3.1 This section presents an assessment on air quality impacts due to the construction and operation phases of the Project. Potential air quality impacts are expected to be dust nuisance during construction phase and air pollutants emissions from OWTF during operation phase. Appropriate mitigation measures are proposed to alleviate the potential air quality impacts.
Environmental Legislation, Standards and Guidelines
3.2 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.
Air Quality Objectives and
EIAO-TM
3.3 The Air Pollution Control Ordinance (APCO) 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 relevant AQOs are listed in Table 3.1 below.
Table 3.1
|
Pollutant |
Maximum
Concentration (µg m-3) (1) |
|||
|
Averaging Time |
||||
|
1 hour (2) |
8 hour (3) |
24 hour (3) |
Annual (4) |
|
|
- |
- |
260 |
80 |
|
|
Respirable Suspended Particulates (RSP) (5) |
- |
- |
180 |
55 |
|
|
800 |
- |
350 |
80 |
|
Nitrogen Dioxide (NO2) |
300 |
- |
150 |
80 |
|
Carbon Monoxide (CO) |
30,000 |
10,000 |
- |
- |
|
Photochemical Oxidants (as Ozone, O3) (6) |
240 |
- |
- |
- |
Notes:
(1)
Measured at 298 K and 101.325 kPa.
(2)
Not to be exceeded more than three times per year.
(3)
Not to be exceeded more than once per year.
(4)
Arithmetic mean.
(5)
Suspended particulates in air with a nominal
aerodynamic diameter of
(6)
Photochemical oxidants are determined by
measurement of ozone only.
3.4
The EIAO-TM stipulates that the
hourly TSP level should not exceed
3.5 In accordance with the EIAO-TM, odour at an air sensitive receiver should not exceed 5 odour units based on an averaging time of 5 seconds for odour prediction assessment.
Air Pollution Control
(Construction Dust) Regulation
3.6 Notifiable and regulatory works are under the control of Air Pollution Control (Construction Dust) Regulation. Notifiable works are site formation, reclamation, demolition, foundation and superstructure construction for buildings and road construction. Regulatory works are building renovation, road opening and resurfacing, slope stabilisation, and other activities including stockpiling, dusty material handling, excavation, concrete production, etc. This Project is expected to include notifiable works (foundation and superstructure construction) and regulatory works (temporary stockpile, dusty material handling, excavation and concrete production). Contractors and site agents are required to inform EPD and adopt dust reduction measures to minimize dust emission, while carrying out construction works, to the acceptable level.
Air Quality Criteria for Non-criteria
Pollutants
3.7 VOCs, Hydrogen Chloride (HCl) and Hydrogen Fluoride (HF) would be released from the gas engine of the OWTF. In the absence of statutory guidelines in HKSAR for non-criteria pollutants, the chronic and acute criteria (the stringent criteria) from international organizations including United States Environmental Projection Agency (USEPA), California Air Resources Board (CARB) and the Office of Health, Safety and Security, US Department of Energy are employed for the assessment criteria. The air quality criteria for non-AQO pollutants employed for this study are presented in Table 3.2.
Table 3.2 Reference Levels for HCl, HF and VOCs Acute and Chronic Exposure
|
Reference
Level ((mg/m3) |
||
|
(1-hour average) |
Cal/EPA Acute reference
level from Office of Environmental Health Hazards Assessment, |
|
|
(Annual average) |
||
|
(1-hour average) |
Cal/EPA Acute REL http://www.oehha.ca.gov/air/acute_rels/allAcRELs.html |
|
|
(Annual average) |
http://www.oehha.ca.gov/air/chronic_rels/AllChrels.html |
|
|
(1-hour average) |
TEEL-0 (the threshold concentration below which most people will experience no adverse health effects) from Office of Health, Safety and Security, US Department of Energy (http://www.hss.energy.gov/HealthSafety/WSHP/chem_safety/teel.html) |
Description of the Environment
3.8
OWTF is proposed to be located
at Siu Ho Wan of
3.9
The proposed Project Site is in
a predominantly rural area. The
potential air pollutants in the study area would be traffic emission from
3.10 There is no fixed air quality monitoring station near the proposed OWTF site. The nearest EPD air monitoring station is at Tung Chung. The latest five years (2004-2008) average monitoring data recorded at this station are presented in Table 3.3. The background concentrations of VOCs, HCl and HF are not available as EPD air monitoring station has not measured these two parameters.
Table 3.3 Annual Average Concentrations of Air Pollutants in the Latest Five Years (Year 2004 - 2008) at Tung Chung Air Quality Monitoring Station
|
Pollutant |
5-year Annual Average Concentration (mg/m3) |
|
Carbon Monoxide |
837 |
|
Total Suspended
Particulate (TSP) |
70 |
|
Respirable Suspended
Particulate (RSP) |
56 |
|
Nitrogen Dioxide (NO2) |
48 |
|
|
23 |
|
Ozone (O3) |
89(1) |
Notes:
(1)
The latest five years (2004 – 2008) annual average
of daily hourly maximum ozone concentrations recorded at EPD’s Tung Chung Air
Quality Monitoring Station.
