DISCUSSION PAPER :GROUNDWATER CLOSURE COST ESTIMATION FOR THE MINING INDUSTRY

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1 DISCUSSION PAPER :GROUNDWATER CLOSURE COST ESTIMATION FOR THE MINING INDUSTRY P.F. Labuschagne 1 GCS Water and Environmental Consultants (Pty) Ltd, Durban, KZN, South Africa; pieterl@gcs-sa.biz. Abstract The increase in awareness of environmental issues and the desire for a cleaner environment by the public has caused mining companies to place greater emphasis on the continuous rehabilitation of harmful effects caused by mining operations. Ongoing rehabilitation is also a requirement of the Government Departments involved in mining in South Africa. The biggest concern for the relevant Government Departments is the possible uncontrolled pollution of water resources in the vicinity of mines, after they have closed. In the compilation of this paper, the unique nature of the South African situation has been considered this refers to a legally acceptable approach towards current legislation and policies. This study leads to the construction of a logical approach towards mine closure specifically to understand issues around costs and financial liability. The final product of this approach should ultimately give more clarity on: The principles followed to identify objectives for mine closure and groundwater assessment, Key steps to follow when assessing site hydrogeology and to determine related impacts, risks, closure costs and liabilities, Overview of methods that could be used for the mitigation of polluted aquifers and a brief sitespecific application. 1. INTRODUCTION The Mineral and Petroleum Resources Development Act (MPRDA), (Act No. 28 of 2002) and its Regulations was promulgated on 1 May Financial provision for environmental rehabilitation and closure requirements of mining operations forms an integral part of the MPRDA, as was the case with the now repealed Minerals Act, 1991 (Act 50 of 1991). Section 41 of the MPRDA and regulations 53 and 54 promulgated in terms of the MPRDA deal with financial provision for mine rehabilitation and closure. These guidelines do not specify how groundwater related impacts can be financially provided for, but rather supplies a vague cost per unit (ha) for groundwater management. This provision usually results in a gap between what is allowed for closure trust funds and what is actually needed to solve a certain groundwater issue. The requirements for mine closure and closure criteria at the mine planning stage are typically uncertain and generally must be based on mine waste rock characteristics determined from drilling and sampling of in-situ rock and laboratory testing of relatively small samples of the material. Waste characteristics are also uncertain and include changing leachate and mine water quality, altered final configuration of the tailings and water pile, as well as variation on open pits and underground mining operations. Finally, regulatory standards can change over the life of the mine introducing further uncertainty to the closure requirements and costs (Hutchison et al., 2011). 2. APPROACH To assess the liability and specific closure cost components of groundwater quantity and quality impacts, hydrogeological data is translated into hydrogeological conceptual site models (HCSM) which are

2 subsequently used as the basis for predictive models to allow simulations of given field conditions. The outcome of these model simulations is used as a guide during the decision making process. Technical data is then further processed as part of financial models and legal considerations. To understand groundwater closure cost requirements and to be able to supply mine management with sound guidance, an approach of step-by-step assessments, based on the Source-Pathway-Receptor principle, was developed by GCS based on various South African and International based guidelines. In this instance, a cost-benefit approach was taken into consideration during the investigation by complimenting existing data with previously undetermined site parameters. The terms source-pathwayreceptor and quantity and quality was applied during the technical assessment phase and for the development of the HCSM. Quantity and Quality refer to the two main variables which supplies a broad overview of status. A flow diagram showing a simplified overview of the required sequence of tasks (Figure 1) was constructed to aid in the estimation of the closure cost. Figure 1: Flow diagram illustrating the groundwater management approach 3. STEP 1: DEVELOPMENT OF A HYDROGEOLOCICAL CONCEPTUAL SITE MODEL (HCSM) The source-pathway-receptor approach is used to describe the hydrological conceptual site model and provides a conceptual understanding of the mode through which sources and sinks act and the potential harm they may inflict on a receiving water body and/or organism. The conceptual model is used to develop management action plans and reclamation alternatives that are directed toward mitigating potentially harmful effects caused by the site activities of concern (i.e. waste storage and/or mine dewatering). The following supplies a brief overview of a logical approach on how to develop a CHSM:

3 Step 1A: Understand Sources The primary objective is to understand the water and contaminant sources and to be familiarised with operational issues that can or already have impacted on local water resources (groundwater and surface water). Groundwater impact sources can be classified as follows: 1. Change in groundwater quantity and water balances: a. Mine de-watering, b. Groundwater supply well- fields, etc. 2. Change in groundwater quality: a. Seepage from waste storage facilities like tailings and waste rock through ARD (acid rock drainage), b. Seepage from unlined dirty water storage facilities, c. Poor quality leakage from old and redundant open pit and/or underground mines through AMD (Acid Mine Drainage), d. Poor quality seepage from other surface infrastructure like metallurgical plants, workshop areas (mainly hydrocarbon contaminants), etc. For the purpose of this paper, the following practical application can be used for discussion purposes. 1. Assessment of de-watering requirements and identification of best fit procedures/applications to de-water a given aquifer. It is important to assess mine de-watering requirements prior to any construction and/or mine development. Sound hydrogeological applications must be applied to understand aquifer characteristics and how de-watering may act as a source of environment risk. This aspect is also discussed under the next heading which deals with pathway understanding. 2. Source Term Evolution. Laboratory analyses on waste material to determine leachate potential and main contaminants associated with the waste material. The process is usually started off by obtaining material samples of mine horizons and waste material for static leach testing and acid base accounting (ABA). Additional and more detailed kinetic testing can be applied to obtain a better idea of long-term leachate characteristics. Information from a number of reference studies is available to guide this process. ABA and kinetic tests will supply answers on the capacity of the material to buffer acidity as well as on subsequent metal and sulphate leaching. the following important aspects related to source term must be considered: Salt and material load assessments, Static ABA testing, Mineralogy, On site monitoring data, Field testing, Geochemical modelling. 3. Water monitoring and other on-site surveys supply additional information on source behaviour. 4. Water Balance calculations will supply an indication of seepages from waste facilities. Unsaturated and saturated seepage models are usually applied and numerical software like SEEPW applied to calculate seepage to groundwater. After the assessment phase has been completed, it is important to capture all data into a dedicated database. Table 1 shows a summary table that can be developed for a given site for database purposes. Table 1: Example of Source List Table

4 Step 1B: Understand the Pathway The second step in conceptual model development is to understand the pathway which the contaminants will follow or the zone of dewatering will developed in. For this discussion pathways relates to subsurface and surface /flow transport. This part of the investigation entails the gathering of geological and hydrogeological reports as well as background information. Intrusive field investigations should also be incorporated. The following list typical steps to be followed to enable a better understanding of site aquifer or pathway systems. Asses the general geographical settings to obtain an understanding of the regional environment, Assessment of all available geological and hydrogeological information, Assessment of all available monitoring data, including surface water sample sites. The following table (Table 3-2) can be used as a guideline of groundwater data that should be collected. Table 2: Typical borehole data to be captured Id X, Y Coo Z [mamsl] Site Description Construction Date Lithology and main water strikes Depth [m] Static Water Level [m] Yield [l/sec] Aquifer Test Main Chemistry 1 2 Conduct a gap analyses to identify information gaps, Field assessments to obtain information to overcome information gaps, these may include geophysical surveys drilling target assessments, drilling and aquifer testing, The end deliverable of the pathway understanding is usually a sequence of conceptual cross-section diagrams presented with tables on aquifer flow parameters and preliminary flow calculations. Some of the important calculations can include simple Darcy Velocity where the aquifer hydraulic conductivity (K [m/day]) and hydraulic head gradient are considered. Aquifer porosity and other aquifer parameters can also be considered. Step 1C: Understand Receptors Receptors can be classified as the end-user of water resources; sensitive environmental entities like an aquifer system with a high yielding capacity; or one of the main rivers in South Africa

