Difference between revisions of "Chapter 4"

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<div id="Figure 4-5" style="text-align:center">'''Figure 4-5: Major Steps Involved in Extraction Metallurgy of Metals'''<br />
 
<div id="Figure 4-5" style="text-align:center">'''Figure 4-5: Major Steps Involved in Extraction Metallurgy of Metals'''<br />
[[Image:MajorStepsInvolvedinExtraction.gif]]</div> (adapted from SME, 2008)
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[[Image:MajorStepsInvolvedinExtraction.gif]]</div>  
  
 
This Section 4.3 describes how the geometry, physical properties, and structure of common mine and process facilities influence or control, or both influence and control, the production and pathways of ARD. Conceptual models illustrate the chemical reactions occurring within each facility, as well as the movement of oxygen, heat, and water that govern sulphide oxidation and transport of oxidation products. More technical detail on sulphide oxidation and transport of oxidation products is also provided in Chapter 2.
 
This Section 4.3 describes how the geometry, physical properties, and structure of common mine and process facilities influence or control, or both influence and control, the production and pathways of ARD. Conceptual models illustrate the chemical reactions occurring within each facility, as well as the movement of oxygen, heat, and water that govern sulphide oxidation and transport of oxidation products. More technical detail on sulphide oxidation and transport of oxidation products is also provided in Chapter 2.

Revision as of 22:11, 26 February 2010

4.0 Defining the Problem – Characterization

4.1 Introduction
4.2 Site Characterization Approach
4.2.1 Conceptual Site Model Development
4.2.2 Mine Phases
4.3 Sources of Acid Rock Drainage, Neutral Mine Drainage, and Saline Drainage
4.3.1 Surface Mining – Open Pit
4.3.2 Underground Mining
4.3.3 Waste Rock and Ore Stockpiles
4.3.4 Tailings Piles and Ponds
4.3.5 In Situ Solution Mines
4.3.6 Heap Leach Piles
4.3.7 Coal and Uranium Mining Specific Acid Rock Drainage Sources
4.4 Components of Site Characterization
4.4.1 Geo-environmental Models
4.4.2 Source Material Geochemical Characterization
4.4.3 Watershed Characterization – The Hydrologic Cycle
4.4.4 Watershed Characterization - Assimilative Capacity of the Receiving Environment
4.4.5 Watershed Characterization – Biological Receptors
4.4.6 Watershed Characterization – Archaeology and Cultural Value
4.5 Selected Characterization Tools
4.5.1 Geophysics
4.6 Summary
4.7 References
List of Tables
List of Figures


4.0 Defining the Problem – Characterization

4.1 Introduction

The generation, release, mobility, and attenuation of acid rock drainage (ARD), neutral mine drainage (NMD), and saline drainage (SD) are complex processes governed by a combination of physical, chemical, and biological factors (see Chapter 2). Whether ARD, NMD, or SD enters the environment depends largely on the characteristics of the sources, pathways, and receptors involved. Characterization of these features is therefore key to the prediction, prevention, and management of ARD, NMD, and SD at mine sites.

Environmental characterization programs are designed to collect sufficient data to answer the following questions:

  • Is ARD likely to occur? What type of drainage is expected (ARD/NMD/SD)?
  • What are the sources of ARD? How much ARD will be generated and when?
  • What are the significant pathways that transport contaminants to the receiving environment?
  • What are the anticipated environmental impacts of ARD release to the environment?
  • What can be done to prevent or mitigate/manage ARD?

To address the above listed questions, expertise from numerous disciplines is required, including geology, mineralogy, hydrology, hydrogeology, geochemistry, biology, meteorology, and engineering (Figure 4-1). Fundamentally, the geologic characteristics of the ore body and host rock (or the coal seam and overburden) define the type of drainage generated as a result of mining. The site climatic and hydrologic/hydrogeologic characteristics define how COIs present in mine drainage are transported through the receiving environment to receptors.

Figure 4-1: Components of Site Characterization Program
ComponentsofSiteCharacterizationProgram.jpg

Because the geologic characteristics of mineral deposits exert important and predictable controls on the environmental signature of mineralized areas both before mining and during mining (Plumlee, 1999), a preliminary assessment of the potential for ARD is typically made based on review of geologic data collected during exploration. Baseline environmental characterization of metal concentrations in various media (i.e., water, soils, vegetation, and biota) may also provide an indication of ARD potential and documents potentially naturally elevated metal concentrations. The initial assessment of ARD potential is refined during mine development and operation as detailed characterization data on the environmental stability of the waste and ore materials are obtained. During mine development, the magnitude and location of sources of mine and process discharges to the environment are identified. The boundaries of the receiving watersheds are delineated based on topography, defining the site characterization boundary. Meteorologic, hydrological, and hydrogeological investigations are conducted to characterize the amount and direction of water movement within the watershed (i.e., the hydrologic cycle) to evaluate COI transport pathways. Potential biological receptors within the watershed boundary are identified. Over the mine life, the focus of the watershed characterization program evolves from establishment of baseline conditions, to prediction of drainage release and transport, to monitoring of the environmental conditions and impacts.

This chapter presents the approach and methods typically applied to characterize the release, transport, and fate of COIs present in ARD, NMD, and SD (i.e., sulphate, metals/metalloids, acidity) at a mine site. Despite inherent differences at mine sites (e.g., commodity type, climate, regulatory framework), the general approach to site characterization is similar, as shown below.

  • Define the quantity and quality of drainage potentially generated by different sources
  • Identify surface and groundwater pathways that transport drainage from sources to receptors
  • Identify receptors that will be affected by exposure to drainage
  • Define the risk of this exposure

Figure 4-2 shows how the information presented in this chapter is integrated with other chapters of the GARD Guide in the development and execution of a site characterization program.

Figure 4-2: Characterization Chapter Road Map
CharacterizationChapterRoadMap.gif

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4.2 Site Characterization Approach

4.2.1 Conceptual Site Model Development

A conceptual site model (CSM) describes what is known about the release, transport, and fate of COIs at a mine site. As such, the CSM includes the following components: sources, pathways, and receptors. The CSM describes the sources of COIs, the mechanisms of their release, the pathways for COI transport, and the potential for human and ecological exposure to these parameters. The most important sources of COI release are mine waste, ore, process waste, and the disturbances resulting from coal or ore extraction and processing. Water is a primary environmental pathway for constituents released from these sources. Transport occurs by groundwater, surface water, or infiltration through the vadose zone. Because water is a primary pathway for COIs, aquatic resources generally are the receptor of most interest.

In addition to water, human and ecological exposure to COIs may occur by other pathways, including air (e.g., exposure to wind-blown tailings) or from direct contact with a solid phase mine or process waste (e.g., vegetation in contact with metal-laden soils). Indirect exposure may occur along the food chain (for example exposure of bioavailable metals to animals that graze on vegetation in contact with contaminated soils).

A CSM can be developed at any stage of a mine’s life; however, CSM development typically begins in the early phases of a project. The CSM is validated and revised, as necessary, over the life of the mine as additional site characterization data are collected.

Where regulatory approval for new mine development is required, early involvement by these agencies in the development and validation of the CSM is key, and should be encouraged. Early involvement is needed to establish the risk considerations for risk assessment discussed in Section 3.6, as differences in risk tolerance can often be best dealt with through consensus on the CSM.

The principal data requirements of a CSM are shown in Figure 4-3. The ability of the CSM to accurately describe the release, transport, and fate of COIs is a function of the amount of available characterization data, which generally is proportional to the mine phase. An example schematic of a CSM is shown in Figure 4-4.

Figure 4-3: Typical Data Requirements of a Conceptual Site Model (CSM)
TypicalDataRequirementsofaConceptualSiteModel.gif
 
 
Figure 4-4: Example Conceptual Site Model Schematic
ExampleConceptualSiteModelSchematic.jpg


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4.2.2 Mine Phases

Table 4-1 describes the phases of mine development. During the early stages of mine development, minimal site-specific information commonly is available and therefore the uncertainty of the CSM is high. Over the life of the mine, the amount of characterization data increases and the uncertainty associated with the CSM decreases.

Table 4-1 is oriented towards hard rock mining, but most is also applicable to coal mining. The key distinction, as discussed in Chapter 2, is that coal seams are more continuous and consistent than most ore bodies.

Table 4-1: Mine Phase Objectives and Activities
MinePhaseObjectivesandActivities.gif

Table 4-2 and Table 4-3 present the chronology of a characterization program and identify the data collection activities typically executed during each mine phase. The bulk of the characterization effort occurs before mining during the mine planning, assessment, and design phase (referred to as the Development Phase throughout this chapter). Identification of potential environmental impacts during this phase and incorporation of appropriate prevention and mitigation measures is intended to minimize environmental impacts. During the commissioning/construction and operation phases, a transition from site characterization to monitoring occurs, which continues throughout the decommissioning and post-closure phases. Ongoing monitoring refines the knowledge of the site, allowing adjustments for new technologies that may evolve during the mine life and whose incorporation will reduce closure costs and better manage associated risks.

Table 4-2: Characterization Activities by Mine Phase
CharacterizationActivitiesbyMinePhase.gif


Table 4-3: Source Material Characterization Activities by Mine Phase
SourceMaterialCharacterizationActivitiesbyMinePhase.gif

4.2.2.1 Exploration Phase

The primary objective of exploration is to locate a mineralized area and determine whether the area contains enough ore to be extracted economically. The techniques employed in mineral exploration include literature review, geologic mapping, geochemical sampling (rock, soil, and water sampling), geobotanical surveys, geophysical testing, remote sensing surveys (surface, subsurface, airborne, and satellite), aerial photography, and drilling (SME, 2008). Exploration data are compiled to characterize the ore deposit, including the deposits size, grade, mineralization style, and the alteration assemblages present. The exploration geologist maps the lateral and vertical distribution of material types across the deposit. Material types may include distinct lithologies or rock units, ore units, alteration assemblages, or soil types that have relatively homogeneous characteristics of importance to mineral extraction and processing, waste management, and other uses such as for construction (e.g., mineralogy, grain size, and porosity). Three-dimensional digital representations of material types, called block models, are generated from borehole data to develop the economic ore estimation models for a feasibility study (see Chapter 5). Geologic block models with an ore evaluation focus can be modified and developed using ARD potential indicator parameters (e.g., total sulphur) to assess ARD potential. However, this is usually accomplished during the mine planning phase when the location of the ultimate pit is known.

