problems 403
aPPendixeS 404
a environmental impact Studies and audits 404
B education, employment, licensing, and certification 408
c leed green Building Project certification Process 413
d review of Basic mathematics, Units, and Unit conversions 414
e glossary and abbreviations 423
f answers to Practice Problems 437 index 438
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BASIC CONCEPTS
Chapter Outline
1-1 Overview of Environmental Technology
Water Supply
Sewage Disposal and Water Pollution Control
Stormwater Management
Solid and Hazardous Waste Management
Air and Noise Pollution Control
Other Environmental Factors
Development of a Master-Planned Community
Environmental Interrelationships
1-2 Public Health
Communicable Diseases
Noninfectious Diseases
1-3 Ecology
Food Chains and Metabolism
Aerobic and Anaerobic Decomposition
Environmental technology primarily involves the application of engineering principles to the planning, design, construction, and operation of the following systems:
● Drinking water treatment and distribution
● Sewage treatment and water pollution control
● Stormwater drainage and runoff control
● Solid and hazardous waste management
● Air and noise pollution control
● General community sanitation
The structures and facilities that serve these functions, including pipelines, pumping stations, treatment plants, and waste disposal sites, make up a major portion of society’s infrastructure—the public and private works that allow human communities to thrive and function productively.
The practice of environmental technology encompasses two fundamental objectives:
1. Public health protection to help prevent the transmission of diseases among humans.
2. Environmental health protection to preserve the quality of our natural surroundings, including air, land, and water.
Biogeochemical Cycles
Stability, Diversity, and Succession
Biological Monitoring in Lakes and Streams
Biological Magnification
Endangered Species Act
1-4 Geology and Soils
Types of Rock
Types of Soil
Soil Survey Maps
1-5 Historical Perspective
An Era of Environmental Awareness
Environmental Regulations
Green Engineering and Environmental Sustainability
1-6 Chapter Synopsis
Actually, there is considerable overlap of these two objectives because of the relationship between the quality of environmental conditions and the health and well-being of people. In fact, the terms “public health” and “environmental health” are often used synonymously.
Public health includes more than just the absence of illness. It is a condition of physical, mental, and social wellbeing and comfort. The cleanliness and esthetic quality of our surroundings—the atmosphere, rivers, lakes, forests, and meadows, as well as towns and cities—have a direct impact on this condition of human well-being and comfort, and sanitation, that is, the promotion of cleanliness, is a basic necessity in the effort to protect public and environmental health.
Environmental engineering technology is part of the broader field of civil engineering. It has had a variety of names, including sanitary engineering, public health engineering, pollution control engineering, and environmental health engineering. The phrase “green engineering” is also used now (in a broader sense), referring to design, construction, and manufacturing activities that focus on environmental sustainability and on energy and natural resource conservation. Low impact (land) development and green
building design are also part of the modern-day civil and environmental engineering lexicon.
Environmental technology is an interdisciplinary field because it encompasses several different technical subjects. In addition to such traditional civil engineering topics as hydraulics and hydrology, these include biology, ecology, geology, chemistry, and others. This variety makes the field interesting and challenging. Fortunately, it is not necessary to be an expert in all these subjects to understand and apply the basic principles of environmental technology. This particular text has been designed so that a student with little academic background in some or all of the supporting subjects can still use it productively.
This chapter is a review of basic and pertinent topics in public health, ecology, and geology. Practical hydraulics is covered in Chapter 2, and the fundamentals of hydrology are presented in Chapter 3. The essential concepts and terminology from chemistry and microbiology are presented in sections of Chapter 4 on water quality. The remaining chapters of the book build on these subjects by presenting specific principles and applications of environmental technology.
1-1 OVERVIEW OF ENVIRONMENTAL TECHNOLOGY
Before beginning a study of the many different topics that make up environmental technology, it would be helpful to have an understanding of the overall goals, problems, and alternative solutions available to practitioners in this field.
To present an overview of such a broad subject, we can consider an engineering project involving the subdivision and development of a tract of land into a new community, which may include residential and commercial centers. Whether the project owner is a governmental agency or a private company, a wide spectrum of environmental issues will have to be considered before construction of the new community can begin. Usually, the owner hires and retains the engineering services of an independent environmental consulting firm to address these issues. Various project reviews are also performed, and permits issued, by local, state, and federal agencies prior to project implementation. (An example of a “master-planned” community project is described on page 4.)
Water Supply
One of the first tasks project developers and consultants must consider is the provision of a potable water supply, one that is clean, wholesome, safe to drink, and available in adequate quantities to meet the anticipated demand in the new community. Some of the questions that must be answered are as follows:
1. Is there an existing public water system nearby with the capacity to connect with and serve the new development? If not,
2. Is it best to build a new centralized treatment and distribution system for the whole community, or would it be better to use individual well supplies? If a centralized treatment facility is selected,
3. What types of water treatment processes will be required to meet federal and state drinking water standards? (Water from a river or a lake usually requires more extensive treatment than does groundwater, to remove suspended particles and bacteria.) Once the source and treatment processes are selected,
4. What would be the optimum hydraulic design of the storage, pumping, and distribution network to ensure that sufficient quantities of water can be delivered to consumers at adequate pressures?
Illustrating the importance of water supply in new community development and environmental planning is the California law (implemented in October 2001) that forces builders to prove that there will be adequate water to supply their new developments. This law imposes strict requirements for cities and counties when issuing permits for new subdivisions of 500 or more homes. The local water agencies must verify that water quantities are ample enough to serve the project for at least 20 years, including periods of drought. California is the first state to pass such strict legislation linking new development to water supply.
Sewage Disposal and Water Pollution Control
When running water is delivered into individual homes and businesses, there is an obvious need to provide for the disposal of the used water, or sewage. Sewage contains human waste, wash water, and dishwater, as well as a variety of chemicals if it comes from an industrial or commercial area. It also carries microorganisms that may cause disease and organic material that can damage lakes and streams as it decomposes. It will be necessary to provide the new community with a means for safely disposing of the sewage, to prevent water pollution and to protect public and environmental health. Some of the technical questions that will have to be addressed include the following:
1. Is there a nearby municipal sewerage system with the capacity to handle the additional flow from the new community? If not,
2. Are the local geological conditions suitable for on-site subsurface disposal of the wastewater (usually septic systems), or is it necessary to provide a centralized sewage treatment plant for the new community and to discharge the treated sewage to a nearby stream? If treatment and surface discharge are required,
3. What is the required degree or level of wastewater treatment to prevent water pollution? Will a secondary treatment level, which removes at least 85 percent of biodegradable pollutants, be adequate? Or will some form of advanced treatment be required to meet federal and state discharge standards and stream quality
criteria? (Some advanced treatment facilities can remove more than 99 percent of the pollutants.)
4. Is the flow of industrial wastewater an important factor?
5. Is it possible to use some type of land disposal of the treated sewage, such as spray irrigation, instead of discharging the flow into a stream?
6. What methods will be used to treat and dispose of the sludge, or biosolids, that is removed from the wastewater?
7. What is the optimum layout and hydraulic design of a sewage collection system that will convey the wastewater to the central treatment facility with a minimum need for pumping?
Stormwater Management
The development of land for human occupancy and use tends to increase the volume and rate of stormwater runoff from rain or melting snow. This is due to the construction of roads, pavements, or other impervious surfaces, which prevent the water from seeping into the ground. The increase in surface runoff may cause flooding, soil erosion, and water pollution problems both on the site and downstream. The following are some of the questions the developer and consultant have to consider:
1. What is the optimum layout and hydraulic design of a surface drainage system that will prevent local flooding during wet weather periods?
2. What intensity and duration of storm should the system be designed to handle without surcharging, or overflowing?
3. Do local municipal land-use ordinances call for facilities that keep post-construction runoff rates equal to or less than the amount of runoff from the undeveloped land? If so,
4. What are the “best management practices” (BMPs) for reducing the peak runoff flows and protecting water quality during wet weather periods?
5. What provisions can be made, during and after construction, to minimize problems related to soil erosion from runoff?
6. What is the best way to manage combined sewer overflows (CSOs) in older sewer systems?
Solid and Hazardous Waste Management
The development of a new community (or growth of an existing community) will certainly lead to the generation of more municipal refuse and industrial waste materials. Ordinarily, the collection and disposal of solid wastes is a responsibility of the local municipality. However, some of the wastes from industrial sources may be particularly dangerous, requiring special handling and disposal methods. There is a definite relationship between public and environmental health and the proper handling and disposal
of solid wastes. Improper garbage disposal practices can lead to the spread of diseases such as typhus and plague due to the breeding of rats and flies.
If municipal refuse is improperly disposed of on land in a “garbage dump,” it is also very likely that surface and groundwater resources will be polluted with leachate (leachate is a contaminated liquid that seeps through the pile of refuse into nearby streams as well as into the ground). However, incineration of the refuse may cause significant air pollution problems if proper controls are not applied or are ineffective.
Hazardous wastes, such as poisonous or ignitable chemicals from industrial processes, must receive special attention with respect to storage, collection, transport, treatment, and final disposal. This is particularly necessary to protect the quality of groundwater, which is the source of water supply for about half the population in the United States. In the second half of the 20th century, a significant number of water supply wells were found to be contaminated with synthetic organic chemicals, many of which are now known to cause cancer and other illnesses in humans. Improper disposal of these hazardous materials, usually by illegal burial in the ground (or “midnight dumping”), has been the main cause of the contamination.
Some of the general questions related to the disposal of solid and hazardous wastes from the new community include the following:
1. Is there a materials recycling facility (MRF, or “murf”) serving the area? What will be the waste storage, collection, and recycling requirements (e.g., will source separation of household refuse be necessary)?
2. Will a waste processing facility (such as one that provides for shredding, pulverizing, baling, composting, or incineration) be needed to reduce the waste volume and improve its handling characteristics?
3. Is there a suitable sanitary landfill serving the area, and will it have sufficient capacity to handle the increased amounts of solid waste for a reasonable period of time? (Despite the best efforts to recycle solid waste or reduce its volume, some material will require final disposal in the ground in an environmentally sound manner.) If not,
4. Is there a suitable site for construction and operation of a new landfill to serve the area? (A modern sanitary landfill site must meet strict requirements with respect to topography, geology, hydrology, and other environmental conditions.)
5. Will commercial or industrial establishments be generating hazardous waste, and, if so, what provisions must be made to collect, transport, and process that material? Is there a secure landfill for final disposal available, or must a new one be constructed to serve the area?
Air and Noise Pollution Control
Major sources of air pollution include fuel combustion for power generation, certain industrial and manufacturing processes, and automotive traffic. Project developers can
exercise the most control over traffic. Private industry will have to apply appropriate air pollution control technology at individual facilities to meet federal and state standards.
The volume of traffic in the area will obviously increase, leading to an increase in exhaust fumes from cars and other vehicles. Proper layout of roads and traffic-flow patterns, however, can minimize the amount of stop-and-go traffic, thus reducing the amount of air pollution in the development.
