In Korea, over 95 percent of the municipal solid wastes (MSW) is disposed by landfilling due to the technical and economical easiness. The problem associated with landfilling in Korea is the fact that most of them are simply open-dumped unsanitary landfills. Since the sites are exposed to surrounding areas without any protection systems, the environmental protection is a supreme issue, and post closure land utilization is greatly desired. The purpose of this study is to provide an effective approach and methodology for evaluating leachate control alternatives in the Nan-ji Do Landfill which is the largest and the most representative unsanitary landfill site in Korea.
Leachate generation and flow characteristics were analyzed to assist decision making for protecting water sources near the site. Using field measurements of water level, hydraulic conductivity, and pollutant concentrations, rain water infiltration and corresponding ground water flow in three dimensions under four conditions of protective systems were simulated along with climatological data to evaluate protective effects and technical, economical efficiency for their constructions and operations.
Installation of final cover on the landfill surface, leachate cutoff wall, and extraction wells for the active hydrogeological control were considered as major remedial alternatives for establishing leachate control system. Seasonal and long-term changes of rainfall infiltration rate through the landfill, subsurface water level, and polluted water discharge rate to surrounding areas in response to the proposed leachate control alternatives were determined through numerical simulations of the ground water flow system.
Among the proposed four alternatives, clay final cover systems with cutoff walls along the Han River side and four extraction wells just inside the cutoff walls, each of which has 400 cubic meters per day of extraction rate, were found to be sufficient to keep the new forming hydraulic gradient in all side downward to the cutoff walls. This alternative has the same protective effects as when the cutoff walls are installed to the whole landfill boundaries and is much easier and cheaper to construct and operate.
The results of this study provide insight into special difficulties associated with verifications of modeling results in unlined landfills without monitoring systems. Even though determination of the most environmentally efficient and cost effective alternative in unsanitary landfills is highly site specific, the framework of approach and methodology proposed in this thesis can be applicable to other unsanitary landfills present in great numbers in Korea and developing countries.
