This section presents the assessment of potential air quality impacts associated with the construction and operation phases of the Project. Dust generated from construction activities is the major source of air pollution during the construction phase, whereas odour from the sewage treatment plant and sludge generated are the primary concerns during the operation phase.

Representative Air Sensitive Receivers (ASRs) within a study area 500 m from the site boundary have been identified and assessed in accordance with Annex 4 and 12 of the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) as well as the requirements stipulated in Clause 3.4.3 and Appendix B of the EIA Study Brief (ESB-289/2015). Suitable mitigation measures, where necessary, are recommended to protect the nearby ASRs and to ensure that the legislative criteria and guidelines can be satisfied.

3.2 Environmental Legislation, Standards and Guidelines

The following legislation and regulations provide the standards and guidelines for the evaluation of air quality impacts and the type of works that are subject to air pollution control:

● Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) (Environmental Impact Assessment Ordinance (EIAO) (Cap. 499.S16), EIAO-TM, Annexes 4 and 12;

● Air Pollution Control Ordinance (APCO) (Cap. 311) and the Air Quality Objectives (AQO);

● Air Pollution Control (Construction Dust) Regulation; and

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

3.2.1 Technical Memorandum on Environmental Impact Assessment Process

The criteria and guidelines for evaluating air quality impacts are laid out in Annex 4 and Annex 12 of the EIAO-TM, respectively. Annex 4 stipulates the criteria for evaluating air quality impacts, which include meeting the AQO and other standards established under the APCO, as well as meeting the hourly Total Suspended Particulate (TSP) criterion of 500μg/m³ and the 5-second average odour concentration of 5 odour units (ou/m³). Annex 12 provides the guidelines for conducting air quality assessments under the EIA process, including determination of ASRs, assessment methodology and impact prediction and assessment.

3.2.2 Air Pollution Control Ordinance

The principal legislation for the management of air quality is the APCO. It specifies AQO which stipulate the statutory limits of air pollutants and the maximum allowable numbers of exceedances over specific periods. The AQO are listed in Table 3.1.

Table 3.1: Air Quality Objectives

Pollutant	Averaging time	Concentration (µg/m³)	Number of exceedances allowed
Sulphur Dioxide (SO₂)	10-minute	500	3
Sulphur Dioxide (SO₂)	24-hour	125	3
Respirable suspended particulates (RSP or PM₁₀)	24-hour	100	9
Respirable suspended particulates (RSP or PM₁₀)	Annual	50	N/A
Fine suspended particulates (FSP or PM_2.5)	24-hour	75	9
Fine suspended particulates (FSP or PM_2.5)	Annual	35	N/A
Nitrogen dioxide (NO₂)	1-hour	200	18
Nitrogen dioxide (NO₂)	Annual	40	N/A
Carbon monoxide (CO)	1-hour	30,000	0
Carbon monoxide (CO)	8-hour	10,00	0
Ozone (O₃)	8-hour	160	9
Lead (Pb)	Annual	0.5	N/A
Total Suspended Particulates (TSP) ⁽¹⁾	1 hour	500	0
Odour ⁽¹⁾	5-second	5 odour units (ou)	0

Note: (1) Criteria under the EIAO-TM, not an AQO
N/A Not Applicable

3.2.3 Air Pollution Control (Construction Dust) Regulation

The Air Pollution Control (Construction Dust) Regulation enacted under the APCO defines notifiable and regulatory work activities that are subject to construction dust control, as listed below:

Notifiable Work

1. Site formation

2. Reclamation

3. Demolition of a building

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

5. Construction of the foundation of a building

6. Construction of the superstructure of a building

7. Road construction work

Regulatory Works

1. Renovation carried out on the outer surface of the external wall or the upper surface of the roof of a building

2. Road opening or resurfacing work

3. Slope stabilisation work

4. Any work involving any of the following activities:

a. Stockpiling of dusty materials

b. Loading, unloading or transfer of dusty materials

c. Transfer of dusty materials using a belt conveyor system

d. Use of vehicles

e. Pneumatic or power-driven drilling, cutting and polishing

f. Debris handling

g. Excavation or earth moving

h. Concrete production

i. Site clearance

j. Blasting

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

The Project scope includes construction of superstructures; and is therefore notifiable. The Project also includes: excavation and backfilling and is therefore regulatory.

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

The Air Pollution Control (Non-road Mobile Machinery) (Emission) Regulation controls emission of dust from non-road vehicles and regulated machines to be used in construction sites. The regulated machines must comply with the emission standards of Stage IIIA of the European Union (EU) or the equivalent, while non-road vehicles must comply with the prevailing emission standards for newly registered road vehicles, which is Euro V. Upon confirmation of their compliance with emission requirement, EPD will issue them with an approval label.

