The Effect of Matrix Properties and Preferential Pathways on the Transport of Escherichia coli RS2-GFP in Single, Saturated, Variable-Aperture Fractures

Fractured aquifers are a relatively under-studied area of groundwater science particularly because of the heterogeneities present in fractures which make it difficult to understand and predict the transport and retention of contaminants. This research was designed to elucidate some of the factors that contribute to particle transport and retention in fractures using solute and particle tracers in a natural rock fracture and a transparent epoxy replica of that same fracture. Significantly less attachment was observed from the tracer experiments conducted in the replica fracture illustrating the large effect that matrix properties have on transport and retention of particles in fractures. The E. coli RS2-GFP tracer experiments conducted in the replica fracture show that increasing specific discharge results in increasing recovery; however, there is a critical specific discharge at which particle recovery seems to steady or slightly decrease. Images were collected of the E. coli RS2-GFP transport through the epoxy replica fracture, which capture for the first time the preferential pathways of E. coli in fractures, and also demonstrate a slight broadening of the dominant preferential pathway under increasing flow conditions. These results are instructive to the development and improvement of predictive models for particle transport in fractured aquifers.