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Abstract: The salinity of groundwater increases with depth in the Canadian Shield (up to 1.3kg/L of density). The existence of brine can be critically important for the safe geologic disposal of radioactive wastes, as dense brine can significantly retard the upward migration of radionuclides released from repositories. Static and flushing conditions of the deep brine are analyzed using a U-tube analogy model. Velocity reduction due to the presence of dense brine is derived under flushing conditions. A set of illustrative numerical simulations in a two-dimensional cross section is presented to demonstrate that dense brine can significantly influence regional groundwater flow patterns in a shield environment. It is implied from the results that (1) the existence of Shield brine can be an indicator of a hydrogeologically stable environment, (2) activities near ground surface may not perturb the stable groundwater environment in the deep brine region, and thus, (3) the deep brine region can be considered as a candidate geologic site for the safe disposal of waste. In addition to brine, other issues associated with long-term waste disposal, such as geological, glacial and seismic events, may need to be considered for the safe storage of spent nuclear fuel in a shield environment. [Copyright &y& Elsevier]

Abstract: When considering natural attenuation as a remediation strategy at a site contaminated by a light non-aqueous phase liquid (LNAPL), it is important to consider the emission of contaminants from the source zone. A quantification of source-zone emissions is essential both for comparison with down-gradient mass fluxes to provide an estimate of fractional mass flux reduction, as well as for estimating the source lifetime. Because the spatial distribution of LNAPL at a field site is strongly dependent on both the spill circumstances and the heterogeneity of the geologic materials, which can be problematic for in-situ determination, alternative methods for estimating source-zone emissions are needed. In this work, a three-dimensional multiphase flow and transport modelling approach is used to investigate the relationship between the lateral extent of an LNAPL body and the emission of contaminants to groundwater at a contaminated site. For simulations involving an LNAPL release in an aquifer comprised of heterogeneous porosity and permeability distributions that were generated geostatistically, it is shown that a simple linear relationship exists between the lateral extent of the LNAPL body in the capillary fringe and the emission to the aqueous phase. The parameters describing the relationship are found to be linear functions of the groundwater flow velocity and the vertical infiltration rate. This site-specific relationship provides a simple method to estimate contaminant emissions to groundwater at LNAPL contaminated sites. [Copyright &y& Elsevier]

• An integrated groundwater – surface water model is developed for a 2056 km2 watershed. • Sub-mesh scale topographic detail utilizes a spatially distributed parameterization. • Topographic depression storage, soil permeability, and land roughness are evaluated. • Depression storage had the strongest influence over flood peak flow reduction. • Landscape factors that promote flood mitigation also enhance groundwater recharge. Optimizing hydrologic resiliency in agricultural landscapes is critical for the sustainability of food production and ecosystem services, and optimization strategies must include a holistic understanding of the hydrologic cycle, including groundwater-surface water interactions. Here, a large-scale (2056 km2), high resolution (50–150 m), structurally complex, fully-integrated groundwater-surface water model was constructed for an agriculturally-dominated watershed in the Northern Great Plains. The sensitivity of surface water flow and groundwater conditions were examined in the context of wetland/depression water storage capacity, soil hydraulic conductivity (K s), field surface roughness (Manning's n), as well as variability in precipitation and potential evapotranspiration (PET). The model evaluation interval extended from 2010 to 2015, which included both flood and drought conditions. Results showed that stream flow rates in the watershed exhibit a larger response to 10 % changes in either precipitation or PET relative to the response associated with a 50 % change in depression storage, a 4x change in K s , or a 50 % change in n , thus highlighting the region's susceptibility to weather variability. Of the landscape parameters examined, increasing depression storage provided a greater reduction in peak flood flows than an increase in K s or n ; however, increases in all three landscape parameters contributed to flood peak mitigation as well as groundwater recharge. When model configuration approximated predevelopment (primarily native prairie) landscape conditions, simulated flood peaks were reduced by 22 to 25 %. This study presents a fully-integrated groundwater-surface water modeling framework to determine the hydrologic influences and risk mitigation value of landscape management practices. [ABSTRACT FROM AUTHOR]