1 Introduction.. 1
1.1 Project Background.. 1
1.2 Designated Projects under EIAO.. 1
1.3 Purpose of this Executive Summary.. 1
2 Project Description.. 1
2.1 Project Scope.. 1
2.2 Sewage Treatment Level and Effluent Disposal
Arrangement. 2
2.3 Construction Arrangement.. 2
2.4 Need and Benefit of the Project.. 2
2.5 Consideration of Alternatives. 3
2.6 Construction Programme. 4
3 Key Findings of the Environmental
Impact Assessment.. 4
3.1 Air Quality Impact.. 4
3.2 Water Quality Impact.. 4
3.3 Ecological Impact.. 6
3.4 Fisheries Impact.. 7
3.5 Landscape and Visual Impact.. 7
3.6 Hazard to Life.. 7
3.7 Landfill Gas Hazard.. 8
3.8 Waste Management Implications. 8
3.9 Land Contamination.. 8
3.10 Noise Impact. 9
4 Environmental Monitoring and Audit
(EM&A). 9
5 Conclusion.. 9
Figure 1.1 Project Location Plan
1
Introduction
1.1.1
The existing Tai Po Sewage Treatment Works
(TPSTW) is located within Tai Po Industrial Estate and has undergone various
stages of extension since it first commissioned in 1979. Currently, the
existing TPSTW is a secondary treatment works with a design capacity of
120,000 m3 per day, serving Tai Po Industrial Estate, Tai Po, Lam
Tsuen and Ting Kok areas. Based on the latest flow records, the existing TPSTW
is already operating close to its design capacity. There is a need to upgrade
the capacity of TPSTW to meet the future sewage treatment demand.
1.1.2
Drainage Services Department (DSD) appointed
Binnies Hong Kong Limited (the consultants) to undertake the consultancy
“Agreement No. CE 50/2019 (DS) Upgrading of Tai Po Sewage Treatment Works –
Investigation” on 31 March 2020. The scope of this consultancy includes the
carrying out of an Environmental Impact Assessment (EIA) study for Upgrading of
TPSTW (the Project).
1.2.1
A Project Profile (No. PP-587/2019) was
submitted to the Environmental Protection Department (EPD) on 5 September 2019 for
application for an Environmental Impact Assessment (EIA) Study Brief under Section
5(1)(a) of the EIA Ordinance (EIAO) and the EIA Study Brief (No. ESB-321/2019)
for the Project was issued on 16 October 2019 under the EIAO.
1.2.2
The Project consists of the following Designated
Projects under Schedule 2, Part I of the EIAO:
n
Item F.1 - Sewage treatment works with an installed capacity of
more than 15,000 m3 per day;
n
Item F.4 - An activity for the reuse of treated sewage effluent
from a treatment plant;
n
Item D.1 – A public utility electricity power plant; and
n
Item D.2 – A public utility gas generation plant.
1.3
Purpose of this Executive Summary
1.3.1
This Executive Summary summarizes the findings,
recommendations and conclusions of the EIA Report for the Project.
2.1.1
The scope of the Project is to upgrade the
existing TPSTW from 120,000 m3 per day to
160,000 m3 per day, with a
view to meeting the future needs of Tai Po District, and allowing provision to
co-digest sludge from TPSTW, other existing and proposed sewage treatment works
in New Territories and pre-treated food waste from the adjoining Organic Waste
Pre-treatment Centre (New Territories East). Total quantities of sewage sludge and
pre-treated food waste to be managed under this Project will be up to 260 dry
tonnes per day.
2.1.2
The energy generated from the proposed
co-digestion of sewage sludge and pre-treated food waste of the Project will be
utilized for electricity supply on site. Any surplus electricity and/or gas
generated from the proposed co-digestion process may be supplied to other government
facilities such as the adjoining Organic Waste Pre-treatment Centre (New
Territories East) as well as private companies such as the CLP Power Hong Kong
Limited and Hong Kong China Gas Company Limited.
2.1.3
The Project mainly comprises the following
works:
(a)
Construction
and operation of new treatment facilities, modification / demolition of
existing treatment facilities of TPSTW;
(b)
Providing
effluent reuse facilities to produce reclaimed water for non-portable use
within the Project site; and
(c)
Providing
co-digestion facilities for sewage sludge and pre-treated food waste.
