3. Air Quality

3.1 Introduction

3.1.1 This section presents the assessment on the potential air quality impacts that are likely to be generated during the construction and operation phases of both the upgrading of the Cheung Chau STW and Pak She SPS and the sewers works of the Project. Appropriate mitigation measures were identified, where necessary, to mitigate the potential air quality impacts to acceptable levels.

3.1.2 This assessment has based on the criteria and guidelines for evaluation and assessment of air quality impacts as stated in Annexes 4 and 12 of the EIAO-TM and has covered the scope outlined in Section 3.4.1 of the EIA Study Brief.

3.2 Relevant Legislations, Standards & Guidelines

Environmental Impact Assessment Ordinance

3.2.1 For construction dust impact assessment, Annex 4 of EIAO-TM stipulates an hourly average of Total Suspended Particulate (TSP) concentration of 500 mg/m³ measured at 298K (25°C) and 101.325 kPa (1 atmosphere) should be met.

3.2.2 For odour impact assessment, Annex 4 of EIAO-TM stipulates an odour limit of 5 odour units based on an average time of 5 seconds at an air sensitive receiver should be met.

Air Pollution Control Ordinance

3.2.3 Hong Kong’s air quality is regulated through the Air Pollution Control Ordinance (Cap. 311) (APCO). The APCO specifies Air Quality Objectives (AQOs), which are the statutory limits for pollutants and the maximum allowable number of times that these may be exceeded over specified periods. These pollutants are defined as Criteria Pollutants (CP). The AQOs that have been defined for these CP are given in Table 3.1.

Table 3.1 : Hong Kong Air Quality Objectives

Pollutant	Concentration (mg/m^3)^(1) Averaging Period
	1 Hour^(2)	8 Hours^(3)	24 Hours^(3)	3 Months^(4)	1 Year^(4)
Sulphur Dioxide, SO2	800	-	350	-	80
Total Suspended Particulate, TSP	500 ^(7)	-	260	-	80
Respirable Suspended Particulates, RSP^(5)	-	-	180	-	55
Nitrogen Dioxide, NO2	300	-	150	-	80
Carbon Monoxide, CO	30,000	10,000	-	-	-
Photochemical Oxidants, (as ozone^(6))	240	-	-	-	-
Lead	-	-	-	1.5	-

Notes:

1) Measured at 298 K and 101.325 kPa (one atmosphere).

2) Not to be exceeded more than 3 times per year.

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

4) Arithmetic means.

5) Respirable Suspended Particulates means suspended particles in air with a nominal aerodynamic diameter of 10 mm or less.

6) Photochemical oxidants are determined by measurement of ozone only.

7) Hourly TSP limit is stipulated in the EIAO-TM.

3.2.4 The Government announced on 17 January 2012 the proposal to adopt the proposed new AQOs. The Air Pollution Control (Amendment) Bill 2013 has passed the Legislative Council and endorsed by Chief Executive on 18 July 2013. The Air Pollution Control (Amendment) Ordinance 2013 will come into operation on 1 January 2014. The proposed new AQOs are summarised in Table 3.2 for reference only.

Table 3.2 : Proposed New Air Quality Objectives for Hong Kong

Pollutant	Concentration (mg/m^3) Averaging Period
	10 Minutes	1 Hour	8 Hours	24 Hours	1 Year
Sulphur Dioxide, SO2	500 ^(1)	--	--	125 ^(1)	--
Respirable Suspended Particulates (PM10)	--	--	--	100 ^(2)	50
Fine Suspended Particulates (PM2.5)	--	--	--	75 ^(2)	35
Nitrogen Dioxide, NO2	--	200 ^(3)	--	--	40
Carbon Monoxide, CO	--	30,000 ^(4)	10,000 ^(4)	--	--
Ozone	--	--	160 ^(2)	--	--
Lead	--	--	--	--	0.5

Notes:

(1) Not to be exceeded more than 3 times per year

(2) Not to be exceeded more than 9 times per year

(3) Not to be exceeded more than 18 times per year

(4) No exceedances allowed

Air Pollution Control (Construction Dust) Regulation

3.2.5 The APCO’s subsidiary regulation Air Pollution Control (Construction Dust) Regulation defines notifiable and regulatory works activities that are subject to construction dust control.

Notifiable Works:

Ÿ Site formation;

Ÿ Reclamation;

Ÿ Demolition of a building;

Ÿ Work carried out in any part of a tunnel that is within 100 m of any exit to the open air;

Ÿ Construction of the foundation of a building;

Ÿ Construction of the superstructure of a building; or

Ÿ Road construction work.

Regulatory Works:

Ÿ Renovation carried out on the outer surface of the external wall or the upper surface of the roof of a building;

Ÿ Road opening or resurfacing work;

Ÿ Slope stabilization work; or

Ÿ Any work involving any of the following activities-

Ø Stockpiling of dusty materials;

Ø Loading, unloading or transfer of dusty materials;

Ø Transfer of dusty materials using a belt conveyor system;

Ø Use of vehicles;

Ø Pneumatic or power-driven drilling, cutting and polishing;

Ø Debris handling;

Ø Excavation or earth moving;

Ø Concrete production;

Ø Site clearance;

Ø or Blasting.

3.2.6 Notifiable works require that advance notice of activities to be given to EPD. The Regulation also requires the works contractor to ensure that both notifiable works and regulatory works will be conducted in accordance with the Schedule of the Regulation, which provides dust control and suppression measures.

Air Pollution Control (Specified Process) Regulation

3.2.7 The APCO provides licence control on certain polluting industrial processes known as "specified processes (SP)". The aim is to properly control and monitor the air pollution caused by the industries that have significant pollution potential. Through the terms and conditions of the licence, the owners of the premises used for the conduct of specified processes are required to use the best practicable means to prevent air pollution. Cement works such as concrete batching plant is classified as a specified process.

3.3 Baseline Environmental Conditions

3.3.1 Cheung Chau is situated at southeast of Lantau Island. It is a densely populated outlying island. Cheung Chau contains mostly developed areas including commercial uses, residential uses and community facilities.

3.3.2 The proposed sewage treatment upgrading works would be undertaken within the existing Cheung Chau STW which is located southwest of Tai Kwai Wan on Cheung Chau Island and adjacent to Pak Kok Tsui Road and Cheung Kwai Road. It is surrounded by the sea at three sides and Cheung Kwai Estate is located further to the east. Cheung Chau Slaughter House is located to the northwest of the Cheung Chau STW.

3.3.3 Buildings located in the immediate vicinity area of the existing Pak She SPS include Cheung Chau Fire Station, Cheung Chau Commercial Centre, an Electricity Sub-station, and low-rise residential buildings along Pak She Praya Road. The existing land uses in the vicinity of the proposed sewerage works are mainly developed areas comprise residential and commercial uses.

3.3.4 There is currently no EPD-operated air quality monitoring station located in Cheung Chau area. Historical air quality monitoring data from the nearest station, namely Tung Chung Air Quality Monitoring Station operated by EPD is taken to present the historical trend of the air quality condition near Cheung Chau area. Table 3.3 summarizes the annual average concentrations of the air pollutants recorded at the Tung Chung Air Quality Monitoring Station from Year 2007 to Year 2011.

Table 3.3 : Annual Average Concentration of Pollutants from Year 2007 to 2011 at EPD’s Air Quality Monitoring Station (Tung Chung)

Pollutant	Annual Average Concentration (mg/m^3)					5-year average (used as background)
	Year 2007	Year 2008	Year 2009	Year 2010	Year 2011
RSP	54	52	46	45	47	49
SO2	23	18	13	12	13	16
NO2	46	49	45	44	51	47
TSP	70	69	60	59	65	65
O3	40	41	47	44	44	43

Note:

Reference made to Air Quality in Hong Kong 2007-2011.

3.3.5 Odour patrol was conducted in areas near the Cheung Chau STW and Pak She SPS to review the existing background odour intensity of ambient air in the vicinity of the two sewage treatment facilities. The odour patrol exercise was conducted on 5^th, 6^th, 7^th and 16^th July 2012 summer time. During the odour patrol, the Cheung Chau STW and Pak She SPS were under normal operation and the temperature was generally higher than 30˚C. The weather conditions such as wind direction and wind speed were also recorded.

3.3.6 Based on the odour patrol survey results, sewage type odour was detected in areas close to the Cheung Chau STW and Pak She SPS. No sewage type odour was detected in other surveyed locations. Details of the odour survey methodology, locations and survey results are provided in Appendix 3.1.

3.3.7 In addition to the odour patrol, on-site odour sampling and laboratory olfactometry measurement for the existing odour condition in the areas near the Cheung Chau STW and Pak She SPS was carried out on 15 May 2013 to provide supplementary details on the existing odour conditions. Field measurements at selected air sensitive receivers near the Cheung Chau STW and Pak She SPS were conducted.

3.3.8 Based on the measurement results, the odour concentration at Cheung Chau Slaughter House (close to the Cheung Chau STW) was measured about 40 OU_E/m³, whilst at locations close to Pak She SPS were measured to be in a range of 11 to 16 OU_E/m³. Details of the odour measurement methodology and results are provided in Appendix 3.1.

