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Impact of micro-karstic flow on Chalk aquifer function and water quality


Project Description

Highlights and Novelty
•Opportunity for investigating the impacts of contaminants on water quality and security.
•Investigation of one of the world’s most important aquifers, the Cretaceous Chalk.
•Determination of micro-karst extent in chalk, to better understand its development, and identify the impact of rapid micro-karstic flow processes on water quality [chalk has previously not been considered a karst aquifer in most areas, as surface karst features absent; recent work has highlighted the widespread nature of micro-karst].
•Working with a very experienced team including British Geological Survey staff to conduct fieldwork using e.g. novel tracer technology to identify micro-karst pathways.
•Identification of preventive actions to be taken by Water Company partner to facilitate improved future groundwater resource management and resource sustainability.

Background

The Cretaceous Chalk aquifer represents the most important groundwater resource in the UK and is also important ecologically for chalk stream ecosystems. Similar aquifers exist in France, Belgium, Netherlands, and Israel. The extent to which chalk aquifers show development of karstic features (widened fractures and conduit development due to dissolution by groundwater flow) is of interest because where karstic features connect sources of contaminants directly to borehole abstractions, water quality may be poor. Where flow is more distributed because karst features less developed, water quality is consistently better.

Karst is generally associated with distinctive and often spectacular landforms, including caves, and results in rapid groundwater flow in subsurface streams and rivers, as well as flow through smaller solution voids, although the latter are less well understood due to their inaccessibility. The Chalk is often not considered a karst aquifer because caves are rare, and surface karst features are small and until recently not well documented. Recent work has highlighted the potential importance of micro-karst development in the Chalk enabling rapid groundwater flow over long distances through relatively small karst features, but its nature and how it impacts groundwater flow and contaminant transport is not well understood.

Recent advances in tracer testing techniques offer the opportunity to study the smaller sized solution voids in karst aquifers, both in classical karst aquifers and in the Chalk. The development of tracers such as bacteriophage (non-harmful virus particles small enough to pass through fractured aquifer systems) and in modelling the development of karst networks enable a new way forward via systematic investigation of the extent of micro-karst development in aquifers like the Cretaceous Chalk. Using these approaches we aim to identify key factors controlling development, the importance of different void types (widened fractures, conduits etc.) in the Cretaceous Chalk, and the impact of these on contaminant transport and therefore water quality.

Objectives
1.To identify key controls on development of micro-karstic flow paths in soluble rocks such as the Chalk.
2.To identify extent of Chalk micro-karst development in areas where surface macro-karst features (swallow holes etc.) are absent, as well as where these surface macro-karst features are evident .
3.To simulate evolution of micro-karstic features in the Chalk aquifer and their impact, and/or predict the pollution vulnerability of groundwater in chalk and karstic aquifers more widely.
4.To investigate how degree of micro-karst development influences nitrate and pesticide concentration trends in Chalk groundwater abstractions, and their response to extreme weather events.

The ultimate goal is to provide a coherent understanding of micro-karst development in chalk aquifers, within the framework of previously-developed models for karst development in soluble rocks, and the impact of micro-karst development on contaminant transport, groundwater pollution vulnerability and therefore on the quality of abstracted groundwater and that of chalk-fed springs and streams.

Student profile

You will have a degree in Geoscience or Environmental Science background (includes Earth Science, Environmental Science, Geology, Geophysics, Hydrology, and Physical Geography), the ability to undertake fieldwork and wet chemical laboratory work and to analyse and interpret numerical data. You will need willingness to EITHER learn to apply numerical modelling codes (using existing modelling software) OR to develop groundwater vulnerability mapping approaches using GIS-based tools. You will need to undertake fieldwork in the field areas relevant to CASE partner (i.e. South East of England), such as geomorphological mapping and tracer testing, with support from the staff at BGS Wallingford and CASE partner staff.

References

Key Supervisor Publications

Allshorn SL; Bottrell SH; West LJ; Odling NE (2007) Rapid karstic bypass flow in the unsaturated zone of the Yorkshire chalk aquifer and implications for contaminant transport, In: Parise M; Gunn J (Ed) Natural and Anthropogenic Hazards in Karst Areas: Recognition, Analysis and Mitigation, Geological Society Special Publications, Geological Society of London, pp.111-122.

Hartmann S; Odling NE; West LJ (2007) A multi-directional tracer test in the fractured Chalk aquifer of E. Yorkshire, UK, J CONTAM HYDROL, 94, pp.315-331. doi: 10.1016/j.jconhyd.2007.07.009

Medici G, West LJ, Banwart SA. 2019. Groundwater flow velocities in a fractured carbonate aquifer-type: Implications for contaminant transport. Journal of Contaminant Hydrology. 222, pp. 1-16

Medici G, West LJ, Chapman PJ, Banwart SA. 2019. Prediction of contaminant transport in fractured carbonate aquifer-types; case study of the Permian Magnesian Limestone Group (NE England, UK). Environmental Science and Pollution Research. 26(24), pp. 24863-24884

Parker AH; West LJ; Odling NE (2018) Well flow and dilution measurements for characterisation of vertical hydraulic conductivity structure of a carbonate aquifer, Quarterly Journal of Engineering Geology and Hydrogeology, . doi: 10.1144/qjegh2016-145

West L J; Odling N (2007) Characterization of a Multilayer Aquifer Using Open Well Dilution Tests, Ground Water, 45, pp.74-84. doi: 10.1111/j.1745-6584.2006.00262.x



Other key references

Edmonds, C. 2008. Improved groundwater vulnerability mapping for the karstic Chalk aquifer of south east England. Engineering Geology 99 (95–108).

El Janyani, S., Dupont, J.P., Massei, N., Slimani, S. and Dörfliger, N., 2014. Hydrological role of karst in the Chalk aquifer of Upper Normandy, France. Hydrogeology Journal, 22(3), pp.663-677.

Foley, A, Cachandt, G, Franklin, J, Willmore, F, and Atkinson, T. 2012. Tracer tests and the structure of permeability in the Corallian limestone aquifer of northern England, UK. Hydrogeology Journal 20, 483–498.

Hartmann A, Goldscheider N, Wagener T, Lange J, Weiler M., 2014. Karst water resources in a changing world: Review of hydrological modeling approaches. Reviews of Geophysics 52(3):218-42

How good is research at University of Leeds in Earth Systems and Environmental Sciences?

FTE Category A staff submitted: 79.20

Research output data provided by the Research Excellence Framework (REF)

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