Wyoming · 020-25 Wyo. Code R. §25-10
Septic system requirements in Wyoming
Tank sizes, drainfield rules, setbacks, permits, and real costs — pulled from Wyoming's own code rather than a national average.
- 3-bedroom tank
- 1,000 gal
- Design flow
- 150 gpd/BR
- Typical install
- $8,000–$21,000
- Permit fee
- $100–$500
- Well setback
- 100 ft
- Permitted by
- State + local
Septic tank sizes required in Wyoming
Wyoming 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 | 1,000 gal | 1,250 gal |
| 5 bedrooms | 750 gpd | 1,150 gal | 1,500 gal |
| 6 bedrooms | 900 gpd | 1,300 gal | 2,000 gal |
Source: 020-25 Wyo. Code R. §25-10. 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 Wyoming 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 | $10,300 |
| Sandy loam | 0.5 gpd/ft² | 900 ft² | 1,800 ft² | $13,100 |
| Loam | 0.4 gpd/ft² | 1,125 ft² | 2,250 ft² | $15,000 |
| Silt loam | 0.3 gpd/ft² | 1,500 ft² | 3,000 ft² | $18,100 |
| Clay loam | 0.2 gpd/ft² | 2,250 ft² | 4,500 ft² | $24,300 |
Estimates use Wyoming's cost index of 0.92× the national average. Build a line-item estimate →
Permits and who issues them
Most counties administer the small wastewater programme; WDEQ permits directly in Carbon, Niobrara, Platte, Weston, and for commercial systems in Campbell.
| Permit required | Yes |
|---|---|
| Typical fee | $100 – $500 |
| Soil evaluation | Required before permit |
| Licensed installer | Not required statewide |
| Turnaround | 2–5 weeks |
| 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
Wyoming DEQ — Water Quality Division, Small Wastewater Systems
deq.wyoming.gov · 307-777-7781
What makes septic hard in Wyoming
Extreme frost depth and high elevation shorten the construction season to a few months.
Shallow bedrock and cobble are common, and excavation costs vary wildly across a single parcel.
Remote sites carry long haul distances for tanks, sand, and aggregate.
Things that catch people out
- Wyoming requires roughly four feet of vertical separation between the trench bottom and the seasonal high water table — that single number disqualifies many valley-bottom sites.
- Only 150 gallons per bedroom is added above four bedrooms, lower than the national norm.
Wyoming septic questions
What size septic tank do I need in Wyoming?
A three-bedroom home in Wyoming requires a minimum 1,000 gallon tank under 020-25 Wyo. Code R. §25-10. 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 Wyoming?
Yes. Most counties administer the small wastewater programme; WDEQ permits directly in Carbon, Niobrara, Platte, Weston, and for commercial systems in Campbell. Fees typically run $100 to $500, with a turnaround of about 2–5 weeks. A soil evaluation or percolation test is required before a permit is issued.
How much does a septic system cost in Wyoming?
A conventional system for a three-bedroom home typically runs $8,000 to $21,000 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 Wyoming 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.
- 020-25 Wyo. Code R. §25-10 — Septic Tanks and Other Treatment Tanks · verified 2026-09-18
- WDEQ Chapter 25 — Septic Tanks, Soil Absorption Systems, and Other Small Wastewater Systems · verified 2026-09-18