Land at Upnor Road, Upper Upnor, Medway

Esquire Developments Ltd

Land at Upnor Road, Upper Upnor, Medway

Odour Constraints Assessment

Wood Environment & Infrastructure Solutions UK Limited – June 2020

2 © Wood Environment & Infrastructure Solutions UK Limited

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Report for

Esquire Developments Ltd

Studio 3 The Old Laundry

Green Street Green Road

Longfield,

Kent

DA2 8EB

Main contributors

Lauren Buchanan

Emma Dunabin

Alun McIntyre (ret.)

Issued by

.................................................................................

Lauren Buchanan

Approved by

.................................................................................

Chris Haigh

Wood

Block 3, Level 2

Booths Park

Chelford Road

Knutsford WA16 8QZ

United Kingdom

Tel +44 (0)1565 652100

Doc Ref. 41635-WOOD-ZZ-XX-RP-OA-0003_A_C01.5

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Document revisions

No. Details Date

1 Draft Report October 2019

2 Draft Report v2 October 2019

3 Final Report November 2019

4 Final Report v3 November 2019

5 Final Report v4 June 2020


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Executive summary

Purpose of this report

Esquire Developments Ltd (Esquire) has commissioned Wood Environment & Infrastructure Solutions UK

Limited (Wood) to compile an odour dispersion model for Whitewall Creek Wastewater Treatment Works

(WwTW) in Kent, operated by Southern Water.

This report has been produced for the purpose of identifying the potential odour constraints regarding the

development of a proposed residential area on land adjacent to the WwTW.

The principal aim of the assessment is to investigate the spatial extent of potential odour impacts from the

WwTW and to evaluate how this may affect the proposed development.

Summary of conclusions

Initially, modelling was undertaken using the geometric mean of emission rates from Wood’s internal

database for each source at the WwTW. However, in order to provide a more accurate prediction of odour

emissions on-site odour sampling was carried out in September 2019.

Using the odour concentrations obtained during sampling, dispersion modelling was used to predict odour

concentrations in the Baseline scenario, representing the current site layout. Also, the inlet works/ detritor

were identified as the greatest source of odour emission at Whitewall Creek WwTW, so a Mitigated scenario,

whereby this source would be enclosed and the air extracted from within the enclosure and treated in an

Odour Control Unit (OCU), was explored.

The odour threshold of 3 ouE m-3 is predicted to be exceeded at the majority of modelled receptors in the

Baseline scenario, with the contour covering up to approximately 62 % of the potential development land.

This is significantly reduced in the Mitigated scenario to approximately 5 % of the Development Site.

A contour plot that shows the difference between the scenarios is presented in Figure i.


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Figure i Contour plot of odour concentrations for the Baseline and Mitigated scenarios


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Contents

1. Introduction 7

1.1 Background 7

1.2 Site description 7

1.3 Sources of information 9

1.4 Report structure 10

2. Assessment methodology 11

2.1 On-site Monitoring 11 Observations during the site survey 11 Sampling methodology 11

2.2 Dispersion Modelling 13 ADMS 5.2 13 Model Scenarios 13 Meteorology 18 Model domain and receptors 20 Terrain 22 Surface characteristics 22

3. Assessment criteria 25

3.1 Relevant legislation and guidance 25 Background 25 Specific criteria 27

3.2 Recent Planning Appeal and Legal Cases 28 Mogden Odour Case 28 Stanton Appeal 29 Cockermouth Appeal 29 Princes Risborough Appeal 29

3.3 Selection of an Appropriate Criterion 29

4. Assessment of impact 31

4.1 Modelling results 31

4.2 Odour contour 32 Potential Mitigation 35

5. Conclusions and recommendations 36

Table 1.1 Report structure 10 Table 2.1 Baseline emission rate and exhaust conditions 14 Table 2.2 Mitigated emission rate and exhaust conditions 16 Table 2.3 Human receptors included in the modelling 20


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Table 2.4 Typical Surface Roughness Lengths for Use in ADMS for Various Land Use Categories 23 Table 4.1 Calculated 98th percentile 1-hour mean odour concentrations at receptors 31

Figure i Contour plot of odour concentrations for the Baseline and Mitigated scenarios 4 Figure 1.1 Site location 8 Figure 2.1 Picture of odour sampling using Lindvall Hood 12 Figure 2.2 Picture of odour sampling using FEP tubing 12 Figure 2.3 Emission rate per source 14 Figure 2.4 Baseline emission sources 15 Figure 2.6 Wind roses from Gravesend 19 Figure 2.7 Map of human receptors close to the site 21 Figure 2.8 Terrain file visualisation 22 Figure 4.1 Contour plot of 98 percentile 1-hour mean odour concentrations – 3 ouE m-3 odour threshold 33 Figure 4.2 Contour plot of 98 percentile 1-hour mean odour concentrations – 1.5 ouE m-3 odour threshold 34

Appendix A Silsoe Odour report Appendix B Odour contours


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1. Introduction

1.1 Background

Esquire Developments Ltd (Esquire) has commissioned Wood Environment & Infrastructure Solutions UK

Limited (Wood) to compile an odour dispersion model for Whitewall Creek Wastewater Treatment Works

(WwTW) in Kent, operated by Southern Water. The WwTW is located adjacent to the land at Upnor Road,

which Esquire is considering for a new residential development. The model will be used to assess the odour

impacts from the WwTW on the potential development land and to evaluate to what extent development of

the land is constrained by these odours.

Initially, an assessment1 was carried out using data collated from Wood’s internal database of emissions,

comprising on-site survey measurements from other, similar WwTW sites. It was predicted that at 23 – 45%

of the potential development area, the 1.5 ouE m-3 odour threshold would be exceeded. Due to this

uncertainty, it was recommended that odour sampling should be carried out at Whitewall Creek WwTW to

more accurately predict the odour emission from the site1.

Detailed dispersion modelling has been used to quantify emissions from the WwTW and the resultant

ambient concentrations across the potential development land, assessed against the relevant odour criteria.

Additionally, dispersion modelling was used to predict the potential reduction in off-site odour with the

implementation of possible mitigation measures.

1.2 Site description

The potential development site is located off Upnor Road, Upper Upnor, Medway. The WwTW is located

immediately adjacent to the south-west corner of the development land. Figure 1.1 shows the location of the

development land and the WwTW.

1 Wood (2019) Land off Upnor Road – Odour Constraints Assessment – Draft issued.


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Figure 1.1 Site location


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1.3 Sources of information

The information used in the assessment comprises:

⚫ Ordnance Survey (OS) maps of the local area;

⚫ Terrain (topographical) data from OS Landform PANORAMA data; and

⚫ Meteorological data supplied by Atmospheric Dispersion Modelling Ltd.


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1.4 Report structure

The remainder of the report contents is set out as contained in Table 1.1 below.

