prepared for: water corporation - henderson, western australia

Woodman Point Waste Water Treatment Plant – Sludge Facility Upgrade Odour Assessment Water Corporation - Henderson, Western Australia EAQ-20014

EAQ20014-WCWA-SludgeUpgrade-FINAL_20210616 P a g e | 2 16 June 2021

Woodman Point Waste Water Treatment Plant – Sludge Facility Upgrade Odour Assessment

Prepared for: Water Corporation - Henderson, Western Australia

Project Ref: EAQ-20014

June 2021

Environment | Air Quality



Contents

Executive Summary ...................................................................................................................................... 6

1 Background & Scope ............................................................................................................................. 7

1.1 Regulatory Guidance for Odour Assessment ................................................................................. 7

2 Sludge Treatment Facility (STF) ........................................................................................................... 10

2.1 Summary of Upgrade Concept Design ......................................................................................... 10

3 WWTP Locality & Meteorology ........................................................................................................... 13

3.1 Locality ......................................................................................................................................... 13

3.2 Meteorology ................................................................................................................................ 16

3.2.1 Representative Meteorological Annual Period .......................................................................... 17

3.2.2 Meteorological Configuration .................................................................................................. 19

3.2.3 Meteorological Data Analysis ................................................................................................... 19

4 Odour Source Assessment (OSA) ........................................................................................................ 23

4.1 Sampling & Analysis Methods ..................................................................................................... 23

4.1.1 Point Source Sampling ............................................................................................................. 23

4.1.2 NATA Accredited Odour Concentration Analysis ....................................................................... 23

4.2 Existing Odour Emission Rates ..................................................................................................... 23

4.3 STF Upgrade Odour Emissions ..................................................................................................... 24

5 Operational Odour Analysis (OOA) ..................................................................................................... 26

6 Odour Field Assessments (OFA) .......................................................................................................... 33

6.1 OFA Preamble .............................................................................................................................. 33

6.1.1 OFA Method ............................................................................................................................ 34

6.1.2 Determination of Plume Extents (EN 16841-2:2016) ................................................................. 34

6.1.3 Determination of Odour Intensity (VDI 3940 Part 3) ................................................................. 35

6.1.4 Odour Impact Criterion ............................................................................................................ 36

6.1.5 OFA Results ............................................................................................................................. 36

7 Odour Impact Assessment Risk Evaluation ......................................................................................... 42

8 Conclusions.......................................................................................................................................... 44

9 Summary Table for Detailed Analysis ................................................................................................. 45

Appendix A: NATA Accredited Odour Concentration Results .................................................................... 46



Appendix B: Photos of Odour Sampling Locations ..................................................................................... 47

Appendix C: OCF Commissioning Validation Report .................................................................................. 48

Appendix D: WP 180 OFA Commissioning Report ..................................................................................... 49

Appendix E: STF OFA Raw Results .............................................................................................................. 50

Figures

Figure 1-1: DWER Odour Guideline – Odour Analysis Procedure ................................................................ 9

Figure 2-1: Layout of Proposed Upgrade to STF ......................................................................................... 11

Figure 2-2: Design of New OCF adjacent to Existing OCF. .......................................................................... 12

Figure 3-1: City of Cockburn Boundaries (orange hashed) and WWTP Landholding (red) ........................ 14

Figure 3-2: Locality Henderson, Western Australia .................................................................................... 15

Figure 3-3-3: Mann Whitney U-Test for Monthly Average Temperature .................................................. 18

Figure 3-4: Annual and Seasonal Windroses for Hybrid derived Site-representative 2017 Meteorology 20

Figure 3-5: Time of Day Windroses for Hybrid derived Site-representative 2017 Meteorology ............... 21

Figure 3-6: Diurnal Trends of Atmospheric Stability for Locality ............................................................... 22

Figure 6-1: OFA #1 (18.12.2020) ................................................................................................................. 38

Figure 6-2: OFA #2 (04.01.2021) ................................................................................................................. 39

Figure 6-3: OFA #3 (14.01.2021) ................................................................................................................. 40

Figure 6-4: OFA #4 (15.01.2021) ................................................................................................................. 41

