The contribution ratio for badly-water system of non-point pollution source including CSOs is on the increase. In the Four River Restoration Project cases, the ratio for non-point pollution source of BOD increased from 22~37% in 2000 to 42~69% in 2003, and will be 65~70% in 2015.
In particular, we need to prepare measures about severely heavy pollution of water system resolting from concentration of non-point pollution source of the surface of the earth and sediment of water supply and sewer system in rainfall caused by CSOs and the initial water.
This study is to identify the rational installation of treatment facilities about the CSOs and the initial water after investigation and analysis of the several cases, and to install the treatment facilities about the CSOs and the initial water.