Arizona Septic Requirements for Vacant Land

In Arizona, a septic system is formally an "on-site wastewater treatment facility." The rules are state rules, written by the Arizona Department of Environmental Quality (ADEQ), but the permit you actually apply for comes from your county. This guide covers how that works, what a site investigation involves, and why soil, slope and nearby wells matter.

Who issues septic permits

ADEQ has authority to permit on-site wastewater systems and has delegated that authority to all 15 counties, which issue permits on ADEQ's behalf. So your application goes to the county environmental, health or development services department, not to ADEQ. The underlying rules are in the Arizona Administrative Code, Title 18, Chapter 9, Article 3.

ADEQ's on-site wastewater page links the forms used statewide, including a Uniform Site Investigation Report and an inspection form for septic systems, plus the general permits for different system types.

System types: the "Type 4" general permits

Household systems are covered by ADEQ's Type 4 general permits, numbered 4.02 through 4.23, which span conventional and alternative systems. The 4.02 general permit covers the conventional setup: a septic tank discharging to a trench, bed, chamber system or seepage pit, for a design flow under 3,000 gallons per day (A.A.C. R18-9-E302). The other Type 4 permits cover alternative systems for sites where a conventional system won't work. Which one you can use depends on what the site investigation finds, so ask the designer which permit type the site points to and what it means for installation and upkeep.

The site investigation (and the "perc test")

Before a system is designed, someone has to investigate the site. Under A.A.C. R18-9-A310:

• Who can do it. An Arizona-registered professional engineer, geologist or sanitarian, or a person holding a certificate of training from a course ADEQ recognizes. In Maricopa County, county staff can also perform the evaluation for trench, chamber or leach-bed disposal; a seepage pit evaluation must be done by a registered engineer or geologist.
• Surface conditions. The investigator documents "limiting conditions." A surface slope greater than 15 percent at the intended location is one. So is a 100-year flood hazard zone shown on the flood insurance rate map that could affect the system.
• Soil testing. Subsurface characterization uses standard soil-evaluation methods or a percolation test. The soil method calls for at least two test locations in the primary disposal area and one in the reserve area. A percolation ("perc") test uses holes dug in undisturbed soil at least 12 inches deep and measures how fast water soaks in over repeated fillings.
• Seepage pits. Testing for a seepage pit requires a test hole at least 18 inches in diameter, drilled to the depth of the proposed pit and at least 30 feet deep.
• Reserve area. The investigation must identify both a primary and a reserve disposal area. A lot has to have room for both, which matters on small parcels.

Counties add their own procedures. Maricopa County's instructions, for example, say to excavate three test holes with a backhoe (two in the primary area, one in the reserve), at least 12 feet deep and 4 feet deeper than the planned disposal field, and to stake and post the site.

Why soil, slope, wells and washes matter

A septic system works by letting treated effluent soak into the ground. That depends on the soil (too tight and it won't absorb; too fast or too shallow over rock and it won't treat) and on keeping effluent away from drinking water. The design rule, A.A.C. R18-9-A312, includes a table of minimum setbacks. Two that matter most on rural land:

• 100 feet from a water supply well, public or private. That includes a neighbor's well near your line.
• 100 feet from a perennial or intermittent stream, measured from the high-water line of a 10-year, 24-hour storm.

The same table sets setbacks from buildings, property lines and washes or drainage easements, some of which can be reduced under conditions. Read the current rule or ask your county before assuming any other distance. On a narrow lot with a well, or one crossed by a wash, setbacks alone can decide whether a conventional system fits.

Existing systems

If the land already has a septic system (an old cabin site, a removed mobile home), find out whether it was permitted and what condition it is in. ADEQ's program includes an inspection process tied to property transfer. Ask the county whether it has a permit on file for the parcel.

How to find your county office and get started

1. Look up which department handles septic in your county. It is often environmental health, environmental services or development services. Start from the county's planning office listed on our Arizona land pages (for example, Maricopa County or Mohave County).
2. Ask for the county's site investigation instructions and permit application, and whether it keeps prior septic records by APN.
3. Check the parcel's flood zone and well neighbors first. See flood zones and the well lookup guide.
4. Hire a qualified investigator to do the site investigation if the county doesn't do it for you.
5. Have the system designed to the results, then apply for the permit for the applicable Type 4 general permit.

For sellers

A favorable site investigation is one of the most useful documents a seller can hand a buyer. If you don't have one, buyers will price in the risk. Arizona's seller affidavit of disclosure for unincorporated land also asks about septic (A.R.S. 33-422). Septic is one item on our full due-diligence checklist, and it feeds directly into whether the land is buildable.

General information, not legal, tax or survey advice. First 48 Offers LLC is a real estate investment company that buys land. It is not a law firm, brokerage, surveyor or title company. Arizona statutes, county procedures and agency boundaries change, and every parcel turns on its own facts. Verify anything important with the county, the agency named, or an Arizona attorney before relying on it.