Microbiological influences on fracture surfaces of intact mudstone and the implications for geological disposal of radioactive waste

Abstract

The significance of the potential impacts of microbial activity on the transport properties of host rocks for geological repositories is an area of active research. Most recent work has focussed on granitic environments. This paper describes pilot studies investigating changes in transport properties that are because of microbial activity in sedimentary rock environments in northern Japan. For the first time, these short experiments (39 days maximum) have shown that the denitrifying bacteria, Pseudomonas denitrificans, can survive and thrive when injected into flowthrough column experiments containing fractured diatomaceous mudstone material and synthetic groundwater under pressurised conditions. Although there were few significant changes in the fluid chemistry, changes in the Microbiological impacts -mudstone 2 permeability of the biotic column were quantitatively monitored. These same methodologies could also be adapted to obtain information from cores originating from a variety of geological environments including oil reservoirs, aquifers and toxic waste disposal sites to provide an understanding of the impact of microbial activity on the transport of a range of solutes, such as groundwater contaminants and gases (e.g. injected carbon dioxide).

Mineralogical comparisons of experimental results investigating the biological impacts on rock transport processes

“…The fourth and most recent approach was based on that taken by Coombs et al 8 but uses anaerobic column experiments in an automatically controlled environmental anaerobic chamber. The constant head reservoirs used by Coombs et al 8 were replaced by 80 syringe pumps to maintain a constant flow rate of 0.625 ml hr -1 and any changes in pressure were logged continuously using a data logging system. The experiment was terminated after 147 days.…”

“…The experiment was terminated after 147 days. A full description of methodologies is given elsewhere 15 .…”

“…Äspö granodiorite and 80 Horonobe mudstone rock were chosen as materials, given that these rock types are analogous to the lithologies that are likely to be considered for radioactive waste repositories. The Äspö URL is located within the Precambrian Transcandinavian Granite Porphyry Belt that comprises predominantly porphyritic quartz monzogranodiorites and granodiorites.…”

“…The Äspö granodiorite samples were taken in immediate proximity to the in situ field-scale experiment (REX -redox experiment in detailed 10 scale) which investigated groundwater redox-buffering capacity of the rock mass within the URL 27 . Horonobe is located in the north-western Hokkaido, Japan 16 . A detailed description of the geological setting of the URL is given by Milodowski et al 24 .…”

“…It provides a detailed analysis and comparison of 65 key mineralogical-, petrographical and geochemical findings that were made during a number of different microbial transport studies undertaken over the past 10 years. These studies were carried out in collaboration with the Äspö Hard Rock Laboratory in Sweden 8,14,15,32 and the Horonobe Underground Research 70 Laboratory (URL) in northern Japan 16 . This provides new insights on the influence that bacteria can have on transport properties within granodiorite or mudstone host rock environments due to the formation of biofilms.…”