020-11 Wyo. Code R. § 11-50
(a) The method for determining the size of a particular land site for accomplishing the treatment level necessary to comply with an NPDES permit or to maintain a groundwater aquifer within its present class shall be based on the number of acres (hectares) required to reduce the waste constituent identified as requiring the largest land area, based on soil assimilative capacity. The ratio used for this determination is expressed as:
Required Land Treatment Area = G/C Where:
G = generation rate = the yearly amount of the controlling constituent to be applied for land treatment. G is listed in kilograms per year (kg/yr) or pounds per year (lbs/yr).
C = plant-soil assimilative capacity = the yearly amount of the controlling constituent that can be assimilated by plant uptake, soil adsorption and accumulation, transformation or degradation, and allow survival and maintenance of indigenous or crop plant species. C is listed in kilograms per hectare per year (kg/ha/yr) or pounds per acre per year (lbs/ac/yr).
Wastewater constituents or categories of constituents from which the land-limiting factor will be selected are generally grouped as:
| Organics | Nitrogen |
| Phosphorus | Heavy metals |
| Salts, acids and bases | Water |
| Oil and grease |
(b) Slope. Slow rate irrigation systems (generally less than 4.0 inches/wk application rate) will not be developed on slopes greater than 15 percent unless the site is terraced, gated pipe is placed on the contour, or vegetation, application rate and soil infiltration rate are such that runoff and erosion would not result.
Overland flow systems will not be developed on sites having less than two percent or greater than eight percent slope.
(c) Soil profile. The minimum depth of unsaturated soil strata on which a land treatment system may be developed is five (5) feet for a slow rate system and ten (10) feet for a rapid infiltration system, unless underdrains or pumped recovery wells are employed for lowering the water table. The applicant should refer to Part A, Section 5 for innovative technology permit requirements.
(d) Runoff and erosion. All land treatment sites will be protected from upslope runoff by diversion ditches capable of intercepting the overland flow from a 10-year 24-hour storm event, unless it is otherwise demonstrated that a storm of this size will not have an impact on the site. A runoff collection ditch is required at the base of overland flow slopes or on sloping irrigation sites where site conditions are such that over application of wastewater and/or seasonal precipitation events may threaten to pollute Surface Waters of the State. Provisions for storage, return and reapplication are required where a runoff collection ditch is required.
020-11 Wyo. Code R. § 11-50
Amended, Eff. 6/29/2018.