Supervising Scientist Annual Report 2002 - 2003

Supervising Scientist, Darwin, 2003
ISBN 0 642 24383 2
ISSN 0 158-4030

2 - Environmental assessments of uranium mines (continued)

There was no further development or mining within the Jabiluka mineral lease during 2002-03. The site remained in a care and maintenance phase involving the implementation and further refinement of processes designed to protect the environment.

The most significant activities on site continued to be associated with water management. Water from the Interim Water Management Pond (IWMP) was irrigated on disturbed areas of the minesite during the 2002 dry season to ensure compliance with the established wet season freeboard requirements. Some minor modifications were made to the irrigation system to reduce the risk of overspray of creek lines on site. The water management system performed satisfactorily during the wet season.

Following the failure of the reverse osmosis treatment plant used by ERA in 2001-02 to treat water from the IWMP prior to irrigation, the Supervising Scientist identified the need to undertake a comprehensive review of the water management system at Jabiluka to ensure that it represented Best Practicable Technology in the context of the site entering a longer period of care and maintenance of the order of ten years. The ten year period was in recognition of the commitment given by ERA to the World Heritage Committee that it would not operate Ranger and Jabiluka at full commercial production simultaneously.

In response, ERA identified approximately 30 water management processes that could be used in various combinations to form a water management strategy and referred these to the MTC for discussion. The MTC undertook a coarse level screening BPT assessment of those options to identify those that should be more closely examined. Returning the mineralised material to the decline and sealing of the decline were added to the range of options considered as a consequence of those discussions. On 30 June 2003, the MTC considered the long-term care and maintenance (LTCM) plan proposed for the site by ERA and determined it to be Best Practicable Technology. The plan was to remove above and below ground infrastructure, cease dewatering the underground workings, place the mineralised material and sludge from the IWMP in the decline together with as much clean waste as possible, seal the decline, and empty and clean the IWMP. Emptying the pond required that up to a maximum of 90 ML of water be irrigated during the 2003 dry season on disturbed areas of the minesite.

The overall result is that the site should require no day to day management as all sources of potential contamination will have been contained below ground or removed from site and the IWMP will become a passively managed facility containing only rainfall. On the basis of the MTC assessment, ERA will apply to the Northern Territory regulator to implement the plan early in 2003-04.

2.3.2 On-site environmental management

Water management

Rainfall at the Jabiluka site was significantly higher than that at Ranger during the 2002-03 wet season. Jabiluka recorded 1792 mm (to the end of May 2003) which was well above average and displays the significant variation that can occur in rainfall between two relatively close sites. Despite the higher than average rainfall, the IWMP remained well below the maximum operating level throughout the wet season. The maximum volume recorded in the IWMP was approximately 119.4 ML. This occurred on 7 May 2003. The maximum operating volume of the IWMP during the wet season is approximately 168 ML.

Between 23 August and 16 November 2002 approximately 40 ML of IWMP water was irrigated at a rate of 485 m³/day over 4.5 ha. This reduced the pond to a volume of 22.8 ML prior to the onset of the 2002-03 wet season.

In anticipation of the measures required to place Jabiluka into a long-term care and maintenance phase, which included emptying and cleaning the IWMP, ERA applied to irrigate IWMP water at a rate of 761 m³/day during the 2003 dry season.The application was approved subject to a review of the system performance after 30 ML had been irrigated. That review concluded that the system was operating satisfactorily and that irrigation at this higher rate could continue. As of 30 June 2003 irrigation had reduced the pond volume to approximately 76 ML. Subject to approval by the Northern Territory regulator, the on-site water management component of the LTCM plan will see the IWMP drained and cleaned, with existing water and sludge being returned to the decline. The IWMP will then contain only clean water which will not require active management.

Investigation of irrigation overspray monitoring technique

Irrigation of the outer batter of the north wall of the IWMP was permitted to maintain vegetation growth and prevent erosion. However, its close proximity to the Tributary North channel resulted in the possibility of some overspray landing in the dry channel, which was to be avoided to the maximum extent practicable.

OSS investigated a monitoring method for the detection of overspray of irrigation water into the dry Tributary North channel. The purpose of the investigation was twofold. Firstly, it was intended to provide information that could assist in the optimisation of the irrigation system to prevent or reduce overspray from the irrigation of the northern batter of the IWMP into the Tributary North channel. Secondly, it could provide data that could assist in the interpretation of monitoring data in Tributary North during the 2002-03 wet season.

