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Dams Safety NSW

Guideline

Mining near declared dams

Published by NSW Department of Planning, Industry and Environment

Dams Safety NSW

Guideline - Mining near declared dams

First published February 2020

More information

Dams Safety NSW

https://www.damsafety.nsw.gov.au

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Disclaimer: The information contained in this publication is based on knowledge and understanding at the time of writing (February 2020) and may not be accurate, current or complete. The State of New South Wales (including the NSW Department of Planning, Industry and Environment), the author and the publisher take no responsibility, and will accept no liability, for the accuracy, currency, reliability or correctness of any information included in the document (including material provided by third parties). Readers should make their own inquiries and rely on their own advice when making decisions related to material contained in this publication.

Dams Safety NSW Guideline – Mining near declared dams

NSW Department of Planning, Industry and Environment | Dams Safety NSW i

Table 1. Document change history

Version Approved date Approved by Notes

1 February 2020

Contents 1. Introduction and purpose of this document ................................................................................ 3

2. Declared dams ........................................................................................................................... 3

3. Dams Safety NSW may direct actions to ensure safety of a declared dam............................... 3

4. Notification areas ....................................................................................................................... 4

4.1. Review of notification areas ................................................................................................ 4

5. General ...................................................................................................................................... 4

5.1. Mining near a prescribed dam before November 2019 – under the Mining Act 1992 ........ 4

5.2. Mining near a declared dam after November 2019 ............................................................ 5

5.2.1. Continuation of existing lease conditions .................................................................... 5

5.2.2. Continuation of notification and consultation requirements in relation to dams safety in the Mining Act 1992 ............................................................................................................... 5

5.2.3. Consents applied for after 1 November 2019 – under the Dams Safety Act 2015 (the Act). 5

6. Mining in notification areas – consideration by Dams Safety NSW ........................................... 5

6.1. Applicant information guidance .......................................................................................... 6

6.2. Dams Safety NSW determination and advice to the consent authority .............................. 7

6.3. Modifications to consents ................................................................................................... 7

Appendix 1 Risk analysis by the applicant ........................................................................................ 8

Risk assessment ........................................................................................................................... 8

Introduction ................................................................................................................................ 8

Risk criteria and limits ................................................................................................................ 8

Hazard Identification .................................................................................................................. 8

Consequences ........................................................................................................................... 9

Geological/hydro-geological analysis ............................................................................................ 9

Ground movement predictions .................................................................................................... 10

Likelihood ................................................................................................................................. 10

Estimate the risk ...................................................................................................................... 11

Evaluate the risks .................................................................................................................... 11


NSW Department of Planning, Industry and Environment | Dams Safety NSW ii

Treat the risks .......................................................................................................................... 11

Management and monitoring ....................................................................................................... 11

Contingency plan ......................................................................................................................... 11

Closure plan ................................................................................................................................ 11

Repair of mining damage to declared dams - agreement with the dam owner ........................... 12

Appendix 2 Monitoring and management ....................................................................................... 13

Introduction .................................................................................................................................. 13

Approach ..................................................................................................................................... 13

Monitoring .................................................................................................................................... 13

Monitoring management plan .................................................................................................. 13

Visual inspection of workings ................................................................................................... 14

Water monitoring ..................................................................................................................... 14

Geological mapping - surface & underground ......................................................................... 14

Surface geological mapping .................................................................................................... 15

Underground geological mapping ............................................................................................ 15

Surface subsidence and strain surveys ................................................................................... 16

Vibration monitoring ................................................................................................................. 17

Drilling ahead of the workings .................................................................................................. 17

Water fingerprinting ................................................................................................................. 18

Additional monitoring ............................................................................................................... 18

Appendix 3 Contingency plans ....................................................................................................... 19

General ........................................................................................................................................ 19

Possible triggers (action indicators) ............................................................................................ 19

Triggers for inflow into mine workings ......................................................................................... 20

Contingency actions .................................................................................................................... 20


NSW Department of Planning, Industry and Environment | Dams Safety NSW 3

1. Introduction and purpose of this document Dams Safety NSW is an independent regulator established under the Dams Safety Act 2015 (the Act). Dams Safety NSW has responsibility for ensuring that dam owners achieve compliance with the Act and the Dams Safety Regulation 2019 (the regulation).

Dams Safety NSW ‘declares’ those dams which have a potential to threaten downstream life, or cause major property, environmental, or public welfare damage. Owners of declared dams must comply with the requirements of the Act and regulation.

Dams Safety NSW publishes guidelines to help declared dam owners comply with the requirements of the legislation. As they are intended to be an aid to industry compliance, the guidelines themselves do not contain compulsory requirements and compliance with the dam safety legislation may be achieved by adopting other methods if they fit better with a declared dam owner’s systems.

The Act also includes requirements for consent authorities to consult with Dams Safety NSW before granting development consent for the carrying out of any mining operations under the Mining Act 1992 in notification areas.

This guideline describes how the Act provisions for mining near a declared dam are administered and suggests methods to reduce risks to declared dams from mining activities. It should assist persons who are mining (or who plan to mine) in the vicinity of declared dams.

