Implications of surcharge on the operability of sewer networks

Thames Water Utilities Limited is the largest water company in the United Kingdom, providing 2600 million litres of treated water for its 8 million clean water customers and treating 4200 million litres of sewage daily for its 13 million waste water customers, in London and across the Thames Valley. Factors such as the scale of removal of sewage from customers, the age of the underground assets and how the system has developed makes Thames Water's sewer network a highly complex system. In the UK there is approximately 302 000km of public sewers worth an estimated value of £108.8 billion, the cost of replacing the entire infrastructure is quoted as being £200 billion (OFWAT, 2002). Thames Water Utilities Limited owns approximately 29% of the whole UK sewer infrastructure. Significant lengths of the network are likely to be over 100 years old and their remaining life expectancy is unknown. In general, as the pipeline ages there is a higher likelihood of failure occurring. There are a variety of factors that influence the deterioration of sewers but the mechanisms which cause these failures are not fully understood. The identified mechanisms of interest include infiltration and exfiltration. These mechanisms can occur at the sewer joints and can be exacerbated during surcharge. This paper presents a literature review of information available on the mechanisms and its perceived main influences. In essence, it is understood that exfiltration could potentially lead to environmental pollution, whereas infiltration could result in operational problems both in the network and at treatment works. There is little published work on issues concerned with these mechanisms and accordingly, there are obvious benefits in investigating these topics further