Provisions for Proper Drainage and Maintenance. All off-street parking, off-street loading and service facilities shall be so drained as to prevent damage to abutting properties or public streets and shall be constructed of materials which will assure a surface resistant to erosion. All parking areas, aisles and loading areas open to the general public shall be paved with six inches of stabilized base or equivalent except that the Planning Board or Board of Adjustment may waive paving in lieu of crushed stone or other material when such is shown to substantially lessen surface runoff. This waiver shall apply only to areas used for employee parking, on-site driveways not connecting directly to the street and loading areas. All such areas shall be, at all times, maintained at the expense of the owners thereof, in a clean, orderly and dust-free condition.