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 25-10 - Septic Tanks and Other Treatment Tanks

Current through July 13, 2024
(a) Septic Tanks
(i) Septic tanks shall be fabricated or
				constructed of concrete, fiberglass, thermoplastic or an approved material.
				Tanks shall be watertight and fabricated to constitute an individual structure,
				and shall be designed and constructed to withstand anticipated loads. As part
				of the application review process, Department of Environmental Quality, Water
				Quality Division (DEQ/WQD) or the delegated small wastewater program shall
				review the design of prefabricated septic tanks for compliance with applicable
				construction standards.
(ii) The
				septic tank shall be placed on a level grade and a firm bedding to prevent
				settling. Where rock or other undesirable protruding obstructions are
				encountered, the opening for the septic tank shall be over excavated, as
				needed, and backfilled with sand, crushed stone, or gravel to the proper grade.
(A) Septic tanks shall not be buried deeper
				than the tank manufacturer's maximum designed depth for the tank. The minimum
				depth of soil cover over the top of the tank is six (6) inches.
(B) Backfill around and over the septic tank
				shall be placed in such a manner as to prevent undue strain or damage to the
				tank or connected pipes.
(C) Septic
				tanks shall not be placed in areas subject to vehicular traffic unless
				engineered for the anticipated load.
(iii) Size
(A) The minimum liquid volume of a septic
				tank shall be 1000 gallons for residences up to a four (4) bedroom capacity.
				Additional capacity of 150 gallons per bedroom shall be provided for each
				bedroom over four (4).
(B) Septic
				tanks for high strength wastewater or non-residential units shall have a
				minimum effective liquid capacity sufficient to provide at least 48 hour
				retention at design flow or 1,000 gallons, whichever is greater.
(iv) Configuration
(A) Single compartment septic tanks shall
				have a length to width ratio of no less than two (2) to one (1), or be
				partitioned to protect against short circuiting flow.
(B) For septic tanks with two (2)
				compartments or more, the inlet compartment shall not be less than one-half
				(1/2) of the total capacity of the tank.
(C) The liquid depth shall be between three
				(3) feet and six (6) feet.
(D) The
				tank partition shall allow the venting of gases between compartments and out
				through the vent stack on the plumbing system of the house.
(E) The inlet and outlet on all tanks or tank
				compartments shall be provided with open-ended sanitary tees or baffles made of
				approved materials constructed to distribute flow and retain scum in the tank
				or compartments.
(I) The tees or baffles
				shall extend above the liquid level a minimum distance of five (5)
				inches.
(II) The inlet tees or
				baffles shall extend below the liquid level at least eight (8) inches but no
				more than 40% of the liquid level. The outlet tees or baffles shall extend
				below the liquid level at least ten (10) inches but no more than 45% of the
				liquid level.
(III) A minimum of
				one (1) inch of clear space shall be provided over the top of the baffles or
				tees for venting.
(IV) The inlet
				pipe shall be at least two (2) inches higher than the outlet pipe. The outlet
				elevation shall be designed to provide a minimum distance of nine (9) inches or
				twenty (20) percent of the liquid depth between the top of the liquid and the
				bottom of the septic tank cover for scum storage and the venting of
				gases.
(v) If
				additional septic tank capacity over 1,000 gallons is needed, it may be
				obtained by joining tanks in series provided the following requirements are
				met:
(A) The inlet of each successive tank
				shall be at least two (2) inches lower than the outlet of the preceding tank,
				and shall have no tee or baffle except for the inlet to the first tank and the
				outlet for the last tank.
(B) The
				first tank or the first compartment of the first tank shall be equal to fifty
				percent (50%) or larger of the total septic tank system volume.
(vi) An access opening shall be
				provided to each compartment of the septic tank for inspection and cleaning.
(A) The access opening(s) in the cover/lid of
				the tank shall have a minimum diameter of twenty (20) inches. Both inlet and
				outlet devices shall be accessible.
(B) The riser from the access opening shall
				terminate at a maximum of six (6) inches below the ground surface. Riser covers
				terminating above grade shall have an approved locking device.
(vii) Land application of domestic
				septage in remote areas that meet the conditions found in Appendix B will be
				permitted as a permit by rule. Delegated small wastewater programs may issue
				individual permits.
(viii) An
				effluent filter with an opening of 1/8-inch or smaller shall be provided on the
				outlet of a septic tank or other tank that precedes a small diameter pressure
				distribution system.