Groundwater-Sewer Interaction in Urban Coastal Areas

Ting Liu,Valentina Prigiobbe,Xin Su

doi:10.3390/w10121774

Abstract

In this paper, a study of the potential causes of the occurrence of high concentration of Enterococcus Faecalis in surface water within urban areas in dry-weather conditions (DWCs) is presented. Two hypotheses were formulated: (1) undersized sewer system; and (2) groundwater infiltration into damaged sewer pipes. In both cases, more frequent combined sewer overflows (CSOs) may occur discharging untreated sewage into surface water. To evaluate the first hypothesis, a hydraulic model of a sewer was developed assuming a water-tight system. The simulation results show that CSOs never occur in DWCs but a rain event of intensity equal to 1/3 of one-year return period may trigger them. To evaluate the second hypothesis, a model combining sewer failure with groundwater level was developed to identify the sections of damaged sewer below the water table and, therefore, potentially affected by infiltration. The risk of infiltration exceeds 50% in almost half of the entire network even at the lowest calculated water table. Considering 50% of infiltration distributed throughout that part of the network, CSOs can occur also in DWCs.

Highlights

Since more than half of the global population resides in urban settings, providing safe, reliable water to city populations is a challenge that defines the 21st century [1]
The simulation results show that there is no flow at the Combined sewer overflows (CSOs) (Figure S8) and no flooding at any catchments, which indicates the sewer system is not undersized under dry-weather conditions (DWCs)
Considering the sections of the sewer at high risk of infiltration, sewer flow simulations were run and the minimum level of infiltration required for the CSOs to occur in outfall 5 (Figure 2) was determined

Summary

Introduction

Since more than half of the global population resides in urban settings, providing safe, reliable water to city populations is a challenge that defines the 21st century [1]. One of the major stressors on natural urban water is the discharge of untreated sewage containing toxic and pathogenic contaminants into natural water bodies, which cause a variety of diseases including diarrhea, the leading cause of illness and death on a global basis [9]. Combined sewer overflows (CSOs) are one of the major causes of uncontrolled discharges of untreated sewage during wet-weather conditions (WWCs). Studies of the impact of sewage overflows on coastal water have shown that the discharge of wastewater can significantly contribute to the accumulation of micro-pollutants (e.g., personal-care products and pharmaceuticals), fecal bacteria, and viruses in the near-shore water and on the sediments, which negatively affect the water quality and present health risks for the population [10,11,12,13].

Methods

Results

Conclusion