3.4 Air Sensitive Receivers

3.4.1 The assessment area for air quality impact is defined by a distance of 500 m from the boundary of the project site. Within the assessment area, representative Air Sensitive Receivers (ASRs) have been identified for this assessment, in accordance with the Annex 12 of the EIAO-TM. Domestic premises, hotel, hostel, hospital, clinic, nursery, temporary housing accommodation, school, educational institution, office, factory, shop, shopping centre, home for the aged and recreational activity areas are classified as ASRs.

3.4.2 The ASRs in the vicinity of the proposed works site are identified for the assessment and the locations of these ASRs and their nearest horizontal separation from the proposed works are listed in Table 3.4. Figure 3.1 to Figure 3.16 show the locations of the ASRs.

Table 3.4 : Representative Air Sensitive Receivers

ASR	Description of ASR	Nature of Use	Horizontal Distance to Nearest Works Area (m)	Nearest Works	Figure No.
TKST2	No.4 Tai Kwai San Tsuen	Residential	1	Sewer	3.1
TKW2*	No.7, Tai Kwai Wan San Tsuen	Residential	1	Sewer	3.1
CSH1*	Chung Shak Hei Home for the Aged	Homes for the Aged	1	Sewer	3.2
CCC1*	No.109, Pak She San Tsuen	Residential	2	Sewer	3.2
CCC2*	No.67, Pak She San Tsuen	Residential	1	Sewer	3.2
CSH2*	Cheung Shun House	Residential	82	Cheung Chau STW	3.3
CCSH*	Cheung Chau Slaughter House	Slaughterhouse	3	Cheung Chau STW	3.3
CKH *	Cheung King House	Residential	113	Cheung Chau STW	3.3
FS*	Cheung Chau Fire Station	Government Quarter	12	Pak She SPS	3.4
CCA*	Cheung Chau Commercial Centre	Office	6	Pak She SPS	3.4
CCB*	Cheung Chau Commercial Centre	Office	1	Pak She SPS	3.4
PSSL*	No. 1A Pak She Second Lane	Residential	35	Pak She SPS	3.4
TKS	Block K, Tung Koon San Tsuen	Residential	2	Sewer	3.5
CCEP	No.7 Cheung Chau Electric Path	Residential	1	Sewer	3.5
CHR	No. 18, Chung Hok Road	Residential	2	Sewer	3.6
SW1	3A Golden Lake Garden	Residential	5	Sewer	3.6
THT	No.24 Tai Hing Tai Road	Residential	5	Sewer	3.6
SWR	No. 3A, Sai Wan Road	Residential	1	Sewer	3.7
ST	Block D Seaview Terrence	Residential	5	Sewer	3.7
SYT1	No.2A Sin Yan Tseng	Residential	2	Sewer	3.7
SYT2	No.37 Sin Yan Tseng	Residential	1	Sewer	3.7
P1	No. 34 Praya Street	Residential	9	Sewer	3.8
TW1	Cheng Chau Fisheries Joint Association Public School	Educational	2	Sewer	3.8
TW2	No. 156, Tung Wan Road	Residential	2	Sewer	3.8
TW3	No. 83, Tung Wan Road	Residential	2	Sewer	3.8
TSB	No. 107, Tai San Back Street	Residential	1	Sewer	3.9
TSB1	No. 123 Tai San Back Street	Residential	1	Sewer	3.9
HSR1	No.35, Hill Side Road	Residential	1	Sewer	3.10
TTY	No. 4, Tai Tsoi Yuen Road	Residential	1	Sewer	3.10
KKPS	Cheung Chau Church Kim Kong Primary School	Educational	11	Sewer	3.10
TG	House 10, Tinford Garden	Residential	3	Sewer	3.10
LTT	No. 9A, Lung Tsai Tsuen	Residential	2	Sewer	3.10
KL	No.49A, King Lau, Lung Tsai Tsuen	Residential	3	Sewer	3.10
LTT1	Cheng Chau Alliance Church	Church	1	Sewer	3.10
LTT2	No.35 Lung Tsai Tsuen Road	Residential	1	Sewer	3.10
P2	No.41A Peak Road	Residential	1	Sewer	3.10
SJH	St. John’s Hospital	Hospital	6	Sewer	3.11
CCS	Warwick Hotel	Hotel	9	Sewer	3.11
HPR	Hak Pai Road Sitting-out Area	Recreational area	2	Sewer	3.12
HC	Block 5, Herald Court	Residential	4	Sewer	3.12
KYW1	No.31 Kwun Yam Wan Road	Residential	7	Sewer	3.12
CCS2	Block G-H Fu Yuen	Residential	1	Sewer	3.12
HSR2	No 22C, Hill Side Road	Residential	2	Sewer	3.13
PR1	No.25B Peak Road	Residential	2	Sewer	3.13
PR2	No.72A Peak Road	Residential	4	Sewer	3.13
KYW2	No.46 Kwun Yam Wan Road	Residential	2	Sewer	3.14
MF1	Caritas Ka Fai House	Residential	2	Sewer	3.14
FP1	No.18 Fa Peng Road	Residential	2	Sewer	3.15
FP2	Bethany Cottage and House	Residential	2	Sewer	3.15
GIC_1 ^[1]	G/IC Area near Pak Kok Tsui Road	G/IC	23	Cheung Chau STW	3.3
GIC_2 ^[1]	G/IC Area near Ping Chong Road	G/IC	68	Pak She SPS	3.4
GIC_3 ^[1]	G/IC Area adjacent Pak She Sewage Pumping Station	G/IC	1	Pak She SPS	3.4
PSSPS_DW ^[2]	North of Pak She Sewage Pumping Station	Public road	3	Pak She SPS	3.4
CCSTW_DW ^[2]	North of Cheung Chau Sewage Treatment Plant	Public road	18	Cheung Chau STW	3.3

Notes:

ASR ID marked with * represents ASR located within the 500 m radius of the boundary of the Cheung Chau STW and Pak She SPS.

[1] The existing land-uses of these locations are storage area and open space. According the Cheung Chau Outline Zoning Plan (No. S/I-CC/5), they are zoned as Government / Institution and Community (G/IC) use which may be used for potential air sensitive use. These are considered planned ASRs.

[2] Reference locations as the downwind locations for the odour measurements near the Cheung Chau STW and Pak She SPS conducted on 15-May-2013. They are not considered as ASR and were included for the odour prediction assessment for reference only.

3.5 Identification of Pollution Sources

Upgrading Works of Cheung Chau STW and Pak She SPS

3.5.1 The potential air quality impacts arising during construction phase would be dust nuisance. The major construction activities involved for the upgrading of the Cheung Chau STW that would be potential source of construction dust include site clearance, excavation, materials handling and wind erosion of stockpile on site. The construction works will be confined within the existing Cheung Chau STW boundary.

3.5.2 For a worst case scenario assessment of construction dust impacts, it is assumed that a concrete batching plant would be provided. According to the current design, the practical proposed concrete batching plant location is shown in Figure 3.17.

3.5.3 In view of the traffic-free nature of Cheung Chau, trucks hauling off site is not expected. Vehicular movement on-site will only be limited to the small scale “VV vehicle” and the number that would be in use is expected to be low.

3.5.4 According to the design information at the time of preparation of this EIA, the new MBR treatment facilities will be constructed first whilst the existing Cheung Chau STW will continue the normal operation. Sewage sludge from the STW will be disposed of via marine route as per the current operation thus no additional odour impacts would arise. Sewage will be diverted to the new MBR facilities upon its completion. The existing treatment facilities will then be decommissioned. There will be no demolition of existing septic tanks under the current design. If it is necessary to demolish the existing septic tank during the construction period, the sludge in the septic tank would be transferred to enclosed container following the same procedure with the regular maintenance works for septic works. Therefore, no additional odour sources would be expected during the construction phase of the Cheung Chau STW upgrading works.

3.5.5 Upgrading of the Pak She SPS will involve replacement of pumps and other E&M equipments, and minor modification of existing pump troughs. Deodourizing units will also be provided to the upgraded Pak She SPS. Appropriate dust control measures should be implemented during the construction stage in accordance with the requirements in the Air Pollution Control (Construction Dust) Regulation. Dust control techniques should be considered to control dust to a level not exceeding the AQOs as well as the 1-hour TSP guideline level of 500 µg/m³. These measures include, but are not limited to, the following:

· Adoption of good site practices;

· Avoid practices likely to raise dust level;

· Frequent cleaning and damping down of stockpiles and dusty areas of the site;

· Covering the exposed areas with tarpaulin;

· Reducing drop height during material handling;

· Provision of wheel-washing facilities for site vehicles leaving the site;

· Regular plant maintenance to minimize exhaust emission; and

· Sweep up dust and debris at the end of each shift.

Sewers Works

3.5.6 The potential dust generating construction activities associated with the sewers works will mainly be localised excavation. It is expected that the sewers works will be carried out by sections. Under normal practice, the sewers would be constructed in section of about 20m to 30m at any one time and each work front would be separated by a clearance distance. With such a typical arrangement, construction works for each section could normally be completed in about 30 days, with each construction activity lasts for about 1.5 days to 9 days.

3.5.7 Given each section of the works would be small scale, localised, and short-term, it would not be useful to perform dust dispersion modelling for this type of transient dust generation activities. Dust suppression and control measures stipulated in the Air Pollution Control (Construction Dust) Regulation would be applied.

3.5.8 These measures include, but are not limited to, the following:

· Adoption of good site practices;

· Avoid practices likely to raise dust level;

· Frequent cleaning and damping down of stockpiles and dusty areas of the site;

· Covering the exposed areas with tarpaulin;

· Reducing drop height during material handling;

· Regular plant maintenance to minimize exhaust emission; and

· Sweep up dust and debris at the end of each shift.

