Supervising Scientist, Darwin, 2004
ISBN 0 642 24391 3
ISSN 0 158-4030
2 - Environmental assessments of uranium mines (continued)
Throughout the reporting period the water management system at Ranger operated satisfactorily.
The rainfall for the 2003-04 wet season was 1619 mm, 106 mm above the long-term average of 1513 mm. The season was highlighted by unseasonable rainfall in both May and June with May receiving 39 mm and June 10 mm. This has led to a slight increase in the total volume of water held in storage on site in the process and pond water systems by approximately 100 ML compared to the end of the previous wet season. Land application recommenced in June/July for the Magela Land Application (MLA) Area, Djalkmara Irrigation and Djalkmara Extension Areas, and the Retention Pond 1 irrigation area. The higher than average rainfall for 2003-04 compares with the rainfall for the 2002-03 wet season of 1199 mm, which was the lowest since the 1991-92 wet season.
Under the Ranger Environmental Requirements, water that is in direct contact with uranium ore during processing (process water) must be maintained within a closed system. It may only be released by evaporation or after treatment in a manner and to a quality approved by the Supervising Scientist.
ERA advised the MTC in October 2003 that plans for a process water treatment plant would be put on hold due to the positive progress made with pond water inventories and a review of its strategy for managing and reducing its inventory of process water.
Since that decision ERA has undertaken further investigations into passive treatment and based on the results has decided to reinitiate the process for construction of a water treatment plant.
During the night of 23 March of 2004, the Ranger and Jabiru East potable water supply was contaminated with process water via an unauthorised connection. This incident is discussed in Section 2.2.4 of this Annual Report.
Two wetland filter systems operated during 2003-04, the Corridor Creek system and the constructed wetland filter in the Retention Pond 1 catchment. Another constructed wetland filter, also near Retention Pond 1, was not utilised and requires reconstruction to improve its water retention characteristics. This has yet to be undertaken.
The Corridor Creek system receives runoff from the southern stockpile area. ERA has undertaken significant works in this area over the past two years to address the sources of the higher than expected uranium concentrations measured at the entrance to the wetland filter that feeds the Corridor Creek system towards the end of the 2001-02 wet season. The top of the No.2 stockpile was recontoured and better integrated with stormwater pipes to prevent 'ponding' of water on its surface (Figure 2.3), and a sump (southern stockpile seepage sump) was constructed to the east of the tailings dam to collect seepage expressing at the base of the No.2 stockpile during the 2002 dry season. These and other associated activities significantly improved the effectiveness with which seepage was separated from surface runoff, the latter reporting to the Corridor Creek system. Uranium concentrations in water entering the wetland filter that feeds the Corridor Creek wetland system (monitoring point VLGCRC2) remain more than 20 times lower than the maximum value recorded in the 2001-02 wet season. This demonstrates that the remedial actions taken continue to be successful.
The pond water system contains water that has been in contact with stockpiled mineralised material and areas of the site other than those contained within the process water system. This also includes water from Pit 3. The water is managed in accordance with the Water Management Systems Operation Manual. The manual describes a system whereby water is managed according to source and quality. The pond water system consists of Retention Pond 1, Retention Pond 2, Pit 3 and Djalkmara Billabong. Retention Pond 1 overflows via a constructed weir into Coonjimba Creek every wet season and was observed to flow between 15 January 2004 and 15 April 2004. Water from Retention Pond 2 or Pit 3 may not be released without prior treatment through wetland filtration and/or irrigation. Water is released from Djalkmara Billabong into Magela Creek each wet season subject to water quality criteria determined by whole of effluent toxicity testing.
In the past few years, the inventory in this system has reduced due to a change from a fixed regime based on catchments to one in which water is managed according to water quality, as well as an optimisation of the wet season stockpile design. However despite a higher than average 2003-04 Wet season, the total volume in the pond water system at the end of March (generally considered the peak storage time) decreased again from 1769 ML in 2003 to 1427 in 2004. This was mainly due to the ability of ERA to undertake strategic releases of water in Djalkmara Billabong in the lead up to Djalkmara being consumed through the expansion works in Pit 3.
As noted above, Djalkmara Billabong was consumed by mining in Pit 3 in June/July 2004. Prior to this, 269 745 m3 of water was discharged to Magela Creek periodically between 31 January 2004 and 21 March 2004. ERA was required to manage the release of waters from Djalkmara to meet criteria for mixing in Magela Creek based on toxicity testing undertaken by eriss staff at the request of ERA. The criteria set were based on toxicity testing using three local species (the water flea, green hydra and the purple spotted gudgeon). Testing using these species provided a No Observed Effect Concentration (NOEC) for each species from which a dilution factor was derived by dividing the lowest NOEC by 10. In this case the resulting 'safe' dilution was calculated to be 1% or 1 in 100. However, this corresponded to a uranium concentration of 6 µg/L which is slightly above the authorised limit for uranium in Magela Creek of 5.8 µg/L. Subsequently ERA were strongly encouraged to set in place a management regime for release of Djalkmara water into Magela creek that sets 0.2 µg/L as the target for water quality. This figure is the current agreed focus level in Magela Creek.
