Explanatory notes on water chemistry results 2010-11

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.

2010-11 wet season notes

Commentary on Magela Creek 2010-11 monitoring data

The Supervising Scientist Division (SSD) modified its wet season monitoring program from 2010-11 to enhance the ability of SSD to independently detect changes in water quality during EC- and turbidity- triggered events with automatic sampling during events; continuous water quality monitoring of pH, EC, turbidity and water temperature; and in situ toxicity monitoring programs. Further details of the changes can be found at SSD wet season monitoring program 2010-11.

In addition to continuous monitoring, manual grab samples are taken every two weeks from Magela Creek for radium analysis and every four weeks water samples are taken and measured for key mine site analytes, including physicochemical parameters, for quality assurance purposes. The sampling point maps show the location of the upstream and downstream sites and key Ranger Mine features. Previous weekly grab sample monitoring data can be found at Magela Creek grab sample monitoring data 2002 - 2010.

The electrical conductivity (EC) and turbidity data from early in November 2010 recorded the water quality of the standing water around the monitoring station before flows commenced. Flow was first recorded at the Magela Creek downstream monitoring station (MCDW) on 13 November 2010 and is noted in the change in EC and peak in turbidity, associated with a rainfall event on 11-12 November 2010. Water levels at the Magela Creek upstream monitoring station had decreased to such a level that between 11-24 November the multi-probe was out of the water therefore no data for EC or turbidity was recorded. EC levels at both sites decreased following a peak in the creek flow rates of 3.4 cumecs on 29 November 2010, which also resulted in peaks in turbidity at both monitoring stations. A short duration peak in turbidity at the downstream site (MCDW) on 10 December 2010 is likely to be caused by turbid surface run-off from a localised rainfall event as there was a small increase in water level but no effect on discharge.

Flow remained very low until mid-December 2010 when flows increased due to rainfall events, which resulted in several large peaks in turbidity at both the upstream and downstream monitoring stations. During December 2010 EC remained

On 15-16 January EC peaked at 50 μS/cm during a 12 hour period with EC remaining above the guideline of 43 μS/cm for 2.5 hours during this time. Uranium data for this EC event remains below 0.3 μg/L (less than 5 % of the 6.0 μg/L uranium limit). Manganese concentration peaked at 19.3 μg/L during the beginning of the EC event, which lies within the historic grab sample range for this site (2.08-48.1 μg/L) and is below the guideline of 26 μg/L. Magnesium and sulfate concentrations closely follow the EC continuous monitoring peak with concentrations peaking at 3.4 mg/L and 12.6 mg/L, respectively. These concentrations are less than 0.5 mg/L greater than the historic grab sample ranges for these analytes at this monitoring site.

In late January and early February EC levels were stable at the upstream monitoring site and showed some minor fluctuations at the downstream site (MCDW) with a maximum EC of around 30 μS/cm.

On 13-14 February EC peaked at 46 μS/cm during a 14 hour period with EC remaining above the guideline of 43 μS/cm for 1.7 hours during this time. Two autosamples were triggered, which contained maximum uranium and manganese concentrations of 0.498 ug/L and 26.3 ug/L respectively. The analysed concentrations of magnesium (3.4 mg/L) and sulfate (11.8 mg/L) are typical of those seen during EC peaks. As the EC peak decreased on 14 February there was a turbidity peak of 42 NTU at MCDW in advance of a peak in Magela Creek discharge of 709 cumecs.

On 22 February the MCDW EC peaked at 57 μS/cm during a 4 hour period with EC remaining above the guideline of 43 μS/cm for 1.75 hours during this time. Two autosamples were triggered, which contained maximum uranium and manganese concentrations of 1.01 ug/L and 16.5 ug/L respectively. This would equate to a filtered uranium value of between 0.6-0.8 ug/L, as compared to the limit of 6 ug/L.  Concentrations of the major ions magnesium and sulfate were 4.2 mg/L and 15.8 mg/L respectively.

