Section 007. Septic Tanks Design And Construction Standards

01. Materials. New septic tanks will be constructed of concrete, or other materials approved by th e Director. Steel tanks are unacceptable. (3-31-22) 02. Design. A professional engineer licensed by the state of Idaho must submit all septic tank design s to the Department for approval. If any design submitted for approval does not meet all requirements in Section 007 , the engineer must demonstrate that any deviation is determined by sound engineering practice and meets the intent o f the rules. (7-1-25) 03. Construction Requirements. All septic tanks will be water tight, constructed of sound, durabl e materials, and not subject to excessive corrosion, decay, frost damage or cracking. (7-1-25) 04. Concrete Septic Tanks. New concrete septic tanks will at a minimum meet the followin g requirements: (3-31-22) a. The walls and floor must be at least two and one-half (2 1/2) inches thick if adequately reinforce d and at least six (6) inches thick if not reinforced. (3-31-22) b. The concrete lids or covers must be at least three (3) inches thick and adequately reinforced. (7-1-25) c. The floor and at least a six (6) inch vertical portion of the walls of a poured tank must be poured at the same time (monolithic pour). (3-31-22) d. The wall sections poured separately must have interlocking joints on joining edge. (7-1-25) e. All concrete outlet baffles must be finished with an asphalt or other protective coating. (3-31-22) 05. Horizontal Dimension Limit. No interior horizontal dimension of a septic tank or compartmen t may be less than two (2) feet. (3-31-22) 06. Liquid Depth. The liquid depth must be at least two and one-half (2 1/2) feet. (7-1-25) 07. Manufactured Tank Markings. Septic tanks manufactured in accordance with a specified desig n approved by the Director, will be legibly and indelibly marked with the manufacturer’s name or trademark, total liquid capacity, and must indicate the tank’s inlet and outlet. (7-1-25) 08. Minimum Tank Capacities. (3-31-22) a. Tanks serving single dwelling units

two and one-half (2 1/2) feet. (7-1-25) 07. Manufactured Tank Markings. Septic tanks manufactured in accordance with a specified desig n approved by the Director, will be legibly and indelibly marked with the manufacturer’s name or trademark, total liquid capacity, and must indicate the tank’s inlet and outlet. (7-1-25) 08. Minimum Tank Capacities. (3-31-22) a. Tanks serving single dwelling units. The minimum tank capacity is one thousand (1,000) gallons . For each bedroom over four (4) in a dwelling unit, add two hundred fifty (250) gallons. (7-1-25) b. Tanks serving all other flows. The minimum tank capacity per structure is one thousand (1,000 ) gallons or a volume equal to at least two (2) times the maximum daily flow, whichever is greater. (7-1-25) 09. Wastewater Flows from Various Establishments in Gallons per Day. ESTABLISHMENTS DWELLING UNIT ESTABLISHMENTS Single Family Dwelling, Apartment, Mobile Home, 3 bedroom. 250/Unit Add/subtract 50 gallons per day/bedroom MULTIPLE RESIDENTIAL Hotel/Motel: With Private Baths 60/Bedspace Without Private Baths 40/Bedspace Overnight Accommodation: Central Toilet 25/Person 35/Person Central Toilet & Shower Rooming House/Bunk House 40/Resident Staff Resident 40/Staff Nonresident 15/Staff INSTITUTIONAL Church/Assembly Hall/Meeting House: 3/Seat With Kitchen 7/Seat Hospital: 250/Bedspace Kitchen only 25/Bedspace Laundry only 40/Bedspace Nursing Home/Rest Home 125/Bedspace Day School: Without Showers 20/Student With Showers 25/Student With Cafeteria, add 3/Student Staff-Resident 40/Staff Nonresident 20/Staff FOOD SERVICE Conventional Service: Toilet & Kitchen Wastes 13/Meal Kitchen Wastes 3.3/Meal Take Out or Single Service 2/Meal Drinking Establishment 2/Person COMMERCIAL AND INDUSTRIAL Laundry - Self Service 50/Wash Service Station 10/Vehicle Shopping Center (No food/laundry) 1/Pkg.Sp

howers 20/Student With Showers 25/Student With Cafeteria, add 3/Student Staff-Resident 40/Staff Nonresident 20/Staff FOOD SERVICE Conventional Service: Toilet & Kitchen Wastes 13/Meal Kitchen Wastes 3.3/Meal Take Out or Single Service 2/Meal Drinking Establishment 2/Person COMMERCIAL AND INDUSTRIAL Laundry - Self Service 50/Wash Service Station 10/Vehicle Shopping Center (No food/laundry) 1/Pkg.Sp. Theaters 5/Seat ESTABLISHMENTS Offices 20/Employee Factories: No Showers 25/Employee With Showers 35/Employee Add for Cafeteria 5/Employee Stores 2/Employee SEASONAL AND RECREATIONAL Swimming Pool: Toilet & Shower Wastes 10/Person Parks & Camps (Day Use): Toilet & Shower Wastes 15/Person Roadside Rest Area: Toilet & Shower Wastes 10/Person Toilet Waste 5/Person Designated Camp Area: Toilet & Shower Wastes 90/Space Toilet Wastes 65/Space Travel Trailer Park with Sewer & Water Hook-up 125/Space Seasonal/Construction Camp 50/Person Country Clubs Resident Member 100/Member Add for Nonresident Member 25/Person Public Restrooms: Toilet Wastes 5/Person Toilet & Shower Wastes 15/Person (7-1-25) 10. Total Volume. The total volume of a septic tank at a minimum must be one hundred fifteen percen t (115%) of its liquid capacity. (7-1-25) 11. Inlets. (3-31-22) a. The inlet into the tank must be at least four (4) inches in diameter and enter the tank three (3) inche s above the liquid level. (7-1-25) b. The inlet of the septic tank and each compartment must be submerged by means of a vented tee or baffle. (7-1-25) c. Vented tees or baffles must extend above the liquid level seven (7) inches or more but not closer than one (1) inch to the lid of the tank. (7-1-25) d. Tees must not extend horizontally into the tank beyond two (2) times the diameter of the inlet. (7-1-25) 12. Outlets. (3-31-22) a. The outlet of the tank must be at least four (4) inches in diameter. (7-1-25) b. The outlet of the septic tank and each compartment must be submerged by a vented tee or baffle. (7-1-25) c

