l Air Pollution Control Ordinance (APCO) (Cap. 311) - this provides the power for controlling air pollutants from a variety of stationary and mobile sources and encompasses a number of Air Quality Objectives (AQOs);

l Air Pollution Control (Construction Dust) Regulation;

l Air Pollution Control (Non-road Mobile Machinery) (Emission) Regulation;

l Air Pollution Control (Fuel Restriction) Regulation; and

l Environmental Impact Assessment Ordinance (EIAO) (Cap. 499), EIAO-TM, Annex 4 and Annex 12.

3.2.2 Air Quality Objectives

3.2.2.1 The relevant prevailing AQOs, as tabulated in Table 3.1 has been in forced since 1 January 2014.

Table 3.1 Hong Kong Air Quality Objectives

Pollutant	Averaging Time	Concentration Limit, µg/m^{3 (1)}	No. of Exceedances Allowed per Year
Fine Suspended Particulates (PM_2.5 / FSP) ⁽³⁾	24-hour	75	9
Fine Suspended Particulates (PM_2.5 / FSP) ⁽³⁾	Annual ⁽²⁾	35	Not applicable
Respirable Suspended Particulates (PM₁₀ / RSP) ⁽⁴⁾	24-hour	100	9
Respirable Suspended Particulates (PM₁₀ / RSP) ⁽⁴⁾	Annual ⁽²⁾	50	Not applicable
Sulphur Dioxide (SO₂)	10-minute	500	3
Sulphur Dioxide (SO₂)	24-hour	125	3
Nitrogen Dioxide (NO₂)	1-hour	200	18
Nitrogen Dioxide (NO₂)	Annual ⁽²⁾	40	Not applicable
Photochemical Oxidants [as Ozone (O₃)]	8-hour	160	9
Carbon Monoxide (CO)	1-hour	30,000	0
Carbon Monoxide (CO)	8-hour	10,000	0
Lead (Pb)	Annual ⁽²⁾	0.5	Not applicable

Notes:

(1) All measurements of the concentration of gaseous air pollutants, i.e., sulphur dioxide, nitrogen dioxide, ozone and carbon monoxide, are to be adjusted to a reference temperature of 293 Kelvin and a reference pressure of 101.325 kilopascal.

(2) Arithmetic mean.

(3) “Fine suspended particulates” means suspended particles in air with a nominal aerodynamic diameter of 2.5 µm or less.

(4) “Respirable suspended particulates” means suspended particles in air with a nominal aerodynamic diameter of 10 µm or less.

3.2.3 Air Pollution Control (Construction Dust) Regulation

3.2.3.1 With reference to the Air Pollution Control (Construction Dust) Regulation, it specifies processes that require special dust control. The Contractors are required to inform the EPD and adopt proper dust suppression measures while carrying out “Notifiable Works” (which requires prior notification by the Regulation) and “Regulatory Works” to meet the requirements as defined under the Regulation.

3.2.4 Air Pollution Control (Non-road Mobile Machinery) (Emission) Regulation

3.2.4.1 The Air Pollution Control (Non-road Mobile Machinery) (Emission) Regulation comes into operation on 1 June 2015. Under the Regulation, non-road mobile machinery (NRMMs), except those exempted, are required to comply with the prescribed emission standards. From 1 September 2015, all regulated machines sold or leased for use in Hong Kong must be approved or exempted with a proper label in a prescribed format issued by EPD. Starting from 1 December 2015, only approved or exempted NRMMs with a proper label are allowed to be used in specified activities and locations including construction sites. The Contractor is required to ensure the adopted machines or non-road vehicle under the Project could meet the prescribed emission standards and requirement.

3.2.5 Air Pollution Control (Fuel Restriction) Regulation

3.2.5.1 The Air Pollution Control (Fuel Restriction) Regulation was enacted in 1990 to impose legal control on the type of fuels allowed for use and their sulphur contents in commercial and industrial processes to reduce sulphur dioxide (SO₂) emissions. In June 2008, the Regulation was amended to tighten the control requirements of liquid fuels. The Regulation does not apply to any fuel-using equipment that is used or operated in premises used solely as a dwelling, or is used or operated in or on a vessel, motor vehicle, railway locomotive or aircraft.