Cumulative Dust Impacts and Control Measures

3.5.9 The following discusses the potential cumulative interface issues between concurrent projects as indicated in Section 2.11. Liaisons with each of the project proponents of these concurrent projects have been made in order to obtain the latest available information and details. The correspondences are shown in Appendix 3.6.

Improvement of Fresh Water Supply to Cheung Chau - Design and Construction

3.5.10 The construction activities of the fresh water supply project are located at Cheung Chau Tai Kwai Wan which potentially interface with the proposed sewers works in the same area for 3 months overlapping period. It is recommended that the construction of sewers at Tai Kwai Wan San Tsuen should be launched after the completion of the Project. The contractor should liaise with the correspondent party to ensure concurrent works are avoided as far as possible. By avoiding concurrent works, adverse cumulative dust impact is not expected to occur.

Replacement and Rehabilitation of Water Mains Stage 3 and Stage 4, Mains on Hong Kong and Islands – Investigation, Design and Construction

3.5.11 Based on the information provided by WSD, Stage 3 of this project has been completed. Construction of Stage 4 commenced in October 2012 and is anticipated for completion in 2015. Close liaison will be undertaken with the project proponent of the interfacing project to avoid concurrent works as far as possible. By avoiding concurrent works, the potential interface issues with this project are not expected to occur.

Improvement to Existing Roads and Drains in Cheung Chau Old Town, Remaining Engineering Works, Stage 3, Cheung Chau

3.5.12 Based on the best available information at time of preparation of this EIA, this project involves the construction of village sewer at Cheung Chau Town Centre, Hill Side Road, Kwun Yam Wan Road, Tai Shek Hau, Lung Tsai Tsuen, Ko Shan Tsuen and Pak She San Tsuen. Close liaison between the two project teams will be undertaken to ensure concurrent works are avoided as far as possible. By avoiding concurrent works and given the small scale works involved, adverse cumulative dust impact is not expected during construction.

3.5.13 In addition, proper mitigation measures as stipulated in the Air Pollution Control (Construction Dust) Regulation would be applied.

3.5.14 As a result, only minimal cumulative impacts from these potential concurrent construction works are anticipated. With the continual monitoring and review of dust impact in the area and close liaison with the contractors of these interfacing projects, adverse cumulative dust impact would not be anticipated.

Operational Phase

3.5.15 It is anticipated that odour impact from the sewers works would be negligible as the sewage collection system is a closed system. The potential air quality impacts during the operational phase will be the potential odour emissions from the upgraded Cheung Chau STW and the Pak She SPS.

3.6 Construction Dust Impact Assessment Methodology

Air Dispersion Model

3.6.1 The air pollutant concentrations were assessed in accordance with the Guidelines for Choice of Models and Model Parameters in Air Quality Assessment published by EPD. The extent of dust impacts arising from the construction phase have been predicted by using the Industrial Source Complex Short-Term 3 (ISCST3) model which has been developed and validated by the United States Environmental Protection Agency (USEPA) and accepted by EPD for regulatory applications.

Emissions Factors

3.6.2 The construction works at the Cheung Chau STW site have the potential to generate fugitive dust from various construction activities and these are included in the ISCST3 dispersion model, including:

Ÿ Traffic from Paved Road;

Ÿ Heavy Construction;

Ÿ Wind erosion;

Ÿ Material Construction; and

Ÿ Operation of the concrete batching plant.

3.6.3 Whilst emissions from the sewers works are expected to be low, the model has included the dust sources of sewers works located within the 500 m of the upgrading works of Cheung Chau STW and the Pak She SPS study area for the evaluation of the potential cumulative impacts.

3.6.4 The emission factors used for the prediction of construction dust emissions impacts were based on typical values referenced from USEPA Compilation of Air Pollution Emission Factors (AP-42), 5th Edition. The calculations of dust emission factors for different dust generating activities are detailed in Appendix 3.2 and summarized below:

Traffic from Paved Road

Emission Factor = k(sL)^0.91* (W)^1.02 (reference: AP-42, Chapter 13.2.1)

Where	E :	particulate emission factor, g/veh-km
	k :	particulate size multiplier for particle size range and units of interest
	sL :	road surface silt loading, g/m^2
	W :	average weight, ton

Heavy Construction

Emission Rate = 1.2 tons arcs/arce/month of activities (reference: AP-42 Chapter 13.2.3.3)

Wind Erosion

Emission Factor = 0.85 Mg/ha/yr (reference: AP-42, Chapter 11.09 Table 11.9-4)

Material Handling

Emission factor = k (0.0016) x (U/2.2)^1.3 / (M/2)^1.4

Where	E :	Emission factor, g/megagram
	k :	Particulate size multiplier, k=0.74 as defined according to Table 2 of AP-42 Section 13.2.4
	U :	Average wind speed at Cheung Chau from 2006 to 2010 (i.e. ~ 4.93m/s)
	M :	Material moisture content; Material handling at construction sites and stone quarrying, and the nature of these activities are similar.. The moisture content for a quarry is estimated between 0.3% and 1.1% according to Section 13.2.4 of AP-42. For conservative scenario, the minimum moisture content value (0.3%) is assumed for the construction sites. .

Unloading of Raw Material

Emission factor = 0.0035 (kg/Mg) (reference: AP-42, Chapter 11.12, Table 11.12-1)

Meteorological Data

3.6.5 Meteorological data from Cheung Chau Automatic Weather Station provided by the Hong Kong Observatory for the year 2010 (the amount of valid data is more than 90 percent for this year) was used for the dispersion model. The following data were included:

Ÿ flow vector of wind;

Ÿ wind speed;

Ÿ air temperature;

Ÿ atmospheric Pasquill stability class; and

Ÿ morning mixing height and maximum mixing height recorded at King’s Park.

Assumptions

3.6.6 The dust impact assessment has made the following assumptions:

Ÿ The study area is defined as “rural”;

Ÿ dry depletion and gradual plume rise options were considered in the model run;

Ÿ A twelve-hour (07:00 to 19:00) working day during construction phase, of which a ten-hour operation 08:00 to 19:00 exclude 1 hour for lunch) for material handling and heavy construction activities;

Ÿ A twelve-hour (07:00 to 19:00) operation hours for concrete batching plant; and

Ÿ The minor VV vehicle movements on site were considered in the model as conservative approach, although it will only be minimal.

3.6.7 Watering of site areas with heavy construction operations, and of paved roads, is recommended to minimize construction dust generation as general good site practice during construction. Table 3.5 shows the calculated dust removal efficiency at different time intervals between watering.

Table 3.5 : Dust Removal Efficiency for Different Watering Frequencies

Time Between Watering (hour)	Dust Removal Efficiency (%)
6	63.7
3	81.9
1.5	90.9

3.6.8 Based on Table 3.5, watering frequencies of heavy construction operations and paved roads are assumed to be 1.5 hours intervals for the heavy construction operation areas and for the paved roads.

3.6.9 According to the “Control of Open Fugitive Dust Sources” cited in AP 42 issued by USEPA, average dust control efficiency (in percent) can be estimated by equation 5-4 of the paper [c=100 – (0.8*p*d*t)/i] based on potential average hourly daytime evaporation rate for the construction site (p in mm/h), average hourly daytime traffic rate (d in veh/hr), watering intensity (in litre/m²), and the time between applications of watering (t in hr). Based on “The Year’s Weather – 2011” issued by Hong Kong Observatory, the total annual evaporation recorded in Hong Kong is 1476.7 mm (58.14 inches). The potential average hourly daytime evaporation rate is calculated by equation 5-5b of the USEPA’s paper based on the mean annual pan evaporation in Hong Kong. The maximum hourly traffic flow is estimated to be 10 vehicles per hour, respectively (round-trip included). To adopt a conservative approach, the peak hourly daytime traffic rate of 10 vehicles per hour is assumed for the dust control efficiency calculation. Based on these assumptions, a minimum 0.5 litres per m² of watering application intensity is required to achieve the target dust removal efficiency. Calculation details are provided in Appendix 3.2.

3.6.10 Watering of site areas with wind erosion will be implemented to minimize construction dust generation as general good site practice during construction. It is assumed the watering application intensity to be 1.5 litres per m² which can achieve the 90% dust removal efficiency. Appendix 3.2 shows the calculation of the water amount and frequency of watering to achieve the dust removal efficiency to 90%.

3.6.11 Construction dust is the key air emission source during construction phase at above-ground works areas. According to Annex 4 of EIAO-TM, Total Suspended Particulates (TSP) is the air pollutant parameter for construction dust impact assessment. According to EPD’s Air Quality Report 2011, the major sources of Respirable Suspended Particulates (RSP) include power generation and road traffic emissions which is not originated by construction activities. As such, RSP are not included in the construction dust impact assessment.

Background TSP Concentration

3.6.12 For background TSP concentration, the 5-years (2007 to 2011) average annual TSP concentration of 64.6 mg/m³ at Tung Chung Station was adopted. This is because Tung Chung is located on an outlying island which is of similar nature of Cheung Chau. The air quality data recorded at the Tung Chung Station is considered to be the most relevant data for Cheung Chau.