A series of trays containing filter papers were located in transects from the northern batter of the IWMP (in the irrigation zone) to the opposite side of the Tributary North channel. Controls and background filter papers were also deployed. Those trays were left in situ for a period of two weeks. The filter papers were collected, leached in dilute nitric acid, and the leachate analysed for uranium. Small amounts of uranium were measured but it was concluded that the minor overspray detected would not result in any measurable increase in the concentration of uranium in Ngarradj. This was confirmed by the Supervising Scientist's monitoring data in the 2002-03 wet season.

Waste rock and mineralised material

During construction of the decline, mineralised material (>0.02% U₃O₈) was segregated and stockpiled on a purpose-built lined pad and then covered with an engineered cover.

Figure 2.12: Jabiluka minesite

The cover has now been in place for four wet seasons and continues to perform adequately. A number of minor holes have appeared in the cover as a result of physical abrasion and wind action, but these are repaired by site staff as they are identified. Holes in the cover allow water to penetrate the mineralised stockpile, but the quantity of water is very small and drainage through the mineralised material stockpile reports to the IWMP.

Independent testing of the cover material has indicted that the material is not degrading at a significant rate and continues to maintain its strength.

Waste rock continues to remain stockpiled on site and is managed passively.

Radiological exposure to employees

The Jabiluka project is a source of radiological exposure to mine employees.

The radiation dose limit for workers recommended by the International Commission on Radiological Protection (ICRP 60) in 1990 and adopted in Australia by the National Health and Medical Research Council is 100 mSv in a five year period with a maximum of 50 mSv in any one year.

As no development work or mining was undertaken during the year, the occupational radiation doses received by workers were very low. The maximum dose reported by ERA for a worker during the 2002 calendar year was 0.51 mSv. Thus, all workers at Jabiluka were classified as non-designated employees (ie, workers who are not expected to receive an occupational radiation dose exceeding 5 mSv in a year).

ERA drafted a new Radiological Management Plan for Jabiluka that was considered and supported at the MTC meeting of 30 June 2003 as part of the BPT assessment of the proposed long term care and maintenance proposal. The plan was required to ensure that the radiological risks associated with the LTCM proposal were adequately addressed, and had been developed in consultation with the MTC members.

ERA did not undertake certain radiological monitoring contained in the Jabiluka Authorisation during 2002-03. This issue is considered further under 'Incidents' later in this section.

Audit outcomes

The mid term review, which is a follow up to the 2002 Annual Audit of the Jabiluka operation (Reported in the 2001-02 Annual report of the Supervising Scientist) was undertaken between 19-21 November 2002. The review team consisted of representatives of oss, NLC and DBIRD.

As was the case at Ranger, the most significant issue under consideration was the progress made in developing and implementing the new Environmental Management System that complies with the requirements of ISO 14001. The conclusion was that there was still considerable work to be done in the development and introduction of an Environmental Management System (EMS).

In May 2003 an audit of the Jabiluka Project Environment Management Plan (EMP) was undertaken by a team made up of members from oss, NLC and DBIRD. The EMP was selected for the audit as ERA had not yet completed the development and implementation of an Environmental Management System at the time of audit.

The procedure was the same as in previous years with the protocol being developed by the audit team to conform with the appropriate ISO standards and then submitted to ERA two weeks prior to the interview and site inspection. The audit took place on 14 May, with the site inspection and interview being completed the same day. The outcome was satisfactory. There were no non-conformances and seven observations (Table 2.8) reported by the audit team.

Table 2.8: Observations from the 2003 Jabiluka Environmental Audit
No documentation was available on washdown for incoming/outgoing vehicles. No site-wide weed location maps showing areas to be avoided or requiring washdowns for returning vehicles were available. No evidence of a training programme for weed identification for site staff. There is a weed identification programme and an associated strategy. ERA staff deal only with terrestrial weeds, PAN do aquatic species. New weed management plan is due by June 2003. The sealing coat on the floor of the bunded oils/chemical storage area is peeling off.

Minesite Technical Committee

The Jabiluka Minesite Technical Committee met eight times during 2002-03. Issues considered at these meetings are listed in Table 2.9.

