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)

2.2 Ranger (continued)

2.2.3 Off-site Environmental Protection

Under the Ranger General Authorisation, ERA is required to monitor and report on water quality in Magela Creek downstream of the mine. Specific water quality objectives must be achieved. The Authorisation specifies the sites, the frequency of sampling, the analytes to be reported, and requires that increases in concentration must not lead to a breach of the annual load limit. In addition, the Supervising Scientist conducts an independent routine monitoring programme which includes chemical monitoring in the Magela Creek.

The Commonwealth Environmental Requirements (ERs) for Ranger further reinforce the existing compliance framework as it relates to the protection of people and the environment. In particular, the ERs require that key variables that indicate the health of the Magela Creek system be defined so that any unusual change triggers an action by the company and/or a response by the Commonwealth.

Water quality criteria for Magela Creek at the monitoring site downstream of Ranger mine have been set in accordance with Australian and New Zealand Environment and Conservation Council (ANZECC) and Agricultural and Resource Management Council of Australia and New Zealand (ARMCANZ) Water Quality Guidelines, and are described in detail in the Supervising Scientist's Annual report for 2001-02. The various thresholds that make up these criteria, in order of decreasing stringency, may be summarised as follows:

Limit (a compliance threshold) - the value of a parameter that must not be exceeded as a consequence of mining operations. Exceedance of a limit due to mining activities may constitute a breach of statutory requirements.
Guideline (management threshold) - set to assist in the interpretation of water quality measurements. The exceedance of a guideline is not a breach of statutory requirements.
Action level (a management threshold) - exceedance of an action level triggers investigative and/or corrective action.
Focus level (a management threshold) - exceedance of a focus level triggers a watching brief and may require further sampling to verify whether an upward trend is occurring.

Collectively these levels are referred to as the 'trigger values'.

Flow commenced on 1 December 2002 in Magela Creek and ceased in the downstream central channel (the downstream monitoring site) in late May 2003. SSD conducted weekly upstream and downstream sampling throughout the 2002-03 wet season. The last compliance monitoring sample was collected on 22 May 2003. SSD monitoring data for water quality in Magela Creek upstream and downstream of Ranger are summarised and compared with previous wet season data in Table 2.6. The SSD water quality data for Magela Creek are in good agreement with ERA data with some notable differences for pH which will be investigated.

Table 2.6: Summary of SSD Magela Creek Water Quality Measurements Upstream and Downstream of Ranger over the 2002-03 Wet Season¹
Parameter	Units	Limit	Median		Range
Parameter	Units	Limit	Upstream	D'stream	Upstream	D'stream
pH	-	5.2 - 7.2*	6.1 (5.8)	6.1 (6.1)	4.8 - 6.7 (5.2 - 6.7)	4.8 - 6.7 (5.7 - 6.7)
EC	µs/cm	43	14 (15)	15 (19)	7.5 - 23 (11 - 19)	9.0 - 23 (11 - 31)
Turbidity	NTU	56	2.0 (2.0)	2.1 (2.5)	0.8 - 9.5 (0.7 - 5.8)	0.9 - 8.9 (1.2 - 9.5)
Sulphate‡	mg/L	EC must comply	0.3 (0.3)	0.6 (1.4)	<0.1 - 0.9 (0.1 - 0.4)	0.2 - 1.6 (0.4 - 3.5)
Magnesium‡	mg/L	EC must comply	0.6 (0.7)	0.7 (1.0)	0.3 - 1.0 (0.3 - 0.9)	0.3 - 1.1 (0.3 - 1.6)
Manganese‡	µg/L	32	5.4 (5.2)	5.8 (7.9)	2.9 - 20 (2.0 - 7.8)	2.8 - 30 (1.8 - 45)
Uranium‡	µg/L	5.8	0.019 (0.011)	0.053 (0.038)	0.007 - 0.079 (0.001 - 0.024)	0.016 - 0.101 (0.014 - 0.198)

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

A full description of SSD monitoring results are available on the internet at www.deh.gov.au/ssd/monitoring/index.html and will be released as an Internal Report by the Supervising Scientist during 2003-04. The SSD monitoring data are summarised below.

In summary, the data show that Magela Creek water was of a very high quality throughout the 2002-03 wet season. Although a signal from the mine was seen at the downstream site (that is, elevated uranium and periods of elevated sulphate), it was less obvious than the previous season (see Figure 2.6). In the 2002-03 wet season the downstream medians and maximum values of all parameters, except uranium and pH, were lower than in the previous season (Table 2.6). While the median uranium concentration is higher in the 2002-03 wet season, the peak concentrations were much lower (Figure 2.6a & b). Uranium and sulphate concentrations remained very low during the 2002-03 wet season, with uranium remaining below 2% of the limit and electrical conductivity (EC) remaining at about 50% or less of the limit at the downstream compliance point.