According to the regulation, mobile machine and equipment (regulated machines) means any mobile machine or transportable industrial equipment that is powered by an internal combustion engine with a rated engine power output that is greater than 19 kW but not greater than 560 kW. Non-road Mobile Machinery (NRMM) is intended to be used in a private road that is within an area wholly or mainly used for the carrying on of construction work/industry. The regulated machines include crawler cranes, excavators, etc., while non-road vehicles include private cars goods vehicles, etc. Therefore, this regulation is applicable to the regulated machines and NRMM to be deployed for construction activities of the Project.

3.3 Study Area

3.3.1 Local Environment and Study Area Description

The proposed effluent reuse facility will be entirely underground and located at the basement level within the proposed sewage treatment plant (STP), inside the Comprehensive Development at Wo Shang Wai, Yuen Long (WSW Development). The WSW Development is designated as “OU(CDWRA)”, which stands for “Other Specified Uses (Comprehensive Development to include Wetland Restoration Area)” under the approved Mai Po & Fairview Park Outline Zoning Plan (S/YL-MP/6). It is bound by Castle Peak Road – Mai Po and San Tin Highway to the east, fish ponds to the north, Wo Shang Wai Village to the south-west, and residential developments such as Royal Palms and Palms Spring to the south. The location of the Project is shown in Figure 2.1.

3.3.2 Background Air Quality

Existing air quality in the 500m Study Area is mainly affected by the traffic flow along major roads near the Project Area such as Castle Peak Road and San Tin Highway to the east of the site. In accordance with the wind data obtained from the nearest wind monitoring station at Lau Fau Shan, the prevailing wind direction was easterly (070 degrees) in year 2016 [1].

With respect to background air quality, the closest EPD general air quality monitoring station located in Yuen Long is referenced. It is noted however that the Yuen Long monitoring station is situated in an urban area surrounded by existing road networks whereas the Project is located in a rural area. Given the differing nature of both locations, the background air quality at the general air quality monitoring station is presented as a conservative indication. Table 3.2 shows the recent five years (2012-2016) monitoring data recorded at the Yuen Long Monitoring Station, which is used as reference to represent the historical background air quality in the Project area. In addition, as part of the on-going EM&A programme for the proposed WSW Development, hourly TSP levels have been recorded at four monitoring locations since 12 May 2010. The four monitoring locations representing the existing sensitive receivers close to the WSW Development are as shown in Figure 3.1. The hourly TSP concentrations measured at these four monitoring locations, which can represent the cumulative TSP impacts due to the construction activities of the proposed WSW Development and other concurrent projects in the vicinity during the monitoring period, are also presented in Table 3.2.

Table 3.2: Historical Air Quality at the Project Area

Pollutant	Averaging Period	Concentration (µg/m³)					Corresponding AQO (µg/m³)
Pollutant	Averaging Period	2012	2013	2014	2015	2016	Corresponding AQO (µg/m³)
Sulphur Dioxide (SO₂)	10 minute - 4^th highest ⁽¹⁾	NM	NM	92	51	58	500
Sulphur Dioxide (SO₂)	24 hour - 4^th highest ⁽¹⁾	29	33	27	17	17	125
Respirable suspended particulates (RSP or PM₁₀)	24 hour - 10^th highest ⁽¹⁾	100	142	124	102	86	100
Respirable suspended particulates (RSP or PM₁₀)	Annual ⁽¹⁾	44	56	50	44	37	50
Fine suspended particulates (FSP or PM_2.5)	24 hour - 10^th highest⁽¹⁾	65	106	86	78	63	75
Fine suspended particulates (FSP or PM_2.5)	Annual⁽¹⁾	29	37	35	30	23	35
Nitrogen dioxide (NO₂)	1 hour - 19^th highest⁽¹⁾	147	183	165	162	149	200
Nitrogen dioxide (NO₂)	Annual⁽¹⁾	49	54	52	45	46	40
Carbon monoxide (CO)	1 hour - 1^st highest⁽¹⁾	2,200	2,690	2,560	2,460	2,080	30,000
Carbon monoxide (CO)	8 hour - 1^st highest⁽¹⁾	1,945	1,950	2,319	2,143	1,474	10,000
Ozone (O₃)	8 hour - 10^th highest⁽¹⁾	NM	NM	177	161	143	160
Lead (Pb)	Annual ⁽¹⁾	NM	NM	0.035	0.029	*	0.5
Total Suspended Particulates (TSP)	1 hour - range	62-272	65-284	51-280	32-211	30-288⁽²⁾	500⁽³⁾

Notes:
(1) Data extracted from EPD’S Air Quality in Hong Kong Reports for Annual Air Quality Monitoring Result (2012-2016) for Yuen Long Monitoring Station
(2) Hourly TSP levels obtained from the EM&A data recorded for the WSW Development from Jan 2016 to Feb 2018
(3) EIAO-TM criterion, not an AQO
NM Not Measured

*: No data is available in 2016 Statistical Summary.
Monitoring results that exceeded prevailing AQO criteria are shown in bold characters.