Usually, the developer’s consultant will have to prepare an environmental impact statement (EIS), which will describe the traffic plan and estimate the expected levels of air pollutants. It will have to be shown that air quality standards will not be violated for the project to gain approval from regulatory agencies. (In addition to air pollution, the completed EIS will address all other environmental effects related to the proposed project.)
Noise can be considered to be a type of air pollution in the form of waste energy—sound vibrations. Noise pollution will result from the construction activity, causing a temporary or short-term impact. The builders may have to observe limitations on the types of construction equipment and the hours of operation to minimize this negative effect on the environment. A long-term impact with respect to the generation of noise will be caused by the increased amount of vehicular traffic. This is another environmental factor that the consultants will have to address in the EIS.
Other Environmental Factors
Not to be overlooked as an environmental factor in any land development project is the potential impact on local vegetation and wildlife. The destruction of woodlands and meadows to make room for new buildings and roads can lead to significant ecological problems, particularly if there are any rare or endangered species in the area. Cutting down trees and paving over meadows can cause short-term impacts related to soil erosion and stream sedimentation. On a long-term basis, it will cause the displacement of wildlife to other suitable habitats, presuming, of course, that such habitats are available nearby. Otherwise, several species may disappear from the area entirely.
Human activity in wetland areas, including marshes and swamps, can be very damaging to the environment. Coastal wetlands are habitats for many different species of organisms, and the tremendous biological productivity of these wetland environments is an important factor in the food chain for many animals. When wetlands are drained, filled in, or dredged for building and land development projects, the life cycle of many organisms is disrupted. Many species may be destroyed as a result of habitat loss or loss of a staple food source. Wetlands also play important roles in filtering and cleansing water and in serving as a reservoir for floodwaters. There is a definite need to control or restrict construction activities in wetland environments and to implement a nationwide wetlands protection program.
Environmental concerns related to general sanitation in a new community include food and beverage protection, insect and rodent control, radiological health protection, industrial
hygiene and occupational safety, and the cleanliness of recreation areas such as public swimming pools. These concerns are generally the responsibility of local health departments.
Development of a Master-Planned Community1
Anthem Community Park in Maricopa County, Arizona, is an example of a large master-planned community, one that exemplifies many of the environmental issues discussed above. Beginning around 2000, this community has gradually been developed on approximately 2400 hectares (ha) [5800 acres (ac)]. Zoning densities on the property allowed for the construction of approximately 14,000 residential units, with about 240 ha (600 ac) set aside for mixed commercial uses. The initial 2001 population of 2500 residents increased to 25,000 in 2010; the ultimate design population is 30,000 residents.
Planned features for the growing Anthem community included school sites, a community center, two golf courses, a water park, single family and multifamily housing, as well as mixed commercial uses. Although the Anthem community is a good example of a project for which the developer must consider a wide range of environmental factors, as mentioned above, the discussion here will focus mainly on water supply and wastewater disposal issues.
As part of the engineering work for this project, the developer hired a consulting engineering firm to create computer programs (also called computer models) of the community’s water supply and wastewater disposal networks. The initial purpose of the computer models was to establish design parameters and construction phasing for the planned infrastructure. They have also served to maintain, operate, and update the system on an ongoing basis. (Computer applications are discussed in more detail in later chapters.)
As it developed, the Anthem community had to meet the guidelines of the Arizona Department of Water Resources, which requires that surface water be used to provide for any new development and that a 100-year water supply be assured. Groundwater could not be used as the sole source of water in the Phoenix Active Management Area in which the project is located, due to overpumping of the aquifers within the area. Wells could be used, but the volume of groundwater withdrawn must be equal to or less than the recharge volume. (Surface water, groundwater, and wells are topics covered in more detail in Chapter 3.)
Since there is no permanent source of surface water supply in Anthem, it was necessary for the developer to obtain an assured 100-year supply from Lake Pleasant on the Central Arizona Project (CAP) canal, a long distance away. A 750-mm (30-in.)-diameter ductile iron pipeline more than 13 km (8 mi) long was built to transport CAP water to the Anthem community. (Water treatment and distribution topics are discussed in Chapters 6 and 7.)
1Adapted from an article that originally appeared in the June 2001 issue of Public Works®, published by Public Works Journal Corporation, 200 South Broad Street, Ridgewood, NJ 07450. © 2001 Public Works Journal Corporation.
The task of providing water to the growing community was further complicated because the Anthem property is located in two different governmental jurisdictions. On the west side, it is within the Phoenix city limits, and on the east, it is in Maricopa County. Each of these governmental entities has different engineering criteria for planning and design; the public infrastructure designed for Anthem must meet the design criteria for both jurisdictions. The computer model used for water and wastewater infrastructure ensures that minimum and maximum pressures are maintained under all water demand conditions, and that maximum flow velocities are not exceeded.
Anthem Community Park wastewater is collected and treated to allow the reuse of the effluent for irrigation of landscaping in roadway medians, parks, and golf courses. Treatment processes include rotary drum screens as well as biological purification and microfiltration. (Wastewater collection is discussed in Chapter 8, and sewage treatment processes are discussed in Chapter 10.) Treated sewage effluent in excess of irrigation needs is allowed to percolate or seep into the groundwater aquifer, using a network of recharge trenches—an example of indirect wastewater recycling. Raw CAP water, potable water, and treated effluent are monitored and managed using automated radio telemetry systems to optimize the reuse of treated wastewater in the planned community.
Environmental Interrelationships
In the preceding overview of environmental technology, we have briefly considered many factors that are very much interrelated and overlapping, as illustrated in Figure 1-1. In a textbook, it is necessary to organize these factors into chapters and sections. But this is only for academic convenience. The interrelationships should always be kept in mind. Water, land, and air pollution are part of a single problem. Sometimes, due to unanticipated interrelationships and overlaps, a solution of one environmental problem
Incineration of solid wastes to conser ve and protect land resources can cause air pollution problems
Cer tain air pollution control systems, such as “scrubbers,” produce a flow of dir ty water that can cause water pollution.
inadvertently causes a different problem to arise. For example, the use of catalytic converters since the mid-1970s to reduce smog caused by automobile exhaust gases has been found to contribute to a different air pollution problem— global warming (or the “greenhouse effect”). Catalytic converters can form significant quantities of nitrous oxide (“laughing gas”), which is a potent gas that can trap heat energy and warm the atmosphere. (The greenhouse effect and atmospheric warming are discussed in more detail later in Section 13-4.)
Another example involves the contamination of groundwater and surface water in some cities by MTBE (methyl tertiary butyl ether), an organic chemical added to gasoline to reduce air pollution. MTBE was used as a fuel additive since the early 1990s to increase gasoline octane levels and help reduce carbon monoxide and ozone concentrations in the air. But it is very soluble in water and can contaminate water sources, largely as a result of leakage from underground storage tanks (see Section 12-3) and the use of motorized watercraft on lakes and reservoirs. MTBE may be a carcinogen (cancer-causing agent), and it can give water a bad taste and odor even at low levels. Its use in the United States started to decline in 2005 when more than two-dozen states banned the chemical.
As more is learned about the potential interrelationships among environmental phenomena, engineers and technologists will be better able to create pollution control systems that will not have any unexpected harmful effects on other components of the environment and will be able to avoid situations like the foregoing.
1-2 Public health
Preventing the spread of disease and thereby protecting the health of human populations is a fundamental goal of environmental technology. Public health protection is, of course, a primary concern of doctors and other medical professionals. But engineering technology also plays a significant role in this effort. In fact, the high standard of health enjoyed by citizens of the United States and other developed nations is largely due to the construction and operation of modern water treatment and pollution control systems. The spread of diseases in countries with inadequate sanitary facilities remains a major problem for more than 2 billion people worldwide. Most medical professionals consider sanitation (i.e., the prevention of human contact with potentially harmful waste materials and other agents of disease) to be the most important aspect of disease prevention and public health protection.
Figure 1-1 Most environmental problems pertaining to air, water, and land quality are interrelated. A problem called acid rain, for example, is caused by air pollution, and it damages both aquatic and terrestrial ecosystems.
Diseases are classified into two broad groups: communicable diseases and noninfectious diseases. Communicable diseases are those that can be transmitted from person to person, commonly referred to as being infectious or contagious. Noninfectious diseases, as the name implies, are not contagious; they cannot be transmitted from one person to another by any means. The kinds of noninfectious diseases of concern in environmental technology are associated with contaminated water, air, or food. The contaminants are
Leachate seeping through sanitar y landfills can contaminate surface water and groundwater resources
usually toxic chemicals from industrial sources, although biological toxins can also cause disease.
Communicable Diseases
Communicable diseases are usually caused by microbes These microscopic organisms include bacteria, protozoa, and viruses (see Section 4-4). Most microbes are essential components of our environment and do not cause disease. Those that do are called pathogenic organisms, or simply pathogens.
The ways in which diseases are spread from one person to another vary considerably. They are called modes of transmission of disease and are summarized in Figure 1-2. It is important to make distinctions among the various modes of transmission to be able to apply suitable methods of control. Direct transmission involves an immediate transfer of pathogens from a carrier (infected person) to a susceptible contact, that is, a person who has had direct contact with the carrier and is liable to acquire the disease. Clearly, control of this mode of transmission is not within the scope of environmental technology; it is in the province of personal hygiene and the medical profession (which provide immunization and quarantine infected persons).
Environmental technology can be applied to intercept many of the modes of indirect transmission. The three indirect modes of disease transmission are airborne, vectorborne, and vehicleborne. Airborne transmission involves the spread of microbes from carrier to contact in contaminated mists or dust particles suspended in air. It is the least common of the indirect modes. (This should not be confused with the noninfectious public health problems associated with chemical air pollution, which is discussed in Chapter 13.)
Vectors of disease include insects, rodents, and other animals that can transport pathogens to susceptible human contacts. The animals that carry the pathogenic microbes are also called intermediate hosts if the microbes have to develop and grow in the vector’s body before becoming infective to humans. Vectorborne disease can be controlled to some extent by proper sanitation measures.
Modes of disease transmission
Direct transmission
Contact or droplet spray (<1 m)
Pathogens
Susceptible human contacts insects, animals water, food, milk aerosol or dust
ne
Indirect transmission
Path of transmission intercepted by environmental technology: water purification, wastewater treatment, air pollution control, solid waste management, and general community sanitation.
Figure 1-2 Communicable diseases are spread in several ways, many of which can be controlled or intercepted by applications of modern environmental technology.
A vehicle of disease transmission is any nonliving object or substance that is contaminated with pathogens. For example, forks and spoons, handkerchiefs, soiled clothes, or even children’s toys are potential vehicles of transmission. They can physically transport and transfer the pathogens from carrier to contact. (Contaminated objects are also called fomites.) Water, food, and milk are also potential vehicles of disease transmission; these are perhaps the most significant with regard to environmental technology and sanitation. Water, in particular, plays a major role in the transmission of communicable diseases, but it is most amenable to engineering and technological controls. Water and wastewater treatment facilities effectively block the pathway of waterborne diseases.
Types of Communicable Diseases
Waterborne and foodborne diseases are perhaps the most preventable types of communicable diseases. The application of basic sanitary principles and environmental technology has virtually eliminated serious outbreaks of these diseases in technologically developed countries.