Tables

Table 3-1: Garden Island BoM AWS chi-squared Outcome........................................................................ 18

Table 3-2: Jandakot BoM AWS chi-squared Outcome ............................................................................... 18

Table 4-1: Existing Odour Concentration Data and derived OERs. ............................................................ 24

Table 4-2: STF Upgrade Design and Airflows .............................................................................................. 25

Table 5-1: Operational Odour Analysis (OOA) of Normal WWTP Operations ........................................... 27

Table 5-2: Operational Odour Analysis (OOA) of Upset WWTP Operations .............................................. 30

Table 6-1: VDI 3940 (Part 3) Odour Intensity Categories ........................................................................... 36



Executive Summary

Environmental & Air Quality Consulting Pty Ltd undertook an Assessment of the proposed Upgrade to

the Woodman Point WWTP, specifically the proposed Upgrade of the Sludge Treatment Facility.

The Upgrade will include increased and improved handling and treatment processes of the DAF, TEAS,

RST, Sludge Hoppers, Storage Tanks and Sludge Loadout Building.

The increase in capacity of sludge processing locations and subsequent increase in process odour

emissions are met with an increase in the odour capture, extraction and odour treatment to mitigate

any increase in odour emissions.

The Upgrade will include a combined air volume extraction rate of 90,800 m3/hr, which is diverted to

the expanded Odour Control Facility (Bioscrubber and Chemical Scrubbing Farm) where treated odour

emissions are compliant with the Odour Control Facility’s performance guarantee.

Odour emissions were quantified for those processes that are proposed to be expanded and the odour

emissions used to determine the expansion volume required for the Odour Control Facility. The increase

in the Odour Control Facility capacity to treat increased odour emissions includes a volume of

contingency. The Odour Control Facility has also been shown to operate at or above its performance

guarantees and therefore any increase in odour emissions due to the Upgrade will be readily handled

within the expanded systems.

The risk assessment of the proposed Upgrade concluded that the risk of impacts is Medium, which may

evoke some regulatory controls for the STF and overall WWTP. Controls are already imposed through

the WWTP’s Prescribed Premises Licence.

It was found that odour emissions from the proposed Upgrade to the STF will not result in an increase in

uncontrolled odour emissions, and therefore; will not result in an unreasonable impact to the amenity

of the nearest sensitive receptor or future sensitive receptor or land use.



1 Background & Scope

Environmental & Air Quality Consulting Pty Ltd (EAQ) was engaged by the Water Corporation (WC) of

Western Australia (WA) to undertake an Odour Impact Assessment (the Assessment) of the WC’s

Woodman Point Wastewater Treatment Plant (WWTP) that will support the WC’s Works Approval

Application for an upgrade (the Upgrade) of the Sludge Treatment Facility (STF) at the WWTP.

The Works Approval application process is regulated by the WA Department of Water and

Environmental Regulation (DWER) under Part V of the Environmental Protection Act 1986 (EP Act). The

WWTP, under the EP Act is classified as a Prescribed Premise licenced as both a Category 54 Sewage

facility, and a Category 61 Liquid waste facility (EPA Licence: L4201/1991/11).

The WWTP liquid stream treatment process was recently upgraded and commissioned in 2019 to

provide a treatment capacity of 180 ML/d, with the potential to further upgrade this to 220 ML/d.

Following this upgrade, it was identified that the sludge treatment process also requires capacity and

infrastructure upgrades due to an expected increase of combined thickened sludge CTS production by

33% on annual average, and by 76% in the theoretical maximum month (summer) compared to the

historical plant operation. This is due to the lower sludge age of the new secondary process, as well as

improvements to solids capture, which were historically lost to ocean discharge. The modelling

conducted during the WP 180 upgrade highlighted an immediate issue in the sludge stabilisation and

treatment capacity, and also in digested sludge dewatering capacity.

The Assessment was commissioned to demonstrate that the proposed Upgrade will not increase the

odour emissions footprint from the STF.

The WC’s current proposal to upgrade the STF will finalise the large scale upgrades scheduled for the

WWTP subsequently improving sludge handling and process treatment, and odour control, capture and

treatment.