Table 3.2 shows that the historical background concentrations for hourly NO₂ and daily SO₂ complied with their respective AQO in all the past 5 years and the hourly TSP levels recorded at the proposed WSW Development are well below the EIAO-TM criterion throughout the monitoring period. The historical daily background levels for RSP and FSP as well as the annual background NO₂ levels, however, exceeded their corresponding AQO in most or all of the 5 past years. For the historical annual RSP and FSP levels, they exceeded their corresponding AQO in 2013.

The predicted future background air pollutant concentrations at the Project area can be extracted from the relevant grids of the PATH-2016 model (for year 2020), as summarised in Table 3.3.

Table 3.3: Future Background air quality from PATH-2016 for year 2020

Pollutant	Averaging Period	Average Concentration (µg/m³) at relevant PATH-2016 grids		Corresponding AQO (µg/m³)
Pollutant	Averaging Period	(28,51)	(28,52)	Corresponding AQO (µg/m³)
Respirable Suspended Particulate (RSP or PM₁₀)	Daily - 10^th highest	81.0	83.0	100
Respirable Suspended Particulate (RSP or PM₁₀)	Annual	34.1	35.3	50
Fine Suspended Particulate (FSP or PM_2.5)	Daily - 10^th highest ⁽¹⁾	60.7	62.2	75
Fine Suspended Particulate (FSP or PM_2.5)	Annual ⁽²⁾	24.2	25.1	35
Nitrogen Dioxide (NO₂)	Hourly – 19^th highest	88.9	91.9	200
Nitrogen Dioxide (NO₂)	Annual	15.6	17.1	40

⁽¹⁾ The daily FSP levels are conservatively estimated by multiplying daily RSP levels, predicted by PATH-2016, by a factor of 0.75, according to EPD’S Guidelines on the Estimation of PM_2.5 for Air Quality Assessment in Hong Kong.

⁽²⁾ The annual FSP levels are conservatively estimated by multiplying annual RSP levels, predicted by PATH-2016, by a factor of 0.71, according to EPD’S Guidelines on the Estimation of PM_2.5 for Air Quality Assessment in Hong Kong.

It can be seen from Table 3.2 and Table 3.3 that while the historical background daily/annual RSP and FSP levels exceeded their respective corresponding AQO in some of the past 5 years, the future background levels for RSP and FSP are below their corresponding AQOs in 2020. The improvement in future ambient air quality can be attributed to the government’s commitment to implementing the various planned emission reduction measures, as published on EPD website ^[2]. It is also noted that an improvement would be expected since the historical background levels are obtained from EPD’s new town Yuen Long monitoring station, whereas the future background levels extracted from PATH-2016 are for over the rural Project area.

3.3.3 Key Pollutants of Concern

As presented in Section 3.2, under the APCO, AQO are stipulated for seven major air pollutants, namely, sulphur dioxide (SO₂), respirable suspended particulates (RSP), fine suspended particulates (FSP), nitrogen dioxide (NO₂), carbon monoxide (CO), ozone (O₃) and lead (Pb) and the EIAO-TM specifies criteria for two parameters, namely total suspended particulates (TSP) and odour. During the construction phase the Project site will have dust emitting activities and potential odour impact from the excavation of sediment. Potential odour may also result from the proposed STP for reclaimed water reuse during the operation phase. Each of the nine pollutants of concern have been reviewed for their relevance to the Project as follows:

Sulphur Dioxide (SO₂)

According to the “2015 Hong Kong Emission Inventory Report” published by EPD in April 2017, 59% of total SO₂ emission in Hong Kong in 2015 is attributed to navigation whereas only below 1% of the total emission is due to road transport. The introduction of ultra-low sulphur diesel for vehicle fleet in 2000 has helped in reducing the SO₂ emission from road transport in Hong Kong. No significant sources of sulphur dioxide emitted from the Project, therefore it is not considered as key air pollutant for air quality impact assessment for this Project, though it is one of the criteria pollutants under the AQO.

Respirable Suspended Particulates (RSP)

According to the “2015 Hong Kong Emission Inventory Report” published by EPD in April 2017, navigation and non-combustion sectors were the top two sources of RSP emissions, accounting for 34% and 17% of total RSP emissions in 2015, respectively. In addition, as can be calculated from Table 3.2, the latest 5-year annual average RSP concentration at Yuen Long Station is about 46.2 μg/m³, which is 92% of the corresponding AQO. As the Project is expected to produce construction dust, RSP has been identified as a key air pollutant of concern during the construction phase of this Project. It is also noted that RSP is one of the criteria pollutants under the AQO.