Assessment Heights

3.6.13 The highest elevation of ASR identified (Cheung Kwai Estate) is about 30 m above ground level. Therefore, the assessment heights were taken as 1.5m (breathing level), 5m, 10m 15m, 20m and 25m above ground level.

Selected ASR for Dispersion Modelling Assessment

3.6.14 All existing ASRs selected and described in Table 3.4 were used for the dispersion modelling assessment.

3.7 Prediction of Construction Dust Impact

Unmitigated Scenario

3.7.1 The worst case modelling results of 1-hour, 24-hour and annual TSP concentrations at all identified ASRs for the unmitigated scenarios are presented in Table 3.6 and Table 3.7 respectively. All the results presented in the tables have included 64.6µg/m³ for background concentration. The predicted results show that the ASRs located close to the construction site and at low elevations would be impacted by elevated dust level if no mitigation measures are applied. Mitigation measures are required to be implemented to reduce the potential dust impacts.

Table 3.6 : Predicted Worst-case 1-hour Average and 24-hour Average TSP Concentration at Different Level above Ground (Unmitigated)

ASR	Worst-case 1-hour Average TSP, µg/m^3						Worst-case 24-hour Average TSP, µg/m^3
	1.5m	5m	10m	15m	20m	25m	1.5m	5m	10m	15m	20m	25m
TKST2	839.2	751.4	526.9	307.4	237.5	197.6	99.7	96.7	89.4	81.6	75.8	72.2
TKW2*	1000.3	857.7	526.9	308.0	251.9	198.6	112.2	107.1	95.2	84.4	77.4	73.3
CSH1*	282.2	272.9	246.3	209.3	170.2	135.3	82.6	81.0	77.4	73.9	71.4	69.5
CCC1*	1871.3	1242.8	382.5	249.1	196.8	179.6	139.9	113.7	90.1	85.0	80.5	77.0
CCC2*	2008.7	1587.4	756.5	426.7	309.0	213.2	151.0	133.1	98.1	81.3	75.9	71.8
CSH2*	2456.0	878.0	528.7	378.4	254.5	171.3	167.5	133.1	91.1	82.2	75.5	70.5
CCSH*	4597.5	1408.2	538.4	327.3	510.5	1481.5	440.3	194.1	120.9	103.3	163.0	150.3
CKH *	4517.1	1013.3	627.0	409.0	253.0	169.1	255.9	135.1	96.7	84.1	75.3	70.2
FS*	1196.3	903.0	392.0	197.8	187.0	174.4	119.5	105.1	81.9	72.6	71.1	70.2
CCA*	2038.2	1350.5	385.0	233.0	215.6	196.0	155.0	125.2	84.3	75.0	73.5	72.1
CCB*	1561.6	988.2	273.8	255.3	232.3	224.9	134.3	108.8	79.8	77.4	75.4	74.3
PSSL*	1214.1	891.0	374.7	184.9	176.1	165.7	119.8	106.1	82.8	72.5	70.6	69.8
TKS	144.3	143.5	140.9	136.9	131.6	125.4	70.9	70.8	70.5	70.0	69.4	68.9
CCEP	120.8	120.3	118.6	115.9	112.4	108.2	69.5	69.4	69.3	69.1	68.8	68.5
CHR	180.7	179.5	175.5	169.2	161.0	151.4	69.5	69.4	69.2	69.0	68.6	68.2
SW1	126.0	125.4	123.4	120.1	115.9	110.9	68.9	68.8	68.6	68.3	67.9	67.4
THT	151.3	150.3	147.1	142.0	135.4	127.7	68.5	68.4	68.2	67.9	67.6	67.2
SWR	126.2	125.6	123.8	120.8	116.8	112.2	69.0	68.9	68.7	68.4	68.0	67.6
ST	151.7	150.8	148.2	144.0	138.5	132.0	71.5	71.4	71.0	70.5	69.9	69.2
SYT1	119.8	119.3	117.6	114.9	111.4	107.2	68.4	68.4	68.2	67.9	67.6	67.2
SYT2	138.4	137.8	135.8	132.6	128.4	123.3	70.4	70.3	70.0	69.7	69.2	68.6
P1	180.2	172.6	151.2	126.6	112.4	98.9	69.4	69.2	68.9	68.4	67.9	67.4
TW1	166.5	160.2	142.1	119.6	99.2	87.9	69.0	68.8	68.0	67.7	67.3	66.8
TW2	629.1	589.0	477.0	343.6	229.9	153.2	88.1	86.5	81.8	76.2	71.5	69.3
TW3	483.5	454.3	372.0	272.4	185.9	126.7	82.1	80.8	77.4	73.3	69.7	68.5
TSB	166.9	164.7	157.7	147.1	134.3	120.8	69.4	69.3	69.1	68.7	68.3	67.9
TSB1	212.3	208.8	197.6	180.9	161.1	140.7	71.0	70.8	70.5	70.0	69.3	68.6
HSR1	172.7	170.7	164.5	154.9	143.0	130.0	69.2	69.1	68.9	68.6	68.2	67.8
TTY	453.0	433.5	376.4	300.9	226.3	165.4	80.8	80.0	77.6	74.5	71.4	68.8
KKPS	204.0	197.7	179.1	153.7	127.3	104.6	70.5	70.2	69.5	68.4	67.3	66.4
TG	220.7	213.8	193.2	165.0	135.7	110.3	71.2	70.9	70.0	68.9	67.6	66.6
LTT	149.6	146.0	135.4	120.7	105.2	91.4	68.1	68.0	67.6	66.9	66.6	66.5
KL	139.1	137.9	134.0	128.0	120.5	112.1	67.9	67.9	67.7	67.6	67.3	67.0
LTT1	128.7	127.6	124.0	118.4	111.5	104.0	67.8	67.8	67.7	67.5	67.3	67.1
LTT2	132.5	131.4	127.7	122.1	115.1	107.3	67.8	67.7	67.6	67.4	67.2	67.0
P2	403.4	388.2	343.0	281.3	217.3	162.0	78.7	78.1	76.2	73.7	71.0	68.7
SJH	163.9	158.9	144.4	125.3	106.5	91.1	68.9	68.7	68.1	67.3	66.5	66.1
CCS	185.5	180.1	163.8	141.7	118.9	99.4	69.8	69.5	68.9	67.9	67.0	66.2
HPR	302.7	294.3	268.9	232.9	193.7	157.3	74.7	74.3	73.3	71.8	70.1	68.6
HC	251.1	243.8	222.0	191.4	158.3	128.2	72.4	72.1	71.2	69.9	68.5	67.2
KYW1	251.3	242.4	216.1	180.7	144.6	114.2	72.4	72.0	70.9	69.4	67.9	67.1
CCS2	107.8	106.0	100.6	93.1	85.3	79.6	66.6	66.6	66.5	66.4	66.2	66.0
HSR2	136.7	135.4	131.4	125.2	117.5	109.0	67.8	67.8	67.7	67.5	67.2	66.9
PR1	141.4	140.1	136.2	130.1	122.4	113.8	67.8	67.7	67.6	67.3	67.1	66.9
PR2	145.1	143.8	139.7	133.3	125.3	116.4	68.1	68.0	67.9	67.7	67.4	67.2
KYW2	152.6	149.3	139.3	125.3	109.9	95.7	68.4	68.2	67.8	67.2	66.6	66.0
MF1	136.4	133.9	126.1	115.2	103.0	91.5	67.7	67.6	67.2	66.8	66.3	65.8
FP1	317.6	309.3	283.9	247.3	206.2	166.6	75.1	74.8	73.7	72.2	70.5	68.8
FP2	287.4	280.2	258.4	226.8	191.0	156.4	73.9	73.6	72.7	71.4	69.9	68.4

Notes:

All the results presented in the table have included 64.6 µg/m³ for background TSP concentration.

Underlined and bold figure indicates exceedance of the relevant AQO.

ASR ID marked with * represents ASR located within the 500 m radius of the boundary of the Cheung Chau STW and Pak She SPS.

Table 3.7 : Predicted Worst-case Annual Average TSP Concentration at Different Level above Ground (Unmitigated)

