轻非水相液体污染源区结构的影响因素数值分析

Numerical analyses of factors affecting the LNAPL source-zone architecture

轻非水相液体(light non-aqueous phase liquid,LNPAL)在地下介质中的运移分布与残余捕获受多种因素影响和控制。LNAPL污染场地概念模型中一般视LNAPL从地表泄漏后穿过包气带至潜水面。然而地下介质的非均质性与包气带含水量的空间变异分布可形成复杂的LNAPL污染源区结构,LNAPL可能无法到达潜水面,而在毛细水带蓄积。文章基于数值模型综合分析了LNAPL泄漏量、介质非均质性与含水量空间变异分布、潜水面周期性变化等多种因素对LNAPL污染源区结构的影响。研究表明:(1)当泄漏量较大时,LNAPL可运移至潜水面;(2)当泄漏量较小时,对于上粗下细的层状非均质条件,LNAPL可能在毛细水带边缘发生蓄积,无法到达潜水面;(3)包气带中黏土透镜体并非都是LNAPL运移的阻碍,LNAPL可以穿透低含水量的黏土透镜体,只有高含水量的黏土透镜体才对LNAPL的入渗有阻碍作用;(4)潜水面周期性变化将导致污染范围扩大。

The migration behavior and entrapment of light non-aqueous phase liquid （LNAPL） in subsurface media are influenced and contMled by a variety of factors. It is generally believed that LNAPL will pass through the vadose zone and transport to the water table after surface leakage. However, the heterogeneity of the subsurface medium and the variability of water content may lead to a complex LNAPL somse-zone architecture. For example, LNAPL cannot reach the water table but accumulates in the capillary zone. In this paper, based on the numerical model, the effects of LNAPL leakage, medium heterogeneity and water content, changes in the water table on the LNAPL source-zone architecture are analysed. The results show that （ 1 ） LNAPL can transport to the water table when there is a large amount of leakage. （2） When the amount of leakage is small, LNAPL may accumulate on the edge of the capillary zone and may not reach the water table under the coarse-fine layered heterogeneous conditions. （3） The clay lens in the vadose zone is not always a hindrance to the migration of LNAPL. LNAPL can penetrate the clay lens with low water content, and only the clay lens with high water content can hinder the infiltration of LNAPL. （4） The periodic change in the water table can increase the polluted range.