Water management in mines
Learn more about the legal requirements and best practices for a water management program in mines.
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This guideline was developed for workplace parties to assist with understanding the requirements in Regulation 854 – Mines and Mining Plants under the Occupational Health and Safety Act (OHSA) for water management programs.
This guideline is meant to:
- provide information to assist workplaces to assess water-related hazards
- provide guidance on what to consider when developing water management programs
- reduce the number of incidents caused by unwanted, excessive accumulations and flows of water in underground mines, reducing the risk of injury to workers
This resource does not replace the Occupational Health and Safety Act (OHSA) and its regulations, and should not be used as or considered legal advice. Health and safety inspectors apply the law based on the facts in the workplace.
Sections of Regulation 854 that apply
In addition, there are other requirements in Regulation 854 that may apply to health and safety issues related to water management, either directly or indirectly, that workplace parties should know. These include but are not limited to:
- section 84: requirements for written procedures where a worker may be endangered by the withdrawal, collapse, shifting or movement of bulk material in a stope, pass, chute or in a storage area
- section 62.1: requirements for non-routine hazardous tasks
- section 64: requirement to make a written record of a potential or actual danger to worker health and safety that has not been remedied or removed at the end of a work shift
Workplace parties should also be aware that, as required by OHSAs section 53 and clause 21(5)(i) of Regulation 854:
where there is an unexpected or uncontrolled run of material, water or slimes in excess of one cubic meter that could have endangered a worker, the employer of a worker who works in the mine or plant is required to provide written notice to the Ministry of Labour, Training and Skills Development (MLTSD) within two days of the occurrence.
It is important that workplace parties recognize and take action to address potential issues that can create problems for mine infrastructure by accumulations of water or wet material (for example control gates in ore or waste passes, dams, bulkheads and backfill fences). This can happen when excessive quantities of the accumulated water combine with other materials to form a hazard.
The failure to take action when needed can result in sudden in-rushes (runs-of-muck) of fluidized material (for example sand or mill tailings introduced as backfill, or blasted ore or rock) that is otherwise relatively harmless in its dry state. Such in-rushes can constitute a serious health and safety hazard to workers.
Contents of the water management program
Underground mines should, as appropriate, make reference in the water management program to other safety or company policies or procedures that may relate to the overall design and/or operation of their water management system. This could include, for example, policies and procedures relating to management of change processes, locking and tagging and/or emergency procedures.
Subsection 87.1(2) of Regulation 854 requires all underground mines to develop and maintain a written water management program that includes the following measures and procedures, listed in order by clause.
Clause 87.1(2)(a): Identify areas of the mine where water is likely to accumulate. These areas may include:
- any locations where water may/is entering the mine
- surface areas where water has the potential to egress into the mine’s sub-terrain levels (exploration diamond drill holes)
- any other common potential sources that are part of the mining process (for example sand plant, process water management etc.)
- where water is being impounded by engineered berms or dams
- identifying and recording the location of underground mine sumps, including shaft bottom
Clause 87.1(2)(b): Control the volume of water that may enter the mine, either naturally or as a result of the mining process. This may include:
- listing any controls identified for water usage for each mining process employed in the mine. These may include but are not limited to: pressure reducing valves, water meters, etc.