ASR	Worst-case Annual Average TSP, µg/m^3
	1.5m	5m	10m	15m	20m	25m
TKST2	65.7	65.6	65.4	65.2	65.0	64.9
TKW2*	65.9	65.7	65.4	65.1	65.0	64.9
CSH1*	65.0	65.0	64.9	64.9	64.8	64.8
CCC1*	66.8	66.5	65.9	65.5	65.3	65.1
CCC2*	66.0	65.8	65.5	65.3	65.1	65.0
CSH2*	68.5	66.8	65.6	65.1	64.9	64.7
CCSH*	148.5	102.6	75.9	69.8	76.9	71.4
CKH *	69.5	67.5	66.0	65.3	64.9	64.8
FS*	65.4	65.2	65.0	64.9	64.8	64.8
CCA*	65.6	65.3	65.0	64.9	64.8	64.8
CCB*	65.7	65.3	65.1	64.9	64.9	64.8
PSSL*	65.3	65.2	65.0	64.9	64.8	64.8
TKS	64.9	64.9	64.9	64.9	64.9	64.8
CCEP	64.9	64.9	64.9	64.9	64.8	64.8
CHR	64.7	64.7	64.7	64.7	64.7	64.7
SW1	64.8	64.8	64.8	64.7	64.7	64.7
THT	64.7	64.7	64.7	64.7	64.7	64.7
SWR	64.8	64.8	64.8	64.7	64.7	64.7
ST	64.8	64.8	64.8	64.8	64.8	64.8
SYT1	64.7	64.7	64.7	64.7	64.7	64.7
SYT2	64.8	64.8	64.8	64.8	64.7	64.7
P1	64.7	64.7	64.7	64.7	64.7	64.7
TW1	64.7	64.7	64.7	64.7	64.7	64.6
TW2	64.8	64.8	64.8	64.7	64.7	64.7
TW3	64.8	64.8	64.7	64.7	64.7	64.7
TSB	64.7	64.7	64.7	64.7	64.7	64.7
TSB1	64.7	64.7	64.7	64.7	64.7	64.7
HSR1	64.7	64.7	64.7	64.7	64.7	64.6
TTY	64.7	64.7	64.7	64.7	64.7	64.6
KKPS	64.7	64.7	64.7	64.6	64.6	64.6
TG	64.7	64.7	64.7	64.6	64.6	64.6
LTT	64.6	64.6	64.6	64.6	64.6	64.6
KL	64.6	64.6	64.6	64.6	64.6	64.6
LTT1	64.7	64.7	64.6	64.6	64.6	64.6
LTT2	64.6	64.6	64.6	64.6	64.6	64.6
P2	64.7	64.7	64.7	64.7	64.6	64.6
SJH	64.7	64.7	64.7	64.7	64.6	64.6
CCS	64.7	64.7	64.6	64.6	64.6	64.6
HPR	64.7	64.7	64.7	64.6	64.6	64.6
HC	64.7	64.7	64.7	64.7	64.6	64.6
KYW1	64.7	64.7	64.7	64.7	64.7	64.6
CCS2	64.6	64.6	64.6	64.6	64.6	64.6
HSR2	64.7	64.7	64.6	64.6	64.6	64.6
PR1	64.7	64.6	64.6	64.6	64.6	64.6
PR2	64.6	64.6	64.6	64.6	64.6	64.6
KYW2	64.6	64.6	64.6	64.6	64.6	64.6
MF1	64.6	64.6	64.6	64.6	64.6	64.6
FP1	64.7	64.7	64.7	64.7	64.7	64.6
FP2	64.7	64.7	64.7	64.7	64.7	64.6

Note:

All the results presented in the table have included 64.6 µg/m³ for background TSP concentration.

ASR ID marked with * represents ASR located within the 500 m radius of the boundary of the Cheung Chau STW and Pak She SPS.

3.7.2 Concentration contour plots of the assessment results of the unmitigated scenario for the cumulative effect of construction activities within the 500 m boundary of Cheung Chau STW and Pak She SPS are presented in Figure 3.18 to Figure 3.35.

Mitigated Scenario

3.7.3 Typical dust control methods include ground watering, equipment and vehicle watering, proper handling of material and stockpile. The assumptions of the dust removal efficiency achieved by dust control measures are provided in Section 3.6.7 to Section 3.6.10 above and detailed in Appendix 3.2.

3.7.4 The TSP concentrations are predicted with the proposed mitigation measures at the identified ASRs. TSP concentrations can be reduced significantly and the predicted results are shown in Table 3.8 and Table 3.9.

3.7.5 From Table 3.8, the predicted maximum 1-hr TSP concentrations at CCSH are exceeding at 20m and 25m above ground level. As the height of CCSH building is below 20m, the exceedance values for CCSH are not applicable. The predicted TSP concentrations at all selected were found to be within the relative AQOs with the proposed mitigation measures incorporated.

Table 3.8 : Predicted Worst-case 1-hour Average and 24-hour Average TSP Concentration at Different Level above Ground (Mitigated)

ASR	Worst-case 1-hour Average TSP, µg/m^3						Worst-case 24-hour Average TSP, µg/m^3
	1.5m	5m	10m	15m	20m	25m	1.5m	5m	10m	15m	20m	25m
TKST2	279.7	257.9	200.7	143.2	106.6	97.4	73.7	72.9	71.2	69.3	67.8	66.8
TKW2*	176.6	163.9	132.7	103.6	96.0	88.4	71.5	71.0	69.8	68.5	67.3	66.5
CSH1*	103.8	102.5	98.8	93.4	87.3	81.4	67.4	67.2	66.8	66.3	65.9	65.6
CCC1*	255.0	205.4	134.6	112.0	98.2	91.9	72.5	70.5	69.3	68.1	67.4	66.9
CCC2*	283.4	243.2	160.6	120.6	105.6	92.3	74.9	73.1	69.6	67.4	66.6	66.1
CSH2*	302.5	242.9	446.4	310.5	158.0	103.4	77.9	76.2	82.0	76.0	70.7	67.7
CCSH*	485.4	186.8	108.6	145.7	510.5	1481.5	107.7	81.2	72.6	80.2	154.9	149.5
CKH *	478.3	251.4	203.0	158.5	114.1	99.2	84.6	75.4	70.9	68.9	67.4	66.4
FS*	192.3	161.1	112.4	110.9	137.6	140.5	70.8	69.4	67.3	67.2	68.3	68.4
CCA*	248.5	185.1	100.8	102.9	104.3	103.0	74.6	71.0	67.5	67.4	67.4	67.2
CCB*	217.1	160.9	117.9	126.2	207.3	224.9	73.5	69.7	68.4	68.5	71.4	72.0
PSSL*	170.9	146.9	106.7	99.5	114.0	115.3	70.5	69.1	67.1	66.7	67.3	67.3
TKS	83.9	83.7	83.1	82.1	80.8	79.4	66.2	66.2	66.1	66.0	65.8	65.7
CCEP	77.7	77.3	75.9	74.0	73.4	72.6	65.6	65.6	65.6	65.6	65.5	65.4
CHR	84.2	84.0	83.5	82.7	81.5	80.2	65.5	65.5	65.4	65.4	65.3	65.3
SW1	78.7	78.6	78.2	77.6	76.8	75.8	65.3	65.3	65.2	65.2	65.2	65.1
THT	76.7	76.6	76.2	75.6	74.9	73.9	65.2	65.2	65.2	65.2	65.1	65.1
SWR	76.8	76.7	76.3	75.7	75.0	74.0	65.4	65.4	65.3	65.3	65.2	65.1
ST	77.7	77.6	77.2	76.6	75.8	74.9	65.8	65.7	65.7	65.6	65.4	65.3
SYT1	74.9	74.8	74.5	74.1	73.5	72.7	65.3	65.3	65.3	65.2	65.1	65.1
SYT2	75.7	75.6	75.3	74.9	74.2	73.5	65.6	65.6	65.5	65.4	65.3	65.2
P1	79.3	79.0	78.1	77.1	76.2	74.9	65.3	65.3	65.3	65.2	65.2	65.1
TW1	80.0	79.6	78.7	78.0	77.0	75.9	65.5	65.4	65.4	65.4	65.3	65.3
TW2	128.2	125.5	118.0	109.0	100.5	93.0	67.3	67.1	66.8	66.4	66.1	65.8
TW3	107.8	105.4	98.8	90.6	83.1	77.2	66.4	66.3	66.0	65.7	65.4	65.3
TSB	84.6	84.3	83.5	82.1	80.3	78.3	65.5	65.5	65.5	65.4	65.4	65.3
TSB1	86.1	85.7	84.6	82.9	80.8	78.5	65.6	65.6	65.5	65.5	65.4	65.3
HSR1	84.4	84.1	83.3	81.9	80.2	78.2	65.4	65.4	65.4	65.3	65.3	65.2
TTY	104.4	103.4	100.3	96.1	91.4	86.6	66.3	66.2	66.1	65.9	65.7	65.5
KKPS	81.5	80.8	78.9	76.3	73.5	71.1	65.3	65.3	65.2	65.1	65.0	64.9
TG	82.6	81.9	79.8	77.0	74.0	71.1	65.4	65.3	65.2	65.1	65.0	64.9
LTT	81.0	80.4	78.7	76.2	73.5	70.9	65.3	65.3	65.2	65.1	65.0	65.0
KL	80.1	79.9	79.2	78.2	76.8	75.3	65.3	65.3	65.2	65.2	65.2	65.1
LTT1	77.3	77.2	76.7	76.0	75.1	74.0	65.2	65.2	65.2	65.2	65.2	65.1
LTT2	78.7	78.5	77.9	77.0	75.8	74.5	65.2	65.2	65.2	65.2	65.1	65.1
P2	101.6	100.1	95.5	89.2	82.5	76.5	66.1	66.1	65.9	65.6	65.3	65.1
SJH	80.0	79.8	78.9	77.5	75.8	74.6	65.3	65.3	65.3	65.2	65.2	65.2
CCS	88.5	87.8	85.7	82.4	78.7	74.9	65.6	65.6	65.5	65.4	65.2	65.1
HPR	103.0	102.5	101.0	98.6	95.3	91.3	66.2	66.2	66.1	66.0	65.9	65.7
HC	89.0	88.1	85.4	81.7	77.5	73.7	65.6	65.6	65.5	65.3	65.1	65.0
KYW1	90.1	89.0	85.7	81.3	76.7	72.6	65.7	65.6	65.5	65.3	65.1	65.0
CCS2	76.0	75.5	74.4	72.7	70.9	69.9	65.1	65.1	65.0	65.0	64.9	64.9
HSR2	75.8	75.6	75.0	74.0	72.8	71.5	65.1	65.1	65.1	65.1	65.0	65.0
PR1	81.5	81.2	80.3	79.0	77.4	75.5	65.3	65.3	65.3	65.2	65.1	65.1
PR2	80.9	80.7	80.0	78.9	77.5	75.9	65.3	65.3	65.2	65.2	65.2	65.1
KYW2	84.5	83.8	81.8	78.8	75.5	72.6	65.4	65.4	65.3	65.2	65.1	65.0
MF1	81.3	80.7	79.0	76.5	73.7	71.8	65.3	65.3	65.2	65.1	65.0	65.0
FP1	95.7	94.7	91.7	87.3	82.4	77.6	65.9	65.9	65.7	65.5	65.3	65.1
FP2	91.5	90.7	88.1	84.4	80.2	76.1	65.7	65.7	65.6	65.4	65.3	65.1

Notes:

All the results presented in the table have included 64.6 µg/m³ for background TSP concentration.