1.1 Regulatory Guidance for Odour Assessment

In accordance with the DWER’s Guideline “Industry Regulation Guide to Licensing” June 2019 [1] the

proposed increase in capacity will include “additional works or emissions not previously assessed….and,

changes to containment structures not previously assessed” and therefore a Works Approval Application

is required.

The Works Approval application process is regulated by the WA Department of Water and

Environmental Regulation (DWER) under Part V of the Environmental Protection Act 1986 (EP Act).

[1]

https://www.der.wa.gov.au/images/documents/our-work/licences-and-works-approvals/licensing%20guidelines/Industry%20Regulation%20Guide%20to%20licensing%20%20June%202019.pdf



The Assessment follows the most recent Government of WA DWER Guideline “Odour Emissions” June

2019 document [2] where the Guideline provides assessment methods for delivering adequate odour

data and information to the DWER for the assessment of applications under Part V of the EP Act; where,

“Part V Division 3 of the EP Act provides the Department with mechanisms for regulating odour, by way

of conditions on works approvals and licences applied to prescribed premises”.

The DWER employs a risk-based approach to its assessment of applications for instruments under Part V

of the EP Act.

In determining the risk posed by odour, DWER considers:

the location, proximity and sensitivity of receptors;

the management of odour sources and activities;

the intensity and offensiveness of the odour;

potential odour impacts from other nearby sources;

the topography and complexity of terrain;

the size and / or complexity of the facility when compared with other Australian operations;

any unusual configuration of odour sources or technology compared with other Australian

operations;

whether the proposal is located in a Strategic Industrial Area (SIA);

the presence of multiple industry categories which may emit odours on the same site;

current and cumulative impacts from odour; and

pathways and impacts on sensitive receptors.

The key components of the odour Assessment in following the DWER Guideline are:

a. Screening analysis; and

b. Detailed analysis (where required).

Given the WWTP is an existing odour source, the need for a screening analysis is superseded by the

detailed analysis.

The Detailed Analysis includes (among others):

Location Review & Meteorology;

Odour Source Assessment (OSA);

Operational Odour Analysis (OOA); and

Odour Field Assessments (OFAs).

The DWER’s odour analysis procedure (step-wise) is as follows:

[2]

https://www.der.wa.gov.au/images/documents/our-work/licences-and-works-approvals/licensing%20guidelines/Guideline%20-%20Odour%20emissions%20v1.0%20FINAL%20(June%202019).pdf



2 Sludge Treatment Facility (STF)

The STF consists mainly of infrastructure that is enclosed and where sludge and other waste streams are

introduced, handled and removed via controlled valves, chutes and other control methods work to

encapsulate the transfer of the sludge without exposure to atmosphere.

The exception to this is the sludge removal process where sludge is loaded into trucks via hoppers. The

hoppers release the sludge into the truck trailers below via a chute(s). The trucks are stationary inside a

shed/tunnel and the doorways are closed during transfer. Nonetheless, there would be some fugitive

odour losses during this process if the shed/tunnel were not completely extracted/evacuated of

odorous air prior to the access doorways being opened.

Figure 2-1 illustrates the configuration of the STF to include the existing airflows’ schematics and

proposed Upgrade schematics for new ductwork to complement new infrastructure.

2.1 Summary of Upgrade Concept Design

The current Concept Design for the Upgrade Works Approval is provided by Jacobs “Woodman Point

Water Resource Recovery Facility Solids Handling Upgrade - Water Corporation Project Number:C-

S03501”.

In summary; the Upgrade to handle additional sludge production from the recent liquid stream upgrade

will include existing infrastructure improvements and additional infrastructure installations, to include:

(a) Additional Dissolved Air Flotation (DAF) capacity via an additional DAF process tank (DAFT 3) to

include supporting machinery and process units for thickened excess activated sludge (TEAS),

feed tanks, TEAS strain presses and buffer tanks;

(b) Additional Rotary Screw Thickeners (RST), feed tanks and supporting machinery and process

units;

(c) New Advanced Digestion Pre-treatment Process - Thermal Hydrolysis;

(d) Additional/expanded Sludge hoppers, digested sludge storage tanks and Sludge loadout building;

and

(e) New/Expanded Odour Control Facility to treat a combined odour emission rate of 90,800 m3/hr.

