CONTROL OF POLLUTANT RUNOFF BY COMBINATION OF STORMWATER RETENTION AND AQUATIC PLANT TREATMENT

Lake Biwa Comprehensive Preservation and Improvement Project was established in 2000 for an environmental management of Lake Biwa. Moriyama River Water Treatment Facility was constructed by combining stormwater retention and aquatic plant treatment under the project. It has been operated in order to improve water quality which runs off into Lake Biwa by a series of facilities of a pre-treatment facility, a stormwater retention pond and a vegetation pond. The objectives of this study are to obtain knowledge on pollutant behaviour and mass balance in the treatment facility and to discuss availability of the methodology for an effective management of pollutant runoff from point/nonpoint sources. Surveys on pollutant runoff were done for dry weather periods and storm events, which observed water quality and flow volume into/through/out of the treatment facility. As a result of discussions through the surveys, it was shown that pollutant removal efficiencies of the treatment facility are not clear during dry weather periods, but they are remarkable during storm events especially in the stormwater retention pond for particulate pollutants. It was also shown that removed pollutant loads in the stormwater retention pond occupied a large ratio for 26-74% in total removed loads in the treatment facility, but these efficiencies depended upon pollutant physical and chemical properties. These findings will leads to more objective environmental management of point/nonpoint pollutants around Lake Biwa.