3.11 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 air sensitive receivers (ASRs). A total of 6 representative ASRs are identified for this assessment in accordance with the criteria set out in the EIAO-TM. The details of the representative ASRs are summarised in Table 3.4 and its locations are shown in Figure 3.1.
3.12
Referring to the latest outline
zoning plan (OZP), there is no other planned ASRs located within
Table 3.4 Air Sensitive Receivers
|
ASR |
Description |
Land Use |
Distance between ASR and closest work
boundary(m) |
No. of storey |
Ground Level (mPd) |
Assessment Height (mAG) |
|
ASR1 |
Siu
Ho Wan Water Treatment Works |
GIC |
90 |
2 |
28 |
1.5, 4.5 |
|
ASR2 |
Siu
Ho Wan Sewage Treatment Works |
GIC |
196 |
2 |
6.5 |
1.5, 4.5 |
|
ASR3 |
Siu
Ho Wan Vehicle Pound Vehicle Examination Centre and Weight Station |
GIC |
25 |
1 |
6.5 |
1.5 |
|
ASR4 |
Bus
Depot of Kowloon Motor Bus Ltd. |
Industrial |
77 |
2 |
6.5 |
1.5, 4.5 |
|
ASR5 |
Bus
Depot of City Bus Ltd. |
Industrial |
15 |
3 |
6.5 |
1.5, 4.5, 7.5 |
|
ASR6 |
North
Lantau Refuse Transfer Station |
GIC |
385 |
3 |
6.5 |
1.5, 4.5, 7.5 |
Construction Phase
3.13 Major construction works of the Project would be construction of the proposed OWTF. The existing site surface is paved with concrete and at an appropriate level for the construction of the facility. Thus, extensive site formation works would not be required. The major potential air quality impact during construction phase of the Project would be dust arising from:
Ÿ
Minor excavation and materials handling;
Ÿ
Construction of superstructure for the office and storage; and
Ÿ Installation of treatment
facilities.
3.14
The area of the Project Site is
approximately
3.15 As mentioned in Section 2, the HyD’s project “Further Landscape Enhancement Works to North Lantau Highway” would be commenced in May 2010 and ended in November 2012. It would have about six months overlapping with this Project. Since the work area for landscape enhancement works would be limited and the excavated materials generated from this Project is in small amount, no adverse cumulative dust impacts would be anticipated. Two WSD’s projects “Extension of Siu Ho Wan Water Treatment Works” and “Integration of Siu Ho Wan and Silver Mine Bay Water Treatment Works” may be commenced in early March 2013. Since the overlapping with these Projects would be 1 – 2 months and the construction of OWTF would be almost completed at this stage, cumulative dust impact would not be anticipated.
Operational Phase
Potential Air Quality Impact from
Operation of OWTF
Waste Acceptance & Pre-treatment Area
3.16 Organic waste would usually be stored for a period of time prior to its collection. This could allow facultative anaerobic degradation of the organic matters in the waste stream, resulting in the generation of odour. Therefore, the unloading and pre-processing of these wastes at OWTF would likely release odour. The waste reception building will be equipped with unloading bays for bulk waste and will operate under negative pressure. Any air circulating inside will be directed to the centralized air pollution control unit where a biofilter would be installed. Therefore, odour emission is expected to be insignificant.
3.17 As the moisture content of the mixed organic waste would not be low, adverse dust emissions during the unloading process and pre-processing of these wastes are not anticipated. In addition, with dust in the vented air be removed after passing through the scrubber, dust impact from the wastes reception hall and pre-treatment area is anticipated to be insignificant.
Digestion
3.18 Mixed organic waste that has high moisture content would be directed to the digesters for processing. Each digester would be equipped with mixing devices to maintain suitable conditions for microbiological activities. The retention time inside the digester would be approximately 40 days to ensure good degradation and maximize biogas.
3.19 The digestion process would be undertaken in an enclosed system. According to the reference design of OWTF, the produced biogas would be cleaned to remove hydrogen sulphide before converting to energy using gas engine generator sets (cogen units). As provided by the manufacturer, the air pollutant emission levels of cogen units are summarized in Table 3.5 below.
Table 3.5 Standards to be Applied for the Emission Level of Cogen Units
|
Parameter |
Emission
Level (mg//Nm3) (1) |
|
Dust (2) |
<15 |
|
Carbon Monoxide |
100 – 650 |
|
NOx |
100 – 300 |
|
SO2 |
< 50 |
|
VOCs |
<50 – 150 |
|
HCl |
< 10 |
|
HF |
< 1 |
Note: (1) All
values refer to an oxygen content in the exhaust gas of 6% and dry basis.
