Open Cut » Environment
Water and salt management over the Northern Bowen Basin was examined through site visits, workshops, one-on-one interviews and site water balance reports. An organising framework for site water management was identified. A framework was developed which includes a conceptual model of demands for water management, a set of best practice considerations and an information system (available online) within which site information is held. A water and salt simulation model was used to show how water quantity and salinity objectives can be set using a “what if?” scenario process.
A compilation of production and water use figures for 21 mines in the region during the period 2003-2005 showed that ~38GL/yr of fresh water and ~52 GL of worked water was used. The term worked water refers to water that has been used to perform a task on a site and is preferred over value-laden terms such as “contaminated”, “poor” or “dirty” water. There is currently no evident relationship between coal production and the use of fresh or worked water. In a more detailed study of 7 mines, it was demonstrated that the lack of a relationship at the overall level was mirrored with lack of any consistent picture at the level of main processes, i.e., CHPP, dust suppression, underground and industrial area water use. No site consistently used less water or had lower losses per unit of coal production across all processes, i.e., the site with lowest in one category of use was not lowest in any other. There was also shown to be considerable variation in the salinity of the worked water.
By applying a coupled water and salt system balance model driven with historical climate data, it was shown that water use could be well organised with respect to coal production. For water quantity, all process scenarios were run based on practices on existing sites. A considerably smaller amount of fresh water could feasibly be drawn into nearly all sites. The costs of doing this were not estimated nor were the policy implications of increasing on-site water capture dealt with. For most sites, reducing fresh water resulted in an increase in worked water salinity. The rationale for controlling salinity was that it would reduce corrosion costs, protect product quality and reduce flotation reagent use. Reduction in salinity was studied by comparing the current practices with dilution and desalination. Fresh water saving and salt control were shown, on average, to have a positive business case if viewed from the perspective of what economic value could be generated using the water saved rather than only considering cost. There is nothing in principle to constrain improved water management. Further research is needed into site water quality dynamics and understanding why processes use less water on some sites.
At the regional level, growth in coal production and water infrastructure was shown to be consistent with the development of the region since the early 1970’s. Currently, water planning across the region indicates scope for water trading and the differences in water systems at different sites provides opportunities for water and void sharing arrangements. Further integration of town and mine water management is suggested as an area for further work.