| Summary: | 碩士 === 國立交通大學 === 土木工程學系 === 100 === Alternative covers of landfills have been proposed and permitted on a case by case basis in the United States. Researches over the past decade indicated that evapotranspiration (ET) cover with either monolithic layer or capillary barrier have been proven to be better or equivalent to traditional RCRA Subtitle D covers. A number of researches and site demonstration projects showed that ET cover can also effectively minimize percolation and meet the requirement of the cover system in regions with wet climate. Thus ET covers may be suitable for the landfills in southern Taiwan where evapotranspiration is greater than precipitation and rainfall often occurs in very short periods. In this study, the effectiveness of ET covers with monolithic fills and capillary barrier has been investigated by computation by Visual HELP and HYDRUS-1D with historical meteorological data representing the northern (Tamsui), central (Taichung), and southern (Tainan). The results show that monolithic covers of a single layer of fine-grained soil with low hydraulic conductivity and a high storage capacity can be quite effective in deterring infiltration. The design of these properties allows monolithic covers to manipulate the water balance by increasing the storage, evaporation, and limiting percolation. The amount of precipitation and the storage capacity of the soils are the critical factors for determining the thickness of these covers. On the other hand, capillary barriers consist of a layer of fine-grained soil underlain by a layer of coarse soil are also very effective by limiting infiltration with the low relative conductivity of the coarse layer.
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