Does freezing affect sediment sampling results?

Sewer sediment sampling is subject to errors, and these can often make a significant contribution to the discrepancies between predictions from mathematical models of pollution transport and what actually happens. Deep freezing of sediment and cutting samples is the most reliable method of sampling, unfortunately it is expensive and is limited mostly to trunk sewers of diameters exceeding 800 mm. The impact of freezing sediment collected from filter backwash water sedimentation tank on the size distribution of particles below 180 mum was investigated, demonstrating that the process had a significant impact. Small particles are known to contribute to heavy metal content in sewer sediments, so they are the subject of special concern.