Collaborative Research on Reactive Transport: Modeling Spatial Cross-Correlation between Hydraulic and Reactive Aquifer Attributes as Determined by Sedimentary Architecture

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0538124Allen-KingCollaborative Research on Reactive Transport:Modeling Spatial Cross-Correlation between Hydraulic and ReactiveAquifer Attributes as Determined by Sedimentary ArchitectureModels for reactive mass transport require a representation of how hydraulic and reactive attributes, such as permeability (k) and the sorption distribution coefficient (Kd), vary in space. No model has yet incorporated the authentic features of the co-variability of these attributesobserved in previous, detailed field studies. This is an important limitation of reactive transport models. We hypothesize that spatial co-variability between hydraulic and reactive attributes in sedimentary deposits depends upon transitions across unit types, much as has been previously shown for spatial variability of hydraulic attributes themselves. The hypothesis is predicated on the concept that sediment erosion, transport and deposition include processes which naturally sort sediment grains and create unit types that differ in composition (mineralogy) as well as grain size.Our hypothesis is based on observations and preliminary testing using lithofacies, k, and Kd data collected for the Borden aquifer. The specific goal of the proposed project is to develop and explore a new model that represents the spatial co-variability of hydraulic and reactive attributes as a function of the hierarchical architecture of sedimentary deposits and the probabilities for transitioning within and between lithologic units across different, relevant scales. The model will represent the following relationships observed in recent field studies: (1)The point-correlation may be positive within some unit types and uncorrelated or negative within others. (2) If correlation exists, it need not be perfect. (3) The lag cross-correlation with translation across unit boundaries may be positive when transitioning across certain unit types and negative across others. (4) There can be multiple, relevant integral scales of correlation associated with the different scale of unit types within the sedimentary architecture. The activities will include developing an appropriate data set from a well-characterized field site, computing theterms of the model which represent relationships within and across hierarchical levels, and gaining an understanding of which of these terms contribute significantly to the cross-correlation at the composite scale, which is the scale at which plume spreading is observed. Once we understand which terms are significant, we will model them as a part of developing the composite model function. The project will involve collaboration among two hydrogeologists, with expertise in geochemistry and geostatistics, and a sedimentologist. Intellectual merit of the proposed activity: Interpretive computational modeling studies have not yet been able to simultaneously reproduce all aspects of nonideal transport behavior that have been observed in controlled field studies. This strongly suggests that fundamental aspects of reactive transport are not yet fully understood. We posit here that lack of proper representation of the co-variability between hydraulic and reactive attributes within theinterpretive reactive transport models is a significant limitation within such studies. The proposed project will enhance overall understanding of co-variabilty of hydraulic and reactive attributes. It will help the research community to move beyond the simplistic paradigm currently used for representing co-variability and lead to development of a well-grounded alternative model built upfrom field observations. Thus, the work we propose will have an important impact on interpretive reactive transport modeling by improving our representation of the hydraulic and reactive attributes within reactive transport models.Broader impacts resulting from the proposed activity: The broader impacts of theproject fall within two general realms: those that enhance student training through direct or indirect participation in the project and those that benefit society through realization of improved understanding of the fate of organic contaminants within sedimentary aquifers