現地反應牆型式對去除地下水中含氯有機溶劑效率之影響

Effect of Configurations of Permeable Reactive Zones on the Remediation Efficiency of Groundwater Contaminated by Chlorinated Solvents

呂政信(Cheng-hsin Lu) ； 單信瑜(Hsin-yu Shan)

《土壤及地下水污染整治》 2卷1期 (2015/01) Pp. 1-10

https://doi.org/10.6499/JSGR.2015.0201.001

摘要

本研究以高雄楠梓加工出口區為例，使用MODFLOW搭配RT3D模擬污染物之傳輸及降解反應，建立當地現存低濃度且範圍廣之污染物環境模型，並模擬注入還原性或氧化性物質及不同形狀之現地透水性反應牆配置，研究結果顯示，現地反應牆形狀配置的不同，對整治污染物有明顯的差異。因氧化劑或還原劑在土層中需要反應的時間，而反應牆通常會搭配置換土壤，換成導水度較高的土壤方便控制水流使污染物通過，但也會使污染物經過反應牆時停留的時間不夠長，故若使用還原性物質（例如：零價鐵）時，其屬階梯式降解反應，來不及於反應牆降解完全，造成降解產生之氯乙烯有超標的現象，而使用氧化性物質（例如：過錳酸鉀）時，則橫向配置之透水性反應牆效果較佳，故針對不同藥劑設計反應牆的形狀變顯得很重要。

關鍵字

含氯有機溶劑 ； 現地透水性反應牆 ； 模擬 ； 地下水污染整治

並列摘要

1. Introduction/Background There are many manufacturing facilities or abandoned locations with groundwater contaminated by chlorinated solvents currently listed as controlled or remediation sites by the Taiwanese EPA. These polluted areas are undergoing remediation to clean up the related aquifers. The source zone of most of these sites has not been located, and the remediation efforts are limited to reducing the concentrations of contaminants in the groundwater and controlling the movement and extent of the plume. In-situ reaction zones/walls have been used in many remediation projects, and the layout and configuration these can have significant effects on remediation effectiveness and efficiency. However, there are very few studies in the literature that discuss using groundwater simulations to optimize the configuration of in-situ reaction walls. This research studied the migration and degradation of a chlorinated solvent plume in an aquifer undergoing in-situ remediation by simulation with MODFLOW and RT3D. The DNAPL contamination site at Nantze Export Zone in Kaohsiung, Taiwan, was chosen as the focal site for the case study. Remediation by injecting reducing or oxidizing agents into permeable reactive zones of various shapes and sizes was simulated. Groundwater in the aquifer beneath the Nantze Export Zone is contaminated with chlorinated solvents, and the plume is moving across the boundary towards Houjin Creek in the north. The hypothesized permeable reactive zone is located near the northern boundary of Nantze Export Zone, and various configurations were simulated to study the effects on remediation efficiency. 2. Materials and Methods This research performed simulation of the DNAPL contaminated plume, which is remediated by insitu reaction walls, with MODFLOW and RT3D. The effectiveness of remediation of pollutants such as TCE, DCE, and VC was evaluated by changing the configuration of the zero-valent iron and potassium permanganate of the permeable reactive zone, including positioning the wall along (longitudinal configuration) or across (lateral configuration) the direction of the groundwater flow, and changing the dimensions of the wall. 3. Results and Discussion 3.1 The Zero-Valent Iron Permeable Reactive Zone Configuration The results of simulation of the zero-valent iron reaction zone indicate that the removal rate of a reaction zone in the longitudinal configuration is higher than when placing the reaction zone in lateral configuration. When the permeability of the reaction zone is significantly higher than that of the aquifer material, significantly more groundwater could flow through the reaction zone in the case of a longitudinal in-situ reaction zone, and thus the reduction in TCE was effective. In addition, if the time that pollutants passed through the permeable reactive zone was long enough, the degradation products, i.e., DCE and VC, could also be reduce to concentrations below the related regulatory standards. 3.2 The Potassium Permanganate Permeable Reactive Zone Configuration The remediation is significantly more efficient for the in-situ reaction zones using potassium permanganate, due to the short reaction time. In other words, once the contaminant in the plume encounters the in-situ reaction zone, it will be removed by oxidation. As a result, as demonstrated by the simulation, a wide lateral in-situ reaction zone which could more effectively intercept the plume and thus capture and remove more of the pollutants. 4. Conclusion The effectiveness and efficiency of in-situ treatment using permeable reductive or oxidative reaction zones can be enhanced and optimized by performing numerical simulations in the design phase to determine the best configuration of the zones. This study showed that this can be accomplished with MODFLOW and RT3D, and that the reaction zones can be successfully incorporated into plume transport modelling.

並列關鍵字

chlorinated solvents ； permeable reactive zone ； DNAPL ； simulation ； ground pollution remediation