This Section summarises
the environmental outcomes associated with the construction, operation,
restoration and aftercare of the Extension.
Potential dust nuisance from construction
activities and gaseous emissions from construction plant have been evaluated. With the implementation of the
recommended standard dust control measures and good construction site
practices, it is not anticipated that the construction of the Extension will
cause adverse dust or air quality impacts.
The following potential air quality
impacts have been evaluated:
·
Gaseous
emissions from the LFG flares, LTP and LFG generator;
·
Odour
and dust from the landfill operation;
·
Volatile
organic compounds (VOCs) from landfill gas emissions from
the landfill’s surface.
The principal
pollutants of concern that could be emitted from the operation of the landfill
gas treatment facility, leachate treatment plant and
generator are nitrogen dioxide (NO2), carbon monoxide (CO), sulphur
dioxide (SO2), benzene and vinyl chloride. The concentrations of these pollutants
predicted due to emissions from these two plants and generator are within the
relevant assessment criteria at air sensitive receivers (ASRs).
The design of the
Extension has incorporated a stringent odour control
management system. Good site practices and housekeeping
measures will be stipulated in the operation contract.
With the exception of those ASRs in the
immediate vicinity of the boundary of the Extension, no exceedances
of the odour criterion were predicted with the implementation of the odour
management and control system.
Residual impacts were predicted in a small area zoned for industrial
development covering part of TKO Area 137 and
The frequency of the exceedances
at
The VOC emissions from the Extension are
not envisaged to cause adverse air quality impact at ASRs. Monitoring data from the existing SENT
Landfill indicate that the ambient VOC concentrations are low at the site
boundary and that levels are within the trigger values specified in the
Contract. Similar types of waste
will be received at the Extension and the operation of the Extension will be
similar to the existing SENT Landfill.
However, the Extension Site will also use an impermeable liner to cover
waste and areas not in use and will have a more comprehensive landfill gas
collection system. VOC emissions
are therefore likely to be lower at the Extension Site. It is therefore not envisaged that the
operation of the Extension will cause adverse air quality impacts to the
identified ASRs with respect to potential VOC emissions.
During the aftercare phase, air emission
sources are primarily associated with the LFG flares and the generator. The Extension will be sealed with a
capping system (including an impermeable liner) and LFG will be extracted to be
flared or utilised. The
vent gas produced in the enclosed tanks will be either diverted to the flares
or to an air scrubber prior to discharge to the atmosphere. Odour sources will be limited to the SBR tanks of the
LTP. As the emission strength and
scale of the Extension operation during this phase are significantly reduced
when compared to the operation/restoration phase, no adverse odour impact is
anticipated.
It is recommended that dust should be
monitored during the construction phase.
For the operation/restoration phase, dust, ambient VOCs,
ammonia and H2S, stack emissions from the flares, thermal oxidizer
and LFG generator, and meteorological condition will be monitored. In addition, regular odour patrols along
the Extension Site boundary will be required. During the aftercare phase, the most of
the monitoring requirements for the operation/restoration phase will be
continued, except for the monitoring of the emission from the thermal
oxidiser. Dust and odour patrols,
which will only be required if there are major maintenance works at the
Extension.
It is recommended that weekly site audits
be carried out during the construction and operation/restoration phases to
determine if the site activities are being managed in accordance with the
recommended good site practices and mitigation measures.
The predicted construction noise levels at
the identified noise sensitive receivers (NSRs) range
from 37 dB(A) to 59 dB(A). These
levels are well below the noise criterion of 75 dB(A) for domestic premises.
Hence, NSRs will not be adversely affected by the
construction/restoration of the Extension.
However, it is recommended that good construction site practices should
be implemented by the Contractor to further minimise the noise impact.
Sources of noise during operations
include:
·
Landfilling operations (eg operation
of compactor vehicles and bulldozers);
·
Fixed
plant (eg the LTP and LFG treatment facility); and
·
Off-site
traffic for the delivery of waste.
The levels of noise generated by the
operation of landfilling and fixed plant items are
predicted to be between 41 dB(A) and 53 dB(A) during daytime and 33 dB(A) and
47 dB(A) during night-time at the NSRs. These levels are well below the day-time
criterion of 60 dB(A) and night-time criterion of 50 dB(A) as set out in the Technical
Memorandum on Noise From Places Other Than Domestic Premises, Public Places or
Construction Sites.
