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Please cite this article as: Cai, Z., Ofterdinger, U., Analysis of groundwater-level response to rainfall and estimation of annual recharge in fractured hard rock aquifers, NW Ireland, Journal of Hydrology (2016), doi: http://dx.doi.org/ 10. 1016/j.jhydrol.2016.01.066 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Despite fractured hard rock aquifers underlying over 65% of Ireland, knowledge of key processes 7 controlling groundwater recharge in these bedrock systems is inadequately constrained. In this study, 8 we examined 19 groundwater-level hydrographs from two Irish hillslope sites underlain by hard rock 9 aquifers. Water-level time-series in clustered monitoring wells completed at the subsoil, soil/bedrock 10 interface, shallow and deep bedrocks were continuously monitored hourly over two hydrological 11 years. Correlation methods were applied to investigate groundwater-level response to rainfall, as well 12 as its seasonal variations. The results reveal that the direct groundwater recharge to the shallow and the relationship between the rainfall intensity and water-table rise reveal that the low rainfall intensity 22 group (≤ 1 mm/h) has greater impact on the groundwater recharge rate than other groups (> 1 mm/h). 23This study shows that the combination of the time-series analysis and the water-table fluctuation 24 method could be an useful approach to investigate groundwater recharge in fractured hard rock 25 aquifers in Ireland.

In highly heterogeneous aquifer systems, conceptualization of regional groundwater flow models frequently results in the generalization or negligence of aquifer heterogeneities, both of which may result in erroneous model outputs. The calculation of equivalence related to hydrogeological parameters and applied to upscaling provides a means of accounting for measurement scale information but at regional scale. In this study, the Permo-Triassic Lagan Valley strategic aquifer in Northern Ireland is observed to be heterogeneous, if not discontinuous, due to subvertical trending low-permeability Tertiary dolerite dykes. Interpretation of ground and aerial magnetic surveys produces a deterministic solution to dyke locations. By measuring relative permeabilities of both the dykes and the sedimentary host rock, equivalent directional permeabilities, that determine anisotropy calculated as a function of dyke density, are obtained. This provides parameters for larger scale equivalent blocks, which can be directly imported to numerical groundwater flow models. Different conceptual models with different degrees of upscaling are numerically tested and results compared to regional flow observations. Simulation results show that the upscaled permeabilities from geophysical data allow one to properly account for the observed spatial variations of groundwater flow, without requiring artificial distribution of aquifer properties. It is also found that an intermediate degree of upscaling, between accounting for mapped field-scale dykes and accounting for one regional anisotropy value (maximum upscaling) provides results the closest to the observations at the regional scale.

Potentially toxic elements (PTEs) including nickel and chromium are often present in soils overlying basalt at concentrations above regulatory guidance values due to the presence of these elements in underlying geology. Oral bioaccessibility testing allows the risk posed by PTEs to human health to be assessed, however bioaccessibility is controlled by factors including mineralogy, particle size, solid phase speciation and encapsulation. X-ray diffraction (XRD) was used to characterise the mineralogy of 12 soil samples overlying Palaeogene basalt lavas in Northern Ireland and non specific sequential extraction coupled with chemometric analysis was used to determine the distribution of elements amongst soil components in 3 of these samples. The data obtained were related to total concentration and oral bioaccessible concentration to determine whether a relationship exists between the overall concentrations of PTEs, their bioaccessibility and the soils mineralogy and geochemistry.Gastric phase bioaccessible fraction (BAF%) ranged from 0.4% to 5.4% for chromium in soils overlying basalt and bioaccessible and total chromium concentrations are positively correlated. In contrast the range of gastric phase BAF for nickel was greater (1.4 to 43.8%), while no significant correlation was observed between bioaccessible and total nickel concentrations. However nickel BAF was inversely correlated with total concentration. Solid phase fractionation information showed that bioaccessible nickel was associated with calcium carbonate, aluminum oxide, iron oxide and clay related components, while bioaccessible chromium was associated with clay related components. This suggests that weathering significantly affects nickel bioaccessibility, but does not have the same effect on the bioaccessibility of chromium. Suggested keywordsoral bioaccessibility, nickel, chromium, basalt, sequential extraction, solid phase distribution 3

Natural gas extracted from hydraulically fractured shale formations potentially has a big impact on the global energy landscape. However, there are concerns of potential environmental impacts of hydraulic fracturing of the shale formations, particularly those related to water quality. To evaluate the potential impact of hydraulically fractured shale on overlying aquifers, we conduct realizations of numerical modeling simulations to assess fluid flow and chloride transport from a synthetic Bowland Shale over a period of 11,000 years. The synthetic fractured shale was represented by a three-dimensional discrete fracture model that was developed by using the data from a Bowland Shale gas exploration in Lancashire, UK. Chloride mass exchange between fractures and the rock matrix was fully accounted for in the model. The assessment was carried out to investigate fluid and chloride mass fluxes before, during, and after hydraulic fracturing of the Bowland Shale. Impacts of the upward fracture height and aperture, as well as hydraulic conductivity of the multilayered bedrock system, are also included this assessment. This modeling revealed that the hydraulically fractured Bowland Shale is unlikely to pose a risk to its overlying groundwater quality when the induced fracture aperture is 200 mm. With the fracture aperture 1000 mm, the upward chloride flux becomes very sensitive to the upward fracture height growth and hydraulic conductivity of the multilayered bedrock system. In the extremely unlikely event of the upward fracture growth directly connecting the shale formation to the overlying Sherwood Sandstone aquifer with the fracture aperture 1000 mm, the upward chloride mass flux could potentially pose risks to the overlying aquifer in 100 years. The model study also revealed that the upward mass flux is significantly intercepted by the horizontal mass flux within a high permeable layer between the Bowland Shale and its overlying aquifers, reducing further upward flux toward the overlying aquifers.

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