2.1.1.1
Several options and alternatives have been considered in
this Project for the refinement and selection of the preferred option for the
workshop to be taken forward for the EIA and detailed design. Details of the options
considered and constraints assessed in adopting the preferred scheme have been
reviewed, including alternative designs and construction methodologies. The review has also taken into account
engineering feasibility, site conditions, programme aspects and environmental
considerations with a view to identifying the optimum arrangement.
2.2.1.1
The existing Hong Kong Workshop at
2.3 “Without Project” Alternative
2.3.1.1
A fundamental project alternative is the option not to
implement the temporary EMSD Hong Kong Workshop in Chai Wan, which in
environmental terms is referred to as the “Do-nothing” option. However, the continuation of the vehicle
repairing and maintenance services of the existing EMSD Hong Kong Workshop in
2.3.1.2
There is currently only one vehicle repairing and
maintenance workshop on
2.3.1.3
Based upon the above reasons, the “Do-nothing” option is not
preferred and not considered to be an environmentally preferred solution to
cope with the current demand of the repairing and maintenance of the small and
light vehicles of the government fleet.
2.4.1
Design of the Workshop
2.4.1.1
The size of this
proposed single-storey workshop is small (only about 2,040 m2) and
the flexibility to distribute individual repairing and maintenance processes
within the workshop is comparatively low.
The following design options were considered and reviewed, however, in
order to optimise the operational and environmental benefits of the facility.
Servicing Capacity Design
2.4.1.2
There were 2 conceptual options for the servicing capacity
design investigated, namely: (i) large servicing capacity; and (ii) small
servicing capacity. The difference
in terms of the scale, extent, layout and configuration are tabulated in Table 2.1.
Table 2.1 Comparison
of Servicing Capacity Design Options
|
Parameter |
(i) Large Servicing Capacity |
(ii) Small Servicing Capacity |
|
Scale |
Covering more government fleet types ranging from
small, medium to large vehicles. |
Covering less government fleet
types. |
|
Extent |
Servicing wider activities e.g. repairing,
maintenance, roller brake testing, tyre balancing, tyre changing, major
vehicle body repair, traffic accident repair, vehicle body painting, vehicle
cleansing, etc. |
Servicing only general activities
e.g. repairing, maintenance, roller brake testing, tyre balancing, tyre
changing, etc. |
|
Layout |
More complicated to accommodate different vehicle
types and servicing activities, hence less flexible to maximise the use of
available space. |
Easier to accommodate small
vehicle types and limited servicing activities, hence more flexible to
maximise the use of available space. |
|
Configuration |
Dependent on the selected site. |
Dependent on the selected site. |
2.4.1.3
The optimisation
of the design to service a smaller number and types of vehicles (small and
light vehicles, i.e. motorcycle, saloon cars and light vans) in the Workshop in
order to reduce any potential environmental issues during the operation phase,
e.g. vehicular emissions, noise, wastewater, chemical waste, etc. A preliminary appraisal of the potential
environmental benefits and dis-benefits of these options are described below
and depicted in Table 2.2.
·
Noise: The design with smaller
number of vehicles to be serviced by the proposed Workshop would offer an
environmental benefit to the nearby sensitive receivers during the operation
phase as a result of the reduced noise sources, e.g. vehicle engine, equipment,
etc. It is anticipated that there
would be no major difference between these options during the construction
phase.
·
Air Quality: The design with smaller
number of vehicles to be serviced by the proposed Workshop would offer an
environmental benefit to the nearby sensitive receivers during the operation
phase as a result of the reduced vehicle emission sources. It is anticipated that there would be no
major difference between these options during the construction phase.
·
Water Quality and
Sewerage: The
design with smaller number of vehicles to be serviced by the proposed Workshop
would require the deployment of lesser staff and vehicle maintenance
activities, thereby reducing the associated generation of sewage and industrial
wastewater during the operation phase. This would relief the pressure on the
loading of sewage treatment infrastructure and capacity on-site and
off-site. It is anticipated that
there would be no major difference between these options during the
construction phase.