Table 1.1 Report structure

Section Aims and objectives

Section 2 Describes the dispersion model, assessment methodology, model inputs and

assumptions used in the assessment

Section 3 Details the assessment criteria

Section 4 Presents an assessment of the potential odour impacts arising from stack emissions

Section 5 Contains a summary and conclusions of the assessment


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2. Assessment methodology

2.1 On-site Monitoring

Odour complaints history

A Freedom of Information Request was issued to Medway Council on Tuesday 19th November 2019 to

ascertain whether any complaints had been received regarding odour from the Whitewall Creek WwTW.

A response was received on 28th November 2019 confirming that no complaints had been received in the

past five years.

Observations during the site survey

On-site monitoring was carried out by Silsoe Odours on Monday 9th September 2019 accompanied by one

Wood employee. Weather conditions during the sampling were relatively stable at approximately 11 °C with

no wind.

It was noted that there was a small hole in the pipework at the back of the sludge tank odour control unit

(OCU) which was allowing untreated air to escape. This assessment has been carried out on the assumption

that the pipework will be repaired.

Sampling methodology

All odour samples were taken using the rigid lung method. This method involves placing an inert sampling

bag within an airtight container and connecting the sample bag to the sampled location by FEP sampling

tubing. The air is evacuated from the rigid lung which draws an equivalent and uncontaminated air sample

into sampling bag.

Samples from area sources including open tanks and aeration surfaces were taken using a Lindvall sampling

hood. The sampling line is attached to a floating Lindvall Hood. The sampling hood is placed on the water

surface and ventilated with activated carbon filtered odour free air during sampling. The air passes through

the hood, picking up any odour emitted from the liquid surface, with a sample being collected at the outlet

using the rigid lung method. A photograph of the sampling method using a Lindvall Hood at the site is

presented in Figure 2.1. It represents the first stage of the method which consists of cleaning the air (purge)

of the FEP tube before connecting it to the sample bag. After the initial purge time, a sample bag is fitted

within the container and attached to the tubing from the hood. Odorous air is drawn into the bag by the

vacuum generated in the barrel using a portable pump, causing the inert bag to inflate ensuring no

contamination of the odour samples occurs.

Samples from point sources such as stacks, were taken by connecting FEP tubing directly to a sampling port

of the stack itself (Figure 2.2).

The odour emission rate for buildings without extraction was calculated based on the odour concentration

measured within the building and the air flows estimated as one air change per hour. Tanks containing

sludge significantly below their rims were assessed by obtaining samples just below the level of the rim and

measuring the average airflow across it during the test. The emission rate is essentially assessed at the mixing

layer occurring at the top of the tank.

Samples taken were analysed by the UKAS accredited Silsoe Odours Ltd. in accordance with BS EN

13725:2003. Where duplicate samples have been obtained, the figures have been averaged using the


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geometric mean. The olfactometry analysis certificate covering all the samples taken on site is provided in

Appendix A.

Figure 2.1 Picture of odour sampling using Lindvall Hood

Figure 2.2 Picture of odour sampling using FEP tubing


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2.2 Dispersion Modelling

ADMS 5.2

The model used in this assessment is the ADMS 5.2 atmospheric dispersion model developed and validated

by Cambridge Environmental Research Consultants (CERC). The model was used to predict the ground level

concentration of odorous compounds emitted to atmosphere from the installation. The model has been used

extensively throughout the UK for regulatory compliance purposes and is accepted as an appropriate air

quality modelling tool by the Environment Agency and local authorities.

ADMS 5 parameterises stability and turbulence in the atmospheric boundary layer by the Monin-Obukhov

length and the boundary layer depth. This approach allows the vertical structure of the boundary layer to be

more accurately defined than by the stability classification methods of earlier dispersion models. In ADMS,

the concentration distribution follows a symmetrical Gaussian profile in the vertical and crosswind directions

in neutral and stable conditions. However, the vertical profile in convective conditions follows a skewed

Gaussian distribution to take account of the inhomogeneous nature of the vertical velocity distribution in the

Convective Boundary Layer.

A number of complex modules, including the effects of plume rise, complex terrain, coastlines, concentration

fluctuations, radioactive decay and buildings effects, are also included in the model, as well as the facility to

calculate long-term averages of hourly mean concentration, dry and wet deposition fluxes, and percentile

concentrations, from either statistical meteorological data or hourly average data.

A range of input parameters is required including, among others, physical data describing the local area,

meteorological measurements and emissions data. The data used in modelling the emissions are given in the

following sections of this chapter.

Model Scenarios

The following model scenarios were included in this assessment:

⚫ Baseline scenario – based on the odour concentrations monitored during the on-site survey

undertaken by Silsoe representing the current odour emission from the WwTW; and

⚫ Mitigated scenario – based on the odour concentrations monitored during the on-site survey,

however represents a mitigation scenario whereby the inlet/ detritor are covered and odour

emissions from this source are expelled through a second odour control unit.

Baseline scenario

The emission rates from the sources sampled during the on-site survey are outlined in Table 2.1 and shown

in Figure 2.4. The location of the sampled sources are shown in Figure 2.3. it can clearly be seen that the inlet

works/ detritor are the largest source of odour at Whitwall Creek WwTW.


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Table 2.1 Baseline emission rate and exhaust conditions

Parameter Inlet works/

Detritor

Primary

Settlement

Tanks (PST)

1 - 3

Humus Tanks

1 – 4

High Rate

Filters 1 - 4

OCU 1*

Type of source Area Area Area Area Point

Height of source (m) 2 2 Ground level/

new tank 6 m

7 6

Exit velocity (m/s) 0.01 0.01 0.01 0.01 15

Temperature (°C) Ambient Ambient Ambient Ambient Ambient

Emission rate (Area source -

ouE/m2/s / Point source –

ouE/s)

135.7 2.64 0.31 0.82 - 0.88 1230

Note the emission rate is based on a geometric mean for each duplicate sample.

*Diameter = 0.26 m – calculated using the flow rate and a design outlet concentration of 1500 ouE m-3.

Figure 2.3 Emission rate per source

0

2000

4000

6000

8000

10000

12000

14000

16000

Inlet/ Detritor PST Humus Tanks High Rate Filters OCU 1

Emission rate (ouE s-1)


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Figure 2.4 Baseline emission sources


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Mitigated scenario

As the inlet works/ detritor were found to be the greatest source of odour from the WwTW, a mitigated

scenario whereby this source is covered and emissions are released to air through a second OCU has been

modelled. This could potentially reduce the total odour emission by 12,301 ouE s-1. The emission rates from

the sources sampled during the on-site survey are outlined in Table 2.2 and shown in Figure 2.5.

Table 2.2 Mitigated emission rate and exhaust conditions

Parameter Inlet works/

Detritor

Primary

Settlement

Tanks (PST)

1 - 3

Humus Tanks

1 - 4

High Rate

Filters 1 - 4

OCU 1* OCU 2**

Type of source Area Area Area Area Point Point

Height of source (m) - 2 Ground level/

new tank 6 m

7 6 5

Exit velocity (m/s) - 0.01 0.01 0.01 15 15

Temperature (°C) - Ambient Ambient Ambient Ambient Ambient

Emission rate (Area source -

ouE/m2/s / Point source –

ouE/s)

- 2.64 0.31 0.82 - 0.88 1230 2083

Note the emission rate is based on a geometric mean for each duplicate sample.

