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Wyoming Septic Tank Regulations — Chapter 25 Small Wastewater

Wyoming Septic Tank Regulations

Wyoming's Small Wastewater Systems rules under Chapter 25 — WY DEQ Water Quality Division oversight, the 48-hour retention or 1,000-gallon-floor rule for high-strength and non-residential systems, Table 4 horizontal setbacks, and realities from Yellowstone to the Powder River Basin.

The Governing Framework

Wyoming regulates small wastewater systems under:

  • Chapter 25 — Septic Tanks, Soil Absorption Systems, and Related Small Wastewater System Design Standards. The substantive rule.
  • 020-25 Wyo. Code R. § 25-10 — Septic Tanks and Other Treatment Tanks.
  • 020-25 Wyo. Code R. § 25-17 — Greywater Systems.
  • Table 4 (in Chapter 25) — Minimum horizontal setbacks for domestic wastewater (feet).
  • Wyoming Statute § 35-11-103(c)(ix) — enabling statutory authority (definition of "small wastewater system").
  • Wyoming Department of Environmental Quality (DEQ) — Water Quality Division — Small Wastewater Systems Program — state-level administrator.
  • County environmental health / permitting offices — field implementation in most areas.
Source: Wyoming DEQ Small Wastewater Systems; Chapter 25 full rule text (PDF); § 25-10 Septic Tanks on Cornell LII.

The 48-Hour Retention Rule

For non-residential or high-strength wastewater, Chapter 25 sets capacity as:

ParameterRequirement
Non-residential / high-strengthMinimum effective liquid capacity sufficient for at least 48-hour retention at design flow, OR 1,000 gallons, whichever is greater
ResidentialPer Chapter 25 residential capacity table
The 48-hour retention rule catches both sizing paths. A small commercial site with 300 gpd design flow needs: 48 × (300/24) = 600 gal retention → 1,000 gal floor controls. A larger commercial site with 800 gpd needs 48 × (800/24) = 1,600 gal retention → 48-hour rule controls. This is effectively a 2× design-flow rule for any site above roughly 500 gpd.

Setback Distances — Table 4

Chapter 25 Table 4 specifies minimum horizontal setbacks for domestic wastewater components. Consult the table or your local authority for complete setback values. Horizontal distance (not straight-line apparent distance) is the controlling measurement on steep terrain.

Greywater Under § 25-17

Wyoming explicitly addresses greywater systems in § 25-17 as a distinct regulatory category. Greywater (from showers, sinks, laundry — but excluding toilet waste) may be used for irrigation and some other applications under Chapter 25 rules with specific design and operational requirements. This is useful for water-scarce properties in a semi-arid state where every gallon of onsite reuse matters.

Permit Process

  1. Contact your county environmental health / permitting office. Wyoming county-level field implementation under DEQ oversight.
  2. Site evaluation. Per Chapter 25 protocols including soil and groundwater depth assessment.
  3. System design submission. Plot plan, soil logs, tank and absorption field sizing per § 25-10.
  4. Permit issuance. Fees typically modest ($200–$500).
  5. Licensed installer construction.
  6. Inspection before cover.

Regional Considerations

  • Cheyenne / Laramie Metro: Capital city with municipal sewer in urban core. Surrounding rural county (Laramie County) uses septic.
  • Teton County (Jackson Hole): Exceptional oversight due to Yellowstone/Grand Teton National Park proximity and sensitive hydrology. Extended setbacks from Snake River and lake frontage. Real-estate-transfer inspections common.
  • Park County (Cody, Powell): Mountain and shoulder-valley terrain. Coordination with Yellowstone NP for parcels near the eastern boundary.
  • Powder River Basin (Gillette, Sheridan): Coal and coalbed methane country. Groundwater-contamination concerns drive stricter site review in some areas.
  • Wind River Reservation: Shoshone and Arapaho tribal environmental authority governs onsite systems on reservation land. Not under Wyoming DEQ jurisdiction.
  • Central basins (Riverton, Lander, Rawlins): Deep soil, semi-arid. Standard systems typical.
  • Mountain resort / second-home markets (Teton, Star Valley): High-end installations with alternative systems, on-lot irrigation reuse under § 25-17 greywater, and premium engineering.