- maintaining a record of the balance between the daily amounts of water used underground versus the daily amount of water being removed
Clause 87.1(2)(c): Prevent unwanted or uncontrolled flows of water in all areas of the mine. This may include:
- designs for ore and waste passes that minimize the likelihood of water infiltration
- designs and procedures for drilling holes into ore and waste passes
- designing effective water removal and drainage plans and maintaining them
- listing of drainage and water lines in inactive areas by location
- roadway maintenance and ditching
- identifying diamond drill holes and boreholes that may transfer water
Clause 87.1(2)(d): Effectively and safely manage and remove water that poses a risk of injury to a worker. This may include:
- identifying any dams and berms used in mines, with design documentation references
- preventing the transmission of water through existing holes into ore and waste passes. These holes (including pre-existing holes) shall be plugged or grouted when they are no longer required and should be identified with proper signage
- identifying drain holes, as well as other holes intersecting ore and waste passes, on any plans, specifications and drawings
- providing training programs to ensure that workers and supervisors are able to recognize and understand the dangerous conditions that water infiltration will have on ore and waste passes
- ensuring that if an accumulation or flow of water that may endanger a worker is encountered, the employer adequately barricades and identifies it with a sign to prevent access. Ensure that work is limited to removing the hazard as required
- developing a material handling (for example saturated material) communication process that includes geology and engineering departments, supervisors and workers providing input to identify and record the hazard of water accumulations or flow in the workplace. Ensure effective communications between all mine departments (such as operating, maintenance, logistics, engineering and geology departments) whose activities could influence ore and waste pass contents, performance and conditions
- implementing safe blasting practices for resolving hang-ups in ore and waste passes involving wet material
- developing procedures to safely manage and remove water that poses a risk of injury to a worker
Clause 87.1(2)(e): Maintain water removal and drainage systems and all of the components of such systems. This may include:
- identifying sump dimensions and depth indicators for site ease of reference and diagnostics
- including sump and drain hole designs in the mine design and engineering plans
- identifying pipe lines and include direction, destination and source of material
- developing procedures to deal with slimes and solids within the water pumping system to limit the migration of solids when pumping water. The management of slimes and solids can be done by allowing the material to decant in a specifically designed and/or designated area of the mine. The recovery of this material upon solidification can then be done safely
- ensuring that all mine process water is diverted away from ore and waste passes and can be effectively managed by mine de-watering systems
- measuring and recording ore and waste pass content levels
- regularly inspecting the water removal and drainage systems, and identifying critical spares/equipment that may be required for the system
- developing contingency plans and/or measures to deal with catastrophic failures to water removal or drainage systems (for example electrical outage, severe weather conditions)
Actions for workplace parties
Monitoring unwanted accumulations or flows of water
Potential sources of water in an underground mine include but are not limited to process water (most commonly because of activities such as drilling, and dust suppression), hydraulic back fill process, slicking (pre-wetting) and flushing out fill lines etc.
If possible, surface water should be kept away from mines by draining ponds, diverting streams, etc.
Monthly water balances are routinely calculated at many underground mines. However, a key challenge in interpreting water balance estimates over time is in understanding the effects of weather conditions. Mines are encouraged to improve upon and/or standardize the manner in which mine water balance calculations are made.
Preventing unwanted accumulations or flows of water
There are a number of generally accepted design and procedural measures that can effectively manage water in underground mines. The overall purpose of such measures are to:
- minimize the amount of water (both naturally occurring and process water) entering underground mines
- remove excessive quantities of water that have entered underground mines
- prevent water that has entered underground mines from getting into ore and waste passes
- safely manage water once it has inadvertently entered ore and waste passes
There may be additional considerations, as follows:
- Provisions in the original design should assess the potential for surface water entry into an underground mine.
- Alternatives to hydraulic backfill should be considered where possible. A calculation of water volume used for backfill and paste fill should be recorded, including slicking of lines, flush and water used in the process.
- Mine sumps should be strategically located. Sump design should consider two separate containments - one for clean water and one for dirty water – that allow solids to settle prior to pumping.
- Vertically oriented openings below the level such as ventilation raises, and sublevel access should be strategically located.
- If possible, ore and waste passes should be eliminated to reduce the hazards associated with potential accumulations of water and to reduce the risk of runs of material (i.e. alternative methods for ore and waste removal from an underground mine, such as conveyor systems, should be used).
- The mine design should include provisions to ensure that mine water drains away from ore and waste passes.
Preventing water from getting into a mine
- Minimize the amount of water entering an underground mine by using methods such as sealing exploration diamond drill holes that emanate from surface and grouting or plugging fragmented rock masses that can serve as a conduit for water transmission.
- Use climatic or topographic study/research as part of mine shaft design to eliminate possible future water flooding. Design the collar of shafts to be of a higher elevation than the surrounding grounds.
Keeping water off of mine levels
- Water supply and drainage lines in inactive areas of the mine should be shut off.
