L. J. West

University of Leeds · School of Earth and Environment

DOC and nitrate in farmland represent key chemical species that determine the water quality in the Karst Critical Zone (KCZ). The work reported here focuses on quantifying fluxes of these species in an experimental farm site (University of Leeds Farm, UK) overlying a dolomitic karst aquifer of Permian age. In this research, the Transect Method was...

Perennial water storage in firn aquifers has been observed within the lower percolation zone of the southeast Greenland ice sheet. Spatially distributed seismic and radar observations, made ~50 km upstream of the Helheim Glacier terminus, reveal spatial variations of seismic velocity within a firn aquifer. From 1.65 to 1.8 km elevation, shear‐wave...

The Cretaceous Chalk is a very important aquifer in England, and its relatively high transmissivity derives essentially from a well-developed network of solutionally-enhanced fractures and conduits. Inspite of the importance of this aquifer, the current regulatory body (Environment Agency of England and Wales) model is unrepresentative of the aquif...

Subglacial water influences the dynamics of ice masses. The state of subglacial pore water, whether liquid or frozen, is associated with differences in electrical resistivity that span several orders of magnitude, hence liquid water can be inferred from electrical resistivity depth profiles. Such profiles can be obtained from inversions of time dom...

Viruses and bacteria which are characterized by finite lives in the subsurface are rapidly transported via fractures and cavities in fractured and karst aquifers. Here, we demonstrate how the coupling of a robust outcrop characterization and hydrogeophysical borehole testing is essential for prediction of contaminant velocities and hence wellhead p...

Fluvio-aeolian sedimentary successions host groundwater aquifers at shallow depths (<~0.15 km), which overlie geothermal and shale-gas reservoirs, and nuclear waste repositories at intermediate depths (~0.15–2.0 km). Additionally, such deposits represent petroleum reservoirs at greater depths (~2.0–4.0 km). The need to improve conceptual understand...

Fast ice flow is associated with the deformation of subglacial sediment. Seismic shear velocities, Vs, increase with the rigidity of material and hence can be used to distinguish soft sediment from hard bedrock substrates. Depth profiles of Vs can be obtained from inversions of Rayleigh wave dispersion curves, from passive or active-sources, but th...

Contaminants that are highly soluble in groundwater are rapidly transported via fractures in mechanically resistant sedimentary rock aquifers. Hence, a rigorous methodology is needed to estimate groundwater flow velocities in such fractured aquifers. Here, we propose an approach using borehole hydraulic testing to compute flow velocities in an un-f...

MuLTI (Multimodal Layered Transdimensional Inversion) is a Markov chain Monte Carlo implementation of Bayesian inversion for the probability distribution of shear wave velocity (Vs) as a function of depth. Based on Multichannel Analysis of Surface Wave methods, it requires as data (i) a Rayleigh-wave dispersion curve and (ii) additional layer depth...

The distribution of channel deposits in fluvial reservoirs is commonly modeled with object-based techniques, constrained on quantities describing the geometries of channel bodies. To ensure plausible simulations, it is common to define inputs to these models by referring to geologic analogs. Given their ability to reproduce complex geometries and t...

In this paper, a testing methodology was developed in the laboratory to measure the tensile strength of large-scale incipient rock joints. In the test, an expansive grout was used to develop the tensile force. Each test comprises two phases: Phase i test and Phase ii test. The Phase i test identified sample failure time, while the Phase ii test mea...

Fluvial and aeolian sedimentary successions host important hydrocarbon resources as well as major groundwater aquifers. This review of the lithological characteristics of Triassic fluvio‐aeolian successions of the Sherwood Sandstone Group (United Kingdom) demonstrates how distance from a fluvial sediment source and rate of rift‐related tectonic sub...

Persistence of geological discontinuities is of great importance for many rock-related applications in earth sciences, both in terms of mechanical and hydraulic properties of individual discontinuities and fractured rock masses. Although the importance of persistence has been identified by academics and practitioners over the past decades, quantifi...

