An impact assessment methodology for urban surface runoff quality following best practice treatment

The paper develops an easy to apply desk-based semi-quantitative approach for the assessment of residual receiving water quality risks associated with urban surface runoff following its conveyance through best practice sustainable drainage systems (SUDS). The innovative procedure utilises an integrated geographical information system (GIS)-based pollution index approach based on surface area impermeability, runoff concentrations/loadings and individual SUDS treatment performance potential to evaluate the level of risk mitigation achievable by SUDS drainage infrastructure. The residual impact is assessed through comparison of the determined pollution index with regulatory receiving water quality standards and objectives. The methodology provides an original theoretically based procedure which complements the current acute risk assessment approaches being widely applied within pluvial flood risk management. ► An easy to use desk-based semi-quantitative approach for assessing residual receiving water quality risks is proposed. ► The impacts of urban surface runoff after treatment within sustainable drainage systems are assessed. ► Source pollutant contributions mitigated by removal efficiencies are compared with receiving water quality standards. ► The procedure is illustrated using an urban regeneration area and a hypothetical section of motorway. ► Stormwater managers and regulators are provided with a tool for planning future urban runoff treatment strategies.