Rate Calculations: Storm and Surface Water Utility rates are calculated differently for two customer categories, residential and non-residential.
- Single-family residential homes are charged a flat rate of $9.79 per account unless they are in a neighborhood with a signed stormwater maintenance agreement with the City. Having this agreement, which assigns responsibilities for maintenance of neighborhood stormwater ponds, lowers the monthly rate to $8.75 per account.
- Non-residential rates are calculated using a formula designed to relate the fee charged to the impact of stormwater runoff from the site. The formula also relates residential and non-residential sites through use of an equivalent residential unit (ERU). An ERU is the average impervious surface of a single-family home in square feet. One ERU is 2,528 square feet.
The table below shows that different non-residential base rates are charged depending on the development year. This is because of differing stormwater management regulations. Prior to 1980, little to no management of stormwater was required when a new site was developed. Between 1980 and 1990, regulations were enacted that required some detention of stormwater onsite. Much more comprehensive requirements were enacted in 1990 and revised in 2005.
2008 City of Olympia Stormwater Rate Structure
| Rate Category |
Monthly Base Rate Calculation |
| Single-family Residential |
$9.79 per utility account |
Single-family approved after 1990
(with maintenance agreements) |
$8.75 per utility account |
| Duplex parcels |
$9.79 per unit ($19.58 when billed as a single account) |
| Non-Residential (pre-1980) |
$9.68 (see formula below) |
| Non-Residential (1980-1990) |
$7.52 (see formula below) |
| Non-Residential (post-1990) |
$3.60 (see formula below) |
| FORMULA to calculate Monthly Non-Residential Rate |
$9.58 + (Base Rate x Total Impervious Surface [sq. ft.] / 2,528) = Monthly Rate |
Non-residential monthly rates are calculated using the formula above. A $9.58 administrative fee is added to the quantity calculated by taking the base rate from the table above, times the total impervious area in square feet, divided by one ERU. Base rates are determined by the year the development was permitted. Impervious surfaces include buildings, concrete, and asphalt surfaces. One ERU (Equivalent Residential Unit) is equal to 2,528 square feet.
More rate information can be found in the Olympia Municipal Code, Section 4.24.010.D. For more information, contact us.