A common factor in landslide activation (or reactivation) is subsurface moisture and associated pore pressure variations linked to rainfall. Monitoring of these subsurface hydrogeological processes is necessary to improve our understanding of water‐induced landslide activation. Geophysical approaches, electrical methods in particular, are increasin...

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 c...

True persistence of rock discontinuities (areas with insignificant tensile strength) is an important factor controlling the engineering behaviour of fractured rock masses, but is extremely difficult to quantify using current geological survey methodologies, even where there is good rock exposure. Trace length as measured in the field or using remot...

Fluvial sedimentary successions represent porous media hosting groundwater, and geothermal resources. Additionally, they overlie crystalline rocks hosting nuclear waste repositories in rift settings. Here, we describe the permeability characteristics of an arenaceous fluvial succession, the Triassic St Bees Sandstone Formation (UK), from core-plug...

Geological discontinuities have a controlling influence for many rock-engineering projects in terms of strength, deformability and permeability, but their characterisation is often very difficult. Whilst discontinuities are often modelled as lacking any strength, in many rock masses visible rock discontinuities are only incipient and have tensile s...

Sandstone aquifers are commonly assumed to represent porous media characterized by a permeable matrix. However, such aquifers may be heavy fractured when rock properties and timing of deformation favour brittle failure and crack opening. In many aquifer types, fractures associated with faults, bedding planes and stratabound joints represent prefere...

Geological discontinuities have a controlling influence for many rock-engineering projects in terms of strength, deformability and permeability, but their characterisation is often very difficult. Whilst discontinuities are often modelled as lacking any strength, in many rock masses visible rock discontinuities are only incipient and have tensile s...

A methodology for developing resistivity-moisture content relationships of materials associated with a clayey landslide is presented. Key elements of the methodology include sample selection and preparation, laboratory measurement of resistivity with changing moisture content, and the derivation of models describing the relationship between resisti...

Fluvial successions comprising the fills of sedimentary basins occur in a variety of tectonic realms related to extensional, compressional and strike-slip settings, as well as on slowly subsiding, passive basin margins. A major rifting phase affected NW Europe during the Triassic and resulted in the generation of numerous sedimentary basins. In the...

Generally, rock discontinuity develops from an original incipient state with a high tensile strength to fully mechanical discontinuities with zero tensile strength (Hencher & Knipe, 2007). Incipient discontinuities have a controlling influence on many projects in terms of strength, deformability and permeability. For engineering simplification purp...

The Cretaceous Chalk aquifer is the most important in the UK for the provision of water to public supply and agriculture. The Chalk has both matrix and fracture porosity and is thus best considered as a dual porosity aquifer system. Although the matrix porosity is large, typically around 0.35 in the study area of East Yorkshire, UK (ESI, 2010), por...

This paper addresses the issue of the tensile strength of incipient discontinuities in rock and presents preliminary results from a series of laboratory studies. In most rock masses rock discontinuities, as veins or incipient fractures, often retain some tensile strength that may approach that of the parent rock. This fact is of high importance to...

Estimates of peat depth are required to inform understanding of peatland development, functioning, and ecosystem services such as carbon storage. However, there is a considerable lack of peat depth data at local, national and global scales. Recent studies have attempted to address this knowledge deficit by using manual probing and Ground Penetratin...

Spectral induced polarization (SIP) phase anomalies in field surveys at contaminated sites have previously been shown to correlate with the occurrence of chemically reducing conditions and/or semiconductive minerals, but the reasons for this are not fully understood. We report a systematic laboratory investigation of the role of the semiconductive...

Diffuse source nitrate leaching from agricultural land threatens groundwater quality worldwide. In the United Kingdom the source of up to 70% of nitrate found in surface and groundwater is thought to have been leached from agricultural land. Rising concentrations approaching or exceeding the maximum permissible concentration level of 11.3 mg/l NO3-...

A ground model of an active and complex landslide system in instability prone Lias mudrocks of North Yorkshire, UK is developed through an integrated approach, utilising geophysical, geotechnical and remote sensing investigative methods. Surface geomorphology is mapped and interpreted using immersive 3D visualisation software to interpret airborne...

The detection and characterization of fractures is important in many engineering practices e.g., rock fall assessment, quarry rock quality determination and mine roof and tunnel stability. Fractures may provide suitable contrasts in electrical properties for detection by GPR instruments. Their ability to reflect radar waves and the dependence of th...

Landslides are complex, strongly heterogeneous natural phenomena. A considerable number of landslide types exist, exhibiting varying states, distributions and styles of activity. If a better understanding of landslide internal processes is to be achieved, firstly, an understanding of landslide internal structure is required. Here, an example of an...

A multi-borehole pumping and tracer test in fractured chalk is revisited and reinterpreted in the light of fractional flow. Pumping test data analyzed using a fractional flow model gives sub-spherical flow dimensions of 2.2-2.4 which are interpreted as due to the partially penetrating nature of the pumped borehole. The fractional flow model offers...

In this study we describe the development of an integrated geophysical/geotechnical sensor network for monitoring an active inland landslide near Malton, North Yorkshire, UK. The network is based around an automated time-lapse electrical resistivity tomography (ALERT) monitoring system, which has been expanded to incorporate geotechnical sensor arr...

The Cretaceous Chalk in Northern Europe and other similar fractured rock aquifers frequently have very thick unsaturated (vadose) zones which control both their hydraulic response to rainfall and the extent to which pollutants are delayed or attenuated before reaching groundwater. Understanding their hydraulic responses is a prerequisite for predic...

The ability of fractures to reflect radar waves and the dependence of this reflectivity on fracture properties (aperture and fill) makes the GPR method a promising tool for rock fracture characterization. Successful characterisation requires quantification of the reflectivity (reflection coefficient (R)) of individual fractures. The AVO method appl...

Spectral induced polarization (SIP) is a promising technique for monitoring biogeochemically induced changes in porous subsurface media, such as biomineral formation during the remediation of contaminated sites. A primary mechanism responsible for low-frequency SIP signatures is the frequency-dependent polarization of the electrical double layer (E...

Recent work has suggested that the electrical self-potential (SP) geophysical technique may be used to noninvasively map redox conditions associated with contaminant plumes or bioremediation schemes. The proposed mechanism linking SP response and redox involves the generation of a current source and sink in the subsurface whereby electrons are tran...

Successful characterisation of fractures requires quantification of the reflectivity (reflection coefficient (R)) of individual fractures. The AVO method involves measuring the reflection amplitude variation with offset (incidence angle)l. Measuring the full AVO response using CMP (Common Mid Point) surveys enables estimation of these fracture prop...

Borehole water levels fluctuate in response to deformation of the surrounding aquifer caused by surface loading due to barometric pressure or strain caused by Earth and ocean tides. The magnitude and nature of this response mainly depend on the hydraulic properties of the aquifer and overlying units and borehole design. Thus water level responses r...

Due to its complex dual porosity nature, flow and contaminant transport in the unsaturated zone of the Chalk are not yet fully understood. Understanding these properties and hence the range of pollutant travel times through the unsaturated zone of the Chalk is vital to predicting trends in groundwater quality. Rising nitrate levels observed in abst...

Ground penetrating radar offers the potential to image individual rock fractures, and can potentially provide much-needed information on fracture aperture and hence permeability. However, estimation of fracture properties from radar requires determination of the reflection co-efficient (R) of individual fractures. The reflected amplitude measured a...

An increasing number of laboratory studies are investigating the link between microbial biogeochemical processes, such as the bioreduction of Fe(III) and sulfate, and geophysical responses. Self Potential (SP) and Induced Polarization (IP) studies both use non-polarisable electrodes to measure these responses. Commonly used electrodes include Ag wi...

Clay-rich till plains cover much of the UK. Such sites are attractive locations for landfills, since clay aquitards lower the risk of landfill leachate entering groundwater. However, such tills often contain sand and gravel bodies that can act as leachate flow routes. Such bodies may not be detected by conventional site investigation techniques suc...

A rigorous and practical approach for interpretation of impeller flow log data to determine vertical variations in hydraulic conductivity is presented and applied to two well logs from a Chalk aquifer in England. Impeller flow logging involves measuring vertical flow speed in a pumped well and using changes in flow with depth to infer the locations...

Environmental change caused by urban development, possibly augmented by climate change, may result in accelerated decay of in situ archaeological resources. Damage may be related to changes in hydrological processes. Such archaeological resources have to be considered in environmental planning. In this paper we highlight the need for improved hydro...

Ice mechanical properties, and hence the response of glaciers to climate change, depend strongly on the presence of liquid water at ice-grain boundaries. The propagation velocities of radar and seismic waves are also highly sensitive to this water. Mixing laws, typically the Looyenga and Riznichenko formulae, have traditionally been used to quantif...

Borehole measurements provide valuable information about how aquifer properties vary in the vertical dimension. Such vertical hydraulic conductivity variations are typically excluded from regional groundwater flow models, as their implications for prediction of sustainable yields are usually small. However, the prediction of groundwater quality tre...

Groundwater forms 70% of the world's freshwater supply, and is typically much cleaner than surface water supplies. It is therefore a key water resource that needs to be carefully managed. In urban areas, groundwater can be overexploited by industry, leading to degradation in quality. In order to regulate groundwater use, an understanding of the key...

A multi-borehole radial tracer test has been conducted in the confined Chalk aquifer of E. Yorkshire, UK. Three different tracer dyes were injected into three injection boreholes and a central borehole, 25 m from the injection boreholes, was pumped at 330 m(3)/d for 8 days. The breakthrough curves show that initial breakthrough and peak times were...

The Cretaceous Chalk is one of the most important aquifers in the UK, supplying 20% of the UK’s drinking water. The Chalk in East Yorkshire is the most northerly exposure of an outcrop that sweeps along the east and south coasts of England. Water flow in the saturated zone of the Chalk is mainly through the fractures owing to its very low matrix pe...

Broadband (100–4000 Hz) cross-hole seismic data have been acquired at a borehole test site where extensive hydrological investigations have previously been performed, including in situ estimates of permeability. The rock type is homogeneous chalk and fractures and bedding planes have been identified from well logs. High values of seismic attenuatio...

The dielectric permittivity of glaciers and ice caps can be measured in field or airborne surveys using ice-penetrating radar. Permittivity contrasts in polar ice caps indicate ice stratigraphy and age, whereas those in temperate glaciers have been interpreted as changes in unfrozen water content, which is an important control on glacier mechanics....

An approach to characterization of multilayer aquifer systems using open well borehole dilution is described. The approach involves measuring observation well flow velocities while a nearby extraction well is pumped by introducing a saline tracer into observation wells and collecting dilution vs. depth profiles. Inspection of tracer profile evoluti...

Tracer tests have been performed on the unsaturated zone of the East Yorkshire chalk aquifer, UK. Rapid tracer travel times through significant thicknesses of unsaturated chalk (15-38 m) indicate that bypass flow must occur through fractures. Transport processes in the unsaturated zone of the chalk aquifer thus have similarities to those in the vad...

We investigate the potential for using resistivity cone penetrometry (RCPT) to constrain 2.5D electrical resistivity tomography (ERT) inversion. ERT data, consisting of several parallel 2D lines, RCPT and EM-31 data were collected at a site on the East Yorkshire coast, U.K. The site is well-characterised, with sand/gravel bodies in clay till. The E...

Environmental change caused by urban development, land drainage, agriculture or climate change may result in accelerated decay of in situ archaeological remains. This paper reviews research into impacts of environmental change on hydrological processes of relevance to preservation of archaeological remains in situ. It compares work at rural sites w...

Electromagnetic signal velocity measurements are commonly used to quantify liquid water contents of near surface geomaterials. Typically, a single-valued function, such as Topp's equation, is used to convert dielectric permittivity (K) into water content (theta). Several factors contribute to error in such water content estimates, including use of...

Ice mechanical properties, and hence the response of glaciers to climatic change, depend strongly on the proportion and distribution of unfrozen water at ice-grain boundaries. Because the dielectric and elastic properties of unfrozen water and ice are significantly different, radar and seismic techniques are also sensitive to pore water content. Th...

The hydraulic behaviour of the vadose zone of a layered sandstone aquifer has been investigated using borehole-based Time Domain Reflectometry (TDR). Both a commercially available portable packer TDR system (TRIME-B3L Borehole Packer Probe) and specially designed borehole-emplaced TDR probes were used to monitor seasonal fluctuations in water conte...

Petrophysical tests were conducted on core samples from the unsaturated zone of the Sherwood Sandstone Group in East Yorkshire. Tests were conducted to determine which physical parameters most influenced its hydraulic conductivity values. The main parameters analysed were grain-size distribution, pore-throat size distribution, clay content, mineral...

Groundwater abstraction from the Triassic Sherwood Sandstone aquifer in the Selby area, Yorkshire, UK, has caused decline of the water level in the aquifer and groundwater quality problems such as high chloride and sulphate concentrations. Geochemical and isotopic analysis of groundwaters and groundwater modelling of an approximately 25 × 30 km are...

A sequence of glacial and alluvial deposits overlying the Cretaceous Chalk in Eastern England was characterised using two geophysical techniques: electrical resistivity imaging and electromagnetic (EM) induction. Extensive geological data were available from trenching and boreholes. Synthetic modelling of the electrical resistivity imaging techniqu...

Areas of clay-rich tills in the UK are attractive sites for landfills. The relatively impermeable clays act as a barrier between landfill contents and surrounding permeable materials, but tills often contain sand and gravel deposits, which may be water-bearing and/or hydraulically connected to aquifers or surface water bodies. The sands and gravels...

Glacier mechanical properties, and hence their response to climatic change, depend strongly on the proportion and distribution of unfrozen water at ice grain boundaries. Glaciologists have characterized unfrozen water content in several ways, notably via thin section microscopic analysis of ice cores to measure porewater contents, and field surveys...

The relationship between dielectric permittivity, water saturation, and clay content for the Sherwood Sandstone from NE England was characterized as part of a wider study of the vadose zone moisture dynamics and pollution vulnerability of this aquifer. Dielectric permittivity was measured over the full range of saturation levels, for various lithol...

The type and amount of organic matter present in industrially contaminated soils will influence the risk they pose. Previous studies have shown the importance of humic and fulvic acids (FAs) (important components of soil organic matter) in increasing the solubility of toxic metals but were not carried out using toxic metal levels and the pH range t...

Understanding the processes controlling recharge to aquifers is critical if accurate predictions are to be made on the fate of contaminants in the subsurface environment. In order to understand fully the hydrochemical mechanisms in the vadose zone it is essential that the dynamics of the hydrology can be suitably characterised. The correlation betw...

The basic principles of the use of regional climate model are presented. The RegCM2 is used for evaluation of the ability of the regional climate model to give better res- olution of the results of climate simulation. The model sensitivity is tested for some changes of its parameters as resolution, location and size of the domain as well as to some...

Characterization of the dynamics of moisture migration in the unsaturated zone of aquifers is essential if reliable estimates of the transport of pollutants threatening such aquifers are to be made. Electrical geophysical investigation techniques, such as ground-penetrating radar, offer suitable methods for monitoring moisture content changes in th...

An investigation of the influence of humate on the mobility of copper(II) ions in a kaolinite soil using leaching tests and electrokinetic experiments is reported. The data are interpreted in terms of humate–copper–clay interactions and humate electrical charge. Humate is mostly immobile below pH8 but is more mobile in alkaline conditions (sorption...

This paper reports the results of geochemical sampling and modelling of leachates from a chromite ore processing residue (C.O.P.R.) pile under rainwater infiltration. The waste pile is located in the north of England and consists of 800,000 m3 of waste. The pH of fresh leachate is similar to that of a solution in equilibrium with portlandite Ca(OH)...