3 AIR QUALITY

Introduction

3.1 This Section presents an assessment of the potential air quality impacts associated with the construction and operation of the Project. The air quality impact assessment has been conducted in accordance with the requirements stipulated in Annex 4 and Annex 12 of the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) as well as the requirements set out under Clause 3.4.1 of the EIA Study Brief.

Environmental Legislation, Policies, Plans, Standards and Criteria

3.2 The criteria for evaluating air quality impacts and the guidelines for air quality assessment are laid down in Annex 4 and Annex 12 of the EIAO-TM respectively.

3.3 The Air Pollution Control Ordinance (APCO) provides statutory control on air pollutants from a variety of sources. The Hong Kong Air Quality Objectives (AQOs), which stipulate the maximum allowable concentrations over specific periods for a number of criteria air pollutants, should be met. The relevant AQOs are listed in Table 3.1.

Table 3.1 Hong Kong Air Quality Objectives

Pollutant	Maximum Average Concentration (µg/m^3) ^(1)
	1-Hour ^(2)	8-Hour ^(3)	24-Hour ^(3)	Annual ^(4)
Total Suspended Particulates (TSP)	-	-	260	80
Respirable Suspended Particulates (RSP) ^(5)	-	-	180	55
Sulphur Dioxide (SO2)	800	-	350	80
Nitrogen Dioxide (NO2)	300	-	150	80
Carbon Monoxide (CO)	30,000	10,000	-	-

(1) Measured at 298 K and 101.325 kPa.

(2) Not to be exceeded more than three times per year.

(3) Not to be exceeded more than once per year.

(4) Arithmetic mean.

(5) Suspended particulates in air with a nominal aerodynamic diameter of 10 mm or smaller.

3.4 The EIAO-TM also stipulates that the hourly total suspended particulates (TSP) level at sensitive receivers should not exceed 500 µg/m³ (measured at 25°C and one atmosphere) for construction dust impact assessment. Mitigation measures from construction sites have been specified in the Air Pollution Control (Construction Dust) Regulation.

3.5 In accordance with the EIAO-TM, odour predicted at an air sensitive receiver should not exceed 5 odour units based on an averaging time of 5 seconds.

Air Pollution Control (Construction Dust) Regulation

3.6 Notifiable and regulatory works are under the control of the Air Pollution Control (Construction Dust) Regulation. Notifiable works are site formation, reclamation, demolition, foundation and superstructure construction for buildings and roads. Regulatory works are building renovation, road opening and resurfacing, slope stabilisation, and other activities including stockpiling, dusty material handling, excavation, concrete works, stockpiling etc. This Project is expected to include both notifiable works and regulatory works. Contractors and site agents are required to inform the Environmental Protection Department (EPD) on carrying out construction works and to adopt dust reduction measures to reduce dust emission to the acceptable level.

Description of the Environment

Baseline Conditions (PTW)

3.7 The Preliminary Treatment Works (PTWs) involved in this study are in North Point, Wan Chai, Central, Sandy Bay, Cyberport, Wah Fu, Aberdeen and Ap Lei Chau on Hong Kong Island. The averages of the 5 years (2002 to 2006) annual average concentrations of the pollutants measured at EPD’s Air Quality Monitoring Stations on Hong Kong Island namely Central / Western, Central, Causeway Bay and Eastern are summarised in Table 3.2.

Table 3.2 Average of 5 Years (2002 to 2006) Annual Average Concentrations of Pollutants recorded at EPD’s Air Quality Monitoring Stations on Hong Kong Island

Monitoring Station	Average of 2002 to 2006 Annual Average Concentrations (mg/m^3)
	NO2	RSP	TSP
Central/Western	54	52	75
Eastern	56	48	No measurement
Causeway Bay	94	83	No measurement
Central	97	74	No measurement

North Point PTW

3.8 The North Point PTW is located within an area of high-rise residential developments in North Point. It adjoins WSD’s HK Regional Building and the King’s Road Playground. Healthy Gardens and Ruby Court are about 35 m to the south of the site. The Island Eastern Corridor is about 120 m to the north and King’s Road is about 5 m to the south. Major local influence on the background air quality is vehicular emissions from the Island Eastern Corridor and King’s Road.

Wan Chai East PTW

3.9 The Wan Chai East PTW is located near the ex-Wan Chai Public Cargo Working Area in Wan Chai East. It adjoins an electric sub-station and the Society for Prevention of Cruelty to Animals. The nearest residential building is about 190 m to the south of the site. Gloucester Road and the Wan Chai Interchange are about 12 m to the south. The portal of the Cross Harbour Tunnel is about 350 m to the northeast. Major local influence on the background air quality is vehicular emissions from Gloucester Road, the Wan Chai Interchange and the portal of the Cross Harbour Tunnel.

Central PTW

3.10 The Central PTW is located in Sheung Wan. It adjoins the Sheung Wan Fire Station and the Victoria Harbour. A high-rise residential/commercial building is located about 120 m to the south. Connaught Road West is about 85 m south of the site. The portal of the Western Harbour Crossing is about 385 m to the west. Major local influence on the background air quality is vehicular emissions from Connaught Road West and the portal of the Western Harbour Crossing.

Fung Mat Road Site

3.11 The Fung Mat Road Site, for the construction of production and junction shafts, is located in Sheung Wan. It adjoins AFCD’s Market Office and the Victoria Harbour. A high-rise residential/commercial building is located about 175 m to the south. Connaught Road West is about 60 m to the south. The portal of the Western Harbour Crossing is about 340 m to the southeast. Major local influence on the background air quality is vehicular emissions from Connaught Road West and the portal of the Western Harbour Crossing.

Sandy Bay PTW

3.12 The Sandy Bay PTW is located to the east of Sandy Bay and adjoins the University of Hong Kong Stanley Ho Sports Centre Pitch. A high-rise residential/commercial building is about 20 m to the east.

Cyberport PTW

3.13 The Cyberport PTW adjoins the Cyber Center in Cyberport to the east of the Telegraph Bay. Le meridian Cyberport is about 25 m to the east. Kong Sin Wan, a natural terrain of approximately 65 m high, is located to the north of the site. Cyberport Road is about 5 m to the northeast. Major local influence on the background air quality is vehicular emissions from Cyberport Road.

Wah Fu PTW

3.14 The Wah Fu PTW adjoins the Waterfall Bay Park in Wah Fu to the east of Pok Po Wan (Waterfall Bay). The Wah Fu Estate, a high-rise residential building, is about 10 m to the east. Waterfall Bay Road is in between the site and the Wah Fu Estate. Major local influence on the background air quality is vehicular emissions from Waterfall Bay Road.

Aberdeen PTW

3.15 The Aberdeen PTW adjoins the Dairy Farm Ice and Cold Storage and the Town Gas Aberdeen Depot in Aberdeen to the north of Kai Lung Wan. Shek Pai Wan Road is about 50 m to the north. The 100 m high Tin Wan Hill is about 95 m to the north. Major local influence on the background air quality is vehicular emissions from Shek Pai Wan Road.

Ap Lei Chau PTW

3.16 The Ap Lei Chau PTW adjoins Shell’s Ap Lei Chau Depot in Ap Lei Chau West to the east of the East Lamma Channel. The nearest residential sensitive receiver is about 170m to north . The Ap Lei Chau Hill is to the northeast. Lee Nam Road is about 5 m to the northeast . Major local influence on the background air quality is vehicular emissions from Lee Nam Road.

Baseline Conditions (SCISTW)

3.17 The Stonecutters Island Sewage Treatment Works (SCISTW) adjoins the Government Dockyard Office on Stonecutters Island. The West Kowloon Refuse Transfer Station is about 30 m to the north east. There is a natural terrain about 50 m to the southwest. Hing Wah Street West and Container Port Road South run along the northeast and northwest sides of the site. Major local influence on the background air quality is vehicular emissions from Hing Wah Street West and Container Port Road South.

3.18 The nearest EPD air quality monitoring station is in Sham Shui Po. The averages of 5 years (2002 to 2006) annual average concentrations of the pollutants measured at EPD’s Sham Shui Po Air Quality Monitoring Stations adjacent to the study area are summarised in Table 3.3.

Table 3.3 Average of 5 Years (2002 to 2006) Annual Average Concentrations of Pollutants recorded at EPD’s Sham Shui Po Air Quality Monitoring Station

Monitoring Station	Average of 2002 to 2006 Annual Average Concentrations (mg/m^3)
	NO2	RSP	TSP
Sham Shui Po	67	55	79

Air Sensitive Receivers

3.19 In accordance with Annex 12 of the EIAO-TM, representative worst affected Air Sensitive Receivers (ASRs) within the study area have been identified for this assessment. Domestic premises, hotel, hostel, hospital, clinic, nursery, temporary housing accommodation, school, educational institution, office, factory, shop, shopping centre, home for the aged and active recreational activity areas are classified as ASRs. Details of representative ASRs are listed in Table 3.4. Figures 3.1 to 3.9 show the locations of the ASRs.

