KEY TERMS
Point-source pollution
The importance of safe drinking water to public health has been clear since John Snow identified polluted water as the source of London’s cholera epidemic in 1855. Major epidemics of cholera and other waterborne diseases broke out periodically in the United States until the end of the 19th century. Ninety thousand people died of cholera in 1885 in Chicago, persuading city officials to stop discharging the city’s sewage into Lake Michigan, which was also the source of municipal drinking water.1(Ch.16) While contaminated water is still a major cause of disease and death in developing countries, Americans expect that their tap water will be safe to drink and, for the most part, it is. Nevertheless, 647 outbreaks of waterborne diseases were documented by the Centers for Disease Control and Prevention (CDC) between 1971 and 1994, including the 1993 cryptosporidiosis outbreak in Milwaukee.2 Each year between 1991 and 2010, the CDC and the Environmental Protection Agency (EPA) recorded an average of 16 outbreaks associated with contaminated drinking water.3,4 Such outbreaks continue, as will be seen later in this chapter.
Common water pollutants include, in addition to microbial pathogens, a wide range of chemicals that may not only be toxic in drinking water, but have harmful effects on fish and wildlife. Many chemicals have been discharged into waterways as industrial wastes, such as the mercury in Minamata Bay or the polychlorinated biphenyls (PCBs) in the Hudson River. People may then be poisoned by eating the fish that have accumulated these toxins in their flesh. Other sources of pollution include deposition from the air, as in acid rain, or runoff from the land.
Until the early 1970s, individual states were responsible for the quality of their waterways and the purity of their drinking water. This arrangement did not control water pollution for the same reason that it could not control air pollution: The sources of pollution and the communities affected by the pollution may be under different political jurisdiction. For example, New Orleans draws its drinking water from the Mississippi River, yet it was helpless to stop cities upstream, located in other states, from discharging sewage and industrial wastes into the river.
A number of infamous pollution cases occurred in the United States in the 1960s and 1970s that inspired the passage of federal legislation. The discovery of PCBs in the Hudson River led to a ban on commercial fishing there because the chemicals were so concentrated in the flesh of the fish. Residents of Duluth, Minnesota, were alarmed to learn that the Reserve Mining Company had been dumping asbestos-containing wastewater into Lake Superior, the source of municipal water, for more than 20 years.5 While no one knew whether asbestos was as carcinogenic when drunk as it was when breathed, bottled water was distributed to the population for over a year until a new water-filtration plant was completed. The James River was so badly polluted with the insecticide Kepone, discharged from a manufacturing plant in Hopewell, Virginia, between 1966 and 1975, that no practical way has ever been proposed to clean it up. The plant was closed, not because of the environmental damage it caused, but because so many of its employees suffered neurological, liver, and other damage from Kepone poisoning.5 Perhaps the most dramatic call to action occurred in 1969, when the Cuyahoga River in Ohio caught fire because it had so much oil floating on its surface.5
The two goals of cleaning up lakes and rivers and ensuring safe drinking water are distinct but related, and Congress has addressed them in separate legislation: the Clean Water Act of 1972, amended in 1977 and several times since, and the Safe Drinking Water Act of 1974, which was rewritten in 1996.1(Ch.15,16) Since half of the drinking water in the United States comes from lakes and rivers, success in meeting the goals of the Clean Water Act is obviously a help in achieving the goals of the Safe Drinking Water Act.
