Pollutant release from sediments in sewer systems and their potential for release into receiving waters

A programme of work funded by the UK Water Research Centre (WRc) has been carried out to investigate the nature, occurrence and re-entrainment into the sewage flow of sewer sediments and their associated pollutants to provide data for the development of UK sewer flow quality models, MOSQITO and MOUSETRAP. Methodologies for the preparation of sewer sediment samples prior to chemical analysis are described. These methods have been developed to determine the level of pollutants released from sewer sediments which will be representative of the conditions found in the sewer environment. Application of progressively lower shear stresses to samples of sediment, from an extreme, via blending, to less severe preparative methods by means of a stirring technique, fractionate sediment samples so that the polluting potential may be assessed separately for both dissolved and resuspendable phases. Stirring preparative methods release less pollutants from a sediment sample than from the blending procedures, with the level of pollutant release being dependent upon the shear stress being applied to the sample, with higher shear values releasing as would be expected, more pollutants.