Proposed Limpopo West Mine Concept Study ... - SRK Consulting

SRK Consulting: 447493: Limpopo West Geochem Page 39Determine and agree effluent discharge standards with Authorities that need to be adhered to bythe mine during the operational and closure phases and resolve the question around currentdischarge qualities and exceedence;Develop and implement a mine water quality monitoring system for mine water generated fromnew mining areas and backfill areas;The mine water generated from these areas should have mine water management infrastructurein place that will allow for the following:If the quality of the mine water falls within the agreed mine water discharge quality parameters, itcan be released to the current mine water reticulation system and managed in the same way asthe current mine water is managed (assuming it is upgraded to handle the additional mine waterflows); andIf the quality exceeds the agreed mine water quality discharge parameters, the mine water willbe managed in a separate mine water reticulation system that either allows for use elsewhere inthe operation and/or storage (unlikely due to safety concerns) and/or treatment, discharge or reuse.An ARD management plan should be developed and implemented to manage the ARD risk from thepit and spoils stockpiles. It should consist of:Acid base accounting (ABA) testing of the individual key lithologies to determine ARD risk andavailability of excess neutralising potential for ARD risk reduction. The ABA monitoring should bedone annually for first two years where after the monitoring programme should be revised aspart of the ARD management plan.Incorporation of ABA results into the existing block model to indicate areas or material types ofhigh, low and medium ARD risk potential.Field kinetic test programme including the installation of field lysimeters on site to assess sitespecific metal leaching rates and drainage quality for inclusion in the monitoring database.6.1.2 Decommissioning and Closure Phase Mitigation MeasuresThe following measures are recommended:Conduct suitable hydrogeological and geochemical investigations to conceptualise the minewater system at closure. These investigations will include the development of baseline data,conceptualisation of the mine workings, modelling of key flow and geochemical processes andevaluation of alternative mine water management strategies using the models. It is proposedthat these investigations be conducted during the operational phase of the mine and completedin time for the last 5 year of planning before closure;In the absence of a detailed understanding of the post closure mine water system, a pump andtreat water management post closure mitigation strategy is recommended. This strategy isrobust against the uncertainty, however, will provide the required environmental protection. Thisstrategy can be changed and optimised should the hydrogeological and geochemicalinvestigations demonstrate alternative and less onerous mitigation strategies.Undertake geochemical modelling to evaluate the potential pit lake chemistry at post closure andwill mainly involve geochemical modelling of key flow and geochemical processes associatedwith the pit, this will include the following tasks to be undertaken:oooooNumerical predictions using hydrogeological flow models to predict potentialgroundwater flow that will influence the pit water quality,Hydrological modelling to demonstrate the filling capacity of the pit once pumpingceases at closure and post-closure phase of the mine,On site water chemistry of the pit water in conjunction with predicted releasechemistries from geochemical characterisation testing will be required as inputparameters in the geochemical model to predict potential water quality,Development of representative conceptual models as a basis for numerical modeldevelopment and to illustrate geochemical, hydrogeological and hydrologicalprocesses;Geochemical modelling to ensure balanced water chemistry will be achieved byusing the United States Geological Survey (USGS) programme PHREEQC andGOGP/LAKJ Report_April2013_19April2013 (1)_Final_Ludi_22052013 April 2013