Table 3.4 Air Sensitive Receivers

Area	ASR ID	Description	Use	No. of storey	Ground Level, mPD	Shortest Distance to site boundary, m
North Point PTW	NP1	Block C, Healthy Gardens	Residential	23	4.6	41
	NP2	Ruby Court	Residential	11	4.6	54
	NP3	King’s Road Playground & Skating Area	Recreational	N/A	4.3	3
	NP4	Customs HQ Tower (planned)	GIC	35	4.3	17
	NP5	K. Wah Centre	Commercial	30	4.3	23
	NP6	Hong Kong & Islands Regional Office, WSD	GIC	4	4.5	26
	NP7	Tin Shui Street Children’s Playground (Relevant to construction phase only)	Recreational	N/A	4.3	16 (To construction site) 127 (To PTW)
Wan Chai East PTW	WC1	HK Yacht Club	Recreational	3	4.3	278
	WC2	Wan Chai Sports Ground	Recreational	N/A	4.0	101
	WC3	Society for the Prevention of Cruelty to Animals	GIC	6	4.0	37
	WC4	Rest Garden near Wan Chai Interchange	Recreational	N/A	4.1	64
	WC5	Elizabeth House	Commercial	21	3.8	186
	WC6	Commercial Buildings at 233 Gloucester Road	Commercial	30	3.8	158
Central PTW	C1	Sheung Wan Fire Station	GIC	3	4.0	2
	C2	Water Front Divisional Police Station	GIC	7	3.7	102
	C3	Sheung Wan Gala Point	Open Space	2	3.7	92
	C4	Fui Nam Building	Residential	18	3.6	121
Fung Mat Road Site	FM1	Block A, Kwan Yick Building Phase III	Residential	24	4.0	187
	FM2	Western Wholesale Food Market	Commercial	3	4.1	80
Sandy Bay PTW	SB1	University of Hong Kong Stanley Ho Sports Centre Pitch	Educational Institution	N/A	5.9	9
	SB2	Home for the Elderly	Homes for the Aged	7	5.4	30
	SB3	Maclehose Medical Rehabilitation Centre	Clinic	12	5.6	40
	SB4	The Duchess of Kent Children’s Hospital	Clinic	2	6.2	14
Cyberport PTW	CB1	Cyber Centre	Commercial	5	6.6	4
	CB2	Le Meridien Cyberport	Hotel	16	6.2	33
	CB3	Aegean Terrace	Residential	3	84.6	125
	CB4	Block 18, Baguio Villa	Residential	10	27.2	258
	CB5	Phase 1, Residence Bel-Air	Residential	39	14.2	521
	CB6	Phase 2, Residence Bel-Air	Residential	44	16.4	516
	CB7	Residential Bel-Air (Scheduled to be occupied in June 2008)	Residential	N/A	30.1	676
Wah Fu PTW	WF1	Wah Yu House, Wah Fu Estate	Residential	11	18.0	40
	WF2	Wah Ming House, Wah Fu Estate	Residential	20	22.0	12
	WF3	Waterfall Bay Park	Recreational	N/A	16.0	68
Aberdeen PTW	AB1	Wah Lai House, Wah Kwai Estate	Residential	35	10.8	210
	AB2	Hing Wai Centre	Industrial	33	3.9	224
	AB3	Shek Pai Wan Road Playground	Recreational	N/A	14.5	298
	AB4	Dairy Farm Ice and Cold Storage	Industrial	3	4.1	36
	AB5	Ka Chun House, Ka Lung Court	Residential	35	7.8	389
	AB6	Ka Sing House, Ka Lung Court	Residential	36	9.0	483
Ap Lei Chau PTW	ALC1	Mei Wah Court, South Horizons	Residential	36	6.0	173
	ALC2	Horizon Plaza	Commercial/ Industrial	28	5.5	323
	ALC3	Shell Ap Lei Chau Depot	Industrial	1	6.5	47
Stage 2A Disinfection Facilities	SCI7	Ngong Shuen Chau Barracks Group 2	Institutional	1^(1)	8.0	74
Stonecutters Island STW	SCI1	Government Dockyard Offices	GIC	4	4.5	80
	SCI2	Ngong Shuen Chau Barracks Group 1	Institutional	2^(1)	4.5	372
	SCI3	COSCO Hit Terminal	Commercial	12	4.8	129
	SCI4	KMB Depot Office	Commercial	6	5.4	209
	SCI5	Planned FSD Diving Rescue and Diving Training Centre	Institutional	5^(1)	5.6	78
	SCI6	Club House	Recreational	1	5.0	65
	SCI8	Hoi Lai Estate	Residential	40	7.5	776
	SCI9	Tack Ching Girl’s Secondary School	Institutional	7	5.5	991
	SCI10	Aqua Marine	Residential	41	6.3	961
	SCI11	Mei Foo Sun Chuen	Residential	21	4.2	822

Note: (1) The number of storeys of the ASR is made reference to the approved EIA report of HATS - Provision of Disinfection Facilities at Stonecutters Island Sewage Treatment Works

Assessment Methodology

Construction Dust

3.20 As discussed in Section 2, construction of the Project would be from 2009 to end of 2013. Based on available information, concurrent projects that may generate cumulative environmental impacts during this Project’s construction period have been identified and summarized in Table 3.5.

Table 3.5 Concurrent Projects for Cumulative Air Quality Assessment

Area	Projects	Remark
North Point PTW	N/A	N/A
Wan Chai East PTW	- Wan Chai Development Phase II (WDII) and Central Wanchai Bypass & Island Eastern Corridor Link (CWB & IECL) - Shatin to Central Link - MTRC South Island Line Extension (East)	- The construction programme for WDII and CWB & IECL is from Yr 2008 to Yr 2013. It would overlap with the Project. The predicted fugitive dust impacts from WDII and CWB & IECL are extracted from the WDII draft EIA report. - No available information on construction programme - Alignment selection is still under consideration (Information is not available)
Central PTW	- MTRC West Island Line Extension - Reprovisioning of Central District Headquarters and Central Divisional Police Station at Chung Kong Road, Sheung Wan	- No interface with Central PTW (the alignment and worksite are outside our study area). - The construction activities would be non-dusty fitting-out works during the overlapping period. Therefore, contribution to cumulative construction dust impact would be minimal.
Fung Mat Road Site	- MTRC West Island Line Extension - Laying of Western Cross Harbour Main and Associated Land Mains from West Kowloon to Sai Ying Pun - Sun Yat Sen Memorial Park, Phase 2 at Waterfront of Sheung Wan	- No overlap with the Fung Mat Road Site (the alignment and worksite are outside our study area). - Dust impact on this project is minimal as described in the approved EIA report. (Register No.: AEIAR-109/2007) - The activities would be non-dusty superstructure work and minor excavation during the overlapping period. Therefore, contribution to cumulative construction dust impact would be minimal.
Sandy Bay PTW	N/A	N/A
Cyberport PTW	- MTRC South Island Line Extension (East) - Drainage Improvement on Northern Hong Kong Island, including the Hong Kong West Drainage Tunnel and the Sheung Wan Stormwater Pumping Station	- Alignment selection is still under consideration (Information is not available). - Dust impact on this project is minimal as described in the approved EIA report. (Register No.: AEIAR-099/2006)
Wah Fu PTW	- MTRC South Island Line Extension (East)	- Alignment selection is still under consideration (Information is not available).
Aberdeen PTW	- MTRC South Island Line Extension (East) - Route 4 (formerly known as Route 7)	- Alignment selection is still under consideration (Information is not available). - No programme (Information is not available).
Ap Lei Chau PTW	N/A	N/A
Stonecutters Island STW and Disinfection Facilities	- Route 8 - FSD Diving Training Centre in the Government Dockyard at Stonecutters Island	- Construction work would be completed in mid-2009. The activities at Route 8 would be non-dusty superstructure work during the overlapping period. Therefore, contribution to cumulative construction dust impact would be minimal. - Dust impact on this project is minimal due to small scale and limited works area as described in the Preliminary Environmental Review Report.

3.21 Fugitive Dust Model (FDM) was used to assess potential dust impact from the construction works. Dust emission was predicted based on emission factors from USEPA Compilation of Air Pollution Emission Factors (AP-42), 5th Edition. The maximum 1-hour and 24-hour average TSP concentrations at the selected ASRs were predicted by FDM based on historic meteorological data described in Section 3.24 below. The major construction activities that are potential sources of construction dust in the Study Area include soil excavation activities at work site, construction of shafts and wind erosion of open site. Table 3.6 gives the relevant clauses for emission factors used in this assessment in AP-42. Detailed calculations of emission rates are presented in Appendix 3.1.

Table 3.6 Emission Factors for Construction Activities

Construction Activities	Emission Rate, g/m^2/s	Remark
Construction of drop shaft at all PTWs.	E = 2.07562E-04	- 100% active area - USEPA AP-42 5th ED., S.13.2.3.3
Works Areas for Sewage Conveyance System (SCS) with surface excavation works and upgrade work at SCISTW	E = 1.03781E-04	- 50% active area - USEPA AP-42 5th ED., S.13.2.3.3
Barging point ^Note 1 and stockpiles: Fung Mat Road SCS Site: North Point SCS Site:	E = 2.12247E-06 E = 2.16386E-06	- USEPA AP-42 5^th ED., S. 13.2.4
Wind Erosion Drop shaft at all PTWs SCS work sites and SCISTW	E = 2.69533E-06 E = 1.34767E-06	- AP-42 5^th ED., S.11.9 Table 11.9.4

Note 1: Based on the latest design information, barging point will not be required at Fung Mat Road and North Point SCS sites. The air emissions from barging points were assumed in this EIA for the purpose of worst-case assessment only.

3.22 The impact of fugitive dust on air quality depends upon the quantity as well as the drift potential of the dust particles emitted into the atmosphere. Large dust particles (i.e. over 100 mm in diameter) will settle out near the source and particles that are between 30 and 100 mm in diameter are likely to undergo impeded settling. The main dust impacts are likely to arise from particles less than 30 mm in diameter, which have a greater potential to disperse over greater distances.

3.23 According to the USEPA AP-42, construction dust particles may be grouped into nine particle size classes. Their size ranges are 0 – 1 mm, 1 – 2 mm, 2 – 2.5 mm, 2.5 – 3 mm, 3 – 4 mm, 4 – 5 mm, 5 – 6 mm, 6 – 10 mm and 10 – 30 mm, and the percentage of particles in each class was estimated to be 4%, 7%, 4%, 3%, 7%, 5%, 4%, 17% and 49%, respectively.

3.24 One year sequential meteorological data for the year 2005 from the Hong Kong Observatory King’s Park or Green Island Weather Station were used to predict the 1-hour and 24-hour average TSP concentrations at representative discrete ASRs close to the construction works. As Green Island Weather Station does not record temperature data, the ambient temperature data at the Hong Kong Observatory Headquarters Station were adopted. For the impact assessments of PTWs at North Point, Wan Chai East, Central and Fung Mat Road Site, meteorological data recorded at the King’s Park Weather Station were used. For the assessments of SCISTW and PTWs at Sandy Bay, Cyberport, Wah Fu, Aberdeen and Ap Lei Chau, meteorological data recorded at the Green Island Weather Station were used. Since the construction activities would be undertaken at ground level, the worst dust impact on the ASRs would be at the ground floor of the ASRs. The height of 1.5m above ground, which is the breathing level of human, was adopted for construction dust impact assessment.

3.25 The five years TSP average monitoring data recorded at EPD’s Central/Western and Sham Shui Po air quality monitoring stations are 75mg/m³ and 79mg/m³ respectively. For this assessment, 79mg/m³ was taken as the TSP background concentration.

