1. science
2. ecology
3. pollution

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Report Number 2 from Norsk Bergindustri/Norwegian Mineral Industry in a
series regarding effects of sea disposal of mine tailings.
The report is version 1 of a guideline for characterization of tailings intended for
sub-sea deposition, the deposition site and receiving environment
The report has been put together by Ingar Walder in Kjeøy Research and
Education Center, commissioned by Norsk Bergindustri.
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This report is number 2 in our series regarding sea disposal.
The initiative to this series has been taken by Norsk Bergindustri/Norwegian
Mineral Industry in order to document the Norwegian practice of disposal of
mine tailings in the sea.
Norsk Bergindustri has several committes, which are made up by internal and
external specialists in different areas. A full overview of these committees and
their responsibilities is available at www.norskbergindustri.no
There is a special committee, deponiarbeidsgruppa/Deposition Working Group,
which is open for all members that practice disposal of mine tailings. The
mandate of this committee is as follows: advisor of the board relating to the
disposal of mineral waste - as well as the sharing of experience and development
of best practices regarding this matter.
Elisabeth Gammelsæter
Roar Sandøy
Secretary General Norsk Bergindustri
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Leader, Deposition Working Group
March 2015
prSN/TR-9432
SUB-SEA TAILINGS DEPOSITION
EVALUATION GUIDELINE
A guideline for characterization of tailings
intended for sub-sea deposition, the deposition
site and receiving environment.
Version 2
March 2015
Guide prepared by:
Ingar Walder, Ph.D.
Geochemist
Director R&D
Kjeøy Research & Education Center
Kjeøy,
8412 Vestbygd
Norway.
Reference/Review Group
- Sverre Høstmark, Norsk Industri
- Roar Sandøy, Sibelco Nordic
- Mona Schanche, Nordic Mining
- Arnstein Amundsen, Hustadmarmor
- Ann Heidi Nilsen, Titania
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FORWARD
This guideline document (prSN/TR-9432:2012) has been prepared by Dr. Ingar Walder
at Kjeøy Research & Education Center. The document has been reviewed by Norsk
Bergindustri (Norwegian Mining Association) Waste Facility Group and by the Scottish
Association of Marine Studies.
This Guideline, written as a Technical Report according to the European Standardization
system, is intended to supplement the existing series of four CEN Technical
Reports/Specifications dealing with characterization of waste from extractive industries:
•
CEN/TR 16376:2012, Characterization of waste - Overall guidance document for
characterization of waste from extractive industries.
• CEN/TR 16365:2012, Characterization of waste - Sampling of waste from
extractive industries.
• CEN/TR16363:2012, Characterization of waste - Kinetic testing for sulfidic
waste from extractive industries.
• CEN/TS16229: 2011, Characterization of waste - Sampling and analysis of
cyanides (WAD) discharged into tailings ponds.
This Guideline focuses on the technical issues related to the recommended
characterization for evaluating sub-sea deposition of tailings from the extractive
industries. General issues concerning characterization of the waste are laid out in the
above listed CEN-documents.
This Guideline considers a range of potential approaches and tools for the
characterization of a prospective receiving sub-sea environment; e.g. bottom flora,
fauna, fish, water current, and water conditions; in addition to, methods for
characterization of waste that will potentially be placed in a sub-sea tailings facility.
This approach enables the project manager to tailor the sampling plan and
characterization to a specific testing scenario. It also allows for flexibility in the
selection of the sampling approach, sampling point, method of sampling and equipment
used, to characterize the receiving environment. It helps generate the necessary
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background information pertaining to factors influencing the chosen characterization
approach required for characterizing the receiving environment. The Guideline also
makes references to the overall guidance document for characterization of waste from
extractive industries (CEN/TR 16376), which provides guidance and recommendations
on the application of methods for the characterization of waste from extractive
industries.
This document provides guidance, not required procedures. It gives recommendations on
what to evaluate during characterization of possible sub-sea deposition environments for
waste from extractive industries. It provides a toolbox with different methods that may
or may not be applicable in a specific case. It is not a legally binding document.
There are many issues specific to sub-sea tailings deposition which are not covered in
the CEN mine-waste guidelines but are covered in this document:
•
•
•
•
•
Sediment dispersion in a Marine environment;
Fish affected by suspended sediments and the effect of suspended sediments of
the Pelagic system;
Leaching of chemicals used during the processing and thickening of tailings;
Release of metals from the tailings due to biogeochemical cycling;
Covering of bottom flora and fauna by sediments.
It is important to understand these issues pertaining to specific sites when evaluating
sub-sea deposition for storage of the tailings.
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TABLE OF CONTENT
FORWARD
5
INTRODUCTION
10
1. SCOPE
14
2. ADMINISTRATIVE PROCEDURES AND LEGAL CONSIDERATIONS
15
2.1. EU LEGAL DOCUMENTS
2.1.1. RELEVANT EU-DIRECTIVES AND BAT-DOCUMENTS
2.1.2. COMMISSION DECISIONS RELATED TO WASTE FROM EXTRACTIVE INDUSTRIES
2.1.3. CEN DOCUMENTS
2.2. INTERNATIONAL CONVENTIONS
2.2.1. OSPAR, LONDON, HELCOM AND BARCELONA CONVENTIONS
2.3. NORWEGIAN LAWS, BYLAWS AND GUIDELINES
2.3.1. NORWEGIAN MINERALS ACT
2.3.2. POLLUTION CONTROL ACT WITH BYLAWS
2.3.3. GUIDELINE FOR CLASSIFICATION OF BOTTOM SEDIMENT
2.3.4. GUIDELINE FOR DEPOSITING CONTAMINATED SEDIMENTS IN THE SEA
2.3.5. CONTAMINATED FJORD COVER DEPOSITION GUIDE
2.3.6. CONCLUDING REMARK
2.4. OTHER NATIONAL REGULATIONS ON SSTD
2.4.1. PAPUA NEW GUINEA DEEP SEA TAILINGS PLACEMENT GUIDELINE
2.4.2. PHILIPPINES
2.4.3. TURKEY
2.4.4. USA
2.4.5. CANADA
2.4.6. AUSTRALIA
2.4.7. JAMAICA
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3. HEALTH AND SAFETY
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4. ENVIRONMENTAL ISSUES
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4.1. TAILINGS CHARACTERISTICS
4.1.1. PARTICLE TRANSPORT / SILTATION / TURBIDITY
4.1.2. ACID/NEUTRAL ROCK DRAINAGE AND POTENTIAL RELEASE OF HEAVY METALS
4.1.3. PROCESS CHEMICALS
4.2. TAILINGS DISCHARGE SYSTEMS
4.2.1. PLUME DENSITY
4.2.2. PIPELINE BREAK
4.3. RECEIVING ENVIRONMENT
4.3.1. FJORD CIRCULATION
4.3.2. VERTICAL WATER COLUMN
4.3.3. CHANGES IN CURRENTS DUE TO DEPOSITION
4.3.4. EFFECTS ON FISH DEPENDENT ON FISH TYPE
4.3.5. SPAWNING AREA (PERMANENT – VARIABLE)
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4.3.6. ECOSYSTEM EFFECTS
4.4. RECOLONIZATION
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5. CHARACTRIIZATION OF DEPOSITION SITE
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5.1.
5.2.
5.3.
5.4.
5.5.
5.6.
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BACKGROUND INFORMATION
MINERAL DEPOSIT
EXPLOITATION METHOD
MINERAL PROCESSING
DEPOSITION SITE
DEPOSITION
6. CHARACTERIZATION OF TAILINGS
48
6.1. SAMPLING PLAN
6.2. PHYSICAL AND HYDRAULIC PROPERTIES
6.2.1. COMPRESSIBILITY AND FRICTIONAL BEHAVIOR
6.2.2. IN-SITU INVESTIGATION OF DEPOSITED WASTE
6.2.3. GRAIN SIZE / SPECIFIC SURFACE AREA
6.3. MINERALOGICAL COMPOSITION AND TEXTURAL INFORMATION
6.4. CHEMICAL ANALYSIS
6.4.1. ANALYSIS OF SOLIDS
6.4.2. ANALYSIS OF LIQUIDS
6.4.3. SULPHUR (TOTAL, SULFATE AND SULFIDE)
6.4.4. ORGANIC AND INORGANIC CARBON
6.4.5. PROCESS CHEMICALS
6.5. A/NRD TESTING METHODS
6.5.1. STATIC TESTING - ACID BASE ACCOUNTING (EN15875)
6.5.2. KINETIC TESTING
6.5.3. SALTWATER/SEAWATER KINETIC TESTING
6.6. LEACHING BEHAVIOUR AND LEACHING TESTS
6.6.1. COMMON LEACHING TESTS
6.7. DISCHARGE SETTLING
6.8. FIELD EXPERIMENTS
6.8.1. EXISTING WASTE FACILITY
6.8.2. SMALL-SCALE FIELD TESTING
6.9. AQUATIC TOXICITY TESTS
6.9.1. ACUTE TOXICITY TESTS
6.9.2. CHRONIC EFFECT TESTS
6.9.3. BIOACCUMULATION TESTS
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7. CHARACTERZATION OF THE RECEIVING ENVIRONMENT
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7.1. FISH AND FISH RESOURCES
7.2. BOTTOM SEDIMENTS
7.3. BOTTOM FLORA AND FAUNA
7.3.1. SOFT-BOTTOM FLORA AND FAUNA
7.3.2. HARD-BOTTOM FLORA AND FAUNA
7.4. WATER QUALITY
7.5. OCEAN-FJORD CURRENTS
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7.6. BATHYMETRY
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8. DATA QUALITY
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9. INTERPRETATION, APPLICATION, AND EVALUATION
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9.1. PARTICLE TRANSPORT
9.2. ACID/NEUTRAL ROCK DRAINAGE AND LEACHING RISK
9.2.1. A/NRD EVALUATION
9.2.2. LEACHING EVALUATION
9.2.3. MARINE ECO-TOXICOLOGY
9.3. UNCERTAINTY – LIMITATIONS
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10. OPERATION, MONITORING AND CLOSURE
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DISCHARGE SYSTEM
FIELD VERIFICATION
MONITORING
EMERGENCY RESPONSE PLANS
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11. DOCUMENTATION AND REPORTING
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12. REFERENCES
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13. WORDS
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10.1.1.
10.1.2.
10.1.3.
10.1.4.
List of Figures
Figure 1. Flow-chart showing the outline of the SSTD evaluation guideline
Figure 2. Simplified sub-sea tailings deposition setting from a mine
Figure 3. Flow chart for a baseline evaluation.
Figure 4. Characterization flow chart.
Figure 5. Experimental setup for long-term leaching tests for SSTD
Figure 6. Flow chart for the steps within the Evaluation of SSTD data
Figure 7. Acid potential vs. neutralization potential
Figure 8. Display of level of organisms and eco-toxicity and leach tests.
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74
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List of Tables
Table 1. List of the main aspects to be covered in a sampling plan
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March 2015
INTRODUCTION
Waste from the extractive industries can only be managed properly if sufficient
knowledge about its geochemical and physical properties and behaviour is available,
together with knowledge of whether or not the receiving environment can handle the
impact of the waste deposition. Such knowledge can be obtained through proper waste
and receiving environment characterization. The Mining Waste Directive, MWD,
(Directive 2006/21/EC of the European Parliament and the Council of March 15, 2006
on the management of waste from extractive industries) and the associated Commission
Decisions (waste facility classification, inert waste definition and waste characterization)
include requirements related to characterization of waste from the extractive industry.
As a follow-up a series of guidelines have also been developed in order to assist
regulators, consultants, and mining operators to characterize the mining waste. These
guidelines have focused on issues regarding land deposition; Sub-sea tailings deposition
has not been specifically addressed.
Norway has a relatively long history of depositing tailings in fjords with approximately
such 22 cases (Kvassnes 2013). Currently, 7 operations are actively depositing tailings
in fjords (Kvassnes 2013). Five of these are primarily industrial minerals operations
(graphite, nepheline syenite, calcite, quartz); and two are iron mines (magnetite,
hematite). Historically tailings from sulphide ore (Cu, Pb, Zn and Ni) and ilmenite ore
have also been deposited in fjords.
The Mining Waste Directive (Directive 2006/21/EC) covers the management of waste
arising from land-based extractive industries. A sub-sea tailings facility is not specified
as “excluded” from the scope of the Mine Waste Directive; and therefore, such facilities
are also covered in the Mining Waste Directive.
The Water Framework Directive (Directive 2000/60/EC) does not preclude sub-sea
tailings deposition (Klima- og forurensningsdirektoratet 2012).
In this document, sub-sea tailings deposition (SSTD) is used to define tailings from
extractive industries being deposited below the lowest water mark registered for an
ordinary outgoing low tide. However, as described in this guideline, a more ideal
placement is considerably deeper than this. The term submarine tailings placement
(STP) and submarine tailings deposits (STD) are also used to mean the same (Ellis,
1995). Deep submarine tailings placement (DSTP) refers to tailings being deposited on
the seafloor with a discharge point of more than 100 m depth (Shimmield, 2010).
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The European Commission Decision on waste characterization (CD 2009/360) states
that: “The purpose of the characterization of extractive waste is to obtain the relevant
information on the waste to be managed in order to be able to assess and monitor its
properties, behaviour and characteristics and thereby ensure that it is managed under
environmentally safe conditions in the long term. Furthermore, the characterization of
extractive waste should facilitate the determination of the options for managing such
waste and the related mitigation measures in order to protect human health and the
environment.”
A multitude of methods and tools are available for various waste characterization
purposes – some are standardised and some are not. Many methods are developed for
characterization of non-mineralogical material and not applicable for waste from the
extractive industry. Tradition, geography, and experience often determine which method
is used. In some cases, the use of specific methods is required by legislation; for
example, “Characterization of waste from extractive industries”. Within EU legislation,
European (CEN) standards and methods are generally preferred, if they are available.
The main methods for the characterization of waste have been included in this SSTD
evaluation guideline. Also included are specific methods used for the evaluation of a
SSTD as a waste disposal method.
This Sub-Sea Tailings Deposition Evaluation Guideline document has been developed
for Standard Norway to support stakeholders in Norway involved in the characterization
and management of extractive waste, in selecting the appropriate tools (standards or
methods) for evaluating the potential for Sub-Sea Tailings Deposition; and to satisfy the
requirements of Directive 2006/21/EC and associated Commission and the Norwegian
implementation of this directive and Commission decisions. It is further meant to
provide information on the possibilities and limitations of the methods, and some
guidance on where to find further information on the interpretation and application of
the waste characterization results. The purpose of the document is to provide authorities,
regulators, operators/waste producers, consultants and testing laboratorieswith a
summary of the specific aspects of characterising waste from the extractive industries
and its suitability for SSTD at a given site.
The outline of the document follows, to a large extent, the outline used in the three CEN
guidelines developed for the characterization of waste from extractive industries (Fig.
1). There are a total of nine chapters. The first chapter, The Scope, is followed by a
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chapter (Chapter 2) on European and other international legal documents and guidelines
including a review of the Norwegian regulations of sea and fjord issues.
Chapter 3, a short chapter on health and safety issues related to sampling, is followed by
a chapter (Chapter 4) on environmental issues related to mining and sub-sea tailings
deposition.
Chapter 5 discusses the baseline issues of waste characterization as described in the
Commission Decision. This guideline further discusses the baseline issues of the
receiving waste facility site. The baseline chapter is followed by an extensive chapter,
Chapter 6, Characterization. This chapter reviews sampling procedures and methods
that can potentially be used for characterizing the waste and the potential receiving
environment.
The Chapter 7 is on data quality, with issues relating to quality control/quality assurance
of the characterization data; while Chapter 8 goes through the evaluation, application
and interpretation of the characterization data. Chapter 9, the last chapter of the
document provides information for proper documentation and an outline of a report
form.
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Figure 1. Flow-chart showing the outline of the SSTD evaluation guideline.
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1. SCOPE
This Guideline document/Technical report provides guidance and recommendations on
the application of methods for the characterization of mine waste and deposition site
when sub-sea tailings deposition is considered. The document covers characterization
methods for both physical and geochemical properties of the waste together with
characterization of the deposition site and receiving environment. Other significant
aspects, from planning to interpretation and reporting, that are not covered in other
Norwegian or European official documents, are also included.
The main purpose of this document is to aid extractive industries and regulatory
agencies on how to plan, determine, perform and evaluate the necessary characterization
for potential sub- sea-tailings deposition. The document includes a discussion on when
and why characterization may be needed, and on the contexts within which
characterization data may need to be applied.
The extractive industry covers many different sectors with very different waste
categories; and characterization may be carried out with many different objectives. For
this reason, a guidance document on characterization cannot be prescriptive or provide
generally applicable instructions on how waste characterization should be performed in
each and every case.
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2. ADMINISTRATIVE PROCEDURES AND LEGAL CONSIDERATIONS
There are very few legal international documents that directly discuss sub-sea/deep sea
tailings deposition. The most important legal documents that have an impact on how
characterization and evaluation of Sub-sea tailings deposition is to be performed are
described below. The EU directives and regulations, together with documents from the
European Standardization Commission, make up the bulk of the documents. This
section also includes a short discussion on how other countries outside Europe have
been dealing with the potential of sub-sea/deep sea tailings disposal.
2.1.
EU Legal Documents
There are several types of documents that legally define the characterization of waste
and the facilities to handle the waste from extractive industries. The first of these are the
EU-directives and Commission Decisions. There is also the European BREF/BAT
(2004) document for specific issues decided by the Commission. This reference
document was decided/accepted by the EU-commission and formed the basis for the
EU-directive on Waste from Extractive Industries (2006). Furthermore, the European
Standardization Commission (CEN) issued standards to be followed, if applicable, and
technical specifications and reports considered as guidelines. These documents are
further described in the following sub-sections.
2.1.1. Relevant EU-Directives and BAT-documents
There are several EU-directives that affect the evaluation of mine waste management in
Norway. The most important directives are:
• EU-Directive on Waste from Extractive Industries (Directive 2006/21/EC)
• EU-Water framework directive (Directive 2000/60/EC)
The Mining Waste Directive was adopted in April 2006, and was to be implemented
from June 2012. As a part of the implementation of the directive, four CEN technical
reports/guidelines and one standard (acid base accounting) have been developed.
The Mining Waste Directive (Directive 2006/21/EC) covers the management of waste
arising from land-based extractive industries. In article 3.15 the directive defines a
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deposition area as a waste facility: “Such facilities are deemed to include any dam or
other structures serving to contain, retain, confine or otherwise support such a facility,
and also to include, but not to be limited to, heaps and ponds, but excluding excavation
voids into which waste is replaced, after extraction of the mineral, for rehabilitation and
construction purposes.” A sub-sea tailings facility is thus included in the scope of the
Mining Waste Directive. According to the directive, inert waste should have less
rigorous guidelines, unless classified as Category A waste facility. Non-hazardous noninert waste may have reduced or waived requirements (Bullet 9) unless classified as
category A waste facility. Bullet 23 states that it is necessary to define when a waste
facility should be closed, and the obligations and responsibilities of the operator after
closure.
The Water Framework Directive (Directive 2000/60/EC) has been in effect from
October 23rd, 2000; and part of the scope of the Directive is to protect territorial and
marine waters (Article 1). Article 11.6 states that member states should take all
appropriate measures not to increase pollution to marine waters, unless these
requirements result in an allowed increase in pollution of the environment as a whole.
The directive also specifies the characterization needed for classification of fresh water
bodies and marine waters.
The BAT (2004) document on management of tailings briefly mentions sub-sea tailings
deposition (SSTD), but does not include the SSTD as a Best Available Technique due to
lack of information on the method. However, the Bref/BAT (2004) document does not
exclude SSTD as a best available technique for tailings management. The document
does, in general terms, describe the Hustadmarmor SSTD system, and states that SSTD
is used since there is no space for land-based deposition. In addition, the document also
states: “This technique is applicable where the tailings slurry will form a high density
plume that will descend to the bottom of the sea, leaving a clear water area above the
pipe outlet.” This Bref/BAT document is under revision.
