Indian standard code of practice for installation of septic tanks (IS: 2470) - Bureau of Indian Standards (1986)

This IS Code provides various requirements that have to be met while constructing a septic tank, so that it meets minimum standards. This Code is dictated by the Bureau of Indian Standards, and ensures that the sewage is treated in a way that maintains health and hygiene of the community.

While the first standard for small septic tanks was first printed in 1963 and then revised in 1968, the standard for disposal of effluent from septic tanks was published later in 1964 and revised in 1971.

This code has been sourced through City Managers' Association Karnataka (CMAK), a non profit that provides technical expertise to urban local bodies.

There are two parts to the code:

• design criteria and construction and
• second secondary treatment and disposal of septic tank effluent

The first part

In the case of location, the tank should not be close to any exterior wall of the building and should be easily accessible for cleaning. A layout with measurements is provided too. There are tables on estimated peak discharge into the septic tank, from different types of residences.

The section on septic tank construction, states that the floor should be impermeable. Various drawings with dimensions provide examples of septic tank size and design for different levels of number of users.

The code, on sludge withdrawal, suggests that tanks should be cleaned atleast once a year. It states that a portion of the sludge not more than 25 mm, should be left behind to act as seeding material. Sludge should not be spread on the ground.

For commissioning of the tank, it is suggested that sewerage system be complete and ready for operation, before connection is made to the building. Further the tank should be filled with water to its outlet before sewage is let in and that there should be a small quantity of well digested sludge to act as a seed.

The second part

This section is broken into 7 parts - however the important parts are preliminary data for design, methods of treatment and disposal of effluent, soil absorption systems, biological filters and upflow anaerobic filter.

Type of soil is key data that is required in designing secondary treatment. The part on preliminary data for design also mentions the need for the soil to be explored to a sufficient depth to determine the soils horizons and types, grading, structure and permeability. External drainage factors, such as slope of ground and position of surface water drains, if any, also needs to be found out.

In the methods of treatment, three types of treatment are described - soil absorption system, biological filters and upflow anaerobic filters. The choice of these depends on position of subsoil water level and subsoil conditions. A table provides recommendations for different soil types.

The part on soil absorption systems provides instructions for contructing a dispersion trench and seepage pit.  The instructions are backed with drawings and a table on allowable rate of effluent applications to soil absorption system.

The code states that biological filters are suitable for treatment of septic tank effluent in areas where the soil is impervious or in water-logged areas or where limited land area is available. Instructions for constructing such a treatment plant is also given.

The code describes the conditions where the upflow anaerobic filter can be used. It is suggested that this be used in areas where the soil is dense, where the water table is high and limited land is available. Drawings with dimensions are able to describe the different types of filters suggested. The code also gives construction features for these filters.

Download the Code here: