Visualizing Environmental Science

Water Pollution 263

Discharge

Leakage from corrosionof casing Confined aquifer

Confined aquifer

Impermeable clay

Nitrates

and

pesticides

seep

into

ground

Leaking

under-

ground

storage

tank

Gasoline

storage

Deep-well injection

of hazardous wastes Septic

tank

Septic

tank

discharge Sewer

leakage

Sewer

Artesian

well

Precipitation puts air

pollutants on land

Landfill

Stream

Unconfined aquifer

Leakage

from torn

plastic liner

Where

groundwater

meets

surface

water

Water table Leakage

from torn

plastic

liner

Surface

impoundment

of hazardous

wastes

Volatile

hazardous

wastes evaporate

and disperse in

the environment

Water table

well

Impermeable rock

methods, such as eliminating chlorine as a bleaching
agent, that produce significantly less toxic effluents.

Groundwater Pollution

Roughly half the people in the United States obtain their
drinking water from groundwater, which is also withdrawn
for irrigation and industry. In recent years, the quality
of the nation’s groundwater has become a concern. The
most common pollutants, such as pesticides, fertilizers,
and organic compounds, seep into groundwater from
municipal sanitary landfills, underground storage tanks,
backyards, golf courses, and intensively cultivated agricul-
tural lands (Figure 10.19). Concern over groundwater
safety has grown over the recent boom in hydraulic frac-
turing, a water-intensive process used to release natural
gas and oil from underground rock formations. Many lo-
cal conflicts have arisen over the potential contamination
of drinking water by fracturing chemicals.

Currently, most of the groundwater supplies in

the United States are of good quality and don’t violate

standards established to protect human health. How-

ever, areas that do experience local groundwater con-

tamination face quite a challenge: Cleanup of polluted

groundwater is costly, takes years, and in some cases is

not technically feasible.

1. What is water pollution?


2. What is biochemical oxygen demand? How is
   BOD related to sewage?


3. How does point source pollution differ from
   nonpoint source pollution? What are some
   examples of each?


4. What are some common sources of
   groundwater pollutants?

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Agricultural practices, sewage (both treated and untreated), landfills, industrial activities,
and septic systems are some of the sources of groundwater pollution. Natural processes
can only remove groundwater contamination very slowly.