Fine Suspended Particulates (FSP)

According to the “2015 Hong Kong Emission Inventory Report” published by EPD in April 2017, major sources of FSP include non-combustion such as construction activities. FSP is a finer component of RSP. As the Project is expected to produce dust during the construction phase, FSP has been identified as a key air pollutant of concern during the construction phase of this Project.

Nitrogen Dioxide (NO₂)

According to the “2015 Hong Kong Emission Inventory Report” published by EPD in April 2017, navigation, public electricity generation and road transport are the top three major sources of nitrogen oxides (NOx) generated in Hong Kong, constituting respectively about 37%, 28% and 18% of the total NOx emission in 2015. NOx is transformed to NO₂ in the presence of O₃ under sunlight. As there are no significant sources of nitrogen dioxide emitted from the Project, nitrogen dioxide is not identified as a key air pollutant for air quality impact assessment for this Project, though it is one of the criteria pollutants under the AQO.

Carbon Monoxide (CO)

According to the “2015 Hong Kong Emission Inventory Report” published by EPD in April 2017, road transport and navigation are the top two major sources of CO emissions in Hong Kong, contributing to respectively about 51% and 23% of the total CO emission in 2015. However, based on the “Air Quality in Hong Kong 2016” published by EPD, the highest 1-hour average (3,130 µg/m³) was recorded in Causeway Bay roadside station and the highest 8-hour average (2,339 µg/m³) was recorded at Tsuen Wan general station, and both were well below the respective AQO limits. Given that the ambient CO levels are well below the relevant AQO with large margins, CO is not identified as a key air pollutant for air quality impact assessment for this Project.

Ozone (O₃)

Ozone is a major constituent of photochemical smog. It is not a pollutant directly emitted from man-made sources but formed by photochemical reactions of primary pollutants such as NOx and volatile organic compounds (VOCs) under sunlight. As it takes several hours for these photochemical reactions to take place, ozone recorded in one place could be attributed to VOC and NOx emissions from places afar. Hence, ozone is a regional air pollution problem. In other words, unlike air pollutants such as NOx and RSP, ozone is not a pollutant directly attributable to emissions from nearby road traffic. As a result, ozone is not identified as a key air pollutant for air quality impact assessment for this Project, though it is one of the criteria pollutants under the AQO.

Lead (Pb)

Since leaded petrol was banned in Hong Kong on 1 April 1999, it is no longer considered as a primary source in Hong Kong. According to the “Air Quality in Hong Kong 2016” published by EPD, the ambient lead concentrations continued to linger at very low levels during 2016 as in previous years, and the overall annual averages, ranging from 14 ng/m³ (at Central/Western) to 20 ng/m³ (at Yuen Long and Tuen Mun), were well below the AQO limit of 500 ng/m³. Therefore, it is not considered as a key air pollutant for the operation phase air quality impact assessment.

Total Suspended Particulates (TSP)

As the project is expected to produce construction dust, TSP has been identified as a key pollutant of concern for assessment, together with RSP and FSP.

Odour

As the excavation works of the Project are expected to encounter sediment, odour may potentially be generated during the construction of the Project. During the operation phase, air quality impacts would be attributed to potential odour emission from the proposed STP. Therefore, odour has been identified as a key parameter of concern during both the construction and operation phases of this Project.

Identified Key Air Pollutants

Based on the above review results, the following key air pollutants of concerns are identified for the purpose of air quality impact assessment of the Project:

1. For construction phase – TSP, RSP, FSP and Odour; and

2. For operation phase – Odour.

3.3.4 Air Sensitive Receivers

Representative Air Sensitive Receivers (ASRs) within 500m of the site boundary have been identified through site inspections and a review of land use plans, according to the criteria set out in the EIAO-TM. ASRs and their horizontal distances from the Project site are summarized in Table 3.4. Locations of the existing and planned ASRs are shown in Figure 3.1.

Table 3.4: Location of Representative Air Sensitive Receivers

ID	Description	Usage	Construction Phase	Operation Phase	Horizontal Distance from the Project site boundary (m)	Horizontal Distance from the Proposed STP Vent
ASR1	Royal Palms	Rs(E)	ü	ü	approx. 23m	approx. 46m
ASR2A	Palm Springs	Rs(E)	ü	ü	approx. 59m	approx. 556m
ASR2B_1	Palm Springs	Rs(E)	ü	ü	approx. 10m	approx. 291m
ASR2B_2	Palm Springs	Rs(E)	ü	ü	approx. 10m	approx. 305m
ASR3	Wo Shang Wai	Rs(E)	ü	ü	approx. 50m	approx. 395m
ASR4	Village House of Mai Po San Tsuen	Rs(E)	ü	ü	approx. 118m	approx. 329m
ASR4A	Village House of Mai Po San Tsuen	Rs(E)	ü	ü	approx. 54m	approx. 290m
P1	Proposed WSW Development - Residential block	Rs(P)	û	ü	Not applicable	approx. 26m
P2	Proposed WSW Development - Clubhouse associated facilities	Rc(P)	û	ü	Not applicable	approx. 31m
P3	Proposed WSW Development - Clubhouse associated facilities	Rc(P)	û	ü	Not applicable	approx. 45m
P4	Proposed WSW Development - Residential block	Rs(P)	û	ü	Not applicable	approx. 58m

