Oregon Septic Tank Regulations — OAR 340, Divisions 71 & 73
Oregon Septic Tank Regulations
OAR Chapter 340 Divisions 71 & 73, DEQ oversight with county-agent permitting, simple tank-capacity tier (1,000 or 1,500 gallons), and Oregon-specific approved-tanks list.
The Governing Framework
Oregon regulates onsite wastewater under the Department of Environmental Quality (DEQ) with county-agent delegation for permitting:
- OAR Chapter 340 Division 71 — On-site Wastewater Treatment Systems — the main program rule.
- OAR Chapter 340 Division 73 — Construction Standards — component design details.
- Oregon DEQ — state-level oversight, approved-tanks list, and field-rule interpretation.
- County-contract agents — most Oregon counties have service contracts with DEQ-authorized agents who administer permits and inspections locally.
Septic Tank Capacity — OAR 340-071-0220
Oregon's capacity rule is refreshingly simple — a two-tier threshold rather than a bedroom-by-bedroom table:
"For dwellings with 4 or fewer bedrooms: the tank capacity must be at least 1,000 gallons. For dwellings with more than 4 bedrooms: septic tank capacity must be at least 1,500 gallons."
— OAR 340-071-0220(3)(a)(C)
— OAR 340-071-0220(3)(a)(C)
| Bedrooms | Minimum Tank Capacity |
|---|---|
| 1–4 | 1,000 gallons |
| 5+ | 1,500 gallons |
The rule also authorizes county agents to require larger capacity as needed for special or unique waste characteristics.
DEQ Approved-Tanks List
Oregon DEQ maintains an approved-tanks list published on its website. Installation in Oregon requires use of a tank that appears on this list. Models from Norwesco, Snyder, Enduraplas, and Chem-Tainer are typically listed; verify your specific model before ordering.
Permit Process — County-Agent Administered
- Identify your county's DEQ-contract agent. Most Oregon counties contract with DEQ-authorized Environmental Health specialists; a handful (Multnomah, Washington, Clackamas) have their own programs.
- Site evaluation. A licensed site evaluator or DEQ-authorized agent conducts the soil profile and percolation assessment. Oregon uses a combination of soil textural classification and percolation rate.
- Design submittal. Licensed installer or engineer prepares the design. Advanced systems (ATU, sand filter, pressure distribution) require engineering review.
- Permit issuance. Typical fee $400–$1,200 depending on county. Timelines 2–8 weeks.
- Installation. By an Oregon-licensed installer.
- Final inspection. County agent or DEQ inspector verifies installation before backfill.
- Certificate of satisfactory completion. Required for occupancy and property-transfer disclosure.
Oregon-Specific Considerations
- Willamette Valley wet soils. Clay-heavy soils in Marion, Linn, Benton, Lane counties may require pressure distribution or advanced treatment. Site evaluation often drives design more than tank sizing.
- Coastal counties. Clatsop, Tillamook, Lincoln, Coos, Curry — high groundwater, coastal-zone setbacks, septic-to-sewer conversion pressure in some towns (Cannon Beach, Seaside).
- Eastern Oregon. Drier soils (Malheur, Baker, Union, Wallowa) often support conventional gravity trench dispersal. Frost depth 30–48 inches depending on elevation.
- Cascade ranges and Hood River area. Volcanic soils have unusual drainage characteristics. Site evaluators familiar with volcanic profiles are essential.
- Portland metro sewer. Portland, Gresham, Beaverton, Hillsboro — most urbanized areas require sewer connection. OSSF installations are limited to outlying parcels.
Frequently Asked Questions
- Why does Oregon use a two-tier capacity rule rather than a bedroom-by-bedroom table?
- The two-tier approach simplifies permitting while still covering the range of real-world occupancy. The design-flow assumptions Oregon uses produce similar per-capita flow between 1-4 bedrooms; the 5+ step accounts for larger families and high-occupancy homes.
- Does Oregon require PE-stamped designs?
- For conventional systems, typically not — a licensed installer can submit the design. Advanced treatment (ATUs, sand filters), pressure distribution, or non-standard sites (steep slope, high groundwater) trigger PE requirements.
- Can I install the tank myself in Oregon?
- Oregon requires a licensed installer for residential OSSFs. Owner installation is not a standard pathway; contact your county agent about any exceptions for rural parcels.
- What's the Approved Tanks list for?
- DEQ maintains a list of pre-approved tank manufacturers and models. Installation in Oregon requires a tank from this list; field-approval of non-listed tanks is rare. Verify your chosen tank model appears on the current list before ordering.
- Are there different rules for coastal-zone installations?
- Coastal counties apply additional setbacks from surface waters and may require elevated or specially-engineered dispersal. No statewide coastal-zone overlay exists, but county-level rules frequently add requirements in coastal jurisdictions. Confirm with your county agent.
Source Citations
- OAR Chapter 340 Division 71 — Onsite Wastewater Treatment Systems
- OAR Chapter 340 Division 73 — Construction Standards
- OAR 340-071-0220 — Septic Tank Design and Construction
- Oregon DEQ Rules and Regulations for Onsite Wastewater Treatment Systems
- Oregon DEQ Approved Tanks and Distribution Units
- OAR 340-071 & 073 combined PDF (Oregon DEQ)
Storing chemicals in your Oregon tank?
Oregon's OSSF rules don't cover chemical-storage tanks — those are specified at the manufacturer level. If you need a tank rated for sulfuric acid, bleach, fertilizer solution, or any of 300+ industrial chemicals, our Chemical Compatibility Database has the full system-of-construction specifications.