*Diameter = 0.26 m – calculated using the flow rate and a design outlet concentration of 1500 ouE m-3.

** Diameter = 0.34 m – calculated using the flow rate and a design outlet concentration of 1500 ouE m-3.


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Figure 2.5 Mitigated emission sources


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Meteorology

For meteorological data to be suitable for dispersion modelling purposes, a number of meteorological

parameters need to be measured on an hourly basis. These parameters include wind speed, wind direction,

cloud cover, relative humidity and temperature. There are only a limited number of sites where the required

meteorological measurements are made. The year of meteorological data that is used for a modelling

assessment can also have a significant effect on ground level concentrations.

This assessment has used meteorological data recorded at Gravesend meteorological station between 2013

and 2017. The meteorological station is located approximately 15 km north-west of the proposed

development site at Upnor and is the nearest synoptic station to the site offering data in a suitable format for

the model.

Figure 2.2 shows the wind roses for each year modelled, illustrating the frequencies of occurrence of

monitored wind direction and wind speed.


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Figure 2.6 Wind roses from Gravesend

2013

2014

2015

2016

2017

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Model domain and receptors

Model domain

A 2 km x 2 km Cartesian grid, centred on the emission sources, and with a receptor resolution of 20 m, was

modelled to assess the impact of emissions on local air quality. This resolution is considered suitable for

capturing the maximum process contribution from site emissions given that the proposed development site

is located adjacent to the WwTW. This modelled grid was used for the purpose of producing concentration

isopleths (contours) and identification of ground level concentrations at receptors which cover a relatively

large spatial area in close proximity to the site.

Receptors

The cartesian grid described above is most useful in this assessment for creating a contour plot of odour

emissions from the WwTW. However, discrete receptors have also been considered in the assessment, these

are intended to show:

⚫ The potential odour impacts at existing residential receptors around the site (R1 – R3); and

⚫ The decrease in odour impacts with increasing distance from the source (R4 – R10). These have

been placed in a transect-type arrangement starting at the source (WwTW) and going across

the development site.

The receptors used in the assessment are detailed in Table 2.3 and Figure 2.7 below.

Table 2.3 Human receptors included in the modelling

Receptor ID Receptor description X Y Z

R1 Residential property 574982 170289 1.6



R4 Transect - WwTW 575128 170226 1.6

R5 Transect - development site 575165 170293 1.6







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Figure 2.7 Map of human receptors close to the site


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Terrain

The ground level concentrations of pollutants arising from emissions in areas of complex terrain differ from

those found in simple, level terrain due to a number of topographical-induced effects on the three-

dimensional flow and turbulent fields over the terrain. These effects are most pronounced when terrain

gradients exceed 1 in 10. The terrain in the model domain approaches or exceeds this criterion and,

consequently, digitally mapped terrain data has been included in the model set up. A visualisation of the

terrain file used is presented in Figure 2.8.

Figure 2.8 Terrain file visualisation

Note: red dot represents the site location. Z-axis is exaggerated.

Surface characteristics

The predominant surface characteristics and land use in a model domain have an important influence in

determining turbulent fluxes and, hence, the stability of the boundary layer and atmospheric dispersion.

Factors pertinent to this determination are detailed below.

Surface Roughness

Roughness length, z0, represents the aerodynamic effects of surface friction and is defined as the height at

which the extrapolated surface layer wind profile tends to zero. This value is an important parameter used by

meteorological pre-processors to interpret the vertical profile of wind speed and estimate friction velocities

which are, in turn, used to define heat and momentum fluxes and, consequently, the degree of turbulent

mixing in the boundary layer.

The surface roughness length is related to the height of surface elements; typically, the surface roughness

length is approximately 10% of the height of the main surface features. Thus, it follows that surface

roughness is higher in urban and congested areas than in rural and open areas. CERC (2014)2 suggest typical

roughness lengths for use in ADMS for various land use categories (Table 2.4).

2 CERC, 2014. ‘The Met Input Module’. ADMS Technical Specification.


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Table 2.4 Typical Surface Roughness Lengths for Use in ADMS for Various Land Use Categories

Type of Surface z0 (m)

Sea <0.0101

Short grass <0.015

Open grassland 0.02

Root crops 0.1

Agricultural areas (min) 0.2

Agricultural areas (max) 0.3

Parkland, open suburbia 0.5

Cities, woodlands 1.0

Large urban areas 1.5

Increasing surface roughness increases turbulent mixing in the lower boundary layer. With respect to

elevated sources under neutral and stable conditions, conflicting impacts in terms of ground level

concentrations often occur due to:

⚫ The increased mixing can bring portions of an elevated plume down towards ground level,

resulting in increased ground level concentrations closer to the emission source; however; and

⚫ The increased mixing increases entrainment of ambient air into the plume and dilutes plume

concentrations, resulting in reduced ground level concentrations further downwind from an

emission source.

The overall impact on ground level concentration therefore depends on the distance of a receptor from the

emission source.

Surface energy budget

One of the key factors governing the generation of convective turbulence is the magnitude of the surface

sensible heat flux. This, in turn, is a factor of the incoming solar radiation. However, not all solar radiation

arriving at the Earth’s surface is available to be emitted back to atmosphere in the form of sensible heat. By

adopting a surface energy budget approach, it can be identified that, for fixed values of incoming short and

long wave solar radiation, the surface sensible heat flux is inversely proportional to the surface albedo and

latent heat flux.

The surface albedo is a measure of the fraction of incoming short-wave solar radiation reflected by the

Earth’s surface. This parameter is dependent upon surface characteristics and varies throughout the year.

Oke (1987) recommends average surface albedo values of 0.6 for snow covered ground and 0.23 for non-

snow covered ground, respectively.

The latent heat flux is dependent upon the amount of moisture present at the surface. The modified Priestly-

Taylor parameter can be used to represent the amount of moisture available for evaporation. Areas where

moisture availability is greater will experience a greater proportion of incoming solar radiation released back

to atmosphere in the form of latent heat, leaving less available in the form of sensible heat and, thus,


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decreasing convective turbulence. Holstag and van Ulden (1983)3 suggest modified Priestly-Taylor values of

0.45 and 1.0 for dry grassland and moist grassland respectively.

Selection of appropriate surface characteristic parameters for this assessment

A detailed analysis of the effects of surface characteristics on ground level concentrations by Auld et al.

(2002)4 led them to conclude that, with respect to uncertainty in model predictions:

“…the energy budget calculations had relatively little impact on the overall uncertainty”

In this regard, it is not considered necessary to vary the surface energy budget parameters spatially or,

temporally, and annual averaged values have been adopted throughout the model domain for this

assessment.

As snow covered ground is only likely to be present for a small fraction of the year, the surface albedo of 0.23

for non-snow covered ground advocated by Oke (1987) has been used, whilst the model default modified

Priestley-Taylor parameter value of 1.0 has also been retained.

