하천·호소 퇴적물 관리 및 준설 물질 활용 방안

Abstract

Freshwater Sediment Management and Beneficial Use of Dredged Material Freshwater sediments of rivers and lakes are important components of water quality and the aquatic ecosystem. As such, the materials produced by dredging activities should be regarded as valuable resources. However, the institutional systems on both sediment and dredged material are not well-organized in Korea. To this end, this study conducted a comprehensive management system of freshwater sediment and the ensuing dredged material. The Korean Ministry of Environment (ME) carried out as a model study a nation-wide investigation on freshwater sediment quality. Other research programs also conducted examinations on the sediment quality including its endocrine-disrupting compounds and persistent organic pollutants. However, the number of samples and sampling frequency were limited in such programs. In response, various criteria and guidelines have been proposed for the sediment management, classified as follows: sediment quality guidelines or criteria for the protection of water quality and aquatic organisms; cleanup screening level for the severely contaminated underwater sediment; disposal and discharge criteria for the dumping of dredged materials; and criteria for beneficial use of dredged materials. Among these guidelines or criteria, sediment quality guidelines (SQGs) are most frequently referred to. SQGs can be derived by different approaches such as those background-based, effects-based, or consensus-based, and so on. The consensus-based SQGs (cSQGs) indicate the statistical means of the published SQGs. These SQGs are used as the primary screening tools rather than the legal standards. And the application of SQGs often accompany the consideration of background or reference sediment qualities. For a more precise analysis, particle size distribution and organic content of sediment should be taken into consideration. If we develop new SQG in Korea, significant time and labor will be required to investigate sediment chemistry, biological effects, reference conditions, etc. Therefore, adapting the published cSGSs as an interim national standard or guideline would provide a practical option. At the same time, the suitability of cSQGs in Korea needs to be studied. Furthermore, the legal basis for sediment management needs to be arranged in environmental laws such as “Framework Act on Environmental Policy,” “Water Quality and Ecosystem Conservation Act,” etc. In Korea, dredging projects at freshwater bodies have been carried out for the purpose of removing contaminated sediment, collecting aggregate (sands), managing river channels, etc. Except for aggregate (sand) collection, most dredged materials were land-filled or disposed to ocean in Korea. In the U.S., however, the eco-friendly utilization and disposal of dredged materials is regarded as the important aim of the environmental policy. The dredged materials are considered for beneficial use (BU) for the following 4 aspects: necessity and opportunity; physical suitability; logistics and management requirements; and environmental suitability. The quality standards of dredged materials are different for each type of BU. In Korea, BU of dredged material does not have a solid legal basis. According to an authoritative interpretation by ME, the objective of a dredging project determines whether the dredged material is soil or solid waste. In case of the Four Major Rivers Restoration Project, BU of dredged materials is mainly focused on the aggregate (sands). At the project sites, a huge amount of dredge materials are produced daily by the dredging activities. Thus, the primary concern is finishing the generated dredged materials rather than utilizing the materials effectively. This indicates that an adequate BU plan of dredged materials needs to be prepared at the project planning stage. In addition, physical, engineering, and biological acceptability as well as chemical suitability need to be considered in the decision-making of BU. In conclusion, this study recommends the following recommendations. First, a comprehensive management plan should be established for freshwater sediment. More specifically, the inventory of freshwater sediment quality needs to be prepared periodically, and a management practice of the contaminated sediment should be established. In this context, the consensus-based SQGs can be used as an interim national guideline. This study proposes a decision-making process for sediment management, and the process is based on the cSQGs and reference value. In the long run, sediment quality standards for freshwater sediment and requirements for BU of dredged materials should be developed from the studies on the assessment of human and ecological risks.