(2)
Dust means Total Suspended Particulates.
3.20
Biogas is being used as a fuel
for the cogen units. If there is a
failure in the cogen units, biogas (after cleaning) would be flared. To eliminate the production of dioxins
by the flare, the flaring temperature and the residence time would be around
Post-treatment
Process
3.21 After the digestion process, residual materials would be passed through a separator to filter out fibrous material from liquid. Wastewater would be re-circulated in the treatment process, while surplus wastewater would be directed to the wastewater treatment unit. Fibrous material (i.e. digestate) would be transported to the composting plant for stabilization. Dewatering process as well as the wastewater treatment unit would be in an enclosed system. The air exhaust from dewatering process area and wastewater treatment unit will also pass through the centralized air pollution control unit to remove the odour before discharging.
Composting
3.22 Digestate would be directed to composting facilities for processing. Supply of air is required by regular aeration to maintain aerobic conditions. The retention time inside the composting process would be about 2 weeks.
3.23 Excluding odour emissions, composting of fibrous materials may emit gaseous pollutants including non-methane volatile organic carbon (NMVOC), VOCs, NH3 and N2O, while the composting equipment would be enclosed inside the building. Air circulation in the building will pass through the centralized air pollution control unit which can remove gas pollutants, particles and odour before it is discharged.
Centralized
Air Pollution Control Unit
3.24 Referring to the reference design of OWTF, vented air extracting from the main buildings of OWTF, including waste reception and pre-treatment area, temporary storage area for shredded materials and dewatering process area, composting area and storage area, and wastewater treatment unit, will be treated in the centralized air pollution control unit before discharging to the atmosphere. Negative pressure system would be provided for the main buildings of OWTF and wastewater treatment area to avoid escape of odour. The design emission levels of the centralized air pollution control unit are summarized in Table 3.6 as follows.
Table 3.6 Standards to be Applied to the Emission Level of the Centralized Air Pollution Control Unit
|
Parameter |
Emission
Level (mg//Nm3) |
|
VOCs (including NMVOC) |
18 – 680 |
|
Dust (1) |
6 |
|
Odour (including NH3 & H2S) |
300 (2) |
|
N2O |
1 – 31 |
Note: (1) Dust means
Total Suspended Particulates.
(2)
The odour unit is ou/Nm3.
Potential Air Quality Impact from
Waste Collection Vehicles during the Transportation of Organic Waste
3.25 Waste collection vehicles and containers to be used during the transportation of organic waste would be properly designed to prevent ingress of rainwater and leakages of leachate, where robust and corrosion resistant material such as stainless steel or hard wearing plastic would be used. In addition, containers should be well-covered to prevent any escape of odour emission. Together with the carrying out of thorough cleaning process on the waste collection vehicles before leaving the waste collection and sorting worksite, odour emission from the waste collection vehicles along the transportation route is therefore not expected. According to the reference design of OWTF, there would be about 50 trips of enclosed waste collection vehicles travelling to and away from OWTF each day and the opening hours for waste reception would be 14 hours a day. It is anticipated that the peak hour periods for unloading the organic wastes would be in the morning and evening. The projected maximum number of waste collection vehicles arriving at OWTF during the peak hour would be 13 vehicles. OWTF has also allowed area for the vehicle queues. As the containers of the waste collection vehicles should be covered, no adverse odour emission from the waste collection vehicles during their queuing process would be expected.
Potential Cumulative Air Quality
Impact
3.26
Within
3.27
The North Lantau Refuse
Transfer Station (NLTS) is located at about
3.28
Vehicle emissions from the
nearby North Lantau Highway, planned Road P1 and marine emissions from NTLS and
planned Lantau Logistics Park (LLP) (the route within
Construction Phase
3.29 As discussed in Section 3.13, dust impact arising from the construction of the Project is considered to be minimal with effective implementation of the dust suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation. With effective implementation of these mitigation measures, adverse construction dust impacts are not expected at the representative ASRs. Qualitative approach is adopted in the assessment.
Operational Phase
PATH
Modelling
3.30 Pollutants in the Atmosphere and the Transport over Hong Kong (PATH) model is used to quantify the background air quality during operation phase of the Project. The commissioning time of OWTF will be around in mid Year 2013 and is expected to build up to the maximum capacity in Year 2015. In order to determine the worst impact from the operation of OWTF, Year 2015 background level predicted by PATH model is considered in the assessment. The emission sources including those in Pearl River Delta Economic Zone, roads, airport, power plants and industries within Hong Kong are all considered in the PATH model. The emission inventories for the PATH model are established based on the confirmed information and reasonable conservative assumptions. The details of the emission inventories are discussed as below.
