TABLE OF CONTENTS

3............. Air Quality Impact. 3-1

3.1.......... Introduction. 3-1

3.2.......... Environmental Legislation, Standards and Criteria. 3-1

3.3.......... Description of Environment 3-3

3.4.......... Identification of Air Sensitive Receivers. 3-4

3.5.......... Identification of Environmental Impacts. 3-6

3.6.......... Assessment Methodology. 3-14

3.7.......... Prediction and Evaluation of Environmental Impacts. 3-20

3.8.......... Mitigation of Adverse Environmental Impacts. 3-26

3.9.......... Evaluation of Residual Impacts. 3-28

3.10........ Environmental Monitoring and Audit Requirements. 3-29

3.11........ Conclusion. 3-29

List of Tables

Table 3.1 New Air Quality Objectives for Hong Kong. 3-1

Table 3.2 Air Quality Standards for Non-AQO Criteria Pollutants. 3-2

Table 3.3 Average Concentrations of Pollutants in the Recent Five Years (Year 2016 – 2020) at Yuen Long EPD Air Quality Monitoring Station. 3-3

Table 3.4 Background Air Pollutants in Year 2025 Extracted from the PATH v2.1 Model 3-4

Table 3.5 Representative Air Sensitive Receivers in the vicinity of YLSEPP. 3-5

Table 3.6 Potential Concurrent Projects. 3-7

Table 3.7 Predicted Construction Phase TSP and RSP Concentrations at ASRs within 500m Assessment Boundary of YLSEPP in Year 2029 extracted from YLS DA EIA Report 3-9

Table 3.8 Predicted Construction Phase 24-hour Average FSP Concentrations at ASRs within 500m Assessment Boundary of YLSEPP in 2029 extracted from YLS DA EIA Report 3-9

Table 3.9 Predicted Construction Phase Annual Average FSP Concentrations at ASRs within 500m Assessment Boundary of YLSEPP in 2029 extracted from YLS DA EIA Report 3-10

Table 3.10 Emission Factor for Dusty Construction Activities. 3-14

Table 3.11 Particle Size Distribution for Construction Dust 3-14

Table 3.12 Conversion Factors from 1-hour to 30-minute Averaging Time. 3-17

Table 3.13 Vehicular Emission Burden in the Study Area. 3-17

Table 3.14 Conversion Factors from 1-hour to 5-second Averaging Time. 3-20

Table 3.15 Predicted Fine Suspended Particulates Concentrations on Representative Air Sensitive Receivers 3-21

Table 3.16 Predicted Respirable Suspended Particulates Concentrations on Representative Air Sensitive Receivers. 3-21

Table 3.17 Predicted Nitrogen Dioxide Concentrations on Representative Air Sensitive Receivers 3-22

Table 3.18 Predicted Sulphur Dioxide Concentrations on Representative Air Sensitive Receivers 3-22

Table 3.19 Predicted Maximum Cumulative Odour Concentrations at Representative Air Sensitive Receivers 3-23

Table 3.20 Predicted Maximum Project-alone Odour Concentrations at Representative Air Sensitive Receivers 3-26

Table 3.21 Predicted Cumulative Construction Dust Impact at Representative ASRs in Year 2028 (Mitigated Scenario) 3-27

List of Figures
Figure 3.1	Locations of Air Sensitive Receivers (Construction Phase)
Figure 3.2	Locations of Air Sensitive Receivers (Operation Phase)
Figure 3.3	Contour of Predicted Maximum Cumulative Hourly TSP Concentration (µg/m^3) at 1.5 mAG (Year 2028, Construction Phase) (Mitigated Scenario)
Figure 3.4	Contour of Predicted 10th Highest Cumulative Daily RSP Concentration (µg/m^3) at 1.5 mAG (Year 2028, Construction Phase) (Mitigated Scenario)
Figure 3.5	Contour of Predicted Cumulative Annual RSP Concentration (µg/m^3) at 1.5 mAG (Year 2028, Construction Phase) (Mitigated Scenario)
Figure 3.6	Contour of Predicted 19th Highest Cumulative Daily FSP Concentration (µg/m^3) at 1.5 mAG (Year 2028, Construction Phase) (Mitigated Scenario)
Figure 3.7	Contour of Predicted Cumulative Annual FSP Concentration (µg/m^3) at 1.5 mAG (Year 2028, Construction Phase) (Mitigated Scenario)
Figure 3.8	Contour of Predicted 10th Highest Cumulative Daily RSP Concentration (µg/m^3) at 1.5 mAG (Year 2041, Operation Phase)
Figure 3.9	Contour of Predicted Cumulative Annual RSP Concentration (µg/m^3) at 1.5 mAG (Year 2041, Operation Phase)
Figure 3.10	Contour of Predicted 19th Highest Cumulative Daily FSP Concentration (µg/m^3) at 1.5 mAG (Year 2041, Operation Phase)
Figure 3.11	Contour of Predicted Cumulative Annual FSP Concentration (µg/m^3) at 1.5mAG (Year 2041, Operation Phase)
Figure 3.12	Contour of Predicted 19th Highest Cumulative Hourly NO2 Concentration (µg/m^3) at 35 mAG (Year 2041, Operation Phase)
Figure 3.13	Contour of Predicted Cumulative Annual NO2 Concentration (µg/m^3) at 30 mAG (Year 2041, Operation Phase)
Figure 3.14	Contour of Predicted 4th Highest Cumulative 10-min SO2 Concentration (µg/m^3) at 35 mAG (Operation Phase)
Figure 3.15	Contour of Predicted 4th Highest Cumulative Daily SO2 Concentration (µg/m^3) at 30 mAG (Operation Phase)
Figure 3.16	Contour of Predicted Maximum Cumulative 5-Second Odour Concentration (OU/m^3) at 1.5mAG (Operation Phase)

List of Appendices
Appendix 3.1	Tentative Construction Programme
Appendix 3.2	Calculation of Construction Dust Emission Sources
Appendix 3.3	Determination of Surface Characteristics
Appendix 3.4	Calculation of Emissions from Stacks of YLSEPP
Appendix 3.5	Traffic Data
Appendix 3.6	Calculation of Vehicular Emission Source
Appendix 3.7	Calculation of Odour Emission Rate
Appendix 3.8	Detailed Prediction Results (Construction Phase)
Appendix 3.9	Detailed Prediction Results (Operation Phase)
Appendix 3.10	Frequency and Magnitude of Odour Exceedance for ASRs within Exceedance Zone

3 Air Quality Impact

3.1 Introduction

3.1.1.1 This section presents an assessment of potential air quality impacts arising from construction and operation of the Project, which has been conducted in accordance with the criteria and guidelines as stated in Section 1 of Annex 4 and Annex 12 of the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) as well as the requirements given in Clause 3.4.4 and Appendix B of the EIA Study Brief (No. ESB-313/2019) (hereinafter “the Study Brief”)

3.2 Environmental Legislation, Standards and Criteria

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

3.2.2 Air Quality Objectives & Technical Memorandum on EIA Process

3.2.2.1 The Air Pollution Control Ordinance provides the statutory authority for controlling air pollutants from a variety of sources. The Hong Kong Air Quality Objectives (AQOs), which stipulate the maximum allowable concentrations over specific periods for typical pollutants, should be met. The Government announced on 19 March 2021 the proposal to adopt the proposed new AQOs. The Air Pollution Control (Amendment) Bill 2021 has passed the Legislative Council and endorsed by Chief Executive on 28 April 2021. The Air Pollution Control (Amendment) Ordinance 2021 comes into effect on 1 January 2022. The new AQOs are summarized in Table 3.1.

Table 3.1 New Air Quality Objectives for Hong Kong

Pollutants	Averaging Time	Concentration Limit (µg/m^3)^[1]	Number of Exceedance Allowed per Year
Respirable Suspended Particulates (RSP or PM10)^[^2]	24-hour	100	9
	Annual ^[4]	50	N/A
Fine Suspended Particulates (FSP or PM2.5)^[^3]	24-hour	50	18 ^[5]
	Annual ^[4]	25	N/A
Nitrogen Dioxide (NO2)	1-hour	200	18
	Annual ^[4]	40	N/A
Sulphur Dioxide (SO2)	10-min	500	3
	24-hour	50	3
Carbon Monoxide (CO)	1-hour	30,000	0
	8-hour	10,000	0
Ozone (O3)	8-hour	160	9
Lead (Pb)	Annual^[^4]	0.5	NA

Note:

[1] Measured at 293K and 101.325kPa

[2] Suspended particulates in air with a nominal aerodynamic diameter of 10µm or smaller.

[3] Suspended particulates in air with a nominal aerodynamic diameter of 2.5µm or smaller.

[4] Arithmetic mean

[5] The number of allowable exceedance for Government projects is 18.

3.2.2.2 Apart from AQOs, the limit of hourly Total Suspended Particulates (TSP) concentration should not exceed 500 µg/m³ (measured at 25°C and one atmosphere) for construction dust impact assessment according to Annex 4 of EIAO-TM.

3.2.2.3 In accordance with Annex 4 of EIAO-TM, the limit of 5 odour units based on an averaging time of 5 seconds for odour prediction assessment should not be exceeded at any air sensitive receiver (ASR).

3.2.3 Air Pollution Control (Construction Dust) Regulation

3.2.3.1 Notifiable and regulatory works are under the control of Air Pollution Control (Construction Dust) Regulation. This Project is expected to include notifiable works (foundation and superstructure construction) and regulatory works (dusty material handling and excavation). Contractors and site agents are required to inform Environmental Protection Department (EPD) and adopt dust reduction measures to minimize dust emission, while carrying out construction works, to the acceptable level.

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 effect 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 Quality Standards for Non-AQO Criteria Pollutants

3.2.5.1 Aside from the AQO criteria pollutants mentioned in Section 3.2.2, Volatile Organic Compounds (VOCs), Hydrogen Chloride (HCl), Hydrogen Fluoride (HF) and formaldehyde would also be emitted from the combustion of biogas at the proposed biogas engine and boilers. In accordance with Annex 4 of EIAO-TM, for air pollutants with no established criteria under the Air Pollution Control Ordinance nor in the EIAO-TM, standards or criteria should be adopted by recognized international organizations. The air quality standards for these pollutants are therefore employed by making reference to standards by recognized international organizations and are detailed in Table 3.2.

Table 3.2 Air Quality Standards for Non-AQO Criteria Pollutants

Pollutants	Averaging Time	Air Quality Standard (µg/m^3)	Reference
Methane	1-hour	600,000	TEEL-0 (the threshold concentration below which most people will experience no adverse health effects) from https://edms3.energy.gov/pac/Docs/Revision_26_Table4.pdf
HCl	1-hour	2100	https://oehha.ca.gov/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary
	Annual	20	Integrated Risk Information System, USEPA
HF	1-hour	240	https://oehha.ca.gov/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary
	Annual	14	https://oehha.ca.gov/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary
Formaldehyde	30-minute	100	World Health Organization Air Quality Guidelines for Europe (https://www.euro.who.int/__data/assets/pdf_file/0005/74732/E71922.pdf)
	Annual	9	Office of Environmental Health Hazard Assessment (OEHHA) Toxicity Criteria Database, California, USA (http://www.oehha.ca.gov/tcdb/index.asp).

3.3 Description of Environment

3.3.1.1 The site area of YLSEPP is about 4.6 hectares and located at the southern tip of Yuen Long South (YLS) Development Area (DA). It is bound by Ma Shan (Kung Um Shan) and Tai Lam Country Park at its south west. There will be a planned reedbed and green belt to its north, and planned government and institutional land use to its east side.

