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Wind, dust dispersal and risk of contamination at Alice Springs

Authors


Correspondence to: Mr Peter Tait, Public Health Association of Australia, Northern Territory Branch, Alice Springs, Northern Territory 0871; e-mail: aspetert@bigpond.com

One concern regarding a potential uranium mine south of Alice Springs is that, in the event of a failure of dust suppression and tailings management, wind will bring dust from operations and tailings into the towns of Alice Springs and Amoonguna. Residents are concerned that this dust would carry radioactive and heavy metal particles into these towns resulting in serious threats to their health from inhaled or ingested radioactive elements causing neoplasia in the long term or heavy metal effects in the shorter term. Recruitment and retention of professional staff may be adversely affected.1 Two further public health factors arise: the issue of the public perception of risk and the actual probabilities of a threat occurring. No published analysis of dust distribution in the vicinity of Alice Springs was found. In order to contribute to an understanding of the probability of a threat, an analysis of the frequencies of wind direction and wind speeds from the Angela Pamela ore deposit site was undertaken.

Records on annual 9.00 am and 3.00 pm wind direction and speed at the Alice Springs Airport were accessed from the Bureau of Meteorology.2 Records cover the period 1941 to 2010. The airport is 9 km from the ore deposit, without intervening topographical features, so close enough to accurately reflect wind behaviour over the ore deposit at synoptic scales.

Both wind speed (force) and direction influence dust pickup and the direction and distance of dust dispersal. Actual analysis of distance and the distribution of particles and of radioactive gases, such as radon, incorporating topographical features (MacDonnell Ranges) and the size and nature of the particles require a high-resolution atmospheric modelling program such as The Air Pollution Model.3 This was outside the resource constraints of this scoping study.

The wind speed at which particles can be picked up and blown a significant distance is about 28 km/h.4 Wind speed data relating to 30 km/h is available from the Bureau of Meteorology so this speed is used for this analysis. Winds gusting greater than 30 km/h during lesser mean wind speed periods cannot be assessed.

Relative to the Angela Pamela uranium deposit, the town of Alice Springs is to the north. Amoonguna is north-north-east of the deposit, as is the Alice Springs airport. North-west of the deposit are the Brewer Industrial Estate, Alice Springs Correctional Facility, the Joint Defence Facility Pine Gap and the rural Ilparlpa subdivision. Stretching more than 50 km north and west are the Iwupataka Aboriginal homelands and West MacDonnell National Park. All the country surrounding the mine is grazing land, which local pastoral families rely on for their livelihood.

Data show the predominant wind directions are between east and south.2 Wind blows towards Alice Springs on 6% of mornings and 12% of afternoons. The Iwupataka homeland, Ilparlpa subdivision, Correctional Facility, Joint Defence Facility Pine Gap and industrial estate have a 42% (morning) and 54% (afternoon) probability of receiving wind from across the mine site.

Wind speed is less in the morning than afternoon; and winter is less windy than summer but the range of wind speed is wider. Wind speed great enough to pick up dust, that is, greater than 30 km/h, occurs only a few per cent of the time.2 Gas dispersion requires much lower wind speed than dust.

Results combining direction, frequency and speed are displayed in Table 1. Wind speeds that can raise dust occur very infrequently in usual conditions. Ascertaining when wind gusts at greater than 30 km/h occur is not possible from this data; daily data would have to be purchased form the Bureau of Meteorology and analysed. Winds strong enough to loft dust would occur during occasional gusts and storm events.

Table 1.  Wind direction and speed frequency.
Combined Direction and Speed9 am Winds3 pm Winds
  1. * Wind speeds that can raise dust

Wind directionWind Speed km/hPer cent of timePer cent of time
East wind10–208–196–19
 20–3019–2619–26
 >30<2*<2*
South East wind10–208–196–19
 20–3019–2619–28
 >30<2*<2*
South wind10–20 4–9
 20–30 9–12
 >30 <2*

Two further factors require consideration. The first is the probability of an event that releases contaminated dust. This study does not seek to quantify that risk. Experience at the Ranger uranium mine demonstrates that such risk is not negligible.

Secondly, the full range of actual weather conditions needs to be modelled using atmospheric modelling programs that incorporate all wind, particulate and topographical factors. Large dust storms are known to occur, which make a contamination event possible. Assessment of the cumulative probability of dust management failure and strong winds is beyond the scope of this study, but would need to be undertaken in any environmental assessment process for mining. In this situation a very conservative approach to protecting local people and livelihoods is necessary.

In conclusion, given the right wind and weather conditions, failure of dust suppression and tailings management at any Angela Pamela mine means workers at the Brewer Industrial Estate, prisoners and officers at the Correctional Facility, staff at the Joint Defence Facility Pine Gap and residents of the Iwupataka Homelands are at a low but still significant risk of dust exposure. Alice Springs itself, workers and tourists at the airport and residents at Amoonguna are at lower but not nil risk. The Ilparlpa subdivision carries an intermediate risk. Grazing cattle and station workers in the surrounding country would always be at some risk.

The potential for damaging health and social consequences despite low risk of contamination needs to be considered when deciding to permit mining. More detailed analysis using a high resolution atmospheric model would give a better understanding of the situation.

Acknowledgements

Catriona Tait for data collection. Clive Rosewarne, Rosalie Schultz (PHAANT) and Blair Trewin (Bureau of Meteorology) for comments on early drafts.

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