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Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Although offshore freshened groundwater (OFG) systems have been documented in numerous continental margins worldwide, their geometry, controls and emplacement dynamics remain poorly constrained. Here we integrate controlled-source electromagnetic, seismic reflection and borehole data with hydrological modelling to quantitatively characterise a previously unknown OFG system near Canterbury, New Zealand. The OFG system consists of one main, and two smaller, low salinity groundwater bodies. The main body extends up to 60 km from the coast and a seawater depth of 110 m. We attribute along-shelf variability in salinity to permeability heterogeneity due to permeable conduits and normal faults, and to recharge from rivers during sea level lowstands. A meteoric origin of the OFG and active groundwater migration from onshore are inferred. However, modelling results suggest that the majority of the OFG was emplaced via topographically-driven flow during sea level lowstands in the last 300 ka. Global volumetric estimates of OFG will be significantly revised if active margins, with steep coastal topographies like the Canterbury margin, are considered. The authors here combine a range of geophysical data, numerical modelling and borehole data to present a high resolution map of an offshore freshened groundwater system in the Canterbury Bight, New Zealand. The study shows the extensions of the offshore freshened groundwater system to be controlled by high permeability shelf sediments, buried paleochannels and onshore rivers. [ABSTRACT FROM AUTHOR]

The flow of terrestrial groundwater to the sea is an important natural component of the hydrological cycle. This process, however, does not explain the large volumes of low-salinity groundwater that are found below continental shelves. There is mounting evidence for the global occurrence of offshore fresh and brackish groundwater reserves. The potential use of these non-renewable reserves as a freshwater resource provides a clear incentive for future research. But the scope for continental shelf hydrogeology is broader and we envisage that it can contribute to the advancement of other scientific disciplines, in particular sedimentology and marine geochemistry. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Mount Simon and Lower Knox Group Formations within the Illinois Basin, USA, are being considered as targets for carbon dioxide (CO $$_2$$ ) storage. Two main concerns related to the subsurface storage process are potential leakage of CO $$_2$$ from the storage formation to the atmosphere and possible migration of CO $$_2$$ or displaced brine into underground sources of drinking water. In this study we use a numerical model to represent the migration of both CO $$_2$$ and brine in the Mount Simon Sandstone and two overlying aquifers, the shallowest of which is considered a potential source of drinking water. A vertically-integrated approach is used to model the fluid flow, leading to a stack of two-dimensional subdomains which are connected by leakage through the aquitards which separate the aquifers. Each formation is discretized into 12,103 grid cells, each $$5 \times 5\,\mathrm{{km}}$$ , and permeability and porosity vary spatially. Two vertical refinements are used for the Mount Simon Sandstone: the first represents the Mount Simon as a single layer, while the second subdivides the formation into subunits within the formation that have varying petrophysical properties. The locations and injection rates of the hypothetical injection operations are based on existing sources of CO $$_2$$ associated with power generation, ethanol production, and oil and gas refineries. A total of 250.5 million metric tons are injected at 118 sites. The injection operations are assumed to continue for 50 years. Results indicate the maximum radial extent of the CO $$_2$$ plume increased from 40 to 50 km between the single layer and multi-layer representations of the Mount Simon. Maximum average pore pressures reached 8.6 MPa and the pressure envelop extended as much as 100 km from the injection wells with significant well-well pressure interference patterns. The maximum well head pressure exceeded the fracture pressure in some cases suggesting more wells may be needed at some of the lower permeability injection sites. Brine leakage into overlying shallower units was not significant. [ABSTRACT FROM AUTHOR]