Analyzing the effects of ionic strength, particle size and particle characteristics on the transport mechanisms of colloids in single, saturated dolomite fractures.

Abstract

<p>A series of experiments were carried out to gain a better understanding of the mechanisms governing the transport of biological and non-biological particles through single, saturated dolomite fractures at the laboratory scale. Fracture apertures and general roughness were characterized using hydraulic and conservative solute tracer experiments.</p> <p>The effects of particle size, surface characteristics and ionic strength of carrying solution were all evaluated. Particulate material studied included MS2, <em>E. coli</em> and two sizes of carboxylated microspheres. To elucidate the effect of ionic strength on particulate transport, the ionic strength of the carrying solution was altered during each experiment. All particulate experiments were completed at a specific discharge of 15 m/day to facilitate comparisons.</p> <p>Recovery of biological particulate material was found to be much less relative to the carboxylated microspheres, even though the energy profiles predicted similar interactions with the fracture surface. This suggests that the biological surface has a significant impact on retention within the fracture. Further, altering the ionic strength of the carrying solution did not spur significant elution of additional particulate material, regardless of surface characteristics. Therefore, it was determined that retention within the secondary energy minimum was negligible under these operating conditions.</p> <p>With respect to carboxylated microspheres, increased retention was observed within the less variable fracture. This suggests that increased variability within a fracture results in increased eddying within the aperture field. This eddying effectively reduces the aperture region available for particle transport, lessening the particle/fracture interaction. Overall, while mean residence times were similar, recovery of biological particles was poorly replicated by microspheres.</p>