2. Declared dams Dams Safety NSW declares those dams that meet the criteria listed in Section 4 of the Regulation:

a dam having a dam wall that is more than 15 metres high an existing or proposed dam that Dams Safety NSW is reasonably satisfied would

endanger a life or result in a major or catastrophic level of severity of damage or loss were there to be a failure of the dam.

Dams Safety NSW publishes a list of declared dams on the website: https://www.damsafety.nsw.gov.au/dams-in-nsw/.

Dams that were ‘prescribed’ under the old Dams Safety Act 1978 became declared dams upon commencement of the new Act.

3. Dams Safety NSW may direct actions to ensure safety of a declared dam

Section 19 (2) of the Act allows Dams Safety NSW to direct a person to do such things as may be reasonably necessary to ensure the safety of a declared dam.

Dams Safety NSW may do this if it is of the opinion that anything done or proposed to be done by a person to or in relation to a declared dam (including the water or other material impounded by the dam) or in the vicinity of a declared dam may endanger the safety of the dam.

To ensure the safety of declared dams, regardless of the consent process described in this guideline, Dams Safety NSW may request specific information regarding proposed mining activity near a declared dam. Dams Safety NSW may also direct that a mine owner carry out particular activities to mitigate the risks to the declared dam. If necessary these may include activities that are described in the appendices of this guideline.



4. Notification areas Dams Safety NSW may declare a notification area surrounding, or in the vicinity of, a declared dam within which mining may have an effect on the dam.

The notification area is defined by straight lines joining a series of coordinates and is also identified on a map. The notification area is set out in an order published in the NSW State Government Gazette.

Not all declared dams have notification areas, only those dams which Dams Safety NSW considers may be affected by mining. Declared dams with notification areas defined are listed on the Dams Safety NSW website https://www.damsafety.nsw.gov.au/mining/.

4.1. Review of notification areas Dams Safety NSW may review and modify a declared dam notification area. A review may result from the receipt of additional information about risks to a declared dam from mining operations, or from a Dams Safety NSW policy determination on the extent of notification areas required for declared dams.

Dams Safety NSW will also consider review requests from a declared dam owner. Requests may be sent via email to: [email protected].

5. General

5.1. Mining near a prescribed dam before November 2019 – under the Mining Act 1992

Prior to commencement of the Act in November 2019, the requirements for mining in notification areas were covered by the Mining Act 1992, which stated that the Dams Safety Committee may recommend to the Minister that a mining lease within a notification area be amended, by the variation of the conditions of the lease or by the inclusion of additional conditions in the lease, so as to prevent or mitigate damage to a prescribed dam.

To administer these requirements the Dam Safety Committee recommended the inclusion of standard conditions in mining leases. These standard conditions required a person to notify the Minister and the Dams Safety Committee if proposing to mine within a notification area.

Subsequently, the Dams Safety Committee may have recommended to the Minister that specific conditions for mining within the notification area be included in the lease. The lease holder was required to comply with the conditions of the lease.

Upon commencement of the new Dams Safety Act 2015 in November 2019, the requirements for mining within notification areas were omitted from the Mining Act 1992.



5.2. Mining near a declared dam after November 2019

5.2.1. Continuation of existing lease conditions Any existing lease conditions that relate to mining in notification areas continue to apply. Any reference to the Dams Safety Committee in those existing lease conditions will be taken to refer to Dams Safety NSW and the conditions remain in force.

For example:

a lease condition that requires notification to the Minister of any plans to mine in a notification area

a specific lease condition that requires regular reporting of mining parameters to the Dams Safety Committee - the lease holder must continue to notify and report in accordance with the lease conditions to Dams Safety NSW.

5.2.2. Continuation of notification and consultation requirements in relation to dams safety in the Mining Act 1992

The Mining Act 1992 (Schedule 6, Part 26 section 180) states:

(1) The amendments made to this Act by the Dams Safety Act 2015 do not apply in relation to an application for a mining lease that:

(a) was made but not granted before the commencement of this clause, or (b) is subsequently made after that commencement,

and accordingly this Act continues to apply in relation to any such application as if it had not been so amended.

This means that the provisions of the previous version of the Mining Act apply for mining lease applications under a consent that was in operation prior to 1 November 2019.

Dams Safety NSW may recommend to the Minister that a mining lease for a mine that comes under this provision be amended by variation of the conditions of the lease or by the inclusion of additional conditions in the lease, so as to prevent damage to a declared dam.

5.2.3. Consents applied for after 1 November 2019 – under the Dams Safety Act 2015 (the Act).

For applications for a development consent in a notification area after 1 November 2019, a consent authority must:

refer the application for development consent to Dams Safety NSW, and take into consideration any matters that are raised by Dams Safety NSW in relation to

the application. Dams Safety NSW is primarily concerned with maintaining the safety of the dam and will be raising matters with the consent authority if mining in a notification area adds risks to the dam that should be addressed by the consent authority or consent applicant.

6. Mining in notification areas – consideration by Dams Safety NSW

In accordance with the Act, the consent authority will refer an application for development consent that includes mining within a notification area (the application) to Dams Safety NSW.



