Cutting down on noise pollution
How to effectively tackle noise pollution at pits and quarries
November 29, 2016 By Ben Coulson and Aaron Haniff
November 29, 2016 – The aggregate extracted from pits and quarries is a key building material used in the construction industry, and where extraction happens, there exists the possibility of occasional noise. Aggregate producers, through site design and the use of berms are generally able to effectively mitigate the noise to acceptable levels. But some designs and locations make it necessary to look for enhanced ways to mitigate noise.
Controlling the potential for noise and the impact it can have on surrounding residences is a key aspect of good aggregate operations. With the right plan in place, the potential for noise complaints can be greatly reduced.
As with many industries, there are some pieces of equipment used in the extraction process that may cause noise vibration. There are also loud sounds created during blasting operations, but the noise levels and nuisance of blasting noise are mitigated in a number of ways, from the timing and frequency of the blasts to scheduling blasts to coincide with appropriate weather conditions.
Pits and quarries that operate within the province of Ontario are regulated under two key pieces of legislation with respect to noise and vibrations. The first is the Environmental Protection Act, administered by the Ministry of the Environment and Climate Change (MOECC formerly MOE). The second is the Aggregate Resource Act, administered by the Ministry of Natural Resources and Forestry (MNRF formerly MNR). The MOECC’s regulations and guidelines control potential environmental impacts, including noise and vibration, while the MNRF grants licences to aggregate producers.
In order for pits and quarries to operate in Ontario, they must meet the noise limits set by the MOECC, and they are some of the most stringent in the world. The more relevant MOECC guidelines deal with sound level limits at receptors, sound and vibration limits relating to blasting activities, and sound levels that specific noisy equipment at sites need to meet.
The most applicable guideline for normal operations of the pit or quarry is MOECC’s Publication NPC-300. Released in August 2013, the document consolidates several formal documents. It outlines sound limits a facility must meet at surrounding receptors, and represents one of the few major changes in MOECC’s documentation dealing with noise and vibration in recent years.
The update includes several major changes. Most notably, it looks at the way receptors and their respective limits are assessed. The sound level limits at receptors change depending on the time of day, with the strictest limits set for the night-time hours when people are trying to sleep, and the most lenient set for the day when people are most active. The limits also depend on the local environment. The lowest limits are designated for rural environments at night, where they can be as quiet as a library, to urban areas during the day where they can be set to levels approximating an average home or the side of a lightly travelled roadway.
For assessment purposes, the worst-case combined sound levels emitted from equipment are examined. Some examples of major sound-generating equipment include: rock drilling, diesel generators, on-site haul trucks, loaders and dozers, crushers, screening plants, conveyor systems and stackers. The sound emissions from each can be determined either by manufacturer sound levels or by measurements taken by acoustic personnel. Depending on the complexity of the facility, basic calculations or a complex sound model, they can then be used to estimate sound levels from the entire aggregate operation at nearby receptors. The combined operations must meet the applicable sound level limits at all surrounding residences.
If the facility cannot meet the designated sound level limits, a mitigation strategy needs to be designed and implemented. The main techniques for mitigation include: changing or limiting the operational times of equipment; adding or upgrading silencers on equipment (e.g., generator sets, etc.); relocating on-site equipment further from receptors or moving it behind barriers (e.g., buildings, berms, quarry face, etc.); selecting quieter equipment; creating higher perimeter berms or adding (portable) on-site barriers (could include permanent stockpiles); and adding a noise monitoring program within the property line with notifications when sound levels reach a set threshold.
The right solution
Different mitigation concepts work better in different cases, but the simplest plan is planning itself. A good site plan and appropriate berms can dampen or even block potentially disruptive noise.
As well, limiting the operational time for equipment can greatly reduce the facility sound level at the surrounding receptor, especially if nighttime operations can be scaled back or removed entirely. Silencers are a great way to reduce stack or wall opening sounds as they are relatively inexpensive and usually last for the life cycle of the equipment.
Noise barriers, walls or on-site structures all work to reduce sound levels by blocking the line of sight between the equipment and the receptor. Unfortunately, long or tall barriers are relatively costly and need to be installed close to the source of noise or to the residence.
If a single source of sound at a facility is dominant, it may be easy to identify and mitigate it with a silencer or barrier. In complex situations where many sources cause compliance issues, a qualified acoustical consultant may be needed to identify and select the appropriate mitigation measures.
Monitoring aggregate sites for noise and vibration helps producers to develop a good understanding of how sound levels change throughout the day, and to identify any problem areas.
The original application and permit should look at worst-case scenarios, but it generally fails to address the transient nature of the operations. This can, however, be achieved by deploying long-term sound and vibration meters at strategic points throughout the site. Some meter deployments have the ability to log various parameters and, combined with a cell signal, can give warnings when sound and vibration levels approach the site-specified limits or when complaints from neighbours occur.
This near real-time communication allows operators to identify and modify site operations immediately and proactively, rather than hours or even days later.
A real-time monitoring station will also allow the data collected to be plotted for real-time viewing. The logged data provides an effective way to demonstrate continuous compliance with the applicable limits or to justify corrective actions on-site.
If neighbours have concerns about the sound or vibration levels, the data can be shared via the Internet with the public, or in a password-protected way with regulators or other stakeholders. This type of action can go a long way in building trust with neighbouring residences, and in reducing complaints.
In summary, the operations of pits and quarries have the potential to create noise and vibration concerns at surrounding sensitive receptors. Proactive planning can reduce many of those potential issues, and a monitoring system is one tool that can help identify potential concerns before they arise and allow corrective action to be taken proactively.
By taking the correct mitigation measures, producers are able to meet the strict Ontario sound and vibration limits, and greatly reduce the potential for complaints from nearby residents. The result is a quieter operation overall, with everyone able to enjoy the natural sounds of the nature all around.
Ben Coulson is a senior consultant for noise, acoustics and vibration at RWDI.
Aaron Haniff is a scientist and engineer for noise, acoustics and vibration at RWDI.
This article originally ran in the Fall 2016 issue of OSSGA Avenues.
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