2009 SWM Fee StudyKing County began charging all developed parcels in unincorporated King County a Surface Water Management fee in 1987. The fee is based on the amount of impervious surface on a property which has a direct correlation to the amount of surface water runoff from a property. SWM fees for properties in unincorporated King County are based on the following chart: Surface Water Management service charges
| Class | Impervious surface | Rate |
|---|
Residential |
NA (it is based on average Impervious Area for all residential properties) |
$133.00/ parcel/ year |
Commercial Classes |
Very Light |
0 to less than or equal to 10 |
$133.00/ parcel/ year |
Light |
greater than 10 to less than or equal to 20 |
$320.61/ acre/ year |
Moderate |
greater than 20 to less than or equal to 45 |
$702.61/ acre/ year |
Moderately Heavy |
greater than 45 to less than or equal to 65 |
$1,199.36/ acre/ year |
Heavy |
greater than 65 to less than or equal to 85 |
$1,641.53/ acre/ year |
Very Heavy |
greater than 85 to less than or equal to 100 |
$2,046.72/ acre/ year |
County Roads |
NA |
Set in accordance with RCW 90.03.525 |
State Highways |
NA |
Set in accordance with RCW 90.03.525 | The SWM fee database used in 1985-86 to determine which class a property would be charged was created using black and white aerial photos and limited field inspection of specific properties. Updates to the database, other than new development, were almost exclusively generated by property owners concerned that a specific property was being incorrectly charged. Many land use changes such as additions, parking lot expansions, or demolitions have occurred since the SWM fee database was created. Many of these changes are not reflected in the current (2010) SWM fee database.
Recent improvements in Geographic Information Systems (GIS) combined with more detailed color aerial photos have enabled King County to more accurately measure impervious surface on a property. In 2009, King County used the improved GIS to compare existing property conditions with those represented in the SWM fee database. The results showed there were approximately 1,700 properties in unincorporated King County that were inaccurately measured and being incorrectly charged. Through a combination of GIS measurements and on site investigation, the SWM Fee Study is correcting the charges for these 1,700 parcels. Aerial photo source data comparison
| 1985 | 2009 |
|---|
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 | Property owners in unincorporated King County who were paying an incorrect SWM fee are receiving updated property tax statements with the corrected SWM fee on them in 2010. If you think your property is being billed incorrectly or have any questions regarding your current or updated SWM fee, please contact Diane Schneider, Finance and Billing Supervisor. For questions about the 2010 Surface Water Management Fee Study, please contact Brian Sleight, Supervising Engineer, King County Stormwater Services Section.
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