Waste Dump Erosion Assessment

Designing Landscapes for the Future

Designing Landscapes for the Future

Erosion of landforms and waste containment facilities is one of the biggest environmental challenges for mining companies. High erosion rates can lead to degradation of cover systems, exposure of reactive mineral waste, acid and metalliferous drainage (AMD) and sub-optimal vegetation outcomes. However, rehabilitation projects are now benefiting from modern technologies and a better understanding of future performance.

In an era where technology such as unmanned aerial vehicles (UAV’s) or drones and terrestrial laser scanners (TLS’s) have made it possible to gather landform scale data within minutes, a shift in best practice landform assessment and design is inevitable. These technologies are now capturing data at unprecedented resolutions, recording details of the landform surface, and providing timelines of rehabilitation performance.

These technologies provide the ability to capture comprehensive landform information in less time and at lower costs than traditional approaches. The geo-referenced outputs provide sub-centimetre topographic survey and mapping capabilities, with such high-resolution aerial imagery that a golf-ball sized feature of interest can be revealed.

Leveraging Drones and Lasers

Traditional landform assessment techniques typically use transect sampling; a repeatable method based on established scientific methods for assessing rehabilitation progress. These methods are labour-intensive, costly, and do not provide the resolution required to confidently extrapolate results to an entire waste landform. Mine waste landforms often cover hundreds of hectares, contain numerous waste classes, have different combinations of geometry, aspect, and placement methods, therefore, homogeneity at a landform scale is rarely observed.

Modern instruments are extremely well-suited for erosional stability assessments due to their accuracy allowing for calculation of many fundamental metrics, including the eroded volume of an erosion feature (Figure1). They are also well suited for vegetation mapping and can be used to identify healthy (and stressed) vegetation using various colour filters in cameras making it possible to quantify vegetation metrics such as plant cover, landscape stem densities (stem/ha), biomass, and litter over entire landforms.

Rill erosion of a cover system on a mined rock stockpile landform.

Figure 1: Rill erosion of a cover system on a mined rock stockpile landform.

Capturing landscape scale erosion and vegetation metrics using new technologies has made it possible to assess landform performance by accurately quantifying parameters such as:

  • Stability trends, and rate of armouring;
  • Sediment loads and transport;
  • Critical failure points;
  • Criticality of various embankment length and gradient combinations;
  • Effectiveness of surface treatments such as contouring ripping and compaction;
  • Plant community development;
  • The effect of vegetation on erosion and sediment loss; and
  • Plant community comparisons between rehabilitated and natural analogue sites.

These metrics tell us how the landform has performed, however, the biggest opportunity is not in the monitoring/retroactive assessments, but rather obtained through predictive and validated assessments to provide confidence in design (i.e. using data to engineer success).

Predicting Future Landform Evolution

A trial landform embankment surveyed using a TLS is shown below (Figure 2). The image crudely visualises the extremely high-resolution data, a cloud of millions of discrete georeferenced points, each in true colour, and of sub-centimetre spatial accuracy.

Trial landform embankment surveyed using a terrestrial laser scanner (TLS).

Figure 2: Trial landform embankment surveyed using a terrestrial laser scanner (TLS).

This baseline data was collected as part of closure planning studies to contain potentially acid forming (PAF) waste. Over time this baseline will allow Okane to compare and monitor the smallest of changes to surface topography after, or during successive wet seasons. Temporal storm patterns collected by the landform weather station records the depth and intensity of rainfall, allowing for assessment of flow regimes, erosive energy and shear stress on surface materials. Subsequent surveys of the surface will record the impacts of individual storm and seasonal events.

Okane uses these correlations of energy and erosion to provide the fundamental relationships required to develop predictive landform evolution models. Once calibrated to rainfall events of various size and intensity, the models can be used for predictive design. Performance can be assessed for longer timeframes, at various geometries and under specific hydrological conditions. Over time, the calibrated model can be refined and optimised for clients to predict landform evolution at operational and closure timescales. Okane can then provide clients with final landform designs that do not rely on monitoring but provide confidence that design objectives will be met.

The use of traditional techniques to assess erosional stability and vegetation remain useful tools for gathering baseline data, however, due the point scale nature of these assessments they are difficult to extrapolate to a whole landform. In an era where drones and TLS’s have made it possible to gather high resolution landscape data, a shift in best practice to assess erosional stability and vegetation on large landforms has occurred. However, simply gathering high volumes of data does not ensure attainment of closure objectives. Okane leverages its multidisciplinary experts in unsaturated hydrogeology, integrated rehabilitation and revegetation, and landform design and evolution modelling to couple plant-soil interaction with landscape scale data to deliver realistic and optimised closure solutions for clients globally. Assessment of landscape scale erosion and vegetation features offer more integrated and comprehensive approaches to landform rehabilitation and mine closure.