Exploration data collected to determine the economic value of a mineral deposit also provide information useful in the assessment of environmental impacts from mining. For example, the presence of acid generating and acid neutralizing minerals associated with the ore and host rock can be determined from mineralogical data. Exploration drilling logs are often a source of useful hydrogeologic data. The depth to water and quantity of water encountered during drilling are information that may be used to characterize groundwater occurrence and flow conditions. Soil, water, and sediment sampling provide information on the occurrence and mobility of trace metals in the watershed. Remote sensing data may provide information on the distribution of secondary minerals formed from weathering of mineral deposits.

Plumlee’s (1999) summary of how the geologic characteristics of a mine deposit affect its environmental signature is reproduced as Table 4-4. Much of this information is obtained during exploration. Seal and Hammarstrom (2003) discuss the application of geoenvironmental models for massive sulphide and gold deposits.

Samples collected during the exploration phase (core, rejects and pulps) should be catalogued and saved for potential future use.

Table 4-4: Geologic Characteristics of Mineral Deposits that Affect Their Environmental Signatures (Plumlee, 1999)
MineralDepositsthatAffectTheirEnvironmentalSignatures.gif


4.2.2.2 Mine Planning Phase

To decide whether a project will be advanced, the economic viability of the project is assessed during the mine planning phase. This phase includes completion of a number of design and feasibility studies, including the environmental and social impact assessment (ESIA) and the feasibility study (FS). The ESIA includes an assessment of the potential environmental impacts associated with development of the deposit. Mine design, development of the mine waste management plan, closure planning, and mine permitting are also conducted during the mine planning phase.

During the mine planning phase, the intensity of site and source material characterization is usually high. A laboratory testing program is initiated to systematically evaluate the environmental stability of waste and ore materials, including the occurrence and nature of sulphide minerals and minerals with neutralization potential and their respective quantities. Intensive baseline monitoring is conducted to characterize existing environmental conditions. This may include establishment of surface water, groundwater, sediment, and climate monitoring stations. The receptors within the watershed are identified and their habitats characterized.

Environmental characterization programs should be integrated with activities of other mine departments to optimize both data collection efforts and the design of the mine facilities. For example, often ARD characterization activities can be integrated with geotechnical investigations (e.g., collection of samples for ARD characterization of ultimate pit walls during drilling to evaluate pit wall stability). Optimal siting of waste facilities should integrate information from multiple disciplines, including geochemistry, hydrogeology, hydrology, geology and geotechnical.

When a positive water balance exists in the beneficiation process, options for water treatment and discharge must be evaluated to manage excess water if it cannot be contained on the mine property.

Characterization during the mine planning phase must be sufficient to allow for accurate estimation of the long-term costs of ARD management for inclusion in the economic evaluation of the project. It may not be possible to profitably mine some marginally economic ore bodies or coal deposits that have high ARD management and closure costs.

Initial design considerations for mine closure should begin as soon as possible during the mine planning phase. This ensures a “design for closure” approach. Issues such as reduced mine footprint, waste rock and tailings (or coal refuse) management, and the avoidance of long-term water treatment should be integrated into the mine design to ensure that the economic model for mine development fully considers the costs of the whole lifecycle, including post-closure.

Where required for open pit mine projects, the ARD block model is developed during this phase. The block model is used to estimate the quantity and characteristics of ore and waste (i.e., potential sources in the CSM). Incorporation of ARD indicator parameters into the block model facilitates consideration of environmental risk in ore development plans and the scheduling of waste production as part of an ARD management plan.

4.2.2.3 Construction and Commissioning Phase

Detailed design typically occurs coincidently with the ESIA review by regulators, communities and other stakeholders, and the securing of mine permits. Modifications to the ARD management plan are made as result of this consultation to reflect permit conditions. Detailed design transitions into construction of all mine facilities (e.g., mine camp, water treatment plant, and waste storage facilities) and infrastructure (e.g., water, power, and roads) required for operation of the mine and associated mineral processing.

The characterization programs initiated during the mine planning phase are usually continued during this construction and commissioning phase. Ongoing laboratory testing of ore and waste materials may now include testing of samples generated during site excavation activities (e.g., pit prestripping). Field scale source material testing programs may also be initiated at this time, particularly when pilot testing of water treatment options is required. Routine surface water, groundwater, sediment, climate, and receptor monitoring programs begin during baseline data collection and continue to be implemented during the construction and commissioning phase. Environmental characterization activities to evaluate the construction of engineering controls intended to prevent ARD, NMD, or SD migration may also occur during this phase (e.g., field testing of liners placed at the base of waste facilities to ensure design permeability criteria are met).

4.2.2.4 Operational Phase

The operational phase is defined as the start of ore extraction and processing. ARD, NMD, or SD sources resulting from ore extraction and establishment of mine waste facilities are created during this phase.

Laboratory and field testing of source materials generally continue during operations to calibrate/validate predictions and validate/modify design of control measures. Testing also supports tracking of waste segregation. Additional testing must be conducted if materials not included in the initial characterization programs are encountered during excavation. The waste management plan commonly stipulates specific testing of waste materials to document the composition of waste facilities or, as part of the waste management protocol, to document operational monitoring (e.g., for segregation of waste materials or alkaline amendment). Source characterization during operations often includes collection of runoff and seepage samples from potential ARD sources. In some cases, instrumentation of waste facilities is required to fulfill specific data needs (e.g., lysimeters or gas monitors within waste rock piles).

Watershed monitoring (i.e., groundwater, surface water, sediment, climatic, and receptor) continues during operational phase with a focus on the identification of environmental impacts and compliance with applicable regulations. The quality of water removed in association with dewatering activities is characterized to assess the need for treatment before discharge.

During the operational phase, source and watershed characterization data collected during operations are reviewed on an ongoing basis and compared to expected conditions and compliance requirements. Trigger levels should be established during this phase that indicate the need to implement contingency measures (e.g., a change or modification to a mitigation measure or engineered source control measure). As needed, predictive models are updated to reflect measured conditions.

4.2.2.5 Decommissioning Phase

The decommissioning phase involves activities aimed to reestablish premining conditions (to the extent possible) or conditions suitable for beneficial post-mining land use. Active mining and the activities associated with mining and processing cease (e.g., cessation of dewatering activities, cessation of heap leaching). Site reclamation and rehabilitation activities, as outlined in the closure plan, are conducted during this phase. If necessary, water treatment facilities continue to operate or passive measures are instituted.

Site water quality monitoring typically continues during the decommissioning phase to assess environmental conditions. Validation of water quality prediction models is critical during this phase to assess the need for additional mitigative measures or long-term monitoring. Site water quality data and long-term kinetic test results are compared to predictive model results for each mine and process facility. If predictions do not agree with the observed data, additional tests are conducted to understand the geochemical system. If necessary, the closure plan is modified to reduce and prevent environmental impacts.

Water table rebound during the decommissioning phase presents an opportunity to assess actual pit lake or underground mine pool water quality. Additional data collection and evaluation, including modeling, may be required to refine long-term water quality predictions and assess the need for mitigation measures, including water treatment. The rate of water table rebound is measured to confirm predictions of the time for mine flooding or establishment of a pit lake and its potential consequences (e.g., discharges).

4.2.2.6 Post-Closure Phase

With the advance of mine waste management techniques, the post-closure phase is characterized by the absence of a continuous presence of personnel on the mine site, though some operations might require ongoing water management and treatment. During the post-closure phase, land use is commensurate with requirements of permits and expectations from adjacent land users and regulatory agencies. The requirements for post-closure monitoring vary with the post-closure objectives and the remaining facilities. Typically, there is a period of one to ten years of performance monitoring over which there is a decreasing frequency of activity, based on achieving the predicted performance for chemical and physical stability. Following performance monitoring, some sites may require longer term monitoring and maintenance of, for example, physical structures such as tailings dams, water retaining structures, or covers. There are a number of management models by which the post-closure monitoring can be achieved (e.g., the company, contractors, regulatory agencies, communities, or research institutions).

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4.3 Sources of Acid Rock Drainage, Neutral Mine Drainage, and Saline Drainage

The disturbances resulting from ore or coal extraction and the wastes generated by the extraction and processing are the primary sources of ARD. The primary methods of extraction are surface mining (e.g., open pit mining), underground mining, and solution mining. The depth of the deposit, the nature of the mineralization (e.g., disseminated vs. veins), the concentration and amenability to processing of valuable metals, and the cost of overburden removal generally dictate whether ore (or coal) is extracted using underground or open pit techniques. The solubility of the ore material determines whether in situ solution mining is an option (SME, 2008).

The selection of mining and mineral processing methods defines which sources of ARD are present (Figure 4-5). Both open pit mining and underground mining create features that are potential sources of ARD (e.g., low-grade ore stockpiles, heap leach piles, waste rock facilities, and tailings storage facilities [TSF]). The mine and process waste management plan describes the size and location of these facilities. Because waste facility design must consider the potential for these facilities to produce environmental impacts, material characterization and facility design is an iterative process. Solution mining changes the geochemistry of the subsurface and has the potential to result in direct ARD impacts to groundwater and impacts to surface water through waste solutions.

Figure 4-5: Major Steps Involved in Extraction Metallurgy of Metals
MajorStepsInvolvedinExtraction.gif

This Section 4.3 describes how the geometry, physical properties, and structure of common mine and process facilities influence or control, or both influence and control, the production and pathways of ARD. Conceptual models illustrate the chemical reactions occurring within each facility, as well as the movement of oxygen, heat, and water that govern sulphide oxidation and transport of oxidation products. More technical detail on sulphide oxidation and transport of oxidation products is also provided in Chapter 2.

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4.3.1 Surface Mining – Open Pit

Mining of relatively shallow deposits or very large low-grade deposits often employs surface open-pit mining techniques. Surface open-pit mining typically involves overburden removal, blasting, mucking, loading, hauling, and dumping. In addition to the commodity being mined, materials overlying, within and adjacent to the ore deposit, are removed. An open pit is formed by the successive removal of layers (termed benches) of rock. The ultimate shape of the pit is a function of the shape of the ore body and the mechanical characteristics of the rock. The ARD potential of the host rock may also be considered in determination of the pit extents (i.e., avoidance of areas with high ARD potential [SME, 2008]).