Water- and foodborne diseases are also called intestinal diseases because they affect the intestinal tract of humans. The pathogens are excreted in the feces of infected people. If these pathogens are inadvertently ingested by others in contaminated food or water, the cycle of disease can continue, possibly in epidemic proportions, that is, when the number of occurrences of a disease in a community is far above normal.
Symptoms of intestinal disease include diarrhea, vomiting, nausea, and fever. Intestinal diseases can incapacitate large numbers of people in an epidemic and sometimes result in the deaths of many infected individuals. Water contaminated with untreated sewage (domestic wastewater) is generally the most common cause of this type of disease.
The most prevalent waterborne diseases include typhoid fever, dysentery, cholera, infectious hepatitis, and gastroenteritis (common diarrhea and cramps). These can also be transmitted by contaminated food or milk products. Diseases caused by bacterial toxins include botulism and Staphylococcus food poisoning. Refrigeration as well as proper cooking and sanitation at food-processing facilities and restaurants are important for control of these foodborne diseases.
Although cholera and dysentery have not generally been a problem in the United States, they are prevalent diseases in Africa, India, and Pakistan and in many other developing countries in Southeast Asia. In fact, they are considered to be endemic (habitually present) in these areas. Typhoid fever is more common in occurrence than cholera or dysentery. Until the beginning of the 1900s, typhoid mortality rates in some urban areas of the United States were as high as 650 deaths per 100,000 population. The beginning of modern water purification technology at about that time helped lower the typhoid death rate to considerably less than 1 per 100,000 people per year. (Immunization and improvements in food and milk sanitation also played a role in reducing the incidence of typhoid.)
Vectorbor ne
Vehiclebor ne
Airbor
Amoebic dysentery, caused by a single-cell microscopic animal called amoeba, occurred in epidemic proportions in Chicago during the early 1930s. About 100 of the approximately 1000 people who contracted the disease died from it. The cause of this epidemic was traced to sewage that contaminated the water supplies of two hotels in the city. Although epidemics of intestinal disease like this one are not at all common in the United States, when they do occur they are usually very localized and can be traced to contaminated water supplies in hotels, restaurants, schools, or camps. Generally, the contamination is caused by cross-connections in the water distribution system, which may allow backflow of wastewater into the drinking water supply.
Giardiasis and cryptosporidosis are two waterborne diseases that can cause gastrointestinal illness and serious public health problems. They are both caused by singlecelled microscopic animals called protozoa (see Section 4-4 for a discussion of microorganisms), which can contaminate drinking water supplies. A very large outbreak of cryptosporidosis, for example, occurred in Milwaukee, Wisconsin, in 1993. The city’s water supply comes from Lake Michigan. An unusual combination of circumstances during a period of heavy rainfall and runoff allowed the protozoan Cryptosporidium to pass through the water treatment plant. More than 40,000 people became ill, about 4000 people were hospitalized, and more than 50 deaths were attributed to this outbreak. The original source of the contamination is uncertain. Since that incident, improved water quality standards and treatment rules make a repetition of this type of outbreak less likely.
Insectborne diseases include those transmitted by the bites of mosquitoes, lice, and ticks. Malaria, yellow fever, and encephalitis are typical diseases spread by certain species of mosquitoes. Flies also transmit disease, but not by biting; the contact of their germ-laden bodies, wings, and legs with food consumed by humans spreads diseases such as typhoid fever and gastroenteritis.
The elimination of the breeding places of insects is one of the most important control measures. Proper garbage disposal reduces fly breeding places, and elimination of standing water is one of the methods available for eliminating mosquito breeding areas. Chemical control with insecticides is usually a last resort because of the environmental and potential health problems associated with the use of toxic substances.
In addition to insects, other vectors of disease transmission are vertebrate animals such as dogs and rats. Rabies is a familiar example of a disease spread by the bite of an infected dog or other mammal, but it is not generally related to environmental conditions. Rodent-borne diseases, such as typhus and bubonic plague, are more readily controlled by applications of environmental technology. Rat populations can be controlled by good community sanitation practices; rodent access to garbage and water should be prevented. Modern building codes include specifications for rodentproof building construction.
Noninfectious Diseases
It is a well-documented fact that the overall death rate for people residing in heavily polluted urban areas is significantly higher than the mortality rate in areas that are relatively pollution free. This is not necessarily because of the incidence of sewage pollution and the spread of infectious diseases. In fact, many current public health problems related to environmental pollution are considered to be the result of contamination of water, food, and air with toxic chemicals. The resulting diseases are noninfectious.
Some noninfectious illnesses associated with toxic chemical pollution have a relatively sudden and severe onset, and the acute or immediate health effects can be readily traced to a specific contaminant. A group of substances known as the heavy metals is particularly notorious in this regard. Other noninfectious diseases may take years to develop and can involve chronic or long-lasting health problems. Generally, various synthetic organic substances cause this type of problem, even in extremely small concentrations. Some organics are considered to be carcinogenic, having the potential to cause cancer in humans.
Lead is one of the heavy metals involved in noninfectious disease. The public health problems related to lead poisoning have long been associated primarily with ingestion by children of peeling lead-based paint. Lead poisoning can lead to blindness, kidney disease, and mental retardation (particularly in children).
The evidence against lead as a dangerous environmental pollutant is overwhelming. It is a cumulative poison; that is, it accumulates in human tissue and can build up to toxic levels over time. As a result, environmental agencies in Europe and the United States have banned the use of lead additives in gasoline.
Mercury is another heavy metal associated with environmental pollution and noninfectious illness. It was first noted as such when it afflicted large numbers of people living in the Minamata Bay region of Japan in the 1950s. Mercury compounds, discharged into the bay in wastewater from a local factory, were ingested by people who ate contaminated fish. A severe epidemic of disease, resulting in blindness, paralysis, and many deaths, was the result. Less severe symptoms included hand tremors, irritability, and depression.
At the time of the Minamata Bay incident, mercury vapor was known to be harmful, although metallic mercury itself was not considered hazardous (it has long been used in dental fillings). Research after the poisoning episode in Japan, however, led to the discovery that certain microorganisms can cause the metallic mercury to combine with other substances in the water, forming harmful mercury compounds, such as methylmercury. This substance was ingested by microscopic organisms in the water, called plankton, and entered the food chain. People who ate the contaminated fish were made ill by the methylmercury.
The episode of mercury poisoning in Japan is one example of a relatively sudden and acute illness related to
environmental pollution. The concentration of the pollutant was relatively high, and the harmful effects were noticed within a short time. Questions remain as to the chronic or long-term effects of lower concentrations of mercury compounds. It is common to detect small amounts of mercury in fish and wildlife even in rivers and lakes far from industrial centers.
Discarded batteries and dry cells are a major source of mercury. This is becoming a very serious problem due to the difficulty in properly disposing of the many batteries generated by the growing electronics industry and the use of calculators, cameras, portable CD players, and watches.
Unfortunately, mercury and lead are not the only harmful chemical substances that become environmental pollutants when poorly managed or controlled. For example, the pesticide Kepone has seriously polluted the James River and Chesapeake Bay. The Hudson River is known to be contaminated with the toxic industrial chemical PCB (polychlorinated biphenyl) (see page 14). This oily substance was widely used in electrical transformer fluids, coolants, paints, and other products. It persists in the environment because it is nonbiodegradable; that is, it does not readily decompose and dissipate by natural processes. PCBs have accumulated in the bottom deposits of rivers, and many species of fish are contaminated with them.
Like the pesticide DDT, PCB has been banned from manufacture and most uses in the United States, but because these substances are extremely persistent in the environment, they remain potential dangers to public health for many years after their initial discharge. Traces of DDT and PCB are still found in the body tissues of animals far removed from the sources of pollution. Both of these chemicals are considered potential human carcinogens.
Environmental pollution with harmful chemicals and the resulting incidences of noninfectious disease are part of a problem now commonly referred to as hazardous waste disposal. This is discussed in more detail in Chapter 12.
Perhaps one of the most publicized environmental disasters in the United States that was related to improper disposal of hazardous wastes occurred in the 1970s at Love Canal in Niagara Falls, New York. Waste chemicals in steel drums were buried in the unused canal over a period of several years. The land was sold and many homes were built on top of the site. Eventually, the chemicals leaked out of the drums and into the soil, water, and air in the vicinity of the old dump site. Soon it was evident that residents in the area of Love Canal were suffering from unusually high rates of cancer, miscarriage, birth defects, kidney disease, and other illnesses. Love Canal was the first polluted site to be put on the federal Superfund list (see Section 12-4). In 2004, the U.S. Environmental Protection Agency (EPA) announced that after more than two decades of cleanup work at the site, at a cost of about $400 million, the Love Canal site was clean enough to be taken off the list.
In incidents like Love Canal, it is difficult to tie a particular chemical to a specific health problem, but the fact that the noninfectious illnesses suffered by the residents of
the area were associated with environmental contamination with chemical wastes is beyond question. Research is being conducted by many universities and governmental agencies to determine some of the long-term effects of heavy metals and synthetic organic chemicals on human health.
Finally, several noninfectious diseases are specifically associated with air pollution. Air pollution and its control are discussed in Chapter 13. Briefly, common diseases related to air pollution include bronchial asthma, bronchitis, and emphysema. Lung cancer also occurs more frequently among people who live in congested industrial and urban areas, and poor air quality is considered to play a role in this. Again, it is difficult to prove a direct cause-and-effect relationship between a specific pollutant and these illnesses, but the overall negative effect of dirty air on public health is obvious: The incidence of respiratory ailments and increased mortality rates are directly related to the severity of air pollution.
1-3 ecOlOgy
Ecology is the branch of biological science concerned with the relationships and interactions between living organisms and their physical surroundings or environment. Living organisms and the environment with which they exchange materials and energy together make up an ecosystem, which is the basic unit of ecology. An ecosystem includes biotic components—the living plants and animals—and abiotic components—the air, water, minerals, and soil that constitute the environment. A third and essential component of most natural ecosystems is energy, usually in the form of sunlight.
Familiar examples of land-based, or terrestrial, ecosystems include forests, deserts, jungles, and meadows. Waterbased, or aquatic, ecosystems include streams, rivers, lakes, marshes, and estuaries. There is no specific limitation on the size or boundaries of an ecosystem. A small pond can be studied as a separate ecosystem, as can a desert comprising hundreds of square kilometers. Even the entire surface of Earth can be viewed as an ecosystem; the term “biosphere” is often used in this context.
If Earth is imagined to be about the size of an apple, then the layer of air that we breathe would not be much thicker than the skin of that apple. This thin envelope of air (called the troposphere) and the shallow crust of land and water just beneath it provide the abiotic components that support life in the biosphere. It is a closed ecosystem because there is essentially no transfer of material into or out of it. Only the constant flow of energy from the sun provides power to sustain the life cycles within the biosphere. Nutrients are continually recycled and reused.
The biosphere seems so big that it is sometimes difficult to believe that humans can affect or disrupt its natural balances. But global problems related to environmental pollution, such as acid rain, the ozone hole, and the greenhouse effect, are significant and must be controlled before irreversible environmental changes occur. These and other pollution problems are discussed later in the text.