As this EC peak decreased due to rising water levels there was a peak in turbidity. Just prior to this event at 2pm on 21 February the primary turbidity sensor at the downstream site malfunctioned. The secondary sensor then developed a fault during the event and produced a magnified turbidity trace. The data shown was validated by comparison with laboratory turbidity readings from autosamples taken during this event and the continuous turbidity trace adjusted accordingly. Accuracy of this data is approximately ± 20 NTU. The turbidity peak occurred following a 190mm rainfall event and is likely to be due to surface runoff from areas both on and off the mine site.

Water levels decreased during March with EC and turbidity being relatively stable. This has continued through April with EC remaining below 30 μS/cm. A brief increase in flow was noted on 6 April in response to a 22 mm rainfall event (BOM data). A local rainfall event on 23 April caused minor peaks in EC and turbidity at both monitoring sites. Flow levels steadily decreased in late April and May.

SSD has now completed an investigation into a low magnitude EC spike noted at the SSD upstream site in the early hours of 22 February 2011, as shown in the figure below, which was not detected at the ERA site further upstream.

Graph showing Magela Creek continuous monitoring data for the period 21-23 February 2011

Magela Creek continuous monitoring data for the period 21-23 February 2011

A field inspection showed that flow from Georgetown Billabong had over-topped the channel divide in Magela Creek and reached the upstream monitoring station. This was caused by an unusual, localised high intensity rainfall event which delivered approximately 170 mm in just over 2 hours. This caused a rapid increase in discharge from the Georgetown catchment prior to flows having risen in Magela Creek. Without the hydraulic dam effect of high flow in Magela Creek, flows from Georgetown Billabong were able to push into the Magela central channel over the top of the channel divide. As flow in Magela Creek increased the effect quickly diminished. Given that such incidents are rare, and their impacts easily identified, SSD does not consider the relocation of the monitoring station warranted at this time.

Recessional flow conditions became established in Magela Creek in late April . These conditions are typified by a falling hydrograph with EC stabilising and rising slowly as groundwater input becomes the dominant contributor to flow.

Continuous monitoring will continue throughout the season until cease to flow is agreed by stakeholders or until the multi-probes are out of water and cannot be lowered any further regardless of flow between upstream and downstream.

Commentary on Gulungul Creek 2010-11 monitoring data

The Supervising Scientist Division (SSD) modified its wet season monitoring program from 2010-11 to enhance the ability of SSD to independently detect changes in water quality during EC- and turbidity- triggered events with automatic sampling during events; continuous water quality monitoring of pH, EC, turbidity and water temperature; and in situ toxicity monitoring programs. Further details of the changes can be found at SSD wet season monitoring program 2010-11.

Grab samples are taken every four weeks for quality assurance purposes. Previous weekly grab sample monitoring data can be found at Gulungul Creek grab sample monitoring data 2002 – 2010.

Flow was observed at the Gulungul Creek downstream monitoring station (GCDS) on 14 December 2010. Continuous monitoring commenced on 15 December 2010 when flow was established and water depths in the creek were sufficient for deployment of the monitoring multi-probes. Water levels have gradually increased due to recent rainfall events, which have resulted in peaks in turbidity at both monitoring stations. Peaks in turbidity recorded during late December 2010 and early January 2011 are primarily associated with increasing water levels within the creek and localised rainfall events.

EC has increased since the end of December and peaked at the upstream and downstream monitoring stations at an EC level of 27.7 μS/cm on 4 and 5 January 2011, respectively. EC peaks were recorded at both the upstream and downstream monitoring sites during 7-11 January 2011 however, the magnitude of the EC increase is much greater at the downstream site (GCDS). Continuous monitoring data from SSD’s Gulungul Creek Mid (GCMid) monitoring station (not shown) suggests the source of the increased EC lies between GCMid and GCDS. Uranium data for these EC events remains below 0.6 μg/L (less than 10% of the 6.0 μg/L uranium limit for Magela Creek). Manganese concentration peaked at 17.8 μg/L, which lies within the historic grab sample range for this site (0.68-18.1 μg/L). Magnesium and sulfate concentrations closely followed the EC continuous monitoring peak and are the dominant major ions contributing to electrical conductivity of surface waters in the Alligator Rivers Region. ERA are currently investigating the source of the increased EC.

