Following the end of World War II there was a major migra tion of population in the United States and Scandinavian countries to urban areas. As a result of this migration and in part due to the public works moratoria imposed during the war, a major pro gram of sewer construction was instigated, which resulted in the collection and subsequent concentration of large volumes of waste water at single discharge points. As the assimilative capacity of these receiving waters was exceeded, it led to or aggravated existing water pollution problems in these waters. To mitigate this degradation of water...