Visualizing Environmental Science

262 CHAPTER 10 Freshwater Resources and Water Pollution

Stream

Copper from

auto brake linings,

worn pipes and

fittings;

asbestos

from roofing

materials, cement

Used

motor

oil;

hydrocarbons

from vehicle

exhaust

Organic wastes,

garbage, animal

droppings,

leaves

and grass

clippings

Nitrogen and

phosphorus

from lawn and

garden fertilizers,

pesticides

Storm

drain

Runoff from

storm drains

Zinc from

weathering

of aging

pipes and gutters;

lead from corroded

plumbing materials

pollution in waterways. To address the problem of run-

off from animal wastes, the U.S. Department of Agricul-

ture developed guidelines to help livestock operations

prepare Comprehensive Nutrient Management Plans to

prevent manure from becoming polluted runoff.

Although sewage is the main pollutant produced

by cities and towns, municipal water pollution also has

a nonpoint source: urban runoff from storm sewers

(Figure 10.18). The water quality of urban runoff from

city streets is often worse than that of sewage. Urban run-

off carries salt from roadways, untreated garbage, animal

wastes, construction sediments, and traffic emissions (via

rain carrying air pollutants). It may often contain such

contaminants as asbestos, chlorides, copper, cyanides,

grease, hydrocarbons, lead, motor oil,

organic wastes, phosphates, sulfuric acid,

and zinc.

Nearly 800 U.S. cities, including New

York and San Francisco, have combined

sewer systems, in which human and in-

dustrial wastes mix with urban runoff

from storm sewers before flowing into

sewage treatment plants. Even the largest

sewage treatment plant can process only a

given amount of wastewater each day, so

when too much water enters the system—

such as after a heavy rainfall or large

snowmelt—the excess, known as com-

bined sewer overflow, flows into nearby

waterways without being treated. Com-

bined sewer overflow, which contains

raw sewage, has been illegal since

passage of the Clean Water Act of

1972 (discussed shortly), but cities

have only recently begun to ad-

dress the problem.

Different industries gener-

ate different types of pollutants.

Food-processing industries

produce organic wastes that

decompose quickly but have

a high BOD. Pulp and paper

mills also release wastes with a

high BOD and produce toxic

compounds and sludge. The

paper industry, however,

has begun to adopt

new manufacturing

According to the Environmental Protection Agency

(EPA), agriculture is the leading source of water qual-

ity impairment of surface waters nationwide and is

r esponsible for 72 percent of the water pollution in U.S.

rivers. Agricultural practices produce several types of

pollutants that contribute to nonpoint source po llution.

Fertilizer runoff causes water enrichment. A nimal wastes

and plant residues in waterways, even treated human

wastes applied to fields as fertilizer, produce high BODs

and high levels of suspended solids as well as w ater en-

richment. Highly toxic chemical pesticides may leach

into the soil and from there into water or may find their

way into waterways by adhering to sediment particles.

Soil erosion from fields and rangelands causes sediment

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Many pollutants may be carried from storm drains on streets to streams and

rivers. The largest single pollutant in urban runoff is organic waste, which removes

dissolved oxygen from water as it decays. Fertilizers cause excessive algal growth,

further depleting oxygen levels. Other everyday pollutants include used motor oil,

which is often illegally poured into storm drains, and heavy metals.