Noise
Potential Sources of Noise
Location
It is obvious that the mineral can only be worked where it occurs, and that the extraction work is carried out in the open air. Therefore the situation is not like developing a new factory, where there is much more choice in the location of the premises, and the factory building can be designed to provide the necessary attenuation or reduction.
Preparatory work
Quarries and other mineral workings produce complex noise fields which vary over time. The initial source of noise on a new mine or quarry is the preparatory works for the site. This will normally entail the provision of a road access, site offices and compound, and usually some mineral processing facilities (although mobile processing plant is increasingly being used, which has a number of significant noise advantages). On some of the larger sites, there may be the construction of a rail access and sidings and/or the diversion of an existing road or river. Most of these activities are similar to the activities carried out for other large scale developments, and usually last for a limited duration.
Soil stripping
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The next activity is the exposure of the mineral for extraction. This will involve the removal of soils and any overburden which may be present. Soils and other soft materials were historically often removed by scrapers (Photograph 2), but these caused excessive damage to the soils, and so hydraulic excavators and dump trucks are now preferred. Nevertheless, by definition the activity takes place on the surface at original ground level, and so often produceshigh noise levels. |
Photograph 2. Scraper depositing soil after scraping and transporting |
| In most cases, advantage is taken of the removal of the soils to construct baffle mounds (Photograph 3). These are soil storage banks or bunds that are generally located on the boundary of the site in order to provide visual and acoustic screening. As the construction takes place on the boundary of the site, the noise levels generated by the formation and removal will almost certainly be the highest experienced during the life of the site. The highest levels will generally only occur for a matter of days at each location. For this reason, higher limits are usually permitted for this activity (which brings subsequent benefits to the noise environment), as given in MPS2: Annex 2 Noise L0180 and discussed in a later section. |  |
Photograph 3. Removed soil utilised as seeded baffle mound |
The next stage will depend on the type of site being operated. For opencast coal sites and some quarries, a thick layer of overburden may need to be removed before exposing the deposit. This has to be stored in an overburden dump, which is usually very visible from the surrounding area, and therefore any noise emitted from the dump (such as vehicle reversing sirens and the squealing of dry caterpillar tracks) is often clearly heard and a common source of complaint. For most quarries, the soil and overburden to be removed is likely to be relatively thin and so is not significantly different to the mineral extraction stage, discussed next.
Mineral Extraction
Once the mineral is exposed, it can then be extracted. Some minerals such as sands, gravels, clays and coal can be extracted by direct use of an excavating shovel or wheeled loader. Other materials such as sandstone and limestone will need to be broken up by blasting or ripping before they can be excavated. Blasting may also occur in the overburden if it is too tough to be excavated directly by shovel.
The mineral will then be removed for initial processing or direct removal off site. Field conveyors can be used on some sand and gravel sites (Photograph 4), but usually the mineral is loaded by excavator or loader into dump trucks (Photograph 5). These are large diesel engine machines which move about the site. The noise will vary in level from each item of plant and will include the noise of material being deposited into dump trucks by excavators. However, the further away from the working area, the less noticeable individual items of plant are. An exception to this is the audible reversing warning device often fitted on trucks, which can be noticeable at considerable distances and be a source of frequent complaints. The squealing of caterpillar tracks can also have a distinctive sound, even at a distance.
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Photograph 4. Use of a field conveyor to transport material from excavation to processing area |
Photograph 5. Shovel and truck operation on a large granite quarry |
| For hard rock there is sometimes a need to use a pecker (Photograph 6) or other hydraulic breaker device on the largest rocks before loading, which can be another very noisy activity. |  |
Photograph 6. Hydraulic breaker breaking the large blocks before loading |
The mineral extraction phase usually takes place well below ground level, which means the quarry faces act as natural barriers to the noise. This is particularly true of hard rock quarries which are often very deep (Photograph 7), whereas sand and gravel quarries may be on the surface or quite shallow (Photograph 8) and therefore more difficult to "hide" the extraction workings from surrounding receptors.
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Photograph 7. Deep workings of a large hard rock quarry |
Photograph 8. Shallow workings of a sand and gravel quarry |
So far, blasting has not been mentioned, although it is required on many hard rock sites. The sound of the blast itself is not usually a major issue, but it can contribute to the overall concern which may be expressed by local residents. The acoustic response of a house to the ground or air vibrations can include the shaking and rattling of objects inside the house, which can be disturbing. Further details on this can be found in the section on Blasting.
Processing
Once the mineral has been extracted and removed from the working area, there will normally be some processing carried out on site. On an aggregate site this is likely to include crushing and screening to produce the desired fractions of material.
Historically, most of this processing has taken place in fixed plant, often housed inside enclosures to reduce the amount of noise and dust that escaped into the environment. Many of these were located at surface level, where there was still a lot of residual impact. However, an increasing amount of processing is now taking place "in pit", either because the fixed plant has been relocated to a lower level, or because mobile processing plant has been selected.
| Some quarry sites may have asphalt coating plants with associated dryers, heaters, mixers and fans (Photograph 9). |  |
Photograph 9. Asphalt plant next to a crushing and screening enclosure |
Transportation
Finally, the material will be ready to be transported off site. This will usually be carried out by heavy goods vehicles, although on some larger sites, the mineral may be transported by other means such as rail or barge. There is increasing demand for road construction and maintenance to be carried out at night. This means asphalt needs to be supplied from some quarries through the night and early morning, which can be a serious noise impact.
The impact of traffic and transport is a separate subject in this website, and issues of "body slap" of empty vehicles and other noise issues are dealt with there.
Restoration
The activity involved in restoration varies tremendously from site to site. For some hard rock sites it may require restoration blasting and re-grading the slopes. For most sites there will be the removal of the soil bunds (which may have been used as screening) and the relaying of the sub-soil and top-soil layers. As with the soil stripping, this is likely to be a noise activity, some of which will be taking place close to the site boundary.
Continued with Acceptable Noise Levels TOP Return to Introduction