Table 2.9: Jabiluka Minesite Technical Committee Meetings
Date	Significant agenda items
15 August 2002	Application and approval for irrigation of IWMP water and the update of the water management review.
17 October 2002	Water management options review update, water management system operations update.
4 December 2002	Status of water management options review, status of water management system, proposed alterations to Jabiluka reporting and monitoring programmes, radiation monitoring and reporting commitments
16 January 2003	Status of options list for water management and BPT assessment, water management system update, Swift Creek monitoring data placed on *oss* website
13 March 2003	Kalf report on the hydrology of the decline
2 May 2003	Draft irrigation proposal, water management review update, proposed alterations to Jabiluka Authorisation in respect of monitoring and reporting and radiation monitoring and reporting , irrigation programme operational details update
6 June 2003	Status of possible care and maintenance long term management proposal, update of water management system, proposed alterations to Jabiluka Authorisation, May Audit, discussion on format for review of irrigation prior to 30 ML application being completed
30 June 2003	Long term care and maintenance proposal, and BPT assessment, review of irrigation programme to date, proposed changes to the Jabiluka Authorisation

Authorisations and Approvals

Changes to, and approvals under, the Authorisation during 2002-03 are listed in Table 2.10.

Table 2.10: Jabiluka Authorisation Changes/Approvals
Date	Issue
15 August 2002	Approval for irrigation during the 2002 dry season.
14 March 2003	Approval of Plan of Rehabilitation #6
28 May 2003	Approval for irrigation during the 2003 dry season

Incidents

As was the case at Ranger during 2002-03, some of the radiological monitoring described in the Jabiluka Authorisation issued by the Northern Territory Regulator (DBIRD) was not undertaken.

During the two quarters ending 30 June 2002 and 30 September 2002, ERA did not undertake personal dust monitoring for the most exposed group of Jabiluka workers, that is, workers who spent time in the underground workings. ERA advised that this monitoring was not completed because the activities undertaken by the workers in the decline did not involve the generation of any dust.

Based upon previous monitoring results, the absence of these data does not give rise to any significant concern about radiation doses received by people. However, the Supervising Scientist expressed the view that ERA should not have taken a decision not to undertake monitoring that was specified in the Jabiluka Authorisation. As a consequence of these discussions, it was agreed that the radiological monitoring requirements at Jabiluka, which were developed in the context of active mining, were not consistent with the very low radiological risk posed by the site whilst in care and maintenance, and that those requirements should be changed accordingly.

Personal dust monitoring of employees going underground was performed during the last quarter of 2002. However, it was again not undertaken in the March 2003 quarter on the basis that ERA considered that there was no potential for a radiological risk to the employee who was maintaining a water pump in the decline. In the absence of any activity at Jabiluka, the Supervising Scientist supported, in March 2003, an application by ERA to remove Schedule C (radiological monitoring) from the Jabiluka Authorisation and include new provisions that require the development and approval of appropriate radiation safety procedures in the event that there is activity involving disturbance of mineralised material. However, the application had not been approved by the regulator during the March 2003 quarter and it is the Supervising Scientist's view that ERA should implement the monitoring specified in the Jabiluka Authorisation until such time as it is removed or amended.

To date, DBIRD (as regulator) has not advised that a breach of the Jabiluka General Authorisation has occurred in relation to this matter.

2.3.3 Off-site environmental protection

Water quality in Ngarradj (Swift Creek)

In accordance with the Jabiluka Authorisation, ERA is required to monitor a range of surface and groundwaters on the lease and to demonstrate that as a result of activities within the project area the environment remains protected. Specific water quality objectives (criteria thresholds are described in section 2.2.3), based on the approach of the ANZECC and ARMCANZ Water Quality Guidelines, must be achieved. In addition to the ERA programme, the Supervising Scientist conducts a routine environmental monitoring programme including chemical monitoring in Ngarradj.

Flow past the Ngarradj main channel downstream monitoring site commenced on 22 December 2002 and ceased in mid-May 2003. Upstream and downstream sampling was conducted weekly by the Supervising Scientist throughout the 2002-03 wet season. The last monitoring sample was collected on 13 May 2003. The SSD water quality data collected during the 2002-03 wet season are summarised, and compared with data from the previous wet season, in Table 2.11.

A full description of the monitoring results will be released as an Internal Report by the Supervising Scientist during 2003-04.

