Permeability measurements from a potential deep geological repository site

The Bruce nuclear site in Canada has been proposed
to host a Deep Geologic Repository (DGR) for Low and
Intermediate Level Radioactive Waste (L&ILW). The
repository would be constructed within a low
permeability, argillaceous limestone, the Upper
Ordovician age Cobourg Formation. Here, we present the
results of two steady-state laboratory hydraulic
conductivity tests performed to measure the intrinsic
permeability of rock core samples from the Cobourg and
overlying Queenston shale formations; both samples were
measured under an isotropic confining pressure using a
constant head approach. Pump pressures and volumes
were recorded for upstream and downstream pumps,
throughout testing. The resulting hydraulic inflow and
outflow rates were measured for each sample under two
different pressure gradients, yielding exceptionally low
values of permeability (on the order of 10-22 m2 or 0.1
nD). These data provide further evidence of the
applicability of existing steady-state experimental
methods to obtain reliable estimates of extremely low
permeabilities from rock core samples under reestablished
in-situ stress conditions. The exceptionally
low permeability of these formations, consistent with insitu
testing and formation scale estimates obtained during
the site characterisation program, along with their low
porosities, renders them an effective barrier to hydraulic
flow for the purpose of geological isolation.