9.1.1
The future development and population growth in Tai
Po and the adjacent area will inevitably increase the sewage flows and loads
and thereby increase the demand for sewage treatment in order to preclude environmental
deterioration. Inevitably, given
projected population levels in the catchment area, the projected sewage flows
and loads would be in excess of the existing treatment capacity of the TPSTW.
In addition the revised, more stringent, discharge standard to be adopted for
the treated sewage of TPSTW also requires the upgrading of the existing sewage
treatment facilities in TPSTW to achieve further improvement in environmental
conditions.
9.1.2
Implementation of the Project
will have several environmental benefits.
Firstly, upgrading of the Tai Po sewage treatment works will provide
greater treatment capacity at an enhanced level of treatment meeting the
revised, more stringent, discharge standard to be adopted to achieve further
improvement in environmental conditions. Thus, despite the projected increase
in sewage flows and loads from the Tai Po catchment, routine effluent
discharges will be of a better quality and will benefit water quality in
Victoria Harbour. In addition,
provision of greater treatment capacity is needed to match the continued
development of Tai Po and proposed extensions of sewerage network under other
projects to capture and treat sewage flows that may otherwise be discharged
without treatment into Tolo Harbour.
Furthermore, there would also be benefits arsing from enhancements to be
made to the existing sewage treatment works and thus the general area in its
vicinity to control odours and noise.
Without the upgrading works, the existing Tai Po sewage treatment works
would not be able to cope with the flow build-up. If the treatment capacity of the plant is exceeded, inadequately
treated sewage may need to be discharged into the vulnerable Tolo Harbour. This, if allowed to happen, will lead to
environmental deterioration.
9.1.1
The development and
population growth in Tai Po and adjacent area will increase the demand of
sewage treatment and be over the treatment capacity of existing TPSTW. The
revised more stringent discharge standard also requires the upgrading of
9.1.3
This EIA study has assessed the potential environmental impacts during
the construction and operation of the Project. Key issues including odourair quality, water qualitywater
quality, solid waste management, landfill gas hazards and noise
impacts have been assessed.
9.2.1
Air quality assessment for the
construction and operation of the Project has been assessed. With the implementation of mitigation
measures specified in the Air Pollution Control (Construction Dust)
Regulation, dust nuisance at ASRs would not be is not expected. An EM&A programme was recommended for
the construction phase to ensure that the dust criteria would be satisfied at
the ASRs.
9.2.2
Odour emission from the TPSTW
would be the main concern during the operation phase. Air dispersion modelling was conducted to simulate the potential
odour impacts of the TPSTW on the ASRs.
It was recommended that the exposed area of inlet pumping stations, grit
removal, weir area of Stage IV primary sedimentation tank,
sludge digestion tank outlet chambers, sludge gravity thickeners and sludge
consolidation tanks
should be covered, with the foul air drawn through deodorization units and
discharged after treatment. The exposed
area of grit
removal, flume channel, weir launders at primary sedimentation tanks, exposed
sewage area of return activated sludge pumping station, screening unit (next to
dewatering house) and wet well of sludge pumping station should also be
covered. Addition of chemical in sewage
at Tai Yuen Ssewage
Ppumping Sstations No. 3 and 4 III and Tai Yuensewage pumping
station IV to reduce odour impact arising
from the Stage IV
inlet pumping station, Stage IV screen house and Stage IV primary
sedimentation tanks is required. Good
house keeping should also be conducted to minimise odour generation from the
TPSTW. With the proposed mitigation,
the residual odour impacts at the ASRs were predicted to be in compliance with
the odour criterion. A field trial test
is recommended to determine the chemical dosage at different sewage flows
before the commissioning the Stage V of TPSTW.
Construction Phase
9.3.1
Minor water quality impact would
be associated with land-based construction, including demolition of existing
facilities and installation of new works. Impacts may result from the surface
runoff and sewage from on-site construction workers. Impacts could be controlled to comply with the WPCO standards by
implementing the recommended mitigation measures. Unacceptable residual impacts
on water quality would not be expected.
Operation Phase
9.3.2
AAn assessment
of water quality impact due to the operation of the Project was made using the
Delft3D model. With this quantitative
modelling tool, impacts were assessed over a year’s duration. Despite the model input parameters being
conservative, comparison between the baseline and operational water quality
modelling results indicated no adverse impact on the marine water quality in
Victoria Harbour during normal operation of the TPSTW after commissioning of
the Project. To cope with the potential
impact of effluent from TPSTW (and STSTW) into Tolo Harbour due to overflow
discharges during normal operation of the TPSTW, upgrading of existing Tai Po
and Sha Tin effluent pumping stations and the associated facilities is
recommended, as described in detail in paragraph 4.7.25. In passing, it is noted that for the 2010
scenario when Phase I of the Project is commissioned, overflow at TPSTW may
occur only occasionally during storm events and the extent of impact is much
less significant as compared to that of the 2016 ultimate flow scenario. And under the Phase I works, mitigation
measures, including dual power supply or ring main from CLP, standby equipments
and treatment units would be provided to avoid the occurrence of any emergency
discharge. An EM&A programme is
recommended to collect water quality data during emergency discharge or THEES
tunnel maintenance to confirm the model predictions.
