Part 2 Expert Answers: what is a Noise Impact Assessment?

If you missed Part One, check it out here.

In my previous insight post, we discussed the basics of noise, associated noise issues, and what is a Noise Impact Assessment (NIA). In part two of this series, we discuss some additional considerations of a Noise Impact Assessment.

What are the considerations of a Noise Impact Assessment?

Even with the difference in the approach between jurisdictions, there are common themes and considerations when carrying out a Noise Impact Assessment including:

1. What sound sources are being introduced?
2. Where and who are receiving the sounds produced by the sources under evaluation, and are they human or not?
3. Are new noise sensitive receptors being introduced near an existing sound source?
4. When will the sound sources operate? Is it a noise sensitive period like the night-time when people are trying to sleep? Or will it only operate at less sensitive times, like the middle of the day?
5. What time of year will the sound sources operate? Seasonal or year-round?
6. How long will the sound sources operate for? Are they permanent or temporary?
7. Does the sound source have any acoustic features or characteristics, such as tonality (honk/tone/ring), impulsivity (banging sounds like a drum kit), intermittency (the sound comes and goes), any other fluctuations or a mix of all the above? The more features a sound has, the more likely someone will be impacted by it, depending on the context. Remember the noise definition scenario in Part One.
8. What is the existing acoustic environment like at the noise sensitive receptor location? Is the receptor in a high sound level location, such as next to a busy road/highway? Or is it a remote location with very low activity and sound level? The existing acoustic environment is often represented by the background sound level and can vary over the course of a day and seasonally.
9. How will the sound travel from the source to the receptor?
10. What is the absolute sound level from the sound source?
11. What is the difference between the sound level from the source under assessment and that from the background sources (nature sounds, existing roads, rail, airports and industry)? The higher the level of the sound source under assessment compared the background acoustic environment, the more prominent it is and, potentially, the higher the impact.
12. To assess the impact of sound, assessment criteria needs be set. The assessment criteria vary with jurisdiction and the attributes of the background acoustic environment. The criteria should typically consider the absolute level of the sound and a comparison against the current or even future baseline sound levels and characteristics of the background acoustic environment.
13. If adverse impacts have been identified, can control measures be provided to reduce the impact of the sound sources on the receptors?

What are the typical stages of a Noise Impact Assessment?

The main stages of a Noise Impact Assessment are:

1. Identify characteristics (sound power level and characteristics such as tonality etc.) and the location of sound source(s) to be assessed.
2. Identify the location and nature of receptors of the sound source(s).
3. Evaluate the sound levels of the existing acoustic environment (often referred to as a baseline or background sound level). This can be done through regulations’ guidance as a desktop assessment (distance from highways/roads etc.), modelling of existing sound sources, review of public sound level contour data such as noise maps, and sound level measurements.
4. Evaluate the sound levels from the sound source(s) through calculation to the receptors with an appropriate methodology. The international standard methodology for this is ISO 9613 – Acoustics – Attenuation of Sound during Propagation Outdoors but there are alternative approaches used in some jurisdictions.
5. Derive the appropriate sound level criteria based on the characteristics of the noise sensitive receptor under assessment.
6. Compare the sound level at the receptors due to the source(s) against the criteria.
7. If required, assess the feasibility and effectiveness of sound control measures/mitigation. It is important to consider potential mitigation options at the early stages of a project/design, as this is where sound control measures/mitigation through orientation of the site and selection of equipment can save time and money down the line. It’s best to look at this sooner rather than later.
8. Assess the impact of the changes to sound (level and characteristics) with consideration of any sound control measures/mitigation.
9. Sometimes other factors come into the assessment process such as the number of people impacted by the changes in sound level.

This is a general guide on what a Noise Impact Assessment is, the general considerations and a typical approach. There are variances in the specific approach of Noise Impact Assessments depending on context of the source/receptor and the jurisdiction it is in.

SLR can help you navigate the complex nature of Noise Impact Assessments and what will or won’t be required for your project/situation.

Feel free to contact us to discuss your project/situation.