Distilling Data

Managing data is challenging.  People borrow from Samuel Taylor Coleridge’s The Rime of the Ancient Mariner when describing the most common challenge with data. “Data, Data everywhere…” they say, highlighting parallels to the author’s anguish over being surrounded by water, but dying of thirst.  Like untreated sea water, untreated data has limited value and it certainly won’t quench your thirst for information.

Big Data is spoken about in hushed voices as if it is a panacea to float upon to salvation. But even Big Data, if untreated, can be disorganized, incomplete, and unreliable. In the context of environmental monitoring, this can be caused by the variety of surveillance sources in inspection and monitoring regimes, institutional data silos, shift changes and personnel turnover, or inconsistent data management policies. Treated data is valuable because it becomes information: information that can be used to make critical decisions about risks, liabilities, and perform accurate and predictive cost benefit analysis.

If you’re like me, you have a tendency to put things in a ‘special place’ and then forget where you left them. Monitoring data is no different. When a mine nears its end of life, how much time do you think is spent just looking for historical monitoring data? Critical monitoring data collected throughout the life of asset- from exploration through to closure - we find juggled between spreadsheets, drop boxes, shared files, or with multiple consulting firms.  Data, that if aggregated, correctly stored and quality-controlled, could inform key closure decisions and help accurately predict long term closure and relinquishment liabilities.

At Okane, we spend a lot of time with a lot of data.  We maintain a comprehensive database of climatic site models, verified through installed monitoring instruments. Our databases combine and store an exhaustive list of data from soil monitoring, water monitoring, snow surveys, gas analyzers, Guelph permeameter measurements, laboratory testing, and field observations. It would be a sea of data one could drown in, except that it is organized, quality controlled, and is summarized in easy-to-understand, site-specific graphics. Our clients invest significantly in capturing critical environmental monitoring data; we ensure that data presented in a format that is useful to support decision making.

Since 2014 we have been following specific data quality assurance and control protocols to ensure data quality and usability for our clients. We think it is important that our clients have access to their data whenever they want, so we store it in a secure database accessible on demand through an easy-to-use web portal. Our clients use this data for regulatory reporting, risk analysis, and predictive modelling. They know that the data we maintain is centralized, secure, accessible, and easy to integrate into their decision-making tools. This is the kind of Advanced Data Management we strive for. The kind of data that gives people the right information to make the right decisions and helps to create a better tomorrow.

It’s like riding a bike

As engineers and scientists, we love the details. We’ll dive deep right into numbers and calculations and come back up for air wondering why no one else has even gotten their ankles wet. This is a common challenge when developing a mine closure plan. Closure teams start with the details and end up drowning.

What if instead, we approached closure planning like learning to ride a bike?

When you teach your child how to ride a bike do you start by explaining the required equilibrium balance forces, the frictional loses employed to brake, the counter steering and lean required to turn? No, of course not. (If you do, I’d really love to meet your kids!)

You start by explaining the big picture, like “keep pedaling”, “put your foot down if you’re going to fall”. Then they try. Sure, they’ll probably fall once or twice, and you’ll show them what they need to correct for, and then they try again. As you advance, maybe you add more information like “look out for that big rock there- see if you can steer around it”, or “that’s a pretty steep hill, what gear should you shift to in order to climb it?”. Whether you realize it or not, you’re helping them identify potential failure modesor risks, and mitigations. Likely you’ll help them plan some safe routes to travel, maybe even teach them how to pump up the tires if they get low orhow to grease the chain. Eventually they’ll start to master the skill with no complex physics models in sight!

We take the same approach to mine closure planning. First start with the big picture,“what is the returning land use”, “what are the closure objectives”, “who are the key stakeholders”. We build a conceptual model (a base case) using the information available and asking ourselves “if we had to implement our closure plan tomorrow, what would we do”. Then we take the conceptual model (base case) for a spin, running it through our Failure Modes and Effect Analysis (FMEA) workflow. The FMEA identifies potential failure modes and quantifies risk with a singular risk profile. Inevitably, the conceptual model(base case) will require enhancement, and we’ll start progressing into the details of the failure modes, identifying appropriate and fit for purpose mitigations to implement. Then we take the enhanced conceptual model through the process again. Likely we’ll identify some specific studies or site-specific monitoring to inform and further enhance the conceptual model.As the project progresses and the asset operations grow, the potential failure modes "live through time" and can be re-visited, throughout the mine life cycle. At every stage of the asset life, you end up with a robust and fit for purpose closure plan and cover system design that identifies and communicates the reality of risks around closure, and optimizes operations to truly implement progressive closure; in short, an approach that fits your site-specific requirements. The liabilities are managed, and the process is controlled, documented, communicated and auditable all the way from the start to the finish.

