Section 49 in Assam Notified Urban Areas (Other than Guwahati) Building Rules, 2014
49. Requirements of Septic tank.
(1)Septic tanks shall have minimum width of 0.75m minimum depth of one meter below water level and a minimum liquid capacity of one cubic meter. Length of tanks shall be 2 to 4 times the width.(2)Septic tanks may be constructed of brickwork, stone masonry, concrete or other suitable material as approved by Authority.(3)Under no circumstance should effluent from a septic tank be allowed in to an open channel, drain or body of water without adequate treatment.(4)Minimum nominal diameter of pipe shall be 100 mm. Further at junctions of pipes in manholes, direction of flow from a branch connection should not make an angle exceeding 45 degree with the direction of flow in the main pipe.(5)The gradients of land drains, under drainage as well as the bottom of dispersion trenches and soak ways should be between 1:300 and 1:400.(6)Every septic tank shall be provided with ventilating pipe of at least 50 mm diameter. The top of the pipe shall be provided with a suitable cage of mosquito proof wire mesh. The ventilation pipe shall extend to a height, which would cause no shell 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.(7)When the disposal of septic tank effluent is to seepage pit, may be of any suitable shape with the least cross- sectional dimension of 90 cm and not less than 100 cm in depth below the invert level of the inlet pipe . The pit may be filled with stone, brick or concrete blocks with dry open joins, which should be backed with at least 7.5 cm 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 slab, 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 cm from the top as an anti mosquito measure.(8)When the disposal of septic tank effluent is to a dispersion trench shall be 50 to 100 cm deep and 30 to 100 cm wide excavated to a slight gradient and shall be provided with 15 to 25 cm of washed gravel or crushed stones. Open jointed pipes placed inside the concrete and shall have minimum internal diameter of 75 to 100 cm. No dispersion trench should be longer than 30m and trenches should not be placed closer than 1.8m.
