Monitored Natural Attenuation Evaluation: Apparent Effects Associated with Heterogeneities in Subsurface

摘要

Monitored natural attenuation (MNA) has been accepted as a remedial alternative at contaminated facilities in the past several years. Estimation of natural attenuation rate plays a significant role in evaluating the effectiveness of MNA. However, it is made technologically challenging by the heterogeneous nature of the subsurface environment. Most field soils exhibit heterogeneities as a result of soil spatial variability and soil pore structure. The challenge in evaluating efficacy of MNA is to account adequately for both types of heterogeneities in the subsurface. Soil spatial variability in hydraulic conductivity is often inadequately represented due to insufficient data. Soil pore structure effects are often ignored or mischaracterized in delineation of a heterogeneous subsurface. In this study, a dual-domain model approach, in comparison with the single-domain model, was utilized to demonstrate the effects associated soil pore structure characterization, which contributes to an apparent natural attenuation rate (ANAR). A heterogeneous hydraulic conductivity field, generated as random functions of spatial coordinates, was used to represent soil spatial variability. The heterogeneous field was utilized to illustrate the effects of preferential flow pathways on estimation of ANAR. In addition, it was discovered that contamination source characterization affects ANAR, which, in turn, exerts an influence in MNA site management.