Environmental Engineering Reference
In-Depth Information
areas where water bodies are no longer fishable and swimma-
ble (goals of the Clean Water Act). Stormwater not only adds
nutrients, but also contributes to flooding in low-lying coastal
areas and cities, which have miles of impervious surfaces that
cannot absorb the water. Urban inputs can be controlled by
reducing the amount of impervious surfaces, sweeping litter
off streets before it gets into the water, and improving sewage
treatment plants. New York City, for instance, has instituted
zoning laws requiring new parking lots to include landscaped
areas to absorb rainwater, established a tax credit for green
roofs with absorbent vegetation, and begun environmentally
friendly infrastructure projects. Philadelphia is building rain
gardens and sidewalks of porous pavement and planting thou-
sands of trees. Rain barrels and rain gardens are the subject of
educational programs for numerous communities and school
groups. These programs provide homeowners with informa-
tion on installation and maintenance and typically include a
hands-on training where homeowners install a rain garden in
a community. These are all excellent ways of chipping away
at the problem. But unless cities require developers to build
in ways to minimize runoff, the volume of rain flowing into
sewers is likely to grow.
What can be done about combined sewer overflow?
Some cities have built retention basins—tanks that hold
sewage until the water volume following a storm decreases.
Other municipalities have reconfigured treatment facilities
to expand and maximize flow rate. Still others have adapted
green infrastructure—green roofs, porous pavements and bio-
swales, or planted ditches that filter contaminants—to reduce
the amount, speed, and toxicity of water drainage after a
storm. A new technology, inflatable dams, has recently been
installed in two locations in Brooklyn, NY. These large cylin-
drical rubber structures are placed within sewer mains and
inflate during heavy rain to block the flow of rain water and
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