3.3.1.2 Currently, the YLS DA is generally rural in character with a mixture of land uses. The predominant uses are brownfield operations including open storage yards, warehouses, industrial workshops, etc. These brownfield operations are intermingled with rural settlements and residential settlements, agricultural land, livestock farms and vacant land.

3.3.1.3 The nearest EPD Air Quality Monitoring Station is located at Yuen Long District Office. The annual average monitoring data recorded at EPD’s Yuen Long Air Quality Monitoring Station has shown a declining trend of pollutants’ concentration in the past five years. The recent five years (2016 – 2020) annual average concentrations of air pollutants relevant to the Project are summarized in Table 3.3.

Table 3.3 Average Concentrations of Pollutants in the Recent Five Years (Year 2016 – 2020) at Yuen Long EPD Air Quality Monitoring Station

Pollutant	Averaging Time	Pollutant Concentration (µg/m^3)
		2020	2019	2018	2017	2016	Mean
Respirable Suspended Particulates (RSP)	10^th Highest 24-hour	77	83	75	87	86	82
	Annual	30	37	37	40	37	36
Fine Suspended Particulates (FSP)	19^th Highest 24-hour	33	38	41	47	48	41
	Annual	16	20	20	22	23	20
Nitrogen Dioxide (NO2)	19^th Highest 1-hour	135	161	150	156	149	150
	Annual	32	44	43	41	46	41
Sulphur Dioxide (SO2)	4^th Highest 10-min	26	42	52	80	58	52
	4^th Highest 24-hour	10	11	16	20	17	15

Remarks:

Bolded value indicates exceedance of the AQO.

3.3.1.4 Apart from the air quality monitoring data, EPD has released a set of background levels from “Pollutants in the Atmosphere and their Transport over Hong Kong” (PATH v2.1) model in July 2021. According to the PATH v2.1 data published by EPD, the concentrations of SO₂, NO₂, RSP and FSP at various averaging times would be lower than the Air Quality Objectives (AQOs) in Year 2025 within the assessment area. The air pollutant concentrations in the Study Area, in reference to the PATH data in Year 2025, are summarized in Table 3.4.

Table 3.4 Background Air Pollutants in Year 2025 Extracted from the PATH v2.1 Model

Pollutant	Averaging Time	Criteria^[1]	Data Summary	PATH v2.1 Grid in Year 2025^[2][5]
				24,43	24,44	25,43	25,44
Fine Suspended Particulates (FSP) ^[3]	24-hr	50 (18)^[6]	Max.	78	78	85	86
			19th Highest ^[6]	39	38	40	42
			No. of Exceedance(s)	10	10	11	11
	Annual	25	-	16	16	16	17
Respirable Suspended Particulates (RSP)^[4]	24-hr	100 (9)	Max.	95	94	102	103
			10th Highest	69	69	71	71
			No. of Exceedance(s)	0	0	1	1
	Annual	50	-	28	27	28	29
Sulphur Dioxide (SO2)	10-min	500 (3)	Max.	57	56	55	54
			4th Highest	57	56	55	54
			No. of Exceedance(s)	0	0	0	0
	24-hr	50 (3)	Max.	17	17	18	18
			4th Highest	11	12	11	11
			No. of Exceedance(s)	0	0	0	0
Nitrogen Dioxide (NO2)	1-hr	200 (18)	Max	134	134	145	148
			19th Highest	99	96	100	101
			No. of Exceedance(s)	0	0	0	0
	Annual	40	-	20	19	19	20

Note:

[1] Values in ( ) mean the number of exceedances allowed per year.

[2] Bolded values mean exceedance of the AQOs.

[3] Annual FSP concentration is adjusted by adding 3.5 µg/m³ with reference to Guidelines on Choice of Models and Model Parameters.

[4] 10^th highest daily and annual RSP concentration is adjusted by adding 11 µg/m³ and 10.3 µg/m³ respectively with reference to Guidelines on Choice of Models and Model Parameters.

[5] All concentration units are in microgram per cubic metre (µg/m³).

[6] The number of allowable exceedance for Government projects is 18.

3.4 Identification of Air Sensitive Receivers

3.4.1.1 In accordance with Annex 12 of the EIAO-TM, any domestic premises, hotel, hostel, hospital, clinic, nursery, temporary housing accommodation, school, educational institution, office, factory, shop, shopping centre, place of public worship, library, court of law, sports stadium or performing arts centre are considered as ASRs.

3.4.1.2 In accordance with Clause 3.4.4.2 of the EIA Study Brief, the assessment area for air quality impact assessment should be defined by a distance of 500m from the boundary of the Project Area and the works of the Project. Illustration of the proposed assessment area is presented in Figure 3.1. For identification of the representative ASRs within the assessment area that would likely be affected by the potential impacts from the construction and operation of the YLSEPP, a review has been conducted based on relevant available information including topographic maps, Outline Zoning Plans (OZPs) (such as OZP Plan No. S/YL-TT/18 – Tai Tong and Plan No. S/YL-TYST/14 – Tong Yan San Tsuen, Revised Recommended Outline Development Plan (RODP) for Yuen Long South Development and other published plans in the vicinity of the Project site. The representative ASRs within the assessment area are identified and given in Table 3.5 below. Their locations are illustrated in Figure 3.1.

Table 3.5 Representative Air Sensitive Receivers in the vicinity of YLSEPP

ASR IDs	Description	Land Use	Shortest Distance from Site Boundary (m)	Assessment Heights (mAG)	Assessment Phase ^[1]
YAE01	117, Wong Nai Tun Tsuen	Residential	395	1.5, 5	C, O
YAE02	125, Wong Nai Tun Tsuen	Residential	255	1.5, 5, 10	C, O
YAE03	121, Wong Nai Tun Tsuen	Residential	250	1.5, 5, 10	C, O
YAE04	128, Wong Nai Tun Tsuen	Residential	270	1.5, 5, 10	C, O
YAE05	67A, Wong Nai Tun Tsuen	Residential	460	1.5, 5, 10	C, O
YAE06	Pui Hong Kui	Community	120	1.5, 5	C (till 2029) ^[2]
YAE07	291, Pak Sha Tsuen	Residential	55	1.5, 5, 10	C (till 2029)^[2]
YAP01	Planned Residential (PDA Zone 3)	Residential	300	1.5, 5, 10, up to 50 at 5m interval	O
YAP02	Planned Residential (PDA Zone 2)	Residential	295	1.5, 5, 10 up to 70 at 5m interval	O
YAP03	Planned Residential (PDA Zone 2)	Residential	290	1.5, 5, 10 up to 75 at 5m interval	O
YAP04	Planned Residential (PDA Zone 2)	Residential	290	1.5, 5, 10 up to 75 at 5m interval	O
YAP05	Planned Residential Zone 2 (with Commercial)	Residential	435	1.5, 5, 10 up to 90 at 5m interval	O
YAP06	Planned Housing (OUMU)	Residential	440	1.5, 5, 10 up to 65 at 5m interval	O
YAP07	Planned School (PDA Zone 2)	Education	345	1.5, 5, 10 up to 40 at 5m interval	O
YAP08	Planned School (PDA Zone 2)	Education	280	1.5, 5, 10 up to 40 at 5m interval	O
YAP09	Planned Residential (PDA Zone 3)	Residential	390	1.5, 5, 10 up to 45 at 5m interval	O
YAP10	Planned Primary School	Education	210	1.5, 5, 10 up to 40 at 5m interval	O
YAP11	Planned Low-rise Residential Developments	Residential	205	1.5, 5, 10, 15, 20	O

Note:

[1] C = Construction Phase; O = Operation Phase.

[2] ASR would be demolished no later than 2029 under YLSDA Stage 3 in accordance with its latest programme.

3.5 Identification of Environmental Impacts

3.5.1 Construction Phase

3.5.1.1 Prior to construction of the YLSEPP, the site formation works of the site would have been completed by CEDD under Agreement No. CE 35/2012 (CE) “Planning and Engineering Study for Housing Sites in Yuen Long South – Investigation”. The potential impact from the site formation works has been addressed in Housing Sites in Yuen Long South EIA Report (Register No.: AEIAR-215/2017) (hereinafter the YLS DA EIA). The construction works of the YLSEPP to be carried out under this Project would only involve excavation works for substructure (substructures defined as the underground structures), pilling works, road paving works, construction for substructures and superstructures works. Based on the tentative construction programme as shown in Appendix 3.1, the construction activities for the YLSEPP would be commenced in 2028 and be completed by 2032. The layout of the YLSEPP is presented in Figure 2.1.

3.5.1.2 According to the latest information, total 4.6 hectares of land would be reserved for construction of YLSEPP. The proposed YLSEPP would not only provide tertiary sewage treatment and sludge treatment but also food waste co-digestion, With the limited space, some of the facilities are required to be placed underground to cater the land constraints. Such provision would incur excavation works for underground facilities during construction of YLSEPP. In addition, reinforced concrete work for substructure is required.

3.5.1.3 Potential construction dust impact would arise from construction activity for the Project. These construction activities include excavation works for substructure, pilling works, road paving, construction for substructures and superstructures. Among which, the excavation works for substructures would cause significant fugitive dust emissions owing to earth movement activities and handling/transportation of excavation/fill materials. Piling works would be conducted using bored piling method under latest design, the piling area would be wet. Due to the wet construction environment during bored piling operation, negligible fugitive dust emission is anticipated. As the site formation has been completed by CEDD prior to the construction of the Project and the road works (internal access only ) included in the Project would involve paving works only, very limited fugitive dust emission would be anticipated from the road paving works with implementation of dust suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation and good site practices. Construction for substructure and superstructure would be reinforced concrete works (which involving steel works and concreting works) for the structures, therefore very limited dust would be generated from construction for substructure and superstructure.

3.5.1.4 The latest construction programme and preliminary site layout of YLSEPP are shown in Appendix 3.1.

3.5.1.5 Fuel combustion from the use of PME during construction works could be a source of NO₂, SO₂ and CO. To improve air quality and protect public health, EPD has introduced the Air Pollution Control (Non-road Mobile Machinery) (Emission) Regulation, which came in operation on 1 June 2015, to regulate emissions from machines and non-road vehicles. Starting from 1 December 2015, only approved or exempted non-road mobile machinery are allowed to be used in construction sites. Hence, with the implementation of the said Regulation, the emissions from PMEs are considered relatively small and will not cause adverse air quality impact to the surrounding ASRs.

Identification of Construction Dust Assessment Year

3.5.1.6 With reference to Appendix 3.1 and above Section 3.5.1.2, the only construction activity of the Project with significant construction dust emission is excavation, which involves the largest amount of earth movement and material handling. All excavation works would be commenced, conducted and completed in 2028 at works area A, B, C and D (3.8ha out of 4.6ha Project site area). While bored piling works, road paving works, reinforced concrete substructure and superstructure works, with very limited dust emission, would be conducted during 2029 to 2031. Testing and commissioning works would be carried out in 2032. In view of the earth movement, material handling nature for excavation, and larger works area of excavation all undertaken in 2028, as comparing with the limited dust emissions from construction activities from 2029 to 2031 and no dust emissions from commissioning test in 2032, the construction dust emission due to the Project in 2028 would be considered representing the worst-case scenario of the whole construction period of the Project. Hence, 2028 was selected as the assessment year for quantitative construction dust assessment in this EIA Study.

Consideration of Cumulative Impact from Concurrent Projects

3.5.1.7 Based on the current construction programme, the Project would likely interact with some other projects, which may have cumulative environmental impacts. With confirmation from CEDD, the updated construction programme of YLS DA is not yet available at the time of this assessment, thus the construction programme stated in the YLS DA Schedule 3 EIA (Register No.: AEIAR-215/2017) is still valid for this assessment.

