3.
Air
Quality IMPACT Assessment
3.1.1
This Chapter presents an assessment of air quality
impact associated with the construction and operation of the Hang Hau Tsuen
Channel at Lau Fau Shan (the Project).
3.1.2
Potential construction phase air quality impact
consists of increased fugitive dust from excavation and other construction
works affecting the nearby air quality sensitive receivers.
3.1.3 The proposed access road along the northern channel bank will be open to public use. In addition, a viewing point and carpark will be constructed at the channel outfall. The potential operation phase air quality impact will be the vehicular emission arising from the increase traffic. In addition, annual maintenance cutting of vegetation and sediment removal may be necessary during operation of the drainage channel. The above activities, however, are not expected to have any significant air quality impacts.
3.2
Air Quality Assessment Criteria
3.2.1
The criteria for evaluating
air quality impacts and the guidelines for air quality assessment are laid out
in Annex 4 and Annex 12 of the Technical Memorandum on Environmental Impact
Assessment Process (EIAO-TM).
3.2.2
The principal legislation regulating air emissions in
Hong Kong Air Quality Objectives (AQOs)
|
Pollutants |
Concentration in Micrograms
per Cubic Meters (µg/m3) |
|||
|
Averaging
Time |
||||
|
1
hourA |
8
hoursB |
24
hoursB |
1
yearC |
|
|
Carbon Monoxide (CO) |
30,000 |
10,000 |
-- |
-- |
|
Nitrogen Dioxide (NO2) |
300 |
-- |
150 |
80 |
|
|
800 |
-- |
350 |
80 |
|
Total Suspended Particulates (TSP) |
500E |
-- |
260 |
80 |
|
Respirable Suspended Particulates (RSP)D |
-- |
-- |
180 |
55 |
Notes:
Concentrations measured at 298K (25°C) and
101.325 kPa (one atmosphere).
A Not
to be exceeded more than 3 times per year.
B Not
to be exceeded more than once per year.
C Arithmetic
means.
D Respirable
suspended particulates means suspended particulates in air with a nominal
aerodynamic diameter of 10 micrometer (µm) or smaller
E This
control limit has no statutory basis but is used as a target level for limiting
fugitive dust emissions generated by construction activities.
3.2.3
The EIAO-TM also stipulates
that the odour level at a sensitive receiver should not exceed 5 odour units
based on an averaging time of 5 seconds for odour prediction assessment.
3.3.1
The Study Area for air
quality impact assessment is defined by a distance of 500 m from the boundary
of the Project works site.
3.4.1 The representative air sensitive receivers (ASRs) that may potentially be impacted by the Project are listed in Table 3.2 and shown in Figure 3.1.
Representative Air
Sensitive Receiver (ASR)
|
Representative ASR |
General Description |
No. of Floors |
Approximate Distance to Works Site Boundary |
Shortest Horizontal Distance to Road Kerb |
|
ASR 1 |
Wing Jan Kindergarten |
1 |
22 m |
82 m to New Road 18 m to |
|
ASR 2 |
Wing Jan Camp |
1 |
4 m |
32 m to New Road 45 m to |
|
ASR 3 |
Village house at No. 84 Hang Hau Tsuen |
2 |
1 m |
10 m to
New Road 154 m to |
|
ASR 4 |
Village house at No. 57 Hang Hau Tsuen |
1 |
1 m |
16 m to
New Road 267 m to |
|
ASR 5 |
Village house at No. 26 Hang Hau Tsuen |
2 |
1 m |
15 m to
New Road |
|
ASR 6 |
Village house at No. 88 Hang Hau Tsuen |
2 |
1 m |
30 m to New Road |
|
ASR 7 |
House at Deep Bay Grove |
3 |
150 m |
175 m to New Road 48 m to |
|
ASR 8 |
Village house at No. 30 Lau Fau Shan |
2 |
210 m |
245 m to New Road 24 m to |
|
ASR 9 |
Planned residential development (TPB application no.
A/YL-LFS/156) |
2-3 |
40 m |
50 m to New Road 5 m to |
|
ASR 10 |
Village house at No. 45A Hang Hau Tsuen |
2 |
1 m |
4 m to New Road |
Note:
The
location of the ASRs is shown in Figure 3.1.
