llandarcy balancing services plant peak gen power 5 ltd · sound power level of between 12 and 20...

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Llandarcy Balancing Services Plant Peak Gen Power 5 Ltd

Noise Assessment 60580051 R4

March 18th 2019

Llandarcy Peak Gen Noise Assessment

60580051 R2 AECOM

Quality information

Prepared by Checked by Verified by Approved by

Mike Hewett MIOA

Regional Director

Chris Skinner

Regional Manager

Revision History

Revision Revision date Details Authorized Name Position

R2 27/9/18 Incorporating responses to feedback from NPT

R3 8/2/19 Incorporating further information requested by NPT

R4 18/3/19 Minor amendments requested by team

Distribution List

# Hard Copies PDF Required Association / Company Name


60580051 R2 AECOM

Prepared for:

Peak Gen Power 5 Limited Gables Lodge 62 Kenilworth Road Leamington Spa CV32 6JX

Prepared by:

AECOM Limited

1 New York Street

Manchester

M1 4HD

UK

T: +44 161 601 1700

aecom.com


60580051 R2 AECOM

Table of Contents

Executive Summary ................................................................................................................................................ 5

1. Introduction .................................................................................................................................................. 6

2. Criteria ......................................................................................................................................................... 6

3. Assessment ............................................................................................................................................... 10

3.1 Statement of qualifications ......................................................................................................................... 10

3.2 Description of the Project Site and sources to be assessed ...................................................................... 10

3.3 Subjective impressions of General Baseline Sound Environment ............................................................. 13

3.4 Context ...................................................................................................................................................... 13

3.5 Measurement locations .............................................................................................................................. 13

3.6 Sound measuring system .......................................................................................................................... 15

3.7 Operational Test ......................................................................................................................................... 15

3.8 Further Mitigation ....................................................................................................................................... 16

3.9 Weather conditions .................................................................................................................................... 16

3.10 Dates and times of measurements ............................................................................................................ 17

3.11 Measurement time intervals ....................................................................................................................... 17

3.12 Reference time intervals ............................................................................................................................ 17

3.13 Specific Sound level................................................................................................................................... 17

3.14 Background and Residual Sound Levels ................................................................................................... 19

3.15 Assessment of impact ................................................................................................................................ 20

3.16 The potential impact of uncertainty ............................................................................................................ 22

Appendix A Glossary of Acoustic Terms ................................................................................................................ 23

Appendix B References ........................................................................................................................................ 26

Figures

Figure 1. Project Layout ....................................................................................................................................... 10 Figure 2. Site and logger locations shown in relation to other land uses in the development masterplan. ........... 11 Figure 3. Aerial view of the Project Site and surroundings showing survey locations .......................................... 12 Figure 4. Current unit noise predictions ............................................................................................................... 17 Figure 5. Noise predictions for SCR modifications (as per Bracknell Units) ......................................................... 18

Figure 6. Noise predictions for SCR modifications and additional noise control measures (BPM) ....................... 18

Figure 7. The results of the unattended logger in 15 minute measurement periods ............................................. 20

Tables

Table 1. Impacts derived from BS 4142 assessment ............................................................................................. 8 Table 2. Measurement Locations ......................................................................................................................... 15 Table 3. Measurement Equipment ........................................................................................................................ 15 Table 4. Measured sound power levels ................................................................................................................ 16 Table 5. Representative background sound level (LA90) at the four measurement locations ................................ 19 Table 6. BS 4142:2014 Assessment with existing plant ...................................................................................... 20 Table 7. BS 4142:2014 Assessment with mitigated plant ..................................................................................... 20 Table 8. Sources of Uncertainty ........................................................................................................................... 22

Llandarcy Peak Gen Power 5 Limited

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Executive Summary

PeakGen Power 5 Limited are applying for planning permission for the Project to support the National Grid and

provide a range of contracted electricity generation services required at periods of peak electricity demand when

there is insufficient electricity generation available to National Grid from the UK’s baseload portfolio of electricity

generation plant at the Project Site.

The constructed Project was commissioned in 2015 (planning reference P2012/1061). Since the plant was

originally built the regulations governing its emissions have changed; the new Regulations come into effect in

January 2019. The Project will be modified by the proposed Internal Modifications and External Modifications to

comply with the Regulations.

The constructed Project consists of ten x 2 MW generating units, each with its own exhaust flue, control room,

switch room, storage locker and associated switchgear to Western Power Distribution’s 33 kilovolt (KV)

substation.

The proposed External Modifications will provide improved noise management to ensure that the Project meets

the revised noise standards and receptor locations agreed with Neath Port Talbot County Borough Council.

This document is a Noise Assessment for the Project based upon national and international legislation and

standards including The Welsh Government Technical Advice Note 11 and British Standards BS 4142:2014 and

BS 8233:2014.

Information was provided to AECOM by PeakGen Power 5 Limited including reports on previous noise surveys

conducted at the Project Site and information on the Project Site and another, similar, installation was used as

the basis for the assessment.

The surveys involved measurement of the existing background and ambient sound levels at noise sensitive

receptors identified around the Project Site and measurement of the sound levels emitted by the existing and

modified units.

The Project Site is surrounded by a large masterplan development which will eventually result in noise sensitive

receptors being constructed closer to the Project Site than those currently present. Both the existing and future

receptor locations have been considered of equal significance. The masterplan development will also result in

an increase in background sound levels at the receptors due to the increase in road traffic and other activities.

Predictions of peaking plant sound levels at the receptor locations were made using the noise source

measurement results. These predictions identified potential high impacts and that further reductions would be

required. Information on additional noise reduction measures was subsequently obtained by PeakGen Power 5

Limited from noise control equipment suppliers. It is understood that the proposed reductions represent the best

that can be achieved without significant impact on the operation of the generators.

These reduction measures were then applied to the noise prediction model. It is considered that these combined

measures represent the application of Best Practicable Means (BPM) and Best Available Techniques (BAT) for

the plant.

The results of the prediction showed very low impacts at the existing receptors and low/medium impacts at night

at the future receptors. The balancing plant is not predicted to change the TAN 11 Noise Exposure

Categorisation of the proposed residential areas to the north and west, though this is a matter for consideration

by those applying for detailed planning permission for those sites. It was considered that, in the context of the

nature of operation of the plant, which will rarely occur during the quietest times of night, and the changes taking

place in the area around the Project Site, these impacts should be considered low.