- Roadways should be regularly maintained to prevent water from pooling.
- Intersecting parts of down ramps or inclines should be designed to minimize water in-rushes. This would apply in relation to roadways, tunnels and ramp elevation or declines in the sump design, and could provide some capacity to absorb any in-rush of water from other levels or pipe line breakage, thus minimizing the risk to the lower infrastructures of the mine.
Water removal and drainage systems
- In some older underground mines, pumping systems have not kept up with the growth or expansion of the mine. These should be reviewed and approved during development and review of the water management program, to make sure the water removal and drainage system remains effective and of sufficient capacity.
- Mine pumps need to be properly maintained on an ongoing basis as do water discharge lines.
- Water lines for water removal and drainage systems need to be inspected on a regular basis, in order to inspect the integrity of the entire water removal and drainage system, including scale build-up. Inspections of water lines should be scheduled at pre-determined intervals and should not be event driven. Design of the mine water removal and drainage system should allow for these inspections. Possible methods include secondary dewatering lines or man machine interface systems. Alternative methods of monitoring using non evasive technology to monitor pressure, volume and pump amperage to identify status and condition of the system should be considered.
- A routine, preventative replacement program of lines should be implemented using data and manufacturers’ recommendations to create a life cycle replacement strategy for lines affected by elevated corrosive material delivery.
- Regular monitoring of water line pressure can be indicative of leaks when pressure drops are realized and conversely can indicate restrictions when pressure increases are realized.
- Managing slimes and solids as part of the water management program is crucial to reliable mine dewatering process. Considerations should be made to sump designs to separate slimes and solids in an effective manner using best practices and new technologies available (for example geotextiles). Basic sump design including clean and dirty water settling can be employed with success. Managing slimes should also include safe areas where saturated material can be decanted for future safe removal/transfer.
Positive displacement pumps
- A positive displacement pump should not be operated against a closed valve on the discharge side of the pump because it has no shut-off head, like centrifugal pumps. A positive displacement pump operating against a closed discharge valve will continue to produce flow until the pressure in the discharge line increases to the point that the line bursts or the pump is severely damaged or both.
- A relief or safety valve on the discharge side of the positive displacement pump is therefore absolutely necessary and is required by regulation.
- The relief valve can be internal or external. An external relief valve installed in the discharge line with a return line back to the suction line or supply tank is recommended.
- The pump manufacturer normally has the option to supply internal relief or safety valves. Generally, the internal valve should only be used as a safety precaution.
- Any drain hole in an underground mine shall be clearly marked by signs that are visible, readable by workers and clearly distinguished from their surroundings; and identified on any drawings, plans and specifications relating to that area of the mine. The signage should identify the location of a drain hole, and its destination.
- Procedures should be put in place for the inspection and maintenance of drain holes.
- Procedures should be put in place for managing plugged drain holes.
- Ensure workers are aware of potential suction hazards associated with maintenance of drain holes.
- Drain holes should be strategically located.
Preventing, guarding and controlling against accumulations or flows of water
Prevention is the key to ensuring water has no impact on mining operations. Water is used for many processes in mining; it needs to be controlled and managed so that it can’t create hazardous conditions.
The following sections will provide important information on how to prevent, guard and control accumulations of water in the workplace.
Runs-of-muck resulting in failures of structures such as control gates in ore or waste passes, dams, bulkheads and backfill fences can occur for many reasons including but not limited to:
- water (either naturally occurring or deliberately introduced into a mine for certain processes) accumulating in ore or waste passes due to inadequate drainage or pumping, or through discontinuities in the rock mass, backfilled or abandoned openings, interconnecting diamond drill holes or stray production holes
- an estimate has not been made of the mass balance of the water being consumed and stored in an underground mine compared to the water outflows, or it has been made incorrectly
- solid material behind such control structures includes a component that is excessively fine (such as sand or backfill) resulting in higher than normal water retention
- the control gate has not been designed in such a way to drain impounded water from behind the structure without requiring the gate to be opened
To mitigate these potential failures, mines should consider the following:
- At least one gate should be capable of holding wet muck for loading pockets that are fed by ore and rock passes where there could be an accumulation of fluidized muck. This gate should be strong enough to hold all muck that is in the ore/rock pass and its enclosure should include a suitable means of control separating off the ore/rock pass in such a way as to prevent an uncontrolled flow of muck, either down the shaft or into the loading pocket where the operator is located. Engineering design is retained and updated in site records reflecting pertinent information of work, changes and omissions.
