Detailed knowledge of the groundwater flow regime is a pre-condition for understanding the geochemicalprocesses in the subsurface. Identification of recharge and discharge areas and mechanisms, as well as flowlines, are essential for delineating trends in geochemical evolution?including changes in As concentrations,and to quantify reaction rates. The Hydrogeology Support Core will provide the tools and expertise forcollection and analysis of a broad range of hydrogeological data for Projects 5, 6 and 7, and the ResearchTranslation Core. The following types of data will be obtained and interpreted: 1) longitude, latitude, andelevation; 2) stratigraphy of the aquifer from core samples and drill cuttings, hydraulic head, conductivity,storativity, and porosity data; 3) geophysical data, primarily frequency EM conductivity, and down-hole logsof resistivity, gamma, flow velocity, and televiewer images; and 4) tracer data (SF6, CH4, Br, 3H/3He, 13C, 14C,13C, 18O, 2H). The equipment to be provided and operated by the Core include: 1) Multilevel wells, 2) aGeoprobe and other push coring and sampling devices, 3) in situ groundwater monitoring devices, 4) afrequency EM conductivity system, 5) various down-hole logging tools, 6) sample preparation systems forisotopic analyses, 7) gas chromatographs, and 8) noble gas mass spectrometers. Carbon (13C, 14C) andwater isotope (18O,2H) analyses will be performed by commercial laboratories. The Core will provide supportfor the various push/pull and forced gradient in situ experiments, with a focus on characterizing the zone ofinjections and tracking injected fluids with tracers. Tracer data will also be used to derive groundwaterresidence times for a range of time scales (from months to 10,000s of years), to identify recharge anddischarge areas and mechanisms and to track groundwater mixing in the aquifers. The research supportcore will provide three-dimensional modeling capabilities for groundwater flow and reactive transportsimulations. We will use hydraulic and tracer data as calibration targets for the model groundwater flow andtransport model, which will then provide the baseline for reactive transport modeling aided withbiogeochemical data obtained by the Biogeochemistry Core.
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