Legend: ü - included in the assessment; û- not included in the assessment
Rs(E) – Existing Residential
Rs(P) – Planned Residential
Rc(P) – Planned Recreational

3.3.5 Cumulative Impacts

The proposed construction programme for the Project is scheduled to commence in Q3 2018, for completion and operation by 2021. Upon availability of public sewerage network, the Project will be decommissioned, which will take approximately 4 months. The concurrent projects that may have cumulative effects during the various phase of the Project include:

Table 3.5: Summary of Concurrent Projects

Concurrent Project	Anticipated Works Period	Possible Cumulative Impact
Comprehensive Development at Wo Shang Wai, Yuen Long (WSW Development)	Q2 2010 – Q1 2021	Yes – dust emissions from the construction of the project
Hong Kong Section of Guangzhou-Shenzhen-Hong Kong Express Rail Link (XRL)	Q1 2010 – Q3 2018*	No
Planned Ngau Tam Mei public trunk sewer at Castle Peak Road (Yuen Long and Kam Tin Sewerage and Sewage Disposal)	Under planning & design	Yes – dust emissions and potential odour emissions from the construction of the project

Note:
* Only the works area of Mai Po Ventilation Building (MPVB) proposed under the XRL Project is located within 500m of the Project site boundary and would hence have potential concurrent impact. Based on on-site observation, the construction of the MPVB structure has been completed in 2014. It is therefore anticipated that no cumulative dust impact would arise from the construction of the Project.

3.4 Air Quality Impact Assessment Methodology

3.4.1 Construction Phase

Activities anticipated during the construction phase that could potentially give rise to fugitive dust emissions include earth moving, transfer of dusty material and construction of the superstructure of the STP building, etc. Other potential sources of air quality impacts may include exhaust emissions from construction vehicles and potential odour generated from the excavation of sediment.

Clause 3 (ii) of Appendix B of the EIA Study Brief (ESB-289/2015) for the proposed Project states that a quantitative assessment shall be carried out to evaluate the construction dust impact at the identified ASRs if it is anticipated that the Project will give rise to significant construction dust impact likely to exceed recommended limits in the EIAO-TM at the ASRs within 500 m from the Project boundary despite the incorporation of dust control measures. Fugitive dust impacts are anticipated to be short-term and could be controlled with the mitigation measures presented in Section 3.6.1. As reviewed in Section 3.3.2, the environmental monitoring and audit (EM&A) data recorded for the WSW Development at the Project site shows no exceedances of the hourly TSP criterion. Therefore, a qualitative assessment of the dust impact is carried out.

3.4.2 Operation Phase

During operation phase, it is anticipated that the ASRs would be subject to potential odour impacts due to the following proposed and existing odour emission sources within the 500m Study Area are:

● the proposed STP;

● sludge generated at the proposed STP;

● existing STP serving Royal Palms residential development;

● existing STP serving Palm Springs residential development; and

● potential odour emissions from the construction of the planned Ngau Tam Mei public trunk sewer at Castle Peak Road.

Clause 4 (ii) of Appendix B of the EIA Study Brief (ESB-289/2015) for the proposed Project states that a quantitative assessment shall be carried out to evaluate the operation phase air quality impacts at the identified ASRs if it is anticipated that the Project will give rise to significant air quality impacts likely to exceed recommended limits in the EIAO-TM at the ASRs despite the incorporation of proposed control/ mitigation measures. As the proposed STP will be fully enclosed and is not of a large scale, the potential odour impact is expected to be minor. In addition, it is anticipated that the operation phase air quality impacts could be controlled with the mitigation measures presented in Section 3.6.2. Therefore, a qualitative assessment of the operation phase air quality impacts is carried out.

3.5 Evaluation and Assessment of Air Quality Impacts

3.5.1 Construction Phase

Fugitive dust emissions

The proposed STP is a 1-storey high building structure with the proposed effluent reuse facility located in the basement of the building, and the footprint of the building is about 225 m². Given the small scale and localized nature of the building construction works together with implementation of the mitigation measures as recommended in Section 3.6.1, the potential construction phase dust emission is anticipated to be short-term and not significant. While the associated works of the Project which will mainly involve laying of piping for the effluent reuse facility will spread over the entire WSW Development site, the required earthworks will be minor with insignificant dust emissions.