2.1.2.
Commission Decisions related to Waste from Extractive Industries
The EU-Commission has made several decisions as part on the implementation of the
EU-Mining Waste directive that also impacts the evaluation of waste handling in
Norway. These are:
• Commission decision on waste characterization (CD 2009/360/EC)
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• Commission decision on classification of waste management facilities (CD
2009/337/EC)
• Commission decision on inert waste (CD 2009/359/EC)
• Commission decision on financial assurance (CD 2009/335/EC)
These four Commission Decisions (CD) describe, in some more detail, issues that are
only briefly mentioned in the Mining Waste Directive.
The Commission Decision (CD) on waste characterization describes, in general, the
issues that need to be addressed with regards to waste characterization in order to make
a mine-waste management plan. These issues have been incorporated into CEN
Guidelines for characterization of waste from extractive industries (chapter 2.1.3).
The CD on waste management facilities describes the criteria for classification of the
facilities. The classification involves determining whether a facility is an A-Facility or
not. An A-Facility, a facility that has the potential risk to cause significant harm to
human health or the environment, has to comply with more stringent regulation and
member states cannot make variances to the EU directives or commission decisions.
The CD on inert waste describes the criteria to be used for classifying waste from
extractive industries as inert. It specifies a maximum content of sulfide, minimum ratio
between acid potential and neutralizing potential, and a list of elements whose
concentrations must be low enough to insignificantly affect human health or the
environment. However, it does not specify methods to be used or threshold values;
these are to be decided by each member state.
The CD on financial assurance outlines the requirement to perform an assessment of the
costs of closure and post closure monitoring and care. The cost is to ensure land
rehabilitation is performed at closure and after closure, including post-operational
monitoring; and/or that treatment of contaminants can be performed.
2.1.3.
CEN Documents
As part of the implementation of the mining directive the European standardisation
committee, CEN has developed several documents via the committee CEN/TC292.
CEN/TC292 handles waste issues and issues related to waste from extractive industries.
The documents developed by CEN as part of the implementation are:
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•
•
•
•
•
2.2.
CEN/TR 16376:2012, Characterization of waste - Overall guidance document for
characterization of waste from extractive industries.
CEN/TR 16365:2012, Characterization of waste - Sampling of waste from
extractive industries.
CEN/TR16363:2012, Characterization of waste - Kinetic testing for sulfidic
waste from extractive industries.
CEN/TS16229: 2011, Characterization of waste - Sampling and analysis of
cyanides (WAD) discharged into tailings ponds.
EN15875 2011, Characterization of waste – Static testing for determination of
acid potential and neutralization potential of sulfidic waste.
International Conventions
There are several International Conventions treating dumping of wastes in marine
waters. None of these conventions prohibit deposition of tailings materials in the sea.
2.2.1.
OSPAR, London, HElcom and Barcelona conventions
The Oslo Convention (1974) and the Paris Convention (1978) were established in order
to reduce the input of contaminant material to the sea (North Sea in particular) (OSPAR
Convention from 1992). The HELCOM convention applies for the Baltic area, and the
Barcelona Convention for the Mediterranean Sea. In 1996 these conventions were
followed up by the “1996 Protocol to the Convention on the Prevention of Marine
Pollution by Dumping of Wastes and Other Matter, 1972" (replacing the 1972 London
Convention), having similar text as the Oslo Convention, but for international waters in
general. The London Convention has a series of Annexes that list hazardous or
potentially hazardous elements and compounds, and specifies limits of those for
accepted deposition. The London Convention also specifies methods of testing.
Among the most important additions of the 1996 Protocol is the inclusion of the
"precautionary approach" and the "polluter pays principle." A major structural revision
of the Convention was the so-called "reverse list" approach. Instead of prohibiting the
dumping of certain (listed) hazardous materials, the dumping of any waste or other
matter that is not listed in Annex 1 ("the reverse list") of the 1996 Protocol was
prohibited. Dumping of wastes or other matter on this reverse list requires a permit.
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The London Convention of 1972, with the Protocol from 1996, sets limits on waste
being disposed in the sea in national and international waters. Article 4, dumping of
wastes or other matters, states: “Contracting parties shall prohibit the dumping of
wastes and other matters with the exception of those listed in Annex 1.” Annex 1,
Wastes and other matters that may be considered for dumping (the reverse list), states:
“The following wastes or other matter are those that can be considered for dumping …..
5. Inert inorganic geological material (e.g. mining wastes)…” However, the protocol
does not specify what criteria to be used for defining inert inorganic geological material.
The European commission has made definitions for inert waste from extractive
industries (CD-Inert Waste, 2009, see Ch. 2.1.2) that can be applied in cases evaluating
SSTD.
The London Protocol applies for all marine waters other than the internal waters of
States, and in this respect it thus not apply for sub-sea tailings deposition in Norwegian
fjords.
2.3.
Norwegian Laws, Bylaws and Guidelines
There are several Norwegian laws that include environmental impact from mining
operations.
2.3.1.
Norwegian Minerals Act
The Norwegian Minerals Act (NFD, 2009), as previously mentioned, primarily regulates
the mineral rights and the exploitation of a deposit. The law briefly discusses the
environmental issues, restating other Norwegian laws that an Environmental Impact
Assessment is required if the disturbed area is above 200 hectares, more than 2 Mm3
material is to be exploited, and/or significant adverse effects on the environment may
occur. The Mining Law states that the operator is required to clean up the site after
closure.
The Directorate for Mineral Resources (DMF) is the agency that sets the requirements
for the restoration and cleanup, and oversees such work. DMF can also require financial
assurance for such restoration and cleanup measures. The Norwegian Ministry of Trade,
Industry and Fisheries (NFD) has issued a guideline that briefly explains the Norwegian
Mining Law (NFD, 2011).
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2.3.2.
Pollution Control Act with bylaws
The Pollution Control Act (Forurensningsloven) of 1981 is designed to protect the
environment against pollution, where discharge of solids and liquids are included as
pollution. It states that it is illegal to pollute (discharge) unless environmental pollution
authorities have issued a permit. The limits for discharge in a permit are commonly
based on mass per time and total concentrations. The Norwegian waste regulation
(Avfallsforskriften) is a follow up to the Norwegian Pollution Control Act.
The Norwegian waste regulation, updated in 2012, is the implementation of the EU
Waste Directive of 2001, and the EU Mining Waste Directive of 2006. The latest
version of the Norwegian waste regulation incorporates the mine waste issues referred to
in the Mining Waste Directive, and the commission decisions described above in section
2.1.2. There is no specific description in the Norwegian Waste Regulation on how to
characterize a potential sub-sea waste facility or how to monitor a SSTD.
The Norwegian water regulation (Vannforskriften) of January 2007 is the Norwegian
implementation of the EU Water Framework Directive (2000). The Norwegian water
regulation does not preclude sub-sea tailings deposition (Klima- og
forurensningsdirektoratet 2012), but includes issues that impact sub-sea tailings
deposition.
There are several other Norwegian regulations (forskrifter) and guidelines (veiledere)
that may be used for parts of characterization for evaluating SSTD at a particular site.
Several of them are discussed in the following sub-sections.
2.3.3.
Guideline for Classification of Bottom Sediment
The Water Framework Directive was implemented in Norway via the Water Regulation
(2010; Vannforskriften). The Norwegian Guideline for Classification of Bottom
Sediments (TA-3001/2012) is a further implementation of the Water Framework
Directive to ensure that all fresh water, groundwater, and coastal water have good
ecological and chemical conditions. This classification follows to a large extent the
Environmental Quality Standard (EQS) Report 55-2011.
The system used for classification of sediments and water is applicable to SSTD. The
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guideline uses distribution coefficients between pore water and sediments to derive the
classification. Tailings to be deposited would also be classified by the same system.
Where there is no data, or there are questions regarding the listed distribution
coefficient, the classification can be derived according to the following equation:
PNECsed = PNEC H2O * Kd
PNEC (Predicted No Effect Concentrations) in the sediments (PNECsed) is based on
PNEC in water (PNEC H2O) and the distribution coefficient (Kd) between sediment and
water for the element/component in question. If the Kd is not known, the Kd can be
derived from sorption tests according to EQS 55-2011.
The classification system uses five different classes:
•
•
•
•
Class I
Class II
Class III
Class IV
• Class V
Natural background concentrations
No toxicological effects; PNEC
Chronicle effects from long term exposure; PNCacute
Acute toxicological effects at short term exposure;
PNECacute*Safety factor
Severe toxicological effects
This classification system is focused around equilibrium between sorbate and sorbant,
and does not take into account the precipitation-dissolution/weathering, which may be as
important for mine-waste material as sorption processes. .
2.3.4.
Guideline for depositing contaminated sediments in the sea
The Norwegian Environment Agency (Miljødirektoratet) has developed a guideline for
depositing contaminated sediments in the sea (TA-2624/2010). This guideline was
developed to ensure that the experience and knowledge gained from recent sea/fjord
deposition of contaminated sediments from harbor dredging was maintained and utilized
in future contaminated sediment cleanup. This guideline applies to the deposition of
sediments, Class III or higher, in accordance with the sediment classification, TA-
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3001/2012 (see Chapter 2.3.3), which is not applicable to the deposition of tailings from
current mining operations.
The Sediment Deposition Guideline specifies the characterization needed for both the
deposition site and the material to be deposited. It also specifies the monitoring
framework during the deposition and after the deposition has been completed.
Some of the required information from a characterization investigation for evaluating
deposition is as follows:
• Seasonal variations in the deposition site, to include biological, physical and
chemical.
• Salinity, temperature, oxygen content, physical oceanography to include currents
• Geotechnical stability of the bottom sediments and natural sedimentary rates.
• Potential for affecting salmon and sea-trout and other fish types
The main purpose for monitoring after deposition is to:
• Evaluate if the sediment deposited is stable;
• Determine if there is leaching of contaminants; and
• Determine re-colonization rates by biota.
The requirement is that there be a natural barrier in the deposition zone so that
contaminated sediments are deposited in a confined area; and that the natural sediments
are not coarser than the sediments to be deposited. If the natural sediments are coarser
than the contaminated sediments, there is a possibility that turbulence of the
contaminated sediments with the natural sedimentation will occur; and the rate of natural
cover development will be slowed down.
2.3.5.
Contaminated fjord cover deposition guide
The Norwegian Environment Agency (Miljødirektoratet) has developed a guideline to
characterize material to be used as cover for contaminated sea-sediments (Klif, TA2143/2005). This guideline describes, in several steps, how to characterize the physical
and geochemical characteristics of a material, so as to be accepted for use in covering
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contaminated sediments. The guideline has also included specifications on ecotoxicological tests. This guideline discusses the following material:
• Rock crushed, milled and physically separated without addition of chemicals;
• Loose material which also includes the fine fraction of sieved material, including
natural sandy material and dredged sea material; and
• Process material, e.g. tailings, smelter slag, and recovered fluidized bed material.
The guideline requires that the material be tested through a series of steps; where if
accepted within a set of criteria at one step level, there is no need to perform tests at the
next step level. If the material is not accepted at one level, it can be tested further to
evaluate if it can be accepted as cover material. The levels of testing are as follows:
• General physical and chemical characteristics
• Chemical stability – leaching potential
• Eco-toxicological characteristics
All suggested cover material needs to be site specifically evaluated. In general, the
characterization of “cover material” is similar to that needed for the characterization of
material evaluated for SSTD. However, since the amount of material to be deposited
from a mining operation commonly constitutes a much larger volume than the material
used for covering contaminated harbor/sea sediments, and the mine material is likely to
be deposited in an area without contaminated sediments, the testing is more rigorous.
In addition, some of the characterization methods described in this guideline are not
appropriate for the purpose designed. The guideline states that mineralogical analyses
are to be performed using X-Ray Diffraction Analysis. However, the detection limits
for this method are too low for the minerals that are often in question, and this may lead
to erroneous results and wrong conclusions.
2.3.6. Concluding remark
There is no specific regulation on mine waste characterization except what has been
incorporated in the waste regulation (Avfallsforskriften). These regulations are
relatively vague without specific guidelines on how to characterize the waste or the
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environment potentially receiving the waste. Chapter 17 does specify the following
requirements:
•
•
•
•
Make a waste management plan,
Evaluate the facility classification,
Design a closure plan, and
Specify financial assurance
It also specifies general issues to be included as part of these requirements, which have
been adopted from the EU-requirements as specified in the EU-Mining Waste Directive
and the following Commission decisions (See 2.1.2).
2.4.
Other National regulations on SSTD
Papua New Guinea (PNG) is currently the only country that has specific regulations for
tailings deposition in the sea. These regulations are for Deep Sea Tailings Placement
(DSTP). DSTP is practiced at two operating mines in PNG. These regulations were
developed under an EU-funded project (SYSMIN). SYSMIN’s aim was to characterize
and assess the impacts of DSTP at three mine sites (two active and one closed
operation), and develop a regulatory framework for DSTP.
The Scottish Association for Marine Science, Research Service (SRSL), Scotland was
funded by the European Commission (8th European Development Fund, 2007-2010) to
produce ‘best-practice’ guidelines of DSTP for the Department of Environment and
Conservation and the Mineral Resource Authority in PNG,. The general guidelines that
were produced by SRSL in 2010 have since been accepted by the PNG government, and
are presently being adopted as regulation within PNG’s legislation. The International
Marine Organisation (IMO) and the Scientific Group of the London Protocol have also
acknowledged the guidelines. More recently, SRSL has been commissioned to produce a
number of site-specific guidelines for individual mines, as a consequence of the highly
site- and conditions dependent nature of DSTP environmental impacts.
Both USA and Canada give an opening for sub-sea tailings deposition in their
environmental regulation, where SSTD may be the most environmentally friendly option
for tailings deposition. The London Dumping Convention also includes SSTD as a
potential viable method for inert inorganic geological material. There are also a few
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countries practicing sub-sea tailings deposition, however, without any specific
regulations for this practice (e.g. Indonesia and Turkey).
2.4.1.
Papua New Guinea Deep Sea tailings placement guideline
A general Deep Sea Tailings Placement (DSTP) guideline for Papua New Guinea
(Guide PNG, 2010) is written to provide developers with a framework for deciding
whether DSTP is an option; and it is different from this guideline and the EU-guidelines
for waste characterization. It is a guideline for 1) evaluating DSTP at a particular site;
and 2) detailing the conditions that must be met to ensure maximum efficiency of
deposition of tailings. The guideline requires the use of an Environmental Impact
Assessment process to ensure best practice development for a potential DSTP project.
However, there are a set of specific guidelines for each operational mine which details
the environmental monitoring and operation that must be carried out at a specific mine.
The PNG guideline discusses the operational requirements in general terms. The
discharge point needs to be sufficiently deep to ensure the following:
• No entrainment or advection of tailings into euphotic zone;
• Minimal production of plumes due to density differences in the water column;
and
• There is acceptable small diffusion of dissolved toxic material into the euphotic
zone.
The guideline specifies that DSTP should be at a minimum depth of 120 meters, where
the euphotic zone is 80 meter or less. Where the euphotic zone is deeper than 80 meters,
the discharge point should be at a minimum of an additional 50% depth. In addition, it
suggests there should be two discharge pipes. The guideline also states that there should
be no potential for long-term adverse effects of the natural bio resources. The guideline
also specifies that the physical oceanographic environment in close proximity and
further away should be monitored for a minimum of 1 year. This 1-year monitoring also
includes weekly monitoring of stratified surface layers. Furthermore, the guideline also
states that the benthic community should be enumerated and characterized for the three
major organism body size classes (meso-fauna, macro-fauna, and mega-fauna).
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2.4.2.
Philippines
The Philippines have covered the environmental issues under the Mining Law in
Chapter XI. All operations are required to perform an Environmental Impact
Assessment regulated by the Environmental Impact Assessment System of the Local
Government Code of 1991. All operating mining companies are required to pay a fee
for generating tailings and mine waste. The fee is to cover potential damages to land,
water and marine environment; and to cover the cost of re-vegetation, rehabilitation, etc.
Even though the Philippines have active sub-sea tailings deposition, there is no specific
law / regulation / guideline for such tailings deposition.
2.4.3.
Turkey
Turkey has one location with tailings deposition, where tailings are deposited at a 350
meters depth in the Black Sea. There has been some consideration to reduce the depth
of the outfall from 350 meters to 250 meters depth. The final tailings deposition zone is
in anoxic water at a depth of over 2000 m. Turkey has no specific regulations for the
sub-sea tailings deposition, but is working on implementing the EU-Mining Waste
directive with the follow-up commission decisions.
2.4.4.
USA
USA has no specific regulation for sub-sea tailings deposition; however, there are
general requirements on the amount of solids in a discharge effluent (15 mg/l). The
result is that sub-sea tailings deposition is practically banned. However, there is an
opening for evaluating sub-sea tailings deposition if no other options are available. This
has been done in a couple of locations: A.J. Gold mine project, Alaska in 1996; and
Quartz Hill molybdenum prospect, Alaska, USA. Both of these projects were halted due
to low metal prices in the mid 1990´s (Ellis and Robertson, 1999).
2.4.5.
Canada
Environment Canada has published a guide to understanding the Canadian
environmental Protection Act of 1999. This guide discusses the practical use of the
Canadian Environmental Assessment Act. Section 8.2.2 explains that deposition of
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mine waste into the sea is subject to a permitting system, based on an environmental
impact assessment.
There is currently no active mining operation with SSTD in
Canada, but there are several closed large scale mining operations (Britannia Copper
mine, BC; Jordan River Copper Mine, BC; Island Copper Mine, BC, Kitsault
Molybdenum Mine, BC, Canada), which have provided a lot of experience/information
that is used in currently active SSTD (Ellis and Robertson, 1999). (Den siste setningen
er litt selvmotsigende hvis det fortsatt er snakk om Canada)
2.4.6.
Australia
Australia has no laws or regulations that specifically prevents the use of SSTD as an
option for tailings displacement, as long as, the project conforms with the Australian and
New Zealand Environmental and Conservation Council´s Interim Disposal Guideline
(December, 1998). There are no active sub-sea tailings disposals or current proposals
for SSTD. The Australian Best Practice Environmental Management of Mining
Modules (2008) do not mentioned SSTD.
2.4.7.
Jamaica
United States Agency for International Development (USAID) has developed guidelines
for dredging in coastal and estuarine region for the Government of Jamaica (USAID,
1992). This guideline includes sections on dredging mineral resources and disposal of
the waste material generated from such dredging. The guideline identifies the
characterization necessary for evaluating base-line conditions, and the issues that should
be a part of an impact evaluation.
The guideline also specifies the importance of long term monitoring during and after
dredging cessation and deposition. The document also states that it is extremely
important to do bioaccumulation studies using fish, crustaceans and molluscs typical of
the disposal site.
The Jamaica guideline for dredging builds upon the World Bank document 0126/1990
on dredging. (World Bank 1990).
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3. HEALTH AND SAFETY
The specific health and safety issues related to the sampler in the context of a sub-sea
waste deposition characterization are mainly related to both the sampling of the waste
and the waste deposition site. During sampling, there are physical and chemical risks to
be aware of. The physical risks related to the waste sampling may be:
•
•
•
•
•
•
•
•
•
Movement of large vehicles, e.g. trucks;
Collapse of waste rock heaps/slopes during sampling;
Trace metal dust inhalation and/or digestion;
Inhalation of dust (e.g. silica, asbestos fibre);
Active waste dumping;
Sink holes and cavities;
Unstable wet tailings etc.;
Safety issues at sea; and
Deployment of sampling gear.
There may also be chemical issues related to the use of potentially hazardous chemicals
in the process, or off-gases resulting from processes in the waste (e.g. hydrogen sulfide
or carbon monoxide).
The majority of sampling at a site, potentially employing deep-sea tailings deposition,
will be performed from a ship utilizing appropriate sampling gear. In this case, the
Ship’s Master will have the final say with respect to health and safety issues on board.
