Characterization of a fluvial aquifer at a range of depths and scales: the Triassic St Bees Sandstone Formation, Cumbria, UK

Fluvial sedimentary successions represent porous media that host groundwater and geothermal resources. Additionally, they overlie crystalline rocks hosting nuclear waste repositories in rift settings. The permeability characteristics of an arenaceous fluvial succession, the Triassic St Bees Sandstone Formation in England (UK), are described, from core-plug to well-test scale up to ~1 km depth. Within such lithified successions, dissolution associated with the circulation of meteoric water results in increased permeability (K~10−1–100 m/day) to depths of at least 150 m below ground level (BGL) in aquifer systems that are subject to rapid groundwater circulation. Thus, contaminant transport is likely to occur at relatively high rates. In a deeper investigation (> 150 m depth), where the aquifer has not been subjected to rapid groundwater circulation, well-test-scale hydraulic conductivity is lower, decreasing from K~10−2 m/day at 150–400 m BGL to 10−3 m/day down-dip at ~1 km BGL, where the pore fluid is hypersaline. Here, pore-scale permeability becomes progressively dominant with increasing lithostatic load. Notably, this work investigates a sandstone aquifer of fluvial origin at investigation depths consistent with highly enthalpy geothermal reservoirs (~0.7–1.1 km). At such depths, intergranular flow dominates in unfaulted areas with only minor contribution by bedding plane fractures. However, extensional faults represent preferential flow pathways, due to presence of high connective open fractures. Therefore, such faults may (1) drive nuclear waste contaminants towards the highly permeable shallow (< 150 m BGL) zone of the aquifer, and (2) influence fluid recovery in geothermal fields

A new approach to using streambed thermal signatures to charaterise spatio-temporal patterns of transitory groundwater-surface water interactions

Despite ephemeral or intermittent streamflow occurring in the majority of the world’s river networks, the spatio-temporal dynamics of transitory groundwater-surface water interactions are poorly understood. Here we present a new method to characterise water flow in variably saturated streambeds which takes advantage of the contrast in diel thermal signatures between dry and saturated conditions. We show how this can be used to detect and characterise short-lived stream flow and groundwater-surface water interactions, first outlining the theory, and then demonstrating the technique using a novel data set from the Maules Creek catchment in NSW, Australia. Analysis of the thermal signatures illustrates that short-lived groundwater-surface water interactions are highly variable in space and time but that a distinct cycle of hydrological regimes can be defined as follows: (1) dry channel, (2) surface runoff, (3) pool-riffle sequences, (4) drying pools. The rate of subsurface redistribution of infiltrated water controls the duration of the pool-riffle sequences regime, which either leads to ephemeral or intermittent stream flow behaviour, and is governed primarily by the heterogeneity of sediments along the channel. Our new approach can be used to better understand how transitory flow regimes support dryland ecology, influence water quality variations, and control rates and spatial distributions of groundwater recharge

Fate and transport of bacteriophage in UK aquifers as surrogates for pathogenic viruses

Recent threats to groundwater quality in the UK (arising from leaking sewers and burial pits used during the recent Foot and Mouth Disease epidemic) have highlighted the need to understand the fate and transport of pathogenic viruses in the subsurface so that a robust assessment of their potential threat to environmental and public health can be made. Non-hazardous microbial tracers (phage) that mimic the movement of pathogenic microorganisms through groundwater systems are being used. Bacteriophage have good potential as surrogates to help us better understand the fate and transport of viral pathogens and are discussed here in the light of their injection as tracers into UK aquifers. Specific bacteriophages (MS2, PRD1 and φX174) that exhibit good potential as tracers and have properties similar to pathogenic viruses of interest are discussed