2.1.4
Owing to the space limitation within the
existing TPSTW and in order to maintain the sewage treatment services of the
existing TPSTW, which is almost fully utilized, a piece of government land to
the south of the existing TPSTW (1.6 hectares) is identified as the proposed
expansion site for the Project. The
location plan of the Project is shown in Figure 1.1.
2.2
Sewage
Treatment Level and Effluent Disposal Arrangement
2.2.1
The existing secondary level treatment of sewage
with disinfection and treated effluent standards will be maintained for this
Project. This Project will follow the same effluent disposal arrangement of the
existing TPSTW that effluent will be diverted and discharged to Victoria
Harbour via the Tolo Harbour Effluent Export Scheme (THEES).
2.4.1
The projected average dry weather flow for the
TPSTW catchment will nearly reach the existing design capacity by 2031 and the
required design average dry weather flow for the TPSTW may reach 160,000 m3 per day by
2041. There is a
need to upgrade the capacity of TPSTW to meet the required sewage treatment
demand.
2.4.2
The
existing West Plant of TPSTW has been in operation for nearly 40 years.
Continuous aging of the existing West Plant is expected, and this may
result in increasing maintenance needs. This
Project will provide an opportunity to develop a New West Plant with improved
sewage treatment technologies and efficiency, minimizing the possibility of
emergency sewage discharge, and release of odour due to equipment failure.
2.4.3
The
upgrading of TPSTW provides an opportunity to co-locate
co-digestion facilities within TPSTW site. The proposed anaerobic
co-digestion of sewage sludge and pre-treated food waste will improve biogas
yield, and thus increase energy recovery from the process. The recycling of
sewage sludge and pre-treated food waste can also preserve precious landfill
space and reduce landfill gas generation at landfills. Thus, this Project will
contribute to the sustainability and circularity for waste management in Hong
Kong.
2.5
Consideration of Alternatives
Sewage Treatment Scheme
Existing Treatment
Level for Discharging to the Victoria Harbour (Recommended Option)
2.5.1
This
option will require the THEES system to accommodate the additional flow of 40,000
m3 per day (i.e. increase from 120,000 to 160,000
m3 per day).
The open channel of Victoria Harbour in general has a higher flushing
capacity and thus a greater pollutant assimilation capacity as compared to Tolo
Harbour. The Project may remain as a secondary treatment works without any
change to the effluent discharge standards. Based on the EIA results, no
unacceptable water quality impact is predicted for this option. This option is recommended for this
Project.
Tertiary Treatment Level
for Discharging to the Tolo Harbour (Not Recommended)
2.5.2
Tolo
Harbour and Tolo Channel are landlocked with poor self-cleansing capacity. This
option may require construction and operation of a new tertiary treatment plant
for further polishing the additional flow of 40,000 m3 per
day to Tolo Harbour. The remaining TPSTW secondary effluent (120,000 m3 per day) will be
discharged to the THEES for disposal. Despite the reduced contaminant
concentration in the tertiary effluent, this option will permanently increase
the pollution load to the sensitive Tolo Harbour, which is not recommended.
Construction
Sequence
2.5.3
Phased construction is recommended to maintain
continuous sewage treatment services throughout the construction phase and
eliminate the chance of temporary sewage bypass into the environment. Phased construction would also reduce the
total construction emissions at one time and minimize the environmental impacts.
Demolition Methods
2.5.4
This
Project will involve demolition of the existing treatment units in TPSTW for
construction of new facilities. Considering environmental benefits and
dis-benefits of the alternative demolition methods as well as the specific
Project constraints, using breaker mounted on excavator is
recommended. There is no noise sensitive receiver located within 300 m
from the Project site. Noise mitigation
measures (e.g. good site practices) will be adopted to minimize disturbance
impact to the environment.
2.5.5
Concrete breaking
using quieter equipment such as crushers and saw cutting can reduce the noise
emissions as compared to
the breakers mounted on excavator. The
demolition rates of using these methods are generally longer. Using these
slower demolition methods will be infeasible to meet the construction programme
and are therefore not selected.