Construction Odour Impact

3.26 An odour impact assessment was conducted in accordance with the following procedures to identify and locate the odour emission sources and to determine the extent and level of odour impact during the upgrading of the PTWs and SCISTW.

· Identify and locate the existing and future odour emission sources within the study area;

· Identify and locate representative ASRs that may be affected by the odour sources;

· Review the construction method that would affect odour emission;

· Assess cumulative odour impact due to other concurrent projects

Operation Odour Impact

3.27 Odour impacts on ASRs were modeled with the air dispersion model, ISCST3 as recommended in EPD’s “Guidelines on Choice of Models and Model Parameters”. Hourly meteorological data for the year 2005 (including wind speed, wind direction, air temperature, Pasquill stability class and mixing height) of the King’s Park or Green Island Weather Station were employed for the model run. For the impact assessments of PTWs at North Point, Wan Chai East Central and Fung Mat Road Site, meteorological data recorded at King’s Park Weather Station were used. For the assessments of SCISTW and PTWs at Sandy Bay, Cyberport, Wah Fu, Aberdeen and Ap Lei Chau, meteorological data recorded at Green Island Weather Station were used. The urban dispersion mode in ISCST3 model was selected.

3.28 The modelled hourly odour concentrations at the ASRs was converted into the 5-second odour concentration so as to compare with the EIAO-TM odour criteria. In accordance with EPD’s “Guidelines on Choice of Models and Model Parameters”, it is recommended to follow the methodologies proposed by Duffee et al.^[1] and Keddie^[2] in performing the conversion from hourly and 5-second average concentration. More recent researches indicated that the peak-to-mean ratio of odour dispersion would depend upon the type of source, atmospheric stability and distance downwind. For the purpose of this assessment to produce more reasonable predictions for odour dispersion from wake-affected point sources, reference was made to the peak-to-mean ratio for wake-affected point source stipulated in “Approved Methods for Modelling and Assessment of Air Pollutants in New South Wales” published by the Department of Environment and Conservation, New South Wales, Australia (NSW Approved Method). As stated in the NSW Approved Method, where nearby buildings interfere with the trajectory and growth of the plume, the source is called a wake-affected point source. A point source is wake-affected if stack height is less than or equal to 2.5 times the height of buildings located within a distance of 5L (where L is the lesser of the height or width of the building) from each release point.

3.29 The dispersion modelling techniques employed for this assessment was followed those described in EPD’s “Guidelines on Choice of Models and Model Parameters” using ISCST3 model except the use of alternative peak-to-mean ratios discussed above. However, it should be noted that the peak-to-mean ratios stated in the NSW Approved Method are derived based on experimental and theoretical analyses and assuming a 0.1% exceedance level (Ref.: Statistical Elements of Predicting the Impact of a Variety of Odour Sources, Peter R. Best, Karen E. Lunney and Christine A. Killip, Water Science and Technology, Australia, 44: 9 pp 157-164 2001). In other words, there would be a 0.1% probability that the actual peak concentration would be higher than those derived with the peak-to-mean ratios stated in the NSW Approved Method.

3.30 In accordance with the NSW Approved Method, the conversion factors are used for converting the 1-hour average concentrations to 1-second average concentrations. As a conservative approach, these conversion factors were directly adopted for converting the 1-hour average concentrations predicted by the ISCST3 model to 5-second average concentrations for compliance checking with the odour criteria. The conversion factors to be adopted in this assessment for different stability classes for wake-affected point sources are shown in Table 3.7.

Table 3.7 Conversion Factors for Wake-affected Point Sources

Pasquill Stability Class	Conversion Factor (1 hour to 5 seconds)
A	2.3
B	2.3
C	2.3
D	2.3
E	2.3
F	2.3

Odour Emission Rate

3.31 In-situ odour sampling was undertaken to measure the odour concentrations of existing odour sources at the PTWs and SCISTW. Odour sampling was conducted in both summer and winter season to evaluate the worst case scenario. The measured results indicated that summer is the worst case scenario and therefore the measured odour emission rates in summer season were adopted in this assessment. Odour concentration was determined by a Forced-Choice Dynamic Olfactometer (Olfactomat-n2) in accordance with the European Standard Method (EN13725). Odour gas samples were collected by using an odour sampling system which includes a battery-operated air pump, a sampling vessel, and an odour bag. A dynamic flux hood was employed in area sources sampling either over water surfaces or solid surfaces. A specific odour emission rate (SOER) at each area source was calculated by the following equation. The baseline odour survey report in summer is given in Appendix 3.2. Summary of odour emission rates at PTW and SCISTW are shown in Table 3.8.

SOER(ou/m^2/s) =	Odour concentration (ou/m^3) xAir flow rate inside hood (m^3/s)
	Covered surface area (m^2)

Table 3.8 Summary of measured or estimated odour emission rate

Location	Emission Rate
SCISTW
Distribution Channel	6.71 ou/m^2/s
Flocculation Tanks	5.68 ou/m^2/s
Primary Sedimentation Tanks	6.93 ou/m^2/s
Effluent Weirs and Drop Shafts of Sedimentation Tanks (detailed calculation of odour emission rate are shown in Appendix 3.4)	1605.08 ou/s/unit
Overflow Chamber near NW KLN Pumping Station	12.29 ou/m^2/s
Flow Distribution Chamber	6.79 ou/m^2/s
Dewatered Sludge	20.17 ou/m^2/s
PTW
Solids Handling Area	14.72 ou/m^2/s

Note: All the emission rates presented in the table are before any correction for ambient temperature described in Sections 3.34 and 3.35 below.

Variation of Odour Emission from Sedimentation Tanks with Different Surface Flow Rate

3.32 To demonstrate that the measured odour emission rate collected under the current SCISTW operation would represent the worst case scenario, the factor for changes of surface flow rate under different operation scenarios were calculated by the following equation (Design Manual: Odor and Corrosion Control in Sanitary Sewerage Systems and Treatment Plants (1985), USEPA).

F = 0.7 (n²V³ / R^4/3)^3/8 [H₂S]

F = V^9/8 K

Where K = 0.7 (n² / R^4/3)^3/8 [H₂S]

F = odour flux (g/m²-hr)

n = Mannings’ Coefficient (0.014 was assumed)

V = velocity of sewage (m/s)

R = hydraulic radius (m)

[H₂S] = H₂S molecule concentration in sewage

Table 3.9 Summary of odour flux under different surface overflow rates

	Current Operation	HAT2A (Design Operation)	HATS2A (with operation of 38 tanks)	HATS2A (with operation of 46 tanks)
Average flow rate (m^3/day)	1,357,000	2,447,000	2,447,000	2,447,000
No. of units (total)	38	46	46	46
No. of units (in duty)	20	40	38	46
Effective surface area (m^2/tank)	815.5	815.5	815.5	815.5
Surface overflow rate (m/hr) in normal operation	3.47	3.13	3.29	2.72
Percentage change of odour flux compare with current operation	N/A	Reduce 11%	Reduce 6%	Reduce 24%

3.33 From Table 3.9, current operation was found to have the highest surface overflow rate. The measured emission rate under current SCISTW operation would therefore represent the worst case scenario and could be applied to different operation modes under HATS2A.

Correction Factor for Ambient Temperature

3.34 To determine the worst case scenario for odour impact assessment, temperature adjustments on the measured odour emission rates at SCISTW were required. The odour surveys at SCISTW were carried out on 28 to 31 August 2006 and the averaged daytime temperature was 29^oC. Based on Year 2005 to 2007 meteorological data from the Hong Kong Observatory, the mean daily maximum ambient temperature in the summer (June – September) were in the range of 29 to 33^oC. With reference to the Hydrogen Sulphide Control Manual (Technological Standing Committee on Hydrogen Sulphide Corrosion in Sewage Works, 1989), the equation below presented by Pomeroy and Parkurst was taken to estimate the variation of odour emissions due to temperature changes:

G = M[BOD₅]1.07^T-20

where G sulphide flux from wall slimes, g/m²h

[BOD₅] 5-day biochemical oxygen demand

T temperature, ^oC

M coefficient, m/h

3.35 Based on the above equation, the sulphide flux increased by about 31% when temperature increased from 29^oC to 33^oC. Therefore, 31% increase or a 1.31 correction factor was applied in the measured odour emission rate to estimate the worst case odour emission in SCISTW and the PTWs.

Deodorization System

3.36 All odour sources in the PTWs and SCISTW will be ventilated to deodorizer for treatment before discharging to the environment. The odour emission rate, exit velocity and diameter of the vent pipe were based on the design specifications of the deodorizing units provided by the Engineer during the course of this EIA study. One or two treatment stage(s) of deodorization system will be installed. For the purpose of this EIA, the assessments were carried out based on the odour removal efficiencies assumed for the deodorization system that are achievable using nowadays technologies. With reference to the “Code of Practice on Assessment and Control of Odour Nuisance from Waste Water Treatment Works, April 2005” published by the Scottish Executive, the odour removal efficiency of two common odour abatement systems namely biofilter and dry scrubbing (carbon or impregnated media) are 95% or more. Therefore, for one stage and two stages of deodorization system, the practicable odour removal efficiency could be up to 95% and 99.75% respectively. For the purpose of this assessment, more conservative odour removal efficiencies of 80% to 90% and 97% were assumed for one stage and two stages deodorization system respectively. For the purpose of this assessment, two stages odour treatment with 97% odour removal efficiency will be adopted for SCISTW (except Chamber 15A), and the Chlorine Contact Tank. For the drop shaft, upgraded facilities of PTWs and the SCISTW Chamber 15A, only one stage deodorization system (e.g. biofilter) with 90% odour removal efficiency will be installed. Table 3.10 shows the performance of deodorization systems that will be installed at different locations. Subject to future detailed design, the Engineer should design the deodorization system to achieve the odour removal efficiency stated in Table 3.10.

Table 3.10 Summary of Required Odour Removal Efficiency for Deodorization System

Location	Possible Treatment Technology	Odour Removal Efficiency
All Drop Shaft and upgraded facilities of PTWs	Biofilter	90%
SCISTW and Chlorine Contact Tank	Biofilter plus activated carbon	97%
SCISTW Chamber 15A	Biofilter	90%
Existing deodorizer at PTWs	Activated carbon	80%

Identification of Environmental Impacts

Construction Dust

Preliminary Treatment Works and Works Areas for Sewage Conveyance System

3.37 With reference to the construction methods described in Section 2, the potential dust impact associated with the proposed construction work would be minimal. The major activities include construction of production/drop shafts and upgrading of the existing facilities.

