Assessing and managing the long-term risks and liabilities at a closed Cornish mine used for waste disposal

摘要

During World War II, a large number of new airfields were established across the UK, one of which was at Portreath on the north coast of Cornwall, some 5 km from the town of Redruth. During the Cold War the site was known as Nancekuke and was used by the Chemical Defence Establishment (CDE} for research and development into chemical warfare agents, with the CDE facility eventually being closed in the late 1970s. When the plant was closed it was fully decontaminated and dismantled, and the wastes were placed in five on-site dumps, two of which were mine shafts associated with Wheal Sally, a former lead and zinc mine also known as Sally's Bottom Mine, which closed in the 1920s. Assessment of the potential for the waste disposal to impact the environment and cost-effective options for managing this potential commenced in the late 1990s. A comprehensive desk-based evaluation of the mine system was therefore undertaken and an inspection programme formulated, consisting of aboveground drilling and closed-circuit television inspections and belowground inspections, including substantial stabilisation works. In parallel with the inspection, a monitoring programme was formulated to establish water quality conditions and the potential for the wastes to impact them. No significant risk to the environment was identified, but long-term management options were evaluated, including the cost benefit associated with each. The final solution included capping three mine shafts for health and safety reasons, using a bespoke system at one shaft to avoid excavation into wastes, and ongoing monitoring of mine discharge water that is scheduled to continue until 2020 and will then cease if, as is currently the case, no pollution has been identified.