ASR ID marked with * represents ASR located within the 500 m radius of the boundary of Cheung Chau STW and Pak She SPS.

Table 3.9 : Predicted Worst-case Annual Average TSP Concentration at Different Level above Ground (Mitigated)

ASR	Worst-case Annual Average TSP, µg/m^3
	1.5m	5m	10m	15m	20m	25m
TKST2	64.9	64.9	64.8	64.8	64.7	64.7
TKW2*	64.8	64.8	64.7	64.7	64.7	64.7
CSH1*	64.7	64.7	64.7	64.7	64.6	64.6
CCC1*	65.0	65.0	64.9	64.8	64.7	64.7
CCC2*	64.8	64.8	64.8	64.7	64.7	64.7
CSH2*	65.3	65.0	64.9	64.8	64.7	64.7
CCSH*	74.7	68.7	65.9	66.5	75.8	71.0
CKH *	65.4	65.1	64.9	64.8	64.7	64.7
FS*	64.8	64.7	64.7	64.7	64.7	64.7
CCA*	64.9	64.7	64.7	64.7	64.7	64.7
CCB*	65.0	64.7	64.7	64.7	64.7	64.7
PSSL*	64.8	64.7	64.7	64.7	64.7	64.7
TKS	64.7	64.7	64.7	64.7	64.7	64.7
CCEP	64.7	64.7	64.7	64.7	64.7	64.7
CHR	64.6	64.6	64.6	64.6	64.6	64.6
SW1	64.6	64.6	64.6	64.6	64.6	64.6
THT	64.6	64.6	64.6	64.6	64.6	64.6
SWR	64.6	64.6	64.6	64.6	64.6	64.6
ST	64.6	64.6	64.6	64.6	64.6	64.6
SYT1	64.6	64.6	64.6	64.6	64.6	64.6
SYT2	64.6	64.6	64.6	64.6	64.6	64.6
P1	64.6	64.6	64.6	64.6	64.6	64.6
TW1	64.6	64.6	64.6	64.6	64.6	64.6
TW2	64.6	64.6	64.6	64.6	64.6	64.6
TW3	64.6	64.6	64.6	64.6	64.6	64.6
TSB	64.6	64.6	64.6	64.6	64.6	64.6
TSB1	64.6	64.6	64.6	64.6	64.6	64.6
HSR1	64.6	64.6	64.6	64.6	64.6	64.6
TTY	64.6	64.6	64.6	64.6	64.6	64.6
KKPS	64.6	64.6	64.6	64.6	64.6	64.6
TG	64.6	64.6	64.6	64.6	64.6	64.6
LTT	64.6	64.6	64.6	64.6	64.6	64.6
KL	64.6	64.6	64.6	64.6	64.6	64.6
LTT1	64.6	64.6	64.6	64.6	64.6	64.6
LTT2	64.6	64.6	64.6	64.6	64.6	64.6
P2	64.6	64.6	64.6	64.6	64.6	64.6
SJH	64.6	64.6	64.6	64.6	64.6	64.6
CCS	64.6	64.6	64.6	64.6	64.6	64.6
HPR	64.6	64.6	64.6	64.6	64.6	64.6
HC	64.6	64.6	64.6	64.6	64.6	64.6
KYW1	64.6	64.6	64.6	64.6	64.6	64.6
CCS2	64.6	64.6	64.6	64.6	64.6	64.6
HSR2	64.6	64.6	64.6	64.6	64.6	64.6
PR1	64.6	64.6	64.6	64.6	64.6	64.6
PR2	64.6	64.6	64.6	64.6	64.6	64.6
KYW2	64.6	64.6	64.6	64.6	64.6	64.6
MF1	64.6	64.6	64.6	64.6	64.6	64.6
FP1	64.6	64.6	64.6	64.6	64.6	64.6
FP2	64.6	64.6	64.6	64.6	64.6	64.6

Note:

All the results presented in the table have included 64.6 µg/m³ for background TSP concentration.

ASR ID marked with * represents ASR located within the 500 m radius of the boundary of Cheung Chau STW and Pak She SPS.

3.7.6 Concentration contour plots of the assessment results of the mitigated scenario for the cumulative effect of construction activities within the 500 m boundary of Cheung Chau STW and Pak She SPS are presented in Figure 3.36 to Figure 3.53. A typical dispersion model output file is shown in Appendix 3.3.

3.8 Operational Phase Odour Assessment Methodology

Air Dispersion Model

3.8.1 The air pollutant concentrations were assessed in accordance with the Guidelines for Choice of Models and Model Parameters in Air Quality Assessment published by EPD. The potential odour emissions arising from the operation of the upgraded Cheung Chau STW and Pak She SPS were predicted by using the Industrial Source Complex Short-Term 3 (ISCST3) model.

Emissions Inventory

Cheung Chau Sewage Treatment Works

3.8.2 Potential odour sources identified in the STW include the following:

Preliminary Treatment Unit:

Ÿ Inlet Works

Ÿ Coarse Screen

Ÿ Distribution Well and Equalisation Tank

Ÿ Fine Screen and Grit Chambers

Ÿ Storm Tank

Ÿ Flow Distribution Tank

Ÿ 1-2mm Fine Screen Channel

Ÿ Wet Well Before MBR Tank

Ÿ Pump House

MBR Treatment Unit:

Ÿ Anoxic Tank

Ÿ Aerobic MBR Tank

Sludge Treatment Unit:

Ÿ Sludge Holding Tank (Pre-thickener)

Ÿ Sludge Digester

Ÿ Sludge Holding Tank (Post-digester)

Ÿ Sludge Dewatering House

3.8.3 Based on the current design, the civil component of the total eight MBR units will be constructed. Six MBR units will be operated and two MBR units will be stand-by use. For planning the worst scenario, it is assumed in the odour impact assessment that total eight MBR units will be operated in full capacity.

3.8.4 The General Layout Plan of the Cheung Chau STW (Figure 2.2) shows the locations of these potential odour sources.

Pak She Sewage Pumping Station

3.8.5 Potential odour sources identified in the SPS mainly include the wet well, screw pump and screening area as shown in Figure 3.54.

Emissions Rates

3.8.6 The odour emission rates from Preliminary Treatment Unit and Sludge Treatment Unit of the Cheung Chau STW, and the Pak She SPS were referenced to the odour emission rates provided in the approved EIA of Harbour Area Treatment Scheme (HATS) Stage 2A (Appendix 3-2) (Register No. AEIAR-121/2008).

3.8.7 Odour measurement of air collected from an operative MBR sewage treatment facility in Hong Kong was conducted for estimating the odour emissions data of the aerobic MBR tank of the MBR treatment unit of the upgraded Cheung Chau STW. MBR Sewage Treatment Facility at Lo Wu Correctional Institution (LWCISTP) was chosen due to similar sewage condition and also using same MBR treatment facility. The correction of changes of surface flow rate under operation scenario of LWCISTP and Cheung Chau Sewage Treatment Works was adopted before the air modelling assessment. Details of the odour measurements at LWCISTP and the calculations of the odour emission rates are provided in Appendix 3.4.

Meteorological Data and Assumptions

3.8.8 Meteorological data from Cheung Chau Automatic Weather Station provided by the Hong Kong Observatory for the year 2010 was used for the dispersion model. .

Selected ASR for Dispersion Modelling Assessment

3.8.9 All ASRs selected and described in Table 3.4 were used for the operational phase odour assessment. In addition, for odour concentration contour plots, assessment grid points were also included to cover the assessment area within 500 m from the Cheung Chau STW and Pak She SPS.

Conversion of 1-Hour Average to 5-Second Average

3.8.10 Odour impact assessment is based on a 5-second average level. Conversion of the ISCST3 modelled output from 1-hour average concentration to 5-second average is needed. The 1-hour average odour concentration is first converted to 3-minute average by the power law relationship which is related to the stability classes. For stability class A to F, multiplying factors of 2.23, 2.23, 1.7, 1.38, 1.31 and 1.31 respectively were applied. The 3-minutes averages were further converted to 5-second averages by applying a multiplying factor of 10 for those hours with atmospheric stability classes A to B, and a factor of 5 for those hours with stability classes C to F. This has made reference to the Guidelines for Choice of Models and Model Parameters in Air Quality Assessment.

