Soak pit design and Septic tank Design calculation
Hello, guys in this article we will discuss the design of the septic tank and soak pit. Septic tank is made up of concrete, polyethylene, fiberglass, etc. It is buried underground which is a watertight container.
Septic tank holds waste and useless water for a long time enough to allow the solid particle in water to settle down in the form of sludge but oil grease and fat remains floating on the surface of the tank as scum.
Now let us discuss the design of the soak pit and septic tank.
Step- One
Suppose we have to Design a Septic Tank & Soak Pit for 10 Residential Buildings.
Given,
No of Buildings = 10 Assume
1. No of persons per family = 6 nos
2. Water supply = 200 lits/day
3.Sewage generation = 85 % of water supply
4. Detention period = 24 Hours
5.Cleaning period = One year
6. Length = 4 x Breath, Height = 1.5 meter
7. Sludge Deposit = 40 lit/person/year
8. Minimum freeboard = 300mm
Step- Two
Calculation for Septic tank
Waste water coming from all Building to septic tank= 10 x 6 x 200 x 0.85 = 10200 lit/day
Detention period = 24 hour
Capacity of tank required = 10200/24 x 24 = 10200 lit
Capacity required for Sludge accumulation = 10 x 6x 40 = 2400 lit/ year
Total volume req = 10200+2400 = 12600 lit or 12.6 cum
Area of tank = 12.6/1.5= 8.4 sqm As L = 4xB 4B x B = 8.4 B= V8.4/4 = 1.44 say 1.5m
So, L = 4 x 1.5 = 6 m
Total Depth of Tank = 1.5+0.3 = 1.8 m
Step- Three
Soak Pit Design calculation
Waste water coming out from septic tank = 10200/day
Percolation rate = 1500 lit/m3/day
Volume of filter media = 10200/1500 =6.8 m3
Assume depth of pit= 2m
Area of soak pit = 6.8/2 = 3.4 sqm
Diameter of Soak well required = 73.4 x 4 / = 2.07 m say 2m.
Video for better Understanding
Hence, in this way we can design a Soak pit for Septic tank Step by Step.
I hope this article on “Design of soak pit” remains helpful for you.
Happy Learning – Civil Concept
Contributed by,
Civil Engineer – Ranjeet Sahani
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Hello,
Why did you consider percolation rate as 1500ltrs/cum/day
Also can you provide its reference (IS code/NBC).
Required Soak Pit Calculation for (1 Bed Room, 2 Bed Room, 3 Bed Room, 4 Bed Room)