Idaho Admin. Code r. 58.01.03.007

Current through September 2, 2024

Section 58.01.03.007 - SEPTIC TANKS DESIGN AND CONSTRUCTION STANDARDS

01.Materials. New septic tanks will be constructed of concrete, or other materials approved by the Director. Steel tanks are unacceptable.

02.Construction Requirements. All septic tanks will be water tight, constructed of sound, durable materials and not subject to excessive corrosion, decay, frost damage or cracking.

03.Concrete Septic Tanks. New concrete septic tanks will at a minimum meet the following requirements:

a. The walls and floor must be at least two and one-half (2 1/2) inches thick if adequately reinforced and at least six (6) inches thick if not reinforced.

b. Concrete lids or covers must be at least three (3) inches thick and adequately reinforced.

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).

d. Wall sections poured separately must have interlocking joints on joining edge.

e. All concrete outlet baffles must be finished with an asphalt or other protective coating.

04.Horizontal Dimension Limit. No interior horizontal dimension of a septic tank or compartment may be less than two (2) feet.

05.Liquid Depth. The liquid depth shall be at least two and one-half (2 1/2) feet but not greater than five (5) feet.

06.Manufactured Tank Markings. Septic tanks manufactured in accordance with a specified design approved by the Director, will be legibly and indelibly marked with the manufacturer's name or trademark, total liquid capacity and shall indicate the tank's inlet and outlet.

07.Minimum Tank Capacities.

a. Tanks serving one (1) or two (2) single dwelling units:

MINIMUM CAPACITY PER DWELLING UNIT
Number of Bedrooms	Minimum Liquid Capacity (Gallons)
1 or 2	900
3 or 4	1,000

For each bedroom over four (4) add two hundred fifty (250) gallons.

b. Tanks serving all other flows. Septic tank capacity shall be equal to two (2) times the average daily flow as determined from Subsection 007.08. The minimum tank capacity shall be seven hundred and fifty (750) gallons.

08.Wastewater Flows from Various Establishments in Gallons per Day.

ESTABLISHMENTS
Single Family Dwelling and Mobile Homes, 3 bedroom. Add/subtract 50 gallons/bedroom	250/Unit
MULTIPLE RESIDENTIAL
Hotel: With Private Baths Without Private Baths	60/Bedspace 40/Bedspace
Motel: With Kitchenette	40/Bedspace 60/Bedspace
Boarding House: Add for each nonresident	150/Bedspace 25
Rooming House/Bunk House Staff Resident Nonresident	40/Resident 40/Staff 15/Staff
Apartments	250/Unit
INSTITUTIONAL
Assembly Hall/Meeting House	2/Seat
Church: With Kitchen	3/Seat 7/Seat
Hospital: Kitchen only Laundry only	250/Bedspace 25/Bedspace 40/Bedspace
Nursing Home/Rest Home	125/Bedspace
Day School: Without Showers With Showers With Cafeteria, add Staff-Resident Nonresident	20/Student 25/Student 3/Student 40/Staff 20/Staff
FOOD SERVICE
Conventional Service: Toilet & Kitchen Wastes Kitchen Wastes	13/Meal 3.3/Meal
Take Out or Single Service	2/Meal
Dining Hall: Toilet & Kitchen Wastes Kitchen Wastes	8/Meal 3.3/Meal
Drinking Establishment	2/Person
Food Service Employee	15/Employee
ESTABLISHMENTS
COMMERCIAL AND INDUSTRIAL
Bowling Alley	125/Lane
Laundry - Self Service	50/Wash
Public Transportation Terminal	5/Fare
Service Station	10/Vehicle
Car Wash: 1st Bay Additional Bays	50/Vehicle 1000 500 each
Shopping Center (No food/laundry)	1/Pkg.Sp.
Theaters (including Concession Stand): Auditorium Drive-in	5/Seat 10/Space
Offices	20/Employee
Factories: No Showers With Showers Add for Cafeteria	25/Employee 35/Employee 5/Employee
Stores	2/Employee
SEASONAL AND RECREATIONAL
Fairground (Peak Daily Attend)	1/Person
Stadium	2/Seat
Swimming Pool: Toilet & Shower Wastes	10/Person
Parks & Camps (Day Use): Toilet & Shower Wastes	15/Person
Roadside Rest Area: Toilet & Shower Wastes Toilet Waste	10/Person 5/Person
Overnight Accommodation: Central Toilet Central Toilet & Shower	25/Person 35/Person
Designated Camp Area: Toilet & Shower Wastes Toilet Wastes	90/Space 65/Space
Seasonal Camp	50/Space
Luxury Cabin	75/Person
Travel Trailer Park with Sewer & Water Hook-up	125/Space
Construction Camp	50/Person
Resort Camps	50/Person
ESTABLISHMENTS
Luxury Camps	100/Person
Country Clubs Resident Member Add for Nonresident Member	100/Member 25/Person
Public Restrooms: Toilet Wastes Toilet & Shower Wastes	5/Person 15/Person

09.Total Volume. The total volume of a septic tank will at a minimum be one hundred fifteen percent (115%) of its liquid capacity.

