Skip to main content

Facts about the King County regional wastewater system

Facts about the King County regional wastewater system

All data current for 2022, the most recent year for which data are available, unless otherwise noted.

2022

  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. -- -- -- -- --
Population Served (estimated) Approximately 1.9 million residents 773,600 835,900 276,500 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
  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 (2022) 185.2 mgd1 95.8 mgd 69.8 mgd 18.1 mgd 0.150 mgd 0.101 mgd
Peak day flow (2022)
720.3 mgd2 384 mgd3 207 mgd4 36.4 mgd5 0.730 mgd6 0.144 mgd7
Septage treated (2022)
33.4 mg/yr
(2,736 dry
tons solids)8
-- 33.4 mg/yr
(2,736 dry
tons solids)
-- -- --
Key:
-- = not applicable or does not apply
1System average includes 1.2 mgd from the CSO Treatment Plants.
2System peak flow includes 92 mgd from the CSO treatment plants; System Peak day occurred on 1/6/2022.
3West Point max day flow occurred on 2/28/2022.
4South Plant max day flow occurred on 1/7/2022.
5Brightwater max day flow occurred on 1/7/2022.
6Vashon max day flow occurred on 1/6/2022.
7Carnation max day flow occurred on 1/6/2022.
8Septage flow and dry tons includes septic haulers plus flow and solids from other treatment plants.
CSO = combined sewer overflow
mgd = million gallons per day
mg/yr = million gallons per year
  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 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
  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
  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

Reclaimed water 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

(Application for NPDES permit renewal was submitted in 2022.)

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

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
  System West Point South Brightwater Vashon Carnation
Electricity produced (2022)

12.699 million kWh

11.921 million kWh
0.778 million kWh -- -- --
Methane gas sold (2022)
(Both West Point & Brightwater also use digester gas to power plant equipment, such as boilers and digesters)
2.737 million therms -- 2.737 million therms -- -- --
Loop biosolids produced (2022) 123,502 wet tons (28,935 dry tons) 42,125 wet tons (11,516 dry tons, average percent solids: 27.3) 67,825 wet tons (14,582 dry tons, average percent solids: 21.5)

Note: South Plant receives untreated solids from Vashon and Carnation plants.
13,552 wet tons (2,837 dry tons, average percent solids: 20.9)

356,115 gallons (25 dry tons, average percent solids: 1.7)

Untreated solids hauled to South Plant for further treatment.

1,040,287 gallons (39 dry tons, average percent solids: 0.9)

Untreated solids hauled to South Plant for further treatment.

Carbon sequestration (2022)
(From Loop biosolids land application)
36,197 MtCO2e
16,059 MtCO2e 16,190 MtCO2e 3,949  MtCO2e
-- --
Reclaimed/recycled water (filtered) used at treatment plants (2022) 783.4 mg/yr 188 mg/yr

Note: Additional lower quality (non-Class A) water is also used for in-plant processes.
68.7 mg/yr

Note: Additional lower quality (non-Class A) water is also used for in-plant processes.
520 mg/yr (as C3 - water, membrane effluent)
-- 5 mg/yr (assumed)
Reclaimed/recycled water (Class A) distributed offsite (2022) 103 mg/yr -- 15.1 mg/yr
(offsite use for irrigation and street cleaning)
54.9 mg/yr
-- 33 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
Wholesale sewer rate $52.11 per month (beginning 1/1/2023)
Sewage treatment capacity charge $72.50 per residential customer equivalent (RCE) per month (beginning 1/1/2023)
Biennial budget (2023-2024) Operating: $383 million
Capital: $620 million (including a disappropriation of $31M of completed projects)
Number of employees (as of Dec. 2022) About 636 full-time equivalents (FTEs); 70 term-limited temporaries (TLTs) and 30 short-term temporaries (STTs), which includes 15 interns.
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) 102
Industrial/commercial facilities with letters and discharge authorizations 517
Approximate number of compliance samples taken (except BOD and TSS)  1,607
Inspections conducted  225
Key:
BOD = biochemical oxygen demand
TSS = total suspended solids
Combined sewer overflows (CSOs)
Baseline volume (1980–83) 2.3 billion gallons per year
Current volume (Jan.–Dec. 2022) 1.7 billion gallons per year
Number of King County CSOs 39 (view CSO location map)
Total rainfall (measured at SeaTac) Total rainfall (2022): 40.27 inches1
Long-term average annual rainfall: 38.29 inches (1945–2016)
1The Seatac website showing 2022 rainfall is missing data on 11/25/22. According to WTD rain gauges there was rain that day, so the Seatac 2022 total listed here may be slightly lower than actual rainfall.
expand_less