Dams Safety will normally have 28 calendar days to assess the application and raise any dam safety matters with the consent authority. Dams Safety NSW may request a time extension from the consent authority if needed.

The aim is to determine that mining operations will not introduce unacceptable dam safety risks, based on the dam’s design and construction and its consequence category.

6.1. Applicant information guidance The consent authority is responsible for making the decision on a development application, but must take into consideration any matters raised by Dams Safety NSW on the application to mine within a notification area.

Dams Safety NSW will determine if there are any dam safety risks that need to be raised as matters to be considered by the consent authority.

To enable this, the applicant for the development consent (the applicant) should provide sufficient information on hazards and risks to the dam, resulting from the proposed mining activity, for Dams Safety NSW to review.

The applicant should be able to demonstrate (using a rigorous scientific approach) that the mining proposal will not introduce unacceptable risks to the dam structure.

The information required for Dams Safety NSW to be able to objectively raise matters with the consent authority depends on the extent and type of the proposed mining and the structures affected. Appendix 1 describes the typical analysis that would be expected when proposing to mine in a notification area. The following is the typical information resulting from that analysis and the background information that would be needed to enable Dams Safety NSW to raise any dam safety matters with the consent authority:

plans showing the proposed mining area(s) in relation to previous mining operations, the 35° Angle of Draw plus half depth of cover from the Full Supply Level of the dam, and the dimensions of all panels, pillars, roadways and cut throughs

detailed plans and cross-sections showing depth of proposed workings, surface and underground geological information such as lineaments, dykes, faults, prominent joints and jointing patterns and ground water flows. Fault and dyke information should be provided. Joint information should include orientation, continuity, spacing and aperture

predictions of changes to the hydro-geological regime in the area of mining and inflows to mine workings

records of surface subsidence and horizontal strain measurements resulting from previous mining operations by the mine in areas where conditions are relevant to the proposed mining within the Notification Area

predictions of surface subsidence and horizontal strains for the proposed mining operations, including a description of the methods adopted for predicting subsidence and strains

if available, information relating to in-situ stress measurements, estimates or interpretations. This should include, if available, data on stress magnitudes and directions

for open-cut operations, a prediction of likely blast vibrations at the dam and comments from a dams engineer on the dam safety impacts of such vibrations.

risk analysis report details of any proposed monitoring programs and details of contingency plans and Trigger Action Response Plans (TARPs) (if required)



6.2. Dams Safety NSW determination and advice to the consent authority

Dams Safety NSW will raise any dam safety matters with the consent authority after reviewing the application information.

6.3. Modifications to consents Modifications to an existing development consent that involves mining in a notification area are treated in the same way as the initial application, in that the consent authority must refer the application for modification of the development consent to Dams Safety NSW.



Appendix 1 Risk analysis by the applicant The material in this appendix has been provided to guide applicants when applying for development consent for carrying out of mining operations in a notification area.

The appendix includes guidance on the risk analysis and specific associated topics that should be addressed by the applicant. An applicant should comprehensively analyse the risks associated with mining in a notification area and produce a report which contains the analysis and conclusions associated with the analysis.

Risk assessment A comprehensive risk assessment should be undertaken for any mining proposal in a notification area. Applicants should carry out a risk assessment that follows the process elements of ISO 31000:2018 – Risk Management – Guidelines. The following has been included for guidance. Other risk assessment methods may be used, such as the International Council on Mining and Metals critical control approach or a ‘bow tie’ risk approach.

Introduction The generic risk assessment process can be summarised in the following steps:

1. Determine risk criteria and risk limits.

2. Identify mining hazards that impact on the dam.

3. Determine the consequences.

4. Determine the likelihood.

5. Estimate the risk.

6. Evaluate the risks, are they tolerable?

7. Treat the risks to reduce them below tolerable limits.

These steps are discussed below in relation to assessing the impact of mining on a dam. Each case will have unique aspects which need to be considered. At each stage it is critical to have experienced persons involved in discussions, as well as the stakeholders. ANCOLD1 guidelines include a list of roles that should be considered for the assessment.

Risk criteria and limits Setting the criteria and limits requires a discussion with stakeholders, including the declared dam owner.

Hazard Identification A comprehensive identification of the hazards to the dam associated with mining should be undertaken.

Mining hazards that may impact a dam include:

large scale subsidence (see the section on ‘ground movements’) vibration due to blasting creation of open cut voids and potential highwall instability changes in permeability due to vertical and horizontal fracturing and collapse of strata, or

opening of pre-existing fractures opening of a drainage point or conduit changes to the stress regime, leading to changes in permeability

1 ANCOLD: Australian Committee on Large Dams



changes to groundwater levels. The section on ‘Geological/hydro-geological analysis’ includes the expected analysis of hazards associated with the geological and hydrological features of the declared dam and its surrounds.

