Final Paper---Pollution Prevention

CHAPTER 19

Botkin, D. B., & Keller, E. A. (2014). Environmental science: Earth as a living planet (9th ed.). Hoboken, NJ: John Wiley & Sons, Inc.

19.1 Water Pollution

Water pollution refers to degradation of water quality. In de- fining pollution, we generally look at the intended use of the water, how far the water departs from the norm, its effects on public health, or its ecological impacts. From a public- health or ecological view, a pollutant is any biological, physi- cal, or chemical substance that, in an identifiable excess, is known to be harmful to desirable living organisms. Water pollutants include heavy metals, sediment, certain radioac- tive isotopes, heat, fecal coliform bacteria, phosphorus, ni- trogen, sodium, and other useful (even necessary) elements, as well as certain pathogenic bacteria and viruses. In some instances, a material may be considered a pollutant to a par- ticular segment of the population, although it is not harmful to other segments. For example, excessive sodium as a salt is not generally harmful, but it may be harmful to people who must restrict salt intake for medical reasons.

Today, the world’s primary water pollution problem is a lack of clean, disease-free drinking water for about 1.1 bil- lion people6 (Figure 19.4). In the past, epidemics (outbreaks) of waterborne diseases such as cholera killed thousands of people in the United States. Fortunately, we have largely eliminated epidemics of such diseases in the United States by treating drinking water prior to consumption. This cer- tainly is not the case worldwide, however. Every year, several billion people are exposed to waterborne diseases. For ex- ample, an epidemic of cholera occurred in Haiti following the 2010 earthquake. Waterborne disease is especially likely following natural disasters such as floods and earthquakes that damage water systems; outbreaks of waterborne diseases continue to be a threat, even in developed countries.

Many different processes and materials may pollute surface water or groundwater. Some of these are listed in Table 19.1. All segments of society—urban, rural, indus- trial, agricultural, and military—may contribute to the problem of water pollution. Most of it results from runoff and leaks or seepage of pollutants into surface water or groundwater. Pollutants are also transported by air and deposited in bodies of water.

Increasing population often introduces more pollutants into the environment, as well as greater demands on finite water resources.7 As a result, we can expect sources of drinking water in some locations to be degraded in the future.8,9

The U.S. Environmental Protection Agency has set thresholds limiting the allowable levels for some (but not all) drinking water pollutants. Because it is difficult to de- termine the effects of exposure to low levels of pollutants, thresholds have been set for only a small fraction of the more than 700 identified drinking water contaminants. If the pollutant exceeds an established threshold, then the water is unsatisfactory for a particular use. Table 19.2 lists selected pollutants included in the national drinking water standards for the United States.

Water withdrawn from surface or groundwater sources is treated by filtering and chlorinating before distribution to urban users. Sometimes it is possible to use the natural environment to filter the water as a service function, saving treatment cost (see A Closer Look 19.1).

The following sections focus on several water pollut- ants to emphasize principles that apply to pollutants in general. (See Table 19.3 for categories and examples of water pollutants.) Before proceeding to our discussion of pollutants, however, we first consider biochemical oxy- gen demand and dissolved oxygen. Dissolved oxygen is not a pollutant but rather is needed for healthy aquatic ecosystems.

19.2 Biochemical oxygen Demand (BoD)

Dead organic matter in streams decays. Bacteria carrying out this decay use oxygen. If there is enough bacterial ac- tivity, the oxygen in the water available to fish and other organisms can be reduced to the point where they may die. A stream with low oxygen content is a poor environ- ment for fish and most other organisms. A stream with an inadequate oxygen level is considered polluted for organ- isms that require dissolved oxygen above the existing level.

The amount of oxygen required for biochemical decom- position processes is called the biological or biochemical oxygen demand (BOD). BOD is often used in water-qual- ity management (Figure 19.6a). BOD measures the amount of oxygen consumed by microorganisms as they break down organic matter within small water samples, which are an- alyzed in a laboratory. BOD is usually expressed in milli- grams of oxygen consumed by biodegradable organic matter per liter (mg/l) of a water sample over five days of incubation at 20°. The test is not considered an accurate quantitative test, but it is a commonly used indicator of water quality. BOD is routinely measured at discharge points into surface water, such as at wastewater treatment plants. At treatment plants, the BOD of the incoming sewage water from sewer lines is measured, as is water from locations both upstream and downstream of the plant. This allows comparison of up- stream, or background, BOD, with the BOD of the water being discharged by the plant.

Dead organic matter—the source of BOD—enters streams and rivers from natural sources (such as dead leaves from a forest), as well as from agricultural runoff and urban sewage. Approximately 33% of all BOD in streams results from agricultural activities. However, urban areas, particu- larly those with older, combined sewer systems (in which storm water runoff and urban sewage share the same line), also considerably increase BOD in streams. This is because during times of high flow, when sewage treatment plants are unable to handle the total volume of water, raw sew- age mixed with storm runoff overflows and is discharged untreated into streams and rivers. For example, when Hur- ricane Sandy caused widespread flooding in 2012, some combined sewer systems in New York City overflowed, creating a water pollution problem.

When BOD is high, as suggested earlier, the dissolved oxygen content of the water may become too low to sup- port life in the water. The U.S. Environmental Protection Agency defines the threshold for a water pollution alert as a dissolved oxygen content of less than 5 mg/l of water. Figure 19.6b illustrates the effect of high BOD on dissolved oxygen content in a stream when raw sewage is introduced as a result of an accidental spill. Three zones are identified:

1. A pollution zone, where a high BOD exists. As waste decomposes, microorganisms use the oxygen, decreas- ing the dissolved oxygen content of the water.

2. An active decomposition zone, where the dissolved oxy- gen reaches a minimum, owing to rapid biochemical decomposition by microorganisms as the organic waste is transported downstream.