It was therefore concluded that with the BPM/BAT mitigations in place, taking into consideration the particular

context of the operation of the Project Site and the nature of the surrounding area the impact of noise from the

peaking plant will be low or very low.


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1. Introduction

PeakGen Power 5 Limited are applying for planning permission for the Project to support the National Grid and

provide a range of contracted electricity generation services required at periods of peak electricity demand when

there is insufficient electricity generation available to National Grid from the UK’s baseload portfolio of electricity

generation plant at the Project Site.

The constructed Project was commissioned in 2015 (planning reference P2012/1061). Since 2015, the new

Regulations have been published1 and come into effect in January 2019. The Project will be modified by the

proposed Internal Modifications and External Modifications to comply with the Regulations.

The constructed Project consists of ten x 2MW generating units, each with its own exhaust flue, control room,


substation.

The proposed External Modifications will provide improved noise management to ensure that the Project meets

the revised noise standards and receptor locations agreed with Neath Port Talbot County Borough Council

This document is a Noise Assessment for the Project based upon national and international legislation and

standards including The Welsh Government Technical Advice Note 11, British Standards BS 4142:2014 and BS

8233:2014.

Information was provided to AECOM by PeakGen Power 5 Limited including reports on previous noise surveys

conducted at the Project Site and information on the Project Site and another, similar, installation was used as

the basis for the assessment.

The surveys involved measurement of the existing background and ambient sound levels at noise sensitive

receptors identified around the Project Site and measurement of the sound levels emitted by the existing and

modified units.

2. Criteria

There are various sources of legislative and standard guidance available in determining the appropriate criteria

for assessing the sound emissions from the Project.

The Environmental Protection Act 1990 (EPA) Part 3 (ref 1) states that noise (and vibration) emitted from

premises (including land) so as to be prejudicial to health or a nuisance constitutes a statutory nuisance.

Local Authorities are required to investigate any public complaints of noise and if they are satisfied that a

statutory nuisance exists, or is likely to occur or recur, they may serve a noise abatement notice. A notice is

served on the person responsible for the nuisance. It requires either simply the abatement of the nuisance or

works to abate the nuisance to be carried out, or it prohibits or restricts the activity. Contravention of a notice

without reasonable excuse is an offence. Right of appeal to the Magistrates Court exists within 21 days of the

service of a noise abatement notice.

In determining if a noise complaint amounts to a statutory nuisance the Local Authority can take account of

various guidance documents and existing case law; no statutory noise limits exist. Demonstrating the use of

‘Best Practicable Means’ (BPM) to minimise noise levels is considered to be an accepted defence against a noise

abatement notice.

The Noise Action Plan for Wales (ref 2) states in Section 1.1 as regards development:

“The challenge therefore is to take a balanced approach to managing noise which considers the needs

of individuals as well as the requirements of business and industry, so that our quality of life is not

reduced in other ways”.

Section 1.2 of the Noise Action Plan for Wales goes on to state:

“Almost everything that people do creates sound, and noise – unwanted sound – is to a certain extent

an inevitable by-product of life. Yet for the reasons described in more detail in the sections below, and

in the interests of a healthy, fair and prosperous society, it is important to have a legal and policy

framework in place that:

1 Environmental Permitting (England and Wales) (Amendment) Regulations SI 2018/110


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• Protects people and wildlife from unacceptable or harmful levels of noise intrusion; and

• Gives everyone access to tranquil places where they can find respite from man-made sights and

sounds.

In Wales, sustainable development means enhancing the economic, social and environmental

wellbeing of people and communities, achieving a better quality of life for our own and future

generations.

The Welsh Government’s vision of a sustainable Wales includes:

• Healthy, biologically diverse and productive ecosystems that are managed sustainably; and

• Communities that are safe, sustainable, and attractive places for people to live and work, where people

have access to services and enjoy good health.”

Guidance on the "need to consider noise when planning a new development, be it a noise generating or a noise-

sensitive" development is set out in Planning Policy Wales and Technical Advice Note 11 (TAN) as described

below:

Technical Advice Note TAN 11 – Noise (1997) (ref 3) is a Welsh Government document that provides guidance on

how the planning system can be used to minimise the adverse impact of noise without placing unreasonable

restrictions on development.

Some detailed guidance is provided on the assessment of noise from a variety of sources, but this guidance

generally refers to other documents for methods of assessment and criteria. This guidance has been taken into

consideration in this assessment.

For the assessment of industrial sound TAN 11 makes reference to BS 4142 (ref 4).

BS 4142:2014 ‘Methods for rating and assessing industrial and commercial sound’ can be used for assessing the

effect of noise of an industrial nature. The method compares the difference between ‘rating level’ of the industrial

sound, with the ‘background sound level’ at the receptor position. The standard uses the following definitions to

describe various aspects of the soundscape of the scenario being assessed:

Background sound level, LAF90,T dB - defined in the Standard as the ‘A-weighted sound pressure level that

is exceeded by the residual sound for 90% of a given time interval, T, measured using time weighting F and

quoted to the nearest whole number of decibels’.

Specific sound level, Ls = LAeq,Tr dB - the ‘sound source at the assessment location over a given reference

time interval, Tr,’.

Rating level, LAr,Tr – the ‘specific sound level plus any adjustment made for the characteristic features of the

sound’.

Ambient sound level, LAeq,T dB - defined in the standard as ‘the totally encompassing sound in a given

situation at a given time, usually composed of sound from many sources near and far when present. The

ambient sound comprises the residual sound and the specific sound.’

Residual sound level, Lr = LAeq,T - the ‘Ambient Sound remaining at the assessment location when the

Specific Sound source is suppressed to such a degree that it does not contribute to the Ambient Sound’.

When assessing a sound source such as the plant it is important to consider the context of the Project Site and

the nature of the existing noise sources in the area. However, it is also necessary to consider the risks of new

sources causing the ambient sound levels in the area to ‘creep’ up.

Whereas the previous version of BS 4142:1997 allowed for a single correction of +5 dB to be made to the

Specific Noise Level if one or more of the distinguishable, impulsive or irregular features were considered to be

present, BS 4142:2014 allows for corrections to be applied based upon the presence or expected presence of the

following:

Tonality: up to +6 dB penalty;

Impulsivity: up to +9 dB penalty (this can be summed with tonality penalty); and

Other sound characteristics (neither tonal nor impulsive but still distinctive): + 3 dB penalty.


