4.1.1
This section presents air
quality impact assessment during construction and operation phases of the
Project. Representative Air
Sensitive Receivers (ASRs) and the potential air quality impact on these
receivers associated with the Project has been identified and assessed. Appropriate mitigation measures are
proposed if necessary.
4.2
Environmental Legislation,
Policies, Plans, Standards and Criteria
4.2.1
The criteria for evaluating air
quality impacts and the guidelines for air quality assessment are set out in
Annex 4 and Annex 12 of the Technical Memorandum on Environmental Impact
Assessment Process (EIAO-TM).
Air Quality Objective & EIAO-TM
4.2.2
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 must be satisfied, stipulate the maximum
allowable concentrations over specific periods for typical pollutants. The relevant AQOs are listed in Table
4.1.
Table 4.1 Hong Kong Air Quality Objectives
|
Pollutant
|
Maximum Concentration (µg m-3) (1)
|
|
Averaging Time
|
|
|
1 hour (2)
|
8 hour (3)
|
24 hour (3)
|
Annual (4)
|
|
Total Suspended
Particulates (TSP)
|
-
|
-
|
260
|
80
|
|
Respirable Suspended
Particulates (RSP) (5)
|
-
|
-
|
180
|
55
|
|
Sulphur
Dioxide (SO2)
|
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 10 mm or smaller.
(6)
Photochemical
oxidants are determined by measurement of ozone only.
Air Pollution Control (Construction Dust) Regulation
4.2.4
Notifiable and regulatory works
are under the control of the 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 both
notifiable and regulatory works.
Contractors and site agents are required to inform the Environmental
Protection Department (EPD) on carrying out construction works and to adopt
dust reduction measures to reduce dust emission to the acceptable level.
Practice Note on
Control of Air Pollution in Vehicle Tunnels
4.2.5
The Practice Note on Control of
Air Pollution in Vehicle Tunnels, prepared by the EPD provides guidelines on
control of air pollution in vehicle tunnels, is applicable to noise
enclosure. Guideline values on
tunnel air quality are presented in Table 4.2.
Table 4.2 Tunnel Air Quality guidelines (TAQG)
|
Air
Pollutant
|
Averaging Time
|
Maximum Concentration
|
|
(mg/m3) (1)
|
ppm
|
|
Carbon Monoxide (CO)
|
5 minutes
|
115, 000
|
100
|
|
Nitrogen Dioxide (NO2)
|
5 minutes
|
1,800
|
1
|
|
Sulphur
Dioxide (SO2)
|
5 minutes
|
1,000
|
0.4
|
Note: (1) Expressed at
reference conditions of 298K and 101.325kPa.
4.3.1
The air quality at the Study
Area is primarily affected by traffic emissions from the existing Tuen Mun Road, Castle Peak Road
and local access roads. There is an
industrial area located close to Tai
Hing Garden
where is about 500m
away from the Project site.
4.3.2
The Project area is in Tuen Mun
while the nearest EPD air monitoring station is located in Yuen Long. According to EPD’s “Guideline on
Assessing the ‘TOTAL’ Air Quality Impacts”, the latest five years average monitoring
data should be adopted as the background concentration. Table 4.3 summarizes the annual
average concentrations of the pollutants (NO2, RSP and O3)
in the latest five years. The
annual average NO2 and RSP concentrations were adopted as background
concentrations for this air quality impact assessment.
Table 4.3 Annual Average Concentrations of Pollutants in the Latest Five Years
(Year 2002 - 2006) at Yuen Long Air Quality Monitoring Station
|
Pollutant
|
Annual Average Concentration in the Latest Five Years (mg m-3)
|
|
NO2
|
60
|
|
RSP
|
62
|
|
O3
|
74 (1)
|
Note: This
is the annual average of daily hourly maximum O3 concentration.
4.4.1
In accordance with the Annex 12
of the EIAO-TM, any domestic premises, hotel, hostel, hospital, clinic,
nursery, school, educational institution, office, factory, shop, shopping
centre, place of public worship, library, court of law, sports stadium or
performing arts centre are considered to be an ASR. Any other place with which, in terms of
duration or number of people affected, has a similar sensitivity to the air
pollutants as the abovementioned places are also considered to be a sensitive receiver,
for example, playground, sitting area of parks/promenade.
4.4.2
The identified representative
existing and planned ASRs are listed in Table 4.4 and the corresponding
locations are shown in Figures 4.1.