10.Inlets.

a. The inlet into the tank will be at least four (4) inches in diameter and enter the tank three (3) inches above the liquid level.

b. The inlet of the septic tank and each compartment will be submerged by means of a vented tee or baffle.

c. Vented tees or baffles will extend above the liquid level seven (7) inches or more but not closer than one (1) inch to the top of the tank.

d. Tees should not extend horizontally into the tank beyond two (2) times the diameter of the inlet.

11.Outlets.

a. The outlet of the tank will be at least four (4) inches in diameter.

b. The outlet of the septic tank and each compartment will be submerged by means of a vented tee or baffle.

c. Vented tees and baffles will extend above the liquid level seven (7) inches or more above the liquid level but no closer than one (1) inch to the inside top of the tank.

d. Tees and baffles will extend below the liquid level to a depth where forty percent (40%) of the tank's liquid volume is above the bottom of the tee or baffle. For vertical walled rectangular tanks, this point is at forty percent (40%) of the liquid depth. In horizontal cylindrical tanks this point is about thirty-five percent (35%) of the liquid depth.

e. Tees and baffles should not extend horizontally into the tank beyond two (2) times the diameter of the outlet.

12.Scum Storage. A septic tank will provide an air space above the liquid level which will be equal to or greater than fifteen percent (15%) of the tank's liquid capacity. For horizontal cylindrical tanks, this condition is met when the bottom of the outlet port is located at nineteen percent (19%) of the tank's diameter when measured from the inside top of the tank.

13.Manholes. Access to each septic tank or compartment shall be provided by a manhole twenty (20) inches in minimum dimension or a removable cover of equivalent size. Each manhole cover will be provided with a corrosion resistant strap or handle to facilitate removal.

14.Inspection Ports. An inspection port measuring at least eight (8) inches in its minimum dimension will be placed above each inlet and outlet. Manholes may be substituted for inspection ports.

15.Split Flows. The wastewater from a single building sewer or sewer line may not be divided and discharged into more than one (1) septic tank or compartment.

16.Multiple Tank or Compartment Capacity. Multiple septic tanks or compartmented septic tanks connected in series may be used so long as the sum of their liquid capacities is at least equal to the minimum tank capacity computed in Subsection 007.07 and the initial tank or compartment has a liquid capacity of more than one-half (1/2) but no more than two-thirds (2/3) of the total liquid capacity of the septic tank facility.

17.Minimum Separation Distances Between Septic Tanks and Features of Concern.

Features of Concern		Minimum Distance to Septic Tank in Feet
Well or Spring or Suction Line	Public Water Other	100 50
Water Distribution Line	Public Water Other	25 10
Permanent or Intermittent Surface Water		50
Temporary Surface Water		25
Downslope Cut or Scarp		25
Dwelling Foundation or Building		5
Property Line		5
Seasonal High Water Level (Vertically from Top of Tank)		2

18.Installation of Manufactured Tanks. If written installation instructions are provided by the manufacturer of a septic tank, those instructions relative to the stability and integrity of the tank are to be followed unless otherwise specified in the installation permit of these rules.

19.Manhole Extension. If the top of the septic tank is to be located more than twenty-four (24) inches below the finished grade, manholes will be extended to within eighteen (18) inches of the finished grade.

20.Sectional Tanks. Sectional tanks will be joined in a manner that will insure that the tank is watertight.

21.Inlet and Outlet Piping. Unless otherwise specified in the installation permit, piping to and from a septic tank or dosing chamber, to points three (3) feet beyond the tank excavation shall be of a material approved by the Director. The following materials are required:

a. ABS schedule forty (40) or material of equal or greater strength piping shall be used to span the excavations for the septic tank and dosing chamber.

b. ASTM D-3034 plastic pipe may be used to span the septic tank and dosing chamber if the excavation is compacted with fill material.

i. The fill material must be granular, clean and compacted to ninety percent (90%) standard proctor density.

ii. Placement of ASTM D-3034 on undisturbed earth is suitable, but in no installation shall there be less than twelve (12) inches of cover over the pipe.

22.Effluent Pipe Separation Distances. Effluent pipes shall not be installed closer than fifty (50) feet from a well.

23.Septic Tank Abandonment. Responsibility of properly abandoning a septic tank shall remain with the property owner. Septic tanks shall be abandoned in accordance with the following:

a. Disconnection of the inlet and outlet piping;

b. Pumping of the scum and septage with approved disposal;

c. Filling the septic tank with earthen materials; or

d. Physically destroying the septic tank or removing the septic tank from the ground.

Idaho Admin. Code r. 58.01.03.007

Effective March 31, 2022