Piling Methods
2.5.6
Non-percussive
piling method (e.g. pre-bored steel H piles) is recommended for construction of
the foundation for new facilities at the Project site. This quiet pilling
method is not applicable for all types of ground conditions. For example, it
will require a longer construction time in areas with a very deep bed rock.
Based on the preliminary ground investigation data available at the EIA stage,
this quiet piling method is considered suitable. It is therefore proposed to
use this method as far as practicable to minimize the noise impact.
2.5.7
If any
updated ground investigation data (to be collected at the design stage of this
Project) reveal that the quiet piling methods are not practical, conventional
percussive pilling should be used as an alternative method and should be
undertaken within non-sensitive hours (e.g. close to noon) as far as
practicable.
2.6.1
The construction works of this Project are tentatively
scheduled to commence in 2025 for completion in 2036.
Construction Phase
3.1.1
During construction phase,
fugitive dust impacts may arise from construction activities including site
clearance and site formation, demolition works, excavation works, and wind
erosion. Mathematical modelling was
undertaken to predict the potential fugitive dust impacts for relevant
parameters including Total Suspended Particles (TSP),
Respirable Suspended Particulates (RSP) and Fine Suspended Particulates (FSP). The modelling has taken into account
the cumulative impact caused by other concurrent sources within the assessment
area. With implementation of mitigation measures
specified in the Air Pollution Control (Construction Dust) Regulation, good
site practices, and Environmental Monitoring and Audit (EM&A) programme, no
adverse dust impact at Air Sensitive Receivers (ASRs) is anticipated due to the
construction activities of the Project.
Operational Phase
3.1.2
During operational phase, odour emission would
arise from the treatment processes. All major emitted odourous gases will be
treated in the deodourizing units before venting to the atmosphere. Mathematical
modelling was carried out to predict the potential odour impact based on the actual
odour emission rates measured in existing TPSTW and other similar facilities. With
implementation of the proposed odour control measures, full compliances with
the odour criterion were predicted at all representative ASRs.
3.1.3
Flue gas will be emitted from combined heat and
power (CHP) generating system of the Project. Parameters of concern include
RSP, FSP, nitrogen dioxide, sulphur dioxide, volatile organic compounds,
hydrogen chloride and hydrogen fluoride. Based
on the modelling results and with consideration of the cumulative impact from the
vehicular emissions and industrial chimney emissions within the assessment area,
full air quality compliances at all representative ASRs were predicted during operation
of the proposed CHP unit without mitigation measure.
3.2
Water Quality Impact
Construction Phase
3.2.1
During construction phase, potential sources of water quality
impact associated with the Project include general land-based construction
activities, construction site run-off, accidental chemical spillage, sewage effluent from construction
workforce, contaminated site runoff and demolition works. These impacts
could be mitigated and controlled to comply with the relevant standards or
assessment criteria by implementing the recommended mitigation measures.
Operational Phase
Project Effluent to Victoria Harbour
3.2.2
The treated sewage effluent of the Project will
be discharged to Kai Tak River and subsequently into the Victoria Harbour
through the THEES. Mathematical modelling was carried out to predict the
potential marine water quality impacts from the Project. Key parameters considered
include Dissolved Oxygen (DO), 5-day Biochemical Oxygen Demand (BOD5),
Suspended Solids (SS), Unionized Ammonia (UIA), Total Inorganic Nitrogen (TIN),
E. coli and sedimentation rates. The model results showed that there would
be no unacceptable water quality impacts arising from the Project at all
representative Water Sensitive Receivers (WSRs) identified in the assessment
area. No adverse water quality impact
upon Victoria Harbour would arise from this Project. A river and marine water quality monitoring
programme is proposed to verify the EIA prediction and identify follow-up
actions or remedial measures as needed.
Project Effluent to Tolo Harbour and Tolo Channel
3.2.3
Maintenance of the THEES is required to ensure
proper functioning and integrity of the system. The occurrence of the THEES
maintenance would be remote with no more than once in every 5 years. During the
inspection or maintenance of the THEES tunnel, temporary suspension of the
normal THEES operation with treated sewage effluent bypass into the Tolo
Harbour is unavoidable to provide a safe and dry zone within the tunnel. In addition, emergency discharge from the Project would occur in case of pump failure, interruption
of the electrical power supply
or failure of treatment units.