Table 4.4 Details of Representative Air Sensitive Receivers
|
ASR
|
Description
|
Use
|
Maximum height above ground (m)
|
Closest Distance to Tuen Mun Road main alignment (m)
|
|
DIC
|
Dragon Inn Court
|
Residential
|
24
|
104
|
|
SSE
|
Sam Shing
Estate
|
Residential
|
88
|
244
|
|
HFG
|
Hanford Garden
|
Residential
|
95
|
236
|
|
KFG
|
Kam Fai Garden
|
Residential
|
56
|
32
|
|
HG
|
Harvest Garden
|
Residential
|
63
|
50
|
|
SST
|
Sam Shing
Temple
|
OU
|
5
|
82
|
|
ABH
|
Chung Sing
Benevolent Society Mrs Aw Boon
Haw Secondary
School
|
Education Institution
|
24
|
86
|
|
SMS
|
Semple Memorial
Secondary School
|
Education Institution
|
24
|
130
|
|
SLS
|
Siu Lun Sports
Ground
|
OU
|
-
|
82
|
|
TSP
|
Tsing Sin
Playground
|
OU
|
-
|
4
|
|
TTP
|
Tung Wah Group
of Hospitals Tai Tung Pui Social
Service Building
|
GIC
|
38
|
10
|
|
HKG
|
Hong King
Garden
|
Residential
|
66
|
14
|
|
JCP
|
JC Place
|
Residential
|
69
|
56
|
|
HTG
|
Hoi Tak
Garden
|
Residential
|
56
|
160
|
|
RG
|
Rainbow Garden
|
Residential
|
66
|
62
|
|
TA
|
Hong Kong Taoist
Association Yuen
Yuen Primary
School
|
Education Institution
|
24
|
94
|
|
TWSP
|
Tsing Wah
Soccer Pitch
|
OU
|
-
|
12
|
|
CLFY
|
Chi Lok Fa
Yuen
|
Residential
|
56
|
14
|
|
TFH
|
On Ting Estate
(Ting Fuk House)
|
Residential
|
89
|
28
|
|
LCKP
|
Lui Cheung
Kwong Lutheran
Primary School
|
Education Institution
|
27
|
82
|
|
STF
|
Shun Tak
Fraternal Association
Leung Kau
Kui College
|
Education Institution
|
24
|
148
|
|
LCK
|
Lui Cheung
Kwong Lutheran
College
|
Education Institution
|
67
|
10
|
|
SOC
|
Siu On Court
|
Residential
|
56
|
24
|
|
LBB
|
Lai Bo
Building
|
Residential
|
96
|
18
|
|
LPB
|
Lee Po
Building
|
Residential
|
99
|
52
|
|
TKB
|
Tuen King
Building
|
Residential
|
38
|
14
|
|
TMF
|
Tuen Mun Fa
Yuen
|
Residential
|
67
|
12
|
|
TMT
|
Tuen Mun
Town Hall
|
GIC
|
20
|
66
|
|
TH
|
Tsing Hoi
Playground
|
OU
|
-
|
18
|
|
LWF
|
Yan Oi Tong Madam
Lau Wong
Fat Primary
School
|
Education Institution
|
32
|
38
|
|
NTM
|
New Town Mansion
|
Residential
|
86
|
46
|
|
YOP
|
Yan Oi
Polyclinic
|
GIC
|
23
|
80
|
|
WG
|
Waldorf Garden
|
Residential
|
99
|
24
|
|
TMTP
|
Tuen Mun
Town Plaza
|
Residential
|
104
|
16
|
|
MON
|
Monastery
|
OU
|
5
|
68
|
|
MSB
|
Man Shing
Building
|
Residential
|
55
|
54
|
|
PC
|
Pak Court
|
Residential
|
20
|
46
|
|
FHB
|
Fu Hang Building
|
Residential
|
58
|
40
|
|
FM
|
Forward Mansion
|
Residential
|
46
|
26
|
|
SC
|
Sun Court
|
Residential
|
53
|
38
|
|
HTB
|
Hing Tai
Building
|
Residential
|
38
|
26
|
|
YOT
|
Yan Oi Tong
Community and Indoor Sports Centre
|
GIC
|
15
|
18
|
|
SHM
|
Tuen Mun San
Hui Market Roof Top Playground
|
OU
|
8.5
|
4
|
|
OC
|
Orchid Court
|
Residential
|
60
|
42
|
|
GC
|
Golden Court
|
Residential
|
38
|
34
|
|
FEC
|
Far East Consortium
Tuen Mun
Central Building
|
Residential
|
47
|
10
|
|
RDG
|
Rose Dale
Garden
|
Residential
|
95
|
28
|
|
KHB
|
Kam Hing
Building
|
Residential
|
89
|
10
|
|
PEN
|
PEN Church of Hong Kong
Sheltered Workshops and Hostel
|
GIC
|
15
|
10
|
|
YLB
|
Yik Lee
Building
|
Residential
|
26
|
16
|
|
EC
|
Eldo Court
|
Residential
|
88
|
62
|
|
TMC
|
Tuen Mun
Church
|
GIC
|
24
|
16
|
|
DST
|
ELCHK Tuen
Mun Lutheran
Church Dzwen Sheng
Tang Kindergarten
|
Education Institution
|
14
|
24
|
|
PAC
|
Parkview Court
|
Residential
|
104
|
22
|
|
PG
|
Proposed
Government, Institution and Community use
|
GIC
|
-
|
24
|
|
PL
|
Tuen Mun Parklane Square (fresh air
intake location)
|
Commercial
|
80
|
16
|
4.4.3
Several elevations have been
chosen for the assessment: 1.5 m
above local ground level (which is the average height of the human breathing
zone), 5.0 m, 10.0 m and 15.0 m above local ground level (mAG). Referring to the finding of the site
visit in August and October 2008, there was no openable window or fresh air intake
louvers below 5mAG of ASR Tuen Mun Parklane Square (PL), and 10mAG of ASR Town
Mun Town Plaza (TMTP) and Tuen Mun Town Hall (TMT) facing Tuen Mun Road. The assessment levels for ASRs TMTP and
TMT are therefore at 10 mAG and 15mAG while the assessment levels for ASR PL are at 5mAG,
10mAG and 15mAG. There is no
openable window or fresh air intake was found at Tuen Mun San Hui market facing
Tuen Mun Road
except the louvers underneath the roof floor. The use of these areas is public
toilets. There are a staff office
and a store room next to public toilet but the windows would not be opened as
advised by the staff. However, as a
conservative approach, assessment was conducted for San Hui Market (SHM) at the
level of this office and the store room, 8.5 mAG.
