These Standards apply for structures with overflows in the overall system of a combined wastewater sewer system within the catchment area of sewage treatment plants. For water management and cost reasons the priority task of the planning of measures for wastewater collection and stormwater treatment is the avoidance of stormwater overflow into the sewer system wherever this is possible. For the remaining discharges, for technical water management and economic reasons, stormwater structures with overflow are located in combined wastewater sewers. With precipitation run-off, high pollutant loads can occur which, with discharge into lakes and rivers, could load these heavily. Although the loadings appear only temporarily these can exceed those from the effluents of sewage treatment plants several times over during rainfall run-off. The task of stormwater treatment is so to limit the rainfall run-off into the sewage treatment plants that there the desired effluent values are maintained and, at the same time, the surge-type loadings of the lakes and rivers remain within acceptable limits. The aim of stormwater treatment must be the best possible reduction of the total emissions from stormwater overflows and sewage treatment plants within the scope of water management requirements. An effective protection of lakes and rivers and of sewage treatment plants from excessive loadings is to be expected if the necessary stormwater treatment takes place according to the criteria of these Standards.