Water Quality Mitigation and Monitoring
Construction Mitigation
The key concern on water quality impacts during the construction phase of the project is sediment
dispersion from dredging, jetting and water pumping operations. Sediment release rates for
sediment dispersion modeling were estimated based on the selected working rate for dredging,
jetting speed of the jetting machine, and pumping rate for seawater removal from suction caissons.
The predicted results showed no adverse water quality impacts. Mitigation measures to minimise
water quality impacts arising from the operations with potential sediment release are
recommended as follows:
Construction Monitoring
Water quality monitoring will be included as part of the Environmental Monitoring and Audit
programme to ensure that water pollution during the construction phase of the project is minimal.
Details of the water quality monitoring and audit requirements are included in the EM&A Manual.
Operational Mitigation and Monitoring
There would be no unacceptable hydrodynamic and water quality impacts during the operational
phase. Water quality monitoring and audit is considered not necessary.
Emergency Plan
An emergency plan would be developed for the wind farm to deal with all eventualities at the wind
farm, including construction and operational related oil releases. Plans would be activated once an
oil spill event due to vessel collision occurs at the wind farm was identified. An Emergency
Response Team would be convened to address the incident and call upon all appropriate and
available resources. These would include (1) the operator’s multi-role wind farm operational
support vessel, that would double as an Emergency Response & Rescue Vessel (ERRV); and (2)
Marine Department patrol vessels directed under the Maritime Oil Spill Response Plan (MOSRP).
The operator’s ERRV is intended to have a near permanent presence at the site and would be in a
position to provide immediate casualty support and oil spill containment and cleanup.
The HKSAR Marine Department would be informed of any oil spill event and take immediate action
to deploy maritime oil spill control vessels to reach the scene of the incident. Depending on the sea
conditions, the travel time from the Marine Department base to the Ninepins is about 3.5 to 4.5
hours. It is expected that control and containment of oil spill from reaching Ninepins would be
undertaken before the oil spill moves further towards the islands. Methods to control and contain
the spill may include the use of spill containment booms, absorbents, etc. Depending on the
situation, oil transfer operations may be carried out to remove the floating fuel oil from the sea
surface.
Given the development of an extensive operational and emergency plan for the wind farm and
support from the Marine Department to deal with accidents, any oil spill events during Project
operation are not anticipated to cause adverse impacts upon nearby water sensitive receivers.
Construction Mitigation
The key concern on water quality impacts during the construction phase of the project is sediment
dispersion from dredging, jetting and water pumping operations. Sediment release rates for
sediment dispersion modeling were estimated based on the selected working rate for dredging,
jetting speed of the jetting machine, and pumping rate for seawater removal from suction caissons.
The predicted results showed no adverse water quality impacts. Mitigation measures to minimise
water quality impacts arising from the operations with potential sediment release are
recommended as follows:
- Working rate for dredging in Junk Bay should not exceed 6,300 m3/day for two dredgers.
- Jetting speed should not exceed 75 m/hr in the section, which starts at the dredging end
point on the seaward side of the transmission power cable in Junk Bay and extends towards
the offshore direction of the transmission power cable. - Jetting speed should not exceed 150 m/hr for jetting operation carried out in the remaining
sections of the transmission power cable and the array cable at the wind farm. - Pumping rate for seawater removal from suction caissons during foundation installation
should not exceed 1,200 m3/hr per foundation or 300 m3/hr per pump. - Closed grab dredgers should be used for sediment dredging in Junk Bay. The mechanical
grabs should be properly maintained to minimise spillage of sediment. - Silt curtains should be provided surrounding the dredging point to minimise dispersion of
sediment plumes. Arrangement of silt curtain is presented HERE. - Barges for disposal of dredged marine sediment:
- Bottom of the barges should be fitted with tight seals to prevent leakage of sediment
during transport. - Filling of dredged marine sediment should only be up to a level that sediment would
not spill over during transport to the disposal site. - Adequate freeboard should be provided to avoid washing the sediment overboard by
wave action. - Dredging operation should be carefully controlled to avoid splashing sediment into
the sea when transferring the dredged sediment to the barge. - Excess material from decks and exposed fitting of barge should be cleaned before
the barge is towed to the disposal site. - The decks of the barges and other marine vessels should be kept clean and tidy,
and are free pollutants, i.e. oil and grease.
- Good site management practices should be implemented to avoid water pollution at all
times during the construction phase.
Construction Monitoring
Water quality monitoring will be included as part of the Environmental Monitoring and Audit
programme to ensure that water pollution during the construction phase of the project is minimal.
Details of the water quality monitoring and audit requirements are included in the EM&A Manual.
Operational Mitigation and Monitoring
There would be no unacceptable hydrodynamic and water quality impacts during the operational
phase. Water quality monitoring and audit is considered not necessary.
Emergency Plan
An emergency plan would be developed for the wind farm to deal with all eventualities at the wind
farm, including construction and operational related oil releases. Plans would be activated once an
oil spill event due to vessel collision occurs at the wind farm was identified. An Emergency
Response Team would be convened to address the incident and call upon all appropriate and
available resources. These would include (1) the operator’s multi-role wind farm operational
support vessel, that would double as an Emergency Response & Rescue Vessel (ERRV); and (2)
Marine Department patrol vessels directed under the Maritime Oil Spill Response Plan (MOSRP).
The operator’s ERRV is intended to have a near permanent presence at the site and would be in a
position to provide immediate casualty support and oil spill containment and cleanup.
The HKSAR Marine Department would be informed of any oil spill event and take immediate action
to deploy maritime oil spill control vessels to reach the scene of the incident. Depending on the sea
conditions, the travel time from the Marine Department base to the Ninepins is about 3.5 to 4.5
hours. It is expected that control and containment of oil spill from reaching Ninepins would be
undertaken before the oil spill moves further towards the islands. Methods to control and contain
the spill may include the use of spill containment booms, absorbents, etc. Depending on the
situation, oil transfer operations may be carried out to remove the floating fuel oil from the sea
surface.
Given the development of an extensive operational and emergency plan for the wind farm and
support from the Marine Department to deal with accidents, any oil spill events during Project
operation are not anticipated to cause adverse impacts upon nearby water sensitive receivers.
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