In addition to natural ecosystems, such as lakes or forests, several types of artificial ecosystems are of particular importance in environmental technology. For example, one of the most common methods of wastewater treatment is based on a biological system called the activated sludge process. This is an engineered ecosystem comprising a steel or concrete tank, a suspended population of microorganisms in wastewater, and a constant input of air. The microbes are the biotic component; the tank, wastewater, and air are the abiotic components. The system removes organic pollutants from the wastewater. This method is discussed in more detail in Chapter 10.
Food Chains and Metabolism
There are two basic principles, or laws, of ecology: the oneway flow of energy and the circulation of nutrients.
Energy is the capacity to do work. It can be transformed from one form to another, such as from mechanical to electrical energy or from energy in the form of sunlight to potential energy stored in food molecules, but it cannot be created or destroyed. No energy transformation is 100 percent efficient; some is always lost to the environment. Because of this, energy cannot be recycled in an ecosystem; it can only flow one way.
In contrast, nutrient materials needed to sustain life can be reused over and over again. They are constantly recycled or circulated through the ecosystem. The one-way flow of energy and the circulation of nutrients are illustrated in Figure 1-3. This is a very simplified diagram of a food chain, showing three broad groups or types of organisms: the producers, the consumers, and the decomposers.
The biological and chemical process by which an organism sustains its life is called metabolism. Two fundamental
metabolic processes of living organisms are photosynthesis and respiration, which is discussed shortly. Living organisms require energy, and, as shown in Figure 1-3, the original or primary source of energy for all natural ecosystems is the sun.
In addition to energy, living organisms need certain chemicals from the environment, called nutrients, in sufficient quantities. All organisms need water, and most require gaseous oxygen. In addition, plants and animals require carbon, hydrogen, phosphorus, potassium, iodine, nitrogen, sulfur, calcium, iron, and magnesium, as well as other elements in smaller amounts. For animals, some of these elements must be in the form of organic molecules, such as carbohydrates or proteins. (A brief review of basic inorganic and organic chemistry is provided in Chapter 4.)
Photosynthesis and Respiration The food chain shown schematically in Figure 1-3 begins with what ecologists call the first trophic level of organisms—the producers. These are the green plants. Green plants are autotrophic, which simply means that they are self-nourishing. They have the unique ability to convert carbon dioxide, water, and some basic nutrients into organic compounds that store the sun’s energy.
This natural process, called photosynthesis, is illustrated in Figure 1-4. The plants utilize solar energy to form carbohydrates from carbon dioxide and water. The carbohydrates can also combine with nitrogen, phosphorus, sulfur, and other elements, forming other organic compounds that are the building blocks of living organisms. Chlorophyll, the pigment that gives plants their characteristic green color, plays a key role in trapping solar energy and converting it into chemical energy. A portion of the energy-rich organic compounds stored in the plant tissue are available for use by other organisms that consume the plants at the next trophic level.
During the process of photosynthesis, gaseous oxygen is released into the atmosphere. Oxygen is essential for the metabolism of the next trophic level in the food chain—the consumers. Actually, the consumer organisms include several intermediate trophic levels, including the herbivores, the carnivores, and the omnivores. Herbivores are plant-eating animals, carnivores are meat eaters, and omnivores eat both plants and animals.
Figure 1-3 Simplified diagram of a food chain. Nutrients are recycled, but energy must be continuously supplied by the sun. The efficiency of energy transfer from one trophic level to the next is less than 10 percent.
Figure 1-4 Schematic diagram of photosynthesis. Energy from the sun is stored in organic molecules and is available for use by the next trophic level.
Energy
Figure 1-5 Schematic diagram of respiration, the opposite of photosynthesis. Organic matter is metabolized or “burned,” thereby releasing the stored energy for use by consumer organisms. Enzymes are chemicals that help the metabolism reactions occur in the living cell.
The consumer organisms are heterotrophic. Unlike the autotrophic plants, which manufacture their own food from simple inorganic chemicals, the herbivores must utilize the energy-rich compounds synthesized by the plants. In turn, the carnivores obtain energy for their metabolism when they consume the herbivores. The process by which the consumers obtain energy from the organic material stored in plants and animals they eat is called respiration
Respiration, illustrated in Figure 1-5, may be viewed as a process of slow combustion or oxidation of organic material during which energy is released. Essentially, respiration is the opposite of photosynthesis. Photosynthesis builds energy-rich organic substances and gives off oxygen; respiration breaks down the organics and gives off carbon dioxide. Photosynthesis requires carbon dioxide, and respiration requires oxygen. This is one of the fundamental balances in nature.
The simplified food chain shown in Figure 1-3 is completed or closed by the decomposers, or decay organisms. These are primarily microscopic organisms, such as bacteria and fungi. During their own metabolism, microorganisms break down the waste products and the remains of dead organisms into simpler inorganic substances, which are then readily usable by the autotrophs. For example, nitrogen in ammonia is not available in plants as a nutrient until it is broken down and converted to inorganic nitrates by certain bacteria. The nitrates can be absorbed by the plants. Not only are decomposers essential for all natural ecosystems, they are the workhorses of engineered water pollution control systems.
Aerobic and Anaerobic Decomposition
Decomposition that occurs in the presence of free oxygen is called aerobic decomposition, and the microorganisms that thrive in oxygen are called aerobes. Aerobic decomposition results in the oxidation of the carbon, hydrogen, sulfur, nitrogen, and phosphorus that are tied up in complex organic molecules. These elements become combined with oxygen, forming carbon dioxide, water, sulfates, nitrates, and other simple substances that can be taken up by green plants for photosynthesis. The energy released from the organic molecules in this process is used by the microbes for growth and reproduction. Aerobic decomposition is an efficient and “clean” biochemical process and does not produce the offensive odors often associated with decay.
Free
Ammonia
Anaerobic
Unstable "smelly" by-products
Volatile
Figure 1-6 Anaerobic decomposition of proteins in the absence of free or molecular oxygen is called putrefaction.
Certain species of microorganisms are able to decompose organic material in the absence of freely available oxygen. These organisms are called anaerobes, and the process is called anaerobic decomposition. As illustrated in Figure 1-6, the end products of anaerobic decomposition include methane, ammonia, hydrogen sulfide, and volatile organic acids, many of which are responsible for the unpleasant odors associated with putrefaction (the anaerobic decay of proteins). Hydrogen sulfide, with the chemical formula H2S, causes the familiar rotten-egg odor. (See Section 4-1 for a review of chemical symbols and formulas.)
Anaerobic decomposition is an inefficient biochemical process. Although the anaerobes get energy from it for their growth and reproduction, the end products are still relatively unstable and can decompose further. In effect, anaerobic decay is similar to incomplete combustion. It plays a key role in some wastewater treatment processes. Methane, CH4, one of the few odorless products of anaerobic decomposition, has a high enough energy value to be useful as a fuel; it is collected for that purpose at some sewage treatment plants and sanitary landfills (see page 2).
A type of anaerobic decomposition that is useful in producing certain foods and beverages is called fermentation, that is, the decomposition of carbohydrates by microbes without free oxygen. Although it is used to produce cheese and alcohol, for example, some kinds of fermentation are not desirable, such as those that sour milk or produce acetic acid in wine.
Biogeochemical Cycles
Although an ecosystem needs a constant source of energy from outside, the nutrients on which life depends can be recycled indefinitely. The pathways in which the chemical nutrients move through the biotic and abiotic components of the ecosystem are called biogeochemical cycles or nutrient cycles
A cycle of particular concern in the field of environmental technology is the hydrologic (water) cycle. This is discussed in some detail in Chapter 3. The important nutrient cycles considered here are the carbon cycle, the nitrogen cycle, and the phosphorus cycle.
Carbon, nitrogen, and phosphorus are considered to be among the macronutrients because they are needed in
relatively large amounts in protoplasm, the fundamental substance of which a living cell is made. Other macronutrients essential to life include hydrogen, oxygen, potassium, calcium, magnesium, and sulfur. The many micronutrients, required only in very small quantities, include iron, manganese, copper, zinc, and sodium.
Carbon Cycle Carbon dioxide (CO2) in the air and dissolved in water is the primary source of the element carbon. Through the process of photosynthesis, the carbon is removed from the CO2 and incorporated with other chemical elements in complex organic molecules. The CO2 eventually finds its way back into the atmosphere when the organics are broken down during respiration. A schematic diagram of this cycle is shown in Figure 1-7.
The combustion of wood and fossil fuels (e.g., gasoline and natural gas) for energy is a human activity that increases the concentration of CO2 in the atmosphere. Carbon dioxide plays a role in absorbing radiated heat and in regulating global atmospheric temperatures. A rise in CO2 levels in the atmosphere tends to cause the average temperature to increase. This problem is called the greenhouse effect (see Section 13-4).
Nitrogen Cycle About 78 percent of the atmosphere is nitrogen gas, N2, but in this molecular form it is not active in biological systems. The nitrogen must first be fixed in the form of nitrates, NO3–, whereby it can be utilized by plants during photosynthesis. Eventually, it is combined with other substances and converted into proteins, consumed by heterotrophs, and broken down again in the process of decay. This cycle is illustrated in Figure 1-8. Nitrification, the process in which nitrogen in the form of ammonia, NH3, is converted to nitrate nitrogen, is of particular significance in water pollution control (see page 2).
Carbon Dioxide (CO2) in air and water Deposits of coal, oil, gas and carbonate rocks
Combustion and weathering
(Producers) Green plants
Bacteria Consumed as food
(Decomposers)
Figure 1-7 Simplified diagram of the carbon cycle. The arrows show the various directions of carbon transfer through the biosphere.
Bacterial action
Atmospheric nitrogen (about 78% of the air)
Bacterial action Bacterial action
Nitrite nitrogen (Inorganic)
Bacterial action
Nitrate nitrogen
Dead animals and wastes "Denitrification"
"Nitrogen fixation" Lightning and bacterial action
Decomposition of dead plants (Organic) (Inorganic) (Organic)
Ammonia nitrogen Decomposition Animal tissue
Absorbed and used by plants for food Plant tissue
Consumed for food
Figure 1-8 Simplified diagram of the nitrogen cycle. Molecular nitrogen must first be fixed (combined with oxygen) into the form of nitrate nitrogen before it can be used by plants as a nutrient.
Phosphorus Cycle Phosphorus is another nutrient that plays a central role in aquatic ecosystems and water quality. Unlike carbon and nitrogen, which come primarily from the atmosphere, phosphorus occurs in large amounts as a mineral in phosphate rocks and enters the cycle from erosion and mining activities. This is the nutrient considered to be the main cause of excessive growth of rooted and free-floating microscopic plants in lakes (algal blooms).
