以TMVOC模擬含水層中低透水性夾層對重質非水相液體污染物之傳輸與蒸汽注入整治之影響

Abstract

本研究以數值模擬軟體TMVOC探討在含水層中含低透水性夾層時，三氯乙烯(Trichloroethylene, TCE)在地下水中污染情形，藉由改變夾層透水性及位置，觀察含水層與其夾層中污染物飽和度及水溶液相濃度，接著針對不同情境加入蒸汽整治，探討夾層透水性及位置對整治期間地下含水層溫度、氣體飽和度、TCE飽和度及水溶液相濃度之影響。 模擬結果顯示在污染階段，夾層位洩漏點下方之情境下，除了在夾層上有部分的淤積外，TCE能夠進入夾層中，在夾層滲透係數為4×10-6 cm/s時，夾層內TCE飽和度為夾層滲透係數為4×10-5 cm/s時的1.5倍；而在夾層位於洩漏點下游之情境下，當污染團經過夾層時，夾層內TCE水溶液相濃度雖會上升，不過在夾層滲透係數為4×10-5 cm/s時，夾層內TCE水溶液相濃度為夾層滲透係數為4×10-6 cm/s時的400倍。 在整治階段，夾層位洩漏點下方之情境下，在夾層滲透係數為4×10-5 cm/s時，TCE純相在35天內整治完畢，不過在夾層滲透係數為4×10-6 cm/s時，需要50天左右，另外低透水性夾層會影響其上方及夾層內整治效率，夾層滲透係數為4×10-5 cm/s時，夾層內及上方均質砂土層區域分別需要100天及80天才能將TCE水溶液相濃度整治至管制標準以下，不過在夾層滲透係數為4×10-6 cm/s時，不管是在夾層內或是上方均質砂土層都只需要約40天；而在夾層位於洩漏點下游之情境下，在夾層滲透係數為4×10-6 cm/s時，夾層內水溶液相濃度整治至管制標準以下時間為滲透係數4×10-5 cm/s時的2倍。

In this study, numerical simulation had been performed with TMVOC, in order to assess the influence of low permeability zone within the aquifer when trichloroethylene (TCE) released into the ground-water system. First of all, the influence of the permeability and position of the low flow zone on the TCE saturation and the aqueous phase concentration was looked into. Then, the effect of steam injection remediation was studied by looking into the saturation of gas, TCE saturation, and the TCE aqueous phase concentration. The results of simulation show that when the low permeability zone is directly underneath the spill position, TCE did not form a pool above the low permeability zone, but rather moved into the low permeability zone. To the low flow zone, when the permeability is 4×10-6 cm/s, TCE saturation is 1.5 times more than the permeability is 4×10-5 cm/s. In the case of low flow zone is downstream of the spill location, the TCE aqueous phase concentration of the low flow zone will be raised when the plume pass by. To the low flow zone, when the permeability is 4×10-5 cm/s, aqueous phase concentration of TCE is 400 times more than the permeability is 4×10-6 cm/s. During steam injection remediation, the case of the low flow zone is underneath the spill location, the results of simulation show that NAPL phase of TCE will disappear after 35 days when the low flow zone permeability is 4×10-5 cm/s, but it takes 50 days when the low flow zone permeability is 4×10-6 cm/s. As for the aqueous phase concentration of TCE, the concentration of TCE will be remediated under the standard after 100 days and 80 days in the low flow zone and above the zone respectively when the low flow zone permeability is 4×10-6 cm/s; it only takes 40 days whatever in the low flow zone and above the zone when the low flow zone permeability is 4×10-5 cm/s. As the case of the low flow zone is downstream of the spill location. When the low flow zone permeability is 4×10-6 cm/s, it takes twice as much time to remediate aqueous phase concentration of TCE under the standard than the low flow zone permeability is 4×10-5 cm/s.