The assessment has adopted a surface roughness length of 0.5 m, based on the land use around the site at

being a mixture of open land and forested areas.

3 van Ulden, A.P. and Holstag, A.A.M., 1983. ‘The Stability of the Atmospheric Surface Layer during Nighttime’. American

Met. Soc., 6th Symposium on Turbulence and Diffusion.

4 Auld, V., Hill, R. and Taylor, T.J., 2002. ‘Uncertainty in Deriving Dispersion Parameters from Meteorological Data’.

Atmospheric Dispersion Modelling Liaison Committee (ADMLC). Annual Report 2002-2003.


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3. Assessment criteria

3.1 Relevant legislation and guidance

Background

Since a landmark public inquiry into Newbiggin-by-the-Sea WwTW in 1993, an ambient odour annoyance

standard of 5 ou/m3, expressed as a 98th percentile of hourly average modelled values at a particular location

over a calendar year5, has been used both by the UK water industry and odour assessment practitioners in

the UK as an assessment criterion. At that time, the protocol used for the determination of odour was a

Dutch standard that used a particular concentration of an odorous chemical in air to screen panellists for

sensitivity. With the advent of the European standard on olfactometry6, a concentration half that of the

original Dutch standard is now used. What this means is that the original 5 ou/m3 is equivalent to 2.5 ouE/m3.

In 2002, the Environment Agency (EA) published a draft copy of its Horizontal Guidance Document H44 and,

in 2011, a final version. This includes a graduated scale of “indicative odour thresholds”, depending upon the

perceived offensiveness of the odour, as follows:

⚫ 1.5 ouE/m3 (98th percentile) for the most offensive odours;

⚫ 3 ouE/m3 (98th percentile) for less offensive odours; and

⚫ 6 ouE/m3 (98th percentile) for the least offensive odours.

These were derived from studies in Holland on the offensiveness of odours from intensive pig farming in

rural areas. It is generally considered that sewage treatment works odours fall into the middle category (3

ouE/m3), unless there are septic wastewater or sludges on the site, in which case the most stringent criterion

would apply.

These thresholds were designed to be applied to those industrial processes regulated by the EA and local

authorities under the Environmental Permitting Regulations (EPR) (formerly PPC Regulations) and it was not

clear, initially, how or whether these would apply to the water industry. In the event, this has now been

clarified to a certain extent and there are a number of WwTW sites across the UK that are permitted and

regulated by the EA, although this normally covers only those operations relating to sludge treatment and

import of wastes. In the case of Whitewall Creek WwTW, the site is not permitted under the EPR to accept

and treat sludges and liquids that are classified as hazardous waste and, therefore, there is minimal sludge

treatment and processing on the site.

Whether a particular odour will cause an annoyance reaction from individuals in their normal everyday

environment is determined by a number of different but interacting factors, including:

⚫ The concentration of the odour in the atmosphere;

⚫ The nature of the odour (how objectionable it is perceived to be); and

⚫ How frequently it occurs and for how long.

5 This equates to experiencing odours above 5 ouE/m3 (regarded as a faint odour) for only 2% of the hours in a year –

approximately 175 hours. For the remainder of the time, the odour experienced would be less than faint. This reflects the

fact that it is not possible to guarantee that sewage treatment will never produce any odours but it is intended to restrict

the number of times that odours could be noticed to a not unreasonable frequency.

6 BS EN 13725:2003. Air quality. Determination of odour concentration by dynamic olfactometry.


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Odour concentration is expressed as European odour units per cubic metre at standard conditions for

olfactometry (ouE m-3) as compared to a European reference concentration of a known standard odorant in

air (n-butanol). The odour concentration, in simple terms, is the number of times an odorous sample of air

has to be diluted with odour free air to reach its odour threshold. Exposure is usually quantified in terms of a

frequency of occurrence over a year of hourly average concentrations above a certain odour concentration.

Odours are not generally additive in the same way as other parameters such as decibels for noise. This

reflects the way in which the brain responds to odour. The human brain has a tendency to ‘screen out’ those

odours which are always present or those that are in context to their surroundings. For example, an

individual is more likely to be tolerant of an odour from a factory in an industrial area than in the countryside.

The human brain will also develop a form of acceptance to a constant background of local odours.

With regard to the concentrations of odour in the atmosphere that can be detected and recognised by the

human olfactory system, and the levels which would cause annoyance or give rise to complaint, there are

clearly a number of factors involved. These factors are commonly associated with the FIDOL acronym:

⚫ Frequency - the number of exposures to an odour within a given time frame;

⚫ Intensity as perceived - the magnitude of the perception of the odour;

⚫ Duration - the time period during which the odour exposure occurs;

⚫ Offensiveness - this is a qualitative judgement to describe the odour; and

⚫ Location – the type of receptor will determine its sensitivity to odour, e.g. residential properties

are likely to be associated with greater sensitivity than industrial locations.

Specific guidance for assessing odour effects for installations subject to the provisions contained within the

H4 Odour Management Guidance provided by the Environment Agency7.

An olfactory response to an odorant will typically occur due to transient peaks or fluctuations in

concentrations over very short periods of time, typically in the order of 1 minute or less. However, the

Environment Agency’s Odour Guidance provides odour benchmarks based on achievement of a 1 hour mean

concentration, not to be exceeded for more than 2% of a year (i.e. a 98th percentile 1-hour mean value).

These odour benchmarks can be considered to represent a criterion for no reasonable cause for annoyance,

rather than a benchmark representative of detection.

Odour generating processes are grouped into three categories dependent upon their perceived

offensiveness:

⚫ Highly offensive - processes involving animal or fish remains, brickworks, creamery, fat and

grease processing, wastewater treatment, oil refining, livestock feed factory;

⚫ Moderately offensive - intensive livestock rearing, fat frying (food processing), sugar beet

processing, these are odours which do not obviously fall within the HIGH or LOW categories;

and

⚫ Less offensive - chocolate manufacture, brewery, confectionery, fragrance and flavourings,

coffee roasting, bakery.

7https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/296737/geho0411bt

qm-e-e.pdf


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Specific criteria

CIWEM Policy Position Statement

The Chartered Institution of Water and Environmental Management (CIWEM) published in February 2011 a

Position Policy Statement (PPS)8 on Control of Odour from sewage treatment works, compiled by its Air

Quality Expert Panel. CIWEM’s position on odour impact criteria is summarised in the document as follows:

“CIWEM considers that the following framework is the most reliable that can be defined on the basis of the

limited research undertaken in the UK at the time of writing:

⚫ C98, 1-hour >10 ouE/m3 - complaints are highly likely and odour exposure at these levels

represents an actionable nuisance;

⚫ C98, 1-hour >5 ouE/m3 - complaints may occur and depending on the sensitivity of the locality and

nature of the odour this level may constitute a nuisance; and

⚫ C98, 1-hour <3 ouE/m3 - complaints are unlikely to occur and exposures below this level are

unlikely to constitute significant pollution or significant detriment to amenity unless the locality is

highly sensitive or the odour highly unpleasant in nature.”