These Upgrades will increase process air capture and extraction to a volume of approximately 78,750

cubic metres per hour (m3/hr). An additional 11,900 m3/hr (approx.) of process air will also be extracted

from existing process machinery and units to improve the efficacy of total odour control, capture,

extraction and odour treatment within the STF.

In total a combined 90,800 m3/hr of odorous air will be captured and treated via the Odour Control

Facility (OCF).

Figure 2-2 illustrates the new OCF/Expanded located next to the existing OCF.



Figure 2-1: Layout of Proposed Upgrade to STF



3 WWTP Locality & Meteorology

3.1 Locality

The Woodman Point WWTP Locality resides in the suburb of Henderson located within the City of

Cockburn. The overall WWTP landholding covers approximately 88 Hectares (Ha).

The WWTP is immediately adjacent to the coastline. To the south of the WWTP are

industrial/commercial land uses. North-west of the WWTP is recreational space to include a caravan

park, and within the north-east quadrant offsite of the WWTP are urban land uses.

The nearest sensitive receiver with respect to residential home(s) is located approximately 530 metres

(m) north-east of the nearest emission source at the WWTP.

Figure 3-1 illustrates the boundaries of the City of Cockburn and the location of the WWTP landholding.

Figure 3-2 presents the Locality within Australia.



3.2 Meteorology

In terms of prevailing winds, the most problematic wind vector is from the south-west (SW). Winds

prevailing from the SW will encapsulate, in general, all odour sources at the WWTP and push fugitive

and process treatment odours toward the nearest residential areas north (N) and north-east (NE) of the

WWTP.

Additionally there are recreational areas, to include a caravan park, to the west (W) and north-west

(NW) of the WWTP. Winds originating from the south-east quadrant (SE) may have an influence on

observable odours from the STF within these recreational areas.

The WC collects meteorological data onsite at the WWTP, however; the data only captures wind speed

and direction. Furthermore, the Locality of the weather station at the WWTP is likely to be influenced by

physical structures such as adjacent process and administration buildings. The use of the onsite weather

station may be appropriate for localised winds across the site but may be less advantageous for macro

scale wind trends moving odours downwind of the WWTP.

The nearest long-term (> 5 years) Bureau of Meteorology (BoM) Automatic Weather Station(s) (AWS) to

the Henderson Locality are Garden Island (Station 009256) and Jandakot (Station 009172). These

stations are approximately 14 kms and 11 kms respectively from the centralized STF at the WWTP.

Meteorological (met) trends at both of these stations would represent sea-breeze (Garden Island) and

in general land-breeze effects (Jandakot). Importantly, the SW winds affecting the nearest residential

areas downwind of the WWTP travel directly across Garden Island and are captured by the Garden

Island AWS.

Both of these met stations, although in some proximity to the Site; represent weather patterns outside

of the localised terrain location of the Site, although the Garden Island AWS would offer close

representation of coastal SW winds affecting the WWTP.

To localise the meteorology on the WWTP, CSIRO’s The Air Pollution Model (TAPM) was utilised to

develop a prognostic met file, and further processing using the Calmet module of the pollution model

Calpuff was undertaken to generate a hybrid meteorological (met) dataset that incorporates surface

observations from Garden Island and Jandakot AWS’s as well as prognostic data generated from TAPM.

To determine which met year (annual period) was the most representative of the Locality for running

the TAPM model in a single representative year, both the Garden Island and Jandakot stations were

reviewed for recent 5-year met trends (2015-2019). Those nearest stations were chosen as surface

observations and given the context of the Locality would represent, in general, those met conditions

most observed at the locale.



2017 Hybridized Annual Windrose

Summer

Autumn

Winter

Spring

Figure 3-4: Annual and Seasonal Windroses for Hybrid derived Site-representative 2017 Meteorology



0100hrs – 0600hrs 0700hrs – 1200hrs

1300hrs – 1800hrs 1900hrs – 0000hrs

Figure 3-5: Time of Day Windroses for Hybrid derived Site-representative 2017 Meteorology



Dispersive conditions based on the vertical met profile can also be illustrated using the diurnal stability

relationship. Figure 3-6 below illustrates the diurnal trends of atmospheric stability during annual wind

conditions across the Locality, by plotting the averaged inverse Monin-Obukhov length (m) against

Stability Class for each hour of the day.