The remaining water within Djalkmara Billabong post wet season was transferred to Retention Pond 2 prior to excavation of the billabong.
Water from the pond water system is irrigated within designated irrigation areas on the minesite.
Waters from Retention Pond 2, Djalkmara Billabong and the Retention Pond 1 wetland are irrigated onto the Magela Land Application (MLA) area, the Djalkmara irrigation area, the Djalkmara Extension irrigation area and the Retention Pond 1 irrigation area. Water from Retention Pond 2 is generally directed to the MLA, Djalkmara Billabong water was directed to the Djalkmara and Djalkmara Extension irrigation areas prior to its removal as part of the Pit 3 expansion, and water from the Retention Pond 1 wetland filter is directed to the Retention Pond 1 irrigation area.
The MLA irrigation area at Ranger has been irrigated since 1986. ERA data show changes in the water quality of the shallow groundwater in the MLA, especially EC and pH levels and uranium and manganese concentrations. Since the capacity of the soils in the irrigation areas to adsorb uranium is finite, the Supervising Scientist has identified the need to review irrigation practices at Ranger to ensure that the current high level of protection of downstream aquatic ecosystems continues to be achieved in the future. eriss plans to investigate the lateral and vertical movement of uranium through the soil profile in the 2004-2005 research year.
Tailings continued to be deposited into Pit 1 using a central deposition point on a pontoon.
If mining and tailings management proceeds as currently planned, it is estimated that tailings will reach RL0 (relative level zero) in Pit 1 sometime in 2006 and that process water will rise above RL0 in Pit 1 during the 2004-05 wet season. Under the current authorisation ERA is limited to deposition of tailings below RL0 within Pit 1 as it is known that the south east corner of Pit 1 intersects a zone of higher permeability rock at and above RL0. In anticipation that process water will rise above RL0 in the 2004-05 wet season, ERA submitted a draft application to the MTC on 23 June 2004 to construct a barrier in the south east corner of Pit 1 and to allow interim deposition of tailings above RL0.
Over the past year ERA has undertaken a range of investigations to characterise the potential risk to the environment of contaminants from tailings/process water and to determine the hydrogeological characteristics of the area surrounding Pit 1. This information along with barrier engineering details form the technical backing for the application, which at the time of reporting is still under consideration by the MTC.
It must be noted that any approved application for tailings above RL0 is an interim approval and ERA will have to undertake further research and investigative work to provide a final tailings containment solution to the MTC for approval. If the proposed interim barrier is not proven to meet the requirements of the MTC for final containment, the Supervising Scientist has advised that tailings should be removed from Pit 1 down to the RL0 level and a suitable containment solution devised.
Allowing the process water level to rise above RL0 in Pit 1 does not require a specific approval. However, the MTC has asked ERA to determine the actions, if any, required to ensure that the environment remains protected and to advise the MTC accordingly.
The annual occupational radiation dose limit recommended by the International Commission on Radiological Protection (ICRP) and adopted in Australia by the National Health and Medical Research Council (NHMRC) is 100 mSv in a five year period, with no single year exceeding 50 mSv. In addition to this requirement, ERA classifies workers as designated and non-designated workers, respectively, where designated workers may potentially receive a radiation dose of greater than 5 mSv per year. All other workers are non-designated.
The primary exposure pathways by which workers may receive a radiation dose are:
- inhalation of radioactive dust;
- inhalation of radon (222Rn) progeny;
- direct exposure to gamma radiation.
The ingestion pathway is generally considered less significant if general safety and hygiene procedures are followed. In March 2004 however, an incident at Ranger resulted in process water contaminating the potable water supply. The maximum total dose that would have been received by an ERA employee via the ingestion pathway due to the incident has been estimated less than 0.5 mSv. This represents a worst-case scenario that assumes that 5 L of the most contaminated water was consumed. The estimated maximum dose is below the occupational dose limit. The incident is dealt with in more detail in Section 2.2.4 of this Annual Report.
Doses received via the three main pathways are calculated using the methodology required by the Code of Practice on Radiation Protection in the Mining and Milling of Radioactive Ores, which is still under review. Radiation doses from each of the three individual pathways are assessed and added up to provide average annual doses to employees. The doses to non-designated employees are calculated using the most exposed group for each of the three exposure pathways therefore representing a hypothetical maximum dose. In the 2003 calendar year the mean and maximum effective dose to designated employees amounted to 1.6 mSv (1.5 mSv in 2002) and 6.5 mSv (5.8 mSv in 2002), respectively. The maximum dose to non-designated workers amounted to 1.0 mSv compared with 0.86 mSv in the previous year. Figure 2.4 shows the trend of the annual effective doses to ERA employees over the last five years. No designated employees have received doses above the recommended occupational dose limit and no non-designated workers have received a dose of higher than 5 mSv in the past five years.