3.5.1
The Study Area is located in the north-western part of
3.5.2
The wind rose from the Lau Fau Shan Station indicates
that the dominant wind direction is mainly easterly with occasional
north-easterly and south-easterly wind.
Existing Air
Conditions
3.5.3
As there is no monitoring station at the Study Area,
EPD's Air Quality Monitoring Station at Yuen Long was used to establish ambient
air quality over the Study Area. Background
concentration for NO2 and RSP are estimated based on 5-year averages
of the most recent monitored air quality data obtained by EPD (i.e. 2003-2007) at the Yuen Long station. Background
concentration for CO is estimated based on 4-year averages (2004-2007) of data
obtained by EPD at the Yuen Long station. The
background data of the air pollutants concentrations at EPD’s Yuen Long Station
are listed in Table 3.3.
Average Background Air Pollutants Concentrations at EPD’s Yuen Long
Station
|
Pollutants |
Annual Average Concentration
(μg/m3) |
AQOs (μg/m3) |
|
CO |
941 |
-- |
|
NO2 |
60 |
80 |
|
RSP |
64 |
55 |
|
TSP |
103 |
80 |
3.5.4
The table indicates that the averaged concentration
of RSP and TSP at Yuen Long exceed the
stipulated AQOs.
3.5.5
The high RSP and TSP levels recorded at EPD's Yuen
Long Station were probably attributable to various construction activities in
the vicinity of the Station and the heavy industrial activities near Shenzhen
as well as vehicular emission from the nearby highways.
3.6
Construction Phase Impact
Assessment
Dust
3.6.1
The principal potential source of air quality impact
arising from the construction of the Project will be fugitive dust. The
temporary dust nuisance, measurable as TSP (Total Suspended Particulates) and
RSP (Respirable Suspended Particulates) will be generated as a result of
construction activities, especially from site clearance / excavation works
where dusty and silty material movement may be involved. The nuisance from
emission of construction vehicles and plant will be relatively small for the
area involved, as the number of construction vehicles and plant is expected to
be limited and small. Moreover, the dust impact is expected to be relatively
insignificant as the excavated material of the area will be mainly from the
stream which have high moisture content.
The major items of the works are:
Ÿ
site clearance;
Ÿ
excavation works to
formation level;
Ÿ
construction of channel
structures / linings, box culverts, drainage pipes, and ancillary drainage
facilities;
Ÿ
construction of
footbridges, maintenance access road and associated road fixtures; and
Ÿ
planting and landscaping
works.
3.6.2
The construction duration is expected to last for
about 3 years within the tentative construction programme timeframe of end 2009
to end 2012.
3.6.3 The most affected air sensitive receivers will be those village houses near and around the works areas. Only minor impacts will be expected due to off-site transportation of spoil materials because the volume of spoil materials requiring disposal is expected to be relatively small. It is expected that the approximate amount of C&D materials to be handled per day is about 30 m3 which equates to approximately 6 trucks per day.
3.6.4
Due to the limited scale of construction works
required, no concrete batching plants will be required for this Project. Construction
tenders / contracts will stipulate that on-site concrete batching shall not be
practised.
3.6.5 Parts of the proposed channel sites are natural stream. Portion of the natural stream bed will be retained to avoid impacting on the established mangrove stands. Hence, the amount of spoil and construction activities is expected to be relatively small.
3.6.6
As the construction works will likely be constructed
section by section, construction dust nuisance is not expected to cause any
significant dust impacts to the nearby sensitive receivers. The quantity of the
spoil materials from site clearance and excavation is unlikely to be large
enough to cause a significant dust nuisance. It is anticipated that excavated
material will only be stockpiled on each local works area and the duration of
the stockpiling will be as short as possible. The feasibility of reusing some
of the excavated materials as backfilling materials will be rigorously examined
during the detailed design stage. As some materials may be used back in the
construction processes, the quantity of material need to be disposed of can be reduced.
Hence construction dust nuisance at nearby representative sensitive receivers
will expect to be insignificant. Provided that proper construction dust
mitigation measures are in place as required by the Air Pollution Control
(Construction Dust) Regulation, adverse dust impact during is not expected.
3.6.7
As the Project is close to existing road, purpose-built
haul road is not expected for the transportation of excavated material and
filling material.