3.2.6 EIAO-TM

3.2.6.1 Annex 4 of EIAO-TM stipulates that hourly Total Suspended Particulate (TSP) level should not exceed 500µg/m³ measured at 298 K and 101.325 kPa (one atmosphere) for the construction dust impact assessment. It also stipulates that the odour level at air sensitive receiver should meet 5 odour units based on an averaging time of 5 seconds for odour prediction assessment.

3.2.6.2 Guidelines for conducting air quality assessment are stipulated in Annex 12 of EIAO-TM, including the determination of air sensitive receivers (ASRs), the assessment methodology, baseline study and impact prediction and assessment.

3.3 Description of the Environment and Future Trend

3.3.1 Baseline Conditions

3.3.1.1 The major existing emission source in the vicinity of the Project site is road traffic emissions from Sai Sha Road at the south of the Project site. The concerned section of Sai Sha Road is a rural road (RR) with annual average daily traffic (AADT) of 18,300 in 2019 according to Transport Department’s “The Annual Traffic Census 2019”. The nearest EPD’s air quality monitoring station to the Project site is Tai Po Air Quality Monitoring Station. The latest available five-year air quality monitoring data measured between 2015 and 2019 at Tai Po Air Quality Monitoring Station are summarised in Table 3.2.

Table 3.2 Summary of the Latest Available Five-Year Air Quality Data at Tai Po Air Quality Monitoring Station (2015 to 2019)

Air Pollutant	Averaging Time		Concentration, μg/m³					AQO, μg/m³
Air Pollutant	Averaging Time		2015	2016	2017	2018	2019	AQO, μg/m³
PM_2.5	24-hour	10^th highest	57	55	55	47	47	75
PM_2.5	Annual		23	20	22	19	20	35
PM₁₀	24-hour	10^th highest	77	74	82	69	65	100
PM₁₀	Annual		36	29	32	31	31	50
SO₂	10-min	4^th highest	56	37	39	24	20	500
SO₂	24-hour	4^th highest	13	10	9	8	10	125
NO₂	1-hour	19^th highest	136	112	127	125	142	200
NO₂	Annual		37	33	39	36	36	40
O₃	8-hour	10^th highest	157	147	181	167	197	160
CO	1-hour	1^sthighest	N.A.	N.A.	N.A.	N.A.	N.A.	30,000
CO	8-hour	1^sthighest	N.A.	N.A.	N.A.	N.A.	N.A.	10,000

Notes:

N.A. Not applicable. CO was not monitored at Tai Po Station.

(1) Monitoring results exceeded the AQOs are shown as bold and underlined characters.

(2) All data were extracted from EPD’s Air Quality Reports.

(3) Reference conditions of gaseous pollutants concentration data: 298 K and 101.325 kPa.

3.3.1.2 As shown in Table 3.2, the 10^th highest 8-hour O₃concentrations exceeded the AQO criteria in 2017 to 2019. High level of O₃ is a regional air pollution problem that the HKSAR government has been strengthening its collaboration with the Guangdong Provincial Government to alleviate the photochemical smog and the associated O₃ problems in the region and continuing to restrict vehicular emission and implement other control measures to reduce local emissions.

3.3.1.3 The concentrations of all other air pollutants monitored at the Tai Po Air Quality Monitoring Station complied with the relevant AQO criteria from 2015 to 2019 – the concentration of annual average NO₂ had been decreasing since 2015 and that of PM_2.5, PM₁₀ and SO₂from 2015 to 2019 were well below the AQO criteria. No 1-hour and 8-hour data was available for CO in Tai Po Station.

3.3.2 Future Background Air Quality

3.3.2.1 The construction of the Project is scheduled to commence in year 2021 Q4 for completion and operation in year 2025 Q2 and hence the air pollutant concentrations in 2020 at the Project area have been adopted as the background concentrations for the Project. Future background air quality concentrations can be predicted from the Pollutants in the Atmosphere and the Transport over Hong Kong-2016 (PATH-2016) model. PATH-2016 model with Year 2020 emission inventory was released by EPD. Air pollutant concentrations for 2020 predicted from PATH-2016 in the Project area are extracted and presented in Table 3.3. No exceedance of the current AQOs is anticipated at the background level based on the prediction.

