Abstract

Non Aqueous Phase Liquids, such as chlorinated solvents (e.g. PCE , TCE), impose a severe threat to the ground water environment and reported health risk to humans via the food chain. Many researchers have analysed and estimated the dissolution mechanisms of spilled NAP Ls into ground water and the transport processes of the dissolved compounds. However, there is still a lack of understanding on governing mechanisms and assessment tools for the prediction of potential risk. Also, the effect of field heterogeneity on the dissolution processes has not been thoroughly investigated.

The present research addresses the need for understanding further the role of heterogeneity in the transport and dissolution of hazardous NAPL compounds in groundwater, based on the NAPL mass flux approach. An analytical solution of the simplified problem is provided and compared to experimental and numerical data. An up-scaled form of the model is shown and compared to numerical results of aquifer scale. Taking into consideration dispersion, rate limiting and flow by-passing effects, a quantitative assessment tool is formulated for evaluating the risk of NAPL contamination. The results show that NAPL spill architecture is a determinant parameter that controls contaminant mass flux through subsurface. In addition, the velocity field around and through the source zone of contamination has a major effect on NAPL mass flux, and is considered to play a vital role in the degree of contaminant discharge in realistic subsurface environments, irrespective of whether the dissolution process is rate limited or not. Evidence from analytical, numerical and experimental results suggests that the reduction of contaminant mass flux is mainly attributed to the effects of bypassing through regions of contrasting contaminant saturation.