mine closure design

cover system design

At many mine sites, the design and construction of a cover system for closure of a waste storage facility is the foremost closure issue, with significant environmental, financial and regulatory implications. Okane has the unique fortune to be involved and to lead the design of cover systems within a large range of climatic conditions around the world. More importantly, Okane is responsible for monitoring over 75 of these locations, and is responsible for continuously managing and interpreting detailed monitoring data.

Our experience in monitoring in many locations worldwide allows for continual evolution of design methodologies by learning through interpretation of detailed monitoring data. Hence, Okane’s design methodology uses an approach of adaptive continual improvement.

This provides integrated solutions for:

  • dust and erosion control;
  • chemical stabilisation of acid-forming mine waste (through control of oxygen ingress);
  • contaminant release control (through control of infiltration); and,
  • provision of a growth medium for establishment of sustainable covers.

There has been a general tendency in the industry to develop performance criteria for cover systems that are tied directly to various cover design objectives. In many cases, this practice has led to the development of overly-conservative targets for cover performance, generally relating to net percolation, oxygen ingress and / or plant density and diversity. Okane provides practical solutions tailored for the site location, climate, scheduling and site constraints, to develop cover performance criteria on a case-by-case basis.

landform design

Okane’s philosophy for design of final landforms for mine waste stockpiles can be summarised as follows:

  • the design of final mine landforms should take place prior to construction to accommodate waste schedules and enable correct placement of mine waste materials;
  • geotechnical stability is paramount, but aesthetics and natural appearance should be considered in the design of mine landforms; and,
  • surface water drainage systems must be designed for the local hydrology and robust, for long-term performance.
Cover System iPad

Landform design for mine closure requires a holistic view of mine operations, where each operational stage and each domain is part of a plan that considers the end land use as well as the immediate need. This plan, which needs to be flexible to accommodate changes in methods and / or technology, is about optimising post-mining land capability, limiting the costs in achieving optimal land use, and minimising long-term maintenance liabilities.

Surface water management systems must be robust to ensure long term stability and environmental performance. Informed landform design considers the specific climate for planning long-term drainage of plateau and embankment surfaces. Okane’s innovative landform designs are provided by highly skilled and experienced personnel using state of the art numerical models.

We routinely use commercial landform evolution models, including WEPP, SIBERIA and CAESAR to create our designs. This, coupled with our capabilities using hydrological models and commercial CAD and GIS software allows Okane to provide first-class engineering designs and visualisations.

integrated rehabilitation

Okane Consultants (Okane) understands the importance of a holistic approach to mine site rehabilitation. The interdisciplinary team at Okane have the capabilities to quantify all aspects of the soil-plant-atmosphere continuum, including plant ecohydrology on disturbed and natural sites. Linking plant water use, health, and root distributions to material properties, cover system characteristics, and landform design vastly improves the performance of rehabilitated sites and the likelihood of reaching stable plant communities.

In Okane’s experience, site specific solutions reduce overall rehabilitation costs and improve the success of rehabilitation efforts. Understanding the movement of water from the growth medium to roots, then from the plant to the atmosphere on a site specific basis allows Okane to tailor solutions to each individual site.

To provide the most cost effective and impactful solutions, Okane focuses on monitoring and sampling key components of soil-plant-atmosphere relations which include:

  • material characterisation as it relates to plant soil type preferences;
  • plant growth and cover;
  • root distribution and morphology;
  • plant water use and physiology; and
  • vegetation response to atmospheric drivers.

Information gained from Okane’s rehabilitation monitoring activities directly inform decisions pertaining to growth medium physical characteristics and thickness, plant species composition, and overall ecosystem function. Effective re-vegetation plans and strategic rehabilitation monitoring can be formulated to ensure plant development achieves desired outcomes.

Once vegetation is established, monitoring metrics may include assessment of plant cover, health, and effects on erosion. Okane’s soil-plant-atmosphere models can also be calibrated using empirical monitoring data collected on site, thus providing robust estimates of cover system and landform performance.