Table 3.3 Air Pollutants Concentrations in 2020 Predicted from PATH-2016 Model

Air Pollutant	Averaging Time		Future Background Concentration, μg/m³(Year 2020) ⁽¹⁾	AQO, μg/m³
PM_2.5	24-hour	10^th Highest	52 – 53 ⁽³⁾	75
PM_2.5	Annual		22 ⁽³⁾	35
PM₁₀	24-hour	10^th Highest	70 ⁽²⁾	100
PM₁₀	Annual		30 ⁽²⁾	50
SO₂	10-min	4^th highest	142 – 143	500
SO₂	24-hour	4^th Highest	22 – 23	125
NO₂	1-hour	19^th Highest	53	200
NO₂	Annual		7 – 8	40
O₃	8-hour	10^th Highest	153 – 155	160
CO	1-hour	1^st Highest	1,027 – 1,029	30,000
CO	8-hour	1^st Highest	834 – 836	10,000

Notes:

(1) Extracted from PATH grids (48, 46) and (48, 45) in which the Project site is located.

(2) With reference to the EPD’s Guidelines on Choice of Models and Model Parameters, PATH-2016’s output of RSP concentration are adjusted as follows:

- 10^th highest daily RSP concentration: add 26.5 µg/m³

- Annual RSP concentration: add 15.6 µg/m³

(3) With reference to the EPD’s Guidelines on the Estimation of PM_2.5 for Air Quality Assessment in Hong Kong, the following conservative formulae are adopted to calculate background FSP concentration from the RSP concentration extracted from the PATH model:

- Annual (µg/m³): PM_2.5 = 0.71 × PM₁₀

- Daily (µg/m³): PM_2.5 = 0.75 × PM₁₀

3.3.3 Representative Air Sensitive Receivers

3.3.3.1 The assessment area for the air quality impact assessment is defined by a distance of 500 m from the boundary of the proposed works site. All existing and planned / committed ASRs in the assessment area were identified (Appendix 3.1 refers) according to the criteria set out in Annex 12 of the EIAO-TM, observations from site visits and review of relevant land use plans including Outline Zoning Plans (OZP), information available in the Statutory Planning Portal of the Town Planning Board (TPB) and land status plans published by Lands Department. Representative ASRs for the construction phase and operational phase were identified as given in Table 3.4 and shown in Figure 3.1.

Table 3.4 Representative Air Sensitive Receivers

ASR ID	Description	Land Use	No. of Storey	Horizontal Distance to Works Boundary, m
A1	Hong Kong Baptist Theological Seminary (HKBTS) Staff & Students Quarters	Residential	6	20
A2	HKBTS Administration and Education Block	Education	5	31
A3a	Planned School with Recreational Area under the Approved Planning Application No. A/MOS/125 ⁽¹⁾	Education	6	30
A3b		Education	6	51
A4	Symphony Bay, Block 11	Residential	7	174
A5	Zessa Vista	Residential	3	227
A6	Recreational Area at Planned School under the Approved Planning Application No. A/MOS/125 ⁽¹⁾	Recreational	-	20
A7	Planned Sitting-out Area and Children's Playground at Nai Chung	Recreational	-	80

Note:

(1) Programme of the planned ASR is uncertain. It is expected that the planned ASR would not exist during the construction of the Project and hence it is only considered as ASR during operational phase.

3.4 Identification of Pollution Sources

3.4.1 Construction Phase

3.4.1.1 Major source of potential air quality impact during construction phase would be fugitive dust generated from wind erosion of the excavated areas and stockpiles, as well as from the following construction activities:

· Site clearance

· Excavation and Lateral Support (ELS)

· Bulk excavation

· Backfilling

· Pipeworks

3.4.1.2 As presented in Section 2.7, there is a concurrent project identified within the assessment area, i.e. Sai Sha Road Widening. Based on the available information, the construction programme of Sai Sha Road Widening would be from Q1 of 2018 to Q4 of 2023. Given the nature of the concurrent project, potential dust impact arising from it would be limited and localised. With the implementation of appropriate mitigation measures, adverse cumulative dust impact would not be anticipated.