(a)
Emissions within Pearl River Delta Economic Zone (PRDEZ)
3.31
The Study of Air Quality in the
Pearl River Delta Region conducted in Year 2000 had recommended various
mitigation strategies to control and improve the regional air quality
problems. In December 2003, the
governments of Hong Kong Special Administrative Region (HKSAR) and
3.32 A Mid-term Review Study on Pearl River Delta Regional Air Quality Management Plan was commissioned by EPD of HKSAR Government and the Guangdong Environmental Protection Bureau (GPEPB) in November 2006 to update the regional pollutant emission for 2003 and 2010 Control Scenario, as well as to review the effect of control measures committed by the governments.
3.33
In addition, the
3.34 In accordance with the Final Report for Review of Air Quality Objectives and Development of a Long Term Air Quality Strategy for Hong Kong Feasibility Study (AQO Review Report), Year 2015, 2020 and post-2020 emission inventories are developed based on the above emission data. Year 2015 inventory, which is estimated based on the interpolation from the emission inventory for Year 2010 from the Mid-Term Review and the Year 2020 inventory compiled from 珠江三角洲環境保護規劃, is the highest emission inventory among three scenarios. As stated in S3.30, the operation of OWTF is expected to build up to the maximum capacity in Year 2015. Therefore, Year 2015 emission inventory as presented in the AQO Review Report considered in the PATH model is reasonable.
(b)
Emissions from
3.35
The emissions from the
operation activities at the
3.36 In accordance with the Hong Kong - Zhuhai - Macao Bridge Hong Kong Boundary Crossing Facilities (HKBCF) EIA Report, the emission inventory for aircraft movements were estimated based on the full operation capacity of the airport by Year 2020. The emission from GSE and APUs would be capped from 2020 onwards. The emissions from engine run-up facility and fuel tanks were also estimated based on the conservative assumptions. Therefore, as a conservative approach, Year 2020 emission inventories for the operation activities at the Hong Kong International Airport as adopted in the HKBCF EIA study are used in the PATH model for this study.
(c)
Emissions from Power Stations within HKSAR
3.37 In accordance with the annual reports from the power stations in HKSAR, they have plans to increase the utilisation of natural gas to 50% by Year 2015. As stated in S3.30, the operation of OWTF is expected to build up to the maximum capacity in Year 2015. It is therefore reasonable to assume that, by the time of operation of the Project, the utilisation rate of natural gas within HKSAR should have reached 50%. The emission inventories for the power stations within HKSAR adopted in the PATH model are based on this assumption.
(d)
Industrial
Sources within HKSAR
3.38 The emissions from other industrial sources have also been considered in the PATH model. As the OWTF is expected to be operated in full capacity in Year 2015, estimation has been made by projecting from the emission level for 2010 in the Mid-Term Review to the emission level for Year 2015.
3.39 Other specific emission sources have been updated based on their respective best available information. The specific industrial emission sources within HKSAR including Ecopark, Sludge Treatment Facilities, Green Island Cement Facilities, Existing WENT Landfill and its Extension and Shiu Wing Steel Mill are also considered in the PATH model and their emissions are based on the full capacity of their operation. Their emissions inventories are make reference to the approved EIA Reports and their Specified Process Licence.
(e)
Marine Emissions within HKSAR
3.40 The emissions from marine emission within HKSAR have also been considered by making reference to 2030 emission inventory (without implementation measure) as mentioned in the AQO Review Report. Due to natural growth, the marine traffic in Year 2030 should be higher than Year 2015. The adoption of Year 2030 emission inventory is considered as conservative approach. In addition, the emissions of the proposed CT10, made reference to the Study on Hong Kong Port – Master Plan 2020 – Final Strategic Environmental Assessment – Part 2 (Port 2020 Study), are also included in the model.
(f)
Vehicular Emissions within HKSAR
3.41
The vehicular emissions within
HKSAR are predicted using EPD’s EMFAC-HK model which takes into account the
exhaust technology, number of trips, different vehicle classes, different speed
fraction etc of the entire
3.42 The vehicular traffic flow is made reference to territory-wide traffic forecast. As a conservative approach, emissions from Year 2031 traffic flow of Tuen Mun – Chek Lap Kok Link, Hong Kong-Zhuhai-Macao Bridge and the roads on Lantau (including North Lantau Highways and Road P1) are considered in the model. With reference to the AQO Review Report, the worse-case at 2015 for major vehicular air pollutants for other roads within HKSAR is adopted for PATH model. As mentioned in S3.30, the OWTF is expected to be in full capacity in Year 2015, the adoption of Year 2015 traffic flow for other roads are expected to be reasonable..