3. A recovery zone, where dissolved oxygen increases and BOD is reduced because most of the oxygen- demanding organic waste from the input of sewage has decomposed and natural stream processes are replenishing the water’s dissolved oxygen. For example, in quickly moving water, the water at the surface mixes with air, and oxygen enters the water.

All streams have some ability to degrade organic waste. Problems result when the stream is overloaded with oxygen-demanding waste, overpowering the stream’s natural cleansing function.

19.3 Nutrients

Two important nutrients that cause water pollution prob- lems are phosphorus and nitrogen, and both are released from sources related to land use. As explained in Chapters 7 (biogeochemical cycles) and 11 (agriculture), phospho- rus and nitrogen are major, essential vegetation nutrients. They are important in fertilizers, and excess amounts ap- plied to farmland run off. Also, domestic animals, includ- ing cattle and sheep, produce large quantities of nitrogen and phosphorus in their wastes. Stream waters on forested land have the lowest concentrations of phosphorus and nitrogen because forest vegetation and vegetation in wet- lands within forests efficiently remove phosphorus and nitrogen. In urban streams, concentrations of these nu- trients are greater because of fertilizers, detergents, and products of sewage treatment plants. Often, however, the highest concentrations of phosphorus and nitrogen are found in agricultural areas, where the sources are fertil- ized farm fields and feedlots (Figure 19.7). Over 90% of all nitrogen added to the environment by human activity comes from agriculture.

Eutrophication

Eutrophication is the process by which a body of wa- ter develops a high concentration of nutrients, such as nitrogen and phosphorus (in the forms of nitrates and phosphates). The nutrients increase the growth of aquatic plants in general, as well as production of photosynthetic blue-green bacteria and algae. Algae may form surface mats that shade the water and block light to algae below the surface, greatly reducing photosynthesis. The bacteria and algae die, and as they decompose, BOD increases, re- ducing the water’s oxygen content, sometimes to the point where other organisms, such as fish, will die.10,11 They die not from phosphorus poisoning but from a chain of events that started with the input of phosphorus and af- fected the whole ecosystem. The unpleasant effects result from the interactions among different species, the effects of the species on chemical elements in their environment, and the condition of the environment (the body of water and the air above it). This is what we call an ecosystem effect.

The process of eutrophication of a lake is shown in Figure 19.8. A lake that has a naturally high concentration of the chemical elements required for life is called a eutrophic lake. A lake with a relatively low concentration of chemical elements required by life is called an oligo- trophic lake. The water in oligotrophic lakes is clear and pleasant for swimmers and boaters and has a relatively low abundance of life. Eutrophic lakes have an abundance of life, often with mats of algae and bacteria and murky, un- pleasant water.

When eutrophication is accelerated by human processes that add nutrients to a body of water, we say that cultural eutrophication is occurring. Problems associated with the artificial eutrophication of bodies of water are not restricted to lakes (see A Closer Look 19.2). In recent years, concern has grown about the outflow of sewage from urban areas into tropical coastal waters and cultural eutrophication on coral reefs.12,13 For example, parts of the famous Great Bar- rier Reef of Australia, as well as some reefs that fringe the Hawaiian Islands, are being damaged by eutrophication.14,15 The damage to corals occurs as nutrient input stimulates al- gal growth on the reef, which smothers the coral.

The solution to artificial eutrophication is fairly straightforward and involves ensuring that high concen- trations of nutrients from human sources do not enter lakes and other bodies of water. This can be accomplished by using phosphate-free detergents, controlling nitrogen- rich runoff from agricultural and urban lands, disposing of or reusing treated wastewater, and using more advanced water treatment methods, such as special filters and chem- ical treatments that remove more of the nutrients.

19.4 Waterborne Disease

As mentioned earlier, the primary water pollution prob- lem in the world today is the lack of clean drinking wa- ter. Each year, particularly in less developed countries, several billion people are exposed to waterborne diseases whose effects vary in severity from an upset stomach to death. As recently as 2010–2012, an epidemic of cholera, a serious waterborne disease, caused widespread suffer- ing. Hundreds of thousands of people were hospitalized and 8000 died of cholera in Haiti after the 2010 earth- quake. Disasters often are followed by disease as people are forced to live in unsanitary conditions. The disease spread to neighboring Dominican Republic, Cuba, and Venezuela.

In the United States, we tend not to think much about waterborne illness. Although historically epidem- ics of waterborne disease killed thousands of people in U.S. cities, such as Chicago, public-health programs have largely eliminated such epidemics by treating drinking water to remove disease-carrying microorganisms and not allowing sewage to contaminate drinking water supplies.

As we will see, however, North America is not immune to outbreaks—or sudden occurrences—of waterborne disease.

Fecal Coliform Bacteria

Because it is difficult to monitor disease-carrying organ- isms directly, we use the count of fecal coliform bacteria as a standard measure and indicator of disease potential. The presence of fecal coliform bacteria in water indicates that fecal material from mammals, including people, or birds is present, so organisms that cause waterborne dis- eases may be present as well. Fecal coliform bacteria are usually (but not always) harmless bacteria that normally inhabit the intestines of all animals, including humans, and are present in all their waste. Because it is so com- mon, it is a convenient and reliable indicator of popula- tion from vertebrate animal wastes. The EPA’s threshold for swimming water is not more than 200 cells of fecal coliform bacteria per 100 ml of water; if fecal coliform is above the threshold level, the water is considered unfit for swimming (Figure 19.10). Water with any fecal coliform bacteria is unsuitable for drinking.

One type of fecal coliform bacteria, Escherichia coli, or E. coli 0157, has caused human illness and death. In the United States, there are about 73,000 cases and 60 deaths per year from E. coli 0157. Outbreaks have resulted from eating contaminated meat (fecal transmission from humans and other animals) and drinking contaminated juices or water.16–19 Table 19.4 lists some recent outbreaks of disease resulting from E. coli 0157.