ches or more but not closer than one (1) inch to the lid of the tank. (7-1-25) d. Tees must not extend horizontally into the tank beyond two (2) times the diameter of the inlet. (7-1-25) 12. Outlets. (3-31-22) a. The outlet of the tank must be at least four (4) inches in diameter. (7-1-25) b. The outlet of the septic tank and each compartment must be submerged by a vented tee or baffle. (7-1-25) c. Vented tees and baffles must extend above the liquid level seven (7) inches or more but not closer than one (1) inch to the inside lid of the tank. (7-1-25) d. Tees and baffles must extend below the liquid level to a depth where forty percent (40%) of th e tank’s liquid volume is above the bottom of the tee or baffle. (7-1-25) e. Tees and baffles must not extend horizontally into the tank beyond two (2) times the diameter of th e outlet. (7-1-25) 13. Scum Storage. A septic tank will provide an air space above the liquid level which will be equal t o or greater than fifteen percent (15%) of the tank’s liquid capacity. (7-1-25) 14. Manholes. Manholes must extend to the finished grade. Access to each septic tank or compartmen t must be provided by a manhole twenty (20) inches in minimum dimension or a removable cover of equivalent size . Each manhole cover must be provided with a corrosion resistant strap or handle to facilitate removal. (7-1-25) 15. Inspection Ports. An inspection port measuring at least eight (8) inches in minimum dimensio n will be placed above each inlet and outlet. Manholes may be substituted for inspection ports. (7-1-25) 16. Split Flows. The wastewater from a single building sewer or sewer line must not be divided an d discharged into more than one (1) septic tank or compartment. (7-1-25) 17. Multiple Tank or Compartment Capacity

Ports. An inspection port measuring at least eight (8) inches in minimum dimensio n will be placed above each inlet and outlet. Manholes may be substituted for inspection ports. (7-1-25) 16. Split Flows. The wastewater from a single building sewer or sewer line must not be divided an d discharged into more than one (1) septic tank or compartment. (7-1-25) 17. Multiple Tank or Compartment Capacity. Multiple or compartmented septic tanks connected i n series may be used if the sum of their liquid capacities is at least equal to the minimum tank capacity in Subsectio n 007.07, and the initial tank or compartment has a liquid capacity of at least one-half (1/2) of the total liquid capacit y of the septic tank facility. (7-1-25) 18. Minimum Separation Distances Between Septic Tanks and Features of Concern. Minimum Distance to Features of Concern Septic Tank in Feet Public Water 100 Well or Spring or Suction Line Other 50 Public Water 25 Water Distribution Line Other 10 Permanent or Intermittent Surface Water 50 Temporary Surface Water 25 Downslope Cut or Scarp 10 Dwelling Foundation or Building 5 Property Line 5 Seasonal High Water Level (Vertically from Top of Tank) 2 (7-1-25) 19. Manufactured Tank Installation. If written installation instructions are provided by th e manufacturer of a septic tank, the installer must follow those instructions relative to the stability and integrity of th e tank unless otherwise specified in the installation permit. (7-1-25) 20. Inlet and Outlet Piping. Unless otherwise specified in the installation permit, piping material t o and from a septic tank or dosing chamber and to the drainfield must be approved by the Director and specified a s follows. (7-1-25) a. ABS schedule forty (40) piping or material of equal or greater strength. (7-1-25) b. ASTM D-3034 or equivalent plastic pipe may be used to span the septic tank and dosing chamber i f the excavation is compacted with fill material. (7-1-25) 21. Effluent Pipe Separation Distances

ptic tank or dosing chamber and to the drainfield must be approved by the Director and specified a s follows. (7-1-25) a. ABS schedule forty (40) piping or material of equal or greater strength. (7-1-25) b. ASTM D-3034 or equivalent plastic pipe may be used to span the septic tank and dosing chamber i f the excavation is compacted with fill material. (7-1-25) 21. Effluent Pipe Separation Distances. Effluent pipes have the same separation distanc e requirements as septic tanks unless otherwise approved by the Director. (7-1-25) 22. Septic Tank Abandonment. The property owner is responsible for septic tank abandonment an d must use the following procedures. (7-1-25) a. Disconnect the inlet and outlet piping; (7-1-25) b. Pump the scum and septage with approved disposal; and (7-1-25) c. Fill the septic tank with earthen materials, physically destroy the septic tank, or remove the septi c tank from the ground. (7-1-25)