3.
Air
Quality IMPACT Assessment
3.1.1
This Chapter presents a qualitative assessment of air
quality impact associated with the construction and operation of the secondary
channels: MUP03, MUP04A, MUP04B, MUP05 &
LMH01 (the Project). Potential construction phase
air quality impact consists of increased fugitive dust at the nearby air
quality sensitive receivers.
3.1.2 Annual maintenance cutting of vegetation and sediment removal may be necessary during operation of the drainage channels. Such activities 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 (TM-EIA).
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 |
24
hourB |
1
yearC |
|
|
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 1
hour criteria not to be exceeded more than 3 times per year.
B 24
hour criteria 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 TM-EIA 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 representative air sensitive receivers (ASRs) that may potentially be impacted by the Project are listed in Table 3.2 and shown in Figures 3.1 – 3.3.
Representative Air
Sensitive Receiver (ASR)
|
Channels |
Representative ASR |
General Description |
No. of Floors |
Approximate Distance to Works Site Boundary, m |
|
MUP03 |
MUP03-1 |
Village house
near |
2 |
34 |
|
MUP03 |
MUP03-2 |
Village house
near |
1 |
14 |
|
MUP04A |
MUP04A-1 |
23 King Ngai Garden near |
3 |
34 (to MUP04B) |
|
MUP04A-2 |
Village house near |
3 |
5 |
|
|
MUP04B |
MUP04B-1 |
|
3 |
23 |
|
MUP04B-2 |
Village house near |
3 |
3 (to 1350mm pipe) |
|
|
MUP05 |
MUP05-1 |
Village house
near |
2 |
20 |
|
MUP05-2 |
Village house at Loi Tung North |
2 |
24 |
|
|
MUP05-3 |
Village house at Loi Tung North |
2 |
7 |
|
|
MUP05-4 |
Village house at Loi Tung North |
2 |
12 |
|
|
MUP05-5 |
Village house
near |
2 |
43 |
|
|
MUP05-6 |
Village house at Loi Tung North |
2 |
4 |
|
|
LMH01 |
LMH01-1 |
Village house at No. 166 Lin Ma Hang |
2 |
8 |
|
LMH01-2 |
Village house at No. 213A Lin Ma Hang |
3 |
6 |
|
|
LMH01-3 |
Village house at No. 139B Lin Ma Hang |
3 |
32 |
|
|
LMH01-4 |
Village house at No. 71 Lin Ma Hang |
2 |
10 |
|
|
LMH01-5 |
Village house at No. 1A Lin Ma Hang |
3 |
116 |
Note:
The
location of the ASRs is shown in Figures 3.1
- 3.3.
3.4.1
The Study Area is located in the northern part of
3.4.2
The wind rose from the Ta Kwu Ling Station indicates
that the dominant wind direction is east-south-easterly and easterly.
Existing Air
Conditions
3.4.3
As there is no monitoring station at the Study Area,
EPD's Air Quality Monitoring Station at Tai Po was used to establish ambient
air quality over the Study Area. According to data collated from the Tai Po
Station, the concentrations of the TSP and RSP in
2003 [3]
are shown in Table 3.3 below.
Air Pollutants Concentrations at Tai
|
Pollutants |
Annual Concentration
in Micrograms per Cubic Meter (μg/m3) |
|
|
|
Average |
AQOs |
|
TSP |
71 |
80 |
|
RSP |
54 |
55 |
3.4.4
The table indicates that the
annual concentration of TSP and RSP at Tai Po are below the
AQOs.
3.4.5
For the study area,
vehicular exhaust emissions from
3.5
Air Quality Impact
Assessment
Construction Phase
Dust
3.5.1
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. However, 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 river
channel which have high moisture content.
The major items of the works are:
Ÿ
MUP03 construction
of approximately 93 m long (1.2 m width) channel using gabion lining and
associated U-channel
Ÿ
MUP04A construction
of approximately 163 m long (4.5 m width) channel using gabion lining and associated
drainage pipes
Ÿ
MUP04B construction
of U-channels and drainage pipes
Ÿ
MUP05 construction
of approximately 1014 m long (of varying widths) channel using gabion lining
The
works also include the various ancillary infrastructure works such as
footbridge, vehicular bridge, maintenance ramp, etc.
3.5.2
The construction duration for this Project as a whole is expected to last for about 3.5 years within the tentative
construction programme timeframe of end 2007 to mid 2011. Each channel would have individual construction programme depending on
the size of the proposed channel.
3.5.3 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 is expected to be relatively small.
3.5.4
Due to the limited scale of construction works
required and the fact that the use of gabions have been proposed for lining the
channels, no concrete batching plants will be required for this Project. Construction
tenders / contracts will stipulate that on-site concrete batching shall not be
practised.