The Monin-Obukhov length describes the effects of buoyancy on turbulent flows, which can simply be

defined as the height at which turbulence is generated more by buoyancy than by wind shear. In other

words, the vertical dispersion of air during daytime convective conditions generates turbulence i.e.

convective turbulence during unstable atmospheric conditions.

As previously discussed, stability refers to the atmosphere’s ability to resist or enhance vertical motion

resulting in turbulence. These trends show that unstable conditions begin around approximately 6AM

and continue through until approximately 5PM.

Again, during this timeframe there is enhanced vertical mixing of airborne plumes and dispersion of

odours is therefore enhanced, however; those 6AM and 5PM nexus points between stable and unstable

atmospheric conditions increase the risk of odour impacts during those daytime hours, in particular

during those cooler seasonal periods of late autumn, winter and early spring.

Figure 3-6: Diurnal Trends of Atmospheric Stability for Locality



4 Odour Source Assessment (OSA)

EAQ undertook a program of odour concentration sampling and testing at various process locations

within the STF. The testing was done to derive existing odour emission rates and therefore determine

Upgraded odour emission rates based on the new infrastructure and process units proposed.

4.1 Sampling & Analysis Methods

4.1.1 Point Source Sampling

Point source sampling was undertaken using a Drum and Pump, also known as the “lung method” and

involves drawing the sample gas through a Teflon™ sampling tube into a single use, Nalophan sample

bag. The bag is housed within a sampling apparatus/drum that is evacuated with an external pump, and

the sample collected by induced flow. The method allows the sample air to be collected without

coming into contact with any potentially odorous material.

Extraction duct emissions were sampled using the Drum & Pump. During odour sampling, the emission

parameters were collected to include velocity to derive an odour emission rate at that sampling

location. All odour samples were collected in duplicate.

4.1.2 NATA Accredited Odour Concentration Analysis

EAQ delivered all odour samples to Ektimo for Olfactory Odour Concentration Analysis. Ektimo are

NATA Accredited operating to the Australian Standard for Odour Measurement ‘Determination of odour

concentration by dynamic olfactometry’ (AS/NZS 4323.3:2001) which prescribes a method for sample

analysis that provides quality assurance/quality control and ensures a high degree of confidence in the

accuracy, repeatability and reproducibility of results.

The concentration results obtained give an odour measurement concentration measured in odour units

(ou.m3). The odour concentration can then be multiplied by a volumetric emission rate to obtain a mass

odour emission rate for each source (ou.m3/s).

4.2 Existing Odour Emission Rates

The site-specific odour emissions data collected, and the observed process characteristics, are

presented in Table 4-1 below.

The final column in Table 4-1 represents the average Odour Emission Rate (OER) for each duplicate set

of odour samples collected.

These OERs represent the current STF odour emission rates at those process locations that will be

affected by the Upgrade.

Appendix A presents the NATA Accredited Laboratory Results, with Appendix B illustrating the sampling

locations.



5 Operational Odour Analysis (OOA)

The following Operational Odour Analysis Tables summarises the current and proposed processes,

odour emissions, process controls, triggers and corrective actions and overall risk rating for odour

impacts. The OOA has been informed, in part; by the site-specific odour field assessment results (refer

Section 6).

The Normal Operations Table, Table 5-1, represents the existing and proposed WWTP configurations

since the proposed infrastructure changes and process augmentations will have existing controls

mirrored to ensure the WWTP has no increase in its odour footprint.

The STF Upgrades do not include new processes or new infrastructure that will increase the existing

odour footprint at those process areas. This is because these Upgraded infrastructure units are enclosed

and the airflows extracted at multiple air exchanges per hour i.e. negative pressure. During EAQ’s onsite

odour sampling and testing program there were no fugitive process odours from the STF infrastructure

that were under negative pressure.