Figure 2.6a: Uranium concentrations in Magela Creek for the 2001-02 wet season

Figure 2.6b: Uranium concentrations in Magela Creek for the 2002-03 wet season

Natural seasonal patterns of slightly elevated metals and ions, particularly manganese, coupled with low pH due to first flush effects and groundwater inputs were seen as expected, at the start and end of the season. Natural first flush waters are typified by relatively low pH and high electrical conductivity (EC) due to dissolution of surface salts and flushing of the soil profile in the catchment, and resuspension of billabong and creek bed sediments. As well as during the first flush, low pH and elevated levels of metals and ions are also common in the late stages of the wet season as groundwater inputs to the system become more noticeable (with diminishing volumes of surface water) and/or dissolved salts in the surface water become concentrated through evaporation.

At the downstream compliance point, pH exceeded the lower guideline on three occasions: twice during the first flush period, when pH at both upstream and downstream sites followed similar trends, and once at the end of the season. Recommended pH values are guideline values rather than strict limits and exceeding a guideline value does not imply that a breach of statutory regulations has occurred.

The values of all measured metals and ions were below the limits throughout the season indicating that there is a high degree of certainty that the Magela Creek aquatic environment remained protected from mining impacts throughout 2002-03 wet season. Results from the biological monitoring programme verify this.

Additional sampling was undertaken in the 2001-02 and 2002-03 wet seasons at the Magela Creek downstream site. The downstream section of the creek consists of three main channels that vary in both flow and water quality. Investigations were undertaken to assess the variation, especially in relation to mine water discharges and the location of the sampling point.

The results of the cross channel variation assessment will be released as an Internal Report by the Supervising Scientist before the start of the 2003-04 wet season.

²²⁶Ra results for 2001-02 and 2002-03

Radium-226 concentration activities in Magela Creek waters are now available for the 2001- 02 wet season and some results are available for the 2002-03 wet season. Based on the available data, no focus, action or limit triggers were exceeded during the 2001-02 wet season.

The wet season arithmetic mean of the difference between the upstream concentration of ²²⁶Ra and the downstream concentration of ²²⁶ Ra was well below the limit of 10 mBq/l (milli becquerel per litre). Because of inherent delays in the analytical procedures used, only a few results are available to date for the 2002-03 wet season. Those results show very low concentrations of ²²⁶Ra, well below the limit. The available data for both sampling seasons indicate that ²²⁶Ra concentrations in Magela Creek are well below concentrations that may cause concern.

Chemical Monitoring in Gulungul Creek

Gulungul Creek flows past the western side of the tailings dam and enters Magela Creek downstream of the principal downstream monitoring point in Magela Creek (GS821009). Gulungul Creek commenced flowing on 31 December 2002 and ceased flowing at the downstream monitoring point in early June 2003. SSD conducted weekly upstream and downstream sampling throughout the 2002-03 wet season. The last monitoring sample collected from that site was on 27 May 2003. This is the second year the Supervising Scientist has monitored these sites and these and future data will be used to set trigger values for future wet seasons. SSD monitoring data for water quality in Gulungul Creek upstream and downstream of Ranger are summarised, and compared with the previous wet season data, in Table 2.7.

Table 2.7 Summary of SSD Gulungul Creek Water Quality Measurements Upstream and Downstream of Ranger over the 2002-03 Wet Season¹
Parameter	Units	Median		Range
Parameter	Units	Upstream	Downstream	Upstream	Downstream
pH	-	6.4 (6.4)	6.4 (6.3)	5.4 - 6.8 (5.9 - 7.0)	5.5 - 6.8 (5.8 - 6.9)
EC	µs/cm	17 (18)	19 (21)	10 - 24 (13 - 24)	8.1 - 24 (16 - 26)
Turbidity	NTU	1.1 (1.1)	1.5 (1.4)	0.4 - 4.5 (0.5 - 3.5)	0.9 - 13 (0.9 - 4.7)
Sulphate‡	mg/L	0.2 (0.2)	0.5 (0.3)	<0.1 - 0.6 (0.1 - 0.5)	<0.1 - 1.4 (0.1 - 0.9)
Magnesium‡	mg/L	0.9 (1.0)	0.9 (1.0)	0.6 - 1.6 (0.7 - 1.4)	0.5 - 1.5 (0.8 - 1.3)
Manganese‡	µg/L	2.7 (1.8)	5.3 (3.5)	1.2 - 6.4 (0.5 - 4.7)	2.3 - 18 (1.3 - 5.8)
Uranium‡²	µg/L	0.069 (0.045)	0.124 (0.071)	0.029 - 0.197 (0.023 - 0.292)	0.056 - 0.251 (0.045 - 0.133)

