Dust is generated from a range of human activities and natural sources. It may be made up of soil, pollen, volcanic emissions, vehicle exhaust, smoke, or any other particles small enough to be suspended or carried by wind. The stonger the wind, the larger the particles lifted, and the more dust carried.

Dust Monitoring
Planning for the new Martha Mine had to take into account that the mine would be operating very near to people’s houses and properties. The planners had to look at ways that dust from the mine and its activities could affect the neighbouring areas.

Dust monitoring equipment was set up around Waihi in 1982, five years before mining started, so that information could be collated about pre-mining dust levels. This information was used to set the standards for dust levels once mining began.

Dust monitoring continues throughout the operation. Technicians take regular weekly and monthly samples around Waihi.

Once a month the bucket is collected and the water is poured through a filter. The filter is dried and weighed. The weight results for each gauge are entered into a database and regularly reported to Environment Waikato. At present there are ten dust deposition gauges that must be checked every month.

below left: The filter from an airborne dust monitor. The monitor contains a pump which sucks air through a filter, just like a vacuum cleaner. Small dust particles are trapped on the filter.

above right: Donna checks a dust deposition gauge.

Air monitors are fixed in raised positions, such as on power poles. A motor drives a pump that sucks in air, just like a vacuum cleaner. The air passes through a filter, drawing airborne dust with it.

Once a week the filter is changed. The volume of air that has passed through the pump is noted. The used filter is taken to the laboratory and weighed. The weight results for each gauge are entered into a database and regularly reported to Environment Waikato. At present there are six air monitors that must be checked every week.

In addition continuous monitoring for PM10/silica has been undertaken by Environment Waikato since 2007. Before that, EW employed a mobile monitoring unit to record data for a few weeks once every two years. The equipment currently used by EW is called a Partisol air sampler. An electric pump sucks in air, just like a vacuum cleaner. The air is first drawn through a special inlet that only accepts particles up to 10 microns and then filters it. The sampler automatically changes filters daily.

How is Dust Measured? … and What are the Permitted Levels?
Dust filters collected by environmental technicians are weighed on a set of sensitive scales. The weight of the clean, dry filter is subtracted and the calculations are made.

The dust collected in dust deposition gauges is measured in grams per square metre per month. The Air Quality Management Plan guidelines allow up to 4 grams per square metre per month (4g/m²/month).

The dust collected in air monitors is measured in micrograms per cubic metre per week. The Air Quality Management Plan guidelines allow up to 45 micrograms per cubic metre averaged over seven days (45µg/m³/7days). One microgram is equal to one-millionth of one gram – those scales must really be sensitive!

How is Dust Managed at the Martha Mine?
The mining company and mining contractor take all practical steps to keep down dust levels by:

• Applying dust suppression product
• Watering haul roads and using sprinkler systems
• Dust collectors and filters on drill rigs and crushers
• Using a windbreak fence adjacent to the crushers
• Keeping stockpiles low so wind is less likely to spread dust
• Planting grass on long term stockpiles
• Planting pasture, shrubs and trees as soon as rehabilitation areas are available
• Washing wheels of all vehicles before they leave the site to travel on public roads