The sampling plans should identify all relevant physical and chemical health and safety
risks; and safety measures should be specified. Health and safety issues should be
streamlined with the health and safety procedures of the operator. Good practice, when
planning a characterization-sampling program, would be to develop a project and sitespecific health and safety plan. It is recommended that, at an operating site, waste
sampling should never be performed by a single individual and that at least one member
of the sampling team should be a local employee. These issues are further discussed in
the sampling standard EN 14899.
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4. ENVIRONMENTAL ISSUES
Sub-sea tailings deposition constitutes a different set of environmental risks not
considered in the CEN/TR 16376:2012, Overall guidance document for characterization
of waste from extractive industries.
The environmental effects of sub-sea tailings deposition depend on how the tailings
interact with the receiving environment. The impact the tailings will have on the
receiving environment will be dependent on their composition, physical characteristics,
and volume, as well as on the tailings discharge systems and waste-material
management.
There are mainly two environmental effects of tailings deposition; smothering of benthic
biota and fauna in the deposition area, and environmental effects from suspended
particles.
The environmental issues are described in the following paragraphs. The different
issues described comprise the physical and chemical characteristics of the tailings that
combined with the characteristics of the receiving environment may potentially affect
the water quality and/or the flora and fauna in the affected area, as well as the
recolonization of the affected area.
Each issue is described individually below; and some overlap may exist. Data obtained
from the following issues are further discussed in Chapter 6.
4.1.
Tailings characteristics
When sediments are deposited, fine particles may remain in the water column for an
extended period of time. Suspended particles may directly affect pelagic biota such as
plankton and fish; and indirectly, by reducing light necessary for growth of flora and
fauna. Discharge into the marine environment below the euphotic zone has generally
less environmental effect since deposition is done below the zone of highest primary
production (Ellis 2008). Never the less deposition will have a negative impact on benthic
biota and fauna in the area of deposition. If the tailings system is not managed correctly
suspended material may rise to shallower water depths and be transported longer
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distances. Correct management and monitoring is therefore important to ensure
controlled deposition in intended area.
Heavy metal contamination from tailings may have en environmental effect if metals are
mobilized in to the environment in harmful concentrations. However, metals in sulfidic
tailings are less likely to be released when placed under water as a result of less oxygen
available for sulfide oxidation.
Another important aspect is to evaluate potential environmental effects related to
processing chemicals that may follow the tailings in to the marine environment. Some
chemicals may have adverse effects on marine life, may not be biologically degradable
and may accumulate in the environment, and may thus be linked with environmental
risk.
4.1.1.
Particle Transport / Siltation / Turbidity
Particle transport by rivers, erosion, landslides and glacial activity are common natural
processes. Substantial amounts of particles are continually being deposited naturally in
lakes, fjords and at sea.. Negative effects of suspended particles are linked to
concentrations that can cause reduction in the growth of the flora and fauna due to
reduced photosynthesis in the euphotic zone. Other effects may be negative effects on
predation caused by reduced visibility, and negative effects on gills.
Particles dispositioning on the sea bottom will smother benthic fauna and flora that are
not mobile and able to move away from the deposition area.
Some organisms are adapted to high turbidity and sedimentation rates; however, these
may not be common in the area where discharged tailings are planned, and will not be
the only species within the receiving environment. The impact from particle transport
and turbidity on pelagic and benthic biota needs to be assessed before any discharge.
Generally a sandy/muddy seabed (sedimentation environment) is more suitable for
deposition than a rocky bottom (high energy erosion environment) (Ellis 2008).
Suspended particulate material has a direct effect on the fish by affecting the outer
protective layer, skin and gills; and indirectly by affecting the ecosystem itself. The
indirect effects may be:
•
Reduced visibility with reduced food uptake
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•
•
Siltation covering the bottom reducing or destroying the spawning and growth
areas, smothering benthic biota and reduced productivity in deposition area
Reduced primary production due to reduced light through the water.
Tailings deposition can to some extent be compared with river deltas, where large
amounts of sediments are being discharged into the sea. Flora and fauna is adapting to
this system; however, the growth is commonly low where there is a high sedimentation
rate, e.g. river deltas.
Particle transport is closely linked to grain size together with the flow system, and the
density difference between the discharge material and the seawater where discharge is
taking place. The amount of fine-grained (less than 20 micron) particles within the
tailings affects the dispersion in the marine environment). The amount of fine-grained
material is a result of the milling and processing techniques required for extraction of the
target minerals. A known effect on fine particles in sea water is flocculation. This is a
process where particles because of their electrostatic charge and inherent stickiness floc
together to form larger particle clusters. This effect increases the sinking velocity of the
particles. Models predicting particle transport should therefore consider this effect that
will largely affect the area of deposition and the concentration of particles in the water
column. In addition to natural flocculation, additional flocculation may occur due to the
use of flocculation additives in the tailings. The flocculation agent is often used for
recovering fresh water, and causes the fine grained tailing to floc together. This will also
affect the tailings settling velocity upon depositing. However, somefine-grained particles
may not flocculate and can be transported with currents outside of intended deposition
area. The concentration of which these particles appear will predict whether the particles
will have a potential environmental effect or not (Skei and Syvitski 2014, Klif 2010).
There are limited studies that investigate how suspended particles affect fish. It is known
that fish have an avoidance behavior in relation to elevated particle concentrations.
There are studies that show that fish seem to be unaffected by moderate elevations of
suspended particles (~25 mg/l) (Hessen 92, Smith et. al 2008).
Change in turbidity may result in a change in spawning areas, and in the areas where
fish are located (Søvik et al., 2012). Fish that live and swim in the upper layers will
likely be much less affected than the fish living/swimming at a lower depth.
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4.1.2.
Acid/Neutral rock drainage and potential release of heavy metals
Acid/neutral drainage is one of the largest environmental issues from mines with sulfidecontaining ores, waste material and wall-rock, and is a well know problem related to
land depositing The exploitation of a mineral deposit results in an increased availability
of surface areas for oxidation of sulfide minerals and, thereby, a potential increase in
element release. Sulfide mineral oxidation can result in acid generation and release of
heavy metals into the environment, especially if the sulfide minerals consist of pyrite
and pyrrhotite. This process is called Acid Rock Drainage (ARD).
Sulfide oxidation will commonly halt if the sulfide containing material is placed under
water, due to low oxygen solubility and a slow oxygen diffusion rate in water. Strong
water currents with oxygenated water will, on the other hand, increase the rate of oxygen
transport to the sulfides and maintain some sulfide oxidation. The sulfide oxidation rate
may also be affected by the salinity of the water due to electrochemical processes.
Seawater has, however, a strong acid buffering capacity, so that acid generation will not
take place in the seawater where there is a relatively high degree of water replacement.
Acid drainage is primarily a problem related to land deposition, but should be evaluated
and examined before tailings are placed in marine environment, if there is a concern
about minerals (metals) possibly leaching during and after deposition (Walder et al, In
prep.).
Heavy metal contamination from tailings may have en environmental effect if metals are
mobilized in to the environment in elevated concentrations. However, metals in sulfidic
tailings are less likely to be released when placed under water as a result of less oxygen
available for sulfide oxidation. This is especially true for anoxic water.
Biogeochemical cycling of elements, including metals, takes place within a marine
environment. This occurs when the redox condition of the water and/or the sediment
changes, causing the elements to be released from particulates/sediments to the
surrounding water; or conversely, elements are removed from the water to the solid
phase. The minerals may be sulfides that oxidize in the saline alkaline seawater,
releasing elements into the seawater, creating a similar condition to neutral rock
drainage. There may also be other minerals that are unstable in the oxidizing highly
saline setting that would release elements/constituents of concern during alteration. In
addition, anoxic conditions in the sediment will affect the metal cycling.
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For some minerals the weathering processes is faster in salt water than fresh water , and
tailings containing these minerals may therefore be in risk for metal contamination.
Chemical alteration and settling rate may be linked. If minerals stay in the water column
for a prolonged period of time before settling they will have a longer exposure time for
alteration/ dissolution if unstable under the oxidizing saltwater conditions.
The waste characterization needed for proper sub-sea tailings deposition is similar to
that described within the Overall guidance document (CEN/TR 16376:2012). However,
some special materials tests of tailings material, and a thorough characterization of the
receiving environment is required in order to properly evaluate the impact of sub-sea
tailings deposition.
4.1.3.
Process chemicals
Process chemicals are mainly used in two operations in mineral processing; froth
flotation for selectively separating economic minerals from waste, and flocculation to
remove fine-grain material in wastewater treatment.
Froth flotation chemicals
There is commonly a need to add chemicals at different stages in the mineral processing,
especially during processing by flotation. When processing is performed by flotation,
chemicals having different functions are added in several steps. These functions may be
the following:
•
•
•
To generating the foam/froth;
As collectors so that certain minerals stick to the bubbles;
To suppress certain minerals from sticking to the foam (e.g. lime to suppress
pyrite from other sulfide minerals); and
Even though many of these chemicals are biodegradable, there is a potential for these to
leach into the environment, whether in a land based tailings pond or sub-sea tailings
disposal.
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The flotation process is strongly dependent upon the type of minerals to be recovered. In
the case of iron ore, this can either be performed with fatty acids or amines as collectors,
or by activation, converting the oxide surface to e.g. a sulfide surface, and using
thiocomplexes as xanthates. There are four main processes used on an industrial scale in
order to separate hematite from primarily quartz in a non-surface activated system
(Somasundaran and Luo, 1999):
•
•
•
•
Flotation of hematite using sulfonates as the collector at pH 2-4;
Flotation of hematite with fatty acids as the collector at pH 6-8;
Flotation of quartz with amines as the collector at pH 6-8; and
Flotation of quartz with calcium ions at pH 11-12, using soaps as the collector
with starch to depress the hematite.
There are many different chemicals used for sulfide flotation. The three main collectors
are xanthate, dithiophosphate and thionocarbamate. By sequentially using additional
chemicals or stronger solutions of collectors, different sulfides can be separated and
collected.
Polypropylene glycol methyl is the standard frother used. New research has shown
enhanced recovery in coarser sulfide particles by using different amounts of frothers
(Klimple, R, 1999).
Success of the flotation depends on the differences in surface charges of the minerals to
be separated. The surface charge depends upon the pH of the solution and is given by
the zeta potential. The pH of the flotation liquid is commonly controlled by the addition
of a low-cost base (lime for raising the pH and hydrochloric acid for lowering the pH).
The tailings water can, therefore, be acidic or basic depending upon the flotation process
(Klimple, R, 1999).
A method for separating chalcopyrite from pyrite using microorganisms has also been
developed. Thiobacillius ferrioxidance rapidly colonizes pyrite but not chalcopyrite.
Pyrite will, therefore, not have a surface charge; while chalcopyrite will maintain the
surface charge and can then be separated from pyrite (Chander, 1999).
Excess chemicals are used in the flotation process. Chemicals that are not associated
with the concentrate will, to a large extent, be collected with water in the thickener.
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This is especially true if the ore minerals are enriched with the collectors. However, if
the collectors used are for the separation of gangue minerals, the recovery of the
chemicals in the thickener will likely be less effective. What is not recovered in the
thickener will be discharged with the tailings material.
Some collectors for silicate flotation, i.e. cationic surfactants, like quaternary ammonium
compounds, are strongly absorbed on the mineral surface and are to a very low extend
effecting the surrounding environment in a deposit for mineral waste. The
biodegradability is ruled by the desorption rate, which is slow, and these molecules can
hardly bio accumulate as they will be stopped on biological membranes. The chemical
equilibrium is strongly shifted towards the solid material and these chemicals can hardly
be found in the water phase.
Flocculation chemicals
Milling may result in a large volume of fine-grained material. In order to reduce the
water content it may be necessary to run the material through a thickener with the
addition of a flocculation chemical (flocculent). Flocculants are polymers that will
flocculate the fine-grain material (colloids to clay- size minerals) with larger grains and,
thereby, improve the water recovery from the tailings. The flocculants is commonly
used in connection with a thickener. There are many producers of flocculant agents.
There are organisms living near the bottom that are likely to eat/digest fine-grained
tailings material near the bottom or directly digest bottom sediments. The larvae and
small fish again eat these organisms and; therefore, existing contaminants can be bioaccumulated up the food chain.
4.2. Tailings discharge systems
The type of tailings discharge system and waste-material management may reduce or
enhance the potential environmental issues of sub-sea tailings deposition.
4.2.1.
Plume density
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Upwelling, having the potential of transporting fine-grain tailings particles to surface
waters, is a concern partly from a fjord current issue and, as well as, a potentially poor
waste-material management issue. If there are air bubbles in the material when
depositing, the bubbles will rise after discharge and pull tailings upwards. Upwelling
may also take place if the interstitial water in the tailings material has lower specific
weight than the water at the discharge point. This will result in upward migration of the
water that will pull tailings material along and possibly spreading the material in the
upper part of the seawater column. Commonly modern tailings discharge is mixed with
seawater prior to deposition to ensure that the plume forms a density plume that settles
on the sea bottom.
4.2.2.
Pipeline break
There is a potential for damage to the pipeline transporting the tailings material from the
processing plant to the discharge point. This may be due to wear and tear of the
material, accidents with boats and onshore equipment, as well as, weather related
incidents. Depending on the damage point, such situations can easily result in a spill to
shallow areas or upwelling from an uncontrolled spill from the designated outfall depth
to shallower waters. These types of pipe breaks have taken place in Papua New Guinea
and Turkey.
4.3. Receiving Environment
All of the issues described above relate to the tailings deposited into the receiving
environment. The receiving environment must also be characterized well enough to be
considered a suitable waste disposal site for tailings deposition.
4.3.1.
Fjord circulation
Upwelling may also be caused by deep water being pushed upwards to shallower areas.
Typically a fjord environment consists of several layers due to salinity and temperature
differences. This layering will commonly result in reduced vertical transport and the
mixing occurring primarily within the layers. Depositing should preferentially be done
below the surface layer since this layer form a barrier for upward transportation of
tailings.
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Fjord circulation can be complex. Environmental factors, such as size of catchment,
fresh water runoff and occurrence of sills at mouths of basins will determine the
circulation and level of mixing between different density layers within the fjord. Depth
to the thermocline and halocline in the fjord are important parameters to obtain. The
depth at which changes occur in temperature (thermocline) and salinity (halocline) are
important when determining whether the receiving environment is suitable for
deposition of tailings, and at what depth a discharge point should be set. Occasionally
deep water replacements can cause deep water to be pressed upwards and being replaced
by water from the sea. This shift may cause fine particles from tailing to be transported
upwards to more shallow layers of the fjord. It is important to determine the effect of
these events on the dispersion of the tailings.
4.3.2.
Vertical water column
Vertical mixing may result in vertical plankton migration together with transport of
oxygen and chemical compounds. This may result in increased oxidising conditions at
the bottom, and transport of potentially harmful elements to higher water layers in the
sea. These mixings may be induced by tidal water flow, variable fresh water input from
rivers throughout the year, and overturn of the water column due to temperature change
in the surface water.
4.3.3.
Changes in currents due to deposition
If the amount of sediments discharged is considerable relative to the capacity of the
receiving environment, the deposition may result in a change in the current pattern that
again, may have an effect on flora, fauna, and organisms in the water column.
4.3.4.
Effects on fish dependent on fish type
There are many different fish types with different habitats and living patterns. Fish that
live in the upper part of the water column are less affected by sedimentation from the
deeper tailings deposition than bottom-dwelling fish. Migrating fish may be affected
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differently from permanent fish types. The different fish types to be concerned about
may include:
o
o
o
o
o
4.3.5.
Pelagic fish (e.g. herring, mackerel)
Farmed fish (salmon, sea trout)
Bottom fish (e.g. flat fish, cat fish)
Stationary fish (e.g. cod, pollock)
Migrating fish (e.g. salmon, sea trout, cod)
Spawning area (permanent – variable)
Fish with different habitation systems also have different spawning requirements. The
spawning areas may be permanent or may move, depending on the environmental
conditions from year to year. Therefore, tailings deposition may affect the spawning,
depending on fish type.
4.3.6.
Ecosystem effects
There may be cumulative effects that are difficult to see without looking at the
ecosystem as a whole. Blocking off part of a fjord bottom may result in a lack of bottom
migration of flora –fauna that are essential to other flora-fauna-fish in a different part of
the fjord; and therefore, the tailings deposition may have an indirect effect on certain
species.
4.4. Recolonization
Where tailings deposition is greatest, the benthic biota will be smothered and suffer
major impacts. The recolonization of an area will depend on the environmental
conditions that exist post-operation (change in sediment type, change in nutrient level,
sea current change, depth change, etc.).
Investigations performed in the Jøssingfjord, Norway; Bøkfjord Norway; and Island
Copper Mine, Canada, after closure of the sub-sea disposal indicates that the natural revegetation of a barren tailings deposition, to reach a sustainable ecological succession,
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can take place relatively rapidly, over 2-5 years. The species are often as varied and rich
as before depositing but may have a different composition compared with the original
flora and fauna. This may be due to:
•
Change in sediment type (grain size and chemistry from the natural sediments;
•
No nutrient in the new sediments (tailings material);
•
Leaching of elements/compounds that are effecting species differently;
•
Shallower than original topography which can result in more sunlight and change
in natural habitats and higher growth; and
•
The weathering may result in change to a mineralogy that forms a crust –
hardpan, as indicated at the shoreline deposit from the former Nussir deposit
flotation plant (Øystein Rushfeldt, Nussir ASA, Pers. Com., 2012). This
hardpan, on land-based tailings, is commonly a mix of gypsum, calcite and iron
hydroxide; however, other minerals can as well be a part of the crust.
The sub-sea tailings deposition described in this document relates to more confined
areas, such as fjord environments, not deep-sea conditions, as is the case of Papua New
Guinea’s tailings deposition. Tailings deposition in Norway will most likely be within a
confined fjord/sea area (Figure 2), where there is some type of geological barrier. This
barrier reduces the spread of tailings material; and it is similar to an on-shore tailings
dam, where tailings material is contained within a constructed dike.
Titania considered an artificial barrier in the Dyngadypet deposit closing off
Knubedalsrenna, in order to reduce spread of tailings material. (Evaluated by
Havnelaboratoriet i 1986)
There may be different options of rehabilitating the tailings by
• Re-introducing the species that where there before;
• Develop a reef that will increase growth; and
•
Fertilize the tailings sediment, before or after deposition, e.g., by establishing a
fish farming plant above the tailings-
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Figure 2. Simplified sub-sea tailings deposition setting from a mine, via processing plant, thickener, and
discharge pipeline to deposition. It also shows mixing in the upper part of the water body, layering in the
sea due to salinity differences, and general flow direction out of the fjord.
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5.
CHARACTRIIZATION OF DEPOSITION SITE
Obtaining baseline information is an essential part of waste characterization, which
again is essential for developing waste management plans. The EU-Commission
Decision on waste characterization has included several areas that, in addition to
understanding the waste properties, will help in determining the short and long term
behaviour of the waste, and the potential impact on soil, surface water, groundwater and
seawater. The CD decision 2009/360/EC specifies five categories of information:
•
•
•
•
•
Background information;
Geological background of deposit to be exploited;
The waste and its intended handling;
Geotechnical behaviour of waste; and
Geochemical characteristics and behaviour of waste.
The first three categories cover supporting information that is discussed briefly in the
Overall Guideline (CEN/TR-16376/2012). The last two categories listed above cover
what is generally considered as waste characterization, and are discussed in detail in the
four CEN guidelines on mine-waste characterization. Information from the disposal site
is briefly mentioned but only for onshore deposition. Figure 3 shows the flow chart for
a baseline evaluation.
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Figure 3. Flow chart for a baseline evaluation.
When evaluating sub-sea tailings deposition, on-shore deposition should also be
evaluated so that it is feasible to compare the potential impacts between the main
alternatives to determine the option that is the safest and has the least environmental
impact.