3.2.4
Mathematical modelling was undertaken to study
the water quality impact arising from the THEES maintenance and emergency discharges.
Key parameters considered include DO, BOD5, SS, UIA, TIN, E. coli, sedimentation
rates and chlorophyll-a. The
model results indicated that the marine water pollution level would be temporally
increased during the THEES maintenance and emergency discharge period. The predicted
pollution elevation would be reversible. The baseline water levels would be
recovered after termination of the THEES maintenance and emergency discharge.
3.2.5
The
THEES maintenance discharge would be scheduled outside the algae blooming
season (December to April/ May) to minimize the risk of red tide occurrence.
The scheduling of the maintenance discharge would also take into account any
ongoing blooming event in the area, which may occur outside the blooming
season. Mitigation measures, including dual power supply or ring main supply
from CLP, standby pumps, treatment units and equipment, shall be provided to
avoid the occurrence of emergency discharge.
The DSD’s Existing Contingency Plan for Incidents Possibly Encountered
in Sewage Treatment Facilities shall be followed to minimize the impact of
emergency discharge and facilitate subsequent management of the emergency
situation. A marine water quality monitoring programme and an event and action
plan including the procedures to be followed in case of the THEES maintenance
and emergency discharge has been developed for the Project and shall be
properly implemented to minimize the potential water quality impacts.
Other Potential Water
Quality Impacts
3.2.6
Other sources of potential water quality impacts
associated with the operational phase are identified as handling and
transportation of pre-treated food waste, wastewater from the sludge /
pre-treated food waste related processes, non-point source surface runoff from
paved areas and accidental chemical spillage. These potential impacts can be
prevented by implementation of the recommended mitigation measures.
3.3
Ecological Impact
Terrestrial Ecology
3.3.2
The Project site and the SWRL supported a
significant number of Collared Crows in Hong Kong. Surveys from this EIA study
revealed that the pre-roosting / roosting sites for Collared Crow are all
located outside the Project site. They are located in the existing SWRL. The
Project site is about 200m away from the nearest pre-roosting site of Collared
Crow, and more than 650m away from the nearest roosting site of Collared Crow. No
direct impact to roosting/pre-roosting sites of Collared Crows is expected. The
Project works will cause a temporary loss of foraging habitat. It is expected
that birds foraging in the TPSTW will become quickly habituated to the upgraded
facilities. For the duration of demolition/construction, the eastern portion of
the TPSTW and other surrounding areas will be available as foraging/loafing
habitats to all bird species currently utilizing this highly disturbed habitat.
No unacceptable impact of this temporary habitat loss (developed area) is
anticipated.
3.3.3
An occasional night roost of non-breeding
ardeids was identified at an existing tree group within the TPSTW. The
concerned tree group, with direct conflict with the Project works, would be
unavoidably removed. The tree group will be compensated by transplanting or
replanting of suitable trees, to provide a potential roosting habitat within
the upgraded TPSTW. Noisy construction works should be ceased within 100 m from
the existing tree group or transplanted / compensated tree group at least 1
hour before the sunset to prevent any disturbance to the night roosting
activities. The removal / felling /
transplantation of the concerned tree group should also be avoided at least 1
hour before the sunset. Given the low frequency of occupancy of the night roost
and that the trees are proposed to be transplanted/compensated within the
Project layout and in view that there are numerous trees in the vicinity that
could also be used by night roosting birds, no unacceptable impact on roosting
of non-breeding ardeids would be expected.
3.3.4
With implementation of recommended mitigation
measures and good site practices, no unacceptable disturbance impacts would be
expected. Ecological monitoring should be conducted during construction phase
to monitor the effectiveness of proposed mitigation measures and during
operational phase to monitor any changes in foraging habitats by the proposed
Project and verify the EIA findings.
Marine
Ecology
3.3.5
The
key marine ecological impact would arise from the changes of water quality due
to THEES maintenance and emergency discharge as presented in Section 3.2 above.
The occurrence of the THEES maintenance and emergency discharge would be remote
and the associated water quality changes would be short-term and reversible.
According to water quality impact assessment results, with implementation of
the recommended water quality mitigation measures, no unacceptable water
quality impact upon the marine ecological resources is anticipated.
