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).

IS 2470 Part 2

: 1985

Code of Practice for Septic Tanks - Part 2: Disposal of Septic Tank Effluent

CurrentFrequently UsedCode of PracticeEnvironmental · Drainage, Sewerage and Sanitary Fittings

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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.

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)

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.