General background information about the deposit to be exploited is as important when
evaluating a sub-sea tailings deposition as for an on-shore tailings deposition. With new
operations, information is gathered during exploration. The amount of information is
variable depending on the type of deposit and how far in the exploration process a
project may be. The amount of information increases as production gets closer. It is
important that specific environmental issues are evaluated as part of the exploration
process.
For on-going operations, gathering information about the deposit is often a natural part
of the operation; and characterization data from produced waste may already exist. The
existing information may not meet current characterization standards, and additional
information may be needed which can be integrated into the operation.
Examples of useful information gathered during exploration and production may be:
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•
•
Three-dimensional geological mapping combined with mineralogical and
geochemical analysis, which is normally an essential part of the exploration data
gathering;
Groundwater and surface water information collected and evaluated before and
during the operation, e.g.;
o Evaluation of process water access;
o Assessment of pumping capacity for open pits and underground
operations; or
o Evaluation of runoff water quality from underground or open pit
operations.
Use of existing information should be complemented with a field visit for verification;
and geochemical/mineralogical data should also be verified by additional analysis.
5.1.
Background Information
General background information and objectives of the extractive operation is helpful in
order to put the waste and the waste characterization process into context. The
background information would typically include general information about the
following:
•
•
•
5.2.
On-going or planned prospecting, extraction, or processing activity;
Type and description of method of extraction and process applied/planned; and
Intended product.
Mineral Deposit
General Information of the mineral deposit is aimed at identifying waste units that will
be exposed by extraction and processing, as specified in the EU-Commission Decision
on waste characterization:
•
•
Nature of surrounding rocks, their chemistry and mineralogy, including
hydrothermal alteration of mineralised rocks and barren rocks;
Style of mineralisation and morphology of mineral deposits, including
mineralised rocks or rock-bearing mineralization;
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•
•
•
Mineralisation typology, including physical properties such as density, porosity,
particle size distribution, water content, economic minerals, gangue minerals,
hydrothermal newly-formed minerals;
Size and geometry of deposit; and
Weathering and supergene alteration from a chemical and mineralogical point of
view.
Not all of this information is relevant for all types of operations. The level of detail of
information to be gathered should be adapted to the type of waste, the potential
environmental risk, and the intended waste facility.
5.3.
Exploitation method
The Exploitation method needs to be described. In general, this is underground and
surface/open pit mining. However, it is also important to describe the mining plan, as
this has a bearing on the amount and potentially the quality/variability of the waste being
generated.
The exploitation method needs to combine information about the potential resources
within the deposit to show how economical the mineral resources are, and to supply
information for a waste minimization evaluation.
5.4.
Mineral Processing
The type of mineral processing depends, to a large extent, on the economic minerals or
elements to be extracted, the mineral assemblage, morphology, grades, the size of
deposit and type of deposition feasible. The mineral processing also affects the type of
waste generated and the type of waste management strategies chosen. Information about
the origin of the waste and the processes generating such waste is, therefore, a natural
part of the waste characterization.
A practical approach could be to document predicted quantities (annual and total) of site
specific waste categories based on factors that affect the waste handling: e.g.
mineralogical characteristics, and type of process the waste has gone through before
being deposited.
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The waste transportation system (e.g. transport by trucks, conveyer belts or pipe lines)
needs to be specified with quantities within each waste stream and transport system. It
is recommended that planned or existing waste transportation systems are documented.
Mineral processing may involve the use of chemical substances: e.g. collectors, frothers,
suppressing agents, flocculants and leaching agents. The substances can end up in the
product which is sold or in the waste stream which is deposited, depending on whether it
is a direct flotation or a reverse flotation. It is, therefore, necessary to list all process
chemicals, where they are used, in what quantities they are being used, and where they
will end up.
In addition, under EU legislation, information should be provided on the classification of
the waste according to the Commission Decision 2000/532/EC, including the hazardous
properties (the so called European Waste Catalogue).
The CD also requires the waste characterization to include information on “type of
waste facility, final form of exposure of the waste and method of deposition of the waste
into the facility”. It should be noted, that for new operations, even though preliminary
plans and information may be available at an early stage, these are management
decisions that should be made based on the results of the waste characterization and
characterization of the waste disposal site.
5.5. Deposition Site
Information regarding baseline properties of the intended waste disposal site (or
alternative sites where relevant) is necessary to evaluate the potential impact from future
waste disposal. The appropriate level of detail will depend on the type of waste and the
disposal scenario planned. Relevant information regarding potential on-shore disposal
sites may include (but not limited to):
•
•
•
•
•
•
Site topography, surface and groundwater hydrology
Climatic conditions;
Dimensions of the planned waste facility,
Physical properties of the foundation soils and bedrock.
Geochemistry of foundation soils and bedrock,
Surface and groundwater geochemistry.
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Relevant information regarding potential sub-sea disposal sites (described in more detail
in Chapter 6.8 and 6.9) may include (but not limited to):
•
•
•
•
•
•
•
•
5.6.
Bottom topography and depths;
Water current variations (vertical and horizontal; seasonal and daily);
Environmental conditions in the water column;
Environmental conditions near the bottom sediments;
Bottom sediment physical and chemical characteristics
Bottom flora and fauna identification and abundance;
Fish density and fish types and other pelagic species such as zooplankton; and
Potential symbioses between different populations within the fjord system.
Deposition
The method of deposition needs to be described in detail. The deposition method needs
to take into consideration the characterization of the waste and waste disposal location.
For a SSTD, this includes the following:
•
•
•
•
•
•
•
Thickener
o Capacity
o Efficiency of water/chemical removal
o Additives
De-aeration system
Saltwater addition system (mixing tank)
Pipeline
o Material
o Dimension
o Length
o Anchoring
o Floating bodies
o Pipe extension systems
o Pipe outlet design; diffusor, branches etc
o Maintenance management system
Discharge point/location/depth
Emergency response system if failure occurs
Twin pipe systems for safe operation
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The whole area assigned for deposition may not be active at the same time. The
depositional system for changing the discharge point needs to be described, if
applicable.
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6. CHARACTERIZATION OF TAILINGS
This chapter describes the characterization of the waste and of the potential sub-sea
deposition area. The characterization of the waste follows the CEN/TR 16376:2012
(Mine waste characterization guideline). However, when evaluating sub-sea deposition,
there are specific waste characterization issues that are not covered in the CEN/TR
16376:2012 and are, therefore, highlighted within this document.
The most common methods used for mineralogical, geotechnical and geochemical
analysis in the extractive industry are presented in this chapter, together with a
discussion of their applicability, together with the methods used for sub-sea disposal site
characterization (Fig. 4).
Figure 4. Characterization flow chart.
The Water Framework Directive specifies many issues that need characterization. The
methods to use in such characterizations are described in section 6.8 and 6.9.
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The methods described should be seen as a set of tools. Which tools to use in a specific
case will depend on the characterization objectives, type of operation, available disposal
scenarios, and other site-specific conditions.
However, before any characterization is performed, a sampling plan must be developed,
as discussed below.
6.1. Sampling Plan
To obtain sufficient data for performing a required waste characterization or
characterizing a site for deposition of waste, a sampling plan needs to be developed. A
field visit will be required as part of developing a sampling/ survey plan.
A specific sampling guideline for the characterization of waste from extractive
industries has been developed (CEN/TR 16365:2012). This guideline builds upon
EN14899, “Sampling of Waste Materials”. The guideline focuses on the development
of the sampling plan but includes sections on sampling equipment, storage, and
transport. The sampling plan guideline does not describe sampling for characterization
of a waste disposal site; however, many of the issues described for a sampling plan are
also applicable for developing a sampling plan for a waste disposal site characterization.
Issues related to sampling of the sub-sea waste storage site are further described in
section 6.8 and 6.9.
According to the sampling guideline, a plan for characterization of waste from extractive
industries should normally cover the aspects listed in Table 1:
ASPECT
Identification of stakeholders
Identify general objectives
Background information
Specific objectives
Determine generic level
Identify constituents and
analytical methods
Identify health and safety
precautions
Select sampling approach
Identify sampling techniques
Sub-sampling
Sample preparation
Transport sample
Document sampling plan and
produce instructions for the
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EXPLANATION
List with contact information of all stakeholders
General objectives as described in Clause 2,
Information of the process type, waste types, known geology, mineralogy,
previously performed characterization etc.
Detailed objectives such as prediction of drainage quality, ARD potential,
mineralogy
Sampling for screening, detailed characterization, confirmation etc.
Elements/constituents of concern e.g. total metal content, pyrite content, and
analytical methods to determine these constituents; animal count, flora count
Health and safety issues for the sampler and the storage and transport of the
samples
Judgemental, unbiased, etc.
Sampling from drill core, auger, shovel, grab etc.
Splitting system of samples after collection for reduction of volume/mass
Freezing, drying, splitting for different analysis, storage requirements
Transport system to the lab and transport documentation
Details on sampling procedure for the sampler
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sampler
Produce a field sample
record
Complete sample record and
document changes
List of information to be included in the field sample record
List deviations to the sampling plan and reasons for the deviation
Table 1. List of the main aspects to be covered in a sampling plan, summarized from CEN/TR 16365,
2012.
6.2.
Physical and hydraulic properties
Obtaining physical and hydraulic properties for on-shore deposition is described in the
Overall Guidance document (CEN/TR 16376:2012). Many of these properties are also
important in assessing sub-sea tailings deposits. These issues are important in
evaluating the physical stability of the disposal sites. Only a few of the parameters
included in physical and hydraulic properties can be obtained prior to generating the
waste deposit. Many of the parameters are included in the waste design and are verified
by sampling and testing afterwards.
It is necessary, for example, to assess the potential buildup of sediments around the
discharge pipe. This can be determined using parameters such as discharge velocity,
sediment grain size distribution, specific gravity, sea current and topography.
Geotechnical investigations may be divided into laboratory and in situ investigations.
Laboratory characterization and testing of the waste material may measure properties
such as: compressibility, shear strength, angle of friction, grain size distribution, density
(bulk density and specific weight), Attenberg limits, plasticity, fracturing, liquefaction
potential, permeability, and erosion potential. Also an accurate composition of the
material must be made.
While laboratory investigations, in general, make more accurate measurements possible,
the average sample size is generally small. Therefore, an accurate sampling strategy to
ensure representative samples is crucial. The sampling plan should be constructed to
avoid possible replication, and analyses should be replicated to allow statistical analyses
of the data. Up scaling of the results should, however, always be done with care.
In-situ tests are, in principle, only applicable to waste already present in existing waste
dumps and tailings storage facilities. Their relevance for initial testing in the planning
stage is limited. However, with advances in ‘smart technology’, it is possible to make
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in-situ measurements of the seabed; and this should be considered as part of the baseline
study of the deposition site.
This short introduction to field and laboratory investigations indicates that there is no
perfect methodology for the characterization of physical properties of the waste material.
There are different, more or less adequate, investigation strategies. All include some
level of inaccuracy that can only be reduced using well-educated and highly experienced
professionals.
It is important to consider the strong interdependence between physical and geochemical
properties. While the physical properties of the waste may have a significant impact on
the long term geochemical performance, chemical weathering of the waste may lead to
changes of the physical properties.
Different sets of testing may be considered for physical characterization of tailings
material for sub-sea deposition.
6.2.1. Compressibility and frictional behavior
Compressibility and frictional behavior are key parameters for the assessment of the
behavior of tailings impoundments. The internal friction is a key element of physical
stability, and in turn, is strongly linked to the level of compaction and dependent on
other processes taking place. Several factors are important in understanding the
compressibility and self-compaction properties of the waste materials, including: the
overall compressibility; its dependence on moisture content; the possible migration
velocity of moisture (seepage velocity); and the grain-size distribution.
6.2.2. In-situ Investigation of Deposited Waste
Sediment core sampling is one way to get direct information from already deposited
waste. Disturbed and undisturbed samples can be collected using core samplers. The
stratigraphy of the impoundment material may be described using a bore log. Disturbed
samples are used to determine the Atterberg-limits, Proctor type, bulk density and
compressibility. From these values, bearing capacity, plastic and elastic soil parameter
values can be estimated. Undisturbed samples can be used for triaxial or uniaxial tests to
determine internal friction and cohesion of the materials. The above mentioned
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properties of disturbed samples or loose soils can also be investigated using shear tests.
In specific cases it may be best to avoid boring.
Besides boring, Cone Penetrometer Testing and Standard Penetrometer Testing can be
used to characterize larger areas. Since they are quick and rather cheap testing methods,
they can be used to refine information from borehole investigations. Moreover, indirect
information on bearing capacity vs. depth can be recorded by special sensors. To
sample tailings deposition on the seabed, specialized multi-corers are used to preserve
the sediment water interface. In addition, multibeam and acoustic seabed surveys are
used to monitor the tailings footprint on the seabed.
6.2.3. Grain Size / Specific Surface Area
Grain size is important for both geotechnical and geochemical evaluations. Grain size
analysis can be performed with a set of sieves for the coarser fraction, and pipette
method for the clay size fractions. Laser diffraction size analysis can also be used for
both coarser and finer fractions. Sieving can be performed either wet or dry. However,
dry sieving results in less finer fraction.
Surface area, used for evaluating reactive surfaces, can be calculated from grain size
analysis (Lapakko and Antonson, 2006), or by using the EMS method (Brunauer et al.,
1938). Both will provide the total surface area, however, surface area of individual
minerals may not be the same as the percentage composition of each mineral.
Morphological analysis is necessary to evaluate available surface area for reactive
minerals within the waste material analyzed.
6.3. Mineralogical Composition and textural information
Knowledge of mineral composition and mineral chemistry is essential in interpreting
chemical composition or leach tests data, and for predicting short and long-term
drainage water quality from waste material. Mineralogy, therefore, provides supporting
information for waste characterization and for the assessment of long-term behavior at a
waste facility, whether on-shore or sub-sea deposition is selected. Detail on
mineralogical analysis related to mine waste characterization is described in the Overall
Guidance document (CEN/TR 16376:2012) and briefly in the following paragraphs.
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Mineralogical information together with physico-chemical conditions may, for example,
provide evidence of the occurrence of weathering processes (weathering potential) like:
•
•
•
•
•
Oxidation (sulfides);
Dissolution (carbonates, sulfates, oxides);
Hydrolysis (silicates);
Sorption (clay minerals, metal oxides); and
Mineral stability/reaction rates.
This information, in combination with geochemical data and leach test results, can be
used to evaluate; long-term leaching potential within the waste material, metal transport
within the waste and into the surrounding environment, and attenuation in the
surrounding material (bedrock, soil etc.).
There are many different mineralogical analyses that can be performed; and their
usefulness varies with the type of issues needing to be solved. However, understanding
the mineralogy, the mineral texture, and mineral assemblages is instrumental in
understanding and predicting geochemical and physical stability.
These methods can provide reliable information on bulk mineralogical composition,
especially on specific questions of mineral heterogeneity and alteration processes. This
guideline provides background information on the capabilities and limitations of the
analytical methods to facilitate dialogue with specialists.
The mineral sciences have become very equipment-focused. The analytical methods are
being developed towards high accuracy determination of small quantities. Having a
well-established purpose with the mineralogy investigation will aid in choosing the right
method(s). Below is a brief summary of the methods:
Microscopic analysis is often the basic form for mineralogy analysis. The microscopy
analysis can give information on the type of minerals and if these minerals have
undergone any alteration/weathering; mineral intergrowth and mineral assemblages.
In addition to microscopy, X-ray diffraction (XRD) methods are commonly used to
identify minerals. This method, however, has detection limits of 2-3 wt %. This means
that the method may not detect minerals that could be of concern even at lower
concentrations, e.g. sulfide minerals. XRD methods are only semi quantitative, and
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additional chemical analyses are necessary to quantitatively (e.g. Rietveld method)
identify minerals when using XRD.
An electron probe micro-analyzer, EPMA, is a micro-beam instrument used primarily
for in situ chemical analysis of minute solid samples. The primary advantage of an
EPMA is the ability to acquire precise, quantitative elemental analyses at very small
"spot" sizes (as little as 1-2 microns), combined with the ability to create detailed images
of the sample. EPMA analysis makes it feasible to evaluate in what mineral form
hazardous elements may be located; and thereby, evaluate the availability of these
elements.
Assessing the texture of the waste material may be important when characterizing the
waste material; as the texture of the rock provides information about the actual
availability of minerals for leaching, and generating acid or neutralizing acidity. If the
reactive minerals are fine grained, this will lead to a large surface area when crushed, i.e.
high availability. If the reactive minerals occur basically encapsulated within nonreactive minerals, they may remain unavailable.
It may also be relevant to assess the degree of liberation; i.e. if the surfaces of the
mineral grains are available for surface reactions. This is relevant for neutralizing
minerals, acid producing minerals, or leachable minerals.
Analysis of the texture of the waste material is commonly performed by classifying the
texture of hand specimens and from microscopic analysis of polished thin sections.
However, MLA (Mineral Liberation Analysis) is becoming more common, as an
addition to traditional methods.
6.4.
Chemical Analysis
Chemical composition of water and solids can be assessed by a variety of methods.
Solids can be analyzed directly using, e.g. X-Ray Fluorescence (XRF), Atomic
Absorption Spectrometry (AAS) with graphite furnace or digestion followed by analysis
of the dissolved substances. There are different options for digestion and which method
to choose partly depends on the objective of the study, and on analytical methods chosen
in earlier studies (to produce comparable data). There are also many options for
chemical analysis of solutions; and which method to choose, again, depends also on the
objective of the study. There are numerous publications on chemical analysis; and
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CEN/TR16376:2012 lists applicability of CEN and ISO standardized tests methods for
waste from extractive industries.
6.4.1.
Analysis of Solids
It is important to recognize that different digestive methods can give very different
results. For example, the most common digestive method for waste characterization is
using aqua regia. Aqua regia is a strong acid, however, it will not dissolve silicate
minerals. Hydrofluoric acid is needed for silicate mineral digestion. Microwave
digestion is a standard method for total digestion of all types of minerals and is
recognized internationally as a reliable and accurate method for sample dissolution.
Handheld XRF can be a very useful tool in the field for both water and solid analysis.
However, the detection limit is poor. It may, therefore, be necessary with follow-up
analysis in the laboratory, using equipment with better detection limits.
Assessing chemical speciation may also be necessary, e.g. Chromium (III)/Chromium
(VI), Iron (II)/Iron (III); and dedicated analytical techniques or several techniques may
be necessary. Speciation may also include evaluating distribution of elements between
different minerals; e.g. lead sorbed to metal oxides, in sulfide minerals and in silicate
minerals. This may be performed with a combination of mineral analysis, EPMA, XRD,
and sequential chemical extraction, and possibly together with geochemical modeling
(Lichtner et. al. 1996, Moritz et al, 2009).
6.4.2.
Analysis of liquids
Chemical analysis of water and the digested solid solutions with a focus towards multielement approaches can be performed using Induced Couple Plasma atomic emission
spectrometry (ICP-AES) or mass-spectrometry (ICP-MS). However, some elements
commonly found in very low concentrations (mercury, arsenic, antimony and selenium)
are better analysed with cold vapor atomic fluorescence AAS (CV-AAS), e.g. mercury;
and hydride-generation AAS (HG-AAS) for the other elements.
Analysis of trace elements in seawater needs to follow a separate approach due to the
very high chloride and sodium contents. A common approach is to dilute the seawater
sample 1:9 with purified water. Trace element analyses with AA-graphite furnace will
also require the use of modifiers. ICP-MS is routinely used for the analysis of seawater,
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and has very low detection limits allowing accurate analysis of very low concentration
of elements.
6.4.3.
Sulphur (total, sulfate and sulfide)
In the characterization of sulfide containing waste, analyzing sulfur and the mineral
forms of sulfur is crucial in assessing acid potential together with determine short term
and long-term acid neutralizing potential. These types of acid potential and neutralizing
potential analysis forms the basis for Acid-Base Accounting (ABA) and acid/neutral
rock drainage (A/NRD) evaluations. ABA analyses are required for most types of
wastes form the extractive industry. Analysis of ABA is described in the EU standard
CEN15875:2011 (Static testing for determination of acid potential in sulfidic waste), and
a discussion on how to evaluate the data is described in the Overall Guidance document
(CEN/TR16375:2012).
