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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.

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