Nano-scale Colloid Particle Transport in Variable-aperture Sandstone Rock Fracture

Fractured rock aquifers are susceptible to contamination from septic tank leakage and municipal landfills due to the high conductivity pathways associated with rock fractures. The transport of virus-sized particles in sandstone fractures has not been previously investigated. Transport tests were conducted in an artificially fractured sandstone rock block with negatively charged carboxylate-modified latex microspheres of three sizes (0.02μm, 0.10μm, 0.50μm ϕ), positively charged amine-modified microspheres (0.05μm ϕ), and a conservative solute (〖Br〗^-). The tests were performed at two specific discharges (0.35mm.s-1, and 0.95mm.s-1), two total ionic strengths (5mM, 15mM), and two ionic compositions (〖Na〗^+and 〖Ca〗^(+2)). The 0.02μm particles were retained the most. The 0.10μm particles were retained the least. The 0.05μm particles were not retained under favorable attachment conditions. Increasing the specific discharge resulted in lower particle retention. Increasing the ionic strength increased particle retention, especially for the smaller colloids. Divalent electrolytes were more effective in retaining the particles permanently.M.A.S