3.43 The emissions from other emission sources (e.g. non-road mobile sources, VOC containing sources etc) within HKSAR have also been considered by making reference to 2030 emission inventory (without implementation measure) as mentioned in the AQO Review Report. Year 2030 emission inventory is expected to be higher than in Year 2015 as there is a positive growth factor in the forecast data.
Emissions
from Centralized Air Pollution Control Unit
3.44
Centralized air pollution
control unit would be used to remove air pollutants, dust and odorous gas in
the air extracted from the main buildings of OWTF and the wastewater treatment
unit. The design emission rates of
the centralized air pollution control unit as stated in Table 3.6 are derived from experiences in the similar plants in
Table 3.7 Emission Level of Centralized Air Pollution Control Unit
|
Parameter |
Emission
Level (mg//Nm3) |
|
VOCs (including NMVOC) |
680 |
|
RSP (1) |
6 |
|
Odour(including NH3 & H2S) |
300 (2) |
Note: (1) Dust
emission levels are considered as RSP in the assessment.
(2)
The odour unit is ou/Nm3.
Emissions
from Cogen Units /Flaring Emission (Biogas)
3.45 The design emission levels for cogen units of OWTF are based on the manufacturing data, which are making reference to the design in Germany plants, are practically achievable. As a conservative approach, the dust emissions are all considered as RSP emissions in the assessment. Based on the preliminary design, the stack height of cogen units would be 8m above ground level with a diameter of 0.5m. The discharge temperature of flue gas would be 733K and the efflux velocity would be 15m/s. The maximum concentration of pollutants from the cogen units (listed in Table 3.5) adopted for the assessment are summarized in Table 3.8 below.
Table 3.8 Emission Level of Cogen Units
|
Parameter |
Maximum
Emission Level (mg//Nm3) (1) |
|
RSP(2) |
15 |
|
Carbon Monoxide |
650 |
|
NOx |
300 |
|
SO2 |
50 |
|
VOCs |
150 |
|
HCl |
10 |
|
HF |
1 |
Note: (1) All
values refer to an oxygen content in the exhaust gas of 6% and dry basis.
(2)
Dust emission levels are considered as RSP in the assessment.
3.46
As mentioned in Section 3.20,
if there is a failure in the cogen units, the produced biogas would be flared
in a high temperature (
Table 3.9 Emission Level of Flaring Gas System
|
Parameter |
Maximum
Emission Level (mg//Nm3) (1) |
|
RSP(2) |
5 |
|
Carbon Monoxide |
100 |
|
NOx |
200 |
|
SO2 |
50 |
|
VOCs |
20 |
|
HCl |
10 |
|
HF |
1 |
Note: (1) All
values refer to an oxygen content in the exhaust gas of 11% and dry basis.
(2)
Dust emission levels are considered as RSP in the assessment.
3.47 In accordance with the engineering design, the cogen units and the flaring gas system would not be operated simultaneously. The maximum emission levels of all air pollutants from cogen units are higher than or equivalent to that from the flaring gas system. For the study of the worst air quality impact from operation of OWTF, the impacts from operation of the cogen units and the standby flaring gas unit are considered in the assessment, respectively. The details of the emission data from OWTF are presented in Appendix 3.1. The assessment results for comparing the air quality impact between the cogen units and the standby flaring gas unit are presented in Appendix 3.6.
Emission
Inventory for Other Sources
Vehicle
Emissions from the
3.48
The vehicular emissions impact assessment
is based on the projected peak hour flows for the worst year within 15 years of
commencement of operation of OWTF, i.e. Year 2028. Vehicle emissions from the North Lantau
Highways and planned Road P1 within
Marine
Emissions within
3.49
Emissions from marine vessels
of NLTS and planned LLP travelling within
Odour
Emissions from Siu Ho Wan Sewage Treatment Works
3.50
As mentioned in Section 3.26,
the potential odour emissions sources would be flocculation tank, primary
sedimentation tanks and exhausted gases from the deodorizing units for Screen
House, Flash Mixer, Sludge Dewatering House,
Odour Emissions from North Lantau
Refuse Transfer Station (NLTS)
3.51 As there is no emission data available for NLTS, the emission rate of tipping face at the landfill, making reference to the approved EIA Report for West New Territories (WENT) Landfill Extension – Feasibility Study, is assumed as emissions from the vent of the tipping hall of NLTS. The emissions from NLTS are litters and its characteristics are similar to the rubbish disposed at the tipping face of the landfill. Air scrubber system is provided for treatment of the exhausted gases from the tipping hall of NLTS before discharging into the atmosphere. The emission rate of tipping face at the landfill should be higher than that of treated gases emitted from the tipping hall of NLTS. Therefore, it is a conservative assumption in the assessment. The detail emission rate and stack parameters of NLTS adopted in the assessment refer to Appendix 3.4.
