(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.
(b) Dosing Tanks
- (ii) High water alarms shall be provided for all tanks that use pumps or siphons. The alarm device shall be an audible alarm or an indoor illuminated alarm or both.
- (iii) The minimum effluent level shall achieve complete submergence of the pump.
- (iv) Dosed systems using a siphon shall have a dose counter installed to check for continued function of the siphon.
(c) Holding Tanks - (i) Holding tanks shall meet the same material requirements as septic tanks. Holding tanks shall have a twenty (20)-inch minimum diameter access opening. A riser shall be brought to ground surface from the access opening.
- (ii) Holding tanks shall not be used for residential systems when other alternative systems are available, except on a temporary, seasonal or intermittent basis, or when used to correct a failed soil absorption system when other alternatives are unavailable.
- (iii) Holding tanks must be located in an area readily accessible to the pump truck and where the tank itself will not float due to high groundwater. If seasonal high groundwater may be present, the tank shall be properly anchored.
- (iv) The minimum liquid volume shall be the greater of 1,000 gallons or seven (7) days storage based upon flow rate determined from Section 5.
- (v) All holding tanks shall be equipped with a high-water level alarm. The device shall be an audible alarm or an indoor illuminated alarm or both. The device shall be installed so that the alarm is triggered when the water level reaches 3/4 of the tank capacity.
- (vi) A design package for holding tanks 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.
(d) Grease Interceptors - (i) A commercial or institutional food preparation facility with a waste stream containing fat, oil, and grease (FOG) in excess of 25 mg/L shall install an exterior grease interceptor or a device approved by the delegated health department or county. Facilities that typically have waste streams high in FOG are, but not limited to, restaurants, cafeterias, slaughterhouses, and institutional kitchens.
- (ii) Waste streams high in FOG shall be plumbed separately and directly to a grease interceptor prior to the waste treatment process.
- (iii) Waste streams from sanitary facilities such as bathrooms, toilets, urinals, or other similar fixtures shall not be discharged into the grease interceptor. These sources must be connected at least four to six (4-6) feet downstream of the grease interceptor's discharge. The design shall prevent any backflow from the sanitary sources into the grease interceptor.
- (iv) Only one source facility per grease interceptor shall be allowed.
- (v) Grease interceptors shall be located so that they are easily accessible for inspection, cleaning, and removal of the collected wastes. The interceptor shall not be closer than fifteen (15) feet from the last discharging fixture and no further away than thirty-five (35) feet.
- (vi) Grease interceptors shall have at least two (2) compartments with a 20-inch minimum diameter access opening for each compartment for cleanout. Each access opening shall have a riser brought to the surface and have a sealed lid that is rated for any anticipated load. There shall be a means provided to sample the effluent.
- (vii) There shall be no internal cleanout tees or bypasses.
- (viii) The inlet and outlet of the grease interceptor shall be vented. The vent pipe shall be at least two (2) inches in diameter. The inlet and outlet vents shall not be interconnected.
- (ix) The outlet pipe invert shall be no more than two (2) inches lower than the inlet invert.
- (x) The dividing wall between compartments shall be the same height as the other walls and the cover should contact the top of the dividing wall. If the partition/dividing wall does not contact the cover, the outlet tee or baffle shall extend below the liquid level, 40-50% of the total liquid depth.
- (xi) The effluent from each compartment shall be drawn from the bottom of a riser pipe that terminates at least eighteen (18) inches below the inlet pipe invert of that same compartment.
- (xii) Grease interceptors shall be accessible during normal business hours without interrupting normal business operations.
- (xiii) Grease interceptors shall be installed in accordance with the manufacturer's instructions and applicable requirements of this section. A copy of the manufacturer's instructions shall be submitted with every permit to construct application submitted to DEQ/WQD.
*Waste flow rate - see Table 2.
**Retention times
| Kitchen waste: | |
| Dishwasher and/or disposal | 2.5 hours |
| Single service kitchen: | |
| Single serving with disposal | 1.5 hours |
***Storage factors
| Fully equipped commercial kitchen | 8 hr. operation: 1 16 hr. operation: 2 24 hr. operation: 3 |
| Single service kitchen: | 1.5 |
- (A) The minimum interceptor size (liquid capacity) shall be 750 gallons.
(e) Other Interceptors - (i) Interceptors are required for oil, grease, sand, and other substances harmful or hazardous to the building drainage system, or the small wastewater treatment system.
- (A) Laundries
- (I) Commercial laundries, laundromats, and dry-cleaners shall be equipped with an interceptor in order to reduce the quantity of lint and silt that enter the collection system.
- (II) The system must be of adequate size and design to allow for cool-down of wastewater so that separation can be more readily achieved.
- (III) The interceptor shall be installed with a wire basket or similar device. The wire basket or similar device shall be removable for cleaning and shall prevent passage into the drainage system of solids 1/2 inch (12.7 mm) or larger in size, such as string, rags, buttons, or other materials that are detrimental to the waste treatment system.
- (IV) Sizing must be in accordance with the following formula: Laundries (grease, lint, silt)
| Total gallons per cycle | X | Cycles per hour | X | Retention time* | X | Storage factor** | = | Interceptor |
| | | | | | | | | |
*Retention times
| Institutional laundries | 2.5 hours |
| Standard commercial laundry | 2.0 hours |
| Light commercial laundry | 1.5 hours |
**Storage factors
| 8 hours of operation | 1.0 |
| 12 or more hours of operation | 1.5 |
- (B) Car Washes
- (I) Where automobiles are washed (including detail shops using hand-wash practices), separators shall have a minimum capacity of 1000 gallons for the first bay, with an additional 500 gallons of capacity for every other bay.
- (II) Additionally, wash racks must be constructed to eliminate or minimize the impact of run-off from rain/storm events. Minimum requirements are roofed structures with at least two walls and appropriate grading to prevent stormwater infiltration into the sanitary sewer.
- (III) An effluent sampling point is required.
(f) Abandonment of Septic and Holding Tanks
The following is the procedure to abandon septic tanks and holding tanks when the system is upgraded, equipment replacement is necessary, or central sewer lines are made available:
- (i) The abandoned tank should be pumped and the septage hauled to a licensed facility approved to receive the waste or the septage pumped into the newly constructed septic or holding tank. Discharging to a central sewer requires coordination with, and the approval of, the owner/operator of the sewer system.
- (ii) Once the abandoned tank is empty, it should be removed and the excavation backfilled. As an alternative to removing the tank, the access covers can be removed; the bottom drilled or broken up sufficient to drain; and the tank filled with native soil, pit run, or sand.
- (iii) If the abandoned tank is part of a Class V UIC facility, the abandonment must also be in compliance with Chapter 27, Section 17.
020-25 Wyo. Code R. § 25-10