6.
Air
Quality Assessment
6.1.1
This section presents a qualitative assessment of air
quality impact associated with the construction and operation of the secondary drainage
channel KT13. Potential construction phase air quality impacts consists of increased
fugitive dust at the nearby air quality sensitive receivers and some odour
issue when contaminate sediments are removed from the stream.
6.1.2 Operation of storm water drainage channel is not expected to have any significant air quality impacts. Maintenance cutting of vegetation and sediments removal may occasionally increase odor in the Study Area but in the long term such incidents are expected to be reduced, as the quality of the sediments improve due to continued implementation of Livestock Waste Control Scheme.
6.2
Air Quality Assessment Criteria
6.2.1
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.
6.3.1 The representative air sensitive receivers (ASRs) that may potentially be impacted by KT13 are listed in Table 6.2 and shown in Figure 6.1.
Representative Air Sensitive Receivers (ASRs)
|
ASR ID. |
Location |
Description |
Approximate Distance from KT13 Site Boundary |
|
13 |
Ma On |
Village House |
35 m |
|
14 |
Ho Pui Village |
Village House |
36 m |
|
15 |
Ma On |
Village House |
4 m |
|
16 |
Ho Pui Village |
Village House |
6 m |
|
17 |
North of Ma On |
Village House |
12 m |
Note: For
location of ASRs, please refer to Figure 6.1.
6.4.1
The Study Area is located in the northwest of
6.4.2
The wind rose from the Shek Kong Station (Figure 6.2)
can be used as an indicator for the Study Area. The wind rose indicates that
the dominant wind direction is north-easterly and easterly.
Existing Air
Conditions
6.4.3
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 in the western end. According to data collated
from the Yuen Long Station, the averages of the NO2, SO2,
TSP and RSP for period between 2003[3]
are shown in the Table 6.3 below.
Air Pollutants Concentrations at Yuen Long EPD Station (2003)
|
Pollutants |
Concentration
in Micrograms per Cubic Meter (μg/m3) |
|||||
|
|
1 hour |
24 hour |
Annual |
|||
|
|
Maximum |
AQOs |
Maximum |
AQOs |
Average |
AQOs |
|
TSP |
N/A |
500* |
389 |
260 |
98 |
80 |
|
RSP |
377 |
N/A |
227 |
180 |
61 |
55 |
|
NO2 |
267 |
300 |
144 |
150 |
60 |
80 |
|
SO2 |
336 |
800 |
85 |
350 |
18 |
80 |
Notes:
N/A means Not Applicable.
* This control limit has no statutory basis but is used as a target level for limiting fugitive dust emissions generated by construction activities.
6.4.4
The table indicates that the concentrations of short
and long-term SO2 and NO2 are below the AQOs. However, the
short-term and long-term concentrations of TSP and RSP exceed the stipulated
AQOs.
6.4.5
The high TSP and RSP levels recorded at EPD's Yuen
Long Station were probably attributable to construction activities in the
vicinity of the Station including works for Village Flood Protection for Yuen
Long, Kam Tin & Ngau Tam Mei (30CD), Drainage Channels for Yuen Long &
Kam Tin (43CD and 60CD), infrastructure provision for Yuen Long South
development and the heavy industrial activities near Shenzhen as well as
vehicular emission from nearby roads. In the long term, TSP and RSP levels in
the Yuen Long area are likely to remain high as construction and industrial
activities will continue.
6.5
Impact
Assessment and Mitigation
Construction
Phase
6.5.1
The principal potential source of air quality impact
arising from the construction of KT13 will be fugitive dust. In order to
minimize impact on air quality, no on-site concrete
batching plant will be erected. Any concrete to be used will be transported to
the work site. When construction tenders/contracts are prepared, these
documents will clearly specify that the Contractor shall not erect and operate
on-site concrete batching plant. The temporary dust nuisance from construction
activities, measurable as TSP (Total Suspended Particulates) and RSP
(Respirable Suspended Particulates) will be generated mainly by site formation
works where large quantity of 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 river channel which have a high moisture content.
6.5.2
The construction duration for KT13 is expected to last
for about 36 months, from mid 2007 to mid 2010.
6.5.3 Thus the most affected air sensitive receivers will be those village houses near and around the works areas. Only minor impacts are expected due to off-site transportation of spoil materials as the number of haulage trips outside the site is limited to approximately 4 per hour (round trip). Most of the spoil will also be excavated in a moist state and directly loaded to trucks for disposal.
6.5.4
Due to the limited scale of construction works
required and the fact that the use of gabions for lining the channel is
proposed for KT13, no concrete batching plants and blasting will be required.
Construction tenders/contracts will stipulate that blasting and on-site
concrete batching shall not be practised.
6.5.5 The proposed construction works will involve site clearance in the works areas, excavation to formation levels of secondary channels, formation of banks of channels and restoration landscaping works after the construction activities.
6.5.6
The existing stream is a semi-natural stream, west of
Tai Kek and near Ho Pui. The proposed works involved construction of two
separate gabion lined secondary channels to the north and to the south of Ho
Pui Area. The northern section (Section A) is about 400m long and the resultant
channel will be about 5m wide and 3m high. While the southern section (Section
B: trapezoidal channel) is about 300m long and the formed channel is about 5m
wide and 2m high. The two will be connected with a twin box concrete culvert
for bypass of storm water flow designed to cope with 1 in 50 years storm.
