- Where a septic tank is used for sewage disposal, the location, design and construction of the septic tank shall conform to the following requirements :-(i)Location of Septic Tanks and Sub-Surface absorption systems. - A sub-soil dispersion system shall not be within 18 metres from any source of drinking water, such as well, to mitigate the possibility of bacterial pollution of water supply. It shall also be as removed from the nearest habitable building as economically feasible but not within 2 metres thereof so that there is no damage to the structures.(ii)Other Requirements :-(a)Dimensions of septic tanks-Septic tanks shall have minimum width of 75 centimetres minimum depth of one metre below the water level and a minimum liquid capacity of one cubic metre. Length of tanks shall be 2 to 4 times the width;(b)Septic tanks may be constructed of brick work, stone masonry concrete or other suitably materials as, approved by the Authority;(c)under no circumstances should effluent from a septic tank be allowed into an open channel drain or body of water without adequate treatment;(d)minimum nominal diameter of pipe shall be 100 millimetres. Further, at junctions of pipes in manholes, direction of flow from a branch connection should 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 soakways should be between 1:300 and 1:400;(f)every septic tank shall be provided with ventilating pipe of at least 50 millimeter 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 2 metres when the septic tank is at least 15 metres away from the nearest building and to a height of 2 metres above the top of the building when it is located closer than 15 metres;(g)when the disposal of septic tank effluent is to seepage pit, the seepage pit may be of any suitable shape with the least cross-sectional dimension of 90 centimetres and not less than 100 centimetres 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 7.5 centimetres 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 reinforced cement concrete cover slabs. Where no lining is used, specially 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 run off. The inlet pipe may be taken down a depth of 90 centimetres from the top as an anti-mosquito measures; and(h)when the disposal of septic tank effluent is to a dispersion trench, the dispersion trench shall be 50 to 100 centimetres deep and 30 to 100 centimetres wide excavated to a slight gradient and shall be provided with 10 to 25 centimetres 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 minimum internal diameter of 75 to 100 millimeters. Each dispersion trench should not be longer than 30 metres and trenches should not be placed closer than 1.8 metres.
