水位波動對地下儲油槽洩漏之影響

Abstract

加油站地下儲槽滲漏的潛勢隨著使用齡期而提高。為了避免油品滲漏導致其中的有毒物質污染土壤與地下水，必須針對地下儲槽進行監測以及早預警。在監測方法中，土壤氣體監測和地下水監測可以直接偵測地下儲槽洩漏出的物質。因洩漏出的有機化合物由流動與擴散傳輸，故其傳輸路徑可能受到地下儲槽與管線和地下水位升降的影響。再者，土壤氣體監測和地下水監測的有效性也會因之而異。本研究以軟體TMVOC模擬儲槽洩漏以評估地下水位變動對監測效果的影響。結果發現土壤透水係數(Kw)較高與孔隙率(n)較小時，由於污染團傳輸速度較快，會提高測漏管的監測效率。且隨著距離洩漏點越遠，效果越明顯。遲滯現象於變動水位模擬的結果雖然有影響，其效果並沒有很明顯，可能是因為洩漏量較少的緣故。

The potential of leakage from underground storage tanks (USTs) of gasoline stations increases with its service life. In order to avoid serious pollution caused by the dissolution of toxic constituents in LNAPLs (Light non-aqueous phase liquids), monitoring measures are employed to provide early warning. Among the monitoring methods, soil gas and groundwater monitoring detect the leaked product directly. The pathway of leaked gasoline flows and diffuses and thus, in turn the effectiveness of soil gas and groundwater monitoring, may be affected by the existence of USTs of gasoline station and the fluctuation of groundwater table such that the effectiveness of soil vapor and groundwater monitoring is affected as a result. In this study, numerical simulation with the software TMVOC was performed in order to assess the effectiveness of soil vapor and groundwater monitoring. The results show that when the leakage occurs at a greater depth, both soil vapor and groundwater monitoring are less effective. Soil vapor monitoring can detect leakage earlier than groundwater monitoring in general; but groundwater monitoring is more effective when the distance from leakage increases. The VOC vapor and groundwater migrate faster when the hydraulic conductivity is higher and porosity is smaller such that the monitoring is more effective. The influence of hysteresis of soil water characteristic curve on the sensitivity of soil vapor and groundwater monitoring is also studied but was found insignificant.