Any construction or alteration upon any lot that results in an increase of impervious surface on such lot equal to or greater than 200 square feet must include facilities for on-site retention and discharge of stormwater runoff from the added area of impervious surface. If the added impervious surface is constructed in separate locations, such that connecting those separate areas of increased impervious surface to a single retention system is impractical, then facilities for the on-site retention and discharge of the additional stormwater may be connected to existing areas of impervious surface, rather than to the newly constructed portions.

Any construction or alteration project subject to site plan review pursuant to Article XIIIC of this chapter must include facilities for the on-site retention and discharge of all stormwater runoff from all impervious surfaces, both existing and proposed; provided, however, that the Planning Board, in connection with its site plan review, may grant relief from the provisions hereof, in its discretion.

Facilities required hereunder shall be designed for the on-site retention and discharge of 100% of runoff calculated on the basis of three inches of rainfall over a one-hour period.