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Once any adjustments have been made, the background sound level and the rating level are compared. The

standard states that:

“Typically, the greater the difference, the greater the magnitude of impact.

A difference of around +10 dB or more is likely to be an indication of a significant adverse impact,

depending upon the context.

A difference of around +5 dB is likely to be an indication of an adverse impact, depending upon the

context.

The lower the rating level is to the measured background sound level, the less likely it is that the

specific sound will have an adverse impact or a significant adverse impact. Where the rating level

does not exceed the background sound level, this is an indication of the specific sound source having a

low impact, depending upon the context.”

Importantly, as suggested above, BS 4142:2014 requires that the rating level of the noise source under

assessment be considered in the context of the environment when defining the overall significance of the impact.

Table 1 illustrates the adopted magnitude of impact scale used in this assessment based upon the difference

between rating level and background sound level, although it should be remembered that the context assessment

(including the absolute level of the sound under consideration) can vary the overall classification of effects.

Table 1. Impacts derived from BS 4142 assessment

BS 4142:204 rating level

– background sound

level (dB)

Magnitude of impact

+14 to ≥+15 High depending on context

+12 to +13 Medium/High depending on context

+9 to +11 Medium depending on context

+7 to +8 Low/Medium depending on context

+4 to +6 Low depending on context

+2 to +3 Very Low/Low

≤ 0 to +1 Very low

For reasons that are discussed in the following paragraphs the nature and context of the Project Site mean that

careful consideration of context will be vital in completing a robust and meaningful BS 4142 assessment of

operational noise impacts. These considerations are discussed in more detail in the following sections.

Areas within the masterplan to the north and west of the balancing plant are understood to have outline, but not

detailed, planning permission for residential development. TAN 11 includes advice on how noise should be

considered when any detailed planning applications for residential development are being determined.

Although TAN 11 specifically refers to BS 4142 for the assessment of the impact of industrial sound it also gives

advice on the impact of other sound sources on the development of land for residential purposes. The document

defines Noise Exposure Categories (NEC) based upon the level of exposure to various types of sound source.

The criteria for the four NEC are listed in Table 2

Table 2. TAN 11 Noise Exposure Categories

Noise Source Noise Exposure Category (NEC)

A B C D

road traffic 07:00-23:00

23:00-07:00

<55

<45

55-63

45-57

63-72

57-66

>72

>66

rail traffic 07:00-23:00

23:00-07:00

<55

<45

55-66

45-59

66-74

59-66

>74

>66


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Noise Source Noise Exposure Category (NEC)

A B C D

air traffic 07:00-23:00

23:00-07:00

<57

<48

57-66

48-57

66-72

57-66

>72

>66

mixed sources 07:00-23:00

23:00-07:00

<55

<45

55-63

45-57

63-72

57-66

>72

>66

Source: Planning Guidance (Wales) Technical Advice Note (Wales) 11 Noise October 1997 (ref 3)

For sites in each category noise should be considered when assessing a proposal for residential development as

follows:

A. Noise does not need to considered

B. Noise should be taken into account and, where appropriate, conditions imposed to ensure an adequate

level of protection

C. Permission should not normally be granted. But if there is no alternative, conditions should be imposed

to ensure commensurate level of protection

D. Permission should normally be refused

Therefore the potential impact of the sound from the balancing plant on the categorisation of the masterplan

areas should be considered. As should the benefits of potential noise controls built into the residential design as

a result of the NEC of each site due to other existing sound sources.

Alternative criteria for noise emissions from the site can be based on WHO Guidelines for Community Noise

(1999) and BS 8233:2014 Guidance on sound insulation and noise reduction for buildings’. (ref 7) The BS 8233

guideline indoor ambient sound level for a bedroom at night to promote undisturbed sleep is 30 dB LAeq,8hour (the

average level over the whole eight hour period). The standard states that “in general” it is desirable that this

level is not exceeded.


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3. Assessment

3.1 Statement of qualifications

The assessment was undertaken by Mike Hewett MIOA who holds a diploma in acoustics, is a corporate member

of the Institute of Acoustics and has more than 28 years’ experience of noise control engineering and undertaking

measurements and assessments to BS 4142 and BS 7445. The original report was prepared by Samuel

Ellwood, under the supervision of Mike Hewett. The revisions in version R3 of the report were written by Mike

Hewett.

At the request of the client reference is also made to background and ambient sound level data obtained as part

of a previous planning application for the Project Site undertaken by Ian Sharland Acoustics in 2011 (ref 5). This

work appears to have been undertaken by qualified personnel working to a procedure based on appropriate

standards.

3.2 Description of the Project Site and sources to be assessed

The Project Site is located on an area of 0.18 hectares within the administrative boundary of Neath Port Talbot

County Borough Council (NPTCBC) to the northeast of Swansea within the D’Arcy Business Park, Land rear of

Unit 6A.

The constructed Project consists of ten x 2MW generating units, each with its own exhaust flue, control room,


substation.

The generators themselves are the dominant sources of sound on the Project Site. In order to meet new

emissions regulations the plant will be modified by fitting Selective Catalytic Reduction equipment (SCR).

Figure 1 shows the layout of the generator compound at the Project Site. The figure shows the proposed layout

with the SCR equipment installed though the generator units themselves will not be moved.

Figure 1. Project Layout

The generator compound is constructed on hard standing and this area is currently surrounded by a mixture of

hardstanding, buildings, roads, grassland and gravel car parks. At the Project Site boundary there is a 3.5 m high

solid wooden fence.

The plant is surrounded by a large masterplan development on a former industrial site. As the masterplan

development develops there will be a larger proportion of the surrounding area made up of roads and buildings.

The masterplan includes several areas of commercial and residential buildings to the south, west and north of the

Project Site. The development is currently under construction with the nearest completed residences being to the

south west of the Project Site. However when complete there will be additional residences to the west and north.

