Do faecal indicator organisms exhibit a first foul flush in combined sewers?

As part of the revised EU Bathing Water Directive, there is scope to discount bathing water quality samples which show poor water quality if poor water quality is predicted and the public forewarned. The Cloud to Coast (C2C) project is developing a model to allow prediction of faecal indicator organism (FIO) concentrations in bathing waters. One of the C2C sub-models is investigating FIO loads from urban catchments. As part of this urban sub-model, the hypothesis of whether FIO loads exhibit a first foul flush in wet weather events is being investigated. This paper presents typical data from two combined sewer overflow outfalls, and based on the data collected suggests there is no first foul flush of FIOs. However sampling took place over a wet summer and hence antecedent dry weather periods (ADWP) were short, and previous research has shown ADWP to be a factor in the first foul flush of pollutants.