Geologic heterogeneity occurs over a range of spatial scales, each with the potential to influence subsurface flow and solute transport. Understanding such controls is fundamental to developing accurate groundwater models for the purpose of understanding contaminant transport and the cause of plume tailing. In response to active remediation strategies, such as pump and treat, chlorinated volatile organic compound (CVOC) plumes often exhibit a relatively short period of rapid mass and concentration decline followed by an extended period of sustained concentration or "tail." The well-established general interpretation is that more permeable zones of the aquifer are rapidly flushed while mass remaining in low hydraulic conductivity (K) zones diffuses slowly into the well-flushed regions. However, the fundamental mechanisms controlling slow mass release, particularly the interplay between mass stored due to sorption and "unsorbed" mass stored within low K regions, are not well understood.

The objective of this project is to systematically evaluate the relative impacts of K and sorption heterogeneity on CVOC mass storage, mass removal, and concentration reduction in sedimentary aquifers. Two types of geochemical heterogeneity will be explored: (1) the larger scale or spatial distribution of sorption and (2) the impact of (sub)grain-scale heterogeneity in sedimentary carbonaceous matter that results in sorption isotherm nonlinearity and concentration-dependent transport.

The technical approach will integrate laboratory experiments, field mapping, and numerical simulations in a multiscale approach to elucidate fundamental rate controlling processes through five tasks. These tasks will (1) determine retarded CVOC diffusion using high sorbing, low carbon content aquifer lithocomponents and aquitard material to evaluate the impact of nonlinear sorption at the (sub)grain scale; (2) map lithofacies at two outcrop analog field sites to provide an authentic geologic framework to constrain the spatial distributions of both K and sorption heterogeneity; (3) "upscale" the results of laboratory studies to assess the role of intragranular diffusion and sorption processes on contaminant tailing through numerical experiments; (4) quantify the impacts of sorption and K spatial heterogeneity on tailing using high resolution, stratigraphically realistic systems; and (5) integrate findings from the previous tasks along with selected large-scale multiprocess simulations, which will be used to populate a practical decision matrix to aid practitioners in site assessments and remedy planning. Contamination history, including release duration and contaminant concentration, will be an important variable in all the transport work.

This project will better define the conditions employed in nonlinear sorption for CVOC plumes and the effect of coarse sedimentary lithocomponents on mass storage and tailing, providing a fundamental understanding of the processes controlling mass storage and release at the grain and subgrain scale to the aquifer scale. Results will be summarized in a decision matrix that will enable site managers to identify potential sources of long-term contamination. (Project Completion - 2023)

Maghrebi, M., I. Jankovic, R.M. Allen-King, A.J. Rabideau, I. Kalinovich, and G.S. Weissmann. 2014. Impacts of Transport Mechanisms and Plume History on Tailing of Sorbing Plumes in Heterogeneous Porous Formations. Advances in Water Resources, 73:123-133. doi.org/10.1016/j.advwatres.2014.07.007.

Maghrebi, M., I. Jankovic, A. Fiori, and G. Dagan. 2013. Effective Retardation Factor for Transport of Reactive Solutes in Highly Heterogeneous Porous Formations. Water Resources Research, 49(12):8600-8604. doi.org/10.1002/2013WR014429.

Maghrebi, M., I. Jankovic, G.S. Weissmann, L.S. Matott, R.M. Allen-King, and A.J. Rabideau. 2015. Contaminant Tailing in Highly Heterogeneous Porous Formations: Sensitivity on Model Selection and Material Properties. Journal of Hydrology, 531:149-160. doi.org/10.1016/j.jhydrol.2015.07.015.

Matott, L.S., Z. Jiang, A.J. Rabideau, and R.M. Allen-King. 2015. Isotherm Ranking and Selection Using Thirteen Literature Datasets Involving Hydrophobic Organic Compounds. Journal of Contaminant Hydrology, 177:93-106. doi.org/10.1016/j.jconhyd.2015.03.011.

Matott, L.S., A. Singh, and A.J. Rabideau. 2017. Parameterizing Sorption Isotherms Using a Hybrid Global-Local Fitting Procedure. Journal of Contaminant Hydrology, 200:35-48. doi.org/10.1016/j.jconhyd.2017.03.006.

Pickel, A., J.D. Frechette, A. Comunian, and G.S. Weissmann. 2015. Building a Training Image with Digital Outcrop Models. Journal of Hydrology, 531:53-61. doi.org/10.1016/j.jhydrol.2015.08.049.

Singh, A., R.M. Allen-King, and A.J. Rabideau. 2014. Groundwater Transport Modeling with Nonlinear Sorption and Intraparticle Diffusion. Advances in Water Resources, 70:12-23. doi.org/10.1016/j.advwatres.2014.04.010.

Weissmann, G.S., A. Pickel, K.C. McNamara, J.D. Frechette, I. Kalinovich, R.M. Allen-King, and I. Jankovic. 2015. Characterization and Quantification of Aquifer Heterogeneity Using Outcrop Analogs at the Canadian Forces Base Borden, Ontario, Canada. Geological Society of America Bulletin, 127(7-8):1021-1035. doi.org/10.1130/B31193.1.

Barbarossa, V. 2015. A Study of Trichloroethylene (TCE) Release Rates from Borden, Ontario Aquifer Sediments through Numerical Modeling (Master’s Thesis). State University of New York at Buffalo. https://www.proquest.com/dissertations-theses/study-trichloroethylene-tce-release-rates-borden/docview/1733672143/se-2?accountid=14169 

Maghrebi, M. 2015. Numerical Modeling of Contaminant Tailing in Physically and Chemically Heterogeneous Formations (Ph.D. Dissertation). State University of New York at Buffalo. https://www.proquest.com/dissertations-theses/numerical-modeling-contaminant-tailing-physically/docview/1658211112/se-2?accountid=14169

Merlo, A. 2015. A Study of Trichloroethylene (TCE) Release Rates from Borden, Ontario Aquifer Sediments through Intermittent Purging (Master’s Thesis). State University of New York at Buffalo. https://www.proquest.com/dissertations-theses/study-trichloroethylene-tce-release-rate-borden/docview/1733235234/se-2?accountid=14169

Munger, Z. W. 2012. Modeling Nonlinear Sorption of Trichloroethene in Natural Sorbents with Kerogen (Master’s Thesis). State University of New York at Buffalo. https://www.proquest.com/dissertations-theses/modeling-nonlinear-sorption-trichloroethene/docview/1112252734/se-2?accountid=14169

Singh, A. 2013. The Effect of Nonideal Sorption on Contaminant Transport in Groundwater and Vapor: Statistical and Modeling Tools (Ph.D. Dissertation). State University of New York at Buffalo. https://www.proquest.com/dissertations-theses/effect-nonideal-sorption-on-contaminant-transport/docview/1317095320/se-2