Consequences It is likely that damage to a dam or water supply would have consequences on a mining company’s operation. However, the risk assessment should focus on the consequences to the dam:

subsidence or settlement, which may reduce freeboard, leading to a reduction in flood capacity and possibly overtopping

changes in slope, causing problems with drains and hydraulic structures. In extreme case instability in the upstream or downstream face due to a steepening of slope

differential movement between the embankment, abutments, spillway, conduits, and other components, possibly leading to physical damage of components, increasing the likelihood of leakage and piping failure, or a failure of particular components (e.g. blocked conduits, burst conduits)

differential movement on geological structures present in the foundation strain concentration, in particular over long structures, leading to cracking and leakage,

and potentially piping dynamic loading, which may result in settlement, liquefaction of foundations or (for

tailings dams) of the storage changes in groundwater, leading to ground movements or changing the groundwater

pressure regime at the dam wall.

Evaluations of the severity of the consequences should take into account the consequence of dam failure in a similar way to the analysis required for assessment of a dam’s consequence category.

Geological/hydro-geological analysis As part of the hazard identification and risk assessment process, an applicant should analyse the influence of the geology of the dam’s surrounds on the potential for mining impacts on the dam. Where the mining may impact a major water supply storage dam, geology and hydrogeology play a critical role and should be given a suitable priority.

Geology can influence:

the stability of the workings; the development of the goaf and other sub-surface impacts; subsidence and other surface ground movements; and groundwater flow paths.

Structural geological features may have a strong influence on the performance of the mining operation and hydro-geological regime, and consequently should be a major focus of the investigations.

The most credible models will be based on inspections of all the available sources: surface, underground, and boreholes. In particular, the combination of surface and underground mapping may permit an assessment of the likelihood that structural features are continuous from the surface to the workings.

The highest level of detail would be required for any higher risk applications. The analysis should integrate all available relevant data, such as:

general surface mapping to determine contacts between geological units, overall structure, domains, structural fabric, etc.

lineament analyses



satellite and airborne geophysical data detailed surface mapping in the vicinity of significant structural geological features or

areas of uncertainty data from boreholes, including lithology, structure, piezometric data, and the results from

permeability testing data from existing workings nearby in-situ stress measurements.

This data will provide important inputs to the hydro-geological modelling to predict mining effects on the groundwater regime and the source and magnitude of potential inflows to the mining operation.

Ground movement predictions Predictions of surface ground movements are critical to analysing risks to a dam.

The prediction of ground movements should consider:

large scale movements: These usually occur over the mine workings and in the immediate vicinity of the workings, perhaps defined by an angle of draw to 20 mm of vertical movement (which is the common criterion in NSW). Angles of draw vary significantly, but an average of 35 degrees from vertical at the underground edge of an extraction is often adopted in NSW. In this realm “normal” or “systematic” mining induced subsidence and strain occur

far-field movements: These are predominantly horizontal movements which increasingly dominate the total ground movements further away from the “limit” of the large scale movements. They have been recorded up to 1.5 km from mine workings

response of the site: ground movements (large scale and far-field) may be modified locally by the characteristics of the site. Valleys in particular are known to sometimes respond to ground movements in a different manner to relatively flat ground. Geological features can also modify the locally recorded movements

response of the structure: Dams in particular tend to be long structures, and may therefore be more susceptible to certain ground movements. The nature of the dam will also contribute to its response. For example, rigid construction (e.g. concrete) will be more susceptible to concentration of strain at discrete points than flexible construction, such as earth or rockfill. For applications relating to open cut mining, blasting predictions should be determined for the maximum likely peak particle velocities and accelerations at critical points on the dam, together with the prediction of the impacts of these blasting effects.

Likelihood Determinations of likelihood should take into account:

the probability of sources of risk (e.g. ground movements due to subsidence, vibrations from blasting) being within predictions, and exceeding predictions

the probability that the workings may not perform as designed or that the geology is not as theorised (e.g. the probability of pillar failure, or the probability of encountering a major fault)

the ability of a dam structure to accommodate ground movements. Generous filter zones, conservative design, and flexible components should improve the capability of a dam to withstand ground movements, whereas brittle components such as a concrete core or face, limited or no filter zones, or poor overall design will lead to greater concern for the safety of the structure

the level of detail, or degree of uncertainty in the available data, models, analyses etc.



Estimate the risk An appropriate process for determining the resultant risk level should be adopted.

Evaluate the risks Risks may be assessed both quantitatively and qualitatively but quantified risks are preferred, where available, as they can be compared to the risk limits. Risks which exceed the limits need treatment to reduce the risks to the required limits.

Treat the risks Risks can be avoided, the likelihood can be reduced, or consequences reduced. For each treatment option the likelihood, consequence and risk should be re-estimated, and the acceptability of the risk re-evaluated.

As an example, it is unlikely that the risks associated with mining operations within 1500m of the dam structure would be sufficiently low for a major water supply dam (particularly a concrete dam).

Management and monitoring All mining activities in notification areas should have some form of monitoring. These should be implemented and procedures for monitoring integrated with a TARP. Refer to Appendix 2 for more guidance.

Contingency plan The nature of mining is such that unexpected conditions are not uncommon. Given the possibility of serious consequences occurring in the event of encountering these conditions, applicants should develop a contingency plan, consistent with the mine TARP, for mining in major water supply dam notification areas. Contingency plans are aimed at minimising damage to the dam in the event that a major connection from the workings to the storage develops. The plans should be reviewed regularly (typically, annually). See Appendix 3 for more details.

