潮汐對地下水中污染物傳輸之影響

Abstract

台灣近數十年來經濟快速發展，公民營工業區林立，其中部分工業區因為廠商的管理不夠完善，導致造成工業區的土壤與地下水污染。自從民國89年土壤與地下水污染整治法通過之後，環保署與工業區的主管單位逐步針對工業區的地下水進行有系統的監測，以期早期偵測污染、即時控制或加以整治。這些工業區中，部分位於沿海地區，而根據監測資料發現，可能因為沿海地區的潮汐作用導致地下水流向不易掌握。為了進一步瞭解潮汐作用之影響，以便在地下水監測井規劃時可以更為妥善，本研究以數值模擬來探討在潮汐作用下對沿海工業區地下水中污染物之傳輸。 本研究以台中港加工出口區作為研究對象，接著考慮到沿海區地下水受到海岸線之潮汐作用的影響，在不同的位置下放置污染源，最後針對潮汐作用對於污染物質影響進行討論。主要以數值軟體Modflow進行模擬，潮汐設定除了在海岸線進行設定，同時也考慮到兩岸河川面受潮汐作用的影響，接著在各個九個不同的位置上設定污染源，藉此分析出污染源的擴散情況。 研究結果顯示出污染物的確會受到潮汐的影響產生出不同的變化，但是在不同的導水度時將會有不同的模擬結果；導水度較小的情況中，污染物受潮汐影響後的擴散範圍較沒有潮汐時廣；導水度較大時，污染物受潮汐影響後的擴散範圍較沒有潮汐作用時小。由前述研究結果可知，在潮汐作用因污染團的形狀與大小會改變，因此在設置地下水監測井應該考慮潮汐之影響。

Due to rapid growth of economy, the amount of government owned or privately owned industrial zone had increased dramatically. In some of those industrial zones, faulty managements may lead to soil and water pollution. From 2000, the regulation of soil and water pollution had passed. EPA and authorities began to monitor, detect pollution, control and remediate groundwater. Among those industrial zones, some of them locate at shoreline. The flow path of groundwater was not easy to predict probably because of tidal influence. In order to understand tidal influence further and to design better groundwater monitoring system, in this research, groundwater transportation with tidal influence in industrial zones in shoreline is discussed with numerical simulation. The Taichung Export Processing Zone was chosen to be the target of case study in this research. Sources of pollutants are set in different locations, and then the influence of tidal change to pollutants is discussed. The groundwater flow simulation codeand contaminant transport code selected for this study were MODFLOW and MT3DMS, respectively. Besides being set up along theshoreline, tide was also set up in two drainage channels along the sides of the Taichung Export Processing Zone at the same time. The sources of pollutions are set in nine locations. The expansion of the plume is analyzed. The results show that the degree of effect of tide on thetransport of contaminantvaried withthe distance between the plume and the tidal boundaries.Furthermore, with low hydraulic conductivity, the degreeof plume expansion is larger than that without considering thetidal effect. With higher hydraulic conductivity, the extentof plume expansion is smaller than the condition with no tide change. According to the results,the shape and size of the plume were affected by the tidal action. As a result, tidal influence should be considered when designing the systemgroundwater monitoring wells.