Water output
The water that we use in our mining and processing operations can be released to a variety of locations. The type of location is dictated by the environment in which the operation is located - for example, ocean, surface waters or evaporation on land.
Different qualities of water can be discharged in accordance with government regulations and we decide on the best way by taking environmental and community concerns into account at each specific site.
Our results
In 2007, we returned 611 billion litres of water to the environment compared to 625 billion litres in 2006. Of the 2007 figure, 77 per cent was process effluent, 14 per cent was from stormwater diverted from our sites to prevent contamination, and a further 8 per cent was water removed to aid mine access (dewatering water).
Other water is lost through evaporation and seepage, entrainment of water in product or process wastes, and process water sent to third parties.
While discharge limits are usually set within permits and other legislation relating to operational conditions, understanding the environmental and social impacts resulting from water return activities is a requirement of our water standard. This is best managed at an operational level because of the site specific nature of water quality.
While each site measures and reports on water quality, these data cannot be aggregated meaningfully at a global level. However, some more common indicators are shown below as an indication of the type of aspects being managed.
- Seven operations in 2007 discharged cyanide at low concentrations and below regulatory limits, but when aggregated across Rio Tinto amount to 46 kilograms well below the 109 kilograms in 2006. All of the seven operations reported cyanide concentrations below discharge permits or below method detection limits.
- In 2007, forty three operations discharged suspended solids at low concentrations that amount to 1.4 million tonnes in total. This figure was 2.5 million tonnes in 2006.
- Fifteen operations reported biological oxygen demand (BOD) at low concentrations. This can be aggregated to 218, 000 tonnes. This an increase from 2006 which was 56, 000 tonnes and is attributed to a full year of monitoring in 2007 at Green's Creek, compared to only a partial year in 2006.
- Twenty five operations measured total metal loading at very low concentrations. Although not a very meaningful reflection of performance at the operational level, this can be aggregated across the Group to 13 tonnes of arsenic, 15 tonnes of copper, 13 tonnes of lead, 11 tonnes of cadmium, 16 tonnes of zinc and seven tonnes of mercury. The comparison to 2006 is that nineteen operations measured total metal loading which can be aggregated to 28 tonnes of arsenic, 12 tonnes of copper, three tonnes of lead, 1.6 tonnes of cadmium, 42 tonnes of zinc and seven tonnes of mercury across the group.