On this basis, it is considered that an appropriate odour criterion threshold for STW odours should be 3 ouE

m-3, as a 98th percentile of hourly average odour concentrations over a calendar year.

IAQM Guidance

The Institute of Air Quality Management (IAQM) have produced guidance9 for assessing odour impacts for

planning purposes. It devotes an entire chapter to odour assessment criteria and recommends the following

scheme in Table 3.1 below (reproduced from table 6 of the guidance document).

Table 3.1 Odour impact descriptors

8 http://www.ciwem.org/knowledge-networks/panels/air/control-of-odour.aspx

9 Institute of Air Quality Management (2018) Guidance on the Assessment of Odour for Planning v1.1.


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This is generally consistent with emerging professional practice in the UK over the last 20 years and criteria

developed by regulatory agencies in Europe.

The receptor sensitivity ratings are included in Table 3.2 below (reproduced from Table 2 of the guidance

document).

Table 3.2 Receptor sensitivity to odours

3.2 Recent Planning Appeal and Legal Cases

Additional support for the use of this particular concentration metric can be found in other documents; a

High Court Judgement relating to odour nuisance at Mogden STW in West London10 and recent Inspectors’

reports and decisions from Public Inquiries into residential developments near to STW sites at Stanton near

Bury St. Edmunds11, Cockermouth in Cumbria12 and Princes Risborough in Buckinghamshire13.

Mogden Odour Case

In the Mogden case, the Judge concluded at paragraph 992 of his Judgement:

“I have to consider whether the odour which has been caused by particular odours has amounted to a nuisance

in law and, if so, to assess damages for that nuisance. It is clear that odour concentrations below 1.5 ouE per m3

would not be considered to be a nuisance but I must bear in mind the fact that, on the basis of my findings,

there are a number of processes at Mogden STW which Thames Water carry out and which do not give rise to

Allen negligence but clearly give rise to odour emissions. It is therefore the additional odour nuisance caused by

10 http://www.bailii.org/ew/cases/EWHC/TCC/2011/3253.html

11 Planning Inspectorate: Appeal Decision Ref: APP/E3525/A/11/2162837

12 http://www.pcs.planningportal.gov.uk/pcsportal/fscdav/READONLY?OBJ=COO.2036.300.12.43652

90&NAME=/Decision%20.pdf

13 Appeal Ref: APP/K0425/W/16/3146838 - Land at Park Mill Farm, Princes Risborough.


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matters for which Thames Water are liable under Allen which I must consider. Such an assessment has no

precise mathematical correlation with odour concentration figures and the application of a particular figure is

difficult in this case because there has been no modelling of the odour conditions for which I have held Thames

Water liable. I would be reluctant to find nuisance if the odour concentration was only 1.5 ouE per m3 but as the

odour concentration rises to 5 ouE per m3 I consider that this is the area where nuisance from Mogden STW

would start and that by the time that 5 ouE per m3 or above is reached nuisance will certainly be established.”

The above reference to “Allen nuisance” refers to the earlier Allen vs Gulf Oil legal case, where it was

determined, in simple terms, that where the source of an odour was an installation that contributed to the

common good, it was to be expected that some small degree of nuisance should be tolerated. In the

Mogden case, as the operation of the WwTW is carried out by a statutory undertaker (Thames Water), the

same applies and, as long as the site is operated in accordance with best practice, some odour should be

tolerated.

Stanton Appeal

In his report on the Stanton Appeal, the Inspector concluded at paragraph 55:

“The parties accepted that annoyance levels producing complaints are subjective and can arise both at levels

below 1.5 OUE/m3 and from events in the 2% frequency. The existence of complaints does not necessarily

demonstrate an unacceptable loss of amenity, but a lack of any is important in terms of the CoP It is material in

this case. On balance, and taking the relevant advice, decisions and practice into account, it seems to me that

the appropriate threshold for this type of small STW is more than the 1.5 OUE/m3 now promoted by Anglian

Water and the Council. I consider that a more appropriate threshold in this case is 3 - 5 OUE/m3, the level of the

DEFRA guidance’s “faint odour”.”

Cockermouth Appeal

In the report on the Appeal Inquiry in Cockermouth, the Inspector concluded:

“I am mindful that the assessment based on a 98th percentile 1-hour average odour concentration (C98,1hour)

would not result in a totally odour free scenario, as there is a likelihood of some occasional odour issues with

sites such as the WWTW. However, any period of exposure to unpleasant odour should be short lived at some

2% of a year. Moreover, there are varying degrees of odour from sewage treatment. At this WWTW, odour from

the sludge holding tanks is abated by use of an odour control unit, which odour sampling has shown to have an

odour removal efficiency of approximately 98%. Thus it seems that highly offensive odours are unlikely to arise

during normal operation. Should odours fall within medium offensiveness, rather than low, the C98,1 hour 3

OUE/m3 level modelled by the appellant indicates that it would not impinge on the appeal dwellings.”

Princes Risborough Appeal

This was an Inquiry into the failure of the local planning authority to determine, within the statutory period,

an application to construct up to 500 homes near Princes Risborough, relatively close to the local wastewater

treatment plant. Whilst the Appeal was rejected by the Inspector on the basis of excessive impact upon the

local highway network, in relation to odour from the WwTW site, the Inspector commented:

“Having regard to the applicant’s unchallenged evidence on the efficacy of the applicant’s odour monitoring

assessments and subject to a condition relating to no residential development within the 3 ouE/m3 odour

concentration contour, I consider there would be no material impact on the living conditions of future residents

from odour”.

3.3 Selection of an Appropriate Criterion

On the basis of the above information and our experience of dealing with odour annoyance cases, from both

Water Industry and developer standpoints, it is considered that the current consensus on criteria applicable


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to sewage treatment works lies around a lower-end figure of 3 ouE m-3, expressed as a 98th percentile metric

of hourly average odour concentrations over a calendar year. This concentration is three times the odour

threshold concentration and is below the “faint odour” level of 5 ouE m-3. This is supported by the

conclusions of the CIWEM PPS, the Mogden Judgement and the Stanton, Cockermouth and Princes

Risborough appeals. It should be noted that odour threshold concentrations (OTC) are determined by odour

panellists under a controlled laboratory environment, in an air-conditioned room fed with air that has been

filtered to remove background odours and held at a constant temperature (~23˚C). In practice, outside in the

“real” environment, a person would be continuously subjected to a plethora of other sensory stimuli,

including background odours from sources other than STWs. Under such circumstances, it is reasonable to

expect that, firstly, the OTC would be at a higher concentration than that determined under controlled,

background stimulus-free laboratory conditions and, secondly, that the concentration at which odours are

detected and become recognisable will also be higher than, say, 5 ouE m-3.