The plant is shown in relation to the masterplan development in Figure 2 Proposed residential areas are shown

in pale yellow, proposed and existing commercial areas are shown in pink. The site is a blue rectangle. The

nearest existing Noise Sensitive Receptors (NSR) to the Project Site are the Holiday Inn Hotel 275 m to the south

east and homes on Fford Coed Darcy 365 m to the south west. In addition there are two houses on Pen-Y-Heol

120 m to the east, but at the time of the survey these appeared to be unoccupied. Homes are either planned or

currently in the early stages of construction 250 m to the west and 70 m to the north. As a result four NSR

locations were selected for the assessment. These are identified with yellow circles on Figure 2 and described in

section 3.14


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The construction details of the proposed housing to the north and west are not known. It is understood that at the

time of preparation of this assessment the two areas had been granted outline planning permission for residential

use as part of the masterplan but that detailed planning permission had not been granted. It is expected that any

applications for detailed planning permission will require the consideration of TAN 11 and the NEC of the plots in

question.

The ambient sound levels in the area are dominated by the M4 motorway and other road traffic. The ambient

levels measured during the survey (see section 3.14) would suggest that homes built on parts of the site close to

the roads and motorway will require acoustic enhancements to glazing and ventilation design to achieve

desirable internal levels. The design of the Holiday Inn hotel appears to feature openable windows on all

facades.

Figure 2. Site and logger locations shown in relation to other land uses in the development masterplan.


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The noise monitoring locations for the survey conducted as part of this assessment are shown in Figure 3 which

also shows the existing buildings and land uses between the site and measurement locations. The measurement

locations are described in detail in section 3.5.

Figure 3. Aerial view of the Project Site and surroundings showing survey locations

The generators themselves are housed within enclosures which have openings for ventilation of the engine

compartments and heat rejection radiators.

Sound power data for use in the noise prediction models was provided by potential suppliers and measurements

by AECOM on the existing units at the Project Site and another PeakGen Power Limited site at Bracknell. The

Bracknell units had already been fitted with SCR equipment. The sound power level data was provided for the

various significant source components in each generator set:

The engine exhaust discharge (one exhaust for each generator located directly above the enclosure);

Engine compartment casing breakout;

Engine compartment ventilation inlets and outlets; and

Engine radiator fans (located within enclosure container).

The assessment described sets out the predicted impacts and effects associated with operation of the Project in

isolation (the operational assessment scenario which would be long-term).

The following assumptions were made when undertaking the operational noise modelling and assessment:

N

site


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It is understood that the operation of the plant is to be driven by the dynamics of the energy market; as a

result the plant could run for shorter or longer periods, at any time of day. The plant would be expected to

operate during periods of peak demand for relatively short periods, typically a few hours at a time. However,

when in operation, it is assumed that the plant will operate continually at full load for periods longer than the

reference period in BS 4142:2014 (one hour during the day and 15 minutes at night).

The prediction methodologies were based on ISO 9613:2 (ref 6).

Corrections for tonality, impulsivity, and intermittency have not been applied, on the assumption that these

potential features will be designed out of the peaking plant during the detailed design phase of the

modifications by the selection of appropriate fans, louvres and silencers/attenuators. However, a +3 dB

correction has been applied to the specific sound levels predicted from the Project, on the basis that the

sound emissions may be distinctive above the residual acoustic environment.

3.3 Subjective impressions of General Baseline Sound Environment During the survey it was observed that the ambient and background sound had audible contributions from the

following sources:

The dominant sound source across the whole study area during both the day-time and night-time the M4

Motorway.

Smaller local roads were also audible. At night this was generally intermittent but during the day almost

constant

In the day-time construction work on the masterplan developments around the Project Site was audible

(care was taken to minimise the impact of this source on the measured levels.

The industrial units around the Project Site. During the day noise from work and radios inside these

building was audible.

3.4 Context

BS 4142 2014 places significant emphasis on giving consideration to the context of a site and its surroundings

when assessing the impact of industrial and commercial noise.

As shown in Figure 2 the Project Site is located in an area with a variety of current and proposed land uses.

There will be housing 250 m to the west and 70 m to the north in addition to the existing housing overlooking the

Project Site to the south west. However the Project Site is also close to areas of existing and proposed industrial

and commercial properties. The main access point to the masterplan development will be close to the Project

Site and as a result road traffic in the area can be expected to increase significantly as more of the masterplan is

completed. The Project Site is adjacent to a railway line although services only run intermittently. There is an M4

junction 250 m away from the Project Site with the M4 running adjacent to the plant as well as the commercial

and housing development. This is the dominant source of background noise.

When considering its impact it is also important to consider the context of the operation of the plant. While the

contracted commitment of the plant to provide power covers any time of the day or night, it is important to

consider the likelihood that such a requirement will actually occur at a time when background levels are very low.

It is possible that this might occur due to some form of extreme stress on the power grid but this is very unlikely to

be a regular occurrence. It is much more likely that operation will be required at times elevated system demand,

which generally occur during the morning rush hour and early evening periods. These periods also have highest

background sound levels and the sensitivity of the general population to noise is likely to be at its lowest.

The existing residual sound in some of the proposed residential areas around the balancing plant may result in a

TAN 11 noise exposure categorisation that will require noise to be taken into consideration when detailed

planning consent is being considered. Therefore the design of the housing will need take noise control into

consideration.

3.5 Measurement locations

The selected measurement locations are shown in Figure 2 and Figure 3 with four sample measurement

locations, one unattended logger location and the location of previous measurements by Ian Sharland Acoustics

(ISA). The measurement locations used were selected to be representative of the closest NSRs to the Project

Site they are listed in Table 3.


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As two of the receptor locations are not currently in existence and access to their approximate locations was not

possible, some of the NSRs are partially represented by more than one measurement location. So the

measurement location numbers should not be used as NSR identification numbers.


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Table 3. Measurement Locations

Measurement Location

Distance from Project Site (m)

Notes:

1 365 Overlooking the Project Site from an elevation of around 8 m with clear view of the exhausts over the Project Site boundary fence. Outside the nearest existing residential receptor to south west. No additional residential buildings are proposed closer to the Project Site in this direction as the intervening land is earmarked for commercial development. Due to the topography this commercial development is unlikely to offer any additional screening when complete.

2 50 Close to Project Site and of a similar distance from the motorway as proposed residences to the north.

3 200 In car park of St Modwen construction site in the approximate location of the proposed nearest residences to the west. Partially screened from both site and motorway by the existing industrial units. Opportunities to measure at this location were limited by the noise created by the ongoing construction activities.

4 270 At the existing Holiday Inn Express hotel. Similar distance from the motorway as the no longer occupied residences to the east of the Project Site.

Logger 30 At the eastern end of the Project Site, 5 m above the ground (1.5 m above the fence line). This location was at a similar distance from the motorway as the proposed nearest house to the plant in the masterplan area to the north, but wasmuch closer to the plant than that house would be.