Identifing sources of E. coli in water is necessary so that aggressive action can be taken to eliminate pollut- ants before they reach our waterways and beaches. DNA fingerprinting studies can be done on E. coli and other living pathogens to identify sources of harmful pollutants. (See Chapter 9 for a discussion of DNA chemistry and form.) DNA patterns of species of E. coli bacteria found

in the gut of people and other animals can be matched (similar to matching human DNA in crime investiga- tions) to identify the source (horses, humans, birds, dogs etc.). Once sources are identified, management plans to minimize pollution are more effective.

19.5 oil

Oil discharged into surface water—usually in the ocean but also on land and in rivers—has caused major pollu- tion problems. Several large oil spills from underwater oil drilling have occurred in recent years (for example, the 2010 spill in the Gulf of Mexico, discussed in detail in Chapter 15). Although spills make headlines, normal shipping activities probably release more oil over a period of years than is released by the occasional spill. The cumu- lative impacts of these releases are not well known.

Some of the best-known oil spills are caused by tanker accidents. On March 24, 1989, the supertanker Exxon Valdez ran aground on Bligh Reef south of Valdez in Prince William Sound, Alaska. Alaskan crude oil that had been delivered to the Valdez through the Trans-Alaska Pipeline poured out of the vessel’s ruptured tanks at about 20,000 barrels per hour. The tanker was loaded with about 1.2 million barrels of oil, and about 250,000 barrels (11 million gal) entered the sound. The spill could have been larger than it was, but fortunately some of the oil in the tanker was offloaded (pumped out) into another vessel. Even so, the Exxon Valdez spill produced an environmental shock that resulted in passage of the Oil Pollution Act of 1990 and a renewed evaluation of cleanup technology.

The long-term effects of large oil spills are uncertain. We know that the effects can last several decades; toxic levels of oil have been identified in salt marshes 20 years after a spill.20,21

Drilling for oil and gas also has the potential for sur- face and groundwater contamination (see Chapter 15). There are also potential threats from abandoned oil wells that have been plugged and, all too often, forgotten. Plugs may eventually fail, and oil and natural gas may seep to the surface to pollute water resources.8

19.6 Sediment

Sediment consisting of rock and mineral fragments— ranging from gravel particles greater than 2 mm in di- ameter to finer sand, silt, clay, and even finer colloidal particles—can produce a sediment pollution problem. By volume and mass, sediment is our greatest water pollut- ant. In many areas, it chokes streams; fills lakes, reservoirs, ponds, canals, drainage ditches, and harbors; buries veg- etation; and generally creates a nuisance that is difficult to remove. Sediment pollution is a twofold problem: It results from erosion, which depletes a land resource (soil) at its site of origin (Figure 19.11), and it reduces the qual- ity of the water resource it enters.22 Water quality not only affects our water supply, it also affects fish and other wild- life. For example, salmon lay their eggs in gravel on the bottom of rivers and streams. But the gravel has to be uni- form in size and of a certain range of sizes. Erosion events can change the characteristic of the sediment and turn an active salmon stream into a poor one for these fish.

Many human activities affect the pattern, amount, and intensity of surface-water runoff, erosion, and sedimenta- tion. Streams in naturally forested or wooded areas may be nearly stable, with relatively little excessive erosion or sedimentation. However, converting forested land to agri- culture generally increases the runoff and sediment yield or erosion of the land. Applying soil conservation procedures to farmland can minimize but not eliminate soil loss. The change from agricultural, forested, or rural land to highly urbanized land has even more dramatic effects. But al- though the construction phase of urbanization can produce large quantities of sediment, sediment production and soil erosion can be minimized by on-site erosion control.23

19.7 Acid Mine Drainage

Acid mine drainage is water with a high concentration of sulfuric acid (H2SO4) that drains from mines—mostly coal mines, but also metal mines (copper, lead, and zinc). Coal and the rocks containing coal are often associated with a mineral known as fool’s gold or pyrite (FeS2), which is iron sulfide. When the pyrite, which may be finely dis- seminated in the rock and coal, comes into contact with oxygen and water, it weathers. A product of the chemical weathering is sulfuric acid. In addition, pyrite is associat- ed with metallic sulfide deposits, which, when weathered, also produce sulfuric acid. The acid is produced when sur- face water or shallow groundwater runs through or moves into and out of mines or tailings (Figure 19.12). If the acidic water runs off to a natural stream, pond, or lake, significant pollution and ecological damage may result. The acidic water is toxic to the plants and animals of an aquatic ecosystem; it damages biological productivity, and fish and other aquatic life may die. Acidic water can also seep into and pollute groundwater.

Acid mine drainage is produced by complex geo- chemical and microbial reactions. The general equation is as follows:

4 FeS 1 15 O 1 14 H O S 4 Fe 1OH2 8 H SO 222324

Pyrite 1 Oxygen 1 Water S Ferric Hydroxide 1 Sulfuric Acid

Acid mine drainage is a significant water pollution problem in Wyoming, Indiana, Illinois, Kentucky, Ten- nessee, Missouri, Kansas, and Oklahoma and is probably the most significant water pollution problem in West Vir- ginia, Maryland, Pennsylvania, Ohio, and Colorado. The total impact is significant because thousands of kilometers of streams have been damaged.

Even abandoned mines can cause serious problems. Subsurface mining for sulfide deposits containing lead and zinc began in the tristate area of Kansas, Oklahoma, and Missouri in the late 19th century and ended in some areas in the 1960s. When the mines were operating, they were kept dry by pumping out the groundwater that seeped in. However, since the mining ended, some of them have flooded and overflowed into nearby creeks, polluting the creeks with acidic water. The problem was so severe in the Tar Creek area of Oklahoma that it was at one time designated by the U.S. Environmental Protection Agency as the nation’s worst hazardous- waste site.

