Exploring subsurface ground water and geochemical rock interactions during drainage of a surface water reservoir in Switzerland

Student thesis: Doctoral Thesis

Abstract

This thesis examines the spatial and temporal controls on groundwater chemistry in a fractured granitic environment. The research was conducted at the Grimsel Test Site, Switzerland (GTS), where draining and refilling of a nearby surface water reservoir induced microseismicity In the surrounding rocks. The GTS is a network of closely monitored tunnels and boreholes approx 300-500m below ground surface. Characterisation of background geochemical conditions over a two-year period consisted of a time series of physiochemical, major and minor dissolved ion chemistry, stable isotope analysis and dissolved organics, for boreholes spanning the length of the GTS. Results show poor fracture connectivity; physiochemical and dissolved ion chemistry are dominated by water-rock reactions between infiltrating meteoric waters and spatially varying host rock lithology. A new technique is developed that compares the differing signatures of dissolved organic compounds (2D-gas chromatographs) found within surface soils, river sediments and the lake, to those found in groundwater samples from the GTS. Results show that organic signatures are well-preserved and that different groundwater samples can be traced to different surface infiltration sites. This organic fingerprinting technique has the potential to be a powerful new tool for determining groundwater origins. Analysing the groundwater data over time, identified no changes to major or minor ion chemistry, but repeated drops in groundwater pH (1-3 units) were observed during periods of reservoir drainage. These drops were concurrent with nearby shallow (
Date of Award2 Jun 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorRichard Lord (Supervisor) & Zoe Shipton (Supervisor)

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