導水度異質性對於含氯有機溶劑污染場址健康風險評估之影響

Abstract

本研究評估導水度異質性對於含氯有機溶劑污染場址之影響，藉由模擬地下水污染溶質傳輸的現象，對導水度垂直向異質性分佈進行系統性的分析。利用RT3D數值模式和健康風險評估來模擬含氯有機溶劑污染場址於地下水傳輸，評估各關切污染物對場址風險之影響。RT3D可模擬四氯乙烯降解作用產生三氯乙烯、二氯乙烯、氯乙烯，各關切污染物的吸附作用使各污染物傳輸速度不同。模擬場址中建立一導水度在垂直方向為異質性的假設場址和選用一國內著名含氯有機溶劑污染場址做研究案例。 研究結果顯示，在模擬一假設場址中，污染源存在於上層含水層，若低導水度分佈於上層，會減緩污染團向外傳輸速度，使得場址內濃度高，場址外濃度低。若高導水度分佈於上層，污染團傳輸快速，使得場址內濃度低，場址外濃度高。模擬結果顯示氯乙烯傳輸速度快，使得24年之間造成場址外嚴重的污染。實際案例場址模擬結果，其上層為低導水度，下層為高導水度之透水層時，模擬濃度漸增，場址內之風險與假設其為均質含水層差異大，場址外之風險與假設其為均質含水層差異小。健康風險評估結果顯示主要危害暴露途徑為吸入途徑，其次為食入，而風險主要由三氯乙稀和氯乙烯所導致。

This research, evaluates the Effect of Heterogeneity of Hydraulic Conductivity on Health Risk at DNAPL Contaminated Sites by simulating groundwater contaminant transport. Using RT3D and Health Risk Assessment to simulate the migration of plume and evaluate the effect of the contamintant of concern on DNAPL contaminated sites. RT3D, which simulates the degradation of Tetrachloroethylene (PCE) and its degradation products, Trichloroethylene (TCE), Dichloroethylene (DCE), Vinyl Chloride(VC), concerns about the absorption of plume causing different velocity of transport. On the simulation site, the site for study was assumed to establish a vertical heterogeneity of hydraulic conductivity. The other DNAPL site in Taiwan was chosen as the case study. The results of the research show that, the assumption that the site point source exists in the upper aquifer pollution, if the low hydraulic conductivity were located on an upper aquifer, plume migration speeds down, making the concentration near the source was high, and the concentration far away the source was low. If high hydraulic conductivity were located on the upper aquifer, plume migration speeds up, and the concentration near the source was low, while the concentration far away the source was high. The results of the simulation show that the rate of transport of Vinyl Chloride is fast, leading to severe pollution beyond the site boundary within a time of 24 years. On the other hand, Results of the Taiwan DNAPL site simulation show that, when assuming low hydraulic conductivity on the upper layer, makes concentration increasing inside the site, the risk shows a big difference with the homogeneous aquifer, and in the outer site the risk difference is low. All the results of health risk assessment show main hazards exposure pathways by mainly inhalation, and followed by ingestion. The risk within the site boundary is primarily caused by both Trichloroethylene (TCE) and Vinyl Chloride (VC).