S Calcium Sulfate 1 Water 1 Carbon Dioxide

One solution being used in Tar Creek and other areas is a passive treatment method that uses naturally occur- ring chemical and/or biological reactions in controlled environments to treat acid mine drainage. The simplest and least expensive method is to divert acidic water to an open limestone channel, where it reacts with crushed limestone and the acid is neutralized. A general reaction that neutralizes the acid is

H2SO4 1 CaCO3 S CaSO4 1 H2O 1 CO2 Sulfuric Acid 1 Calcium Carbonate 1crushed limestone2

Another solution is to divert the acidic water to a bio- reactor (an elongated trough) containing sulfate-reducing bacteria and a bacteria nutrient to encourage bacterial growth. The sulfate-reducing bacteria are held in cells that have a honeycomb structure, forcing the acidic water to follow a tortuous path through the bacteria-laden cells of the reactor. Complex biochemical reactions between the acidic water and bacteria in the reactor produce metal sulfides and in the process reduce the sulfuric acid con- tent of the water. Both methods result in cleaner water with a lower concentration of acid being released into the environment.

19.8 Surface-Water Pollution

Pollution of surface water occurs when too much of an undesirable or harmful substance flows into a body of wa- ter, exceeding that body of water’s natural ability to re- move it, dilute it to a harmless concentration, or convert it to a safe form (see A Closer Look 19.3).

Water pollutants, like other pollutants, are catego- rized as being emitted from point or nonpoint sources (see Chapter 8). Point sources are distinct and confined, such as pipes from industrial and municipal sites that empty into streams or rivers (Figure 19.13). In general, point source pollutants from industries are controlled through on-site treatment or disposal and are regulated by permit. Municipal point sources are also regulated by permit. In older cities in the northeastern and Great Lakes areas of the United States, most point sources are outflows from combined sewer systems. As mentioned earlier, such sys- tems combine storm water flow with municipal wastewa- ter. During heavy rains, urban storm runoff may exceed the capacity of the sewer system, causing it to overflow and deliver pollutants to nearby surface waters.

Nonpoint sources, such as runoff, are diffused and intermittent and are influenced by factors such as land use, climate, hydrology, topography, native vegetation, and geology. Common urban nonpoint sources include runoff from streets or fields; such runoff contains all sorts of pollutants, from heavy metals to chemicals and sedi- ment. Rural sources of nonpoint pollution are generally associated with agriculture, mining, or forestry. Nonpoint sources are difficult to monitor and control.

Reducing Surface-Water Pollution

From an environmental view, two approaches to dealing with surface-water pollution are: (1) reduce the sources of pollution; and (2) treat the water to remove pollutants or convert them to forms that can be disposed of safely. Which option is used depends on the specific circumstances of the pollution problem. Reduction at the source is the environmentally preferred way of dealing with pollutants. For example, air-cooling towers, rather than water-cooling towers, may be used to dispose of waste heat from power plants, thereby avoiding thermal pollution of water. The second method— water treatment—is used for a variety of pollution problems. Water treatments include chlorination to kill microorganisms such as harmful bacteria and filtering to remove heavy metals.

There is a growing list of success stories in the treat- ment of water pollution. One of the most notable is the cleanup of the Thames River in Great Britain. For cen- turies, London’s sewage had been dumped into that riv- er, and there were few fish to be found downstream in the estuary. In recent decades, however, improved water treatment has led to the return of a number of species of fish, some of which have not been seen in the river for centuries.

Many large cities in the United States—such as Bos- ton, Miami, Cleveland, Detroit, Chicago, Portland, and Los Angeles—grew on the banks of rivers, but the riv- ers were often nearly destroyed by pollution and concrete. Today, there are grassroots movements all around the country dedicated to restoring urban rivers and adjacent lands as greenbelts, parks, and other environmentally sen- sitive developments. For example, the Cuyahoga River in Cleveland, Ohio, was so polluted by 1969 that sparks from a train ignited oil-soaked wood in the river, setting the surface of the river on fire! The burning of an Ameri- can river became a symbol for a growing environmental consciousness. The Cuyahoga River today is cleaner and no longer flammable—from Cleveland to Akron, it is a beautiful greenbelt (Figure 19.15). The greenbelt changed part of the river from a sewer into a valuable public re- source and focal point for economic and environmental renewal.24 However, in downtown Cleveland and Akron, the river remains an industrial stream and parts remain polluted.

Two of the newer surface-water cleanup techniques involve nanotechnology and bioengineering. Nanotech- nology uses extremely small material particles (10−9m size, about 100,000 times thinner than human hair) de- signed for a number of purposes. Some nano particles can capture heavy metals such as lead, mercury, and arsenic from water. The nano particles have a tremendous surface area to volume. One cubic centimeter of particles has a surface area exceeding a football field and can take up over 50% of its weight in heavy metals.25

Bioengineering uses plants and soil in an engineered landscape (especially urban lands) to minimize water pol- lution. Urbanization significantly changes the hydrology of a landscape. Open land (forest or grasslands) with na- tive vegetation is replaced by surfaces such as rooftops, parking lots, streets, and sidewalks that are impervi- ous (water can’t infiltrate them). Lawns and gardens are planted, and pesticides and fertilizers are applied. Urban runoff from streets and parking lots contains trash, oil, gasoline, and other pollutants that are directed to storm water drains that may directly enter local streams, lakes, or the ocean.

Engineering technology is being used to treat urban runoff before it reaches streams, lakes, or the ocean. One method is to create a “closed-loop” local landscape (biore- tention facility) that does not allow runoff to leave a prop- erty. Bioretention facilities are designed to collect urban runoff and store it in landscapes that allow water to be used by plants and to infiltrate the soil for additional natural fil- tration.26 Examples of bioretention facilities include “rain gardens” below downspouts and parking lots that direct wa- ter to landscape instead of the street (Figure 19.16).27 The use of bioretention facilities such as landscape areas parallel to roadways or “islands” in parking lots represents a fun- damental change in how urban land is developed. Runoff from five large building complexes, such as Manzaneta Vil- lage at the University of California, Santa Barbara, can be directed to engineered wetlands (bioswales) where wetland plants remove contaminants before water is discharged into the campus lagoon and then the ocean. Removing nutri- ents has helped reduce cultural eutrophication of the lagoon (Figure 19.17).

