The Town measures the amount of impervious surface (roofs, sidewalks, driveway, parking lot, etc.) using the number of Equivalent Residential Unit (ERU) per property. 1 ERU is equal to 3,473 square feet, which is the median amount of impervious area found on a typical single-family residential property in Fort Mill. All single-family residential properties are charged one ERU.
Other properties are charged in proportion to this billing unit based on the calculated number of ERUs for the existing impervious area multiplied by the ERU rate. For example, if your property has four times the amount of impervious area of one ERU, you will be charged four times the base rate of $72 per year (i.e. 4 ERUs or $288 per year). This billing methodology is typical for other stormwater funding programs in the United States. The impervious surface is calculated using the County’s 2009 aerial photography. If a property owner believes that the area of impervious surface has changed since the 2009 aerial photography was produced, the property owner can apply for an evaluation.