Geology Reference
In-Depth Information
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What Would You Do
Americans generate tremendous amounts of waste. Some
of this waste, such as battery acid, paint, cleaning agents,
insecticides, and pesticides, can easily contaminate the
groundwater system. Your community is planning to construct
a city dump to contain waste products, but it simply wants to
dig a hole, dump waste in, and then bury it. What do you think
of this plan? Are you skeptical of this plan's merits, and if so,
what would you suggest to remedy any potential problems?
groundwater contamination. The United States alone must
dispose of several thousand metric tons of hazardous chemi-
cal waste per year. Unfortunately, much of this waste has
been, and still is, being improperly dumped and is contami-
nating the surface water, soil, and groundwater.
Examples of indiscriminate dumping of dangerous
and toxic chemicals can be found in every state. Perhaps the
most famous is Love Canal, near Niagara Falls, New York.
During the 1940s, the Hooker Chemical Company dumped
approximately 19,000 tons of chemical waste into Love Ca-
nal. In 1953, Hooker covered one of the dump sites with dirt
and sold it for one dollar to the Niagara Falls Board of Edu-
cation, which built an elementary school and playground on
the site. Heavy rains and snow during the winter of 1976-
1977 raised the water table and turned the area into a muddy
swamp in the spring of 1977. Mixed with the mud were
thousands of toxic, noxious chemicals that formed puddles
in the playground, oozed into people's basements, and cov-
ered gardens and lawns. Trees, lawns, and gardens began to
die, and many of the residents of the area suffered from seri-
ous illnesses. The cost of cleaning up the Love Canal site and
relocating its residents exceeded $100 million, and the site
and neighborhood are now vacant.
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Figure 13.17
Oil Field Subsidence, Long Beach, California
The withdrawal of petroleum from the Long Beach, California, oil fi eld
resulted in up to 9 m of ground subsidence in some areas because
of sediment compaction. In this photograph, note that the ground has
settled around the well stems (the white “posts”), leaving the wellheads
up above the ground. The levee on the left edge of the photograph was
built to keep seawater in the adjacent marina from fl ooding the oil fi eld.
It was not until water was pumped back into the reservoir to replace the
extracted petroleum that ground subsidence fi nally ceased.
A major problem facing our society is the safe disposal of
the numerous pollutant byproducts of an industrialized
economy. We are becoming increasingly aware that streams,
lakes, and oceans are not unlimited reservoirs for waste and
that we must fi nd new safe ways to dispose of pollutants.
The most common sources of groundwater contamina-
tion are sewage, landfi lls, toxic waste disposal sites, and ag-
riculture. Once pollutants get into the groundwater system,
they spread wherever groundwater travels, which can make
their containment diffi cult (see Geo-Focus on pages 346 and
347). Furthermore, because groundwater moves so slowly, it
takes a long time to cleanse a groundwater reservoir once it
has become contaminated.
In many areas, septic tanks are the most common way
of disposing of sewage. A septic tank slowly releases sewage
into the ground, where it is decomposed by oxidation and
microorganisms and filtered by the sediment as it perco-
lates through the zone of aeration. In most situations, by the
time the water from the sewage reaches the zone of satura-
tion, it has been cleansed of any impurities and is safe to use
(
Finding groundwater is rather easy because it is present be-
neath the land surface nearly everywhere, although the depth
to the water table varies considerably. But just fi nding water
is not enough. Suffi cient amounts in porous and permeable
materials must be located if groundwater is to be withdrawn
for agricultural, industrial, or domestic use. The availability
of groundwater was important in the westward expansion
in both Canada and the United States, and now more than
one-third of all water for irrigation comes from the ground-
water system. As we mentioned in the Introduction, ground-
water provides 80% of the water used for rural livestock and
domestic use in rural America and it is the primary source
of water for a number of large cities. Furthermore, as one
would expect, quality is more important here than it is for
most other purposes.
If we discount contamination by humans from land-
fi lls, septic systems, toxic waste sites, and industrial effl uents,
groundwater quality is mostly a function of (1) the kinds of
materials that make up an aquifer, (2) the residence time of
Figure 13.18a). If the water table is close to the surface
or if the rocks are very permeable, however, water entering
the zone of saturation may still be contaminated and unfi t
to use.
Landfills are also potential sources of groundwater
contamination (Figure 13.18b). Not only does liquid waste
seep into the ground, but rainwater also carries dissolved
chemicals and other pollutants down into the groundwater
reservoir. Unless the landfi ll is carefully designed and lined
with an impermeable layer such as clay, many toxic com-
pounds such as paints, solvents, cleansers, pesticides, and
battery acid will fi nd their way into the groundwater system.
Toxic waste sites where dangerous chemicals are either
buried or pumped underground are an increasing source of
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