POLLUTANT RELEASE FROM SEDIMENTS IN SEWER SYSTEMS AND THEIR POTENTIALFOR RELEASE INTO RECEIVING WATERS

A programme of work funded by the UK Water Research Centre (WRc) has b een carried out to investigate the nature, occurrence and re-entrainme nt into the sewage flow of sewer sediments and their associated pollut ants to provide data for the development of UK sewer flow quality mode ls, MOSQITO and MOUSETRAP. Methodologies for the preparation of sewer sediment samples prior to chemical analysis are described. These metho ds have been developed to determine the level of pollutants released f rom sewer sediments which will a representative of the conditions foun d in the sewer environment. Application of progressively lower shear s tresses to samples of sediment, from an extreme, via blending, to less severe preparative methods by means of a stirring technique, fraction ate sediment samples so that the polluting potential may be assessed s eparately for both dissolved and resuspendable phases. Stirring prepar ative methods release less pollutants from a sediment sample than from the blending procedures, with the level of pollutant release being de pendent upon the shear stress being applied to the sample, with higher shear values releasing as would be expected, more pollutants.