Open-pit mining may alter either surface water or groundwater, or both surface water and groundwater conditions near the open pit. Diversion of surface water or dewatering activities to lower the groundwater table may be required to access the ore body. Fractures generated during blasting alter the hydraulic properties of the host rock and may change groundwater flow patterns. Surface water and groundwater quality may also be affected. When sulphides are present, dewatering and blasting activities alter the ARD potential of the host rock by increasing the exposure of sulphide minerals to atmospheric oxygen and humidity or water. Chemicals introduced during mining can also affect water quality, for instance ammonia and nitrate introduced by the use of nitrogen-based explosives such as ammonium nitrate/fuel oil (ANFO).

Operational Conditions - Figure 4-6 schematically illustrates the primary water pathways and geochemical reactions that occur within an open-pit mine during operations. When necessary, dewatering wells are sited around the perimeter of the pit to lower the groundwater table to beneath the floor of the open pit. Alternatively, sumps within the pit may be used for dewatering. Precipitation falling within the pit capture zone becomes pit wall runoff, or infiltrates into the unsaturated zone. Infiltration flows downward to the groundwater table or horizontally toward the pit wall, where it discharges as seepage. High-porosity blast-generated fractures within the adjacent rock zone and historical mine tunnels intersecting the open pit provide preferential pathways for groundwater flow. The quality of pit wall runoff and groundwater inflow to the pit is a function of the composition and reactivity of the rocks these waters encounter and the contact time. Sulphides exposed to atmospheric oxygen and humidity or water on the pit walls or blast fractures oxidize, resulting in generation of ARD. Therefore, if the pit is to be filled and reclaimed after mining is completed, and if mining is proceeding laterally, the backfilling process should be coordinated with excavation to minimize the amount of time that the mineral sulphides are exposed. ARD neutralization may occur due to dissolution of buffering materials, when they are present. Sulphide oxidation products, which accumulate on pit walls and fracture surfaces, are flushed by groundwater or surface runoff. Pit wall runoff may collect in pools where the haul road meets the pit wall. During dry periods, evaporation results in the accumulation of secondary minerals. These soluble mineral phases are flushed during storm events and might release metals, sulphate, and acidity, depending on their characteristics. Ultimately, runoff collects in a shallow pool at the bottom of the pit. Water on the floor of the pit may infiltrate into the groundwater system, evaporate, or be actively removed with sumps. Infiltrated water mixes with underlying groundwater and may be captured by dewatering wells.

Figure 4-6: Sources and Pathways of ARD, NMD, and SD in a Pit during Operation and Closure
SourcesandPathwaysofARDNMDandSDinaPit.jpg

Post-Closure Conditions - At the cessation of mining, a pit lake will form if total water inflow to the pit is greater than water outflow (Figure 4-6). A pit lake will form in pits that extend below the groundwater table. For pits that do not extend to the depth of the groundwater table, a pit lake may form in regions where annual precipitation exceeds the sum of evaporation and infiltration through the bottom of the pit (bathtub effect). During the decommissioning phase, dewatering activities are typically ceased. The groundwater table rebounds to the premining level and if the pit has not been backfilled, produces a pit lake. In some cases, filling of the pit may be accelerated by diversion of surface water into the pit. For example, the Island Copper Pit in British Columbia, Canada was flooded with sea water in less than half a year; the Martha Mine Pit in New Zealand is expected to fill from river water and groundwater in 5 years.

At the opposite end of the spectrum, open-pit mines in arid regions with limited surface water resources, low groundwater discharge rates, and high evaporation rates may take tens to hundreds of years to achieve a steady-state lake level, extending lake filling conditions well into the post-closure phase. Alternatively, open-pit mines may not contain water at all if the natural groundwater table is below the pit bottom.

Similar to natural lakes, pit lake water quality may vary seasonally and with depth. Pit lake water quality will be a function of the geology (i.e., reactivity) of the wall rock, climatic conditions (i.e., the amount of precipitation and evaporation), the rate and quality of groundwater and surface water inflows, the type and extent of biological activity, and pit limnology (Geller et al., 1998).

Pit lake water quality can present a long-range environmental concern, especially considering the volume of water that some pit lakes contain. Acidic conditions may develop within a pit lake because of the oxidation of wall rock sulphides, flushing of reactive waste materials backfilled in the pit, the addition of ARD in runoff or groundwater, and the precipitation of iron hydroxide minerals within lake water. An example of a highly acidic pit lake is the Berkeley Pit Lake in Butte, Montana, which has a pH of approximately 2.5 and copper and zinc concentrations of approximate 150 mg/L and 600 mg/L, respectively (Gammons and Duaime, 2006). Fortunately, pit lakes with these extreme characteristics are rare on a global scale and appear to be limited to some porphyry copper deposits with high sulphur contents and minimal carbonate or other neutralizing lithologies. Abandoned coal mine pits in eastern Germany and Pennsylvania, USA, and uranium mines in central Canada have also developed acidic waters. Neutral to basic waters have developed in pit lakes hosted in limestone deposits, where the dissolution of calcite buffers pit lake pH. Saline waters also occur in pit lakes, particularly in extremely arid environments where the evaporative loss of fresh water raises the concentration of dissolved solids. Stratification within pit lakes and the presence of thermoclines and chemoclines may result in waters of very different composition with depth.

Because pit lakes may potentially represent a long-term source of ARD that persists after mine closure, prediction of the quality and environmental impacts of these lakes is a key part of the ARD management plan. If impacts are predicted, mitigative options should be considered, including accelerated flooding, raising the flooded water level, and batch treatment. As a final option, pumping and treatment may be required.

A pit lake may be incorporated into the site water management plans for post-closure (e.g., Island Copper Mine, Selbaie Mine, and Mt. Milligan Project in Canada). If local and national regulations permit, wastes can be stored in pit lakes where very low oxygen or anoxic conditions essentially prevent ARD formation. Physical (e.g., sedimentation), chemical (e.g., mineral precipitation and sorption), and biological (e.g., sulphate reduction) processes that occur in pit lakes can be used to ameliorate water quality.

Additional references on pit lake characteristics, predictive modeling, remediation and post-closure utilization include Geller and Salomons (1998), Castendyk and Eary (ADTI-MMS workbook, in press), and Bowell (2003).

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4.3.2 Underground Mining

Underground mining methods are used to mine deeper ore bodies. Underground mining typically involves blasting, stoping, mucking, hauling, and skipping (vertical haulage) of waste and ore to surface. Where employed, block caving mining methods may create a large mass of fractured rock above the underground workings. The rubblized zone may extend all the way to the ground surface. The physical and chemical properties of this large mass of fractured or rubblized rock can be similar to the properties of waste rock. Similar to open-pit mining, dewatering activities are typically required to remove groundwater from the underground workings, commonly through use of dewatering wells and sump pumps. In some cases, a drainage tunnel can be constructed below the mining level that permits gravity drainage of groundwater to land surface. Mining exposes sulphides present on mine walls or blast fractures to atmospheric oxygen that enters the underground workings through shafts and other openings that intersect the land surface. The underground workings, as well as the ore and waste piles generated by mining, might be sources of ARD.

Operational Conditions - Figure 4-7 shows the water pathways and geochemical reactions associated with underground mines. Dewatering activities during operations alter groundwater flow paths near the underground workings. Depending on the depth of the underground workings, the primary source of groundwater inflow into the underground workings may be from the regional groundwater system (deep mines) or the local groundwater system (shallow mines). The shallow groundwater flow system is recharged by precipitation that falls within the underground working capture zone and infiltrates into the ground. The quality of groundwater inflow into the underground workings is a function of the composition and reactivity of the rock it encounters and the contact time. Oxidation of exposed sulphides in the underground workings (mine walls or blast fractures) results in the accumulation of sulphide oxidation products. During mining, a constant supply of oxygen is maintained through the ventilation system and mine shafts and adits that intersect the land surface. Sulphide oxidation products are flushed by inflowing groundwater. Underground mine water quality may also be affected by chemicals introduced during mining activities (e.g., diesel, nitrogen from blasting residuals, grout) or by materials backfilled into the mine during operations or at closure (e.g., paste tailings, waste rock). Groundwater removed as part of dewatering activities may require treatment before discharge to the environment. Although the underground mine is typically a groundwater sink during operations, release of impacted mine water to the environment may occur by infiltration to groundwater or surface discharges at mine openings.

Figure 4-7: Sources and Pathways of ARD, NMD, and SD in Underground
Workings during Operation and Closure

SourcesandPathwaysofARDNMDandSDinUnderground.jpg

Post-Closure Conditions - At the cessation of mining, dewatering ceases and groundwater inflow into the underground workings results in development of a mine pool. In some cases, the workings are backfilled during mining with mine waste (tailings, waste rock, inert material such as sand, or a combination of these). The mine workings, due to their elevated permeability and porosity relative to the host rock, become preferential pathways for local groundwater flow. Even collapsed or backfilled voids and block cave rubble zones exhibit greater permeability than the surrounding fractured rock and therefore strongly influence groundwater movement. As the water table rebounds, sulphide oxidation products present on mine walls or backfilled waste are flushed, resulting in release of sulphate, metals, and acidity to the mine water. Inundation of sulphide minerals prevents further sulphide oxidation. However, sulphides that remain above the water table represent a long-term source of ARD. As is the case for pit lakes, underground mine pools are frequently stratified (Wolkersdorfer, 2008). In Pennsylvania, USA, water levels in flooded underground coal mines show considerable fluctuation in composition owing to variability in meteoric conditions and local groundwater pumping.

As the water table rebounds, the underground workings may transition from a groundwater sink to a groundwater source. Discharge of mine pool water to the environment may occur by groundwater or mine openings. In some cases, these openings are plugged to prevent discharge to surface (ERMITE-Consortium, 2004).

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4.3.3 Waste Rock and Ore Stockpiles

Smith and Beckie (2003) provide a comprehensive summary of the hydrologic and geochemical processes occurring in a waste rock pile. Figure 4-8 shows the water pathways and geochemical reactions associated with waste rock piles. The primary factors controlling the hydrologic characteristics of a waste rock pile are (a) material grain size distribution, and (b) the proportion and spatial arrangement of matrix-supported and matrix-free zones created during construction (Smith and Beckie, 2003)  

Figure 4-8: Sources and Pathways of ARD, NMD, and SD in a Waste Rock Pile
ARDNMDandSDinaWasteRockPile.jpg

Typically, waste rock is hauled in dump trucks to the disposal site. The loading process and truck vibrations during hauling result in segregation of the rock into layers of similar grain size, a process called sorting. Waste rock dumping from the crest of a steep slope further enhances sorting because large grained material travels further down slope than fine grained material. Consequently, waste rock piles (and ore stockpiles) are generally composed of inter-layered beds of coarse grained material and fine grained material inclined at the angle of repose (33 to 37 degree angle). This method of construction creates the following structures with potential hydrologic significance: coarse rubble zones at the base of the pile, discrete zones within the pile containing little to no granular material between larger rock fragments, sloping surfaces between coarse and fine grained layers, and internal low permeability pavement surfaces formed by truck movement during pile construction. The grain size and structural characteristics of a pile also influence oxygen movement within the pile (Smith and Beckie, 2003).