Annual effective doses to employees depend on the work category and were, as in previous years, dominated by the external gamma pathway for mill and mine production workers and by the dust pathway for mill maintenance workers and electricians.
ERA and EWL Sciences prepared a discussion paper for the ARRTC meeting in March 2004 compiling the results of the Ranger radiation monitoring programme from 1980 to present. The paper provides an extensive statistical analysis of historical occupational radiation data and has shown that occupational doses via the various exposure pathways are highly predictable. Sporadically, elevated results for personal dust monitoring in the Product Packing group, where every employee has to wear compulsory respiratory equipment, and the Mill Maintenance group indicate that these areas should be a focus of future monitoring and engineering design efforts.
The follow-up Environmental Audit Review to the 2003 annual Audit of the Ranger operation (reported in the 2002-2003 Annual Report of the Supervising Scientist) was undertaken on 17-18 November 2003 The review team consisted of representatives of oss, NLC and DBIRD.
The audit review found no Category 1 or Category 2 non-conformances. The majority of the issues raised in the May 2003 audit have been addressed, with the one conditional issue raised in the May 2003 audit closed out.
The 2004 annual Environmental Audit of the Ranger operation was undertaken between 24-28 May 2004. The audit objectives were: to determine the current status of the Draft Mining Management Plan; to identify any statutory non-compliance; to identify areas for improvement; and to present findings as non-judgmental feedback on the performance of ERA as perceived by the audit team at the time of the audit.
The main areas visited during the audit were the tailings corridor, the corridor sump, the GCMBL Bund, the Brockman Bund, the half pipes (VCGL), the Corridor Creek Wetland Filter, Pit 1, the Southern Stockpile, the Southern Stockpile Seepage Sump, the Western Stockpile, Pit 3, and the Workshop and Mill Area.
The audit team identified two Category 1 non-conformances, three Category 2 non-conformances, and made 22 conditional comments. These generally referred to items planned in draft MMP but not yet completed. A number of observations were also made by the team (Table 2.3).
The Ranger Minesite Technical Committee met four times during 2003-04. Dates of meetings and significant issues discussed are shown in Table 2.4.
|Date||Significant agenda items|
|17 October 2003||Process water treatment programme update, RL0 application update, status of operational monitoring plan and Mine Management Plan, monitoring sites MCUS, GCUS and GCC, SSD revised trigger values, stockpile runoff proposal for 2003-04 wet season and status of Senate Inquiry recommendations.|
|28 November 2003||Process water treatment programme update, RL0 application update, status of operational monitoring plan and Mine Management Plan, monitoring sites MCUS and GCUS, SSD revised trigger values, stockpile runoff proposal for 2003-04 wet season, Lea Report recommendations and status of Senate Inquiry recommendations.|
|19 February 2004||Water treatment programme update, RL0 application update, status of operational monitoring plan and Mine Management Plan, SSD revised trigger values, stockpile runoff proposal for 2003-04 wet season, threshold levels for reporting, routine periodic inspections, review of radiological monitoring update, and first flush issues|
|23 June 2004||Pond water treatment programme, RL0 application update, status of Mining Management Plan and approvals, SSD revised trigger values, threshold levels for reporting, review of radiological monitoring, first flush issues, tailings beach, closure of MTC-related items from OSS leak report, radiation clearance procedures and schedule of operational monitoring programme/research activities.|
There was only one approval under the Authorisation during 2003-04 (see Table 2.5).
|12 May 2004||Approval of Ranger Rehabilitation Plan #29|
There were several reportable incidents at Ranger during the year.
On 11 October 2003 an incident occurred involving two contractors in the Product Packing area of the Ranger mill. The workers had attempted to repair a rotary valve in the mechanism that fills drums with uranium product and uranium product spilled onto the floor, generating a dust cloud. Both contractors were wearing appropriate personal protective equipment (airstream helmets) at the time. ERA investigated the incident, including estimating the dose that might have been received by the contractors resulting from the incident. Based on the information available, in particular that the contractors were wearing airstream helmets as appropriate, it was concluded that dose limits were not exceeded.
On 23-24 March 2004 an incident occurred in which the Ranger potable water supply was contaminated with process water. This incident was the subject of an investigation by the Supervising Scientist and is discussed in detail in Section 2.2.4 of this Annual Report.
Three separate incidents involving vehicles leaving the Ranger site without appropriate radiation clearance processes being undertaken also occurred during the year. These incidents were investigated by the Supervising Scientist and are discussed in Section 2.2.5 of this Annual Report.
- Letter of Transmittal
- Supervising Scientist's Overview
- 1 - Introduction
- 2 - Environmental Assessments of Uranium Mines
- 3 - Environmental Research and Monitoring
- 4 - Statutory Committees
- 5 - National Centre for Tropical Wetland Research
- 6 - Communication Liaison
- 7 - Administrative Arrangements
- Appendix 1 - ARRTC Key Knowledge Needs
- Appendix 2 - List of Publications 2003-04
- List of Tables
- List of Figures