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Supervising Scientist Environmental Monitoring Program
Background descriptions about the nature and sources of mine-related contaminants which could reach Alligator Rivers Region streams from the Ranger and Jabiluka mine sites may be found in the 'Background Paper' on environmental monitoring.
Data are provided for three streams on ERA leases. These streams are Magela Creek, which flows immediately east of the Ranger mine, Gulungul Creek, which flows immediately west of Ranger, and Ngarradj (Swift Creek) which flows east of the Jabiluka minesite.
The Supervising Scientist Division (SSD) modified its wet season monitoring program in 2008-09 to enhance the ability of SSD to independently detect changes while reducing replication of monitoring activities that are already carried out by other agencies.
From the 2008–09 wet season (and in subsequent seasons), there is closer integration of the grab sampling water quality monitoring program with continuous water quality monitoring and in situ toxicity monitoring programs. Routine water chemistry weekly grab sample collections were relocated to SSD’s upstream and downstream continuous monitoring and in situ toxicity monitoring sites to provide better overlap amongst these methods. These weekly samples, as for previous seasons, are measured for key mine site analytes, including physicochemical parameters. The sampling point maps show the location of the upstream and downstream sites and key Ranger Mine features.
The downstream site incorporating chemistry (continuous and grab) and in situ toxicity monitoring is located in the west channel of Magela Creek whereas the previous downstream chemistry grab sampling site was located in the central channel of Magela Creek. The west channel has historically shown elevated contaminant levels when compared to the central channel, particularly in relation to events emanating from Ranger Retention Pond 1 (RP1). Water released from RP1 enters Coonjimba Billabong, which then eventually drains into the western side of Magela Creek. Continuous and grab sample electrical conductivity monitoring in previous years show that RP1 contributed water mixes incompletely in the western channel and preferentially follows the western bank, particularly during low flow periods.
Statistical analysis (ANOVA) comparisons of water chemistry of the downstream central channel site with the western channel downstream site for similar sampling periods over the last six years (water chemistry data from the toxicity monitoring program) shows that there are differences between these two sites, with the western channel site having slightly higher concentrations of uranium, magnesium and sulfate than the central channel site.
These higher concentrations measured at the western channel site are minor and are not regarded as sufficiently different to impact on the decision to relocate the sampling sites, particularly as sampling at the western channel site will result in a more conservative assessment of the contribution of the mine site to solutes in Magela Creek.
The first water chemistry samples for the Supervising Scientist's 2008-09 wet season surface water monitoring program were collected from Magela Creek on 26 November 2008 immediately after commencement of surface flow. Weekly sampling continued throughout the season with the last samples collected on 10 June 2009. On 16 June 2009, key stakeholders agreed that continuous surface flow had ceased in Magela Creek and monitoring of the creek was no longer required.
On 11 February 2009, electrical conductivity (EC) measured 45 µS/cm at the downstream site, which exceeds the statistically derived guideline value of 43 µS/cm. This corresponds with elevated magnesium (3.3 mg/L) and sulfate (12.2 mg/L). Continuous monitoring data (not shown) confirms that this was the peak of an EC event that lasted 30 hours and for which electrical conductivity remained above the guideline level of 43 µS/cm for 5 hours.
SSD considers the increased concentration of magnesium and sulfate had likely originated from RP1 (via Coonjimba Billabong). Water levels were low in Magela Creek prior to this EC event. SSD propose that an observed increase in flow (and water level) in Magela Creek restricted flow from Coonjimba Billabong and as Magela Creek water level dropped, drainage from Coonjimba Billabong caused the increase in EC at the downstream site.
Preliminary ecotoxicological research work by SSD suggests that there has been no detrimental environmental impact from this short lived event.
On 18 February, uranium was approximately 6 per cent of the limit and measured 0.37 µg/L at the downstream site compared to 0.028 µg/L at the upstream site. This concentration is similar to uranium concentrations measured by the creekside field toxicity monitoring program on two occasions in 2002/2003 and once in the 2006/2007 wet season. On each of these occasions, field toxicity monitoring (including the in situ test conducted 16 – 20 February, 2009) has shown no biological effects.
The routine grab sampling on 18 March 2009 coincided with another EC event at the downstream site, resulting in elevated concentrations of magnesium (3 mg/L) and sulfate (10 mg/L). Continuous monitoring data (not shown) confirms that this event peaked at 47 µS/cm and lasted about twenty hours, with EC exceeding the guideline level of 43 µS/cm for 8 hours. There had been increased discharge in Magela Creek during the previous day (from increased rainfall in the catchment) and the resultant water level decrease on 18 March would have increased drainage from Coonjimba Billabong back into Magela Creek and hence an increase in EC.
From mid–April, typical end of season trends were apparent as the water level decreased. Manganese concentrations at the downstream site increased as groundwater influences started dominating, and electrical conductivity between the upstream and downstream sites became similar as mine site influences decreased.
Overall, the results from the in situ toxicity monitoring, continuous monitoring and grab sample monitoring programs suggest that water quality in Magela Creek was comparable to previous seasons (for the west channel), providing reassurance that the aquatic environment of Magela Creek remained protected from activities at the Ranger Mine.
Weekly grab sampling at the upstream site for routine analysis of water chemistry variables has discontinued commencing with the 2008–09 wet season, as this site does not represent a useful reference site (i.e. water chemistry measured at this site may show upstream (natural) catchment influences that compromise its effectiveness for assessing downstream impacts from the mine). Weekly grab sample monitoring continued at the downstream site. The continuous monitoring of EC and turbidity was maintained at both the downstream and upstream sites (data not shown).
The first water chemistry samples for the Supervising Scientist's 2008-09 wet season surface water monitoring program were collected from Gulungul Creek on 30 December 2008 immediately after commencement of surface flow. Weekly sampling continued throughout the season with the last samples collected on 20 May 2009. On 22 May 2009, key stakeholders agreed that continuous surface flow had ceased in Gulungul Creek and monitoring of the creek was no longer required.
There was considerable work during 2008 on the Ranger Mine Tailings Storage Facility (TSF) with substantial quantities of waste rock used to raise the TSF wall. Water run-off from this waste rock may have contributed to the observed elevations in EC, uranium and sulfate concentrations at the Gulungul Creek downstream site. In addition, discharge in Gulungul Creek was lower than previous years due to less rainfall in the catchment, and hence dilution of solutes may have also decreased compared to previous years.
The turbidity measurement at the downstream site on 18 February 2009 (14 NTU) coincided with a turbidity event recorded by SSD continuous monitoring sondes at both the upstream and downstream site (results not shown).