3.9 Prediction of Odour Impact

Unmitigated Scenario

3.9.1 It should be noted that deodourizing units will be installed at the Cheung Chau STW and Pak She SPS. Thus, the “unmitigated scenario” prediction results, assuming no deodourizing units, are presented for comparison only. The predicted unmitigated cumulative odour levels at the selected ASRs are summarized in Table 3.10. The predicted unmitigated odour concentration contour plots at 1.5m, 5m, 10m 15m, 20m and 25m above ground level are shown in Figure 3.55 to Figure 3.60.

Table 3.10 : Predicted Worst-case 5-second Average Odour Concentration at Different Level above Ground (Unmitigated – for Comparison Only)

ASR	Predicted Worst-case Odour Concentration, 5-second Average Odour Units
	1.5m	5m	10m	15m	20m	25m
TKST2	24.1	25.6	29.1	30.9	28.7	24.6
TKW2*	23.4	23.3	23.0	22.5	21.8	20.9
CSH1*	41.1	48.6	63.1	64.6	56.8	51.8
CCC1*	48.3	47.7	45.8	42.8	38.9	34.4
CCC2*	41.2	40.9	39.9	38.4	36.3	33.8
CSH2*	267.6	264.1	245.7	204.5	147.7	96.0
CCSH*	153.7	184.4	325.0	350.8	275.4	180.8
CKH *	229.1	226.1	257.9	279.3	196.2	158.8
FS*	49.0	50.3	63.4	95.3	100.6	86.8
CCA*	245.0	339.5	242.2	97.3	98.4	84.0
CCB*	61.4	60.8	58.6	55.1	54.9	47.0
PSSL*	47.3	49.9	66.2	100.2	103.3	90.2
TKS	16.5	16.6	16.9	16.7	15.8	14.1
CCEP	8.8	8.5	7.6	6.5	6.0	6.0
CHR	14.4	14.8	15.8	16.5	16.0	15.1
SW1	13.4	13.1	12.2	10.6	9.1	8.4
THT	7.1	7.0	7.4	7.8	7.6	7.2
SWR	11.1	11.0	10.6	10.0	9.0	7.8
ST	9.1	9.1	9.2	9.3	9.0	8.4
SYT1	9.6	9.4	8.7	7.9	7.0	6.3
SYT2	7.6	7.3	6.6	5.7	5.7	5.7
P1	11.6	12.0	12.9	13.3	12.5	11.9
TW1	18.5	18.5	18.2	16.8	15.0	14.0
TW2	17.8	18.3	19.5	19.7	18.3	17.3
TW3	16.9	17.1	17.4	16.7	15.1	14.2
TSB	21.9	21.9	21.7	20.6	18.2	16.9
TSB1	15.4	15.8	17.0	17.8	17.2	16.2
HSR1	22.7	22.6	21.9	20.6	18.3	16.6
TTY	14.4	14.7	15.6	16.2	15.9	14.9
KKPS	8.5	8.2	7.4	6.3	5.0	4.3
TG	8.3	8.0	7.2	6.1	4.8	4.1
LTT	8.4	8.2	7.7	6.8	5.8	4.8
KL	18.2	18.0	17.3	15.9	14.0	12.5
LTT1	12.3	12.4	12.4	12.1	11.2	10.3
LTT2	16.7	16.5	15.8	14.6	12.8	11.5
P2	8.1	7.8	7.0	6.0	4.8	4.0
SJH	13.6	13.5	13.1	12.1	10.7	10.1
CCS	17.2	16.9	16.1	14.5	12.5	11.6
HPR	19.6	19.6	19.4	18.8	17.4	15.9
HC	6.9	6.6	6.0	5.2	4.2	3.2
KYW1	8.4	8.1	7.3	6.2	4.9	4.5
CCS2	7.8	7.5	6.8	5.8	4.6	3.9
HSR2	9.2	9.1	8.8	8.5	8.0	7.2
PR1	14.5	14.5	14.6	14.4	13.8	12.6
PR2	19.6	19.4	18.6	17.2	15.1	13.5
KYW2	12.3	12.1	11.4	10.3	8.8	7.8
MF1	8.8	8.7	8.4	7.9	7.3	6.5
FP1	5.4	5.2	4.7	4.1	3.4	2.7
FP2	5.1	5.0	4.5	4.0	3.3	2.6
GIC_1 ^[1]	175.2	155.0	270.1	236.6	162.7	114.5
GIC_2 ^[1]	69.7	68.9	66.2	89.8	84.1	74.1
GIC_3 ^[1]	68.0	97.9	150.6	87.8	86.2	73.6
PSSPS_DW ^[2]	60.6	59.9	82.1	96.8	98.7	83.5
CCSTW_DW ^[2]	119.0	132.0	359.5	345.1	238.1	170.9

Note:

Underlined figure indicates exceedance of the assessment criteria stipulated in the EIAO-TM.

ASR ID marked with * represents ASR located within the 500 m radius of the boundary of Cheung Chau STW and Pak She SPS.

[1] The existing land-uses of these locations are storage area and open space. According the Cheung Chau Outline Zoning Plan (No. S/I-CC/5), they are zoned as Government / Institution and Community (G/IC) use which may be used for potential air sensitive use. These are considered planned ASRs.

[2] Reference locations as the downwind locations for the odour measurements near the Cheung Chau STW and Pak She SPS conducted on 15-May-2013. They are not considered as ASR and were included for the odour prediction assessment for reference only.

3.9.2 Without any odour removing measures, elevated odour levels were predicted.

3.9.3 Odour prediction was also conducted at two reference locations where odour measurements were conducted near the Cheung Chau STW (CCSTW_DW) and Pak She SPS (PSSPS_DW).  These two locations (1.5m above ground level) were downwind locations from the Cheung Chau STW and Pak She SPS that were to capture a representative existing odour level.  The odour modeling results of the unmitigated scenario at the two reference locations (at 1.5m above ground) were predicted to be 60.6 OU and 119.0 OU (PSSPS_DW and CCSTW_DW, respectively).  These modeling results were based on an unmitigated scenario with the upgraded treatment facilities operation.  In comparison with the odour measurement results at the two reference locations, PSSPS_DW and CCSTW_DW, that were 14 OU and 64 OU, respectively, the modeled results of the unmitigated scenario are higher.  This is considered generally in order as the modeled scenario was based on higher treatment capacities, no deodourisation facilities and no covering structures, which is expected to have resulted a higher predicted odour level than the measurement results.

Mitigated Scenario

3.9.4 Based on the current design, the identified odour sources within the Cheung Chau STW would be enclosed and all the odour emissions from the enclosed sources would be ventilated to a deodourizing unit. The deodourizing unit is designed to be able to achieve an odour removal efficiency of 99% for Cheung Chau STW and 99% for Pak She Pumping Station. The design information of deodourizing unit is summarized in Table 3.11. The odour emission rate and odour removal efficiency in Table 3.11 shall be verified during commission test and periodic performance tests.

Table 3.11 : Design Information of Deodourizing Units (Mitigated)

		Odour removal efficiency of deodourization unit	Number of emission point	Total emission area (m^2)	Emission Rate per emission point (with mitigation) (OU/s)
Cheung Chau STW	Room 1 – Preliminary Treatment Unit	99%	5	12	10.095
	Room 2- Treatment Unit	99%	6	12.8	3.255
	Room 3 – Sludge Treatment Unit	99%	2	3.5	36.199
Pak She Pumping Station		99%	1	3.5	3.808

3.9.5 The treated air would then be emitted at 2.5 m above ground level based on the current design information. The predicted maximum mitigated odour levels at the selected ASRs are summarized in Table 3.12. With the odour removing measures, predicted odour levels at all selected ASRs will be significantly reduced to meet the 5 odour units criteria.

3.9.6 The predicted mitigated odour concentration contour plots at 1.5m, 5m, 10m 15m, 20m and 25m above ground level are shown in Figure 3.61 to Figure 3.66. A typical odour modelling output file is shown in Appendix 3.5.

Table 3.12 : Predicted Worst-case 5-second Average Odour Concentration at Different Level above Ground (Mitigated)

