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- The Unraveling Biogeochemical Pathways Challenge focuses on quantifying critical and interrelated microbial metabolic and geochemical mechanisms associated chromium in situ reductive immobilization and reoxidation. A key scientific goal is to determine if there are diagnostic biomolecular signatures indicative of important aquifer biogeochemical processes that can be used to (a) help discriminate between direct (enzymatic and indirect (abiotic) oxidation-reduction processes relevant to bioremediationand (b) to inform and constrain reactive transport models even when geochemical field measurements do not reveal all relevant processes. This Challenge is aligned with biostimulation experiments being conducted at the Hanford 100 Area.
- The Evolution of Pore Structures and Flowpaths Challenge focuses on developing a predictive understanding of feedbacks between biogeochemical transformations and flow dynamics (manifest from the pore to the field scale), the impact of such feedbacks on overall system behavior, and the discovery of diagnostic signatures of critical system transitions or "tipping points." This Challenge is aligned with and leverages on field experiments being conducted at the uranium contaminated Rifle, Colorado site by the Rifle IFRC Team.
- The Predicting Contaminant Mobility at the Plume Scale Challenge explores the impact of a migrating pH gradient and the use of a "reactive facies" concept as an organizing principle to integrate laboratory and field information about properties and mechanisms as needed, to make reliable and computationally tractable predictions of long term plume (U and iodine) mobility. This Challenge also explores the minimal but necessary level of detail required for adequate predictions of plume mobility. This Challenge is being carried in collaboration with EM-supported SRNL scientists and the Advanced Simulation Capability for Environmental Management (ASCEM) team at the Savannah F-Area.
Several crosscutting themes encourage fertilization across the SFA. Complexity, scale transitions, and multidiciplinary are scientific themes that cross-cut the Sustainable Systems SFA Challenges. Recognition of subsurface system complexity (with inherent emergent processes and feedbacks) is common to all of the SFA challenges. Each Challenge uses a hybrid approach whereby fundamental whereby fundamental processes and their interactions are explored and diagnostic (or integrative often microscopic ) signatures of system responses are identified. Scale transitions are considered in each Challenge: the Unraveling Challenge explores processes from the molecular (<10-6) to the local field scale (10-2-10 m); the Evolution Challenge from the pore to the field scale; and the Plume Challenge from the pore to the plume (>100 m) scale. Each Challenge is multidisciplinary in nature and takes advantage of integrated and recognized LBNL expertise.