Effect of Geochemical Conditions on Bacterial activity

Observations within different experiments have shown that perturbations in Boom Clay appear to be accompanied by bacterial activity. The increased sulphate concentrations in Boom Clay due to the oxidation of pyrite could activate sulphate reducing bacteria (SRB) resulting in the production of sulphide which could cause corrosion of the overpack. The supercontainer design aims to create a buffer environment with corrosion-favorable characteristics. The high pH environment and the elevated temperature could have a severe influence on the activity of SRB near the repository. The influence of both factors on the growth/activity of SRB was investigated via incubation experiments using Boom Clay water and simultaneously the amount of sulphide produced by SRB was measured. These incubation experiments showed that: - SRB activity inside the concrete buffer, with pH values higher than 12.5, is highly unlikely. - SRB activity on the concrete-Boom Clay interface, with pH value in the range of 10-10.5 and an increased temperature between 40 and 70°C, can not be excluded. - The sulphide concentrations in the range of 4.7 to 9.4 mM (150 to 300 ppm) could be expected.