Supervising Scientist Division

Appendix 2 - Ranger Environmental Requirements explanatory material relating to Section 3.3 background values for key variables in water quality (amended November 2004)

Supervising Scientist Annual Report 2004–2005

Supervising Scientist, Darwin, 2005
ISBN 0 642 24395 6
ISSN 0 158-4030

Foreword

Section 19.2 of the Environmental Requirements of the Commonwealth of Australia for the Operation of the Ranger Uranium Mine (the Ranger ERs) provides for the publication of explanatory material agreed to by the major stakeholders to assist in the interpretation of provisions of the Ranger ERs.

This document has been published by the Supervising Scientist under section 19.2 to assist in the interpretation of the Ranger ERs (ER 3.3) which relates to water management and should be read in conjunction with ER 3.3. This replaces the Explanatory Material relating to section 3.3 previously published in Klessa (2001) and Supervising Scientist (2002).

1 Key variables (ie water quality parameters) for monitoring, interpretation and reporting at GS 009

In this paper, key variables are those identified as

Table 1 Key variables for monitoring interpretation
and reporting at GS009
Key variable Relevance
pH Stipulated under ER 3.3; master variable influencing speciation and toxicity of potential contaminants; and ecosystem character (ie structure and function)
EC As given above for pH
U† Stipulated under ER 3.3; principal contaminant of public concern; potential ecological impact
Turbidity No evidence of mine effect but becomes increasingly important as physico-chemical indicator of potential ecological impact from surface disturbance during rehabilitation
Mg† Evidence of mine effect; potential water potability impacts; potential ecological impact unclear
SO4 As given above for Mg
Mn† Evidence of mine effect; contaminant arising primarily from use of pyrolusite in U3O8 production; potential ecological impact
226Ra No evidence of mine effect; potential human health impact
Ca† No direct effect envisaged but required for the interpretation of potential ecological impact from Mg imbalance (ie Ca:Mg ratio)

† refers to the soluble (<0.45 �m) fraction; 226Ra is measured as a total fraction

2 Water quality objectives for Magela Creek (assessed at GS 009)

Coupled narrative and numeric water quality objectives have been derived for Magela Creek (tables 2 & 3). The numeric values support the primary management aim of aquatic ecosystem protection and allow scientific interpretation of the data. The narrative statements support the secondary management aim of minimising water quality changes downstream of the mine, in line with the wishes of the Traditional Owners. The methodology used in the setting the water quality objectives is contained in Iles (2004).

Numeric water quality objectives form a hierarchy of values that trigger increasingly stringent management responses. The responses are detailed in section 3 below. Apart from the key variables discussed in the dot points below the trigger values have been based on local biological effects data (toxicity of uranium to local species) or on the natural distribution of reference site data. Focus, action and guideline trigger values determined by the latter method are set at the 80th, 95th and 99.7th percentiles (and the 0.3rd, 5th and 20th percentiles for lower pH triggers) respectively.

The water quality objectives will be reviewed and updated regularly by the Supervising Scientist in consultation with major stakeholders.

Table 2 The Water Quality Objectives for Magela Creek
Parameter Objective Trigger values
Focus Action Guideline Limit
pH To retain the natural distribution of pH in
Magela Creek and report and act on any
trigger value exceedances at MG009.
5.9 – 6.5 5.6 – 6.7 5.0 – 6.9 N/A
Turbidity To retain the natural distribution of
turbidity in Magela Creek and report and
act on any trigger value exceedances at
MG009.
5 NTU 10 NTU 26 NTU N/A
Electrical Conductivity   To (i) report and act on any exceedances
of the focus, action and guideline trigger
values, and (ii) to sustain the improved
water quality seen in the last two wet
seasons when practical.
  21 �S/cm 30 �S/cm   43 �S/cm N/A
Magnesium To minimise the magnesium mine signal
at the downstream site and sustain the
improved water quality seen in the last
two wet seasons when practicable.
Use EC as
proxy
Use EC as
proxy
Use EC as
proxy
N/A
Sulfate To minimise the mine related sulfate
signal at the downstream site and sustain
the improved water quality seen in the last
two wet seasons when practicable.
Use EC as
proxy
Use EC as
proxy
Use EC as
proxy
N/A
Manganese When flow is dominated by surface flow
(> 5 cumecs) the reference site distribution is
achieved and any trigger value
exceedances at MG009 are reported
and acted on.
7 �g/L 11 �g/L 26 �g/L N/A
Uranium To (i) report and act on any trigger value
exceedances at MG009, and (ii) to sustain
the lower uranium concentrations
measured in the last two wet seasons
when practicable.
0.3 �g/L 0.9�g/L N/A 6�g/L
Radium-226 The median total 226Ra activity
concentration for the wet season at the
downstream site will not be more than
10 mBq/L greater than that at the
upstream site.
N/A N/A N/A 10 mBq/L
wet season
median
difference
Table 3 The measures of success of meeting the Water
Quality Objectives
Parameter Measure of success
pH The focus, action and guideline trigger values are not exceeded at the downstream
site alone (ie exceedance not reflected at the upstream site) more often than
statistically expected. And, all exceedances are reported and investigated as
outlined in Appendix 1, Actions Invoked by Exceedance of a Trigger Value.*
Turbidity The focus, action and guideline trigger values are not exceeded at the downstream
site alone (ie exceedance not reflected to the upstream site) more often than
statistically expected. And, all exceedances are reported and investigated as
outlined in Appendix 1, Actions Invoked by Exceedance of a Trigger Value.
Electrical Conductivity

(i) All exceedances are reported and investigated as outlined in Appendix 1,
Actions Invoked by Exceedance of a Trigger Value
.

