A new sewage exfiltration model – parameters and calibration

Abstract

Exfiltration of waste water from sewer systems represents a potential danger for the soil and the aquifer. Common models, which are used to describe the exfiltration process, 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. But, due to the complexity of the exfiltration process, the calibration of these models includes a significant uncertainty. In this paper, a new exfiltration approach is introduced, which implements the dynamics of the clogging process and the structural conditions near sewer leaks. The calibration is realised according to experimental studies and analysis of groundwater infiltration to sewers. Furthermore, exfiltration rates and the sensitivity of the approach are estimated and evaluated, respectively, by Monte-Carlo simulations.

Harmonized assessment of nutrient pollution from urban systems including losses from sewer exfiltration: a case study in Germany

“…Studies on sewer exfiltration at pipe scales indicate that the leakage process is ruled by a number of key parameters, including leakage area, depth of wastewater in the pipe, clogging layer, hydraulic permeability and soil characteristics, and hydraulic gradient from pipe surface to the groundwater (Wolf and Hötzl 2007 ; Karpf et al 2009 ; Peche et al 2017 ). These parameters describe structural and dynamic components of sewer exfiltration processes, which data demand at the catchment scale is often not available or subject to large uncertainties (Rutsch et al 2008 ; Karpf and Krebs 2011 ; Peche 2019 ). The common approach for large-scale studies is so far based on mapping analysis of sewer network deteriorations (structural condition, distribution of pipes), surveying and indirectly correlating with population-based sewer discharge, or simplified assumptions of nationwide fixed rates of water loss from defective sewer pipes (e.g.…”

“…For the thickness of colmation layer parameter, the value of 0.04 m is used for dwf and 0.01 is used for swf conditions, since at a thickness of 0.05 m the layer is considered stabilized and no exfiltration might occur (Vollertsen and Hvitved-Jacobsen 2003 ; Ellis et al 2009 ). Meanwhile, the value of the hydraulic conductivity parameter is adjusted for validating the final exfiltration rates at single defect sites using the recommended range by Wolf and Hötzl ( 2007 ) and Karpf and Krebs ( 2011 ), due to the fact that no specific value is reported for large-scale studies for this parameter. As a result, the estimated rates of sewer leakage of public and private sewers under dwf fit well with the literature data, with the mean value of sewer leakage from private sewers being lower than from public sewers.…”

“…To help overcome some of the abovementioned issues and to provide a better solution for water emission control in large urban wastewater systems, several upscaling approaches have been proposed (e.g. Wolf and Hötzl 2007 ; Karpf and Krebs 2011 ; Peche et al 2019 ). The review by Rutsch et al ( 2008 ) states the necessity to develop a ‘standard’ defect area as an alternative parameter for site-specific exfiltration-relevant damages.…”

High groundwater levels: Processes, consequences, and management

“…The flow direction depends on the potential difference between groundwater and sewer water levels. Studies in Dresden (Karpf, 2012; Karpf & Krebs, 2011) have shown that the typical flow rates for the direction from the sewer into the aquifer are one to two orders of magnitude lower than the rates of groundwater flow into the sewer. With respect to high groundwater levels caused by sealing of the sewer system, only the case of groundwater flowing into the sewer is of relevance.…”

Submerged appurtenances and pipelines: An assessment of water levels and contaminant occurrence

“…Under low‐ and/or negative‐pressure conditions, leaks in drinking water pipes may become intrusion pathways if submerged under groundwater. Saturated soil conditions around pipes may be caused either by leaking water mains or sewers, with potentially large exfiltration rates (Karpf & Krebs, 2011), or by groundwater. On the basis of a survey conducted by Kirmeyer and colleagues (2001), 15 to 30% of the total length of pipes in some systems may be located below the shallow groundwater table, either permanently or for a few months at a time.…”