Frequently Asked Questions

What's a "small wastewater system" under Wyoming law?
Defined in Wyoming Statute § 35-11-103(c)(ix). Generally encompasses individual residential and small-commercial onsite wastewater systems below certain flow thresholds. Larger systems fall under different DEQ Water Quality rules (point-source discharge permits).
Can I reuse greywater for irrigation?
Yes, under § 25-17 with specific design and operational requirements. Wyoming's semi-arid climate makes greywater reuse operationally attractive. The system must meet Chapter 25 greywater design specifications to qualify.
Why is Teton County oversight stricter?
Jackson Hole / Teton Village proximity to Yellowstone and Grand Teton National Park creates elevated hydrological and environmental concerns. Snake River and area lakes support fragile ecosystems. Additional review layers (county planning, NPS coordination) apply. Expect longer permit timelines and higher fees than average Wyoming installations.
Do polyethylene tanks meet Chapter 25?
Yes. Major OEM rotomolded polyethylene tanks meeting IAPMO/NSF listings and § 25-10 construction standards qualify. Verify with your county.

Source Citations

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Storing chemicals in your Wyoming tank?

Wyoming'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.

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Agricultural Tank Regulations — Wyoming Department of Agriculture (WDA)

The Wyoming Department of Agriculture regulates pesticide, fertilizer, and commercial feed storage under Wyoming Statutes Title 11, Chapter 22 (Pesticides) and related chapters, with rules in WDA Rules Chapter 5:

  • WDA Rules Chapter 5 — Pesticides: registration, labeling, applicator licensing, and RUP handling.
  • W.S. 11-22-101 et seq. — Wyoming Environmental Pesticide Control Act.
  • W.S. 35-12 — Hazardous materials and commercial fertilizer authorities.

Wyoming agriculture is livestock-dominant (cow-calf, sheep, irrigated alfalfa and hay for finishing and winter feed) with sugar beets, dry beans, and malting barley concentrated in the Big Horn Basin and the North Platte corridor. Bulk liquid fertilizer and pesticide storage at commercial ag-retail facilities follows 110% SPCC-style containment as industry standard; WDA does not publish an Illinois-style prescriptive agrichemical rule, but general-duty obligations under the Wyoming Environmental Quality Act (W.S. 35-11) and federal SPCC drive the operational floor. Anhydrous ammonia storage references ANSI K61.1 with coordination from WDA and local fire jurisdictions. The Big Horn Basin (Park, Big Horn, Washakie, Hot Springs counties) runs significant nurse-tank volume during spring pre-plant for barley and beets.

Source: WDA Technical Services Division; Wyoming Rules.

Oil & Gas Produced Water — Wyoming Oil and Gas Conservation Commission (WOGCC)

The Wyoming Oil and Gas Conservation Commission regulates upstream oil and gas under WOGCC Rules and Regulations Chapter 3, with statutory authority at W.S. 30-5-104:

  • WOGCC Ch. 3 — Operational rules including pits, ponds, tanks, and produced-water management.
  • WOGCC Ch. 4 — Environmental rules.
  • W.S. 30-5-104 — Commission rulemaking authority.

Wyoming is a major oil and gas state — Powder River Basin (Campbell, Converse, Johnson counties), Jonah Field and Pinedale Anticline in the Green River Basin, and legacy Wind River and Bighorn basin production all move large produced-water volumes. WOGCC permits produced-water pits, requires tank-battery containment, and coordinates with Wyoming DEQ on Class II injection wells through the WYPDES program and EPA Region 8. Polyethylene tanks are common at chemical-injection skids (scale inhibitor, biocide, methanol); fiberglass and steel dominate high-volume produced-water service. Closed-loop drilling and centralized produced-water handling have grown as Powder River operators chase efficiency and environmental footprint reduction.

Source: WOGCC Rules; Wyoming Statutes Title 30.

Petroleum USTs — Wyoming DEQ Storage Tank Program

The Wyoming Department of Environmental Quality regulates petroleum storage tanks through the Storage Tank Program under Wyoming Storage Tank Regulations Chapter 1, with statutory authority at W.S. 35-11:

  • Wyoming Storage Tank Regulations Ch. 1 — UST technical standards, release detection, corrective action, and closure.
  • W.S. 35-11-1401 et seq. — Financial Responsibility Account (state fund reimbursement).
  • WYPDES — Wyoming Pollutant Discharge Elimination System permits, applicable to industrial stormwater from tank facilities.

Wyoming UST owners register with DEQ, keep annual fees current, maintain release detection and spill/overfill prevention to 2018 federal rule standards, and report suspected releases within 24 hours. The Financial Responsibility Account reimburses eligible corrective-action costs above a deductible. AST facilities above federal SPCC thresholds coordinate with DEQ Water Quality Division on spill-response planning.