5 All receptors must be identified and mapped. This will potentially require a comprehensive GIS exercise and a field hydro-census. 4. STEP 2: DEFINE ZONE OF IMPACT Step 2A: Numerical Applications After comprehensive conceptualisation of the mining, aquifer and regional surface water systems, the direction and extent of contaminant transport and zone of dewatering in groundwater needs to be determined. The main objective of this step is to graphically illustrate the zone of impact and to determine the extent and volume of required mitigation or capital required to resolve the identified issues. The first step in this process entails the collation of data so that it can be imported into a numerical groundwater modelling code. Several numerical codes can be applied from which MODFLOW and FEFLOW is the most popular codes. The simulations will ultimately provide answers on groundwater flow direction, characteristics regarding the interconnection between the waste sources, the groundwater and the receiving water bodies and behavior of contaminants in the aquifer. The real value of hydrogeological modelling should be unlocked by using results for further conceptualisation, scenario predictions and decision-making purposes. After the numerical model is calibrated to satisfactory confidence levels the following logical steps are recommended: a) Delineation of a sulphate plume for a coal or gold mine may be sufficient as a start. Site specific applications needs to be confirmed and presented. This may involve only one chemical element or a suite of elements. The main objective is to graphically present the zone of contamination. b) Apply numerical model to determine the total extend of groundwater de-watering, the 0.5 or 1m contour lines are usually applied to delineate the total extent of de-watering. c) A critical risk and an acceptable risk contour line must be identified. These are usually linked to a final closure plan and regional land use after closure. In a case study completed by GCS the 200mg/l sulphate contour line was selected to delineate the acceptable risk plume and the 1000mg/l contour line was selected to delineate the critical risk plume. d) Determine the coverage / extent of these plume areas (in square meters [m 2 ]) e) The same to be done with the de-watering plume and the footprint to be expressed in m 2. f) All identified receivers are then identified within these plumes listed and risk ranked according to acceptable risk ranking methodology. Step 2B: Water and Salt Balance During this stage the numerical model can be applied to determine a salt and water balance for each impact zone. The volume of contamination is determined by applying the numerical model. The extent of each identified plume is expressed in terms of area (ha) and volume (m 3 ). The volume of each plume is based on the area times the assumed depth of pollution times the porosity. The porosity is based on the average or combined porosity of the aquifer matrix, fractures, cavities, etc. 5. STEP 3: RISK MATRIX AND FINAL HCSM All identified variables in terms of source; pathway and receivers can now graphically be presented to enable a system for future management purposes (refer to Figure 2). GIS or any form of graphical interpretation can be applied. A summary excel spreadsheet or database system is usually very handy to keep track of all source entities and to start off with preliminary impact ratings per identified source/plume by considering a normal rating technique to include:

6 Quantity of waste expressed in m 2, and/ or extent of de-watering expressed in time and area (m 2 ), Leakage potential of waste (normally based on a seepage model), Toxicity of leakage, Infiltration potential of aquifer (look at porosity and hydraulic conductivity), Mass Transport, Depth to Groundwater, Aquifer vulnerability, Receptors, Legal compliance issues, Closure implications. This allows for a better understanding on which problem to focus during the next steps of cost estimation. Once the calculations for diffuse seepage from individual pollution sources are completed, a percentage of contribution to individual plumes are awarded by simply dividing the potential mass flux from individual sources by the total contribution of all the sources in a specific plume area. Water balance data obtained from numerical model simulations needs to be translated into a salt balance for this purpose. This will ultimately provide input to the risk assessment on receiving water bodies in terms of salt load. 6. STEP 4: FINANCIAL MODEL Figure 2: Typical plume delineation plan (ITRC, 2008) The technical aspects that have been assessed in steps 1 to 3 can now be translated into costs and financial terms to assist with long term planning, legal compliance and feasibility of mine site rehabilitation. Uncertainties with regards to the legal requirements, standards and benchmarks, time aspects, environmental impacts, cost, etc. are all factors currently hampering closure planning. Incorporating true life cycle (i.e. from cradle to grave) costs into financial feasibility studies for mines is an essential feature of sound mine development planning. This requires, however, that reliable mine closure and post-closure costs be established before the mine is even put into production. The technical challenges in forecasting what closure elements will be required, particularly in wetter climates where water management can be a significant part of closure, or in areas where extreme events (earthquakes, floods) may occur and then consequently dealing with the uncertainty as to how the regulatory framework may evolve, makes reliable cost forecasting difficult, and requires a significant amount of judgment. The financial modelling exercise is undertaken to identify costs associated with each management option.

