Geology Reference
In-Depth Information
pollution abatement, recreation, and fish and wildlife
habitat. All of these uses provide benefits to humans in
the Earth system.
Water use is considered to be
consumptive
when it
is withdrawn and does not go directly back to the
immediate water supply system. It includes water that
is evaporated, transpired, incorporated in products
and crops, and consumed by humans and livestock.
Although we don't use all of our share of the
nation's water supply directly in our homes, we con-
sume goods that require water to produce. When we
buy a car, each pound of steel in it required 60,000 gal-
lons of water; production of a pound of beef may have
required more than 2,000 gallons of water. Shortages of
water for irrigation of crops can translate to a shortage
of food, forcing up food prices globally (Brown, 2006).
In this way a water shortage on the other side of the
world may impact you here in North America; a local
drought can become a "global drought."
public understanding of contamination. Still 20% of
U.S. community drinking water systems violate some
public safety requirement and in 1995 fish advisories
for consumption covered all of the Great Lakes, (Great
Lakes Information Network, 2005) and many rivers
and smaller lakes. About half the population in 45 least
developed countries lack access to safe drinking water.
Understanding water contamination and remediation
is essential in improving the quality of life for hundreds
of millions of humans.
CONTAMINATION OF GROUND
AND SURFACE WATERS
Contamination of water occurs from domestic, indus-
trial, and agriculture wastes produced by society.
Some contamination is from systems designed to place
waste on the land or in the water: septic tanks with
drain fields (nitrates might be the world's number one
contaminant), land disposal of sludge, and disposal
wells. Some contamination occurs because the wastes
are accidentally discharged: animal feedlots, acid mine
drainage, and landfills. In addition, sometimes non-
wastes contaminate water: accidental spills from truck
and train accidents, highway salt, fertilizers and pesti-
cides, and leaky underground storage tanks (USTs).
The types of pollutants include inorganic solids, min-
erals, metal ions, salts, bacteria and viruses, undecom-
posed organic matter such as grease, volatile organic
compounds (VOC), radioactive waste, and silt. Of the
VOC, the chlorinated solvents (TCE, PCE, and TCA)
1
are widespread as they were used as cleaning agents at
many sites and have produced plumes of contami-
nated water far from the source.
Contamination of slow-moving groundwater
may last for centuries and be difficult to clean up.
Pulses of recontamination of a groundwater aquifer
occur from contaminated soils above the water table
during recharge events. We need proper waste han-
dling systems to prevent groundwater and surface
water contamination, and we need to protect the zones
of groundwater recharge from contamination.
Addressing past contamination is a more diffi-
cult job. How do we clean up sites? Options include
removal and reburial or decontamination of the fluid
or the soils; on-site destruction of the hazardous mate-
rial by biological, mechanical, and chemical techniques;
or sealing off the site from further use and letting nat-
ural long-term remediation occur. These and other
options are topics of research on clean-up of contami-
nated groundwater aquifers.
Finally, in discussions of potential pollution by
human activity, we must always consider
background
or baseline levels
in a watershed. Simply finding high
levels of dissolved solids, for example, in a basin does
not mean that humans are responsible. Some bodies of
WATER QUALITY
Natural water is not necessarily "pure" or distilled; even
water from glacier ice has ions precipitated from the
atmosphere. Natural water contains minerals and ele-
ments from the atmosphere and the enclosing river
channel or groundwater aquifer (calcite, silica, calcium,
sodium, nitrates, iron, etc.), dissolved gases (oxygen,
C0
2
, etc.), organic wastes from plants and animals, and
microbes (viruses, bacteria, and parasites such as
Giardia
and
Cryptosporidium). A
quick measure of the inorganic
content of water is the total dissolved solids (TDS) which
can be obtained using a conductivity meter. Evaporation
of seawater provides a good demonstration of the min-
eral matter than can be dissolved in clear water.
The content of dissolved organic and inorganic
material in water is usually given as ppm or even ppb
(parts per billion). One ppm is 1 drop in 13 gallons of
water. A ppb is a very small quantity. It is equal to: 1
inch in 16,000 miles; 1 second in 32 years; and 1 square
foot in 36 square miles. Yet these ppb and ppm quanti-
ties are important in water quality as contaminants in
water at these levels can cause health problems.
In discussions of water quality criteria, one must
specify the use of the water. Water that is good for irri-
gation, may not be good for other uses such as drinking,
boiler feed, bathing, or food processing. For swimming
the important factor is not dissolved solids but fecal col-
iform bacteria, which indicate sewage pollution—a
health hazard—and closure of beaches. For fish habitat,
the dissolved oxygen level is important. For public
water supplies in the United States, the USEPA has Pri-
mary Regulations for Human Health and Secondary
Regulations based on aesthetics. For example, the Sec-
ondary Maximum Contaminant Level (SMCL) for Total
Dissolved Solids (TDS) is 500 mg/L.
Waterborne diseases in the developed world are
much reduced because of water treatment systems and
' TCE, Trichloroethelyne; PCE, Tetrachloroethylene; and TCA,
Trichloroe thane.
