The Nuances of Noise

The Frontiers Report published by the UN Environment Programme (UNEP)¹ in February 2022 identified noise pollution as one of three looming environmental issues (alongside wildfires and disruptive timing of life cycles) that merit attention and action from governments and the public at large. As such, control of noise pollution is a significant component of sustainable development.

In most noise pollution matters, Environmental Noise Monitoring is an essential part of the process and this may relate to new industrial, infrastructure, commercial and residential developments, planning, licensing and dispute resolutions. 

Environmental Noise Monitoring is usually required to:

1. Make a record of the levels and sources of prevailing ambient/background noise around a proposed site, so that appropriate noise criteria can be recommended for noise emitted from a completed development
2. Quantify the levels of environmental noise incident upon proposed building façades so that the sound insulation requirements can be established
3. Calibrate a computer 3D noise map model
4. Investigate noise complaints
5. Understand noise trends (whether noise levels decrease or increase over time)
6. Comply with a requirement (e.g. IPPC², planning or licensing condition)
7. Quantify the emissions from noise sources to allow assessment/modelling

Assessment of noise impacts

The science of Acoustics is often called a “black” art, and this may be due to the lack of a clear relationship between sound levels and human reaction, and no clear definition of what constitutes an unacceptable impact or a significant effect. As such, great professional care is required in order to link monitored noise levels with the effects on humans (and these include physiological as well as behavioural effects). However, noise can be an important contributor to other environmental effects acting either directly, indirectly or in combination. For instance, noise may disturb wildlife, alter the character of the landscape, and air overpressure cause structural damage. 

Noise impact assessments are complex and can vary greatly with every site needing a bespoke solution. There is a dearth of specific guidance on how to undertake a noise impact assessment and whilst relevant guidance is available, it has not been specifically developed to assist with the process of undertaking a noise impact assessment. The process of a noise impact assessment is an iterative process in which there are multiple feedback loops. This means that while there is a series of commonly accepted and well-understood steps, their application will vary between individual assessments. 

In the UK, planning and noise impact assessment works within a complex land use planning decision making process. Planning attempts to mediate between conflicting interests in the use and development of land. 

UK planning is a complex system which is presently defined by: 

• Legislation: TCPA 1990, Planning Act 2008, Localism Act 2011, Transport and Works Act 1992, Scotland, Wales, Northern Ireland. 
• Regulation and Orders: EIA Regulations, Infrastructure Planning EIA Regulations 2009, Scotland Regulations, 2011 etc.
• Judicial and appeal precedence.
• National policy and advice: NPPF, NPS and Planning Practice Guidance, NPF, PPW, SPSS. 
• Local policy and guidance.

In a noise impact assessment relating to new development, the existing noise levels will be assessed in conjunction with the predicted noise levels introduced due to the development proposals in order to review the nature and extent of the associated noise impact. Apart from an assessment of the change in noise levels, other factors of the change may need to be considered to determine the extent of any effect and its significance. 

A noise impact assessment adhering to good practice principles should be: 

Transparent

For instance, the reporting ought to be in a format that is understandable to the layman, the terminology defined, the methodology described, limitations and uncertainties identified and constraints explained.

Focused 

Through the identification of key issues.

Practical

By producing information that is sufficient, relevant and reliable for use in the decision making, environmental noise monitoring data and analysis should be achievable within the limits of available data, time, resources and methods considered as robust and tested.

Participative 

By including consultation with a range of stakeholders (although not possible in all cases).

Credible 

By being objective, impartial, rigorous, balanced, fair and ethical.

Thorough 

By including an assessment of alternatives, where appropriate, including where appropriate alternative sites, design, technology and mitigation measures; the assessment also ought to include an assessment of a viable worst-case scenario. 

The subjective nature of noise in conjunction with the difficulties encountered with linking sound levels with human effects, makes it impossible to set out a prescriptive methodology for noise impact assessments. As such, a degree of professional judgement is required where the assessor must clearly set out the approach taken for a particular project, which has to be bespoke to the constraints and opportunities of the issue at hand.

