Surface water sewer misconnections in England and Wales: Pollution sources and impacts

•Multiple method “weight-of-evidence” approaches for source verification of illicit discharges•Continued and persistent impairment of urban water quality and ecological status by polluted stormwater outfalls•Inefficiency of existing compliance and enforcement procedures for misconnections•Significance of misconnected household appliances to potential in-stream pollution loadings•Variability in national/local estimates of misconnection rates and remediation cost-estimates

In urban areas served by separate sewerage consisting of separate pipe systems it is not uncommon for misconnections to be made either accidentally or deliberately, whereby the wrong effluent is connected to the wrong sewer. The main focus of this problem has been on in-household appliances that are wrongly connected to separate surface water sewers, potentially leading to pollution of receiving waters and non-compliance with statutory water quality standards. This paper examines the available evidence to evaluate the potential scale, severity and cost of the problem in England and Wales in comparison to that reported from investigations in the United States. The particular difficulties associated with distinguishing specific sewage sources in the wastewater “cocktail” discharged at polluted surface water outfalls are reviewed. The deficiencies of existing legislation and enforcing compliance with respect to misconnections are also discussed and the pollution potential resulting from domestic misconnections is explored based on sampled data.