Each assessment should detail the following:
Weather conditions
Noise surveys must be carried out in suitable conditions for example, in the absence of strong winds, rain and snow. For road traffic noise, road surfaces should be dry. The survey should not commenced until at least 1 hour after the cessation of any rainfall, or until roads are visibly dry. The microphone of the sound level meter must be fitted with an appropriate windshield when taking measurements outdoors. Details of weather conditions during the survey must be given in the report. The report must include a location plan showing the measurement position in relation to the development site.
Attendance at survey
It is preferable for the noise consultant to attend during the survey. Then there can be certainty about the origins of any noise that has been measured and recorded. When long-term measurements are needed, they should be supplemented with attended measurements. This way, variations seen on the record for the longer-term measurements can be accounted for.
Baseline survey
Before any judgement can be made on the likely impact of a development, it is necessary to have full understanding of the existing noise climate in the vicinity of the receptor.
This is achieved by carrying out a survey of background and ambient noise levels over periods of time which are representative of the times and days when the source will be operational.
Expected noise survey duration is 72 hours for most situations, to include weekdays and weekend periods.
Noise sources and times of operation
A detailed knowledge of the noise source (or in the case of a proposed development, the likely noise source) is essential.
Where the noise source already exists, the data from the noise survey should give information on noise levels, duration, frequency content and variability during and between days.
Measurements should be made at the receptor. However, calculations from alternative positions may be acceptable where this is not possible. Alternative measurement locations must be representative of conditions at the receptor.
If the noise source arises from transport, considering the future growth for that method of transport. It will be necessary to consider projected noise levels from that mode of transport fifteen years after the noise assessment.
Report format and content
The noise impact assessment report should set out all the required information in a format which is logical and understandable.
It will provide the council with information about the proposal, including:
- its location
- the agreed criteria
- surveys undertaken
- the instrumentation used
- the noise source(s)
- the receptors
- mitigation measures
- the impact with respect to acceptability criteria
As a minimum the report should include:
- An introduction.
- Statement of qualifications, competency, professional memberships, and experience.
- Description of the site and proposal including the noise source and associated detail.
- Identification of the receptor, proximity to source and their sensitivity.
- Acceptability criteria.
- Details of the noise measurement survey to include (but not limited to) details of the device(s) used, the chosen methodology, location, duration, meteorological conditions, interpretation of results, data summary and any additional calculations.
- Impact assessment – analysis of the results against acceptability criteria.
- Noise mitigation measures - discussion of any need for, options available to mitigate observed noise levels, and the improvements various options might provide.
- Conclusions.
- Recommendation.
- Appendices, for raw measurement data, calibration certificates, calculations, additional maps, plans, details, and specifications for mitigation measures.