Stores retail business: one space for each 250 square feet of total floor area, excluding basements. In the CA District if the establishment is within 500 feet of a public parking lot that has more than 40 parking spaces available for local commercial use, and all on-site, off-street parking is located in the rear or side yards of the property, the standard shall be one space for each 500 square feet of total floor area, excluding basements.