Encyclopedia of Global Resources part 141 ppsx

See also: Clean Water Act; Environmental engineer-ing; Environmental Protection Agency; Eutrophica-tion; Solid waste management; Streams and rivers; Water pollution and water pollution c

Trang 1

tant reason that separate sewers, even though more

expensive, are favored by public health officials The

biologic processes can also be severely affected by toxic

industrial waste that can kill the “good” bacteria,

which are crucial to the treatment process

Accord-ingly, many communities require pretreatment for

industrial wastes

Tertiary treatment is the most advanced form of

waste treatment It includes a number of practices

such as the use of ozone, which is a strong oxidizing

agent, to remove most of the remaining BOD, odor,

and taste, and the addition of alum as a phosphate

precipitator A recent and innovative method of

ter-tiary treatment is to spray chlorinated effluent on

ei-ther croplands, wooded areas, or mine tailings after it

has been given secondary treatment This method has

several distinct advantages over the traditional direct

discharge of the effluent into surface watercourses

First, biologic digestion in the soil removes almost

all of the remaining BOD Second, soil and plants

are capable of absorbing large amounts of

nitro-gen and phosphorus during the growing season,

which slows their release into the environment

Other benefits include increased crop and timber

yields and groundwater recharge The land area

needed to handle treated wastewater by the spray

irrigation method is approximately 6.4 square

ki-lometers per 100,000 people

Wastewater Disposal in Rural and

Suburban Areas

In areas where population densities are less than

about 1,000 people per square kilometer, the cost

of a sewer system and treatment plant are difficult

to justify Septic systems are commonly used in

residential areas for disposal of domestic

waste-waters Household effluent is piped to a buried

septic tank, which acts as a small sedimentation

basin and anaerobic (without oxygen) sludge

di-gestion facility The effluent exits from this tank

into a disposal field where aerobic (with oxygen)

biologic breakdown of dissolved and solid

or-ganic compounds occurs In order to operate

ef-fectively, the soil must be of sufficient depth and

permeability so that microbial decomposition can

take place prior to the effluent reaching the water

table The Environmental Protection Agency

esti-mates that 25 percent of the homes in the United

States use some form of a septic disposal system

Robert M Hordon

Further Reading American Water Works Association, and American

Society of Civil Engineers Water Treatment Plant De-sign Edited by Edward E Baruth 4th ed New York:

McGraw-Hill, 2005

Drinan, Joanne E Water and Wastewater Treatment: A Guide for the Nonengineering Professional Boca Raton,

Fla.: Lewis, 2001

Gray, N F Biology of Wastewater Treatment 2d ed

Lon-don: Imperial College Press, 2004

Hammer, Mark J., and Mark J Hammer, Jr Water and Wastewater Technology 6th ed Upper Saddle River,

N.J.: Pearson/Prentice Hall, 2008

McGhee, Terence J Water Supply and Sewerage 6th ed.

New York: McGraw-Hill, 1991

Metcalf & Eddy, Inc Wastewater Engineering: Treatment and Reuse 4th ed Revised by George

Tchoban-oglous, Franklin L Burton, and H David Stensel Boston: McGraw-Hill, 2003

Paper &

paperboard products 32.7%

Yard wastes 12.8%

Food wastes 12.5%

Plastics 12.1%

Metals 8.2%

Rubber, leather,

& textiles 7.6%

Wood 5.6%

Glass 5.3%

Other 3.2%

Waste in the United States: 2007 Facts and Figures Note:

U.S Environmental Protection Agency,

Total U.S municipal solid waste generated in 2007 was about 230 million metric tons, or 2.1 kilograms per person per day Not included in these figures are mining, agriculture, industrial, and construction wastes; junked automobiles and equipment; or sewage.

U.S Municipal Solid Waste, 2007

Trang 2

Qasim, Syed R Wastewater Treatment Plants: Planning,

Design, and Operation 2d ed Lancaster, Pa.:

Tech-nomic, 1999

Laak, Rein Wastewater Engineering Design for Unsewered

Areas 2d ed Lancaster, Pa.: Technomic, 1986.

