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Wastewater Treatment

King County, Washington

For questions about the Wastewater Treatment Division website, please send an e-mail message or contact us at:

King Street Center
201 S. Jackson St., Suite 500
Seattle, WA 98104-3855
Phone: 206-477-5371
Fax: 206-684-1741
Telecommunication device for the deaf (TTY): 711

Get Directions to our office location in Seattle, Washington.

Staff Contacts

Facts about the King County regional wastewater conveyance and treatment system

All data current for 2013,
the most recent year for which data is available, unless otherwise noted.

-- means "not applicable" or "does not apply"
XX means "information not available at this time"
mgd means "million gallons per day" and
mg/yr means "million gallons per year."

System and treatment plant data

Customers and service area

  System West Point South Vashon Carnation Brightwater 
34 local agencies
(includes 17 cities, 16 sewer districts, and the Muckleshoot Indian Tribe)
-- -- 1 sewer district City of Carnation  --
Population Served (estimated)
1.5 million residents 660,000
(varies summer to winter)
(varies summer to winter)
(based on census data)
2,000 190,000
415 square miles 105 square miles 241 square miles 660 acres
(by 2050)
832 acres
(in city and surrounding Urban Growth Area)
67 square miles

Sewage treated

  System West Point South Vashon Carnation  Brightwater
Sewage Treated
(Volume expected in Average Rainfall Year)
About 180 mgd (average) 96 mgd 67 mgd 0.12 mgd 0.09 mgd 17 mgd
Sewage Treated (2013)
167.3 mgd 82.2 mgd 70.1 mgd
(0.6 mgd is Brightwater effluent)
0.098 mgd 0.090 mgd 14.8 mgd
-- -- 29.77 million gallons -- -- --

Facilities and Equipment

  System West Point South Vashon Carnation Brightwater
Treatment plants
5 West Point Treatment Plant,
South Treatment Plant,
Vashon Treatment Plant,
Vashon Island
Carnation Treatment Plant,
Brightwater Treatment Plant, Snohomish County north of Woodinville
Pump Stations
47 -- -- 4 --  1
Regulator Stations
-- 25 -- -- -- --
CSO treatment facilities
Alki, Carkeek, Mercer/Elliott West, Henderson/Norfolk
-- -- -- -- --
King County sewer conveyance lines
about 391 miles -- -- 3.2 miles 1.6 miles --
Sewer pipe diameter
6 inches to 17 feet -- -- 2.5 to 8 inches 12 inches 48 to 66 inches
Outfalls, length and depth
-- 3,600 ft long;
240 ft deep;
600 ft diffuser

Discharge to Puget Sound.
10,000 ft long;
625 ft deep;
4 diffusers @ 500 ft L ea.

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.
2 parallel pipes 4,600 ft long

600 ft deep

2 diffusers @ 250 ft L ea

Discharge to Puget Sound.

Design criteria

  West Point South Vashon Carnation Brightwater
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) but does not include extraordinarily large storms in the average. It is based on an average that does not show the maximum flows that can be handled at a plant.
133 mgd 115 mgd 0.26 mgd (est.) 0.22 mgd 30 mgd (2012-2016)
Maximum monthly average flow
215 mgd 144 mgd 0.52 mgd 0.27 mgd 40.9 mgd (2012-2016)
Average dry-weather flow
110 mgd 96 mgd -- 0.21 mgd 25.2 mdg (2012-2016)
Biological oxygen demand (BOD) influent loading (annual average)
168,000 lbs/day 220,000 lbs/day 526 lbs/day 314 mg/L 66.063 lbs/day (max month 2012-2016)
Total suspended solids (TSS) influent loading (average annual)
181,000 lbs/day 201,000 lbs/day 526 lbs/day 314 mg/L  61.400 lbs/day (max month 2012-2016)
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 1.14 mgd
(2.05 mgd with on-site storage)
1.4 mgd 130 mgd

Permit information

  System West Point South Vashon Carnation  Brightwater
Permit (NPDES) renewal dates:
View permit limits (BOD, TSS, fecal coliform, chlorine residual) for each treatment plant.
-- NPDES permit 6/30/2014 (permit renewal underway; expected by 6/14) NPDES permit 10/31/2014
(permit renewal underway; expected by 10/14)

Reclaimed Water permit 10/31/2014
(permit renewal underway; expected by 10/14)
NPDES permit 8/31/2016 NPDES and Reclaimed water permit (combined) 12/30/2018  NPDES permit 7/31/2016

Reclaimed Water permit 8/1/2016

Resource recovery

  System West Point South Vashon Carnation Brightwater
Electricity produced annually
-- 6.506 million kilowatt hours 0.384 million kilowatt hours -- --  --
Methane gas sold annually
(Both West Point & South Plant also use digester gas to power plant equipment, such as boilers and digesters)
-- Not applicable 1.51 million therms -- --  --
Biosolids produced annually
115,801 wet tons
(or 28,395 dry tons) 
42,048 wet tons at 27.9% solids (or 11,717 dry tons) 

60,399 wet tons at 23.2% solids (or 14,007 dry tons)

Note: South Plant receives sewage sludge from Vashon and Carnation plants.

595,856 gallons at 1.5% solids (or 37.5 dry tons). Untreated solids hauled to South Plant for further treatment 544,566 gallons at 0.7% solids (or about 15.5 dry tons). Untreated solids hauled to South Plant for further treatment  13,335 wet tons (or 2,680 dry tons at 20.1% solids)
Reclaimed/Recycled water (Class A) used
About 65 million gallons per year of reclaimed water is distributed off-site; 607 million gallons per year is used for internal industrial treatment at the plant.

189.2 million gallons per year (used for industrial process at treatment plant).

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

2.94 million gallons per year (off-site customer use for irrigation, street sweeping, and sewer flushing).

81.7 million gallons per year (industrial use at the treatment plant)

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

-- 31.93 million gallons per year (distributed to Chinook Bend Natural Area wetland enhancement site)

30.2 million gallons per year (distributed to for irrigation, toilets/urinals, and public art).

336 million gallons per year (industrial use at the plant)

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Financial and budget information

Wholesale sewer rate $39.79 per month (1/1/2014)
Sewage treatment capacity charge $55.35 per month (beginning 1/1/2014) 
Annual budget (2014) Operating: $126.8 million 
Capital-related: $299.0 million
Number of employees 
(as of Jan 2014)
About 561 full-time equivalents (FTEs); 18 term-limited temporary (TLT) employees, and 7 temporaries (4 interns, 2 veterans in the HERO Intern program, and 2 administrative staff).
Brightwater Treatment Plant estimates Cost: $1.859 billion (with inflation) 
Serves: South Snohomish and North King counties 
Capacity: 30 mgd, 2013; 54 mgd, 2040
WTD expenditures for capital facilities through 2030 
>> view projects under construction
$2.8 billion (2013-2030)

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Other data (rainfall, industrial pretreatment, combined sewer overflows)

Total Rainfall 
(measured at SeaTac)
Total rainfall 2013 Water Year, 47.41 inches; 
Long-term average annual rainfall 38.22 inches
Industrial Pretreatment Program
Significant industrial users 121
Industrial/Commercial facilities with discharge authorizations 342
Approximate number of compliance samples taken 1,610
Inspections conducted 363
Combined Sewer Overflows (CSOs) 
CSO Control Program
Baseline volume 
2.3 billion gallons per year
Current volume 
(Jan.-Dec. 2013)
386 million gallons per year 
(view CSO reduction graph)
Number of King County CSOs 38; (view CSO location map)

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Ratepayer Report, April 2014
Ratepayer Report
, April 2014