19.9 Groundwater Pollution

Approximately half of all people in the United States to- day depend on groundwater as their source of drinking water. (Water for domestic use in the United States is dis- cussed in A Closer Look 19.4.) People have long be- lieved that groundwater is, in general, pure and safe to drink. However, groundwater can be easily polluted by any one of several sources (see Table 19.1), and the pollutants, though very toxic, may be difficult to recognize.

In the United States today, only a small portion of the groundwater is known to be seriously contaminated. However, as mentioned earlier, the problem may become worse as human population pressure on water resources increases. Our realization of the extent of the problem is growing as the testing of groundwater becomes more common. For example, Atlantic City and Miami are two eastern cities threatened by polluted groundwater that is slowly migrating toward their wells.

It is estimated that 75% of the 175,000 known waste-disposal sites in the United States may be spewing plumes of hazardous chemicals that are migrating into groundwater resources. Because many of the chemicals are toxic or are suspected carcinogens, it appears that we have inadvertently been conducting a large-scale experi- ment on how people are affected by chronic low-level exposure to potentially harmful chemicals. The final results of the experiment will not be known for many years.28

The hazard presented by a particular groundwater pollutant depends on several factors, including the con- centration or toxicity of the pollutant in the environment and the degree of exposure of people or other organisms to the pollutants.29 (See Section 8.6 on risk assessment in Chapter 8.)

Principles of Groundwater Pollution: An Example

Some general principles of groundwater pollution are il- lustrated by an example. Pollution from leaking under- ground gasoline tanks belonging to automobile service stations is a widespread environmental problem that no one thought very much about until only a few years ago. Underground tanks are now strictly regulated. Many thousands of old, leaking tanks have been removed, and the surrounding soil and groundwater have been treated to remove the gasoline. Cleanup can be a very expensive pro- cess, involving removal and disposal of soil (as a hazardous waste) and treatment of the water using a process known as vapor extraction (Figure 19.18). Treatment may also be accomplished underground by microorganisms that con- sume the gasoline. This is known as bioremediation and is much less expensive than removal, disposal, and vapor extraction.

Pollution from leaking buried gasoline tanks em- phasizes some important points about groundwater pollutants:

• Some pollutants, such as gasoline, are lighter than water and thus float on the groundwater.

• Some pollutants have multiple phases: liquid, vapor, and dissolved. Dissolved phases chemically combine with the groundwater (e.g., salt dissolves into water).

• Some pollutants are heavier than water and sink or move downward through groundwater. Examples of sinkers include some particulates and cleaning solvents. Pollutants that sink may become concentrated deep in groundwater aquifers.

• The method used to treat or eliminate a water pollutant must take into account the physical and chemical prop- erties of the pollutant and how these interact with sur- face water or groundwater. For example, the extraction well for removing gasoline from a groundwater resource (Figure 19.18) takes advantage of the fact that gasoline floats on water.

• Because cleanup or treatment of water pollutants in groundwater is very expensive, and because undetected or untreated pollutants may cause environmental dam- age, the emphasis should be on preventing pollutants from entering groundwater in the first place.

Groundwater pollution differs in several ways from surface-water pollution. Groundwater often lacks oxygen, a situation that kills aerobic types of microor- ganisms (which require oxygen-rich environments) but may provide a happy home for anaerobic varieties (which live in oxygen-deficient environments). The breakdown of pollutants that occurs in the soil and in material a meter or so below the surface does not occur readily in groundwater. Furthermore, the channels through which groundwater moves are often very small and variable. Thus, the rate of movement is low in most cases, and the opportunity for dispersion and dilution of pollutants is limited.

Long Island, New York

Another example—that of Long Island, New York— illustrates several groundwater pollution problems and how they affect people’s water supply. Two counties on Long Island, New York (Nassau and Suffolk), with a population of several million people, depend entirely on groundwater. Two major problems with the groundwater in Nassau County are intrusion of saltwater and shal- low aquifer contamination.30 Saltwater intrusion, where subsurface salty water migrates to wells being pumped, is a problem in many coastal areas of the world. The general movement of groundwater under natural condi- tions for Nassau County is illustrated in Figure 19.19. Salty groundwater is restricted from migrating inland by the large wedge of fresh water moving beneath the island. Notice also that the aquifers are layered, with those closest to the surface being the most salty.

In spite of the huge quantities of water in Nassau County’s groundwater system, intensive pumping has lowered water levels by as much as 15 m (50 ft) in some areas. As groundwater is removed near coastal areas, the subsurface outflow to the ocean decreases, allowing salt- water to migrate inland. Saltwater intrusion has become a problem for south shore communities, which now must pump groundwater from a deeper aquifer, below and iso- lated from the shallow aquifers that have saltwater intru- sion problems.

The most serious groundwater problem on Long Island is shallow aquifer pollution associated with ur- banization. Sources of pollution in Nassau County in- clude urban runoff, household sewage from cesspools and septic tanks, salt used to deice highways, and in- dustrial and solid waste. These pollutants enter sur- face waters and then migrate downward, especially in areas of intensive pumping and declining groundwater levels.30 Landfills for municipal solid waste have been a significant source of shallow-aquifer pollution on Long Island because pollutants (garbage) placed on sandy soil can quickly enter shallow groundwater. For this reason, most Long Island landfills were closed in the past few decades.

19.10 Wastewater treatment

Water used for industrial and municipal purposes is often degraded during use by the addition of suspended solids, salts, nutrients, bacteria, and oxygen-demanding material. In the United States, by law, these waters must be treated before being released back into the environment.

Wastewater treatment—sewage treatment—costs about $40 billion per year in the United States, and the cost keeps rising, but it will continue to be big business. Con- ventional wastewater treatment includes septic-tank disposal systems in rural areas and centralized wastewater treatment plants in cities. Recent innovative approaches include apply- ing wastewater to the land and renovating and reusing waste- water. We discuss the conventional methods in this section and some newer methods in later sections.