¹ Italicised data are values from the 2001-2002 wet season
² limit = 5.8 µg/L
‡ dissolved (<0.45 µm)

A full description of SSD monitoring results is available on the internet at www.deh.gov.au/ssd/monitoring/index.html and will be released as an Internal Report by the Supervising Scientist during 2003-04. The SSD monitoring data are summarised below.

During the first month of flow, daily monitoring was carried out at the Gulungul Creek downstream site to establish if there had been any impact arising from the new toe-loading earth works on the south wall of the tailings dam (particularly on uranium concentrations). First flush effects were noticeable in the uranium, sulphate and manganese data. However, the concentrations of these solutes and electrical conductivity levels (EC) were within historical ranges for the downstream site throughout the season indicating no additional mine related effects on the water quality due to the new toe-loading works.

EC data at both sites followed a bowl shaped curve, that is, elevated levels at both ends of the wet season and low levels during mid season. This results from first flush effects at the start of the season and groundwater inputs and evapoconcentration of solutes toward the end of the season. EC, pH, and uranium data followed similar trends at both upstream and downstream sites throughout most of the wet season, as did turbidity, apart from one high downstream value in the first flush period, which is not unusual.

Higher concentrations of uranium and sulphate were seen at the downstream site compared with the upstream site and the downstream concentrations recorded were generally higher this season than last (Table 2.7) (the downstream medians and maximums of several parameters are higher this wet season than last but are within historical ranges recorded at this site by ERA). Elevated sulphate concentrations have been observed before in drier years (such as 1991-92 and 1992-93).

The observed magnesium and sulphate concentrations are decoupled indicating that the sulphate is not of mine origin. It has also been noted before² that black soils in the catchment may be contributing to the sulphate signal downstream of the mine. It is possible that the higher uranium concentrations at the downstream site were caused by mining. However, the concentration increases were very low compared with the limit which is 5.8 µg/L. There is, consequently, no concern that the environment was adversely affected.

Apart from elevated manganese during the first flush period, other parameters showed similar trends and values to the upstream site giving a high degree of certainty that the aquatic environment of Gulungul Creek remained protected from impacts of mining.

Apart from uranium concentrations, and sulphate concentrations at the end of the season, the SSD water quality data for Gulungul Creek are in good agreement with ERA data. ERA is investigating a problem with the handling of their Gulungul Creek water samples that is probably responsible for the higher uranium concentrations measured in the ERA samples.

Biological Monitoring in Magela Creek

Based upon eriss research since 1987, biological monitoring techniques have been developed that can be used to assess the environmental impact of uranium mining on aquatic ecosystems downstream of the Ranger mine. Two broad approaches are used: early detection studies and studies of natural animal populations and communities, the latter providing a better measure and assessment of overall ecosystem-level responses and their importance arising from any potential impact.

For early detection, creekside monitoring procedures have been developed and employed in Magela Creek; ERA staff have collaborated with eriss on this programme in past years. For ecosystem-level responses, benthic macroinvertebrate and fish communities from Magela Creek sites are measured and the results compared with historical data and comparable data gathered simultaneously in analogue control streams. Results of creekside monitoring and fish community studies conducted during the 2002-03 wet and early dry seasons and macroinvertebrate studies carried out up to 2002 are reported here.

Creekside monitoring

In this form of monitoring, effects of Ranger mine waste water dispersion are evaluated using responses of aquatic animals held in tanks on the creek side to effluent waters. The responses of two test species are measured over a four-day period:

reproduction (egg production) in the freshwater snail, Amerianna cumingi, and
survival of black-banded rainbowfish, Melanotaenia nigrans, larvae.

