For lots served by public utilities, the number of dwelling units permitted shall not exceed the number of dwelling units customarily developable in the zoning district in which the proposed development is located, developed with a conventional layout and all applicable ordinances and laws observed. In order to calculate density with a conventional subdivision or site condominium layout, the applicant shall submit a concept site plan of the property with a conventional layout. The plan shall indicate the topography of the site at two-foot contour intervals and the limits of all floodplains, water bodies, wetlands, easements, and other areas which would be set aside and preserved due to impracticality, economic infeasibility, contractual prohibition, or based upon applicable law or ordinance. In addition, the concept plan with the conventional layout shall include the general street pattern and lot configurations. In general, the plan shall be drawn with sufficient detail to permit the Planning Commission to determine the density that would be achieved by conventional development.