- This may not be necessary for installations where the source of ore is a conveyor belt as the possibility of wet muck running out of a feeder and flowing the 15 meters or more to the transfer car, down the chutes, into the measuring pocket and into the shaft, is quite remote.
- This may also not be necessary for lip pockets, where muck usually comes from LHDs, or for spillage pockets, where the muck comes from spill doors in the shaft.
- The location of the loading pocket in the shaft can influence the degree of hazards. An intermediate pocket subjects the shaft inspectors and passengers on a skip-cage combination to an increased probability of a run-of-muck accident. Although it is not easy to eliminate an intermediate loading pocket where the mine design requires it, these intermediate pockets require more stringent design measures and procedural measures than a lower loading pocket.
- Mine haulageways should have drainage ditches located on the other side of the drift from the ore pass. Waterlines in the vicinity of ore pass dumps and car washing stations should be limited to prevent accidental leaks of water. Consider using steel pipe only (vs. plastic pipe) if water lines are to be located in the vicinity of ore/waste pass dumps.
- There should be curb rings around the inlets of bins as an additional design measure. Shut-off valves should be provided to shut the water off in areas where it is not required so that leaks can be reduced. Instrumentation can be used to monitor drain lines in problem areas so that action can be taken to control leaks.
Preventing water from entering mine ore and waste passes
- The grade of level headings should be set such that water drains away from ore and waste pass dump locations.
- Proper positioning, size and dip of ore and waste passes are essential.
- Ore and waste pass entry points need to be above level grade.
- The number of ore and waste pass entry points should be minimized.
- Where an accumulation of water is likely to be present, a borehole shall be drilled at least six meters ahead of the working face to protect against a sudden breakthrough of water. This work will be guided by the engineering group and could be completed with jumbo drill rigs using extension steel. The borehole can be completed during normal face drilling development prior to loading of explosives.
- A drill or blast hole that is located in an area of the mine where an accumulation or flow of water is likely to be present shall be identified on any drawings, plans and specifications relating to that area of the mine. Any drill holes and blast holes that intersect with ore and waste passes shall also be identified on mine plans. These holes should have appropriate signage with a description of their point of destination.
- A drill or blast hole that could allow water to enter a chute, raise or waste or ore pass shall be filled or plugged to prevent water from entering the chute, raise or waste or ore pass. This task may include, where appropriate, grouting these holes.
- Wet material including slimes, sand or soupy wet muck should not be introduced into a chute, raise or ore/waste pass. Any transfer of such material within the mine should occur only after completion of a risk assessment and a procedure that has been developed jointly with the joint health and safety committee (JHSC) or health and safety representative (HSR), if any, to eliminate, where possible, or mitigate the associated risks.
Addressing accumulations or flows of water
Communication/notification of hazard
- Upon discovery of the accumulation or flow of water that may endanger a worker, the hazard must be reported to a supervisor and documented so that the information can be communicated to all affected workplace parties. The employer must notify any worker in the area of any accumulation or flow of water that may endanger him or her.
- Methods of communication/notification may include pre-shift meetings, five-point safety cards or zero harm cards that include specific written comments and/or instructions regarding the hazard, and operation shift logs.
- Areas of a mine where water has entered must be immediately and adequately barricaded to prevent worker access.
- Workers must not be allowed to enter the area unless it is to perform work related to addressing the hazard and all reasonable precautions have been taken to protect them. This may include non-routine hazardous task procedures, job hazard analysis or field level risk assessments.
Determining material content and water levels
- If water has entered ore and waste passes, inspection programs and camera systems should be used to monitor the contents of the water/material, and to determine the proper positioning of controls for operating pass control gates.