On 25 February 2009, uranium measured 0.57 µg/L at the downstream site (<10% of the Magela Creek limit) coinciding with slightly elevated electrical conductivity (28 µS/cm) and sulfate concentration (2.7 mg/L). On 4 March 2009, uranium measured 0.36 µg/L at the downstream site, again coinciding with slightly elevated EC (24 µS/cm) and sulfate concentration (2.7 mg/L). None of these excursions are considered to be environmentally significant.
Since mid March 2009, uranium levels decreased to concentrations less than 0.2 µg/L (< 2% of the limit) which is comparable to previous season’s measurements.
From early April, recessional flow characteristics became apparent with electrical conductivity at the upstream and downstream sites becoming more similar and manganese concentrations increasing as groundwater inputs started to dominate.
Overall the water quality of Gulungul Creek suggests that the aquatic environment remained protected from activities at the Ranger Mine.
Jabiluka has been in a long-term care and maintenance phase since late 2003 and poses a low risk to the environment. As a consequence of this low risk and the good data set acquired over the last six years indicating the environment has been protected, the monitoring program has been systematically scaled down (see Commentary on Ngarradj (Swift Creek) 2004-05 monitoring data and Commentary on Ngarradj (Swift Creek) 2003-04 monitoring data for full explanation on previous monitoring changes). Since 2007-08, the Supervising Scientist Division has collected monthly samples from the downstream statutory compliance site only. Energy Resources of Australia (ERA) also samples monthly but to a different schedule and from both the upstream and downstream site.
Ngarradj Creek commenced flow late December, 2008, with the first water samples collected at the downstream site by SSD on the 23 December 2008. The last water sample was collected on 15 April 2009. Flow in the creek had ceased by 7 May 2009.
All variables are consistent with measurements from previous seasons.
Overall, water quality measured in Ngarradj during the 2008-09 wet season provides reassurance that the aquatic environment of Ngarradj remains protected from any impacts from the Jabiluka site.
Maps showing Magela Creek, Gulungul Creek and Ngarradj (Swift Creek)
The first water chemistry samples for the Supervising Scientist Division’s (SSD) 2007-08 wet season surface water monitoring program were collected from Magela Creek on 28 November 2007. Weekly sampling continued throughout the season while the creek was flowing, with the last sample collected on 2 July 2008. On 9 July 2008, key stakeholders agreed that continuous surface flow had ceased in Magela Creek and monitoring of the creek was no longer required.
Overall, water quality is comparable with previous years with all variables consistent with patterns observed in the last five years, with the only discernible variation being the effect on turbidity from the movement of soil from landslips in the upper Magela catchment (and well upstream of the mine) into the Creek. These landslips formed last year as a result of a record three day period of torrential rain that occurred in the Magela catchment during late February/early March. In 2008, during periods of heavy rainfall in the part of the catchment containing the landslips, soil moved into the Magela Creek and caused periodic increases in turbidity at both the upstream and downstream sites.
Continuous monitoring of turbidity showed that there were five turbidity events as a result of soil movement from these landslips (data not shown), with the routine monitoring program coinciding with two of those events. On 24 January, turbidity was measured at 8 NTU at the upstream site which was the leading edge of a landslip turbidity event which lasted 24 hours. On 13 March, the near peak of a 36 hour landslip turbidity event was measured at the downstream site (15 NTU) and the receding edge of the same event was measured at the upstream site (8 NTU). SSD is currently investigating the contribution of mud load from these events and the impact on Magela Creek.
With respect to the other variables, in late December rainfall increased in the Magela catchment and the subsequent increase in flow resulted in decreased magnesium concentration, electrical conductivity and pH, and increased turbidity at both the upstream and downstream sites. With rainfall continuing during the following week, Ranger Retention Pond 1 (RP1) commenced seasonal discharge into Magela Creek, via Coonjimba Billabong (approximately a month earlier than observed in previous years). This RP1 input saw a corresponding increase in concentration of uranium, magnesium, sulfate and conductivity at the downstream site. All variables were within guideline values or limits, with uranium only 3% of the limit.
ERA measured a uranium concentration of 0.93 µg/L on the 7 January 2008 at the downstream site which is 16% of the limit. Water sampling by ERA (investigative and routine) and SSD (routine) show that over the following week uranium concentrations decreased to levels consistent with previous wet seasons at less than 2 % of the limit.
Magela Creek stopped receiving water from RP1 on 11 April, with electrical conductivity, magnesium, sulfate and uranium concentrations decreasing over the following weeks.
From late April typical end of season trends became apparent with magnesium, pH and electrical conductivity increasing at the downstream and upstream sites (indicative of increasing groundwater influence as the volume of surface water in the creek decreases). Sulfate and uranium concentrations decreased as run-off from the mine decreased. The shallow groundwater near the Magela downstream site is known to contain naturally elevated concentrations of soluble manganese, and as surface flow continued to decrease at the downstream site, manganese levels increased.
On June 2, flow was observed to have ceased in the channel where water sampling at the downstream site normally occurs. Water sampling at the downstream site was transferred to the nearby western channel of Magela Creek (which continued to flow) until flow had completely ceased across the creek. This change in sampling site explains the decrease in manganese concentrations measured on water samples collected on June 5 compared to the previous week. There was better surface flow in this western channel compared to the downstream central channel measured in the previous week and therefore less influence from groundwater.
Overall, the water quality in Magela Creek was good during the 2007-08 wet season providing reassurance that the aquatic environment of Magela Creek remained protected from impacts of mining activities at the Ranger site.
The first water chemistry samples for the Supervising Scientist's 2007-08 wet season surface water monitoring program were collected from Gulungul Creek on 27 December 2007 immediately after commencement of surface flow. Weekly sampling continued throughout the season with the last samples collected on 12 June 2008. On the 19 June 2008, key stakeholders agreed that continuous surface flow had ceased in Gulungul Creek and monitoring of the creek was no longer required.
Turbidity measured on the 14 February 2008 at the upstream and downstream site increased from the previous week coinciding with increased rainfall experienced in the catchment over that week.
From February to May, although uranium, sulfate and electrical conductivity measured slightly higher in concentrations at the downstream site compared to the upstream site, they were well within guideline values or limits and were comparable to previous wet seasons.
Water samples from early April onwards show magnesium at the upstream site, and pH and electrical conductivity at both upstream and downstream sites generally increasing. Sulfate and uranium concentrations at the downstream site decreased, with uranium remaining at less than 3% of the limit since late April. These trends are normally seen towards the end of the wet season as groundwater inputs become more dominant in the creek (refer to Explanatory Notes Gulungul creek 2002-03).