Precipitation falling on the pile will evaporate, flow over the surface of the pile as runoff, or infiltrate into the pile. The quality of waste rock seepage and runoff is a function of contact time and the composition and reactivity of the waste rock. Oxygen transport within the pile and waste rock grain size are important controls on waste rock reactivity (see Chapter 2).

Saturated conditions may exist within the waste rock pile. Development of a perched water table at the base of the pile may occur because of the presence of a low permeability layer beneath the pile. Perched water may also be present at higher elevations in a pile because of areas of low permeability (e.g., former haul road surfaces). Waste rock seepage may exit along slope faces at the toe of the pile or may infiltrate into the subsurface underneath the pile.

To prevent infiltration of waste rock seepage into the underlying groundwater system, waste rock piles and any other sources of material that may generate ARD may be sited in areas where surficial soils have low permeability. Siting such facilities is best accomplished by an assessment of the entire development site to map the levels of permeability for the purposes of determining the optimum location of all facilities. In potentially sensitive areas, drilling to fully understand the subsurface conditions may be required. In cold climates, permafrost may act as a barrier to the migration of seepage; however, because of the heat generated during sulphide oxidation, the permanence of the permafrost below waste facilities requires evaluation. In some cases, engineered liners may be used as a barrier to seepage migration and drains may be installed to collect drainage.

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4.3.4 Tailings Piles and Ponds and Coal Refuse and Slurry Piles

Tailings are discharged to surface storage facilities by several methods, including subaerial slurry, subaqueous slurry, and dry deposition. The methods of transport and disposal are a function of the water content of the tailings (e.g., thickened and paste tailings may be disposed subaerially using pipeline transport, whereas fully dewatered tailings are disposed by dry deposition methods, including use of conveyors and trucks) and the topography and placement of the tailings dam. Tailings may be segregated by grain size (e.g., use of cycloning to separate the sand fraction from the slimes) before discharge. Compared to waste rock, tailings are homogenous with a more consistent distribution of acid generating and acid neutralizing minerals; however, if these minerals are associated with a particular size fraction, segregation may occur during deposition. The fine particle size of tailings results in lower permeability to oxygen and water.

The tailings grain size, disposal method, and deposition history govern the hydrogeological characteristics of a TSF (Blowes et al., 2003). The sulphide content of the tailings and the availability of oxygen will govern the reactivity of sulphidic tailings. Water covers present, in the case of subaqueous disposal, act as a barrier to oxygen ingress into the tailings. Other tailings design features intended to limit oxygen or water ingress include use of engineered covers and maintenance of a high degree of saturation (e.g., in tailings paste).

In addition to surface disposal, tailings may be disposed in underground workings. Underground disposal may simply fill void spaces or may be designed to provide structural support for ongoing mining. Reagents may be added to increase strength or improve environmental stability before backfill. Addition of a binder (i.e., cement) to acid generating tailings may provide some, although generally limited, neutralization potential. Tailings segregation (e.g., removal of slimes) or dewatering (e.g., for disposal as a paste) may be performed before backfill. Mine drainage collection systems are designed to capture tailings seepage during operations.

Discharges associated with tailings facilities include runoff and seepage for all disposal methods. Runoff and seepage quality are a function of tailings composition, reactivity, and contact time. Residual process reagents may also affect water quality (e.g., cyanide). Facilities may be sited in areas with low permeability surface soils or an engineered liner may be constructed to prevent migration of tailings seepage. In cold climates, migration of the permafrost into the base of the facility may prevent generation or movement, or both generation and movement, of ARD.

Coal processing typically includes crushing, grinding, and sizing followed by physical separation of pyrite and shale (waste materials) by gravity or floatation. The waste material (locally known as coal refuse, gob, slurry, etc.) from coal beneficiation (also known as coal cleaning, washing, or preparation) generally has a higher acid generation potential than the coal itself because sulphide minerals contained in the coal and waste rock are concentrated in the waste during the coal cleaning process. Coal reject piles, largely consisting of fine-grained shale and pyrite, are typically located near the coal processing plant. Because of the mineral composition, grain size, and high-surface area of these wastes, coal reject piles may be strongly acid generating depending upon their sulphur content (SME, 2008). This waste material is often deposited as a slurry behind a dam, just like tailings. Where it is deposited fairly dry, it should be compacted frequently to minimize the ingress of oxygen. Additional measures may be taken to minimize ARD formation, as discussed in Chapter 6.

Figure 4-9 shows the flow paths and geochemical reactions occurring in a subaqueous TSF. A dam is first constructed to impound the tailings and supernatant. For stability reasons, tailings dam embankments are commonly designed to be unsaturated and well drained so if they are constructed with sulphide-bearing waste rock or tailings, the tailings dam embankments may be particularly prone to ARD generation. Precipitation onto the surface of the facility contacts the tailings beaches (tailings exposed to atmospheric oxygen), the dam, or falls directly on the tailings pond. During large storm events, discharge through an overflow drain or discharge down the face of the dam may occur. This water may be captured for treatment. Infiltration through the tailings enters into the subsurface or is captured in a seepage collection system. The seepage rate is a function of the permeability of the underlying natural or engineered materials and the infiltration rate through the tailings. During operations, ARD is not normally a concern because most mill circuits add lime to the tailing. Also, during subaqueous disposal, fresh tailings added to the beaches normally maintain a relatively high water content. Active management of the tailings pond supernatant (e.g., addition of lime) can be conducted to prevent low pH conditions and mobilization of metals. During post closure, remedial measures that have been designed from the outset are implemented to prevent ARD and improve seepage quality (see Chapter 6).

Figure 4-9: Sources and Pathways of ARD, NMD, and SD in a Subaqueous Tailings Storage Facility

ARDNMDandSDinaSubaqueousTailings.jpg
Downstream Construction Method
 
ARDNMDandSDinaSubaqueousTailings2.jpg
Upstream Construction Method
 
ARDNMDandSDinaSubaqueousTailings3.jpg

Centerline Raise Construction Method


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4.3.5 In Situ Solution Mines

Solution mining makes use of a series of injection and recovery wells to circulate a leach solution through an ore zone. Solution mining is applied to extract solids that are easily leached or dissolved. Leach solutions may be acidic, neutral or basic, heated, or unheated. Blasting may be conducted in boreholes before injection to increase the permeability of the ore zone. Solution mining has been used in uranium, copper, manganese, halite, potash, nahcolite, and sulphur mining (SME, 2008).

Solution mining alters groundwater geochemistry and flow paths near the ore zone. In some applications, leach solutions are oxidants and may promote ARD. If not contained, leaching solutions, particularly oxidizing solutions and acids, may degrade local or regional groundwater quality. To avoid groundwater impacts, solution mining requires rigorous evaluation of the groundwater flow system (e.g., flow paths, capture zone analysis) before injection of leach solutions. Characterization of the groundwater system must include hydrogeologic units in hydraulic connection with the ore body and aquifers above and below the ore zone. Disposal of waste solutions may pose a concern for surface water resources.

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4.3.6 Heap Leach Piles

Sulphuric acid leaching and sodium cyanide heap leaching are two metallurgical processes used to extract metals (copper and gold, respectively) from ore material under different conditions. In both leaching processes, cobble-sized or finer grains of ore materials are piled onto lined pads, either directly from the mine or after size reduction. The leaching fluid, applied to the top of the pile, infiltrates through the material, dissolving the ore bearing mineral. The “pregnant” or metal-bearing solution is collected from the bottom of the pile and processed to recover the ore metals.

Improper handling of both the acid leach solutions and the pregnant solution can result in the release of acidic process solutions to the environment. Leakage through the lined or unlined base of the leach pad could impact groundwater quality, while seepage flowing from the toe of the facilities and direct runoff may impact surface water.

When leaching is concluded, the draindown water or rinse water must also be handled properly. Acidic leaching solutions and drainage may precipitate very fine-grained acid-generating secondary minerals such as jarosite and melanterite, onto grain surfaces particularly under dry conditions. During rain events, these secondary minerals will readily dissolve, releasing the stored acidity and metals. Whether these solutions exit the mine waste depends on the climatic and physical characteristics of the mine wastes and the presence or absence of engineering controls (e.g., liner).

Sulphide minerals remaining in the pile after conclusion of leaching can also contribute to acid formation, depending on the residual sulphide mineral content and climatic conditions. If a basic cyanide solution is used for ore leaching, some cyanide compounds may remain sorbed to grain surfaces or dissolved in pore waters after leaching concludes. At the cessation of mining, cyanide present in gold heap leach piles can be removed by rinsing or can be allowed to degrade naturally (SME, 2008). Maintenance of the residual alkalinity (pH 10 to 11) from cyanide leaching through the addition of a cover may also provide environmental benefits. Best operating practices from closed heap leach sites in Nevada have demonstrated that preserving the alkaline conditions, which were essential during the cyanide leaching operations, is best achieved by not rinsing the heaps. However, an engineered cover may be needed to limit infiltration of precipitation and prevent natural leaching of alkalinity to a level that could allow ARD processes to begin depending on the nature of the material.

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4.3.7 Coal and Uranium Mining Specific Acid Rock Drainage Sources

Coal is formed when plant remains are preserved over geologic time from oxidation and biodegradation. Coal is a sedimentary rock; however, the harder forms may be regarded as metamorphic due to exposure to elevated temperature and pressure. Coal is often found in beds a meter or more in thickness that are widespread in extent. As discussed in Chapter 2, iron sulphide is often associated with coal deposits and adjacent strata.

The nature of sedimentary strata affects coal mine hydrology. Coal is typically derived from peat that forms in a swampy or marshy area, and the strata immediately underlying a coal seam typically have low permeability (e.g., an underclay). The coal itself, because it contains fractures known as face and butt cleats, can be an aquifer. Overlying strata can also be aquifers or aquitards. Mining typically disrupts such flow patterns, creating a new aquifer consisting of fractured and broken rock. Thus, the effects of coal mining on local hydrology may not diminish once the water table rebounds.