3.38 The major upgrading works inside PTWs would involve replacement of sewage treatment facilities (such as raked screen, vortex-type grit separator, washpress and screw grit classifier), installation of biofilter for gaseous treatment, and/or construction of new pumping station. The construction activities would be minor excavation works, material handling and concreting operation.

3.39 Referring to the construction sequences of each PTW as recommended in the “Preliminary Design Report on PTW Upgrading Works” prepared by the engineer under this Study, the construction activities for the PTW upgrading works would mostly be carried out within the PTW site. Given the limited work area for the PTWs upgrading works, the potential dust impacts at the ASRs in the vicinity of the PTWs would be low. All the above activities are not expected to generate considerable amount of construction dust. With the implementation of the control measures stipulated in the Air Pollution Control (Construction Dust) Regulation, construction dust impact to the surrounding air sensitive receivers would be minimal.

3.40 Other construction works within the site boundary of each of the PTWs mainly are the construction of drop shafts in all the PTWs. According to the Preliminary Design Report on PTW Upgrading Works, the upgrading works for each PTW would commence after the completion of the major works of the drop shaft construction at the respective PTW. The upgrading works of PTWs would therefore not overlap with the drop shaft construction works.

3.41 Surface excavation works (for construction of production and/or drop shafts) were also proposed at some works areas for the sewage conveyance system (SCS). With the implementation of the control measures stipulated in the Air Pollution Control (Construction Dust) Regulation, construction dust impact to the surrounding air sensitive receivers would be minimal.

Stonecutters Island Sewage Treatment Works

3.42 The major works for SCISTW would be the expansion of the existing chemical enhanced primary treatment capacity to cope with the anticipated population and economic growth (i.e. increase the number of primary sedimentation tanks and expansion of sludge dewatering/handling facilities and chemical storage and dosing facilities). The major dusty construction activities would be site clearance, piling works, excavation works for the new primary sedimentation tanks, construction of box culverts and the main pumping station. Most of the works would involve superstructure construction and concreting works which are not dusty construction activities.

Construction Odour Impact

Preliminary Treatment Works

3.43 The existing sewage treatment facilities at PTWs would require temporary sewage structures/facilities during upgrading works. With reference to the information provided by the engineer, phased implementation of the proposed works and temporary flow diversion at each PTW would be required to minimize disruption to plant operation and maintenance.

3.44 The construction sequence of the proposed upgrading works for the PTWs would be formulated in such a way to avoid any additional odour emissions from the operation of the PTWs during the construction stage. The enclosing structure as well as any associated deodorization facilities for the existing odour sources within the PTWs would not be altered prior to the decommissioning of the affected odour sources during the construction phase. All the new / temporary odour sources related to the future interim operation of the upgraded PTW would either be enclosed within building structure or located underground with odorous air collected to temporary / permanent deodorization facilities for treatment before discharging to the environment. A typical construction sequence is (1) construct a new/temporary facilities/effluent channel and install temporary/permanent deodorizer; (2) divert sewage to new/temporary facilities/effluent channel which would be fully enclosed and odorous air would be collected to temporary/permanent deodorizer for treatment; (3) demolish the existing facilities/effluent channel; (4) discharge effluent to drop shaft; (5) install new deodorization system; and (6) landscaping works and roadworks. In addition, the discharges of the temporary / permanent deodorizer to be installed during the construction phase would not be placed closer to the nearby ASRs as compared with the existing odour sources of the respective PTW. Therefore, potential odour impacts during PTW upgrading should not be worse than the existing situation.

3.45 Based on the latest information, no odour source from nearby concurrent projects is anticipated. Cumulative odour impact is therefore not anticipated.

Stonecutters Island Sewage Treatment Works

3.46 The construction works would not affect or involve the existing sewage treatment facilities. Therefore no temporary sewage treatment structure would be provided at SCISTW during construction period and no additional odour impact would be expected.

Operation Odour Impact

Preliminary Treatment Works and Works Areas for Sewage Conveyance System

3.47 The PTWs are designed to provide screening and grit removal to the incoming sewage before conveying the flows through a network of deep SCS to SCISTW for treatment and final disposal.

3.48 For the PTWs with inlet pumping stations, i.e. North Point PTW, Wan Chai East PTW, Central PTW, Sandy Bay PTW, Cyberport PTW and Aberdeen PTW, sewage collected will first pass through coarse screens to remove large objects in the sewage to protect the pumps. Sewage will then be lifted up by the sewage pumps before entering the downstream screening and degritting facilities. There is no inlet pumping station in Ap Lei Chau PTW and Wah Fu PTW, at which the sewage from the incoming sewers will be conveyed to the inlet chamber immediately upstream of the screening facilities. Potential odour emission would be expected in the inlet pumping station and the inlet chamber.

3.49 Sewage will then pass through fine screens and grit removal to further screen out the large objects or particles. The collected solids will be compacted by the screening’s handling equipment to reduce water content. Those exposed facilities would cause odour nuisance if not properly mitigated.

3.50 The sewage treatment facilities and screen/grits storage area would be enclosed. A new deodorization system will be installed in the PTWs to treat odorous gases collected from the enclosed channels/tanks and building structures. The air within these facilities would be ventilated to deodorizers for treatment before discharging to the environment. The ventilation system would also maintain a slight negative pressure within the facilities. The discharge locations of the existing and future deodorization systems are shown in Figures 3.10 to 3.17.

3.51 Potential odour sources for different treatment facilities in the PTWs were identified during site visits. Some odour sources are currently mitigated with deodorization facilities. However, to further reduce odour emissions from those existing facilities that would not be upgraded under this Project, it is proposed to upgrade the deodorization facilities at the PTWs in Wan Chai East and Sandy Bay to biofilter. Besides, it is also proposed to relocate the discharge location of the existing deodorizer at Aberdeen PTW further away from nearby ASRs and to increase the discharge velocity of the existing deodorizer at the Central PTW to 10 m/s. Existing and future odour mitigation measures are summarized in Table 3.11.

Table 3.11 Potential Odour Sources and Existing/Proposed Odour Mitigation Measures at PTWs

PTWs	Potential odour source	Existing odour control measures	Existing odour control measures to be upgraded	Planned odour control measures
North Point PTW	Wet well of inlet pumping station	Covered	N/A	Covered and single stage of odour treatment will be provided.
	Screens	Enclosed with provision of deodorizer
	Distribution Channel	Covered
	Grit Traps	Enclosed with provision of deodorizer
	Effluent Channel	Covered
	Screenings/Grit Handling Area	Enclosed with provision of deodorizer
	New inlet pumping station	N/A	N/A	Covered and foul air will be ventilated to deodorizer (biofilter) for treatment which is constructed under the other project.
	Drop Shaft (for future PTW)	N/A	N/A	Covered and foul air will be ventilated to deodorizer for treatment.
Wan Chai East PTW	Inlet pumping station (Wet well & coarse screen)	Enclosed with provision of deodorizer (Activated Carbon)	One of the existing deodorizer will be kept. Another existing deodorizer will upgrade to stage 1 of odour treatment.	N/A
	Screens
	Distribution Channel
	Grit Traps
	Effluent Channel
	Screenings/Grit Handling Area
	New Transfer Pumping Station	N/A	N/A	Covered and single stage of odour treatment will be provided.
	Drop Shaft (for future PTW)	N/A	N/A	Covered and foul air will be ventilated to deodorizer for treatment.
Central PTW	Inlet pumping station (Wet well & coarse screen)	Enclosed with provision of deodorizer	Existing deodorizer will be kept and the discharge velocity will increase to 10m/s.	N/A
	Screens	Covered / enclosed without provision of deodorizer	N/A	Covered and single stage of odour treatment will be provided.
	Distribution Channel	Covered without provision of deodorizer
	Grit Traps
	Effluent Channel
	Screenings/Grit Handling Area	Open, but mitigated by spraying of deodorant
	Drop Shaft (for future PTW)	N/A	N/A	Covered and foul air will be ventilated to deodorizer for treatment.
Fung Mat Road	Junction Shaft	N/A	N/A	Covered and foul air will be ventilated to deodorizer for treatment.
Sandy Bay PTW	Influent Channel	Enclosed / covered with provision of deodorizer (Activated Carbon)	Existing deodorizer will be upgraded to achieve 90% odour removal efficiency	N/A
	Screens
	Distribution Channel
	Grit Traps
	Effluent Channel
	Screenings/Grit Handling Area
	New Transfer Pumping Station	N/A	N/A	Covered and single stage of odour treatment will be provided.
	Drop Shaft (for future PTW)	N/A	N/A	Covered and foul air will be ventilated to deodorizer for treatment.
Cyberport PTW	Influent Channel	Enclosed / covered with provision of deodorizer	Existing deodorizer will be kept.	N/A
	Screens
	Distribution Channel
	Grit Traps
	Effluent Channel
	Screenings/Grit Handling Area
	New pumping station	N/A	N/A	Covered and single stage of odour treatment will be provided.
	Drop Shaft (for future PTW)	N/A	N/A	Covered and foul air will be ventilated to deodorizer for treatment.
Wah Fu PTW	Influent Channel	Covered without provision of deodorizer	N/A	Covered and single stage of odour treatment will be provided.
	Screens
	Distribution Channel
	Grit Traps
	Effluent Channel
	Screenings/Grit Handling Area
	Drop Shaft (for future PTW)	N/A	N/A	Covered and foul air will be ventilated to deodorizer for treatment.
Aberdeen PTW	Inlet pumping station (Wet well & coarse screen)	Enclosed with provision of deodorizer	Existing deodorizer will be kept and the discharge location will be relocated further away from ASRs.
	Screens	Enclosed / covered without provision of deodorizer	N/A	Covered and single stage of odour treatment will be provided.
	Distribution Channel
	Grit Traps
	Effluent Channel
	Screenings/Grit Handling Area
	Drop Shaft (for future PTW)	N/A	N/A	Covered and foul air will be ventilated to deodorizer for treatment.
Ap Lei Chau PTW	Influent Channel	Enclosed / covered without provision of deodorizer.	N/A	Covered and single stage of odour treatment will be provided.
	Screens
	Distribution Channel
	Grit Traps
	Effluent Channel	Without cover
	Screenings/Grit Handling Area	Enclosed / covered without provision of deodorizer.
	Night Soil Disposal Area	Without cover		The night soil will be discharged to inlet chamber through the discharge pipe of septic waste tanker. Disposal area will be enclosed and foul air will be ventilated to deodorizer for treatment. A potential odour source namely a sump pit (0.25m^2) will be constructed for collection of wastewater.
	Drop Shaft (for future PTW)	N/A	N/A	Covered and foul air will be ventilated to deodorizer for treatment.

