Section 49(8) in Assam Notified Urban Areas (Other than Guwahati) Building Rules, 2014
(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.
