BRÄDDNING – ETT FÖRORENINGSPROBLEM? / Overflow- a Pollution Problem?
A large number of measurements and field studies on the quality of combined sewer overflow discharge quality have been carried out during the recent years. These measurements indicate that commonly used calculation methods for determining the pollution load from combined sewer overflows may greatly underestimate the actual load. This is due to the fact that the calculation methods used do not consider accumulation and related sediment wash-out from the combined sewer system. In order to make relevant estimations of pollution discharge from combined sewers it is important to take into account sediment wash-out during overflow periods. It is concluded that standard values of the pollution concentration in the combined sewer overflow discharge is better to use as compared to dilution calculations. In spite of the severe pollution problem originating from combined sewer overflows, the Swedish Environmental Protection Board has not yet formulated any general policy regarding the functioning of and permissible pollution load from the overflows.