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Water Catchment Protection


An important land use for the northern jarrah forest is the supply of potable water to Perth, regional communities and local properties. It is therefore essential that Alcoa manages its mining operations to minimise any negative effects on both stream water quality and yields are maintained.
 
Alcoa’s comprehensive hydrological monitoring and research programs covers the High Rainfall Zone (HRZ, long-term average rainfall >1,100 mm/yr) and the Intermediate Rainfall Zone (IRZ, 900 to 1,100 mm/yr) of the northern jarrah forest. The main issues for water quality relate to turbidity in the HRZ, and in the IRZ, the potential for increasing stream salinity.
 
Current research is focused on the HRZ’s catchment water yields. Monitoring and modelling of catchments where mining and rehabilitation have been completed have shown streamflow initially increases due to the clearing of the vegetation but eventually approaches pre-mining levels and may drop below these levels.

Research programs instigated in 2007 are examining the cause and longevity of the streamflow decline and also how fire and silvicultural management of the rehabilitation influences streamflow.

The primary area of interest in the IRZ is stream salinity. The potential for mining in the IRZ to affect the salinity of drinking water reservoirs was recognised almost 30 years ago and a comprehensive research program began in 1979.

About 40% of the ore contained within Alcoa’s mineral lease is in the IRZ. Alcoa has made a commitment to not mine in the IRZ until research demonstrates that no salinity impact will occur as a result of mining. This is to ensure the protection of the drinking water catchments.

A Trial Mining Project (TMP) was started in 2004 in the IRZ at the Huntly Mine to help demonstrate that mining and rehabilitation will not lead to an increase in salinity in drinking water reservoirs. Mining and rehabilitation of the trial mining area is on track to be completed by 2011.
 
In 2007, an approval process focussing on analysis and research of proposed mining in the IRZ has been agreed with the MMPLG and the Bauxite Hydrology Committee (BHC). The BHC is a technical sub-committee of the MMPLG which has a role of overseeing Alcoa’s hydrological research program.
 

Monitoring

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Monitoring ensures Alcoa maintains streamflow and water quality at acceptable levels.

Turbidity monitoring station

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A turbidity monitoring station sends real-time data to the mine office.

Discharge Sump

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A multi-stage discharge sump removes sediment from mine runoff before it is released to a nearby streamzone.