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Facts about the King County regional wastewater system
All data current for 2023, the most recent year for which data are available, unless otherwise noted.
Customers and service area
| System | West Point | South | Brightwater | Vashon | Carnation | |
|---|---|---|---|---|---|---|
| Wholesale customers | King County has sewage disposal contracts with 18 cities, 15 sewer districts, and the Muckleshoot Tribe to provide wholesale wastewater treatment services. | -- | -- | -- | 1 sewer district | City of Carnation |
| Population Served (estimated) | Approximately 2 million residents | 785,300 | 866,200 | 293,100 | 1,100 (based on 2020 census data) |
2,167 |
| Area served | 424 sq mi | 113 sq mi | 240 sq mi | 69 sq mi | 660 ac (by 2050) | 821 ac (in city and surrounding urban growth area) |
|
Key: -- = not applicable or does not apply sq mi = square miles ac = acres |
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Sewage treated
| System | West Point | South | Brightwater | Vashon | Carnation | |
|---|---|---|---|---|---|---|
| Sewage treated (volume expected in average rainfall year) |
178 mgd | 95 mgd | 65 mgd | 18 mgd | 0.15 mgd | 0.100 mgd |
| Sewage treated (2023) |
182.3 mgd1 | 91.9 mgd | 71.1 mgd | 18.5 mgd | 0.154 mgd | 0.104 mgd |
| Peak day flow (2023) |
731.1 mgd2 | 411 mgd3 | 195.4 mgd4 | 38.2 mgd5 | 0.779 mgd6 | 0.157 mgd7 |
| Septage treated (2023) |
23.8 mg/yr (1,810 dry tons solids)8 |
-- | 23.8 mg/yr (1,810 dry tons solids) |
-- | -- | -- |
|
Key:
-- = not applicable or does not apply |
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Facilities and pipelines
| System | West Point | South | Brightwater | Vashon | Carnation | |
|---|---|---|---|---|---|---|
| Treatment plants | 5 | West Point Treatment Plant, Seattle | South Treatment Plant, Renton | Brightwater Treatment Plant, Snohomish County north of Woodinville | Vashon Treatment Plant, Vashon Island | Carnation Treatment Plant, Carnation |
| Pump stations | 48 | 20 | 19 | 4 | 5 | -- |
| Regulator stations | 26 | 24 | 2 | -- | -- | -- |
| CSO wet weather treatment facilities | 5: Alki, Carkeek, Georgetown Henderson/Norfolk, Mercer/Elliott West |
-- | -- | -- | -- | -- |
| CSO storage facilities | 4: Murray, North Beach, Rainier Valley, South Magnolia | -- | -- | -- | -- | -- |
| Conveyance storage | 2: Logboom, North Creek | -- | -- | -- | -- | -- |
| King County sewer conveyance lines | About 383 mi sewer lines (and 15 mi reclaimed water lines) | -- | -- | -- | 3.9 mi | 1.75 mi |
| Sewer pipe diameter (smallest to largest) | 2.5 in. to 14 ft, 8 in. | 8 in. to 14 ft, 8 in. | 8 in. to 14 ft, 8 in. | 8 in. to 14 ft, 4 in. | 2.5 in. to 8 in. | 8 in. to 12 in. |
| Outfalls, length and depth | -- | 3,600-ft long; 240-ft deep; 1 diffuser at 600 ft-long Discharge to Puget Sound. |
2 parallel pipes, 10,000-ft long each; 625-ft deep; 4 diffusers at 500-ft long each Discharge to Puget Sound. |
2 parallel pipes, 4,600-ft long each; 600-ft deep; 2 diffusers at 250-ft long each Discharge to Puget Sound. |
2,850-ft long; 200-ft deep; no diffuser Discharge to Puget Sound. |
Primary discharge: Chinook Bend Wetland Enhancement Project Backup: Snoqualmie River at Carnation Farm Road Bridge |
|
Key: -- = not applicable or does not apply CSO = combined sewer overflow ft = feet in. = inches mi = miles |
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Design criteria
| West Point | South | Brightwater |
Vashon | Carnation | |
|---|---|---|---|---|---|
| Average wet-weather flow (non-storm): This number is often used to describe the size of the treatment plants. It is based on average wet-season flow (November through April). For West Point, the average does not include flow on days with rainfall. For all plants, this number is based on an average that does not show the maximum flows that can be handled at a plant. |
133 mgd | 115 mgd | 30 mgd |
0.26 mgd | 0.37 mgd |
| Maximum monthly average flow: | 215 mgd | 144 mgd | 40.9 mgd |
0.52 mgd | 0.48 mgd |
| Average dry-weather flow: | 110 mgd | 96 mgd | 25.2 mgd |
-- | 0.37 mgd |
| Biochemical oxygen demand (BOD) influent loading (annual average) | 168,000 lb/day | 220,000 lb/day | 66,063 lb/day (maximum month) |
526 lb/day | 321 pounds/day |
| Total suspended solids (TSS) influent loading (annual average) | 181,000 lb/day | 201,000 lb/day | 61,400 lb/day (maximum month) |
526 lb/day | 321 pounds/day |
| Instantaneous maximum capacity: Maximum flows that can be handled at the plants—often for short periods; some portions of these flows get minimal treatment. | 440 mgd | 325 mgd | 100 mgd |
1.14 mgd (or 2.05 mgd with on-site storage) | 1.40 mgd |
|
Key: -- = not applicable or does not apply IPS = Influent Pump Station lb = pounds mgd = million gallons per day mg/L = milligrams/liter |
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Permit information
| West Point | South | Brightwater | Vashon | Carnation | |
