Hydraulic modelling of sewage exfiltration

Abstract

Exfiltration of waste water in sewer networks represents a potential danger for the soil and the aquifer. Various modelling approaches have been proposed to quantify sewerage exfiltration and its spatial and temporal variation. Common models are based on the law of Darcy, extended by a more or less detailed consideration of the expansion of leaks, the characteristics of the soil and the colmation layer. In the paper investigations are introduced, which are focused on the actual water content of the soil and its influence on exfiltration rates. Modelling results with HYDRUS 1D show, that under unsaturated conditions initial exfiltration rates are increased compared to saturated conditions. In experiments it was found, that the matrix potential increases the tightness of the colmation layer. Further a colmation model was deduced, which allows the calculation of the thickness and conductivity of the colmation layer.

A Review of Surfactant Role in Soil Clogging Processes at Wastewater Exfiltration Locations in Sewers

“…One of the principal hypotheses put forward to explain the decrease in exfiltration rate over time at a sewer defect and which has been noted to occur in both experimental and field studies, is that organic and inorganic wastewater microparticles, accumulate in the void space of the porous colmation medium causing a decrease in its effective porosity (Rice, 1974;Rauch and Stegner, 1994;Karpf et al, 2009).…”

A new sewage exfiltration model – parameters and calibration

“…The exfiltration process is controlled by the potential height (∆H), the leak area (A L ), the length of the sewer pipes (L), the hydraulic conductivity (K C ) and the thickness (Z C ) of the colmation layer between pipe and backfill material. The potential height depends on the water level in the sewer pipes (gravitation potential) and the matrix potential of the soil (Beal et al, 2004;Karpf et al, 2009).…”

“…For deducing the parameter K EX , data of experimental studies (Karpf et al, 2009) and groundwater infiltration analysis in the investigation area -the sewer catchment of the city of Dresden (Karpf and Krebs, in preparation-b) are used. An overview about the database and the use of it is given in Tab.…”

“…Besides the examination of the potential height H and its influence on the clogging process (Karpf et. al, 2009), the conductivity of the trench backfill was identified as a factor which has a major influence on the clogging process and thus the exfiltration rate.…”

Sewer exfiltration and the colmation layer

“…Therefore moisture changes in the enveloping transition soil layer can strongly influence the matrix potential and in turn, the exfiltration rate (Karpf et al 2009). Increasing hydraulic potential leads to deeper particle penetration into the transition zone and thus both the matrix potential and the overlying sewer pressure gradient are significant influences in the development of the colmation layer.…”