Construction Phase
4.5.1
The construction period for the
Project would be commenced in late 2009 for completion in late 2012. The major construction activities for
the Project with air quality concern include:
Ÿ
Excavation
Ÿ
Road works
Ÿ
Slope works
Ÿ
Foundation works
for noise barriers/enclosures
Ÿ
Installation of noise barrier supporting frame
Ÿ
Installation of noise barrier panel
4.5.2
According to Transport
Department’s requirement, 2-lane traffic is required to be maintained for each
direction of traffic during construction.
A single lane of 3.5m
wide will be closed at most in one time.
On the other hand, the maximum length of work front is estimated to be 170 m. The maximum size of the work front would
be about 595 m2 (170 m x 3.5 m).
The total volume of generated C&D materials is estimated to be 13,850 m3. The construction programme is about 35
working months and 26 working days for each working month are assumed for this
Project. The major construction
activities would be undertaken within 24 months, as a conservative estimation,
the maximum amount of excavated/handled materials for all work fronts per day
is about 22 m3, which is small amount of excavated materials. The dust impact from this Project is
considered to be minimal with the adoption of mitigation measures stipulated in
the Air Pollution Control (Construction Dust) Regulation.
4.5.3
During the construction period,
another road improvement works at Tsing Tin Interchange which located 500m away from the Project would be
overlapped by a few months.
However, for the ASRs located between the two project sites, the worst
case wind angles for dust emissions from these two projects were opposite. Hence, no cumulative dust impacts would
be expected. Regarding the ASRs
located at the downwind location of both projects, insignificant cumulative
dust impact would be anticipated as the shortest distance between the ASRs and
the Project/Tsing Tin Interchange project would be about 500m.
4.5.4
The commencement date of
another project, Reconstruction and Improvement of Tuen Mun Road - Sam Shing
Hui Section, would be in mid 2009 which would also
overlap with the Project. However,
the major works of this project is widening of road verge at Sam Shing Hui work
site, maximum of 1-2 trucks per hour to be operated would be expected. For the proposed Project itself, the
major construction activities at Sam Shing Hui area would be road widening
works and installation of noise barriers/enclosures, small amount of excavated
materials is anticipated (maximum of one truck per hour at Sam Shing Hui road
section work front is expected), therefore, adverse cumulative dust impacts
arising from the Project and other concurrent projects would not be anticipated
with the adoption of dust suppression measures stipulated in Air Pollution
Control (Construction Dust) Regulation and good site practices.
Operation Phase
4.5.5
Potential air quality impact in
the surrounding ASRs during the operation phase of the Project includes:
Ÿ
Background pollution levels based on five years averaged
monitoring data from EPD monitoring station at Yuen Long which summarised in Table 4.3;
Ÿ
Vehicle emissions from open road sections of the existing
and widened Tuen Mun Road Town Centre Section with the incorporation of the
proposed vertical barrier, cantilevered noise barriers, semi-enclosures and
full enclosures;
Ÿ
Portal emissions from the proposed full enclosures along
Tuen Mun Road Town Centre Section;
Ÿ
Portal emissions from the existing full enclosures along Wong Chu Road;
Ÿ
Portal emissions from the existing deckover near On Ting
Estate Commercial Complex over Tuen
Mun Heung Sze Wui Road; and
Ÿ
Portal emissions from the existing deckover of Tuen Mun
Town Plaza
over Tuen Mun Road.
4.5.6
In accordance with the approved
fleet averaged emission factors derived from EMFAC-HK Model for the approved
EIA Study for Widening of Tuen Mun Road at Tsing Tin Interchange, the ratio of
total NO2, RSP and CO emissions to the corresponding 24-hour average
AQO (there is no 24-hour average AQO for CO, the AQO of CO
for shorter period of 8-hour CO is used) was 0.0072, 0.0032 and 0.0015
respectively. Besides, the ratio of
total NO2 and CO emissions to the corresponding 1-hour average AQO
was 0.0036 and 0.0005 respectively.
This indicated that NO2 and RSP were the most critical air
pollutants of road traffic emission.
In other words, if the predicted NO2 and RSP concentrations
complied with the corresponding AQO, air pollutants like CO with lower ratio
would also comply with their respective AQO. NO2 and RSP were therefore
selected as the most critical air pollutants for the purpose of this
assessment.
Construction Phase
4.6.1
As mentioned in Section 4.5, insignificant
dust impact would be expected during construction phase of the Project,
therefore, only qualitative assessment was undertaken in the study.
Operation Phase
4.6.2
The air dispersion model CALINE4,
which was recommended by EPD, was employed to predict the vehicle exhaust
pollutants from the Project and surrounding open road network; whereas ISCST3,
was employed to predict portal emissions from the proposed and existing
enclosures/deckovers. All major
roads within 500m
of the study area were included in the model. The hourly and daily average NO2
and daily average RSP were calculated in the model.