Odour
3.6.8
Odour is not expected from the excavated stream material. In the unlikely event that potential odourous materials are
encountered during construction, excavation works should be conducted in the
shortest time span possible. Programming of the works should be carried out to
ensure that the time for such works can be minimised. If necessary, the Contractors
should also liaise with local resident to inform them of the duration of
potential odour nuisance, and that efforts are made to minimise and mitigate
such nuisance. Excavated material, if found to be odorous,
should be placed as far away from air sensitive receivers as possible.
Temporary stockpiles of odorous excavated material should be removed off-site
as soon as practically possible within 2 days to avoid odour nuisance arising.
3.7
Operational Phase Impact
Assessment
Introduction
3.7.1
Potential air
quality impacts during operational phase of the Project are identified as
follow:
§
Traffic emission from the
proposed access road (which will be open for public use) and the associated
carpark near the viewing point; and
§
Dust and odour from the
routine maintenance of the proposed channel.
3.7.2
Apart from
maintenance, there are no other potential odour impacts at the ASRs during
normal operation of the Hang Hau Tsuen Channel.
Traffic Emission Impact
3.7.3
The proposed access road will
be open to public use. According to the HKPSG, a minimum buffer distance of 5 m
to ASRs is recommended for local distributor road. As shown in Table
3.2, majority of the ASRs would have adequate buffer distance to the
proposed access road, except ASR 10 (at 4 m). However, it should be noted that the
HKPSG recommendation is relevant to local distributor road with continuous free
flowing through traffic. As there is no through traffic for the access road and
only a very few parking spaces (8-9 nos.) will be provided, the worst case
forecast peak traffic flow in 2027 is expected to be 50 vehicles with 10% heavy
vehicles per hour only. With such very limited traffic flow on the access road,
the expected vehicular emission at the ASR 10 would still be acceptable. In addition, traffic management will be
implemented to restrict vehicles longer than 7 m from using the access road. With
the very low traffic flow and buffer distance, adverse traffic emission impact
from the proposed access road to the nearby ASR is therefore not expected.
Maintenance Impact
3.7.4
Maintenance would be necessary for the constructed channel to
remove excessive silts, vegetation, debris and obstructions in order to
maintain its hydraulic performance and structural integrity. Siltation will
generally be allowed to accumulate and removal of excess silt would be carried
out at locations where specific flooding or safety issue is identified. The
excavated sediment will be properly stored and disposed of to minmise dust and
odour nuisance. Little or no maintenance will be necessary for the natural
stream bed sections of the channel. Therefore, maintenance of the channel
during the operational phase is unlikely to cause any adverse air quality
impacts in terms of dust and odour.
Construction Phase
Construction Dust
3.8.1
In order to comply with Air Pollution Control
Ordinance (APCO), the Contractor should undertake at all times measures to
prevent dust nuisance as a results of his activities. The Contractor should
follow all the requirements for dust control stipulated in the Air Pollution
Control (Construction Dust) Regulation. Dust suppression measures should be
installed as part of good construction practice, and they should be
incorporated in the Contract Specification and implemented to minimize dust
nuisance to within acceptable levels arising from the works. The followings are
examples of the dust suppression measures.
(i)
The area in which excavation takes place shall be
sprayed with water immediately prior to, during and immediately after the
excavation to minimise dust generation.
(ii)
The Contractor shall frequently clean and water the
site to minimize fugitive dust emissions.
(iii)
Effective water sprays shall be used during the
delivery and handling of aggregate, and other similar materials, when dust is
likely to be created and to dampen all stored materials during dry and windy
weather.
(iv)
Watering of exposed surfaces shall be conducted at least 2 times per day especially during dry and
windy weather.
(v)
Areas within the site where there is a regular
movement of vehicles must be regularly watered as often as necessary for
effective suppression of dust or as often as directed by the Engineer.
(vi)
Where dusty material are being discharged to vehicle
from a conveying system at a fixed transfer point, a three-sided roofed
enclosure with a flexible curtain across the entry shall be provided. Exhaust
fans shall be provided for this enclosure and vented to a suitable fabric
filter system.
(vii)
The Contractor shall restrict all motorised vehicles
within the site, excluding those on public roads, to a maximum speed of 15 km
per hour and confine haulage and delivery vehicles to designated roadways
inside the site.
