Explanatory notes on water chemistry results 2012-13

2012-13 Wet season notes

Commentary on Magela Creek 2012-13 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.

Water 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 water sample monitoring data can be found at Magela Creek grab sample monitoring data 2002 - 2010 and the previous year's continuous monitoring data at Magela Creek monitoring data 2010-12.

Flow was first recorded at the Magela Creek upstream and downstream monitoring stations on 7 January 2013.  Flow has remained very low due to below average rainfall so far this wet season.

On 17 January 2013 Jabiru airport recorded a rainfall event of 81.8 mm. This appears to have been a localised rainfall event resulting in decreased EC and increased turbidity observed only at the downstream monitoring site. Water quality parameters returned to previous levels within a few hours. The effects of this rainfall event were also observed at both the upstream and downstream monitoring sites in Gulungul Creek (see below) and impacts on water quality are therefore due to rainfall run-off and not mine-derived water releases.

Continued low rainfall conditions have seen flow in the creek gradually reduce through most of February. March has seen an increase in the frequency of rainfall events which has increased the flow levels in Magela Creek.

On 30 and 31 March 2013 a low pressure system resulted in a lot of rainfall over Arnhemland. Jabiru Airport recorded total rainfall of 240 mm over the two days. Flow rates within Magela Creek quickly rose and peaked at 800 cumecs. During this period managed release water from RP1 was released into the Coonjimba Billabong catchment. This discharge of more saline water resulted in slightly increased EC levels at MCDW. However due to the vast dilution rates during this rainfall event the EC did not exceed the focus trigger level of 21 µS/cm. During falling water levels after this rainfall event the EC levels increased at both monitoring sites, however, levels have generally remained less than 20 µS/cm.

In April recessional flow conditions became established within Magela creek with sustained flow at

During early May the mine site released pond water treatment plant permeate (good quality water) into the Corridor Creek system. This relatively small input resulted in increased water levels and outflow from Georgetown Billabong into Magela Creek. As the billabong waters typically have a higher EC than the creek waters, which is increased during the dry season due to evapoconcentration, the outflow from Georgetown Billabong was detected at MCDW via an increase in EC to 25 µS/cm on 5 May 2013. This EC is just above the Focus trigger value of 21 µS/cm. The mine site stopped the discharge of permeate into Corridor Creek and in turn Georgetown Billabong ceased flowing into Magela Creek so the EC decreased.

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. During recessional flow conditions data will be updated on a monthly basis unless there are water quality incidents to report.

Commentary on Gulungul Creek 2012-13 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.

Water samples are taken every four weeks and measured for key mine site analytes, including physicochemical parameters, for quality assurance purposes. Previous weekly grab sample monitoring data can be found at Gulungul Creek grab sample monitoring data 2002 – 2010 and the previous year's continuous monitoring at Gulungul Creek monitoring data 2010-2012.

Flow was first recorded at the Gulungul Creek upstream and downstream monitoring stations on 23 December 2012.  Flow has remained very low due to below average rainfall so far this wet season.

On 17 January 2013 Jabiru airport recorded a rainfall event of 81.8 mm. This appears to have been a localised rainfall event resulting in increased EC and increased turbidity observed at both the upstream and downstream monitoring sites. Water quality parameters returned to previous levels within a few hours.

Continued low rainfall conditions have seen flow in the creek remain low through most of February. March has seen an increase in the frequency of rainfall events which has increased the flow levels in Gulungul Creek.

On 30 and 31 March 2013 a low pressure system resulted in a lot of rainfall over Arnhemland. Jabiru Airport recorded total rainfall of 240 mm over the two days. Flow within Gulungul Creek quickly rose and with a corresponding decline in EC due to dilution with low salinity rainfall. EC increased in early April as flow levels decreased.

On 9 April 2013 an increase in EC coincided with a localised rainfall event. The EC at the downstream monitoring site peaked at 45 µS/cm and remained above 42 µS/cm for a period of 5 hours. Under the Ecotoxicology Electrical Conductivity-Magnesium Pulse Framework a 5 hour pulse duration would have an EC trigger value of 581 µS/cm, thus with a peak of 45 µS/cm the downstream aquatic ecosystem is very unlikely to have been impacted by this event.

From mid-April recessional flow conditions became established within Gulungul creek with sustained low flows and slowly rising and converging EC at upstream and downstream monitoring sites. During early to mid May the monitoring multi-probe sensor at GCDS was out of the water due to very low flow levels.

A localised rainfall event in the upper Gulungul Creek catchment on 22 May 2013 flushed solutes into the creek resulting in an EC peak of 113 µS/cm at the upstream monitoring site, GCUS, and is thus not mine derived. These solutes were washed down the creek and progressively diluted, producing EC peaks of 76 and 46 µS/cm at GCMID and GCDS monitoring sites. The EC at the downstream monitoring site remained above 42 µS/cm for a period of 3.3 hours. Under the Ecotoxicology Electrical Conductivity-Magnesium Pulse Framework a 3.3 hour pulse duration would have an EC trigger value of 1140 µS/cm, thus with a peak of 46 µS/cm the downstream aquatic ecosystem is very unlikely to have been impacted by this natural event.

Flow levels have since decreased and the EC of the upstream and downstream monitoring sites have converged.

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.  During recessional flow conditions data will be updated on a monthly basis unless there are water quality incidents to report.

Commentary on Ngarradj (Swift Creek) 2012-13 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 and water level) from the downstream statutory compliance site only. Energy Resources of Australia (ERA) collect monthly grab samples from both the upstream and downstream site.

Multisonde performance checks are made every two weeks for quality assurance purposes. Previous grab sample monitoring data can be found at Ngarradj (Swift Creek) grab sample monitoring data 2001-2009 and and the previous year's continuous monitoring at Ngarradj (Swift Creek) monitoring data 2010-2012.

Flow was first recorded at the Ngarradj (Swift Creek) monitoring station on 17 January 2013.  Continued low rainfall conditions have seen flow in the creek remain low through most of February. March has seen an increase in the frequency of rainfall events, which has increased the flow levels in Ngarradj with a corresponding decrease in EC.

On 30 and 31 March 2013 a low pressure system resulted in a lot of rainfall over Arnhemland. Jabiru Airport recorded total rainfall of 240 mm over the two days. Flow within Ngarradj quickly rose and with a corresponding decline in EC due to dilution with low salinity rainfall. EC increased in April and May as flow levels decreased; typical of recessional flow conditions.

There are intermittent communications issues between the monitoring stations and the server. Data will be manually downloaded and updated when available.

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. During recessional flow conditions data will be updated on a monthly basis unless there are water quality incidents to report.