The levels of façade traffic noise along
While no adverse noise impacts are
expected during the operational phase of the Extension, it is recommended that
good site practices be implemented to further minimise any impact.
The aftercare of the restored Extension
will involve limited construction works and is expected to have an
insignificant noise impact compared with the construction, operation and
restoration of the Extension, for which noise levels were already predicted to
be within relevant criteria. The
LTP and LFG treatment plant will continue to operate during the aftercare
period and the predicted noise levels at the NSRs due
to the operation of these plants are well within the criteria set out in the Technical
Memorandum on Noise From Places Other Than Domestic Premises, Public Places or
Construction Sites. Noise impact during the aftercare phase
is anticipated to be negligible.
It is recommended that weekly site audits
be carried out during the construction and operation/restoration phases to
determine if the site activities are being managed in accordance with the
recommended good site practices and mitigation measures.
Potential sources of impacts to water
quality during the construction phase are construction runoff and sewage
generated by the workforce. With
the implementation of the mitigation measures set out in the EIA and good
construction site practices, there will be no adverse impacts to the receiving
water bodies.
Potential sources of impact on water
quality during the operation/restoration phase include uncontrolled discharge
of leachate from the active tipping area into the
surface water drainage system, sub-surface off-site migration of leachate into groundwater and marine water through any
defects in the landfill liner and discharge of improperly treated effluent from
the LTP.
The hydrogeological
assessment concludes that, while the landfill cap remains intact and leachate control is maintained, there will be no adverse
impacts on groundwater quality.
Even in the very long term (on a timescale of several hundred years),
when the landfill cap degrades and the active leachate
control system can no longer performs its full function, the potential impacts
on groundwater quality are predicted to be slight. Under such conditions, the quality of
groundwater discharges to
A temporary surface water drainage system
will be constructed around the active tipping area to prevent stormwater from entering the landfill, and to prevent contaminated
rainwater from discharging off-site.
Contaminated runoff will be collected by this system and treated with
the leachate.
A comprehensive leachate containment system
will be installed to contain leachate generated from
the landfill. Construction quality
control / quality assurance procedures will be implemented to ensure that
joints are properly sealed and to avoid damage to the impermeable liner during
construction of this system.
Leachate and sewage collected from the Extension
will be treated at the on-site leachate treatment
plant. Treated effluent will be
discharged to the public sewer and conveyed to the Government treatment works
for further treatment. Treated
effluent entering the sewer will comply with the effluent discharge standards
set out in the Technical Memorandum Standards for Effluents Discharged into
Drainage and Sewerage Systems, Inland and Inshore Waters. There will be no adverse water quality
impact.
Potential sources of impacts to water
quality during the aftercare phase are:
·
Sub-surface
migration of leachate off site and into groundwater
and marine water; and
·
Discharge
of improperly treated effluent from the leachate
treatment works.
In the very long term, the potential impacts on
groundwater quality are predicted to be slight from both these sources.
Leachate collected from the restored landfill will
be treated to comply with effluent discharge
standards as set out in the Technical Memorandum Standards for
Effluents Discharged into Drainage and Sewerage Systems, Inland and Inshore
Waters for discharge to foul sewer
leading to a sewage treatment works.
No adverse water quality impact is anticipated.
It is recommended that weekly site audits
be carried out during the construction and operation/restoration phases to
determine if the site activities are being managed in accordance with the
recommended good site practices and mitigation measures. Monitoring of surface water and
groundwater quality and effluent discharged from the LTP has been recommended.
The key potential impacts during the
construction phase are related to wastes generated from site clearance, site formation,
demolition of the existing SENT Landfill infrastructure and construction of new
infrastructure for the Extension.
It is estimated
that approximately 1.1 Mm3 of excavated materials (eg soil and rock) will be generated by the construction works,
mainly from the slope formation works.
Some of these excavated materials will be reused on-site for the site
formation work and the landfill operation itself. The remaining excavated materials
(approximately 517,000 m3) will be disposed off site. The construction of the Extension will
require fill material to be imported onto the site. These materials could be obtained from
local construction industries, Construction and Demolition Material Handling
Facilities and the quarry, subject to review and the prevailing operational
condition at these facilities.
