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Water level and hydrochemical parameters from groundwater monitoring wells can be effectively used for interpreting changes in the groundwater system when aquifers are appropriately characterized. Groundwater levels in six paired monitoring wells of alluvial and sedimentary bedrock aquifers in the Gyeongju area, southeastern South Korea were analyzed to evaluate their abrupt changes due to earthquakes, and to identify the differences in responses of groundwater level to the earthquakes and precipitation based on confining conditions of the aquifers, which was verified by principal component analysis (PCA) of water level and major ion concentrations, and lithologic logs. When earthquakes occurred in 2016 near the study area, the different responses of groundwater level to the earthquakes were detected in the two well pairs under confined condition. In particular, wells with single screened interval showed dissimilar patterns in water level fluctuation and hydrochemical water type. The PCA results of groundwater levels and hydrochemical parameters also substantiated the different aquifer types in the two well pairs. These results suggest that groundwater monitoring data should be acquired and analyzed considering the well design and aquifer type to properly evaluate impacts of earthquakes on the aquifers, which can contribute to establishment of earthquake monitoring systems.

This study uses a combination of conventional and high resolution field and laboratory methods to investigate processes causing attenuation of a hexavalent chromium (Cr(VI)) plume in sedimentary bedrock at a former industrial facility. Groundwater plume Cr(VI) concentrations decline by more than three orders of magnitude over a 900 m distance down gradient from the site. Internal plume concentrations generally exhibit stable to declining trends due to diffusive and reactive transport in the low permeability matrix as fluxes from the contamination source dissipate due to natural depletion processes and active remediation efforts. The strong attenuation is attributed to diffusion from mobile groundwater in fractures to immobile porewater in the rock matrix, and reactions causing transformation of aqueous Cr(VI) to low-solubility Cr(III) precipitates, confirmed by high spatial resolution rock matrix contaminant concentrations and comparisons with groundwater concentrations from multi-level sampling within the plume. Field characterization data for the fracture network and matrix properties were used to inform 2-D discrete-fracture matrix (DFM) numerical model simulations that quantify attenuation due to diffusion and reaction processes, which show consistency with field datasets, and provide insights regarding future plume conditions. The combination of field, laboratory and modeling evidence demonstrates effects of matrix diffusion and reaction processes causing strong attenuation of a Cr(VI) plume in a sedimentary bedrock aquifer. This approach has important implications for characterization of sites with Cr(VI) contamination for improved site conceptual models and remediation decision-making.

Disposal of highly radioactive waste (HLW) can be environmentally acceptable if radionuclides are kept isolated from the groundwater, which has inspired planners of repositories to work out multibarrier concepts that postulate defined functions of the host rock and engineered waste confinements. Assessment of the role of the host rock involves groundwater flow modelling and rock mechanical analysis, which are both highly speculative and ignore future changes in rock structure, stress conditions, and groundwater flow. Widening the perspective by considering the integrated physical performance of interacting geological strata respecting groundwater flow conditions can provide excellent isolation of HLW with a minimum of engineered barriers as illustrated by the principle of very deep boreholes (VDH) for which the very high salt content of deep water is the primary barrier by maintaining possibly contaminated groundwater at depth. Such isolation of groundwater regimes can also be obtained by constructing repositories in crystalline rock covered by clay-containing sedimentary rock in regions with no or very low hydraulic gradients, particularly if the two principles are combined. The paper describes a possible case of this type, showing that effective isolation of HLW in repositories of commonly discussed types, KBS-3H and VDH, can be achieved under present and foreseeable climatic conditions. The paper compares the short- and long-term functions of repositories located at the southern end of the Swedish island Gotland, being an example of desired geological conditions that are found also in other parts of Sweden and in Lithuania, Germany, Holland and the UK. Here, 500 m of sediment rock series cover gneiss bedrock in which a KBS-3H repository of SKB-type can be built under virtually “dry” conditions because of the tightness of the overlying sedimentary rock and lack of hydraulic gradients in the crystalline rock. Shafts leading down from the ground surface to the repository level are constructed by use of freezing technique and lined with low-pH concrete before installation of waste after which they have to be sealed with expanding clay. Use of initially largely water-saturated clay provides suitable physical properties of the embedment of waste containers. Alternatively, a VDH repository consisting of a number of steep 4 km deep boreholes with about 800 mm diameter can be driven for installing waste below 2 km depth, leaving the upper 2 km for sealing with clay. The geological conditions, which are also believed to provide acceptable rock pressure conditions for construction of a KBS-3H repository at about 600 m depth, are believed to be suitable for the construction and short- and long-term performance of either repository type. Upprättat; 2016; 20150726 (svek)

There is growing concern in Prince Edward Island as groundwater nitrate concentrations in the bedrock aquifer have increased since the mid-1980s due to intensive agriculture, with associated ecological impacts evidenced by surface water eutrophication. While, agricultural beneficial management practices have been implemented, subsurface heterogeneity and matrix diffusion processes appears to be limiting their effectiveness. The objective of this study was to quantify nitrate concentrations in lower K zones and hydrogeochemical influence on concentration via porewater analysis of discrete samples from cores, and application of multi-level systems for high-resolution spatial and temporal monitoring of hydraulic head and hydrochemistry. Results show elevated nitrate persists in the shallow subsurface, suggesting minimal denitrification due to lack of electron donors / oxygenated conditions and matrix storage effects. Such data improves conceptual models of nitrate migration and fate in sedimentary bedrock aquifers to allow adjustments to agricultural practices that can meet source water protection goals. Canadian Water Network, University Consortium for Field-Focused Groundwater Contamination Research, Natural Sciences and Engineering Research Council of Canada Industrial Research Chair (2011-2012), Agriculture and Agri-Food Canada, Cavendish Farms, PEI Department of Environmental, Labour and Justice, PEI Department of Agriculture and Forestry, the City of Charlottetown, Nova Scotia Environment, and PEI Potato Board