only those constructed in granite geologic formations have operated without incident. as of 2015 there were DGR facilities in Finland which operated without incident constructed in crystalline rocks such as granite. Accident risk and long-term safety The lack of precedent in using limestone as a host formation for a DGR makes it very difficult to predict potential failures of the DGR that is not constructed in granite formation. OPG’s presentation of assumptions about the DGRs geochemistry is an underestimation of the potential risks of constructing a DGR in limestone formation, as seen in the case of the Waste Isolation Pilot Plant in New Mexico that leaked radioactive plutonium to the surface after a drum barrel leaked: "These accidents illustrate how difficult it is to predict potential failures of such a disposal system over millennia. For example, assumptions about the repository's geochemistry or the likelihood of drilling into it can lead to underestimation of the risks." Western University professor, Erika Simpson observed that DGRs constructed in geological formations other than granite have a risky track record. In an op-ed for a London newspaper, she wrote, "It didn’t help soothe critics that the only example OPG offered of a similar DGR — the Waste Isolation Pilot Plant in New Mexico — is no longer operating, after an underground fire and loss of containment resulted in radioactive releases to the surface in 2014. Likewise, Germany’s vaunted salt mine solution for low-level nuclear waste has also proven to be full of holes as thousands of litres of groundwater continue to leak into the Asse mine every day mixing with radioactive waste." Furthermore, research conducted in China revealed that Exposure to mechanical and chemical weathering has been proven to mechanically destabilize limestone, leading to geohazards including sinkholes and rapid erosion of limestone into soil. This could occur during construction and in the highly extended lifetime of the DGR. See also Schacht Asse II Waste Isolation Pilot Plant References Environment of Ontario Radioactive waste repositories