Explanatory notes on water chemistry results 2005-10

Wet season notes 2005-10

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.

2009-10 wet season notes

Commentary on Magela Creek 2009-10 monitoring data

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 and enable closer integration of the grab sampling water quality monitoring program with continuous water quality monitoring and in situ toxicity monitoring programs. Further information on the background to the changes to sampling site locations can be found in the commentary on Magela Creek 2008–09 monitoring data.

The weekly grab 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.

Flow was first recorded at the Magela Creek upstream monitoring station on 24 December 2009. At the downstream monitoring station flow started on 27 December 2009.

The first water chemistry grab samples for the Supervising Scientist's 2009-10 wet season surface water monitoring program were collected from Magela Creek on 30 December 2009. Weekly sampling continued throughout the season until cease to flow was agreed by stakeholders on 27 July 2010. Continuous monitoring of EC and turbidity was maintained at both the downstream and upstream sites for the whole wet season.

The increase in rainfall in the Magela Creek catchment in late December 2009 resulted in increased flow, with consequent decreased manganese concentration, electrical conductivity and pH, and increased turbidity at both the upstream and downstream sites. This behaviour is typical of first flush conditions.

During late January the continuous monitoring data showed there were a series of minor electrical conductivity events. There are likely to be associated with the release of mine-derived solutes from Retention Pond 1 (RP1) to Coonjimba Billabong. These EC events lasted between 9 and 13 hours. During two of these events the EC remained above the EC guideline value of 43 µS/cm for periods of 2.25 and 0.83 hours.
On 3 February, uranium concentration peaked at approximately 3% of the limit and measured 0.175 µg/L at the SSD downstream site compared with 0.024 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.
Water levels within Magela Creek remained low during mid-February. High rainfall in late-February resulted in high creek levels from 26 February – 3 March 2010. Below average rainfall during March resulted in very low creek levels and increased values for electrical conductivityand pH and higher magnesium and sulfate concentrations. Heavy rainfall during mid-April resulted in seasonally low solute concentrations and increased turbidity due to high water flows. Continuous monitoring data show several EC events during this period of high creek levels. These events coincided with increased discharge of water from Retention Pond 1 (RP1), with values of EC exceeding the EC guideline of 43 µS/cm for between 2.75 and 8.5 hours, with maximum conductivities from 48 to 90 µS/cm.

SSD considers these pulses of high conductivity water likely originated from RP1 (via Coonjimba Billabong). It is probable that an increase in flow (and water level) in Magela Creek had initially restricted flow from Coonjimba Billabong. As the Magela Creek water level dropped, water held back in Coonjimba Billabong drained out causing the increase in EC at the downstream site as a consequence of the reduced dilution. Ecotoxicological research conducted by SSD suggests that no detrimental environmental impacts would have resulted from these short-lived EC events.

From late-April, typical end of wet-season trends were apparent as the water level decreased. Manganese concentrations at the downstream site increased as groundwater influences started to dominate, and electrical conductivity between the upstream and downstream sites became similar as minesite influences decreased. Cease to flow was called by stakeholders on 27 July 2010.

Overall, the data from the continuous monitoring and grab sample monitoring programs indicate that water quality in Magela Creek was comparable with previous seasons for the west channel. Uranium concentrations measured during the 2009-2010 wet season are comparable with previous seasons for the downstream west channel of Magela Creek.

Commentary on Gulungul Creek 2009-10 monitoring data

Weekly grab sampling at the upstream site for routine analysis of water chemistry variables was discontinued from 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.

The first water chemistry samples for the SSD 2009-10 wet season surface water monitoring program were collected from Gulungul Creek on 30 December 2009. Weekly sampling from the downstream site continued throughout the season while the creek was flowing. On 24 June 2010 MTC stakeholders agreed that surface flow had ceased in Gulungul Creek and monitoring was terminated.

All weekly grab sample data show electrical conductivity measurements (EC) below the Magela Creek guideline value of 43 µS/cm. However, continuous monitoring data shows two exceedances of this guideline during the peak of EC events on 26 January and 24 March 2010. These events lasted 14 and 21.5 hours respectively, during which time the EC remained above the guideline value for 3 hours during the January EC event and 1.25 hours during the March event.

Uranium concentrations measured by SSD at the downstream Gulungul Creek monitoring site for the 2009-10 wet season show a peak in concentrations on 6 January 2010, when uranium was 0.32 µg/L at the downstream site (

Overall, the water quality measured in Gulungul Creek for the 2009-10 wet season indicates that the aquatic environment in the creek has remained protected from mining activities.

Commentary on Ngarradj (Swift Creek) 2009-10 monitoring data

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 seven years indicating the environment has been protected, the monitoring program has been systematically scaled down (see Commentary on Ngarradj (Swift Creek) 2008-09 monitoring data, 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 2009-10, the Supervising Scientist Division has collected continuous monitoring data (electrical conductivity, pH and turbidity) from the downstream statutory compliance site only. Energy Resources of Australia (ERA) collect monthly grab samples from both the upstream and downstream site. Previous grab sample monitoring data can be found at Ngarradj (Swift Creek) grab sample monitoring data 2001-2009.

2008–09 wet season notes

Commentary on Magela Creek 2008–09 monitoring data

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.

Commentary on Gulungul Creek 2008–09 monitoring data

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 (

Since mid March 2009, uranium levels decreased to concentrations less than 0.2 µg/L (

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.

Commentary on Ngarradj (Swift Creek) 2008–09 monitoring data

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.

2007-08 wet season notes

Commentary on Magela Creek 2007-08 monitoring data

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.

Commentary on Gulungul Creek 2007-08 monitoring data

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.

Commentary on Ngarradj (Swift Creek) 2007-08 monitoring data

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.

2006-07 wet season notes

Commentary on Magela Creek 2006-07 monitoring data

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.

Commentary on Gulungul Creek 2006-07 monitoring data

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.

Commentary on Ngarradj (Swift Creek) 2006-07 monitoring data

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.

2005-06 wet season notes

Commentary on Magela Creek 2005-06 monitoring data

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 (

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.

Commentary on Gulungul Creek 2005-06 monitoring data

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.

Commentary on Ngarradj (Swift Creek) 2005-06 monitoring data

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).