Meteorological
Data
3.52 The Mesoscale Model 5 (MM5) meteorological data has been extracted from the PATH model and the hourly values for atmospheric stability from meteorological surface observations are calculated by PCRAMMET for use in the CALINE4 and ISCST3 modelling.
3.53 The study area of OWTF is at Grids (14,25), (14,26), (15,25) and (15,26). Raw MM5 meteorological data was extracted from these grids for the Project. The hourly stability class from the PCRAMET output files are used for CALINE4 and ISCST modelling. The details of the meteorological conditions to be used in the models are presented as follows:
CALINE4 Model
l Wind Speed: hourly wind speed from MM5 meteorological data;
l Stability Class: hourly data from PCRAMMET output file;
l Wind direction: hourly data from MM5 meteorological data;
l Surface roughness: 100 cm for the study area
l Directional variability: calculated according to the stability class in PCRAMMET output file; the standard deviation of wind direction (sA) for stability classes A to G are 33°, 33°, 26°, 18°, 11°, 6° and 6°.
l Mixing height: hourly data from MM5 meteorological data (for the mixing height of MM5 lower than the minimum mixing height measured at King’s Park Meteorological Station in Year 2003, the minimum mixing height of 129 is adopted); and
l Temperature: hourly data from MM5 meteorological data.
ISCST Model
l Wind Speed: hourly wind speed from MM5 meteorological data;
l Stability Class: hourly data from PCRAMMET output file;
l Wind direction: hourly data from MM5 meteorological data with 180 degrees inversion;
l Mixing height: hourly data from MM5 meteorological data (for the mixing height of MM5 lower than the minimum mixing height measured at King’s Park Meteorological Station in Year 2003, the minimum mixing height of 129 is adopted);
l Temperature: hourly data from MM5 meteorological data (unit changed from degree Celsius to Kelvin); and
l Anemometer height: 10m
Air
Dispersion Model
Odour
emissions from the Centralized Air Pollution Control Unit, SHWSTW and NLTS
3.54 Air quality impacts of air pollutants and odour from the centralized air pollution control unit are modelled with the air dispersion model, Industrial Source Complex Short Term (ISCST3).
3.56
The modelled hourly odour
concentrations at the ASRs are converted into the 5-second odour concentration
so as to compare with the EIAO-TM odour criteria. According to EPD’s “Guidelines on Choice
of Models and Model Parameters”, it recommends the use of methodologies
proposed by Duffee et al.[1] and Keddie[2] in performing the conversion
from hourly to 5-second average concentration. However, it is not appropriate to adopt
this peak-to-mean ratio for all types of odour sources. More recent researches indicated that
the peak-to-mean ratio of odour dispersion would depend upon the type of
source, atmospheric stability and distance downwind. For the purpose of this assessment to
produce more reasonable predictions for odour dispersion from point sources
(wake-affected and non-wake-affected) and area sources, reference is made to
the peak-to-mean ratio stipulated in “Approved Methods for Modelling and
Assessment of Air Pollutants in New South Wales” published by the Department of
Environment and Conservation, New South Wales, Australia (NSW Approved Method). As stated in the NSW Approved Method,
where nearby buildings interfere with the trajectory and growth of the plume,
the source is called a wake-affected point source. A point source is wake-affected if stack
height is less than or equal to 2.5 times the height of buildings located within
a distance of
3.57 The dispersion modelling techniques employed for this assessment are to follow those described in EPD’s “Guidelines on Choice of Models and Model Parameters” except the use of alternative peak-to-mean ratios for wake-affected point sources and area sources. However, it should be noted that the peak-to-mean ratios stated in the NSW Approved Method are derived based on experimental and theoretical analyses and assuming a 0.1% exceedance level (Ref.: Statistical Elements of Predicting the Impact of a Variety of Odour Sources, Peter R. Best, Karen E. Lunney and Christine A. Killip, Water Science and Technology, Australia, 44: 9 pp 157-164 2001). In other words, there would be a 0.1% probability that the actual peak concentration would be higher than those derived with the peak-to-mean ratios stated in the NSW Approved Method.
3.58 In accordance with the NSW Approved Method, the conversion factors are used for converting the 1-hour average concentrations to 1-second average concentrations. As a conservative approach, these conversion factors would be directly adopted for converting the 1-hour average concentrations predicted by the ISCST3 model to 5-second average concentrations for compliance checking with the odour criteria. The conversion factors for different stability classes for wake-affected point sources are shown in Table 3.10.
