Facts about the King County regional wastewater system
All data current for 2021, the most recent year for which data are available, unless otherwise noted.
2021
| System | West Point | South | Brightwater | Vashon | Carnation | |
|---|---|---|---|---|---|---|
| Wholesale customers | 34 local agencies (includes 18 cities, 15 sewer districts, and the Muckleshoot Indian Tribe) |
-- | -- | -- | 1 sewer district | City of Carnation |
| Population Served (estimated) | Approximately 1.9 million residents | 787,000 | 839,000 | 268,000 | 1,100 (based on 2020 census data) |
2,000 |
| 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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| 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 | 0.10 mgd |
| Sewage treated (2021) |
183 mgd* | 95.2 mgd | 68.8 mgd | 18.7 mgd | 0.165 mgd | 0.100 mgd |
| Peak day flow (2021) |
580 mgd** | 370 mgd | 176 mgd | 32.6 mgd*** | 0.805 mgd**** | 0.162 mgd***** |
| Septage treated (2021) |
28.3 mg/yr | -- | 28.3 mg/yr (2,360 dry tons solids) |
-- | -- | -- |
|
Key: -- = not applicable or does not apply *System average includes 0.5 mgd from the CSO Treatment Plants. **System peak flow includes 59 mgd from the CSO treatment plants; System Peak day occurred on 1/12/2021. ***Brightwater max day flow occurred on 1/12/2021; South Plant's max day flow occurred on 1/13/2021 but South Plant's flow was still very high on 1/12/2021 at 175.4 mgd. ****Vashon max day flow occurred on 1/12/2021. *****Carnation’s max day flow which occurred on 10/26/2021, was not due to rainy weather, but due to flow that was stored the day before but released on 10/26/2021. CSO = combined sewer overflow mgd = million gallons per day mg/yr = million gallons per year |
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| 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 | 25 | 23 | 2 | -- | -- | -- |
| CSO wet weather treatment facilities | 4: Alki, Carkeek, 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 14 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 | 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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| 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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| 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 2/1/2015-1/31/2020 (Permit renewal application for NPDES was submitted in 2019. Permit administratively extended until new permit.) |
NPDES permit 8/1/2015-7/31/2020 (Permit renewal applications for separate NPDES and reclaimed water permits were submitted in 2019. Both permits were administratively extended until new permit.) |
NPDES permit 3/1/2018-2/20/2023 Reclaimed Water permit: 5/1/2019-4/30/2024 |
NPDES permit 3/1/2017-2/28/2022 (Permit renewal application for NPDES was submitted in 2021. Permit administratively extended until new permit.) |
NPDES and reclaimed water permit (combined) 11/1/2021-10/31/2026 |
|
Key: BOD = biochemical oxygen demand NPDES = National Pollutant Discharge Elimination System TSS = total suspended solids |
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| System | West Point | South | Brightwater | Vashon | Carnation | |
|---|---|---|---|---|---|---|
| Electricity produced (2021) |
13.467 million kWh |
12.687 million kWh |
0.780 million kWh | -- | -- | -- |
| Methane gas sold (2021) (Both West Point & Brightwater also use digester gas to power plant equipment, such as boilers and digesters) |
2.630 million therms | -- | 2.630 million therms | -- | -- | -- |
| Loop biosolids produced (2021) | 116,182 wet tons (or 28,417 dry tons) | 43,090 wet tons (or 11,819 dry tons). Average percent solids: 27.4. | 57,655 wet tons (or 13,420 dry tons). Average percent solids: 23.3. Note: South Plant receives untreated solids from Vashon and Carnation plants. |
15,437 wet tons (or 3,179 dry tons). Average percent solids: 20.6. |
244,844 gallons (or 20.4 dry tons). Average percent solids: 2.0. Untreated solids hauled to South Plant for further treatment. |
1,156,594 gallons (or 43.4 dry tons). Average percent solids: 0.9. Untreated solids hauled to South Plant for further treatment. |
| Carbon sequestration (2021) (From Loop biosolids land application) |
35,270 MtCO2e (the equivalent of taking almost 8,000 cars off the road) |
16,485 MtCO2e | 14,407 MtCO2e | 4,378 MtCO2e |
-- | -- |
| Reclaimed/recycled water (filtered) used at treatment plants (2021) | 678.8 mg/yr | 200 mg/yr Note: Additional lower quality (non-Class A) water is also used for in-plant processes. |
69.8 mg/yr Note: Additional lower quality (non-Class A) water is also used for in-plant processes. |
404 mg/yr |
-- | 5 mg/yr (assumed) |
| Reclaimed/recycled water (Class A) distributed offsite (2021) | About 77.8 mg/yr | -- | 5.2 mg/yr (offsite use for irrigation, street cleaning, and sewer flushing) |
37.3 mg/yr |
-- | 35.3 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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| Wholesale sewer rate | $47.37 per month (beginning 1/1/2021) $49.27 per month (beginning 1/1/2022) |
|---|---|
| Sewage treatment capacity charge | $68.34 per residential customer equivalent (RCE) per month (beginning 1/1/2021) $70.39 per residential customer equivalent (RCE) per month (beginning 1/1/2022) |
| Biennial budget (2021-2022) | Operating budget: $346 million Capital budget: $620 million (including a disappropriation of $31M of completed projects) |
| Number of employees (as of Dec. 2021) | About 620 full-time equivalents (FTEs); 43 term-limited temporary (TLTs) employees and 9 short-term temporaries (STTs) in December. |
| WTD expenditures for capital facilities View projects under construction |
$2.3 billion (2021–2026) |
| Industrial pretreatment program |
|
| Industrial/commercial facilities with permits (aka Significant Industrial Users) | 103 |
| Industrial/commercial facilities with letters and discharge authorizations | 567 |
| Approximate number of compliance samples taken (except BOD and TSS) | 1,580 |
| Inspections conducted | 220 |
|
Key: BOD = biochemical oxygen demand TSS = total suspended solids |
|
| Combined sewer overflows (CSOs) CSO control program |
|
| Baseline volume (1980–83) | 2.3 billion gallons per year |
| Current volume (Jan.–Dec. 2021) | 1.14 billion gallons per year |
| Number of King County CSOs | 39 (view CSO location map) |
| Total rainfall (measured at SeaTac) | Total rainfall (2021): 43.33 inches Long-term average annual rainfall: 38.29 inches (1945–2016) |
Sustainability at WTD
2019 Highlights -- Sustainability in King County's Wastewater Treatment Division