Ian Sharland (2011)

70 To the north of the railway line at the approximate location of the proposed homes to the north of the Project Site

Representative background sound levels were established for both the day-time and night-time period at each

location. This was based upon review and statistical analysis of all 15-minute interval results throughout the

night-time periods surveyed.

3.6 Sound measuring system

Table 4. Measurement Equipment

Dates used Manufacturer and equipment Model Serial number Date of last traceable calibration

17-18/05/2018 Norsonic Sound Level Meter 140 1403909 23/01/2018

6 – 17/05/2018 Norsonic Sound Level Meter 116 19697 28/10/2016

Nor Calibrator 1251 34393 23/01/2018

GRAS Microphone 40AF 102590 29/07/2016

The Norsonic 116 was used for the long term unattended measurements and the Norsonic 140 for the attended

measurements at locations 1 to 4. The meters were mounted upon a tripod with the microphone at least 1.5

metres above ground. A windshield was fitted at all times. Details of on-going activities and typical noise sources

in the area were recorded during visits to the monitoring locations to set up and collect the measurement

equipment.

The sound level meters were calibrated before and after the measurements. No significant variation in the

calibration signal was noted.

The sound level meters have been traceably calibrated to national standards and copies of calibration certificates

are available on request.

3.7 Operational Test

Detailed sound source measurements were undertaken on one of the existing units at Llandarcy on July 17. The

purpose of the measurements was to determine the sound power radiated by the major source components on

each unit. The instrument used was the Norsonic 140 listed in Table 4.

The procedure was based upon the principles of ISO 3746 adapted to the specific conditions of each site. The

procedure involved measuring sound pressure close to each source and then correcting for measurement

surface area to give the sound power.


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On August 9 a similar set of measurement was undertaken on a unit at the PeakGen Power 5 Limited site in

Bracknell. This unit was the same model as those at Llandarcy but had already been fitted with the SCR

equipment proposed for the Project Site.

The results of the sound power measurements are summarised in Table 5.

Table 5. Measured sound power levels

Unit Source Sound Power Level

LWA (dB re 1 pW)

Llandarcy Unit 9t Exhaust 111

Llandarcy Unit 9t Radiator inlets 90

Llandarcy Unit 9t Radiator discharge 97

Llandarcy Unit 9t Canopy fans 97

Bracknell Unit 10 Exhaust 98

Bracknell Unit 10 Radiator inlets 89/92

Bracknell Unit 10 Radiator discharge 98/101

Bracknell Unit 10 Canopy fans 97

The radiator fans operate at variable speeds depending on the unit temperature. As a result the actual fan speed

at any given time will depend on ambient temperature. The tests at the Project Site were conducted during

operation on a day with moderate ambient conditions. At Bracknell two tests were conducted one with the fans at

full speed and one with the units operating normally in moderate ambient conditions.

The normal operation values were used in the noise prediction modelling.

3.8 Further Mitigation

One option for further noise reduction that was considered was an increase to the height of the site boundary

fence on the northern side of the compound. It is understood that an increase to the height of the compound

fence is not possible due to potential; effects on the cooling of the generators, dispersion of exhaust gases and

height restrictions imposed by Network Rail due to the proximity to the rail lines. This option has therefore been

determined to be impracticable.

Subsequent to the measurements at Bracknell and the resulting noise predictions (presented below) PeakGen

Power 5 Limited consulted suppliers and noise control companies to determine the possibilities for further

reductions in the sound emitted by the units. The best reductions that could be obtained were as follows:

Further reduction in exhaust sound power by fitting higher performance attenuator than that used for the

Bracknell units. Data was obtained from suppliers for the highest performance exhaust silencer that could

be fitted without an unacceptable impact on engine performance. Reduced sound power 83 dB LWA.

Reduction of radiator and canopy fan noise by replacement with more aerodynamic fan installations. These

will be non-standard units in a bespoken installation. In addition modifications to the compound to reduced

reflections of sound in the direction of the nearest receptors. A package of control measures covering these

areas has been prepared by a specialist noise control company who have predicted a total reduction in

sound power level of between 12 and 20 dB LWA, giving a reduced sound power for casing and fans

combined of 88 dB LWA.

It is therefore considered that the application of the additional mitigation measures listed above represents Best

Practicable Means (BPM) and Best Available Techniques (BAT) for noise control of the peaking plant.

3.9 Weather conditions

Observations regarding weather conditions were made whilst attending the Project Site.

Survey days were chosen as to have favourable weather conditions, being dry with no precipitation and low wind

speeds. At the start of each survey period, weather conditions were observed and noted.

Overall, the meteorological conditions were within the limits considered suitable by relevant standards for

collecting sound level measurements.


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3.10 Dates and times of measurements

The logger measured in 15 minute samples from the May 6 to the May 17. The attended noise surveys took

place during both the day-time and night-time, generally covering the hours between 22:30 and 12:00 on May 17

and May 18. These were measured in a mixture of 5-minute and 15-minute samples.

The results of the noise surveys are deemed consistent enough to give a sufficient representative background

and residual sound information in appropriate and favourable weather conditions and during representative site

operations.

3.11 Measurement time intervals

Measurements were made over 5 minute and 15 minute logging periods.

3.12 Reference time intervals

The sound produced by the generator sets will be constant during operation. Therefore the reference time

interval is not significant in terms of the assessment. However the assessment is based nominally on a reference

period of 15 minutes at night.

3.13 Specific Sound level

The predictions of specific sound were made using input sound power data listed in 3.7 and 3.8. Three scenarios

were modelled as follows:

1. Ten units in their existing form as tested on site.

2. Ten units with standard SCR equipment fitted similar to the units at Bracknell.

3. Ten units with the SCR fitted and additional noise reduction as described in 3.8.

The results are shown on the following figures in the form of noise contours and spot levels at the existing and

proposed receptors. The displayed levels are specific sound levels without any character correction added

Figure 4. Current unit noise predictions

LAeq


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Figure 5. Noise predictions for SCR modifications (as per Bracknell Units)

Figure 6. Noise predictions for SCR modifications and additional noise control measures (BPM/BAT)

LAeq

LAeq


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3.14 Background and Residual Sound Levels

Table 6 presents the representative background sound levels at the 5 measurement locations and that presented

in the Ian Sharland Acoustics Report. Three values are given for some of the locations one for the full daytime

period (07:00 to 23:00), one for the full night time period (23:00 to 07:00), and a third for the period at the end of

the night time period (05:30 to 07:00). This third value was included to illustrate the levels during the part of the

night when the peaking plant has a higher likelihood of operating than in the very quiet early parts of the night.