It is estimated
that approximately 2,800 m3 of inert construction and demolition
material will be generated from the construction and demolition of the existing
infrastructure. These materials will
be reused on-site as fill material and in miscellaneous engineering works.
Approximately
1,500 tonnes of construction waste will be generated from site clearance works
and about 700 m3 of construction waste will be generated
from the construction and demolition of infrastructure. Construction waste will be disposed of
at the existing SENT Landfill. A
small amount of chemical waste (less than a hundred litres per month), sewage
(about 25.5 m3 per day) and general refuse (about 110.5
kg per day) will be generated during the construction phase.
With the implementation of standard good
construction site practices, the construction of the Extension will not cause
adverse waste management or environmental impacts.
It is estimated
that dewatered sludge (maximum of about 4.9 m3 per day at 30% dry
solids), chemical waste (less than a hundred litres per month), sewage (22.5 m3
per day) and general refuse (97.5 kg per day) will be generated during the
operation/restoration phase. With
good site practices, the storage, handling, collection, transport and disposal
of waste arising from the operation and restoration of the Extension will meet
the requirements set out in the EIAO-TM. No adverse waste management impacts
are anticipated.
A small quantity
of dewatered sludge (about 0.33 m3 per day), sewage (3 m3 per
day) and general refuse (13 kg per day) will be generated during the aftercare
of the Extension. While the sewage
will be treated in the leachate treatment plant, the
sludge and general refuse will require off-site disposal at other waste
disposal facilities.
With good site practices, the potential
environmental impacts associated with the storage, handling, collection,
transport and disposal of the small quantity of waste arising from the
aftercare of the Extension will be within acceptable limits set out in the EIAO-TM. No adverse waste management impacts are
anticipated.
It is recommended that weekly audits of the
waste management practices be carried out during the construction and
operation/restoration phases to determine if wastes are being managed in
accordance with the recommended good site practices. Audits of waste management practices
during the aftercare phase are not considered necessary given that the amount
of waste to be handled is small.
The potential hazards associated with
sub-surface migration of landfill gas from the existing SENT Landfill to the
Extension and from the Extension to the adjacent existing and future
developments have been assessed.
Both the existing SENT Landfill and the Extension are considered as a
“medium” source due to the comprehensive and proven landfill gas control
measures installed or to be installed.
The source-pathway-target analysis shows that landfill gas risk posed by
the SENT Landfill and the Extension is medium to high during both the
construction and operation phases within the Extension. The risk posed by the Extension to the
adjacent developments ranges from very low to low, depending on the nature and
location of the these developments.
In general, underground rooms or voids
should be avoided as far as practicable in the design of the Extension
infrastructure area. Other
precautionary and protection measures during construction, design and
operation/restoration phases of the Extension have been recommended. It is expected that with the proposed
precautionary measures in place, the potential risk of landfill gas migration
to the respective targets will be minimal.
Regular monitoring of landfill gas in the perimeter landfill gas
monitoring wells and service voids within the Extension Site and the along the
Site boundary will be undertaken to ensure that no unacceptable off-site
migration of landfill occurs.
The Extension Contractor will be required
to undertake regular monitoring of landfill gas along the Extension boundary as
required by the Contract Specification.
The terrestrial and aquatic ecological resources
recorded within the Study Area (including the Extension Site and the 500m
buffer area) include plantation, shrubland,
grassland, developed area, seasonal stream and subtidal
habitats, as well as associated wildlife.
Of these habitats, shrubland has a moderate
ecological value, whilst other habitats are of low or low to moderate
ecological value. The ecological
value of the developed area is negligible.
The majority of
the proposed Extension will be located in habitats which are already disturbed/developed,
including the existing SENT Landfill and the fill bank in TKO Area 137.
The
proposed Extension will encroach into a small strip (approximately 5 ha) of the
CWBCP, comprising shrubland and grassland habitats of
low to moderate ecological value. The potential impacts on these habitats
within the CWBCP are considered to be low to moderate. With the implementation of the
recommended mitigation measures, no adverse residual impact is expected. There are no marine works involved and
no marine habitats and species will be affected.
