Fee Calculation

How the Utility Fee is Calculated
Storm drain outlet in riverMuch like a kilowatt or a therm serve as the basis for other utilities, the Equivalent Runoff Unit (ERU) is the base unit for a stormwater utility. An ERU is a measure of the amount of impervious surface on a property. Impervious surfaces, like a concrete parking area or a rooftop, do not allow stormwater to soak into the ground. These surfaces increase the amount of stormwater that runs off of the property and must be managed by the stormwater system.

A single ERU represents 2,628 square feet of impervious surface. This amount is the average size of the impervious area found at a single-family property here in Athens-Clarke County. That base amount is then applied to larger properties across the county. For example, City Hall on College Avenue has over 14 times the amount of impervious surface as an average single-family home and is charged 14.6 ERUs.

Residential customers are classified as small, medium, or large single family properties, based entirely on the amount of impervious surface on the property (not the occupancy, number of bedrooms, or heated square footage of the house). A small single family property has less than 1500 square feet of impervious surface, a medium single family property has between 1500 and 4000 square feet of impervious surface, and a large single family property has more than 4000 square feet of impervious surface. 

Please note that the following image shows example properties. Your bill may differ from the amount listed below due to account-specific differences, such as differences in the water quality factor, which is explained further below.

residential customers fee diagram

Commercial property owners are charged based on the exact square footage of impervious surface on the parcel.

Water Quality Factor

The water quality portion of the fee takes into account the land use of the property in determining the stormwater utility fee. A Water Quality Factor is assigned to several categories of land use:

Land Use CategoryDefinitionWater Quality Factor
Low Density DevelopmentSingle family, duplex, or triplex properties with lot size greater than half an acre0.5
Medium Density DevelopmentSingle family, duplex, or triplex properties with lot size less than half an acre1
Multi-family/Institutional DevelopmentSchools, hospitals, churches, and residential development with four or more dwelling units per structure1.3
Commercial/Industrial DevelopmentAll remaining developed properties not covered by the classification above1.9
UndevelopedProperties with less than 300 square feet of impervious area.0

Calculation Formula

The amount of your stormwater utility fee is the sum of the ERUs multiplied by the base rate of $2.07, the ERU multiplied by the quantity rate of $0.86, and the ERU multiplied by the appropriate ID factor and the quality rate of $0.57:

  • (ERU x Base Rate) + (ERU x Quantity Rate) + (ERU x Quality Rate x ID Factor) = Monthly Stormwater Fee

The formula above calculates the monthly stormwater fee. When comparing this amount to your utility bill, be sure to remember that the stormwater utility bill is for three months of stormwater charges. An average single-family homeowner is charged for one ERU. For properties charged one ERU, the fee is around $3.50 per month.