Closure plan The life of a typical major water supply dam is probably an order of magnitude greater than a typical mining operation. Mine workings remain for a very long time after mining has ceased and constitute an ongoing dam safety hazard.

Applicants should develop a plan for mine closure which takes into account:

the need for stabilisation or sealing of the workings in order to achieve acceptable levels of risk in the long-term

the likelihood that deterioration of the workings after completion will lead to additional mining impacts

the combined effect of any future mining together with that under current consideration.

Closure plans are particularly important where layouts are used which provide some support to the strata, (e.g. first workings or partial extraction layouts) as these have components which can deteriorate or fail over a long period. They are also important for applications that are close to the risk limit.

Applicants should consider all possible post-mining failure scenarios, determine that there are feasible technical solutions to these and that they have the capacity to implement a solution. It may be difficult to fully develop these plans at the outset, so it may be appropriate to plan to review the performance of the workings at the completion of mining in an area.



Repair of mining damage to declared dams - agreement with the dam owner In the event that the safety of a dam structure is compromised due to mining induced impacts Dams Safety NSW may decide that it is necessary to issue a direction under the Act to ensure the safety of the dam.

The Act allows Dams Safety NSW, if it is of the opinion that a declared dam is unsafe or is in danger of becoming unsafe, to direct the owner of the dam to do such things as may be reasonably necessary to ensure the safety of the dam.

The Act also allows Dams Safety NSW, if it is of the opinion that anything done or proposed to be done by a person to or in relation to a declared dam (including the water or other material impounded by the dam) or in the vicinity of a declared dam may endanger the safety of the dam, to direct the person to do such things as may be reasonably necessary to ensure the safety of the dam.

In an emergency quick action may be required. Matters such as the roles of the various parties, access rights in the event of an emergency, the responsibility for costs and the like should be discussed and agreed before an emergency occurs. The contingency plan and TARP should consider and work together with the declared dam owner’s emergency response plan.

A written agreement between the mining company and the dam owner should be established to clarify the above.



Appendix 2 Monitoring and management

Introduction Mining applicants should establish and implement a monitoring programme so that:

the package of controls to mitigate mining risks to the safety of the dam is complete predictions on which the risk analysis was based are verified areas of uncertain knowledge are clarified unexpected behaviour is recognised during mining which provides triggers for action or

additional monitoring

Approach Management and monitoring programs are generally aimed at controlling residual risks, ensuring good management of activities, and facilitating the interaction between the declared dam owner and the mining company. Many competing priorities present themselves to mine management. It is important that adequate resources be applied to the dam safety aspects and a management program can help ensure that this happens. In situations where there is an extensive monitoring program, the interface between the mining company and the dam owner needs to be well defined to ensure that the flow of information is handled efficiently by both parties.

Monitoring Ongoing monitoring is important in determining the impacts of mining including the need for baseline monitoring prior to extraction (preferably for at least two years), to provide a basis against which to assess mining impacts. Where there are a number of monitoring streams, it can be a challenge to keep a program on track. An effective management plan will assist in keeping track of what has to be done, who does it, where the resources come from etc.

Monitoring management plan The monitoring management plan (developed in conjunction with the declared dam owner) should include details of monitoring trigger levels and actions to be taken, including all roles and responsibilities.

The plan should specify at least:

what is required to be done what is required to be delivered and when who is responsible for each task.

Some more common components include:

inspection of workings; water monitoring; geological mapping; surface subsidence and strain surveys; vibration monitoring; drilling ahead of the workings; water fingerprinting and other monitoring conditions



Visual inspection of workings A record of any features encountered or events which occurred should be kept (e.g. if significant floor heave or pillar spalling occurs, or if a dyke or joint zone is encountered). For open cut mining it would include the location of the pit with respect to the dam, the levels in the pit, and areas of active mining. Face location records are also useful in determine how the mine is progressing with respect to the predicted locations of identified hazards.

Water monitoring The presence or rate of water flow into the workings can be a useful, readily measured indicator of the performance of the workings. Unexpected water inflows can provide a useful trigger for further investigation or increased surveillance in accordance with the TARP. There are two types of programs: routine and emergency. As a general guide, if the workings are unlikely to have an effect at the surface (e.g bord and pillar workings with a reasonable depth of cover and no significant geological structures) then only "emergency water monitoring" will apply. Otherwise both routine and emergency monitoring are required. A declared dam owner who also operates a mine in a notification area must report an incident to Dams Safety NSW that results in a significant amount of groundwater entering the mine (Section 19 (1) (h) of the Dams Safety Regulation 2019). Note that a code of practice is available for reference at: https://www.resourcesregulator.nsw.gov.au/__data/assets/pdf_file/0011/543935/NSW-code-of-practice-Inundation-and-inrush-hazard-management.pdf Regular measurement (typically daily or weekly) and reporting (typically monthly) of water entering and leaving an area of the mine is normally required. The detail required in these surveys varies depending on the importance of the storage, the type of workings, the history of water make in the seam to be extracted, and on the geological conditions in the mine in general. If full monitoring is considered to be necessary, the mining company should monitor all water entering and leaving the approval area. This may involve regularly measuring water coming in and out by ventilation, leaving in the coal or ore, or pumped out or in; that is, a complete water balance for the approval area. In some cases water fingerprinting may also be required.