It is also important to consider the nature of the odours involved. Human beings are conditioned during their

early years to react adversely to faecal and sewage-type odours. Therefore, the most offensive odours arising

from STW sites, those from septic (aged) sewage and untreated sludge that has been stored for more than a

day, are most likely to generate complaints. At Whitewall Creek STW, there is no import or on-site treatment

of sludge. This means that the residual odour emissions from the site will consist of less offensive odours

(from the trickling filters and final settlement tanks) and abated odours from the odour control units.

This provides further weight to the selection of an odour criterion of 3 ouE m-3 as opposed to 1.5 ouE m-3, the

latter being proposed in the EA H4 document in relation to the most offensive odours. On this basis, it is

considered that, at worst, a criterion level of 3 ouE m-3 applied to a typical external environment is

appropriate and also offers a “margin of safety”.


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4. Assessment of impact

4.1 Modelling results

Table 4.1 presents the results for the odour impact assessment of the baseline scenario and mitigated

scenario compared to the 1.5 ouE m-3 and 3 ouE m-3 odour thresholds.

Table 4.1 Calculated 98th percentile 1-hour mean odour concentrations at receptors

Receptor Baseline scenario Mitigated scenario

Odour 98%-ile

of 1 hour mean

(ouE m-3)

Odour

concentration

as a percentage

of the 1.5 ouE

m-3 threshold

Odour

concentration

as a percentage

of the 3 ouE m-3

threshold

Odour 98%-ile

of 1 hour mean

(ouE m-3)

Odour

concentration as

a percentage of

the 1.5 ouE m-3

threshold

Odour

concentration as

a percentage of

the 3 ouE m-3

threshold

R1 0.9 59% 30% 0.5 35% 18%

R2 5.0 336% 168% 1.2 82% 41%

R3 1.0 67% 33% 0.5 31% 15%

R4 59.5 3967% 1983% 9.6 637% 319%

R5 32.9 2191% 1096% 3.2 213% 107%

R6 11.6 774% 387% 1.9 128% 64%

R7 6.7 448% 224% 1.4 96% 48%

R8 4.5 302% 151% 1.1 76% 38%

R9 3.2 215% 108% 0.8 54% 27%

R10 2.3 152% 76% 0.6 37% 19%

In the Baseline scenario, the results in Table 4.1 show that, as expected, receptor R4, situated on the site for

reference, is predicted to experience the highest odour concentration. Receptors R1 – R3 represent the

existing receptors in the vicinity of the WwTW of which R2, located directly downwind, is the only one that

exceeds the odour concentration threshold (both 1.5 ouE m-3 and 3 ouE m-3). Receptors R5 – R7 are situated

on the Development Site, all of which exceed both the 1.5 and 3 ouE m-3 odour thresholds indicating that

odour complaints could be possible across the potential development site.

In the Mitigated scenario the predicted odour concentration at modelled receptors is significantly less than in

the Baseline scenario at all modelled receptors. After implementation of the proposed mitigation measures,

the 3 ouE m-3 odour threshold is predicted to be exceeded at receptors R4 (onsite) and R5 on the

development site close to the site boundary. This indicates that odour complaints could well occur from

future residents across a small portion of the site. When comparing to the 1.5 ouE m-3 odour threshold, as

well as receptors R4 and R5, R6 is predicted to exceed, however it is not considered likely that odour will be

sufficiently offensive to cause odour complaints.


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4.2 Odour contour

A contour plot of the 98th percentile odour results for the extent to which it is predicted that the 3 ouE m-3

odour threshold will be exceeded across the development site for each scenario is presented in Figure 4.1

below. A contour plot of the 98th percentile odour contour for the 1.5 ouE m-3 odour threshold (Southern

Water preferred criterion) is included for reference in Figure 4.2.

With reference to the wind roses shown in Figure 2.6, it is possible to explain the shape of the contour, as the

winds are predominantly from a south-westerly direction. This has the effect of dispersing emissions from the

WwTW across the development site to the north-east.

In the Baseline scenario is can be seen that approximately 62 % of the Development Site is predicted to

exceed the 3 ouE m-3 odour threshold (91 % when compared to 1.5 ouE m-3), which is reduced in the

Mitigated scenario to approximately 5 % (32 % when compared to 1.5 ouE m-3). Areas within the 3 ouE m-3

contour may experience odour concentrations that are high enough to trigger complaints.

Appendix B shows 3 ouE m-3, 5 ouE m-3 and 10 ouE m-3 contour plots for both scenarios, indicating that these

areas will experience higher concentrations of odour.


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Figure 4.1 Contour plot of 98 percentile 1-hour mean odour concentrations – 3 ouE m-3 odour threshold


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Figure 4.2 Contour plot of 98 percentile 1-hour mean odour concentrations – 1.5 ouE m-3 odour threshold


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Potential Mitigation

The odour survey and modelling identified that the inlet works and detritor processes in the north-east

corner of the WwTW site made the greatest contribution to odour emissions from the site and, consequently,

had the greatest impact upon odour concentrations on the proposed development site, in excess of those

considered to be acceptable for residential areas. The mitigation measures proposed to reduce the area of

land contained within the 3 ouE m-3 C98 contour surrounding Whitewall Creek WwTW site involve the

following elements:

⚫ Enclosure of the inlet works channels with GRP covers with four air extraction points, ducted to

OCU (see below);

⚫ Enclosure of the detritor process in the north-east corner of the site, by erecting a steel-framed

portal cladded building (15 m x 12 m x 5 m) over the process units, with roller-shutter door;

⚫ Installation of a local and general exhaust ventilation ducting system (u-PVC or stainless steel);

⚫ Duty and standby ventilation extract fans, to achieve a routine 3 air changes per hour in the

building envelope (2,700 m3/h);

⚫ A dedicated odour control unit (OCU), most likely an advanced biofilter, consisting of either

crushed mussel shell or pumice media, with an integrated automatic pumped and filtered final

effluent irrigation system; and

⚫ Discharge ductwork and 6-metre stack.


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5. Conclusions and recommendations

This assessment has used detailed dispersion modelling to undertake an odour impact assessment from the

Whitewall Creek WwTW near Upper Upnor. Odour sampling was carried out in September 2019 and

monitored site specific odour concentrations were used to calculate actual odour emission rates from each

source.

A review of the available Guidance and case law on odour annoyance criteria has concluded that an

annoyance criterion of 3 ouE/m3, expressed as a 98th percentile of hourly average odour concentrations over

a calendar year is the appropriate benchmark for wastewater treatment works.

Odour concentrations for the current site layout (Baseline scenario) were predicted, as well as a Mitigated

scenario whereby the inlet/ detritor were covered and odour released through an odour control unit. In the

Baseline scenario 62 % of the Development Site is predicted to exceed the 3 ouE m-3 odour threshold,

however this is predicted to reduce to approximately 5 % of the development site in the mitigated scenario.

Given the significant reduction in odour concentration across the Development Site, it is clear that, with

mitigation in place, development can proceed and accords with paragraph 170 (e) of the NPPF (2019). It is

recommended that the detail of potential mitigation options be explored further with Southern Water, the

operator of Whitewall Creek WwTW.

