A separate stormwater retention permit, issued by the Incorporated Village of East Hills, shall be required for the installation or construction of any dry well or retention system.

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. Impervious surfaces include, but are not limited to, roofs, driveways, on-grade and raised patios, athletic courts, swimming pools and spas, accessory equipment, retaining walls, window wells, areas of artificial turf, stepping stones, piers, egress wells, walkways and stoops. Areas of permeable materials and decks are excluded from calculations of impervious surfaces. In instances where runoff from new rear yard patios, athletic courts and impervious surfaces, in the opinion of the Code Enforcement Official, will not have an adverse effect on adjoining or down-slope properties, the Code Enforcement Official shall have the authority to allow exceptions to these requirements.

All new or substantially improved structures shall provide for the on-site stormwater retention for the entire structure and all impervious surfaces on the subject property. A "substantially improved structure" is defined as the enlargement, replacement or alteration of any structure where the new work area exceeds 50% of the existing building area or which would classify as a Level 3 alteration by the Existing Building Code of NYS.

If added impervious surfaces are constructed in separate locations and connecting the additional stormwater areas into 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, providing that the area retained is equal to, or greater than, the combined area of the added impervious surface.

Where drainage is needed or required for new cellar entranceways, emergency exits, window wells and other below-grade openings that have the potential for stormwater entering and flooding the cellar, such openings shall be provided with a dry well or retention system that is separate from all other dry wells or retention systems. This shall not prohibit combining more than one such below-grade opening on the same dry well or retention system.

All stormwater retention systems installed which require approval under the provisions of this article shall be inspected and approved by the Building Inspector or Code Enforcement Official. In instances where, in the opinion of the Code Enforcement Official, spatial constraints, soil composition or other site conditions prevent the installation from conforming to generally accepted practices, the Code Enforcement Official may require alternate design and certification by a duly licensed design professional.