3.52 The estimated unmitigated and mitigated odour emissions from the PTWs are summarized in Table 3.12 below. The emission sources from the exhaust vent pipes of the deodorizing units were modeled as point sources in the ISCST3 model. The odour emission rate for existing unit, exit velocity and diameter of the vent pipe were based on the design specifications of the deodorizing units as provided by the Engineer. Detailed odour emission rate calculations are provided in Appendix 3.3.

Table 3.12 Odour Emission Rate at PTWs

Location	Unmitigated Odour Emission Rate, ou/s	Deodorizer Requirement						Mitigated Odour Emission Rate, ou/s
		Deodorizer Discharge ID		Discharge Height, m	Total Discharge cross-sectional Area, m^2	Discharge velocity, m/s	Odour removal efficiency
North Point PTW
PTW treatment works	5.0045E+03	F-NP-DO1		8	1.51	8	90%	5.0045E+02
New inlet pumping station	2.8099E+03	E-NP-DO1 E-NP-DO2 E-NP-DO3		14.3	0.64 0.64 0.64	8	90%	2.8099E+02
Drop Shaft	3.5160E+02	F-NP-DO2		4	0.05	8	90%	3.5160E+01
Wan Chai East PTW
New Transfer Pumping Station	3.5160E+03	F-WC-D01		8	0.35	8	90%	3.5160E+02
Existing inlet pumping station and treatment works	4.3950E+02 2.7334E+03 6.2919E+03	E-WC-DO1 E-WC-DO2 E-WC-DO3		9.1	0.27 0.85 0.82	8	80% 90% 90%	8.7900E+01 2.7334E+02 6.2919E+02
Drop Shaft	3.5160E+02	F-WC-DO2		4	0.16	8	90%	3.5160E+01
Central PTW
PTW treatment works	7.2020E+03	F-CE-DO1	10		1.87	8	90%	7.2020E+02
Existing inlet pumping station	1.3882E+03 6.0600E+02 6.0600E+02	E-CE-DO1 E-CE-DO2-1 E-CE-DO2-2	13		0.98 0.43 0.43	10	80% 80% 80%	2.7763E+02 1.2120E+02 1.2120E+02
Drop Shaft	3.5160E+02	F-CE-DO2	4		0.18	8	90%	3.5160E+01
Fung Mat Road Site
Junction Shaft	1.7580E+03	F-FM-DO1	4		1.08	8	90%	1.7580E+02
Sandy Bay PTW
New Transfer Pumping Station	3.5160E+03	F-SB-DO1	8		0.35	8	90%	3.5160E+02
Drop Shaft	3.5160E+02	F-SB-DO2	4		0.12	8	90%	3.5160E+01
Existing preliminary treatment works complex	2.8439E+03	E-SB-DO1	10		0.89	8	90%	2.8439E+02
Cyberport PTW
New Pumping Station	3.5160E+03	F-CB-DO1	13		0.35	8	90%	3.5160E+02
Existing preliminary treatment works building	2.2286E+03	E-CB-DO1	5		0.25	13.1	80%	4.4572E+02
Drop Shaft	3.5160E+02	F-CB-DO2	4		0.1	8	90%	3.5160E+01
Wah Fu PTW
PTW treatment works	1.9479E+03	F-WF-DO1	9.5		0.73	8	90%	1.9479E+02
Drop Shaft	1.7580E+02	F-WF-DO2	4		0.03	8	90%	1.7580E+01
Aberdeen PTW
PTW treatment works	5.0754E+03	F-AB-DO1	12		1.37	8	90%	5.0754E+02
Existing inlet pumping station	1.9848E+03	E-AB-DO1	12		1.09	10	80%	3.9696E+02
Drop Shaft	3.5160E+02	F-AB-DO2	4		0.06	8	90%	3.5160E+01
Ap Lei Chau PTW
PTW treatment works	3.9009E+03	F-AL-DO1	11		1.32	8	90%	3.9009E+02
Drop Shaft	1.7580E+02	F-AL-DO2	4		0.01	8	90%	1.7580E+01

Stonecutters Island Sewage Treatment Works

3.53 Existing odour sources at the SCISTW were identified based on the findings from on-site survey and odour patrol.

3.54 The work flows of the SCISTW (for both HATS Stage 1 and HAT Stage 2A) are described as follow:

· Main pumping station for pumping sewage from PTW followed by Influent Channels and distributing them equally to the Rapid Mix Chambers. Currently, parts of the Influent Channels and Rapid Mix Chambers have been covered and the exposed sections would be potential sources of odour emissions.

· Rapid Mix Chambers for mixing chemicals into the raw sewage flow to enhance the sedimentation process.

· Followed by the Flocculation Tanks for providing an environment to allow the chemicals to form a floc that will make the sedimentation process more efficient. Currently, the exposed surfaces have the potential to release odour.

· Followed by the Main Aerated Distribution Channels for distributing the flocculated flow equally to the Sedimentation Tanks. The exposed surfaces have the potential to release odour.

· In the Sedimentation Tanks, the flocculated sewage will be settled and collected by sludge collection system. Most of the lighter-than-water scum will float to the top of the Sedimentation Tanks and be collected. In the Sedimentation Tanks, the turbulence resulting from the flow over weirs and evaporative losses from quiescent liquid surfaces of the wastewater treatment tanks would be the main sources of odour emissions.

· Sludge collected from the Flocculation and Sedimentation Tanks by the sludge collection system will be pumped to the Sludge Tanks.

· The sludge treatment facilities at SCISTW mainly includes sludge/scum collection system, sludge holding tanks, and sludge dewatering centrifuges, dewatered sludge conveying system, dewatered sludge silo, and dewatered sludge loading bay.

· Scum collected by the scum collection system will be pumped to the Sludge Treatment Facilities via a sludge conveying system. The sludge conveying system is totally enclosed with gas extraction. Chemical wet scrubbers are installed for treating the odorous gases generated from the dewatering house and sludge conveyors, as well as the sludge loading bay. A new deodorizer for sludge facilities will be installed.

· The sewage will enter the disinfection facilities for disinfection where located at a site off Container Port Road. The exposed surfaces of chlorine contact tank have the potential to release odour.

· Treated sewage flows will exit the disinfection facilities through effluent culverts that connect to the plant outfall system.

3.55 Some existing treatment facilities have already been enclosed/covered and odour emission to the atmosphere is not expected. For those existing odour emitting areas that are not covered, they will be enclosed with air ventilated to deodorizers for treatment before discharge to the environment.

3.56 The reference design of the SCISTW for the purpose of this HATS Stage 2A EIA study comprises of the expansion of existing chemically enhanced primary sedimentation tanks and sludge dewatering, handling and disposal facilities together with the provision of disinfection works. These treatment facilities are additional odour emission sources. The air within these facilities will be ventilated to deodorizers for treatment before discharge to the environment. The ventilation system will also maintain a slight negative pressure within the facilities. Leakage of odour from these facilities to the outside environment is not expected. Two treatment stages of deodorization system will be installed in the SCISTW, Stage 1 is biofilter and Stage 2 is activated carbon. Layouts of the planned upgraded treatment facilities and two proposed deodorizer system options are shown in Figure 3.19. The identified potential odour sources for the existing and the upgraded sewage treatment facilities are summarized in Table 3.13.

Table 3.13 Potential Odour Sources of Existing & Upgraded Treatment Facilities in SCISTW

Sewage Treatment Facilities	Existing Odour Control Measures	Planned Odour Control Measures
Existing Treatment Facilities
Main Pumping Station and Riser Shaft	Enclosed and air exhausted via a deodorizing unit	Odour sources to be covered or enclosed. The foul air will be ventilated to deodorizer for 2 stages treatment before discharging to the atmosphere.
Influent Upflow Structure	Covered / enclosed and air exhausted via a deodorizing unit
Rapid Mixing Tank
Flocculation Tanks	Nil
Distribution Channels
Sedimentation Tanks, weir & Drop Shafts
Scum Pit
Sludge Storage Tanks	Enclosed and air exhaust via a deodorizing unit
Sludge Dewatering Building
Sludge Cake Silos
Sludge Conveyors
Sludge Loading Bays
Flow Distribution Chamber	Nil
North West Kowloon PTW
North West Kowloon PTW – Pumping Station
North West Kowloon PTW – Overflow Chambers
Sludge Transfer Tanks	Normal Operation including installed rubber seal at unloading door and manual washing and cleaning of sludge tankers	Refurbishment of sludge tanks with air-tight seal and implementation of thorough cleaning process for the sludge tankers
Upgraded Treatment Facilities
Main Pumping Station and Riser Shaft	N/A	Odour sources to be covered or enclosed. The foul air will be ventilated to deodorizer for 2 stages treatment before discharging to the atmosphere.
Influent Upflow Structure
Rapid Mixing Tank
Flocculation Tanks
Distribution Channels
Sedimentation Tanks, weir & Drop Shafts
Scum Pit
Sludge Storage Tanks
Sludge Dewatering Building
New Sludge Cake Silos
New Flow Distribution Chamber
Chlorination Contact Tank
Drop Shaft and Chamber 15A		Covered and foul air will be ventilated to deodorizer for treatment.

3.57 As described above, all odour sources (including HATS Stage 1 and HATS Stage 2A facilities) will be enclosed or covered with foul air ventilated to deodorizing units. The emission sources from the exhaust vent pipes of deodorizing units were modeled as point sources in the ISCST3 model. The exit velocity and diameter of the vent pipe would be based on the design specifications of the deodorizing units provided by the Engineer, which should achieve at least 97% odour removal efficiency as advised by the Engineer.