3.4.1.3 Toxic air pollutants (TAPs) in the form of volatile organic compounds (VOC) are anticipated from the use of chemicals, such as solvents, cleaning agents and fuels, for the maintenance and servicing of construction plants and vehicles during construction phase. Considering that the quantities of chemicals to be used would be limited, the amount of VOC generated would be small. The aboveground works areas would be in outdoor setting, and the underground works areas would be well-ventilated, such that the VOC would be able to disperse and would not accumulate at the works areas. With proper handling of the chemicals, environmental and health impacts associated with TAPs is anticipated to be insignificant.

3.4.1.4 Likewise, fuel combustion from the use of PMEs during construction works could be a potential source of air pollutants such as NO₂, SO₂ and CO. To reduce SO₂ emission, Air Pollution Control (Fuel Restriction) Regulation was enacted in 1990 to impose legal control on the types of fuel allowed for use and their sulphur contents in commercial and industrial processes. To improve air quality and protect public health, EPD has introduced the Air Pollution control (Non-road Mobile Machinery) (Emission) Regulation in since 1 December 2015, only approved or exempted non-road mobile machinery are allowed to be used in construction sites. In addition, all construction plants are required to use ultra-low-sulphur diesel (ULSD) (defined as diesel fuel containing not more than 0.005% sulphur by weight) as stipulated in Environment, Transport and Works Bureau Technical Circular (ETWB-TC(W)) No. 19/2005 on Environmental Management on Construction Sites. Furthermore, given the localized and small scale of the Project, as well as the small number of PMEs involved, adverse air quality impacts due to emissions from the use of PMEs would be unlikely.

3.4.2 Operational Phase

3.4.2.1 Odour from the operation of the proposed SPS would be the key source of air quality impacts during the operational phase of the Project. Odour would potentially arise from the inlet chamber, screen house and wet well of the proposed SPS.

3.4.2.2 TAPs are not anticipated to be generated during the normal operation of the proposed SPS, but from the use of chemicals, such as solvents, cleaning agents and fuels, for the maintenance of the SPS. Since the maintenance works would not be frequent, and the quantities of chemicals used would be limited, the amount of VOC generated would be small. Considering the small amount, with proper handling of the chemicals, environmental and health impacts associated with TAPs is anticipated to be limited.

3.5 Assessment Methodology

3.5.1 Construction Phase

3.5.1.1 The construction programme, plant inventory and construction works area of the Project were reviewed to evaluate the dust impacts on the nearby ASRs. Given that the construction activities and site area are limited and the scale of construction would be minor, the potential dust impact would be limited and could be well controlled through the dust suppression measures as stipulated in the Air Pollution Control (Construction Dust) Regulation (Cap. 311R) of Air Pollution Control Ordinance (APCO) (Cap. 311) and good site practices. Therefore, qualitative approach was adopted for the assessment.

3.5.2 Operational Phase

3.5.2.1 The potential odour sources including inlet chamber, coarse screen channel, distribution chamber and wet well would be located underground and enclosed with air- and water-tight covers. The covers would be opened occasionally during routine maintenance of the SPS including screen cleaning. The SPS would be equipped with deodorising unit of at least 90% (99.5% in terms of target odour species, i.e. H₂S) odour removal efficiency at the exhaust. With proper design of the SPS, adverse odour nuisance from the operation of the SPS would not be anticipated. Nonetheless, quantitative assessment for potential odour impact associated with the Project operation was conducted to ensure the compliance of the EIAO-TM odour criterion.

3.5.2.2 The emission parameters and odour emission rate of the odour control system as provided and confirmed to be practical and adequate for the scale of the proposed SPS by the project engineer are detailed in Appendix 3.2. It was assumed that the deodorising unit of the Project would operate continuously on a 24-hour-per-day, 7-day-per-week basis with steady state ventilation rate and exhaust gas velocity in the assessment.