3.4.1
The Project will only involve land-based
construction works in Tai Po Industrial Estate. There will be no direct loss of
fishing grounds under this Project.
3.4.2
Only treated and disinfected effluent will be
allowed for discharging into the Victoria Harbour. The water quality model
predicted that the treated sewage effluent of the Project would not change the
overall degree of water quality levels in the assessment area. No unacceptable
water quality impact upon the fisheries resources in Victoria Harbour would
arise from this Project.
3.4.3
Indirect fisheries impacts due to water quality
changes under the THEES maintenance and emergency discharge during the
operational phase were assessed to be short term and reversible (see Section 3.2 above).
The frequency of such occurrence would be remote. The THEES maintenance
discharge would be avoided in the algae blooming season (December to
April/May). The scheduling of the THEES maintenance discharge would also take
into account any ongoing blooming event in the area, which may occur outside
the blooming season. With implementation of mitigation measures recommended for
water quality impact (which would also serve for fisheries protection), no
unacceptable fisheries impacts are predicted.
3.5
Landscape and Visual Impact
3.5.1
The affected landscape resources would be the
amenity planting in the Project site. Approximately 456 nos. of trees in the
Project site would be unavoidably affected by the Project. Among the affected
trees, 10 nos. of Ficus microcarpa or Ficus benjamina are mature
trees with direct conflict with the proposed works and would be unavoidably
removed. The
affected trees in the Project site shall be transplanted as far as possible.
Any unavoidable tree felling shall be mitigated by compensatory tree planting
in accordance with DEVB TCW No. 4/2020. Compensatory planting for the same
species of the affected mature trees (Ficus microcarpa or Ficus
benjamina) should be
provided with sufficient planting space within the Project site or nearby
off-site area. In addition, good site practice, erection of decorative screen
hoarding are recommended for the Project construction.
3.5.2
The most affected visual sensitive receivers would
be the occupants of Tai Po Industrial Estate and travellers along Dai Kwai
Street. Key sources of visual impacts include the construction activities and
construction plant during the construction phase as well as the new Project
facilities during operational phase. During
operational phase, infill planting, tree planting along the site boundary,
green roof, vertical greening and responsive design of building will be
provided for the Project.
3.5.3
It is considered that no unacceptable landscape
and visual impact is anticipated with mitigation measures implemented during
construction and operational phases.
3.6.1
Quantitative
Risk Assessment (QRA) was carried out to assess the potential hazard to life
impact due to generation, storage, utilization, processing and transmission of
biogas within the Project site and due to neighbouring hazardous facilities
including Tai Po Gas Production Plant, liquefied petroleum gas storage
facilities at Apex Print Limited and Zama Industries Limited and dangerous
goods storage at Linde HKO Limited.
3.6.2
Overall,
the QRA has confirmed that the construction and operation of the proposed
Project would not cause significant increase to the existing risk levels of the
TPSTW and neighbouring hazardous facilities. Risk mitigation measures are
proposed to further minimize the hazard to life impacts.
3.6.3
Upon implementation of all proposed mitigation
measures, no unacceptable hazard to life impacts would arise from the Project.
3.7.1
The landfill gas hazards posed by the Shuen Wan
Restored Landfill to the Project site were qualitatively assessed to be Low to
Medium during both construction and operational phases. Key mitigation measures recommended include
the provision of safety measures and landfill gas monitoring during the
construction phase as well as the adoption of building protection design and safety
measures for entry into the confined space during the operational phase. Upon
implementation of all proposed mitigation measures, no unacceptable landfill
gas hazard would arise from the Project.
3.8.1
Wastes generated by the Project construction
activities would include Construction and Demolition (C&D) materials,
excavated sediments, general refuse and chemical waste. Approximately 338,770 m3
of inert C&D materials would be generated of which 50,810 m3
would be reused on-site and 287,960 m3 would be disposed of at
designated Public Fill Reception Facility. Approximately 25,850 m3
of non-inert C&D materials would be generated of which 18,090 m3
would be recycled and 7,760 m3 would be disposed of at designated landfill. Approximately
26,200 m3
of excavated
sediments would be generated during construction phase. Based on
the results of the chemical and biological screening, approximately 21,800 m3
of sediment is suitable for Type 1 – Open Sea Disposal (Dedicated Sites), and 4,400
m3 of sediment requires Type 2 – Confined Marine Disposal in
accordance with the requirements of the ETWB TCW No. 34/2002. It is estimated that about 50
litres of chemical waste would be generated per month and collected by licensed
chemical waste collector for disposal at licensed chemical treatment
facilities. About 260 kg of general refuse would be generated per day and
collected by waste collector for disposal of at waste transfer/disposal
facilities and then to landfill.
