Surfaces covered by impenetrable materials such as asphalt, compacted gravel, concrete, brick, and stone are impermeable. These impermeable materials seal surfaces, repel water, and prevent precipitation from infiltrating into soils and groundwater. Removal of these impermeable materials, when combined with permeable pavement or vegetation establishment, is intended to reduce stormwater runoff rate and volume, as well as associated pollutants transported from the site by stormwater runoff.
The process of urbanization, characterized by increases in impermeable or impervious areas, causes a substantial increase in stormwater runoff. One obviously beneficial stormwater management practice is to reduce the amount of impervious surface area in a given urbanized area. If an area has already been urbanized, this can be accomplished by removing impervious areas that can be replaced with pervious areas and still serve the intended purpose.
Patios, walkways, parking areas, and driveways can all be converted to pervious areas that increase infiltration to groundwater. Gardens, lawns, and permeable pavers all can be used in place of the impervious area removed. In order for impervious surface removal costs to be offset by the Program, they must be accompanied by an approved stabilization plan.