Emergency water monitoring

Any significant inflow of water should be reported immediately to the dam owner. “Significant” in relation to groundwater flows into the workings is defined on a case-by-case basis, however a starting point might be:

the volume or rate of flow, or the change in the volume or rate of flow, or the location causes surprise among persons familiar with the workings

the volume or rate of flow doubles over a few days, or the volume or rate of flow is more than 3 standard deviations above the mean value (i.e.

larger than about 99% of recent readings, or in the top one percentile).

Geological mapping - surface & underground The section on Geological/hydro-geological analysis describes the analysis that should be carried out to develop a credible geological/hydrogeological model to address the hazards associated with the geology of the dam’s surrounds. Development of the model should continue during the operation of the mine. The conditions requiring underground geological mapping and additional surface mapping contribute to this.



For underground workings the geological/hydrogeological models are critical to understanding the interaction between the mine workings and the surface. The geology can influence:

the stability of the workings the development of the goaf and other sub-surface impacts subsidence and other surface ground movements and groundwater flow paths.

Structural geological features may have a strong influence on the performance of the system, and consequently should be a major focus of the investigations.

The most credible models will be based on inspections of all the available sources: surface, underground, and boreholes. In particular the combination of surface and underground mapping may permit an assessment of the likelihood that structural features are continuous from the surface to the workings. The highest level of detail would be required for any high risk applications, and medium risk applications that may impact on valuable stored water.

In the case of open cut mining, geological mapping facilitates the assessment of highwall stability (where this could impact on the safety of the dam structure) and of the likelihood that a flow path will develop between the storage and the pit.

Surface geological mapping Surface geological mapping involves developing a traditional surface geological map with additional emphasis on structural geology and significant lineaments. Lineaments are defined by an investigation of air photos or satellite images. “Significant” lineaments may be defined by their persistence, proximity to the dam or stored water, or magnitude. The significant lineaments are then a focus of surface inspection aimed at determining the conditions that gave rise to the lineament. The following features would typically be shown on the surface geological map:

topographic contours at 10 m intervals (small intervals may obscure other detail) surface boundaries of major geological units the results of detailed surface geological mapping in the vicinity of each significant

lineament, aimed at determining the surface conditions giving rise to the lineament. Features considered may include: outcrop mapping, with fracture, joint, or bedding patterns; soil cover; vegetation changes; slope changes; wet areas, seepage, springs or creeks

the outline of past extraction and the significant results of underground mapping in these areas. These include all faults (including major slickensided joints, sheared or crushed zones which may not show displacement) and

the areas of proposed extraction.

These maps should integrate, as far as possible, the significant features determined from any relevant investigation undertaken as part of the application, in particular borehole data, results from geophysical investigations, and the results from in-situ stress investigations. These maps should be prepared by suitably qualified persons (i.e. geologist, etc).

Underground geological mapping This involves the preparation of a geological map based on an inspection of the underground workings. Its focus is on the elements that may impact on the behaviour of the workings, the stability of the workings, or that may indicate a connection from the underground to the surface. These elements include:



structural features: faults, major joints, crushed seams, and sheared zones igneous features: dykes, sills, other intrusions evidence of the impact of in-situ stress on the workings (guttering, roof falls, etc.)

other features that may impact on the level of extraction (e.g. thinning or dip of seam) and

other features that may impact on the performance of the workings (sedimentary features such as channels, changes in roof or floor conditions, etc.).

These maps should be prepared by suitably qualified persons (geologist, geotechnical engineer, etc).

Surface subsidence and strain surveys For almost all applications relating to underground workings predictions of surface ground movements are required and are critical to the decision whether to permit mining or not. Accurately predicting ground movements in valleys and at points remote from mining, where movements may be small, is difficult. Both these situations are relevant to the impact of mining on major dam structures, and the former is also relevant to the impact of mining on stored water.

Consequently, measurement of actual ground movements is usually incorporated into a monitoring program to verify the predictions, to allow for the early detection of unexpected ground movements, and to increase the overall understanding of the impact of mining on dams and stored water.

When designing a measurement system it is useful to characterise the type of movements to be measured. Ground movements might be characterised as:

large scale movements: These usually occur over the mine workings and in the immediate vicinity of the workings, perhaps defined by an angle of draw to 20 mm of vertical movement (which is the common criterion in NSW). Angles of draw vary significantly, but an average of 35 degrees from vertical at the underground edge of an extraction is often adopted in NSW. This is the realm of “normal” or “systematic” mining induced subsidence and strain. This monitoring:

o allows for the verification of overall subsidence predictions o will be closely related to the progress of mining o contributes to the understanding of the development of the overall subsidence

profile, which can then be compared or correlated with ground movements at specific locations.

far-field movements: These are predominantly horizontal movements which increasingly dominate the total ground movements further away from the “limit” of the Large Scale Movements. Cases have been recorded up to 1.5 km from mine workings.

response of the site: Ground movements (large scale and far-field) may be modified locally by the characteristics of the site. Valleys in particular are known, under some circumstances, to respond to ground movements in a different manner to relatively flat ground. Geological features can also modify the locally recorded movements.

response of the structure: Dams in particular tend to be long structures, and may therefore be more susceptible to certain ground movements. The type of dam will also contribute to its response. For example, rigid construction (e.g. concrete) will be more susceptible to concentration of strain at discrete points than flexible construction, such as earth or rockfill.

