(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.
