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Supervising Scientist Division
| Composite sample | Weekly grab samples are collected at Magela creek, with every second sample analysed individually for 226Radium. The alternate week samples not analysed individually are pooled at the end of the season and are referred to as the composite sample. This composite sample is analysed for 226Radium. |
| First flush | 'First flush effects' refers to rapid changes in water quality that occur after early season rains or to the quality of the first flows in a stream. Soil and vegetation particles wash into the streams, sediments on the bed of the creek are stirred up and dissolved substances from soil and shallow groundwater can be flushed into the streams. During this time the electrical conductivity, turbidity and concentration of metals and dissolved ions are higher than usual, pH is often lower. The same type of effects can also follow intense storm events throughout the season. |
| Guideline | 'Guidelines' are set to assist in the interpretation and management of water quality. Guidelines are based on the range of values that occur naturally at the upstream reference site and so are expected to be exceeded occasionally at the downstream site. Guidelines are updated occasionally by the Supervising Scientist to reflect changes in the range of values measured at the upstream reference site. |
| Limit - general | A 'limit' is the value that an indicator must not exceed as a result of mining operations. Limits apply to uranium and radium. Exceedence of a limit, due to mining related activities, would normally be regarded as a breach of statutory regulations. The limit for uranium is based on toxicity to local species in accordance with the ANZECC/ARMCANZ Water Quality Guidelines to protect 99% of the species present. The uranium limit was updated in 2004 in light of additional toxicity data. For 226Ra, the limit is set in accordance with International Commission on Radiological Protection recommendations. |
| Limit for total 226Ra activity concentration | Definition of the limit of 10 mBq.L-1 for an increase above natural background in total 226Ra concentration in surface waters downstream of the mine was established following recommendations of the International Commission on Radiological Protection. Additional safety factors are incorporated. The limit is based on a dose constraint of 0.3 mSv per year above natural background from the ingestion of 226Ra in freshwater mussels ( Velesunio angasi ), a 10 year old child consuming 2 kg of mussels annually and a concentration factor of 19 m3.kg-1 for 226Ra from the water column. |
| Wet season median difference | The median of all data collected over the whole of the 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 is called the 'wet season median difference'. |