Tillman, Glenn M Water Treatment: Troubleshooting and

Problem Solving Chelsea, Mich.: Ann Arbor Press,

1996

See also: Clean Water Act; Environmental

engineer-ing; Environmental Protection Agency;

Eutrophica-tion; Solid waste management; Streams and rivers;

Water pollution and water pollution control; Water

supply systems

Water

Categories: Ecological resources; energy resources;

mineral and other nonliving resources

Water is an odorless, tasteless, and transparent

com-pound that is a critical factor in all chemical, physical,

and biological processes As far as is known, water

ex-ists freely and in great abundance on only one planet

in our solar system, Earth.

Background

Although water could exist on the Earth without life,

life could not exist without water It is the most

abun-dant liquid on the Earth In its solid and liquid forms,

water covers about 70 percent of the Earth’s surface It

exists in gaseous form as water vapor in the lower

at-mosphere, varying from close to 0 percent to about

4 percent by volume from region to region Water

constitutes most of the living tissue in humans: about

92 percent of blood plasma, 80 percent of muscle

tissue, 60 percent of red blood cells, and more than

50 percent of most other tissues

Water Properties

Water is a compound of two atoms of hydrogen and

one of oxygen, giving it the well-known chemical

for-mula H2O It has some unique properties It can exist

naturally in three states on Earth: solid, liquid, and

gaseous Furthermore, under normal pressure, when

heated from 0° Celsius, the melting point of water, to

4° Celsius, it contracts and reaches its highest density

This unusual thermal condition contrasts sharply with

most other substances, which expand and experience decreasing density when they are heated Therefore, ice is less dense than water and will float This prop-erty has substantial implications, as it allows water to freeze from the surface downward, thereby allowing circulation to continue under the frozen surface so that fish can survive Submarines that travel under the Arctic Ocean ice pack could not do so were it not for water’s unusual thermal property

Water is an excellent solvent, so much so that “pure water” is hard to find in nature Water has the highest specific heat of all common substances Specific heat

is the amount of heat that a fluid needs to raise the temperature of a unit volume by 1 degree This is an important property, as the enormous heat capacity of water has an equalizing effect on the Earth’s climate

A Salvadoran boy uses water from a common faucet to bathe himself.

(AP/Wide World Photos)

Trang 3

Maritime locations have a milder climate than those

that are located in continental interiors Thus, the

av-erage annual temperature range between the

warm-est and coldwarm-est months for Winnipeg, Canada, and

the Isles of Scilly, England, is 39° and 8.3° Celsius,

re-spectively Even though both places are at 50° north

latitude, the temperatures in the Isles of Scilly are

moderated by their oceanic location, whereas

Winni-peg is in the middle of a large continent

The high heat capacity of water is closely associated

with some other unusual properties of water, namely,

the latent heat of fusion and vaporization The latent

heat of fusion is the amount of heat per unit mass (80

calories per gram) that is necessary to change a

sub-stance completely at its melting point to a liquid at the

same temperature This means that if heat is applied

to ice at 0° Celsius, the temperature of the ice remains

constant until all of the ice has melted Note that the

term “latent” indicates a change in state without a

change in temperature In a similar manner, the

la-tent heat of vaporization is the amount of heat per

unit mass (539 calories per gram) required to change

a liquid completely at its boiling point to a gas at the

same temperature This means that if heat is applied

to water at 100° Celsius, the water begins to boil and

the temperature remains the same until all the water

has boiled away The old saying “a watched pot never

boils” reflects the fact that water needs an enormous

amount of heat before it can reach its boiling point

and undergo a phase change from liquid to vapor

The processes of fusion and vaporization are

revers-ible and thereby represent two of the most important

energy transformations in the environment, as they

strongly influence the Earth’s climate

Water boils at 100° Celsius at sea-level pressure,

which is one of the highest boiling points of any fluid

on Earth This property differs from the general rule

that the boiling point of a fluid goes up as its

molecu-lar weight increases This rule does not apply to water

that has a relatively low molecular weight Viscosity

in-creases with increasing pressure for nearly all fluids

This is not the case with water, for which viscosity

de-creases as pressure inde-creases This property explains

why water, which is under high pressure in a

water-distribution system, is able to flow, rather than

drib-ble, out of a kitchen tap

The hydrogen bonding of water allows its surface

tension to be two to three times greater than that of

most common liquids This property explains why

certain insects can “walk on water” and why steel

nee-dles can float Surface tension (cohesion) and the ten-dency of water to wet solid surfaces (adhesion) cause capillarity, which allows water to “climb” a wall or tube If water had a much weaker or smaller surface tension (and therefore weaker capillary forces), soil water, which is necessary for plant life, would be un-able to overcome gravity

