Environmental Engineering Reference
In-Depth Information
lower concentrations of dissolved oxygen (which
helps decompose many contaminants) and smaller
populations of decomposing bacteria. The usually cold
temperatures of groundwater also slow down chemi-
cal reactions that decompose wastes.
It can take hundreds to thousands of years for
contaminated groundwater to cleanse itself of
degrad-
able
wastes. On a human time scale,
nondegradable
wastes
(such as toxic lead, arsenic, and fluoride) are
there permanently.
Solutions
Groundwater Pollution
Prevention
Cleanup
Find substitutes for
toxic chemicals
Pump to surface,
clean, and return
to aquifer (very
expensive)
Keep toxic
chemicals out of
the environment
Install monitoring
wells near landfills
and underground
tanks
Global Outlook: Extent
of Groundwater Pollution
Leaks from chemical storage ponds, underground
storage tanks, piping used to inject hazardous waste
underground, and seepage of agricultural fertilizers
can contaminate groundwater.
On a global scale, we do not know much about ground-
water pollution because few countries go to the great
expense of locating, tracking, and testing aquifers.
Nevertheless, the results of scientific studies in scat-
tered parts of the world are alarming.
According to the EPA and the U.S. Geological Sur-
vey, one or more organic chemicals contaminate about
45% of
municipal
groundwater supplies in the United
States. An EPA survey of 26,000 industrial waste ponds
and lagoons in the United States found that one-third
of them had no liners to prevent toxic liquid wastes
from seeping into aquifers. One-third of these sites are
within 1.6 kilometers (1 mile) of a drinking water well.
In 2002, the U.S. General Accounting Office estimated
that at least 76,000 underground tanks storing gaso-
line, diesel fuel, home heating oil, or toxic solvents
were leaking their contents into groundwater in the
United States.
During this century, scientists expect many of the
millions of such tanks installed around the world to
corrode, leak, contaminate groundwater, and become
a major global health problem. Determining the extent
of a leak from a single underground tank can cost
$25,000-250,000, and cleanup costs range from $10,000
to more than $250,000. If the chemical reaches an
aquifer, effective cleanup is often not possible or is too
costly.
Bottom line:
Wastes we think we have thrown
away or stored safely can escape and come back to
haunt us.
Toxic
arsenic
contaminates drinking water when a
well is drilled into aquifers where soils and rock are
naturally rich in arsenic. According to the WHO, more
than 112 million people are drinking water with ar-
senic levels 5-100 times the WHO standard, mostly in
Bangladesh, China, and West Bengal, India.
There is also concern over arsenic levels in drink-
ing water in parts of the United States. The EPA plans
to lower the acceptable level of arsenic in drinking wa-
Inject
microorganisms to
clean up
contamination
(less expensive
but still costly)
Require leak
detectors on
underground tanks
Ban hazardous
waste disposal in
landfills and
injection wells
Pump
nanoparticles of
inorganic
compounds to
remove pollutants
(may be the
cheapest, easiest,
and most effective
method but is still
being developed)
Store harmful
liquids in
aboveground tanks
with leak detection
and collection
systems
Figure 11-27
Solutions:
methods for preventing and cleaning
up contamination of ground water.
Critical Thinking: which two
of these solutions do you believe are the most important?
ter from 50 to 10 parts per billion (ppb). According to
the WHO and other scientists, even the 10 ppb stan-
dard is not safe. Many scientists call for lowering the
standard to 3-5 ppb, which would be very expensive.
Solutions: Protecting Groundwater
Prevention is the most effective and affordable way to
protect groundwater from pollutants.
Figure 11-27 lists ways to prevent and clean up ground-
water contamination. Pumping polluted groundwater
to the surface, cleaning it up, and returning it to the
aquifer is very expensive.
Preventing contamination is
the most effective and cheapest way to protect groundwater
resources.
11-7
OCEAN POLLUTION
Science: How Much Pollution Can the
Oceans Tolerate?
Oceans, if they are not overloaded, can disperse
and break down large quantities of degradable
pollutants.