6.4.4.
Organic and Inorganic Carbon
Total organic carbon can be analyzed using high temperature combustion (1350 dC).
This takes both organic and inorganic carbon. It may be necessary, therefore, for a
pretreatment stage, where the sample is acidified, and thereafter, CO2 gas is vented,
prior to combustion. Alkalinity analysis of a water sample and subtracting the carbon
content from alkalinity will also make it feasible to obtain total organic carbon.
Total inorganic carbon in a solid sample would consist of carbonate minerals. Analysis
of this can be performed using high temperature combustion, assuming that there is no
organic carbon present. Otherwise, the sample can be analyzed using the ABA method
(CEN-15875) section 6.5.1.
6.4.5.
Process chemicals
Additives may be used in many different steps in mineral processing, especially in a
flotation process: collectors, frothers, modifiers, depressants, activators, and flocculants.
Flotation collectors are made of polar groups and one or more non-polar hydrocarbon
groups. Activators may be copper sulfate or sodium sulfide for many of the sulfide
minerals and some carbonate minerals. Collectors are often amyl, butyl, or ethyl
xanthates or in some settings kersosene or tall oil. Modifiers are commonly lime or soda
ash. The frothers used are commonly a type of oil, pine oil, beret oil etc. The type and
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amount of additives used depends strongly upon the type of economic minerals to be
recovered and the gangue minerals to remove.
The analysis of these will vary depending upon the components. Some of the additives
will be difficult to detect because the elements are already within the mineral matrix.
Some collectors, i.e. for silicates will be very difficult to detect as they are strongly
bound to the mineral surfaces. Often only the producer of the chemicals can do the
analyses.
The additives used for leaching may be strong acids (sulfuric acid, hydrochloric acid) or
strong bases (soda ash, lime) often with carbonate as a complexing agent for anions, or
cyanide for precious metals.
Analysis of most inorganic additives is included in section 6.5.2, while cyanides analysis
is described in CEN/TS16229: 2011 (Sampling and analysis of cyanides discharged into
tailings ponds). Analysis of organic additives depend upon the type of chemical but
may be analyzed by ion-chromatography, gas chromatography, and ICP-MS, depending
upon what compounds are analyzed.
6.5.
A/NRD Testing Methods
The EU Mining Waste directive (2006) requires the use of a new static test method for
evaluating A/NRD potential. As part of the implementation of the directive, a static test
method was developed EN15875 (2011) which is built upon the most commonly used
ABA methods in the mining industry, Modified Sobek (Lawrence and Wang, 1998). The
Overall Guidance document (CEN/TR 16376:2012) describes how to interpret the data
and when to use kinetic testing for further evaluation of the A/NRD potential. These
methods are described within the next few sections.
6.5.1.
Static Testing - Acid Base Accounting (EN15875)
Static testing is a requirement in the EU Mining Waste directive and included in the
Norwegian law in the updated Avfallsforskriften, 2012. In addition to the method
EN15875 (2011), developed for the Mining Waste directive, the Overall Guideline for
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characterization of mine waste (CEN/TR 16376:2012) describes other methods.
However, these methods are not recommended for basic characterization, but are
recommended for verification during production.
6.5.2.
Kinetic Testing
Kinetic tests are experiments set up to allow naturally occurring reactions to take place,
and are a special form of leach tests designed for mineral reactions that has a strong rate
change with time. These reactions will commonly change the behavior of the tested
material over time. The concept of kinetic tests could include any test that allows for,
and measures, changes over time. Commonly, kinetic testing refers specifically to tests
run to evaluate acid generation behavior of sulfidic wastes, i.e. to quantify reaction rates
for acid producing and buffering reactions and to evaluate if the material actually will go
acidic or not. However, these tests can also have other more specific objectives, and the
design can be tailored to achieve these objectives.
Both long-term and short term leaching takes place during sub-sea tailings deposition.
This has not been described in the mine waste guidelines.
• Long-term leaching from bottom material after settling
• Short-term leaching from the material while settling
The Overall Guideline (CEN/TR 16376:2012) specifies the use of kinetic testing if the
neutralizing potential (NP) to acid potential (AP) is NP:AP<3. In the case of depositing
tailings under water, specific kinetic tests for sub-sea tailings deposition should always
be performed.
Kinetic testing to evaluate long term leaching behavior from tailings deposited under
water is different than the kinetic testing described in CEN/TR16363:2012; where the
purpose is primarily to achieve a maximum sulfide oxidation. In a sub-sea tailings
deposition, mine waste material will be permanently placed under water shortly after
production; and as long as, the deposition system works according to the handling plan,
there will be no change to this. Usually, kinetic testing is commonly performed under
optimal conditions for sulfide oxidation where leaching of reactive material takes place
once a week (typical humidity cell test).
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Even though the intended handling of the mine waste material is placement under
water, the material should be tested under atmospheric conditions, as well, if the acid
generation is more than 1/3 of the acid neutralizing potential (CEN/TR 16376:2012).
This testing should then follow the Kinetic testing guideline (CEN/TR16363: 2012).
The more standardised kinetic test methods (ASTM 2001, 2011: USEPA 1978, Morin
and Hutt, 2002) are designed to evaluate/calculate (as mentioned above) the maximum
sulphide oxidation rate relative to neutralising reactions, and not to simulate waste
behaviour under field conditions (Lapakko, 2004). Adjustments to the standardised
methods are being used to evaluate leaching rates (Price, 2009); adjustments that take
into account more site-specific conditions such as airflow, grain size and climate.
Information on leaching rates and drainage chemistry is also achieved from scaled up
experiments and field tests. More information on running kinetic tests under strongly
oxidizing conditions can be found in the Overall Guidance document, CEN/TR
16376:2012 and the Kinetic testing guideline (CEN/TR16363: 2012).
In order to simulate and evaluate the leaching potential from sub-sea tailings deposition,
it is suggested to place tailings in the bottom of a Plexiglas tube. To avoid the
experiment being affected by oxygen diffusion through the Plexiglas and to control
temperature, experiments can be place in a water bath.
The bottom water in the area of deposition may be oxygenated or reduced depending
upon the organic activity and the current in the area. Site-specific information is needed
for input parameters. Sulfide oxidation rates will be higher in an oxygenated setting
than in reduced setting for tailings deposition containing sulfides. Oxygenated condition
is, therefore, recommended for the experiments, however it may be very useful to run
parallel experiments with reducing conditions for comparison, especially if the seabed
measurements indicate reducing conditions, a setting that may change seasonally.
The following parameters should be monitored on a frequent basis during kinetic tests
for sub-sea tailings deposition, :
•
•
•
•
•
Temperature;
Salinity;
pH;
pe;
Oxygen content; and
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•
Element concentrations.
These leach tests should be run for several months until they reach a steady release rate.
Due to the high alkalinity and carbonate content in seawater, the seawater will not
become acidic; however, secondary minerals may, thereby, control the long-term release
rate.
Sulfur release is commonly the best way of monitoring and calculating sulfide oxidation
rates. However, sulfate in seawater is in the range of 2-3000 mg/l. The release of
sulfate into the column may be in the order of a few mg/l to maybe a few tens mg/l. It
may, therefore, be beneficial to run such tests with water spiked with NaCl and Na2CO3.
This can give the chloride content of water with its corrosive capabilities and the
alkaline seawater a pH of around 8. Unpublished ongoing work by Repzka and Walder
(2013) indicate that the sulfide oxidation rate is lower in such designed saline water
compared with normal seawater possibly due to differences in the ionic strength of the
solutions.
A more detailed look at Kinetic tests for sub-sea tailings deposition is described in the
following section.
6.5.3.
Saltwater/Seawater Kinetic Testing
It is necessary to perform specific leach tests designed for sub-sea tailings deposition in
order to evaluate the potential for mineral weathering and element leaching from
material potentially placed under water. The CEN guidelines (ref) only mention this
issue, referring to this specific guideline for more detailed information.
Salt water has a corrosive effect possibly enhancing the reaction rate of minerals. This
has been analyzed primarily by comparing reaction rates in high ionic strength solutions
relative to low ionic strength solutions (Langmuir, 1997). High chloride and sulfate
content has an additional effect where the corrosive processes are increasing. In
addition, the high ionic strength of the water will result in increased solubility of
minerals. It is, therefore, recommended that long-term leaching tests are run using
salt/seawater and in replicated environmental conditions of the tailings deposition site.
This requires physical and chemical information of the proposed location described in
Section 6.9.
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There are several issues that should be evaluated as part of the parameters controlled in
these leaching experiments for sub-sea tailings disposal. These could be:
•
•
•
•
•
•
•
•
Salinity,
Flow rate,
Oxygen concentration,
Temperature,
Grain size/surface area,
Deposition area,
Mineralogy/mineral chemistry, and
Amount and quality of organic matter at deposition site.
.
A leaching set-up can monitor or control the first four parameters (Figure 5). The last
three are input parameters for evaluating the result of the leach tests.
Figure 5. Experimental setup for long-term leaching tests for sub-sea tailings deposition.
As mentioned before, salinity is an important parameter, due to the corrosion issue of
chloride and the ionic buffering capacity of seawater. If deposition is suggested in
narrow fjords, there may be a high influx of fresh water reducing the salinity. One
option is to use the seawater from the potential location of deposition. If there is a
potential for sulfide oxidation, this can be assessed by monitoring the sulfate content in
the leachate. However, seawater has relatively high sulfate content (average 2600 mg/l,
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Stumm and Morgan, 1998) and the excess sulfate from the sulfide oxidation is likely to
be insignificant relative to the background value of the seawater. To circumvent this,
salt water consisting of only sodium chloride to achieve the appropriate ionic strength
and carbonate-bicarbonate to buffer the pH at level of the applicable seawater is a
possible option.
Local seawater (from site of deposition) or other seawater of similar properties can be
used. Using local seawater will have the benefit of having the correct starting water
quality with the microbial activity from the site. However, using seawater collected
from another area with similar quality should give a similar result. The seawater needs
to be filtered preferably with filter size of 0.2 µm to remove most colloids, as well as,
other particles in the water.
Water with the same salinity and pH as from the site of deposition can also be used.
Since the reaction process, especially for sulfides in salt water is poorly known, salt
water should only be used to evaluate the sulfate release rate and seawater should be
used to assess metal release rates.
Water current measurements are a natural part of evaluating potential impact from a
sub-sea tailings deposition (See section 6.9). Some areas may be stagnant, while other
areas may have a relatively high flow rate. These measurements are usually performed
both in upper part of the water body and deeper part of the water body, but seldom at the
bottom. However it is important to understand the currents near the seabed as these may
redistribute tailings after deposition. The experiments could easily be set up with a flow
through system if that is the condition of the potential deposition area. The flow would
ensure that there is a constant mix of water near the tailings surface such that the water
does not become stagnant. High flow rates, as measured in the Kvalsund, a potential
tailings deposition site for the Nussir mine, have a flow rate of 50-150 m/hour 2 meters
above the bottom (Akvaplan-Niva, 2011). Implementing this flow rate in column
experiments would require larger pumps. Lower flow rate would, therefore, be more
applicable for laboratory experiments. However, there is no point in carrying out
laboratory experiments that do not replicate conditions.
Oxygen content in the water is an indication of bacteriological decomposition and
organic activity growth together with a mixing rate. Oxygen content is an indication of
the redox content, which affects mineral stability. Sulfide minerals will not oxidize and
release elements in reducing conditions. Therefore, monitoring and controlling the
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oxygen content is important for understanding the processes and evaluating the result
from the leaching experiments to predict and assess any potential impact to the receiving
environment.
Temperature will affect the reaction rate of minerals. The temperature is a component
that can be controlled, however, high pumping rates commonly generate higher
temperature in the lines transporting the leachate, making it more difficult to control the
lower range temperatures.
Grain size – surface area can be used to calculate reaction rate relative to the mass of
certain grain-size or to a mineral surface area. However, as described in the mineral
section 6.3, only the available mineral surface of the reacting minerals is of interest.
Therefore, the best option is to run the tests with tailings material from flotation
experiments following the designed outline of the processing scheme.
There are two possible leaching scenarios taking place when using SSTD; 1) Short term
leaching during deposition that is related to the tailings mass, and long-term leaching
rates that are related to the tailings area (Walder and Repzka, in prep.). Probably, only
the upper part of the tailings will be a part of the reacting system after the tailings has
settled to the bottom. However, as the tailings are buried along with organic material,
the sediments become sub-oxic then anoxic. How deep in the sediments this occurs is
dependent on the amount of organic material, the oxygen content of overlying water,
currents and the degree of bioturbation of the sediments. When the tailings become
anoxic, the biogeochemical cycling of the elements will take place. This can lead to a
release of metals to the pore water and diffusion upwards in the pore water, where it
may re-precipitate in oxygenated sediments or be released to the overlying water
column.
The surface area of the tailings in the column, relative to the total area of deposition, can
be useful in calculating the long-term release rate and in the impact evaluation.
However, the long-term redox condition of the sediments containing the tailings is
extremely important, as there can be currents affecting the oxygen content of the near
surface water; bioturbation of the sediments increases oxygen availability. This again
can lead to biogeochemical cycling of elements and possible transport of elements to the
surface.
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Mineralogy and mineral chemistry together with the leachate chemistry is important
in evaluating the leaching processes taking place. Mineralogy and mineral chemistry
together with sequential chemical extraction (SCE) can be very valuable in
understanding the processes taking place during the experimental period. In particular,
SCE analysis can be very informative on evaluating the amount of mineral
transformation and secondary mineral precipitation. The high carbonate and sulfate
concentration in the seawater with high pH measurements, results in sulfate and
carbonate minerals being formed at very low metal concentrations.
The length of time for these tests can be several months depending upon the results. As
for kinetic tests, these leach tests evaluate mineral reaction rates and should, therefore,
also be run until there is a stable release rate of the primary elements of concern. For
kinetic tests, the activity is commonly dependent upon a microbial process, which takes
place in a reduced pH environment setting. This can take 6 months to years in an
oxygenated freshwater setting. Similar microbial processes are also taking place in
seawater. Leaching in seawater is likely not affected by the same high microbial
buildup, or a change in pH. Therefore, these tests may have to be run for as long as tests
run in a fresh water setting.
Buildup of secondary carbonate and sulfate minerals on the surfaces of the sulfide
minerals are likely to result in encapsulation of the sulfide minerals. These again will
result in reduced release rate and improved long-term condition. The duration of the
tests should be long enough to ensure that these processes can be evaluated.
Field scale/pilot scale testing is the type of testing that is closest to practice, as it
considers natural exposure conditions. This type of test includes pilot scale tests with
exposure of waste rock or exposed rock surfaces to the atmosphere (O2) and local
weather conditions or imposed rainfall regimes. Tailings may also be placed in a
smaller confined area in a fjord during pilot scale operations to evaluate actual leaching
and settling. However, these types of tests are costly and must run for a long period of
time (years) before meaningful results may be obtained. This can be circumvented by
using mesocosum tests which allows for the assessment of leaching, eco-toxicity, and
physical effects in-situ.
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6.6.
Leaching Behaviour and Leaching Tests
Constituent leaching from waste materials is a natural part of an A/NRD evaluation;
however, leaching can also be of environmental significance where there are no sulfide
minerals. Wastes from the extractive industry can, for example, be very alkaline where
strong bases are used in processing (e.g. alumina refining or gold leaching), very salty
(salt mines), or acidic where acids have been used for leaching metals from oxide
minerals and silicate minerals. The tests discussed here are short-term leach tests that
will be applicable for older waste or waste that will reach a constant leach rate within the
leach test time. For new wastes, where there may be a lag-time before reaching longterm stable leaching conditions, these tests would be not applicable.
6.6.1.
Common Leaching Tests
Leaching tests may in principle, be applicable to any type of residue from the extractive
industry. If they are appropriate or not will depend on whether they offer an efficient
way, with sufficient accuracy, to produce the information sought after in a specific case.
The percentage of a specific constituent that can be leached from a waste at a relevant
pH is a measure of the potential leachability. The leachability varies strongly for each
material and each element. It may range from close to 100 % to 0,001 %, demonstrating
that total composition is a poor measure for predicting the potential environmental
impact of an element.
There are a large number of standardized leaching tests available. The characterization
leaching tests comprise methods for measuring:
•
•
•
solid-aqueous partitioning as a function of pH;
solid-aqueous partitioning as a function of liquid to solid ratio (L/S); and
mass transfer rates for monolithic or compacted granular materials.
Most of these tests have been developed for the characterization of waste in general, but
not specifically for waste from extractive industries. The preferred and most commonly
applied leaching test for waste characterization is the CEN/TS 14405 column-leaching
test.
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The column-leaching test (CEN/TS 14405) is an up-flow percolation test designed to
resemble common percolation scenarios. The liquid to solid ratio can be related to a
time scale via the infiltration rate, density and height of the material. The liquid used in
these types of tests is distilled/de-ionized water, but in this case, it may be applicable to
use salt water.
It should be noted that, in the case of oxidizing waste material, e.g. sulfide mineral
containing waste, this test (CEN/TS 14405) does not capture the change of leachability
over time. In addition, this test is not very replicable to the environmental conditions at
the bottom of the sea, where the flora and fauna may be using/interacting with the 5-10
cm upper part of the bottom sediments.
Different tests use different solutions for leaching, e.g. acetic acid, sulfuric acid,
carbonic acid (rain water) etc. None of the tests have been specifically designed for
leaching evaluations in sea/saline waters. However, running tests with salt water instead
of meteoric water or distilled water may be applicable for evaluating leaching for
tailings to be stored in seawater.
The first eluate collected from a column test reflects the pore water conditions of the
material considered; while eluates collected later are more representative of the leaching
rate in a flow through system. Control measures can be taken for testing materials
sensitive to oxidation to avoid changes in initial conditions, e.g. using pH or Eh-buffers.
The effect of preferential flow can be difficult to quantify. Preferential flow may be
generated in sub-sea tailings deposits from bio-turbation (e.g. sea-cucumbers) from
boring into the sediments or stirring up the top surface of the bottom sediments.
6.7. Discharge settling
The discharges material settles via two different routes: Given high solid content the
discharge will form a high density current, and most of the discharge will follow this
current to the seabed. A minor fraction will disperse from the density plume and mix
with the seawater. These particles will settle at a slower rate and may be transported
longer distances, by way of water currents.
The speed of the turbidity current is governed by:
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C = 0.7√((d1-d2)/d2*gh) where:
d1 is density of the turbidity current;
d2 is density of the ambient fluid (seawater);
g is gravity(980 cm/s2); and
h is thickness of the head of the current.
The settling rate of the tailings sediments is often a critical parameter for modeling
sediment transport. Stokes law defines settling rates:
V0 = ((ds-dw) g D2)/18µ, where
V0 terminal settling velocity (cm/sec);
ds is density of the solid (gr/cm3);
dw is density of the water (gr/cm) – seawater;
g is gravity(980 cm/s2);
D is particle diameter (cm) ; and
µ is molecular velocity (gr/sec*cm).
Experiments can be set up to determine the terminal settling velocity; however, the
tailings have a grain size range, and different minerals have different densities.
Flocculation:
The particles have primarily a negative surface charge and with the high salinity of the
seawater, will act as a flocculant. Sea currents in the deposition area may sea current in
affect the settling rate (given a vertical component) and the settling point. Can be
modeled, provided data for current direction, strength and distribution
There are different methods designed for performing settling tests. However, the bulk of
the material from a tailings deposition is thick and heavy and settles in a way most
experimental setups are not designed to replicate. The majority of the effluent will form
a density current and travel to the seabed, provided the tailings density is greater than the
seawater. However, fine material will shear off at density changes within the water
column and will travel further and take longer to settle. This material will, therefore, be
subjected to more a common settling system and experiment.
