Hydrophobic organic contaminant transport property heterogeneity in the Borden Aquifer

Abstract

We determined that the spatial heterogeneity in aquifer properties governing the reactive transport of volatile organic contaminants is defined by the arrangement of lithofacies. We measured permeability (k) and perchloroethene sorption distribution coefficient (K d ) for lithofacies that we delineated for samples from the Canadian Forces Base Borden Aquifer. We compiled existing data and collected 57 new cores to characterize a 30 m section of the aquifer near the test location of Mackay et al. (1986). The k and K d were measured for samples taken at six elevations from all cores to create a data set consisting of nearly 400 colocated measurements. Through analysis of variance (corrected for multiple comparisons), we determined that the 12 originally mapped lithofacies could be grouped into five relatively distinct chemohydrofacies that capture the variability of both transport properties. The mean of ln k by lithofacies was related to the grain size and the variance was relatively consistent. In contrast, both the mean and variance of ln K d were greater for more poorly sorted lithofacies, which were also typically more coarse-grained. Half of the aquifer sorption capacity occurred in the three highest-sorbing lithofacies but comprised only 20% of its volume. The model of the aquifer that emerged is that of discontinuous scour-fill deposits of medium sand, generally characterized by greater K d and k, within laterally extensive fine-grained to very fine-grained sands of lower K d and k. Our findings demonstrate the importance of considering source rock composition, transport, and deposition processes when constructing conceptual models of chemohydrofacies.

Characterization and quantification of aquifer heterogeneity using outcrop analogs at the Canadian Forces Base Borden, Ontario, Canada

“…1-Gravel 2-Lenticular fi ne to medium sand 3-Tabular fi ne to medium sand 4-Silt and clayey silt Note: Equivalent lithofacies described by Allen-King et al (2015) are included for comparison. The following differences were observed between lithofacies reported by Allen-King et al (2015) other possible data sources, including various types of point measurements (e.g., grain size or paleocurrent direction), geophysical data, cores, stratigraphic sections, and lithological measures, to produce an interpreted map of geologic features on the 3-D outcrop surface (Bellian et al, 2005).…”

“…However, few geologic studies have focused on the nature of the sediments that form this important aquifer at a scale (e.g., decimeter or less) appropriate for evaluating plume migration at this location (e.g., Allen-King et al, 2015). A better understanding of facies geometry and continuity will greatly improve our understanding of subsurface heterogeneity and its infl uence on these tracer tests (e.g., Ramanathan et al, 2010), and so maps that capture the fi ne-scale facies geometries in three dimensions are needed to improve modeling efforts at the Borden site and will prove useful in other studies, as well.…”

What have we learned from deterministic geostatistics at highly resolved field sites, as relevant to mass transport processes in sedimentary aquifers?

“…As explained by Kalinovich et al (2012),  is related to abundance of dark carbonate lithocomponents containing kerogen within the mineral matrix, and Y - point correlation is not uniform and varies from weak positive to weak negative among the facies types (Ritzi et al, 2013;Allen-King et al, 2015). Again, the structure common to…”

“…Details of the data sets are given in (Ritzi et al, 2013 andAllen-King et al, 2015). indicating that the approximation in equation (4) represents the sample correlation structure (i.e, the shape of the rise and the correlation range) quite well.…”

“…This included highly resolved data characterizing the sedimentary architecture in fluvial, alluvial, and lake shoreline deposits. The studies have created a body of literature studying the link between sedimentary architecture and heterogeneity in attributes such as permeability and sorptive properties (e.g., Anderson, 1989Anderson, , 1991aAnderson, , 1991bDavis et al, 1993;Davis et al, 1997;Allen-King et al, 1998;Barrash and Clemo, 2002;Divine, 2002;Guad et al, 2004;Biteman et al, 2004;Kalinovich et al, 2012;Ritzi et al, 2013;Ritzi, 2014, andAllen-King et al, 2015). In these studies, data populations were subdivided according to facies type.…”