Abstract

Two key problems in studying the interaction of various contaminants with soils in environmental remediation problems are (1) the monitoring of the contaminant evolution in the soil matrix and (2) the understanding of soil/fluid interactions. To study these two problems we have developed a combination of routine analysis (density and grain size analysis techniques) and novel instrumental monitoring techniques. These monitoring techniques are X-ray computer assisted tomography (CAT) scanning, nuclear magnetic resonance (NMR) and X-ray diffraction (XRD). This paper shows how these methods can be combined to study contaminant interaction with soil, as well as the identification of different states of an aqueous phase in the soil pore space. From this combination of techniques, we have been able to monitor qualitative changes in the soil matrix induced by the presence of an aqueous phase and a contaminant phase. Our results indicate that the contaminant (that happened to be a pesticide in these tests) interacts with the soil matrix and reduces the ability of water to interact with the soil.

Introduction

Environmental-contaminant and soil interaction phenomena are of great importance in remediation problems, and have received a large amount of attention in the literaturel. The understanding of these interactions will allow for a better modeling of contaminant transport, biodegradability, and toxicity. To study the interactions of a contaminant with a given soil, one must first have a full understanding of the soil properties (stationary phase). The reason for this is that soils are of a complex heterogeneous nature2 In this study, we have used the Armadale soil (also known as Mossy Point soil), which has been extensively studied at the University of Calgary1,3,12. This soil has been analyzed in its native state both chemically and physically. The chemical analysis consisted of conventional wet chemistry and XRD for mineral determination. The physical analysis consisted of density and grain size distribution measurements. The next step was to study the water/soil interaction with water being considered as a single mobile phase. To do this type of analysis, the preferred technology must be non-destructive and must have the ability to perform time-controlled measurements. There are two techniques that are well suited for this work and have the above properties (1) NMR imaging (MRI) and/or NMR relaxometry (2) CAT scanning. The imaging via MRI of water in soils has been shown to be feasible if the soil is low in iron (especially ferromagnetic iron) and other paramagnetic species4,5. These same conditions hold for any type of NMR study on soils. In parallel to NMR and CAT scanning testing, capillary pressure measurements were also made. The final step was to measure contaminant properties in soil in the presence of water.

In this paper, a high concentration pesticide solution was used as the contaminant. The developed methodology is presented through a series of preliminary tests. The results of these tests are presented in terms of the interaction of a contaminant with soil under different water saturation conditions.

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