A1 © Wood Environment & Infrastructure Solutions UK Limited

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Appendix A

Silsoe Odour report

CR/SO1989/19/ARUP020 v2 1 of 17 Report date: 24 September 2019

Draft Draft Draft Draft ReportReportReportReport ToToToTo

Lauren Growns, Lauren Growns, Lauren Growns, Lauren Growns, Wood Environment & InfrastructureWood Environment & InfrastructureWood Environment & InfrastructureWood Environment & Infrastructure

Solutions UK LtdSolutions UK LtdSolutions UK LtdSolutions UK Ltd

Odour Emissions from Odour Emissions from Odour Emissions from Odour Emissions from Whitewall CreekWhitewall CreekWhitewall CreekWhitewall Creek Wastewater Treatment WorksWastewater Treatment WorksWastewater Treatment WorksWastewater Treatment Works

9999thththth September 2019September 2019September 2019September 2019 v2v2v2v2

Date of report Date of report Date of report Date of report 24242424 SeptemberSeptemberSeptemberSeptember 2019201920192019

Robert Sneath, CEnv, MIAgrE

Silsoe Odours Ltd

Building 42 Wrest Park, Silsoe,

Bedfordshire, MK45 4HP.

01525 860222

[email protected]

Author: Author: Author: Author: ---- Robert SneathRobert SneathRobert SneathRobert Sneath


ContentsContentsContentsContents

1. OBJECTIVE AND DETAILS OF THE SITE ............................................................................ 3

1.1. DESCRIPTION OF SITE WORK .................................................................................. 3

1.2. ODOUR SAMPLING ................................................................................................. 3

2. METHODOLOGY FOR SAMPLING .................................................................................... 4

2.1. SAMPLING THE AREA SOURCES ............................................................................. 4

2.2. HYDROGEN SULPHIDE SAMPLING .......................................................................... 4

2.3. LABORATORY ODOUR ANALYSIS ............................................................................ 5

3. SAMPLING LOCATIONS ................................................................................................... 6

3.1. SITE PLAN ................................................................................................................ 6

4. SAMPLING SOURCES ...................................................................................................... 8

4.1. HIGH RATE FILTER ................................................................................................... 8

4.2. PST .......................................................................................................................... 9

4.3. OCU STAGE 1 ........................................................................................................ 10

4.4. DAMAGED CONNECTION IN OCU PIPEWORK, BETWEEN STAGE 1 AND STACK .. 11

4.5. SLUDGE OCU (STACK) ........................................................................................... 12

5. RESULTS OF ODOUR MEASUREMENTS ........................................................................ 13

APPENDIX 1 ....................................................................................................................... 15

Silsoe Odours LtdSilsoe Odours LtdSilsoe Odours LtdSilsoe Odours Ltd.

Silsoe Odours Ltd is an odour laboratory in Bedfordshire offering complete odour management and

consultancy services. We are accredited by UKAS for odour concentration measurements by dynamic

olfactometry and collection of odour samples specified in BSEN13725 and our own accredited

procedures.


1. Objective and Details of the Site

The objective of the baseline odour survey is to quantify the odour emissions from the wastewater

treatment plant at Southern Waters Upnor Wastewater Treatment Works (WwTW) to facilitate the

development (by Wood) of an odour dispersion model of the whole works.

The work will require:

• An odour survey

• Provision of the odour survey results in a form ready for use in a dispersion model.

The address of the site is

Whitewall Creek WTW

Upnor Road,

Rochester,

ME2 4UZ

1.1. Description of site work

Samples were taken on 9 September 2019 at Whitewall Creek WTW.

Sources sampled were high rate filters, humus, primary settlement tank, detritor, sludge OCU (stack),

OCU stage 1.

1.2. Odour sampling

Sampling was be carried out to the requirements of BSEN13725.

Samples were taken from key area and point sources for odour analysis to enable an odour dispersion

model to be built. The sample locations were agreed with Wood and Southern Water.

Silsoe Odours collected a total of 7 sources listed in Table 1 below.


2. Methodology for sampling

The odour samples were collected into Nalophan NA sample bags through PTFE sampling tubes. The

sample bags were fitted in rigid "barrels" which are partially evacuated to provide the vacuum to draw

air along the sample tube into the bags (lung principle). The vacuum will be generated by portable 12v

battery electric pumps.

2.1. Sampling the area sources

For area sources a Lindvall hood was used to collect the samples, this method followed the guidance in

the EA draft H4 document (2003 version) and BSEN13725;2003 to provide an emission rate from surface

sources. Sampling was undertaken by covering a portion of the surface with a suitable ventilated hood.

A Lindvall type sampling hood of approximately 0.6m2 was used and ventilated with odour free air at a

known volumetric flow rate. An odour sample was then collected at the outlet of the canopy. The rate

of air injected into the hood was monitored and adjusted as close to 1.6 m/s as possible for each sample

and used to calculate a specific odour emission rate per unit area per second (Esp) as follows:

Esp = Chood x L x V

Where,

Chood is the odour concentration measured from the sample bag.

L is the hood factor, which is equal to the path length (m2) of the hood divided by the covered area (m2).

V is the velocity (m/s) of air presented through the hood.

The hood can be placed on open solid surfaces, but floats were used when using the hood on liquid

surfaces.

2.2. Hydrogen Sulphide sampling

Samples were analysed with a Jerome 631-X Hydrogen Sulfide analyzer (Arizona Instruments, USA) by

Silsoe Odours prior to olfactometry analysis.


2.3. Laboratory Odour analysis

The Principle of Olfactometry technique is as follows: -

The odour concentration of a gaseous sample of odorants is determined by presenting a panel of

selected and screened human subjects with that sample, varying the concentration by diluting with

neutral (odourless) gas, in order to determine the dilution factor at the 50% detection threshold (Z50 ≡

panITE,Z ).

At that dilution factor the odour concentration is 1 ouEm-3 by definition. The odour concentration of the

examined sample is then expressed as a multiple (equal to the dilution factor at Z50) of one European

Odour Unit per cubic metre [ouEm-3] at standard conditions for olfactometry.

The Silsoe Odours Ltd laboratory operate a forced choice olfactometer, it has two outlet ports from one

of which the diluted odour flows and clean odour-free air flows from the other.

The measurement starts with a dilution of the sample large enough to make the odour concentration

beyond the panel members’ thresholds, the concentration is increased by factor between 1.4 and 1.5

in each successive presentation. The port carrying the odorous flow is chosen randomly by the control

sequence on each presentation. The assessors indicate from which of the ports the diluted odour

sample is flowing using a personal keyboard. They also indicate whether their choice was a guess,

whether they had an “inkling” or whether they were certain they chose the correct port. Only when

the correct port is chosen and the panel member is certain that their choice was correct is it taken as a

TRUE response. At least two consecutive TRUE responses must be obtained for each panel member.