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The following issues need to be evaluated when designing settling tests:
• Use of different flocculation chemicals and seawater for control
• Tests combined with evaluation of mineral dissolution
• Settling experiments should be performed with a stirring that is similar to the
measured current in the deposition area.
Salt water is, by itself, a good flocculation agent. Therefore, saltwater should be used in
these experiments. However, it would be useful to also run, simultaneously, freshwater
experiments for comparison, which would aid in modeling the particle transportation.
The key variable for the models is understanding of the water masses and currents.
6.8. Field experiments
Field experiments may be difficult to design in a mining setting where sub-sea tailings
deposition is proposed, since it is not common to build a pilot plant prior to a full-scale
operation. However, if the processing method is somewhat new or with a new ore type,
it may be beneficial to start with a pilot scale operation, e.g. Kolsvik Gold, Bindalen,
Northern Norway. At Kolsvik Gold deposit, the plan has been to start with a pilot scale
operation processing 20-50.000 tons of material on-site. It is planned to discharge most
of this material in the fjord, where the mine is hoping to obtain a discharge permit for
full scale operation.
It is important to use monitoring systems to evaluate the sediment spread during a test
operation. Measurements of current and other parameters that vary over time need to be
monitored also during a test deposition (see Chapter 6.9).
6.8.1.
Existing waste facility
Investigation of existing extractive waste facilities may be part of the monitoring/
confirmation to follow up on an earlier comprehensive waste characterization and
predictions of future drainage/leaching water quality.
It may also be a part of
characterizing the waste in closed facilities, with no or insufficient existing information.
This may be former sub-sea/shore line tailings deposit (e.g. Nussir deposit, Sydvaranger
mine). A detailed study of the behavior of the deposited tailings and their effect/impact
on the surrounding environment will give valuable information for evaluating how a
new or increased operation using the same ore will behave.
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Investigations of existing SSTD sites may be seen as the ideal field scale test set up
providing the receiving environment’s conditions are the same or similar especially
salinity, water masses, currents, natural sedimentation rates, biology etc. In the existing
facility it may be possible to evaluate the sea conditions, geotechnical stability, and
geochemical processes that are taking place, much depending on how long the facility
has been in place. This information may then be used for evaluation and verification of
models and predictions for continued deposition, adjustment to the deposition system, or
to evaluate new SSTD sites.
6.8.2.
Small-scale field testing
Tests performed in the field during field experiments of sub-sea tailings deposition
would be similar to those performed for water quality and water current analysis. These
could be:
•
•
•
•
•
•
•
•
•
Turbidity analysis;
Water current measurements;
Water quality analysis;
Temperature;
Salinity;
Sediment settling pans;
Effect on the marine life from sediment transport and settling;
Characterization of natural sedimentation material; and
Identification and abundance of benthic and pelagic biota.
These methods are discussed in Chapter 6.9. Solid sample collection should be
performed from near the discharge point, to a point in transect away from the discharge,
to a site far enough away so as not to be impacted by tailings. The last sampling point is
a control site.
6.9. Aquatic Toxicity Tests
Aquatic toxicity tests are used to evaluate the impact of anthropogenic chemical
substances and sediments/water affected by human activity. Common tests include;
standardized short time acute and acute test, to longer time chronic tests (OECD 201,
2006; OECD, 202, 2004; OECD, 203, 1992; OECD 204, 1984; ISO 10253). These tests
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measure endpoints, such as survival, growth, reproduction, of each concentration in a
gradient, along with a control test. It is common, and recommended, to use organisms
with ecologically relevant sensitivity to toxicants, with a well-established literature
background. There are several aquatic toxicity tests available, and several of them are
commonly performed in parallel to evaluate the toxicity. There are three toxicological
issues that may need to be evaluated.
•
•
•
Acute toxicity;
Chronic toxicity; and
Bioaccumulation.
It is important to test fish, crustacean, mollusk, and algae that occur at the site of
potential deposition. These tests can be performed following the leach tests, that can
indicate potential concentrations of the compounds/elements that potentially will
increase due to the tailings deposition, both compounds (organic or inorganic) used as
part of the processing of the ore and easily leached, and elements/compounds released
due to digenesis (e.g. desorption, mineral dissolution).
When designing toxicity tests, as well as, preparing samples prior to the tests, it is
important to remember the complexity of the material to be discharged. EN-14735/2006
is a background document describing steps to be performed before performing the ecotoxicity tests. This standard provides guidance on taking a sample, transport, and
storage, and defines preparation of a sample. The standard is for both solid and liquid
samples.
6.9.1.
Acute Toxicity Tests
Acute toxicity tests are short-term tests, from a few hours to a few days. Acute toxicity
tests can be performed as static non-renewal, static renewal, and as a flow through
system. Each setup has their benefits and drawbacks:
•
•
Static non renewal
o May result in depletion of oxygen
o Loss of toxicants
o Buildup of metabolic waste
o Easy and inexpensive
Static renewal
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•
o Improved conditions for oxygen, loss of toxicants and metabolic buildup
o Require greater volume of effluent
Flow through tests
o Maintain O2 conditions
o Require large volume of effluent
More representative tests for an acute toxicity evaluation will require more space and
volume of effluent, normally used for onsite tests. However, there are sophisticated
mesocosm experimental setups that can replicate onsite conditions, and are more
appropriate than the smaller laboratory setups.
A mesocosm is an experimental tool that brings a small part of the natural environment
under controlled conditions. Mesocosms provide a link between observational field
studies, with or without replication, and controlled laboratory experiments performed
under un-natural conditions (http://mesocosm.eu/node/17).
The toxicity tests may also vary depending upon the contaminants being introduced into
the water column, compared with what may be sorbed/assimilated with the solid phase.
Pelagic organisms would rarely come in direct contact with sediment-associated
contaminants; but indirectly they would, by feeding on the benthic organisms or material
suspended in the water column.
Effluent acute toxicity is generally tested using multi-concentrations, consisting of a
control and at least five concentration levels. The test should provide dose-response
information, expressed as the percent effluent that is lethal to 50 % of the organisms
within the prescribed period of time (commonly 1-4 days). It may also be prescribed as
the highest effluent concentration in which survival is not statistically significantly
different from the control. Negative results from this test do not preclude chronic
toxicity or bioaccumulation effects.
The “Marine algal growth inhabitation tests with Skeletonema costatum and
Phaeodactylum tricornutum” (ISO 10253) is a screening test for readily water-soluble
substances or mixtures of substances. The substances should not be significantly
degraded or eliminated in any other way from the test medium.
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6.9.2.
Chronic effect tests
There are several tests that are designed to evaluate chronic toxicity on marine life. The
most commonly used tests are:
•
•
•
•
EPA 600/R-01/020, method for assessing the chronic toxicity of marine and
estuarine sediment-associated Contaminants with the Amphipod Leptocheirus
plumulosus
EPA821 chronic toxicity test for water soluble pollutants
USEPA-USACE 2001 determination of the chronic toxicity of contaminants
associated with whole sediments with the amphipod Leptocheirus plumulosus in
laboratory exposures
OECD 204, Fish toxicity testing framework, 14 days test period
The EPA 600/R-01/020 guideline describes chronic toxicity of contaminants with
whole sediments. The sediments may be from marine environments or estuarine
environments, or could be spiked with compounds in the laboratory. The method is
based on using the amphipod Leptocheirus plumulosus. The test is performed in a 1 liter
glass chamber containing 175 ml sediments and 725 ml of overlying water, with 28 days
of testing. The endpoint in the tests is survival, growth, and reproduction of amphipods.
The test is applicable for sediments from oligohaline to fully marine environments with
silt content >5% and clay content <85%.
EPA821 is a chronic test designed for five species for which toxicity test methods are
provided: the sheepshead minnow, Cyprinodon variegatus; the inland silverside,
Menidia beryllina; the mysid, Mysidopsis bahia; the sea urchin, Arbacia punctulata; and
the red macroalga, Champia parvula.
The EPA821 states further: “Four of the methods incorporate the chronic endpoints of
growth or reproduction (or both) in addition to lethality. The sheepshead minnow 9-day
embryo-larval survival and teratogenicity test incorporates teratogenic effects in addition
to lethality. The sea urchin sperm cell test uses fertilization as an endpoint and has the
advantage of an extremely short exposure period (1 h and 20 min).”
USEPA-USACE 2001 is a chronic toxicity test designed for a 28 days test period, in a
1-liter glass chamber containing 175 ml of sediment with about 775 mL overlying
seawater. Four hundred milliliters of the seawater is renewed three times per week. The
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organisms are fed at time of seawater renewal. Tests are initiated with neonate
amphipods that mature and reproduce during the 28-d test period. After the 28 days
survival rate (percentage of amphipods that has survived), growth rate, and reproduction
are determined.
6.9.3.
Bioaccumulation Tests
If there are organics or chemicals present that are not included in priority lists, and
bioaccumulation is not already known for the biota, bioaccumulation potential tests may
be necessary. Two tests designed for testing bioaccumulation are described in the
following paragraphs.
•
•
OECD (2012),Test No. 305. Standard for bioaccumulation testing of fish
ASTM-E1688 − 10, Standard Guide for Determination of the Bioaccumulation
of Sediment- Associated Contaminants by Benthic Invertebrates
The OECD (2012), Test No. 305 describes a procedure for characterizing
bioaccumulation potential of substances in fish, using an aqueous or dietary exposure,
under flow-through conditions. The test is divided in two phases; bioaccumulation and
post-exposure. During the uptake phase (usually 28 days but can be extended), a group
of fish of one species is exposed to the test substances at one or more chosen
concentrations (depending on the properties of the test substance). For the depuration
phase, they are then transferred to a medium free of the test substance, or fed with clean,
untreated feed. Concentration of the test substance in the fish is followed through both
phases of the test. The aqueous exposure test yields a bioconcentration factor (BCF) and
the dietary approach yields a biomagnifications factor (BMF); greater emphasis is put on
kinetic BCF estimation (when possible), estimating the BCF at steady state.
The ASTM-E1688−10 is a toxicity tests design to evaluate the bioaccumulation from
sediment-associated contaminants using benthic invertebrates digesting sediments. The
method design is such that it can use single or multiple species. There should always be
a control column without contaminants. Light, temperature oxygen content, and flow
rate (if not static setup) need to be controlled. Test period may be between 10 to 78
days, with food supplied and water replaced at certain intervals. The method describes
how to determine the amount of duplicates, and what invertebrates to use for specific
contaminants. The tissue of the benthic invertebrates is tested for the contaminant in
question. The guideline describing the method provides an extensive description on
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how to calculate the results of bioaccumulation, and issues to be aware of to obtain best
test result.
7. CHARACTERZATION OF THE RECEIVING ENVIRONMENT
The receiving environment is defined in this guideline, as the area for tailings
deposition. Even though the onshore receiving environment from tailings dams and
waste rocks are poorly described in other EU documents and guidelines, it is outside the
scope of this guideline. The characterization of the receiving environment, as referred to
in this guideline, is focused on sub-sea tailings deposition sites.
The main issues that need investigating with regards to the receiving environment for
sub-sea tailings deposition are:
•
•
•
•
•
•
•
•
•
Visual observations of the bottom ecological system (corals, sponges, etc.)
Fish resources (quantities, types, spawning areas, economics etc.);
Bottom flora-fauna;
Zooplankton (types and concentrations etc.);
Indicator species;
Bottom sediments (grain size, chemical composition, pore water chemistry etc.);
Ocean (e.g. eufotic-afotic zone, thermocline, oxycline, halocline);
Water quality;
Water currents, including identifying different water masses, circulation and
potential for turnover in the fjord; and
• Bathymetry.
Visual observations of bottom marine activity such as corals and sponges give an
indication of the natural nutrient conditions in the area potentially used for SSTD. The
observations can be used to evaluate spawning and feeding areas. This gives a starting
point for evaluating the potential impact from tailings deposition, e.g. potential for
spawning areas. Visual observations can be performed with sub-sea cameras, small submarine vessels and divers. In addition, a complete benthic survey should be carried out
using sediments collected by an appropriate corer that recovers sediment with sediment
water interface samples. The samples should then be analyzed for micro and macro
fauna using internationally recognized methods.
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It is important to identify flora-fauna indicator species (and agree upon) during the
characterization. These indicator species should then be monitored during operation and
after closure.
Methods to obtain this information are described in the following sub-sections.
7.1. Fish and Fish Resources
Particle discharge may affect the fish by irritating the gills; while increased turbidity
may result in the fish moving to areas with better water quality. Particles from crushing
and milling have sharper edges than natural formed fine particles. Due to the sharper
edges, tailings particles may be more harmful to gills than natural fine particles. The
discharge may also affect the growth potential by reducing light and covering the sea
bottom, which again affects the fish habitat and food supply.
Different species of fish will often use area potentially affected by tailings deposition in
different ways. For Atlantic salmon and sea trout, the area may only be used as a
transport route near the surface, while other fish may have spawning or feeding areas at
the bottom, where the tailings potentially will be deposited.
The fish resource in the potential depositional area should, therefore, be studied. This
can be done by investigating records describing catches, and interviewing local
fishermen. The information to obtain should include:
•
•
•
•
•
Historically sizes/amount of fish catches combined with boat types and fishing
equipment used;
Identify the type of fish that is in the area (local and migrating fish) and in what
depth that they typically exist in potentially affected areas;
Spawning areas and feeding areas for the different fish types should also be
identified;
Identify salmon protected areas within the potentially affected area; and
Identify areas designated for fish farming.
There may be a need to actually fish within the designated area to better evaluate the
type of fish that exist within the potentially affected area. All of this information can
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then be used to evaluate the potential impact of fish resources from tailings deposition.
Salmonid fish (Atlantic salmon, sea trout, arctic char) have been protected by the
Norwegian legislation with the introduction of the National Salmon Water Courses and
National Salmon Fjords legislation. No negative impact will, therefore, be allowed for
salmon as a result of tailings material deposition. Salmon is also protected via the North
Atlantic Salmon Convention (NASCO) established in 1983.
Atlantic salmon smolt, sea trout, Tout and arctic char can be tagged with acoustic tags,
and an array of receivers along the migration route can be deployed throughout the fjord
area. This will indicate migration routes, residence time, migration periods, and depths
of the salmonides, all information to be used for evaluating potential impact. It may be
beneficial to divide the salmon cycle into the juvenile stage (larvae to smolt), post-smolt
(migration stage), and spawning stage.
The information for pelagic fish (herring, mackerel, etc.), white fish (cod, red fish,
haddock etc), and bottom fish (flat fish, halibut) is commonly collected from local
fishermen and government records of fish catches. The information to be collected
should follow Norwegian guideline for fish resource mapping (Fiskeridirektoratet 2010).
Chemical analysis should be performed primarily of liver and muscles of the local fish
to evaluate baseline conditions. This will also be used as a reference level for
monitoring during mining and after secession of the mining operation.
7.2. Bottom Sediments
Physical and chemical analyses of bottom sediments should be performed for
monitoring purposes and environmental assessments. ISO 5667-19:2004 provides
guidance for bottom sediment sampling. The guideline encompasses sampling strategy,
requirements for sampling devices, observations made and information obtained during
sampling, sediment sample handling, and sediment packaging and . It should be noted,
that it is extremely important to use correct sampling equipment, otherwise the results
may be useless.
The amount of samples and locations can be estimated based on different statistical
approaches described in the waste sampling guidelines (EN 14899:2005; CEN/TR
16376:2012) and other geo-statistical sampling documents.
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Sediment cores should be described visually prior to analysis. Bottom sediment
sampling should be performed using a multi or mega-corer that is hydraulically dumped,
and recovers undisturbed sediment with the sediment water interface intact. Common
practice for the sediment analysis is to use the upper 0-2 cm layer for grain size, total
organic carbon (TOC) and metals, when carrying out a baseline study. Down core
analysis should be undertaken, as this will provide information on the redox conditions
of the sediments and indicate what biogeochemical cycling is taking place. Pore water
samples should also be collected and analyzed. Mineralogical analysis e.g. MLA
(mineral liberation analysis; see Chapter 6.3) would also be advantageous. This will
give a good indication of the environmental condition (environmental classification
system SFT 97:03) at present and provide background data prior to potential tailings
deposition.
There is also a need to select one or several locations as reference stations that will be
outside the expected tailings deposition influence area. These reference stations should
have similar bottom fauna and geochemical characteristics as within the influence area.
Pore water analysis is also recommended for evaluating background conditions. Pore
water can be extracted from core samples of bottom sediments and analyzed as water
samples, as described under Chapter 6.4.2.
7.3. Bottom Flora and Fauna
7.3.1.
Soft-Bottom Flora and Fauna
The bottom fauna (for the same samples as described above) should be sorted and
species abundance determined. The data should be presented in species lists together
with univariate parameters, amount of species, amount of individuals, Shannon Wiener
diversity indexes, and Hulberts diversity indexes.
There should be 3-5 replicates for each sample location for the soft bottom analysis,
where each sample represents at least 0.1 m2. In some cases, this may be increased to 10
replicates if there is a considerable variation between replicates. This can be performed
by sampling more replicates at one time, and storing them until results are obtained from
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the initial 3-5 replicates analysis. The amount of stations to be sampled will depend
upon the variation of conditions and fauna in the potential influence area. Sampling
should be performed according to the standards NS 9422 (ISO 5667-19:2004) and NS
9423.
7.3.2.
Hard-Bottom Flora and Fauna
The hard bottom flora and fauna evaluation is divided into the littoral zone (0-5 meters
depth) and the sub-littoral zone (to 20-25 meters depth). Permanent macro-algae and
animals are to be analyzed by species types and amounts.
The analyses of species types, and amounts of flora and fauna in the littoral zone, should
be performed within a set frame of 0.5*0.5 m, divided into 25 squares. All squares
should be analyzed according to NS 9424. These frames should be set at every onemeter depth to below the tidal water area (with one replicate for each depth level). The
amount of stations required depends on the potential influence area and variation within
the influence area. In addition, reference areas should also be selected and analyzed.
The analysis of the sub-littoral zone (below the littoral zone described above) can be
performed by a specialist (e.g. diver/marine biologist) using visual analysis, together
with photo image analysis for each meter depth.
7.4. Water Quality
Assessment of the water quality in the potential affected area needs to be performed.
The water quality should be taken into account when sampling. Sampling can be
performed according to ISO-5667-9, 1992 Guidance on sampling marine water. Water
quality data is used both as input for water current modeling and for evaluating
geochemical leaching potential:
•
•
•
•
•
Salinity;
Turbidity;
Temperature;
Redox potential –oxygen content; and
Chemical composition.
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The first four parameters can be measured using probes, while chemical composition
requires samples to be analyzed in a laboratory. The first four parameters can be
measured in continuous depth profiles, from the top to bottom, in selected locations. All
of these parameters should be performed within the potential influence area, at different
locations, during different seasons.
7.5. Ocean-Fjord Currents
Current measurements are necessary to evaluate particle transport in the potential impact
area. Current measurements should be performed using both stationary measurement
and mobile devices, e.g., gliders or AUVs. Both current direction and velocity need to
be monitored at different depths. Measurements should be performed at several
locations within the potential influence area. The data from these measurements can
then be used to plot direction velocity maps for different depths.
There are commonly large seasonal differences due to snow melting in the spring (wet
season) and freezing conditions in the winter (dry season) and low fresh water input.
Measurements need to be taken during both of these seasons, over a minimum of a two
month period.
There are moon cycles affecting tidal water currents with daily, monthly and yearly
cycles that may need to be assessed. These may be evaluated during the 2 by 2 month
monitoring explained in the above paragraph. In addition, the possible occurrence of
internal waves needs to be explored.
By deploying mooring lines with different instruments at different depths, it is possible
to gather the required information by high-resolution monitoring. Examples of
stationary equipment that may be used include the RCM9 current meter from Aanderaa
instruments.
