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 Post-Construction
Run-Off Control
Regulated municipalities must have a program requiring new
and redevelopment projects to implement controls on sites,
which will reduce pollutant loads in stormwater run-off.
Why Is The Control of Post-Construction Runoff Necessary?
Post-construction stormwater management in areas undergoing
new development or redevelopment is necessary because runoff
from these areas has been shown to significantly affect
receiving water bodies. Many studies indicate that prior
planning and design for the minimization of pollutants in
post-construction stormwater discharges is the most
cost-effective approach to stormwater quality management.
 There
are generally two forms of substantial impacts of
post-construction runoff. The first is caused by an increase
in the type and quantity of pollutants in stormwater runoff.
As runoff flows over areas altered by development, it picks up
harmful sediment and chemicals such as oil and grease,
pesticides, heavy metals, and nutrients (e.g., nitrogen and
phosphorus). These pollutants often become suspended in runoff
and are carried to receiving waters, such as lakes, ponds, and
streams. Once deposited, these pollutants can enter the food
chain through small aquatic life, eventually entering the
tissues of fish and humans.
The second kind of post-construction runoff impact occurs
by increasing the quantity of water delivered to the water body
during storms. Increased impervious surfaces (e.g., parking
lots, driveways, and rooftops) interrupt the natural cycle of
gradual percolation of water through vegetation and soil.
Instead, water is collected from surfaces such as asphalt and
concrete and routed to drainage systems where large volumes of
runoff quickly flow to the nearest receiving water. The
effects of this process include stream bank scouring and
downstream flooding, which often lead to a loss of aquatic
life and damage to property.
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