Investigation of bacterial transport in the large-block test, a thermally perturbed block of topopah spring tuff

摘要

Transport of bacteria is investigated as part of the Large-Block Test (BLT), a thermally perturbed block of Topopah Spring tuff. Two bacterial species, Bacillus subtilis and Arthrobacter oxydans, were isolated from the Yucca Mountain tuff. Natural mutants that can grow under the simultaneous presence of the two antibiotics, streptomycin and rifampicin, were selected from these species by laboratory procedures, cultured, and injected into the five heater boreholes of the large block hours before heating was initiated. The temperature, as measured 5 cm above one of the heater boreholes, rose slowly over a matter of months to a maximum of 142 deg C and to 60 deg C at the top and the bottom of the block. Samples were collected from boreholes located approximately 5 ft below the injection points. Double-drug-resistant bacteria were found in the collection boreholes nine months after injection.