1 Introduction
1.1 Mining on the West Coast and in Southland
1.1.1 Coal mining
1.1.2 Gold mining
1.2 Potential environmental effects of mining
1.2.1 Mine drainage chemistry
1.2.2 Biological effects
1.2.3 Reducing impacts – management and treatment
1.3 Development of a framework to assess mining impacts on streams
1.3.1 Regulation of the mining industry
1.3.2 The Framework
1.4 Document structure
2 Predicting potential ecological impacts on streams
2.1 Introduction
2.2 Historical data
2.3 Baseline information
2.3.1 Site hydrogeology
2.3.2 Baseline chemical water quality
2.3.3 Baseline biological monitoring
2.4 Checklist
3 Mine drainage and downstream water chemistry
3.1 Introduction
3.1.1 Commodity and region
3.2 Analysis of rocks from the proposed mine site
3.2.1 Important minerals and field observations
3.2.2 Sampling strategies for geochemical characterisation of rocks
3.2.3 Acid–base accounting (ABA)
3.2.4 Geochemical testing to assess the trace element content of rocks
3.2.5 Assessing the reactivity of rocks – kinetic tests
3.3 Prediction of water quality downstream of a mine
3.3.1 Site hydrogeology
3.4 Checklist
4 Coal - potentially acid-forming
4.1 Introduction
4.2 Predicted water quality
4.2.1 Mine drainage
4.2.2 Downstream water quality
4.3 Predicted ecological impact
4.4 Operational management and treatment
4.4.1 Operational management
4.4.2 Treatment
4.4.3 AMD from historical mining activities – additional considerations for treatment
4.5 Checklist
5 Coal – non-acid-forming
5.1 Introduction
5.2 Predicted water quality
5.2.1 Downstream water quality
5.3 Predicted ecological impact
5.4 Operational management and treatment
5.5 Checklist
6 Gold – hard rock
6.1 Introduction
6.2 Predicted water quality
6.2.1 Downstream water quality
6.3 Predicted ecological impact
6.4 Operational management and treatment
6.4.1 Prevention and mitigation
6.4.2 Treatment
6.5 Checklist
7 Gold – alluvial
7.1 Introduction
7.2 Predicted water quality
7.3 Predicted ecological impact
7.4 Operational management and treatment
7.5 Checklist
8 Decision making and monitoring
8.1 Decision-making steps
8.2 Ongoing monitoring
8.2.1 Monitoring of rock geochemistry
8.2.2 Leachate monitoring
8.2.3 Treatment system monitoring
8.2.4 Water quality
8.2.5 Biological monitoring
8.3 Checklist
9 Worked example and service providers
9.1 Worked example
9.1.1 Overview
9.1.2 Step 1: Collate background and baseline information
9.1.3 Step 2: Collect rock samples
9.1.4 Step 3: Geochemical testing to determine acid-forming status
9.1.5 Step 4: Predict mine drainage chemistry
9.1.6 Step 5: Predict stream water chemistry
9.1.7 Step 6: Determine the ecological impact
9.1.8 Step 7: Consider whether impacts are acceptable
9.1.9 Step 7a: Decide on management and treatment
9.1.10 Step 8: Design ongoing monitoring
9.2 Service providers
10 References
11 Additional reading
11.1 Further reading
11.1.1 General
11.1.2 Geochemistry
11.1.3 Biological effects
11.1.4 Operational management and treatment
11.2 Publications arising from the research programme
11.3 New Zealand case studies authored or co-authored by the research team
11.3.1 Hard rock gold
11.3.2 Alluvial gold
11.3.3 Treatment options for mine drainage
List of Figures
Figure 1 Unimpacted tributary (left) mixes with AMD-contaminated water, Cascade Creek (Denniston).
Figure 2 Simplified food web of a stream ecosystem. Effects of mine drainage on fish can be direct, such as toxicity from low pH, or indirect, such as effects on algae which affect invertebrates and, in turn, fish.
Figure 3 General framework and detailed step-by-step guide for predicting and managing water quality (pH and metal) impacts from mining on streams
Figure 4 Outline of document structure.
Figure 5 Examples of macroinvertebrates that commonly live in streams and rivers throughout New Zealand. Top left: the spiral-cased caddisfly Helicopsyche. Top right: the stonefly Zelandoperla. Bottom left: ubiquitous mayfly, Deleatidium. Bottom right: the common stonefly Zelandobius.
Figure 6 Before-after-control-impact (BACI) sampling designs for assessing the environmental effects of human impacts on stream ecosystems. Each circle represents a sampling site. A rigorous BACI design includes multiple sampling sites in impacted reaches, and upstream and additional stream controls, both before and after an impact.
Figure 7 Formations that could be disturbed by coal and gold mining on the West Coast and in Southland.