·
Waste and Land
Contamination: The design with smaller number of vehicles to be serviced by the
proposed Workshop would require the deployment of vehicle maintenance
activities, thereby reducing the associated generation of waste arising and
potential risk of land contamination during the operation phase. It is
anticipated that there would be no major difference between these options
during the construction phase.
·
Landscape and Visual: It is anticipated that
there would be no major difference in environmental benefits between these
options during the construction and operation phases.
Table 2.2 Potential
Environmental Benefits and Dis-benefits of Servicing Capacity Design Options
|
|
Servicing Capacity Design Options |
|||
|
Environmental Issues |
Large Number and Types of
Vehicles |
Small Number and Types of
Vehicles |
||
|
|
C |
O |
C |
O |
|
Noise |
- |
X |
- |
ü |
|
Air Quality |
- |
X |
- |
ü |
|
Water Quality and Sewerage |
- |
X |
- |
ü |
|
Waste and Land Contamination |
- |
X |
- |
ü |
|
Landscape and Visual |
- |
- |
- |
- |
Note: “C” = Construction phase; “O” = Operation
phase; “ü” = Environmentally preferred option; “X” = Environmentally not preferred
option; “-” = No environmental preference
Building Design
2.4.1.4
There were two conceptual options for the building design investigated,
namely: (i) ordinary built form; and (ii) shed built form. Their difference in terms of the scale,
extent, layout and configuration are tabulated in Table 2.3.
Table 2.3 Comparison of Building
Design Options
|
Parameter |
(i) Ordinary Built Form |
(ii) Shed Built Form |
|
Scale |
Multi-storey design, depending on height
restriction. |
Single storey open shed. |
|
Extent |
More spacious to accommodate more activities. |
Small size and restricted to less
activities. |
|
Layout |
Stronger building envelope to withstand inclement
weather. |
Less favourable to adverse
weather. |
|
Configuration |
More variety, depending on height limit, size and
configuration of the selected site. |
Simple and standard. |
2.4.1.5
The use of a simple open steel shed design instead of a
typical building design of the workshop so as to reduce the duration of
construction works and hence potential environmental impacts during the
construction phase, e.g. construction dust, noise, site effluent, C&D
waste, etc. A preliminary appraisal
of the potential environmental benefits and dis-benefits are described below
and depicted in Table 2.4.
·
Noise: The open shed design for
the building structure of the proposed Workshop would offer an environmental
benefit of reduced construction noise nuisance to the nearby sensitive
receivers as a result of the shortened construction period, but the dis-benefit
of adopting an open shed would be the potential noise nuisance arising from the
maintenance activities during the operation phase.
·
Air Quality: The open shed design for
the building structure of the proposed Workshop would offer an environmental
benefit of reduced construction dust impact to the nearby sensitive receivers
as a result of the shortened construction period. It is anticipated that there would be no
major difference between these options during the operation phase.
·
Water Quality and
Sewerage: The
open shed design for the building structure of the proposed Workshop would
offer an environmental benefit of reduced construction site effluent and sewage
impacts to the nearby sensitive receivers as a result of the shortened
construction period. It is
anticipated that there would be no major difference between these options
during the operation phase.
·
Waste and Land
Contamination: The open shed design for the building structure of the proposed
Workshop would offer an environmental benefit of reduced construction waste
arising as a result of the shortened construction period. It is anticipated that there would be no
major difference for waste and land contamination aspects between these options
during the operation phase.
·
Landscape and Visual: It is anticipated that
there would be no major difference in environmental benefits between these
options during the construction and operation phases.
Table 2.4 Potential
Environmental Benefits and Dis-benefits of Building Design Options
|
|
Building Design Options |
|||
|
Environmental Issues |
Simple Steel Shed |
Typical Building |
||
|
|
C |
O |
C |
O |
|
Noise |
ü |
X |
X |
ü |
|
Air Quality |
ü |
- |
X |
- |
|
Water Quality and Sewerage |
ü |
- |
X |
- |
|
Waste and Land Contamination |
ü |
- |
X |
- |
|
Landscape and Visual |
- |
- |
- |
- |
Note: “C” = Construction phase; “O” = Operation
phase; “ü” = Environmentally preferred option; “X” = Environmentally not preferred
option; “-” = No environmental preference
2.4.1.6
It has been considered that, as the Workshop is a temporary
facility, the use of chain-link fence rather than a solid boundary wall would
facilitate a simple, lean design concept to attain more environmental benefits
from the significant saving of building material and natural ventilation and at
the same time without compromising the environmental quality due to any
environmental impacts during the construction and operation of the
Workshop.