7 Step 4A: Determine Rehabilitation Technologies Groundwater rehabilitation methods were identified during the HCSM and numerical modfelling steps and a cost estimate per unit must now be established. It is very important to focus on source rehabilitation and then on pathway interception. Source control usually does not form part of the groundwater closure costing as it is more a direct mine closure and rehabilitation function. The ultimate goal of source control is to minimize the amount of waste by reclamation activities and secondly to minimize rainfall infiltration to less than 1% by applying sound cover and vegetation. It is important to determine what sources can be mitigated/minimized during the operational phase if a mine is still in operation. It is obviously better to apply more resources and capital during operations and less during and after closure. For this paper it will be assumed that sources are dealt with during operation and that source control was already applied. Pathway interception is a secondary function and usually more difficult to apply. Typical pathway interception/treatment technologies include: Active Pathway Interception: interception boreholes and trenches; Passive Pathway Interception: tree plantations; Reactive Barriers and passive treatment technologies; Water treatment technologies: RO plants, lime dosing; and Passive water treatment: wetland systems. At least one treatment option or, if possible, a combination of options must be identified for each plume area based on the best application for the given aquifer system, depth of the plume, duration of mitigation required, etc. Step 4B: Time frame After mitigation technology selection the time period that the closure / rehabilitation will continue for needs to be determined. This can be determined through the aid of the numerical model or geochemical model. Some mine decant problems may occur for a very long time while some plumes will require only limited interception. The following diagram shows the numerical simulation for sulphate concentration at a receptor considering 4 different remediation scenarios. It was determined that this specific plume will require borehole interception for at least 35 years to be able to obtain sulphate concentration of 500 mg/l at a given point. Figure 3: Typical scenario model simulation to show optimal time frame of pathway interception.

8 Step 4C: Costing and Case Study The Financial Model or cost estimation for a typical mine seepage problem is demonstrated by means of a case study. For discussion purposes the following plume delineation information was generated by following all the steps listed in this paper (refer to Table 3 below). For this particular case study a 1000mg/l sulphate plume was mapped as a result of seepage from a typical gold tailings storage facility (TSF). The total plume coverage is approximately 1500ha. Source control will be applied by looking at full reclamation of tailings material and rehabilitation of the footprint area. Interception adjacent to the source will require a block of 45ha of eucalyptus trees around the source area and interception boreholes hydraulically down-gradient of the trees to intercept the sulphate plume before it seeps into the Vaal River. Considering all the aquifer data it was determined that groundwater flow is between 2000 and 3500m3/day across the plume area and that the plume consist of between 7.5m and 15M m3 of storage capacity. If 5 to 7 interception boreholes were constructed, each suppling yields between 4 and 6l/sec, a total pump treatment life of 12 to 18 years will be required to pump sulphate rich groundwater. The water can be used for process water during the remainder of the operational phase and must be treated afterwards. Table 4 below, supplies an overview and example of a typical cost table to supply a capital cost requirement (CAPEX) and an operational cost requirement for the minimum and maximum operational life time (OPEX). It can be seen that significant financial resources will be required and around R34M (ZAR) and operational cost around R4M/annum if all water is treated by RO (reverse osmosis) technology. It can further be seen that approximately R67M will be required over an 18 year period as running and maintenance cost. The ongoing cost or OPEX are usually not included in closure cost estimations and it is clear from this exercise that long term operational costs added significantly to required closure costs. Table 5 supplies an example of a cost breakdown for production boreholes; bill of quantities must be worked out for each identified management option with cost. Table 3: Typical example of sulphate plume management /mitigation plan

