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Green Roofs Could Clean Rivers in More Ways than One.
It has long since been known that green roofs
contribute to minimizing pollution in the local
watersheds that surround municipalities. In areas
that combine stormwater and wastewater in the
same sewer to be treated centrally (combined
sewer systems), the ever increasing area of
impermeable surfaces such as roads, parking lots,
and rooftops create tremendous peak flows that
can be difficult to manage by wastewater
treatment facilities which can result in combined
sewer overflows that cause treatment facilities to
dump untreated sewage into local water bodies.
Green roofs absorb rainwater and delay runoff.
This translates to easier to manage peak flows and less combined sewer overflow events.
New studies in Washington D.C. predict that the benefit to local water quality may go well beyond
minimizing overflow events. Stormwater itself carries surface pollutants that collect on
impermeable surfaces and carry them through stormwater drains and in some areas, directly to
local water bodies untreated. Stephen MacAvoy of American University is studying green roofs
ability to filter these common pollutants out of rainwater and keep them from running into local
water bodies.
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