Clean Water Act
The Clean Water Act set national goals that lakes and rivers should be “fishable” and “swimmable” and that all pollutant discharges should be eliminated. First attempts at cleaning up the nation’s waterways focused on “point-source” pollution—well-defined locations that discharge pollutants into lakes and rivers. Most point-source pollution comes from municipal sewage and industrial discharges. The 1972 and 1977 legislation imposed strict controls on these sources; it also provided billions of dollars of funding to assist municipalities in building wastewater treatment facilities. With the success of these efforts, it became apparent that a great deal of pollution washed into waterways from the air and the land. The 1987 reauthorization of the Clean Water Act focused on cleaning up nonpoint-source pollution, which has proven to be a much more difficult task.1(Ch.16)
Laws governing point-source pollution set requirements for treating wastewater so that it can be discharged into waterways without causing human health problems or disrupting the aquatic environment. In the case of sewage treatment plants, this requires several steps. The primary step is to remove suspended solids by screening them and then allowing them to settle out by gravity in settling tanks. The secondary stage is to break down the remaining organic material using biological processes: The wastewater is mixed with bacteria and plenty of oxygen, resulting in conversion of the organic wastes into carbon dioxide, water, and minerals. The wastewater is then usually disinfected with chlorine before being discharged into the environment.1(Ch.16)
While the treatment process produces a liquid discharge that meets standards of environmental safety, it also generates “sludge,” the solid waste left behind on screens and at the bottom of settling tanks. Enormous amounts of sludge are generated by municipal sewage plants, creating a major disposal problem. In the past, sludge was often dumped in the ocean or incinerated, but these methods create other pollution problems. Congress prohibited the ocean dumping of sludge in 1992. Some communities bury it in landfills, but landfill space is running low. Since sludge is rich in nutrients, the EPA encourages the use of treated sludge as a fertilizer and soil conditioner to improve marginal lands and increase forest productivity. The EPA has developed strict regulations on sanitizing and removing hazardous contaminants from the sludge—known after treatment as biosolids—before it can be used on land. Currently, 55 percent of the estimated 8.2 million tons of sewage sludge generated every year is used as fertilizer.1(Ch.16)
About 70 percent of the U.S. population is served by sewage treatment plants. Most of the other 30 percent use onsite septic systems, which function as miniature sewage treatment plants including the use of bacteria to break down organic wastes. Like the larger plants, septic systems produce sludge, which must be pumped out periodically. Improperly constructed and poorly maintained septic systems contribute to pollution of waterways and often result in public health problems.1(Ch.16)
Despite the laws and some occasional funding from the federal government, many cities have inadequate sewer systems that back up into basements or overflow and dump untreated sewage into waterways. In part the problems are due to population growth, which has placed additional burden on aging systems, and in part they occur because most systems combine rainwater runoff with sewage, overwhelming the system when it rains. According to an analysis of EPA data by the New York Times, sewage systems are the nation’s most frequent violators of the Clean Water Act.7 The American Society of Civil Engineers has estimated that $298 billion will be needed over the next twenty years to fix the nation’s sewage infrastructure.8
Discharges from industrial sources are the second major category of point-source pollution, which is strictly regulated by the Clean Water Act. The EPA is required to develop standards for the release of various categories of pollutants into the environment. Industries that discharge directly into the nation’s waterways are required to obtain a permit specifying allowable amounts and constituents of pollutants they may discharge. They must routinely monitor their discharges, and they must report regularly to the EPA.1(Ch.16)
Industrial wastes may cause special problems if they are discharged into sewer systems and pass through a municipal sewage treatment plant, occasionally with disastrous consequences. In 1977, pesticide wastes illegally dumped into the sewers of Louisville, Kentucky, killed all the microbes responsible for the secondary treatment process, rendering the plant ineffective. For nearly two years while the plant was being cleaned up at a cost of millions of dollars, 100 million gallons of untreated sewage were discharged into the Ohio River every day. In 1981 in Cincinnati, a paint factory discharged hydrochloric acid into the city sewers, corroding the sewer pipe and causing it to collapse, leaving a hole in the street 24 feet in diameter.9(Ch.15)
To prevent such problems, the Clean Water Act requires pretreatment of industrial wastes that are discharged into sewers. But standards have not been set for many smaller commercial establishments, including car washes and photo processing plants. Hazardous chemicals also enter sewer systems from residences, when people dispose of bleaches, toilet bowl cleaners, paint thinners, and other household substances by flushing them down the drain.
As strict limits have been set on pollution from sewage systems and industry, nonpoint-source pollution has become an increasingly important threat to water quality. These contaminants come from stormwater runoff from farmland, construction sites, and urban streets. Agriculture is the leading source of water pollution in the United States, contributing soil, manure fertilizers, and pesticides that wash into streams and lakes. Agricultural runoff is believed to have been the source of the Milwaukee cryptosporidiosis outbreak. Construction activities also contribute soil to runoff water, together with oil, tar, paint, and cleaning solvents. Contaminants contributed by urban street runoff include sand, dirt, road salt, oil, grease, heavy metal particles, pesticides and fertilizers from lawns, and animal and bird droppings.
