Mound Septic System Cost in Washington
Estimated 2026 installed range: $12,800 – $28,200
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Open the cost calculatorWhy Washington prices differ
Statewide cost drivers here are hard ground, terrain and remote access. Locally, wet soils and strict local health rules drive design costs. That is why a mound system in Washington can land well above or below the national range of $10,000–$22,000.
All system types in Washington
| System | Low | High |
|---|---|---|
| Conventional | $4,500 | $10,200 |
| Chamber | $6,400 | $14,100 |
| Aerobic / ATU | $10,200 | $23,000 |
| Mound | $12,800 | $28,200 |
| Sand filter | $10,200 | $20,500 |
What mound systems are for
A mound system raises the drain field above the ground when the water table is high or soil is shallow. It is one of the most expensive common options.