3.58 Total 2 design arrangements of the deodorizing system are proposed namely (1) Centralized design, which centralizes all foul air for treatment by 4 deodorizers and discharges from 4 locations; and (2) Decentralized design, which treats foul air with 9 deodorizers and discharges from 9 locations. The estimated unmitigated and mitigated odour emissions from the SCISTW are summarized in Table 3.14 below. Odour emission rate calculations are provided in Appendix 3.4.

Table 3.14 Odour Emission Rate at SCISTW

Facility	Unmitigated odour Emission Rate, ou/s	Deodorizer Requirement					Mitigated Odour Emission Rate, ou/s
		Deodorizer Discharge ID	Discharge Height, m	Total Discharge Cross-sectional Area, m^2	Discharge velocity, m/s	Total no. of discharge point
Option 1 - Centralized Design
Stage 1 MPS & Riser Shaft	317032.03	S-O1-DO1	25	7.84	20	4	9510.96
Stage 2A MPS & Riser Shaft
CEPT Facilities
Sludge Storage Tanks
Sludge Dewatering Building 1
Sludge Dewatering Building 2
NWKPS
NWKPS O/F Chamber
Flow Distribution Chambers
Existing Sludge Cake Silos
New Flow Distribution Chamber
New Sludge Cake Silos
NWKPTW	19963.88	S-O1-DO2	13	2.26	12.28	8	598.92
Chlorination Contact Tank	37776.64	S-C-DO1	11	1.13	7.2	4	1133.30
Drop Shaft and Chamber 15A	2630.22	S-C-DO2	4	0.57	8.84	2	263.02
Option 2 - Decentralized Design
CEPT Facilities (Odd No. Units) & Flow Distribution Channel)	146162.21	S-O2-DO1	12	1.86	20	1	4384.87
CEPT Facilities (Even No. Units) & NWKPS + NWKPS O/F chamber	136086.21	S-O2-DO2	12	1.86	20	1	4082.59
Sludge Treatment Facilities (include Sludge Storage Tanks, Sludge Dewatering Building 1 & 2, Existing and New Sludge Cake Silos)	19057.82	S-O2-DO3	6	2.40	12.58	3	571.73
Stage 1 MPS & Riser Shaft	6518.89	S-O2-DO4	18	1.13	12.28	4	195.57
Stage 2A MPS & Riser Shaft	6518.89	S-O2-DO5	18	1.13	12.28	4	195.57
NWKPTW	19963.88	S-O2-DO6	13	2.26	12.28	8	598.92
Flow Distribution Chambers	2688.01	S-O2-DO7	4.5	0.32	10.48	2	80.64
New Flow Distribution Chamber
Chlorination Contact Tank	37776.64	S-C-DO1	11	1.13	7.2	4	1133.30
Drop Shaft and Chamber 15A	2630.22	S-C-DO2	4	0.57	8.84	2	263.02

Note: (1) CEPT facilities include Influent upflow structure, distribution channel, flocculation tanks, sedimentation tanks & effluent weirs, drop shafts, scum pit and rapid mixing tank of sedimentation tanks

(2) MPS is Main Pumping Station

(3) NWKPTW, NWKPS & NWKO/F chambers are North West Kowloon PTW, NWKPTW Pumping Station & NWKPTW Overflow Chamber, respectively

(4) The emission rate included a 1.31 ambient temperature correction factor.

3.59 Other potential odour emission would be expected from the nearby West Kowloon Refuse Transfer Station (WKRTS). It is noted that the tipping hall is fully enclosed and provided with an air scrubbing system to control odour emission from the tipping hall before discharging to the atmosphere. Tipping hall is also maintained with a negative air pressure to prevent odour gas escaping from the entrance of the tipping hall. In accordance with the finding of the Approved Project Profile of “Development of a grease trap waste treatment facility at West Kowloon Transfer Station” (Application No.: DIR133/2005), operation of WKRTS shall comply with the 2 odour units criterion at the WKRTS site boundary. Taking into consideration further dispersion and hence dilution of the potential odour emissions from WKRTS to the nearby ASRs, the odour levels associated with WKRTS on the nearby ASRs would be expected to drop below 2 odour units.

Prediction and Evaluation of Environmental Impacts

Construction Dust (Unmitigated)

3.60 The maximum predicted 1-hour and 24-hour average TSP levels for construction of the Project are summarised in Table 3.15. Dust impacts are high at ASRs under the “unmitigated” scenario, and the predicted hourly and 24-hour average TSP concentrations exceeded the respective guideline level or criterion at a number of ASRs. The maximum predicted TSP hourly concentration would be 1,785µg/m³ at the Tin Shui Street Children’s Playground (NP7). No exceedance was predicted at the ASRs near the Cyberport PTW and the Ap Lei Chau PTW under the unmitigated scenario. The TSP contour plots in the vicinity of those two sites are shown in Figures 3.20 to 3.23. For the ASRs near the SCISTW, the highest predicted TSP hourly concentration would be 1,663µg/m³ at the Ngong Shuen Chau Barracks (SCI7). Details of the assessment results are given in Appendix 3.5.

Table 3.15 Predicted Maximum 1-hour Average TSP Concentrations at 1.5m above ground

ASR ID	Description	Predicted 1-hr TSP conc.^[1]	Predicted 24-hr TSP conc.^[2]
NP1	Block C, Healthy Gardens	345	168
NP2	Ruby Court	340	129
NP3	King’s Road Playground & Skating Area	709	232
NP4	Customs HQ Tower (planned)	1081	281
NP5	K. Wah Centre	862	269
NP6	Hong Kong & Islands Regional Office, WSD	675	113
NP7	Tin Shui Street Children's Playground	1785	789
WC1	HK Yacht Club	163	100
WC2	Wan Chai Sports Ground	483	271
WC3	Society for the Prevention of Cruelty to Animals	919	604
WC4	Rest Garden near Wan Chai Interchange	740	168
WC5	Elizabeth House	228	90
WC6	Commercial Buildings at 233 Gloucester Road	309	94
C1	Sheung Wan Fire Station	1038	316
C2	Water Front Divisional Police Station	232	89
C3	Sheung Wan Gala Point	267	98
C4	Fui Nam Building	193	111
FM1	Block A, Kwan Yick Building Phase III	216	118
FM2	Western Wholesale Food Market	542	295
SB1	University of Hong Kong Stanley Ho Sports Centre Pitch	633	195
SB2	Home for the Elderly	386	109
SB3	Maclehose Medical Rehabilitation Centre	350	123
SB4	The Duchess of Kent Children’s Hospital	477	124
CB1	Cyber Centre	347	124
CB2	Le Meridien Cyberport	417	101
CB3	Aegean Terrace	148	94
CB4	Block 18, Baguio Villa	103	80
CB5	Phase 1, Residence Bel-Air	85	80
CB6	Phase 2, Residence Bel-Air	85	80
CB7	Residential Bel-Air (Scheduled to be occupied in June 2008)	82	80
WF1	Wah Yu House, Wah Fu Estate	435	119
WF2	Wah Ming House, Wah Fu Estate	673	261
WF3	Waterfall Bay Park	247	111
AB1	Wah Lai House, Wah Kwai Estate	165	90
AB2	Hing Wai Centre	708	276
AB3	Shek Pai Wan Road Playground	612	143
AB4	Dairy Farm Ice and Cold Storage	870	346
AB5	Ka Chun House, Ka Lung Court	115	84
AB6	Ka Sing House, Ka Lung Court	120	85
ALC1	Mei Wah Court, South Horizons	104	84
ALC2	Horizon Plaza	93	80
ALC3	Shell Ap Lei Chau Depot	204	96
SCI1	Government Dockyard Offices	511	191
SCI2	Ngong Shuen Chau Barracks Group 1	305	131
SCI3	COSCO Hit Terminal	610	198
SCI4	KMB Depot Office	432	180
SCI5	Planned FSD Diving Rescue and Diving Training Centre	663	152
SCI6	Club House	924	222
SCI7	Ngong Shuen Chau Barracks Group 2	1663	1052
SCI8^(5)	Hoi Lai Estate	197	89
SCI9^(5)	Tack Ching Girl’s Secondary School	175	87
SCI10^(5)	Aqua Marine	162	87
SCI11^(5)	Mei Foo Sun Chuen	162	102

Note: (1) An hourly averaged TSP guideline level of 500µg/m³ should not be exceeded.

(2) A 24-hour averaged TSP criteria of 260µg/m³ should not be exceeded.

(3) Background TSP concentration of 79µg/m³ was included.

(4) Bold value indicates exceedance of TSP guideline or criterion.

(5) The worst affected height was detected at 5m above ground.

Construction Dust (Mitigated)

3.61 The unmitigated TSP concentrations are high at the ASRs near some PTWs and works areas. However, with the implementation of good site practice with regular watering, dust suppression could be achieved. According to USEPA AP-42, watering twice a day could generally reduce dust emission by half and hence the dust concentration by 50%. Hence, on the same basis, watering 4 and 8 times a day would achieve a dust removal efficiency of 75% and 87.5% respectively. Assessment results indicate that the following watering measures would be required to control the fugitive dust impacts:

· Watering twice per day within the worksites at North Point PTW, Wan Chai East PTW, Fung Mat Road Site, Sandy Bay PTW, Wah Fu PTW, Aberdeen PTW and SCS worksite at Aberdeen;

· Watering 4 times per day within worksites at the Central PTW;

· Continuous watering will be implemented at the barging points, if any, throughout the whole unloading process (a dust removal efficiency of 75% was assumed for the purpose of this assessment); and

· Watering 8 times per day within worksites at the SCS works area at Wan Chai East and North Point, SCISTW and the Disinfection Facilities of SCISTW.

3.62 With the above watering throughout the construction phase, no exceedance of the TSP guideline level or criterion was predicted at the ASRs near the PTWs and the works areas. The predicted 1-hour and 24-hour average TSP levels are shown in Table 3.16. Details of the assessment results are given in Appendix 3.6 and the TSP contour plots in the vicinity of the above PTWs and nearby works areas are given in Figures 3.24 to 3.37. Exceedances of the 1-hour average TSP of 500 m/m³ and the 24-hour average TSP AQO of 260 mg/m³ are noted in some areas at 1.5m above ground. However, they are not ASRs and no air sensitive areas use within these exceedance areas.

