Environmental Engineering Reference
In-Depth Information
5) m
−
1
, and objects can be discerned as far as 80 to 400 km (of course, the latter distance
is only visible from a height or to a height, so as to reach over the earth's curvature). In polluted
air,
b
ext
can be as large as E
to 5E(
−
m
−
1
, when objects disappear at a few kilometers distance.
Visibility impairment is a significant and unpleasant side effect of fossil fuel use. Visibility
improvement can be accomplished by reducing fine-particle and gaseous precursor emissions from
fossil fuel combustion and other fossil fuel usage. In practice this means improved emission control
devices for primary particles, SO
2
,NO
x
, and VOC (see Chapters 5 and 8). In the United States,
visibility improvement is addressed in Section 169A of the Clean Air Act Amendment of 1977,
which requires that visibility impairment at U.S. national parks must be lessened by reducing
particles and their precursor emissions from nearby sources. As a consequence of better and wider
use of emission control devices on stationary and mobile sources, visibility has improved steadily
in the past decades, and regional haze occurrences in the United States are now less frequent than
they were in the 1960s and 1970s.
(
−
3
)
9.3
WATER POLLUTION
The consumption of fossil fuel entails a significant impact on water quality and water usage. The
contamination of water starts at the mining and extraction stage, through transport and refining, all
the way to leaching into the groundwater of ash and scrubber sludge left behind after combustion of
fossil fuels. We shall limit this section to the effects of acid mine drainage, coal washing, leaching
from coal and ash piles, and water pollution due to atmospheric deposition of toxic byproducts of
fossil fuel combustion.
The major environmental disasters due to collisions or grounding of supertankers carrying
crude oil have been documented in scientific journals and the press and will not be treated here in
detail. Suffice it to say that in 1978, the
Amoco Cadiz
ran aground off the coast of France, spilling
223,000 metric tons of crude oil. In 1979, in the collision of the
Atlantic Empress
with the
Aegean
Captain,
50 miles northwest of Tobago, more than 287,000 t were spilled. In 1983, the
Castillo de
Bellver
spilled 252,000 t off the coast of South Africa. In 1989, the
Exxon Valdez
spilled 37,000 t of
crude in the environmentally sensitive Prince William Sound in Alaska. In 1991, the
ABT Summer
spilled 260,000 t off the coast of Angola. It is estimated that between 3 to 4 million metric tons
of oil is spilled annually into the world rivers, lakes, seas and oceans. Oil spills seem to be a high
environmental risk associated with fossil oil usage.
9.3.1
Acid Mine Drainage and Coal Washing
In terms of sheer quantity, the most serious water pollution problem associated with coal use is acid
drainage from mines, especially surface mines, coal piles, and coal washing. Precipitation falling on
open coal seams and on coal piles will leach out mineral matter. The leachate contains acids, toxic
elements, and often radioactive isotopes. Leachates with a pH as low as 2.7 have been measured.
The acid is a product of oxidation and hydrolysis of the pyritic sulfur in coal. The following toxic
elements are found in coal mine and pile drainage in concentrations that exceed drinking water
standards: arsenic, barium, beryllium, boron, chromium, fluorine, lead, mercury, nickel, selenium,
vanadium, and zinc. U.S. federal and state regulations now require that the leachate be either