6.5.7 The proposed construction works will mainly involve site clearance in the works areas and formation of access road, excavation to formation levels of secondary channels, formation and concreting of bypass culvert, formation of channel banks and landscaping restoration works after the construction activities.
6.5.8 For the construction of secondary drainage channel KT13, the amount of spoil generated and filling material required is estimated to be about 81,283 m³. Based on a typical truck load of 6 m3 spoil, for a period of about 30 months and 10 hours per working day, the amount of vehicle trips is estimated to be 4 per hour (roundtrip). Therefore, dust impact arising from construction traffic is considered negligible.
6.5.9
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, since some of the excavated materials
will be used back as backfilling materials. As some materials will be used back
in the construction processes, the quantity of material need to be disposed of
or import will be limited. Hence construction dust nuisance at nearby
representative sensitive receivers will expect to be insignificant. In
addition, the distance between the construction works and nearest air sensitive
receiver is about 4m. 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. As part of the ecological mitigation measure to
minimise impact on the existing stream course, a restriction to minimised the
working area to 75m length of stream has been proposed. Such restriction would
also reduced the likely dust impact.
6.5.10
Dedicated haul road is not expected as access to the
site is accessible via existing public road, e.g.
Odour
6.5.11
In order to minimize the impact of potential odour
during construction, excavation works should be conducted in the shortest time
span possible. Programming of the works should be carried out well in advance
to ensure that the time for such works can be minimized. 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 minimize and
mitigate such nuisance. For earth and other materials excavated from the
ground, these should be transported away from the site within 1 day. In the
event that on-site storage cannot be avoided, the stockpiling should be
temporary. Also, all such stockpiled materials must be stored in covered skips.
Any leachate from storage skips should be stored in covered buckets and tanks.
It should be collected along with toilet waste by licensed contractor to be
disposed at government sewer.
Dust and Odour
Mitigation Measures
6.5.12
In order to comply with the Air Pollution Control
Ordinance (APCO), the Contractor should undertake at all times 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 proper 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 and odour suppression measures.
Dust
Mitigation Measures
(i) The
Contractor shall frequently clean and water the site to minimize fugitive dust
emissions.
(ii) 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.
(iii) Watering
of exposed surfaces shall be exercised as often as possible depending on the
circumstances.
(iv) Areas
within the site where there is a regular movement of vehicles shall be
regularly watered as often as necessary for effective suppression of dust or as
often as directed by the Engineer.
(v) 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.
(vi) 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.
(vii) 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.
(viii) All
vehicle exhausts shall be directly vertically upwards or directed away from the
ground.
(ix) Any
materials dropped on paved roads shall be cleaned up immediately to prevent
dust nuisance.
Odour Mitigation Measures
(x) Any
odourous excavated material shall be placed away from sensitive receivers. The
material shall be removed within 1 day.
(xi) Any
odourous material stockpiled shall be of the shortest duration. Also, all
stockpiled materials shall be stored in covered skips. Any leachate from these
storage skips shall be collected in covered tanks or buckets and removed from
site with toilet waste by licensed collectors for discharging to government
sewer.
Operation
Phase
6.5.13
During the operation phase, any excavated sediments
arising from maintenance dredging should be stored in covered impermeable skips
and removed from site within 1 day.
Concurrent
Construction Activities
6.5.14
Concurrent major projects in the North West New
Territories (NWNT) include the proposed Deep Bay Link (6.5 km away), Yuen Long
Highway Widening Works (4 km away) and Yuen Long Floodway Bypass (4 km away).
Since all these projects are located far away from this Project, potential
cumulative dust nuisance is not expected.
6.5.15
Other secondary drainage channels will be constructed
within the same timeframe as KT13. All are spread out across the Kam Tin area,
the nearest of which (KT12, 200m in length) is at least 350m to the east of KT13.
The other nearby projects include the secondary drainage channels KT14 and KT15
which is approximately 650m and 1300m away from KT13. Despite the three years
construction period of KT13, the cumulative dust impacts as a result of
concurrent channel works within the Kam Tin areas are not expected to be
significant given the large distance separation and provided that the
recommended dust suppression measures are implemented.
6.6.1 With the implementation of the proposed mitigation measures, no adverse residual impacts are expected during the construction and operation of KT13.
6.7
Monitoring and Audit Requirements
6.7.1 Dust impacts during the construction phase can be readily mitigated through implementation of standard mitigation measures and proper housekeeping practices.
6.7.2
An
Environmental Monitoring & Audit (EM&A) program in respect of dust
issues will be carried out at ASR14 and ASR15 at Ma On Kong and Ho Pui Villages
respectively to ensure that the proposed mitigation measures are implemented
and that they are effective. These representative sensitive receivers are close
to the construction works areas and hence, are most likely to be impacted if
dust suppression measures are not properly implemented.
6.7.3
No monitoring is required
during operational phase.
6.7.4
The details of EM&A
requirements are presented in Chapter 11 of this Report.
6.8.1 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 AQOs. Mitigation measures have been proposed in order to minimise the impact of potential odour during construction.
6.8.2 Operational stage odour nuisance is expected to be complied with the EPD’s criteria as regular cleaning and drainage improvement will improve the sediment deposition situation in all the proposed drainage.