油品多相抽除法整治之模擬

Abstract

為預防及整治土壤及地下水污染，確保土地及地下水資源永續利用，環保署於2000年制定土壤及地下水污染整治法。在土壤與地下水污染整治法通過後，受污染場址的土地轉移、土地使用將受到限制，在業者時限壓力下工程師常被要求在短時間內完成整治工作。而多相抽除法為近十幾年來快速發展之現地整治方法，惟在效率評估上多半仰賴工程師經驗，缺乏量化的指標。本研究以大型儲油槽汽油洩漏在砂質土層造成的污染作為研究對象，以數值模擬軟體TMVOC探討多相抽除法在該場址中，佈井位置、孔隙率、井底壓力此三變數對整治效率的影響。模擬結果顯示佈井於洩漏點下游10 m處整治效率最佳，由此點向上游或下游佈井效率將降低，距離此點越遠效率越差。大孔隙率之場址整治效率較高。井底壓力與大氣壓力的壓差和整治效率有正相關性，但非成正比，加大負壓對回收速率的影響在整治前期較為明顯，整治後期影響降低。

To protect ground water from contamination, the Environmental Protection Administration of Taiwan had promulgated the Soil and Groundwater Pollution Remediation Law in 2000. Land use rights of contaminant sites are strictly restricted under this law. The land owners, thus, often ask engineers to complete remediation events within very short period. Multi-phase extraction (MPE) is a rapidly emerging in-situ remediation technology with good performance on recovery of LNAPL. However, the efficiency estimation of MPE has usually been bases on engineer experience. In this study, numerical simulations had been performed with TMVOC, in order to assess the influence of well location, well bottom pressure and porosity on the efficiency of MPE. A hypothesized aquifer of sandy soil had been assumed to receive gasoline from oil spill from tank farms and thus to be remediated with MPE. The results of simulation show that the extraction well placed 10 m downstream from spill point gives the best efficiency. Efficiency decreases as the extraction well was located away from that particular point, either upstream or downstream. Furthermore, the aquifer of which a higher porosity has been assumed shows a better efficiency than one with lower porosity. In addition, the efficiency of extraction exhibits a positive correlation with the difference between well bottom pressure and atmospheric pressure. Nevertheless, the benefit of high negative pressure is obvious only in the earlier few months after which the benefit decreases with time.