Southwest Environmental Limited

Noise Impact Assessment

A Noise Impact Assessment is a report that attempts to gauge the impacts on an existing receptor from a planned development (new factory next to some houses), or it may assess noise from an existing source on planned buildings (new homes planned next to a quarry).

Do you require a noise impact report, if so then please contact Southwest Environmental for a quotation. We also offer noise monitoring services.

During construction their will normally be an increase in noise, which can impact on neighbors.

Some developments will have a negative noise impact, as they may replace older developments with a higher noise footprint one example of this might be the redevelopment of a dockyard to seafront residential apartments.

In most cases there will be an positive noise impact, new roads, wind farms and industrial centers will all generally create more noise than the previous site use.

Noise is considered as a form of pollution and as such any "noise" component of an environmental impact assessment will include:

- Baseline Studies- Impact Prediction

- Noise Mitigation

- Noise Monitoring

Picking up on one of the above point. Mitigation: Mitigation of noise can be accomplished in an umber of ways, one such way is to control the noise at source, this might include fitting larger silencers to motorised plant, or the specialize detuning, of outlets etc.

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Noise Impact Modeling

FAQS for Noise and Vibration Impact

Typical Noise Levels in London

Noise Levels Explained

Noise Impact Modeling

Noise Impact Modeling is is a a critical part of the noise impact assessment process.

Noise impact baseline studies must be prepared, but then it is necessary to derive a post development figure for noise at a particular location.

The sound level must be considered along with barriers, that may attenuate sounds on its path to the receptpr.

Receptors for noise can be humans, and natural. Amenity areas should therefore be considered that offer a degree of tranquility.

Dependent on the level of detail required within the model noise modeling can be a relatively simple, or extremely complex affair.

FAQS for Noise and Vibration Impact

Below discussed are some common ideas that relate to the measurement of Noise & Vibration, and their impacts. In order to keep this description simple this guide strays from official guidance and should be considered as an introductory note only.

What are Noise and Vibration?

Noise (Unwanted Sound) and Vibration are both vibrations. Noise is a vibration that we can hear, whilst “vibration” we feel.

How are Noise and Vibration Measured?

Monitoring equipment is used to record sound levels. A microphone is used and any sound is recorded and the “volume” recorded. The results are recorded in decibels (dB). Vibration is measured using an accelerometer. This measures movement in 3 different directions (up-down, side to side and forward-backwards). Results are presented in mm/s that is a measure of movement over time.

What are the Trigger Limits for Vibration?

For people there is no limit as such, although 10mm/s is thought to be “intolerable”. However, humans all differ and some may tolerate more vibration, and some less. We would typically consider a vibration level of 5 mm/s as a trigger level where residents should be protected. For a building the trigger levels differ depending on the strength of the building. But past 15mm/s investigations should be made, to try and reduce vibrations affecting the building.

What is the Trigger Level for Noise?

Noise limits are different to vibration in that there is normally background noise, which louder noises have to overcome in order to be a nuisance. For example talking loudly in a quiet library will disturb people nearby, whilst talking loudly at a football match; you may not even be heard.  With noise we typically measure a back ground (or baseline) level and then add 5dB on top of this to give a Trigger level.

 How do Sound and Vibration Travel?

The travel path is the path the sound takes from the source (digger) to the receiver (ear). Outdoor barriers can block travel paths, for example traffic noise. The effectiveness of barriers is dependent on factors such as its distance from the noise source and the receiver, its height and construction.

Typical Noise Levels in London

Secondary data collected in the Kings Cross Station EIS (London), indicates Basic Noise Level, dB LA10, 1hr  of 73.5 dBA on Camden Road, the report includes monitoring locations in 16 other locations between the site and Kings Cross Station. Noise levels range from 68.7 dBA to 76.7. A US90 certainty value for this data set is 74.22 dBA.

The LA90 15min sound level on Bayham Place (to the rear of Camden High Street, London )  was calculated at 54dBA. Which is noted being representative of "night time back ground sound level". This sound level has been adopted as a worst case to assess impact of heat pump units on nearest noise sensitive windows.

Observing daytime levels from we can see LAeq Levels of 65dBA. The LA90 15min level peaks at 58dBA. Noise Levels Explained.

Noise Levels Explained

Many have tried to explain noise level simply, but many are too clever to do this. The main two expressions of noise used in reports that you may read on planning websites for example are LA90 and LA10, they can be both recorded at the same time with the same equipment yet they give different values, why is this?

Step 1 - First of all we measure the noise using a noise meter. So we might have data that looks like this: 70, 75, 72, 74, 70, each number is the average noise level for a time period perhaps 1 minute. For a 24 hour period we would have approx. 3600 numbers in a row.

We can then make a graph using these numbers, a histogram to be precise, where we label the noise levels along the x (bottom) axis and noise level on vertical (y) axis. We end up with something that looks like the chart to the right.

We gather up our number that we have recorded and group them together in "bins" of whole number noise levels, that increase incrementally. We then make of histogram to show what percentage of of measurements are made up by each of these "bins".

The first bar from left to right that passes 90% is 71, that is our LA90 Level. We can see it is quite low and as such represents back ground noises, it is a good value to use for "base level" noise.

The first bar to pass 10% from right to left is 74, that is our LA10 Level as you can see it represents all of the louder noises that we might be subject o of the course of a day, it is quite useful for describing how annoying  noise might be.

So you can now see that a LA90 shows noises as a bit quieter than they might be. But both do not tell you how loud the loudest noises are, as you can see from the graph some noises might be 76dB but using LA90 and LA10 you would not know that.