The expanded OCF to include newly installed Bioscrubber vessels is one piece of infrastructure that will

have emissions to atmosphere, however; the design and construction will mirror the existing bioselector

odour extraction to include complete capture, extraction and treatment of odour emissions within the

existing odour treatment facility. As a consequence the single emission stack from the existing and

newly proposed OCF will be the only increase in air emissions to atmosphere from the STF Upgrade. This

increase in emissions however represents treated odours, to include Hydrogen sulphide (H2S), released

to atmosphere which have had an odour reduction of at least 95%.

Table 5-2 presents a summary of Upset Conditions for Operations.



6 Odour Field Assessments (OFA)

As part of this Assessment, EAQ undertook and ambient odour intensity and frequency sampling

program to determine the extent of offsite odour impacts (if any) from the existing STF.

Given the onsite odours in and around the STF are largely negligible where the processes are enclosed

and extracted, the main source of fugitive odour losses and potentially odour impacts offsite is the

sludge loadout tunnel.

The topography of the WWTP and the sludge loadout tunnel means that these fugitive odours are

within a “cut-out” at the WWTP. This cut-out is considerably lower in elevation that the DAFT, RST and

other supporting process areas and therefore fugitive odours are far more likely to be retained in the

base of the cut-out and under SE winds readily pushed offsite toward Cockburn Road that runs along

the coastline to the west of the WWTP.

EAQ utilised three (3) field based odour assessors during each OFA and undertook a total of eight (8)

individual OFA sampling days, where;

Four OFAs targeted the wet process; and

Four OFAs targeted the STF.

The OFAs targeting the wet process were undertaken in August 2020 under specific atmospheric

stability and wind conditions to “isolate” the wet process within a SW wind vector. The results of these

OFAs are presented in Appendix D.

Those OFAs that targeted the STF were undertaken between December 2020 and January 2021. Winds

originating from the SE vector were targeted to ensure that any odours from the STF can be discerned

directly downwind of the STF.

6.1 OFA Preamble

OFAs were undertaken using a methodology that determines the extent of the odour plume emitted,

and its perceived impact from the odour source using field methods based on the most recent European

Methodology (BS EN 16841-Parts 1 & 2:2016) “Ambient air – Determination of odour in ambient air by

using field inspection” which determines the downwind plume width and length; and the standard

known as “Measurement of Odour Impact by Field Inspection” defined by the German Standard VDI

3940 (Part 3), where the system by which those observed odours are ranked according to the strength

(intensity) of the odour, sensation experienced and in the case of hedonic tone, the quality of the odour

impression for each detection interval within each measurement cycle.

The VDI 3940 (Part 3) Standard (guideline) states that:



“the frequency of recognizable facility odours has proven to be a suitable indicator for the

assessment of the investigated odour situation in terms of the nuisance impact of facility odours”

(page 5).

The Measurement of Odour Impact by Field Inspection, otherwise referred to as OFAs, collects field

data observations by ‘ground-truthing’ detectable odours from a pre-defined odour source to assess the

plume length and width, the odour intensity of an observed odour, and the frequency of observation of

those intensities.

Field odours are detected by a panel of field technicians (assessors) that have been calibrated for their

olfactory sensitivity according to the Australian/New Zealand Standard AS/NZS4323.3:2001; Stationary

source emissions: Determination of odour concentration by dynamic olfactometry.

6.1.1 OFA Method

For the purpose of the Assessment, the Plume Measurement method is chosen to determine the plume

extent downwind of the WWTP and in consideration of those measurement points most aligned with a

line-of-sight to the STF.

The European Standard EN 16841-2:2016 describes the plume method for determining the extent of

recognisable odours from a specific source using direct observation in the field by human panel

members under specific meteorological conditions.

The plume method involves the determination of the presence or absence (YES/NO) of recognisable

odours in and around the plume originating from a specific odorant emission source, for a specific

emission situation and under specific meteorological conditions (specific wind direction, wind speed and

boundary layer turbulence). The unit of measurement is the presence or absence of recognisable

odours at a particular location downwind of an odour source.

The extent of the plume is assessed as the transition of absence to presence of recognisable odour. The

results are typically used to determine a plausible extent of potential exposure to recognisable odours.

