Above: Regular monitoring of dust deposition both on and off site is an important aspect of environmental management.

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. By far the most effective method for controlling dust generation is by sprinkling potential sources with water.

What is Dust?

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.

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 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. 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 no guidelines 4g/m2 per 30 days or 150 mg/m2 over 24 hrs Inhalable Particulate 60µg/m3 averaged over 24 hours 120µg/m3 averaged over 24 hours. 40µg/m3 annual av. 50µg/m3 averaged over 24 hours

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2004 Air Quality Report 2004 Air Quality Report (406k) Download Now

Monitoring

	Above: A water truck in the open pit. All attempts are made to minimise dust generated by mining activities.

Dust monitoring programmes were first set up in 1982 as interest increased in the old Martha Mine area. The monitoring has provided a continuous dust database as good as, or better than, anywhere else in New Zealand.

Results from dust monitoring are highly variable. This is a common feature, dependent on every day events. Pollen, agricultural and commercial activities and even volcanic events have all been recorded. The effects of eruptions at White Island and Mt Ruapehu have been recorded in Waihi.

Deposited and suspended particulate are measured continuously around the Waihi area. There are now more than 20 measuring stations plus one in Katikati and one in Paeroa to provide useful comparisons. In addition, monitoring of inhalable particulate and the silica (quartz) contents are carried out from time to time.

Monitoring shows:

• 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.
  
  
• Continuous monitoring since the start of the project shows that 99% of all dust measurements are below the levels required by consent conditions.
  
  
• Measured inhalable particulate levels range from 5 to 10 microns per cubic metre. This is well below the levels set to protect against health effects.
  
  
• 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 (urban area levels are much higher).

Above: A dust monitoring station and sample collection. Results for Waihi are comparable with those from other small urban areas, and 99% of all dust measurements are below the levels required by consent conditions.

How is Dust Controlled?

The company is required to minimise dust emissions. Site wide emissions to air are covered by a regional consent from Environment Waikato. This requires the company to produce an Air Quality Management Plan which must be approved by the Regional Council.

Dust is managed by the following methods:

• watering haul roads
• sprinkler systems
• dust collectors and filters on drill rigs and crushers
• water sprays where required
• keeping stockpiles low
• vegetation cover on long-term stockpiles
• progressive rehabilitation
• wheel washing

This section contains technical data and terms. A brief glossary of terms is provided at the bottom of the page.

Concentrations of Respirable Dust in Waihi and Silica Content in Dust

As part of Newmont Waihi Gold’s air discharge consent, the mine is required to undertake monitoring of fine particulate (respirable dust) and silica (or quartz) particle size distribution. This is conducted every two years for three months in summer.

During the last round of monitoring three particle samplers were operated side by side at the meteorological station in the vicinity of the open pit. These samplers measured TSP and particulate matter sized 0 to 2.5 microns and 0 to 10 microns. Samples were collected for 24 hours every third day. These samples are analysed for total amount of dust in each size fraction, and the amount of silica present in the dust collected from each size fraction. Respirable dust includes dust particles up to 10 microns.

Monitoring Results:

Concentrations of respirable dust in Waihi and silica content in dust

There are no ambient air quality guidelines for silica, but the workplace exposure standard for crystalline silica (quartz) in respirable dust is 200 µg/m3 for an 8-hour average. Even allowing for the difference in averaging times, and general public exposures rather than workers, the measured concentrations in PM2.5 and PM10, (maximum silica concentration in respirable dust of 8.4 µg/m3 for a 24-hour average) are less than the level that would indicate a potential health concern converted from workplace exposure standards.

Past and recent analyses on dust particle size and silica content concluded that dust from the mining operation is not a health hazard.

Regular Dust Monitoring

The current Martha Mine dust monitoring programme was initiated in 1982, five years prior to the resumption of gold mining in Waihi. The programme was set up for the Department of Health to determine what, if any, impact mining activities might have on air quality in Waihi.

Today, Newmont Waihi Gold operates one of the most extensive dust monitoring programmes in New Zealand. In addition to the sites within the Waihi area there are two sites in neighbouring towns outside the Waihi region. These provide useful comparisons. One is situated in Katikati and another in Paeroa.

A Brief Glossary of Terms

Deposited particulate 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.

EPA Environmental Protection Agency (USA)

TSP 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.

PM_2.5 particulate matter sized 0 to 2.5 microns

PM₁₀ particulate matter sized 0 to 10 microns
(an average human hair is approximately 70 microns thick)

µg/m³ micrograms per cubic metre