Distribution of Water Earth is a well-watered planet Thus, hypothetically, if the entire surface of the Earth could be leveled off and the ocean depths filled with the continents, the planet would be covered with water to a depth of more than 3 kilometers By far, most of the world’s water (97 percent) is contained in the oceans Another 2 per-cent is locked in ice caps and glaciers This means that almost all the water in the world (99 percent) is either salty or frozen The remaining water is accounted for

by groundwater to a depth of 4 kilometers, freshwater lakes, saline lakes and inland seas, soil moisture and water in the unsaturated zone, and the atmosphere Finally, if one measured the average volume of all the rivers on Earth, the estimated amount would only be 0.0001 percent of the total water on the planet

Water as a Resource There are several characteristics that pertain to water

as a resource First, water is a renewable resource As governed by the hydrologic cycle, it is continuously going through the processes of evaporation, convec-tion, and advection in the atmosphere; precipitation; interception and transpiration by vegetation; over-land flow; infiltration and percolation through the soil and unsaturated zone to the groundwater in shal-low, intermediate, and deep aquifers; and base flow from groundwater to streams for eventual transport

to the ultimate sink on Earth, the oceans In the oceans, it evaporates again to continue the cycle The quantity of water on Earth is relatively fixed, although the quality is affected by numerous anthropogenic ac-tivities

Second, water is ubiquitous on the Earth It can be found almost anywhere, although it may be too salty

or frozen to use directly Available and abundant freshwater resources, like mineral resources, are un-evenly distributed Thus, water must be transported long distances to supply the needs of major metropol-itan areas For example, New York City gets most of its water from Delaware River basin reservoirs, some 200 kilometers away Los Angeles depends on water that is

Trang 4

transported hundreds of kilometers from Northern

California, the Owens Valley east of the Sierras, and

the Colorado River

Third, water can be considered a common

prop-erty that has poorly defined propprop-erty rights Even

during droughts, when potential consumers may be

excluded, water is sometimes treated as a free

com-modity Society recognizes the expenses associated

with the diversion, treatment, and distribution of

water but does not recognize the cost of the water

it-self The western United States stands out as a major

exception to the common property concept, because

ownership of water does occur, usually on a

first-come, first-served basis

Fourth, water is relatively inexpensive (although in

certain drought-prone regions, in the face of

popula-tion growth, its scarcity is a growing concern) The

combination of the common property aspect of water,

water-supply technology, and economies of scale make

water an unusually cheap commodity even though it is

essential for life and has no substitute For example,

treated public water in the United States delivered to

a domestic user costs about 13 cents per liter (5 cents

per gallon)

Water Use

The various ways that water is used can be

dichoto-mized into offstream and instream use Offstream

use pertains to water that is diverted (withdrawn) from surface water or groundwater sources and trans-ported to the place of use This includes water that is used for domestic, commercial, irrigation, livestock, industrial, mining, and thermoelectric power pur-poses Each of these seven categories of offstream water use has a different effect on the potential for re-use of the return flows For example, the return flow for irrigation is often contaminated by pesticides, her-bicides, salts, and fertilizers to such an extent that it has minimal reuse potential An unfortunate illustra-tion of this situaillustra-tion occurs on the lower Colorado River near Yuma, Arizona, where the United States built a large desalinization plant in order to reduce the salinity of the water for the irrigated areas in nearby Mexico The plant opened in 1992 and has ex-perienced numerous operating problems In con-trast, the reuse potential of most of the water dis-charged from thermoelectric plants is high, because the major change in the water is an increase of tem-perature

Instream water use occurs without the water being diverted from surface or groundwater sources These uses include navigation, low flow maintenance to ben-efit aquatic ecosystems, hydroelectric power genera-tion, and wastewater assimilation Although instream uses have an impact on the quality and quantity of water resources for all uses, numerical estimates of the

U.S Water Use Per Day

(billions of gallons)

Per Capita (gallons) Irrigation

Public

Industrial

& Misc

Steam Electric Utilities

Source: U.S Department of Commerce, Statistical Abstract of the United States, 2004, 2004.

