Waste Rock and Tailings Characteristics

Tailings Storage Facilities

Embankment Design

Surface Water and Stormwater

Embankment Zoning

Acid Drainage Control

Hydrogeology

Subsurface Drainage

Processes of Water Movement

Construction Control and Monitoring

Long Term Management of the Tailings Storage Facilities

Introduction.
In many mines throughout the world, waste rock and tailings are disposed of separately to form waste dumps and tailings dams. At Waihi the situation is unusual, in that waste rock is used to form embankment is progressively raised in order to 'keep up' with tailings production, allowing for sufficient storage capacity to ensure that the water within the tailings pond will be contained, even in extreme rainfall events. Storage capacity is provided for a 1200 mm rainstorm, (the Probable Maximum Precipitation), plus an additional 1.0 metre minimum freeboard.

There are two tailings storage facilities, known as Storage 2 and Storage 1A. Construction of Storage 2 commenced in 1987, and has reached its final crest height. It was decommissioned from tailings deposition in 2005. A substantial database spanning more than ten years demonstrates that the performance of Storage 2 has been very good. The design of Storage 1A is based largely upon the design of Storage 2. While there are some technical differences, for the purposes of explanation on this website the description of Storage 2 can also be applied to Storage 1A.

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A number of environmental considerations have been taken into account in planning and designing the waste disposal area:

• Identification of the best location for the tailings storage facilities, taking into account the status of the land with respect to ownership, geology, archaeological features, flora and fauna.
• The design and construction of the embankments, considering short and long term structural stability.
• Ways that potentially significant adverse effects such as noise, dust, visual effects, acid drainage, and cyanide can be avoided, remedied and mitigated.
• The surface and subsurface drainage systems required to ensure that potentially contaminated water can be collected and managed.
• The water management and water treatment facilities required to ensure that there are no significant adverse effects on the surrounding rivers and streams.
• The requirements for rehabilitation and closure of the site.

To address these issues, advice has been sought from a team of experts including archaeologists, geologists, hydrogeologists, engineers, geochemists, rehabilitation consultants and landscape architects. The following sections describe the design and construction of the tailings storage facilities with particular emphasis on structural stability, acid drainage control, and the drainage systems, for surface water and underdrainage.