(viii)
Wheel washing facilities shall be installed and used
by all vehicles leaving the site. No earth, mud, debris, dust and the like
shall be deposited on public roads. Water in the wheel cleaning facility shall
be changed at frequent intervals and sediments shall be removed regularly. The
Contractor shall submit details of proposals for the wheel cleaning facility.
Such wheel washing facilities shall be usable prior to any earthworks
excavating activity on the site. The Contractor shall also provide a
hard-surfaced road between any washing facility and the public road.
(ix)
All vehicle exhausts shall be directly vertically
upwards or directed away from the ground.
(x)
Any materials dropped on paved roads shall be cleaned
up immediately to prevent dust nuisance.
Odour
3.8.2
In the event that excavated materials are found to be odourous,
the following measures should be implemented by the Contractor.
(i)
Place odorous
excavated material as far away (say, at least 20m)
from air sensitive receivers as possible.
(ii)
Temporary stockpiles of
odorous excavated material should be properly covered with tarpaulin and should
be removed off-site as soon as practically possible within 2 days to avoid any
odour nuisance arising.
Operational Phase
3.8.3
No adverse air quality impact is identified during
operational phase. In the event that sediment excavated during maintenance are
found to be odourous, the following measures should be implemented by DSD (or
DSD’s maintenance contractor).
(i)
Place odorous
excavated material as far away (say, at least 20m)
from air sensitive receivers as possible.
(ii)
Odorous excavated material
should be properly covered with tarpaulin or packed in plastic bags or stored
in enclosed skips and should be removed off-site as soon as practically
possible within 2 days to avoid any odour nuisance arising.
3.9.1
There will likely be one concurrent project in the vicinity
of the proposed Project (see Section 2.9). As the concurrent
project is located about 150 m from the Project and given the small scale works
of the concurrent project, cumulative air quality impact is not expected.
3.10
Monitoring and Audit Requirements
3.10.1 Dust impacts during the construction phase can be readily mitigated through implementation of standard mitigation measures and good housekeeping practices.
3.10.2
However,
if the proposed construction dust mitigation measures are not fully
implemented, it is likely that some nearest air sensitive receivers would
suffer unacceptable impact. It is therefore recommended that an Environmental
Monitoring & Audit (EM&A) programme in respect of dust issue be carried
out at representative sensitive receivers to monitor the effectiveness and
efficiency of the dust suppression measures.
3.10.3
It
is recommended that at least the following representative ASRs (Table
3.4) should be selected for monitoring purpose during the construction phase.
These representative sensitive receivers have been selected for monitoring
because of their locations are close to the construction works areas, and/or
are downwind from the sites under the most predominant meteorological
conditions and hence, are the mostly likely being impacted if dust suppression
measures are not properly implemented.
3.10.4
No monitoring is required
during operational phase.
3.10.5
The monitoring requirement is
broadly presented in Chapter 10 of this Report. Details
of the monitoring and audit of construction dust will be presented in the
separate EM&A Manual.
Representative ASRs chosen for Air Quality Monitoring during
Construction Phase
|
Air Quality Monitoring Station |
ASR ID |
General Description |
|
A1 |
ASR 2 |
Wing Jan Camp |
|
A2 |
ASR 4 |
Village house at No. 57
Hang Hau Tsuen |
Notes:
Subject to the location of the construction works and
to be proposed by the ET Leader.
3.11.1 The construction dust impact assessment has identified air sensitive receivers within the Study Area. Construction works that may cause potential construction dust nuisance is also identified. Mitigation measures, as required by Air Pollution Control (Construction Dust) Regulation, are also highlighted. Provided that the Contractor implements all the necessary mitigation, air quality at nearby air sensitive receivers during construction phase is expected to comply with the 1 hour TSP guideline and the daily TSP Air Quality Objectives.
3.11.2 Air quality monitoring is recommended at selected air sensitive receivers during the construction period to check for compliance with the permissible dust levels and effectiveness of the proposed mitigation measures.
3.11.3 During the operational phase of the Project, given the low volume of vehicles expected to use the access road, vehicular emission impact from the proposed access road upon the nearby air sensitive receivers is not expected. Maintenance of the channel is also unlikely to cause any adverse impact during operational phase.