Table 2.1: Summary of SSD Ngarradj (Swift Creek) Water Quality Measurements Upstream and Downstream of Jabiluka over the 2002-2003 Wet Season¹
Parameter	Units	Limit	Median		Range
Parameter	Units	Limit	Upstream	D'stream	Upstream	D'stream
pH	-	3.92-6.00*	5.2 (5.1)	5.6 (5.4)	3.7 - 5.5 (4.4 - 6.0)	4.2 - 5.8 (4.4 - 5.7)
EC	µs/cm	21	14 (16)	14 (15)	10 - 26 (13 - 20)	9 - 26 (11 - 21)
Turbidity	NTU	-	0.7 (0.9)	1.2 (1.7)	0.3 - 1.5 (0.1 - 3.9)	0.7 - 3.4 (0.7 - 3.3)
NO₃ (as NO₃)	mg/L	1.26	0.04 (0.01)	0.04 (0.01)	0.02 - 0.49 (0.01 - 0.01)	0.02 - 0.53 (0.01 - 0.03)
Sulphate‡	mg/L	1.5	0.4 (0.4)	0.3 (0.3)	<0.1 - 1.1 (0.2 - 0.8)	0.1- 1.3 (0.1 - 0.7)
Magnesium‡	mg/L	0.76*	0.3 (0.3)	0.4 (0.5)	0.2 - 0.6 (0.2 - 0.5)	0.3- 0.9 (0.3 - 0.9)
Manganese‡	µg/L	-	3.9 (5.7)	3.8 (5.3)	3.0 - 15 (4.1 - 11)	2.9 - 16 (3.2 - 12)
Uranium‡	µg/L	5.8	0.007 (0.009)	0.012 (0.011)	0.002 - 0.018 (0.001 - 0.026)	0.003 - 0.026 (0.003 - 0.024)

¹ Italicised data are values from the 2001-2002 wet season
* pH and magnesium limits are guidelines only
‡ dissolved (<0.45 µm)

In summary, uranium, sulphate, turbidity and electrical conductivity (EC) trends and values were almost identical at the upstream and downstream sites. Uranium concentrations remained extremely low (less than one half of 1% of the limit) at both sites throughout the season. Natural seasonal patterns can be seen in the data, namely, elevated magnesium concentrations and EC values at the beginning and end of the wet season, elevated uranium concentration and sulphate values during the first flush event, with values decreasing throughout the season, and low pH values at the beginning of the season during the first flush period. The pH and magnesium guidelines were exceeded once each. Both incidences were not unexpected, fitting the natural seasonal pattern, and neither of the exceedances were considered to be a breach of environmental standards.

As no limits were exceeded at any time during the season there is a high degree of certainty that the aquatic environment of Ngarradj Creek remained protected from mining impacts throughout the 2002-03 wet season. Results from the biological monitoring programme will be used to verify this. Furthermore, the data trends amongst years (including data collected prior to the commencement of mine workings) are almost identical for all parameters, and between-site trends this year are also almost identical for most parameters - turbidity, magnesium and pH are the exceptions and although these parameters remained within natural variations. Therefore, no mine-related signal can be inferred from the 2002-03 data. ERA's data compares well with SSD data for the upstream and downstream sites. There are some differences in physical data (EC, pH and turbidity) particularly at the beginning of the wet season. ERA and SSD sampled on different days of the week so a disparity in physical values is expected. Metal and ion concentrations and trends, however, were very similar for both datasets. On several occasions ERA recorded higher uranium values than SSD for the same week but the ERA downstream and upstream concentrations were similar on those occasions.

Biological monitoring in Ngarradj Creek

Benthic macroinvertebrates and fishes have been selected as key 'indicator' groups to monitor and assess potential impacts upon aquatic ecosystems arising from the Jabiluka mine. Strategic baseline sampling of both indicator groups has been conducted in the past five wet seasons (1998-99 to 2002-03 wet seasons) with results of the macroinvertebrate studies reported in the Supervising Scientist's Annual reports for 1999-2000, 2000-01 and 2001-02

Monitoring using macroinvertebrate community structure

Benthic macroinvertebrate results are being used to assess whether or not mine contaminants reaching Ngarradj (Swift Creek) downstream of the Jabiluka minesite during the wet season are adversely affecting the aquatic biota. Such contaminants may include suspended solids, or residual contaminants such as nutrients (from explosives) or uranium from waste water spray-irrigated on land during the dry season.