Table 6 also presents residual sound levels measured at the five locations

Table 6. Measured background and residual sound levels at the measurement locations

Location 1 2 3 4 Logger ISA

Day-time LAF90 42 42 40 53 44 -

05:30-07:00 LAF90 39 - - - 45 -

Night-time LAF90 36 37 33 50 43 40

Night-time LAeq 50 42 42 52 47 -

These levels were used to derive representative background sound levels for the four NSR locations as

summarised in Table 7 below.

Table 7. Representative background and residual sound levels at NSRs

NSR Based on data from measurement location(s)

Day-time background sound level LAF90

05:30-07:00 background sound level LAF90

Night-time background sound level LAF90

Night-time residual sound level LAeq

Homes on Fford Coed Darcy 1 42 39 36 50

Holiday Inn 4 53 53* 50 52

Proposed homes north Logger, ISA 44 45 43 47

Proposed homes west 3, 2 40 40* 33 42

* estimated from trends at other locations

The results of the logger measurements are shown in Figure 7.

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LAF,90


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Figure 7. The results of the unattended logger in 15 minute measurement periods

The large peak during the day on Jul 12 was due to an operation of the plant to meet a peak in electricity demand

with all ten units running at full load. As mentioned in Table 3 the location of the logger was closer to the plant

than the nearest house would be (though a similar distance from the motorway). So the sound level experienced

at the residential location during plant operation would be lower than the peak level on Figure 7. The smaller

peak on last day was due to operation of single unit for onsite acoustic tests.

The background and ambient levels in the area are likely to be changed by the completion of the masterplan

development particularly during the day and rush hour periods. The construction of new roads serving several

hundred homes and addition commercial premises will result in significant increases in traffic noise compared

with current site. The homes and commercial premises themselves are also likely to result in increased ambient

and background sound levels. These changes will be present every day.

3.15 Assessment of impact

Table 8 and Table 9 show the BS4142 assessment for the existing units (Scenario 1 above) and the mitigated

units (Scenario 3 above)

Table 8. BS 4142:2014 Assessment with existing plant

NSR Night time background sound level

(dB LAF90)

Specific sound level

(dB LAeq)

Rating level

(dB LAr)

Difference between rating level and background sound level

Impact (see Table 1)

Homes on Fford Coed Darcy 36 54 57 +21 High

Holiday Inn 50 53 56 +6 High

Proposed homes north 43 71 74 +31 High

Proposed homes west 33 59 62 +29 High

Table 9. BS 4142:2014 Assessment with mitigated plant

NSR Night time background sound level

(dB LAF90)

Specific sound level

(dB LAeq)

Rating level

(dB LAr)

Difference between rating level and background sound level

Effect (see Table 1)

Homes on Fford Coed Darcy 36 32 35 -1 Very low

Holiday Inn 50 32 35 -15 Very low

Proposed homes north 43 48 51 +8 Low/Medium*

Proposed homes west 33 38 41 +8 Low/Medium*

* Depending on context

Table 9 shows that the mitigated plant has a very low impact on the existing occupied receptors and a borderline

low/medium impact on the future receptors.

These assessments are based upon the representative background sound levels for the full night. As discussed

in section 3.4, operation during the quietest part of the night is possible but unlikely. The majority of occasions

upon which the plant will operate will occur in the day time or in the morning at the very end of the ‘night time’

period. The values in Table 6 show that the background sound levels during these periods are higher than for the

night. Therefore for the significant majority of periods when plant operation might occur the impacts will be lower.

It should also be considered that background sound levels are expected to increase when the masterplan

development is fully complete. In the context of these increased levels the impact of the mitigated plant would be

further reduced. The level of tranquillity currently present around the Project Site at certain times of day is

unlikely to be maintained when the masterplan is complete. The future operation of the peaking plant will be in

the context of that environment.

The guidelines in BS 8233 are based on sound levels inside buildings whereas the measured residual sound

levels and predicted specific sound levels apply outdoors. The indoor levels resulting from these outdoor levels

will depend upon the sound insulation performance of the building construction. This is usually calculated as a

worst case by assuming that windows facing the sound source will be partially open for ventilation purposes. The


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closest noise sensitive receptors to the peaking plant, the homes to the north and west, are yet to be constructed

so their exact locations and construction details are not known. The measured residual levels would suggest that

the design of the homes to the north of the site will need to incorporate measures to insulate them from the

existing road traffic noise. But it is not known whether this will involve ventilation systems that will avoid the need

for openable windows. For the purposes of this worst case assessment it has been assumed that ventilation will

be provided by openable windows resulting in an outside to inside sound reduction of between 10 and 15 dB LA.

The reduction achieved with windows closed would be much greater.

As stated in section 2, the BS 8233 guideline level is based on the ambient level of “steady” sound sources over

the full eight hour night time period. The peaking plant is extremely unlikely to operate for eight hours at night

time but it is possible as the plant will operate in accordance with the requirements of the grid.

Table 10 presents a worst case BS 8233 assessment based on the ambient levels inside bedrooms with open

windows in facades facing the peaking plant and peaking plant operation for a full eight hour night time period.

Levels when windows are closed, or in those rooms which do not face the peaking plant directly, will be lower.

The outdoor ambient levels were calculated by combining the measured residual sound levels with the predicted

specific sound levels for the mitigated scenario.

Table 10. BS 8233:2014 night time assessment with mitigated plant

NSR Residual sound level

(dB LAFeq,8hr)

Specific sound level of plant

(dB LAeq,8hr)

Outdoor ambient sound level*

(dB LAeq,8hr)

Increase in outdoor ambient level

(dB)

Estimated internal ambient sound level (with open windows)

(dB LAeq,8hr)

BS 8233

Homes on Fford Coed Darcy

50 32 50 0 35-40 Exceeds guideline but there is no contribution from peaking plant

Holiday Inn 52 32 52 0 37-42 Exceeds guideline but no contribution from peaking plant

Proposed homes north

47 48 51 4 36-41 Exceeds guideline with contribution from peaking plant with open windows. However this area is in TAN 11 NEC B due to motorway noise so detailed planning permission will require noise ingress to be considered and controlled. These controls will also have benefit for the balancing plant sound.will

Proposed homes west

42 38 44 2 29-34 Potentially exceeds guideline with minor contribution from peaking plant

* with peaking plant in operation for full eight hours

Table 10 shows that the estimated internal ambient levels with open windows at all four NSRs exceed the BS

8233 guideline of 30 dB LAeq,8hour. However, the primary reason for those exceedances is the existing residual

sound in the area.