Local Exhaust Design
2.4.1.7
There were two conceptual options for the local exhaust
design investigated, namely: (i) mechanical ventilation; and (ii) natural ventilation. Their difference in terms of the scale,
extent, layout and configuration are tabulated in Table 2.5.
Table 2.5 Comparison
of Local Exhaust Options
|
Parameter |
(i) Mechanical Ventilation |
(ii) Natural Ventilation |
|
Scale |
Tasks oriented installation of extraction systems |
Designing with available space and
roof height to enhance natural ventilation. |
|
Extent |
Extensive, depending on the provision of the type of
services |
Designing with available space and
roof height to enhance natural ventilation. |
|
Layout |
Fixed layout for provision of local exhaust system
for specific activities. |
More flexible open layout plan to
suit different use of space for different activities requiring ventilation. |
|
Configuration |
Flexible design and installation, and facilitated by
provision of ductworks. |
Depending on whether existence of
adjacent obstacles or barriers on-site.
|
2.4.1.8
The enhancement of utilising natural ventilation by
providing a 5.2m high clearance instead of using mechanical ventilation systems
for local exhaust of emissions from the workshop so as to minimise any
potential noise impacts to the nearby sensitive receivers during the operation
phase. A preliminary appraisal of the
potential environmental benefits and dis-benefits are described below and
depicted in Table 2.6.
·
Noise: The design for using
natural ventilation in the proposed Workshop would offer an environmental
benefit of reduced noise nuisance to the nearby sensitive receivers during the
operation phase as a result of the reduced noise sources from mechanical
ventilation fans. It is anticipated
that there would be no major difference between these options during the construction
phase.
·
It is anticipated that there would be no major difference in
environmental benefits on air quality, water quality and sewerage, waste and
land contamination, and landscape and visual aspects between these options
during the construction and operation phases.
Table 2.6 Potential
Environmental Benefits and Dis-benefits of Local Exhaust Design Options
|
|
Local Exhaust Design Options |
|||
|
Environmental Issues |
Natural Ventilation |
Mechanical Ventilation |
||
|
|
C |
O |
C |
O |
|
Noise |
- |
ü |
- |
X |
|
Air Quality |
- |
- |
- |
- |
|
Water Quality and Sewerage |
- |
- |
- |
- |
|
Waste and Land Contamination |
- |
- |
- |
- |
|
Landscape and Visual |
- |
- |
- |
- |
Note: “C” = Construction phase; “O” = Operation
phase; “ü” = Environmentally preferred option; “X” = Environmentally not preferred
option; “-” = No significant environmental preference
2.4.1.9
As a result of the environmental
benefits of the alternatives considered with respect to revising the design to service a
smaller number and types of vehicles, using an open steel shed design and using
natural ventilation, these design alternatives have been adopted in the
preferred scheme as discussed further in Section 3.
2.4.2
Construction Methodology
2.4.2.1
Construction of the workshop would be comparatively
uncomplicated as it mainly involves the erection of a shed, underneath which
the vehicle repairing and maintenance activities would be carried out. As such, consideration of alternatives
was focused on the design of the foundation works and two typical construction
methods being studied and compared, namely Steel-H Driven Piling and Raft
Foundations.
Steel-H Driven Piling
2.4.2.2
Steel-H driven piling is a percussive piling method and
comprises the following engineering features for the construction of this
workshop:
·
capable of providing high load bearing capacities when
driven into ground on hard stratum;
·
can be driven with high energy to achieve deep penetration
in bearing strata when compared with concrete piles;
·
smaller size but high capacity pile allows for close pile
spacing;
·
supplied in a wide range of sizes;
·
can be supplied with coated surfaces to cater for different
ground conditions capable of inducing negative skin friction and aggressive
soils; and
·
easy to handle without the need to pre-drill and driving
does not cause large soil displacements, therefore, ground heave can be
minimal, with minimum site disruption and no added expense of site clean
up.