Note: Per capita figures are gallons; all other values are in billions of gallons.

Trang 5

amount of instream use are difficult to obtain with the

exception of hydroelectric power generation

Diversion of freshwater resources varies

consider-ably from country to country One useful measure of

existing or potential water shortages is to examine

to-tal annual diversions as a percentage of the annual

re-newable water supplies for that country Some

coun-tries, such as Canada (1.4 percent) and the United

States (15.5 percent), are well within the limits of

their overall renewable water supplies, although the

drier areas of the Southwest are reaching the limits

of local resources Other countries in arid regions

such as Libya (712 percent) and Saudi Arabia (722

percent) are clearly in excess of their renewable

sup-plies and are therefore mining their groundwater

reserves

Water-use data for the United States have been

compiled at five-year intervals by the U.S Geological

Survey on a statewide basis since 1950 These five-year

water-census reports provide an invaluable summary

of water-use trends and patterns As expected, total

water withdrawals increased from 1950 to 1980 as the

population increased However, beginning in 1985

and contrary to expectations that water use would

simply continue to increase as population increased,

water use actually declined and then remained stable

through 2000 It is hypothesized that technological

changes, such as irrigation practices, the introduction

of low-flow toilets, and a growing awareness of water

conservation, led to a more efficient use of water

Excluding water withdrawn for thermoelectric

power, irrigation represents the largest use of fresh

water in the United States, accounting for

approxi-mately 65 percent of total water withdrawals The

three states with the largest irrigation withdrawals are

California (22.4 percent), Idaho (12.5 percent), and

Colorado (8.4 percent) In terms of source, surface

water and groundwater account for 76 percent and 24

percent, respectively, of the total amount of

freshwa-ter withdrawals

Public water supply pertains to the diversions made

by public and private (investor-owned) systems that

are delivered to many users for domestic (residential),

commercial, industrial, and thermoelectric power

pur-poses Surface water accounts for 63 percent of the

total fresh water diverted by public water systems It

does not include industrial self-supplied water or the

thousands of individual homes and farmsteads in the

United States that have their own wells About 15

per-cent of the U.S population have their own wells Even

in the most densely populated state in the nation (New Jersey), the estimated portion of the population that has its own wells has remained at about 10 per-cent for several decades

Water Disputes Because water is essential for life, disputes over its use not only are numerous but also have been going on for several thousand years In arid areas, such as the Middle East, water is crucial for irrigated agriculture Thus, Turkey’s decision to build reservoirs for irriga-tion in the headwaters of the Tigris and Euphrates rivers, which are in its territory, may deprive the down-stream states Iraq and Syria of water on which they have come to depend The allocation of the waters of the Jordan River among the neighboring states of Is-rael, Jordan, Lebanon, and Syria in another politically sensitive and drought-prone area is related to the via-bility of peace in the region With the small exception

of some limited reserves of groundwater that accrued from ancient pluvial periods, Egypt is totally depen-dent on the Nile River, which originates in Ethiopia and Lakes Albert and Victoria in east-central Africa Any large diversion of the Nile by the upstream states would have a major impact on Egypt

The Colorado River and its tributaries begin in the Rocky Mountains in Wyoming, Colorado, and New Mexico and flow for 2,333 kilometers through Utah, Arizona, Nevada, and California before emptying into the Gulf of California in Mexico Although agree-ments exist among the seven states and Mexico re-garding water allocation, problems have developed and are likely to worsen in the future, because the ini-tial allocation was predicated on an average flow that was based on an above-normal precipitation cycle In the face of drier or more normal precipitation cycles, the allocations have to be reduced, with obvious harm

to the large users in the basin, particularly those who use the water for irrigation

The Chicago diversion scheme provides a good ex-ample of an international agreement on water alloca-tion that was settled amicably As Chicago grew during the late nineteenth century, drinking water was ob-tained from a nearby and abundant source, Lake Michigan Serious health problems developed when Chicago’s sewage was sent back to the same lake In or-der to maintain the quality of the drinking water, the Chicago Sanitary and Ship Canal was connected with the Illinois River, which flows into the Mississippi River Because excessive out-of-basin diversions from