The survey method depends on the type of movements to be measured. The following notes are intended to provide some guidance only:



large scale movements: A traditional subsidence and strain survey grid (i.e. perpendicular lines extending over the panels), or aerial methods can be used to determine these movements. Precision of not less than 1% of the maximum predicted movements should be acceptable. For traditional subsidence surveys over longwalls this equates to acceptable error bands of the order of 10 mm for vertical movement, and 1 mm for horizontal movement per nominal 20 m bay length. The lower precision of aerial surveys is acceptable when the magnitude of maximum subsidence is around 1 m or greater, and where specific points or areas are targeted with higher precision surveys.

far field movements: The nature of these movements is such that high precision survey techniques utilising long-baseline survey grids are required in order to record acceptable results.

response of the site: If the site is a valley, traditional surveying techniques across the base, or along the top of the valley may produce acceptable results, in particular if the predicted magnitude of movements is small. Alternatively, 3D survey marks can be installed on the valley walls and floor, monitored by EDM. Other sites (e.g. adjacent to a geological feature of interest) would typically be monitored by traditional surveying techniques.

response of the structure: Dams for which a dam movement monitoring program is required would typically already have an existing survey monitoring grid on which measurements have been taken and recorded for a number of years. Ideally, “during mining” monitoring of the dam would utilise the same grid and equipment, thus allowing the pre-mining movement history to be used as baseline data. Survey techniques on dams typically utilise high precision EDM to give 3D movement vectors.

Vibration monitoring Where mining may result in significant ground vibrations, for example as a result of blasting, peak particle velocity limits or other limits may be set at critical structures. Typically, a conservatively low limit should be applied initially, for example 10 mm/s PPV at a dam wall.

Vibration monitoring will normally be required to ensure that the limits have not been exceeded. However the information obtained from a vibration monitoring program can be used by a mining company to more accurately predict ground vibrations.

The mining company should develop a plan to monitor ground vibrations. Where blasting is the source of vibrations, blasts should be designed to maintain vibrations below the limits. The involvement of a blasting specialist would normally be required in this process. Monitoring is typically conducted in conjunction with an event (i.e. a blast) and at or close to the critical components. Generally the following conditions apply:

the dam owner is advised prior to a blast a management plan may be required; this may include evacuation of persons

downstream of the dam prior to blasting or inspections of the dam following blasting exceeding set limits may trigger:

o an immediate notification of the dam owner o a cessation of blasting while the cause is investigated and procedures refined to

ensure future blasts are within limits and o an inspection of the affected components (the dam wall).

Drilling ahead of the workings In-seam drilling ahead of workings has become a relatively common practice in underground coal mines in NSW. Typically these holes are not cored. Information on geology is determined by inspection of the cuttings, consideration of the rate of advance and pressure on the drill, and roof and floor “touches”.



Drilling ahead of the workings can assist in the detection of significant geological features before the heading intersects them. Particular interest are major water bearing features which might represent a flow path from the surface to the underground workings. The method may be applied as an additional check on geology when mining near major dam structures.

Generally drilling ahead is not a substitute for adequately developing a geological model as part of the application, as only coarse geological features can be detected by this method.

Water fingerprinting An understanding of the source of an inflow may allow for a more focussed remedial plan in the event that an uncontrolled inrush occurs.

A water fingerprinting program should be developed with considerable care as the outcomes depend on a robust and defensible system of collection and analysis. A typical program might include:

the collection of background samples of likely source waters (surface, workings, groundwater, etc);

analysis of these samples to determine typical properties: chemical, algal, pH, etc; and collecting samples in the event of an inrush and comparing these to the database of

samples to determine the likely source.

Additional monitoring Additional monitoring may be required in special cases; for example when large scale extraction is proposed in much wider panels, or at much shallower depths than previously attempted beneath important storages. In these instances the monitoring program may include groundwater monitoring, sub-surface subsidence monitoring, pillar stress monitoring, geophysical surveys, or other techniques to assist in evaluating the impact of the mining on the surrounding strata and the affected surface feature.



Appendix 3 Contingency plans

General The purpose of a contingency plan for the protection of a declared dam is to provide effective procedures that will assist in minimising damage to the dam in the event that unexpected conditions are encountered during mining operations. The plan is not a substitute for adequate pre-mining investigation nor does the existence of a plan allow mining in areas that would otherwise have an unacceptable risk. This document is intended as a guide only. The plan should be consistent with the mine TARP and may be included as part of the other plans developed by the mine to mitigate risks - where contingency or emergency plans already exist for other reasons it may be more appropriate to extend one of these plans rather than develop a completely new plan.