(ii) The existing trigger values are not exceeded more often than in the last two
wet seasons without reasonable cause

Magnesium The magnesium concentrations this wet season will not significantly differ to those
of the last two wet seasons without reasonable cause.
Sulfate The sulfate concentrations this wet season will not significantly differ to those
of the last two wet seasons without reasonable cause.
Manganese The focus, action and upper guideline trigger values are not exceeded at
the downstream site alone (ie exceedance not reflected to the upstream site)
more often than statistically expected during periods where flow exceeds
5 cumecs. And, all exceedances are reported and investigated as outlined in
Appendix 1, Actions Invoked by Exceedance of a Trigger Value.
Uranium

(i) 100% of downstream uranium concentrations are below the limit and there
are no sustained increases above the focus and action triggers. And all
exceedances are reported and investigated as outlined in Appendix 1,
Actions Invoked by Exceedance of a Trigger Value
.

(ii) The uranium concentrations this wet season will not significantly differ
to those of the last two wet seasons without reasonable cause.

Radium-226 The downstream median total 226Ra activity concentration for the wet season minus
the upstream median total 226Ra activity concentration for the wet season is not
greater than 10 mBq/L.

* Appendix 1, Iles 2004

3 Actions invoked by exceedance of a trigger value

Exceedances of triggers based on natural variations are expected occasionally and the responses triggered have been slightly modified to take account of this. The main change is that where trigger values are based on natural variations in water quality the upper triggers (and lower for pH) are now ‘guidelines’. Where the value is based on local biological effects data or dietary modelling (as for uranium and radium respectively) the upper trigger remains a ‘limit’.

The responses invoked by an exceedance of a trigger value are described below. The following general rules apply.

Exceedance of a focus trigger

Statistically expected ~20% of the time when triggers are based on the natural range of values measured at a reference site.

Values that are higher than the focus level but lower than the action level will result in a watching brief. A watching brief involves keeping an eye on the data in the coming weeks, or further sampling, to verify whether an upward trend is occurring.

An exceedance of a focus trigger does not have to be reported immediately but shall be reported in the Weekly Water Quality Report provided by the company to the Supervising Authorities and the Northern Land Council.

Exceedance of an action trigger

Statistically expected ~5% of the time when triggers are based on the natural range of values.

Values that are higher than the action level but lower than the guideline/limit must be reported13 to the Supervising Authorities and the Northern Land Council immediately.

Confirmation of such a value by virtue of

will result in an investigation of the cause and correction of the cause if mining related.

An explanation of the cause (and any corrective action taken) shall be reported in the Weekly Water Quality Report provided by the company to the Supervising Authorities and the Northern Land Council.

Exceedance of a guideline

Statistically expected ~0.3% of the time when triggers are based on the natural range of values.

The company shall treat values in excess of the guideline the same as a limit exceedance except when there is a corresponding increase at the upstream site, and for manganese, when the flow is less than five cumecs. Under these circumstances a guideline exceedance will be treated as for an action exceedance.

Exceedance of a limit

Company action

Values in excess of the limit must be reported both verbally and in writing to the Supervising Authorities and the Northern Land Council immediately. The company will also provide a detailed written report as soon as practical to the Supervising Authorities and the Northern Land Council detailing:

Supervising Scientist action

If in the opinion of the Supervising Scientist the exceedance of a limit is due to operations at Ranger the Supervising Scientist will advise the Minister with regard to

In drawing a conclusion that the exceedance of the limit for 226Ra constitutes a breach of the ERs, the Supervising Scientist must be convinced that the anthropogenic dose to the critical group has exceeded 1mSv in one year.

4 Reporting of results

The presence or absence of short- and long-term trends in chemistry at 009 should be reported by the company and incorporated as appropriate into weekly water quality and annual wet season reports.

5 Glossary of terms and abbreviations

abrupt change an abrupt change is one where values exceed trigger values and are maintained over at least two consecutive samples.
cumec measure of flow velocity, cubic meters per second.
EC electrical conductivity.
eriss Environmental Research Institute of the Supervising Scientist.
ERs Environmental Requirements
Minister Minister means the Minister for the time being administering section
41 of theAtomic Energy Act 1953.
trend an upward trend is established when three consecutive values x1, x2 and x3, show x1<x2<x3 .

6 References

ANZECC & ARMCANZ 2000. Australian and New Zealand guidelines for fresh and marine water quality. National Water Quality Management Strategy Paper No 4, Australian and New Zealand Environment and Conservation Council & Agriculture and Resource Management Council of Australia and New Zealand, Canberra.

Hogan AC, van Dam RA, Markich SJ & Camilleri C 2003. Chronic toxicity of uranium to the tropical green alga Chlorella sp. for the derivation of a site specific Trigger Value for Magela Creek. Internal Report 412, December, Supervising Scientist, Darwin. Unpublished paper.

Iles M 2004. Water quality objectives for Magela Creek – revised November 2004. Internal Report 489, December, Supervising Scientist, Darwin. Unpublished paper.

Klessa D 2001. Water quality in Magela Creek upstream and downstream of Ranger: A summary of performance for 2000–2001 and derived triggers and limits for 2001–2002. Internal Report 380, Supervising Scientist, Darwin. Unpublished paper.

Supervising Scientist 2002. Annual Report 2001–2001. Supervising Scientist Darwin.

Footnotes

13 Reporting by way of verbal communication is acceptable (Ranger Minesite Technical Committee 17/10/2003).