The design and approach of the macroinvertebrate study for Jabiluka are similar to those described above for the Ranger macroinvertebrate study (see Section 2.2.3 of this Annual report). Macroinvertebrate samples were gathered from sites in Ngarradj Creek (draining the minesite) upstream and downstream of Jabiluka, and also from paired upstream and downstream sites in three adjacent streams currently unaffected by any mining activity at Jabiluka (control streams). For the three wet seasons, 1998-99, 1999-2000 and 2000-01, samples were collected from each site at three to four weekly intervals for the period of creek flow. In the 2001-02 wet season, this sampling effort was reduced so that only Ngarradj and one of the control creeks were sampled monthly during the wet season, while all four streams were sampled on the final sampling occasion in March. For each sampling occasion and for each pair of sites for a particular stream, a dissimilarity index was calculated - see explanation of this index in the section 2.2.3 of this Annual report, 'Biological monitoring in Magela Creek'. Sample processing and data analysis have now been completed for wet seasons up to and including 2001-02 with results plotted in Figure 2.13.

As may be seen from Figure 2.13, dissimilarity values for Ngarradj Creek over the four wet seasons are reasonably constant and similar to values reported in adjacent control streams over the same time period. Relatively high dissimilarity values - indicating differences in types of macroinvertebrate taxa and/or their abundances between the two sites - were observed in Ngarradj at the end of the 1998-99 and 2000-01 wet seasons, and over the 2001-02 wet season.

Figure 2.13: Paired upstream-downstream dissimilarity values (using the Bray-Curtis measure) calculated over four wet seasons for community structure of macroinvertebrate families in several streams near the Jabiluka minesite.

Note: Missing data indicate absence of flow (7J Creek, 3rd wet season) or no sampling (7J and North Magela creeks, 4th wet season).

There are two explanations for this:

Macrophyte habitat from which macroinvertebrates are sampled is naturally sparse at the upstream Ngarradj site, particularly at the end of the wet season when available habitat has been near-exhausted after earlier sampling in the season. Moreover, the upstream site appears to have become progressively (and naturally) scoured and eroded over the past several years to the extent that macrophyte beds have almost been eliminated. Loss of habitat has contributed to the lower densities of animals observed at the upstream site. In 2002-03, the upstream site was re-located about 300 m upstream to a location with more abundant macrophyte habitat.
Relatively high dissimilarity values in Ngarradj also correspond with occasions when total macroinvertebrate abundance was much higher (three to six times) at the Ngarradj downstream site compared with values recorded at both the upstream and downstream sites on other occasions sampled during the respective wet seasons. Taxa contributing to these high abundances included baetid and caenid (mayfly) nymphs, chironomid (midge) larvae and leptocerid (caddisfly) larvae. Collectively, and from literature records of the known sensitivities of various macroinvertebrate taxa to human-related disturbances, high abundances of these taxa at the downstream Ngarradj site are not indicative of mining impact.

Relatively high dissimilarity values as observed in Ngarradj are also observed in control streams (Figure 2.13), though not necessarily at the same times. These results support conclusions drawn in previous Annual reports that up to and including the 2001-02 wet season, there were no adverse effects of runoff from the Jabiluka minesite upon macroinvertebrate communities downstream in Ngarradj Creek.

Monitoring using fish community structure

Fish studies associated with Jabiluka are conducted in billabongs as well as streams. The stream study has the same design as the Jabiluka macroinvertebrate study described above. Thus, bankside visual observations upon fish communities are gathered from sites in Ngarradj (draining the minesite) upstream and downstream of Jabiluka, and also from paired upstream and downstream sites in three adjacent streams currently unaffected by any mining activity at Jabiluka (control streams). Data have generally been collected from each site in March and April of each of the past five wet seasons, 1998-99 to 2002-03, though flow conditions that are too high or too low have prevented sampling on some occasions. Only one sample was obtained in 2002 because of very low flow and the sampling in March 2003 was aborted because of high flows. In 2003 fish were sampled in Ngarradj and Catfish Creeks in February to examine seasonal variation in fish assemblages and evaluate the possibility of including an extra sample in the routine monitoring programme.

As with the macroinvertebrate study, a dissimilarity index was calculated for each sampling occasion and for each pair of sites for a particular stream. Paired-site dissimilarity values for Ngarradj and three control streams are compared for the five-year period in Figure 2.14.

Figure 2.14: Paired upstream-downstream dissimilarity values calculated for fish community structure in four streams near the Jabiluka minesite over the past several wet seasons.

Note: Calculations made using Bray-Curtis measure with log (X + 1) transformed abundance data. Not all sites were sampled on each sampling occasion.

In two control streams, Wirnmuyurr and Catfish creeks, the dissimilarities for 2003 were very similar to those of previous years indicating that in each stream the fish communities at different sites continued to respond in similar ways to natural variation in environmental conditions. However, in the other control stream, North Magela Creek, and in the exposed stream, Ngarradj Creek, marked declines in dissimilarity were recorded in 2003. Such declines could be as much an indication of a mine-related effect as an increase in dissimilarity but in this instance they appear to result from natural causes that are unrelated to mining operations. Different causes are suggested for each stream, as follows.