3.5.1.8 Table 3.6 summarise the concurrent projects located within 500m from the Project boundary that would contribute to the cumulative environmental impacts during construction phase of Year 2028 - 2032.

Table 3.6 Potential Concurrent Projects

Potential Concurrent Projects	Tentative Construction Commencement Year	Tentative Commissioning Year
Water Reclamation Facilities	Under YLS DA Stage 2 Works. The construction programme is yet to be confirmed
YLS DA Stage 2	2022	2033 (Full population intake)
YLS DA Stage 3 works	2031	2038 (Target intake year)

Remarks:

- YLS DA Stage 1 and Stage 2 works are located more than 1km from the YLSEPP, respectively. No construction phase cumulative impact would be anticipated.

- With reference to Appendices 4.1, 5.4 and 5.12 of YLS DA EIA, land clearance and resumption would be conducted in Year 2022 – Jun 2023 for YLS DA Stage 2 works, while dusty construction activities, such as site formation works for YLS DA Stages 2 will not begin until Jul 2023.

- With reference to Appendices 4.1, 5.4 and 5.12 of YLS DA EIA, land clearance and resumption would be conducted in Year 2031 – Jun 2033 for YLS DA Stage 3 works, while dusty construction activities, such as site formation works for YLS DA Stages 3 will not begin until Jul 2033.

3.5.1.9 According to the approved YLS DA EIA Study, which is the best available information for YLS DA project, YLS DA Stage 2 works, which will tentatively be commenced in Year 2022 and completed for population intake in Year 2033; whilst YLS DA Stage 3 works will tentatively be commenced in 2031 and the intake year will be targeted in 2038. According to YLS DA EIA, only land resumption and decontamination works would be conducted during Year 2022 to June 2023 for Stage 2 works and during Year 2031 to June 2033 for Stage 3 works. Dusty construction activities, such as site formation works for YLS DA Stage 3 will not begin until July 2033. Hence, no cumulative construction phase air quality impact would be anticipated from YLS DA Stage 3 works during construction of the YLSEPP. Comparing the latest best available information under the YLSEPP EIA Study (this Study) against YLS Sewage Treatment Works (YLS STW) in YLS DA EIA Report, the latest footprint and construction area is expanded.

3.5.1.10 The potential cumulative construction dust impact arising from the entire YLS DA, including the construction of YLSEPP and Water Reclamation Facilities were identified and assessed in the YLS DA EIA Report for YLS DA. According to Table 4.7 of the approved YLS DA EIA Report, the highest dust emission year would be Year 2028, with 632 tonne dust emission per year, while during Year 2029 and 2030, the dust emission per year would be respectively reduced to 448 and 71 tonne per year. During Year 2031 and 2032, there will be superstructures works, road paving works or landscaping works only in these years, significant dust emission due to YLS DA construction would not be anticipated. Therefore, Year 2028 would also be the worst-case year for assessment of YLS DA. During Year 2028, which is the worst-case year for YLSEPP and YLS DA, no site formation works of YLS DA would be conducted within 500m assessment area of this Project, while road works on existing Kung Um Road would be expected. Heavy construction at the existing Kung Um Road would be assumed for worst-case assumption in this Study. While the construction programme of Water Reclamation Facilities is yet to be confirmed at the time of assessment, heavy construction works would also be assumed at the planned Water Reclamation Facilities for worst-case assumption in the cumulative impact assessment.

3.5.1.11 As mentioned in Section 3.5.1.6, after Year 2028, only very limited construction dust emission would be anticipated from the construction of the Project during Year 2029 - 2031 and no dusty construction work would be conducted in Year 2032, very limited dust impact from the Project contribution to the cumulative construction dust impact would be anticipated during the period of Year 2029 -2032.

3.5.1.12 Referring to YLS DA EIA Report, some construction activities of YLS DA would be undertaken within 500m assessment area of this Project during Year 2029 – 2030. These construction dust impacts due to YLS DA construction works during Year 2029 – 2030 have been addressed in YLS DA EIA. Year 2029 was selected as assessment year in YLS DA EIA to represent the worst-case year during this period. YLS DA EIA identified 3 representative ASRs, A33, A34 and A35 (equivalent to YAE05, YAE04 and YAE01 in this EIA Study) located within YLSEPP 500m assessment boundary. With reference to Appendix 4.7 of the YLS DA EIA, the predicted construction dust concentration in Year 2029 at YAE01, YAE04 and YAE05 are listed in below Table 3.7, Table 3.8 and Table 3.9. In accordance with Table 3.7, the maximum 1-hour average TSP concentration were predicted in the range of 226 – 228 µg/m³, complying the EIAO-TM criterion of 500 µg/m³, with over 54% margin. The 10^th highest 24-hour average RSP concentration were predicted in the range of 83 – 86 µg/m³, complying the AQO of 100 µg/m³ with a 14% margin. The annual average RSP concentration were predicted to be 36 – 37 µg/m³, would comply with the AQO of 50 µg/m³ with a 26% margin. Given large margins to the corresponding criteria, and very limited dust impact arising from the construction works for YLSEPP, no adverse cumulative TSP and RSP impact were anticipated in Year 2029 and 2030. Table 3.8 and Table 3.9 present the 10^th highest 24-hourly average FSP and annual average FSP concentrations extracted from YLS DA EIA, which would exceed the current AQO. However, the predicted concentrations were based on the background FSP concentration from the previous PATH model (PATH-2016). Excluding the background FSP concentration from the PATH-2016, the YLS DA contribution to the overall FSP concentration would be less than 1 µg/m³. The background 19^th highest 24-hour average and annual average FSP concentrations extracted from the latest PATH v2.1 are presented in Table 3.8 and Table 3.9. Taking into account the latest daily and annual FSP background concentrations at YAE01, YAE04 and YAE05 from PATH v.2.1, predicted daily and annual FSP concentrations from YLS DA would respectively be 39 – 43 µg/m³ and 17 - 18 µg/m³, comply with the 19^th highest 24-hourly average FSP and annual average FSP criteria with a respectively margin of 14% and 25%, during Year 2029 and 2030. Given large margins to the corresponding criteria, and very limited dust impact arising from the construction works for YLSEPP, no adverse cumulative FSP impact would be anticipated in Year 2029 and 2030.

Table 3.7 Predicted Construction Phase TSP and RSP Concentrations at ASRs within 500m Assessment Boundary of YLSEPP in Year 2029 extracted from YLS DA EIA Report

ASR	Predicted Concentration, µg/m^3
	Max. 1-hour Average TSP	10^th Highest 24-hour Average RSP	Annual Average RSP
YAE01 (A35 in YLS DA EIA)	228	86	37
YAE04 (A34 in YLS DA EIA)	226	86	36
YAE05 (A33 in YLS DA EIA)	228	83 – 84	36

Table 3.8 Predicted Construction Phase 24-hour Average FSP Concentrations at ASRs within 500m Assessment Boundary of YLSEPP in 2029 extracted from YLS DA EIA Report

ASR	PATH Grid	24-hour Average Concentration, µg/m^3
		Predicted 10^th Highest	Previous PATH-2016 10^th Highest Background	YLS DA Contribution	Latest PATH v2.1 19^th Highest Background for Year 2025	Estimated 19^th Highest based on Latest PATH v2.1 for Year 2025^[1]
YAE01 (A35 in YLS DA EIA)	24,43	65	65	<1	39	40
YAE04 (A34 in YLS DA EIA)	24,44	64	64	<1	38	39
YAE05 (A33 in YLS DA EIA)	25,44	62	62	<1	42	43

Remarks:
[1] YLS DA contribution assumed as 1 µg/m³ as worst-case assumption.

Table 3.9 Predicted Construction Phase Annual Average FSP Concentrations at ASRs within 500m Assessment Boundary of YLSEPP in 2029 extracted from YLS DA EIA Report

ASR	PATH Grid	Annual Average Concentration, µg/m^3
		Predicted	Previous PATH-2016 Background	YLS DA Contribution	Latest PATH v2.1 Background for Year 2025	Estimated Concentration based on Latest PATH v2.1 for Year 2025 ^[1]
YAE01 (A35 in YLS DA EIA)	24,43	26	26	<1	16	17
YAE04 (A34 in YLS DA EIA)	24,44	26	25	<1	16	17
YAE05 (A33 in YLS DA EIA)	25,44	25	25	<1	17	18

Remarks:
[1] YLS DA contribution assumed as 1 µg/m³ as worst-case assumption.

3.5.1.13 During Year 2031 and 2032, YLS DA EIA indicated that only superstructure works, road paving works and landscaping works would be conducted in the whole YLS DA, significant dust emission and adverse construction dust impact are not anticipated. For YLSEPP, only very limited dust impact from construction works in Year 2031 and no dusty activities in Year 2032, therefore no adverse cumulative dust impact would be anticipated in Year 2031 and 2032.

3.5.1.14 Should there be any change to the YLS DA construction programme, a separate environmental review would be conducted under YLS DA project to address the associated environmental impact. The dust levels would be monitored regularly during the construction period and managed under an EM&A programme as specified in the EM&A Manual.

Vehicular Emission

3.5.1.15 Within 500m assessment boundary, the only existing open road emission source would be the existing Kung Um Road, which would be under YLS DA road works construction during Year 2028. Hence, no vehicular emission source is identified within the 500m assessment boundary.

3.5.1.16 The number of construction vehicles to/from the Project site would be anticipated to be 10 veh/hr during construction hours, which is considered limited. It is anticipated that the associated tailpipe emission would also be limited. No significant air quality impact from the construction vehicle emission would be anticipated.

3.5.2 Operation Phase (Air Pollutant Emission Impact)

Flue Gas Emission

3.5.2.1 During the operation of YLSEPP, biogas is expected to be generated as a by-product from the anaerobic digestion process in the co-digestion of sludge and food wastes. Biogas generated will be stored in the biogas holders. The stored biogas will go through the sulphur absorption vessels to remove the hydrogen sulphide (H₂S) before passing either to the combined heat and power (CHP) units or steam boilers. Biogas will be combusted in the CHP generator to produce electricity and combusted at the steam boilers for heating demands in the sludge treatment process use. There will be 2 duty plus 1 standby CHP units to ensure process continuity. In view of the high operation reliability of CHPs, residue biogas for flaring would only be carried out during emergency. The flue gas will be discharged to the atmosphere at the exhaust stacks at a design temperature of 180 °C. Since continuous heating is required in the anaerobic co-digestion process for the biomass feeding to the digesters and heat loss compensation from the digesters, steam will be produced by the boiler to supply heat for the digestion process. Sludge dryers will be utilized to achieve the required dry solids content in the digested sludge for disposal. Steam from the steam boiler will also be utilized to provide the needed thermal energy for the dryer to achieve the required dryness. The exhaust gas from CHP will be emitted to the atmosphere through two stacks and exhaust gas from the steam boiler will emit exhaust gas via a separate stack. The locations and emission parameters of the stacks for the operation of YLSEPP is shown in Appendix 3.4.

Identification of Key Air Pollutants of Flue Gas Emission

3.5.2.2 As identified in Section 2.4.3, NO₂ and SO₂ would be the major pollutants of emissions from biogas combustion at CHPs and boiler. The proposed YLSEPP would employ biogas IC engine as CHP units. The biogas IC engine would utilize biogas from anaerobic digesters. Similar CHP units have been used in Organic Waste Treatment Facilities (OWTF). Similar air pollutants would be expected from CHP units in the proposed YLSEPP and from that in the OWTF. While the boiler would combust biogas as in the CHP units, similar air pollutants would be expected. With reference to the EIA study for OWTF Phase I (AEIAR-149/2010) and the associated VEP (i.e. Application No. VEP-488/2015), particulates, methane (CH₄), hydrogen chloride (HCl) and hydrogen fluoride (HF) were considered as emitted pollutants from the CHPs.

