Fee Calculation

How the 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.

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 Category Definition Water Quality Factor
Low Density Development Single family, duplex, or triplex properties with lot size greater than half an acre 0.5
Medium Density Development Single family, duplex, or triplex properties with lot size less than half an acre 1
Multi-family/Institutional Development Schools, hospitals, churches, and residential development with four or more dwelling units per structure 1.3
Commercial/Industrial Development All remaining developed properties not covered by the classification above 1.9
Undeveloped Properties 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.

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