WHEAL JANE MINEWATER STUDY ENVIRONMENTAL APPRAISAL AND TREATMENT STRATEGY f\lRA - SoJ VV> “f-4 '-f WHEAL JANE MINEWATER STUDY Environmental Appraisal and Treatment Strategy NRA National Rivers Authority South Western Region Knight Piesold RPA Kanthack House Risk & Policy Analysts Ltd Station Road Warren House, Beccles Road Ashford, Kent Loddon, Norfolk TN23 1PP NRJ4 6JL WHEAL JANE MINEWATER STUDY ENVIRONMENTAL APPRAISAL AND TREATMENT STRATEGY Contents EXECUTIVE SUMMARY 1. INTRODUCTION 2. BACKGROUND 3. THE RELEASE OF MINEWATER FROM WHEAL JANE 4. EXISTING TREATMENT SYSTEM 5. THE CURRENT SITUATION 6. HYDROLOGICAL MODELLING 7. DEVELOPMENT OF WATER QUALITY OBJECTIVES 8. LOCATION OF LONG TERM TREATMENT PLANT 9. PREVENTION & CONTROL OF DISCHARGES 10. PASSIVE TREATMENT TECHNOLOGY 11. ACTIVE TREATMENT TECHNOLOGY 12. SLUDGE DISPOSAL 13. ECONOMIC BENEFITS OF IMPROVEMENTS IN WATER QUALITY 14. TREATMENT OPTIONS Final Version NRA South Western Knight Piesold Wheal Jane Minewater Study Executive Summary Environmental Appraisal and Treatment Strategy EXECUTIVE SUMMARY INTRODUCTION Wheal Jane is an abandoned underground tin mine in Cornwall. After mine closure in 1991, underground pumping ceased, allowing groundwater levels to recover, releasing acidic metal laden minewater into the Camon River. The result was a highly visible and widely reported pollution incident extending into the Fal Estuary. In 1992 the NRA set up a project with the following objectives: - • Amelioration of the effects of the metal rich minewater from Wheal Jane on the Camon River and Fal Estuary. • Development of water quality objectives for the Camon River. • Research into the most appropriate and cost effective long term treatment strategies for achieving various water quality objectives. This report provides the basis for the NRA’s recommendations, to the DoE, on the long-term options for treating the Wheal Jane minewater. BACKGROUND The mines in the Camon Valley have been worked as far back as 2000 BC, although extensive mining only began in the 17th Century. By the 1850s the mines in the Camon Valley were the largest group of copper producers in the world. The effect of this industrial activity on the valley has been: • The deposition of metal-rich silt in the Camon River, Restronguet Creek and Carrick Roads. • Dewatering and lowering of the groundwater table by both pumping and the construction of drainage tunnels (adits). • Elevated metal concentrations in the local watercourses and the Fal Estuary. THE RELEASE OF MINEWATER FROM WHEAL JANE Following mine closure and the cessation of dewatering, it became apparent that a release of minewater into the Camon River was inevitable. As minewater rose to the level of drainage adits, the NRA exercised its statutory powers to instigate an emergency treatment system. Despite attempts at treatment, there was an uncontrolled release of minewater on January 13, 1992 after an adit plug failed. Final Version NRA South Western Page EX/1 Knight Piisold Wheal Jane Minewater Study Executive Summary Environmental Appraisal and Treatment Strategy Water quality in the Camon River and the estuary was greatly affected, with concentrations of many metals exceeding Environmental Quality Standards (EQS) by up to two orders of magnitude. The release of high iron loadings also caused short-term discolouration of Restronguet Creek and the Carrick Roads. The treatment system, instigated by the NRA, has since been progressively upgraded and comprises: • pumping of minewater from underground; • the addition of hydrated lime to neutralise the acidic water, resulting in the formation of a metal hydroxide precipitate (metalliferous sludge); • flocculation, to promote rapid settlement of the metalliferous sludge; • sedimentation and storage of the resultant metalliferous sludge in the Clemows Valley Tailings Dam. The existing treatment system is located on the Wheal Jane mine site and is operated on behalf of the NRA by South Crofty pic. The system currently treats on average 155 1/s but now has sufficient capacity to handle up to 300 1/s. Monitoring has indicated that on average 97.5% of the metals are recovered from the treated minewater. By the end of 1994, the system had removed some 12 500 t of metal from the outflowing minewater and has been responsible for minimising the environmental impact on the Fal Estuary. Monitoring has demonstrated that the effects of the minewater release on both water quality and discolouration were short-lived. There appears to have been no major adverse effects from the incident on the biota of the estuary. THE CURRENT SITUATION Although the existing treatment strategy has significantly reduced the release of untreated minewater to the Camon River, an overflow of untreated minewater still occurs during the winter and spring from Nangiles Adit. Metal concentrations in the Wheal Jane mine have declined since 1992 and are typically one order of magnitude