Coal is typically mined using surface (strip mining or open pit), or underground methods (primarily stope and pillar or longwall). At surface mines, virtually all of the coal is typically removed, and so the presence of pyrite and carbonate minerals in the strata just below the coal, exposed during the mining process, and the overburden, has to be considered when deciding if ARD is a potential problem. In contrast, at underground coal mines, much of the coal remains behind, while the overburden may remain largely intact. At such sites, pre-mine prediction of post-closure water quality is largely based on the amount of pyrite in the coal and the strata immediately above and below it, and whether or not the coal that will remain behind will be inundated after mine closure.

Uranium is mined in open pits, underground mines or by in situ leaching. Waste rock and tailings generated by uranium mining may contain elevated concentrations of radioisotopes. Dust, air, and water are all potential exposure pathways for radiation to receptors. Leaching, often with sulphuric acid, is used at some mines for uranium recovery (typically, in a mill but occasionally in heap leaches or underground). Sulphuric acid leaching may produce waste with ARD characteristics because of the presence of residual acidity. In some cases, waste materials from uranium mining may also contain primary sulphides and therefore have potential to generate ARD. The presence of radioisotopes can require different reagents (e.g., barium sulphate) in the treatment of ARD at uranium mines. Otherwise, sources of ARD and measures to prevent its formation are similar to other types of mining.

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4.4 Components of Site Characterization

This section presents a summary of the components and methods commonly used to characterize ARD sources, pathways, and receptors. A comprehensive listing of the tools used in environmental assessments of mining projects, including references and a description of their use, is presented in Plumlee and Logsdon (1999). Price (1997 and 2009) presents guidelines for the development of a characterization program, including laboratory testing and interpretation of test results.

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4.4.1 Geo-environmental Models

A geo-environmental model of a mine deposit is defined as “a compilation of geologic, geophysical, hydrologic, and engineering information pertaining to the environmental behavior of geologically similar mineral deposits (1) prior to mining, and (2) resulting from mining, mineral processing and smelting.” (Seal et al., 2002). The key elements of the geo-environmental model include deposit type, deposit size, host rock, wall-rock alteration, mining and ore processing method, deposit trace element geochemistry, primary and secondary mineralogy, topography and physiography, hydrology, and climatic effects. Geo-environmental models are empirical data compilations that are best used as guidelines for the potential range of environmental impacts at a site (Seal et al., 2002). Geo-environmental models should not be used to predict absolute pH or metal concentrations that will develop at a site or in lieu of site characterization (Plumlee, 1999).

Geo-environmental models provide a starting basis for the level of characterization that will be required at a mine site. These geo-environmental models provide valuable information in the development of the CSM. Additional discussion on geo-environmental models and their use in water quality definition and prediction is presented in Chapters 2 and 5, respectively.

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4.4.2 Source Material Geochemical Characterization

4.4.2.1 Laboratory and Field Testing

Laboratory and field testing is conducted to characterize the acid generation and metal leaching potential of mine materials. Geochemical characterization programs typically follow a phased approach, beginning with laboratory testing followed by field testing. The design of most testing programs is dynamic, with each successive phase building on the results of previous phase or phases. A brief summary of the testing approach is provided below, with more detail presented in Chapter 5.

A geochemical characterization program will typically include the following laboratory analyses:

  • Static Test - chemical composition (i.e., whole rock and elemental analysis), mineralogical analysis, acid base accounting (ABA), and short-term static leach testing
  • Kinetic Test - long-term leach testing

Static testing is typically the first phase of geochemical characterization, and usually is a precursor to kinetic testing. The objective of static testing is to describe the bulk chemical characteristics of a material. These tests are designed to evaluate the potential of a particular rock type to release acid, neutralize acid, or leach metals. Static tests provide an indication of the presence of minerals that may generate acid as well as minerals that may act to neutralize any acid formed (see Chapter 5 for additional information on the interpretation of static test results). In some cases, testing may indicate that a surrogate parameter may be used as an indication of ARD potential (e.g., iron as an indicator of the amount of sulphide, calcium as an indicator of the amount of neutralization potential [NP]).

Elemental analysis results are commonly compared to average crustal abundance values to provide a screening level assessment of COIs. A high concentration of a particular element does not necessary imply that this element will indeed be mobilized in concentrations that may lead to environmental or health impacts.

Short-term leach test results provide additional information on metal leaching potential. The disposition of the sample (e.g., unoxidized vs. oxidized; oxidation products absent vs. oxidation products present), test solution to solid ratio, lixiviant, reaction time, and sample particle size reduction should all be considered in the evaluation and comparison of leach test results. ABA and mineralogical analysis results are used to assess the relative proportions of acid generating and acid consuming materials. ABA analysis typically includes analysis of paste pH, sulphur speciation, NP, and total inorganic carbon (TIC). Paste pH is used as an indicator of the presence of stored acidity. Sulphur speciation data, which includes information on the presence of nonacid generating sulphur minerals, are used to calculate the acid generation potential of the material. NP provides an estimate of the acid neutralizing potential of a material. TIC analysis allows assessment of the fraction of available NP attributed to carbonate mineral phases.

An essential component of static testing is mineralogical analysis that, at a minimum, includes identification of all sulphide minerals and all minerals with neutralization potential. If possible, mineralogical analysis should be quantitative. A description of how minerals with acid generation and acid neutralization potential occur (e.g., grain size, grain morphology, disseminated, fracture coatings, as inclusions) is also relevant in the assessment of reactivity (i.e., rate of oxidation or dissolution) (see Chapter 5 for additional information on interpretation of mineralogical data).

Although the results of static testing may indicate a potential for acid rock drainage or metal leaching (or both acid rock drainage and metal leaching), kinetic testing is commonly required to assess the relative rates of various ARD and metal leaching potentials. Field scale leach tests may be initiated before or during the construction or operational phases of mine development to provide a better representation of material reactivity under site conditions.

Physical properties of the testing materials (e.g., surface area, particle size distribution) are also determined because these properties affect material reactivity. This information of the physical properties is needed in the scale-up of laboratory and field testing results to represent field scale and operational conditions.

Figure 4-10 shows the typical components and evolution of a geochemical characterization program for selected potential source materials. Any waste, construction, or process stream residues that have the potential to generate ARD must be included in the mine characterization program so that appropriate disposal practices and mitigation measures can be employed (e.g., treatment sludges, quarried materials for construction, heap leach residues, hydromet residues, slag). Chapter 5 presents detailed descriptions of the laboratory and field scale testing methods and their interpretation for the prediction of environmental impacts.

Figure 4-10: Source Material Geochemical Testing Program Components
GeochemicalTestingProgramComponents.gif

4.4.2.2 Sample Selection

A fundamental component to the success of a geochemical characterization program is the selection of representative samples. The available sources of material for testing are typically related to the phase of mine development. Drill core is the most common material source for geochemical testing during the early stages of mine development. Because exploration drilling programs target discovery and delineation of the ore zone, the selection of samples to characterize waste material must include careful examination of the spatial coverage of the drill core relative to the anticipated extents of the pit or underground workings (Downing and Mills, 2007). Other sources of material for testing that are frequently available include rock chips from borehole drilling, hand samples from outcrops, samples from existing waste facilities, development rock, ore composites, and residues from metallurgical testing. Use of samples from analogue sites can also be considered as a last resort. The mine geologist is a valuable resource and should be consulted in the selection of representative samples for testing. Determination of the appropriate disposal methods for wastes generated during exploration necessitates initiation of testing early in the mine life.

As mentioned previously, any material with the potential to generate ARD or release COIs should be characterized. Construction materials for roads and site infrastructure are often quarried from the area around a mining development. The ARD potential of these materials should also be evaluated before construction. Due to the spatial extent of placement, use of construction materials with ARD potential may result in a widespread source of ARD. The potential for land disturbances associated with the construction of mine facilities to expose rock with ARD potential should also be considered.

Selection of representative samples should consider the following:

  • Material Type – Individual samples selected for testing should be representative of a single material type (e.g., lithology, alteration type). The exploration geologist should be consulted regarding the initial definition of mine units and material types. Based on the results of the geochemical characterization program, material type classifications may require further refinement. For instance, a classification suitable for mineral extraction may not be sufficient to identify the environmental characteristics and corresponding ore and waste management requirements of the various material types. Construction materials should be included in the characterization program. Ore materials should also be included for prediction of ore stockpile runoff.
  • Spatial Representation (x, y, z) – Sample selection should ensure good spatial representation (vertical and horizontal) of the area to be mined. In practice, sample locations may be restricted to a one-dimensional line defined by a borehole or mine tunnel, or a two-dimensional plane, such as the wall of an open pit or cross section through the deposit. Additional boreholes increase the distribution of sample points and improve the definition of mine units. Because mine plans change, the spatial representativeness of samples should be reassessed throughout operations. For example, if the location of the pit wall changes, additional testing may be required to characterize pit wall runoff. Mining may also extend into areas that were not characterized during feasibility testing and such mining may encounter new materials.
  • Compositional Representation – Sample selection should include all major material types and cover the range of pertinent characteristics for each material type (e.g., pH, carbonate, sulphur, and NP content). Personnel tasked with sample selection must be familiar with the geological characteristics of the deposit, including rock types, fracture patterns, weathering, alteration, and mineralization.
  • Focused (Biased) versus Random Sampling – Use of focused or random sampling depends on the objective of the characterization program. For example, sample selection may target areas with visual sulphides to provide an indication of worst-case drainage quality. Similarly, focused sampling may be more effective in ensuring a sample set with a complete range of compositional characteristics than random sampling. Random sampling may be appropriate during operations in determining the appropriate location for waste disposal (e.g., waste segregation based on total sulphur content). In this context, random still implies a rationale-based program, which may be part of a phased program but lacks adequate samples to be geostatistically complete. Ultimately, if a major ARD problem is predicted from earlier phase test work, the waste should be characterized by a geostatistical model which includes an adequate number of samples as well as a geological interpretation. From this model, key indicators can then be selected for the operations to use in separating materials, if such efforts are warranted as a part of the ARD prevention and control program.
  • Sample Storage and Handling – Appropriate sample storage and handling procedures should be defined. Preference regarding the use of weathered or fresh materials for testing must be determined. In either case, the type of material used for testing must be documented. A photographic log of geochemical test samples is recommended.

