The Colmation of Leaks in Sewer Systems During Dry Weather Flow

This paper examines the performance of infiltration of wastewater into the groundwater due to leaks in sewer systems. Experiments were carried out under a variety of conditions using domestic sewage and uniform bedding material ranging in grain-size from 0 to 40 mm. The results indicate that the infiltration is determined solely by the physical process of the colmation of the bedding sand zone. Due to the accumulation of particles in the porous media the permeability of this zone and therefore the amount of infiltrated sewage is decreased rapidly with time. This effect is commonly known as colmation. A strong influence of both solids concentration of the sewage and grain-size of the bedding material can be seen on the temporal development of the colmation. Still a steady state flow was reached under all experimental conditions in less than an hour of infiltration. The characterisation of the colmated zone by the leakage factor presents the possibility to calculate the infiltrated sewage according to Darcy's law. The infiltration of sewage into the groundwater is therefore linear dependent on the area of the leak and the pressure head. The observed values for the steady state leakage factor range between 0.001 and 0.01 1/s depending mainly on solids concentration and grain-size.