Tailings Storage Facility Management

Cover image for a guide to surface tailings storage facility management under Queensland guidance note QGN 29

A tailings storage facility is the largest structure most mines will ever build, it is built incrementally by the people who operate it, and when it fails the consequences are measured in lives and catchments. QGN 29, the Queensland guidance note on surface tailings storage facility management, describes the regime that keeps that from happening: sound design, construction, operation and maintenance, validated through inspection and auditing.

This guide covers why TSFs fail, what the surveillance regime has to catch, what QGN 29 expects around wet season and seismic events, and where the record keeping usually breaks down.

Why TSFs are a different kind of hazard

Poorly designed, operated or maintained tailings facilities have contributed to a number of high consequence accidents and environmental disasters. That sentence appears in the guidance note, and the international record behind it is unambiguous.

What makes a TSF unlike most mining hazards is the time constant. A haul road hazard is created and resolved within a shift. A tailings embankment accumulates its problem over months or years: a slightly steeper lift than designed, a rate of rise faster than the consolidation allows, a decant that has not been moved, a seepage face that has been damp for a while and is now wetter. Every one of those is survivable alone and the combination is not.

The corollary is that the control is surveillance over time, and surveillance over time is a record keeping problem before it is an engineering one. The engineer who assesses the facility can only assess what was observed and written down.

The four phases QGN 29 addresses

The guidance note frames a regime across design, construction, operation, and maintenance or modification, with inspection and auditing validating all four. The separation matters because responsibility moves.

  • Design is usually external, by a specialist engineer, and produces the operating envelope: freeboard, rate of rise, beach length, decant position, phreatic surface expectations.
  • Construction is often done by the mine, in lifts, over years, sometimes by people who were not there for the previous lift.
  • Operation is deposition management, water balance and decant control, done daily by operators.
  • Maintenance or modification is where facilities drift, because a change made for a good operational reason can sit outside the design assumptions nobody reread.

The gap that matters is between what the designer assumed and what the operation actually does. That gap is only visible if operational records are legible to the engineer, which is a higher standard than being legible to the operator.

What the surveillance regime has to catch

Routine TSF inspection is looking for change, not for a pass or fail. The items that matter are the ones that mean something different this week than last week.

  • Freeboard against the design minimum, and the trend, not just today’s number.
  • Beach length and pond position. A pond migrating towards the embankment is one of the clearest warnings available.
  • Seepage. Location, flow, clarity and whether it is carrying fines. Clear seepage in a known location is a design feature. Cloudy seepage in a new location is not.
  • Cracking, settlement and bulging on the crest and downstream face, with position recorded well enough that the same crack can be found and compared next month.
  • Erosion and rilling on the outer face.
  • Instrumentation. Piezometers, survey monuments and inclinometers, and whether they are actually working. QGN 29 specifically expects assessment of all monitoring equipment, because a dead piezometer reads as reassuringly steady.
  • Decant and spillway condition, including debris and obstruction.
  • Rate of rise against what the design permits.

Wet season and seismic triggers

QGN 29 calls out two event driven expectations that routine monthly inspection does not cover.

Wet season preparedness and compliance against plan. In Queensland this is the dominant annual risk cycle. Storage capacity, freeboard, spillway condition, pump capacity and the water balance all have to be in position before the season, and the check has to be a documented one against a plan rather than a general sense that things look right. The equivalent thinking for pit water is covered in water management, dewatering and inrush.

Inspection after regional seismic events. An earthquake felt at the site, or a regional event of sufficient magnitude, triggers an inspection regardless of where it falls in the routine schedule. The trigger needs to be defined in advance, with a magnitude and distance threshold and a named person responsible, because deciding whether an event qualifies while everyone is talking about the earthquake is how it gets skipped.

People and training

The guidance note expects training and education of mine personnel to ensure safe management of the facility. This is less obvious than it sounds.