Standard operating procedures (SOPs) for geological logging and the collection and documentation of sample selection should be developed and followed. SOPs should include quality assurance/quality control (QA/QC) protocols (e.g., collection and analysis of duplicate samples, sample chain of custody procedures, and inclusion of standard samples with known values). Sample size should be large enough to provide material for all potential geochemical tests and sample for archiving purposes. Archived samples should be easily retrievable. If compositing of samples is required, protocols should be defined. Compositing may be useful for identification of the characteristics of a sample representing a larger core interval or rock volume, such as an open-pit mine bench depth or waste zone. However, information on the smaller-scale characteristics may be lost due to the “smearing” of geochemical properties and analytical results. This “smearing” may lead to samples with anomalous qualities not being recognized, even though it may be those materials that govern the composition of a mine or process effluent. In general, it is recommended to collect discrete samples with clearly-defined characteristics, the testing results of which can be combined numerically to evaluate the properties of mixtures.

The mine geologic model and the block model may be used in the selection of representative samples. If geochemical testing indicates that special handling of waste materials will be required, the block model may be populated with diagnostic ARD indicator parameters (e.g., total sulphur). In this case, a comprehensive set of discrete samples would be needed to build the geostatistical model.

4.4.2.3 Number of Samples Required

The number of samples required for source characterization of each material type depends on the following: (a) the amount of disturbance (i.e., the volume/mass of material extracted or the amount exposed on pit/mine walls or production tonnage as determined by the block model); (b) the compositional variability within a material type; and (c) the statistical degree of confidence that is required for the assessment. Initial estimates of sample numbers are typically based on professional judgment, and experience. The number of required samples typically grows during each of the early phases of mine development as the knowledge base and project needs grow. Ultimately, for sites characterized as having ARD potential, a full geostatistical model often provides the basis for control plans where material segregation is part of the mine plan.

Few guidelines are available regarding sample requirements. Table 4-5 provides an example of Australian guidelines for the number of samples during the early phases of the mine life. Although characterization testing is likely to occur during all phases of mine development, the peak of the laboratory testing programs often occurs during the feasibility phase.

Table 4-5: Australian Guidance on Sample Numbers (adapted from Australian Government Department of Industry,
Tourism and Resources, 2007).
Mine Phase Number of Samples Description
Exploration

(1)  Prospect Testing – Include sulphur in list of elements being analysed for all samples tested; include the full range of pathfinder elements as defined by ore deposit/exploration model; collect and record mineralogical data as per exploration/ore deposit model; where the geology of the deposit is known include static testing of at least 3 to 5 representative samples of each key material type (i.e., lithology, alteration type); analysis of ground water and surface water for acidity and representative pathfinder elements.

(2)  Resource Definition – All samples tested for sulphur and representative samples tested for mineralogy as per ore deposit model. Static testing of at least 5 to 10 representative samples of each key material type.
Collect groundwater and surface water data. Surface water and groundwater analysis to include acidity as well representative metal ions

All testing to include QA/QC samples

By the end of the resource definition phase, there should be adequate information to accurately characterize the ARD potential of the ore body (high and low grade), although further test work will normally be required to characterize the ARD potential of waste rock and ore and hence tailings.
Pre-Feasibility

Static testing of several hundred representative samples of high and low grade ore, waste rock and tailings, the number dependent on the complexity of the deposit geology and its host rocks;

All drillhole samples analysed must include sulphur analysis and identified representative metal ions. Sampling density is dependent on complexity of ore deposit and host rock geology interval of representative drill holes but should be restricted to single rock units or lithologies - include minimums

Kinetic testing of at least 1 to 2 representative samples of each material type

Surface water and groundwater analysis to include acidity as well as pH, EC and representative metal ions, including Al, Fe, Mn,

All testing to include QA/QC samples.

Where required, the number of samples must be sufficient to populate a “resource”block model of the ore and host rocks that will be affected by mining with a reliable distribution of NAPP[1] data (e.g., acid producing potential (APP), sulphur and acid neutralizing capacity (ANC) (or NPR data) on ore, waste rock and wall rock.

Mine Planning, Feasibility and Design

Where required, additional static testing as required for block waste resource model refinement – increase density of NAPP (or NPR) characterization

Inclusion of confirmatory testing (e.g., NAG testing for comparison to NAPP (i.e. APP, or sulphur, and ANC) for metalliferous deposits; and mineralogy or NPR values)

Continuation of kinetic testing. 

Upgrade drillhole database and waste resource model for new ore positions.

All testing to include QA/QC sample(s). Apply QA/QC to all analyses, not only ore. Include wall rock.

Data set must be sufficient to assess ARD potential to support a management plan.  If data are insufficient, additional testing will be required.


Statistical analysis of test results is advisable to confirm that a representative data set has been obtained. For example, histograms may be used to ensure that the entire distribution has been captured in sample selection (Runnells et al., 1997) and samples with “extreme” characteristics have not been overlooked. The number of samples will increase as the heterogeneity (e.g., particle size and composition) of a material type increases. For this reason, characterization of process tailings typically requires fewer samples than characterization of waste rock. Sample representativeness must continually be assessed during the mine life. For example, a change in ore type over the mine life may produce process tailings with different characteristics. Operational monitoring (see Chapter 8) should include a program of systematic ongoing tailings testing to identify changes and implement alternative waste management practices, if required.

The goal of material management is to prevent or minimize ARD, which is preferable to mitigation and treatment following onset. Characterization programs must be designed to provide adequate information to make cost-effective, sustainable, and environmentally protective decisions regarding the management and disposal of waste materials. For materials with an uncertain ARD potential, resolution of this uncertainty by additional characterization efforts may not be necessary if a decision is made to manage the waste with the assumption that the material has ARD potential. For example, detailed characterization of the sulphide content of tailings over time may not be necessary if the tailings will be placed in a contained impoundment with a water cover.

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4.4.3 Watershed Characterization – The Hydrologic Cycle

Because water is the primary pathway for transport of ARD, the quantity, quality, and movement within the mine’s watershed must be characterized. Delineation of the watershed boundary is the first task in watershed characterization. Topographic maps and site reconnaissance are used to determine the surface water boundaries, or divides, that separate the watershed containing the ore deposit from surrounding watersheds. Geographic information systems (GIS) and digital elevation models (DEM) may be used for this task. Groundwater watershed divides are initially assumed to coincide with surface-water divides, with refinements added based on the results of subsequent hydrogeological investigations. The watershed boundary generally defines the site characterization boundary.

Although groundwater watershed divides are typically initially assumed to coincide with surface water divides, groundwater regimes and their boundaries can be complex. When mining in an area with karst, investigations should be conducted very early in the site characterization program to identify karstic limestone features within the watershed boundary. Karst features can be major preferential flow paths which can govern local groundwater regimes and the transport pathways of any seepage from tailings and waste rock containment areas. Siting of mine infrastructure should also consider the presence of major karst features.

4.4.3.1 Climate

The quantity of water within a watershed is a function of climate. The key components of climatic characterization are precipitation and temperature. Information on the amount, temporal distribution, and form of precipitation (rain or snow) is used in association with temperature data to characterize the quantity and seasonal distribution of recharge to a watershed. These data are used in development of a site wide water balance (see Section 4.4.3.4).

Characterization of the climatic conditions at a site typically begins with identification and review of available regional data. Site-specific climatic data are obtained by installing a meteorological station to record daily values of temperature, precipitation, wind speed, wind direction, and relative humidity. In cold climates, snowpack should be measured. Evaporation pans or empirical equations are used to estimate site evapotranspiration rates.

Site precipitation data are typically compared to regional data collected concurrently to assess the representativeness of the regional data set. Because the period of record for regional data sets is typically longer, these data are often used to estimate the occurrence, frequency, and magnitude of extreme weather events (e.g., floods and droughts). Characterization of these events is needed to assess ARD release, fate, and transport. During dry periods, sulphide oxidation products will accumulate. ARD loading is often greatest during a rain event that follows an extended dry period.

4.4.3.2 Hydrology

Hydrologic characterization begins with identification of all surface water features within the watershed (i.e., lakes, streams, and rivers) and points of discharge (i.e., lakes and ocean). Surface water quality, quantity, and direction of flow within the watershed boundaries are characterized. Baseline conditions are characterized before exploration or, more commonly, during the development phase. Monitoring is conducted during the construction and operations phases, and possibly during decommissioning and post-closure phases to assess impacts.

Streamflow measurements are required to characterize the amount and rate of flow to evaluate constituent fate and transport and to characterize aquatic habitat. Streamflow is measured using a current meter or weirs (see Chapter 8). The degree of seasonal variation will dictate the required monitoring frequency. Continuous monitoring systems can be established using data loggers with solar or battery power. These systems characterize changes in flow in response to climatic events.

Water quality sampling is conducted to characterize baseline water quality conditions. If possible, water quality sampling should precede any land disturbances such as exploration drilling. Multiple sampling events may be required to capture baseline conditions and seasonal variation in water quality related to seasonal variation in flow. The initial water quality survey should be spatially comprehensive, with samples collected throughout the watershed, both upstream and downstream of the ore deposit and future land disturbances. Typically, samples are collected above and below the confluences of each relevant tributary in the watershed, as well as above and below any historical mine features and natural exposures of ARD, ND, and SD. This approach allows anomalous high values to be systematically traced to their source. Some of the sampling sites in the initial survey will become part of a long-term monitoring program if and when a mine is developed. With this in mind, siting of sampling locations should consider the locations of future mining features. Sample sites should be surveyed with a satellite based navigations system such as Global Positioning System (GPS), GALILEO (European Global Satellite Navigation System), or GLONASS (Global’naya Navigatsionnaya Sputnikovaya Sistema [global navigation satellite system]).

Because metal concentrations may be naturally elevated in mineralized areas, characterization of baseline conditions is critical in later assessments of water quality impacts related to mining. Baseline data may be used to support establishment of site-specific water quality guidelines based on premining conditions. In the absence of adequate and defensible baseline data, water quality impacts may be erroneously attributed to mining operations or post-closure water quality criteria may be set to unachievable levels. For these reasons, special emphasis is placed on historical mine features and natural sources of drainage. These data may be provided to regulatory agencies in advance of mine development to ensure documentation of premining conditions.

Water quality sampling and flow monitoring continues during the operation phase to evaluate environmental impacts.