3.5.2.3 The EPD approved air dispersion model, AERMOD was used to predict the odour impact from the operation of the Project at the representative ASRs. Odour emission from the exhaust outlet of the DO was modelled as point source in the assessment.

3.5.2.4 Hourly meteorological conditions including wind data, temperature, relative humidity, pressure cloud cover and mixing height of Year 2010 were extracted from the WRF meteorological data adopted in the PATH-2016 system. The minimum wind speed was capped at 1 metre per second. The mixing height was capped between 121 metres and 1667 metres according to the observation in Year 2010 by Hong Kong Observatory (HKO). The height of the input data was assumed to be 9 above ground for the first layer of the WRF data as input. The meteorological data was inputted as on-site data into AERMET.

3.5.2.5 Surface characteristic parameters such as albedo, Bowen ratio and surface roughness are required in the AERMET (the meteorological pre-processor of AERMOD). The land use characteristics of the surrounding are classified and these parameters of each landuse are then suggested by AERMET by default according to its land use characteristics. Flat terrain in AERMOD was adopted for this assessment. The detailed assumptions are presented in Appendix 3.3.

3.5.2.6 According to the latest design, the building height of the SPS would be about 9mAG, while the deodorizer exhaust would be located at the façade of the SPS at 4mAG height. Building wake effect would be expected. According to the EIAO-TM, the odour criterion is 5 OU units based on an averaging time of 5 seconds. Therefore, it is required to convert the predicted odour concentration in 1-hour averaging time from the AERMOD model to 5-second average. Reference was made to the peak-to-mean ratio 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). In accordance with the NSW Approved Method, the conversion factors for converting 1-hour average concentration to 1-second average concentration were adopted as a conservative approach. The conversion factor is 2.3 for wake-affected point sources under Pasquill Stability Class of A to F.

3.5.2.7 PCRAMMET was applied to generate Pasquill-Gifford stability class hour by hour based on the WRF meteorological data. The hourly emission rate was multiplied by the conversion factor corresponding to the estimated stability class in order to predict the 5-second average odour concentrations.

3.6 Prediction and Evaluation of Environmental Impacts

3.6.1 Construction Phase

3.6.1.1 Albeit the Project site would be in close proximity to the ASRs, considering the minor scale of the Project, dust emissions would be limited and could be well controlled through the dust suppression measures as stipulated in the Air Pollution Control (Construction Dust) Regulation (Cap. 311R) and good site practices. With proper implementation of the dust suppression measures, adverse air quality impact due to the construction of the Project would not be anticipated.

3.6.2 Operational Phase

3.6.2.1 The main air quality impact would be the odour nuisance from the operation of the proposed SPS (installed capacity per day of about 20,600m³). Site visits to several typical SPSs with capacities ranging from about 12,100 to 36,900 m³ per day, including Yuen Long South SPS, Au Tau SPS, Yuen Long Kau Hui SPS and Tai Po Tai Wo Road SPS, were conducted in July 2017. These existing SPSs were all provided with odour removal system with odour removal efficiency of at least 99.5% in terms of target odour species, i.e. H₂S, and all the potential odour sources were enclosed within the building structures. Exhausts of the odour removal system of these SPSs were all located at the building facades and the shortest horizontal separation distance between the exhausts and the SPS’s site boundaries was less than 10m. Odour was not noticed at the site boundaries of these SPSs during the site visits.

3.6.2.2 Based on the latest engineering design, air ventilated from the enclosed structure of the proposed SPS would be treated by deodorising unit with odour removal efficiency of at least 99.5% in terms of target odour species, i.e. H₂S, before discharging to the atmosphere. The exhaust outlet of the deodorising unit would be located away from the nearby ASRs as far as practicable, i.e. facing east of the Sai O Trunk Sewer SPS. The shortest horizontal separation distance to the nearest ASRs (A1 and A6) is approximately 20 m from the site boundary of the Project, while the odour exhaust of the proposed Sai O Trunk Sewer SPS would be located at least 100 m and 30 m from A1 and A6, respectively. In addition, odour sources would be fully enclosed or tightly covered and equipped with deodorising unit. The odour impact of the proposed Sai O Trunk Sewer SPS is therefore expected to be similar to or not worse than that of the SPSs visited.

