浅层地下水氯代烃污染天然衰减速率的估算

Estimation of natural attenuation rate of chlorinate solvents contamination in shallow groundwater

天然衰减恢复技术是恢复和控制浅层地下水氯代烃污染的技术之一,如何简便获取可靠的氯代烃衰减速率常数是该技术应用的一个关键。趋势线分析方法是一种简便有效的方法,在污染羽状体稳定的条件下,通过地下水流向上至少3口监测井的资料,能够比较准确地估算出污染物的天然衰减速率常数和生物降解速率常数。某氯代烃污染典型区的应用实例研究表明,该区四氯乙烯(PCE)的天然衰减速率常数和生物降解速率常数分别为0·000925d-1和0·000537d-1,证实该区浅层地下水中的PCE存在天然生物降解,但降解速率比较缓慢。忽略吸附作用的天然衰减容量计算所得出的天然衰减速率常数明显小于实际结果,说明尽管典型区包气带及含水层介质的有机碳含量很少,但它们对PCE的吸附作用不容忽视。

Natural attenuation is one of the cost-effective techniques for the remedy or containment of chlorinated solvent contamination. How to achieve credible attenuation rates of contaminants simply would play an important role in decision-making and site management. A Trend Line Analysis （TLA） is a simple and effective method. Using this method, natural attenuation rates and specific biodegradation rates can be estimated, preferably under the steady state of the contaminant plume, by using contaminant data from at least three monitoring wells. These wells should be situated along a transect parallel to groundwater flow and as close to the een- terline of the plume as possible. A case history in a typical chlorinated solvent contaminated area shows that the natural attenuation rate and specific biodegradation rate of PCE are 0. 000 925 d^-1 and 0. 000 537 d^-1 respectively. This confirms the existence of biodegradation of PCE in this area, but the rate of biodegradation is slow. Natural attenuation rate estimated from Natural Attenuation Capacity calculation, neglecting sorption, is clearly smaller than that estimated by TLA method. The result shows that the effect of a small amount of organic carbon in the aquifer media on sorption of PCE cannot be neglected.