Trang 6

Lake Michigan would affect navigation farther

down-stream at Montreal and Quebec on the St Lawrence

River, an international agreement between Canada

and the United States was reached early in the

twenti-eth century that allowed a diversion of 85 cubic

me-ters per second

Water Quality

Until relatively recently, societies were more

con-cerned with water quantity than with water quality

However, this began to change as growing

concen-trations of industry and increased population density

led to larger amounts of impurities being released

into local water sources By the end of the nineteenth

century, the Thames River near London and other

rivers near large European cities were so polluted

that the rivers became anaerobic (containing no

dis-solved oxygen) and emitted offensive odors Fish could

not survive in these waters It became obvious that

wastewater from residential and commercial sources

had to be treated prior to release into a receiving

watercourse

One solution to the problem in urban areas has

been to construct public sewers that connect to

waste-water treatment plants, which have helped to improve

water quality In more rural areas, septic systems and

well-constructed latrines are generally used to handle

wastewater However, there are countries where

unim-proved sanitation facilities, such as public and

open-pit latrines, are used by large segments of the

popula-tion Thus, access to improved sanitation for the total

population (urban and rural) varies from an

esti-mated low of 9 percent for Chad and Eritrea in Africa

to 100 percent for such countries as Canada, Israel,

Ja-pan, and the United States

The types of water pollution can be categorized on

the basis of their effect on human health and the

envi-ronment Organic wastes are decomposed by

chemi-cal and biologichemi-cal processes that can use up the

dis-solved oxygen in water that is essential for fish and

other aquatic organisms Excessive amounts of

ni-trates and phosphates entering surface waters can

lead to accelerated aquatic plant growth and organic

debris buildup, a process known as eutrophication

Sediments from agricultural and urban land uses can

cover benthic (bottom) organisms, clog steam

chan-nels, and destroy certain aquatic organisms Bacteria

and viruses that come from animal and human wastes

can enter drinking water supplies and cause such

dis-eases as dysentery, hepatitis, and cholera Heavy metals

such as lead and mercury, fibers such as asbestos, and industrial acids are harmful to humans and aquatic ecosystems Synthetic organic compounds that in-clude water-soluble materials (cleaning compounds and insecticides) and insoluble materials (plastics and petroleum residues) can cause a variety of ail-ments in humans and animals, such as kidney disor-ders, birth defects, and possibly cancer Radioactive wastes from commercial and military sources release toxic radiation that causes cancer Thermal pollution results from heated water being discharged into re-ceiving watercourses, usually from power plants The additional heat can lead to species change and in-creased growth rates in many types of aquatic organ-isms

As if the foregoing list were not extensive enough,

an additional problem has developed with the discov-ery that endocrine-disrupting compounds (pharma-ceuticals) and personal care products, collectively known as (PPCPs), can be excreted from humans and livestock (animals that are given food additives such

as antibiotics, growth promoters, and pharmaceuti-cals) The array of PPCPs that have been detected in drinking water sources include antibiotics, painkill-ers, beta-blockpainkill-ers, and sex steroids The majority of the PPCPs wind up in wastewater treatment plants, where they are only partially removed by existing technology The remaining PPCPs end up in surface streams from overland runoff or get directly into groundwater from septic systems Currently, there is minimal change in drinking water legislation regard-ing these products by government regulatory bodies, although there is growing recognition that an increas-ing amount of PPCPs are enterincreas-ing drinkincreas-ing water sup-plies without humans’ full knowledge of the dangers

to health

Water pollution sources are often dichotomized as point and nonpoint Point sources of pollution refer

to a known discharge point or outfall from a facility such as a wastewater treatment plant Although these are individually important, most of the stream pollu-tion comes from nonpoint sources, which are diffuse and scattered throughout the landscape Nonpoint sources include storm-water runoff from urbanized areas and agricultural runoff from rural areas Many contaminants from agricultural operations (herbi-cides and pesti(herbi-cides) are adsorbed onto soil particles, which are washed into the stream during storm events and transported downstream

Robert M Hordon

Trang 7

Further Reading

Brooks, Kenneth N Hydrology and the Management of

Watersheds 3d ed Ames: Iowa State University

Press, 2003

Cech, Thomas V Principles of Water Resources: History,

Development, Management, and Policy 2d ed.