At Fford Coed Darcy and The Holiday Inn the peaking plant is making no contribution to the ambient level, so the

exceedance of the guideline level would be the same regardless of whether the peaking plant is in operation or

not. The estimated indoor ambient sound level at these receptors due to the peaking plant alone would be 17 to

24 dB LAeq.

At the proposed homes to the west the peaking plant sound contribution results in an ambient level 2 dB LAeq

higher than the residual level. So the estimated exceedance of the guideline is 2 dB greater when the peaking

plant is in operation. The sound resulting from the peaking plant operation alone would not exceed the BS 8233

guideline.

At the proposed homes to the north the peaking plant sound contribution is greater than the residual sound and

results in an ambient level 4 dB LAeq higher than the residual level. So the estimated exceedance of the guideline

is 4 dB greater when the peaking plant is in operation. The sound resulting from the peaking plant operation

alone would exceed the BS 8233 guideline by between 6 and 11 dB LA. However the measured residual levels

indicate that the guideline level would be exceeded by the residual sources even when the peaking plant is not in

operation


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The results in Table 7 indicate that the night time TAN 11 NEC of the residential receptors to the north of the site

is NEC B due to noise from the M4 motorway. Therefore noise will need to be considered when the detailed

planning permission for this area is being determined. The design of the homes will therefore need to incorporate

means of controlling ingress of this noise such as systems that will allow the homes to be ventilated without the

use of open windows. These measures will also reduce the ingress of sound from the balancing plant

Table 10 shows that when the balancing plant predicted sound level is added to the existing residual sound level

the resulting ambient sound level would be 51 dB LAeq. This still falls within the parameters for NEC B for mixed

sources. So the TAN 11 categorisation of the area around the assessment location is unchanged by the

operation of the balancing plant.

It must be noted that the survey conducted for this environmental assessment was designed to provide data for

the assessment of the impact of the balancing plant on the nearest residences so the results do not provide

information to determine the NEC of the whole proposed residential area. The levels of motorway noise will vary

across the area as will the level of sound from the balancing plant. However the potential impact of the balancing

plant will be greatest at the assessed location.

The conclusion of the BS 8233 assessment is therefore similar to the BS 4142 assessment, with no effect at

Fford Coed Darcy and The Holiday Inn, a small increase in levels at the homes to the west and a slightly larger

increase at the homes to the north. These assessments only apply to bedrooms with open windows in facades

facing the peaking plant. The levels in rooms facing in other directions and when windows are closed will be

lower. It is estimated that if the homes to the north and west are constructed to provide sufficient sound

insulation to protect them from the existing residual sound levels then they will also be adequately protected from

the peaking plant sound.

It is important to consider the nature of the expected typical operation of the peaking plant. The BS 4142 and

BS 8233 assessment methods make no distinction between sources that operate every day and those which only

operate occasionally when demand requires. This will have an impact on how the sound effects people

particularly in the context that operation is most likely to occur during periods when other activities are at their

highest. It is understood that operation of the peaking plant is more likely during the winter when there is less

likelihood that residents will have their windows open.

Although it is not possible to say that the plant will never operate during a very quiet night time period at some

point it is clear that it is very unlikely that such an occurrence would be regular. Therefore frequent medium

effects, which might lead to community annoyance, are unlikely.

In light of these observations it is considered that the low/medium impact predicted by the BS 4142 and BS 8233

methods overestimate the actual impact that the operation of the mitigated peaking plant will have and the actual

impacts will be low.

3.16 The potential impact of uncertainty

Table 11. Sources of Uncertainty

Source Mitigation

Effects of wind due to wind generated noise

The survey was conducted during a period of low windspeeds

Possibility of unrepresentative activities affecting background sound

Study of Project Site prior to survey and drive-around inspection before and after survey indicated no major road or rail disruption in the area. The potential impacts of construction noise at some locations were reduced by selection of measurement periods. Undertaking continuous logged survey captures the underlying sound climate in the area.

Uncertainties in measurement procedure

Minimised by following standard procedure (BS 4142).


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Appendix A Glossary of Acoustic Terms

Many words have more specific meanings when used in acoustics than in every-day language.

Sound is used to describe the physical phenomenon of the transmission of energy through

gaseous or liquid media via rapid fluctuations in pressure.

Level used solely to describe values measured in decibels

Loudness is the human perception of the level of sound

noise has no strict definition and is often used interchangeably with sound however it is

usually taken to mean unwanted sound

index a value based on the mathematical processing of raw data

indicator a value used to indicate the likelihood of a particular response of effect

eg. L10,18hr is an index based on statistical processing of sound pressure data that is

used as an indicator for road traffic noise response.

weighted values modified to reflect sensitivities at particular frequencies.

attenuation amount by which sound or vibration is reduced when passing through a structure or

system

directivity the amount by which a source radiates more sound in one direction than another.

decibels

dB

The decibel is not a true measurement unit nor is it exclusive to acoustics.

The decibel is a logarithmic ratio of two values of a variable. Decibels are used because they can represent very wide ranges of ratios (from trillionths and billionths to billions and trillions) with a small range of decibel values. Decibels can be used to represent measured values by using a known reference value in the ratio. When using decibels to measure something it is therefore important to specify what variable is actually being measured and what reference level has been used. This is done by adding a reference value statement in the form “dB re x units”, where the units indicate the variable being measured and x is the reference value.

Decibels are used in acoustics because the human ear responds to sound in a logarithmic way and the quantities measured in acoustics vary over wide ranges. However, decibels are used in acoustics to measure several different things which it is important not to confuse with each other.

To avoid confusion there is a notation system that identifies what a decibel value is for. The notations take the form of an italic capital letter and some subscript characters. The capital identifies the general type of value and the subscripts give specific details of what is being represented.