- Field level risk assessment should be conducted to manage risks associated with impounded water. The supervisor should initially visit the hazardous area to inspect it, speak to affected workers and record the status of the hazard. If the risk is undetermined or high, the supervisor, joint health and safety committee or health and safety representative and affected workers should develop a plan or procedure, setting out the next steps that need to occur prior to the movement of any material (for example, the use of remote operations, the use of a camera to monitor the situation and safely accommodate the action plans). Mine ore pass cavity monitoring surveys should be reviewed during the job planning.
- Simple tools can be used to verify water content in ore/waste passes from the top area or suspected point of entry of water. Such tools can be steel and wood measuring balls to determine the content of the materials and water levels.
- Knowing the estimated volume of water in the pass from the measurements can indicate what action plan is required. If the pass is holding a large amount of water, for example, a plan to pump the water out can be taken from the top by lowering a pump.
- If the pass is known to be holding large amount of slimes determined by the measurement, the pass should be barricaded (top and bottom), and the water decanting from the bottom or lower exit point of the pass should be monitored. Further measurement can be taken over time to determine if the water or slimes are being lowered by naturally occurring drainage.
- Upon monitoring results, the evaluation of risk can be made and an action plan to remotely empty the pass can be made. All plans need to have a completed risk assessment prior to action.
Workers and supervisors need to be aware of the hazards that they could be exposed to, the controls that are in place to prevent harm and their responsibilities implementing the controls and participation in water management programs. Workers, the Joint Health and Safety Committee (JHSC) and representatives must also understand their roles in the program and how to control water hazards that are part of their work. Additionally, workers must be informed about where to seek solutions to concerns or answers to questions related to these hazards.
A basic workforce education and training program should include:
- an overview of the requirement for a water management program and the purpose of the program
- general information regarding water-related hazards and their locations
- factors that influence runs of material, water and slimes
- the controls that are in place to minimize water accumulation
- how water is to be used and effectively removed at a mine
- an overview of the procedures and expectations of the water management program and where to seek additional information if questions arise
The program should recognize that different training may be needed depending on a worker’s role in the workplace and the risk of exposure to dangerous conditions.
As changes to the program are made through the annual review or the introduction of new controls, workers and the Joint Health and Safety Committee (JHSC) or Health and Safety Representative (HSR) may require additional training, information and instruction. Documentation and records of all training must be retained and be available for review. Training facilities such as Workplace Safety North (WSN) can help workplaces with these training requirements.
Consultation with committee or representative
Employers shall develop and maintain a water management program in consultation with the joint health and safety committee (JHSC) or a health and safety representative (HSR), if any (subsection 87.1 (1)).
Where the OHSA or its regulations require that an action be taken in consultation with another party, including but not limited to the JHSC or representative, the Ministry of Labour, Training and Skills Development expects that the employer will engage in a meaningful interaction (for example, including but not limited to dialogue, discussion and providing all relevant information) with the JHSC or HSR.
There should be a genuine opportunity for the JHSC to comment, and those comments should be received and considered in good faith. This includes taking into account any feedback and responses from the JHSC or HSR before taking action (i.e. implementing a plan, program etc.) and responding to any recommendation arising out of the consultation.
Consultation is not simply informing the JHSC or the HSR that the employer intends to take action.
Review of the program
Underground mines are required to review the water management program annually, and as soon as possible following any significant alteration to the water removal or drainage system. As part of this review, mines should create a document for each mine site that outlines a mutually agreeable process between the mine employer and the JHSC members, and that can be used for record keeping purposes. The employer should ensure that the water management program is available for review by the JHSC or HSR to facilitate the review.
Some examples of events that could occur that would trigger a review of the water management program could include:
- a rockburst or fall of ground that could significantly alter the water removal or drainage process
- closing or limiting access to an area of the mine which includes the infrastructure for water removal or drainage
- loss or exceeding of water storage capacity (for example environmental conditions, dam or berm failures)
- new processes introduced at the mine (for example, equipment, mining methods, backfill)