3.5.5 Parts of the proposed secondary channel sites are natural streams. The proposed construction works will involve site clearance in the works areas, excavation to formation levels of secondary channels, lining of channel banks and bases, and restoration landscaping works following the construction activities.
3.5.6 Portion of the natural stream banks and beds at MUP05 will be retained, while MUP03 and MUP04B will be small channels or drainage pipes. The amount of spoil and construction activities is expected to be relatively minor.
3.5.7 Ready mixed concrete would mostly likely be supplied by existing batching plant nearby.
3.5.8 Alternative solutions to flooding problem at Lin Ma Hang stream (LMH01) instead of a bypass channel have been recommended under this Project to avoid impacts on the valuable ecological resources in the area. The revised works for Lin Ma Hang comprise the local improvement of crossings, footbridges, stream banks as well as improvement to the existing security grille at the outlet of Lin Ma Hang stream. It also includes the installation of several flood alarm system in the village. As a consequence, construction activities are substantially scaled down. Given the small scale works, construction dust is considered to be negligible.
3.5.9
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 or
imported can be reduced. Hence construction dust nuisance at nearby
representative sensitive receivers will expect to be insignificant. In
addition, the distance between the channel construction
works and most of the air sensitive receiver is over 5 m or more.
This buffer distance is adequate to alleviate the ASR from the construction
dust nuisance provided that proper construction dust mitigation measures are in
place as required by the Air Pollution Control (Construction Dust) Regulation.
3.5.10
As the proposed channels are close to existing roads,
purpose-built haul road is not expected for the transportation of excavated
material and filling material. Nonetheless, the Contractor should identify any
alternative access route away from any
Odour
3.5.11
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. Odorous excavated material 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 24 hours to avoid odour nuisance arising.
Operational Phase
3.5.12
Maintenance would be necessary for the proposed gabion channels
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 it would impede water flow. Little or no maintenance
will be necessary for the ‘two-stage’ channel at MUP05 and the natural stream
sections of LMH01. Therefore the operation phase of this Project would unlikely
cause any adverse air quality impacts in terms of dust and odour.
Construction Dust
3.6.1
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 Contractors are
required to 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 should be directly vertically
upwards or directed away from the ground.
(x)
Any materials dropped on paved roads will need to be
cleaned up immediately to prevent dust nuisance.
Odour
3.6.2
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 24 hours to avoid
any odour nuisance arising.
3.7.1
There are projects in the vicinity of the proposed drainage
channels. These are described in Chapter 2. Many do not have
significant influence on the Project, some are on-going projects that will be
completed by the time works commences for this Project.
3.7.2
The major public works project in the area is the Fanling
Bypass for the Ping Che / Ta Kwu Ling Development proposed under the NENT
Study. However, there is still no programme for the preliminary design or
implementation of this project and thus will not be consider in the cumulative
impact assessment.
3.7.3
The only likely potential cumulative impact would be from
construction works of the drainage channels under this Assignment, specifically
the Non-DP channels at MUP01 and MUP02 (which drains into
MUP05). Works associated with the Non-DP channels at MUP01 and MUP02 will be
limited as only short sections of gabion banks / landscaped embankment slopes
will be required. As such, adverse cumulative air quality impact is not
expected.
3.8
Monitoring and Audit Requirements
3.8.1 Dust impacts during the construction phase can be readily mitigated through implementation of standard mitigation measures and good housekeeping practices.
3.8.2
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.
3.8.3
It
is recommended that at least the following representative ASRs (Table 3.4)
should be selected for monitoring purposes during the construction stage. 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/or are
close to concurrent construction activities and hence, are the mostly likely
being impacted if dust suppression measures are not properly implemented. Given the relatively small scale improvement works, monitoring at
Lin Ma Hang is not required.
3.8.4
No monitoring is required
during operational phase.
3.8.5
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 Stage
|
Air Quality Monitoring Station |
ASR ID |
Representative for |
Secondary Channels |
|
MUP-A1 |
MUP05-2 |
Village north of Loi
Tung |
MUP05 and potential concurrent activities at MUP01,
MUP02, MUP03, MUP04A and MUP04B |
|
MUP-A2 |
MUP05-4 |
Village north of Loi
Tung |
MUP05 and potential concurrent activities at MUP04A
and MUP04B |
|
MUP-A3 |
MUP04A-2 |
Village house near Loi
Tung |
MUP04A |
Note: Channels MUP01, MUP02 are non-DPs.
3.9.1 The construction dust impact assessment has identified Air Sensitive Receiver (ASR) within the Study Area. Potential 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, construction dust nuisance at nearby representative sensitive receivers is expected to be complied with Air Quality Objectives.
3.9.2 No operational phase air quality impact is expected.