3.6.2.3 Odour concentrations from the operation of the proposed SPS at the representative ASRs has been predicted using the assessment approach described in Section 3.5.2. The results are summarised in Table 3.5 below and detailed in Appendix 3.4.

Table 3.5 Predicted Maximum 5-second Average Odour Concentration at Representative Air Sensitive Receivers

ASR ID	Description	Predicted Maximum 5-second Average Odour Concentration, OU/m³
A1	HKBTS Staff & Students Quarters	0.15 - 0.89
A2	HKBTS Administration and Education Block	0.17 - 0.82
A3a	Planned School with Recreational Area under the Approved Planning Application No. A/MOS/125	0.12 - 0.85
A3b		0.08 - 0.88
A4	Symphony Bay, Block 11	0.10 - 0.41
A5	Zessa Vista	0.36 - 0.40
A6	Recreational Area at Planned School under the Approved Planning Application No. A/MOS/125	2.91
A7	Planned Sitting-out Area and Children's Playground at Nai Chung	0.70

Note:

(1) According to EIAO-TM, odour concentrations limit is 5 OU/m³ based on an averaging time of 5 seconds

3.6.2.4 As shown in Table 3.5, the 5-second average odour concentrations at the representative ASRs were predicted to be well below the EIAO-TM odour criterion of 5 OU, ranging from 0.08 OU/m³ to 2.91 OU/m³. No adverse odour impact arising from the operation of the proposed SPS would be anticipated. Based on the detailed results in Appendix 3.4, the worst-affected level would generally be at 1.5mAG for all representative ASRs. Therefore, the maximum odour concentrations at 1.5mAG in the form of contour plot is presented in Figure 3.2, which shows that no exceedance zone was predicted within the 500m assessment area.

3.6.2.5 Although no adverse odour impact was predicted, implementation of the commonly adopted good site practices as detailed in Section 3.7.2 is recommended to further minimise any odour nuisance from the operation of the proposed SPS.

3.6.2.6 Screening wastes will be stored in covered containers, packed and handled carefully inside the screen house, and remained in the covered containers before disposal of at landfill site to avoid off-site odour nuisance along the disposal route. Therefore, adverse on-site or off-site odour impacts due to the removal / handling of the screening wastes would not be anticipated.

3.7 Recommended Mitigation Measures

3.7.1 Construction Phase

3.7.1.1 Sufficient dust suppression measures as stipulated under the Air Pollution Control (Construction Dust) Regulation (Cap. 311R) and good site practices such as enclosing stockpiles of sand with three-side enclosure, covering the dusty materials with clean impervious sheet, water spraying of all access roads and site areas, and good house-keeping of the site should be properly implemented in order to minimise the construction dust generated. These measures include the followings:

a) Use of regular watering, to reduce dust emissions from exposed site surfaces and unpaved roads particularly during dry weather;

b) Use of frequent watering in particularly dusty construction areas close to ASRs;

c) Use of frequent watering or water sprinklers for major haul roads, material stockpiling areas and other dusty activities within the construction site;

d) 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;

e) Provide hoardings of not less than 2.4 m high from ground level along the site boundary except for site entrance or exit;

f) Open temporary stockpiles should be avoided or covered. Prevent placing dusty material storage plies near ASRs;

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

h) Establishment and use of vehicle wheel and body washing facilities at the exit point of the site;

i) Imposition of speed control for vehicles on unpaved site roads. 8 km/hr is the recommended limit;

j) Routing of vehicles and positioning of construction plants should be at the maximum possible distance from ASRs;

k) Avoid position of material stockpiling areas, major haul roads and dusty works within the construction site close to concerned ASRs; and

l) Avoid unnecessary exposed earth.