Stability, Diversity, and Succession
Each species of living organism occupies a particular habitat and serves a particular function in an ecosystem. The function and habitat constitute the organism’s ecological niche. A basic characteristic of a healthy or well-balanced ecosystem is an overlapping of niches occupied by different species. The more complex the ecosystem, in terms of the numbers and interrelationships among different species, the more stable it will be. A stable ecosystem can withstand some external stress, such as pollution, construction, or hunting, without being completely disrupted or damaged. In a stable ecosystem, if any one species disappears because of natural or artificial causes, other species are available to occupy its niche and take over its role in the food chain. Actually, the term food web is more appropriate for a healthy ecosystem because of the overlapping nature and complexity of the eat-and-be-eaten-by relationships. A tropical rain forest is a good example of a stable ecosystem because of the tremendous number of plant and animal species thriving in it. The loss of one species of tree or one species of animal is not likely to have a significant impact on the whole ecosystem.
In an ecosystem with little diversity, that is, only a few different species of organisms, the situation is more unstable and susceptible to the effects of stress. The disappearance of a group of organisms from the food web is more likely to break the chain of trophic levels and severely disrupt the ecosystem. Diversity of species, then, provides a factor of safety or buffer against ecological disruptions by increasing the likelihood of adaptation to changing environmental conditions. The greater the diversity of species, the healthier is the ecosystem.
Although aquatic ecosystems such as streams and lakes are generally stable, they are sensitive to disruption from human activity. A diagram of an aquatic system is shown in Figure 1-9. Most desirable organisms, from the fish down to the microscopic plankton and bacteria (see Section 4-4), need oxygen to survive.
One effect of water pollution is the reduction of the dissolved oxygen level in the water. This type of pollution changes the ecological balance, favoring a smaller number of species of organisms that are tolerant of low oxygen levels. In heavily polluted water, only maggots and sludge worms may survive.
In studying the health or quality of a stream or lake, ecologists may use a formula to compute a diversity index for the ecosystem. In a field survey the number of different species is counted, and the population of each species is estimated by sampling limited areas. These data are used in the diversity index formula, and a single number or index is determined to characterize the condition of the ecosystem.
Generally, a low diversity index is indicative of a polluted ecosystem, and the pollution-tolerant species are readily identified. In a clean stream, for example, many different species of fish may be found, including trout. But in a
polluted stream, only a few species of more tolerant organisms, such as catfish, may be found.
When evaluating the biodiversity of an ecosystem, it is important to account for the relative abundance of each species (called evenness) and the number of different species present (called richness). Diversity increases as both species evenness and richness increase. For example, consider two areas, each having 10 different species and a total population of 100 organisms. Suppose the first area has 10 members of each species, but the other has 91 members of one dominant species and one member of each of the other nine species. Both areas have the same richness, but the first has greater evenness and would have a higher diversity index. An example of a biological diversity index that incorporates both richness and evenness in the calculation is the Simpson’s Diversity Index.
It is important to realize that even healthy or wellbalanced ecosystems change over time in a process called natural succession. For example, a lake will eventually become shallower as silt and organic material accumulate in bottom sediments. As time goes on, the lake will eventually turn into a marsh and finally a meadow. These natural changes in a lake, called eutrophication, are discussed in more detail in Chapter 5. As shown there, this natural process can be affected by human activity and pollution.
Although the lake, marsh, and meadow may be stable and healthy ecosystems during their individual lifetimes, natural geological and biological processes will cause the succession from one stage to another. If geological and weather conditions are suitable, the process of natural succession will continue until a climax stage is reached. For example, the meadow, once a lake, will eventually become a hardwood forest in many temperate ecosystems. Natural
Figure 1-9 An aquatic ecosystem showing the various biological components of a freshwater or marine habitat.
(Courtesy of the U.S. Environmental Protection Agency.)
Microscopic animals
Microscopic plants (algae)
Clam
Rooted plants
PLANKTON
succession, though, takes place over very long periods of time, and the changes are not ordinarily visible during a human life span.
Biological Monitoring in Lakes and Streams
Small insects and other organisms that live on the bottom of streams and lakes form an important part of the aquatic food web. Ecologists call them benthic (which means “bottom dwelling”) macroinvertebrates. They are sensitive to many factors in their environment and are useful as indicators of the condition or “health” of streams and lakes. Routine macroinvertebrate monitoring or sampling (e.g., about six times a year) can indicate problems that may not easily be detected by chemical testing and can detect pollution problems that may no longer be evident in water samples (e.g., from a chemical spill that washes downstream).
Macroinvertebrates depend on adequate water quality for survival. The time required for insect communities to return to their natural state after disturbances, such as those from point-source industrial pollutants, can be on the order of many years for streams and decades for lakes. As a result, changes in their numbers and species can indicate pollution from various sources. Biological sampling and monitoring of these communities provide an effective method for determining if a watercourse has been impacted by pollution. (It is best to sample either in the spring, when late-stage larval forms are present but have not yet begun their final maturation, or in late fall, after most species have mated.)
More than 4000 species of aquatic insects have been reported. These benthic macroinvertebrates are therefore a highly diverse group, which makes them excellent candidates for studies of changes in biodiversity. Changes in population numbers or behavior of these organisms can indicate that the physical or chemical conditions are outside their preferred limits. Also, the presence of numerous families of highly tolerant organisms usually indicates poor water quality.
Biological Magnification
When a living organism cannot metabolize or excrete an ingested substance, that substance gradually accumulates in the organism. This phenomenon, called biological accumulation (or bioaccumulation), refers to the process by which a substance first enters a food chain. The extent to which bioaccumulation will occur depends on an organism’s metabolism and on the solubility of the substance. If the substance is soluble in fat, it will typically accumulate in the fatty tissues of the organism. Bioaccumulation is of particular concern when the substance being concentrated is a toxic environmental pollutant and the organism is of a relatively low trophic level in a food chain.
When many contaminated organisms are consumed by a second organism that can neither metabolize nor excrete the substance, the concentration of the substance will build to even higher levels in the second organism. This effect is
magnified at each successive trophic level, and the process is called biological magnification (or biomagnification). In other words, biomagnification is the steadily increasing concentration of a substance as it moves from one level of a food chain to the next (e.g., from plankton to fish to birds or to humans). Biomagnification is of particular importance when chemicals are concentrated to harmful levels in organisms higher up in the food chain. Even very low concentrations of environmental pollutants can eventually find their way into organisms in high enough doses to cause serious problems.
Biomagnification occurs only when the pollutants are environmentally persistent (last a long time before breaking down into simpler compounds), mobile, and soluble in fats. If they are not persistent, they will not last long enough in the environment to be concentrated in the food chain. (Persistent substances are generally not biodegradable.) If they are not mobile, that is, not easily transported or moved from place to place in the environment, they are not likely to be consumed by many organisms. Finally, if they are soluble in water rather than fatty tissue, they are much more likely to be excreted by the organism before building up to dangerous levels.
Impact of DDT The incidence of mercury poisoning in people who consumed contaminated fish in the Minamata Bay region of Japan in the 1950s is just one example of the detrimental effects of biomagnification (see page 13). Another classic example involves DDT, an abbreviation for the organic chemical dichlorodiphenyltrichloroethane. It is a type of chemical known as a chlorinated hydrocarbon, and it takes a long time to break down in the environment. With a “half-life” of 15 years, if 10 kg of DDT were released into the environment in the year 2000, 5 kg would still persist in the year 2015, about 2.5 kg would remain in 2030, and even after 100 years had elapsed, in the year 2100, more than 100 g of the substance would still be detected in the environment. Of course, long before that time span elapsed, some of the DDT could be inadvertently consumed by living organisms as they forage for food, and thereby enter a food chain.
DDT is toxic to insects, but not very toxic to humans. It was much used in World War II to protect U.S. troops from tropical mosquitoborne malaria as well as to prevent the spread of lice and liceborne disease among civilian populations in Europe. After the war, DDT was used to protect food crops from insects and to protect people from insectborne disease. As one of the first of the modern pesticides, it was overused, and by the 1960s, the problems related to biomagnification of DDT became very apparent. Rachel Carson’s book Silent Spring, published in 1962, raised the public awareness of the environmental dangers involved in its continued use (see page 20). DDT has since been banned from most applications in the United States.
If DDT is not very toxic to humans, why was there a problem with its use? The difficulty lies in the adverse ecological impact of DDT on bird populations, particularly the thinning of egg shells and the detrimental effect on egg hatching and brood survival. Ospreys and bald eagles were
severely impacted, as were other species (the title of Rachel Carson’s book alluded to the disappearance of songbirds). Since the ban on DDT in the United States in 1972, many bird populations have recovered, but exposure in other countries may still be a problem for some species of birds. (Note: In addition to the impact on bird populations, before its ban, DDT had also been found in human mothers’ milk at seven times the level permitted for milk sold in stores and may have had adverse impacts on human health.)
Many other substances in addition to mercury and DDT exhibit bioaccumulation and biomagnification in an ecosystem. These include copper, cadmium, lead, and other heavy metals, pesticides other than DDT, and cyanide, selenium, and PCBs.
PCBs in the Hudson River PCBs are a group of organic industrial chemicals that become very persistent contaminants when released into the environment. (They were used as insulating materials in transformers and other electrical equipment before being banned from such use in 1977.) One example of PCB contamination involves the Hudson River in New York State, into which large amounts of PCBs were discharged (legally, at the time) from two General Electric plants between 1947 and 1977; over 136,000 kg (300,000 lb) of PCBs remain concentrated in bottom sediments of the Hudson River. The extensive spread of PCBs throughout the food chain of the Hudson River is considered to be one of the most significant hazardous waste pollution problems in the nation. [In fact, about 320 km (200 mi) of the Hudson River bottom are considered to be a Superfund site.]
Small amounts of PCBs are consumed by microorganisms in the riverbed and are passed up and through the food chain in ever-increasing concentrations. People who consume fish contaminated with PCBs are in jeopardy. PCB levels in most fish found in the Hudson exceed the 2-ppm limit set by the federal government; commercial fishing is banned in most of the Hudson River because of this. (PCB was classified as a carcinogen by the EPA).
The danger of exposure to PCB will remain as long as it remains in the river. In spite of the ban on commercial fishing in the Hudson and periodic issuance of recreational fishing advisories, many people continue to eat contaminated fish from the river. Many scientists believe the best way to reduce PCB levels in Hudson River fish (as well as in the people who eat the fish) is to remove the contaminated sediments from the river. Studies have been conducted to determine if dredging the contaminated sediments from the riverbed is the optimum solution to the problem. The EPA has recommended the removal of 2 million m3 of sediment from hundreds of so-called PCB hotspots along a 64-km stretch of the river north of Albany. This project involves dredging only the most contaminated portions of the river rather than extensive bank-to-bank dredging. The sediment would be transported away from river communities by railroad for
proper disposal. General Electric would be responsible for the cleanup under the Superfund law (see page 331).
Endangered Species Act
Although extinction is a natural process, a number of species of fish, wildlife, and plants in the United States have become extinct as a consequence of economic growth and development that took place without adequate ecological concern and conservation measures. Some species of fish, wildlife, and plants have been depleted in numbers to the point that they are now threatened with extinction. These species are of esthetic, ecological, educational, historical, recreational, and scientific value to the nation and its people. Because of this, the Endangered Species Act was drafted. As defined in the act, endangered species means “any species which is in danger of extinction throughout all or a significant portion of its habitat.” The term “threatened species” means “any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range.”