Source: Wyoming DEQ Storage Tank Program.

Septic System Sizing Deep Dive

Wyoming DEQ Water Quality Division regulates onsite wastewater under Wyoming Small Wastewater Systems Rules Chapter 25:

BedroomsMinimum Septic Tank Capacity
1–3 BR1,000 gallons
4 BR1,250 gallons
5 BR1,500 gallons
6+ BR+250 gallons per additional bedroom

Wyoming soils and terrain are harsh for OWTS: shallow bedrock, thin rocky profiles in the foothills, high-altitude cold climate, and wind-scoured topsoil. Chapter 25 requires site and soil evaluation, licensed installer, and DEQ or delegated-county review. Alternative systems where conventional trenches fail include mounds, sand filters, aerobic treatment units, and pressure-dosed systems. Cold-climate design — deep bury depths, insulated tanks, freeze-protected piping, and careful summer-season installation — is the operational reality across most of the state. High-altitude counties often default to mounds with pressure dosing to manage shallow bedrock and slow percolation.

Chemical Storage Secondary Containment & Spill Reporting

Federal SPCC (40 CFR 112) applies at 1,320 gallons aggregate aboveground oil. Wyoming layers on:

  • W.S. 35-11-901 and related — Release notification under the Wyoming Environmental Quality Act; reporting to DEQ Water Quality Division.
  • WOGCC Ch. 3 — Spill reporting for upstream oil and gas releases to WOGCC.
  • Wyoming Office of Homeland Security (WOHS) — EPCRA Tier II and State Emergency Response Commission coordination.
  • Wyoming Hazardous Materials Response Team — incident response coordination.

Report non-oil-and-gas releases to DEQ and federal RQ releases to the National Response Center at 1-800-424-8802. Upstream oil and gas releases go to WOGCC. Secondary containment at 110% is the SPCC and industry default. For state-specific RQ thresholds that diverge from 40 CFR 302.4, consult DEQ directly.

Source: Wyoming DEQ Water Quality Division; WOGCC.

Permit Pathways at a Glance

  • Small wastewater (septic): DEQ Water Quality Division or delegated county under Ch. 25.
  • Fertilizer & pesticide registration: WDA under WDA Rules Ch. 5 and W.S. 11-22.
  • Pesticide applicator license: WDA under Wyoming Environmental Pesticide Control Act.
  • Oil & gas produced water storage: WOGCC under Ch. 3 / Ch. 4.
  • Petroleum UST: Wyoming DEQ Storage Tank Program under Wyoming Storage Tank Regulations Ch. 1.
  • SPCC > 1,320 gal oil aggregate: Federal SPCC plan; state spill reporting to DEQ or WOGCC.
  • WYPDES industrial stormwater: Wyoming DEQ Water Quality Division.

Current fees change; verify with WDA, DEQ, or WOGCC before budgeting.

More Wyoming FAQs

Does WOGCC require containment around every tank battery?
Yes — WOGCC Chapter 3 requires construction, integrity, and containment standards for produced-water and oil tank batteries. Berm sizing, liner requirements, and freeboard are prescriptive; inspection records must be retained.
Can I reuse Powder River produced water for dust suppression?
Produced-water reuse is tightly controlled. CBM (coalbed methane) produced water has historically been used for livestock watering and irrigation under specific permits; conventional produced water with higher TDS typically goes to Class II disposal. Any beneficial-use plan requires WOGCC and DEQ approval.
How does high altitude affect septic in Jackson or Sheridan?
Short treatment seasons, frozen soils, and shallow bedrock push high-altitude counties toward mounds with pressure dosing, insulated tanks, and deep bury depths. Some Teton County sites require ATU plus drip dispersal to meet setback and treatment targets.
Who enforces anhydrous ammonia regulations in Wyoming?
WDA inspects commercial ag facilities; OSHA PSM applies above 10,000 pounds stored; DOT 49 CFR applies in transport. Wyoming does not publish a standalone prescriptive anhydrous ammonia rule separate from the Pesticides Act and referenced ANSI K61.1 standards.
Does Wyoming have a state LUST fund?
Yes — the Financial Responsibility Account under W.S. 35-11-1401 reimburses eligible petroleum tank owners and operators for corrective-action costs above a deductible. Registration and fee payment must be current to qualify.

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