AAC R18-9-E302 is Arizona's general permit for a conventional septic system: a septic tank with a gravity disposal field built as a trench, bed, chamber, or seepage pit. It covers systems under 3,000 gallons per day of design flow. The disposal field is sized from a soil test. ADEQ writes the rules; counties run day-to-day permitting.
This is a government work (Arizona statute, administrative rule, or city ordinance) in the public domain. Always confirm the current official text at the source before relying on it.
Homes without a sewer line handle their own wastewater. Most use a septic system: a tank plus a buried disposal field. Arizona regulates how these are built. AAC R18-9-E302 is the general permit for the most common design. This page explains what it covers and when it applies.
What this permit covers
R18-9-E302 is a general permit. That means the state sets standard rules ahead of time. If your system fits the design, you get the permit by meeting those rules, instead of a custom review. The rule's title spells out the design: "Septic Tank with Disposal by Trench, Bed, Chamber Technology, or Seepage Pit, Less Than 3000 Gallons Per Day Design Flow." In plain terms, that is a septic tank that sends its water to a buried disposal field.
The two flow and design limits
Two limits define this permit:
- Design flow. It covers systems with a design flow of "less than 3000 gallons per day." A single home is far below that. This size fits houses and small buildings, not large developments.
- Gravity only. The rule states that "only gravity flow of wastewater from the septic tank to the disposal works is authorized by this general permit." So water moves downhill on its own, not with a pump. A system that needs a pump to lift the effluent falls under a different permit.
How the disposal field is sized
The tank holds the waste and lets solids settle. The disposal field is where the treated water soaks into the soil. This permit lets you spread that water through a trench, a bed, chamber technology, or a seepage pit. The right size depends on your dirt. Sandy soil drains fast. Clay drains slow. So the rule ties the field size to a soil test. Arizona's design rules (R18-9-A310 and R18-9-A312) set the soil absorption rate used in that math. A site evaluation and a soil or percolation test come before the design is final.
Who permits it, and what this means for you
The Arizona Department of Environmental Quality (ADEQ) writes these rules. In Maricopa County, the county environmental department runs the day-to-day permitting under that authority. If you build or replace a conventional septic system near Phoenix, this is usually the permit path.
Note that this is the construction permit for a new or replaced system. It is different from the inspection required when a property with septic changes owners, which is covered by AAC R18-9-A316. To see how a tank and a field split the work, see septic tank vs leach field. For typical price ranges, see septic system cost. Not sure which system you have? See do I have septic or city sewer. This page is general information, not legal advice. Confirm the current rule text and local permit steps with ADEQ or Maricopa County before you build.
Keep Reading
- AAC R18-9-A316: Septic Inspection When a Property Transfers
- Arizona Administrative Code R18-4-215: Backflow Prevention and Annual Testing
- AAC R18-9-D701: Arizona's Type 1 Gray Water Permit Rules
- A.R.S. 32-1101: How Arizona Classifies Contractor Licenses
- What's the difference between a septic tank and a leach field?
- How much does a septic system cost?
- How do I know if I have septic or city sewer in Phoenix?