Septic-Tank Disposal Systems

In many rural areas, no central sewage systems or waste- water treatment facilities are available. As a result, individ- ual septic tank disposal systems, not connected to sewer systems, continue to be an important method of sewage disposal in rural areas as well as outlying areas of cities. Because not all land is suitable for a septic-tank disposal system, an evaluation of each site is required by law before a permit can be issued. An alert buyer should make sure that the site is satisfactory for septic-tank disposal before purchasing property in a rural setting or on the fringe of an urban area where such a system is necessary.

The basic parts of a septic-tank disposal system are shown in Figure 19.20. The sewer line from the house leads to an underground septic tank in the yard. The tank is designed to separate solids from liquid, digest (bio- chemically change) and store organic matter through a period of detention, and allow the clarified liquid to dis- charge into the drain field (absorption field) from a pip- ing system through which the treated sewage seeps into the surrounding soil. As the wastewater moves through the soil, it is further treated by the natural processes of oxidation and filtering. By the time the water reaches any freshwater supply, it should be safe for other uses.

Sewage drain fields may fail for several reasons. The most common causes are failure to pump out the septic tank when it is full of solids, and poor soil drainage, which allows the effluent to rise to the surface in wet weather. When a septic-tank drain field does fail, pollution of groundwater and surface water may result. Solutions to septic system problems include siting septic tanks on well- drained soils, making sure systems are large enough, and practicing proper maintenance.

Wastewater Treatment Plants

In urban areas, wastewater is treated at specially designed plants that accept municipal sewage from homes, busi- nesses, and industrial sites. The raw sewage is delivered to the plant through a network of sewer pipes. Following treatment, the wastewater is discharged into the surface- water environment (river, lake, or ocean) or, in some limited cases, used for another purpose, such as crop ir- rigation. The main purpose of standard treatment plants is to break down and reduce the BOD and kill bacteria with chlorine. A simplified diagram of the wastewater treat- ment process is shown in Figure 19.21.

Wastewater treatment methods are usually divided into three categories: primary treatment, secondary treatment, and advanced wastewater treatment. Prima- ry and secondary treatments are required by federal law for all municipal plants in the United States. However, treatment plants may qualify for a waiver exempting them from secondary treatment if installing secondary treat- ment facilities poses an excessive financial burden. Where secondary treatment is not sufficient to protect the quality of the surface water into which the treated water is dis- charged—for example, a river with endangered fish spe- cies that must be protected—advanced treatment may be required.31

Primary Treatment

Incoming raw sewage enters the plant from the munici- pal sewer line and first passes through a series of screens to remove large floating organic material. The sew- age next enters the “grit chamber,” where sand, small stones, and grit are removed and disposed of. From there, it goes to the primary sedimentation tank, where particulate matter settles out to form sludge. Some- times, chemicals are used to help the settling process.

The sludge is removed and transported to the “digester” for further processing. Primary treatment removes ap- proximately 30 to 40% of BOD by volume from the wastewater, mainly in the form of suspended solids and organic matter.31

Secondary Treatment

There are several methods of secondary treatment. The most common treatment is known as activated sludge, because it uses living organisms—mostly bacteria. In this procedure, the wastewater from the primary sedimenta- tion tank enters the aeration tank (Figure 19.21), where it is mixed with air (pumped in) and with some of the sludge from the final sedimentation tank. The sludge contains aerobic bacteria that consume organic material (BOD) in the waste. The wastewater then enters the final sedimentation tank, where sludge settles out. Some of this “activated sludge,” rich in bacteria, is recycled and mixed again in the aeration tank with air and new, incoming wastewater acting as a starter. The bacteria are used again and again. Most of the sludge from the final sedimenta- tion tank, however, is transported to the sludge digester. There, along with sludge from the primary sedimentation tank, it is treated by anaerobic bacteria (bacteria that can live and grow without oxygen), which further degrade the sludge by microbial digestion.

Methane gas (CH4) is a product of the anaerobic digestion and may be used at the plant as a fuel to run equipment or to heat and cool buildings. In some cases, it is burned off. Wastewater from the final sedimentation tank is next disinfected, usually by chlorination, to elimi- nate disease-causing organisms. The treated wastewater is then discharged into a river, lake, or ocean (see A Closer Look 19.5), or in some limited cases used to irrigate farm- land. Secondary treatment removes about 90% of BOD that enters the treatment plant in the sewage.31

The sludge from the digester is dried and disposed of in a landfill or applied to improve soil. In some instances, treatment plants in urban and industrial areas contain many pollutants, such as heavy metals, that are not re- moved in the treatment process. Sludge from these plants is too polluted to use in the soil and must be disposed of. Some communities, however, require industries to pre- treat sewage to remove heavy metals before the sewage is

sent to the treatment plant; in these instances, the sludge can be more safely used for soil improvement.

Advanced Wastewater Treatment

As noted above, primary and secondary treatments do not remove all pollutants from incoming sewage. Some addi- tional pollutants, however, can be removed by taking more treatment steps. For example, phosphates and nitrates, organic chemicals, and heavy metals can be removed by specifically designed treatments, such as sand filters, car- bon filters, and chemicals applied to assist in the removal process.31 Treated water is then discharged into surface water or may be used for irrigating agricultural lands or municipal properties, such as golf courses, city parks, and grounds surrounding wastewater treatment plants.

Advanced wastewater treatment is used when it is particularly important to maintain good water qual- ity. For example, if a treatment plant discharges treated wastewater into a river and there is concern that nutrients remaining after secondary treatment may cause damage to the river ecosystem (eutrophication), advanced treatment may be used to reduce the nutrients.