|---|---|---|---|---|---|
| Permit (NPDES) renewal dates: View permit limits (BOD, TSS, fecal coliform, chlorine residual) for each treatment plant. |
NPDES permit 6/1/2024 - 5/31/2029 |
NPDES permit 8/1/2015-7/31/2020 (Application for NPDES permit renewal was submitted in 2019. Permit administratively extended until renewed.) Reclaimed water permit: application for reclaimed water permit renewal was submitted in 2019. Permit administratively extended until renewed. |
NPDES permit 3/1/2018-2/20/2023 (Application for NPDES permit renewal was submitted in 2022. Permit administratively extended until renewed.) Reclaimed water permit: application for reclaimed water renewal permit was submitted in 2023. Permit expected to be administratively extended in prior to expiration in April until renewed. |
NPDES permit 3/1/2017-2/28/2022 (Application for NPDES permit renewal was submitted in 2021. Permit administratively extended until renewed.) |
NPDES and reclaimed water permit (combined) 11/1/2021-10/31/2026 |
| Puget Sound Nutrient General Permit: South Plant, West Point, Brightwater, and Vashon: coverage issued 4/1/22; expiration 12/31/26 | |||||
|
Key: BOD = biochemical oxygen demand NPDES = National Pollutant Discharge Elimination System TSS = total suspended solids |
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Resource recovery
| System | West Point | South | Brightwater | Vashon | Carnation | |
|---|---|---|---|---|---|---|
| Electricity produced (2023) |
8.82 million kWh |
8.355 million kWh | 0.465 million kWh | -- | -- | -- |
| Methane gas sold (2023) (Both West Point & Brightwater also use digester gas to power plant equipment, such as boilers and digesters) |
2.911 million therms | -- | 2.911 million therms | -- | -- | -- |
| Loop biosolids produced (2023) | 124,195 wet tons (28,776 dry tons) | 42,120 wet tons (11,796 dry tons, average percent solids: 28.0) | 66,544 wet tons (13,769 dry tons, average percent solids: 20.7) Note: South Plant receives untreated solids from Vashon and Carnation plants. |
15,530 wet tons (3,211 dry tons, average percent solids: 20.7) |
397,872 gallons (33 dry tons, average percent solids: 2) Untreated solids hauled to South Plant for further treatment. |
997,842 gallons (42 dry tons, average percent solids: 1) Untreated solids hauled to South Plant for further treatment. |
| Carbon sequestration (2023) (From Loop biosolids land application) |
34,644 MtCO2e |
16,437 MtCO2e | 13,725 MtCO2e | 4,481 MtCO2e |
-- | -- |
| Reclaimed/recycled water (filtered) used at treatment plants (2023) | 783.4 mg/yr | 187 mg/yr Note: Additional lower quality (non-Class A) water is also used for in-plant processes. |
69.4 mg/yr Note: Additional lower quality (non-Class A) water is also used for in-plant processes. |
522 mg/yr (as C3 - water, membrane effluent) |
-- | 5 mg/yr (assumed) |
| Reclaimed/recycled water (Class A) distributed offsite (2023) | 39.6 mg/yr | -- | 4.1 mg/yr (offsite use for irrigation and street cleaning) |
0 mg/yr Note: No reclaimed water was distributed to customer sites due to pipe failures throughout the conveyance system. |
-- | 35.5 mg/yr (distributed to Chinook Bend Natural Area Wetland Enhancement Site) |
|
Key: -- = not applicable or does not apply kWh = kilowatt-hour mg/yr = million gallons per year MtCO2e = metric tons of carbon dioxide equivalents |
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Financial information
| Wholesale sewer rate | $55.11 per month (beginning 1/1/2024) |
|---|---|
| Sewage treatment capacity charge | $74.23 per residential customer equivalent (RCE) per month (beginning 1/1/2024) |
| Biennial budget (2023-2024) | Operating: $391.8 million Capital: $984 million (including a disappropriation of $65 million of completed/legacy projects) |
| Number of employees (as of Dec. 2023) | About 719 full-time equivalents (FTEs); 39 term-limited temporaries (TLTs) and 36 short-term temporaries (STTs), which includes 18 high school and college interns. |
| WTD expenditures for capital facilities View projects under construction |
$3.3 billion (2023–2028) |
Industrial pretreatment
| Industrial pretreatment program |
|
| Industrial/commercial facilities with permits (aka Significant Industrial Users) | 99 |
| Industrial/commercial facilities with letters and discharge authorizations | 503 |
| Approximate number of compliance samples taken (except BOD and TSS) | 1,619 |
| Inspections conducted | 233 |
|
Key: BOD = biochemical oxygen demand TSS = total suspended solids |
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Combined sewer overflow and rainfall
| Combined sewer overflows (CSOs) CSO control program |
|
| Baseline volume (1980–83) | 2.3 billion gallons per year |
| Current volume (Jan.–Dec. 2023) | 644 million gallons per year |
| Number of King County CSOs | 38 (view CSO status map) |
| Total rainfall (measured at SeaTac) | Total rainfall (2024): 34.97 inches Long-term average annual rainfall: 38.29 inches (1945–2016) |