ASR	Predicted Worst-case Odour Concentration, 5-second Average Odour Units
	1.5m	5m	10m	15m	20m	25m
TKST2	0.2	0.3	0.3	0.3	0.3	0.2
TKW2*	0.2	0.2	0.2	0.2	0.2	0.2
CSH1*	0.4	0.5	0.6	0.6	0.6	0.5
CCC1*	0.5	0.5	0.5	0.4	0.4	0.3
CCC2*	0.4	0.4	0.4	0.4	0.4	0.3
CSH2*	2.7	2.6	2.5	2.0	1.5	1.0
CCSH*	1.5	1.8	3.3	3.5	2.8	1.8
CKH *	2.3	2.3	2.6	2.8	2.0	1.6
FS*	0.5	0.5	0.6	1.0	1.0	0.9
CCA*	2.5	3.4	2.4	1.0	1.0	0.8
CCB*	0.6	0.6	0.6	0.6	0.5	0.5
PSSL*	0.5	0.5	0.7	1.0	1.0	0.9
TKS	0.2	0.2	0.2	0.2	0.2	0.1
CCEP	0.1	0.1	0.1	0.1	0.1	0.1
CHR	0.1	0.1	0.2	0.2	0.2	0.2
SW1	0.1	0.1	0.1	0.1	0.1	0.1
THT	0.1	0.1	0.1	0.1	0.1	0.1
SWR	0.1	0.1	0.1	0.1	0.1	0.1
ST	0.1	0.1	0.1	0.1	0.1	0.1
SYT1	0.1	0.1	0.1	0.1	0.1	0.1
SYT2	0.1	0.1	0.1	0.1	0.1	0.1
P1	0.1	0.1	0.1	0.1	0.1	0.1
TW1	0.2	0.2	0.2	0.2	0.2	0.1
TW2	0.2	0.2	0.2	0.2	0.2	0.2
TW3	0.2	0.2	0.2	0.2	0.2	0.1
TSB	0.2	0.2	0.2	0.2	0.2	0.2
TSB1	0.2	0.2	0.2	0.2	0.2	0.2
HSR1	0.2	0.2	0.2	0.2	0.2	0.2
TTY	0.1	0.1	0.2	0.2	0.2	0.1
KKPS	0.1	0.1	0.1	0.1	0.0	0.0
TG	0.1	0.1	0.1	0.1	0.0	0.0
LTT	0.1	0.1	0.1	0.1	0.1	0.0
KL	0.2	0.2	0.2	0.2	0.1	0.1
LTT1	0.1	0.1	0.1	0.1	0.1	0.1
LTT2	0.2	0.2	0.2	0.1	0.1	0.1
P2	0.1	0.1	0.1	0.1	0.0	0.0
SJH	0.1	0.1	0.1	0.1	0.1	0.1
CCS	0.2	0.2	0.2	0.1	0.1	0.1
HPR	0.2	0.2	0.2	0.2	0.2	0.2
HC	0.1	0.1	0.1	0.1	0.0	0.0
KYW1	0.1	0.1	0.1	0.1	0.0	0.0
CCS2	0.1	0.1	0.1	0.1	0.0	0.0
HSR2	0.1	0.1	0.1	0.1	0.1	0.1
PR1	0.1	0.1	0.1	0.1	0.1	0.1
PR2	0.2	0.2	0.2	0.2	0.2	0.1
KYW2	0.1	0.1	0.1	0.1	0.1	0.1
MF1	0.1	0.1	0.1	0.1	0.1	0.1
FP1	0.1	0.1	0.0	0.0	0.0	0.0
FP2	0.1	0.0	0.0	0.0	0.0	0.0
GIC_1 ^[1]	1.8	1.6	2.7	2.4	1.6	1.1
GIC_2 ^[1]	0.7	0.7	0.7	0.9	0.8	0.7
GIC_3 ^[1]	0.7	1.0	1.5	0.9	0.9	0.7
PSSPS_DW ^[2]	0.6	0.6	0.8	1.0	1.0	0.8
CCSTW_DW ^[2]	1.2	1.3	3.6	3.5	2.4	1.7

Note:

ASR ID marked with * represents ASR located within the 500 m radius of the boundary of Cheung Chau STW and Pak She SPS.

[1] The existing land-uses of these locations are storage area and open space. According the Cheung Chau Outline Zoning Plan (No. S/I-CC/5), they are zoned as Government / Institution and Community (G/IC) use which may be used for potential air sensitive use. These are considered planned ASRs.

[2] Reference locations as the downwind locations for the odour measurements near the Cheung Chau STW and Pak She SPS conducted on 15-May-2013. They are not considered as ASR and were included for the odour prediction assessment for reference only.

3.9.7 No exceedances of odour level arising from the operation of the upgraded Cheung Chau sewage treatment facilities were predicted under the mitigated scenario.

3.10 Mitigation Measures

Construction Phase

3.10.1 For the construction activities under the Project, the suitable requirements stipulated in the Air Pollution Control (Construction Dust) Regulation shall be implemented during the construction activities to minimise the dust impact. It is recommended that typical dust control methods including the following good site practices should also be incorporated during construction phase:

Ÿ Watering every 1.5 hours on active works areas and paved haul roads to reduce dust emissions by 90.9% (e.g. watering intensity at 0.5 litres/m². Actual application shall depend on the site condition and weather conditions).

Ÿ Watering every hour on unpaved areas and stockpiles of dusty materials (if no tarpaulin is provided) to reduce dust emissions by 90% (e.g. watering intensity at 1.5 litre/m² during the first hour, subsequent application at 0.2 litre/m². Actual application shall depend on the site condition and weather conditions).

Ÿ Use of regular watering, with complete coverage, to reduce dust emissions from exposed site surfaces and unpaved roads, particularly during dry weather.

Ÿ Use of frequent watering for particularly dusty construction areas and areas close to ASRs.

Ÿ Vehicle washing facilities should be provided at every vehicle exit point.

Ÿ 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.

Ÿ Stockpiles of imported material kept on site shall be contained within hoarding, dampened and/or covered during dry and windy weather.

Ÿ Material stockpiled alongside trenches should be covered with tarpaulins.

Ÿ Open stockpiles shall be avoided or covered. Where possible, prevent placing dusty material storage piles near ASRs.

Ÿ Any excavated or stockpile of dusty material should be covered entirely by impervious sheeting or spayed with water to maintain the entire surface wet during the non-working hours.

Ÿ All dusty materials shall be sprayed with water prior to any loading, unloading or transfer operation so as to keep the dusty materials wet.

Ÿ Water sprays shall be used during the delivery and handling of sands aggregates and the like.

Ÿ All demolished items that may emit dust particles should be covered entirely by impervious sheeting or placed in an area sheltered on the top and the 3 sides within a day of demolition.

Ÿ Good site practices for Concrete batching plant:

- Every stock of more than 20 bags of cement or dry pulverized fuel ash (PFA) should be cover entirely by impervious sheeting or placed in an area sheltered on the top and the sides.

- Cement or dry PFA delivered in bulk should stored in a closed silo fitted with an audible high level alarm which is interlocked with the material filling line and no overfilling is allowed.

- Loading, unloading, transfer, handling or storage of bulk cement or dry PFA should be carried out in a totally enclosed system or facility, and any vent or exhaust should be fitted with effective fabric filter or equivalent air pollution control system (Maximum TSP emission factor of silos and mixing tower: 50 mg/m³)

Operational Phase

3.10.2 The design of enclosing the odour sources of the upgraded Cheung Chau STW and Pak She SPS and the installation of deodorization units would readily reduce the potential odour impacts. Odour impacts after the upgrading works will be significantly reduced. The current design information of deodourizing units is summarized in Table 3.13.

Table 3.13 : Design Information of Deodourizing Units (Mitigated)

		Odour removal efficiency of deodorisation unit	Number of emission point	Total emission area (m^2)	Emission Rate per emission point (with mitigation) (OU/s)
Cheung Chau STW	Room 1 – Preliminary Treatment Unit	99%	5	12	10.095
	Room 2- Treatment Unit	99%	6	12.8	3.255
	Room 3 – Sludge Treatment Unit	99%	2	3.5	36.199
Pak She Pumping Station		99%	1	3.5	3.808

3.10.3 In addition, good housekeeping practices listed below should be followed to control odour emissions 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 and screened materials should be transferred to closed containers to minimize odour escape;

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

· Sludge should be transferred to closed containers; and

· Sludge containers should be flushed with water regularly.

3.11 Environmental Monitoring and Audit Requirements

Construction Phase

3.11.1 Mitigation Measures are recommended to reduce the dust impact to an acceptable level. With the implementation of the dust suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation and good site practices, construction dust impacts could be eliminated. Environmental monitoring and audit (EM&A) for air quality will be carried out during the construction period of Cheung Chau STW and Pak She SPS to ensure proper implementation of construction phase mitigation measures with consideration of practicability in local level.

3.11.2 Further details of the specific EM&A requirements for the construction activities of Cheung Chau STW and Pak She SPS are provided in the EM&A Manual, together with event action plans and procedures for complaints.

Operational Phase

3.11.3 All the odorous gas arising from the sewage would be collected and properly treated by deodorization unit with 99% odour removal efficiency for Cheung Chau STW and Pak She SPS. The predicted odour levels at the ASRs would comply with the EIAO-TM criterion. Odour monitoring and audit should be carried out during the commissioning stage to ensure the continuing effectiveness of the odour control measures. Details of monitoring and audit programme of odour due to the operation of Cheung Chau STW and Pak She SPS are presented in the EM&A Manual. Commissioning test of the deodorization unit is also a mandatory requirement to confirm the effectiveness of the odour removal efficiency is in compliance with the design criteria.

3.12 Conclusion

3.12.1 Dust generating activities were identified and evaluated. If unmitigated, construction of the Cheung Chau STW upgrade would have short term fugitive dust emissions impacts at the identified ASRs. Mitigation measures including watering of on-site construction area are expected to limit fugitive dust levels to acceptable levels. Provided proper implementation of mitigation measures is adopted, no unacceptable construction dust emissions impacts are anticipated. An EM&A programme will be implemented to ensure construction dust impacts are controlled to acceptable level.

3.12.2 During the operational phase of the Project, all the potential odour generating facilities would be enclosed by air-tight covers. Odourous gas generated from the Cheung Chau STW and Pak She SPS would be ventilated to the deodorization facility for treatment before discharge. The deodorization facility is designed to be able to achieve an odour removal efficiency of 99% for Cheung Chau STW and Pak She SPS. During sludge transportation, it is recommended that the sludge should be carried by enclosed container to avoid unacceptable odour nuisance. With proper mitigation measures incorporated into the design, odour impacts after the upgrading works will be significantly reduced, and no unacceptable odour impacts are anticipated. An EM&A programme will be implemented to ensure the continuing effectiveness of the odour control measures.