DUNDEE PRECIOUS METALS - TSUMEB SMELTER: 3D GROUNDWATER FLOW AND CONTAMINANT TRANSPORT Prepared for: Dundee Precious Metals Tsumeb (Pty) Limited SLR Project No.: 733.04040.00010 Revision No. 1: Month/Year: March 2018 Dundee Precious Metals Tsumeb (Pty) Limited Dundee Precious Metals - Tsumeb Smelter: 3D Groundwater Flow and Contaminant Transport File name: Appendix E Addendum - SLR Project No.: 733.04040.00010 Month/Year: March 2018 DPMT_Groundwater_flow_and_transport_model_Report_v1.1 DOCUMENT INFORMATION Title Dundee Precious Metals - Tsumeb Smelter: 3D Groundwater Flow and Contaminant Transport Project Manager Arnold Bittner Project Manager e-mail [email protected] Author Markus Zingelmann, Winnie Kambinda Reviewer Arnold Bittner Keywords Keywords Status Final Authority Reference No SLR Project No 733.04040.00010 DOCUMENT REVISION RECORD Rev No. Issue Date Description Issued By Revision No. 0 January 2018 Client Draft report issued to client AB Revision No. 1 March 2018 Final Report AB BASIS OF REPORT This document has been prepared by an SLR Group company with reasonable skill, care and diligence, and taking account of the manpower, timescales and resources devoted to it by agreement with Dundee Precious Metals Tsumeb (Pty) Limited part or all of the services it has been appointed by the Client to carry out. 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Information, advice, recommendations and opinions in this document should only be relied upon in the context of the whole document and any documents referenced explicitly herein and should then only be used within the context of the appointment. i Dundee Precious Metals Tsumeb (Pty) Limited Dundee Precious Metals - Tsumeb Smelter: 3D Groundwater Flow and Contaminant Transport File name: Appendix E Addendum - SLR Project No.: 733.04040.00010 Month/Year: March 2018 DPMT_Groundwater_flow_and_transport_model_Report_v1.1 EXECUTIVE SUMMARY The Environmental Impact Assessment (EIA) for the proposed Dundee smelter expansion required a ground- and surface water study to investigate the likely impacts that additional infrastructure could have on the environment and for these results to be included in a cumulative site impact assessment. From the Groundwater and Surface water Study (SLR 2016), it is been concluded that the planned smelter expansion will have a relatively small impact on the groundwater quantity, but potentially a cumulative negative impact on the groundwater quality. However, there is already a negative impact on the groundwater quality existing, due to significantly intensive smelter operations during the past 100 years. For this purpose, a reliable estimation of the groundwater flow and contaminant transport was needed. In line with the Environmental and Social Impact Assessment (ESIA) Amendment Process for the Proposed Tsumeb Smelter Upgrade and Optimisation Project, a 3D groundwater flow and transport model has been setup to meet these requirements. This model provides firstly the results for regional and local groundwater flow conditions and secondly a realistic and reliable assessment of potential groundwater contaminant transport. The model has been setup using the finite-element based software FEFLOW 7 with a steady-state flow and a coupled transient transport solution. Applied hydraulic conductivity values range between 0.002 m/d within the Basement-Complex (aquiclude) and 55 m/d in the fractured and karstified Hüttenberg-Formation (dolomite aquifer). In addition, since site specific porosities are not available, default values according to empirical investigations and groundwater models developed in similar environments were assumed. Porosity values range between 0.1% in the low permeable basement and up to 8% in the fractured dolomites of the Tsumeb- Subgroup (e.g. Hüttenberg-Formation). Regional and local faults and fracture systems have been included as discrete-features into the finite-element model, assuming that they are acting as groundwater pathways. Groundwater recharge has been taken into consideration and varies from 0.01% to 10% of mean annual rainfall (i.e. recharge ranges from 1 to 55 mm/a). For the model calibration existing water level records from a previous hydrocensus (GCS 2016) and further groundwater level readings were used. The calibrated model results meet requirements for a reliable and robust flow model solution (see Reilly & Harbaugh 1996) with an absolute model error of 2.51%. In general, the groundwater flow pattern is comparable to the existing regional flow (see GKW & BICON Namibia 2003). Based on the calibrated flow solution, groundwater contaminant transport has been simulated. The transient non-reactive transport modelling does not consider adsorption, precipitation and retardation processes, which could further reduce the transport of contaminants. No specific source concentration was modelled and the plumes are illustrated in percentages of the relative source concentration. This is a worst case assumption as in reality seepage concentration will decline over time due to the above mentioned processes. The potential pollution scenarios are showing the predicted situation after 10 years, 25 years, 100 years, and 200 years after the initial contamination started from the relevant source areas. The following results can be summarised: After 10 years, the plume is predicted to spread mainly towards the general flow direction and concentrations decrease rapidly over a short distance. After 25 years, the plume is predicted to spread mainly in the general flow direction to the north of the Tsumeb Smelter site. After approximately 800 m, the contaminant concentrations drop to general background concentrations. After 100 years, at a maximum distance of around 3.2 km from the origin concentrations drop to below 5% of the initial concentration. Although, the plume is spreading further towards the northeast, concentrations do not change, in general (this scenario represents most likely the current situation). After 200 years, there is no significant change of the plume extent, although minor changes of the concentrations in the close vicinity of the source can be seen. At this stage, a kind of equilibrium has been reached, where reduction processes and dispersion cancel each other out. The hydraulic barrier, represented by the Maieberg Formation limestone and shale, potentially also retards the pollution plume to the north and into the irrigation farming area. ii Dundee Precious Metals Tsumeb (Pty) Limited Dundee Precious Metals - Tsumeb Smelter: 3D Groundwater Flow and Contaminant Transport File name: Appendix E Addendum - SLR Project No.: 733.04040.00010 Month/Year: March 2018 DPMT_Groundwater_flow_and_transport_model_Report_v1.1 CONTENTS EXECUTIVE SUMMARY ................................................................................................................................ II 1. INTRODUCTION ................................................................................................................................. 1 1.1 BACKGROUND................................................................................................................................................ 1 1.2 MODEL OBJECTIVES ....................................................................................................................................... 2 1.3 SOFTWARE AND MODEL FUNCTION .............................................................................................................. 2 2. GENERAL SETTINGS ............................................................................................................................ 2 2.1 FOOTPRINT OF THE TSUMEB SMELTER ......................................................................................................... 2 2.2 TOPOGRAPHY AND HYDROLOGY ................................................................................................................... 3 2.3 GEOLOGY AND HYDROGEOLOGY ................................................................................................................... 4 2.1 GROUNDWATER QUALITY AND CONTAMINANTS .......................................................................................... 7 3. CONCEPTUAL MODEL ......................................................................................................................... 8 3.1 PREVIOUS MODEL SOLUTIONS .....................................................................................................................