Influence of Sedimentary Bedding on Reactive Transport Parameters under Unsaturated Conditions

Abstract

Moisture and contaminant transport in partially saturated, heterogeneous, layered sediments is typically anisotropic. Solute transport parameters, including dispersivity and the adsorption coefficient, and the modeled concentration of reactive minerals may depend on the direction of flow with respect to sedimentary layering. Reaction rates, in contrast, should be independent of flow direction. We determined the influence of flow direction on transport parameters for nonreactive (Br−) and reactive (cobalt ethylenediaminetetraacetic acid [Co(II)EDTA2−]) solutes under partially saturated conditions by imposing flow either parallel to or across sedimentary bedding in 11 intact sediment cores of various textures. Higher dispersivity of nonreactive tracers in parallel‐bed cores suggested fluid channeling through permeable layers, while low‐conductivity layers dampened channeling in cross‐bed samples. Rates of transformation of Co(II)EDTA2− into Co(III)EDTA− and of disassociation of Co2+ and EDTA4− were modeled assuming that the reaction rates were independent of the flow direction. The concentration of Mn oxides that was responsible for the transformation reaction was dependent on the flow direction, which governed the extent of contact between the solution and the solid phase. Similarly, the adsorption constants of Co(II)EDTA2− and Co(III)EDTA− were dependent on the flow direction but were also unique for each experiment. The modeled concentration of reactive minerals was the most sensitive parameter describing the reaction and transformation of Co(II)EDTA2−

Mercury Remediation Technology Development for Lower East Fork Poplar Creek—FY 2017 Progress Report

“…This finding clearly suggests that diffusion was not very important. Although the degree of dispersion and the separation of the multiple nonreactive tracers suggests that diffusion was more important in the intact soils than in the sieved soils, the magnitude of these effects was minor compared with observations in more structured soils (Reedy et al 1996;Mayes et al 2003Mayes et al , 2009. Overall, these findings are consistent with the lack of response to flow interruption.…”

“…In comparison, the intact soils might exhibit a slower approach to equilibrium because diffusion can limit the rate of transport into and out of the aggregates. Researchers applied several tests-analysis of dispersion in breakthrough curves of nonreactive tracers, multiple nonreactive tracers with different diffusion coefficients, and flow interruption (Mayes et al 2003;Mayes et al 2009;Reedy et al 1996).…”

Comparison of Average and Point Capillary Pressure–Saturation Functions Determined by Steady‐State Centrifugation

“…Th e Hanford samples consisted of both disturbed and undisturbed sediments. Th e disturbed sediments were the same as the fi ne-to medium-grained sand used in the fl ow and transport experiments reported by Pace et al (2003) and Mayes et al (2009) and referred to as HL (the same notation is used here). Th e other Hanford samples were all undisturbed cores excavated in August 2007 from an outcrop exposing three distinct sandy sedimentary layers (an upper coarse layer, UCL, a middle fi ne layer, MFL, and a lower coarse layer, LCL) at the ERDF.…”