From early May, turbidity measurements were reported from the field instrument rather than by laboratory measurements (due to technical issues). The slight increase in turbidity recorded at the downstream site, though very low at less than 4 NTU, was likely an artifact due to the shallowness of the water and resulting interference from natural light and the sediment bed on the turbidity sensor beam.
Overall, all variables at both upstream and downstream sites are comparable to routine monitoring over the last five years.
Jabiluka has been in a long-term care and maintenance phase since late 2003 and poses a low risk to the environment. As a consequence of this low risk and the good data set acquired over the last six years indicating the environment has been protected, the monitoring program has been systematically scaled down (see Commentary on Ngarradj (Swift Creek) 2004-05 monitoring data and Commentary on Ngarradj (Swift Creek) 2003-04 monitoring data for full explanation on previous monitoring changes). In 2007-08, the Supervising Scientist Division collected monthly samples from the downstream statutory compliance site only. Energy Resources of Australia (ERA) also sampled monthly but to a different schedule and from both the upstream and downstream site.
Ngarradj Creek commenced flow late December, 2007, with the first water samples collected at the downstream site by SSD on the 3 January 2008. The last water sample was collected on the 25 April 2008, after which time it was observed that the creek had ceased to flow.
Variables are consistent with measurements from previous seasons with uranium less than 0.4% of the limit. Overall, water quality in Ngarradj was good during the 2007-08 wet season providing reassurance that the aquatic environment of Ngarradj remained protected from any impacts from the Jabiluka site.
The first water chemistry samples for the Supervising Scientist Division's (SSD's) 2006-07 wet season surface water monitoring program were collected from Magela Creek on 14 December 2006. Weekly sampling continued throughout the season until the creek ceased to flow on the 8 August 2007.
During the first four weeks of sampling Magela creek had variable flow and at times almost ceased to flow due to lack of consistent rainfall. Continuous surface water flow was fully established by mid-January.
Magnesium and sulfate levels at the downstream site for the first two weeks of flow were the highest observed in Magela creek since the SSD commenced its routine monitoring program in 2001. During the 1990's and up to 2001, similar levels (and higher) were consistently observed by ERA during routine monitoring, however, similarly to the current wet season, no biological impacts were observed by the SSD's biological monitoring programme. Historically, the elevated levels were detected later in the season, reflecting the onset of point discharge from the mine. The elevated levels measured at the beginning of the current wet season were observed prior to release of mine waste waters.
Turbidity, uranium, manganese and pH values at both upstream and downstream sites were comparable to recent year's routine monitoring data. The pH measured at the upstream site on 25 January 2007 was below the lower guideline level for the downstream compliance site and was likely an outlier, as a simultaneous field pH measurement (not shown) was higher and comparable to those observed in previous weeks. Importantly, the downstream site was within the expected range and all subsequent results for both sites have been well within the guideline.
On the 18 and 22 February 2007, magnesium and sulfate concentrations, and consequently electrical conductivity, increased at the downstream site, with no corresponding increase at the upstream site. Results of an SSD investigation conducted on the 22 February 2007 indicate that the probable source of the magnesium and sulfate was RP1 (via Coonjimba Billabong). Assessment of electrical conductivity data collected as part of the continuous monitoring project showed that the total estimated magnesium load at the downstream site for the monitoring period up to the 23 February 2007 was lower than the load estimated during the same period last wet season. This indicates that the increased magnesium and sulfate concentrations were likely a result of decreased water volume in Magela Creek compared to previous years, effectively concentrating the solutes present.
Between 27 February and 2 March 2007, the Magela creek catchment (like the Gulungul and Ngarradj catchments) experienced an extreme rainfall event resulting in overbank flow both at the upstream and downstream sites that covered the gauge boards. The discharge measured over the three day period corresponded to the highest flood levels recorded in Magela Creek since recording began in 1971. This record period of rainfall caused Ranger to close its mining and milling operations due to excess water contained on site. Turbidity increased in Magela Creek at both the upstream and downstream site indicating catchment-wide storm effects. The downstream site showed no guideline or limit exceedences for any of the variables in the water samples collected on the 1 March. Rather, as a result of the increased stream flow in Magela Creek, decreased electrical conductivity, pH, uranium, manganese, magnesium and sulfate concentrations were observed. All these variables were similar between the upstream and downstream sites, except for uranium. While uranium concentration decreased, the concentration at the downstream site was higher than the upstream site, though still only 1% of the limit. During mid-March the uranium concentration reached a season high of 0.15 μg/L (2.5% of the limit) at the downstream site.
Typical end of season trends became apparent in mid-April, with magnesium, pH and electrical conductivity increasing at both upstream and downstream sites (indicative of groundwater influence dominating as the volume of surface water in the creek decreased) and uranium and sulfate concentrations decreasing at the downstream site as runoff from the mine decreased. As flow continued to decrease, manganese levels increased similar to previous years (refer to last paragraph in Explanatory Notes Magela creek 2003-04). Manganese measured at the downstream site on 12 July 2007 decreased from 20 μg/L (measured the week prior) to 6.4 μg/L, similar to the concentration measured at the upstream site, reflecting the variability in manganese behaviour during the recessional flow period.
Overall, the water quality in Magela Creek was good during the 2006-07 wet season providing reassurance that the aquatic environment of Magela Creek remained protected from impacts of mining activities at the Ranger site.
The first water chemistry samples for the Supervising Scientist Division's (SSD's) 2006-07 wet season surface water monitoring program were collected from Gulungul Creek on 4 January 2007, the first week after continuous surface water flow was observed in the creek. Weekly sampling continued throughout the season until the 28 June 2007 when the last samples were collected. On the 4 July 2007, key stakeholders agreed that continuous surface flow had ceased in Gulungul Creek and monitoring of the creek was no longer required.
Between 27 February and 2 March 2007, the Gulungul creek catchment (like the Magela and Ngarradj catchments) experienced an extreme rainfall event resulting in overbank flow both at the upstream and downstream sites. This record period of rainfall caused Ranger to close its mining and milling operations due to excess water contained on site. As a result of the increased stream flow in Gulungul Creek, increased turbidity and decreased electrical conductivity, pH, magnesium and sulfate were observed at the upstream and downstream sites. However, all these variables remained within the range observed in previous years.
During March, uranium and sulfate concentrations increased at the downstream site, but were consistent with levels seen in recent years. Although the uranium concentrations downstream of the mine were elevated relative to the upstream concentrations, the increase was very low compared to the limit (6 μg/L). From early April, uranium and sulfate concentrations at the downstream site decreased, becoming more similar to the upstream site.
Magnesium, pH and electrical conductivity began increasing at both upstream and downstream sites from early April, which is the trend normally seen toward the end of the wet season as groundwater inputs become more dominant in the creek (refer to Explanatory Notes Gulungul creek 2002-03).
Overall, the water quality in Gulungul Creek was good during the 2006-07 wet season providing reassurance that the aquatic environment of Gulungul Creek remained protected from impacts of mining activities at the Ranger site.
The first water chemistry samples for the Supervising Scientist Division's (SSD's) 2006-07 wet season surface water monitoring program were collected from the Ngarradj downstream statutory compliance point and the upstream sites on 31 January 2007. Monitoring continued on a monthly basis until 25 May 2007 when the last samples were collected and after which time it was observed that the creek had ceased to flow. ERA commenced monitoring at the upstream site on the 16 January 2007 and both downstream and upstream sites on the 23 January 2007 after flow first established.
Magnesium concentrations and conductivity were above the guideline level at both the upstream and downstream site in the first week of sampling. This initial high magnesium concentration has been observed in previous seasons (2001-02 and 2002-03) and is most likely influenced by groundwater inputs (see Explanatory notes 2001-02). All other variables were within guideline values and comparable to previous seasons data.
Between 27 February and 2 March 2007, the Ngarradj catchment (like the Magela and Gulungul catchments) experienced an extreme rainfall event resulting in overbank flow both at the upstream and downstream sites. As a result of the increased stream flow in Ngarradj, turbidity increased slightly at both upstream and downstream sites but was still comparable to turbidity measurements from previous years. During this period, all variables were within guideline values and comparable with previous seasons.
From late April, trends reflecting reduced volume of surface flow were apparent with magnesium concentrations increasing at the downstream site as groundwater influences began to dominate. On the 18 June, after a month of nearly no rain, 71 mm of rain was recorded at Oenpelli. This rainfall corresponded with slight increases in turbidity, uranium and sulfate at both downstream and upstream sites and an increase in conductivity and magnesium at the downstream site measured by ERA.
Overall, the water quality in Ngarradj was good during the 2006-07 wet season providing reassurance that the aquatic environment of Ngarradj remained protected from impacts of activities at the Jabiluka site.
The first water chemistry samples for the Supervising Scientist's 2005-06 wet season surface water monitoring program were collected from Magela Creek on 6 December 2005, one day after flow was observed at the downstream statutory compliance point. Weekly sampling was conducted throughout the wet season, and ceased in the last week of August when the creek stopped flowing, except on the following occasions. Following an accidental irrigation, on 21-22 January, of the Magela Land Application Area with pond water, additional sampling of Magela Creek was undertaken on 23 January. In the last week of April, sampling did not occur after cyclone Monica passed over Jabiru on the 25th April and sites became inaccessible.
All indicators throughout the wet season, including the period following the irrigation incident and the cyclone, were within limits/guidelines set by the Supervising Scientist for the protection of the aquatic environment and were within the range seen in previous years. Uranium concentrations at the downstream site were generally slightly higher than at the upstream site but remained well below (<3% of) the limit throughout the season. Magnesium and sulfate concentrations were also generally higher at the downstream than the upstream site as magnesium sulfate enriched surface waters from the mine entered Magela Creek.
At the start of the wet season (late December - mid January) turbidity measurements were slightly higher at both upstream and downstream sites compared to values measured during routine monitoring in the last few years. However, the turbidities reported during that period were not high compared to values measured in other regional creeks (eg Gulungul and Ngarradj) during rising water levels and were well below the guideline which is based upon the natural range of turbidities measured over a decade at the upstream site. (Turbidity is an analogue measure of suspended sediment and so is elevated when turbulence in the water is high - such as when waters are rising following heavy rainfall.) Sulfate concentrations at the downstream site were lower than usual for the same period.
In the mid part of the season sulfate and magnesium peaked at the downstream site, the concentrations measured on 23 March were 3.4 mg/L and 1.4 mg/L respectively. These two values were probably caused by a combination of a large storm over the mine site the day before sampling (witnessed by the monitoring team) and decreasing Magela Creek water levels leading to less dilution of mine origin inputs in the creek. Those concentrations are within the range measured in Magela Creek before the establishment of SSD's routine monitoring program (not shown here) and are not considered to be environmentally significant; biological monitoring showed that aquatic ecosystems were not impacted at those levels.
Tropical Cyclone Monica passed in the vicinity of Ranger mine as a category 3 cyclone on April 25 extending the period of flow in the creek and therefore delaying typical end of season trends. These trends became apparent mid-May with magnesium, pH and EC increasing at both upstream and downstream sites -indicative of groundwater influence dominating as the volume in the creek decreased - and uranium and sulfate concentrations decreasing at the downstream site as runoff from the mine decreased. The elevated manganese recorded in the last week of flow is not unusual, similar trends were seen in 2001-02 and 2003-04.
The first water chemistry samples for the Supervising Scientist's 2005-06 wet season surface water monitoring program were collected from Gulungul Creek on 29 November 2005, the first week after flow began in the creek. Weekly sampling was conducted throughout the wet season, and ceased mid-August when the creek stopped flowing, except in the last week of April, after cyclone Monica passed over Jabiru on the 25th April and sites became inaccessible.
Uranium spikes at the downstream site were seen at the start of the wet season, when manganese was also slightly elevated, and in mid January when an uranium concentration of 0.393 µg/L (less than 7% of the 6 µg/L limit determined for Magela Creek) was accompanied by a sulfate concentration of 2.3 mg/L. None of these excursions is considered to be environmentally significant. The uranium and sulfate concentrations reduced subsequently and by June were almost identical upstream and downstream of the mine. Magnesium and EC began increasing at both upstream and downstream sites in mid-May, which is the trend normally seen toward the end of the wet season as groundwater inputs become more dominant in the creek.
The first water chemistry samples for the Supervising Scientist's 2005-06 wet season surface water monitoring program were collected from Ngarradj on 10 January 2006 and ERA collected samples from Ngarradj on 29 December 2005 from the downstream only (the upstream site was not yet flowing). The Supervising Scientist Division (SSD) collected samples monthly until June. Energy Resources of Australia and the NT Department of Primary Industry, Fisheries and Mines have also sampled monthly but to a different schedule. ERA have collected samples up to the first week in August after which the creek stopped flowing. The charts displayed on this site show both SSD and ERA data.
Values and trends for key variables measured by ERA & SSD this wet season are similar to those seen in previous years. Uranium is marginally higher at the downstream site however it is less than 0.5% of the limit, sulfate is lower at the downstream site compared to upstream of the mine, and magnesium at the downstream site increased toward the end of flow when groundwater inputs dominate the flow. These trends have been observed since monitoring began (refer to the explanatory notes for 2001-02).
The first water chemistry samples for the Supervising Scientist's 2004-05 wet season surface water monitoring program were collected from the Magela Creek downstream statutory compliance point on 21 December 2004, one day after the commencement of flow past the site . Weekly sampling continued throughout the wet season with the last of the routine monitoring samples collected on 25 May 2005, the week before flow past the downstream compliance point ceased. Investigative monitoring continued for several weeks at other sites in Magela Creek. Results from those investigations will be used to assess aspects of the monitoring program.
All indicators remained within limits/guidelines throughout the 2004-05 wet season and the quality of water was comparable to that seen in previous years.
Uranium, magnesium and sulfate were generally slightly higher downstream of the mine but the concentrations were very low and not of environmental concern. The downstream sulfate concentrations were slightly higher this season than in the last two seasons but were lower than those measured most years since the mid 1980's. Uranium was less than 1% of the limit for most of the season. Manganese and the general parameters - pH, electrical conductivity (EC) and turbidity - were almost identical at upstream and downstream sites for the season, except for a slightly elevated manganese concentration in the first week of monitoring.
Flow rates greater than 500 cubic metres per second, the largest flows recorded in Magela Creek for the season, occurred within hours of sample collection on the 23 March 2005. Turbidity peaked and the dilution effects of the storm-related flows are evident in the downstream magnesium, sulfate and conductivity data that week.
Gradual changes in Magela Creek water quality began in April. By May the signal from the mine became less noticeable with magnesium and sulfate concentrations similar at both sites. Magnesium-sulfate enriched surface water discharges from the mine decreased reducing the concentrations downstream. At the same time magnesium concentrations upstream increased as a result of the progressively increasing influence of magnesium rich groundwater to the diminishing volumes of surface flow. Similar trends have been noted in previous years (for example see Commentary on Magela Creek 2002-03 monitoring data).
The water quality objectives set to protect the aquatic ecosystems downstream of the mine were achieved. Available biological monitoring data (see Creek side monitoring results) also indicate that the environment remained protected throughout the season.
The first water chemistry samples for the Supervising Scientist's 2004-05 wet season surface water monitoring program were collected from Gulungul Creek on 23 December 2004 , the first day of flow in the creek for the wet season . Weekly sampling continued throughout the season with the last of the routine monitoring samples collected on 8 June 2005, during the week in which flow past the downstream compliance point ceased.
Uranium concentrations in Gulungul Creek are slightly higher than those in Magela Creek. Like Magela Creek, the concentrations at the Gulungul Creek downstream site are slightly higher than those at the upstream site. However, the uranium concentrations in Gulungul Creek were well below the limit throughout the season, with the concentration at both the upstream and downstream sites ranging between about 1 and 4% of the limit.
Sulfate concentrations in Gulungul Creek were similar to those seen in previous years, with the downstream concentrations generally higher than those upstream but still well below levels of environmental concern.
The small difference in electrical conductivity (EC) between the upstream and downstream sites shows that the sulfate increase has little effect on the overall solute levels downstream of the mine. The EC trend at both upstream and downstream sites closely follows that of magnesium which is not influenced by the mine, ie concentrations are very similar upstream and downstream of the mine. Manganese, pH and turbidity were also similar at the upstream and downstream sites.
Seasonal effects similar to those described for Magela Creek can also be seen in Gulungul Creek. A gradual increase in magnesium concentrations and EC both upstream and downstream of the mine and a downstream decrease in sulfate began in April. A slightly elevated manganese concentration was measured downstream during the last week of flow. Similar trends in Gulungul Creek have been noted in previous years (for example see Commentary on Gulungul Creek 2002-03 monitoring data).
Toward the end of 2003 Jabiluka entered a long-term care and maintenance phase. The site poses a very low risk to the environment (see Commentary on Ngarradj (Swift Creek) 2003-04 monitoring data). Consequently, the Supervising Scientist's water chemistry monitoring program at Ngarradj was reduced to monthly sampling for the 2004-05 wet season, augmented by a utomatic recordings of turbidity and hydrological data at 6-minute intervals. The NT Department of Business, Industry and Resource Development (DBIRD) resumed the role of performing check monitoring at Ngarradj, also on a monthly basis. These independent programs complement each other, providing fortnightly water sampling and a combined dataset to assess the water quality at Ngarradj. ERA continued to carry out independent monitoring on a weekly basis.
The first water chemistry samples for the Supervising Scientist's 2004-05 wet season surface water monitoring program were collected from the Ngarradj downstream statutory compliance point on 6 January 2005 . ERA commenced monitoring at that site on the 29 December 2004, the day flow was first observed, and DBIRD commenced monitoring in the second week of January. The last samples were collected from Ngarradj on 10 May 2005, by ERA, shortly before flow ceased.
ERA & SSD data, which agree well, show values and trends similar to those seen in previous years. The water quality was very good throughout the season with only one exceedance of the electrical conductivity (EC) and the magnesium guideline. All other key indicators remained within limits/guidelines, with uranium remaining less than 0.5% of the limit.
EC at both sites was low throughout the season except for one occasion in early January (SSD data) when EC at the downstream site was just above the guideline value. However, the corresponding EC at the upstream site was of a similar value, indicating that the elevation was part of a natural fluctuation in the system.
The magnesium concentration exceeded the upper guideline in May just before flow ceased. When the water level in the creek drops toward the end of the season we expect to see increases in magnesium concentrations, particularly at the downstream site, which naturally has higher concentrations than upstream. Therefore, the upper level for magnesium has always been a guideline and not a limit. This trend has been noted in previous years in Ngarradj ( for example see Commentary on Ngarradj (Swift Creek) 2002-03 monitoring data ) and at other creeks in the region (eg Magela and Gulungul Creek).
The water quality objectives set to protect the aquatic ecosystems downstream of Jabiluka were achieved providing assurance that the environment remained protected throughout the season.
The first water chemistry sample for the Supervising Scientist's 2003-04 wet season surface water monitoring program was collected from the Magela Creek downstream statutory compliance point on December 23rd , one day after the commencement of flow past the site for this wet season . Weekly sampling continued throughout the wet season with the last of the routine monitoring samples collected on July 2nd . Further sets of samples were collected in Magela Creek for investigative purposes (rather than for compliance monitoring) on:
All indicators measured at the Magela Creek compliance point during flow have been well within limits this season, even during the first weeks when first flush effects often result in limits or guidelines being approached and occasionally exceeded ( see 2002-03 wet season notes ). The final manganese measurement (discussed below), while above the limit, is not considered a breach of compliance, as there was no flow past the compliance point at the time of sampling. Compliance with the water quality limits and guidelines throughout the season provides reassurance that the aquatic environment has not suffered any deleterious effects from mining during the previous year. The results of the biological monitoring program , when available, are expected to confirm this.
Overall, the water quality in Magela Creek this wet season was similar to that seen last season, and was demonstrably improved compared to that seen during the 2001-02 season (note the smaller differences in upstream-downstream electrical conductivity and concentrations of uranium, magnesium and sulfate seen in the last two seasons compared to the 2001-02 season). These improvements are likely due to a range of remedial works and water management practices implemented at the mine in recent years. Values for electrical conductivity (EC), pH, turbidity and manganese concentration were almost identical at both sites throughout most of the season. Magnesium and sulfate values were similar at both sites at the beginning and end of the season, but were higher at the downstream site during the greater part of the wet season proper when waste-water inputs to the creek are received from the mine site via Retention Pond 1, Georgetown Creek and, for a short period of controlled release, Djalkmara Billabong.
Intermittent pumping of Djalkmara Billabong water into Magela Creek began on the 31st of January and ceased in late March. (This pumping is permitted under strict conditions based on results of 'Whole of Effluent' ecotoxicological testing, flow rates in Magela Creek and predictive modelling of expected concentration increases at the downstream Magela Creek statutory compliance point.) During Djalkmara pumping, a slight rise in uranium concentration downstream of the mine was noticeable in the early February data and again in early March - the uranium concentrations did not exceed 2% of the ecotoxicological limit on those occasions. The other downstream parameters showed little, if any, additional change during the pumping of Djalkmara Billabong.
The charts for water quality in Magela Creek include the daily measurements (in late March - early April) of uranium, manganese, electrical conductivity and pH made during the Supervising Scientist's investigation into the contamination of drinking water by process water at the Ranger Mine. The results demonstrate that no uncharacteristic change in any of the key water quality variables occurred at the downstream Magela Creek statutory compliance point throughout the incident, with all results within the normal range of measurements.
Toward the end of the wet season, pH, electrical conductivity and magnesium concentrations at both the upstream and downstream sites increased. These trends are typical of late wet season flow conditions when water level in the creek begins to reduce; the fact that increases occurred upstream of the site indicates that they are not attributable to mining.
Elevated manganese concentration at the very end of the season was expected (based on previous years results) but was not seen this year while the creek was flowing at the compliance point. This prompted continuation of sampling, despite the lack of flow at the compliance point, to identify the conditions under which these increases occur. The results indicate, as expected, that the manganese increase is brought about by water quality changes related to the flow conditions, ie the low dissolved oxygen in the near stagnant water causes the manganese present to dissolve. While the seasonal increases in manganese levels are not detrimental to the environment (supported by findings of the biological monitoring program), investigations of their occurrence and causes will be ongoing.
The first water chemistry sample for the Supervising Scientist's 2003-04 wet season surface water monitoring program was collected from Gulungul Creek on December 23rd , one day after the commencement of flow past the site for this wet season . Weekly sampling continued throughout the wet season with the last of the routine monitoring samples collected on July 10th when the creek had all but stopped flowing.
In the first three months of the wet season, the uranium concentrations at the Gulungul Creek downstream site were moderately higher than at the upstream site. The difference, which was greater than in previous years, was most noticeable in mid to early January when the downstream uranium concentration trended away from the upstream concentration. From mid-March, the uranium concentrations at the downstream site were almost the same as those measured at the upstream site, though as in previous years the downstream concentrations are slightly higher than the upstream concentrations. The higher uranium concentrations measured at the downstream site, while probably mine related, are not considered to have posed an environmental risk, the values remaining less than five percent of the limit at the most. Nevertheless, an investigation into the cause of the elevated uranium concentrations at the downstream site will be undertaken.
From early April, pH remained steady at the downstream site while increasing slightly at the upstream site. The measured pH values were similar to those observed in previous years at both upstream and downstream sites, with this season's results showing fewer fluctuations over the season. EC and turbidity measurements recorded this wet season are similar to values measured in previous years and are similar at both the upstream and downstream sites for most of the season. As occurred last wet season, EC generally increased from the middle of the season at both sites (compare to 2002-03 data). However, as was the pattern last season, EC exhibited a sharp increase in the last month. The cause of the elevated EC will be investigated. It cannot be attributed to the common mine-related salts magnesium and sulfate as concentrations of those variables at the downstream site were actually lower during this period than in previous weeks.
Although the uranium concentrations downstream of the mine were elevated relative to the upstream concentrations, the increase was very low compared to the limit. Overall, the water quality in Gulungul Creek was good during the 2003-04 wet season providing reassurance that there is a high degree of certainty that the aquatic environment of Gulungul Creek remained protected from impacts of mining. The results of the biological monitoring program, when available, are expected to confirm this.The first water chemistry sample for the Supervising Scientist's 2003-04 wet season surface water monitoring program was collected from the Ngarradj downstream statutory compliance point on December 23rd. Water samples were collected weekly for the first seven weeks of the wet season. After considering the reduced risk to the environment posed by the site (which is now in a care and maintenance mode) and the high water quality measured in the early part of the season, the sampling of water for chemical analyses was reduced to fortnightly from February 4th. Automatic gauging stations in Ngarradj upstream and downstream of the Jabiluka site continued to record continuous pH, turbidity and hydrological data, while the biological monitoring program did not change from the previous year. Fortnightly water quality sampling ceased in mid May, when the flow at the downstream compliance site was negligible and by which time flow at the road crossing, further downstream, and in the tributaries had ceased; the last sample for the season was collected on April 25th.
The following points summarise the data collected at Ngarradj as part of the routine water chemistry monitoring program:
Flow commenced on the 1st of December 2002 in Magela Creek and ceased in the downstream central channel (the downstream monitoring site) in late May 2003. The last monitoring sample collected from that site was on May 22nd. The water quality data collected during the 2002-2003 wet season are described below.
Water quality data for the first few weeks show typical first flush effects at both upstream and downstream sites. Natural first flush waters are typified by relatively low pH and higher electrical conductivity (EC) and metal and ion concentrations than occur during the main period of wet season flow. This is due to flushing of the soil profile and resuspending of billabong and creek bed sediments. Thus during this period pH at both upstream and downstream sites followed similar trends; exceeding the lower guideline twice, while metal and sulfate concentrations and EC were higher at both upstream and downstream sites compared to mid-season values. The manganese concentrations at the downstream site were noticeably higher than the upstream site but remained below the limit. By late December first flush effects ceased and metal and sulfate concentrations and EC fell at both upstream and downstream sites.
Magnesium and sulfate values increased downstream in mid January for a short period. Elevated concentrations of both these ions occurred again towards the end of March at the downstream site. These increased concentrations are associated with dispersion of mine waste waters, mainly from Ranger Retention Pond 1. However, magnesium and sulfate concentrations are interpreted with reference to EC (a surrogate indicator), and these levels remained well below the limit for the whole wet season, with similar values reported at both upstream and downstream sites. Magnesium concentrations at both the upstream and downstream sites increased toward the end of the season as the surface flow receded.
Uranium concentrations at the downstream site rose slightly during active release of Djalkmarra Billabong water to Magela Creek (intermittent during mid February - mid March). Release of water from Djalkmarra is permitted under strict conditions determined primarily by biological toxicity testing. Both ERA and SSD increased the frequency of their water quality monitoring for the release period. SSD also monitored at extra sites in Magela Creek during the release to determine the variation in concentrations across the creek at the downstream compliance point, and conducted routine biological creekside monitoring. SSD monitoring data for the release period show that uranium remained within the natural range of concentrations and was always below 2% of the allowable limit. After the releases ceased, uranium levels at the downstream site quickly returned to levels similar to the upstream site (i.e. ~ 0.5% of the limit).
Throughout the season, EC, turbidity and pH fluctuated but were almost identical at upstream and downstream sites.
As well as first flush, low pH and elevated levels of metals and ions are also common in the late stages of the wet season as a consequence of the increasing contribution of higher-concentration groundwaters as surface flows are declining (see 2001-2002 data and comments). Concentrations of manganese increased sharply at the downstream site in the last few weeks of flow coupled to a sudden decrease in pH (manganese solubility is very responsive to pH changes), with the last pH measurement of the season exceeding the lower guideline. Such natural excursions mean that recommended pH values are guideline values rather than strict limits. Exceeding a guideline value does not imply that the environmental standard has been breached.
In summary, the data show that the Magela Creek water was very high quality throughout the 2002-2003 wet season. Although a signal from the mine can be seen at the downstream site, i.e. elevated uranium during active release and periods of elevated sulfate, the concentrations of these constituents remained very low, with uranium remaining below 2% of the limit and EC remaining at about 50% or less of the limit. Natural seasonal patterns of slightly elevated metals and ions coupled with low pH were seen, as expected, at the start and end of the season (for reasons explained above) - pH exceeded the lower guideline and manganese approached, but did not exceed, the limit during these times. Apart from the seasonal manganese elevations, the values of all measured metals and ions were well 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 2002-2003 wet season. Results from the biological monitoring program verify this.
Gulungul Creek commenced flowing on the 31st of December 2002 and ceased flowing at the downstream monitoring point in early June 2003. The last monitoring sample collected from that site was on May 27th. The water quality data collected during the 2002-2003 wet season are described below.
First flush effects are noticeable in the uranium data, which shows a general decrease in uranium concentrations at both sites throughout the wet season. EC, pH, turbidity and uranium data followed similar trends at both upstream and downstream sites throughout most of the wet season. Uranium concentrations were slightly higher at the downstream site on most occasions but remained well below (<5%) the limit. On one occasion in late February, a natural increase in uranium concentration at the upstream control site coupled to increased turbidity and EC were observed. This is a good example of how a local storm event can affect water quality by washing soil and organic matter into the creek and stirring up the creek bed sediments. These effects were very localised; the same phenomenon was not seen at the downstream site.
Electrical conductivity (EC) began increasing in mid-March at both upstream and downstream sites. Upstream EC decreased toward the end of the wet season while downstream EC remained elevated. Elevated EC is a typical late season effect that manifests as volumes of surface water diminish toward the end of the wet season and groundwater inputs to the system become more noticeable and/or dissolved salts in the surface water become concentrated as surface water evaporates. The uranium concentrations at the downstream site also rose slightly at the end of the season, probably due to same seasonal effects or to the slight increase in turbidity.
In summary, while it is possible that the higher uranium concentrations at the downstream site were caused by mining, the concentration increases were very low compared to the limit. Hence there is no concern the environment was adversely affected. Further, no limits were exceeded in Gulungul Creek during the 2002-2003 wet season and the chemical data indicate that there is a high degree of certainty that the aquatic environment of Gulungul Creek remained protected from impacts of mining. Results from the biological monitoring program verify this.
Flow past the Ngarradj main channel downstream monitoring site commenced on the 22nd of December 2002 and ceased in mid May 2003. The last monitoring sample was collected on May 13th. The water quality data collected during the 2002-2003 wet season are described below.
First flush effects can be seen in the electrical conductivity (EC) data, which was above the limit at both sites in the first two weeks of flow then fell to within limits in early January. EC remained below the limit throughout the remainder of the wet season, with similar trends observed at both upstream and downstream sites.
Throughout the season, turbidity levels followed similar trends at both sites and, apart from the first upstream measurement, pH remained within the recommended guidelines. Uranium concentrations, which are extremely low (near the limit of detection), were slightly higher at the downstream site but remained well within the limits set and followed similar trends at both sites. The slightly higher uranium concentrations at the downstream site are apparently natural; the same pattern is seen in historical data collected prior to development activities at Jabiluka. For most of the season similar trends were seen at both sites for sulfate and magnesium, though concentrations of sulfate were lower and magnesium higher at the downstream site. These are natural patterns that have also been observed in previous years (see 2001-2002 data and comments).
Magnesium increased suddenly at the downstream site toward the end of the season and exceeded the guideline value. There is a natural source of magnesium present between the upstream and downstream monitoring sites that enriches the groundwater with this ion. With diminishing surface flow, the groundwater entering the creeks makes up a higher proportion of the flow and therefore has a greater impact on the surface water quality. Hence, elevated magnesium at the downstream site is expected during the final stages of flow (see 2001-2002 data and comments). The effect of higher groundwater contribution can also be seen in the increasing EC levels at both sites in the late stage of the wet season.
Because elevated magnesium is natural at the downstream Ngarradj Creek site no limit can be set, only a guideline value. Thus exceeding this value does not imply that the environmental standard has been breached.
In summary, uranium, sulfate, turbidity and EC trends and values were almost identical at the upstream and downstream sites. Uranium concentrations remained extremely low (less than 1% of the limit) at both sites throughout the season. Natural seasonal patterns can be seen in the data, i.e., elevated magnesium concentrations and EC values at the beginning and end of the wet season, elevated uranium concentration and sulfate 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 2002-2003 wet season. Results from the biological monitoring program 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 (magnesium and pH are the exceptions). Therefore, no mine-related signal can be inferred from the 2002-2003 data.