4.6.3
The construction of the Project
is originally to be commenced in late 2008 and completed by 2010. Due to a
number of factors and various design developments, the commencement of the
Project is postponed and the completion date will be delayed to 2012. Based on the initial programme, the
highest predicted traffic flow year within 15 years after completion of the
Project should be 2025. A set of
2025 traffic data obtained from 2003-based TPEDM SI planning data was predicted
and has been endorsed by Transport Department. As a result from the
change of completion date to 2012, a review on the traffic figures adopted in
this assessment has been carried out. The 2025 traffic forecast endorsed by TD
for use in this assessment was derived from the 2003-based TPEDM SI planning
data. However, this set of planning data is now superseded by the 2006-based TPEDM
SI planning data which was released by PlanD in mid 2008. Comparing the 2027
population and employment data in NWNT from the 2006-based TPEDM SI against the
assumed 2025 population and employment data adopted in the 2025 traffic
forecast, the 2027 figures obtained from the 2006-based TPEDM SI planning data
are even smaller than the assumed 2025 figures adopted in the 2025 traffic
forecast which were developed with reference to the 2003-based TPEDM SI
planning data. There are some reductions in population and employment
assumptions in the 2006-based TPEDM SI planning data. Since the traffic flows
on TMRTCS are in proportion to the population and employment of NWNT (i.e. Tuen
Mun/Tin Shui Wai/Yuen Long areas), the endorsed 2025 traffic forecast for the
EIA are derived from a set of relatively higher population and employment
assumptions. Hence even the assessment year of the EIA is postponed to 2027 and
the traffic forecast for the EIA is to be updated with the latest set of
2006-based TPEDM SI planning data, the 2027 traffic forecast so produced would
still be anticipated to be less than the endorsed 2025 traffic forecast.
Therefore, the endorsed
2025 traffic data, which are the highest emission
strength from the road within next 15 years after the operation of the Project,
used for estimating the vehicular impacts in the assessment is on a conservative side. The projected 2025
peak hour traffic flows and vehicle composition are attached in Appendix 4.1. The letter from Transport Department for
the agreement on the traffic flow and mix data for this EIA Study is attached
in Appendix 3.4.
Fleet Average Emission Factors
4.6.4
Widening of Tuen Mun Road at Tsing Tin Interchange
EIA Study and this Project are located at the same district. For calculation of the fleet average
emission factors, hourly traffic flow should be calculated with reference to
the Annual Traffic Census. Within
the study area of these two projects, there is only one major core
station. The calculation of the
hourly traffic flow for both projects are based on the same station, therefore,
the characteristics of road traffic at Tsing Tin Interchange are similar to
that of the Project. In addition,
the assessment year for Widening of Tuen Mun Road at Tsing Tin Interchange EIA
Study is one year early than this Project, the calculated fleet average
emission factors are expected to be larger than that of this Project. As a conservative assumption, the fleet
average emission factors adopted in Widening of Tuen Mun Road at Tsing Tin
Interchange EIA Study were applied for this Study. The methodology/assumption adopted in
the EMFAC-HK model for calculation the emission factors and the emissions
factors for “trunk road” and “other road” under peak hour traffic speed and
congestion condition (10 kph) are presented in Appendix 4.2. The adopted
vehicular emissions for different vehicle categories (peak hour speed) are
listed in Table 4.5.
Table 4.5 Emission Factors For Different Vehicle Classes (Peak Hour Flow Speed)
|
Vehicle Class
|
Description
|
Emission Factors, g/mile-veh
|
|
NOX
|
RSP
|
|
Trunk Road
|
Other Road
|
Trunk Road
|
Other Road
|
|
MC1
|
Petrol Private Cars (PC) & Light Goods Vehicles (LGV)
|
0.2272
|
0.2818
|
0.0053
|
0.0083
|
|
MC3
|
Diesel Private Cars & Light Goods Vehicles<2.5t
|
0.9498
|
1.0722
|
0.3164
|
0.4021
|
|
MC4
|
Diesel Private Cars & Light Goods Vehicles 2.5-3.5t
|
0.5317
|
0.5866
|
0.1633
|
0.2095
|
|
MC5
|
Public Light Buses
|
0.7523
|
0.7675
|
0.6154
|
0.6869
|
|
MC6
|
Light Goods Vehicles >3.5t
|
3.4661
|
3.7633
|
0.3939
|
0.4999
|
|
MC7
|
Medium & Heavy Goods Vehicles with GVW 5.5-15t
|
7.3436
|
7.8873
|
0.7244
|
0.8988
|
|
MC8
|
Medium & Heavy Goods Vehicles with GVW >=15t
|
9.2875
|
10.0082
|
0.7963
|
1.0268
|
|
MC10
|
Double Deck Franchised Buses
|
5.1323
|
5.8073
|
0.2475
|
0.3305
|
|
MC11
|
Motor Cycles
|
1.0231
|
1.1372
|
0.0400
|
0.0625
|
|
Taxi3
|
Taxi
|
0.2514
|
0.2819
|
0.0233
|
0.0328
|
|
Taxi4
|
Private Light Buses <3.5t
|
0.0000#
|
0.0000#
|
0.0000#
|
0.0000#
|
|
Taxi5
|
Private Light Buses >3.5t
|
0.7471
|
0.8242
|
0.4687
|
0.6083
|
|
Taxi6
|
Non- franchised Buses <6.4t
|
0.0000#
|
0.0000#
|
0.0000#
|
0.0000#
|
|
Taxi7
|
Non- franchised Buses 6.4-15t
|
6.4663
|
7.0735
|
0.5716
|
0.7392
|
|
Taxi8
|
Non- franchised Buses >15t
|
0.0000#
|
0.0000#
|
0.0000#
|
0.0000#
|
|
Taxi10
|
Single Deck Franchised Buses
|
5.1323*
|
5.4401
|
0.2475*
|
0.8151
|
Notes:
# - Since there is no private light
buses, no non-franchised buses <6.4t, no non-franchised buses >15t
travelled within the study area, the calculated emission factors for these
vehicle classes are zero.
