Section 25-15 - Small Wastewater Lagoons (a) Selection Criteria: - (i) Lagoons shall only be considered in areas of Wyoming where the annual evaporation exceeds the annual precipitation during the active use of the lagoon.
- (ii) Lagoons shall only be allowed when the percolation rate exceeds sixty (60) minutes per inch and the soil extends vertically down at least two (2) feet from the bottom of the lagoon to the seasonal high groundwater table or bedrock formations.
- (iii) A lagoon shall not be constructed within the 100 year floodplain.
(b) General Design Requirements: - (i) Beyond the horizontal setback distances requirements specified in Section 7(g) of this rule, the lagoon shall not be placed within one hundred (100) feet of the owner's property line.
- (ii) The use of a septic tank that meets the specifications in Section 9 of this rule shall be required before the small wastewater lagoon.
- (iii) The lagoon shall be located and constructed so it will not receive surface runoff water.
- (iv) The slope of the lagoon site shall not exceed five percent (5%).
- (v) The lagoon site must be located in an area of maximum exposure to sun and wind.
- (vi) The lagoon shall be designed for complete retention.
- (vii) The area of the lagoon shall be calculated based on the following formula.
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A = Area of the lagoon (in square feet) at the maximum operating depth of five (5) feet.
Q = Average daily sewage flow, gallons per day. (Multiply values from Table 1 or 2 by 0.6 to get average daily flow.)
E = Average annual lake evaporation in inches per year. (Note: lake evaporation is less than pan evaporation; lake evaporation equals pan evaporation times a pan coefficient of 0.7)
P = Average annual precipitation rate in inches per year.
S = Seepage rate in decimal form, in inches per day.
- (viii) The slopes of the dikes shall not be steeper than three (3) horizontal to one (1) vertical. The minimum width of the top of the dike shall be four (4) feet.
- (ix) All fill shall consist of impervious material that is well compacted and free of rocks, frozen soil, or other large material.
- (x) The minimum operating depth shall be two (2) feet. The dikes shall provide a minimum freeboard of two (2) feet.
- (xi) The floor of the lagoon shall be level and maintained free of all vegetation.
- (xii) The influent line into the lagoon must discharge near the center.
- (xiii) A cleanout, with a tightly fitting cap, or manhole shall be provided in the influent line near the dike.
- (xiv) The area around the small wastewater lagoon shall be fenced to preclude the entrance of livestock, pets, and humans. The fence shall be equipped with a locking gate. The gate shall have a sign indicating "NO TRESPASSING - WASTEWATER LAGOON".
(c) A design package for a small wastewater lagoons is provided online at the Division's website to assist the applicant in submitting a completed application for coverage under the general permit for small wastewater systems. The worksheet and calculations were prepared by a registered professional engineer employed by the Wyoming Department of Environmental Quality, Water Quality Division. The general design requirements stated in this section are incorporated into the worksheets such that by properly completing the forms and installing the components, the system will comply with these requirements.
020-25 Wyo. Code R. § 25-15