Noise And Dust - It Pays To Talk

Mark Dawson, a technical director with Wardell Armstrong and one of the firm’s experts in noise and air quality, looks at some of the issues

By the very nature of the processes involved, mining and quarrying can sometimes create real or perceived problems for people living or working near to sites where minerals are being extracted. Noise and dust are often seen as the chief culprits. But with careful thought and design, and good early dialogue, a lot of the concerns can be well managed and mitigated. It is, after all, in nobody’s interests to have endless complaints or a reputation for being a bad neighbour.

Necessary – or nice to have?

A good first step is to think about and design the assessment work that is needed for the cost-effective control of noise and dust in the particular situation that is under consideration. This can either be part of a detailed environmental impact assessment (EIA) or concentrate on specific issues (more about this later).

There can be a natural tendency for operators thinking about a new development to keep their cards close to their chest. But this sometimes results in not getting the dialogue with the local authority opened early enough. And in a mineral area, planners will be experienced in dealing with applications and the issues that arise.

It makes sense, therefore, to discuss the development proposals with them, to agree the right assessment methodologies and to identify any local issues that might need to be taken into consideration. Early guidance can have a positive influence on design and will generally prove to be much more cost-effective than trying to correct a problem later on or attempting to re-engineer things having already gone a long way down the planning route. For example, the shortest route for an access road to a pit may be down a lane that runs past a row of cottages – but an alternative that is only slightly longer can avoid all the upset that this can cause.

At the same time, it is important to keep the assessment to a realistic level and not be pressured into unnecessary work or ‘nice to haves’. Twenty four-hour noise monitoring, or even a 12-month programme of dust monitoring before operations start, may be asked for without being strictly necessary. Discussion and negotiation are therefore key.

Another important step is to identify sensitive receptors around the site. In many cases the same receptors will be applicable for both the noise and dust assessments, but not always. For example, a surfaced access road could be a dominant source of noise but generate little dust.

Noise limits and mitigation

Noise criteria for minerals sites in the UK are set out in Mineral Planning Statement 2 (MPS 2). This allows certain short-term operations needed to get the extraction works   under way to be assessed against a relatively high noise limit – and it is important to use this facility to the full. For example, a 5m high screening mound using overburden to shield properties can be justified if a net benefit can be shown.

Longer-term operations are assessed against a lower noise limit which largely depends on the existing background noise levels. Obtaining these in a way that is truly representative is a skilled job. It is all too easy to understate or (even worse) overstate them, and this can have a significant effect on the noise limits subsequently applied to the operation. A good appreciation of atmospheric conditions and local land-use practices is important.

Operational noise levels should be calculated for each phase, or possibly part phase, throughout the life of the mineral site. Accurate noise data for the plant to be used is important, as is a clear understanding of how the plant will be used at all relevant times. Attention to this kind of detail is critical for a realistic assessment.

Prediction calculations need to follow accepted procedures and be detailed enough to include all noise mitigation provided by site features and the natural contours of the ground.

Once operational noise levels at all receptors are known, any exceedences above agreed limits need to be dealt with. Mitigation measures can be modelled until the optimum solution is reached. Soil storage and overburden mounds can provide very effective noise mitigation, and can be incorporated into the initial design of each phase.

Controlling dust  

Dust emission rates and propagation paths are much more difficult to predict and quantify, with no empirical way to model them. What might constitute an unacceptable level of dust at receptors is, therefore, less well prescribed. But effective site layout, the use of wind speed and direction data, and the logical phasing of operations can all reduce exposure substantially.

The most significant dust-generating operations should be identified for each phase, or part phase, of the life of the mineral site. Local meteorological data showing wind speed and direction throughout the year can be used to estimate the number of hours during which winds are likely to blow on dry days from each dusty operation to each receptor. This, together with the distance to each receptor, rates the need for dust control for each situation.

Mitigation measures can then be designed to target the most significant situations and provide the most cost-effective control. Water sprays and grass seed are common techniques, as well as managing vehicle drop heights and speeds. Detailed in a dust-management plan, they will trigger levels at which additional mitigation is required in particular circumstances. Their effectiveness can then be checked by monitoring programmes at critical phases of the operation.

Experience

Also it is often possible to find ways of solving several problems at once. Large mounds of overburden or bunds, for example, can be used very effectively to store material, control noise, and screen operations from sight.

It pays to think about the environmental issues early on, and to talk to people with experience of how best to mitigate them. Involving the right experts in areas such as assessment, monitoring, modelling, design of mitigation, limits and reporting on exceedences can help to ensure that things are done the right way from the start – and in a way that balances getting the best possible financial returns with being a good neighbour.

For further information visit: www.wardell-armstrong.com