* - Since there is no single deck
franchised buses travelled within the study area of Widening of Tuen Mun Road
at Tsing Tin Interchange, as a conservative approach, the calculated emission
factor for double deck franchised buses would be adopted for single deck
franchised buses.
Model Assumptions for Open
Road Vehicle Emission
4.6.5
As mentioned in section 4.6.2,
CALINE4 dispersion model was used for calculation of the hourly average NO2,
24-hour average NO2 and 24-hour average RSP concentrations. The areas in the vicinity of concerned
section of Tuen Mun Road
are high density of mid-rise and high-rise residential developments. The study area is therefore considered
as “urban”. In accordance with EPD “Guidelines on Choice of Models and Model
Parameter”, the typical value used for urban developments is 370cm and was therefore adopted in the
model run. The following summarizes
the meteorological conditions adopted in the CALINE4 model:
Ÿ
Wind speed : 1m/s
Ÿ
Wind direction : 360 wind
directions
Ÿ
Resolution : 1°
Ÿ
Wind variability : 7° (F Class)
Ÿ
Stability class : F (Night-time)
Ÿ
Surface roughness : 370cm
Ÿ
Mixing height : 500m
4.6.6
Secondary air quality impacts
arising from the implementation of roadside noise barriers and enclosures were
also incorporated into the air quality model. For the proposed cantilevered noise barrier
and noise semi-enclosure along the Tuen Mun Road (as shown in Figures 3.3A – 3.3C), it was assumed that dispersion of the
traffic pollutants would have effect similar to that traffic pollutants would
be emitted from the top of the canopies and semi-enclosures. The calculation of open road emissions
is presented in Appendix 4.2.
Model Assumptions for Portal Emissions
4.6.7
The portal emissions (NO2
and RSP) of the proposed and existing full enclosures/deckovers were calculated
based on the vehicle emission derived from the adopted fleet average emission
factors and vehicle flows in 2025.
A figure showing the locations of the enclosures/deckovers portal
emissions and the calculations of portal emissions are attached in Appendix 4.3.
4.6.8
Portal emissions were modeled
in accordance with the Permanent
International Association of Road Congress Report (PIARC, 1991). In normal case, pollutants were assumed
to eject from the portal as a portal jet such that 2/3 of the total emissions
was dispersed within the first 50m
of the portal and the other 1/3 of the total emissions within the second 50m.
However, the separation distance between the two full enclosures at some
locations along Tuen Mun Road
is between 50m - 100m. The pollutants were assumed to eject
from the portal as a portal jet such that 2/3 of the total emissions was
dispersed within the first 50m
of the portal. If the length of
remaining open road section is less than 50m,
the other 1/3 of the total emissions was assumed to eject within the remaining
of the open road section and to the next enclosures. As the separation distance between
proposed Enclosure D, E1, E2 and landscape deck of Tuen Mun Town Plaza
(Enclosure F) at Tuen Mun Road
would be less than 100m
from each other, the calculation of portal emission at these enclosures was
taking into account the looping effect.
4.6.9
The decked section of Tuen Mun Road (Pui
To Road) was assumed as semi-enclosure structure and the portal emission was based
on its total surface area of this semi-enclosure. The opening of this semi-enclosed
structure is 688m2
(lateral opening: 44m in
length x 6m high x 2 sides; top
opening: 4m in length x 40m in width), about 30% of the total
surface area of this semi-enclosure structure (2282m2). As this road section is not fully open,
only part of portal emission from Enclosure E1 (see Figure A4.3, Sheet 2
of 4) would be dispersed at this open section (Kowloon bound direction) and part of portal
emission would be ejected into next enclosure E2. Taking into account of 30% of openable
area of this semi-enclosure structure, about 17.6% portal emission to be
dispersed out and 82.4% portal emission would be ejected into next enclosure.
4.6.10 Apart from the portal emission at the Pui To Road bridge section,
traffic emission of this road section is also included in the CALINE4 model.
The detail emission calculation is presented in Appendix 4.3.
4.6.11 Between the landscape deckover of Tuen
Mun Town
Plaza (Enclosure F) and proposed
Enclosure E2, a semi-enclosure is proposed to cover Kowloon bound as well as part of Yuen Long
bound of Tuen Mun Road. Taking into account of extended
structure from Tuen Mun Town Plaza, the portal emissions from landscape deckover
(Yuen Long bound) and Enclosure E (Kowloon
bound) were considered to be dispersed on Tuen Lung Street. The two third of total portal emission
was considered to be dispersed on the first 50m of Tuen Lung Street, while the one third of the
total portal emission was considered to be dispersed on the second 50m of Tuen Lung Street. The width of the volume source is based
on the width of the semi-enclosure to Tuen
Lung Street.