The extent of the STP building construction works for the proposed Project represent only a small part of the proposed WSW Development. The construction programme for the Project is expected to overlap with the construction of the proposed WSW Development in Q3 2018 to 2021. The cumulative impact however is expected to be limited given the small scale and localized nature of the STP building construction works.

Based on the information provided by the Drainage Services Department (DSD) and EPD, a gravity trunk sewer will be provided along Castle Peak Road between Ngau Tam Mei and San Tin under PWP Item 235DS. This has been assessed in a separate EIA report for “Yuen Long and Kam Tin Sewerage and Sewage Disposal Stage 2” (EIA Application No. EIA-094/2004). The tentative construction period mentioned in the EIA was from 2009 to 2012, however, the latest status of the implementation programme of the public trunk sewer has yet to be confirmed, and the construction has not yet commenced. While it is uncertain at this stage whether construction of the public trunk sewer would overlap with that of the proposed Project, this concurrent project is far away (over 200m) from the Project Area and proper mitigation measures have been proposed in the EIA study. As such, the cumulative impact that can be caused by this concurrent project is anticipated to be insignificant.

Another concurrent project identified within the 500m Study Area is the construction of the Mai Po Ventilation Building (MPVB) and the associated railway section of the XRL with part of the works area encroached in the WSW development. However, based on on-site observations, the construction of the MPVB structure appears to have been largely completed in 2014 and therefore no cumulative dust impact arising from the construction of the Project is anticipated since then.

An EM&A programme is currently being undertaken for the proposed WSW Development to monitor the dust impacts associated with its construction to ensure no adverse impacts on the adjacent ASRs and to verify the effectiveness of the dust control measures. The historical EM&A findings since its commencement are summarised in Table 3.2. The measured hourly TSP concentrations ranged from 30 to 456 μg/m³ during the monitoring period from May 2010 to February 2018, which are all below the EIAO-TM criterion of 500 μg/m³. Since March 2011, the hourly TSP levels were in a lower range of 30 to 288 μg/m³, which are well below the EIAO-TM criterion. A number of these readings were taken whilst site formation works were being conducted and other concurrent projects such as the construction of the MPVB were still underway, hence representing the short-term cumulative construction dust levels at the nearby ASRs due to the proposed WSW Development and other concurrent projects. Hence, it is anticipated that with proper implementation of the recommended control measures as detailed in Section 3.6.1 the TSP, RSP and FSP levels at all the identified ASRs would be in compliance with the relevant criteria during the construction phase of the Project.

Construction vehicle and machine emissions

Given the small scale of construction works for the Project and with the enforcement of the Air Pollution Control (Non-road Mobile Machinery) (Emission) Regulation, the regulated machines and non-road vehicles must comply with the relevant emission standards. Therefore, the particulates, SO₂ and NO₂ emissions from these machines and vehicles should be limited and will not be significant. It is anticipated that emissions from these machines are small and would not result in exceedances of the relevant AQOs at the identified ASRs.

Potential odour impact from excavation of sediment

As indicated in the Waste Management Implications section, Chapter 6, approximately 800m³ of sediment will be excavated from the Project site during the construction phase. As described above, the proposed STP is a 1-storey high building structure with the proposed effluent reuse facility located in the basement of the building, and the footprint of the building is about 225 m². Given the small scale and localized nature of the building construction works, potential odour nuisance to the surrounding environment would be avoided by following control measures as recommended in Section 3.6.1.3. Hence, with proper measures, potential odour impact is considered to be short-term and controllable.

3.5.2 Operation Phase

Odour emission from proposed interim on-site sewage treatment plant

The proposed STP will serve the WSW Development until the commissioning of the public gravity trunk sewer that is planned along Castle Peak Road. It will adopt Membrane Bioreactor (MBR) technology with UV disinfection system and the effluent generated from the STP will be fully reused at the WSW Development for toilet flushing and irrigation of landscaped areas. Upon commissioning of the public trunk sewer, the sewage from the proposed development will be connected to the public sewerage system as a long-term measure. The STP will then be decommissioned but not demolished.

The proposed housing development for the WSW Development is anticipated to be occupied by 2021. It will consist of a 400-unit proposed development, with a design population intake of 1,245 persons, for which all the sewage generated is expected to be treated and re-used on-site. The design average dry weather flow (ADWF) of the proposed STP will be 482m³/day as presented in Section 5.5.2.1.

The proposed STP and associated effluent reuse facility will be housed indoors with full enclosure and maintained at negative pressure. The STP will be designed with an inlet chamber and wet well which will be located underground and enclosed by airtight cover. A high-efficiency deodorizer (with at least 99.5% odour removal efficiency) with a forced ventilation system will also be installed at the STP building to remove odour before discharge into open air. In addition, discharge point of the proposed STP will be directed away from nearby ASRs. The dewatered sludge of the STP will be loaded onto a truck at underground level for off-site disposal. Details of the odour containment and control measures for the STP are presented in Section 3.6.2.

