A. All persons engaged in any land disturbing activity shall provide stormwater retention in accordance with the following standards unless otherwise approved by the erosion control administrator:
1. Retention for any property/project that will result in a total impervious area between five thousand (5,000) square feet and one acre may at the discretion of the erosion control administrator be based on the rational method for the calculations included as part of the application for a permit. The erosion control administrator shall determine the suitability of the rational method based on location of property/project, history of drainage in the affected area, and topography.
2. Retention for any property/project that will result in a total impervious area over one acre shall be based on the soil conservation service (SCS) method for calculations or an alternative method approved by the erosion control administrator.
3. Retention for the addition of impervious area shall be calculated as the cumulative impervious area. For example, in year one, a commercial site increases the parking lot by twenty thousand (20,000) square feet. In year two, the same commercial site adds a building with an area of thirty thousand (30,000) square feet. In year one, if approved by the erosion control administrator, the rational method may be used for stormwater detention calculations required by this chapter. In year two, stormwater calculations shall be submitted and shall be based on the total increase of fifty thousand (50,000) square feet of impervious area and the SCS method for calculation or an approved alternate method. (Ord. 2017-1503, 4-4-2017)