加油站柴油洩漏與抽取模擬

Abstract

國內自開放民營加油站設立後，加油站的數量大量增加。近年來土壤與地下水污染的控制與整治場址中，加油站所佔的比例亦逐漸提升。柴油相對於汽油而言，其揮發性較低，可能導致其滲漏監測較汽油困難。因此，國內柴油污染場址的污染量與程度均較汽油污染嚴重的現象。在國內絕大多數加油站僅利用測漏管進行土壤氣體監測以評估油品滲漏的監測效果，但仍是難以即時掌握油品滲漏的發生時機與污染程度。此外，在油品的污染傳輸與整治模擬方面，也因柴油的餾分較廣且成分複雜，使得在油品污染相關的數值模擬幾乎都以汽油的滲漏與整治為主。本研究將以柴油在加油站地下油槽洩漏為研究對象，利用TMVOC針對多成分柴油精確地模擬柴油滲漏與抽取狀況，以土壤氣體與地下水中柴油與其成分之濃度來評估監測有效性。由模擬結果顯示出柴油滲漏點位於非飽和區時，氣體監測會優於以地下水監測井監測地下水體；當滲漏點位於地下水面下，氣體監測和地下水體監測均難以偵測到柴油污染。土壤氣體及水中濃度監測效果方面，高滲透係數會比低滲透係數佳，地下水位越深其監測效果越差。抽取應用於柴油整治，在高滲透係數及孔隙率會有較高移除率。在相較同樣的汽油污染情況下，監測井設置在距離洩漏點3 m範圍內，可偵測到一定程度之柴油或汽油油氣濃度變化。但汽油揮發性高，其監測井之氣體監測會比柴油較早達到氣體濃度標準，而汽油洩漏至一年時之油氣濃度幾乎為柴油油氣濃度的數十倍。在地下水含苯濃度監測方面，汽油也明顯比柴油優越許多。

The number of filling stations in Taiwan increased dramatically after the government lifted the ban on private ownership. However, the filling stations account for a large proportion of the soil and groundwater pollution sites. Most filling stations in Taiwan use soil vapor monitoring to monitor leakage of underground storage tanks and pipelines. Since the vapor pressure of diesel fuel is much lower than that of gasoline, diesel fuel leakage is more difficult to detect. As a result, the amount and extent of diesel fuel pollution could be more serious. On the other hand, the composition of diesel fuel is much more complicated than that of gasoline such that the assumption of its composition for multi-components simulation becomes more difficult. Therefore, almost all of numerical simulations of LNAPL leakage and remediation has been focused on gasoline. This study performed multi-component transport simulation of diesel fuel leakage and pumping by TMVOC to evaluate the effectiveness of monitoring. The results of simulation show that diesel fuel leakage in the unsaturated zone, gas monitoring will be better than groundwater monitoring. When leakage located on the below the groundwater, the gas and groundwater monitoring are difficult to detect diesel fuel contamination. The monitoring soil vapor and contaminants in groundwater is more effective in soil with higher permeability. While the grounswater table is low, the monitoring soil vapor and contaminants in groundwater is more effective in soil with higher the grounswater table. Diesel fuel pumping used has a higher removal rate in the soil with high permeability and porosity soil. Compared to the same in the case of gasoline contamination, the monitoring soil vapor can detect a certain degree of diesel or gasoline hydrocarbon concentration which set up at a distance of 3 m leak point range. Because gasoline volatility is high, the monitoring soil vapor will be reached standards earlier than diesel gas concentration.