Table 3.16 Predicted Maximum 1-hour Average TSP Concentrations at 1.5m above ground under “Mitigated” Scenario

ASR ID	Description	Predicted 1-hr TSP conc^[1]	Predicted 24-hr TSP conc^[2]
NP1	Block C, Healthy Gardens	212	123
NP2	Ruby Court	209	103
NP3	King’s Road Playground & Skating Area	394	156
NP4	Customs HQ Tower (planned)	257	147
NP5	K. Wah Centre	470	174
NP6	Hong Kong & Islands Regional Office, WSD	312	92
NP7	Tin Shui Street Children's Playground	297	170
WC1	HK Yacht Club	100	84
WC2	Wan Chai Sports Ground	166	106
WC3	Society for the Prevention of Cruelty to Animals	277	153
WC4	Rest Garden near Wan Chai Interchange	162	98
WC5	Elizabeth House	100	81
WC6	Commercial Buildings at 233 Gloucester Road	108	84
C1	Sheung Wan Fire Station	319	138
C2	Water Front Divisional Police Station	117	82
C3	Sheung Wan Gala Point	126	84
C4	Fui Nam Building	108	87
FM1	Block A, Kwan Yick Building Phase III	146	98
FM2	Western Wholesale Food Market	309	185
SB1	University of Hong Kong Stanley Ho Sports Centre Pitch	356	137
SB2	Home for the Elderly	233	94
SB3	Maclehose Medical Rehabilitation Centre	215	101
SB4	The Duchess of Kent Children’s Hospital	278	102
WF1	Wah Yu House, Wah Fu Estate	257	99
WF2	Wah Ming House, Wah Fu Estate	376	170
WF3	Waterfall Bay Park	163	95
AB1	Wah Lai House, Wah Kwai Estate	122	84
AB2	Hing Wai Centre	393	178
AB3	Shek Pai Wan Road Playground	345	111
AB4	Dairy Farm Ice and Cold Storage	475	212
AB5	Ka Chun House, Ka Lung Court	97	81
AB6	Ka Sing House, Ka Lung Court	99	82
SCI1	Government Dockyard Offices	133	93
SCI2	Ngong Shuen Chau Barracks Group 1	107	85
SCI3	COSCO Hit Terminal	145	94
SCI4	KMB Depot Office	123	92
SCI5	Planned FSD Diving Rescue & Diving Training Centre	152	88
SCI6	Club House	185	97
SCI7	Ngong Shuen Chau Barracks Group 2	275	199
SCI8^(4)	Hoi Lai Estate	94	80
SCI9^(4)	Tack Ching Girl’s Secondary School	91	80
SCI10^(4)	Aqua Marine	89	80
SCI11^(4)	Mei Foo Sun Chuen	89	82

Note: (1) An hourly averaged TSP guideline level of 500µg/m³ should not be exceeded.

(2) A 24-hour averaged TSP criteria of 260µg/m³ should not be exceeded.

(3) Background TSP concentration of 79µg/m³ was included.

(4) The worst affected height was detected at 5m above ground.

Cumulative Dust Impacts from both Wan Chai East PTW and Concurrent Project (Mitigated Scenario)

3.63 The construction works of Wan Chai East PTW and works area next to the PTW would overlap with the Wan Chai Development Phase II (WDII). The construction activities of WDII also include reclamation and construction of Central-Wan Chai Bypass (CWB). Cumulative dust impacts have been assessed based on the latest information from the EIA Report for WDII & CWB project dated December 2007. A summary of the construction activities during the overlapping period of the two projects is given in Table 3.5.

3.64 It is identified that the worst affected month from the WDII Project is Nov 2012 (i.e Scenario 4 of WDII Project). In addition to ASRs WC1 to WC6, representative ASRs (A35 to A37, A40 & A41) within the study area that are closest to the construction sites of the WDII project was included for the construction dust assessment. Results indicate that with proper watering throughout the construction of Wan Chai East PTW and WDII projects, there would be no adverse cumulative dust impact. The following frequencies of watering are recommended:

· Twice a day for Wan Chai East PTW

· Eight times a day for the SCS works area next to PTW; and

· Four times a day for the WDII project

3.65 The emission rates for the WDII project were made reference to the WDII EIA report and summarized in Table 3.17. Detailed calculation of emission rate is presented in Appendix 3.1.

Table 3.17 Emission Factors for Construction Activities and Wind Erosion for WDII Project

Construction Activities	Emission Rate (g/m^2/s)	Remark
Road Construction, Building Construction and Material Handling (as Heavy Construction)	E = 3.113426E-05	- 50% work area - 75% reduction by water suppression (watering four times a day) -USEPA AP-42 5^th ED., S.13.2.3.3
Wind Erosion	E = 1.347666E-06	- 50% work area - AP-42 5^th ED., S.11.9 Table 11.9.4

Note: Table extracted from the Table 3.5 of WDII EIA report

3.66 As the major dust sources in the vicinity of the Wan Chai East PTW are associated with the WDII Project, this assessment has adopted the WDII EIA modelling approach in estimating the cumulative dust impacts as tabulated in Table 3.18 below. Worst case meteorological data was used to predict the cumulative worst-case 1-hour and 24-hour average TSP concentrations at representative discrete ASRs close to the construction works. The meteorological data used in the model were:

· Wind speed: 1 m/s

· Wind direction: 360 wind direction

· Stability class: D (daytime) & F (night time)

· Surface roughness: 1m

· Mixing height: 500 m

3.67 Daily TSP concentrations were calculated as follows:

Daily TSP concentration = (number of working hour)/24 x (1-hour average maximum TSP concentration during working hours) + (number of non-working hour)/24 x (1-hour average maximum TSP concentration during non-working hours) + Background

3.68 As stated in WDII EIA report, 10 working hours per day was assumed for the dusty construction work for WDII project. However, 12 working hours per day was adopted for the works of HATS2A project. For conservative approach, 12 working hours per day was adopted for calculation of daily TSP concentration.

3.69 A summary of mitigated cumulative 1-hour and 24-hour average TSP concentrations is shown in Table 3.18 and the TSP contour plots are given in Figures 3.25a and 3.32a. Results show that all ASRs are within the respective guideline or criterion.

Table 3.18 Predicted Cumulative Maximum 1-hour Average TSP Concentrations at 1.5m above ground under the “Mitigated” Scenario

ASR ID	Description	The Project^[1]		Cumulative^[1] [2]
		Predicted 1-hr TSP conc	Predicted 24-hr TSP conc	Predicted 1-hr TSP conc^[3]	Predicted 24-hr TSP conc^[4]
WC1	HK Yacht Club	100	84	197	143
WC2	Wan Chai Sports Ground	166	106	241	167
WC3	Society for the Prevention of Cruelty to Animals	277	153	297	196
WC4	Rest Garden near Wan Chai Interchange	162	98	163	125
WC5	Elizabeth House	100	81	139	112
WC6	Commercial Buildings at 233 Gloucester Road	108	84	140	113
A35^(5)	Great Eagle Centre	89	83	278	185
A36^(5)	Causeway Centre (Block A)	97	83	207	147
A37^(5)	Wanchai Swimming Pool	102	91	413	258
A40^(5)	Gloucester Road 169-170	101	87	154	119
A41^(5)	Gloucester Road 210	115	92	148	116

Note: (1) Background TSP concentration of 79µg/m³ was included.

(2) Predicted results based on the WDII & CWB EIA modelling approach.

(3) An hourly averaged TSP guideline level of 500µg/m³ should not be exceeded.

(4) A 24-hour averaged TSP criteria of 260µg/m³ should not be exceeded.

(5) Additional ASRs for WDII & CWB Project. The ASR ID and location is reference to WDII & CWB EIA Report.

Construction Odour Impact

3.70 As mentioned in Sections 3.42 to 3.45, there would be no additional odour emission from the PTWs and the SCISTW during their upgrading/expansion works. Additional odour impact from these facilities during the construction phase would not be expected.

Operation Odour Impact

3.71 Odour levels at the ASRs under the mitigated scenario have been predicted and the results are summarized in Tables 3.19 and Table 3.20. Details of the assessment results are given in Appendix 3.7. The modeling results showed that with the implementation of the proposed odour mitigation measures, the predicted odour levels at all the identified ASRs would be within the odour criterion. The odour contours at the worst hit level are illustrated in Figures 3.38 to 3.46. Exceedances of the 5OU are noted in some areas. However, no air sensitive uses are identified within these exceedance areas.

Table 3.19 Predicted maximum odour levels at ASRs (PTWs)

Area	ASR ID	Description	Odour level (5 seconds average) (ou)
North Point PTW	NP1	Block C, Healthy Gardens	1.93
	NP2	Ruby Court	1.88
	NP3	King’s Road Playground & Skating Area	0.17
	NP4	Customs HQ Tower (planned)	3.07
	NP5	K. Wah Centre	2.12
	NP6	Hong Kong & Islands Regional Office, WSD	1.83
Wan Chai East PTW	WC1	HK Yacht Club	0.60
	WC2	Wan Chai Sports Ground	0.46
	WC3	Society for the Prevention of Cruelty to Animals	3.03
	WC4	Rest Garden near Wan Chai Interchange	0.53
	WC5	Elizabeth House	0.69
	WC6	Commercial Buildings at 233 Gloucester Road	1.09
Central PTW	C1	Sheung Wan Fire Station	0.63
	C2	Water Front Divisional Police Station	1.32
	C3	Sheung Wan Gala Point	0.35
	C4	Fui Nam Building	0.94
Fung Mat Road Site	FM1	Block A, Kwan Yick Building Phase III	0.20
	FM2	Western Wholesale Food Market	0.20
Sandy Bay PTW	SB1	University of Hong Kong Stanley Ho Sports Centre Pitch	0.43
	SB2	Home for the Elderly	1.22
	SB3	Maclehose Medical Rehabilitation Centre	1.30
	SB4	The Duchess of Kent Children’s Hospital	0.41
Cyberport PTW	CB1	Cyber Centre	1.51
	CB2	Le Meridien Cyberport	1.50
	CB3	Aegean Terrace	1.05
	CB4	Block 18, Baguio Villa	0.55
	CB5	Phase 1, Residence Bel-Air	0.22
	CB6	Phase 2, Residence Bel-Air	0.25
	CB7	Residential Bel-Air (Scheduled to be occupied in June 2008)	0.16
Wah Fu PTW	WF1	Wah Yu House, Wah Fu Estate	1.34
	WF2	Wah Ming House, Wah Fu Estate	2.63
	WF3	Waterfall Bay Park	0.15
Aberdeen PTW	AB1	Wah Lai House, Wah Kwai Estate	0.60
	AB2	Hing Wai Centre	0.49
	AB3	Shek Pai Wan Road Playground	0.50
	AB4	Dairy Farm Ice and Cold Storage	0.31
	AB5	Ka Chun House, Ka Lung Court	0.25
	AB6	Ka Sing House, Ka Lung Court	0.27
Ap Lei Chau PTW	ALC1	Mei Wah Court, South Horizons	0.30
	ALC2	Horizon Plaza	0.16
	ALC3	Shell Ap Lei Chau Depot	0.15

Note: There is 0.1% probability of exceeding the predicted odour concentration inherent in the calculation method.