The contingency plan is required to be an ‘action plan’ and include:

relevant, reliable and readily measured parameters identified for use as ‘triggers’ identified levels or events for triggers explanation of the monitoring or other information supporting each trigger level an explanation of the actions required to be implemented at each trigger level. For

example, for mine inflows, procedures will specify levels of inflow above which key personnel, both at the mine and in other organisations, are to be informed of the situation, and what actions are required of these personnel

definition of the roles, responsibilities and contacts for persons involved in any trigger or action

outlining the resources required to monitor the parameters and implement any required actions as is the process for obtaining these resources and

arrangement such that the plan can be implemented rapidly by someone in the event of an emergency.

Where the plan calls for an action which requires the use or installation of equipment, such as pumping inflow water or constructing bulkheads, the time required for deployment of the equipment should be considered in the plan. Where necessary the equipment should be stored or installed at the commencement of mining, to be readily available.

Possible triggers (action indicators) Triggers should be based on physical parameters which are relevant, reliable, and readily measured. Inflow into the workings is usually a prime candidate for an information source as it is relevant, and usually readily measured. However, the possibility of flow paths which do not intersect the workings developing as a result of mining should be considered. Other indicative parameters are:

development of caving towards a known aquifer or flow path changes in groundwater levels water loss from reservoir unexpected ground movements at the surface, particularly at the dam structure, or

underground or deterioration of pillars.

These should be considered in the context of risks to the dam. Typically a number of trigger levels would be set. Defined in terms of the broad actions required at each level, these might include:


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1. Watch; 2. Notify, increase surveillance, mitigate (pump); 3. Investigate, slow mining; 4. Prepare for remedial measures, stop mining; and 5. Implement remedial measures progressively (there may be more than 1 stage of remedial works).

Levels for triggers may need fine tuning based on their performance in the first few months. This is particularly the case for low level triggers, such as a ‘watch’ or ‘notify’ trigger. Activating low level triggers too frequently may reduce their perceived importance. However an occasional (say, less than 3 times in 12 months) low level trigger will provide evidence that the system is working.

Triggers for inflow into mine workings At the upper end of the scale, mining should cease when the rate or volume of loss of stored water approaches the set limits. At this stage, implementation of the remedial works should have begun.

Levels could be set based on the rate of flow, rate of change of flow, appearance of flow (discolouration), etc.

In order to be reliable and readily measurable, systems must be in place to determine the background levels. Usually this would involve maintaining a water balance for an area. It may also incorporate some form of water fingerprinting to allow discrimination between different sources of water. This might minimise the number of false alarm triggers.

Options for detecting water inflows include:

an awareness program for staff and an informal visual inspection program; formal visual inspections; and review of the water balance recordings for the mine (i.e. recording volume of water

pumped in an out of an area of the mine, recording volumes in holding and recording moisture lost from an area in coal or ore or from ventilation).

Typically a program would be developed that incorporated a number of these options. The more reliability there is in a program, the smaller the chance that the operation is interrupted by false alarms.

The total volume of water is an important consideration too, in particular if there are limited means of removing water from the workings. Access to certain areas will be restricted as the workings fill with water, so actions that require access to these areas need to be scheduled before access is lost.

Where water is to be stored behind plugs or dams in the workings, the pressure on the plug as a result of the height of water behind it may determine the schedule as well. For example, a plug may be designed for a maximum pressure equivalent to 10 m of head. A plan would need to assume that the plug will fail at this point, and that any action to be done in the area that would be flooded by the failure of the plug needs to be completed well before the pressure builds up to 10 m.

Contingency actions Table 2 lists generic contingency actions, and provides some specific examples relevant to the loss of stored water. (Note that a similar approach would be required for responding to


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unexpected mining effects on the structural integrity of dam structures). Also refer to Appendix C of the following code for guidance: https://www.resourcesregulator.nsw.gov.au/__data/assets/pdf_file/0011/543935/NSW-code-of-practice-Inundation-and-inrush-hazard-management.pdf

Table 2 Generic actions related to trigger levels

Generic Trigger

Generic Action Example of specific actions related to an inflow

Watch Visual inspection or observation of existing monitoring data, conducted irregularly but frequently during normal operations.

Arranging to walk past and look at an area of seepage or drippers a few times during a shift.

Notify Formal advice that an event has occurred, or is occurring.

Contact the dam owner and advise them that there is persistent leakage from a heading, that it will continue to be monitored, and that an update will be provided.

Increase surveillance

Implement a higher frequency of measurement or observation of existing data streams, or implement additional monitoring aimed at improving the understanding of the behaviour of the event.

Direct seepage water to a point where it can be measured and recorded, so that a clearer understanding develops of the rate and volume of inflow from a particular point.

Investigate Undertake desk or on-site investigations to determine the source, path, or cause of an event.

Drill holes to determine if a flow path from the surface to underground exists. Undertake water fingerprinting to determine the source. Re-evaluation of geological/hydrogeological model. Geophysical testing to determine water bearing fissures.

Mitigate Implement measures to reduce the consequence of the event.

Turn on existing pumps, or install additional pumps; NB this mitigates the consequence to the operation but does nothing to mitigate the threat to the dam. Stop mining. Draw down the reservoir.

Remediate Implement measures to reduce the cause.

Install a grout curtain or sheet, or attempt to grout a specific flow path. Seal the area of the mine where the stored water is entering.

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