9 Table 4: Typical cost table for CAPEX and OPEX Table 5: Example of cost breakdown for a production borehole

10 7. STEP 5: CONTINUOUS REFINING AND IMPROVEMENT A process of annual evaluation, gap analyses, field work, assessments, sensitivity analyses and calibration needs to be incorporated within the process. There should be a list of critical identified aspects that need more data, clarification and/or field investigations. This includes the main uncertainties which comprises other aspects that usually require more attention. A more compressive scientific approach and analysis could therefore be required. The following list some of the potential required refinement: Sensitivity analyses of the models applied, Simulation of different scenarios and trade-off assessment, Confirmation of land use options after closure, Ongoing health and environmental risk assessment. 8. CONCLUSIONS AND STRATEGIC GROUNDWATER MANAGEMENT CONCEPT The main objective of this paper was to illustrate a logical approach towards Groundwater Closure Cost Planning and Management. The following main phases form an essential part of the process: Development of a Hydrogeological Conceptual Site Model by incorporation and assessment of the source, pathway and receiver concept. Development of a stable and efficient database to support the above. Essential to apply the life cycle approach; the process needs to be started as early as possible, preferably during the construction phase of a mine. Define the zone of impact by applying analytical and numerical applications. Apply the source pathway receptor principle to enable sound and realistic scenario predictions. Develop a risk and rehabilitation matrix that feeds into the conceptual site model. Start with a preliminary financial closure cost model and repeat tasks above on a bi-annual time frame. Cost models need a clear understanding of the required mitigation and rehabilitation requirements. Refine and apply continuous improvement. 9. REFERENCING Bell, F.G. (1999). Geological Hazards, their assessment, avoidance and mitigation. Published by E&FN Spon, London. ISBN BHP Billiton, (2012). Mine closure and rehabilitation plan for the Olympic Dam. Department of Minerals and Energy, (2005).Guideine Document for the evaluation of the quantum of closure related financial provision provided by a mine. PRETORIA, Republic of South Africa Department of Water Affairs and Forestry. (2000). Guideline document for the implementation of regulations on use of water for mining and related activities aimed at the protection of water resources. Second edition. Published by The Department of Water Affairs and Forestry, PRETORIA, Republic of South Africa.

11 Department of Water Affairs and Forestry, (2003). Summery Technical Procedure Required for Mine Closure Applications Draft Document. Published by The Department of Water Affairs and Forestry, PRETORIA, Republic of South Africa. Fetter, C.W, (1998). Applied Hydrogeology. Third Edition. Macmillan College Publishing Company, New York. Government of Western Australia Department of Mines and Petroluem and Environmental Protection Authority, (2011). Guidelines for preparing Mine Closure Plans. Hatting R.P., Lake J., Boer R.H., Aucump P., Voljoen C. (2003). Rehabilitation of contaminated gold tailings dam footprints. WRC Report no.1001/1/03, Water Research Commission, Pretoria, South Africa. Hodgson, F.D.I, Usher B.H, Scott, R, Zeelie S, Cruywagen L.M. and de Necker E. (2001). Prediction techniques and preventative measures relating to the post-operational impact of underground mines on the quality and quantity of groundwater resources. Water Research Commission, report no. 699/1/01. Water Research Commission, Pretoria, South Africa. Hutchison, I. and Dettore R (2011). Statistical and Probabilistic Closure Cost Estimating. Proceedings Tailings and Mine Waste Vancouver, BC, November 6 to 9, Kruseman, G.P., and De Ridder, N.A., (1994). Analysis and evaluation of pumping test data. ILRI publications number 47. Second Edition (Completely Revised). International Institute for Land Reclamation and Improvement, Wageningen, The Netherlands. Lake, J. and Hattingh, R.P. (2001). A Guideline to the Development of Rehabilitation management Strategies for Reclaimed Gold Mine Residue Deposits in South Africa. WRC report to be published. Rösner, T., Boer, R.H., Reyneke, R., Aucamp, P. and Vermaak, J. (2001). A Preliminary Assessment of Pollution Contained in the Unsaturated and Saturated Zone Beneath Reclaimed Gold-Mine Residue Deposits, WRC Report K5/797/0/1. Pretoria, South Africa. Scott, R. (1995). Flooding of Central and East Rand gold mines: An investigation into controls over the inflow water, water quality and the predicted impacts of flooded mines. WRC Report no.486/1/95, Water Research Commission, Pretoria, South Africa. Van Zyl, D. (1987). Seepage and Drainage Analysis of Tailings Impoundments Is it Really That Simple? Proceedings of the International Conference on Mining and Industrial Waste Management, Johannesburg.