Further assessment of the plume’s odour impact was undertaken by reference to the VDI Standard

where the intensity and frequency of odour observations was determined within, and at the plume

extents (length and width). This provided further insight as to the plume’s potential for odour decay as

assessor(s) move further away from the odour source.

Additionally, the measure of odour intensity within the plume allows a determination of Risk (existing

and future) for odour impacts.

6.1.2 Determination of Plume Extents (EN 16841-2:2016)

Calibrated assessors are used to determine the presence or absence of the specific odour under

investigation at different points downwind of an odour source, and often under pre-defined

meteorological conditions. These conditions are chosen to ensure that the extent of the plume is



sufficiently defined and can be observed within locales that are relatively free of obstructions such as

dense forest, scrub, high density housing etc.

The meteorological conditions during the field observations are live tracked using the nearest BoM AWS

data which informs each assessor of the typical meteorological conditions across the site.

Importantly, the local meteorological aren’t always specifically aligned with the nearest BoM

AWS if that station is sufficiently far away from the odour source, or influenced by coastal or

terrain effects; and

In the case of the Garden Island BoM AWS, the location of this AWS is coastal and approximately

14 kms away from the WWTP which is also located on the coastline. Consequently, the AWS

readings are likely to be similar to the WWTP locale; however, it is expected that some of those

instantaneous readings from the AWS may be variable to onsite wind observations in particular

when winds are prevailing from inland vectors.

Typically, the measurement is repeated to reduce uncertainty to an acceptable level. In this way

variability due to random variations in meteorological conditions, panel member performance and

odorant emission is averaged out.

Assessors cross the plume at intervals while conducting stationary single measurements at single

measurement locations. By successively entering and exiting the plume over these location intervals the

transition between absence and presence of recognisable odour, and subsequently the extent of the

plume is defined.

The plume direction is crossed at different distances from the source. This includes crossings at

distances where no recognisable odour is detected. The maximum plume reach can then be estimated.

6.1.3 Determination of Odour Intensity (VDI 3940 Part 3)

Following the determination of the Plume extent, the assessor then referred to VDI for determining

odour intensity at single measurement points downwind of the odour source.

With this method:

Calibrated and experienced assessors conduct a single measurement(s) at discrete measurement

points within the downwind odour plume offsite of the upwind odour source;

Each measurement cycle comprises 60 grab measurements every 10 seconds for a single

measurement cycle of 10 minutes. Each grab measurement results in a single odour sample. The

Assessment/Grid/Plume Measurement Area represents a specific, preferential wind condition;

An OFA survey comprises the total individual discrete measurement points, and the total single

measurement(s) undertaken within the assessment/grid/plume measurement area on the

measurement day;

The survey period is often reflective of worst-case meteorological conditions when it is sub-

annual, or all wind conditions when it is annual. A survey may be undertaken at any interval



The maps are illustrative and do not specifically represent the exact locations down to the nearest

metre (+/- 20m), they do however show the relative position of observations and the wind vector within

which observations are made, and:

White pie charts indicate no odour was detected;

Pie charts with detection frequencies in varying colours depict the Intensity & Frequency of

odour observations at that measurement point, for all discrete measurements taken at each

measurement point, and in reference to the VDI 3940 (Part 3) scale;

Pie charts on the ‘edge’ of each wind vector (blue hashed polygons) are the extent of odours

observable laterally of those single measurement points, and/or where topographical

constraints prevent further assessment of odours past that single measurement point; where:

o At those lateral single measurement points the edge of the plume has been identified;

and

The light blue polygon represents the average wind direction for the duration of each OFA day.



Figure 6-1: OFA #1 (18.12.2020)



Figure 6-2: OFA #2 (04.01.2021)



Figure 6-3: OFA #3 (14.01.2021)



Figure 6-4: OFA #4 (15.01.2021)



7 Odour Impact Assessment Risk Evaluation

In referring to the (then) Department of Environmental Regulation (DER)’s Guidance Statement: Risk

Assessments (February 2017), and in consideration of:

OOA Tables describing the emission sources, controls, triggers and responses and overall odour

controls;

OFA results demonstrating the intensity and frequency of odours observed from the STF; and

Design and upgraded Infrastructure for the STF, to include contingency within the existing OCF,

where the STF odour emission sources are captured, extracted and treated.