3.5.2.3 Referring to the findings of the literature review^[[1]^], nitrogen oxides (NO_X), sulphur dioxide (SO₂), carbon monoxide (CO), and non-methane volatile organic compounds (VOCs), such as formaldehyde (CH₂O) may emit from combustion of biogas.

3.5.2.4 NO_X is a major pollutant from fuel combustion, such as biogas combustion in the CHP and boiler. In the presence of O₃ and VOC, NO_X would be converted to NO₂. Hence, NO₂ is one of the key pollutants for the operational air quality assessment of the Project. Thus, operation phase assessment on cumulative NO₂ impact would be conducted. 1-hour and annual average NO₂ concentrations at each identified ASRs would be assessed and compared with the relevant AQOs to determine the compliance.

3.5.2.5 SO₂ emissions from biogas combustion mainly depend on desulphurization degree of biogas. As presented in Section 2.4, H₂S removal unit will be installed to remove sulphur content in the biogas as far as practicable prior to combustion at CHPs and boiler. SO₂ concentrations at each identified ASRs would be quantitatively assessed and compared with the relevant AQOs to determine the compliance.

3.5.2.6 Respirable Suspended Particulates (RSP) refers to suspended particulates with a nominal aerodynamic diameter of 10µm or less. Biogas combustion would induce RSP emission. Cumulative RSP concentrations from the Project and vehicular emission at each identified ASRs would be quantitatively assessed and compared with the relevant AQOs to determine the compliance.

3.5.2.7 Fine Suspended Particulates (FSP) refers to suspended particulates with a nominal aerodynamic diameter of 2.5µm or less. Biogas combustion would induce FSP emission. Cumulative FSP concentrations from the Project and vehicular emission at each identified ASRs would be quantitatively assessed and compared with the relevant AQOs to determine the compliance.

3.5.2.8 CO is produced in all oxidation process of carbon containing materials and is an important by-product of incomplete combustion of biogas. Control and monitoring system will be installed at CHP to maintain optimal air to fuel ratio and monitor the performance of the CHPs and boiler in order to minimize incomplete combustion during operation. Such that CO emission could be minimised. With reference to the “Air Quality in Hong Kong 2020”, the highest 1-hour average (2,850 µg/m3) and the highest 8-hour average (1,685 µg/m3) CO concentrations were recorded. These values were around one tenth and one fifth of the respective AQO limits. In view that there is still a large margin to the AQOs, CO would not be a critical air pollutant of concern. Quantitative CO assessment of the concentrations at representative ASRs would be carried out in this study.

3.5.2.9 Biogas is rich in volatile organic compounds (VOCs). Generally, biogas combustion would reduce 99% VOC, with reference to the literature review^[1]. While methane would easily be oxidized to carbon dioxide and water during combustion, non-methane VOC (NMVOC) would generally consider for environmental assessment. Literature^[1] indicated VOC emission from biogas combustion plant would contribute minimal amount of total VOCs in the area. CH₂O is a by-product during incomplete combustion of biogas. CH₂O emission were found in some biogas engines, which could contribute up to 2% of CH₂O concentration in the environment. Control and monitoring system will be installed at CHPs and boiler to maintain optimal air to fuel ratio and monitor the performance of the CHPs and boiler in order to minimize incomplete combustion during operation. VOCs in terms of methane and CH₂O (representing NMVOCs) are quantitatively assessed in this study.

3.5.2.10 For incoming food wastes, pre-treatment to avoid food packaging films and plastics in the organic wastes shall be performed before transferring to YLSEPP for digestion. Therefore, it is expected that the food waste are unlikely to contain chlorinated materials and the emission of HF and HCl from the process is expected to be minimal. In view of presence of common salt (sodium chloride) in food waste and bleach (Sodium hypochlorite) in sewage as inorganic chlorine containing material, quantitative assessments of the concentrations at representative ASRs would be carried out for HF and HCl in this study.

Vehicular Emission

3.5.2.11 Vehicular emission is another source of air pollutants (NO_X, RSP and FSP) within 500m study area from the Project boundary. The open road emission sources associated with operation phase of the Project include the improved Kung Um Road and proposed roads under YLS DA, which are presented in Appendix 3.5. Cumulative pollutant concentrations from flue gas emission and vehicular emission would be considered in this study.

Other Emission

3.5.2.12 No diesel-powered equipment would be operated on-site. No existing or planned PTI or bus terminus or bus depots is identified within 500m assessment area. No air quality impact due to these concerned facilities is anticipated. A site survey was conducted on 9^th December 2021. No industrial chimney was identified within the 500m assessment area. Also, there is no major stack source within 4 km from the project boundary. No direct impact from any other major sources on the study area is anticipated.

3.5.3 Operation Phase (Odour Impact)

Odour Emission from Proposed Sewage Treatment works and Co-digestion Facilities

3.5.3.1 The potential odour impact on the neighbour ASRs would be the major environmental concerns for the operation of YLSEPP. Odour emission would be anticipated from inlet works (screen, inlet pump, conveyor, compactor, grit classifier, equalization tank, and skip), sewage treatment units (sedimentation tanks, and biological treatment unit), sludge treatment units (sludge blend tank, centrifuge, sludge holding tank, dryer, sidestream treatment facilities and skip) and organic waste reception facilities (food waste bunder, and preparation tank). These facilities will be designed to be covered and the exhausted air will be conveyed to deodourizers (DOs) for treatment before releasing to the environment. The potential odour emission sources during the operation phase of YLSEPP would therefore be the exhaust of the DOs. Five DOs (DO1, DO2, DO3, DO4 and DO5) will be equipped for all treatment units with odour emission.

3.5.3.2 The odour impact from sludge transfer tanks, if any, could be controlled by proper design and good cleaning practices of sludge transfer tanks. The potential odour source during the transportation would be the gap between the tank opening and its cover. Sludge tanks which its air-tightness has been proved by DSD should be deployed for transporting sludge. With thorough cleaning practice and regular condition test of the sludge tanks, odour emission and leachate leakage during storage and transportation are not anticipated.

3.5.3.3 The organic waste reception facility at YLSEPP would receive organic waste for co-digestion with sludge generated from sewage treatment. The incoming organic waste will be transported by fully enclosed pipes or trucks to avoid odour nuisance. The organic waste reception area in the co-digestion facility for imported organic wastes would be another odour source within the Project Site. The organic waste reception area will be enclosed and the odorous air in this facility will be vented to DO (DO5) for odour treatment prior to discharge to the environment.

3.5.3.4 To remove aqueous ammonia during the sidestream treatment, Anammox technology has been selected. With reference to Section 2, the Anammox technology would convert aqueous ammonia to nitrogen gas, which is non-odourous, to reduce potential odourous ammonia emission. During the process, insignificant emission of ammonia and nitrous oxide (N₂O) from the sidestream treatment facilities would be conveyed to DO for treatment prior to discharge to the atmosphere.

3.5.3.5 Odourous air from inlet works and sedimentation tank will be conveyed to DO1. Odourous air from sludge treatment units, including the sidestream treatment facilities, will be conveyed to DO2. Odourous air from biological treatment unit will be conveyed to DO3 and DO4. Odourous air from organic waste reception facilities will be conveyed to DO5. All DO1 -DO5 are two-stage deodourizers. The detailed deodourization technology has been presented in Section 2.

3.5.3.6 As described in Section 2, this project will treat the collected sewage to a tertiary treatment level. The high effluent standard is suitable for further production of reclaimed water. Most tertiary treated effluent will be reused. Any surplus tertiary effluent will be discharge to Yuen Long Nullah for river vitalization. In addition, the water reclamation facility is proposed under CEDD's D&C consultancy for YLS DA Stage 2 Phase 2 Works, all the treated effluent would be discharged to Yuen Long Nullah in the interim. With the tertiary treatment from YLSEPP, the treated effluent will bring a flow to Yuen Long Nullah and prevent the Nullah from being stagnant. Such flow will bring beneficial effect to the Yuen Long Nullah.

Cumulative Odour Sources from Existing Livestock Farms

3.5.3.7 With reference to the approved YLS DA EIA Report, six existing livestock farms (3 chicken farms and 3 pig farms) are located within the YLS DA. Two chicken farms and all three pig farms will be removed under the YLS DA development no later than Year 2031, i.e. before operation of the Project. One chicken farm (Farm Code: 18/16/F203) will be retained and is located within 500m assessment area from the proposed YLSEPP. Cumulative odour impact from the retained chicken farm would be anticipated and has been addressed in the YLS DA EIA.

3.6 Assessment Methodology

3.6.1 Construction Phase

3.6.1.1 Construction activities with significant particulates emission were identified from the construction method according to engineering design. Construction dust impact was predicted based on emission factors from United States Environmental Protection Agency (USEPA) Compilation of Air Pollution Emission Factors (AP-42), 5th edition and activity information from the engineer design.  The major construction activities of concern include excavation, and construction vehicle movement were considered in the assessment as heavy construction activities during working hours. Wind erosion of open construction work site was considered during non-working hours.  The construction vehicle movement is limited within the construction site of YLSEPP and Kung Um Road. The relevant emission factors identified from AP-42 are summarized in Table 3.10. Detailed calculation of dust emission sources is presented in Appendix 3.2.

Table 3.10 Emission Factor for Dusty Construction Activities

Emission Source	Activity	Emission Factor	Remarks
Excavation, construction vehicle movement	Heavy Construction Activities	E(TSP) = 2.69 Mg/hectare/month of activity	Ref. from AP-42, Section 13.2.3, 1/95 ed.
	Wind Erosion	E(TSP) = 0.85 Mg/hectare/year	Ref. from AP-42, Section 11.9, 11/06 ed.

3.6.1.2 Construction dust emission factors in USEPA AP-42 are expressed in terms of TSP.  Fractions of finer particulates were estimated from the TSP emission factor with the size distribution of the concerned process, in order to compare against the AQOs.  Construction activity generally involves aggregate handling, therefore the particle size distribution of aggregate handling, which is available in AP-42 by USEPA, was adopted for heavy construction activities.  Particle size distribution of construction dust is listed in Table 3.11.

Table 3.11 Particle Size Distribution for Construction Dust

Process	Cumulative % of TSP
	RSP	FSP	Reference
Aggregate Handling (equivalent to Heavy Construction Activities)	47.3%	7.2%	Page 13.2.4-4, Section 13.2.4, AP-42, USEPA (Version 11/06)

3.6.1.3 As discussed in Section 3.5.1, based on the tentative construction programme, the major construction activities including excavation works in Workfront A, B, C and D which would happen simultaneously within 2028, causing significant dust emission in that year. Between Year 2029 to 2031, bored piling, road paving works, reinforced concrete substructure and superstructure works will be carried out, which is less dusty than excavation works. Only testing and commissioning works would be conducted in Year 2032. Thus, Year 2028 is selected as the assessment year of the construction phase.

3.6.1.4 All construction works areas were assumed to be active for the assessment purpose. 12 hours (07:00-19:00) a day, 7 days a week was assumed as the construction period in the modelling assessment.  Wind erosion is assumed for the other non-working hours (19:00 to 07:00 of the following day).

3.6.1.5 With reference to Section 3.5.1.16, no significant vehicular emission from the 10 veh/hr construction trucks would be anticipated. Therefore, no vehicular emission modelling is considered necessary.

Concurrent Project

3.6.1.6 As discussed in Section 3.5.1, in Year 2028, the whole construction site of the proposed water reclamation facilities, was assumed to be active for the assessment purpose. 12 hours (07:00-19:00) a day, 7 days a week was assumed as the construction period in the modelling assessment.  Wind erosion is assumed for the other non-working hours (19:00 to 07:00 of the following day).

