Mining related dust and its control
We are required to minimise air emissions. Site-wide emissions to air are covered by a regional consent from Waikato Regional Council. This requires the Company to produce an Air Quality Management Plan which must be approved by the Regional Council.
There is a certain level of dust in the air at all times. The amount and type of dust varies considerably and depends on many factors including source, climate, wind direction, and traffic. Dust is generated from many man-made and natural sources and 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 stronger the wind the larger the particles lifted and the more dust carried.
Dust particles of different sizes behave differently, and are measured by the following size fractions:
Deposited Particulate refers to particles that settle out of the air, that are greater than about 10 to 20 microns. The primary effect is a nuisance one, in that particles may show up as a deposit on clean surfaces such as cars and window ledges.
Total Suspended Particulate (TSP) refers to particles that can remain suspended in the air for significant periods of time, ranging from several minutes for the larger particles to several days for very fine material. Elevated levels can affect visual quality and can also have effects on human health, generally by irritating the eyes, mucous membranes and skin. Wind-blown pollen is a source of suspended particulate that can exacerbate effects on health such as hay-fever.
Comparison of human hair and dust particle size.
The method used for measuring suspended particulate picks up all particles up to about 100 microns in size. The size fraction less than 10 microns (PM10) is referred to as inhalable particulate. Because the particles are small enough to be inhaled, they can have an effect on human health. While levels are set for deposited particulate and total suspended particulate to protect against nuisance dust effects, PM10 levels are set to protect against health effects.
All attempts are made to minimise dust generated by mining activities in Waihi. Dust generated is mostly what is called 'nuisance dust'. It is visible and can be annoying, but is not a health hazard.
Air quality guidelines
|Air Quality Management Plan Trigger Level||Ministry for the Environment Guideline||Proposed Waikato Regional Plan Guideline|
|Suspended Particulate||45µg/m3 averaged over seven days||no guidelines||no guidelines|
|Deposited Particulate||4g/m2/month averaged over one month||4g/m2/month (above background) averaged over one month||4g/m2 per 30 days or150 mg/m2 over 24 hrs|
|Inhalable Particulate||60µg/m3 averaged over 24 hours||120µg/m3 averaged over24 hours. 40µg/m3annual av.||50µg/m3 averaged over 24 hours 50µg/m3 averaged annually|
Air quality monitoring programmes were first set up in 1982 as interest increased in the old Martha Mine area. The monitoring has provided a continuous air quality database as good as, or better than, anywhere else in New Zealand.
Results from air quality monitoring are highly variable. This is a common feature, dependent on every day events. Pollen, agricultural and commercial activities and even volcanic events and Australian bushfires have all been recorded. The effects of eruptions at White Island and Mt Ruapehu have been recorded in Waihi.
Deposited, suspended and inhalable particulate are measured continuously around the Waihi area.
- results for Waihi are comparable with those from other small urban areas. This is what might be expected for a township located adjacent to a major highway
- measured inhalable particulate levels are well below the levels set to protect against health effects
- crystalline silica levels (quartz) are very low. Levels measured at the mine site are lower than those measured at Waihi Beach
- metal concentrations of the dust are very low and compare with levels in other rural areas (city urban area levels are much higher)
- no employee or contractor has displayed health effects related to air quality. Mine employees or contractors would be the first to display any such effects as they work on site close to potential dust sources (we have an occupational health monitoring programme to monitor employee exposure to dust)
- air quality in and around Waihi is not deteriorating
- air quality is often at its worst in winter due to air contaminants from domestic fires
- continuous monitoring since the start of the project shows that 99% of all dust measurements are within compliance with consent conditions and that the other 1% was mostly attributable to activities that were not mining-related.
How is dust controlled?
Dust is managed by the following methods:
- Maintaining conservative speed limits on site
- watering haul roads and using sprinkler systems and water sprays where required
- 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 to cover long-term stockpiles
- planting pasture, shrubs and trees as soon as rehabilitation areas are available
- washing wheels of vehicles before leaving site to travel on public roads.
- Covering the conveyor as it passes through town.
Glossary of terms
Particles that settle out of the air that are greater than about 10 to 20 microns. The primary effect is a nuisance one rather than a health hazard. Particles may show up as a deposit on clean surfaces such as cars and window ledges.
Environmental Protection Agency (USA).
Total Suspended Particulate. Suspended particulate refers to particles that can remain suspended in the air for significant periods of time, ranging from several minutes for the larger particles to several days for very fine material. Elevated levels can affect visual quality and can also have effects on human health, generally by irritating the eyes, mucous membranes and skin. Wind blown pollen is a source of suspended particulate that can exacerbate effects on health such as hay fever. The size fraction less than 10 microns (PM10) is referred to as inhalable particulate. Because the particles are small enough to be inhaled, they can have an effect on human health. PM10 levels are set to protect against health effects.
Particulate Matter sized 0 to 2.5 microns.
Particulate Matter sized 0 to 10 microns (an average human hair is approximately 70 microns thick).
micrograms per cubic metre. One microgram is one millionth of one gram.
More information about air quality can be found on the Ministry for the Environment and Waikato Regional Council websites.
Waikato Regional Council:
Air Quality Monitoring Report for Hamilton, Tokoroa, Taupo,Te Kuiti, Matamata, Putaruru, Ngaruawahia, Waihi and Turangi 2011
Ministry for the Environment:
For various publications about air quality go to: www.mfe.govt.nz/publications/air