Hoboken, N.J.: John Wiley & Sons, 2005

Chapelle, Frank Wellsprings: A Natural History of

Bot-tled Spring Waters New Brunswick, N.J.: Rutgers

University Press, 2005

Clarke, Robin, and Jannet King The Water Atlas New

York: New Press, 2004

De Villiers, Marq Water: The Fate of Our Most Precious

Resource Boston: Houghton Mifflin, 2000.

Gleick, Peter H., et al The World’s Water, 2008-2009:

The Biennial Report on Freshwater Resources

Washing-ton, D.C.: Island Press, 2009

Glennon, Robert Jerome Water Follies: Groundwater

Pumping and the Fate of America’s Fresh Waters

Wash-ington, D.C.: Island Press, 2002

Hunt, Constance Elizabeth Thirsty Planet: Strategies for

Sustainable Water Management New York: Zed

Books, 2004

Hutson, Susan S., et al Estimated Use of Water in the

United States in 2000 Reston, Va.: U.S Geological

Survey, 2004

Manning, John C Applied Principles of Hydrology

Illus-trated by Natalie J Weiskal 3d ed Upper Saddle

River, N.J.: Prentice Hall, 1997

Powell, James L Dead Pool: Lake Powell, Global

Warming, and the Future of Water in the West Berkeley:

University of California Press, 2008

Spellman, Frank R The Science of Water: Concepts and

Applications 2d ed Boca Raton, Fla.: CRC Press,

2008

United Nations World Water Assessment Programme

Water: A Shared Responsibility New York: Berghahn

Books, 2006

Ward, Andrew D., and Stanley W Trimble

Environ-mental Hydrology 2d ed Boca Raton, Fla.: Lewis,

2004

Whiteley, John M., Helen M Ingram, and Richard

Warren Perry, eds Water, Place, and Equity

Cam-bridge, Mass.: MIT Press, 2008

Web Site

U.S Geological Survey

Water Science for Schools

http://ga.water.usgs.gov/edu/

See also: Deep drilling projects; El Niño and La Niña; Eutrophication; Groundwater; Hydroenergy; Hydrol-ogy and the hydrologic cycle; Irrigation; Lakes; Mon-soons; Oceans; Streams and rivers; Thermal pollution and thermal pollution control; United Nations Con-vention to Combat Desertification; Water pollution and water pollution control

Water pollution and water pollution control

Category: Pollution and waste disposal

Water may become polluted by humans above the con-centrations of constituents normally produced by the dissolution of minerals, the atmosphere, and the bio-sphere High concentrations of toxic materials such as benzene, lead, and mercury may pose major health con-cerns The toxic constituents in natural waters must be reduced in concentration by chemical or physical pro-cesses known as remediation propro-cesses Major issues include decisions as to the desirable levels of pollution reduction and who should pay for the cleanup.

Background There are natural cycles of water compositional change that are not considered pollution Most pre-cipitation contains only tiny amounts of dissolved constituents obtained from the atmosphere, except for a relatively high concentration of carbon dioxide

in the form of carbonic acid Precipitation may also pick up small amounts of dissolved constituents as it moves through plants As the water from the precipi-tation moves through the soil, the soil becomes more acidic from the carbon dioxide in the soil This acid water can dissolve the common constituents found in minerals so the water becomes enriched in calcium, magnesium, potassium, sodium, chloride, sulfate, and

a complex ion formed from the carbonic acid, bicar-bonate These constituents are healthful to organisms

as long as they remain in low concentrations Other constituents are present in only tiny quantities in most minerals so that they are present in water in only dilute concentrations Natural organic compounds from the decomposition of plants and animals may also become dissolved in water

Trang 8

The soil water may move farther down into permeable

rocks (rocks through which water readily flows) such

as sandstones (rocks composed mostly of sand) or

limestones (composed mostly of calcium carbonate)