In Ngarradj the paired site dissimilarity for the February sample (16%) was much lower than recorded in March and April of previous years (range 23 to 42%). This low dissimilarity was the result of a very low number of species present in the creek at that time, only two species upstream and three species downstream, and the numerical dominance of one species (blackbanded rainbowfish, Melanotaenia nigrans) at both sites. This species comprised over 99% of fish present. The effect of this was to reduce the influence of any differences between sites in other less abundant species on the calculation of the dissimilarity value, resulting in lower values.

The low species richness in February may be the normal pattern of the recruitment process of many species of fish into Ngarradj from downstream habitats on the Magela floodplain or from residual pools within Ngarradj itself. Most of the stream channel of Ngarradj dries out each year leaving a few small pools. The dominance of M. nigrans at this time suggests this species survives these conditions well and can reproduce rapidly when the stream channels begin to fill in the early wet season. Recruitment of fish from the floodplain is likely to be delayed until the floodplain fills (typically January) and breeding has taken place. In Magela Creek near Ranger, upstream migration from the floodplain typically commences some time in February. The late start to high flows in Ngarradj in 2003 could also have delayed recruitment of some species.

Nevertheless, the later sampling in Ngarradj in April produced a larger array of species (that is, seven) and a higher dissimilarity that was within the range of those values found in previous years.

In North Magela Creek, the low dissimilarity in 2003 (6%; Figure 2.14) resulted from a different aspect of fish migration. The one sample obtained, in April, coincided with the last surge of upstream fish migration from the floodplain that often occurs at the start of recessional flows. As a result, samples from upstream and downstream sites were dominated by very large numbers of sail-fin glassfish (Ambassis agrammus), 50 times higher than recorded in previous years, and greater than normal numbers of chequered rainbowfish (Melanotaenia splendida inornata). Again, this domination of the samples at both sites by two species has resulted in much reduced dissimilarity values.

The constancy of dissimilarity values for April samples in Ngarradj Creek and two control streams over the past several years supports the conclusion that there were no adverse effects of runoff from the Jabiluka minesite on fish communities in Ngarradj. Unusual changes in paired-site dissimilarities from Ngarradj and Catfish creeks appear to be chance results relating to coincidence of sampling with fish recruitment behaviour.

Implicit in this design is the comparison of fish community structure between the paired sites in Ngarradj with that in control streams. However, this approach is confounded by possible movement of fish between the two sites. Greater reliance will need to be placed, if data accrue in future, on the comparisons between sites in Ngarradj and those in independent control streams.

Radiological exposure to the public

The group of people most at risk of receiving a radiation dose from operations at Jabiluka are the 60 or so residents of Mudginberri, which is located approximately 10 km south of the Jabiluka site. The Supervising Scientist maintains a radiological monitoring station at Four Gates Road, approximately 1 km west of Mudginberri Billabong. ERA monitors radon decay products and long lived alpha activity (radioactive dust) concentrations on the Jabiluka lease on Jabiluka Hill, but not at Mudginberri as the Aboriginal Traditional owners have withheld the necessary permission. Figure 2.15 shows radon decay products (Figure a) and long lived alpha activity (radioactive dust) (Figure b) monitoring results at Four Gates Road and Jabiluka Hill since April 2000.

Figure 2.15: Radon decay products (RDP) and LLAA (radioactive dust) concentrations at Four Gates Road radon station (eriss) and Jabiluka Hill (ERA)

The data were collected by ERA and, since January 2002, also by the Supervising Scientist when his routine radiological monitoring programme commenced. Radon progeny and radioactive dust concentrations at both of these sites are extremely low and consistent with natural background levels. The annual radiation dose received by residents of Mudginberri attributable to activities at Jabiluka is too small to be quantified.

Theoretically, some of the radon progeny to which residents at Mudginberri are exposed will be attributable to mining operations at Ranger. However, determining the radiation dose to Mudginberri residents arising from 'Ranger origin' radon is extremely difficult because it is very small compared with the radiation dose received from radon present naturally in the atmosphere. One way of making such an estimate is through mathematical modelling. Such modelling has previously been carried out by eriss the result being a dose that is less than 1% of the dose limit for members of the public.

Supervising Scientist Division