Environmental Engineering Reference
In-Depth Information
Figure 2-9
Sediment-laden runoff following rainfall in a developing watershed.
and human detritus that cover our impervious surfaces. A constant dust-fall from
the atmosphere takes place during dry periods, and most of the atmospheric par-
ticulate matter is scrubbed by rainfall. Also contained in this surface runoff are
all the microbes that are hard at work breaking down the organic constituents
found on the urban street, from pet wastes to food materials. These bacteria are
also of the same general type that are found in a wastewater effluent, but usually
do not present as great a risk of disease transmission as do those in human waste
matter.
This does not mean to suggest that stormwater will not pollute a raw water
supply source as severely as sewage, but that the health concerns take a somewhat
different form. The drippings of petroleum hydrocarbons and metals from our
automotive vehicles are hardly what we would consider a suitable constituent
in our drinking water supply, nor are the small concentrations of herbicides,
pesticides, and other synthetic chemicals that are washed from the landscape
with every storm. As our lifestyles have become more complex, so have our
residual wastes, and their discharge into our waterways have health implications
well beyond our present level of scientific measurement.
One of the more insidious issues at the current time is the formation of
“estrogen mimickers” in the environment, and the potential long-term effect of
low-level exposure (probably through our water supply) to human health. The
decomposition products of several common chemicals can be found everywhere
in our modern water supply sources, and have been suspected of reducing the
potency of American males over the past six decades.
Impervious surfaces and maintained landscapes generate pollutants that are
conveyed in runoff and discharged to surface waters, but the transport process
is neither constant nor uniform. The technical solutions developed over the past
decades to remove pollutants from our point source wastewaters were based on a
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