Contaminant Transport in Fractured Chalk: Laboratory and Field Experiments

Abstract

Laboratory experiments were performed on chalk samples from Denmark and Israel to determine diffusion and distribution coefficients. Batch tests were used to define sorption isotherms for naphthalene and o-xylene. Linear sorption isotherms were observed and described with Henry-isotherms. Because of the high purity and low contents of clay minerals and organic carbon, Danish and white Israeli chalk generally have low retardation capacities. Contrarily, gray Israeli chalk, with organic carbon fractions as high as 1.092%, remarkably retards organic contaminants. The K(OC) concept is not applicable to predicting distribution coefficients based on the organic carbon content in the chalk samples. Effective diffusivities of o-xylene, naphthalene, and several artificial tracers were determined using through-diffusion experiments. Based on measured diffusion coefficients and available literature values, a chalk specific exponent of 2.36 for Archie's law was derived, allowing a satisfactory estimate of relative diffusivities in chalk. A field-scale tracer test with uranine and lithium was performed in the Negev desert (Israel) to examine the transferability of diffusivities determined on small rock samples in the laboratory. Due to low recovery rates of the tracer, a modified single fissure dispersion model was used for inverse modeling of the breakthrough curves. Resulting diffusivities deviate insignificantly from the laboratory values, which are considered to be representative for the investigated part of the aquifer and applicable in transport models.

Enhanced gas recovery with CO2 sequestration: The effect of medium heterogeneity on the dispersion of supercritical CO2–CH4

“…Rhodes et al, 2008)). While the early breakthrough of the solute at the field scale is caused by high permeability flow channels dominating at large length scale, diffusive retardation of solute plume at the pore scale may result in long residence times and is seen as prolonged tailing of the breakthrough curves (Gouze et al, 2008;Witthȕser et al, 2003). One of the main contributions of our study is to demonstrate how complex carbonate pore structures with a significant portion of pore space at the sub-micron scale can have a different impact on the transport behaviour.…”

Contaminant transfer and hydrodispersiveparameters in basaltic lava flows: artificial tracertest and implications for long-term management

“…This was attributed to the existence of slow groundwater flows that would have been identified with longer monitoring. This hypothesis was proposed by Witthüser et al [66] in a fractured chalk aquifer to explain a recovery rate of about 4% between two wells located 10 m apart.Similar explanations have been proposed in works focusing on alpine karst systemswhere some springs showed a recovery rate lower than 1% [40]. Slower flows should likely occur in a fine-grained system such as the scoriaceous layers of the aquifer (Figure 1B).…”

Comparison of modeling methods for the determination of effective porosities and diffusion coefficients in through‐diffusion tests

“…[12] The solution for the receiving cell concentration takes the form [Crank, 1975;Bradbury and Green, 1985;Skagius and Neretnieks, 1986;Witthüser et al, 2003] …”

“…[4] The application of the through-diffusion method has been well established in literature as a method for measuring the intrinsic diffusion coefficient of a porous media [Feenstra et al, 1984;Bradbury and Green, 1985;Skagius and Neretnieks, 1986;Gilling et al, 1987;Snyder, 2001;Lü and Viljanen, 2002;Witthüser et al, 2003]. In a typical through-diffusion test, two cells are separated with a porous media sample centered between the two cells.…”