3.7.1.2 Guidelines stipulated in EPD’s Recommended Pollution Control Clauses for Construction Contracts should be incorporated in the contract documents to abate dust impacts. The clauses include:

l The Contractor shall observe and comply with the APCO and its subsidiary regulations, particularly the Air Pollution Control (Construction Dust) Regulation.

l The Contractor shall undertake at all times to prevent dust nuisance as a result of the construction activities.

l The Contractor shall ensure that there will be adequate water supply / storage for dust suppression.

l The Contractor shall devise and arrange methods of working and carrying out the works in such a manner so as to minimise dust impacts on the surrounding environment, and shall provide experienced personnel with suitable training to ensure that these methods are implemented.

l Before the commencement of any work, the Contractor may be required to submit the methods of working, plant, equipment and air pollution control system to be used on the site for the Engineer inspection and approval.

3.7.2 Operational Phase

3.7.2.1 In addition to the proposed deodorising unit and odour control measures as mentioned in Section 3.6.2.2, the following good site practices should be implemented to further minimise any potential odour nuisance from the proposed SPS:

l The odour sources including inlet chamber, coarse screen channels, distribution chamber and wet wells should be enclosed with air- and water-tight lids at all times except during checking, maintenance and cleaning;

l Negative pressure should be maintained within the facilities;

l Screening wastes should be stored in a covered container or sealed plastic bag and handled carefully inside the screen houses before transporting outside the SPS building;

l Screening wastes should be regularly removed from the proposed SPS by a reputable waste collector. They should be transported in an enclosed type carrier or vehicle and disposed of on the same working day; and

l The deodorising unit should be regularly checked and maintenance to maintain the odour removal efficiency.

3.8 Evaluation of Residual Impacts

3.8.1 Construction Phase

3.8.1.1 With proper implementation of the mitigation measures as stated in Section 3.7.1, adverse construction dust impact would not be expected.

3.8.2 Operational Phase

3.8.2.1 With proper design of the proposed SPS and effective implementation of the mitigation measures as stated in Section 3.7.2, odour impact during operational phase of the Project would not be anticipated.

3.9 Environmental Monitoring and Audit

3.9.1 Construction Phase

3.9.1.1 While adverse construction dust impact would not be expected with proper implementation of the mitigation measures as stated in Section 3.7.1, dust monitoring is recommended during the construction phase to ascertain that there would be no adverse dust impacts at the nearby sensitive receivers. Details of the monitoring and audit programme are contained in a stand-alone EM&A Manual. Weekly site audit is also recommended to be undertaken to ensure the proposed mitigation measures are implemented in an appropriate manner and are effective.

3.9.2 Operational Phase

3.9.2.1 Adverse odour impacts would not be anticipated during operational phase. Nonetheless, it is recommended to conduct odour measurement in terms of hydrogen sulphide (H₂S) at the deodoriser prior to operation to ensure the odour removal performance requirement can be met, and monitoring of the exhaust odour emission rate of the deodoriser upon operation to ascertain the validity of the air quality impact assessment. In addition, odour patrol should be carried out during the period of regular (generally once to twice every year) and any ad hoc maintenance or cleaning of the deodorisation system when the deodoriser might not be working at its full capacity as specified and assumed in assessment.

3.10 Conclusion

3.10.1 Construction Phase

3.10.1.1 With implementation of regular site watering and good construction practices for dust minimization, construction dust impacts are not expected to be significant on the surrounding sensitive receivers. Requirements of Air Pollution Control (Construction Dust) Regulation and EPD’s Recommended Pollution Control Clauses for Construction Contracts are proposed to be incorporated into the contract.

3.10.2 Operational Phase

3.10.2.1 Odour emission from the proposed Sai O Trunk Sewer SPS would be the main concern during operational phase. Air ventilated from the enclosed structure of the proposed SPS should be treated by deodorising unit with odour removal efficiency of at least 90% (99.5% in terms of target odour species, i.e. H2S) before discharge to the atmosphere. The exhaust outlet of the deodorising unit would be located away from the nearby air sensitive receivers as far as practicable, i.e. facing east of the Sai O Trunk Sewer SPS. With incorporation of the proposed odour control measures in the design of the SPS, the predicted odour concentrations at all representative ASRs would comply with the EIAO-TM odour criterion. No adverse odour impact would be anticipated during the operation of the proposed SPS.