lower, as can be seen on Figure EX. 1. Metal concentrations in the Camon River have also declined rapidly and are now at pre-incident levels. However, due to other sources of contamination, the concentrations of a number of metals in both the Camon River and Restronguet Creek still exceed EQS under the European Community (EC) Dangerous Substances Directive. Zinc levels in part of the Fal Estuary also exceed the EC Shellfish Waters Directive. The Wheal Jane complex, together with County Adit, are the major sources of contamination in the Camon River. However, significant amounts of metals also are contributed from other tributaries and non-point sources. For this reason there would still be a significant metal loading in the Camon River even if the two major point sources (Wheal Jane and County Adit) were treated. Final Version NRA South Western Page EX/2 Knight Piesold Wheal Jane Minewater Study Executive Summary Environmental Appraisal and Treatment Strategy Photograph Ex.l Camon River - Catchment above Grenna Bridge Final Version NRA South Western Knight Piesold Wheal Jane Minewater Study Executive Summary Environmental Appraisal and Treatment Strategy Figure EX 1 Measured Total Zinc and Iron Concentrations in No.2 Shaft Iron Concentration (mg/1) NRA South Western Final Version Knight Piesold Wheal Jane Minewater Study Executive Summary Environmental Appraisal and Treatment Strategy WATER QUALITY OBJECTIVES FOR THE CARNON RIVER Based on statutory ana other requirements, the following water quality objectives have been adopted for the Camon River: • The "No Deterioration" objective : to maintain water quality at 1993-1994 levels. • The "North Sea Commitments" objective : to achieve a reduction in the zinc loading in line with UK commitments made at the 1985 North Sea Conference. • The "EC Directive" objective : to achieve full compliance with the EC Dangerous Substances Directives. In addition a "No Treatment" scenario (do nothing option) has been considered. The maximum permissible metal concentrations allowable for each of water quality objectives are summarised in Table EX-1, together with the predicted metal concentrations for the "No Treatment" scenario. Table EX-1 : Water Quality Objectives for the Carnon River Predicted Water Quality Objectives "No Treatment" Substance Water Quality No North Sea EC Directive Deterioration Commitments Cadmium 95 %ile 11 (T) -- as /ig Cd/1 AA 21 (T) 6 (T) - 1.0 (T) Copper 95 %ile 0.9 (T) -- as mg Cu/1 AA 0.8 (T) 0.6 (T) - 0.028 (D) Zinc 95 %ile 13 (T) - - as mg Zn/1 AA 26 (T) 6 (T) 3 (T) 0.5 (T) Arsenic 95 %ile 0.3 (T) - - as mg As/1 AA n/a 0.1 (T) - 0.050 (T) Iron 95 %ile 17 (D -- as mg Fe/1 AA 52 (T) 8 (T) - 1.0 (D) Manganese 95 %ile 1.0 (T) -- as mg Mg/1 AA 1.7 (T) 0.7 (T) - - Aluminium 95 %ile 4.0 (T) -- as mg Al/1 AA 6.2 (T) 2.1 (T) - - PH 95 %ile 4.2 - 6.0 as pH units 5 %ile n/a 7.1 - 9.0 Notes : EC Directive EQS values based on hardness > 250 mg/1 CaCOj/1. AA ... Annual Average (T) ... Total metal; (D) ... Dissolved metal. n/a ... not available Where a particular objective does not contain targets for every parameter, the values ascribed in the prcccding obj*xlive have been applied. Final Version NRA South Western Page EX/3 Knight Piesold Wheal Jane Minewater Study Executive Summary Environmental Appraisal and Treatment Strategy An assessment was made of how much minewater from Wheal Jane would need to be treated in order for the river to meet the various water quality objectives. The treatment requirements necessary to achieve the "No Deterioration" and "North Sea Commitments" water quality objectives are summarised in Table EX-2. Table EX-2 : Minewater Treatment Capacity to meet each Water Quality Objective Annual probability of non- 50% 5% compliance Maximum Average Maximum Average capacity flow capacity flow (I/s) (I/s) (1/s) (1/s) No Deterioration Annual Average 190 160 270 180 95%ile 210 170 300 190 North Sea Commitments Annual Average 230 175 300 190 EC Directive Unable to meet all EC Directive Requirements Modelling of water quality in the Camon River has indicated that the EC Directive Objective cannot be achieved, even if all the waters from both Wheal Jane and County Adit were treated. This is due to the presence of unidentified diffuse sources of contamination associated with other abandoned mineworkings. THE LONG TERM STRATEGY As part of the development of a long-term treatment strategy, studies have been undertaken to assess the potential for minimising the environmental impact of the minewater by: • Passive treatment. • Active treatment. • Prevention and control. PASSIVE TREATMENT TECHNOLOGY The treatment of acidic metal-rich minewaters using passive systems is well established, with the design of each passive system dependent upon site specific criteria. A pilot treatment plant has been constructed in the Camon Valley and has been designed to treat up to 1.7 1/s of minewater (1% of the average outflow).