Patterson, TL & Trevor, M 2019, 'Three case studies: mechanisms other than spillage and leaks that change groundwater quality and inhibit closure certification', in AB Fourie & M Tibbett (eds), Mine Closure 2019: Proceedings of the 13th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1201-1216, https://doi.org/10.36487/ACG_rep/1915_95_Patterson
(https://papers.acg.uwa.edu.au/p/1915_95_Patterson/)
Abstract: Baseline groundwater quality at mines is often poor, containing naturally occurring constituents at elevated concentrations. Groundwater quality changes at mine sites during operations and closure, and the changes are typically attributed to releases from mine waste or spillage of process solutions or waste water. If the changes are related to release of mine waste or water, then remediation is required before closure can be certified as complete. However, there is a long list of other mechanisms that can cause groundwater quality changes at mines, ranging from changes to recharge and flow patterns caused by construction to oxidation of minerals in the walls of a monitoring well.
This paper presents case studies for two closed gold mines where groundwater quality changes were preventing closure certification and many of the changes were not due to release of mine waste or water. The paper also describes the information developed to demonstrate that the changes were a consequence of constructing and operating the mine and represented a new baseline condition. The paper also describes how anticipation of such changes as part of environmental permitting would help streamline closure, and elaborates on what and where such information should be incorporated in permitting.

Keywords: closure, groundwater monitoring, geochemical changes, impacts