수 환경 복원을 위한 퇴적물 준설 깊이 및 면적 설정에 관한 연구

Abstract

Abstract A study on designation of dredging depth and area in sediment for restoration of water environment

By : Jeon Gee-Seok Advisor : Prof. Cheong Kyung-Hoon Ph. D Department of Environmental-Biological Engineering Graduate School of Chosun University

Heavy metals in water have a potential toxicity and continue to remain. That's why they can threat human health through the food chain system. Many of them are removed by adsorption and sedimentation, but more many of them are extracted into water due to pH or ORP change. And they move to the upper layer of sediments especially by extraction from settlements, dissolution, anion exchange, biological process of microorganism, and deteriorate the water quality. So, when planning the dredge and drainage of river, you have to consider the portion of heavy metals in sediment. There are two sediment management methods for water purification. One is a site-treatment system of extraction prevention, the other is a dredge of sediment. In my country heavy rain falls in summer and a big amount of soil erosion occurs into the lake. Therefore, dredge often suggested as an alternative. But there are no sediment control standards for water improvement in the lake. Whenever dredge method is considered, many problems are suggested and the foreign dredge standards for building harbor are applied directly. But we have to think about whether the standards for building harbor is reasonable or not for water improvement. sediment standards have to be divided considering water usage, regional situation, characteristics of pollutants. So it is necessary to make the environmental-friendly and economical standards considering the regional characteristic. The objective of this study is to evaluate the heave metals' concentration and the toxicity of sediments in Hyungsan-river and Youngil-bay and the results are as follows. There are a lot of clay and weak sediment in the upper side of Hyungsan-river, the sand layer in the surface is getting thinner along down the river, and the mixture of sand and clay is getting darker by microorganism decomposition as the river is deeper. And in the middle and downstream of Youngil-bay, the portion of organic matter and clay is so high that it is important to make the dredge technology capable to minimize the turbulence of sediment layers. In Hyungsan-river, the concentration of heavy metals was Zn> Pb> Ni> Cu> Cr> Cd> As> Hg and heavy metal concentration in upper stream was high in sed. 1, 6, 7 and was high in the downstream. It was higher than the standards of America, Canada. Heavy metal concentration of Youngil-bay was higher than Hyungsan-river's one in the middle and down streams. Especially concentrations of heavy metals in the Posco and harbor area were high. The concentration of heavy metals did not change a lot according to the depth in Hyungsan-river but in Youngil-bay, the concentration change was very big according to the increasing amount of water in summer and the difference between the rise and fall of the tide affecting to sediment. In upper part of sediment, The total heavy metal concentration was high by small organic matters in that area or by heavy metal absorbtion or enrichment in water. This kind of heavy metal absorbtion or enrichment came from partial anhydrization and decomposition from sediment section. Thus there are some relations between sediment and particle size in Youngil-bay sediments. Especially, in 20cm layer which contains rich organism there is a high concentration of heavy metals. Zn in the sediment was found in all kinds of heavy metals, bound to Fe-Mn oxides > bound to carbonate> bound to residual> bound to organic matter> absorbed type. Pb was combined type with oxidized Fe and Mn, residual type. The portion of Cu in Youngil-bay was high as organic combined type but that in Hyungsan-river was high as combined type with oxidized Fe and Mn. According to pre-treatment, concentration difference was high as this order : EPA 3050 A method> EPA 3051 method> Korean standard method of soil analysis(leaching test)> Korean leaching test. After the evaluation of contaminates according to sediment's depth of Youngil-bay, I could know the change of heavy metal concentration. As a result, there were not a big necessity about sediment dredge in Hyungsan-river. In Youngil-bay the necessary sediment dredge area is about 348,243㎡ which is about 49.8% of the planned area(699.036㎡). Considering to prevent the water deterioration due to the sediment turbulence, the capable amount of dredge is about 208,946㎥ which is 33.2% of the planned amount(629,132㎥). In this study, I suggested such a minimized dredge amount and area for sediment treatment that the cost efficient dredge can be possible. And I think that it could be the best way to water treatment in this area.