Enacted by Congress in 1973, the law provides for the protection and conservation of threatened or endangered plants and animals and their habitats. A list of more than 1100 endangered species and about 300 threatened species is maintained by the U.S. Fish and Wildlife Service (FWS), a branch of the Department of the Interior. This list includes a wide variety of insects, crustaceans, birds, fish, reptiles, and mammals, as well as flowers, grasses, and trees. The law prohibits any action that would adversely affect or reduce the numbers of the listed organisms. Anyone can petition the FWS to include a particular species on the list. The final determination of a species’ listing by the FWS is based on available scientific data.
Protecting endangered and threatened species and restoring them to a secure status in the wild is the basic objective of the endangered species program; administration of the program includes the following responsibilities:
● Listing, reclassifying, and delisting species
● Providing biological opinions to federal agencies on their activities that may affect listed species
● Overseeing recovery activities for listed species
● Providing for the protection of important habitat
● Providing grants to states to assist with their endangered species conservation efforts
Since the enactment of the Endangered Species Act, there have been several successful recoveries of endangered species. For example, the American alligator was delisted in 1987, the American peregrine falcon was delisted in 1999, and the bald eagle was delisted in 2007 because of recovery. (Species are also delisted if they become extinct.) The FWS has established recovery program goals for listed species and has a specific protocol for down listing a particular species from endangered to threatened, or for delisting it entirely.
1-4 geOlOgy and SOilS
To a large extent, both liquid and solid wastes are disposed of on top of or below the ground surface. An important concern in environmental technology is the interaction between such waste materials and naturally occurring bodies of water. The protection of groundwater quality is of particular concern. This involves soil types and characteristics (see Section 10-5). Because soil comprises unconsolidated rock particles, it will be helpful for the student who has little or no background in the subject of geology or soils to first review the brief discussion in this section.
Types of Rock
Rocks are composed of inorganic substances called minerals. Some common minerals are quartz, mica, feldspar, calcite, magnetite, and kaolinite. The fundamental chemical elements making up these minerals include silicon, potassium, aluminum, calcium, iron, oxygen, and many others.
The three major types of rocks are igneous, sedimentary, and metamorphic. Igneous rocks, which compose most of the solid crust of the planet, have cooled and solidified from a hot molten state. Granite, composed primarily of the minerals quartz and feldspar, is a common type of igneous rock.
Even the hardest and most durable igneous rocks that are exposed at Earth’s surface are subject to physical disintegration and chemical decay. Changes in the composition and structure of the rock are constantly occurring because of the action of wind, water, temperature changes, carbon dioxide, and oxygen. This gradual process is called weathering. The solid rock made up of consolidated minerals is broken down into relatively small unconsolidated fragments called soil.
When the soil particles are moved by wind or water and deposited elsewhere, they form sediments. These sediments may be covered under additional deposits of material; eventually, they are compacted and consolidated under the load of overlying layers. With time, the rock fragments can become cemented together, forming a second type of rock called sedimentary rock. Sandstone, formed from cemented sand grains, and shale, formed from consolidated and lithified mud (silt and clay), are common sedimentary rocks. Limestone, consisting primarily of the mineral calcite (calcium carbonate, CaCO3) crystallizing in a marine environment, is also a widely occurring sedimentary rock type.
Under conditions of excessive heat and pressure caused by environmental conditions, both the igneous and sedimentary rock types can be changed from their original forms and mineral structures. The newly formed rock is called metamorphic rock. Marble and slate are familiar examples of this third fundamental type of rock. Marble is formed as calcite in limestone recrystallizes due to heat and pressure. Slate is the metamorphic equivalent of shale.
Igneous rocks
Heat and pressure
Heat and pressure
Weathering, transpor t, deposition, consolidation
Weathering, transpor t, deposition, consolidation
y rocks
Both sedimentary and metamorphic rocks can again be subject to the weathering, transportation, and deposition process in a continual cycle of rock formation. This is illustrated in Figure 1-10.
The physical properties of rock that are of primary interest in environmental technology include those that are related to the underground storage and flow of water. Two terms are of significance in this regard: porosity and permeability. Rock is not entirely solid through and through. Porosity refers to the percentage of total rock volume that is occupied by voids, or pore spaces. Permeability refers to the characteristic of the rock that enables water to flow through the pore spaces. This is called the matrix permeability. Note that porous rocks are not necessarily highly permeable, particularly if the pore spaces are very small or are not interconnected.
Sedimentary rocks are generally porous and relatively permeable, whereas most igneous and metamorphic rocks are impermeable. Carbonate sedimentary rocks, such as limestone, are relatively soluble. In this type of rock, solution cavities may form as water slowly flows through the pore spaces and dissolves the mineral calcite. The solution cavities increase the rock’s permeability.
Rock formations have characteristic structural features that may also affect permeability. For example, a feature called layering or stratification is usually present in sedimentary rocks. This comes about because the unconsolidated soil particles are deposited as sediments by water or wind in horizontal layers; these layers may differ in particle size or mineral composition. As a consequence, permeability is generally higher in the direction parallel to the layers in sedimentary rocks.
Rock masses can gradually bend and fold because of environmental changes and earth movements. When the rocks shatter and crack from excessive stresses, fractures or fissures are formed; these are called joints. Joints in which one side of the rock mass moves or is displaced relative to the other side, as occurs during an earthquake, are called faults. Unless cemented or tightly closed, both joints and faults serve as convenient pathways for the flow of water and add fracture permeability to the rock mass. In soluble rocks like limestone, the joints can be enlarged by solution to form caves.
Sedimentar
Metamor phic rocks
Figure 1-10 Schematic diagram of the rock cycle.
Types of Soil
Soil, the unconsolidated rock fragments formed from weathering, may be classified or grouped on the basis of texture, or the size and shape of the soil particles. There are four major textural classifications of soil:
1. Gravel: rock fragments between 4.75 mm and 75 mm in size
2. Sand: rock particles larger than 0.075, but less than 4.75 mm in size
3. Silt: fine, powderlike particles larger than 0.002, but less than 0.075 mm
4. Clay: very small particles, less than 0.002 mm in size
Natural soil deposits may include organic materials (about 5 percent) and mineral rock fragments (about 45 percent). The remaining volume formed by the spaces, called pores (voids), which exist among and between adjacent soil particles, contains water (20 to 30 percent) and air (20 to 30 percent). When the pore spaces are completely filled with water, the soil is saturated.
The term “loam” is used for a combination of silt, sand, and clay; it may or may not contain organic material. Clay differs from gravel, sand, and silt not only in size but also in particle shape and mineral composition. Gravel, sand, and silt consist of relatively coarse grained, bulky particles; the very finely divided clay particles are platelike in shape and have a strong affinity for water.
The permeability of soil decreases as the particle size decreases. Gravel and sand are porous and highly permeable, readily allowing the flow of water through the spaces between the soil grains. Silt is considerably less permeable because of the small particle and void size, and clay, although a porous material, is virtually impervious to the flow of water. This is basically because the water in the clay is held by molecular forces on the platelike clay particles. The impermeability of clay soil can be used to advantage in building a sanitary landfill for solid waste disposal, but it is a serious disadvantage for subsurface disposal of wastewater. This is discussed in more detail in subsequent chapters.
In addition to “porosity” and “permeability,” other terms related to the flow of water in soil include infiltration and percolation. Infiltration refers to the penetration of the water through the ground surface layer of soil or rock, and percolation refers to the continuing movement or flow of water through the pore spaces under the force of gravity.
Generally, the tight soils, which contain a significant percentage of silt and clay, have low infiltration and percolation rates. However, coarse-textured soils, containing mostly sand or gravel, have high infiltration and percolation rates. Tight soils are not suitable for on-site subsurface disposal of sewage. The percolation or “perc” test, which may be used when designing on-site septic systems, is discussed in Section 10-5.
Soil Gradation Although soils can be classified according to particle size as gravel, sand, silt, or clay, naturally occurring soil deposits are not usually found in such distinctive groupings. They are generally mixed, containing a variety of
Figure 1-11 Typical soil gradation curve. The uniformity coefficient Cu can be used to classify the soil.
(From D.F. McCarthy, Essentials of Soil Mechanics and Foundations, 2nd ed., Reston Pub. Co., Reston, VA. Copyright 1982. Reprinted and electronically reproduced bt permission of Pearson Education, One Lake Street, Upper Saddle River, NJ 074580.)
soil particle sizes. The distribution and percentage of different particle sizes in the soil is referred to as soil gradation.
Soil gradation can be easily determined mechanically by separating the different soil particles in sieves or screens with varying sizes of mesh openings. The result of this mechanical analysis is usually expressed graphically in a gradation curve. A typical gradation curve is shown in Figure 1-11, where the vertical axis shows the percentage of the soil particles that are finer than a specific particle size, and the horizontal axis shows the particle size. This particular curve shows that 60 percent of the soil is less than 0.7 mm in size and 10 percent of the soil is less than about 0.12 mm.
The particle size for which 10 percent of the soil is smaller is called the effective size of the soil because there is a reasonably consistent relationship between the size and soil permeability. The effective size, designated D10, is used as a factor when specifying sand for filters used in water or wastewater treatment systems. Another gradation factor, called the uniformity coefficient, is also used in this regard. The uniformity coefficient is the ratio of two particle sizes: the 60 percent finer size and the effective size, or D60>D10. The soil depicted in the gradation curve in Figure 1-11 has an effective size of 0.12 mm and a uniformity coefficient of 0.7 mm/0.12 mm = 5.8.
Mixed soils can be described as being well graded or poorly graded, depending on the distribution of particle sizes. Good gradation is represented by curve A in Figure 1-12. There is a wide variation of particle sizes in this kind of soil; the smaller particles fit into and fill up most of the pore spaces between the larger particles. As a result, a well-graded soil tends to have relatively low porosity and permeability. It is also resistant to erosion and scour.
Gradation curve B is typical of a poorly graded soil, which consists primarily of soil grains in a very narrow range of sizes. In a soil of this type, the porosity and permeability are relatively high because there are not enough small particles to fill the voids between the larger particles. Poorly graded soils generally have uniformity coefficients of less than 10.
Mixed soils are ordinarily classified or grouped in order to help predict their behavior and characteristics. Several classification systems are used in soil mechanics technology, most of which are based on sieve analysis and other laboratory tests. One of the simplest methods, the USDA Textural
Figure 1-12 Well-graded soil (curve A) has lower porosity and permeability than poorly graded soil (curve B).
classification system makes use of a triangular classification chart, as illustrated in Figure 1-13.
The triangular classification chart relies only on the relative amounts of sand, silt, and clay in the soil sample. For example, a soil that contained 30 percent sand, 40 percent silt, and 30 percent clay would be characterized as clay loam on the chart. Generally, when the proportion of clay exceeds 20 percent of the total soil sample, the clay will tend to dominate the soil characteristics and behavior, and the primary soil type or designation will be clay. A classification scheme more common than the triangular chart, called the Unified Soil Classification System (USCS), makes use of additional lab test data to classify the soil. The textural characteristics of mineral soils, in terms of their feel and appearance, are summarized in Table 1-1. (Soil structure is discussed in Section 10-5).
