Environmental Engineering Reference
In-Depth Information
(a)
(b)
Figure 6.29.  Range and pasture management: (a) rangeland; (b) grass drill in a pasture. Source : Natural Resources Conservation
Service (2005b).
the pollution falls, it may end up in streams, lakes, or
estuaries, and can affect the water quality.
The deposition of an air pollutant on land or water
can take several forms. Wet deposition occurs when air
pollutants fall with rain, snow, or fog. Dry deposition is
the deposition of pollutants as dry particles or gases. The
pollutants can reach bodies of water as direct deposition
falling directly into the water, or as indirect deposition ,
falling onto land and washing into the body of water as
runoff.
There are five categories of atmospheric pollutants
with the greatest potential to affect water quality: nitro-
gen compounds, mercury, other metals, pesticides, and
combustion emissions. These categories are based on
both method of emission and other characteristics of the
pollutants. Mercury is in its own category since it behaves
so much differently in the environment than do other
metals. Combustion of fossil fuels is a major source of
nitrogen oxides to the atmosphere. however, nitrogen
is in its own category since its effects on ecosystems are
so different from those of other combustion emissions.
Pesticides and combustion emissions are exclusively
human-made, whereas mercury, other metals, and nitro-
gen compounds arise from both natural and human-
made sources.
rus is normal, estimate the median and 90th per-
centile load of phosphorus contained in the runoff.
6.2. A 25-km 2 area is to be developed into residential
and commercial districts from which the runoff
will be routed to a large recreational lake. To avoid
the recreational lake becoming impaired, a TP
load allocation of 1300 kg TP/year should not be
exceeded. The residential area is expected to be
30% impervious, and the commercial area is
expected to be 60% impervious. If the annual rain-
fall in the area is 1500 mm and 30% of this rainfall
does not generate any runoff, estimate the
maximum percentage of the developed area that
should be commercial so as not to exceed the load
allocation.
6.3. A 150-m segment of a 10-m-wide urban roadway
drains into a nearby river. Field reconnaissance
indicates that the roadway segment has a litter and
street refuse deposition rate of 15 g/m·d, a dry
deposition rate of 5 g/m 2 ·d, a traffic emission rate
of 0.1 g/axle·m, a traffic density of 100 axles/d, and
a road condition factor of 0.5. The height of the
curb is 15 cm, the average traffic speed is 80 km/h,
and the average wind speed is 10 km/h. It is esti-
mated that the urban washoff coefficient is
0.15 mm −1 . Five days before a recent 3-hour storm
produced 100 mm of runoff, the solids on the
roadway segment was estimated to be 1 kg/m.
PROBLEMS
6.1. An urban (residential) area is estimated to be
45% impervious and to have an average annual
rainfall of 700 mm, and it is estimated that 60% of
the annual rainfall does not produce runoff.
Assuming that the EMC distribution of phospho-
(a) Estimate the mass of solids entering the river
from the storm runoff.
(b) What is the equilibrium level of solids on the
roadway?
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