Alcoa of Australia Residue Management
 
Residue Rehabilitation
Residue is stored in large fully-confined impoundments within Alcoa of Australia’s landholdings. The Residue Rehabilitation group has a major focus on developing a sustainable vegetation cover based on a detailed understanding of the various physical, chemical and microbial limitations of residue sand as a growth media.
 
There are two categories for the rehabilitation of the residue areas;
 
1. progressive rehabilitation
2. closure rehabilitation
 
Progressive rehabilitation refers to the ongoing rehabilitation of long-term external embankments of the residue footprint. When a residue embankment is built that is planned to be part of the final external footprint of the residue area, the rehabilitation of that embankment commences soon after construction, and while the residue area is still operational.
 
While the residue mud is generally not visible outside Alcoa of Australia’s operations because it’s contained within engineered dykes, we are committed to rehabilitating the embankments of the dykes to attempt to give the residue area as natural an appearance as possible for nearby communities.  The aim of embankment rehabilitation is to generate a self-sustaining ecosystem, but this can take years to establish. As the external embankments are lifted to contain the residue, the new embankment sections are progressively rehabilitated. In effect this allows a great majority of the overall residue footprint to be rehabilitated before the residue drying areas close.
 
Final closure rehabilitation is where the area remaining open at the end of a residue area’s life (usually because Alcoa of Australia has made a commitment to close an area or it has reached its design height) is rehabilitated.  What is involved in final rehabilitation closure will depend on the final land-use planned for the area, and may vary from site to site. Typically however it will involve contour shaping, revegetation and dewatering of the residue area after closure.
 
Field trials and fundamental research on residue rehabilitation as a means of optimising the vegetation performance is undertaken at all three Alcoa of Australia refinery residue areas.  This work varies from large scale field trials such as demonstration areas at Pinjarra, to bench scale laboratory experiments by local, interstate and international universities. This research aims to better understand water-nutrient-plant-residue sand dynamics as a means of optimising the rehabilitation prescription and identifying potential residue area closure strategies.
 
At the Pinjarra Refinery, we have rehabilitated a former residue area and are trialling a range of treatment options.  Currently the rehabilitated residue area at Pinjarra is being used for agriculture (Alcoa Farmlands) and features native species.
 
Alcoa has also closed residue areas at Kwinana, some of which have been returned to the State and used as the site for the Kwinana Motorplex.
 
Currently, all of Wagerup Refinery’s residue storage areas are still operational.
 
At closure, many of the potential challenges arising during operations will no longer exist, for example dust generation and water use. However other issues, such as managing the deposit to reduce potential groundwater impacts will remain important.
 
The current closure strategy has three main objectives, being that decommissioned residue areas should:
  • have the capability to be used for productive community benefit,
  • be a safe and self-sustaining structure in the long term, and
  • allow future access to residue for alternate uses.