The Inver Grove Heights stormwater utility assigns costs to land parcels based on the premise that owners of parcels that have a high percentage of impervious surface, such as commercial and industrial areas, which generate larger volumes of runoff, would be charged more than the owners of land parcels that have a small amount of impervious surface, such as single-family or rural residential areas, which generates less runoff.
The following activities were completed by City staff to establish a stormwater rate structure for the City of IGH:
- Grouping parcels into 15 utility groups based on zoning and existing land use.
- Using code-allowed percentage of impervious areas for parcel zoning classifications, calculating stormwater runoff volume using actual rainfall for April through November from 1995 to 2004.
- Using one acre of single-family residential property as the reference (given a value of 1.0); the residential equivalency factor (REF) for each utility group was determined by the following ratio:
The runoff volume for an acre of given utility group land / The runoff volume of an acre of single-family residential land
- The base fee for a parcel is determined by multiplying the REF by the base rate to get the per acre or per lot charge. The surcharge fee amount is calculated the same way, using the surcharge rate in place of the base rate.
- The stormwater fee structure has three different final rates:
- Rural Rate: for parcels that are outside the current Municipal Urban Service Area (MUSA) boundary and are zoned as agricultural or estate district, and for undeveloped land in the Northwest Area (NWA).
- Urban Rate: for parcels within the current Municipal Urban Service Area (MUSA) boundary.
- NWA Developed: for developed property in the Northwest Area.
Rural property is charged the base rate. Urban property is charged the base rate plus the urban surcharge rate. Developed property in the Northwest Area is charged the base rate plus the NWA developed surcharge rate. The fee uses a minimum per-parcel annual fee. This was established to ensure that annual costs for citywide planning/management/permit tasks are covered.