The geometric mean of the dilution factors of the last FALSE and the first of at least two TRUE

presentations determines the individual threshold estimate (ITE) for a panel member. The odour

concentration, ouEm-3, for a sample, is calculated from the geometric mean of at least two ITEs for each

panel member.


3. Sampling locations

3.1. Site plan

(

Figure 1: Aerial photo of Whitewall Creek WTW


Table 1: List of locations for odour concentration and emission rate determinationTable 1: List of locations for odour concentration and emission rate determinationTable 1: List of locations for odour concentration and emission rate determinationTable 1: List of locations for odour concentration and emission rate determination

LOCATIONLOCATIONLOCATIONLOCATION No. of SamplesNo. of SamplesNo. of SamplesNo. of Samples MethodMethodMethodMethod

1 High rate filter 4 2 Samples Lindval Hood

2 High rate filter 3 2 Samples Lindval Hood

3 Humus 2 Samples Pump & Barrel

4 PST 2 Samples Lindval Hood

5 Detritor 2 Samples Lindval Hood

6 Sludge OCU (stack) 2 Samples Pump & Barrel

7 OCU (stage 1) 2 Samples Pump & Barrel

1

7 6

5

4

3

2


4. Sampling Sources

4.1. High Rate Filter


4.2. PST


4.3. OCU Stage 1


4.4. Damaged connection in OCU pipework, between stage 1 and stack


4.5. Sludge OCU (stack)


5. Results of Odour measurements

The Laboratory results are contained in Appendix 1.

Table Table Table Table 2222: Average results for : Average results for : Average results for : Average results for Whitewall Creek WTWWhitewall Creek WTWWhitewall Creek WTWWhitewall Creek WTW emission rates on emission rates on emission rates on emission rates on 9999 SeptemberSeptemberSeptemberSeptember 2019201920192019

Sample source Geometric

mean odour

concentration,

ouE/m3

odour emission

rate, ouEm-2s-1

High rate filter 4 94 0.82

High rate filter 3 102 0.88

Humus tank 4 42 0.31

PST 372 2.64

Detritor 16,631 135.7

Sludge OCU

(stack)

2,052 24.63

OCU stage 1 3,974

167.01


TTTTable able able able 3333: : : : Emission ratesEmission ratesEmission ratesEmission rates for for for for Whitewall Creek WTWWhitewall Creek WTWWhitewall Creek WTWWhitewall Creek WTW processesprocessesprocessesprocesses on on on on 9999 SeptemberSeptemberSeptemberSeptember 2019201920192019

Sources Total Area,

m2

Contains odour

emission rate,

ouEm-2s-1

Total

emission,

ouE/s

High rate filter 4 (new) 433.5 0.82 356

High rate filters (old) 314 Tank 1,2,& 3 0.88 829

Humus Tank 4 (new) 318.2 Humus feed tank 0.31 99

Humus Tanks (old) 226.9 Tank 1,2 & 3 0.31 211

PST 247.1 HRF feed tank 2.64 1,954

Detritor 106.3 Inlet, screens &

channel to pst 135.7 14,428

Sludge OCU (stack) 25

OCU stage 1 167


APPENDIX 1

Olfactometry Report

CR/SO1951/19/REC011 16 of 17 Report date: 6 June 2019

Contract report number: CR/SO1992/19/WE010

Customer reference: P.O. 318926

Measurements carried out by:

G. A. Liddle

1. Contact: Alun McIntyre

Wood Environment & Infrastructure Solutions UK Ltd

Floor 12, 25 Canada Square

Canary Wharf, London E14 5LB

Mobile +44 (0) 758 300 3631

Office +44 (0) 203 215 1650

2. Odour source: Wastewater Treatment Works

3. Sampler: * R. W. Sneath; J. R. Sneath

4. Sampling date: * 9 September 2019

5. Laboratory temperature and CO2 23.1oC; 1,084 ppm

6. Measurement date 10 September 2019

7. Presentation mode: Forced choice

8. Olfactometer: Olfasense GmbH

TO-Evolution

9. Pre-Dilution Gas Meter: Durecom KG-2 2017-009020

10. Reference odorant/accepted reference value n-butanol. 60 ppm / 40ppb

11. Calibration Status of Laboratory Aod = 0.048; r = 0.213

12. Method: Following Odour Lab Procedure OL2 which

incorporates BSEN13725 “Air quality – Determination

of odour concentration measurement by dynamic

olfactometry”.

13. Special remarks: Nalophan NA bags 25µm thick

14. Approved by

R. W. Sneath, Head of Laboratory.

Compiled by

G. A. Liddle, Laboratory Operator

“This laboratory is accredited in accordance with the recognised International Standard ISO/IEC 17025:2005. This accreditation

demonstrates technical competence for a defined scope and the operation of a laboratory quality management system (refer joint

ISO-ILAC-IAF communiqué dated April 2017)”

CR/SO1951/19/REC011 17 of 17 Report date: 6 June 2019

Results:Results:Results:Results:

Table 1: Table 1: Table 1: Table 1: Results Results Results Results forforforfor Whitewall Creek WTWWhitewall Creek WTWWhitewall Creek WTWWhitewall Creek WTW odour samples analysed onodour samples analysed onodour samples analysed onodour samples analysed on 9999 September 2019September 2019September 2019September 2019

*Sample insufficiently odorous to complete 2 run – result from 9 ITEs or fewer.

Deviation from the standard: Deviation from the standard: Deviation from the standard: Deviation from the standard:

None

The following data is not covered by our UKAS Accreditation:The following data is not covered by our UKAS Accreditation:The following data is not covered by our UKAS Accreditation:The following data is not covered by our UKAS Accreditation:

S. O. H2S measurements in Table 1 not accredit

Samples

collected

09/09/19

at:

Samples

analysed

10/09/19

at:

Sample No. Sample Source

and Position

S. O.

H2S

ppm

Odour

Panel

Threshold,

ouE m-3

Lab. Pre-

dilution

factor

Odour concentration

of sample, ouE m-3

(including laboratory

pre-dilution)

11:33 09:26 20190910 U1 High rate Filter 4 0.000 89 None 89




12:26 09:17 20190910 U5 Humus 0.000 41* None 41*

12:31 09:10 20190910 U6 Humus 0.000 43** None 43**

12:48 10:02 20190910 U7 PST 2 0.018 434 None 434

12:53 10:12 20190910 U8 PST 2 0.022 319 None 319

13:23 11:33 20190910 U9 Detritor 2.0 12,545 None 12,545

13:27 11:49 20190910 U10 Detritor 2.4 22,047 None 22,047

13:48 10:27 20190910 U11 Sludge OCU 0.24 1,696 None 1,696

13:53 10:39 20190910 U12 Sludge OCU 0.25 2,482 None 2,482

14:15 10:51 20190910 U13 OCU Stage 1 0.68 3,676 None 3,676

14:18 11:00 20190910 U14 OCU Stage 2 0.79 4,295 None 4,295


June 2020

41635

Baseline Scenario


June 2020

41635

Mitigated scenario

June 2020

41635

Land at Upnor Road, Upper Upnor, Medway

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