Figure 1-13 Triangular soil classification chart.
(Courtesy of the Natural Resources Conservation Service, United States Department of Agriculture.)
Soil Survey Maps
A group of related soils that has developed from similar parent rock formations is called a soil series. Soils within a specific soil series are essentially alike in all basic characteristics. They are designated on the basis of their textural classification and the name of the geographic location that is particularly representative of the soil type.
Table 1-1 Textural Properties of Mineral Soils—Feel and Appearance
Soil
Sandy Gravel Loose stones and single grains that feel gritty. Squeezed in the hand, the soil mass falls apart when the pressure is released.
Silty sand Aggregates easily crushed; very faint velvety feeling initially, but with continued rubbing, the gritty feeling of sand soon dominates.
Sandy silt Aggregates are crushed under moderate pressure; clods can be quite firm. When pulverized, soil has velvety feel continued rubbing. Casts bear careful handling.
Clayey silt Aggregates are firm but may be crushed under moderate pressure. Clods are firm to hard. Smooth, flour-like feel dominates when soil is pulverized.
Silty clay Very firm aggregates and hard clods that strongly resist crushing by hand. When pulverized, the soil takes on a somewhat gritty feeling due to the harshness of the very small aggregates.
Clay Aggregates are hard; clods are extremely hard and strongly resist crushing by hand. When pulverized, it has a grit-like texture due to the harshness of numerous very small aggregates which persist.
Squeezed in the hand, it forms a cast that crumbles when touched. Does not form a ribbon when rubbed between thumb and forefinger.
Forms a cast that bears careful handling without breaking. Does not form a ribbon between the thumb and forefinger.
Casts can be handled quite freely without breaking. Very slight tendency to ribbon between the thumb and forefinger. Rubbed surface is rough.
Cast can be freely handled without breaking. Slight tendency to ribbon between thumb and forefinger. Rubbed surface has a broken or rippled appearance.
Cast can bear much handling without breaking. Pinched between the thumb and forefinger, it forms a ribbon whose surface tends to feel slightly gritty when dampened and rubbed. Soil is plastic, sticky, and puddles easily.
Casts can bear considerable handling without breaking. Forms a flexible ribbon between thumb and forefinger and retains its plasticity when elongated. Rubbed surface has a very smooth, satin feeling. Sticky when wet and easily puddled.
Source: National Small Flows Clearinghouse, 800-624-8301, http://www.nesc.wvu.edu/nsfc.
The Natural Resource Conservation Service (NRCS), formerly called the Soil Conservation Service (SCS), of the U.S. Department of Agriculture has surveyed local areas of the country and prepared countywide soil survey maps Soil survey maps show the location of different soil series in an area and are readily available in print form from most county NRCS offices and in digital form through the NRCS’s website. A part of a typical NRCS soil survey map is illustrated in Figure 1-14.
Soil survey maps are superimposed on top of aerial photographs of the area. In addition to the soil series distribution, they show lakes, roads, and other physical land features. They are particularly useful as an aid for good landuse planning and development. The letter symbols, such as HnB and RrD, designate the soil series. For example, HnB stands for “Hibernia very stony loam, 3 to 8 percent slopes.” RrD stands for “Rockaway rock outcrop association, sloping and moderately steep.” Hibernia and Rockaway are the geographic locations in Sussex County, New Jersey, where these soils have been identified.
Soil series boundar y line
Figure 1-14 Typical NRCS soil series map. The symbols identify the different soil series in an area. The characteristics of each soil series are described in the NRCS publications. (Courtesy of the Soil Conservation Service, United States Department of Agriculture.)
Figure 1-15 The slope of the ground surface is important in environmental planning. Slopes of over 15 percent are generally considered to be steep.
The slope of the ground is of importance in environmental planning and land development. Slopes expressed in percent (%) represent the change in elevation of the ground per 100 m or 100 ft of horizontal distance. For example, a hill with a 20 percent slope changes 20 m in elevation in a distance of 100 m. This is illustrated in Figure 1-15.
Slopes of less than 5 percent are usually considered to be gentle, whereas those over 15 percent are considered to be steep. Steep slopes are much more susceptible to high rates of stormwater runoff and soil erosion than are gentle slopes. In contrast, areas of very flat topography (0 to 2 percent slopes) may suffer from poor stormwater drainage and flooding problems. Modern municipal land-use ordinances may limit the extent of home building and other development allowed on steep slopes, and proper hydraulic design of storm drainage systems is important for the very flat areas.
The descriptive material in the NRCS soil survey reports contains a lot of information regarding soil characteristics and behavior. Data on depth to bedrock and depth to the water table are given. Bedrock is the unweathered rock formation underlying the surface soils. The water table represents the depth at which the soil is saturated with water, as is discussed in more detail in Chapter 3. Depth to bedrock and the water table are important with respect to designing solid or liquid waste disposal facilities. Other NRCS data include soil index properties, gradation, permeability, erosion potential, and suitability of the land for various types of development. For example, the HnB series is described as having a seasonal high water table that severely limits the use of the ground for a sanitary landfill or septic tank absorption fields.
1-5 hiStOrical PerSPective
Water was an important factor in the location of the earliest settled communities, and evolution of public water supply systems is the first focus of environmental technology (which, of course, is a modern expression). In the development of water resources beyond their natural condition in local rivers, lakes, and springs, the digging of shallow wells was perhaps the first innovation. As the need for water increased
and tools were developed, the wells were made deeper. The need to move water supplies from distant sources was an outcome of the growth of urban communities.
Piped water supply systems have been in existence for well over 3000 years. Archeological findings show that pipes were made out of hollow logs, clay, and other materials that could not withstand much in the way of pressure. Even the most sophisticated of the ancient systems, the masonry aqueducts and tunnels constructed by the ancient Romans (many of which are still standing), were not capable of carrying water under pressure.
Ancient Rome had sewers as well as aqueducts, but these were used primarily as storm drains rather than for sanitary disposal of human wastes. At that time in history there was no knowledge of the relationship between improper waste disposal and the spread of disease.
Not until the mid-1800s did people realize that there was a direct connection between contaminated drinking water and disease. The cause of a localized cholera epidemic in London was traced by Dr. John Snow to a polluted community well, known as the Broad Street well. People who drew their water from the well were affected by the epidemic, whereas people with other water sources were not affected at all. When the well was taken out of service by simply removing the pump handle, the outbreak of cholera subsided.
The Broad Street well incident of 1854 pointed to the need for proper disposal of human wastes and for clean water supplies. Today, it is common knowledge that sewage carries “germs” that can spread disease, but in 1854 the germ theory of disease had not even been postulated. The only evidence of the need for sanitation was the coincidence of the dirty well water and the epidemic. It was not until the late 1800s that Robert Koch proved that the presence of certain microscopic living organisms caused disease in humans. Koch’s famous postulates state that (1) a specific organism can always be found in association with a given disease. (2) The organism can be isolated and grown in pure culture in the laboratory. (3) The pure culture will produce the disease when inoculated into a susceptible animal. (4) It is possible to recover the organism in pure culture from the experimentally infected animal.
In the United States, a piped water supply system was used for the first time in 1801 when a steam-powered waterworks station was put into operation in Philadelphia. By the end of the 1800s, about 25 percent of all urban households in the country had running water. During the mid-1800s, sewers began to replace cesspools for waste disposal because of the rapid growth of urban populations and the provision of running water in individual homes. Construction of the first large sewage collection systems in the United States was completed in Chicago and Brooklyn in the late 1850s. Serious outbreaks of cholera and other epidemics of waterborne disease were frequent in American cities throughout the 1800s.
Water filtration plays an important role in disease prevention. The first slow sand filters in the United States were built in Poughkeepsie, New York, in 1872 to treat water from the Hudson River, called “one of the most polluted and
potentially dangerous water sources in the world” by engineers and scientists of that time. A filter plant was also constructed in Lawrence, Massachusetts, in 1892, dramatically reducing the number of typhoid outbreaks caused by the polluted Merrimac River water source. The Lawrence filter plant proved to be a turning point in establishing the practice of “sanitary engineering” on a scientific basis.
Beginning in the first decade of the 20th century, newly applied water purification techniques, mostly by disinfection using chlorine, started to drastically reduce the incidence of waterborne diseases in the United States. The dramatic inverse relationship between the number of American water supplies being chlorinated and the decline in waterborne disease is clearly evident from the historical record. At the beginning of the 20th century, there were more than 250 reported waterborne disease outbreaks occurring each year in the United States, but there were no water chlorination plants. By 1960, when there were about 9000 chlorination plants in operation, fewer than about 10 waterborne disease outbreaks were reported each year. Chlorine was used for the first time in the United States for disinfecting the Jersey City, New Jersey, water supply in 1908.
In the first half of the 20th century, many public health authorities believed that “the solution to pollution is dilution.” They felt that the best and most economical way to protect public health was to purify drinking water, not wastewater. Most sewage was discharged untreated (or “raw”) into streams and rivers. The first facility for “primary sewage treatment” was built in New Jersey, in 1911, and the first “secondary sewage treatment” plant was built in Texas, in 1916. A large-scale municipal sewage treatment plant was built in Milwaukee, Wisconsin, in 1919. But it was not until the late 1950s that it really became apparent that wastewater treatment was important for water pollution control and public health protection. (Primary and secondary wastewater treatment is discussed in Chapter 10.)
The first “Earth Day” celebration in 1970 heralded a new environmental era in the United States, when air quality and solid and hazardous waste disposal joined with drinking water supply and water pollution control as major concerns. The more comprehensive profession called environmental engineering replaced the field called sanitary engineering. This new environmental era is discussed further, below. (The historical development of solid and hazardous waste disposal methods are discussed in Chapters 11 and 12, and air pollution control requirements are discussed in Chapter 13.)
An Era of Environmental Awareness
In the 1960s, a broad awareness of environmental pollution problems developed among the general public. Many people came to realize the value and importance of protecting environmental quality. Clean air and clean water were worth rallying about, and public demonstrations were held. People wanted streams and lakes that could be used for swimming and fishing as well as for safe drinking water supplies.
The words ecosystem and biosphere became popular buzzwords, and newspaper articles about local pollution problems became more common. Educational programs that focused on ecology and environmental issues were developed for grade school through the university level and grew in popularity.
In addition to stopping air and water pollution, solving problems related to refuse disposal, radiation, noise, pesticides, and wildlife preservation became important in the modern quest for environmental quality. Although infectious diseases like typhoid and cholera had virtually disappeared in the United States, people became aware of other types of problems caused by human and ecosystem exposure to industrial toxic chemical substances.
Rachel Carson’s influential book, Silent Spring, a “bestseller” in the early 1960s (as of 2012, 2 million copies had been sold), focused attention on the environmental damage caused by improper use of pesticides. DDT and other synthetic chemicals used to protect agricultural crops were seriously disrupting the natural balance of ecosystems on a wide scale. After DDT was finally banned for most uses in the United States in 1972, the concentrations of this chemical found in human and animal tissues was observed to decline significantly, and several endangered species, such as the bald eagle and osprey, began to thrive once again. (American chemical companies continued to export DDT until the mid-1980s; China ceased manufacturing the pesticide in 2007.)
