Estimation of Basic Unit Pollution Load of an Urban Area in the Lake Biwa Basin

From field surveys of roof runoff conducted in general residential houses in the Lake Biwa basin, the pollution loads of buildings in an urban area were evaluated. The samples were collected from the total roof drainage during a rainfall event, and the water pollutants investigated were total organic carbon （ TOC ） , total nitrogen （ TN ） , and total phosphorus （ TP ） . As a result, it was estimated that 67.7% of the total precipitation flowed out as roof wastewater, and it was clarified that the proportion of dissolved components was high in all cases. The calculated loads of TOC, TN, and TP from buildings were 60.4, 18.1, and 0.64 g ha -1 day -1 , respectively. By applying these loads and roadway loads in the Lake Biwa basin, the basic unit pollution loads of TOC, TN, and TP in the urban area of the Lake Biwa basin were estimated to be 140, 24.2, and 1.1 g ha -1 day -1 , respectively.