So next time you find yourself underwater in a sea of closure studies and complex numerical models, give us a call. When we’re finished, maybe we can all go for a bike ride.

Thinking Above the Line

Lately there is so much information available to us, it can be difficult to know what to listen to. Especially now in the current crisis, a lot of anxiety can be developed due to false perceptions, fears or uncertainty. This reminds me a lot of a facilitation process we use when applying Failure Mode and Effects Analysis (FMEA) for closure planning. Often, closure planning meetings are filled with lengthy discussions around what people believe to be true or debates about missing information, or the veracity of information. Frequently these debates become a distraction, and the meeting spirals. This creates conflict or disinterest, and never results in an accurate picture of the risks or the appropriate mitigations. Other times people get distracted, making false assumptions about the desired state of the returning land use instead of asking the right questions. Ever heard a story about the perfect wet cover design…except the local community and stakeholders were expecting a terrestrial landform, not a lake! Let’s not forget about the closure planning teams that end up doing study after expensive study just because they didn’t frame the desired outcomes and alternatives properly to start with.

Taking the time to set up for closure planning risk assessments is critical. Our team develop detailed fact sheets (Just the Facts Ma’am!), establish key closure objectives, landform specific objectives and criteria, while working with our clients and their stakeholders to understand the specific site risk tolerances and the desired returning land use. Then, once site specifics are fully understood, conceptual landform and cover system designs can be proposed. This ensures all the alternatives can be evaluated against the same criteria and risk quantifiers, and the optimized solution can be selected; an optimized solution based on informed risk-based decisions.

The benefits of this process are not just the reduction of time spend in frustrating meetings or the costs savings of avoiding inapplicable studies. This process can be repeated at every stage of the mine life cycle to ensure that a closure plan, if even conceptual, is not only technically the best option, but also cost-effective, implementable (you better be able to build it!) and meets expectations of all stakeholders. As the mine life evolves you can revisit and update the original fact sheets, see the impacts to the original risk assessments, and adjust the mitigations in a structured and deliberate fashion. The potential failure modes live through time. We call this “thinking above the line”.

It is the same type of thinking we’re calling for from our leaders in crisis. Check your assumptions, fears and preconceived notions at the at the door. Establish the facts, ask the right questions, and make decisions confidently on what we know to be true; what is so. When you get new information, reevaluate the risks and take the right steps to mitigate. Not unlike closure planning, we have an opportunity here to leave a positive long-term legacy.

Okane Nova Scotia Image Merge

Spring Update

It’s spring and that means Tara Baker and Graham Hay are off to Fort McMurray for work on oil sands mine tailings dewatering!

International Network for Acid Prevention (INAP)

Philippe Garneau and Jared Robertson are in Brisbane meeting with members of the International Network for Acid Prevention (INAP). Jared is presenting Okane’s latest work on the INAP project in collaboration with Earth Systems.

Tailings Remediation Plan

Travis Polkinghorne joins the Okane Saskatoon Office as a Junior Engineer and this summer will be working on rotation at Gunnar Mine to conduct the QA/QC program for the Tailings Remediation Plan construction project. Travis has his Bachelor’s in Civil Engineering from the University of Saskatchewan, and has worked at SNC Lavalin as a Geotechnical Engineering Assistant and most recently at the Water Security Agency as a Project Engineer in Training.

Professional Development

Okane’s Oceania staff held their 2019 Professional Development Seminar in Noosa, Queensland, sharing technical presentations and knowledge transfer from staff across the Oceania region and Canada – and visiting the beach, of course!

Revegetated Cover Systems Program

Okane are excited to be leading the Revegetated Cover Systems Program (RCSP), a five-year collaboration between OKC, Kings Park Science (KPS) of the Department of Biodiversity, Conservation and Attractions (DBCA), the University of Western Australia (UWA), and Industry. The program aims to quantify actual plant water use (transpiration) on cover systems, optimise species biodiversity to ameliorate cover system performance, and improve revegetation of engineered cover systems in the Pilbara.