Chlorine Treatment

As mentioned earlier, chlorine is frequently used to dis- infect water as part of wastewater treatment. Chlorine is very effective in killing the pathogens responsible for outbreaks of serious waterborne diseases that over time have killed many thousands of people. However, chlorine has been discovered to have another, less benign poten- tial: Chlorine treatment also produces minute quantities of chemical by-products, some of which are potentially hazardous to people and other animals. For example, a recent study in Britain revealed that in some rivers, male fish sampled downstream from wastewater treatment plants had testes containing both eggs and sperm. This is likely related to the concentration of sewage effluent and the treatment method used.32 Evidence also suggests that these by-products in the water may pose a risk of cancer and other human health effects. The degree of risk is con- troversial and is currently being debated.33

19.11 land Application of Wastewater

The practice of applying wastewater to the land arose from the fundamental belief that waste is simply a resource out of place. Land application of untreated human waste was practiced for hundreds if not thousands of years before the development of wastewater treatment plants, which have sanitized the process by reducing BOD and using chlorination.

Many sites around the United States are now recy- cling wastewater, and the technology for wastewater treat- ment is rapidly evolving. An important question is: Can we develop environmentally preferred, economically vi- able wastewater treatment plants that are fundamentally different from those in use today? An idea for such a plant, called a resource-recovery wastewater treatment plant, is shown in Figure 19.22. The term resource recovery here refers to the production of resources, including methane gas (which can be burned as a fuel), as well as ornamental plants and flowers that have commercial value.

Wastewater and Wetlands

Wastewater is being applied successfully to natural and constructed wetlands at a variety of locations.35–37 Natural or human-made wetlands can be effective in treating the following water-quality problems:

municipal wastewater from primary or secondary treat- ment plants (BOD, pathogens, phosphorus, nitrate, suspended solids, metals)

storm water runoff (metals, nitrate, BOD, pesticides, oils)

industrial wastewater (metals, acids, oils, solvents)

agricultural wastewater and runoff (BOD, nitrate, pesticides, suspended solids)

mining waters (metals, acidic water, sulfates)

groundwater seeping from landfills (BOD, metals, oils, pesticides)

Using wetlands to treat wastewater is particularly at- tractive to communities that find it difficult to purchase traditional wastewater treatment plants. For example, the city of Arcata, in northern California, makes use of a wet- land as part of its wastewater treatment system. The waste- water comes mostly from homes, with minor inputs from the numerous lumber and plywood plants in Arcata. It is treated by standard primary and secondary methods, then chlorinated and dechlorinated before being discharged into Humboldt Bay.35

Louisiana Coastal Wetlands

The state of Louisiana, with its abundant coastal wetlands, is a leader in the development of advanced treatment us- ing wetlands after secondary treatment (Figure 19.23). Wastewater rich in nitrogen and phosphorus, applied to coastal wetlands, increases the production of wetland plants, thereby improving water quality as these nutrients are used by the plants. When the plants die, their organic material (stems, leaves, roots) causes the wetland to grow vertically (or accrete), partially offsetting wetland loss due to sea-level rise.38 There are also significant economic sav- ings in applying treated wastewater to wetlands, because the financial investment is small compared with the cost of advanced treatment at conventional treatment plants. Over a 25-year period, a savings of about $40,000 per year is likely.37

In sum, the use of isolated wetlands, such as those in coastal Louisiana, is a practical way to improve water qual- ity in small, widely dispersed communities in the coastal zone. As water-quality standards are tightened, wetland wastewater treatment will become a viable, effective al- ternative that is less costly than traditional treatment.38,39

Phoenix, Arizona: Constructed Wetlands

Wetlands can be constructed in arid regions to treat poor- quality water. For example, at Avondale, Arizona, near Phoenix, a wetland treatment facility for agricultural wastewater is sited in a residential community (Figure 19.24). The facility is designed to eventually treat about 17,000 m3/day (4.5 million gal/day) of water. Water en- tering the facility has nitrate (NO3) concentrations as high as 20 mg/l. The artificial wetlands contain naturally occurring bacteria that reduce the nitrate to below the maximum contaminant level of 10 mg/l. Following treat- ment, the water flows by pipe to a recharge basin on the nearby Agua Fria River, where it seeps into the ground to become a groundwater resource. The cost of the wetland treatment facility was about $11 million, about half the cost of a more traditional treatment facility.

19.12 Water Reuse

Water reuse results when water is withdrawn, treated, used, treated, and returned to the environment, followed by fur- ther withdrawals and use. Water reuse is very common and a fact of life for millions of people who live along large riv- ers. Many sewage treatment plants are located along rivers and discharge treated water into the rivers. Downstream, other communities withdraw, treat, and consume the water.

Water reuse is a planned endeavor. In fact, reused wa- ter is a water source (see Chapter 18). For example, in the United States, treated wastewater is applied to numerous sites to recharge groundwater and then reused for agricul- tural and municipal purposes.

Direct water reuse refers to use of treated wastewater that is piped directly from a treatment plant to the next user. In most cases, the water is used in industry, in agri- cultural activity, or in irrigation of golf courses, institu- tional grounds (such as university campuses), and parks. Direct water reuse is growing rapidly and is the norm for industrial processes in factories. In Las Vegas, Nevada, new resort hotels that use a great deal of water for fountains, rivers, canals, and lakes are required to treat waste- water and reuse it (Figure 19.25). Because of per- ceived risks and negative cultural attitudes toward using treated wastewater, there has been little direct reuse of water for human consumption in the Unit- ed States, except in emergencies. However, that is changing. In Orange County, California, there is an ambitious program to reuse treated wastewater. The program processes 70 million gallons a day by injecting treated wastewater into the groundwater system to be further filtered underground. The water is then pumped out, further treated, and used in homes and businesses.40

19.13 Conditions of Stream Ecosystems in the United States

Assessment of stream ecosystem conditions in the United States has been an important research goal since passage of the Clean Water Act of 1977. Un- til recently, no straightforward way to perform this evaluation had been seriously attempted, so the condition of small streams that can be waded was all but unknown. That void has now been partly filled by recent studies aimed at providing a cred- ible, broad-scale assessment of small streams in the United States. A standardized field collection of data was an important step, and the data at each site include the following:

• measurement of stream channel morphology and habitat characteristics

• measurement of the streamside and near-stream vegetation, known as the riparian vegetation

• measurement of water chemistry

• measurement of the assemblage and composition of the stream environment (biotic environment)

The evaluation includes two key biological indicators: (1) an index of how pristine a stream ecosystem is and (2) an index that represents a loss of biodiversity. Results of the study are shown in Figure 19.26. The top graph is for the entire United States, while the three lower graphs are done on a regional basis. The ratings range from poor conditions— that is, those most disturbed by environmental stress—to good conditions that mostly correspond with undisturbed stream systems. Streams with poor quality are most numer- ous in the northeastern part of the United States, as well as in the midsection of the country. The percentage of stream miles in good condition is considerably higher in the West.

