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Water management


The responsible management of water is critical to minerals industry operations and to the maintenance of a ‘social license to operate’. While the industry accounts for less than 4% of annual water use, it can be a significant water user at a local or regional level.

Gold companies in Australia have put in place a range of strategies for responsible water use. They include monitoring programs for water supply, storage, usage and discharge, risk assessments, development and maintenance of site-wide water balances and water conservation programs that address significant risks at all stages of the mine life cycle. They have invested heavily in the development and application of innovative technologies for the management, recovery, recycling and beneficial use and re-use of water. Gold companies have also been at the forefront of adopting risk management approaches to ensure that climate variability is factored into water management planning.

The Minerals Council of Australia (in conjunction with the Sustainable Minerals Institute) has developed a leading practice Water Accounting Framework for the minerals industry. The framework allows mining operations to account for and to report water use in a consistent way. This industry-driven initiative aims to build greater understanding and community confidence in the way water use is managed and reported.

Case Study: Cadia Valley Operations Water Account

Newcrest’s Cadia Valley Operations have pioneered the framework and an example of the 2011-12 water account is provided below. The framework is used to drive continuous improvement in water management and re-use.

The Input and Output statements provide information on all water into and out of Cadia Valley Operations. Through deliberate design, Cadia Valley Operations source the majority of water needed on site, including water flow from waste rock dumps and natural catchment within the mining area. Around 10% of the operation’s water needs are sourced from town effluent under a special arrangement.

The quality of water inputs and outputs and the potential transformation through its use in site operations is an essential part of the water story. A consistent approach to “water quality” categories is a key component of the framework based on three categories of water:

  • Category 1 – Low salt content and only requiring minimal and inexpensive treatment to bring to drinking water quality standards
  • Category 2 – Low to medium salt content or moderately acidic/basic and may contain other components requiring additional treatment to bring to drinking water standards
  • Category 3 – Medium to high salt content or highly acidic/basic and may contain levels of harmful metals requiring significant treatment to bring to drinking water quality standards.

While category 1 is viewed as better water quality than categories 2 or 3, this does not necessarily mean that categories 2 and 3 pose a greater “hazard” than the category 1. An example of category 3 is seawater, used in some operations.

Of interest at Cadia Valley Operations is the large output of Category 1 water over the reporting period. This volume is explained in the account’s “Notes” and contextual “Statement” which records that due to the high rainfall conditions during the 2011-12 reporting year, more than 6 billion litres of surplus water was released from the onsite dam contributing to catchment flows.

Another key figure to note is the “entrained” volume of Category 2 water in the Cadia Valley Operations’ Output Statement. This volume of category 2 water represents the amount of water contained within the ore that is transported from the site over the reporting period.

Table 1: Inputs table

 

Inputs Megalitres Quality
Surface water
Precipitation and runoff1 10,152 Category 1
Precipitation and runoff2 6,548 Category 2
Surface storages 0  
Rivers and creeks3 2,523 Category 1
Groundwater
Aquifer interception4 506 Category 2
Bore fields 166 Category 1
Entrainment5 572 Category 2
Sea Water
Estuary 0  
Sea/ocean 0  
Third party water
Town effluent 2,525 Category 1
Entitlement transfer 426 Category 1
Total inputs 23,418

 

 

 

Table 2: Outputs table

 

Outputs Megalitres Quality
Surface water
Discharge6 <1  
Environmental flows7 6,167 Category 1
Groundwater
Seepage8 576 Category 2
Re-injection 0  
Sea Water
Discharge to sea 0  
Discharge to estuary 0  
Third party water
Entitlement transfer 0  
Other
Evaporation 5,003 Category 1
Entrainment9 4,635 Category 2
Vent loss 303 Category 1
Other10 144 Category 2
Total outputs 16,828  

 

The site’s water balance summary provides a high level view of the change in water held by the site over the reporting period. It can be seen that Cadia Valley Operations increased stored water volume by 6,950 mega litres over the 12 month period.

 

Table 3: Water balance (ML)

 

Inputs – outputs 6,590
Storage at start 12,434
Storage at end 19,024
Change in storage 6,590

 

Notes

 

  1. Includes Cadiangullong creek dam inflow, Cadia Creek extraction, Flyers Creek extraction, Copper Gully Creek to Cadia Hill Pit, Rodds Creek into URC dam
  2. Stormwater runoff from waste rock dumps, tailings storage facilities and active mining areas
  3. Extraction from the Belubula River
  4. Total groundwater interception from mining operations minus entrainment
  5. Assume 22Mt @ 2.6% insitu moisture
  6. Releases from sediment dams (CD11 &T6) and overflow of Belubula Pond, less than 1ML in total
  7. Releases from Cadiangullong dam to maintain minimum flow and overflow through the dam spillway
  8. Modelled seepage loss from Cadia East Environmental Assessment
  9. Tailings, concentrate and Cadia East waste rock entrainment
  10. Estimated haul road dust suppression usage

 

The accuracy statement reflects the way these flow volumes in the account have been calculated. This is a useful guide for site managers when trying to identify areas for improved monitoring or measurement.

 

Table 4: Accuracy statement

 

Type of flow Percent of total flow
Measured 23%
Estimated 41%
Calculated 37%

 

Table 5: Water balance summary (ML/year)

 

  Category 1 Category 2
Input summary by source and quality
Surface water 12,675 6,548
Sea water    
Third-party water 2,951  
Output summary by destination
Surface water 6,167  
Groundwater   576
Seawater    
Third-party water    
Evaporation 5,003  
Entrainment   4,635
Other 303 144

 

The statement of operational efficiencies provides a consistent way for operations to determine the proportion of water they reuse (without treatment) and recycle (with treatment) within their operations. The consistency provided by the framework not only provides a clear benchmark for site improvement, but also allows reuse to be compared across operations for the purposes of identifying areas for investment and improvement.

 

As provided in the statement of operational efficiencies for Cadia Valley Operations, more than 73% of water used by the site is reused within its operation. This high reuse value is representative of the site’s drive to manage its water use efficiently.

 

Table 6: Statement of operational efficiencies

 

Total flows into tasks (ML) 40,080
Volume of water (ML) reused 29,419
Reuse efficiency 73%
Volume of recycled water (ML) 24
Recycling efficiency 0.06%

 

Statement

 

Rainfall in 2011-12 was close to average at 860mm (average 880mm), following the very wet year in 2010-11 (1413 mm). High rainfall in February and March resulted in the onsite storage of Cadiangullong Dam again filling to capacity and spilling over 5,000ML during March to May. Carcoar Dam on the Belubula River also filled to capacity and spilled, this was the first time the dam had greater than 90% since 2001.

 

During the year works were completed on enlarging Upper Rodds Creek Dam, with capacity increasing from 3,700 to 14,500ML. Completion of this work and other modifications to the Cadia Valley Operation water management system allowed continued building of onsite storage by a further 6,590ML. Water supply reliability has improved significantly since July 2010 when total site water storage was 2,645ML compared to the 19,024ML in June 2012.

 

Cadia Valley Operation holds a number of water licenses that allow the extraction of regulated and unregulated flows in the Belubula River catchment. Pumping capacity and available storage limited license extraction with effectively 100% of entitlement available on the Belubula River, taking into consideration carry-over provisions.

 

The major water sources were quite different from previous years, the percentage of the total water sources were:

 

  • TSF stormwater 31%
  • Belubula River 22%
  • Orange effluent 18%

 

Extraction from Flyers Creek, Belubula River and delivery of effluent from Orange recommenced after being temporarily suspended in 2010-11 to minimise the risk of discharge from site.

 

Cadia Valley Operations Water Balance