If lakes are present in the watershed or the watershed discharges to an ocean, characterization and monitoring of these systems may be necessary. Chapter 8 discusses lake and marine water quality monitoring and determination of a lake water balance.

4.4.3.3 Hydrogeology

Hydrogeologic characterization includes determination of groundwater occurrence, groundwater quality, current and potential future groundwater usage, and groundwater flow direction and velocity. Characterization of groundwater conditions is required to evaluate constituent fate and transport, to design dewatering operations, assess compliance with regulatory criteria for designated uses (e.g., drinking water), and to site mine and process facilities (e.g., preference for siting waste facilities in groundwater discharge zones over groundwater recharge zones and preference for siting of waste facilities over aquitards rather than aquifers).

Topographic maps, site reconnaissance, and aerial photographs are used to identify areas of groundwater recharge (i.e., hill tops) and groundwater discharge areas (i.e., springs, streams, rivers, ponds, lakes, and wetlands). Information on existing groundwater wells and their use is compiled.

Existing geologic information for the watershed is reviewed to evaluate the nature and distribution of aquifers and aquitards. Aquifers are saturated geologic units that readily transmit groundwater (e.g., fractured bedrock, unconsolidated sand, and gravel), whereas aquitards are geologic units that do not transmit significant quantities of groundwater (e.g., unfractured crystalline bedrock, most shales, and clay). In many cases, collection of information on the lithology, stratigraphy, and structural features (e.g., fractures, folds, and faults) of the subsurface will result in an understanding of the distribution of aquifers and aquitards. The geologic data collected during exploration and regional geologic survey data should be included in the assessment of geologic watershed information

Groundwater occurrence and the depth of the water table are determined by drilling. Shallow exploration boreholes provide excellent locations to measure the depth to the water table. Exploration drilling logs may also include information on depth to water and volume of water encountered during drilling that can be used in the development of the subsequent field investigations. During the Development Phase, a monitoring well network is established. Groundwater levels are measured to create a potentiometric map for the study area from which groundwater flow directions are determined. Groundwater flows from regions of high hydraulic head (e.g., hill tops) to regions of low hydraulic head (e.g., stream valleys). Hydrostratigraphic cross sections for the site are created showing depth to groundwater, aquifer and aquitard thicknesses, and extents. The location of seeps and springs and their flow rates should be documented.

Laboratory or field testing is conducted to characterize the pertinent hydraulic properties of aquifer units (i.e., porosity and hydraulic conductivity). Hydraulic conductivity is estimated from laboratory testing of drill core samples or from hydraulic testing in the field, including piezometer tests (slug test) or larger scale pumping tests. Because pumping tests provide in situ measurements of hydraulic conductivity averaged over a larger aquifer volume than piezometer tests, pumping tests are often the preferred testing method. Pumping tests also allow for determination of the specific storage and transmissivity of the aquifer. Porosity is determined by laboratory testing or estimated from literature values (Freeze and Cherry, 1979).

Groundwater flow velocity is calculated from the hydraulic gradient (determined from water-level data), hydraulic conductivity, and porosity. Groundwater flow velocities are required for evaluation of constituent fate and transport. Characterization of the physical flow system is also required to select an appropriate dewatering system and for dewatering system design. When dewatering wells are employed, the dewatering time is a function of the pumping rate, which is dictated by the number of pumps and pump capacity. Dewatering rates dictate the required capacity of the water treatment plant (if treatment is deemed necessary) and this information is also needed for surface water discharge permits. Numerical modeling software is often used to create a two- or three-dimensional representation of the groundwater flow system, which may be used as a tool in constituent fate and transport and dewatering evaluations. The groundwater model may also be used to define inputs to the water balance (see Section 4.4.3.4 and Chapter 5).

Groundwater quality sampling is conducted at all monitoring wells, seeps, and springs to establish baseline conditions. Monitoring wells are sited upgradient and downgradient of sources of mine drainage. Groundwater quality monitoring continues throughout the operation phase, and as required during the decommissioning and post-closure phases to evaluate environmental impacts.

For underground mines, characterization of the hydrogeologic conditions is essential to assess dewatering during operations and flooding at closure. Geologic maps are reviewed to identify structural controls on groundwater flows. Exploration drill holes may be converted to piezometers or for measurement of groundwater levels or hydrogeologic testing.

4.4.3.4 Site Wide Water Balance

Climatic, hydrological, and hydrogeologic data are combined to develop a watershed water balance. The water balance is a fundamental component of the environmental impact assessment as it defines the amount of water available to “dilute” a constituent load released from a source, thereby defining the concentration of a constituent in a water resource. An accurate water balance is therefore key to the accurate prediction of constituent concentrations. The water balance is also used to manage site water consumption, predict discharge from water treatment plants, determine design criteria for stormwater collection systems, and predict post-mining pit lake filling (if applicable).

The water balance describes the hydrologic regime of the watershed. The water balance is an accounting of all water inputs and outputs and changes in storage. For a watershed in which the surface water and groundwater divides coincide and for which there are no external inflows or outflows of groundwater, the water balance is described as follows (Freeze and Cherry, 1979):

P = Q + ET + ΔS (Equation 4-1)

where P is precipitation, Q is runoff, ET is evapotranspiration, and ΔS is the change in storage of the groundwater and surface-water reservoir. A simplified box and arrow representation of the components of a watershed water balance is shown in Figure 4-11. This figure illustrates the interaction between surface water and groundwater resulting in additional components (i.e., overland flow [OF], infiltration to soil and groundwater [IS and IG], and groundwater base flow [B]).

Figure 4-11: Water Balance Box and Arrow Diagram
WaterBalanceBoxandArrowDiagram.gif

To develop a site wide water balance, each of the water inputs and outputs must be defined using site characterization data. When site data are unavailable, inputs are derived using regional data or established relationships. For example, the precipitation and evapotranspiration inputs may initially be based on regional data and then updated with data from the site meteorological station. The Thornthwaite Method provides a means to estimate monthly ET rates as well as IS and IG values based on average monthly air temperature, latitude, and soil characteristics (Dingman, 2002). The Rational Equation can be used to estimate monthly OF values (Fetter, 2001).

Site requirements will dictate the temporal resolution of the water balance. Typically, a daily or monthly time step is applied. Spreadsheet programs, databases, and decision analyses software (e.g., MS Excel, MS Access, and GoldSim) are well designed for water balance calculations. To evaluate conditions under a range of rainfall events, a multiyear precipitation record is generated. This record typically includes extreme climatic conditions (e.g., droughts and storms) to evaluate the effects of such extreme events. Statistical analysis of historical precipitation records is conducted to determine the frequency and magnitude of extreme events.

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4.4.4 Watershed Characterization - Assimilative Capacity of the Receiving Environment

The sensitivity of the downstream aquatic life and the ability of the receiving environment to attenuate COIs must be characterized to predict the fate and transport of constituents in the environment. The buffering capacity of the receiving environment will affect the fate and transport of acidity and metals present in ARD. For historical mining or natural ARD releases, neutralization of acidity may occur following mixing with alkaline waters or interactions with solid mineral phases. Movement of an acidification front will be slower in a well-buffered system than a poorly-buffered system. The transport of COIs will also be affected by geochemical conditions within the receiving environment, and as such, key geochemical parameters should be measured (i.e., pH and redox). Characterization programs should include collection of solid phase data for stream and lake sediments and aquifer materials that may affect metal transport (e.g., presence of clay and total organic carbon).

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4.4.5 Watershed Characterization – Biological Receptors

The first step in biological characterization is to identify the receptors within the watershed that may be affected by release of ARD, NMD, or SD. Biological receptors may include vegetation, aquatic life, terrestrial wildlife, livestock, and humans. Consideration should be given both to current and future use of water resources by humans. During the Development Phase, receptor baseline conditions are characterized, including receptor habitat, when applicable. These studies are completed by ecologists or biologists familiar with the local habitats and biota. During the construction and operation phases, receptor monitoring is conducted to assess impacts. In some cases, potential impacts to receptors are determined indirectly (e.g., monitoring of groundwater quality to ensure drinking water obtained from wells for human consumption and use is not affected). If operational monitoring identifies impacts to biological receptors, the objective of monitoring during the decommissioning phase is to measure recovery in impacted areas. Chapter 8 provides additional detail on receptor characterization and monitoring.

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4.4.6 Watershed Characterization – Archaeology and Cultural Value

Because society values cultural and historical aspects of landscapes, characterization should include identification of potential sites of historical and cultural value within the watershed. In some instances, historical sources of ARD, NMD, or SD can be considered of cultural or archaeological value (see Figure 4-1). For example, under Spanish law, industrial sites of historical significance receive considerable protection and are intended to be preserved, which may include the ARD present at certain historical mining sites. If archaeological items are likely to be unearthed, it is important that personnel involved in site investigations be trained to recognize artifacts and be provided with the proper procedures and protocols to be followed when artifacts are discovered. Depending on relevant national legislation, these requirements can be quite strict and specific and must not be overlooked.

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4.5 Selected Characterization Tools

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4.5.1 Geophysics

4.5.1.1 Introduction

Surface geophysical methods provide a non-invasive way to obtain information on the geologic and hydrologic characteristics of the subsurface or waste facilities. Geophysics can also be employed to map subsurface contaminant plumes and locate acidic underground mine pools, primarily through the use of electromagnetic methods (e.g., Hammack et al., 2003a, b) or to detect seeps from abandoned mines in rural areas (Sams and Veloski, 2003). Another useful application of electrical methods is the evaluation of extraction efficiency and reactivity in heap leach piles by identifying the portions of the pile in which moisture is present as well as the conductivities of the various wet zones. The USGS provides a bibliography of geophysical methods for characterizing mine waste (USGS, 2008) which is accessible at: http://crustal.usgs.gov/projects/minewaste/geophysics_mine_pubs.html. For further explanation of common geophysical methods, see Burger et al. (2006).

