Physical and geochemical modelling (SWIFT-PHREEQC) of British aquifers for aquifer storage and recovery purposes. Part 2 : geochemical modelling

Gaus, I.. 2001 Physical and geochemical modelling (SWIFT-PHREEQC) of British aquifers for aquifer storage and recovery purposes. Part 2 : geochemical modelling. Nottingham, UK, British Geological Survey, 37pp. (CR/01/054N) (Unpublished)

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Abstract/Summary

This report describes the progress that has been made in developing models simulating both the physical and geochemical aspects of Aquifer Storage Recovery (ASR) schemes. This work is part of a 30 month project, entitled ASR-UK, which started in April 1999. This report follows on from the work reported in Gaus et al., BGS report WD/00/08, published in March 2000. The aim of this report is to explore and to assess the chemical limitations or benefits in applying ASR in the major UK aquifers: the Chalk, the Lower Greensand, the Triassic Sandstone and the Jurassic Limestone. The implications for the quality of the recovered water using different types of injection water and different types of native water are assessed using two types of modelling: mixing modelling and cycle modelling. A total of 13 different combinations were developed. An example of more detailed geochemical modelling based on observations from an ASR-site in the Chalk is also included. More complex modelling requires detailed knowledge, particularly on the solid phases in the aquifer, but such data are generally limited. To assess the likely chemical quality of the recovered water when planning an ASR-scheme three components have to be taken into account: • chemical aspects of the injected water; • chemical aspects of the native water in the aquifer; • geochemistry of the aquifer and the chemical interaction with the injected water (e.g. dissolution of pyrite). Major chemical changes to the quality of the injected water during recovery are expected when one or more of the following conditions are met: • there is a large difference in chemical condition between the injected and the native water; this can cause large differences in pH or redox condition. • the native water or the sediment do not possess a sufficient pH buffering capacity (e.g. in the case of acidic waters where no calcite is present for dissolution) • there is a large difference in elemental concentrations between the injection and the native water (e.g. fluoride) and significant mixing occurs (e.g. in dual porosity aquifers) • a change in chemical condition of the water having contact with the sediment is able to trigger major (e.g. dissolution of gypsum) or minor (e.g. dissolution of heavy metals) reactions. The conclusions are based on the modelled cases only, and highlight the main chemical reactions likely to occur when implementing an ASR-scheme. Other chemical interactions may determine the quality of the recovered water when other injection waters are used, the native water has a different quality, or the geochemistry of the aquifer is different from the one assumed here. Also minor reactions and elemental concentrations are in general not modelled. Within this study it was also clearly illustrated that the geochemical model can be used at different levels when planning an ASR-scheme. At the initial desk-study level, geochemical modelling can be used as a crude assessment of the chemical viability of the scheme. In subsequent stages of the ASR-scheme trial and implementation, geochemical modelling can be supported by the observed data, used to assess the impact of specific geochemical reactions as illustrated for fluoride in the ASR-trial in the Chalk.

Item Type:	Publication - Report
Programmes:	BGS Programmes > Groundwater Management
Funders/Sponsors:	British Geological Survey, Foresight Link Award, UKWIR
Additional Information. Not used in RCUK Gateway to Research.:	This item has been internally reviewed, but not externally peer-reviewed.
Additional Keywords:	GroundwaterBGS, Groundwater, Groundwater modelling
Date made live:	07 Apr 2020 13:22 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/527413

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