This deeper water is called groundwater If the

ground-water encounters other soluble minerals, then the

water composition may gradually change For

exam-ple, if groundwater encounters the soluble mineral

gypsum (a calcium sulfate mineral), it produces

wa-ters with high concentrations of calcium and sulfate

up to the point at which no more gypsum will dissolve

If the groundwater encounters a much more soluble

mineral such as halite (a sodium chloride mineral),

the water can become enriched in sodium and

chlo-ride Most deep groundwaters have high

concentra-tions of sodium, chloride, calcium, and sulfate,

sug-gesting contact with halite and gypsum, which make it

unfit to drink or to use in irrigation Even shallow

groundwaters in some places in central Kansas

be-come contaminated with near-surface gypsum and

halite

Groundwater may encounter rarer minerals such

as iron, lead, mercury, and zinc minerals combined

with sulfur, which react and produce acid waters with

high concentrations of the toxic metals This process

may be accelerated by mining: The chemically

reac-tive minerals may be exposed to air and water and may

dissolve even more rapidly than if left unmined below

the surface

Pollution

Mining may expose fine minerals so that weathering

processes may more rapidly decompose the minerals

Industrial processes produce a plethora of toxic

con-stituents, including mercury, lead, arsenic, cadmium,

chromium, nitrate, selenium, radioactive materials,

and hydrocarbons (organic compounds composed of

hydrogen, carbon, and often oxygen, nitrogen, or

sul-fur) Pollutants such as mercury become

concen-trated in the food chain and can produce serious

problems in humans For example, a number of

peo-ple were poisoned by mercury near Minamata, Japan,

in the 1950’s Industrial waste enriched in mercury

was dumped into the bay, where it was concentrated

by shellfish that people ate People in many areas of

the world have been poisoned by drinking water from

lead pipes If the water passing through the pipes is

moderately acidic, the water dissolves the lead In

Nova Scotia, arsenic polluted groundwater to a

con-centration of up to 5 milligrams of arsenic per liter as

a result of an arsenic mineral being discarded in gold-mining waste piles

There are also hundreds of hydrocarbon com-pounds produced by industry on the list of potential carcinogenic substances which are not desirable to have in any amount in drinking water The maximum concentration of toxic elements or compounds al-lowed in drinking water in the United States is set by the Environmental Protection Agency (EPA) Some toxic organic compounds, such as benzene, are relatively insoluble in water Benzene can move from the water as a separate liquid if there is consid-erable benzene present (much as oil and water can separate when they are mixed together) Some com-pounds—again, benzene is a good example—are vol-atile, as they readily vaporize from the liquid Thus a volatile, benzene-type liquid under buildings can pro-duce a vapor that migrates and concentrates in the basements of the buildings Other hydrocarbon com-pounds, such as alcohols, are relatively soluble in water, so considerable amounts of these hydrocar-bons may move dissolved in groundwater

Health effects as a result of exposure of these toxic substances are varied Some, such as arsenic, chro-mium, mercury, lead, and many organic compounds, are carcinogens Chromium may also cause skin ul-cers Mercury can cause fatigue and energy loss Lead, which is highly toxic, inhibits hemoglobin formation

U.S Drinking Water:

Maximum Allowed Concentrations

of Key Toxic Compounds

Constituent

Milligrams per Liter

Benzene (volatile organic) 0.005

Trang 9

Water Pollution Control

Water pollution can be controlled by passive and

ac-tive methods Passive methods include the storage of

hazardous wastes under conditions that reduce the

movement of toxic constituents into the groundwater

system Ideal storage would be in areas of low rainfall

with little population in rocks of low permeability so

that the toxic constituents remain in place Rocks of

low permeability include unfractured mudrocks and

many igneous and metamorphic rocks For example,

high levels of radioactive waste materials become

ex-tremely hot and are highly corrosive Much of the

ra-dioactive material in these high-level wastes will take

hundreds of thousands of years to decay Plutonium,

for example, concentrates in the bones of vertebrates

and takes more than 240,000 years to decay Thus,

al-ternative long-term storage must be found

It is not economically feasible to transport

house-hold or industrial garbage very far, so local landfills

must accommodate much of this waste unless it is very

hazardous No one wants these landfills nearby, so

large cities incur significant expense to their

moun-tains of garbage Moreover, rainfall is high in the

cen-tral and eastern United States, so it is important to

iso-late waste physically from the groundwater (ideally by

storing it where there are impermeable rocks), since

rain will infiltrate and move the soluble materials into

the groundwater Unfortunately, many old landfills

were sited in permeable rocks or in sediment such

as sands and gravels in river floodplains in which

groundwater moves directly through the landfill The

locations of many old, unused dumps or landfills have

been forgotten, so they continue their slow pollution

of the groundwater

More active methods must be used to control

pollu-tion in cases where groundwater or soil has already

been contaminated One problem is determining who

will pay for the expensive cleanup or remediation If

a specific industrial polluter is identifiable, the

sus-pected polluter usually must be sued The industry will

have to pay for cleanup if it is proved to have caused

the pollution If no industry can be responsible, then

individual landowners or the government may have

to pay for the remediation Exceedingly widespread

or hazardous cases of pollution may become EPA

Superfund cleanup sites if no industry or other

gov-ernment agency can be held liable for the pollution

Every cleanup site is different in terms of

pollut-ants, geology, and precipitation, so a variety of

meth-ods must be used One method is to remove all the

contaminated material physically and move it to a better landfill Organic compounds that evaporate may be removed to the air by pumping the polluted water from the ground and vaporizing it in a chamber This procedure is not used frequently, as it simply pol-lutes the air instead of the water Some organic com-pounds may be removed by carbon filters, although this is expensive Industrial organic compounds may

be burned at high temperature instead of buried to form harmless carbon dioxide and water Large vol-umes of soils or groundwater contaminated by petro-leum products may be aerated with nutrients and mi-crobes so that the organisms change the petroleum to harmless materials

Removal of multiple contaminants from waters may involve many processes in combination that re-move specific contaminants Besides the methods dis-cussed above, such processes include chemical precipi-tations of insoluble solids, exchange of contaminants onto special resins, and filtration of contaminants

History of Legislation in the United States During the industrialization of the United States in the nineteenth century, garbage and sewage were allowed

to collect in streets and near water supplies and were dumped untreated into rivers This led to epidemics

of diseases spread by water, such as cholera, hepatitis, and typhoid fever The Rivers and Harbors Act of 1899 prohibited the dumping of trash into bodies of water

In the latter part of the nineteenth century, some cit-ies began to filter their water supplcit-ies through sand

By the beginning of the twentieth century, drinking water had begun to be chlorinated to kill harmful or-ganisms Thus, by the mid-twentieth century, disease spread by water became rare in the United States, and the focus of pollution control began to shift to chemi-cal wastes Public awareness began to increase because

of well-publicized problems produced by pollution such as fish kills, human illness (such as the mercury poisioning that occurred at Minamata Bay, Japan), and lakes choked by abundant plant growth

Excessive plant growth may be produced by exces-sive nitrogen and phosphorous nutrients in waters Algae, for example, may cover much of a lake’s sur-face, producing foul-smelling water and using up the dissolved oxygen from the water as the algae die and decay With insufficient oxygen, fish may begin to die rapidly

The first real response by the federal government

to the need for water pollution control was the

Trang 10

Fed-eral Water Pollution Control Act of 1948 This weak

law stated that the states were responsible for water

quality and that the federal government would

vene only if the states could not resolve issues of

inter-state pollution The original act was extended in 1956

and 1961, and some of the original weaknesses were

addressed For example, money was included to help

states and towns fund water treatment plants

As a response to growing pollution problems, the

federal government passed the Federal Water Quality

Act of 1965, commonly known as the Clean Water Act,

in which the federal government took the

responsibil-ity for water pollution control The enforcement of

the law involved various federal agencies until it wound

up with the Environmental Protection Agency in 1970

According to this act the states were supposed to

de-velop criteria and enforcement policies regarding

water quality, but they were slow to do so Therefore

the Water Quality Act of 1970 was passed; it

strength-ened federal control of discharges of hazardous wastes

Federal grants were given to some industries for

treat-ment control of pollutants

The Water Pollution Control Act of 1972 was the

first law that gave the federal government the power

to set minimum standards for water quality and to

re-quire strict enforcement of these standards through

the EPA It became illegal to discharge any pollutant

into a stream unless a permit was obtained Violations

were enforced by large daily fines Some rivers, such as

the Willamette River in Oregon, have made

incredi-ble recoveries as a result of these laws The Willamette

River changed from a foul-smelling, organic-rich

sewer in which few fish could survive into a healthy,

oxygen-rich river with abundant fish Beginning in

the 1970’s the list of organic chemicals not allowed in

U.S streams and lakes increased to many hundreds of

compounds

Robert L Cullers

Định dạng
Số trang	10
Dung lượng	136,39 KB