4.5.1.2 Remote Sensing

Remote sensing techniques provide a means to rapidly map potential sources of ARD at a mine site, particularly for historical sites where ARD controls were not implemented. Airborne imaging spectrometers, such as NASA’s airborne visible/infrared imaging spectrometer (AVIRIS) can spectrally identify surface exposures of Fe-rich, hydroxyl, or water-bearing secondary minerals commonly associated with ARD (e.g., copiapite, jarosite, schwertmannite, ferrihydrite, goethite, and hematite). Because jarosite forms under more acidic conditions than schwertmannite, ferrihydrite, and goethite, the relative distribution of these minerals can be used to locate potential acid producing areas. Swayze et al., (2000) applied this method to identify potentially acid producing areas at the California Gulch Superfund Site in Leadville, Colorado, USA. Swayze et al. (2000) concluded that the presence of jarosite at the surface is likely indicative of ongoing acid production and surface exposures of jarosite warranted field investigation. The method cannot detect all sources of acidic drainage. For example, jarosite is not associated with all ARD discharges. Some sources of ARD (e.g., tunnels and adits) may be too small to identify using the large pixel sizes commonly associated with remote sensing. Nonetheless, the USEPA estimated that the mineral maps generated by the AVIRIS program at Leadville saved over $2 million in investigation costs and reduced sampling and interpretation time by more than 2 years.

Others have used airborne frequency domain electromagnetic conductivity flown at lower altitudes (using helicopters) to map subsurface contaminant plumes and locate acidic underground mine pools at relatively shallow depths (50 m). It may be possible to use time domain electromagnetic conductivity to detect such pools at depths up to 100 m (Hammack et al., 2003a). Hand-carried geophysical techniques can also prove useful. For example, terrain conductivity has been successfully used to locate where water is being lost from a stream to an underground mine, allowing a small section of the stream bed to be remediated. This is discussed in more detail in Chapter 7 (Section 7.1.3.3).

4.6 Summary

Development of an ARD characterization program at a mine site is critical to the prediction, prevention, and management of ARD, NMD, and SD. The development of a site characterization program begins with development of a conceptual site model to identify sources of ARD, pathways for transport, and the receptors within the watershed. This chapter identifies and discusses the common components and data collection activities associated with a mine site characterization program. Because the distinctions between characterization, prediction, and monitoring are loosely defined, the contents of this chapter should be reviewed in association with Chapter 5, Prediction, and Chapter 8, Monitoring.

Identification and characterization of source materials is fundamental to the accurate assessment of whether ARD is likely to occur at a particular mine site. Characterization of materials to assess their ARD and metal leaching potential should begin during the early phases of a mine life and continue through to the end of operation. At a minimum, the characterization program should include testing of the ore (high and low grade) and waste materials (e.g., tailings and waste rock). At coal mines, this characterization is directed primarily at overburden for surface mines, while the nature of the coal and surrounding strata is more critical at underground mines. Inclusion of other materials (e.g., construction material and process waste streams) may also be appropriate.

The scope and development of an ARD characterization program is ultimately site specific. In some cases, engineering controls may be selected as the preferred or most economical method to address uncertainty in material characterization (e.g., placement of tailings in a lined facility for tailings with uncertain metal leaching or ARD behaviour).

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4.7 References

Australian Government Department of Industry, Tourism and Resources, 2007. Managing Acid and Metalliferous Drainage, February.


Blowes, D.W., Ptacek, C.J., and J. Jurjovec, 2003. Mill Tailings: Hydrogeology and Geochemistry. In: J.L. Jambor, D.W. Blowes, and A.I.M. Ritchie (Eds.), Environmental Aspects of Mine Wastes, Short Course Series Vol. 31, Mineralogical Association of Canada, 95-116.


Bowell, R. (Ed.), 2003. Pit Lake Systems: A Special Issue. Mine Water and the Environment, 22(4).


Burger, H.R., Sheehan, A.F., and C.H. Jones, 2006. Introduction to Applied Geophysics: Exploring the Shallow Subsurface. W.W. Norton & Company, New York, NY.


Castendyk, D.N., and L.E. Eary, (Eds.), in press. Mine Pit Lakes; Characteristics, Predictive Modeling, and Sustainability. ADTI-MMS Handbook Series Vol. 3, Society for Mining, Metallurgy, and Exploration, Colorado.


Dingman, S.L., 2002. Physical Hydrology, 2nd edition. Prentice Hall, Upper Saddle River, NJ.


Downing, B.W., and C. Mills, 2007. Quality Assurance/Quality Control for Acid Rock Drainage Studies.


ERMITE-Consortium, 2004. Mining Impacts on the Fresh Water Environment: Technical and Managerial Guidelines for Catchment Scale Management. In: P. Younger and C. Wolkersdorfer (Eds.), Mine Water and the Environment, 23(Supplement 1):S2-S80.


Fetter, C.W., 2001. Applied Hydrogeology, 4th edition. Prentice-Hall, Inc., Upper Saddle River, NJ.


Freeze, A.R., and J.A. Cherry, 1979. Groundwater. Prentice-Hall, Inc., Englewood Cliffs, NJ.


Gammons, C.H., and T.E. Duaime, 2006. Long-Term Changes in the Limnology and Geochemistry of the Berkeley Pit Lake, Butte, Montana. Mine Water and the Environment, 25(2):76-85.


Geller, W., Klapper, H., and W. Salomons (Eds.), 1998. Acidic Mining Lakes – Acid Mine Drainage, Limnology and Reclamation. Springer, Berlin, Heidelberg, New York.


Hammack, R.W., Love, E.I., Veloski, G.A., Ackman, T.E., and W. Harbert, 2003a. Using helicopter electromagnetic surveys to identify environmental problems at coal mines. Mine Water and the Environment, 22(2):80-84.


Hammack, R.W., Sams III, J.I., Veloski, G.A., and J.S. Mabie, 2003b. Geophysical investigation of the Sulphur Bank mercury mine Superfund site, Lake County, California. Mine Water and the Environment, 22(2):69-79.


Plumlee, G.S., 1999. The Environmental Geology of Mineral Deposits. In: G.S. Plumlee and M.J. Logsdon (Eds.), The Environmental Geochemistry of Mineral Deposits, Part A: Processes, Techniques and Health Issues, Reviews in Economic Geology Vol. 6A, Society of Economic Geologists, Inc., 71-116.


Plumlee, G.S., and M.J. Logsdon, 1999. An Earth-System Science Toolkit for Environmentally Friendly Mineral Resource Development. In: G.S. Plumlee and M.J. Logsdon (Eds.), The Environmental Geochemistry of Mineral Deposits, Part A: Processes, Techniques and Health Issues, Reviews in Economic Geology Vol. 6A, Society of Economic Geologists, Inc., 1-27.


Price, W.A., 1997. Draft Guidelines and Recommended Methods for the Prediction of Metal Leaching and Acid Rock Drainage at Minesites in British Columbia. Reclamation Section, Energy and Minerals Division, Ministry of Employment and Investment, Smithers, BC.


Price, W.A., 2009. In press.


Runnells, D.D., Shields, M.J., and R.L. Jones, 1997. Methodology for adequacy of sampling of mill tailings and mine waste rock. In: Proceedings of Tailings and Mine Waste 97, Rotterdam, Balkema, 561-563.


Sams III, J.I., and G.A. Veloski, 2003. Evaluation of airborne thermal infrared imagery for locating mine drainage sites in the Lower Kettle Creek and Cooks Run basins, Pennsylvania, USA. Mine Water and the Environment, 22(2):85-93.


Seal II, R.R., Foley, N.K., and R.B. Wanty, 2002. Introduction to Geoenvironmental Models of Mineral Deposits. In: R.R. Seal II and N.K. Foley (Eds.), Progress on Geoenvironmental Models for Selected Mineral Deposit Types, U.S. Geological Survey Open-File Report 02-195.


Seal II, R.R. and J.M. Hammarstrom, 2003. Geoenvironmental Models of Mineral Deposits: Examples from Massive Sulfide and Gold Deposits. In: J.L. Jambor, D.W. Blowes and A.I.M. Ritchie, Environmental Aspects of Mine Wastes, Short Course Series Vol. 31, Mineralogical Association of Canada, 11-50.


Smith, L., and R. Beckie, 2003. Hydrologic and Geochemical Transport Processes in Mine Waste Rock. In: J.L. Jambor, D.W. Blowes and A.I.M. Ritchie, Environmental Aspects of Mine Wastes, Short Course Series Vol. 31, Mineralogical Association of Canada, 51-72.


Society for Mining, Metallurgy, and Exploration, Inc. (SME), 2008. Management Technologies for Metal Mining Influenced Water – Basics of Metal Mining Influenced Water. V.T. McLemore (Ed.).


Swayze, G.A., Smith, K.S., Clark, R.N., Sutley, S.J., Pearson, R.M., Vance, J.S., Hageman, P.L., Briggs, P.H., Meier, A.L., Singleton, M.J., and S. Roth, 2000. Using Imaging Spectroscopy to Map Acid Mine Waste. Environmental Science and Technology, 34:47-54.


United States Geological Survey (USGS), 2008. Bibliography of Geophysical Methods for Characterizing Mine Waste.
http://crustal.usgs.gov/projects/minewaste/geophysics_mine_pubs.html


Wolkersdorfer, C., 2008. Water Management at Abandoned Flooded Underground Mines – Fundamentals, Tracer Tests, Modelling, Water Treatment. Springer, Heidelberg.

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List of Tables

Table 4-1: Mine Phase Objectives and Activities
Table 4-2: Characterization Activities by Mine Phase
Table 4-3: Source Material Characterization Activities by Mine Phase
Table 4-4: Geologic Characteristics of Mineral Deposits that Affect Their Environmental Signatures (Plumlee, 1999)
Table 4-5: Australian Guidance on Sample Numbers (Australian Government Department of Industry, Tourism and Resources, 2007)

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List of Figures

Figure 4-1: Components of Site Characterization Program
Figure 4-2: Characterization Chapter Road Map
Figure 4-3: Typical Data Requirements of a Conceptual Site Model (CSM)
Figure 4-4: Example Conceptual Site Model Schematic
Figure 4-5: Major Steps Involved in Extraction Metallurgy of Metals
Figure 4-6: Sources and Pathways of ARD, NMD, and SD in a Pit during Operation and Closure
Figure 4-7: Sources and Pathways of ARD, NMD, and SD in Underground Workings during Operation and Closure
Figure 4-8: Sources and Pathways of ARD, NMD, and SD in a Waste Rock Pile
Figure 4-9: Sources and Pathways of ARD, NMD, and SD in a Subaqueous Tailings Storage Facility
Figure 4-10: Source Material Geochemical Testing Program Components
Figure 4-11: Water Balance Box and Arrow Diagram

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  1. NAPP – Net Acid Producing Potential expressed as kg H2SO4 per tonne. Calculated by subtracting acid neutralizing capacity (ANC) from acid producing potential (APP). The Australian Guidelines use NAPP as a measure of the ARD potential. NPR may be used in place of NAPP