Current velocity can be measured using an Acoustic Doppler Current Profiler (ADCP), a
hydroacoustic current meter similar to a sonar. Water current velocities are measured
over a depth range using the Doppler effect of sound waves bouncing off off particles
within the water column. There are no moving parts, so biofouling is not an issue. Such
an instrument is enough to cover up to 1000 m of water column, this allows for more
accurate estimations of flow patterns. The ADCP is an acoustic instrument which may
affect cetacean navigation and ecolocation (Hogan, 2011). However, if the water
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column is layered, e.g. with thermocline or halocline, mechanical instruments may be
more appropriate.
The length of time for the current measurements will vary based on locations for
deposition. One year monitoring may be enough at one place; while other potential
locations may need measurements collected over several years, especially if there are
large variations from year to year and more accurate data is needed for performing
transport modeling.
If the potential area for deposition is strongly affected by tidal cycles, it may be
necessary to take several full month measurements. If the potential area for deposition
is strongly affected by variation in freshwater input, it may be necessary to have current
measurements taken over several years to see the difference from one year to another.
It is difficult to describe, in general terms, where to place monitoring systems.
However, if there is a threshold that is used to enclose the sediments, the current
velocity and direction across it should be monitored. The potential of upwelling needs
to be monitored, as well as, the current near the sea bottom where deposition is taking
place. Surface current data is also important in order to develop a possible threedimensional flow system. This flow system can be used to model particle transport.
7.6. Bathymetry
Mapping the bottom topography is an important part of evaluating the potential impact.
Bottom topography data can be used in identifying potential thresholds that can be used
as dykes for the deposition; estimating potential volume for deposition, and identifying
locations for bottom test locations.
Kartverket (Norwegian Map Authority) has produced hydrographic maps for most areas
of the Norwegian coast. However, more detail information may be necessary. One
method for performing more detailed mapping is using, e.g. Simrad 38/200 kombi D
transducer and an EA400SP transceiver. Collected data is then transferred to a map
using a computer mapping programme. For the Simrad 38/200, the mapping programme
Nobeltec is commonly used. Depth measurements can also be performed using sonar in
connection with the OLEX system. Depth maps using color differences for depth
variations are recommended.
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8. DATA QUALITY
The Overall Guidance document, CEN/TR 2012 for characterization of waste states:
“Assessing current physical and geochemical properties and predicting how these will
develop in the future under the influence of weathering, with possible different closure
alternatives, is a complex undertaking. Especially, the prediction of future behaviour is
no exact science and will always include a level of uncertainty. The level of accuracy
and precision that is required /acceptable will vary depending on the context. In
situations where the test result and predictions will be the key factor in the choice
between different management options, a high level of accuracy will be needed
(alternatively high safety factors will have to be applied). On the other hand, in clear-cut
cases, whether clearly benign or clearly problematic material, there may be no need for a
high precision. This may be the case when assessing if drainage collection and treatment
will be needed (while dimensioning of a treatment system will still require a higher level
of precision)”. This statement also applies to the SSTD Evaluation Guideline, where the
precision of the species and amount of species, may not have the high precision
requirement; while metal leaching and particle transport may need high precision,
especially in sensitive environments. .
Data quality and uncertainty can be understood in several ways ISO 5667-14:1998.
•
•
•
•
•
Uncertainty related to the representativeness of the samples that are collected;
Uncertainty of a specific test result (e.g. leaching and analysis);
Variability in materials taken at different times or locations;
Seasonal variation; and
Uncertainty in the prediction of release behaviour under field conditions.
These uncertainties are not easy to measure or calculate; however, the sampling plan
needs to address the issues and design an approach for the possible uncertainties. The
sample representativeness can often give a higher uncertainty than the lab analysis,
where uncertainties are routinely dealt with.
Predictive modeling will often be a part of developing waste management plans and
closure plans (e.g. particle transport; long-term leaching rates; ground-water transport).
Considerable uncertainty is inherent in determining many of the parameters that are
required for modeling drainage quality from waste rock or tailings. The inherent
uncertainty in model predictions is rarely stated or recognized; however, sensitivity
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analysis should be a part of the modeling, evaluating important output parameters that
are sensitive to the input parameters.
The uncertainties of modelling outputs may stem from incomplete characterization or
incomplete knowledge of the geochemical conditions, lack of data on thermodynamic/
kinetic properties, and/or insufficient knowledge of the sea conditions at the potential
deposition site. The Overall guidance document for waste characterization
(CEN/TR16367, 2012) states: “Methods used to evaluate or account for model
uncertainty include Monte Carlo analysis, stochastic methods, and an evaluation of a
range of model parameters to develop a range of deterministic outcomes. Rather than
parameters being described by a single value, as required in the model, parameters are
better described with a probability distribution (i.e., a mean value with standard
deviation, etc.)”.
Model uncertainty should be described in predicting leaching quality of waste material.
These uncertainties should include the different potential setting for the waste
management options and for the closure scenarios. Field verification is commonly
needed to reduce uncertainties in the conceptual model, as omission of an important
release controlling process may lead to a faulty prediction. In this context, the
interrelations between laboratory test results, field studies, and actual measurements at
full scale operations can provide a higher level of understanding, and thus increase the
reliability of data developed to support management decisions, keeping in mind that
management options are strongly reduced by the time full scale operation begins.
The uncertainty level and type of uncertainties change at different stages of the
characterization process (GARD Guide, 2009; MEND Prediction Manual, Price, 2009).
The MEND Prediction Manual emphasizes the use of sensitivity analysis and risk
assessment as part of the characterization program; and both the MEND and the GARD
Guide recommends using characterization and modeling results cautiously.
Quality Control/Quality Assurance (QA/QC) is important in this context, dealing
primarily with measurable quantities, such as physical parameters, chemical analysis and
leaching test results; and helping to create a process where sampling or laboratory
analysis are performed consistently. General laboratory practice is important in this
context and described in EN17025.
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9. INTERPRETATION, APPLICATION, AND EVALUATION
Data from the many different analyses will not mean much if it is not evaluated,
interpreted and used in the correct context. Specialist in the different disciplines should
perform this work. When there is a possibility for a land-based deposition, then an
environmental cost-benefit analysis for these main two deposition forms should be
performed.
Some of the issues that would be incorporated in such an evaluation may be:
• Fine grained tailings on top of natural fine-grained material/slime etc.;
• Stability at the bottom of the sea/fjord relative to dam failures from land based
deposition
• Temporary destruction of sea-bottom relative to temporary destruction of a
surface area housing a tailings dam;
• Difference in the air/water flow through a land based deposition relative to subsea tailings deposition, where this is close to non-existent.
• Leaching from a SSTD in a high acid buffering capacity sea, compared with a
land-based weathering setting;
• Natural geological barrier that reduces sediment migration and provides high
stability relative to a land based tailings dam failure;
• Shallow area (tailings filling) gives higher biological activity; and
• Recovery after sub-sea deposition ends relative to reclamation of a surface
tailings dam.
This guidance document will aid in obtaining proper information from the potential
SSTD, while the CEN documents will guide in obtaining the proper information for the
land based tailings dams.
One of the purposes with the SSTD evaluation is to develop acceptance criteria for the
different tailings deposition issues. Such criteria may be:
•
•
•
•
•
Solid concentrations near and far from the deposition area
Element concentration near and far from the deposition area
Amount of discharge relative to environmental limits (how much the area can
take without significantly being impacted, short term and long term.
Metals in the food chain
Process chemicals
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Developing such acceptance criteria could be through an open dialog with regulatory
agencies, interest groups (NGOs) and experts in the different fields. The basis for such
discussions would be the data and interpretations obtained through the SSTP evaluation
report guided by this document (Fig. 6).
Fig. 6. Flow chart for the steps within the Evaluation of SSTD data
Through this type of an SSTD evaluation, it is recommended that indicator species for
flora and fauna are identified. Monitoring should then focus on these indicator species
on a frequent basis. Non- indicator species could be monitored on a less frequent basis;
however, this is open for debate. The type of indicator species would depend on type of
environmental issues that are dealt with. There may be a need for several indicator
species, where environmental issues, e.g. turbidity, siltation, metal leaching, and organic
contaminant leaching (additives) exist.
9.1. Particle Transport
Particle transport is an important part of the sub-sea tailing evaluation because:
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•
•
•
•
Particles may transport contaminants a long distance;
Enhance the length of time for leaching;
Affect the gills of fish;
Reduce the light to and growth of the bottom flora and fauna and depending on
the amount and rate of deposition; and
• Smother the flora and fauna in the deposition area.
It is necessary to understand the sea current at least throughout the year, the structure in
the sea (e.g. layering and internal mixing), bottom topography, water salinity in addition
to the effluent characteristics to be able to evaluate the particle transport distance and
residence time in the water column.
This information will then be used as input to particle tracking modeling programs.
Some of the sea-current particle tracking programs are as follows:
•
•
•
•
•
•
•
•
CORMIX/CDFATE (Schroeder et al, 1998)
PLUMES (VISUAL PLUMES) (USEPA)
BJET (developed by DNV and NTNU, documented by Sørgård, 1992)
DREAM –and Sintef, Trondheim
NCOM - Navy Coastal Ocean Model (Martin, 2000)
BOM-Bergen Ocean Modeling (Berntsen, 2000)
MOHID – Instituto Superior Técnico, Technical University, Lisbon
GEMS - NIVA program
There are likely more programs available, or programs that could be modified to serve
the purpose of modeling fjord current. The following is a brief description of these
modeling programs.
CORMIX/CDFATE is a numerical modeling program developed to evaluate dilution
and spreading from a continuous discharge of particles from a discharge point. The
model simulates the spread and dilution at different layering and current velocities. The
input data to CDFATE and BJET are:
•
Receiving Environment
o Current direction and velocity
o Temperature variations
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•
o Salinity variations
Discharge material
o Particle grain size (silt:clay ratio)
o Salinity
o Temperature
o Amount of discharge with solid to liquid ratio
o Discharge velocity
o Diameter of discharge pipe
Visual Plumes (VP), (USEPA) is a Windows-based computer application for modeling
a mixing zone system. VP simulates single and merging submerged aquatic plumes in
arbitrarily stratified ambient flow and buoyant surface discharges. It contain features
such as graphics, time-series input files, user specified units, a conservative tidal
background-pollutant build-up capability, a sensitivity analysis capability; and a multistressor pathogen decay model that predicts coliform bacteria mortality based on
temperature, salinity, solar insolation, and water column light absorption.
VP includes the DKHW model based on UDKHDEN (Muellenhoff et al., 1985. Initial
mixing characteristics of municipal ocean discharges. EPA/600/3- 85/073a and b), and
the surface discharge model PDS (Davis, 1999, Fundamentals of environmental
discharge modeling. CRC Press).
.
MOHID is a three-dimensional water modeling system, developed by MARETEC
(Marine and Environmental Technology Research Center) at the Instituto Superior
Técnico, Technical University of Lisbon. The MOHID modeling system allows the
adoption of integrated processes modeling (physical and biogeochemical), at different
scales (e.g. use of nested models) and systems (estuaries and watersheds).
The integration of MOHID’s different tools, (MOHID Water, MOHID Land and
MOHID Soil) can be used to study the water cycle in an integrated approach. Since
these tools are based on the same framework, coupling them is easily achieved
(www.mohid.com).
MOHID includes a baroclinic hydrodynamic module for the water column, a module for
the sediments, and corresponding eulerian and lagrangian transport modules. The system
is composed of pre-processing and post-processing systems plus a graphical interface for
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the implementation of the model (Neves et al., 2008). The model has been used in
several fjord sediment transport investigations (Marin, 2012)
Bergen Ocean Model (BOM) can be used as a mean in investigating the dynamic
interaction between the slope, shelf, and fjord, thereby aiding interpretation of the
observational data (Cotier et al., 2005). The primitive equations used in the BOM,
sigma-coordinate ocean model, assumes Boussinesq and hydrostatic approximation, and
solves for the barotropic field at higher resolutions in time than the baroclinic field
(Berntsen, 2000). This model does not include particle transport, only current
movement.
DREAM model is developed by SINTEF, Trondheim, Norway and currently used in the
offshore industry to evaluate spreading of drill-mud material from the North Sea
drilling. Also used for tailings Hustad, Nordic Mining The modeling program is tailings
deposition.
The DREAM model can be used to potentially describe the following (Rye, 2012):
• Near zone characteristics: content of particles, grain size distribution, content of
chemicals, fresh water, seawater, discharge system, creation of sub-sea plume.
• Testing of chemicals. Chemicals used in the production should be tested for
toxicity, biodegradation, and bioaccumulation. What is used for the oil industry
can also be used in the evaluation of SSTD.
• The DREAM model can simulate spreading of fine particles from a point source
discharge taking into account plume behavior of the discharging material. This
modeling will include near zone deposition and far zone transport of fine grained
particles, e.g. clay fraction to colloids where input data can include: e.g. salinity
layering, temperature layering, sea current at different levels, and flocculation
potential for the particles
• Simulation may also include environmental effect from chemicals used, where
data from toxicity tests and sorption onto particles of the chemicals are included,
as well as, the above input factors.
The choice of modeling program depends on the complexity of the modeling required.
Important issues that may need to be handled by the program are as follows:
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•
•
•
•
•
•
•
•
•
The grid spacing needs to be small enough that that it will catch the processes
taking place,
Pipe discharge
Dual density fluids,
Salinity variations,
Temperature variations,
Tidal variations,
Fresh water input from rivers,
Variable depth,
Particle transport,
Other necessary issues may include fate and transport of chemicals, either from
additives or from weathering and leaching of minerals. Mineral precipitation and
dissolution may also be included in the modeling evaluation in order to understand the
potential environmental impact of SSTD.
9.2. Acid/Neutral Rock Drainage and Leaching Risk
Understanding the mineralogy is essential in performing prediction on material stability,
A/NRD, and/or leaching behaviour. Using the methods described within this document
and/or other guidelines will give the basic mineralogical information required for
characterization. This mineralogical information may need to be combined with
chemical, leaching, and reaction rate analysis of the waste material to perform any longterm behaviour prediction.
The tests will often give indications of the geochemical processes that are or could take
place. This will commonly have to be followed up by geochemical modeling to predict
long-term behaviour. Geochemical modeling will commonly be the tool used when
predicting how different closure scenarios may affect the long-term behaviour.
This section discusses the interpretation of the required ABA (EN15875) test for
potential waste from the extractive industry; and the required test if there is less than
three times the neutralising capacity relative to acid production capacity based on the
ABA test. There is then a discussion on the use of leach tests, followed by the use of
geochemical modelling for A/NRD prediction.
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9.2.1.
A/NRD Evaluation
A/NRD can be a major environmental effect from mining operations if not understood
and handled properly. ABA accounting gives a first evaluation of the acid and
neutralising potential for analysed material. It is not always applicable, as a lot of mine
waste material, especially from industrial minerals operations, does not contain sulfides;
and therefore, the issue of A/NRD does not apply.
Inert waste is defined by EU-commission decision (CD 2009/359/EC on inert waste) as
waste material that has less than 0.1 wt.% sulfide, or waste with maximum 1 wt.%
sulfide content and the neutralizing potential is 3 times higher (based on method
EN15875). In addition, the contents of potentially harmful elements (Cd, Co, Cr, Cu,
Hg, Mo, Ni, Pb, and Zn) are insignificant. If the waste material has a significantly high
content of these potentially harmful elements, the availability of these potentially
harmful elements should be evaluated by leaching and /or kinetic testing methods. The
level of insignificance is to be defined by each member state. This insignificance is
commonly defined by the contaminant levels classification for soils not affected by
contamination. (e.g., background level).
If the waste cannot be classified as inert waste, further A/NRD evaluation is needed. A
first step in this evaluation is to have an understanding of the mineral phases that can
potentially leach elements, and/or affect the chemical condition of water, e.g.
neutralization or acidification.
The data should be evaluated based on acid (producing) potential (AP) relative to (acid)
neutralization potential (NP) (EN15875). The data is commonly plotted in a diagram
where AP vs NP and AP vs Net Neutralizing Potential (NNP = NP-AP). If the ABA
analyses are using total sulfur content for calculation of AP (that means all sulfur is as
pyrite sulfur), the AP will be a conservative estimate. If sulfide is used, the result may
not be conservative, depending upon the mineralogy (Fig. 7).
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AP (tCaCO3 eq./1000t)
Potentially
acid generating
1:1
C - sulfate
addition
D - carbonate
reduction.
Uncertainty
zone
B - Non-carbonate
neutralization
A - sulfide
reduction
3:1
Non-acid
generating
NP (tCaCO3/1000t)
Figure 7. Acid potential (AP) relative to neutralization potential (NP) based on ABA analysis. In
addition, included are the mineralogical effects on AP and NP that are not included in the ABA analysis.
A-sulfide reduction – material containing sulfide minerals that are not acid generating; B-Noncarbonate
neutralization – long term silicate weathering consuming hydrogen ions; C-Sulfate addition – acid
generating sulfate minerals; D-carbonate addition – iron carbonate and dolomite (Modified from Walder
et al., 2005).
The method required in Europe to be used is the same as most other methods; it analyzes
only for the rapid carbonate neutralizing potential. This is not necessarily a conservative
estimate, since it depends upon the carbonate mineralogy. Some carbonate minerals can
be acid generating (iron carbonate mineral- siderite; D Fig. 7), and some have very low
reaction rate (dolomite - calcium magnesium carbonate). In a slow moving water
system, (e.g. groundwater or tailings flow), either in seawater or onshore, a long
residence time for the acid production will result; silicate minerals may also be acid
consuming (B, Fig. 7).
When there is a potential for element leaching and/or acid generation, kinetic tests
should be run as specified in CEN/TR 16376 (Overall Guidance document). The
method for kinetic testing is described in CEN/TR16363 (Kinetic Testing guideline).
This document specifies the issues to be dealt with for an on-shore placement of tailings;
while sub-sea tailings placement are not dealt with, but rather described within this
document.
Data from kinetic testing for SSTD evaluation should be plotted as cumulative
concentration relative to time. This will show immediate release rate and afterwards,
long-term release rate (2-3 months). Since the seawater is highly alkaline, acid rock
drainage is not likely to be an issue when tailings are placed under water in the sea.
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There may be microbial buildup in these environments, however, not in the same way as
in on-shore placement, where the neutralization is only from the minerals within the
waste material.
There are likely two different element/metal leaching processes taking place (Walder et
al, 2013; Repzka et al, 2013):
•
•
Short term leaching is based on the initial leaching of the material either from
secondary minerals and/or from leaching taking place in the tailings prior to
deposition. This short term leaching rate is relative to the total mass of the
material deposited.
Long-term leaching is from metal desorption, mineral digenesis, dissolution,
and oxidation. This process will primarily take place near the surface of the
tailings, which are in contact with fresh seawater, and also where the products of
the mineralogical processes can be incorporated into the water column.
Microbial processes and bio-turbation in the upper 5-10 cm of the bottom
sediments may result in an exchange of compounds of leach elements in the
water column.
Since the second process is dependent on three geochemical processes: transport of
reactant to the surface, mineral transformation, and transport of products away from the
surface, this process will likely slow down with time. If the reactive minerals on the
surface layer of the tailings are being consumed, there will be a propagation downwards
dependent only upon diffusion. This will slow down the reaction process. If the
products are elements-compounds that are becoming saturated in the high alkalinity,
high sulfate setting, these will precipitate and potentially encapsulate either individual
minerals or the surface of the tailings (possibly forming a hardpan). This will slow
down both the transport of reactants to the surface and products away from the surface.
However, bio-turbation and microbial processes may also be involved. There may be a
lag-time as well for these processes, as seen for sulfide oxidation in aerated conditions.
Native sediments may, therefore, also be included in the kinetic cell tests to make sure
that the specific microbes are included.
If microbial processes are significant to the metal leaching rates, it is important that the
tests are run long enough to be able to evaluate what mineralogical and geochemical
processes are taking place within the tailings material. It is also necessary to evaluate if
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the leaching rates observed are in a setting similar to the expected setting in the tailings
deposition area.
