Hydrophobic organic contaminant transport property heterogeneity in the B orden A quifer

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. VOC Kd and k correlated to facies define their heterogeneity Only 20% of the aquifer volume accounts for 50% of aquifer sorption Coarse‐grained units have greater sorption capacity than fine‐grained units