Lxxx denotes a level (ie a value measured in dB by comparison with a reference value);

Dxxx denotes a difference between two levels; Rxxx denotes a rating (or index), which is measure of the generalised

acoustic performance of a material or construction based on a difference between two levels;

Cxxx denotes a correction (or constant)

Of these only those with L notations require a reference value statement. Those with D or R notations are effectively ratios of two measured values not one measured value and a reference value and those with C notations are not based on reference values at all. A reference value statement therefore has no meaning when describing D, R and C decibels.

Because decibels are logarithmic they have to be added, subtracted, multiplied, divided and averaged using different techniques from normal numbers.

Sound Pressure Level

Lp

obsolete – SPL

This is the basic measure of how much sound there is at a given location. It is a measure of the size of the pressure fluctuations in the air that we perceive as sound.

Sound Pressure Level is expressed in decibels with a reference level of 20 Pa (Lp

in dB re 20 Pa)

Sound Power Level

LW

obsolete – SWL

This is the total amount of sound produced by a source. It cannot be measured directly but it can be calculated from Sound Pressure Level measurements in known conditions. It can be used to predict the Sound Pressure Level at any point.

Sound Power Level is expressed in decibels with a reference level of 1 pW (LW in dB re 1 pW). In the US a reference of 100 fW is sometimes used


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Pitch, frequency

tonal sound broadband sound impulsive sound

frequency analysis

The sound we perceive can have different characteristics. These can range from low-pitched hums to high-pitched squeals and impulsive sounds.

In engineering acoustics the word frequency rather than pitch tends to be used when describing the characteristics of a sound. The unit of frequency is the Hertz (Hz), which is the number of pressure fluctuations per second.

Any sound can be defined by its frequency content. Some sounds comprise just one discrete frequency (tonal sounds). Others are distributed over wide frequency ranges (broad band sound). Impulsive sounds are made up short pulses of high frequency components. Sources often produce all of these types of sound at the same time.

There are different ways of analysing and displaying the frequency content of a sound:

Octave Band Analysis is the simplest method. The audible range of frequencies is divided into 10 bands.

Third-Octave Band Analysis more detailed with 30 bands Narrow Band Analysis 12

th Octave (120 bands), 24

th Octave (240),

Fast Fourier (FFT) Analysis a high resolution technique that can give extremely detailed information on frequency content

A-weighting

LA or LpA, LWA,

obsolete – dBA, dB(A)

similar – C-weighting

LC or LpC, LWC

The human ear does not sense all frequencies of sound equally. Our sensitivity is at a maximum at around 2 kHz and steadily decreases above and below. Below 20 Hz and above about 20 kHz we can’t hear at all.

Within its operating limits a precision measurement microphone measures all frequencies the same so the output it produces does not reflect what we would actually hear. The A-weighting is an electronic filter that matches the response of a sound level meter to that of the human ear. When A-weighted the Sound Pressure Level Lp becomes LpA (or LA) and the Sound Power Level LW becomes LWA.

It used to be common to identify that a level was A-weighted by writing dB(A) or dBA instead of dB. These terms are now obsolete and should not be used as they conflict with other, non-acoustic, uses of decibels

The response of the human ear varies depending on how loud the sound is. A-weighting matches the response of a sound level meter to human hearing at low levels (~ 40-90 dB). For higher levels there are other weightings the most common of which is the C-weighting.

Lp

LpA (or LA)

LAF, LAS

The instantaneous sound pressure level (Lp)

The A-weighted instantaneous sound pressure level (LpA or LA)

This is the root mean square size of the pressure fluctuations in the air. This level can fluctuate wildly even for seemingly steady sounds. To make sound level meters easier to read the values on the display are smoothed or damped out. This is effectively done by taking a rolling average of the previous 0.125 s (FAST time constant) or the previous 1 s (SLOW time constant).

The letters F or S are added to the subscripts in the notation to indicate when the FAST or SLOW time constant has been used. These are often omitted but it is good practice to include them.

Lmax

LAmax

LAFmax

Lmin , LFmin

The maximum instantaneous sound pressure level (Lmax),

The A-weighted maximum instantaneous sound pressure level (LAmax)

The A-weighted maximum instantaneous sound pressure level with a FAST time constant (LAFmax).

This is the highest instantaneous sound pressure level reached during a measurement period.

The opposite of the Lmax is the minimum instantaneous sound pressure level or Lmin etc.

It is good practice to include the letter which identifies the time constant used as this can make a significant difference to the value.


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LN,T

LAN,T LAFN,T

N = %age value, 0-100

T = measurement time

eg. LA90, LA10, LAF90, 5 min

The percentage exceedence sound pressure level (LN,T),

The A-weighted percentage exceedence sound pressure level (LAN,T), the A-weighted percentage exceedence sound pressure level with a FAST time constant (LAFN,T).

This is the sound pressure level exceeded for N% of time period T. eg. If an A-weighted level of x dB is exceeded for a total of 6 minutes within one hour, the level will have been above x dB for 10% of the measurement period. This is written as LA10,1hr = x dB.

LA0 (the level exceeded for 0 % of the time) is equivalent to the LAmax and LA100 (the level exceeded for 100 % of the time) is equivalent to the LAmin.

It is good practice to include the letter which identifies the time constant used as this can make a significant difference to the value.

Leq,T

LAeq,T

T = measurement time

eg. LAeq,5min

The equivalent continuous sound pressure level over period T (Leq,T),

The A-weighted equivalent continuous sound pressure level over period T (LAeq,T).

This is effectively the average sound pressure level over a given period. As the decibel is a logarithmic quantity the Leq is not a simple arithmetic mean value.

The Leq is calculated from the raw sound pressure data. It is not appropriate to include a reference to the FAST and SLOW time constants in the notation


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Appendix B References

1 Her Majesty’s Stationary Office (1990) Environmental Protection Act 1990.

2 Noise Action Plan for Wales 2013-2018. Welsh Government.

3 Planning Guidance (Wales) Technical Advice Note (Wales) 11 Noise, October 1997

4 British Standards Institute (2014) BS 4142 – Methods for rating and assessing industrial and commercial

sound.

5 Assessment of Noise from Proposed Generators at Llandarcy Business Park Ian Sharland Acoustics 18

October 2011

6 International Standards Organization (1996) ISO 9613-2 – Attenuation of Sound during Propagation

Outdoors, Part 2: General Method of Calculation.

7 British Standards Institute (2014) BS 8233 Guidance on sound insulation and noise reduction for buildings’


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