The proposed upgrade of the Woodman Point WWTP STF Consequence of odour impacts at the nearest

existing and future urban receptor is Moderate; where:

Onsite impacts: mid-level;

Offsite impacts local scale: low-level;

Offsite impacts wider scale: minimal; and

Local scale impacts: mid-level impact to amenity.

And, the Likelihood of the risk occurring is Rare, where:

The risk event may only occur in exceptional circumstances when considering the nearest

sensitive receptors from the STF.

Based on the above, and in consideration of the OOA (refer Section 5) the future risk is considered to be

Medium and accounts for the forward planning within the Henderson locale, the existing and future

separation distances and the lack of urban encroachment on the western side of the WWTP.

This Medium risk assessment is likely to align with the existing risk analysis for the WWTP.

Importantly, the STF Upgrades will not a pose a risk for increases in fugitive odour losses from the STF

given that:

Proposed STF sources will be enclosed, extracted and the odour emissions treated through the

expanded OCF.

The sludge transfer shed/tunnel is the only source of fugitive odour release that at times may be

uncontrolled when the access doorways are opened for truck ingress/egress, however; the historic

operations of the sludge loadouts and improved management practices that will support the Upgrade

would ensure that fugitive odour losses from the sludge loadout are minimised.

Importantly, these fugitive odours tend to remain trapped in and around the sludge loadout

shed/tunnel due to the terrain features of the WWTP site. Under specific wind conditions these fugitive

odours can be emitted to the W, NW and N along Cockburn Road that runs adjacent to the coastline.

Along this pathway there are recreational areas and further NW and N are a recreational camp and



caravan park. Those residential areas due N of the STF are sufficiently separated from these fugitive

odours to avoid odour nuisance.

The odour plume observed during the OFAs showed that the length of the observable plume was

approximately 750 m from the corner of the sludge loadout shed/tunnel. At this distance of observation

there is a negligible risk of observable STF odours at the recreational camp, caravan park and those

residential areas N of the STF.



8 Conclusions

The Assessment of the proposed Upgrade to the Woodman Point WWTP has shown that the proposed

expansion of the STF throughputs will not increase the existing odour footprint from the WWTP.

The Upgrade will include an increase in capacity at sludge processing locations where those increases

are met with an increase in the odour capture, extraction and odour treatment of those increases in

odour emissions.

The Odour Source Assessment quantified those process sources where an intended increase in capacity

is proposed. The increased capacity, resulting in increased odour emissions, is managed by a further

increase in the capacity of the Odour Control Facility which comprises Bioscrubber and Carbon

Scrubbing Tanks. The increase in the Odour Control Facility capacity to treat those captured odour

emissions includes a volume of contingency. The Odour Control Facility has also been shown to operate

at or above its performance guarantees and therefore any increase in odour emissions due to the

Upgrade will be readily handled within the expanded systems.

The Operational Odour Analysis also lists those controls and contingencies in place for the proposed

Upgrade where the Upgrade will be managed within the existing WWTP systems and where applicable,

those systems expanded to include those new infrastructure locations within the STF.

The Odour Field Assessment program further demonstrated that STF odours are markedly confined to

the STF proximity, in general, and where odours were detected offsite of the STF, those odours did not

impact upon existing or future sensitive receptor locations. STF odours have not been detected in other

sensitive receptor localities from previous studies undertaken for the WWTP.

The risk assessment of the proposed Upgrade concluded that the risk of impacts is Medium, which may

evoke some regulatory controls for the STF and overall WWTP. These controls are already imposed

through the WWTP’s Prescribed Premises Licence. The existing controls are unlikely to be increased

based on the Upgrade given that the Upgrade does not introduce additional sources of uncontrolled

odour emissions.

Based on the study methods utilised within this Assessment, it is the view of EAQ that odour emissions

from the proposed Upgrade to the STF will not result in an increase in uncontrolled odour emissions,

and therefore; will not result in an unreasonable impact to the amenity of the nearest sensitive receptor

or future sensitive receptor or land use.

prepared for: water corporation - henderson, western australia

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