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Septic Services in Seattle, WA

King County County · Pop. 749,256

Seattle and King County represent one of the most challenging septic system environments in the Pacific Northwest due to the combination of glacially-derived soils with restrictive till layers, high seasonal rainfall, and the ecological sensitivity of Puget Sound. Although Seattle's urban core is entirely sewered, King County is home to over 85,000 permitted onsite sewage systems serving rural communities on the Eastside, Enumclaw Plateau, Vashon Island, and other areas. King County's OSS program is among the most rigorous in Washington State, with mandatory O&M reporting, biennial inspection requirements for many alternative system types, and enhanced standards for systems near Puget Sound shorelines. Alderwood soils, which cover much of King County's forested uplands, are well-known for their cemented till layer that perches groundwater and limits system options to mound or drip irrigation designs.

Services in Seattle

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Drain Field Repair

Restore or replace failed leach fields and drain lines to prevent sewage surfacing and groundwater contamination.

$2,000 – $15,000

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Grease Trap Pumping

Commercial grease trap cleaning and pumping to prevent sewer blockages and maintain health code compliance.

$200 – $800

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Septic Inspection

Comprehensive evaluation of your septic system's condition, required for real estate transactions in most states.

$300 – $600

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Septic System Installation

Complete new septic system design and installation, from perc testing to final inspection.

$3,500 – $20,000

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Septic Tank Pumping

Regular pumping removes accumulated solids from your septic tank, preventing backups and extending system life.

$275 – $600

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Septic Repair

Diagnose and fix septic system problems including leaks, clogs, baffle failures, and component replacements.

$500 – $5,000

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Well Drilling

Professional water well drilling for residential and commercial properties without access to municipal water.

$6,000 – $25,000

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Well Pump Repair

Diagnose and repair well pump failures, pressure tank issues, and water flow problems.

$300 – $3,000

Septic Providers in Seattle (7)

SS

Scott's Septic Service Verified

Seattle, WA 00000

Scott's Septic Service provides professional septic services in Seattle, WA and surrounding areas. Contact them for septic pumping, repair, and inspection services.

Septic PumpingSeptic RepairSeptic Inspection
(253) 261-3453 View Profile

Septic Service Costs in Seattle

Service Average Cost
Septic Tank Pumping $300 - $550
Septic System Installation $12,000 - $35,000

Soil Conditions

Seattle and King County soils are dominated by Alderwood gravelly sandy loam—a glacially-derived, moderately well-drained soil over dense glacial till ortstein layer typically found at 20 to 40 inches depth. The ortstein or cemented till layer severely restricts percolation below that depth, causing perched seasonal groundwater. Norma fine sandy loam and Tukwila muck occur in lowlands and are hydric soils unsuitable for conventional systems.

Alderwood gravelly sandy loam (USDA series) is the dominant soil across King County uplands, characterized by 20 to 40 inches of moderately permeable material over a dense, nearly impermeable glacial till ortstein. This profile causes perched seasonal groundwater that saturates the lower half of conventional drainfields. Norma fine sandy loam and Tukwila muck in valley bottoms are hydric soils classified as unsuitable for any type of OWTS. Indianola loamy sand, present on higher-elevation outwash terraces, has good permeability and is the most favorable soil for conventional systems in King County.

Water Table: Seasonal high groundwater perches at 12 to 30 inches in Alderwood soils during the wet season (October through April). Lowland and valley areas along the Duwamish, Cedar, and Green rivers show groundwater within 0 to 18 inches seasonally.

Local Regulations

King County Environmental Health Services administers OSS permits under WAC 246-272A with locally-adopted additional requirements. All new systems require a licensed OSS designer evaluation. Systems within 200 feet of Puget Sound, Lake Washington, or other listed water bodies require enhanced treatment technology. King County mandates biennial inspections for ATUs, drip irrigation, and mound systems. O&M reports must be submitted electronically to King County's OSS tracking database.

Seattle proper is entirely connected to King County's regional sewer system. Rural King County unincorporated areas and smaller cities use OSS permitted by King County Environmental Health Services under WAC 246-272A. King County requires a licensed OSS designer evaluation, annual or biennial inspections for many alternative systems, and O&M reporting via King County's online tracking system.

Frequently Asked Questions — Seattle

Does Seattle have septic systems?
The city of Seattle itself is entirely served by King County's regional sewer system. However, the broader King County area—including Vashon Island, the Enumclaw Plateau, rural east King County, and unincorporated communities—has over 85,000 onsite septic systems that are regulated by King County Environmental Health Services.
Why are septic installation costs so high in the Seattle area?
King County's challenging Alderwood soils with restrictive till layers, combined with high labor costs and the prevalence of mound and drip irrigation systems, drive installation costs significantly above national averages. Engineered systems required by King County's proximity-to-water-body rules further increase costs. Material transport and the density of permits requiring licensed designer oversight also contribute.
How does King County's OSS program differ from other Washington counties?
King County has adopted stricter standards than the Washington State minimum, including mandatory biennial inspections for alternative systems, an electronic O&M reporting requirement, and enhanced treatment requirements within 200 feet of Puget Sound shorelines. The county also operates a loan program to help low-income homeowners repair or replace failing systems.
What happens to my septic system during Seattle's wet season?
King County's wet season (October through April) can cause seasonal groundwater to perch at or above the bottom of conventional drainfields in Alderwood soils, temporarily reducing system function. Homeowners should minimize water use during extended wet periods, avoid running laundry on rainy days if possible, and ensure inspection covers access to risers that may be flooded.
What is required for a septic system on Vashon Island?
Vashon Island is entirely dependent on onsite sewage systems—there is no municipal sewer. All OSS on Vashon must be permitted through King County Environmental Health and meet WAC 246-272A requirements. Vashon soils are predominantly Alderwood series, and most systems require pressure distribution or mound design. Proximity to Puget Sound means many systems require enhanced treatment. King County's OSS loan program is available to Vashon residents.