3.6.1.7 As stated in Table 3.6, YLS DA Stage 2 works will tentatively be commenced in Year 2022 and completed for population intake in Year 2033. During the worst assessment scenario Year 2028, YLS DA Stage 2 Works that will be located within the 500m assessment area of this Project were assessed. In Year 2028, those work areas will be undergoing heavy construction are included in the quantitative assessment. In view of the insignificant construction dust emission from the Project during Year 2029 – 2031 and no dusty construction work would be conducted in Year 2032, as mentioned in Section 3.5.1.11, significant cumulative construction dust impact from YLSEPP and YLS DA are not anticipated. The assessment scenario of Year 2028 is considered the worst-case during Year 2028 – 2032, i.e. the whole construction period of YLSEPP. The emission inventory of the works were directly adopted from the YLS DA EIA Report and presented in Appendix 3.2.

Dispersion Modelling & Modelling Approach

3.6.1.8 According to Guidelines on Assessing the ‘TOTAL’ Air Quality Impacts by EPD, an integrated modelling system PATH v2.1 which is developed and maintained by EPD was applied to provide background pollutant concentrations in assessing the total impact in the study area. In addition, Weather Research and Forecast (WRF) meteorological data were adopted for modelling.

3.6.1.9 American Meteorological Society (AMS) and USEPA Regulatory Model (AERMOD), the EPD approved air dispersion model, was applied to predict the air quality impacts from the operation of the YLSEPP at the representative ASRs.

3.6.1.10 Hourly meteorological conditions including wind data, temperature, relative humidity, pressure cloud cover and mixing height of Year 2015 were extracted from the WRF meteorological data adopted in the PATH v2.1 system. The minimum wind speed was capped at 1 metre per second. The mixing height was capped between 131 metres and 1941 metres according to the observation in Year 2015 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. In order to avoid any missing hours misidentified by AERMOD and its associated components, the WRF met data was handled manually to set wind direction between 0° – 0.1° to be 360°. The meteorological data was inputted as on-site data into AERMET.

3.6.1.11 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 land use are then suggested by AERMET by default according to its land use characteristics. The detailed assumptions are discussed in Appendix 3.3. Flat terrain in AERMOD is adopted for this assessment.

3.6.1.12 Considering the locations of the YLSEPP located within the YLS DA, which would be built into an urban area. Urban heat island effect in AERMOD has been adopted with the assumed population of 101,200, with reference to the RODP in the Revised Draft Supplementary Report for Ultimate Development Option of Yuen Long South Revised RODP under Planning and Engineering Study for Housing Sites in Yuen Long South.

3.6.1.13 Hourly average of TSP, Daily and annual averages of RSP and FSP concentrations were predicted at each identified ASRs at respective assessment heights. As particulates are concerned, dry deposition was applied in the model run. Particle size distribution is assigned for particles with aerodynamic diameters smaller than 10 µm to each type of source in the AERMOD in order to account for the particle deposition. The particle size distributions for construction dust are summarized in Table 3.11.

3.6.2 Operation Phase (Air Pollutant Emissions Impact)

Flue Gas Emission

3.6.2.1 During operation phase, flue gas emission from the Project would be anticipated from the combustion of biogas for operation of the CHPs and boiler. The locations of the CHPs and boilers are presented in Appendix 3.4.

3.6.2.2 Biogas is produced as a by-product from the co-digestion process. Biogas will be stored in the gas holders and then be utilized by two CHP units to produce heat and electricity. The exhaust gas from CHPs will be vented to the atmosphere through 2 stacks (CHP1 and CHP2). As a worst-case scenario in the assessment, the emission rates of the pollutants from the stacks were estimated based on the maximum design sewage treatment capacity of 65,000 m³ / day.

3.6.2.3 The maximum consumption rate of the boiler installed in YLSEPP would be 215 m³/hr (provided by engineer). The flue gas from boiler will be vent to a stack, BO.

3.6.2.4 In the assessment, the pollutant level at the exhausts of the CHPs and the boiler are provided by Engineer and presented in Appendix 3.4. It is assumed that 10% of the NO_X emissions are NO₂ at the chimney exhaust, with reference to EPD’s Guidelines on Choice of Models and Model Parameters and 10% initial NO₂/NO_X ratio in the Heathrow Airport EIA report. Ozone Limiting Method (OLM) was applied for the rest of NO_X. The OLM method is detailed below at Section 3.6.2.16. The emission levels of other pollutants such as RSP and SO₂ are referenced from the design parameters in the approved EIA for Organic Waste Treatment Facilities Phase I (AEIAR-149/2010) and the associated VEP (i.e. Application No. VEP-488/2015). As a conservative assumption, 100% RSP are assumed as FSP for this operation phase assessment. Daily and annual averages of RSP, daily and annual averages of FSP, hourly and annual averages of NO₂, 10-minute and daily averages of SO₂, hourly and 8-hourly averages of CO, hourly and annual averages of HCl, hourly average of methane, hourly and annual averages HF, 30-minute and annual averages formaldehyde concentrations were predicted at each identified ASRs at respective assessment heights. The emission parameters from the CHPs and the boiler are summarized in Appendix 3.4.

Dispersion Modelling & Modelling Approach

3.6.2.5 The methodology stated in Sections 3.6.1.8 - 3.6.1.12 have also been applied to flue gas modelling.

3.6.2.6 It was assumed that the flue gas emissions of YLSEPP from its CHPs and boiler operate continuously on a 24-hour-per-day basis with steady state ventilation rate and exhaust gas velocity in the assessment. Flue gas emission was modelled as point source in the assessment.

3.6.2.7 The 1-hour to 30-minute conversion factors for formaldehyde were calculated via a power law relationship with reference to Duffee et al., 1991[2]. Such that the 1-hour average concentrations predicted by the AERMOD model would be converted to 30-minute average concentrations. The conversion factors for different Pasquill stability classes are listed in Table 3.12 below.

C_l = C_s(t_s/t_l)^p

where

C_l = concentration for the longer time-averaging period;

C_s = concentration for the shorter time-averaging period;

t_s = shorter averaging time;

t_l = longer averaging time; and

p = power law exponent in Table 3.12

Table 3.12 Conversion Factors from 1-hour to 30-minute Averaging Time

Pasquill Stability Class	Power Law Exponent	1-hour to 30-minute Conversion Factor
A	0.5	1.41
B	0.5	1.41
C	0.333	1.26
D	0.2	1.15
E	0.167	1.12
F	0.167	1.12

3.6.2.8 As a conservative approach, the AERMOD predicted maximum 1-hour average formaldehyde concentrations at each ASRs would be converted to 30-minute average concentration using the highest conversion factor of 1.41 in Table 3.12, as a conservative approach.

Vehicular Emission

3.6.2.9 For vehicular emission from open roads, the associated key air pollutants are NO₂, RSP and FSP. Open road emission sources within 500m study area would be included in the assessment, as shown in Appendix 3.5. The associated vehicular emission factors are presented in Appendix 3.6.

Determination of Assessment Year

3.6.2.10 The Project is expected to be completed by Year 2032. The assessment year for open road vehicular emission will be determined by the year with the highest vehicular emission burden in the study area in 15 years after Project commissioning, i.e. Year 2032 – Year 2047. With reference to the TIA, the traffic forecast showed that the traffic in the study area would peak in Year 2041, owing to the peak of Hong Kong population in Year 2041 and decreasing trend afterwards, referring to Hong Kong Population Projections by Census and Statistics Department. The predicted peak traffic flow year would also be Year 2041. The vehicular emission burdens of NO_X and RSP for Year 2032, Year 2036 and Year 2041 were estimated with EMFAC-HK v4.3 and are presented in Table 3.13. The traffic data is presented in Appendix 3.5 and the assumption adopted in EMFAC-HK is presented in Appendix 3.6. Year 2041 was found to have the highest vehicular emission burden in NO_X and RSP in 15 years after commencement, and hence selected as assessment year.

Table 3.13 Vehicular Emission Burden in the Study Area

Year	Vehicular Emission Burden (kg per day)
	NOX	RSP
2032	0.74	0.01
2036	0.66	0.02
2041	1.64	0.04

Dispersion Modelling & Modelling Approach

3.6.2.11 EMFAC-HK v4.3 was adopted to estimate the vehicular emission factors in NO_X, NO₂, RSP and FSP in various travelling speeds, and the worst ambient conditions, i.e. the lowest temperature and relative humidity for the year with reference to the observation in Year 2020 by HKO Lau Fau Shan meteorological station. The emission factor in NO was then derived by assuming NO_X consists of NO and NO₂ only.

3.6.2.12 The traffic data for open roads in 500m study area, comprises 24-hour traffic flow with vehicle percentage, travelling speed in 18 vehicle classes and is presented in Appendix 3.5. Transport Department (TD) agreement on the adopted traffic data is also presented in the appendix. With reference to the traffic data, hourly emission factor of each open road was determined by summation of emission by each vehicle class which is product of traffic flow and emission factor at specific speed and ambient condition. The hourly emissions factors of NO, NO₂, RSP and FSP were further divided by the hourly flow to obtain a composite emission rate in gram per miles per vehicle, ready for input to the dispersion model. The detailed calculation of vehicular emission source is presented in Appendix 3.6.

3.6.2.13 CALINE4, the HKEPD approved air dispersion model for road source developed by the California Department of Transport, was used to assess the contribution due to vehicular emission from road networks within 500m study area.

3.6.2.14 The surface roughness is dependent on the land use characteristics, which is estimated to be 10% of average height of physical structure within 1 km radius of the Subject Site. Typically, the value is assumed to be 370 cm and 100 cm for urban and new development respectively. Given that the low-rise industrial buildings and structures of the Project, surface roughness of 100 cm was assumed in the assessment.

3.6.2.15 Under the current EPD guideline, the hourly meteorological data including wind speed, wind direction, and air temperature from the relevant grids from the WRF Meteorological data (same basis for PATH v2.1 model), were employed for the model run. PCRAMMET was applied to generate Pasquill-Gifford stability class for the meteorological input to CALINE4 model based on the WRF meteorological data.

3.6.2.16 Ozone Limiting Method (OLM) has been adopted for the conversion of NO_X to NO₂ based on the ozone background concentration from PATH v2.1. Regarding vehicular emission, NO₂ and NO were predicted separately in CALINE4. Following the principle of OLM, the total predicted vehicular NO2 is estimated as below:

[NO₂]_vehicular = [NO₂]_predicted + MIN {[NO]_predicted, or (46/48) ´ [O₃]_PATH}

where

[NO₂]_vehicular is the total predicted vehicular NO₂ concentration

[NO₂]_predicted is the predicted NO₂ concentration

[NO]_predicted is the predicted NO concentration

MIN means the minimum of the two values within the bracket

[O₃]_PATH is the representative O₃ PATH concentration (from other contribution)

(46/48) is the molecular weight of NO₂ divided by the molecular weight of O₃

3.6.2.17 Cumulative air pollutant concentration at ASRs was derived by the sum of contributions by open roads and YLSEPP and background contribution from PATH v2.1 on hour-by-hour basis. The cumulative air pollutant concentrations at ASRs are compared against the respective standard as stated in Section 3.2.

3.6.3 Operation Phase (Odour Impact)

3.6.3.1 Cumulative odour impact from the operation of the proposed YLSEPP and the retained chicken farm was predicted and compared against the EIAO-TM criterion of 5 OU.

