Day 2 Major Advances in Reclamation Mineral site closure planning, reclamation, rehabilitation & remediation Day 2 Major Advances in Reclamation

After land clearing, the next step is topsoil removal After land clearing, the next step is topsoil removal. Soil is a thin layer of the Earth's crust that has been modified by the natural actions of agents such as water, plant-life, and microorganisms. Most terrestrial plants could not survive without soil, so topsoil management plays an important role in mine reclamation planning. Prior to mining, topsoil is carefully removed and stored at separate areas to be used for subsequent mine site rehabilitation. Timing and storage of topsoil removal are important. Topsoil which is too wet or too dry can result in compaction and loss of soil structure, and long-term stockpiling will reduce its quality. Where practical, the mine's environmental manager aims for an early return of the topsoil for rehabilitation of the reconstructed landforms.

Transferable skills learned by heap leach personnel include pipe laying, irrigation systems, operating and maintenance of pumps and controls, surveying, earthworks, liner construction and maintenance, slope and erosion control, reclamation and revegetation, and various other aspects of civil construction.

Montana is the only state in the USA to have implemented a ban on cyanide leaching of gold ores. Three primary reasons have been given for the decision to phase-out existing projects and prohibit new developments involving cyanide leach mining in Montana:

CASE 6.3 Cyanide and Groundwater 1. Open pit, cyanide leach mines threaten the private property rights of neighboring landowners (e.g. Landowners downstream of the Golden Sunlight mine were forced to sell their properties to Placer Dome Corp. after their drinking water well was contaminated with cyanide)

2. Open pit, cyanide leach mines expose Montana taxpayers to the costs of reclamation and leave liabilities for future generations (e.g. Pegasus Gold Corp. declared bankruptcy in 1997 leaving the State with insufficient funds to reclaim the Zortman/Landusky mine, Montana's largest gold mine. The State has estimated that water treatment will have to occur at the mine site in perpetuity).

3. Open pit, cyanide-leach mines consistently contaminate Montana's water resources with cyanide and other pollutants placing human and environmental health at risk. Since 1982, there have been 50 cyanide releases at Montana mines, releasing millions of gallons of cyanide solution into Montana's soil, surface and groundwater resources. Cyanide can persist for very long periods of time in groundwater because the sunlight and oxygen needed to break it down to less harmful substances are largely absent. Groundwater contamination is the most prevalent form of cyanide contamination at Montana's open pit cyanide leach mines because the liner systems designed to prevent this type of occurrence are not impermeable and are prone to structural damage (punctures or tears).

7.3 THE HYDROSPHERE – STORAGE AND MOVEMENT OF WATER For a mining project water may be both friend and foe. Mining project operations invariably require water, sometimes in very large quantities. The uses vary widely: dust suppression, milling and processing, transport of tailings and/or concentrates, recovery of metals by leaching, and reclamation of mined lands. Waste waters may be generated from dewatering, runoff from disturbed land, or excess water from tailings impoundments or water storages. Impacts on the local hydrologic cycle in terms of quantity, quality, or both, often constitute the most prominent or the most serious environmental impacts associated with mining.

Loss of Visual Amenity Surface mining commonly causes scars on the Earth's surface. While the extent of such scarring is much less than that associated with rail and road construction, the scars themselves tend to be larger and more unsightly, potentially causing a loss of visual amenity. Visual impacts may diminish public enjoyment, or may impair the character or quality of a natural landform. Reclamation and eventually mine closure aim to re-instate a stable and pleasing landform but full rehabilitation of natural vegetation is likely to require several decades, if it's possible at all. Reclamation and eventually mine closure aim to re-instate a stable and pleasing landform but full rehabilitation of natural vegetation is likely to require several decades, if it's possible at all.

Safe on-land storage of tailings slurry is difficult to achieve and reclamation of wet tailings storages requires long-term planning and financing. A recent trend is to reduce the water content of tailings prior to final disposal by using paste and thickened tailings technologies (Jewell and Fourie–2005). Tailings with reduced water contents involve lower environmental risks. However, such dewatering technologies are relatively expensive and are used mainly in cases of severe water shortage, to recover expensive process reagents, or in situations where secure conventional tailings systems cannot be constructed.

Safe on-land storage of tailings slurry is difficult to achieve and reclamation of wet tailings storages requires long-term planning and financing. Tailings with reduced water contents involve lower environmental risks.

Factors Controlling Water Erosion universal soil loss equation The widely accepted universal soil loss equation (USLE, US Department of Agriculture 1980) relates average soil loss to five factors: rainfall and runoff (R), soil erodibility (K), a combined slope length and steepness factor (LS), vegetative ground cover and cover management (C), and support practices (P) (Figure 20.2). It

FIGURE 20.2 Factors Controlling Water Erosion

The structure of the original USLE remains unchanged, but the estimation of the five factors has been refined to characterize the special site conditions resulting from mining, construction and reclamation activities. RUSLE is a very powerful tool that can be used to estimate soil loss under a wide variety of site-specific conditions. The equation can include the full spectrum of land manipulation, including rock cover, mulches, random surface roughness, effects of mechanical equipment on soil roughness, terraces and vegetation types. Its successful application is directly related to the experience of the model user in estimating site-specific empirical control factors as model input data.

Permanent or temporary vegetation and mulching can be employed for areas of occasional or no construction traffic (e.g. reclamation areas). Preventive measures include minimizing surface areas to be disturbed, timing the sequence of site clearing activities to coincide with actual mining activities in each area, and controlling the numbers and activities of vehicles on a site at any given time. Phasing of land clearing is considered to be especially critical for cleared sites greater than 40 hectares in size (Cheminfo Services 2005). Where feasible, clearing should be started at the location that is upwind with reference to the prevailing wind direction.

Rehabilitation and reclamation are the most commonly used terms for the procedures and practices applied to return land disturbed by mining to a functional condition. Rehabilitation is the term most commonly used in the Australian mining industry, while reclamation is the term favored in the USA

Revegetation is another commonly used term, its meaning being confined to that part of the rehabilitation process involving establishment and maintenance of plants. Restoration is a more specific term which refers to rehabilitation that returns the land surface to its pre-existing function and condition.

Main Environmental Challenge Apart from Tailing management, handling, and relocation of waste rock continues to remain one of the main challenges in the mining industry. Will be covered when we discuss approaches to waste rock disposal (Ch. 19 – Mining and the Environment – Spitz & Trudinger)