Figure 8 NAG pH vs NAPP graph. Samples that are acidic according to both NAG and NAPP tests plot in the PAF field, while those that are non-acidic by both tests plot in the NAF field. Samples where one of the analyses indicates acidic and the other indicates non-acidic plot in the uncertain field and require further investigation.
Figure 9 NAG pH vs MPA/ANC. This plot is interpreted in the same manner as Fig. 8.
Figure 10 Basic process for determining water quality downstream of a mine.
Figure 11 Potential water chemistry from PAF coal measures.
Figure 12 Potential ecological outcomes arising from a PAF coal mine on the West Coast. Metal limits are dissolved metals and refer to the sum of Fe and Al concentrations.
Figure 13 Options and effectiveness with time (TEAM NT 2004, in INAP 2009).
Figure 14 Prioritisation for consideration of applicability of different waste-rock management strategies. Refer to above text for details on different techniques.
Figure 15 Flow chart to guide selection between active and passive treatment for AMD (modified from Waters et al. 2003).
Figure 16 Flow chart to design a site-specific active treatment system for AMD (modified from Rajaram et al. 2001). The generic treatment step is shown on the side of the diagram. Note for treatment of suspended solids see also Appendix B.
Figure 17 Summary of the key benefits of the five most commonly used chemicals for the dosing-with-alkali step.
Figure 18 Comparison of potential costs for active treatment of two hypothetical AMDs over 5 and 20 years using the five most commonly used chemicals. These costs were determined using AMDTreat (Means et al. 2003) and are based on cost of chemicals in New Zealand in 2010 and default parameters for labour and construction costs provided in AMDTreat. A low-flow, low-acidity (30 L/s, 500 mg/L) option is compared with a high-flow, high-acidity (80 L/s, 1000 mg/L) option over 5- and 20-year treatment periods.
Figure 19 Flow chart to select among AMD passive treatment systems based on water chemistry (high Fe), topography, and available land area (Trumm 2007).
Figure 20 Flow chart to select among AMD passive treatment systems based on water chemistry (low Fe), topography, and available land area (Trumm 2007).
Figure 21 Treatment system costs for a hypothetical AMD determined using AMDTreat (Means et al. 2003) using 2010 cost of limestone in New Zealand and default parameters for labour and construction costs provided in AMDTreat. Aew, aerobic wetland; Anw, anaerobic wetland; OLC, open limestone channel; ALD, anoxic limestone drain; RAPS, reducing and alkalinity producing system; SLB, slag leaching bed; LLB, limestone leaching bed; DW, diversion well; Bio, bioreactor. Hatched area indicates the non-chemical costs. Note: the costs shown in this figure cannot be directly compared with those shown in Figure 18 as the hypothetical AMDs considered in these two examples are markedly different (Appendix F).
Figure 22 Potential ecological impacts arising from drainage from coal mining in non-acid-forming regions.
Figure 23 Predicted water quality associated with a hard-rock gold mine on the West Coast, depending on mineralogy of mineralised rock (ore), mine processing system, and topography of the site where waste is deposited.
Figure 24 Ecological impact outcomes arising from hard-rock mine drainage based on predicted water chemistries.
Figure 25 Summary of mitigation strategies for environmental issues at a West Coast gold mine. The principal strategy is to remove As and Sb from discharge waters via adsorption to Fe oxyhydroxide. If insufficient natural Fe oxyhydroxide formation occurs, a treatment system is required.
Figure 26 Selection of passive or active treatment for As removal.
Figure 27 Flow chart of the potential aquatic impacts arising from an alluvial gold mine, bolding indicates most likely outcome.
Figure 28 Framework for predicting and managing water quality impacts on streams from mining.
Figure 29 Topographic map showing mine and waste dump footprint.
Figure 30 Map showing drill-hole location and cross-section line from geological report.
Figure 31 Cross section A-A’.
Figure 32 Cross section B-B’.
Figure 33 Cross section C-C’.
Figure 34 Cross section D-D’.
Figure 35 Cross section E-E’.
Figure 36 Cross section F-F’.
Figure 37 Modifed Figure 11 to illustrate the path followed to predict generic water chemistry for the proposed mine.
Figure 38 Modified Figure 12 showing the pathway to determine the potential ecological outcome for the proposed mine.
Figure 39 Modified Figure B1 showing the pathway for determining treatment of total suspended solids for the hypothetical example mine.
Figure 40 Modified Figure 16, showing the decision pathway for the selection of a treatment system for the hypothetical example mine.
Figure 41 Location of treatment system and monitoring points.
List of Tables
Table 1 Summary to interpreting acid–base accounting results.
Table 2 Active treatment systems to remove As.
Table 3 Hypothetical ABA results of samples collected during exploratory drilling.
Table 4 Companies providing services relevant to mining impact assessment.
Appendices
Appendix A Regulatory requirements
Appendix B Suspended solids
Appendix C Geochemistry
Appendix D Biological impacts
Appendix E Operational management
Appendix F Reducing impacts – treatment techniques
Appendix G Extreme events