Table 3.20 Predicted maximum odour levels at ASRs (SCISTW)

ASR ID	Description	Odour level (5 seconds average) (ou)
		Option 1 Centralized Design	Option 2 Decentralize Design
SCI1	Government Dockyard Offices	1.2	1.5
SCI2	Ngong Shuen Chau Barracks Group 1	0.8	1.6
SCI3	COSCO Hit Terminal	1.6	1.8
SCI4	KMB Depot Office	1.3	1.9
SCI5	Planned FSD Diving Rescue and Diving Training Centre	1.3	2.2
SCI6	Club House	0.6	0.8
SCI7	Ngong Shuen Chau Barracks Group 2	1.6	1.7
SCI8	Hoi Lai Estate	0.8	1.0
SCI9	Tack Ching Girl’s Secondary School	0.7	0.8
SCI10	Aqua Marine	0.9	0.8
SCI11	Mei Foo Sun Chuen	0.8	1.0

Note: There is 0.1% probability of exceeding the predicted odour concentration inherent in the calculation method.

3.72 As described above, the peak-to-mean ratios stated in the NSW Approved Method are derived based on experimental and theoretical analyses and assuming a 0.1% exceedance level (Ref.: Statistical Elements of Predicting the Impact of a Variety of Odour Sources, Peter R. Best, Karen E. Lunney and Christine A. Killip, Water Science and Technology, Australia, 44: 9 pp 157-164 2001). In other words, there would be a 0.1% probability that the actual peak concentration would be higher than those derived with the peak-to-mean ratios stated in the NSW Approved Method.

Cumulative Odour Impacts Associated with WKRTS

3.73 As discussed in S3.59 above, operation of WKRTS shall comply with the 2 odour units criterion at the WKRTS site boundary. Taking into consideration further dispersion and hence dilution of the potential odour emissions from WKRTS to the nearby ASRs, the odour levels associated with WKRTS on the nearby ASRs would be expected to drop below 2 odour units. For conservative assessment, 2 odour units were added to the predicted maximum odour levels at ASRs (Table 3.20) to account for the worst-case cumulative odour impacts associated with WKRTS. The highest cumulative odour level of 4.2 OU is predicted at ASR SCI5 and the predicted worst-case cumulative odour levels at all the identified ASRs would be within the 5OU criterion. The cumulative odour contours at the worst hit level (40 m above ground for Option 1 & 20 m above ground for Option 2) are illustrated in Figure 3.47 and no ASRs are identified within the areas with predicted exceedances of the 5OU criterion except ASRs SCI4 & SCI5. However, the maximum height of ASRs SCI4 & SCI5 are less than 20m high and the highest predicted cumulative odour levels at ASRs SCI4 & SCI5 are less than 5OU. In other words, exceedances of the odour criterion due to cumulative odour impacts associated with WKRTS are not predicted at any air sensitive uses.

Mitigation of Environmental Impacts

Construction Phase

3.74 As discussed in Sections 3.63 to 3.69, the cumulative maximum 1-hour average and 24-hour average TSP concentrations were predicted to comply with the TSP guideline or criterion at all representative ASRs with the implementation of dust suppression measures. It is recommended that the requirements of the Air Pollution Control (Construction Dust) Regulation shall be adhered to during the construction period. In addition, good site practices and a comprehensive dust monitoring and audit programme are recommended to minimise cumulative dust impacts. Control measures relevant to this Project are listed below:

· Skip hoist for material transport should be totally enclosed by impervious sheeting;

· Vehicle washing facilities should be provided at every vehicle exit point;

· The area where vehicle washing takes place and the section of the road between the washing facilities and the exit point should be paved with concrete, bituminous materials or hardcore;

· Where a site boundary adjoins a road, streets or other areas accessible to the public, hoarding of not less than 2.4 m high from ground level should be provided along the entire length except for a site entrance or exit;

· Regular watering, with complete coverage, to reduce dust emissions from exposed site surfaces and unpaved roads, particularly during dry weather;

· Side enclosure and covering of any aggregate or dusty material storage piles to reduce emissions. Where this is not practicable owing to frequent usage, watering should be applied to aggregate fines;

· Open stockpiles should be avoided or covered. Where possible, prevent placing dusty material storage piles near ASRs;

· Tarpaulin covering of all dusty vehicle loads transported to, from and between site locations;

· Control of vehicle speed on unpaved site roads. Ten kilometers per hour is the recommended limit;

· Every stock of more than 20 bags of cement should be covered entirely by impervious sheeting placed in an area sheltered on the top and the 3 sides;

· Every vehicle should be washed to remove any dusty materials from its body and wheels before leaving the construction sites; and

· Instigation of an environmental monitoring and auditing program to monitor the construction process in order to enforce controls and modify method of work if dusty conditions arise.

Operation Phase

3.75 The fully covered design of the odour sources of the upgraded PTWs & SCISTW and the installation of deodorization system at the exhaust of ventilation system would adequately control potential odour impact. Adverse odour impact from the PTWs & SCISTW is not anticipated.

3.76 In addition, good housekeeping practices for the SCISTW and PTWs listed below should be followed to ameliorate any odour impact from the plant and these standard practices should be included in the plant operator manual.

· Screens should be cleaned regularly to remove accumulated organic debris

· Grit and screening transfer systems should be flushed regularly with water to remove organic debris and grit

· Grit materials should be transferred to closed containers to minimize odour escape

· Scum and grease collection wells and troughs should be emptied and flushed regularly to prevent putrefaction of accumulated organics

· Skim and remove floating solids and grease from primary clarifiers regularly

· Sludge should be frequently withdrawn from tanks to prevent the production of gases

· Sludge cakes should be transferred to closed containers

· Sludge containers should be flushed with water regularly

3.77 Besides, in order to avoid excessive extraction of the foul air from the drop shafts of the sedimentation tanks and also from the effluent flume structure of SCISTW to deodorization system, the extraction vent(s) of the deodorization system should be located away from the top openings of the drop shafts.

3.78 The odour impact from sludge transfer tanks could be controlled by properly design and good cleaning practices of the sludge transfer tanks. The loading opening of sludge transfer tank is the potential odour source during the transportation when there are gaps between the tank opening and its cover. DSD has issued a contract for the refurbishment works of the sludge transfer tanks and works are scheduled to be completed in early 2008. The first few lots of refurbished sludge tanks should be deployed for transporting sludge to the SENT Landfill since more sensitive receivers would be encountered during the road transportation. The air-tightness of the refurbished sludge tanks has been proved by DSD through trial tests. With thorough cleaning practice and regular condition test of the refurbished sludge tanks, odour emission and leachate leakage during storage and transportation are not anticipated. Further assessment and performance tests on the sludge tanks with regards to potential odour emissions would be conducted under the future EM&A programme for verification and monitoring purposes.

Evaluation of Residual Impacts

Construction Phase

3.79 With the implementation of dust suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation during construction, no adverse residual air quality impact would be expected.

Operational Phase

3.80 Air quality at the ASRs has been predicted to comply with the odour assessment criteria with the proposed mitigation measures, and adverse residual impact is not expected. To facilitate compliance of the odour criterion stipulated in the EIAO-TM, commissioning tests for all deodorization systems should be included in the Design and Construction Contract Document.

Environmental Monitoring and Audit

Construction Phase

3.81 With the implementation of mitigation measures stipulated in the Air Pollution Control (Construction Dust) Regulation, dust levels at all ASRs would comply with the dust criteria. Details of the monitoring requirements are presented in the stand-alone EM&A Manual.

Operational Phase

3.82 The predicted odour levels at the ASRs would comply with the EIAO-TM criterion. It is recommended that odour monitoring should be carried out during the operation phase to verify that the odour criteria are satisfied at the ASRs. In addition, for SCISTW, odour measurement should also be conducted at the exhaust stacks of the deodorization system to ensure that the total odour emission rate from SCISTW would not exceed the total mitigated odour emission rate estimated in this EIA (Table 3.14 refers). Details of the monitoring programme are presented in the EM&A Manual.

Conclusions

Construction Phase

3.83 Air quality impact from the construction of the Project was assessed. With the implementation of mitigation measures specified in the Air Pollution Control (Construction Dust) Regulation, dust nuisance at these ASRs would not be expected. An EM&A programme was recommended for the construction phase to verify that the dust criteria would be satisfied at the ASRs.

Operational Phase

3.84 Odour emission from the PTWs and SCISTW would be the main concern during the operation phase. Air dispersion modelling was conducted to simulate the potential odour impacts of the SCISTW and the PTWs on the ASRs. It is recommended that all the identified odour sources in the PTWs and SCISTW should be properly enclosed or covered, with the foul air drawn through deodorization units and discharged after treatment by biofilter and/or activated carbon. Good house keeping (regular cleansing schedule) should be conducted to minimize odour generation from the PTWs and SCISTW. It should be pointed out that the preceding odour modelling represents a worst-case scenario, i.e. maximum flow coupled with most adverse meteorological conditions, and the percentage reduction in odour to be achieved. With the proposed mitigation, the residual odour levels at the ASRs were predicted to comply with the odour criterion. It is also recommended that odour monitoring should be carried out during the operation phase to verify that the odour criterion is met at the ASRs.

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[1] Richard A. Duffee, Martha A. O”Brien and Ned Ostojic (1991). Odour Modelling – Why and How, Recent Developments and Current Practices in Odour Regulation, Controls and Technology, Air & Waste Management Association.

[2] Keddie, A. W, C(1980). Dispersion of Odours, Odour Control – A concise Guide, Warren Spring Laboratory.