HR: 1340h
AN: H53E-1463    [Abstracts]
TI: Effects of Low-Conductivity Regions Near Grain-to-Grain Contacts on Early Colloid Breakthrough at the Column Scale
AU: * Ochiai, N
EM: ochiain@gmail.com
AF: Oregon State University, Dept. of Crop & Soil Science 3017 ALS Bldg., Corvallis, OR 97331, United States
AU: Dragila, M
EM: maria.dragila@oregonstate.edu
AF: Oregon State University, Dept. of Crop & Soil Science 3017 ALS Bldg., Corvallis, OR 97331, United States
AB: Effects of fluid velocity (2 to 60 m day^-1) on bulk transport of carboxylate-modified microspheres (5.0μm) was investigated using saturated sand (450μm)-packed columns and pore-scale colloid movement was observed in glass bead (3mm)-packed flow-cells. At all flow rates, the colloid peak emerged from columns approximately 0.1 pore volume earlier than the dissolved conservative tracer, suggesting a consistent pore volume from which colloids were excluded. Retention of colloids within columns increased with decreasing fluid velocity. Visualization of colloid movement in pseudo-3D pore networks did not indicate presence of preferential transport paths, as would be expected for size exclusion. Direct observation, however, revealed zones of reduced hydraulic conductivity near grain-to-grain contacts. Fewer than expected colloids entered zones of reduced conductivity and subsequently returned to faster flow streams or meandered until becoming associated with a solid-water surface. We investigate whether colloid exclusion or removal from low-conductivity regions and advection of remaining colloids in reduced pore volume can explain the observed early breakthrough of colloids.
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2007 Fall Meeting