IS 2470:1985 Part 2 is the Indian Standard (BIS) for septic tanks - part 2: disposal of septic tank effluent. This code provides guidelines for the safe and sanitary disposal of effluent from septic tanks. It details the design, sizing, and construction of soil absorption systems like seepage pits and dispersion trenches, as well as biological filters, based on soil percolation rates and groundwater conditions.
Outlines methods for the disposal of treated effluent from septic tanks, including absorption pits and drainage fields.
Overview
- Status
- Current
- Usage level
- Frequently Used
- Domain
- Environmental — Drainage, Sewerage and Sanitary Fittings
- Type
- Code of Practice
Also on InfraLens for IS 2470
Practical Notes
! A soil percolation test is mandatory to determine the suitability of the soil and to accurately size the absorption area.
! Do not use seepage pits (soak pits) in areas where the soil is rocky, has a percolation rate exceeding 30 minutes, or where the water table is high.
! Upflow anaerobic filters or underdrained sand filters are recommended where the soil is highly impervious or space is severely limited.
! Ensure dispersion trenches follow the natural contours of the land to maintain uniform depth and a gentle gradient.
Frequently referenced clauses
effluentsoilgravelsandfilter mediabrickbats
International Equivalents
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Key Values7
Quick Reference Values
Minimum clearance from bottom of absorption system to ground water table1.5 m
Minimum distance from drinking water well18 m
Maximum length of a single dispersion trench30 m
Minimum diameter of seepage pit0.9 m
Minimum depth of seepage pit below invert level2.0 m
Maximum gradient of distribution pipe in trench1 in 200
Minimum spacing between dispersion trenches2.0 m
Key Formulas
C = 130 / sqrt(t) — Maximum rate of effluent application (l/m2/day), where t is the standard percolation rate in minutes (empirical rule of thumb referenced in practice)
Tables & Referenced Sections
Key Tables
Table 1 - Allowable Rate of Effluent Application to Soil Absorption System
Key Clauses
Clause 3 - Soil Percolation Test
Clause 4 - Seepage Pit (Soak Pit)
Clause 5 - Dispersion Trench
Clause 6 - Biological Filters (Upflow Anaerobic Filter)
Clause 7 - Underdrained Sand Filters
Frequently Asked Questions4
What dictates the choice of the effluent disposal method?+
The soil percolation rate and the position of the sub-soil ground water table (Clause 2.1).
What is the maximum acceptable soil percolation rate for using a soil absorption system?+
30 minutes for a 1 cm drop; beyond this, the soil is considered unsuitable for standard absorption (Table 1).
What is the minimum safe distance between a soak pit and a drinking water source?+
At least 18 meters to prevent contamination of the water supply.
What is the recommended width and depth for a dispersion trench?+
Width should be 0.3 m to 1.0 m, and depth should be 0.5 m to 1.0 m (Clause 5.3).
QA/QC Inspection Templates
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