Septic system requirements in Washington County, Oregon
The septic rules landplan.io applies in Washington County, what a septic tank costs there, and the parcel data we hold.
Updated
Design a septic system for an address in Washington County
Oregon's state rules apply in Washington County: landplan.io has no county rules of its own here. State rules: Reviewed See Oregon's rules
Septic systems allowed in Washington County
The system types landplan.io permits in Washington County:
- Standard Subsurface Systems
- Pressure Distribution System
- Drip systems
- Bottomless Sand Filter Systems
Septic tank size in Washington County
The daily design flow of a home: 75 gal/day per bedroom, at least 300 gal/day. The septic tank is sized from that flow:
| Daily design flow | Minimum tank |
|---|---|
| up to 240 gal/day | 1,000 gallons |
| 240 to 360 gal/day | 1,500 gallons |
| 360 to 600 gal/day | 2,000 gallons |
| 600 to 720 gal/day | 2,500 gallons |
| 720 to 840 gal/day | 2,750 gallons |
| 840 to 920 gal/day | 3,000 gallons |
| 920 to 1,040 gal/day | 3,250 gallons |
| Bedrooms | Daily design flow |
|---|---|
| 1 | 300 gal/day |
| 2 | 300 gal/day |
| 3 | 375 gal/day |
| 4 | 450 gal/day |
| 5 | 525 gal/day |
| 6 | 600 gal/day |
| 7 | 675 gal/day |
| 8 | 750 gal/day |
| 9 | 825 gal/day |
| 10 | 900 gal/day |
| 11 | 975 gal/day |
| 12 | 1,050 gal/day |
| 13 | 1,125 gal/day |
| 14 | 1,200 gal/day |
| 15 | 1,275 gal/day |
Septic setbacks in Washington County
| From | To | Distance |
|---|---|---|
| LineString | Groundwater Interceptors slope 3% or less | 20 Ft |
| LineString | Groundwater Interceptors slope greater than 3% Downgradient | 50 Ft |
| LineString | Groundwater Interceptors slope greater than 3% Upgradient | 10 Ft |
| LineString | Intermittent Streams | 20 Ft |
| LineString | Irrigation Canals Lined (watertight canal) : Downgradient | 25 Ft |
| LineString | Irrigation Canals Unlined: Downgradient | 50 Ft |
| LineString | Irrigation Canals Unlined: Upgradient | 25 Ft |
| LineString | Underground Utilities | 10 Ft |
| LineString | Water line | 10 Ft |
| Point | Groundwater Supplies and Wells | 100 Ft |
| Point | Springs Downgradient | 100 Ft |
| Point | Springs Upgradient | 50 Ft |
| Polygon | Existing Septic Component to be Abandoned | 5 ft |
These are the values the landplan.io design engine applies in Washington County. Confirm a design with the Oregon health department or your county's before you build.
Parcel data in Washington County
landplan.io has parcel boundaries for Washington County (100% of its area): type an address and the design starts from the parcel.
Septic companies, designers and jobs in Oregon
Where the rules come from
The regulations and documents landplan.io's Washington County, Oregon rules are read from:
- OAR 340 Division 71 - Onsite Wastewater Treatment Systems (current text from OARD) (OAR 340-071)
- OAR 340-071-0800 - Division 71 Tables (Table 1 Minimum Separation Distances and the other tables)
Near Washington County
- Yamhill County
- Columbia County
- Tillamook County
- Multnomah County
- Clatsop County
- Polk County
- Clackamas County
- Marion County
- All of Oregon
Questions
What septic systems are allowed in Washington County?
landplan.io designs by Oregon's state rules there and permits: Standard Subsurface Systems, Pressure Distribution System, Drip systems and Bottomless Sand Filter Systems.
What size septic tank do I need in Washington County?
landplan.io sizes the septic tank in Washington County from the daily design flow: up to 240 gal/day: 1,000 gallons; 240 to 360 gal/day: 1,500 gallons; 360 to 600 gal/day: 2,000 gallons; larger flows need larger tanks. A home's design flow is 75 gal/day per bedroom, at least 300 gal/day.
How far must a septic system be from a well in Washington County?
landplan.io keeps these distances in Washington County: Point to groundwater supplies and wells: 100 Ft.
Does landplan.io have parcel data for Washington County, Oregon?
Yes: parcel boundaries cover Washington County (100% of its area).