Section 54(3) in Tamil Nadu Combined Development and Building Rules, 2019
(3)Sewerage. - (a) Taking into account the site conditions, land and building uses, and nature of wastes within the site, outlet connection ( i.e. the availability of sewers or other outlets, sub-soil conditions etc.), sewage and waste water collection and disposal system for a building or a group of buildings or for a layout shall be designed and it shall conforming to National Building Code.(b)Septic Tanks. - (i) Where a septic tank is used for sewage disposal, the location, design and construction of the septic tank shall conform to requirements of the National Building Code and as per provisions in G.O.Ms. No 106, MAWS Dept., dated 01.09.2014 (operative guidelines for sept age management for local bodies)(ii)Location of the Septic Tanks and Subsurface Absorption System: A subsoil dispersion system should preferably not be closer than 18m from any source of drinking water, such as well, to mitigate the possibility of bacterial pollution of water supply.(iii)Requirements.-(a)Dimensions of septic tanks - Septic tanks shall have a minimum width of 75cm, a minimum depth of 1m below the water level and a minimum liquid capacity of 1 cu.m. The length of tanks shall be 2 to 4 times the width;(b)Septic tanks may be constructed of brickwork, stone masonry, concrete or other suitable materials as approved by the Authority;(c)Under no circumstances shall effluent from a septic tank be allowed into an open channel, drain or water body without adequate treatment;(d)The minimum nominal diameter of the pipe shall be 10cm. Further, at junctions of pipes in manholes, direction of flow from a branch connection shall not make an angle exceeding 45 degrees with the direction of flow in the main pipe;(e)The gradients of land drains, under-drainage as well as the bottom of dispersion trenches and soak ways shall be between 1:300 and 1:400;(f)Every septic tank shall be provided with ventilating pipe of at least 5cm diameter. The top of the pipe shall be provided with a suitable cage of mosquito-proof wire mesh. The ventilating pipe shall extend to a height which would cause no smell nuisance to any building in the area. Generally, the ventilating pipe may extend to a height of about 2m, when the septic tank is at least 15m away from the nearest building and to a height of 2m above the top of the building when it is located closer than 15m.(g)When the disposal of septic tank effluent is to a seepage pit, the seepage pit may be of any suitable shape with the least cross-sectional dimension of 0.90m and not less than 1.00m in depth below the invert level of the inlet pipe. The pit may be lined with stone, brick or concrete blocks with dry open joints which should be backed with at least 7.5cm of clean coarse aggregate. The lining above the inlet level should be finished with mortar. In the case of pits of large dimensions, the top portion may be narrowed to reduce the size of the RCC cover slabs. Where no lining is used, especially near trees, the entire pit should be filled with loose stones. A masonry ring may be constructed at the top of the pit to prevent damage by flooding of the pit by surface runoff. The inlet pipe may be taken down a depth of 0.90m from the top as an anti-mosquito measure; and(h)When the disposal of the septic tank effluent is to a dispersion trench, the dispersion trench shall be 0.50m to 1.00m deep and 0.30m to 1.00m wide excavated to a slight gradient and shall be provided with 150mm to 250mm of washed gravel or crushed stones. Open jointed pipes placed inside the trench shall be made of unglazed earthenware clay or concrete and shall have a minimum internal diameter of 7.5cm to 10cm. Each dispersion trench shall not be longer than 30m and trenches shall not be placed closer than 1.8m.
