Explanatory notes on water chemistry results 2011-12

2011-12 Wet season notes

Commentary on Magela Creek 2011-12 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 23 November 2011. A peak in EC occurred at the downstream monitoring site (MCDW) on 4 December 2011. The source of the contamination was identified as solute-laden groundwater expressing from a creekline within Djalkmara Land Application Area. This was exacerbated by low flow conditions, and hence low dilution capacity, within Magela Creek. EC reduced during periods of increased flow during mid to late December. Low rainfall during early January 2012 resulted in low flow conditions. EC remained less than 20 µS/cm at both the upstream and downstream monitoring sites from 4 January 2012; with the exception of a rainfall event on 12 January 2012 (26.6 mm of rain was recorded at Jabiru Airport). During this event EC at MCDW reached 23.23 µS/cm prior to and 22 µS/cm following the event peak flows. A 38.2 mm rainfall event (recorded at Jabiru Airport) on 18 January 2012 resulted in a peak in EC at MCDW, associated with the rising hydrograph of the water flow, where EC reached 35.8 µS/cm.

Water levels increased and EC levels decreased at MCUGT and fluctuated at MCDW during rainfall events throughout late January, February and early March 2012. An increase in discharge on 15 and 16 March 2012 related to monsoonal activity resulted in a decrease in EC at both the upstream and downstream sites. Recessional flow conditions became established in April with low water levels and rising, converging EC levels at both the upstream and downstream monitoring sites. Rainfall events during late April and early May 2012 resulted in short-term peaks and troughs in EC and turbdity.

Continuous monitoring continued until 07 August 2012 when discontinuity of flow between upstream (MGUCT) and downstream (MCDW) was confirmed.

Commentary on Gulungul Creek 2011-12 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 24 November 2011. There was a peak in EC on 3 December 2011 at the upstream monitoring site (GCUS), which was associated with first flush conditions and was followed by a turbidity event which reached 116.7 NTU. Increased rainfill during mid-late December 2011 resulted in water levels remaining above 0.8m at the downstream monitoring site (GCDS). During late December 2011/early January 2012 there was a steady decline in water level and a corresponding increase in EC. EC remained less than 25 µc/cm at both the upstream and downstream monitoring sites.

On 12 January 2012 26.6 mm of rainfall was recorded at Jabiru Airport. Prior to the rainfall event peak water flows the EC reached 31.3 µS/cm at GCUS and 28.7 µS/cm at GCDS. A 38.2 mm rainfall event (recorded at Jabiru Airport) on 18 January 2012 also resulted in peaks in EC associated with the rising hydrograph of the water level. EC reached 33.35 µS/cm at GCUS and 34.85 µS/cm at GCDS. EC-triggered gamet samples from GCUS and GCDS show conformance between uranium, and to a lesser extent, magnesium concentrations. Upsteam and downstream differences in EC, manganese and sulfate concentrations suggest a localised source of run-off between GCMID monitoring station (data not shown) and GCDS.

Water levels increased and EC levels decreased during subsequent rainfall events throughout late January, February and early March 2012. An increase in discharge on 15 and 16 March 2012 related to monsoonal activity resulted in a decrease in EC at both the upstream and downstream sites. Recessional flow conditions became established in April with low water levels and rising, converging EC levels at both the upstream and downstream monitoring sites. Rainfall events during late April and early May 2012 resulted in short-term peaks and troughs in EC and turbdity.

Continuous monitoring continued until 17 June 2012 when falling water levels resulted in the multi-probes being out of the water and could not be lowered any further.

Commentary on Ngarradj (Swift Creek) 2011-12 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 4 December 2011. EC remained less than 20 µc/cm from the start of monitoring this wet season and decreased to less than 15 µc/cm with increased water levels during mid-late December 2011. The decline in water levels observed during late December 2011/early January 2012 were accompanied by a corresponding increase in EC, with notable decreases in EC associated with the rainfall events throughout late January, February and March 2012. Recessional flow conditions became established in April with low water levels and rising EC. Data was lost between 5 and 12 April 2012 due to a communications malfunction with the local data logger. Rainfall events during late April and early May resulted in short-term peaks and troughs in EC.

Continuous monitoring continued until 26 June 2012 when cease to flow was agreed by stakeholders.