滲流狀況對於廢棄物掩埋場穩定性之影響

Abstract

廢棄物掩埋場設置滲出水集排水系統(Leachate collection system, LCS)之目的為收集滲 出水，輸送至滲出水處理廠進行處理後排放或返送(Recirculation)。目前台灣採取滲出水 返送的掩埋場有一百三十餘場，其中有些掩埋場周邊雨水截流系統已經破壞、有些滲出 水收集系統已經堵塞，但這些掩埋場並未評估滲出水淤高後對於邊坡穩定之影響。這些 掩埋場中有一半為山坡地掩埋場，因此評估滲出水淤積狀況以及邊坡穩定狀態為當務之 急。本研究將以美國掩埋場設計通用之水文平衡分析模式HELP 針對假設之山坡地掩埋 場進行模擬，再將其結果利用SEEP/W與FEMWATER 進行場內滲出水滲流模擬，最後 以SLOPE/W進行邊坡穩定分析，以完整瞭解掩埋場滲出水集排水系統效能與其他條件 對於滲出水淤積以及邊坡穩定之影響程度。因HELP 在模擬時可考量氣象、水文、植生、 排水以及場內各層之導水與貯水性質，故可以極為精確地估算掩埋場內各層所貯留與排 放之水量。利用HELP 所得之結果，則可作為SEEP/W或FEMWATER 模擬時之輸入條 件，以進一步掩埋場內滲出水淤積水位之分佈。本研究亦將透過系統參數之變化，探討 降低滲出水導致邊坡破壞風險之可行方法。本研究亦將針對二至三場山坡地掩埋場，利 用實際資料進行分析，以評估推廣應用之可行性。

Leachate collection systems (LCSs) are designed to efficiently remove leachate from solid waste landfills. This prevents ponding of the leachate on the liner system, thus minimizing leachate migration to the environment. The potential of LCS drainage materials (sand, gravel, and geotextiles) to clog as a result of biological growth and particulate clogging is an important issue that should be addressed in landfill design. However, almost all of the landfills in Taiwan adopted outdated LCS design and thus most of the LCS systems suffer from clogging. On the other hand, leachate recirculation is used in most of these landfills to achieve zero discharge since the leachate treatment plant of these landfills had failed due to lack of proper maintenance. More than 70 such landfills are located in mountainous areas such that the reduced slope stability as a result of the elevated leachate level should be a major concern for the regulatory agencies and the public. The objective of this research is to study the effect of clogged LCS on the risk of slope failure of landfills. The research proposed using HELP, which is a hydrological balance model for landfill design in the United States, to compute the water balance in all the layers in the landfills as a first step. The resulted water balance data will then be processed as the initial and boundary conditions for groundwater simulation model SEEP/W and FEMWATER used to compute the distribution of leachate head in the landfill. Consequently, the slope stability will be analyzed with the 2D slope stability software, SLOPE/W, to access the factor of safety of critical leachate distribution. The research will also study the effectiveness of the alternatives of reducing leachate generation or leachate removal on improving the slope stability. The study will also include modeling 2 to 3 actual mountainous landfills in Taiwan to access the feasibility of widespread application of the proposed analytical procedures