Wyoming Administrative Code
Agency 020 - Environmental Quality, Dept. of
Sub-Agency 0011 - Water Quality
Chapter 25 - SEPTIC TANKS, SOIL ABSORPTION SYSTEMS, AND OTHER SMALL WASTEWATER SYSTEMS
Section 25-7 - Site Suitability
Current through September 21, 2024
(a) Small wastewater systems must be located where the surface drainage is sufficient to allow proper operation of the small wastewater system. Avoid depressions and bases of slopes and areas in the path of runoff from roofs, patios, driveways, or other paved areas unless surface drainage is provided. Small wastewater systems shall not be located beneath buildings, parking lots, roadways, driveways, irrigated landscaping, or compacted areas.
(b) The site must include area for both the proposed soil absorption system and a future replacement soil absorption system. Both the proposed and replacement soil absorption systems shall be sized to receive one-hundred (100%) percent of the wastewater flow. If a trench system is used, the replacement soil absorption system may be located between the trenches of the proposed soil absorption system if there is at least nine (9) feet of spacing between trench sidewalls.
(c) For standard soil absorption systems, effective suitable soil depth shall extend at least four (4) feet below the bottom of the soil absorption system to any restrictive layer, fractured rock, or highly permeable material.
(d) The depth to high groundwater shall be at least four (4) feet below the bottom of the absorption surface for all treatment systems except pressure distribution. For pressure distribution systems, the depth to high groundwater shall be at least three (3) feet below the bottom of the absorption surface if the percolation rate of the soil is five (5) minutes per inch or greater (5-60 mpi).
(e) Slope
Table 3. Slope and Percolation Rates for Absorption Systems
| Percolation Rate (minutes/inch) | Maximum Slope1 |
| 5 | 25% |
| 6-45 | 20% |
| 46-60 | 15% |
1 Flatter slopes may be required where the effluent surfaces downslope.
(f) Soil Exploration Pit and Percolation Tests
(g) Minimum horizontal setback distances (in feet) are as follows:
Table 4. Minimum Horizontal Setbacks for Domestic Wastewater in Feet 1, 2
| From | To Septic Tank Or Equivalent | To Absorption System |
| Wells (includes neighboring wells) | 50 | 100 |
| Public Water Supply Well | 100 | 2002 |
| Property Lines | 10 | 10 |
| Foundation Wall (w/o drains) | 5 | 10 |
| Foundation Wall (with drains) | 5 | 25 |
| Potable Water Pipes | 25 | 25 |
| Septic Tank | N/A | 10 |
| Surface Water, Spring (including seasonal and intermittent) | 50 | 50 |
| Cisterns | 25 | 25 |
1 For disposal of non-domestic wastewater, the setback distance shall be determined by a hydrogeological study in accordance with Section 17(b) of Chapter 3, but shall not be less than the distances shown in Table 4.
2 Small wastewater systems that discharge to the same aquifer that supplies a public water supply well and are located within Zone 1 or 2 (Attenuation) of the public water supply well, as determined by Wyoming Department of Environmental Quality Source Water Assessment Project (2004) or as established in Section 2 of the Wyoming Wellhead Protection Guidance Document (1997), shall provide additional treatment. These systems will be required to obtain an individual permit to construct and will require that a PE sign, stamp, and date the application, as stated in Section 2 of this chapter. The additional treatment shall be in accordance with Chapter 3 Section 2(b)(ii). The treatment system shall be designed to reduce the nitrates to less than 10 mg/L of NO3- as N and provide 4-log removal of pathogens before the discharge leaves the property boundary of each small wastewater system.