•
•
9.2.2.
There may be mineral precipitation taking place in the tests that is not likely to
take place in the natural setting because of buildup of element concentrations in
the leach solution that would be removed by high water current.
The flow near bottom in the experiments may be higher than in the natural
setting and, therefore, mineral saturation is not reached in the experiments that
may take place in the natural environment, a common issue for kinetic tests run
under aerated conditions as well.
Leaching Evaluation
The potential impact on water (surface water, groundwater, seawater) is a key aspect in
the waste characterization evaluation. The concentrations of different elements in the
waste material (tailings and waste rocks) are controlled by the water in contact with the
waste. The concentration in the water can be equilibrium based (if water flow is low
relative to the rate of solid solution exchange); or reaction rate based, by weathering and
diffusion (reacting elements to the surface of the minerals e.g. oxygen), and products
transported away from the reacting surface. In many cases, these reaction rate processes
are biologically mediated, especially for sulfide oxidation. Many factors control the
resulting concentrations in water that come in contact with the waste, such as pH, Eh,
EC, L/S, minerals, and sorptive phases.
Only a few leaching tests have been designed specifically for waste from the extractive
industry, and most have been designed for specific purposes. All tests have to be used
cautiously, since they are designed for specific purposes, and not necessarily for the
required purpose. All test results have to be used carefully since leaching of the material
is mineralogically controlled mineral precipitation and dissolution, together with the
physiochemical conditions both in the laboratory and in the field. There is often a large
difference between the laboratory-controlled condition and what is taking place in the
natural setting.
Leaching addresses the release of substances by dissolution from the surface of particles.
These substances may be dissolution of primary waste minerals or secondary minerals
formed after short term/long term weathering. When evaluating the water quality, it is
the dissolved elements that are of concern. Factors controlling solubility under realistic
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exposure conditions are: mineral precipitation/dissolution, sorption on iron-oxide
phases, binding to clay surfaces, ionic strength of the solution, and cation exchange.
Dissolution of mineral phases and ingestion by bottom fauna and fish can also be of
concern. This information is not obtained through the normal leaching methods
described for the waste characterization. Bioavailability tests may be needed for this
purpose.
The short-term leach tests are most useful for older mine waste that has been exposed to
on-shore weathering or mineralisation and digenesis in a marine environment, for some
time (months to years) and are in a quasi-stable leaching mode. Test results can then be
used to evaluate leachability during the operational phase (short to medium term); e.g. to
assess what will be released in the water phase during the next rainfall on land. Shortterm leach tests may also be used to evaluate the immediate leaching potential when
depositing the tailings in seawater, but the result cannot be used to evaluate the longterm leaching after deposition.
When evaluating short-term storage of new waste material, or when the release rate is
controlled by equilibrium reactions of sorption, dissolution/precipitation etc., the shortterm leach tests can be useful.
Results from leaching tests can be used as input to geochemical modelling programmes,
as a calibration of parameters used in geochemical modelling. Calibration in
geochemical modelling can be done through comparing modelling results with leach test
results. If leach test results are used for calibration, geochemical modelling of the
leaching tests data should be adjusted at least for the water: rock ratio and the grain
size/surface area used in the modelling.
Kinetic testing of waste material in saltwater generates difficulties in the interpretation
and in the quality of the data. Seawater has high concentrations of chloride, sulfate and
bicarbonate-carbonate. Chloride may complex with some of the positively charged
elements (Cu, Ag, Zn, Cd) increasing the solubility of minerals that otherwise would
precipitate e.g. tenorite (copper oxide), and other copper minerals. Also the high ionic
strength may result in an increased dissolution relative to dissolution in fresh water. On
the other hand, sulfate and carbonate in solution results in the formation of secondary
minerals like azurite, malachite, and cerrusite. These minerals may, therefore, reduce
the availability of elements of concern. The leach solution needs to reflect this by either
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using seawater from the location, or design seawater with the components that affects
the solubility of these elements. To understand the result, it is often necessary to run
geochemical modeling programs to specifically evaluate saturation index of easily
soluble or precipitating minerals.
The bottom seawater is usually oxygenated; and there is a water current at the bottom. It
is, therefore, essential to obtain information about the bottom water oxygen level to
reflect this in the reaction rate/leaching tests.
Leaching of tailings at the bottom of the sea is very different than for tailings (and waste
rocks) deposited on shore, where water and air can freely flow through and more easily
generate A/NRD. Tailings deposited in a lake or a tailings pond with a water table
above the surface of the tailings, have a very slow through-flow. Tailings deposited in
the sea would have little or no water flow-through, resulting in mineral reactions
occurring only near the surface depending on colonization and bio-turbation.
9.2.3.
Marine Eco-toxicology
Marine eco-toxicity tests may be a natural step after leach tests have been performed.
The concentrations of compounds from the applicable leach tests should be reflected in
the eco-toxicity tests (short term and long term). The type of test(s) may vary with the
results of the leach tests.
•
Compounds used in the processing may decompose rapidly and, thereby, rapidly
reduce in concentration. In those settings, acute toxicity may be the most
applicable.
•
Compounds used in the processing may slowly leach, and therefore, the
concentration used in the tests needs to reflect this.
•
Minerals may, with time, weather and release elements. The release may
increase with time or reduce with time and the tests needs to reflect this.
The connection between the different eco-toxicity test types, leach tests, and the level of
marine life forms are displayed in Figure 8. The eco-toxicity tests are commonly
performed on water-soluble compounds; however, the bottom sediments may, through
the digestive system of several species at different levels, enter the food chain. EcoKREC-Norsk Bergindustri
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toxicity tests should also be set up to reflect this, depending upon the material that is
evaluated for sub-sea deposition.
Figure 8. Display of the connections between the level of organisms, eco-toxicity tests and leach tests.
In the framework of CEN/TC292 (Waste), standardization work was initiated to validate
methods to characterize the eco-toxicological properties of waste. While some choose
methods predominantly using chemical analyses, others are more in favor of direct ecotoxicological measurements.
Observed toxicity may be a final result of a number of processes occurring during all
preparation steps, from sampling to the preparation of a concentration series. Critical
aspects can be found within the selection of the leaching conditions (for example pH and
solid/liquid ratio), and the choice between batch procedures versus percolation tests.
Within the EN 14735 (standard for preparation of material for eco-toxicity testing),
several choices have already been made concerning these aspects. In order to understand
the results of the eco-toxicity tests, the variation of test conditions need to be such that
speciation models can be used. This will increase the understanding of the toxicity
result, since toxicity often depends on the species available, not the total concentration
of a component. This type of speciation modeling may need to include, organic and
inorganic components, sorption processes, and solid phases (e.g. LeachXS, Geochemical
Work Bench, PhreeqC),
Solid –liquid separation has a major influence on DOC and colloid levels in solution.
The decision to filter or centrifuge the eluate or to abstain from liquid-solid separation
cannot be taken lightly, as these parameters have a major influence on the outcome of an
eco-toxicity test. For many decisions on waste use, treatment, and disposal, a low liquid
to solid ratio is of importance. Inferring effects at a low L/S from results at L/S=10 is
impossible. During tailings deposition, the fine-grained material will shear off and
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remain suspended for a longer time period indicating that a high L/S ratio would be the
most applicable for tailings deposition.
When chemicals are accumulated into the bottom sediments, the direct bio-availability
for pelagic organisms is reduced. The exposure to benthic organisms, however, is
increased. The bioaccumulation into the pelagic organisms is, therefore, dependent
upon feeding of the benthic organisms (EPA821). However, suspended fine-grained
material from the deposition process may be indigested by pelagic organisms. The
bioaccumulation is more complex with respect to human health. There will be an
ecologic impact on the communities.
Performing bioaccumulation tests based on sediment-associated contaminants is very
difficult. Taking natural sediments into the laboratory for controlled bioaccumulation
can easily disturb the complex nature of the sediments and, thereby, stress the benthic
organisms and change the microenvironments (redox and temperature conditions). This
would, thereby, make it difficult to interpret the result.
9.3. Uncertainty – Limitations
Uncertainty and limitations are very important issues in a sub-sea tailings deposition
evaluation. Much of what is discussed in this section has already been mentioned in
Chapter 7. However, due to their importance, the information is repeated here.
Assessing current physical and geochemical properties of waste material is relatively
straight forward; however predicting how the waste material will develop in the future
under the influence of weathering is complex. When adding different closure scenarios,
this becomes an even more complex task. The prediction of future behaviour of the
waste material is no exact science and will include a level of uncertainty. When the
result of the predictions is a key factor in a choice of a waste management option, a high
level of accuracy or safety factors will be needed. In clear-cut cases, however, whether
clearly benign or clearly problematic material, there may be no need for high precision.
Data quality and uncertainty can be understood in several ways. It can be the uncertainty
related to the representativeness of the samples that are collected, the uncertainty of a
specific test result (e.g. leaching and analysis), the variability in materials taken at
different times or locations; and it can relate to the uncertainty in the prediction of
release behaviour under field conditions.
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In case of sea/fjord evaluation uncertainties can include;
•
•
•
•
Variations throughout the years, when growth potential is variable;
Migrating fish;
Bottom flora fauna is highly variable between different locations; and
Salinity is dependent upon variable currents and freshwater input.
These uncertainties are not easy to measure or calculate, but it is important to get a sense
of the magnitude of uncertainty when trying to draw conclusions based on test results
and predictions.
Predictive modeling will, in many cases, be part of the evaluation. The inherent
uncertainty in model predictions should be recognized and clearly stated. Considerable
uncertainty is inherent in determining many of the parameters that are required for
modeling sea currents, sediment transport, and leaching rates from mineral weathering.
The uncertainties of modeling outputs may result from:
•
•
•
•
Incomplete characterization;
Incomplete knowledge of the;
o Conditions;
o Leaching rates;
o Thermodynamic data in general or for the specific conditions;
Lack of data on flocculation; and/or
Insufficient knowledge of the hydrological conditions at the site.
The Overall guidance document for waste characterization (CEN/TR16367, 2012)
states: “Methods used to evaluate or account for model uncertainty include Monte Carlo
analysis, stochastic methods, and an evaluation of a range of model parameters to
develop a range of deterministic outcomes. Rather than parameters being described by a
single value as required in the model, parameters are better described with a probability
distribution (i.e., a mean value with standard deviation, etc.).”
The model uncertainties should also recognize and describe the difficulties of up-scaling
test results from e.g. leaching tests and flocculation tests. Taking into account the
uncertainty in model parameters will still not address uncertainties in the conceptual
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model. Field verification is commonly needed to reduce uncertainties in the conceptual
model, as omission of an important release controlling process may lead to a faulty
prediction. In this context, the interrelations between laboratories test results and field
tests can provide a greater level of understanding, thus increasing the reliability of data
developed to support management decisions.
Quality Assurance /Quality Control (QA/QC) is also important, and deals primarily with
measurable quantities, such as physical parameters, chemical analysis and leaching test
results, and helping to create a process where sampling or laboratory analysis are
performed consistently. EN17025 is a European standard that specifies good laboratory
practice. Issues of sampling quality are described in CEN/TR 15363 specific for mines
waste. There are no specific guidelines dealing with QA/QC in monitoring sea currents.
10. OPERATION, MONITORING AND CLOSURE
The characterization of the waste and the area of deposition are essential in evaluating
the impact. The level of impact needs to be evaluated based on different types of
discharge; electing a method for discharge that gives the minimal impact to human
health and the environment. When the system for minimal or accepted level of impact
has been decided, the design of the monitoring program should include:
•
•
•
•
•
•
•
Discharge parameters (salinity, L:S ratio, air content);
Turbidity measurements in the surrounding sea;
Soft-bottom flora –fauna monitoring in a distant from discharge point at border
of no-influence;
Fish amount and quality;
Water quality;
Interstitial water from the tailings; and
Redox potential at the bottom and within the tailings sediments.
10.1.1. Discharge System
The discharge system includes the transport from the processing plant to the discharge
point in the sea. The issues to deal with in the discharge systems are the following
parameters:
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•
•
•
•
•
Pipeline;
Flocculation;
Salt water addition;
Temperature; and
Air bubble trap.
The parameters are issues that deal with reduction of material spreading. If there are air
bubbles in the tailings then discharging the tailings will result in a greater mixing and
possible upwelling. If the tailings are warm, and have low salinity, the water within the
tailings will have buoyancy and rise, increasing the mixing and spread. The same effect
may take place if fresh water is within the tailings. The fresh water can be partly
replaced with cold saltwater, and thereby, reduce the effect of buoyancy, and reduce the
effect of mixing.
The characterization data of the seawater at a deposition site is part of the input data to
be used in evaluating how much seawater is required, and how reduction in temperature
is necessary to get an acceptable density to reduce particle spreading.
Experiments on flocculation using different flocculation agents will also give input to
such modeling. Salt water is assumed to act as a flocculation agent due to the high
salinity.
If salt-water addition is not efficient enough as a flocculation agent, then other chemicals
are needed, causing other effects that will need evaluating based on the chemical used,
e.g. Magnafloc, which can be carcinogenic at certain concentrations .
10.1.2. Field verification
Most of the analysis and methods described in this document are based on relatively
short-term analysis of small samples. Kinetic tests, that may last for a year or more, are
considered short term when taking into account that the analysis/methods are in some
cases used to evaluate long-term effects over hundreds to thousands of years.
Long-term onsite field scale tests can be very useful if there is a potential for
mineralization or digenesis affecting the chemical and geotechnical stability of the
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waste. During the exploration phase, there is usually not enough material available for
such tests; however, when a project moves into the feasibility phase and excavation for
full production has begun, material will become much more available. Field scale tests
can and should then be initiated. These tests can be in place throughout the life of the
mine, and provide feedback to update waste handling and closure plans. Information on
water chemistry, turbidity, flora-fauna, fish impact etc. provide valuable on going
information on the stability of the waste and deposition process. These onsite long-term
field-testing would be a natural part of the operational environmental and management
plan. The monitoring can be based on indicator species, together with a well-developed
accepted criteria system.
The long-term stability is both a physical and geochemical issue. Both long-term
physical and geochemical stability needs to be evaluated using the receiving
environmental setting, design criteria, and leach tests, but primarily from a theoretical
and analogue site evaluation with the input of the above listed issues.
The geochemical stability is partly evaluated though the long-term leach tests.
However, these tests will seldom be run long enough to observe silicate mineral
alteration and/or hard pan formation. It is, therefore, necessary to evaluate the
geochemical stability using geochemical modeling tools that can incorporate reaction
rates. Input parameters for such geochemical modeling will include, but not necessary be
limited to:
•
•
•
•
•
•
Initial solution geochemistry,
Initial mineralogy,
Potential secondary mineral precipitation or alteration of primary minerals,
Reaction rates of initial and secondary minerals,
Seawater chemistry (salinity, alkalinity, oxygen concentration, element
concentration etc.)
Infiltration rate of seawater into the tailings material and transport mechanism
out of the tailings.
Geochemical programs that potentially can be used for this evaluation include e.g.
PhreeqC, Geochemical Work Bench (Bethke, 2010), FlowTran (Lichtner, 2001), and
LeachEX. Cuipers et al, 2005 gives an overview of potential geochemical modeling
programs to use. Most of these programs do not include the high salinity issue of
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seawater in the geochemical data base and adjustments to the programs may have to be
done.
There are few physical stability analyses that can be performed prior to tailings
deposition. Ore processing tests will result in data on grain size. If sufficient material is
available, stability tests can be performed in salt-water tanks. These tests may be
performed alongside the testing for useful flocculants. These types of analyses can then
be used to make criteria for a tailings deposition design. However, in many cases, only
monitoring will tell if the design fulfils the physical stability criteria.
10.1.3. Monitoring
Defining monitoring plans is a natural step in evaluating SSTD. The monitoring plan
for SSTD should be designed to evaluate:
.
• Sea-fjord current and mixing;
• Salinity of seawater and possible change in layering over time;
• Geochemistry of the discharging material;
• Solid transport above the tailings deposition area and away from this area;
• Seawater chemistry with a focus on elements that potentially can leach from the
tailings – tailings water;
• Amount of material deposited;
• Fish habitat changes;
• Flora – fauna changes relative to reference monitoring stations; and
• Water and solids discharge from rivers to the fjord potentially used for tailings
deposition.
These issues should be monitored on a regular basis during and after closure of the
tailings deposition.
10.1.4. Emergency Response Plans
There is always the potential for failures in a production system, which is also applicable
to a tailings deposition system. A failure in a pipe, especially the tailings pipeline, could
have a catastrophic short-term effect, and potentially long-term effect, on the marine
environment. It is, therefore, essential to perform a risk assessment for potential
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failures. From there, a response systems should be developed that can effectively be
implemented to reduce potential affects due to failures. The emergency response plans
may include:
•
•
•
•
Failure in the pipe line above the sea;
Failure in the pipe line below sea level;
Failure in the mixing tank; and
Failure in the air removal system,
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11. DOCUMENTATION AND REPORTING
Proper documentation and reporting is important in building trust between involved
parties (operator, regulators, general public, NGOs) and for the credibility and
traceability of test results. The documentation of the waste characterization and the
characterization of the receiving environment (on-shore and off-shore) should cover all
steps, from describing the rationale behind performing the characterization to the
evaluation and conclusions.
The structure of the documentation of the results and interpretations should follow good
reporting practices and any applicable legal requirements. A recommended structure,
including the documentation of relevant supporting information, is given below;
1.
2.
3.
4.
5.
6.
7.
8.
9.
Introduction
Background information of the (future) operation
• Type and description of extraction method,
• Nature of the intended product
Geology of the site
• Nature of surrounding rocks
• Chemistry and mineralogy, mineralization typology, including physical
properties, size and geometry of deposit,
• Weathering of the deposit
Objective(s) and approach(s) to the characterization
Sampling procedures
Analytical procedures
Baseline data for the site of disposal
Presentation of the results of the characterization
• Waste characteristics
Field data
Analytical data
• Deposition location characteristics
Field data
Analytical data
Evaluation and discussion of the result
• Waste types and its intended handling
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•
10.
11.
12.
Mineralogical and geochemical description of the waste including
leaches tests/kinetic tests etc.
• Volume/mass of different types of waste and when waste is produced
• Description of potential geotechnical and geochemical impact
• Sub-sea deposition system
Pipeline
Spreading/settling
Chemical effect of additives
Conclusions and Recommendations for follow up work
References to sited documents
Attachment
• Laboratory reports
• Field reports (field analysis and observations)
• Sampling plan
Copies of all reports should be stored at the operator’s office for possible future
auditing.
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12. REFERENCES
ASTM 2001:
Bakke, S.M. and Jensen, T., 2004: Titania AS. Miljøundersøkelser i Jøssingfjorden
2003. Report 2004-0083 by Det Norske Veritas.
Bref/BAT, 2004: Reference Document on Best Available Techniques for Management
of Tailings and Waste-Rock in Mining Activities, Sevilla, Spain, July 2004, Internet:
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13. WORDS
TAILINGS means the waste solids or slurries that remain after the treatment of
minerals by separation processes (e.g. crushing, grinding, size-sorting, flotation and
other physico chemical techniques) to remove the valuable material/minerals/metals
(from the Mining Waste directive)
WASTE FACILITY means any area designated for the accumulation or deposit of
extractive waste, whether in a solid or liquid state or in solution or suspension, (from
the Mining Waste Directive)
HEAVILY MODIFIED WATER BODY means a body of water, which as a result of
physical alterations by human activity is substantially changed in character (from the
Water Framework Directive)
GOOD ECOLOGICAL POTENTIAL means the status of a heavily modified water
body or an artificial body of water, so classified in accordance with relevant provisions
of Annex V in the water framework Directive.
ECOLOGICAL STATE is an expression of the quality of the structure and functioning
of aquatic ecosystem associated with surface waters, classified in accordance with
relevant provisions of Annex V in the water framework Directive.
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