Animals are exposed to a continuous flow of water pumped from upstream of the minesite (control site) and to water collected from the creek at gauging station GS8210009, some 5 km downstream of the mine. At the end of each four-day trial, the mean number of eggs per snail pair and mean number of fish surviving per replicate, are noted and compared for each of the upstream and downstream sites. Specifically, when data from the upstream site are subtracted from those at the downstream site, a set of 'difference' values can be derived. These difference values may be compared statistically for different parts of the time-series. For example, 'difference' data for the wet season of interest may be compared with those from previous years; if they differ significantly, using a Student's t test, it may indicate a mine-related change. Since about 1996, creekside trials have been performed approximately every other week during the wet season. Trials usually commence in December and cease in early April, the period of significant creek flow in Magela Creek.

The results of the creekside trials are plotted as part of a continuous time series of actual and 'difference' data in Figure 2.7A for snail egg production, and in Figure 2.7B for larval fish survival. Part of this time series of data was acquired by ERA because of the earlier intent for the company to routinely conduct chemical and biological monitoring. Descriptions of the sources of creekside data and data quality issues are provided in the Supervising Scientist's Annual report for 2001-02.

Eight creekside tests were conducted in the 2002-03 wet season (16-20 December 2002, 30 December 2002 - 3 January 2003, 13-17 January 2003, 27-31 January 2003, 10-14 February 2003, 24-28 February 2003, 10-14 March 2003 and 24-28 March 2003). Using the data shown in figures A and B, 'difference' values for 2002-03 were compared with those from previous years. The difference data shown and subsequently used in statistical analyses are those for valid tests only.

Snail egg production at upstream and downstream sites was very similar across all tests (Figure 2.7A). Moreover, the results of statistical analysis showed no significant difference in the 'difference' values of 2002-03 data compared with data from previous years (P >0.05).

Larval fish survival was high at both upstream and downstream sites for the first, third, fifth, sixth and seventh tests (Figure 2.7B). In the second, fourth and eighth tests, fish survival at the downstream site was relatively high but was low at the upstream site. For the entire time series of fish survival data (1992-2003), there is a significant (P = 0.01) decline in the difference values as a consequence of a decline in upstream larval fish survival. This downward trend, however, is stepped - that is, there is no significant trend when data within the periods 1992-96 and 2000-03 are analysed separately; the difference lies between these two periods of creekside testing.

The generally poor control survival of larval fish observed in recent years could be related to: (i) a small change in location of upstream pumps to the centre of the main channel where water quality may be slightly more adverse (lower pH and solute concentrations); and/or (ii) in recent years flow rates in the creek have generally been above average as a consequence of a series of wetter wet seasons. It is known that water quality under high flow conditions is characterised by relatively lower pH and lower solute concentrations and under these conditions stress may be placed on aquatic organisms of Magela Creek. Some protection (that is, higher survival) may be conferred to test animals at the downstream site because these are exposed to waters emanating from Georgetown and Coonjimba Billabongs. Relative to creek waters, billabong waters are enhanced in nutrients and are less acidic.

From these results, it is concluded that there were no adverse effects of mine waste waters on either of the creekside test species over the 2002-03 wet season.

Figure 2.7: Creekside monitoring results for: A. freshwater snail egg production, and B. larval black-banded rainbowfish survival, for wet seasons between 1992 and 2003

Monitoring using macroinvertebrate community structure

Macroinvertebrate communities have been sampled from a number of sites in Magela Creek at the end of significant wet season flows, each year from 1988 to the present. The design and methodology have been gradually refined over this period to meet the needs of cost efficiency and improved ability to confidently attribute any observed changes to mining impact. The most significant refinement that took place in the study occurred in 1994 when there was a reduction from ten sites sampled in Magela Creek to just three, as well as commencement of sampling at sites in three additional control streams. Since 1994, there have also been three changes to sampling and sample processing methods.

The original design for this macroinvertebrate study was based upon the principle of gathering macroinvertebrate samples from sites in Magela Creek upstream and downstream of Ranger, and also from similar paired upstream and downstream sites in three adjacent 'control' streams that are generally unaffected by any mining activity (Figure 2.8). In recent years, it has become evident that Gulungul Creek has been receiving some small quantities of mine contaminants from Ranger (see section earlier, 'Chemical monitoring in Gulungul Creek'). Given its doubtful role as a true control stream, it is more appropriate now to consider this stream in the same category as Magela Creek, that is, 'potentially disturbed'. The design of this study, therefore, is now a balanced one comprising two 'potentially disturbed' streams and two control streams.