4.6.12 As mentioned in Section 4.6.5,
360 predetermined meteorological conditions were used. The following summarizes the
meteorological conditions adopted in the ISCST3 model:
Ÿ
Wind speed : 1m/s
Ÿ
Wind direction : 360 wind
directions
Ÿ
Resolution : 1°
Ÿ
Wind variability : 7° (F Class)
Ÿ
Stability class : F
(Night-time)
Ÿ
Mixing height : 500m
Sensitivity Test for 100% Portal Emission
4.6.13 As mentioned in Section 4.6.8,
the separation distance between the two full enclosures at some locations along
Tuen Mun Road
would be less than 100m. Other than portal emissions were modeled
in accordance with the PIARC assumption, a sensitivity test for 100% portal
emission within these open road section was also conducted. It was assumed that the portal emission
would ALL disperse at the opening (if the separation distance between the two
full enclosures at some locations along Tuen Mun Road is about 50 -100m), without drawn into the next full
enclosure. The 2/3 of the total
emissions were assumed to eject and disperse at the first half of the opening
while 1/3 of the total emissions were assumed to be eject and disperse at the
second half of the opening. If the
separation distance between the two full enclosures at some locations along Tuen Mun Road is
less than 50m, it
was assumed that all emissions would eject and distribute evenly at the
opening. The calculation of portal
emissions, assessment results and contour plots for 100% portal emission
assumption are presented in Appendix 4.6. The meteorological conditions in the
CALINE4 and ISCST3 model runs are similar to PIARC assumption. Comparing with the discrete results of
both assumptions, higher air pollutants levels predicted at more ASRs and the
highest predicted level of the pollutants to be occurred under PIARC
scenario. Referring to the contour
plots, the predicted pollutant concentrations in the vicinity of the portal
openings under both scenarios are negligible in difference. Therefore, the PIARC assumption is
considered to be more representative to present the results for the worst
affected ASRs in this assessment.
NO2/NOX Emissions Conversion
4.6.14 The NO2/NOX conversion for all vehicle
emission sources for all averaging periods was estimated based on the Ozone
Limiting Method. The latest five
years (2002 – 2006) annual average of daily hourly maximum ozone concentrations
recorded at EPD’s Yuen Long Air Quality Monitoring Station of 74µg/m3
was adopted for the calculation.
The NO2/NOX conversion was calculated as follows:
[NO2]pred
= 0.1 ´ [NOX]pred + MIN {0.9 ´ [NOX]pred,
or (46/48) ´ [O3]bkgd}
where
[NO2]pred is the predicted NO2
concentration
[NOX]pred is the predicted NOX
concentration
MIN means
the minimum of the two values within the brackets
[O3]bkgd is the representative O3
background concentration
(46/48) is the molecular weight of NO2
divided by the molecular weight of O3
Concentration Calculation
4.6.15 As mentioned in Section 4.5.5,
background pollutant levels recorded at Yuen Long Station, vehicle emissions
from open sections of the existing and planned road networks, portal emissions
from existing and proposed full enclosures/deckovers would contribute to the cumulative impact.
4.6.16 The CALINE4 and ISCST3 models would calculate hourly concentrations
only. The highest predicted hourly
concentration between daytime and evening time was assumed to be maximum 1-hour
average concentration. With
reference to the Screening Procedures for Estimating the Air Quality Impact of
Stationary Source (EPA-454/R-92-019), a conversion factor of 0.4 is used to
convert the 1-hour average concentrations to 24-hour average concentrations.
4.6.17 The pollutant concentrations at the ASRs at different wind
directions (1degree resolution) were predicted by both CALINE4 and ISCST3
models, where
Ÿ
The CALINE4 model was used to predict the open road emissions
from the existing road networks and widened Tuen Mun Road Town Centre Section
Ÿ
The ISCST3 model was used to predict all the portal
emissions from existing and proposed full enclosures/deckovers
4.6.18 The pollutant concentrations at the ASRs at each specific wind
direction were calculated by summing up the results obtained from the two
models. The highest pollutant
concentrations at the ASRs amongst the 360 wind directions were identified as
the worst predicted pollutant concentrations.
Vehicular Emission Impact (Inside the existing and proposed full
enclosures/deckovers)
4.6.19 The existing and proposed full enclosures/deckovers assumed for the
in-tunnel air quality model run were summarized as follows:
Ÿ
Proposed full enclosures along Tuen Mun Road Town Centre
Section in front of Golden Court;
Ÿ
Proposed
full enclosure along Tune Mun Road Town Centre Section in front of Pui To Road
Flyover;
Ÿ
Proposed full enclosure along Tuen Mun Road Town Centre
Section in front of Tuen Mun Town Plaza Block 1 & 2;
Ÿ
Proposed full enclosures along Tuen Mun Road Town Centre
Section near Tuen King
Building;
Ÿ
Proposed full enclosures along Tuen Mun Road Town Centre
Section near Chi Lok Fa Yuen;
Ÿ
Proposed
full enclosures along Tuen Mun Road Town Centre Section near Tsing Sin
Playground;
Ÿ
Proposed
full enclosure along Tuen Mun Road
near Kam Fai Garden, and
Ÿ
Existing deckover under Tuen Mun Town Plaza
along Tuen Mun Road.
4.6.20 The air quality under the existing and proposed full
enclosures/deckovers was calculated based on the empirical formulas of fluid
dynamics. A conversion factor of
12.5% including tailpipe NO2 emission (taken as 7.5% of NOX)
plus 5% of NO2/ NOX for tunnel air recommended in PIARC
for air expelled from the tunnel was taken in this assessment as the inside tunnel
conversion factor. Two scenarios
were considered in the assessment, i.e. normal traffic flow condition and worse
traffic flow condition (i.e. congested condition). It was assumed that the vehicles are at
peak hour flow speeds of Tuen Mun Road (as the emission factors of the peak
hour speeds are more conservative than using the design speed) under normal
traffic flow condition,, whereas under congested mode, the vehicles are at a
speed of 10 kph, the separation between vehicles is assumed to be 1m. The emission factors for “other road”
were adopted for assessment as its emission factors are higher than “trunk
roads” (see Appendix 4.2).