3.6.3.2 To simulate the potential odour impact from the operation of the proposed YLSEPP, specific odour emission rate (SOER) from other effluent polishing plants (EPPs) in Hong Kong are referenced. Similar to YLSEPP, Yuen Long EPP (YLEPP) also serve Yuen Long District and are nearest to the proposed YLSEPP. However, odour emission from YLEPP would be anticipated higher due to high sulphur content from seawater flushing catchment area, unlike YLSEPP collect sewage from fresh water flushing catchment area. YLEPP collect both domestic sewage and industrial sewage from Yuen Long Industrial Estate, unlike YLSEPP collect mainly domestic sewage. To have a more realistic reference, odour emission rate from Shek Wu Hui EPP (SWHEPP) is considered. Sewage sources of both YLSEEP and SWHEPP are domestic sewage from public and private housing, village sewerage and major development districts (YLSEPP serving YLS DA, while SWHEPP serving Kwu Tung South Potential Development Area, Kwu Tung North New Development Area and Fanling North New Development Area, which all uses non-salt water flushing systems). In terms of treatment process, both YLSEPP and SWHEPP would uses MBR sewage treatment processes. As a conservative approach, odour emission rates from the SWHEPP, which serves larger catchment area, were adopted.

3.6.3.3 With reference to the “Code of Practice on Assessment and Control of Odour Nuisance from Waste Water Treatment Works, April 2005” published by the Scottish Executive, odour removal efficiency of two common odour abatement technologies, namely bio-filters and dry scrubbing (carbon or impregnated media) are of at least 95%, while 90% odour removal efficiencies could be achieved by most types of deodourizers. With reference to SWHEPP and Yuen Long Effluent Polishing Plant (YLEPP), two-stage DOs could achieve 95% odour removal efficiencies. Therefore, odour removal efficiencies of 95% are assumed for the two-stage DOs in this project, respectively. Detailed deodourization technology of the DOs have been presented in Section 2.4.4.

3.6.3.4 The locations, emission rates and emission parameters of the odour emission sources from the proposed YLSEPP (i.e. the exhaust of the deodourizers) are presented in Appendix 3.7.

3.6.3.5 To simulate the potential odour impact from the retained chicken farm, reference is made to the approved YLS DA EIA Report. In the approved YLS DA EIA Report, night-time temperature adjustment to the chicken farm odour emission rate was applied. However, in view of the latest EPD PATH v2.1 night-time temperature data, the maximum night-time temperature would be 35°C, i.e. only 1°C below the temperature of 36°C during the YLS DA chicken farm odour survey. To avoid potential underestimate of the odour emission during night-time in the current global warming trend, no night-time temperature adjustment would be applied. The odour source locations, type and other emission parameters followed the approved YLS DA EIA Report in the assessment.

3.6.3.6 According to the latest YLSEPP layout shown in Appendix 3.7, the exhaust points of DOs of the Project are found at 11.5 – 16m above ground and are located adjacent to building structures with heights up to 17m above ground, building wake effect is expected. For the retained chicken farm, the odour emission sources were classified as area and volume sources in the approved YLS DA EIA Report. The 1-hour to 1-second conversion factors from Approved Methods for the Modelling and Assessment of Air Pollutants in New South Wales were adopted directly to convert the 1-hour average concentration predicted by the AERMOD model to 5-second average concentration as a conservative approach. The conversion factors for different types of source and stability classes are listed in Table 3.14 below. PCRAMMET was applied to generate Pasquill-Gifford stability class hour by hour based on the WRF meteorological data from PATH v2.1.

Table 3.14 Conversion Factors from 1-hour to 5-second Averaging Time

Pasquill Stability Class	Conversion Factor
	Wake-Affected Point Source	Area Source	Volume Source
A	2.3	2.5	2.3
B	2.3	2.5	2.3
C	2.3	2.5	2.3
D	2.3	2.5	2.3
E	2.3	2.5	2.3
F	2.3	2.5	2.3

3.6.3.7 The methodology stated in Sections 3.6.1.8 - 3.6.1.12 have also been applied to odour modelling.

3.7 Prediction and Evaluation of Environmental Impacts

3.7.1 Construction Phase

3.7.1.1 The cumulative construction dust impact due to the Project, open roads, and construction works of YLS DA development within 500 m assessment area at representative ASRs in Year 2028 have been predicted and presented in Appendix 3.8. The predicted unmitigated cumulative air quality impact were 488 – 3135 µg/m³ in maximum hourly TSP, 69 – 167 /m³ in 10^th highest daily RSP, 29 – 81 µg/m³ in annual RSP, 38 – 47 µg/m³ in 19^th highest daily FSP and 16 – 25 µg/m³ in annual FSP. It is noted that exceedance of hourly TSP, daily and annual RSP would be expected at the representative ASRs, thus mitigation measures are deemed necessary.

3.7.2 Operation Phase (Air Pollutant Emissions Impact)

3.7.2.1 The cumulative air quality impact due to the Project (CHPs and boiler) and open roads within 500m assessment area at representative ASRs have been evaluated. The detailed prediction results are presented in Appendix 3.9 and summarised in Table 3.15 - Table 3.17. The prediction results indicated the 19^th highest daily average FSP concentrations would range from 38.2 to 42.4 µg/m³, complying with the respective AQO of 50 µg/m³. The annual average FSP concentration would range from 15.6 to 16.8 µg/m³, complying with the respective AQO of 25 µg/m³. The prediction results indicated the 10^th highest daily average RSP concentrations would range from 69.1 to 71.4 µg/m³, complying with the respective AQO of 100 µg/m³. The annual average RSP concentration would range from 27.3 to 28.8 µg/m³, complying with the respective AQO of 50 µg/m³. The prediction results indicated the 19^th highest hourly average NO₂ concentrations would range from 96.0 to 108.3 µg/m³, complying with the respective AQO of 200 µg/m³. The annual average NO₂ concentration would range from 18.8 to 22.2 µg/m³, complying with the respective AQO of 40 µg/m³.

3.7.2.2 The SO₂ emissions from CHP and boiler at representative ASRs have been evaluated. The predicted SO₂ concentrations at the ASRs are detailed in Appendix 3.9 and summarized in Table 3.18. The prediction results indicated the 4^th highest 10-minute average SO₂ concentrations would range from 54.4 to 58.5 µg/m³, complying with the respective AQO of 500 µg/m³. The 4^th highest daily average SO₂ concentration would range from 11.5 to 13.9 µg/m³, complying with the respective AQO of 50 µg/m³.

Table 3.15 Predicted Fine Suspended Particulates Concentrations on Representative Air Sensitive Receivers

ASR ID	Predicted FSP Concentration, µg/m^3
	19^th Highest Daily Average	Annual Average
Criteria	50	25
YAE01	38.7	16.0
YAE02	38.2	15.6
YAE03	38.2	15.6
YAE04	38.2	15.6
YAE05	42.4	16.8 - 16.8
YAP01	38.2 - 38.3	15.6 - 15.8
YAP02	38.2 - 38.3	15.6 - 15.7
YAP03	38.2 - 38.4	15.6 - 15.7
YAP04	38.2 - 38.3	15.6
YAP05	38.2 - 38.3	15.6
YAP06	38.2	15.6
YAP07	38.2	15.6
YAP08	38.2	15.6
YAP09	38.2	15.6
YAP10	38.2	15.6
YAP11	38.2	15.6

Table 3.16 Predicted Respirable Suspended Particulates Concentrations on Representative Air Sensitive Receivers

ASR ID	Predicted RSP Concentration, µg/m^3
	10^th Highest Daily Average	Annual Average
Criteria	100	50
YAE01	69.1	28.1
YAE02	69.2	27.3
YAE03	69.2	27.3
YAE04	69.2	27.3
YAE05	71.3 - 71.4	28.8
YAP01	69.3 - 69.9	27.3 - 27.5
YAP02	69.2 - 69.4	27.3 - 27.4
YAP03	69.2	27.3 - 27.4
YAP04	69.2	27.3 - 27.4
YAP05	69.1 - 69.2	27.3
YAP06	69.1 - 69.2	27.3
YAP07	69.2	27.3
YAP08	69.2	27.3
YAP09	69.2	27.3
YAP10	69.2	27.3
YAP11	69.2	27.3

Table 3.17 Predicted Nitrogen Dioxide Concentrations on Representative Air Sensitive Receivers

ASR ID	Predicted NO2 Concentration, µg/m^3
	19^th Highest Hourly Average	Annual Average
Criteria	200	40
YAE01	99.7	20.3
YAE02	96.0 - 96.1	19.0
YAE03	96.0 - 96.1	19.0
YAE04	96.0 - 96.1	19.0
YAE05	101.2 - 101.3	20.0
YAP01	97. 5 - 108.3	19.7 - 22.2
YAP02	96.0 - 102.7	18.9 – 21.0
YAP03	96.0 - 102.9	18.9 - 20.4
YAP04	96.0 - 99.1	18.8 - 20.2
YAP05	96.0 - 98.4	18.8 - 19.7
YAP06	96.0 - 97.2	18.9 - 19.4
YAP07	96.1 - 99.1	19.3 - 19.5
YAP08	96.3 - 100.4	19.3 - 19.6
YAP09	96.0 - 98.5	19.1 - 19.3
YAP10	96.0 - 101.2	19.1 - 19.4
YAP11	96.0 - 97.0	19.1 - 19.3

Table 3.18 Predicted Sulphur Dioxide Concentrations on Representative Air Sensitive Receivers

ASR ID	Predicted SO2 Concentration, µg/m^3
	4^th Highest 10-minute Average	4^th Highest Daily Average
Criteria	500	50
YAE01	57.3 - 57.4	11.7
YAE02	55.8 - 55.9	11.8 - 11.8
YAE03	55.8 - 55.9	11.8 - 11.8
YAE04	55.8	11.7 - 11.7
YAE05	54.4	11.5 - 11.5
YAP01	55.8	11.9 - 13.9
YAP02	55.8	11.7 - 13.0
YAP03	55.8	11.7 - 12.0
YAP04	55.8	11.7
YAP05	55.8	11.7
YAP06	55.8	11.7
YAP07	55.8	11.7
YAP08	55.8 - 58.5	11.7
YAP09	55.8	11.7
YAP10	55.8	11.7
YAP11	55.8	11.7

3.7.2.3 According to the detailed results in Appendix 3.9 the 19^th highest daily average and annual average FSP concentrations, and 10^th highest daily average and annual average RSP concentration would occur at 1.5 mAG. The maximum 19^th highest hourly average and annual average NO₂ concentrations, the 4^th highest 10-minute average SO₂ concentrations 4^th highest daily average SO₂ concentrations would occur at 35, 30, 35, 30 mAG, respectively. Contour plots of the cumulative pollutant concentrations at these worst affected levels are thus predicted and presented in Figures 3.8 – 3.15. As presented in Figure 3.12, 3.13 and 3.15, exceedance zone is observed around the effluent polishing plant. However, there are no air sensitive uses located within the exceedance zone.

3.7.2.4 Furthermore, the predicted concentrations of other pollutants, including formaldehyde, CO, methane, HCl and HF, at representative ASRs have been presented in Appendix 3.9. All of the pollutants would be well below the respective criteria as stated in Section 3.2.

3.7.2.5 Hence, no adverse air quality impact would be anticipated from the operation of CHPs and boiler of YLSEPP.

3.7.3 Operation Phase (Odour Impact)

3.7.3.1 Based on the methodology presented in Section 3.6.3, the predicted cumulative odour impact in terms of maximum 5-second average odour concentrations at the representative ASRs have been predicted and the results are presented in Appendix 3.9 and summarized in Table 3.19. The predicted cumulative odour concentrations at all planned ASRs YAP01 -YAP11 would be 0.1 to 3.6 OU/m³, complying with the 5 OU EIAO-TM criterion. The predicted cumulative odour concentrations at existing ASRs YAE03, YAE04 and YAE05 would be 0.6 – 4.5 OU/m³, complying with the 5 OU EIAO-TM criterion. However, the predicted cumulative odour concentrations at the existing ASRs YAE01 and YAE02 would be 5.6 to 6.7 OU/m³, non-compliance with the EIAO-TM criterion of 5 OU. According to the detailed results presented in Appendix 3.9, the predicted maximum 5-second average cumulative odour concentration would occur at 1.5 mAG. Contour plot of the cumulative odour concentrations at the worst affected level are thus predicted and presented in Figure 3.16.

