Distribution of sewer exfiltration to urban groundwater

Abstract

Sewer leakage, which leads to the occurrence of infiltration or exfiltration, is a chronic problem in sewer systems for many cities worldwide. Exfiltration can result in deterioration of groundwater quality and serious public health risks if groundwater is subsequently used for potable supply. Throughout the world there is evidence of contaminated groundwater leading to outbreaks of waterborne diseases. The UK has witnessed about 70 officially documented sewer-related waterborne disease outbreaks. As a first step in the assessment of microbiological risks to urban groundwater from leaking sewers, this study reviewed the recent literature on, and summarised estimates of, exfiltration. Furthermore, an algorithm to estimate the spatial distribution of exfiltration was developed using Nottingham as the case study area. The results show that out of the total 34 km2 beneath Nottingham, around 23 km2 is susceptible to exfiltration. Some 67% and 4% of the exfiltration-susceptible area receives higher (>500 l/day) and lower (<50 l/day) rates of exfiltration, respectively. The higher rates are closely associated with older sewers. With the current replacement/renewal frequency of once every 1300 years, sewers of all ages are therefore a potential risk to urban groundwater.

Evaluation of Decentralized, Closely-Spaced Precipitation Water and Treated Wastewater Infiltration

“…Alongside the aging of existing water infrastructure (e.g., References [5][6][7]), more sustainable systems for an adaptive and future-proof water resource management concept are required. Here, decentralized systems that are designed especially for storm water infiltration, as well as for wastewater on-site treatment, have become increasingly relevant for building owners and operators (e.g., Reference [8]).…”

Assessing “Urban Karst” Effects from Groundwater–Storm Sewer System Interaction in a Till Aquitard

“…An exfiltration rate of 6.6 L/s is estimated for a total length of approximately 500 m of storm sewer of diameter varying from 0.375 to 0.975 m from injecting 71.2 m 3 of water at close to a constant head over a 3h period after the second filling. This level of sewer exfiltration is much higher than the range given in the review by Chisala and Lerner (2008); estimated at 0.01-0.1 L/s per km for the UK, but up to 3.5 L/s per km from studies reviewed across Europe. In the present study, the high rates of storm sewer system exfiltration are considered due to much of the exfiltration coming from surcharging and backup of water through the catch basins and outflow through the subdrains into the roadway subgrade ( Figure 5); this is a consequence of the shallow and flat design of the storm sewer system.…”

“…The groundwater literature has tended to focus on the impacts to urban aquifers with the emphasis on recharge (e.g., Yang et al 1999;Lerner 2002) and water quality, particularly associated with exfiltration from sanitary sewer systems (e.g., Bishop et al 1998;Chisala and Lerner 2008;Vroblesky et al 2011;Wolf et al 2012). This is not surprising as urban aquifers are important sources of water supply and their effective management may be critical to the well-being of the cities that they supply (Schirmer et al 2013).…”

Sewer exfiltration and the colmation layer

“…However, the universal validity of the results derived from these direct sewer rig and field studies do not agree with a number of indirect modelling studies, which would suggest much lower levels of exfiltration losses (Yang et al 1999;Chisala & Lerner 2008). How robust therefore are the loss rates quantified from experimental sewer studies and are equilibrium exfiltration loss rates maintained over extended time periods?…”