Table 3.10 Conversion Factors for Wake-affected Point Sources and Area Sources
|
Pasquill
Stability Class |
Conversion
Factor (1 hour to 5 seconds) |
|
|
Wake-affected
Point Sources |
Area
Sources |
|
|
A |
2.3 |
2.5 |
|
B |
2.3 |
2.5 |
|
C |
2.3 |
2.5 |
|
D |
2.3 |
2.5 |
|
E |
2.3 |
2.3 |
|
F |
2.3 |
2.3 |
Air
Pollutant Emissions from OWTF
3.59 For potential air quality impact (except odour impact) due to the emissions from centralized air pollution control unit, combustion of biogas and the flaring emissions, an air dispersion model, ISCST3, are used to simulate their respective dispersion. “Rural” model is adopted in the model run.
3.60 As a worst case scenario, it is assumed that the centralized air pollution control unit and the cogen units are operated continuously on a 24-hour-per-day basis in the assessment.
Emissions
from Marine Vessels
3.61 For potential air quality impact due to the emissions from marine vessels, the air dispersion model, ISCST3, is used to simulate their respective dispersion. “Rural” mode is employed for the model run.
Vehicle
Emissions from Open Roads
3.62 CALINE4 dispersion model is used for the calculation of hourly, 24-hour and annual NO2, and 24-hour and annual RSP concentrations.
Concentration
Calculation
3.63 The locations of the stacks of OWTF, emission sources of SHWSTW and NLTS, and marine emission sources considered in the model are shown in Appendix 3.5.
3.64
The Ozone Limiting Method (OLM) has been adopted for the conversion of
NOx to NO2 based on the predicted O3
concentrations in Grids (14,25), (14,26), (15,25) and (15,26) from the PATH
modelling output for emissions from OWTF, vehicle and marine emissions. A tailpipe emission NO2/NOx
ratio of 7.5% according to the EPD’s “Guidelines on Choice of Models and Model
Parameters” has been assumed for vehicle emission. i.e. The NO2/NOx
conversion is:
[NO2]pred = 0.075 x [NOX]pred + MIN {0.925 x [NOX]pred, or (46/48) x [O3]PATH}
3.65
The NO2/NOx conversion for marine emissions and
emissions from OWTF has been calculated as follows:
[NO2]pred = 0.1 x [NOX]pred
+ MIN {0.9 x [NOX]pred, or (46/48) x [O3]PATH}
3.66 The hourly, daily and annual average NO2 and SO2 concentrations, daily and annual RSP concentrations, hourly average VOCs, as well as hourly and annual HCl and HF concentrations at each ASR due to each source group are assessed and then added together with the background air quality. The ratio of guideline standard of hourly CO concentration to hourly NO2 concentration in mg/m3 is 100 to 1, however, the ratio of CO emission rate to NO2 emission rate is only 1.3 times in accordance with the emission data of OWTF. Therefore, CO would comply with the AQO if the predicted NO2 concentration is below the AQO.
3.67 For the prediction of air pollutants emissions, the CALINE4 and ISCST3 models calculate hourly concentrations based on one year Mesoscale Model 5 (MM5) meteorological data in Grids (14,25), (14,26), (15,25) and (15,26) extracted from PATH model. The pollutant concentrations at the ASRs at each hour are predicted by both CALINE4 and ISCST3 models, where
·
The CALINE4 model is used to predict the open road emissions from the
road networks
·
The ISCST3 model is used to predict all emissions from OWTF and marine emissions
3.68 The future background concentrations for air pollutants are extracted from PATH model. The PATH model output is added to the sum of CALINE4 and ISC results sequentially on an hour-to-hour basis to derive the short-term and long-term cumulative impacts at the ASRs. The highest pollutant concentration predicted at the ASRs amongst the 8760 hours (a year) is identified as the worst predicted hourly pollutant concentration. The maximum 24-hour average pollutant concentration at the ASRs is the highest daily average concentration amongst the 365 days. The annual average pollutant concentration at the ASRs is the average of 8760 hourly concentrations.
3.69 The odour concentrations based on averaging time of 5 seconds at each ASR due to source groups (OWTF, NLTS and SHWSTW) are also predicted.
Prediction and Evaluation of Impacts
3.70
The potential dust emission
sources would be excavation, material handling, spoil removal and wind erosion
of the work site. As the size of the
work site is limited and the maximum amount of excavated materials per day
would be about
Operational
Phase
3.71 The hourly, daily and annual average NO2 and SO2 concentrations, daily and annual RSP concentrations, hourly average VOCs, as well as hourly and annual HCl and HF concentrations at each ASR due to each source group are assessed and compared against the relevant air quality criteria as stated in Tables 3.1 and 3.2. The assessment results are presented in Appendix 3.6. Results indicate that all assessed AQO parameters at the ASRs would comply with the respective criteria as stated in Table 3.1. The predicted hourly VOCs, hourly and annual HCl and HF would also comply with the chronic and acute criteria of USEPA, CARB and the Office of Health, Safety and Security, US Department of Energy as stated in Table 3.2. Results indicate in Appendix 3.6 that the impact from cogen units at the ASRs would be worse than or similar to that from standby flaring gas unit. Therefore, the predicted cumulative air pollutants concentration contour plots at the worst affected levels under normal operation of OWTF (i.e. operation of cogen units and centralized air pollution control unit) are shown in Figures 3.2 – 3.14. Referring to the contour plots, no ASRs including the planned LLP would be located within the exceedance zones.