4.6.21 For illustration purpose, the proposed full enclosures would be
divided into different portions. These
enclosures are designed with various length and some of them are proposed on
the slip roads and combined at the merged section along Tuen Mun Road. The emissions from looping effect for
Enclosure D, E1, E2 and F were also considered in the calculation. The
assessment assumptions for each proposed enclosure are summarized as follows
and the locations of all enclosures/deckovers are shown in Figure A4.4:
Proposed full enclosures along Tuen
Mun Road Town Centre Section in front of Golden Court –
Enclosure D
4.6.22 A 117m long full enclosure and a
83m long full enclosure
are proposed along the elevated slip road to Pui To Road and Tuen Mun Road southbound, where the first
50m of the enclosures
are merged together. The longest
length of the enclosure, i.e. 117m,
was considered in the calculation with total flow inside the proposed Enclosure
D as a worst case scenario.
Proposed full enclosure along Tuen Mun Road Town Centre Section in front
of Pui To Road Flyover – Enclosure E1
4.6.23 A 82m
long full enclosure is proposed to be located in front of Pui To Road
Flyover. The total vehicular
emission inside enclosure E1 was calculated by summing vehicular emissions at Kowloon bound and Yuen
Long bound of Tuen Mun Road
inside the enclosure.
Proposed full enclosure along Tuen Mun Road Town Centre Section in front
of Tuen Mun Town Plaza Block 1 & 2 – Enclosure E2
4.6.24 A 73m
long full enclosure at the south of Pui
To Road will abut
on the existing deckover under the Pui
To Road. The total vehicular emission inside enclosure E2 was
calculated by summing the vehicular emissions at Kowloon bound and Yuen Long bound of Tuen Mun Road
inside the enclosure.
Proposed full enclosures along Tuen
Mun Road Town Centre Section near Tuen King Building – Enclosure G
4.6.25 The calculation of vehicular emissions inside the full enclosure G
are divided into 2 groups, Group 1 - enclosure no. 16 (on the slip road from
Tuen Hing Road), and Group 2 - enclosure no. 14 & 15 (in front of YOT Madam
Lau Wong Fat Primary School) and enclosure no. 17 & 18 (in front of Tuen
King Building). The lengths of
Group 1 and Group 2 enclosure to be considered in the calculation are 136m and 200m, respectively. As a worst case scenario, assuming
the pollutants inside the two enclosure groups would be thoroughly mixed and
the sum of their vehicular emissions was adopted to represent the vehicular
emission inside the proposed enclosure G.
Proposed full enclosures along Tuen
Mun Road Town Centre Section near Chi Lok Fa Yuen
– Enclosure H
4.6.26 A 78m
long full enclosure is proposed along Tuen
Mun Road near Chi Lok Fa Yuen which would cover Kowloon bound and Yuen
Long bound of Tuen Mun Road. Vehicular emission inside enclosure no.
19 and 20 were calculated and the sum of the above vehicular emissions was
represented as the total vehicular emissions inside enclosure H.
Proposed full enclosures along Tuen Mun Road Town Centre Section near
Tsing Sin Playground
and Kam Fai Garden – Enclosure I & J
4.6.27 A 112m
long full enclosure and a 180m long
full enclosure are proposed along Tuen
Mun Road near Tsing Sin Playground and Kam Fai
Garden. Both enclosures would cover
Kowloon bound
of Tuen Mun Road
only. Vehicular emissions inside
the enclosures at one direction were calculated in the assessment.
Existing deckover under Tuen
Mun Town
Plaza along Tuen Mun Road –
Enclosure F
4.6.28 The calculation of vehicular emissions inside the existing deckover
under the Tuen Mun Town Plaza (96m in length) could be simplified by direct
comparison with each other. The
vehicular emissions inside this existing deckover could be calculated directly
since the deckover length at both directions are the same.
4.6.29 The calculations of in-tunnel air quality for section of existing and
proposed full enclosures/deckovers were presented in Appendix 4.4A-4.4H. As mentioned in Section 4.5.6,
the most critical air pollutant of NO2 was assessed for the
existing/proposed full enclosures/deckovers.
Construction Phase
4.7.1
In view of site constraint, the
maximum length of road section to be widened (each work front) would be about 170m at a time. One dump truck would be allowable on
site for unloading materials due to limited work area. Therefore, no adverse dust impact would
be expected at the nearby ASRs. No
unacceptable dust impact would be expected after proper implementation of dust
control and suppression measures stipulated in the Air Pollution Control
(Construction Dust) Regulation. As
mentioned in Section 4.5.3, the cumulative adverse
dust impact from another project, Reconstruction and Improvement of Tuen Mun
Road – Western Section, is not anticipated as limited amount of soil materials
to be generated from the road verge widening work.
Operation Phase
Traffic Emission Impact (Open
Road)
4.7.2
Taking into account vehicle
emissions from open road networks, portal emissions from the existing and
proposed full enclosures/deckovers and the background pollutant concentrations,
the predicted 1-hour average NO2, 24-hour average NO2 and
RSP concentrations were predicted and the highest pollutant concentrations at
each ASR under the worst wind directions were calculated and presented in Appendix
4.5.
