Alaska · 18 AAC 72
Septic system requirements in Alaska
Tank sizes, drainfield rules, setbacks, permits, and real costs — pulled from Alaska's own code rather than a national average.
- 3-bedroom tank
- 1,000 gal
- Design flow
- 150 gpd/BR
- Typical install
- $14,000–$38,000
- Permit fee
- $250–$900
- Well setback
- 100 ft
- Permitted by
- State + local
Septic tank sizes required in Alaska
Alaska sizes systems on a design flow of 150 gallons per day per bedroom. The tank must meet both the bedroom table below and a 2× daily-flow detention requirement — whichever produces the larger number governs.
| Bedrooms | Design flow | Code minimum | Recommended |
|---|---|---|---|
| 1 bedroom | 150 gpd | 1,000 gal | 1,000 gal |
| 2 bedrooms | 300 gpd | 1,000 gal | 1,000 gal |
| 3 bedrooms | 450 gpd | 1,000 gal | 1,000 gal |
| 4 bedrooms | 600 gpd | 1,250 gal | 1,250 gal |
| 5 bedrooms | 750 gpd | 1,500 gal | 1,500 gal |
| 6 bedrooms | 900 gpd | 1,750 gal | 2,000 gal |
Source: 18 AAC 72. The recommended column rounds the governing requirement up to a tank size manufacturers actually stock.Run your own numbers →
Drainfield size and cost by soil type
For a three-bedroom home in Alaska at 450 gpd. This single table explains most of the variation between quotes — the area scales inversely with how fast your soil accepts water, and the drainfield is the largest line item in the job.
| Soil | Loading rate | Absorption area | With reserve | Typical total install |
|---|---|---|---|---|
| Medium sand | 0.8 gpd/ft² | 563 ft² | 1,126 ft² | $14,500 |
| Sandy loam | 0.5 gpd/ft² | 900 ft² | 1,800 ft² | $18,400 |
| Loam | 0.4 gpd/ft² | 1,125 ft² | 2,250 ft² | $21,000 |
| Silt loam | 0.3 gpd/ft² | 1,500 ft² | 3,000 ft² | $25,300 |
| Clay loam | 0.2 gpd/ft² | 2,250 ft² | 4,500 ft² | $34,000 |
Estimates use Alaska's cost index of 1.28× the national average. Build a line-item estimate →
Permits and who issues them
ADEC runs the program statewide, but the Municipality of Anchorage and the Fairbanks North Star Borough operate their own delegated programs with stricter rules.
| Permit required | Yes |
|---|---|
| Typical fee | $250 – $900 |
| Soil evaluation | Required before permit |
| Licensed installer | Not required statewide |
| Turnaround | 3–8 weeks; the season is short |
| Ongoing inspection | Not mandated statewide |
| Reserve area | 100% replacement area required |
Minimum setback distances
Measured horizontally from the drainfield unless noted. Local rules are frequently stricter, and on a small lot these numbers — not the soil — often decide the layout.
| Private water well | 100 ft |
|---|---|
| Well (septic tank) | 50 ft |
| Property line | 10 ft |
| Surface water | 100 ft |
| Building foundation | 10 ft |
Regulatory contact
Alaska Department of Environmental Conservation — Wastewater Discharge
dec.alaska.gov · 907-269-6285
What makes septic hard in Alaska
Permafrost makes conventional trenches impossible across much of the interior. Systems must be built above the permafrost table or insulated, and both add cost.
The construction window is short. Excavation is realistically limited to roughly May through September in most of the state.
Freight dominates the budget. In off-road communities the barge or air cost of a tank can exceed the tank itself.
Things that catch people out
- Anchorage and Fairbanks North Star Borough have their own on-site programs — the state rules are the floor, not the whole story.
- A 100-foot setback from any lake, river, stream, spring, or slough applies to every component, which rules out a lot of otherwise buildable waterfront.
Alaska septic questions
What size septic tank do I need in Alaska?
A three-bedroom home in Alaska requires a minimum 1,000 gallon tank under 18 AAC 72. Design flow is 150 gallons per day per bedroom, and the tank must also hold 2 times daily flow, so the practical recommendation is 1,000 gallons.
Do I need a permit for a septic system in Alaska?
Yes. ADEC runs the program statewide, but the Municipality of Anchorage and the Fairbanks North Star Borough operate their own delegated programs with stricter rules. Fees typically run $250 to $900, with a turnaround of about 3–8 weeks; the season is short. A soil evaluation or percolation test is required before a permit is issued.
How much does a septic system cost in Alaska?
A conventional system for a three-bedroom home typically runs $14,000 to $38,000 installed. Soil quality moves this more than anything else — on tight clay requiring a mound, budget two to three times the low end.
How far must a Alaska drainfield be from a well?
100 feet from a private water well, with the septic tank itself allowed at 50 feet. Local rules can be stricter.
Sources
Every figure on this page traces to one of these documents.
- 18 AAC 72 — Wastewater Treatment and Disposal · verified 2026-09-18
- 18 AAC 72.035 — Conventional onsite systems · verified 2026-09-18