The potential odour impacts due to the proposed STP has been reviewed by making reference to the approved EIA report of Expansion of Sha Tau Kok Sewage Treatment Works (STKSTW) (EIA Register No.: AEIAR – 207/2017). The sewage treatment technology and the sludge handling approach of the proposed STP for WSW Development is similar to that of the STKSTW in terms of odour generation activities. According to the approved EIA report for STKSTW, the odour control measures of the proposed STKSTW are similar to those of the proposed STP for WSW Development, as exemplified below:

● Enclosure of the major process equipment inside building structure, which is equipped with ventilation system to ensure adequate air exchange within the structure (in other words, maintaining negative pressure inside the structure);

● MBR system equipped with deodorizer (at least 99.5% odour removal efficiency) for treating odorous emissions;

● Regular maintenance of the deodorizer to ensure the odour removal efficiency is maintained at/above the design requirement; and

● Locating the exhausts of deodorization facilities away from the nearby ASRs.

The design ADWF of the STKSTW is 5,000m³/day, which is more than 10 times of the design ADWF of the proposed STP (i.e. 482m³/day). It is therefore considered as a conservative approach to review the potential odour impacts due to the proposed STP by making reference to the odour impact assessment findings of the approved EIA report for STKSTW.

According to Table 3-3 of the approved EIA report for STKSTW, the shortest separation distance between the nearest ASR (i.e. A8) and site boundary of the proposed STKSTW is 20m. The predicted 5-second odour concentrations at the ASR A8 would be in the range of 0.03OU to 0.13OU at the heights of 1.5m to 10.5m above ground (Table 3.7 of the approved EIA report for STKSTW refers), which are well below the odour criterion of 5OU. As presented in Table 3.4 above, the shortest horizontal distance between the nearest ASR (i.e. P1) and the proposed ventilation exhaust of the STP is approximately 26m, and the approximate height of ASR P1 is 8m above ground. Given that the STKSTW is of similar design to the proposed STP but the design ADWF of STKSTW is over 10 times of that of the proposed STP; and that the nearest ASR A8 assessed in the approved EIA for STKSTW is of similar distance and height to those of the nearest ASR P1 in this EIA, the potential odour level at the nearest ASR P1 due to the proposed STP would be conservatively comparable to those predicted at the ASR A8 due to the STKSTW, i.e., well below the odour criterion of 5OU. In other words, with the scale of the proposed STP and with the appropriate odour containment and control measures in place to confine and reduce the potential odour emissions at sources, it is anticipated that adverse odour impact due to the proposed STP is not expected.

Cumulative odour impact from existing and planned odour emission sources

There are two existing private STPs serving Royal Palms and Palm Springs residential developments, which are respectively about 200m and 250m from the Project Area. According to the approved EIA for the proposed WSW Development (EIA Register No.: AEIAR-120/2008), site walks conducted near these two STPs detected no sewage odour. Moreover, based on the information provided by EPD no odour complaints related to the two existing private STPs were received by EPD in the last 5 years (2012 to 2016). As reviewed in the previous paragraphs, there would not be significant odour impact due to the proposed STP on the nearby ASRs. As a result, the odour impacts caused by the two existing STPs are minor, and thus unacceptable cumulative odour impact is not anticipated.

The implementation programme for the planned Ngau Tam Mei public trunk sewer at Castle Peak Road is uncertain since it is currently under the planning and design stage. However, it is assumed that the public trunk sewer will be designed in accordance with the relevant standards and guidelines published by DSD. With appropriate sewage septicity management and ventilation/ odour control, no adverse odour nuisance from the new sewerage system is expected and therefore unacceptable cumulative odour impact is not anticipated.

3.5.3 Decommissioning Phase

Upon implementation of the public trunk sewer, the proposed STP will be decommissioned, but the structures will be retained in-situ and will not be demolished. Hence no adverse air quality impacts on the surrounding ASRs are anticipated during the decommissioning phase of the Project.

3.6 Mitigation Measures

3.6.1 Construction Phase

3.6.1.1 General Practices for Dust Control

It is recommended that the following dust mitigation measures are implemented to maintain dust emissions at acceptable levels during the construction phase:

● Any dusty activities should be regularly sprayed with water to maintain damp conditions of the works area.

● Any dusty materials should be covered with tarpaulin or similar material during transportation.

● Any dusty materials stockpiles should be either (i) covered entirely by impervious sheeting; or (ii) sprayed with water.