3.72 Referring to the odour impact assessment results as stated in Appendix 3.6, the predicted odour concentration at the ASRs due to operation of OWTF would range from 0.2 – 3.5 ou/m3. The maximum odour concentration would be predicted at ASR 1, while the odour concentrations at other ASRs would not be higher than 0.5 ou/m3. Over 96% per annum, the predicted odour concentrations at the ASRs due to OWTF would be below 0.15 ou/m3 (i.e. well below 1 ou/m3 which is not detectable by most people), the odour impact is considered negligible and would not contribute to cumulative impacts. Cumulative odour impacts due to emissions from SHWSTW, NLTS and OWTF have also been assessed The predicted cumulative odour concentrations at the ASRs would be in the range of 0.5 – 4.6ou/m3. The predicted odour concentration contour plots at worst hit level due to the operation of OWTF are shown in Figure 3.15. Referring to the odour contour plots, no ASRs including the planned LLP would be located within the exceedance zones.
Recommended Air Quality
Mitigation Measures
Construction Phase
3.73 Implementation of dust suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation and good site practices should be carried out to further minimize construction dust impact.
·
Use of regular watering, with complete coverage, 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 should be applied to
aggregate fines.
·
Open stockpiles should be avoided or covered. Where possible, prevent placing dusty
material storage piles near ASRs.
·
Tarpaulin covering of all dusty vehicle loads transported to, from and
between site locations.
·
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 points, 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.
·
Imposition of speed controls for vehicles on unpaved site roads. 8 kilometers per hour is the recommended
limit.
·
Where possible, routing of vehicles and positioning of construction
plant should be at the maximum possible distance from ASRs.
·
Every stock of more than 20 bags of cement or dry pulverised fuel ash
(PFA) should be covered entirely by impervious sheeting or placed in an area
sheltered on the top and the 3 sides.
·
Cement or dry PFA delivered in bulk should be stored in a closed silo
fitted with an audible high level alarm which is interlocked with the material
filling line and no overfilling is allowed.
·
Loading, unloading, transfer, handling or storage of bulk cement or dry
PFA should be carried out in a totally enclosed system or facility, and any
vent or exhaust should be fitted with an effective fabric filter or equivalent
air pollution control system.
Operational Phase
3.74 There is no adverse air quality impact expected from the operation of the Project.
Evaluation of Residual Impacts
3.1 With the implementation of the mitigation measures as stipulated in the Air Pollution Control (Construction Dust) Regulation, dust control measures and good site practices, no adverse dust impact at the ASRs would be expected.
3.2
No adverse air quality impact
during the operation of the Project is expected.
Environmental Monitoring and Audit
Construction Phase
3.3 With the implementation of practicable dust suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation, adverse construction dust impact is not expected during construction of the Project. Yet, regular site environmental audits during the construction phase of the Project as specified in the EM&A Manual should be conducted to ensure that the recommended dust suppression measures are implemented.
Operation Phase
3.4 Commissioning tests will be conducted to confirm the centralized air pollution control unit, the cogen units and the standby flaring gas unit against the design emission levels as stated in Tables 3.7 – 3.9. During operation phase of the Project, stack monitoring will be installed for centralized air pollution control unit and cogen units of OWTF to ensure that the air emissions from OWTF would be complied with the design emission limits as well as EPD criteria. Besides, odour patrol at the plant boundary is also proposed to monitor any odour impact arising from the operation of the OWTF. Details of the monitoring and audit programme are contained in a stand-alone EM&A Manual.
Construction Phase
3.5 Air quality impacts from the construction works of the Project would mainly be related to construction dust from excavation, materials handling, spoil removal and wind erosion. With the implementation of mitigation measures specified in the Air Pollution Control (Construction Dust) Regulation, proposed dust suppression measures and good site practices checked by regular site environmental audits, no adverse dust impact on the ASRs in the vicinity of the construction sites would be anticipated.
Operation Phase
3.6 No adverse air quality impact would be expected from the operation of the Project. Stack monitoring and odour patrol are recommended for monitoring any adverse impact arising from the operation of OWTF.
[1] Richard A.
Duffee, Martha A. O”Brien and Ned Ostojic (1991). Odour Modelling – Why and How, Recent
Developments and Current Practices in Odour Regulation, Controls and
Technology, Air & Waste Management Association.
[2] Keddie, A.
W, C(1980). Dispersion of Odours, Odour Control – A concise Guide, Warren
Spring Laboratory.