Samples were collected from each site at the end of each wet season (between April and May). For each sampling occasion and for each pair of sites for a particular stream, a dissimilarity index is calculated. This index is a measure of the extent to which macroinvertebrate communities of the two sites differ from one another. A value of 'zero' indicates identical macroinvertebrate communities while a value of 'one' indicates totally dissimilar communities, sharing no common taxa. Research elsewhere in the Alligator Rivers Region has shown significantly 'higher' dissimilarity values for locations upstream and downstream of point sources of disturbance compared with values recorded in both the pre-disturbance, baseline period and in undisturbed control streams; the higher dissimilarity is a consequence of the 'altered' (disturbed) macroinvertebrate community structure at (the) site(s) downstream of such point sources.

Analysis of the full macroinvertebrate data set from 1994 to 2002, the period over which sampling in additional control streams occurred, has been completed and results are shown in Figure 2.8. This figure plots the paired-site dissimilarity values using family-level (log-transformed) data, for the two Magela catchment streams and two Nourlangie catchment (control) streams.

Inferences that may be drawn from the data shown in Figure 2.8 are weakened because there are no pre-mining (pre-1980) data upon which to assess whether or not significant changes have occurred as a consequence of mining. Notwithstanding, the plots show that the mean dissimilarity value for each stream across all years is approximately the same (~0.3) and that the values are reasonably constant over time. This provides good evidence that changes to water quality downstream of Ranger as a consequence of mining in the period 1994 to 2002 are not sufficient to have adversely affected macroinvertebrate communities.

Figure 2.8: Paired upstream-downstream dissimilarity values (using the Bray-Curtis measure) calculated for community structure of macroinvertebrate families in several streams in the vicinity of the Ranger uranium mine for the period 1994 to 2002.

Note: The dashed vertical lines delineate periods for which a different sampling and/or sample processing method was used. Dashed horizontal lines indicate mean dissimilarity across years.

Monitoring using fish community structure

Sampling of fish communities in billabongs is conducted in late April to the end of June of each year. Two types of data are gathered, using non-destructive sampling methods:

Visual observation data from two deep, channel billabongs: Mudginberri Billabong on Magela Creek about 12 km downstream of Ranger, and directly exposed to any released mine waters ('exposure' billabong, 1989-present); and Sandy Billabong on Nourlangie Creek (control billabong, independent catchment, 1994-present).
Data from 'pop-nets' set in shallow, weedy, lowland billabongs, in various combinations, from 1994 to the present:
- 'exposed' billabongs in Magela Creek adjacent to and downstream of Ranger mine;
- 'unexposed' billabongs in Magela Creek downstream of the mine but not directly receiving mine waste waters ('pseudo'-controls);
- 'control' billabongs in Nourlangie Creek and East Alligator River (true controls).

The design for both approaches is amenable to the comparisons: (i) exposed billabong(s) versus control billabong(s) from independent catchments (Nourlangie Creek and East Alligator River); and/or (ii) 'exposed' billabongs versus 'unexposed' billabongs in Magela Creek, recognising that this second approach is confounded by possible movement of fish between the two billabong types in the same stream system.

The comparison of visual observation data on fish community structure in exposed and control channel billabongs since 1994 was examined by calculating multivariate dissimilarity indices. These indices are explained above in the section, 'Monitoring using macroinvertebrate community structure'.

The dissimilarity between the two sites for 2003 (14%) was very similar to that in the previous year (15%) and slightly lower than in earlier years (mean dissimilarity 21%). Thus the fish communities in both control and exposed sites have responded in similar ways to natural environmental variation amongst years.

The pop-net sampling data for fish in shallow billabongs (Figure 2.9) show that some billabongs consistently yield more fish than others and that there is a considerable year to year variation in fish numbers. However, the pattern of this variation is quite similar amongst most sites and is not related to exposure type. Of some note, is Corndorl Billabong, a downstream unexposed site; the extremely low numbers of fish recorded in 2002 were not repeated in 2003. This billabong is contaminated with Salvinia molesta, an exotic floating fern, which at higher densities chokes the water column making the habitat unsuitable for fish. In 2002, samples contained larger amounts of this weed than in other years including 2003.

Multivariate ordination (explained in the research highlight entitled, 'ecological effects of magnesium sulphate', elsewhere in this Annual report) was used to compare the fish community structures in the three exposure types (Figure 2.10). The data points for different sites tend to occupy different areas of the ordination indicating differences in community structure among sites. The area enclosed by data points for each billabong in years prior to 2003 is shown as a polygon to indicate their 'natural' location in the ordination space. There is considerable overlap amongst the exposed and unexposed sites and one control site, Buba Billabong, indicating that these differences amongst sites are natural differences and are not related to any form of exposure to potential mining effects. The other two control sites lie at opposite sides of the scatter plot indicating they differ from the fish communities at the other sites in different ways.