A variety of approaches must be used to minimize pollution caused by stormwater runoff. These include preventing soil erosion by planting vegetation on exposed soil, incorporating more green space into urban areas, minimizing the use of chemical fertilizers and pesticides, and controlling litter.
Air pollution is also a source of water pollution. In addition to acid rain, a number of other chemicals are deposited into lakes, rivers, and oceans from the air. These include lead, asbestos, PCBs, and various pesticides. It has been shown that the major portion of PCBs in the Great Lakes comes from the air. Industrial accidents and spills also contribute to pollution of waterways.10
To conform to the requirements of the Clean Water Act, the EPA regularly collects data from the states on water quality of rivers, lakes, and estuaries. The most recent reports available, which include data that are more or less up to date, depending on the state, showed that the nation still has a long way to go meet the fishable and swimmable requirements. Of the water bodies that were assessed, only 57 percent of river miles, 59 percent of lake acres, and 41 percent of bay and estuaries square miles were rated “good” for both fishing and swimming.10
Safe Drinking Water
Almost half of the drinking water in the United States comes from rivers and lakes. Thus it is likely to be contaminated by the point-source and nonpoint-source pollutants discussed above. The other half comes from underground aquifers; these are generally of better quality but are increasingly susceptible to contamination by leaching from landfills, leaky oil and gas storage tanks, and other sources of toxic chemicals. Improvements in surfacewater quality brought about by the Clean Water Act make the job easier for community water systems, which must, however, meet much higher standards to produce potable water—water that is safe for human consumption.
All community systems need to treat their water so that, theoretically, all contaminants are removed. The steps needed to produce potable water vary depending on the source of the water and the type of contaminants. The basic steps common to most systems include sedimentation, coagulation, filtration, and disinfection. Incoming water is first allowed to sit quietly while suspended material settles out. Then alum is added, causing small particles to coagulate and settle out. Filtration through beds of sand or similar materials removes the smaller particles that do not settle, and chlorine is added to kill remaining pathogens. In areas of the country where water is “hard”—containing high concentrations of dissolved calcium or magnesium—or where it has objectionable tastes or odors due to dissolved iron or gases, additional treatments may be used. As a last step, fluoride is often added to protect community residents from tooth decay. A typical drinking-water purification plant is diagrammed in (FIGURE 22-1).
To ensure that the treatment process is working effectively, regular laboratory tests are generally done on the final product. The traditional measures of water purity are turbidity and coliform levels. Turbidity indicates the presence of suspended particles, a failure of the sedimentation and filtration steps. Suspended particles may interfere with the germicidal action of the chlorine. After the cryptosporidiosis outbreak, which accompanied an increase in the turbidity of Milwaukee’s water, national turbidity standards were tightened. If coliform bacteria are detected, there has probably been a failure of disinfection. These bacteria are common inhabitants of the intestines of humans and other animals and, while they are usually not pathogenic themselves, their presence indicates that other, more harmful microorganisms may have survived the treatment process.1(Ch.16)
The general approach to water treatment described above is directed primarily against bacterial diseases, the most common and historically devastating type of waterborne disease. It is not very effective, however, against viruses and the parasites Cryptosporidia and Giardia, which are resistant to chlorine. Furthermore, it does nothing to address the problem of contamination with common chemical pollutants such as pesticides, herbicides, fertilizers, PCBs, lead, and other metals that may be harmful to health. Most community water systems are totally unprepared even to test for these pollutants.
The Safe Drinking Water Act of 1974 required the EPA to set standards for local water systems and mandated that states enforce the standards. Uniform guidelines were set for drinking-water treatment, and regular monitoring and testing were required, with the results to be reported to state governments. However, no deadlines were established for the standard setting, and state agencies were lax in enforcing the requirements that were in place. The 1986 reauthorization of the Safe Drinking Water Act specified 83 contaminants to be regulated by the EPA and set deadlines for action. In addition, it required water systems to take measures to prevent contamination with Giardia and Cryptosporidia.9(Ch.16) The EPA stepped up the pace of regulation. Now, maximum contaminant levels have been set for 87 identified contaminants, including microorganisms, disinfectants, disinfection byproducts, inorganic chemicals, organic chemicals, and radionuclides. A selected list of these contaminants is shown in (Table 22-1). In addition, secondary standards have been set for 15 contaminants that do not cause health risks but that may affect taste, odor, or color, or that cause discoloration of skin or teeth.