Table 3.19 Predicted Maximum Cumulative Odour Concentrations at Representative Air Sensitive Receivers

ASR ID	Predicted Maximum Cumulative 5-second Average Odour Concentration, OU/m^3
Criteria	5
YAE01	5.9 - 6.7
YAE02	5.6 - 6.3
YAE03	4.0 - 4.5
YAE04	3.0 - 3.5
YAE05	0.6 - 0.9
YAP01	0.1 – 1.0
YAP02	0.2 - 1.6
YAP03	0.2 - 1.7
YAP04	0.2 - 1.8
YAP05	0.1 - 1.4
YAP06	0.2 - 1.7
YAP07	0.3 - 2.0
YAP08	0.3 - 2.2
YAP09	0.3 - 2.1
YAP10	0.4 - 2.8
YAP11	2.1 - 3.6

Remarks:

- Boldfaced values indicate exceedance to the EIAO-TM criterion of 5 OU.

Comparison of Existing and Future Odour Conditions

3.7.3.2 The Project, i.e. the proposed YLSEPP, is an essential component of the YLS DA development, which planned to remove five out of the existing six livestock farms, while retaining a chick farm in the vicinity of the Project. Location of the retained chicken farm is presented in Figure 3.16. With reference to the approved YLS DA EIA Report, by removing the livestock farms, the total odour emission in the YLS DA area would be substantially reduced. With the implementation of the Project and YLS DA, the existing odour conditions at existing representative ASRs in the YLS DA area would be substantially improved in the future. Without the Project in place, the YLS DA development and the removal of five livestock farms would not be feasible. The odour condition would maintain the current condition and the ASRs would be affected by the odour arising from all 6 livestock farms.

3.7.3.3 The odour modelling methodology applied in this study and in the approved YLS DA EIA study are highly similar in terms of the model domain location (both are YLS DA), the selected air dispersion model (both are AERMOD), meteorological data (both are from EPD PATH model), 1-hour to 5-second average concentration conversion factor (both are the same as listed in Table 3.14), generation of Pasquill-Gifford stability class by PCRAMMET and the same odour emission rate from the retained chicken farm. The differences would only be (a) temperature adjustment for odour emission rate of chicken farm was included in YLS DA EIA, but not included in this Study (see Section 3.6.3.5) and (b) the odour emission rate of the proposed YLSEPP under YLS DA EIA was based on Lok Ma Chau Loop Sewage Treatment Works, while the odour emission rate of the proposed YLSEPP are based on latest design information in this Study. The removal of temperature adjustment in this Study would result in a more conservative odour concentrations associated with the retained chicken farm which is the major odour emission source. Hence, even the design of the proposed YLSEPP has been updated, based on the similarities on the assessment approaches and more conservative odour impact results for chicken farm in this Study, the odour prediction results under basecase scenario (existing condition) in the approved YLS DA EIA Report would be considered still valid for comparison purpose against the latest odour prediction results in Table 3.19.

3.7.3.4 Identified by YLS DA EIA Study, six existing livestock farms (chicken farms with farm code 18/16/X002N, 18/16/D93 and 18/16/F203; pig farms with farm code 18/16/C72,C73, 18/16/C86 and 18/16/G112)[3] are located within the 500m assessment boundary of YLS DA EIA. Three existing pig farms (farm code 18/16/C72,C73, 18/16/C86 and 18/16/G112) and two existing chicken farms (farm code 18/16/X002N and 18/16/D93) would be removed under YLS DA project, while chicken farm 18/16/F203 would be retained. The chicken farm 18/16/X002N and the pig farm 18/16/C72,C73 are located more than 800m from the representative ASRs in this Study, the associated odour contribution to the representative ASRs would be very limited. In addition, the improvement of future odour condition at the representative ASRs are mainly due to the removal of the other nearby livestock farms, i.e. 18/16/C86, 18/16/G112 and 18/16/D93. The locations of these three to-be-removed livestock farms and the retained chicken farm 18/16/F203 are presented in Appendix 3.10.

3.7.3.5 Within the 500m assessment boundary, three common ASRs are identified under both YLS DA EIA and this Study, namely YAE01, YAE04 and YAE05 (A35, A34 and A33 in YLS DA EIA, respectively). The locations of these ASRs are presented in Figure 3.2. In particular, YAE01 is located inside the odour exceedance zone, while YAE03 and YAE04 are located about 270m and 80m outside the odour exceedance zone, respectively. The odour improvement at YAE02 and all other ASRs within the odour exceedance zone could be estimated by referencing the odour assessment results from the two common ASRs which located inside/nearest to the odour exceedance zone, i.e. YAE01 and YAE04 (A35 and A34). Below estimation of the future odour improvement by referencing the data from the two representative ASRs in YLS DA inside/nearest to the exceedance zone, i.e. YAE01 and YAE04. Comparing the cumulative odour impact under with-Project scenario (Table 3.19) and YLS DA EIA basecase scenario, the odour concentration at the worst-affected ASR YAE01 would be improved[4] by about 25 OU/m³, while the improvement[5] at YAE04 would be about 13 OU/m³. As shown in Appendix 3.10, YAE01 and YAE04 are located from the two existing to-be-removed pig farms by about 260 – 480m and by about 480 - 530m, respectively. While YAE01 is located closer to the pig farms than YAE04, the odour reduction due to removal of these two existing pig farms for YAE01 (about 25 OU/m³) would hence be larger than that for YAE04 (about 13 OU/m³). Since YAE02 lies between YAE01 and YAE04 and the separation distance between YAE02 and the two existing pig farms is about 390 – 470m, therefore it is expected that the odour improvement at YAE02 would also be lain between that for YAE01 and YAE04, i.e. from 13 OU/m³ to 25 OU/m³.

3.7.3.6 The contour plot in Figure 3.6 indicates a potential odour exceedance zone surrounding the retained existing chicken farm 18/16/F203 and covered the representative ASRs YAE01 and YAE02, and nearby village houses which are also ASRs. With reference to the locations shown in Appendix 3.10, the distance from the to-be-removed livestock farms to the village houses No. 112, 113, 114 and 116, 118, 123, 124 and 126 Wong Nai Tun Tsuen would be between that of YAE01 and YAE04. Hence, it is expected that the odour improvement at these village houses would also be in the range of 13 OU/m³ to 25 OU/m³.

Exceedance Magnitude, Frequency and Odour Contribution by the Project

3.7.3.7 The exceedance magnitude, exceedance frequency and odour contribution by the Project at representative ASRs YAE01 and YAE02, as well as all ASRs (village houses No., 112, 113, 114, 116, 118, 123, 124, 125, 126) within the odour exceedance zone are presented in Appendix 3.10. The frequency of exceedance in odour concentrations is up to 0.51% of the time in a year for ASRs located within the exceedance zone. During this period, the Project would contribute up to 0.45 OU/m³, less than 1.0 OU. The major odour contribution would be from the retained existing chicken farm during the time of exceedance. No other existing/planned ASR has been identified located within the predicted exceedance zone.

Project-alone Scenario

3.7.3.8 Consider a hypothetical Project-alone scenario, the design capacity of the Project has been increased from 24,000 m³/day in the approved EIA Report for YLS DA development, to 65,000 m³/day in latest design, as mentioned in Section 2. Optimal design against the potential odour impact has been considered, including covering all odourous sources for collecting and conveying odourous gas for treatment at DOs with 95% odour removal efficiency before venting to the atmosphere. The proposed DOs would be two-stage biotrickling filter followed by activated carbon filter deodourization technologies, with reference to Section 2.4. The exhausts of the DOs are also designed to locate farthest away and pointing away from the representative ASRs as far as practicable to further minimise any odour impact to the ASRs. Further relocation of DO exhaust to locations farther away from the ASRs would be limited by engineering constraint, such as limitation of space and height restriction. It is therefore considered that the odour mitigation measures for the Project have been exhausted. The predicted odour concentration at various levels of representative ASRs under the hypothetical Project-alone scenario are presented in Appendix 3.9 and summarized in Table 3.20. The predicted maximum 5-second average odour concentration among the representative ASRs due to the Project alone would range from <0.1 to 0.8 OU/m³ below 1 OU.

Table 3.20 Predicted Maximum Project-alone Odour Concentrations at Representative Air Sensitive Receivers

ASR ID	Predicted Maximum Project-alone 5-second Average Odour Concentration, OU/m^3
Criteria	5
YAE01	0.5
YAE02	0.5 - 0.6
YAE03	0.6
YAE04	0.6
YAE05	0.4 - 0.5
YAP01	<0.1 - 0.6
YAP02	<0.1 - 0.7
YAP03	<0.1 - 0.7
YAP04	<0.1 - 0.7
YAP05	<0.1 - 0.4
YAP06	<0.1 - 0.4
YAP07	<0.1 - 0.5
YAP08	0.1 - 0.7
YAP09	0.1 - 0.7
YAP10	0.1 - 0.8
YAP11	0.4 - 0.8

Summary for Operation Phase Odour Impact

3.7.3.9 From both cumulative and project-alone perspectives, the Project would give rise to odour nuisance of below 1 OU. The Project would support the YLS DA development, which would remove 5 existing livestock farms and hence improve the existing odour condition in the vicinity of the YLS DA. There is an overall net reduction in odour impacts for all ASRs within the exceedance zone with the removal of 5 livestock farms and the presence of the proposed YLSEPP under the whole YLS DA project, no adverse residual odour impact would be expected due to the Project and due to the YLS DA development as a whole.

3.8 Mitigation of Adverse Environmental Impacts

3.8.1 Construction Phase

3.8.1.1 In order to minimise the construction dust impact, watering once every two hours on heavy construction work areas to reduce dust emission by 91.7% shall be implemented. Detailed calculations of the dust suppression efficiency is presented in Appendix 3.2. Any potential dust impact and watering mitigation would be subject to the actual site condition. For example, a construction activity that produces inherently wet conditions or in cases under rainy weather, the above water application intensity may not be unreservedly applied. While the above watering frequency is to be followed, the extent of watering may vary depending on actual site conditions but should be sufficient to achieve the removal efficiency. The dust levels would be monitored and managed under an EM&A programme as specified in the EM&A Manual.

3.8.1.2 Dust suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation and good site practices listed below should be carried out to minimize the construction dust impact.

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

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

· 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 shall be applied to aggregate fines.

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

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

· Establishment and use of vehicle wheel and body washing facilities at the exit points of the site.

· Provision of wind shield and dust extraction units or similar dust mitigation measures at the loading area of barging point, and use of water sprinklers at the loading area where dust generation is likely during the loading process of loose material, particularly in dry seasons/ periods.

· Provision of not less than 2.4m high hoarding from ground level along site boundary where adjoins a road, streets or other accessible to the public except for a site entrance or exit.

· Imposition of speed controls for vehicles on site haul roads.

· Where possible, routing of vehicles and positioning of construction plant should be at the maximum possible distance from ASRs.