2.4.2.3
However, the strict control on the use of percussive piling
methods in
·
Comparatively less excavated C&D materials arising; and
·
Better site control and, hence, lower risk of site effluent
runoff during the rainy season due to smaller exposed soil surfaces.
2.4.2.4
Notwithstanding these minor benefits, there are some notable
downsides to the use of percussive piling. The most notable is the
significant noise and vibration impacts that would be caused due to the
mechanical impaction induced by the hydraulic hammer. In addition, the limited times for
undertaking percussive piling would affect the programme as noted above and
therefore prolong the noise impacts to adjacent sensitive receivers. Also, potential construction dust
impacts could be experienced as a result of excavation of soil for the
construction of the pile caps.
Raft Foundations
2.4.2.5
Raft foundation has the following engineering features for
the construction of this workshop:
·
a type of shallow foundation with shallow footings
preferable for when the surface soil is strong and stiff as it can withstand
the imposed load;
·
spreading loads from the structure over a large area, with a
slab extending over the entire load which can be stiffened by the use of
ribs/beams in the foundation; and
·
mainly used on soft/loose soils with low bearing capacity.
2.4.2.6
While the raft foundation may increase the amount of
excavated C&D materials arising, present a slightly bigger challenge to
control the potential risk of site effluent runoff and have a slightly higher
potential construction dust impacts due to the larger exposed soil surfaces,
this method does have the benefit of notably reducing the noise and vibration
impacts as no percussive piling machines will be used.
2.4.2.7
A preliminary appraisal of the available construction methodology
options is described below and depicted in Table
2.7.
·
Noise: The choice of using raft
foundation for the construction of the proposed Workshop would offer an
environmental benefit of reduced noise nuisance to the nearby sensitive
receivers.
·
It is anticipated that there would be no major difference in
environmental benefits on air quality, water quality and sewerage, waste and
land contamination, and landscape and visual aspects between these options
during the construction phase.
Table 2.7 Potential
Environmental Benefits and Dis-benefits of Construction Methodology Options
|
|
Construction Methodology Options |
|||
|
Environmental Issues |
Steel-H Driven Piling |
Raft Foundation |
||
|
|
C |
O |
C |
O |
|
Noise |
X |
- |
ü |
- |
|
Air Quality |
- |
- |
- |
- |
|
Water Quality and Sewerage |
- |
- |
- |
- |
|
Waste and Land Contamination |
- |
- |
- |
- |
|
Landscape and Visual |
- |
- |
- |
- |
Note: “C” = Construction phase; “O” = Operation
phase; “ü” = Environmentally preferred
option; “X” = Environmentally not preferred option; “-” = No significant
environmental preference
2.4.2.8
As the benefits and dis-benefits concerning dust, run-off
and the amount of waste are not significantly different between the two
techniques and can be adequately controlled in both cases, it is considered
that the ability to generate noise is the most notable environmental
factor. Percussive piling can
generate significant noise and vibration disturbance to the surrounding sensitive
receivers and as a result of this, and the constraints imposed by this
technique on the programme, the raft foundation technique is considered to be
overall environmentally preferable and has been selected for the preferred
option.
2.5.1.1
Based on the above considerations of the design and
construction methodology options, a preferred option has been selected in the
Scheme and Preliminary Design phases of this Project as summarised below, based
on which the detailed design of this project will be proceeded and this EIA
study was carried out:
·
Optimum design for small servicing capacity of vehicles,
simple open steel shed facility and natural ventilation for emissions exhaust;
and
·
Optimum construction methodology using raft foundation.
2.5.1.2
This preferred option is determined based on the comparison
of the environmental benefits and dis-benefits of the various options and
alternatives and has been selected on the basis that it minimises environmental
impacts and presents overall environmental benefits over the other options and
is considered the optimum scheme from an environmental perspective.