地下水流速及介质非均质性对重非水相流体运移的影响

重非水相流体(DNAPL)在地下介质中的运移分布受多种因素影响,包括DNAPL的物化性质、泄漏速率、地下水流速和介质非均质性等。本文采用地质统计方法生成渗透率随机场刻画非均质性,运用T2VOC模拟不同流速情形下DNAPL在均质/非均质介质中的运移分布,以评估地下水流速和非均质性对DNAPL运移的影响。研究结果表明,地下水流速的增大显著促进了DNAPL的水平和垂向运移。相同流速情形下,非均质性的增强使得DNAPL污染羽分布形态及运移路径的空间变异性增强,出现明显的蓄积和绕流。当DNAPL运移的优势通道方向与流速方向相反时,水流对DNAPL水平运移的促进作用将减弱,反之,其促进作用增强。随着流速与非均质性的同时增强,水平方向上污染羽的扩散范围增大,另外水平和垂直方向上质心位置(一阶矩)及展布范围(二阶矩),污染池起始位置及其长度的空间变异离散程度增大。

Influence of groundwater flow velocity and geological heterogeneity on DNAPL migration in saturated porous media

The migration behavior and distribution of Dense Non-aqueous Phase Liquid (DNAPL) in subsur-face is influenced by lots of factors including phys icochemical properties of DNAPL,leakage rate,ground-water flow velocity, and geological heterogeneity. This study investigates the influence of flow velocity and heterogeneity on DNAPL migration in the saturated zone. Heterogeneity is described by random permeability field based on geological statistical method, and migration processes of released DNAPL at varying ground-water flow velocity are simulated using T2VOC. The results show that enhanced flow velocity promotes both the lateral and vertical migration of DNAPL. In the cases of fixed flow velocity,increased heterogeneity leads to an increased spatial variability in morphology of DNAPL plume and percolation paths. DNAPL is captured in high permeabiliy zone and bypass flow around the low permeability zone. With increased stan-dard deviation of log-permeability, the promotion effect on lateral DNAPL migration resulting from water flow is reduced when the direction of preferential pathway of DNAPL migration is opposite to water flow, inversely, the promotion effect is enhanced when these two directions are similar. The plume spread in the horizontal direction, and the spatial variability of both centroid (first moment) and variance (second moment) of plume,start position of DNAPL pool as well as pool length increase with synchronously increased flow velocity and heterogeneity.