This finding is not surprising, given the extent of stream channel modifications and changes in land use in the eastern half of the country, compared to the western half. Western states tend to have more mountains and more areas of natural landscape that have not been modi- fied by agriculture and other human activities. However, streams in the West were deemed to have a higher risk of future degradation than those in other areas because the West has more pristine streams to measure changes against and because it also has more high-quality stream ecosystem conditions that can potentially be degraded than those in other parts of the country.41

19.14 Water Pollution and

Environmental law

Environmental law, the branch of law dealing with conservation and use of natural resources and control of pollution, is very important as we debate environmental issues and make decisions about how best to protect our environment. In the United States, laws at the federal, state, and local levels address these issues.

Federal laws to protect water resources go back to the Refuse Act of 1899, which was enacted to protect navi- gable streams, rivers, and lakes from pollution. Table 19.5 lists major federal laws that have a strong water resource/ pollution component. Each of these major pieces of legis- lation has had a significant impact on water-quality issues. Many federal laws have been passed with the purpose of cleaning up or treating pollution problems or treating wastewater. However, there has also been a focus on pre- venting pollutants from entering water. Prevention has the advantage of avoiding environmental damage and costly cleanup and treatment.

From the standpoint of water pollution, the mid- 1990s in the United States was a time of debate and controversy. In 1994, Congress attempted to rewrite major environmental laws, including the Clean Water Act (1972, amended in 1987). The purpose was to give industry greater flexibility in choosing how to comply with environmental regulations concerning water pol- lution. On the one hand, industry interests favored the proposed new regulations that, in their estimation, would be more cost effective without causing increased envi- ronmental degradation. Environmentalists, on the other hand, viewed attempts to rewrite the Clean Water Act as a giant step backward in the nation’s fight to clean up our water resources. Apparently, Congress had incorrectly as- sumed it knew the public’s values on this issue. Survey after survey has established that there is strong support for a clean environment in the United States and that people are willing to pay to have clean air and clean water. There is a consensus that the Clean Water Act was a huge suc- cess in cleaning U.S. waters. However, achieving water sustainability will require modification of the Clean Water Act in order to:42

• better target pollution abatement, based on watersheds • better integrate the Clean Water Act with drinking

water standards

• better integrate water pollution to global change

• better control nutrients causing widespread problems in the Gulf of Mexico and other areas

• better manage storm water runoff and pollution.

Congress has continued to debate changes in environ- mental laws, but little has been resolved.43

SUMMARY

• The primary water pollution problem in the world to- day is the lack of disease-free drinking water.

• Water pollution is degradation of quality that renders water unusable for its intended purpose.

• Major categories of water pollutants include disease- causing organisms, dead organic material, heavy metals, organic chemicals, acids, sediment, heat, and radioactivity.

• Sourcesofpollutantsmaybepointsources,suchaspipes that discharge into a body of water, or nonpoint sources, such as runoff, which are diffused and intermittent.

• Eutrophication of water is a natural or human-induced increase in the concentration of nutrients, such as phos- phorus and nitrogen, required for living things. A high concentration of such nutrients may cause a population explosion of photosynthetic bacteria. As the bacteria die and decay, the concentration of dissolved oxygen in the water is lowered, leading to the death of fish.

• Sediment is a twofold problem: Soil is lost through ero- sion, and water quality suffers when sediment enters a body of water.

• Acid mine drainage is a serious water pollution problem because when water and oxygen react with sulfide min- erals that are often associated with coal or metal sulfide deposits, they form sulfuric acid. Acidic water draining from mines or tailings pollutes streams and other bodies of water, damaging aquatic ecosystems and degrading water quality.

• Urban processes—for example, waste disposal in land- fills, application of fertilizers, and dumping of chemi-

cals such as motor oil and paint—can contribute to shallow aquifer contamination. Overpumping of aqui- fers near the ocean may cause saltwater, found below the fresh water, to rise closer to the surface, contami- nating the water resource by a process called saltwater intrusion.

• Wastewater treatment at conventional treatment plants includes primary, secondary, and, occasionally, ad- vanced treatment. In some locations, natural ecosys- tems, such as wetlands and soils, are being used as part of the treatment process.

• Water reuse is the norm for millions of people living along rivers where sewage treatment plants discharge treated wastewater back into the river. People who with- draw river water downstream are reusing some of the treated wastewater.

• Industrial reuse of water is the norm for many factories.

• Deliberate use of treated wastewater for irrigating agri- cultural lands, parks, golf courses, and the like is grow- ing rapidly as demand for water increases.

• Use of treated wastewater that is applied to the land and later withdrawn as a municipal water source is becom- ing more common.

• Cleanup and treatment of both surface-water and groundwater pollution are expensive and may not be completely successful. Furthermore, environmental damage may result before a pollution problem is identified and treated. Therefore, we should continue to focus on preventing pollutants from entering water, which is a goal of much water-quality legislation.

Botkin, D. B., & Keller, E. A. (2014). Environmental science: Earth as a living planet (9th ed.). Hoboken, NJ: John Wiley & Sons, Inc.