Late January and early February has seen a rise in EC levels at both monitoring sites as water levels have decreased. Turbidity peaks which occurred at the upstream site on 15 and 24 January 2011 were also observed at the downstream site at a much lower magnitude. On 14 February there was a turbidity peak of 84 NTU at GCUS in advance of a peak in Gulungul Creek water level due to heavy rainfall. At GCDS the turbidity remained relatively low peaking at 15 NTU. During the high water levels EC decreased at both monitoring to

During early April EC at GCDS remained comparable with the upstream site and below 20 μS/cm. Turbidity likewise remained relatively low and stable. A local rainfall event on 23 April caused peaks in minor peaks in EC and turbidity at both monitoring sites.

Recessional flow conditions became established in Gulungul Creek in late April. These conditions are typified by a falling hydrograph with EC stabilising and rising slowly as groundwater input becomes the dominant contributor to flow.

Monitoring ceased for the season in Gulungul Creek in the week of 22 June as water levels dropped below the sensors requiring their removal.

Commentary on Ngarradj (Swift Creek) 2010-11 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. Since 2009-10, the Supervising Scientist Division has collected continuous monitoring data (EC, 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.

The electrical conductivity (EC) and water level data from early in November 2010 recorded the water quality of the standing water around the monitoring station before flows commenced. Flow was first recorded at the Ngarradj monitoring station on 13 November 2010 and is noted in the change in EC, associated with a rainfall event on 11-12 November 2010. Water levels within Ngarradj had decreased to such a level that between 7-11 November, 24-27 November and 6-12 December 2010 the EC sensor was out of the water therefore no data was recorded. Water levels increased considerably in late December 2010 and mid-January 2011 with reduced EC levels. Water levels were relatively low in late January with EC stable at around 10 μS/cm. Periods of high water levels from February to early April have resulted in low, stable EC levels of 4-8 μS/cm.

Rainfall has largely ceased since mid-April and consequently EC levels are slowly rising, typical of low flow conditions at the beginning of the dry season.

Rainfall largely ceased since in mid-April and consequently EC levels slowly rose, typical of low flow conditions at the beginning of the dry season. On 20 May 2011 continuous monitoring of Ngarradj ceased as the multi-probes were out of water and could not be lowered any further.

Radium-226 in Magela Creek and Ngarradj (Swift Creek)

Radium-226 in Magela Creek 2001-2011

Radium-226 (226Ra) results for the 2010-11 wet season can be compared to previous wet season data from 2001-02 through to 2009-10. 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. From 2010-11 wet season onwards samples for routine radium analysis will also be collected from the Magela Creek stations during these regular QA/QC site visits. Two fortnightly radium samples will be combined to make a four week composite sample from each site. This monthly routine monitoring program is complemented by radium analysis on composite event-based samples from the autosampler, which will provide a more comprehensive assessment of the variation in radium concentrations over the wet season. Typically only one site’s autosampler is triggered during EC events (MCDW) as EC remains low at the upstream site. During these occurrences where only one site is sampled the other site’s radium activity is estimated using the median of the previous data set from 2001. This will allow a whole of wet season median difference to be calculated.

Radium-226 results received to date for the 2010-11 wet season include monthly composite samples collected from MCUGT and MCDW from 8 and 22 December 2010. Composite samples from MCDW were collected during an EC events on 15-16 January 2011, 14 and 22 February 2011. As there was no upstream samples collected to enable an activity difference to be calculated the median of all previous upstream routine radium-226 results (2001 – 2010) was used.

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.

Wet season median differences (shown by the grey horizontal lines in the chart) from 2001 to 2011 are close to zero, indicating that the majority of 226Ra levels at both sites in Magela Creek are due to the natural occurrence of radium in the environment.

Radium-226 in Ngarradj (Swift Creek) 2001-2009

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 water quality 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 radium-226 samples. Previous 226Ra monitoring data can be found at Ngarradj (Swift Creek) radium monitoring data.