Tommi Kauppila, Geological Survey of Finland, PO Box 1237, 70211 Kuopio, Finland; tommi.kauppila(at)gtk.fi
Mine closure always includes a period of post closure monitoring of the environment and, increasingly, socio-economic indicators, to ensure compliance and to make sure that closure has been successful. In certain jurisdictions, post closure monitoring may be employed when seeking relinquishment of the site. This resource contains a separate section on the technical aspects of monitoring and this article only discusses the general principles of post closure monitoring.
A post closure management plan, which includes topics such as monitoring, inspections, maintenance, record keeping, reporting, and funding, may be included in the Closure Management Plan or it may be a separate document. A post closure management plan also may be required by legislation, particularly for waste facilities, in which case its form and contents may be prescribed (e.g. U.S. EPA 2015, under review). In any case, a post closure plan is essential to make sure that the crucial, and often quite long, period after the main decommissioning and reclamation activities is taken care of in a structured manner. This is especially important for small mine operators that may not have a separate department at the corporate level to take care of the post closure maintenance and monitoring requirements of their closed mines.
As with all closure activities, the aim should be to minimize the need for post closure monitoring and maintenance. Understandably, this should not be at the expense of the quality and usefulness of the monitoring program. Monitoring should be designed based on the body of knowledge of the main risks remaining after the mine has closed, accumulated during the closure process. It should also cover all the relevant mine closure objectives because one of the aims of monitoring is to verify that closure has been successful. The program should also be revised according to the needs identified during the monitoring period. Importantly, mere reporting of monitoring results as such is not sufficient or effective. Instead, the monitoring reports should seek to identify trends in the data and investigate the reasons behind these trends to detect any problems as early as possible.
The time period for which post closure monitoring is needed varies from case to case. There may be requirements set out in legislation or permits that exactly prescribe the monitoring period. However, it is the nature of the mine site that usually dictates how long a monitoring period is needed to verify the stability of the site. The monitoring period should be long enough to include all the slow processes that may affect the closed site such as the initiation of acid rock drainage, infilling of open pits and underground workings, slow transport of contaminants in groundwater, long term performance of passive water treatment facilities, waste caps and other closure structures etc. In most cases a fairly long monitoring period is required although the monitoring frequency may be gradually reduced if no alarming trends are detected.
Besides a long enough post closure monitoring period, good documentation of the monitoring and maintenance activities and the performance of the closure structures provide assurance that the site is stable and closure has been successful. Such documentation is essential to fulfil regulatory requirements and provides a good basis for due diligence investigations if the site changes ownership.
U.S. EPA 2015. Draft Post-Closure Care (PCC) Guidance. Guidelines for Evaluating and Adjusting the Post- Closure Care Period for Hazardous Waste Disposal Facilities under Subtitle C of RCRA.