The person walking the embankment weekly is usually not a geotechnical engineer. They need to know what normal looks like on this facility, which observations are significant, and what to do immediately rather than at the end of the shift. A generic inspection form handed to someone who has not been taught what a developing seepage face looks like produces a complete record of nothing.

Competency for TSF inspection is a good example of the kind of position specific requirement that RS22 management structure asks the site senior executive to determine and document. No ticket is prescribed for it. That does not mean nothing is required.

Where sites come unstuck

  • Inspections record a state, not a trend. Twelve monthly forms each saying “satisfactory” contain no information about whether anything is moving.
  • Observations cannot be relocated. “Crack on the northern crest” is unfindable next month. Without a position, comparison is impossible and the record is decorative.
  • Instrumentation is read but not assessed. Readings are logged, nobody confirms the instrument still works, and a flat line is mistaken for stability.
  • The design intent is not on site. Operators manage deposition without knowing the rate of rise limit or the design freeboard, because those live in a report in a consultant’s file.
  • Modifications are made without reference back to the design. A pipeline rerouted, a decant relocated, a road built on the embankment. Each is reasonable and each changes an assumption.
  • Records are not available to the reviewing engineer. The annual assessment is done from a site visit and a conversation, because a year of operational observation is not in a usable form.

Running TSF surveillance so the trend is visible

HazView runs TSF surveillance on live sites, so this is a use case rather than an analogy.

Every observation is placed on the facility. A seepage point, a crack, a settlement area or an instrument is a located feature with its own history, so the next inspection opens the same point and compares against the last photograph rather than starting a fresh form. That single property is what turns a stack of inspections into a trend, and it is the property paper and spreadsheets cannot provide.

Inspection routines are scheduled and assigned, with wet season and post seismic inspections as their own triggered routines rather than as an item somebody remembers. Overdue inspections are visible. Photographs, timestamps and the inspector’s identity are attached to every entry and kept permanently, which is what the reviewing engineer needs and rarely receives.

Piezometer and survey data usually come from other systems, and they should. The REST API brings those readings in against the same facility, so instrumentation trends and visual observations sit on one map instead of in two reports that get compared once a year. Records can be pushed back out to corporate or consultant systems the same way, which removes the retyping that makes people summarise instead of record.

The platform is not a geotechnical assessment and does not replace the design engineer or the annual review. It makes sure that when those people arrive, the year of observation they need actually exists and can be read.

See how HazView works for geotechnical engineers, or book a demo.

Frequently asked questions

What is QGN 29?

The Queensland guidance note on surface tailings storage facility management, published in 2018. It outlines a regime of design, construction, operation and maintenance or modification, validated through inspection and auditing. It is guidance, not law, and compliance with it is not by itself proof of compliance with the legislation.

How often should a TSF be inspected?

There is no single number, because it depends on the facility, its consequence category and its rate of rise. What matters is that routine frequency is set deliberately, that event based triggers exist for wet season and regional seismic events, and that the regime is actually followed and recorded.

What should a TSF inspection look for?

Change. Freeboard and its trend, beach length and pond position, seepage location and clarity, cracking and settlement on the crest and downstream face, erosion, instrumentation function, decant and spillway condition, and rate of rise against the design.

Does a seismic event require an inspection?

QGN 29 expects inspection after regional seismic events. The threshold that triggers one should be defined in advance with a named responsible person, so it does not become a judgement call made in the middle of the event.

Who is responsible for the TSF?

The site senior executive carries the safety and health obligation, with design and periodic assessment typically from a specialist engineer and daily management from operations. The failure mode is the space between those three, so the accountability for each part belongs in the documented management structure.

Is clear seepage a problem?

Clear seepage at a known location with a stable flow is often a designed part of the facility. Seepage that is new, increasing, or carrying fines is a different matter entirely, because material moving with the water means internal erosion. Which is why location and clarity have to be recorded, not just the presence of water.