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 run-off necessary?

 

Post-construction stormwater management in areas undergoing new development or redevelopment is necessary because run-off 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 run-off:

 

The first is caused by an increase in the type and quantity of pollutants in stormwater run-off. As run-off flows over areas altered by development, it picks up harmful sediment and chemicals such as oil and grease, pesticides, heavy metals, and nutrients (ex: nitrogen and phosophorus). 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 occurs by increasing the quantity of water delievered to the water body during storms. Increased impervious surfaces (ex: parking lots, driveways, and rooftops) interrupts 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 run-off 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.

 

Click here for the Minimum Control Measure (MCM) regarding Post-Construction Run-off (PDF)