Noise monitoring technique

The style of monitoring will depend on the type of noise survey undertaken and the information that is required. Sometimes fully manned noise surveying may be necessary (e.g. complaints investigation). However, in general, unmanned monitoring will usually be appropriate. With modern equipment, continuous monitoring over a few hours to a few weeks can be undertaken at multiple locations in order to review the fluctuations in the local sound environment. 

In the case of long-term continuous monitoring (say over a few months), and if secure locations with a power supply and reliable internet/mobile connection are available, modern equipment can be utilised where the recorded levels are downloaded remotely, or even viewed online via a web-based platform. If required, alerts can be set up and even automatic audio³ recordings can be set up to aid in the investigation (for instance, the sound level meters may record a minute of audio when a predetermined trigger level is exceeded, assuming there are no privacy issues). 

If required, multi-channel systems capable of measuring several parameters in addition to noise levels can be utilised (e.g. vibration, dust, weather data).

In the case of unattended noise monitoring, and especially if the noise climate is complex and is not dominated by one source, or a specific source needs to be identified within a complex sound field, the use of conventional equipment may be cumbersome and potentially very time consuming (e.g. when having to listen back to lots of audio samples to try to understand the noise climate better). Moreover, such monitoring can be inconclusive in a lot of cases. For instance, how do you know that the noise affecting the nearby hospital is emanating from your construction site rather than from the one next to yours? Advances in signal processing have meant that state of the art sound level meters can process more information than previously possible and therefore overcome some if not all of the constraints encountered with conventional sound level meters.

A recent development is the multi-channel microphone for environmental measurements, to help automate the location of noise sources. The directional 3D functionality enables, for example, aircraft to be picked out from normal community noise, identification of the direction of significant noise sources, and separate analysis of particular noise sources (say a road or railway is near your construction site, and you want to be in a position to only consider the noise coming from your construction site).

It should be noted that sometimes, it may be preferable to predict rather than measure environmental noise levels. For instance the proposals may significantly change the existing levels and the assessors may be tempted to rely only on predictions. However, even in such scenarios, environmental noise monitoring in conjunction with extrapolation should be the preferred option. Assessors may gain assistance from any noise maps that have been produced for the area of interest, however, the assessment should not rely solely on such information and great care is needed to ensure that such maps are fully understood. Rather than trying to extract the exact noise level at a location, such maps may be more useful in providing information in relation to how noise levels change at different locations around the assessed area. 

Selection of receptors

In order for the Environmental Noise Monitoring to be effective, all relevant noise sensitive receptors must be identified, and it should be borne in mind that these will not have the same degree of sensitivity. Such sensitive receptors may include non-residential buildings, animals and even land areas. 

The assessor must be able to identify the location of such receptors and assign different degrees of sensitivity. It should be noted that in some projects, the proposals may introduce new noise sensitive receptors, and as such it will be imperative to include such uses as potential receptors in the assessment and review the impacts of existing noise at these receptors.

Consultation

It is advisable to consult the competent authority prior to undertaking any Environmental Noise Monitoring and even prior to defining the scope of the study. Of course, there may be specific commercial or other reasons for confidentiality and as such, such consultation may not occur (at least initially). It should be noted that although the local planning authority may have an environmental health department with expertise in noise, the competent authority may not be the relevant planning authority. 

Consultation has the following advantages: 

• Receptors may be more readily identified, and their significance quantified (as far as possible)
• Local concerns may surface
• Information on existing noise levels maybe known and available 
• Monitoring requirements may be identified
• Assistance with the surveys may be provided for instance, by arranging access, or receiving agreement to place a sound level meter on a lamp post
• Agree suitable receptor locations
• Agree on a methodology for the assessment of the impacts 

Information required

Whilst planning the survey the surveyor needs to understand the brief and engage with the instructing parties in order to plan appropriate survey methods.