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

3.8.1.3 With the implementation of the above measures, the cumulative TSP, RSP and FSP concentrations at the representative ASRs were predicted and are summarized in Table 3.21. The predictions showed that the hourly average of TSP, daily and annual averages of RSP, daily and annual averages of FSP at representative ASRs would comply with the criteria as stipulated in the TM-EIAO and the AQOs. The detailed prediction results are presented in Appendix 3.8.

Table 3.21 Predicted Cumulative Construction Dust Impact at Representative ASRs in Year 2028 (Mitigated Scenario)

ASRID	Maximum Hourly average TSP Conc. (µg/m^3) (EIAO-TM: 500 µg/m^3)	10^th Highest Daily average RSP Conc. (µg/m^3)  (AQO: 100 µg/m^3)	Annual average RSP Conc. (µg/m^3)  (AQO: 50 µg/m^3)	19^th Highest Daily average FSP Conc. (µg/m^3)  (AQO: 50 µg/m^3)	Annual average FSP Conc. (µg/m^3)  (AQO: 25 µg/m^3)
YAE01	201	69.2	28.5	38.6	16.0
YAE02	274 - 281	69.6	28.2 - 28.5	38.2	15.7
YAE03	279 - 289	69.7	28.3 - 28.6	38.2	15.7 - 15.8
YAE04	284 - 289	69.8 - 69.9	28.5 - 28.9	38.2	15.7 - 15.8
YAE05	173	73.8 - 74.3	29.6 - 29.7	42.5	17.0
YAE06	301 - 339	73.9 - 84.2	33.0 - 42.6	39.1 - 41.6	16.5 - 18.2
YAE07	269 - 498	72.6 - 79.3	34.3 - 44.2	39.7 - 41.6	16.7 - 18.4

3.8.1.4 With reference to the detailed prediction results in Appendix 3.8, the maximum TSP, RSP and FSP concentrations are predicted at 1.5 mAG. The contour of mitigated construction dust concentrations at 1.5mAG have been presented in Figures 3.3 - 3.7.

3.8.1.5 In order to help reduce carbon emission and pollution, timely application of temporary electricity and water supply would be made and electric vehicles would be adopted in accordance with DEVB TC(W) No. 13/2020 – Timely Application of Temporary Electricity and Water Supply for Public Works Contracts and Wider Use of Electric Vehicles in Public Works Contracts in the Project.

3.8.2 Operation Phase (Air Pollutant Emissions Impact)

3.8.2.1 With reference to the prediction results in Section 3.7.2, no adverse air quality impact is anticipated during the operational phase of the Project, thus mitigation measure is deemed not necessary.

3.8.3 Operation Phase (Odour Impact)

3.8.3.1 With reference to above Section 3.7.3, no adverse odour impact is anticipated during operation phase due to the Project alone, with the implementation of proposed odour control measures as mentioned in Section 3.5.3. Overall improvement to the odour condition in the vicinity of the YLS DA is expected with the YLS DA project, including the Project as an essential component. No adverse residual cumulative odour impact is anticipated.

3.8.3.2 In view of the predicted exceedance of the maximum cumulative odour concentrations at the existing ASRs as presented in Section 3.7.3, odour mitigation measures have been considered. With reference to Section 2.4, the odour sources of the YLSEPP have all been designed to minimise the potential odour emission. These emission sources are covered/enclosed. The odourous gas in the covered/enclosed space are conveyed to the two-stage DOs, which equipped with the best available technology in the market to achieve at least 95% odour removal efficiency. The exhausts of the DOs are located farthest away and pointing away from the representative ASRs as far as practicable from dispersion point of view to further minimise any odour impact to the ASRs. It is therefore considered that the odour mitigation measures at the Project have been exhausted.

3.8.3.3 No further mitigation measure would be required during the operation phase.

3.9 Evaluation of Residual Impacts

3.9.1 Construction Phase

3.9.1.1 With the implementation of the mitigation measures as stipulated in the Air Pollution Control (Construction Dust) Regulation and good site practices on the work sites, no adverse residual impact would be expected from construction of YLSEPP.

3.9.2 Operation Phase (Air Pollutant Emissions Impact)

3.9.2.1 No adverse flue gas impact is expected during the operation phase of YLSEPP.

3.9.3 Operation Phase (Odour Impact)

3.9.3.1 With the implementation of the recommended mitigation measures at the Project mentioned in Section 2.4.4, 3.5.3 and 3.7.3, the odour mitigation measures have been exhausted. The predicted odour concentrations due to the Project alone would be less than 1 OU/m³ at all ASRs.

3.9.3.2 Considering the cumulative odour impact due to the Project and the retained chicken farm, the predicted cumulative odour concentrations at all planned ASRs within the 500m assessment area would comply with the EIAO-TM criterion of 5 OU during operation phase of the Project. No adverse residual odour impact would be expected at the planned ASRs.

3.9.3.3 Potential odour exceedances to the EIAO-TM criterion of 5 OU are predicted at two existing representative ASRs, YAE01 and YAE02, and nearby ASRs for a short duration of time (up to 0.51% of the time in a year) during operation phase of the Project. The Project contribution to the overall exceedance would be up to 0.45 OU/m³, less than 1 OU/m³. The details are presented in Appendix 3.10. Nonetheless, as detailed in Section 3.7.3, the Project will support the YLS DA and bring about a net improvement in cumulative odour impact for the YLS DA area. Despite the predicted odour exceedance at some existing ASRs, the cumulative odour impacts will be substantially improved (by approximately 13 – 25 OU/m³ for all the ASRs located within the exceedance zone, including YAE01 and YAE02) compared to that of existing condition without removal of the five livestock farms.

3.9.3.4 It is therefore concluded that there is no adverse residual odour impact arising from the Project.

3.10 Environmental Monitoring and Audit Requirements

3.10.1 Construction Phase

3.10.1.1 EM&A for potential dust impacts should be conducted during construction phase so as to check compliance with the legislative requirements. Details of the monitoring and audit programme are contained in a stand-alone EM&A Manual.

3.10.1.2 Regular site audits and monitoring for potential dust impact are recommended to be conducted during the entire construction phase of the Project so as to ensure the dust mitigation measures and the dust suppression measures stipulated in Air Pollution Control (Construction Dust) Regulation are implemented in order.

3.10.2 Operation Phase

3.10.2.1 No adverse air pollutant emissions impact would be generated during the operation phase of this Project. Therefore, the Environmental Monitoring and Audit (EM&A) works related to air quality during the operational phase is considered not necessary. However, commissioning test should be conducted for the CHP units and the boiler to ensure proper operation of the facilities. As H₂S is the major odour source associated with the effluent polishing plant, it is recommended to conduct the odour monitoring in terms of hydrogen sulphide (H₂S) at the deodorizers upon commissioning and in the first three years to determine whether it can meet the 95% odour removal performance requirement. Upon the third-year monitoring, the odour monitoring should be reviewed and agreed with EPD if the monitoring is required to be continued. An Odour Complaint Registration System is also proposed in the EM&A programme to check whether the deodorizing units can fulfill the recommended odour removal performance. In addition, odour patrol should be carried out during regular and ad hoc maintenance or cleaning of the deodourizers after operation of YLSEPP to ensure no adverse odour impact arisen from the operation of the YLSEPP. Details of the monitoring and audit programme are contained in a stand-alone EM&A Manual.

3.11 Conclusion

3.11.1 Construction Phase

3.11.1.1 The potential air quality impacts from the construction works of the YLSEPP would mainly be related to the construction dust from the excavation, pilling works, road paving works, construction of substructures and superstructures works. With the implementation of mitigation measures specified in the Air Pollution Control (Construction Dust) Regulation, good site practices, regular watering and EM&A programme, no adverse dust impact at ASRs is anticipated due to the construction activities of the Project.

3.11.2 Operation Phase (Air Pollutant Emissions Impact)

3.11.2.1 Flue gas emission would be emitted from the stacks of CHP and boiler in the YLSEPP. Cumulative air quality impact arising from YLSEPP operation, the vehicular emissions from the open roads within the 500m assessment area has been assessed for operation of YLSEPP. The assessment results conclude that the predicted cumulative the 19^th highest 1-hour average and annual average NO₂, the 10^th highest daily and annual average RSP, the 19^th highest daily and annual average FSP, 10-min average and daily average SO₂, and the maximum 1-hour and the maximum 8-hour average CO at representative ASRs would comply with the corresponding new AQOs. The predicted maximum 1-hour average and annual average HCl, maximum 1-hour average and annual average HF, maximum 1-hour average methane, maximum 30-minute average and annual average formaldehyde would comply with the corresponding international standards. No adverse air quality impact is anticipated arising from the flue gas emission associated with the operation of YLSEPP.

3.11.3 Operation Phase (Odour Impact)

3.11.3.1 All odour sources in YLSEPP are fully enclosed. The potential odour emission from the sewage treatment facilities, sludge treatment facilities and organic waste co-digestion facilities would all be treated in the deodourizers before discharge into atmosphere. With implementation of the best-available deodourizers in the market with 95% odour removal efficiency, locating deodourizer exhaust away from ASRs as far as practicable, the assessment results show that the predicted Project-alone 5-second average odour concentration at the representative ASRs within the Study Area would be below 1 OU.

3.11.3.2 Considering the cumulative odour impact due to the Project and the retained chicken farm, the predicted cumulative odour concentrations at all planned ASRs would comply with the EIAO-TM criterion of 5 OU. No adverse odour impact would be expected at the planned ASRs.

3.11.3.3 Cumulative odour exceedances to the EIAO-TM criterion of 5 OU are predicted at two existing representative ASRs, YAE01 and YAE02, and nearby village houses for a short duration of time during operation phase of the Project. The frequency of exceedance in odour concentrations at ASRs within the exceedance zone is up to 0.51% of the time in a year. During the time of exceedance, the proposed YLSEEP would contribute less than 0.45 OU/m³, while the major odour contribution would be from the retained existing chicken farm. Nonetheless, the Project will support the YLS DA and bring about a net improvement in cumulative odour impact at the YLS DA area. Despite the predicted odour exceedance at some existing ASRs, the cumulative odour impacts at these ASRs will be substantially improved compared to that of existing condition without removal of the five livestock farms. With the removal of the five livestock farms, an overall reduction in odour impacts at all the ASRs would be anticipated.

3.11.3.4 It is therefore concluded that there is no adverse residual odour impact arising from the Project.

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[1] Valerio Paolini, Francesco Petracchini, Marco Segreto, Laura Tomassetti, Nour Naja & Angelo Cecinato (2018) Environmental impact of biogas: A short review of current knowledge, Journal of Environmental Science and Health, Part A, 53:10, 899-906, DOI:10.1080/10934529.2018.1459076

[2] Richard A. Duffee, Martha A. O'Brien and Ned Ostojic, 'Odor Modeling - Why and How', Recent Developments and Current Practices in Odor Regulations, Controls and Technology, Air & Waste Management Association, 1991

[3] Locations of the livestock farms are available at https://www.epd.gov.hk/epd/english/laws_regulations/enforcement/lw_map.html

[4] YLS DA EIA predicted the odour concentration at ASR A35 of 6.0 OU/m³ under its ultimate scenario (with Project) and an improvement of 25.4 OU/m³. This Study predicted the odour concentration of up to 6.70 OU/m³ under with Project scenario, the respective improvement would be approximately (25.4 + 6.0 – 6.70) = 24.70 OU/m³. The rounded value of 25 OU/m³ is presented.

[5] YLS DA EIA predicted the odour concentration at ASR A34 of 2.0 OU/m³ under its ultimate scenario (with Project) and an improvement of 14.0 OU/m³. This Study predicted the odour concentration of up to 3.46 OU/m³ under with Project scenario, the respective improvement would be approximately (14.0 + 2.0 – 3.46) = 12.54 OU/m³. The rounded value of 13 OU/m³ is presented.