The method of determining slopes classified as "moderate" and "critical" shall be based upon two-foot contours and measured over a distance having a minimum change in vertical elevation of two feet. A plan and calculations prepared by a licensed professional engineer or land surveyor shall be submitted to determine the extent of moderate and critical slope areas. Said plan shall be clearly and legibly drawn or reproduced at a scale of no less than one inch equal to 30 feet for tracts of one acre or less and no less than one inch equal to 50 feet for tracts greater than one acre. All topography and elevations shall be related to a benchmark noted on the plan and, wherever possible, shall be based on the United States Geological Survey mean sea level data. Existing contours of the site under review shall be presented at no greater than two-foot intervals.

The permitted lot coverage and building coverage of any site shall be calculated by excluding all critical slopes and 50% of the moderate slopes from the lot area.

There shall be no site disturbance, no structures and no impervious coverage permitted within critical slope areas. Excluded from this limitation are utility improvements, both public and privately controlled, such as electric, telephone, cable lines, potable water, sanitary and storm sewer lines, driveways, utilities and roads, both public and private. Driveways, however, must be designed and constructed with a maximum grade of 15% at any point and disturb no more than 25 feet of width parallel to the driveway. Utility crossings within critical slopes shall be located to fall within the driveway disturbance area where possible in order to minimize critical slope disturbance.

Within moderate slope areas, no more than 50% of the rate of coverage for each developable lot(s), pursuant to the applicable zone district standards, may be utilized for building and/or lot coverage. For example, in a residential zone district which permits a maximum of 65% lot coverage and 25% building coverage for each developable parcel, no more than 32.5% of that area classified as moderate slope may be improved with impervious coverage and no more than 12.5% of that area classified as moderate slope may be improved with building coverage.