3.8.2
During
operational phase, 43 m3 screenings and grits would be generated at
the inlet works per day while 586 m3 dewatered sludge
would be generated from sewage treatment and co-digestion per day. The
collected screenings and grits would be disposed of at landfill by a reputable
waste collector while the dewatered sludge/digestate would be disposed of at T·
Park in Tuen Mun.
3.8.3
Provided
that these wastes are handled, transported and reused/disposed of using
approved methods and that the recommended good site practices are strictly
followed, adverse impacts on waste management during construction and
operational phases would not be anticipated.
3.9
Land Contamination
3.9.1
As documented in the Contamination Assessment
Plan (CAP) prepared under this EIA, based on the site appraisal, there are
areas in the existing TPSTW and the proposed expansion site with potential land
contamination concerns. As the existing facilities in all the concerned areas are
still in operation and will continue to operate during the EIA stage, further
assessment and, if required, remediation works are recommended to be carried
out after decommissioning of the concerned facilities / areas but prior to the
construction works at the concerned facilities / areas.
3.9.2
After decommissioning of the existing facilities
in the concerned areas of the Project and before commencement of the
construction work at these areas, site re-appraisal and preparation of a
supplementary CAP covering the whole construction works area of the Project
should be undertaken for EPD’s approval. Land contamination site investigation
should be conducted in accordance with the approved supplementary CAP. A
Contamination Assessment Report (CAR) shall be prepared to summarize the
results of the SI and confirm the extent of land contamination. If land
contamination is identified, a Remediation Action Plan (RAP) shall be prepared
to provide details of the proposed remediation methods. Remediation action, if
necessary, should be carried out according to EPD’s approved RAP(s) and
Remediation Report(s) (RR(s)) should be submitted after completion of the
remediation action. The RR(s) should be
endorsed by EPD prior to the commencement of construction works at the
respective identified contaminated areas (if any).
3.9.3
With the implementation of the recommended
further works for the Project, any soil/groundwater contamination would be
identified and properly treated prior to the construction works. No unacceptable
land contamination impacts are therefore anticipated.
3.10.1
No existing / committed / planned Noise Sensitive
Receivers (NSRs) are identified in the noise impact assessment area. Key noise mitigation
measures recommended in the EIA include the adoption of good construction site
practices, quieter construction methods (where practicable), quieter and more
environmentally friendly construction equipment listed in the EPD website as
well as enclosing noise emitting plants (pumps, air blowers, etc.) within
building structures during the operational phase. With the
implementation of the recommended mitigation measures, no unacceptable noise
impacts are anticipated.
4
Environmental Monitoring and Audit (EM&A)
Environmental
Monitoring and Audit (EM&A) requirements for air quality impact, water
quality impact, ecological impact, fisheries impact, landscape and visual
impact, hazard to life, landfill gas hazard, waste management implications,
land contamination and noise impact have been recommended. The recommended
EM&A programme comprises baseline and impact monitoring for construction
and operational phases of the Project to verify the EIA predictions and
effectiveness of the recommended mitigation measures. The programme also includes
regular environmental site inspections
and audits to ensure that the recommended mitigation measures and good site
practices are properly implemented. The
EM&A requirements are specified and detailed in the separate EM&A
Manual.
5.1.1
The EIA has identified and assessed the
potential environmental impacts during the construction and operation of the Project
in accordance with the guidelines of the EIAO-TM and the EIA Study Brief. The
EIA has, where appropriate, identified mitigation measures to ensure compliance
with environmental legislation and standards. The EIA has concluded that with
the implementation of the recommended mitigation measures, no unacceptable
residual environmental impacts are envisaged as a result of the construction
and operation of the Project.
5.1.2
An EM&A programme has been recommended to
monitor the environmental performance of the Project and ensure the mitigation
measures recommended would be properly implemented.