Depending on the purpose of the monitoring, various types of information is likely to be required:

• Time histories of parameters such as background noise levels, maximum or average levels
• Differentiation of noise climate between day and night-time periods 
• Number of exceedances of defined sound levels
• Frequency analysis of sound levels
• Specific analysis of individual noise ‘events’ such a train passing
• Levels within buildings (as well as external levels)

It should be noted that the type of analysis to be undertaken may dictate particular measurements/information: e.g. if using BS4142 (when assessing impacts from industrial premises) it is important to measure background sound levels with specific time samplings which are different for daytime and night-time periods, or if providing an assessment for compliance with Approved Document O, it is important to establish the number of individual maximum noise levels during the night-time. 

Monitoring locations

Ideally, monitoring locations should be at the position of the receptor (e.g. a dwelling) and since we spend most of our time indoors⁴, the measurement location ought to be indoors as well. This is clearly not practicable or even desirable (due to the possible interference from internal sound sources). 

However, after consideration for the necessary access requirements, security concerns and potential need for a power supply it is understandable to expect most monitoring locations to be located at the site boundary. 

With appropriate planning, it may be possible to establish a measurement location near a receptor (e.g. by placing a sound level meter on a lamp post), however, there may be instances when such locations are not useful (e.g. locations where other nearby noise sources may prohibit measurements near the receptor locations). 

In any case, since the monitoring locations are rarely 100% representative of the noise climate that is the subject of the assessment, various corrections will need to be applied to the measured sound pressure level readings and this will require great professional care in order to acquire the best representative readings and minimise any challenges from various stakeholders. 

Effects of meteorology

When undertaking environmental noise monitoring the effects of meteorology must be considered. 

It is common to avoid monitoring when: 

• The wind speed exceeds 5 m/s
• Unusual temperature conditions are occurring
• When there is significant precipitation (unless these are the normal conditions for the area)

Care should be taken to ensure that the equipment is capable of operating satisfactorily under the prevailing conditions. The calibration of the equipment should not be compromised under cold or wet conditions. 

However, if non-ideal weather conditions cannot be avoided, such periods of poor conditions should be indicated in the data records, and any relevant account taken of their effects in describing the noise climate under review. 

If the receptors are located at long distances, it will be crucial to also consider atmospheric effects (e.g. temperature gradient, air absorption) as well as weather effects. 

Conducting the survey

The survey ought to be conducted in a competent matter and some pertinent points to consider include:

• Ensure arrival on site at the specific time
• Ensure all relevant paperwork is in order
• Ensure adherence to all relevant health and safety requirements
• Review the variables used to derive pre-selected monitoring locations and if new evidence is found, re-select (if possible whilst on site) a new monitoring location
• Understand the location orientation of nearby receptors and assess their significance status
• Leave a good impression with home or business owners if setting up equipment at their premises

Competence

As discussed above, noise monitoring is a complex endeavour. As such, if your project requires noise monitoring you need to ensure that this is undertaken only by qualified and experienced practitioners. In the UK, normally these will be qualified acousticians who are corporate members of the Institute of Acoustics. They should be experienced in the measurement and prediction of noise and have a good understanding of the issues involved in the assessment of noise. In addition, if the company undertaking the monitoring is a member of the Association of Noise Consultants then this should provide additional confidence in the competency of the assessors due to the rigorous selection process for member companies.

References

1. https://www.unep.org/news-and-stories/press-release/deadly-wildfires-noise-pollution-and-disruptive-timing-life-cycles
2. Environmental permitting guidance: Integrated pollution prevention and control (IPPC) directive
3. Meaning recordings that can be listened back in contrast to sound or noise readings.
4. According to a study (see https://www.ribblecycles.co.uk/ The Not-So Great Outdoors? | Ribble Cycles) Britons spend around 92% of the time indoors.