Data for a number of variables for the monitoring period show strong concordance between upstream and downstream values (pH, turbidity) indicating no detectable mine-related effects. These variables are not significantly enhanced or altered in mine waste waters compared with levels found naturally in Magela Creek.
The most evident difference between the upstream and downstream sites for Magela Creek is the presence of elevated concentrations of uranium, magnesium, and sulfate at the downstream location. These differences are almost entirely due to the contribution from Retention Pond 1 (RP1) mine waste-water overflow to Coonjimba Billabong and thence to Magela Creek. When RP1 ceases to overflow, indicator values at the paired sites converge. Relatively minor contributions from Georgetown Billabong, via Georgetown Creek and Corridor Creek, Djalkmara Billabong releases and washoff from the Magela land application area are also probable, especially early in the wet season. The concentrations of manganese diverge, particularly towards the end of the season. The basin-shaped profile for manganese, particularly at the downstream site, is thought to be due to intrusion of natural groundwater to Magela Creek. The shallow groundwater near the Magela downstream site is known to contain elevated concentrations of soluble manganese. During recessional flow, the groundwater contribution increases as a proportion of total flow, leading to higher values for this element. Although electrical conductivity (EC) is notably higher at the downstream site, this indicator is a less sensitive measure of mine-related contribution than either magnesium or sulfate.
While mine-related changes were evident over the period of monitoring in the 2001-02 wet season, limits were rarely exceeded for any constituent, indicating no environmental harm arising from mine waste water dispersion.
The downstream site at Gulungul Creek has a consistently higher sulfate concentration than the upstream site. This would normally be interpreted as evidence for mine-related impact. However, the concentration of magnesium is not higher at the downstream site whereas elevation would be expected if there was an influence from Ranger mine. This decoupling of magnesium and sulfate suggests that the source of the latter constituent may be the oxidation of sulfide minerals in the catchment, and unrelated to the mine. This interpretation is supported by the generally lower pH at the downstream site, which is the reverse of the observations from Magela and Ngarradj Creeks (and some tributaries of Ngarradj Creek, not shown). Sulfide oxidation is accompanied by a decrease in pH. Gulungul Creek flows through black soils and associated swamps in the vicinity of Ranger, and these may be a source of low levels of sulfide minerals and some heavy metals. The downstream site shows elevated (though not environmentally significant) concentrations of copper and possibly lead. Charts for these metals are shown below. These (particularly copper) are not likely to be attributable to the mine, and strengthen the hypothesis that Gulungul Creek receives a measurable indicator input from riparian soils. Gulungul downstream also has a higher uranium concentration, compared with the upstream site. There is no clear indication of whether this is mine-related or not However, the uranium limit was not exceeded at any time indicating no environmental harm arising from the elevated levels.
The indicators measured for Ngarradj Creek included pH, conductivity, turbidity, uranium, magnesium, manganese, sulfate and calcium. For all indicators, concordance in concentration values was maintained between the upstream and downstream sites throughout the monitoring season. In no case did values measured at the sites diverge in any significant way. These observations allow a high degree of confidence that no measurable mine-related additions of target indicators were observed during the 2001-02 wet season.
The most evident difference between the upstream and downstream sites at Ngarradj Creek is the higher sulfate concentration at the upstream site. This observation is consistent over the wet season and mirrors the baseline data of previous years. The reason is that the west branch of Ngarradj Creek (not routinely sampled), which joins the creek between the two monitoring sites contains lower sulfate than the main branch. This difference is natural and may be related to spatial differences in the previous estuarine character of this region. This consistent reversal of the typical concentration pattern for sulfate (upstream indicator concentrations are usually lower than downstream ones) provides a very sensitive indication of whether mine-related sulfate is entering Ngarradj Creek.
The only other significant divergence between the two sites relates to magnesium. A basin-shaped profile is evident for magnesium measured at both sites, but particularly downstream. Basin-shaped profiles are usually an indication of groundwater intrusion. Although this effect has been observed in previous years (the baseline period), it was more evident for the 2001-02 monitoring season. This may be due to the 2001-02 wet season having below average rainfall, but also a grossly abnormal distribution, where most precipitation fell in January and February. Under these circumstances surface flow will decline much earlier than usual (Ngarradj Creek stopped flowing in early May 2002), but groundwater flows may be much less affected. In this case, magnesium-charged groundwater will make a greater contribution to surface flow, and earlier in the season.
Radium-226 (226Ra) results for the 2008–09 wet season can be compared to previous wet season data from 2001–02 through to 2007–08. The data from sample composites (weekly collected samples were combined in 2006–07 onwards to give monthly averages) show that the levels of 226Ra are very low in Magela Creek, including downstream of the Ranger mine. The anomalous 226Ra concentration of 8.8 mBq/L in a sample collected in 2005 was probably due to a higher contribution of 226Ra-rich soil or finer sediments that are present naturally in Magela creek. This has been explained previously in the Supervising Scientist Annual Report series.
From the 2008-09 wet season onwards, collection of water samples are undertaken from the upstream and downstream sites for continuous physicochemical monitoring and in situ toxicity monitoring in Magela Creek. An explanation of the site changes is given in the commentary on Magela Creek 2008–09 monitoring data.
The limit for total 226Ra activity concentrations has been defined for human radiological protection purposes. The median of all 226Ra data collected over the current wet season is calculated for both the upstream site and for the downstream site. The median of the upstream data is then subtracted from the median of the downstream data. This difference value, called the ‘wet season median difference’, quantifies any increase at the downstream site and should not exceed 10 mBq/L.
All wet season median differences (shown by the green line in the graphs) from 2001 to 2009 are close to zero, indicating that 226Ra levels at both sites in Magela Creek are due to the natural occurrence of radium in the environment. Thus, it is concluded that there is no significant input of 226Ra from the Ranger mine site into Magela Creek.
Radium-226 (226Ra) results for the 2008-2009 wet season at the Ngarradj downstream site (monthly collected samples) can be compared to previous wet season's data. Since previous monitoring (2002-2007) has shown that human health has been protected, from 2007-08 Wet Season onwards, monitoring will occur at the downstream site only. This is only while Jabiluka is in long-term care and maintenance. Visual comparisons of the charted downstream data are made to ensure that the ecosystem and human health downstream of the mine are still protected.
The first season is the only season that the wet season median difference (shown by the solid line in the graphs) - which is the downstream median for the season minus the upstream median for the season - is greater than zero, indicating that this was the only season when 226Ra is higher downstream of Jabiluka compared to upstream. Even in that season the wet season median difference was very low indicating human health was not at risk from the presence of 226Ra in Ngarradj. For the 2009 wet season, the downstream site is comparable with the previous three years data.