A survey recorded 11 wildlife species of
conservation interest (including birds, butterflies, bat and reptile) at the
Extension Site. As these species are highly
mobile and as there is a large extent of similar habitat in the vicinity of the
Extension, the impacts on wildlife are considered to be minimal.
The EIA sets out mitigation measures to
reduce ecological impacts. These
include the adoption of surface water, groundwater, leachate
and landfill gas management systems, good construction practices and provision
of compensatory planting. These
measures will reduce potential disturbance to the surrounding environment and
will also help provide a habitat of higher ecological value than that of the
existing site once the restoration works are complete.
It is recommended that weekly site audits
be carried out during the construction and operation/restoration phases to
determine if the site activities are being managed in accordance with the
recommended good site practices and mitigation measures.
With mitigation measures in place, the
landscape impacts would range from “insubstantial” to “substantial” at
landscape resources during the construction phase. The landscape impacts will be reduced to
“insubstantial to moderate” during the operation/restoration phase and further
reduced to “insubstantial to slight” at year 10 of the aftercare phase when the
restored landscape is fully mature.
There will be “Slight positive” landscape impacts on the reclaimed TKO
Area 137.
Most of the sensitive residential
receivers are relatively distant from the Extension (ie
greater than 1.6 km). With
mitigation measures in place, the visual impacts to the sensitive residential
receivers would range from “Insubstantial” to “slight” during the construction
phase and slightly worsen to “Insubstantial to moderate” during the
operation/restoration phase as the volume and height of the landfill gradually
increase. During the aftercare
phase, the impact will be reduced to “Insubstantial to slight” on day 1 of the
aftercare phase, when landfilling operations have
ceased; and further reduced to “Insubstantial” as the landscape restoration
gradually matures.
It is recommended
that EM&A for landscape and visual resources is undertaken during the
design, construction, operation and restoration/ aftercare phases of the
Extension. The design,
implementation and maintenance of landscape mitigation measures should be
checked to ensure that they are fully realised and
that potential conflicts between the proposed landscape measures and any other
Extension works and operational requirements are resolved at the earliest
possible date and without compromise to the intention of the mitigation measures. In addition, implementation of the
recommended mitigation measures should be monitored through the site audit programme.
The environmental impact assessment has
concluded that no unacceptable environmental impacts are envisaged as a result
of the construction, operation, restoration and aftercare of the Extension,
provided that the recommended mitigation measures are implemented. It is predicted that there will be a
residual odour impact on air sensitive receivers in the immediate vicinity of
the Extension Site boundary. Taking account of
the nature of the developments affected, the number of people impacted, the
transient nature, low frequency and magnitude of the exceedances,
the residual impacts are considered acceptable.
The EIA has concluded that residual
impacts are only related to odour while other environmental impacts are found
to be acceptable.
With the implementation of good odour management
practices and control measures at the Extension, the population in the
The environmental friendly design features
of the Extension include:
·
Double-liner
system at the base of the landfill to ensure full containment of leachate and LFG and to prevent off-site migration.
·
Comprehensive
leachate and LFG management systems to contain, collect and treat leachate
and LFG in a safe manner without polluting the environment.
· A comprehensive surface water management system to prevent contaminated runoff entering the surrounding environment while preventing clean surface water from the surrounding environment entering the landfill site.
As each of the three strategic landfills
plays an important integral part of the waste management strategy in
The Extension Site is currently occupied
by developed land and a hillslope in the CWBCP,
neither are easily accessible nor used by the public. When the Extension is restored, it can
provide around 50 ha of space for the development of beneficial afteruse(s), eg recreational
uses, linkage to the CWBCP and providing access from the TKO area to the
The design and operation of the landfill
has incorporated stringent odour management and control system to avoid odour
impact to residential populations.
The design described in Section
12.10.2 will avoid leachate, LFG and contaminated
water from migrating off-site affecting the nearby environment.
Mitigation measures and good site
practices have been recommended through the impact assessment to minimise the
potential impacts to the environment.
The Extension will unavoidably impact a small area of natural habitat
comprising shrubland and grassland of low to moderate
ecological value. Compensation of
woodland plantation with native species on the restored Extension has been
recommended to provide a habitat of higher ecological value.