The emergence of an environmental awareness on the part of the general public in the 1960s was apparently more than just a passing fad. It was a genuine concern that served to focus the attention of politicians, lawmakers, and governmental agencies on the need for an appropriate legal and regulatory framework for environmental quality control.
In 1970, the National Environmental Policy Act (NEPA) was signed into law in the United States. NEPA established a national policy to “maintain conditions under which humans and nature can exist in productive harmony, and fulfill the social, economic, and other requirements of present and future generations of Americans.” The concept of using EISs as a planning tool to minimize the harmful effects of land development and urban growth was developed for the first time under NEPA. In 1970, the EPA was also created, consolidating into one independent federal agency a means for establishing and enforcing pollution control and environmental quality standards.
The EPA is basically a regulatory agency, but it has other responsibilities in addition to establishing and enforcing environmental standards. It is a research organization with a scientific and technical staff that collects environmental data and studies the causes, effects, and methods of control for all types of pollution. The EPA also provides technical and financial assistance to state governments. Individual states have set up their own environmental protection agencies to provide similar assistance to county and municipal governments.
Environmental Regulations
Since 1970, many laws have been enacted by Congress to establish and implement standards of environmental quality for water, land, and air. Many of these laws have been revised and amended several times since their enactment, and some remain under congressional review. A few of the key environmental laws are listed next and are discussed in pertinent sections of this book:
● Clean Air Act (CAA)
● Clean Water Act (CWA)
● Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA)
● Resource Conservation and Recovery Act (RCRA)
● Safe Drinking Water Act (SDWA)
Implementing and enforcing these and other environmental laws is very expensive. To some people, the objectives of environmental protection seem to be at odds with other goals—industrial growth and economic “progress.” But in the long run, the external diseconomies caused by environmental degradation are likely to be far greater than the costs of regulation. In other words, if the environment is damaged now in the interest of profits, society will have to “pay the piper” in the future, either in the form of expensive cleanup operations and increased health problems and medical costs or in a generally lower quality of life.
Although there is often controversy on just what steps to take and how much to spend for environmental protection, most people agree that the problem cannot be ignored altogether. A certain amount of governmental regulation will always be necessary. Eventually, a balance will be reached in which environmental, economic, energy, and social problems will be solved without one preempting or overshadowing the others. Meanwhile, there is a need for technical personnel at all levels of training and education to plan, design, build, and operate environmental control systems. (See Appendix B.)
Green Engineering and Environmental Sustainability
The need for enforceable governmental regulations to preserve environmental quality and to protect public health became well established over the second half of the 20th century. As successful as these laws and regulations have been, it has gradually become clear that more efforts are needed to protect the environment, conserve energy, and preserve natural resources. At the beginning of this century, a distinct environmental trend has emerged in this regard and taken root in many industrial and construction practices, including the production of chemicals, the manufacture of appliances and other consumer items, and the design and construction of commercial, institutional, and residential buildings. This trend is generically called “green engineering.”
The earth’s natural resources are limited in quantity as well as in capacity to absorb the ecological impacts of human activities. A primary goal of green engineering is “environmental sustainability,” a phrase that reflects the long-term need to conserve as well as to protect those resources from contamination or depletion. Current governmental regulations do not explicitly mandate application of green engineering principles. But many industrial, engineering, and architectural organizations, building owners and project developers, and professional design practitioners, are voluntarily adopting and applying its goals and practices. Environmental considerations are factored in to the entire planning, design, production, and construction process from the very beginning of a project.
“Green chemistry,” for example, is a discipline-specific area of green engineering. It involves the design of chemical processes and development of products in a way that conserves resources and energy, and reduces or eliminates the generation of hazardous wastes over the life cycle of the product. The U.S. Environmental Protection Agency (USEPA) promotes green chemistry by awarding Presidential Green Chemistry Awards.
Another application of green engineering is called “green building design and construction,” which mitigates negative environmental impacts related to the siting and construction as well as the operation and maintenance of various types of buildings. It has the added benefits of reducing building operation and maintenance costs and enhancing building marketability. In year 2000, the U.S. Green Building Council (USGBC) initiated the Leadership in Energy and Environmental Design (LEED) Green Building Rating System to provide a method for ranking and certifying “green buildings.” This program has evolved over the years; the LEED system is an internationally recognized program. The Canada Green Building Council (CaGBC), for example, uses the LEED certification protocol (adapted for Canadian conditions).
(See Appendix C for more information on LEED certification; green building design and construction technology is included in related sections of the text.)
Low-impact development (LID), a component of green building design, is the application of green engineering principles to site preparation and stormwater management. LID is an array of land planning and development practices used to manage stormwater and reduce pollution to streams, lakes, wetlands, and coastal areas. A key objective in LID is designing a landscape so that the movement, treatment, and storage of stormwater are similar to what occurs on a natural landscape. By promoting infiltration of stormwater, reducing overland runoff, and protecting vegetated areas, LID practices can help reduce groundwater depletion, reduce the number and magnitude of flooding events, improve water quality, and enhance neighborhood beauty. (LID is discussed in Chapter 9.)
1-6 chaPter SynOPSiS
Environmental technology is a broad, interdisciplinary field involved in providing water supply, pollution control, and waste management infrastructure. Generally a part of civil engineering, it encompasses the objectives of public health protection and environmental quality control. These objectives are achieved by the efforts of a knowledgeable team of engineers, technologists, and technicians who have training in many diverse disciplines, including hydraulics, hydrology, biology, chemistry, geology, physics, and mathematics. Environmental technology is also an integral component of modern green building design and low impact development projects, which all endeavor to protect environmental quality and sustainability.
Practitioners in environmental technology work on projects related to drinking water purification and distribution; sewage collection, treatment, and disposal; stormwater management and flood control; solid and hazardous waste disposal; air and noise pollution control; community sanitation; and the general protection of air, water, and land environments.
Environmental quality control involves the application of basic ecological principles. Public health protection involves prevention of the spread of communicable and noninfectious diseases. Although biologists and doctors are involved in these activities, they are supported to a large degree by engineering and technological activities. Pathogenic microbes such as bacteria, protozoa, and viruses cause communicable diseases. Toxic chemical pollution is often the cause of noninfectious disease. Environmental technology serves to break the cycle of transmission of disease, and most water purification systems involve the construction of synthetic ecological or biological systems. One of the easiest ways to protect public health and environmental quality is to provide water and wastewater treatment, as well as proper sanitation.
Two basic principles of ecology involve the one-way flow of energy and the circulation of nutrient materials, which are manifested in a food chain comprising producers, consumers, and decomposers. The sun is the primary source of the energy, and two fundamental metabolic processes, photosynthesis and respiration, keep the cycle of the food chain going. In the process of photosynthesis, plants (the producers) use the solar energy to form carbohydrates from carbon dioxide and water, releasing oxygen into the air. Oxygen is essential for the next trophic level of a food chain (the consumers), which eats the plants to obtain nutrients and energy for growth and reproduction, using the process of respiration. A food chain cycle is completed by microscopic decay organisms (the decomposers), which break down the waste products and remains of dead consumer organisms into simpler substances that are once again available for the producers.
A healthy and stable ecosystem is one that is occupied by many different species of living organisms, and the
greater the diversity of species, the healthier is the ecosystem. All ecosystems change over time in a process called natural succession until a climax stage is reached. Pollution of an ecosystem, particularly by nonbiodegradable toxic substances such as DDT and PCBs, can lead to bioaccumulation and biomagnification, causing great harm throughout the higher trophic levels. The extinction of species is a natural process that can be accelerated as a consequence of human activity and pollution. A basic objective of the Endangered Species Act is to protect both endangered and threatened (likely to become endangered) species of fish, wildlife, and plants.
Earth’s mantle (soil and rock) serves not only as the foundation of structures but also as the depository of many of civilization’s waste products. Consequently, geology is of particular significance within the discipline of environmental technology, particularly with regard to the protection of groundwater resources. Soil, the unconsolidated rock fragments formed from weathering, comprises four major textural classifications: gravel, sand, silt, and clay. Gravel and sand are porous and highly permeable, readily allowing the flow of water through the pore spaces between the soil grains. Silt is somewhat less permeable, and clay is very impermeable. Naturally occurring soil deposits comprise a
review Questions
1. Give a brief definition of environmental technology, including mention of basic activities and objectives.
2. List at least 15 technical factors or options related to the environmental aspects of a land development project.
3. Define the term “pathogen.”
4. Briefly discuss the modes of transmission of communicable disease.
5. List five common intestinal diseases. What is the most common mode of transmission of these diseases?
6. Briefly discuss the environmental aspects of noninfectious diseases with reference to some specific illnesses.
7. What constitutes an ecosystem? Give examples of five different types and sizes of ecosystems.
8. Make a sketch that illustrates the two basic principles of ecology.
9. Briefly describe two fundamental metabolic processes of living organisms.
10. What is the difference between a heterotrophic and an autotrophic organism?
11. What is the difference between aerobic and anaerobic decay?
12. What is the difference between putrefaction and fermentation?
variety of soil particle sizes and the distribution of particle sizes is called the soil gradation or texture. Other important soil characteristics include soil structure and color. Soil series (a group of related soils) are depicted on countywide soil survey maps available from the NRCS.
The field of environmental technology, as it is now practiced, is only a little more than 50 years old. In the United States, an era of environmental awareness began primarily in the early 1960s. In 1970, the NEPA was signed into law in the United States. Other federal and state laws and regulations enacted since that time provide a framework within which public and environmental health protection rules are legally enforceable. Protecting public health and environmental quality costs money, but direct and indirect costs of not applying environmental technologies can be even greater. Practically speaking, it is not possible to completely eliminate environmental pollution. However, it is possible to apply basic mathematics, science, economics, and engineering knowledge in an effort to minimize or avert most adverse effects of air, water, and land pollution caused by human activities, and to conserve energy and natural resources. This textbook provides a “user-friendly” learning tool for students who seek to understand the fundamentals of environmental technology.
13. Sketch a biogeochemical cycle for two different macronutrients.
14. What are plankton, and what role do they play in the aquatic food web?
15. Why is species diversity important for an ecosystem?
16. What is meant by natural succession of an ecosystem?
17. Briefly describe three types of rock and give one example of each type. Briefly compare their permeabilities. What role do structural features such as layering, joints, and faults play in permeability?
18. What is the difference between the terms “porosity” and “permeability”? What is the difference between infiltration and percolation?
19. What is soil? List four basic types of soil and compare their permeability characteristics.
20. What is meant by soil gradation? What is meant by the effective size and uniformity coefficient of soil? Why is soil gradation important in environmental technology?
21. What is the difference between a well-graded soil and a poorly graded soil? Illustrate the difference by sketching typical gradation curve shapes for each. If a soil sample had a uniformity coefficient of 50, would it be considered well graded or poorly graded?
22. A soil sample is determined to contain 25 percent sand, 20 percent silt, and 55 percent clay. Using the triangular classification chart in Figure 1-13, how would you
