비점오염원 저감을 위한 우수유출수 관리방안

Abstract

So far, the management of water pollution has been focused mainly on the post-treatment of point pollutions such as urban sewage and industrial waste water. Considerable improvement has been made to the water quality and the reduction of pollution. However, this post-treatment oriented policy has no countermeasures for non-point pollution that occupies considerable portion of water pollution. Moreover, increased impermeable rate accompanied by urbanization changed the characteristics of storm runoff. It added to the damage from flood due to rapid storm runoff seen from the water volume aspect. Seen from the aspect of water quality, it caused the water quality to be deteriorated with the runoff of various polluting materials into the water system along with the storm runoff. Therefore, immediate action shall be taken to properly control the storm runoff to reduce the risk of flood by rapid storm runoff and to improve the water quality. The review on the runoff characteristics of non-point pollution materials by storm runoff showed that BOD, CDO, SS, T-N and T-P featured the first-flushing effect, showing relatively high concentration in early-stage storm runoff, however, the heavy metal(Zn, Cd, Pb, Cu) showed no meaningful significance with the first-flushing effect and storm runoff tendency. Another review on the Site Mean Concentration(SMC) of non-point pollution materials according to the use of land revealed that the SMC of BOD was in relatively low concentration in the range of 5.3～12.1mg/L, no meaningful significance by the use of land. The SMC of COD and SS ranged from 115.9～67.7mg/L and 22.7～126.6mg/L, respectively, and showed the highest concentration in motorway. T-N SMC from 3.26～9.62mg/L and highest in commercial areas and T-P SMC from 0.09～0.48. Heavy metal (Zn, Cd, Pb, Cu) SMC featured relatively high concentration in motorway and parking lots, which seems to be caused by the vehicular traffic. The analysis on the effect of reducing non-point pollution by existing rainwater runoff prevention facilities revealed that the rainwater pumping station's reservoir can be utilized as the storm runoff treatment facilities for the reduction of non-point pollution materials. The result of storm runoff precipitation test showed, on the whole, relatively precipitation characteristics. 12 hours of precipitation was sufficient to remove 60～90% of suspended solid. In order to utilize the pumping station's reservoir to remove non-point pollution materials, the storm runoff must be stored/precipitated for at least 12 hours and the upper portion shall be drained out first followed by properly treated lower portion. When examined the runoff characteristics of general receiving reservoir and infiltration receiving reservoir, the runoff volume in general receiving reservoir increased in proportion to the increase of rainfall while the runoff volume in infiltration receiving reservoir remarkably decreased compared to general reservoir. Little runoff was found in the rainfall volume under 20mm. Considering that the non-point pollution materials have high pollution in the early-stage storm runoff, the infiltration receiving reservoir is expected to reduce considerable amount of non-point pollutions. To build a foundation for the management of storm runoff to reduce the non-point pollution, the management plans for the rainwater runoff in cities and industrial areas that exceed certain scale shall be established first. With the management plan carried out, the restriction on the storm runoff shall be implemented after building the foundation for non-point pollution control. Therefore, it is important that the self-governing communities and carriers recognize the importance of storm runoff control and make efforts to reduce the pollution from storm runoff. Since the characteristic of pollution material runoff by rainfall shows relatively high pollution concentration in early stage runoff and more than 80% of the entire rainfall are 20mm and below in Korea, the storm runoff treatment facilities for the reduction of non-point pollution may be designed to cover approximately 20mm rainfall. It will be able to treat more than 80% of the entire rainfall and contribute to reduce considerably the non-point pollution burden in appropriate drainage area. However, when establishing the storm runoff treatment facilities in certain area, the geomorphologic peculiarities, hydrographical and hydrological characteristics as well as the climate and applicable technologies must be taken into consideration when determining the scale of the facilities. Moreover, the peculiarity of Korean climate, which has more than 70% of rainfall in summer, shall also be considered when selecting the storm runoff treatment technology and designing the facilities. There are many types of storm runoff treatment facilities applicable to each local peculiarity. In Korea, where the use of land is limited, the size of land required for the treatment facilities shall be the main consideration in selecting the location. Generally, the urban areas where wide area is not usually unavailable, adopt infiltration facilities that occupy relatively small area. Especially, the appropriate measures are needed to enable the control of non-point pollution by supplementing existing manhole and to improve the rainwater pumping station's reservoir to make it possible to treat the first flush non-point pollutions. The installation of apparatus type facilities such as Stormceptor, Stormfilter and Swirl/Vertex needs sufficient preliminary study in terms of their effectiveness in peculiar climate and geographical features of Korea. Compared to urban areas, rural areas have more earth/sand runoff and periodic maintenance is more troublesome. Therefore, rather than infiltration or apparatus type facilities that require much maintenance works, the rural areas shall adopt multi-purpose retention reservoir, artificial wetland, vegetation waterway and filtering belt that require wide area but easier maintenance. When building new towns, appropriate measures shall be taken to limit the town's impermeable area ratio in certain level to prevent the rapid change of runoff features by the increase of impermeable rate, and to install infiltration facilities to control the increased runoff after the development. For the control of non-point pollutions, preliminary efforts to remove the source of pollution shall be made along with the installations of storm runoff treatment facilities. The efforts to remove the source of non-point pollutions in urban areas can be made through the periodic cleaning of cities, inspection/cleaning of manhole and rainwater irrigational facilities, dredging the bottom of detention reservoir and installation of storm runoff blocking slope in construction areas. Future studies shall focus on the understanding of non-point pollution runoff features and quantification of its effect on the water quality. For this, model site shall be selected to analyze the water quality and water quantity according to the storm runoff and water discharging system all the year round, and the concepts set forth in this report, various storm runoff treatment facilities and rainwater pumping station, shall be embodied to understand the efficiency of each facility and finally to develop the storm runoff treatment facilities that are customized to the characteristics of Korean climate and geographical features.