4.7.3
Based on the prediction, no
exceedance of 1-hour average NO2, 24-hour average NO2 and
24-hour average RSP AQO would occur at any representative ASR in the Study
Area. In accordance with the
results, it was found that the maximum pollutant concentrations would occur at
1.5mAG for most ASRs and 10mAG for two ASRs (ASR LCK and TKB). The predicted pollutant concentrations
at all representative ASRs would decrease at 15mAG. The predicted maximum hourly average NO2,
24-hour average NO2 and RSP concentration contours at 1.5mAG and
10mAG are shown in Figures 4.2 to 4.7. For ASR SHM, hourly and 24-hour average
NO2 concentration contours at 8.5mAG are shown in Figures 4.8
and 4.9. Referring to the
1–hour and 24-hour average NO2 and RSP concentration contour plots
at 1.5mAG, 8.5mAG and 10mAG, the following areas are found exceedance of AQO:
Ÿ
1-hour NO2 contour plot at 1.5mAG – San Hui
Market, Yan Oi Tong Community and Indoor Sports Centre, Tuen Mun Town Hall, Tuen Mun Parklane Square
Ÿ
24-hour NO2 contour plot at 1.5mAG – San Hui Market,
Yan Oi Tong Community and Indoor Sports Centre, Tuen Mun Town Hall, Tuen Mun Parklane Square
Ÿ
24-hour NO2 contour plot at 8.5mAG – Yan Oi Tong
Community and Indoor Sports Centre
Ÿ
24-hour NO2 contour plot at 10mAG –Yan Oi Tong
Community and Indoor Sports Centre, Tuen
Mun Town
Hall
4.7.4
Actually,
in accordance with findings of the site visits conducted in August and October
2008, there were no opening façades and fresh air
intakes for Yan Oi Tong Community and Indoor Sports Centre and Tuen Mun
Town Hall from 1.5mAG to
10mAG and higher level within the exceedance zones. Also, there were no opening facades and
fresh air intakes for Tuen Mun
Parklane Square lower than 5mAG, and between 5mAG
and 10mAG within the exceedance zones.
Discrete results show that no exceedance is found at the fresh air
intake location of Tuen Mun
Parklane Square at the height of 5mAG, 10mAG and
15mAG, and a decrease in pollutant concentrations from low to higher level is
noted. For San Hui Market, there
were no opening facades and fresh air intakes at 1.5mAG to 8.5mAG within the
exceedance zone. The minimum height
of opening facades at San Hui Market facing Tuen Mun Road was 8.5mAG. Discrete results indicate that no
exceedance is found at this ASR with the height of 8.5mAG and higher
level. Therefore, no air sensitive
areas are located within these exceedance areas.
Vehicular Emission Impact (Inside the full enclosure/deckover)
4.7.5
For the air quality assessment
inside the proposed and existing full enclosures/deckovers along Tuen Mun Road, the
predicted maximum NO2 concentrations under normal traffic flow and
congested traffic flow would be 909 mg/m3 and 1129 mg/m3 respectively.
These comply with the Tunnel Air Quality Objective (1800mg/m3). Detailed calculations and results of
each enclosure/deckover are presented in Appendix 4.4A to 4.4H.
Construction Phase
4.8.1
To ensure compliance with the
relevant standards, dust mitigation measures stipulated in the Air Pollution Control
(Construction Dust) Regulation and good site practices should be incorporated
in the contract document to control potential dust emission from the site. The major dust suppression measures
include:
Ÿ
skip hoist for material transport should be totally enclosed
by impervious sheeting
Ÿ
every vehicle should be washed to remove any dusty materials
from its body and wheels before leaving the construction site
Ÿ
the area where vehicle washing takes place and the section of
the road between the washing facilities and the exit point should be paved with
concrete, bituminous materials or hardcores
Ÿ
where a site boundary adjoins a road, streets or other
accessible to the public, hoarding of not less than 2.4m high from ground level should be provided along
the entire length except for a site entrance or exit
Ÿ
every stack of more than 20 bags of cement should be placed
in an area sheltered on the top and the 3 sides and be covered entirely by
impervious sheeting
Ÿ
all dusty materials should be sprayed with water prior to
any loading, unloading or transfer operation so as to maintain the dusty
materials wet
Ÿ
the height from which excavated materials are dropped should
be controlled to a minimum practical height to limit fugitive dust generation
from falling and landing
Ÿ
the load of dusty materials carried by vehicle leaving a
construction site should be covered entirely by clean impervious sheeting to
ensure dust materials do not spread from the vehicle
Ÿ
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
Operation Phase
4.8.2
The predicted air quality
impacts on the ASRs would comply with the AQO. No mitigation measure would be required
during operation phase.
Construction Phase
4.9.1
With the implementation of dust
suppression measures stipulated in Air Pollution Control (Construction Dust) Regulation
during construction, no adverse residual dust impact would be expected.
Operation Phase
4.9.2
No adverse residual traffic
emission impact is predicted.
Construction Phase
4.10.1 With the implementation of the proposed dust suppression measures,
good site practices and dust monitoring and audit programme, acceptable dust
impact would be expected at the ASRs.
Details of the monitoring requirements such as monitoring locations,
frequency of baseline and impact monitoring are presented in the stand-alone
EM&A Manual.
Operation Phase
4.10.2 Since the predicted air quality in the study area complies with the
AQO, no environmental monitoring and audit is proposed.
Construction Phase
4.11.1 In view of nature of the works and the site conditions, adverse dust
impact at the ASRs would not be expected from the Project. Nevertheless, appropriate dust control
and suppression measures as stipulated in the Air Pollution Control
(Construction Dust) Regulation should be implemented to minimize any potential
dust impact.
Operation Phase
4.11.2 The potential impacts arising from the background pollutant levels
within and adjacent to the Project site, vehicle emissions from open road networks
and the implementation of roadside noise barriers and enclosures were
assessed. Results showed that the
predicted air quality at the ASRs would comply with the AQOs. No mitigation measures are proposed.