9.1
n assessment of water
quality impact due to the operation of the Project was made using the Delft3D
model. With this quantitative modelling
tool, impacts were assessed over a year.
Although the model input parameters were conservative, comparison
between the baseline and operational water quality modelling results suggested
that there should be no adverse impact on the marine water quality in Victoria
Harbour during normal operation of the TPSTW after commissioning of the
Project. To cope with the potential
impact of effluent from TPSTW (and STSTW) into Tolo Harbour due to overflow
discharges during normal operation of the TPSTW, upgrading of existing Tai Po
and Sha Tin effluent pumping stations and the associated facilities is
recommended. The need
for the upgrading of the Tai Po effluent pumping station and Sha Tin effluent
pumping station, has been identified in a previous consultancy study ‘Review of
North District and Tolo Harbour Sewerage Master Plan Study’conducted
by EPD. It is
noted that the upgrading of Shatin effluent pumping station is currently in the Category C
of the Public Works Programme (PWP), whilst the inclusion of upgrading of the
Tai Po effluent pumping station into the PWP is being processing processed by the EPD. Nevertheless, for 2010
scenario, overflow at TPSTW may occur only occasionally occur only during storm events and the extent of impact is
considered minor. Other mitigation
measures, including dual power supply or ring main from CLP, standby equipments
and treatment units would be provided to avoid the occurrence of any emergency
discharge. An EM&A programme is
recommended to collect water quality data during emergency discharge or THEES
tunnel maintenance to confirm the model predictions. The monitoring results shall be
employed to identify areas for any further necessary mitigation measures to
avoid, rectify and eliminate environmental damage associated with the Project.
9.4.1
Wastes generated by the
construction activities are likely to include C&D material from the site
formation and demolition works at the existing TPSTW site, general refuse from
the workforce and used bentonite slurry. Provided that these identified waste
arisings are to be handled, transported and disposed of using the recommended
methods and that good site practices are to be strictly followed,
adverse environmental impacts are not anticipated during the construction
works.
9.4.2
Waste management will be the
contractor’s responsibility to ensure that all wastes produced during the
construction of the Project are handled, stored and disposed of in accordance
with good waste management practices and EPD’s regulations and requirements.
The recommended mitigation measures shall should form the basis of the site Waste
Management Plan to be developed by the Contractor at the commencement of the
construction phase.
9.5.1
A landfill gas (LFG) hazard assessment
has been undertaken to assess the potential hazard posed by the Shuen Wan
Landfill to TPSTW which is located within the Consultation Zone of Shuen Wan
Landfill. The results suggest that the
overall level of the landfill gas hazard is High.
9.5.2
Some appropriate protection measures
have been proposed to minimise the landfill gas hazard for the proposed project
site during the construction phase and operational phase.
9.5.3
Construction stage
·
Prior to and during development or construction,
contractors would be advised of the possible presence of LFG in the subsurface
for them to take into account in the design, construction and maintenance of
their works. Procedures shall be established for pre-entry monitoring for
ducts, manholes, and chambers.
·
Portable gas detectors shall be used to regularly check
the levels of methane, carbon dioxide and oxygen in depressions, trenches, and
excavations area. The regular monitoring shall be undertaken at least for the
beginning of each half working day (i.e. morning and afternoon) for the entire
period the excavation remains open. If elevated LFG level is measured during
monitoring at depressions, trenches and excavations, ventilation of such area
shall be provided and sources of ignition shall be kept away from areas where
build-up of LFG is possible.
Operational
stage
·
Procedures shall also be established for pre-entry
monitoring of ducts, manholes, and chambers. The atmosphere within utility
manholes and chambers shall be checked for methane, carbon dioxide and oxygen
prior to entry. The frequency of
routine monitoring is recommended to be monthly at least during the initial
stage (first 3 months) of the operational phase of the project in order to make
sure no accumulation of landfill gas. The frequency can be subsequently relaxed
to a quarterly basis or eventually terminated with the approval of EPD based on
available monitoring data for methane, carbon dioxide and oxygen.
9.5.4
Provided that the recommended
protection measures (details in section 6 of the report) are implemented
properly, the health and safety of the site workers/personnel working at the
proposed project site will be safeguarded and there would be no adverse impact
arisen from the proposed project.
9.6.1
Construction noise impacts and
the operation noise impacts arising from the Project have been identified as
key environmental issues. The potential noise impacts arising from the Project
have been assessed and evaluated.
Construction Phase
9.6.2
For the construction phase, the
unmitigated noise levels at the identified NSR in Tai Po Sewage Treatment Plant
would be in the range of 67 dB(A) to 82 dB(A).
To
alleviate the noise impact, sufficient nNoise control measures would be required to
mitigate the potential construction noise impacts. The rRecommended mitigation
measures include the use of silenced types PMEs and implementation of good site
practices.
9.6.3
With the recommended control
measures in place, the mitigated noise levels at the identified NSR due to the
Tai Po STW would comply with the daytime construction noise standard as set out
in the EIAO-TM. In addition, an EM&A programme would be implemented to
monitor the construction
noise impact.
Operation Phase
9.6.4
The noise impacts associated
with the operation of the Project were also assessed. According to the
assessment result, the predicted unmitigated noise levels would comply with the
daytime and night-time noise criteria. Thus, no mitigation measure would be
required.