Figure 2.9: Abundance of fish in different billabongs with different forms of exposure to contaminants from Ranger uranium mine, 1994-2003.

Note: Exposed sites are adjacent to the mine and receive surface flows direct from the mine site; unexposed sites are downstream from the mine and can receive contaminated creek water by back flow; and control sites cannot receive contaminated water as they are on different catchments with no mining activity. Not all sites have been sampled each year. Sampling in Djalkmara Billabong was discontinued after mining at Pit 3 closed its connection to Magela Creek.

Figure 2.10: Ordination plots of fish communities in shallow billabongs near Ranger uranium mine with different potential exposure to contamination from mine wastes for 1994 to 2003: (a) control sites on different catchments (Nourlangie Creek and East Alligator River); (b) unexposed sites downstream on Magela Creek; and (c) exposed sites on Magela Creek adjacent to Ranger mine.

Note: Ordination calculated for 2 dimensions, stress= 0.18. The areas enclosing points for years 1993 to 2002 for each billabong are shown as polygons. (Only the relevant polygons are highlighted.) The position of data for 2003 is indicated separately as filled symbols for comparison with previous years.

The data points for 2003 are displayed separately in the ordination (Figure 2.10) to compare the position of billabongs with those in previous years. In all cases they lie close to, if not within, the area occupied in previous years. The relatively small scatter of data points for the fish community in each billabong indicates that, although the fish community structure has changed from year to year, in most cases this change has not been of a size that would indicate a significant departure from the natural variation for that site. An exception to this was the location of the data point for Corndorl Billabong in 2002. As mentioned above, this outlier is possibly related to an unusual level of weed (Salvinia) infestation in that year.

The small variation in dissimilarity values for fish communities in channel billabongs and the similarity of 2003 fish communities in shallow billabongs to the respective communities found in previous years indicate there is no evidence of any adverse effects of mine waste waters arising from the Ranger minesite on fish communities of Magela Creek.

Radiological Exposure to the Public

As the Ranger uranium mine is a potential source of radiological exposure to the local community, the Supervising Scientist's radiological monitoring programme focuses on the local population centres closest to the mine, which are Jabiru, Mudginberri and Jabiru East.

The annual radiation dose limit for members of the public recommended by the International Commission on Radiological Protection and adopted in Australia by the National Health and Medical Research Council is 1 mSv. This does not include the natural background radiation dose, which is approximately 2 mSv per year in Australia.

The only potentially significant exposure pathways for members of the public due to Ranger operations are the inhalation of radioactive dust or radon decay products dispersed from the mine in the atmosphere and the ingestion of radionuclides in bush foods taken from the Magela Creek system downstream of Ranger.

Figure 2.11 shows radon decay products (Figure a) and long lived alpha activity concentrations (radioactive dust) (Figure b) monitoring results at Jabiru and Jabiru East since April 2000. The data were collected by ERA and, since January 2002, also by the Supervising Scientist when his routine radiological monitoring programme commenced.

ERA uses a model developed by eriss in 1988 that correlates radon decay product measurements with wind direction to calculate the mine-derived dose from the inhalation of radon decay products to residents of Jabiru. For 2002, ERA estimated that the mine contributed approximately 0.03 mSv to the annual dose to Jabiru residents, which amounts to 3% of the dose limit. The contribution from dust to the annual dose is negligible.

It is possible to estimate the dose received by people from the ingestion of bush foods taken from the Magela Creek system downstream of Ranger considering the two major sources of radionuclides to Magela Creek, ie, water released from Retention Pond 1 and Djalkmara Billabong. Using a model developed by eriss, the dose from these two sources is estimated to be of the order of 10-20 µSv or 1-2% of the dose limit. There are other sources of radionuclides at Ranger that would also contribute to the dose from ingestion of bush foods. However, considering the relatively large uncertainties in estimating such a small dose, they do not alter the dose estimate quoted above.

Figure 2.11: Radon decay product and long lived alpha activity concentrations (radioactive dust) at the monitoring stations in the Alligator Rivers Region.

Note: According to ERA, the apparent high LLAA (radioactive dust) result that was obtained at Jabiru East at the end of 2001 was due to contamination of the sampler used in the quarter.

² Supervising Scientist Monitoring Programme: Instigating an environmental monitoring programme to protect aquatic ecosystems and humans from possible mining impacts in the ARR. Background paper - www.deh.gov.au/ssd/monitoring/background.html

Supervising Scientist Division