South West/OO-TO E n v ir o n m e n t A g e n c y Wheal Jane Minewater Project Consultancy Studies 199G-1999 Appraisal and Selection of Long Term Treatment Option December 1998 Knight Piesold in association with Plymouth M arin e Laboratory RPA ENVIRONMENT AGENCY (SOUTH WEST) Wheal Jane Minewater Project Consultancy Services 1996 - 1999 Appraisal and Selection of Long Term Treatment Option E n v ir o n m e n t Ag e n c y NATIONAL LIBRARY & INFORMATION SERVICE SOUTH WEST REGION Manley House. Kestrel Way, Exeter EX2 7LQ Knight Piesold Limited Kanthack House Station Road Ashford, Kent TN231PP Telephone: 01233 658200 December 1998 Fax: 01233 658299 11139\R11369 Email: [email protected] Environment Agency (South West) Wheal Jane Minewater Project Appraisal and Selection o f Long Term Treatment Option Consultancy Studies J 996-1999 CONTENTS Page EXECUTIVE SUMMARY.........................................................................................................................1 1. INTRODUCTION..................................................................................................................... 1-1 1.1 PROJECT DESCRIPTION........................................................................................... 1-2 1.1.1 Previous Studies................................................................................................1-2 1.1.2 The Current Project.......................................................................................... 1-2 1.2 APPROACH...................................................................................................................1-5 1.2.1 Report Structure................................................................................................1-6 1.3 ACKNOWLEDGEMENTS.......................................................................................... 1-7 2. BACKGROUND....................................................................................................................... 2-1 2.1 REGIONAL CONTEXT............................................................................................... 2-1 2.1.1 Site Description and Catchment Characteristics............................................. 2-1 2.1.2 Economic Perspective;...................................................................................... 2-1 2.1.3 Geology and Mining History........................................................................... 2-2 2.2 THE MINEWATER LEGACY.....................................................................................2-3 2.2.1 Mechanisms and Historic Levels.....................................................................2-3 2.2.2 Effectof Closure of Wheal Jane...................................................................... 2-4 2.2.3- Recent Changes to the Minewater Regimes .................................................... 2-7 3. EXISTING TREATMENT...................................................................................................... 3-1 3.1 INTRODUCTION......................................................................................................... 3-1 3.2 DESCRIPTION AND PERFORMANCE..................................................................... 3-1 3.2.1 Contingency Design......................................................................................... 3-2 3.2.2 Cessation of Mining by SCP............................................................................ 3-2 3.3 MANAGEMENT AND OPERATION......................................................................... 3-3 3.3.1 Discharge Consent.............................................................................................3-3 3.3.2 Treatment Costs................................................................................................3-3 4. WATER QUANTITY AND QUALITY................................................................................. 4-1 4.1 WATER QUANTITY AND QUALITY..................................... ..................................4-1 4.2 INFLUENT WATER QUANTITY AND QUALITY..................................................4-2 4.3 WATER QUALITY OBJECTIVES..............................................................................4-3 4.4 STATUTORY REQUIREMENTS................................................................................4-3 4.5 REQUIRED METAL REMOVAL................................................................................4-4 5. PROCESS ROUTE ALTERNATIVES.................................................................................. 5-1 5.1 INTRODUCTION......................................................................................................... 5-1 5.2 PREVENTION AND CONTROL OF DISCHARGES................................................5-1 5.3 ACTIVE TREATMENT................................................................................................5-2 5.3.1 Oxidation and Chemical Neutralisation (OCN)...............................................5-2 5.3.2 Biochemical Sulphidisation (BCS).................................................................. 5-3 5.3.3 Ion Exchange (IEX).......................................................................................... 5-4 5.3.4 Treated Effluent Quality (TEQ)....................................................................... 5-4 5.3.5 Alternative and Emerging Technologies......................................................... 5-5 K n igh t Pie sold Final Version (i) V:\REPORTSM1139\fU722\t722FLnildoc 06/12/99 Environment Agency (South West) Wheal Jane Minewater Project Appraisal and Selection o f Long Term Treatment Option Consultancy Studies 1996-1999 5.4 PASSIVE TREATMENT............................................................................................. 5-6 5.4.1 Introduction.......................................................................................................5-6 5.4.2 Descriptions......................................................................................................5-6 5.4.3 Performance and Results.................................................................................5-7 5.4.4 Applicability of Passive Treatment................................................................. 5-7 5.4.5 Summary........................................................................................................... 5-9 5.5 SLUDGE MANAGEMENT.........................................................................................5-9 5.6 COMPARISON OF ALTERNATIVES.................................................................... 5-10 5.6.1 Sustainability...................................................................................................5-10 6. DERIVATION OF TREATMENT OPTIONS..................................................................... 6-1 6.1 INTRODUCTION......................................................................................................... 6-1 6.2 IDENTIFICATION OF TARGET TREATMENT ALTERNATIVES...................... 6-1 6.3 TREATMENT SCENARIOS........................................................................................6-1 6.4 DESCRIPTION OF MODELLING..............................................................................6-3 6.5 MODELLING RESULTS............................................................................................. 6-3 6.6 TREATMENT OPTIONS............................................................................................. 6-6 7. BIOLOGICAL IMPACTS....................................................................................................... 7-1 7.1 INTRODUCTION......................................................................................................... 7-1 7.2 SUMMARY OF FINDINGS.........................................................................................7-1 7.2.1 Estuarine Chemistry.........................................................................................7-2 7.2.2 Predicted Effect of Minewater Treatment........................................................7-3 7.2.3 Conclusions.......................................................................................................7-4 8. TREATMENT COSTS............................................................................................................ 8-1 8.1 DEVELOPMENT OF TREATMENT OPTIONS........................................................8-1 8.1.1 Plant Location.................................................................................................. 8-1 8.1.2 Site Descriptions.............................................................................................. 8-1 8.1.3 Land Ownership...................................... ........................................................ 8-2 8.1.4 Proximity.......................................................................................................... 8-2 8.1.5 Minewater Supply............................................................................................8-3 8.1.6 Planning Implications.......................................................................................8-4 8.1.7 Summary of Treatment Options...................................................................... 8-5 8.2 TREATMENT COST ESTIMATES............................................................................8-6 8.2.1 Scope of Evaluation..........................................................................................8-6 8.2.2 Capital Costs.....................................................................................................8-7