3.6.1.2 Best Practices for Dust Control

It is recommended that the relevant best practices for dust control as stipulated in the Air Pollution Control (Construction Dust) Regulation should also be adopted to further reduce the construction dust impacts of the Project. These best practices include:

Good Site Management

● Good site management is important to help reduce potential air quality impact down to an acceptable level. As a general guide, the Contractor should maintain high standard of housekeeping to prevent emission of fugitive dust. Loading, unloading, handling and storage of raw materials, wastes or by-products should be carried out in a manner so as to minimise the release of visible dust emissions. Any piles of materials accumulated on or around the work areas should be cleaned up regularly. Cleaning, repair and maintenance of all plant facilities within the work areas should be carried out in a manner minimising generation of fugitive dust emissions. The material should be handled properly to prevent fugitive dust emission before cleaning.

Loading, Unloading or Transfer of Dusty Materials

● All dusty materials should be sprayed with water immediately prior to any loading or transfer operation so as to keep the dusty material wet.

Debris Handling

● Any debris should be covered entirely by impervious sheeting or stored in a debris collection area sheltered on the top and the three sides.

● Before debris is dumped into a chute, water should be sprayed so that it remains wet when it is dumped.

Transportation of Dusty Materials

● Vehicle used for transporting dusty materials/spoils should be covered with tarpaulin or similar material. The cover should extend over the edges of the sides and tailboards.

Wheel washing

● Vehicle wheel washing facilities should be provided at each project site exit. Immediately before leaving the project site, every vehicle should be washed to remove any dusty materials from its body and wheels.

Use of vehicles

● Immediately before leaving the Project site, every vehicle should be washed to remove any dusty materials from its body and wheels.

● Where a vehicle leaving the Project site is carrying a load of dusty materials, the load should be covered entirely by clean impervious sheeting to ensure that the dusty materials do not leak from the vehicle.

Site hoarding

● Where a site boundary adjoins a road, street, service lane or other area accessible to the public, hoarding of not less than 2.4m high from ground level should be provided along the entire length of that portion of the site boundary except for a site entrance or exit.

3.6.1.3 Odour control measures

During excavation works, the following mitigation measures are recommended in order to contain potential odour from excavated sediment:

● all malodorous excavated material should be placed as far as possible from any ASRs;

● the stockpiled malodorous materials should be removed from site as soon as possible; and

● the stockpiled malodorous materials should be covered entirely by plastic tarpaulin sheets.

3.6.2 Operation Phase

For the potential odour impact due to the proposed STP, it is recommended to implement the following measures to contain and mitigate the potential odour impact:

● The STP will be totally enclosed.

● Negative pressure ventilation will be provided within the enclosure to avoid any fugitive odorous emission from the STP.

● Further odour containment will be achieved by covering or confining the sewage channels, sewage tanks, and equipment with potential odour emission.

● Proper mixing will be provided at the equalization and sludge holding tanks to prevent sewage septicity.

● Chemical or biological deodorization facilities with at least 99.5% odour removal efficiency will be provided to treat potential odorous emissions from the STP including sewage channels / tanks, filter press and screening facilities so as to minimize any potential odour impact to the nearby ASRs.

● The deodorization facilities should be regularly maintained so as to ensure at least 99.5% odour removal efficiency.

● The deodorization facilities should be designed such that the discharge point is directed away from nearby ASRs.

3.7 Residual Impacts

3.7.1 Construction Phase

With proper implementation of the recommended mitigation measures, no adverse residual air quality impacts are anticipated for the Project during the construction phase.

3.7.2 Operation Phase

During the operation phase, the potential cumulative odour impacts at all ASRs due to the proposed STP and the two existing STPs serving Royal Palms and Palm Springs are anticipated to be not significant. Hence, no adverse residual air quality impacts are anticipated for the Project during the operation phase.

3.8 Environmental Monitoring and Audit

3.8.1 Construction Phase

With implementation of the recommended mitigation measures, no significant dust impact is expected and regular dust monitoring is therefore not considered necessary during the construction phase of the Project.

3.8.2 Operation Phase

The proposed effluent reuse facility will be entirely underground, enclosed within the STP building and equipped with a high efficiency deodorizer. With proper operation of the STP and proposed effluent reuse facility, no additional mitigation measures are required and hence odour monitoring and audit is considered not necessary during the operation phase.

3.9 Conclusion

3.9.1 Construction phase

Given the small scale and localized nature of the STP building construction works together with implementation of the recommended mitigation measures, no adverse air quality impacts on the surrounding ASRs are anticipated during the construction phase of the Project.

3.9.2 Operation Phase

With proper operation of the proposed STP and effluent reuse facility, as well as the recommended odour containment and control measures in place to confine and reduce the potential odour emissions at sources, adverse odour impacts on the surrounding ASRs are not anticipated.

[1] Hong Kong Observatory, “Summary of Meteorological and Tidal Observations in Hong Kong 2016”, published in August 2017, http://www.hko.gov.hk/publica/smo/smo2016.pdf

[2] http://www.epd.gov.hk/epd/english/environmentinhk/air/prob_solutions/strategies_apc.html