Non-Aqueous Phase Liquid Contamination of Aquifers
Key staff: Professor Steve Leharne
The focus of this research is the challenge to the sustainable use of land and groundwater by the widespread presence of nonaqueous phase liquids (NAPLs) in sub-surface soils and rocks.
Exemplar NAPLs include petroleum hydrocarbons, wood-treating oils such as creosote, transformer and insulating oils containing polychlorinated biphenyls, coal tar, and chlorinated hydrocarbon solvents such as trichloroethene. NAPLs have been widely produced and used in industry since the late 1800s. They enter sub-surface soils and rocks by spillage, leakage from underground storage tanks and improper disposal to ground by industrial users.
NAPLs are slightly soluble in water, and therefore exist in the subsurface as a separate fluid phase, immiscible with both water and air. NAPLs are conveniently characterised by their specific gravity. Dense (D)NAPLs have specific gravities greater than 1. If released at ground surfaces, DNAPLs can migrate to significant depths below the water table, where they slowly dissolve into flowing groundwater, giving rise to aqueous phase contaminant plumes.
Light (L)NAPLs have a specific gravity less than 1. Typically they are unable to penetrate the water table but can form a depression in the water table, where they slowly dissolve in groundwater. Both DNAPLs and LNAPLs can form contaminant plumes in the vapour phase of the unsaturated zone, which often represents a critical hazard to various key receptors. Contamination of groundwater and the vapour phase are the key risk drivers informing our concern at NAPLs.
Recent Projects
Predicting aquifer penetration
We have received funding from the Engineering and Physical Sciences Research Council (EPSRC) to address the key questions of how far a DNAPL spill will penetrate an aquifer. We have had to combine measurements of the physical properties of DNAPLs – such as surface and interfacial tension, contact angle and viscosity, with an understanding of the geology of the aquifer. This has made us examine issues such as the role that components in DNAPLs can play in altering these physical properties, and how they can alter the wetting properties of aquifer rocks.
How can you clean up a contaminated aquifer?
We have addressed this question with two projects, both funded by the EPSRC. The first examined how surfactants can be used to remove residually trapped DNAPL. Surfactants are used to reduce the water/DNAPL interfacial tension, which is pivotal in trapping the DNAPL droplets.
A second approach to achieving clean-up is to attack the plume. In this project we examined the use of iron to clean up a plume of tetrachloroethene, an industrial solvent often used in leather manufacturing to remove fats from animal carcasses.
Which aquifers are likely to be contaminated?
The Environment Agency has funded our examination of how to predict which public water supply wells are likely to be contaminated by DNAPLs. This work has largely been achieved through using the GIS (Geographical Information System) to examine the regional-scale issues of pollutant transport.
Publications
Dong. J., Chowdhry, B. Z., and Leharne, S. A. (2004) Investigation of the wetting behaviour of coal tar in three phase systems and its modification by poloxamine block co-polymeric surfactants. Environmental Science and Technology, 38 (2), pp. 594–602.
Dong, J., Chowdhry, B. Z., and Leharne, S. A. (2005) Altering the spreading coefficient of coal tar systems using ethylene oxidepropylene oxide block copolymers. Colloids and Surfaces A-Physicochemical and Engineering Aspects. 266 pp., pp. 191–199.
Gooddy, D. C., Bloomfield, J. P., Harrold, G., and Leharne, S. A. (2002) Towards a better understanding of tetrachloroethene entry pressure in the matrix of permo-triassic sandstones. Journal of Contaminated Hydrology. 59, pp. 247–265.
Harrold, G., Gooddy, D. C., Lerner, D. N., and Leharne, S. A. (2001) Wettability changes in trichloroethylene contaminated sandstone. Environmental Science and Technology. 35, pp. 1504–1510.
Harrold, G., Gooddy, D. C., Reid, S., Lerner, D. N., and Leharne, S. A. (2003) Changes in interfacial tension of chlorinated solvents following flow through UK soils and shallow aquifer material. Environmental Science and Technology. 37, pp. 1919–1925.
Harold, G., Lerner, D., and Leharne, S. A. (2005) The impact of additives found in industrial formulations of TCE on the wettability of sandstone. Journal of Contaminant Hydrology. 80, pp. 1–17.
Kueper, B., Wealthall, G., Smith, J., Leharne, S., and Lerner, D. (2003) An Illustrated Handbook of DNAPL Transport and Fate in the Subsurface. ISBN 1844320669. Bristol: Environment Agency.
Tait, N. G., Lerner, D. N., Smith, J. W. N., and Leharne, S. A. (2004) Prioritisation of Abstraction Boreholes at Risk from Chlorinated Solvent Contamination on the UK Permo-Triassic Sandstone Aquifer using a GIS Science of the Total Environment. 319 pp., pp. 77–98.
Tait, N. G., Davison, R. M., Whittaker, J. J., Leharne, S. A., and Lerner, D. N. (2004) Borehole Optimisation System (BOS) – A GIS-based risk analysis tool for optimising the use of urban groundwater. Environmental Modelling & Software. 19, pp. 1111–1124.