1
Introduction
1.1
Project Background
Keppel Seghers Zhen Hua Joint Venture (KSZHJV) was appointed by the Project Team of the Integrated Waste
Management Facilities (IWMF) Phase 1 of the Environmental Protection Department
(EPD) for the design, construction and operation of IWMF Phase 1 near Shek Kwu
Chau under Contract no. EP/SP/66/12 (the Contract).
The Project involves reclamation of land
near the south-western coast of Shek Kwu Chau as shown in Figure 1.1. Upon
the completion of reclamation, the incinerator and associated facilities will
be constructed on the reclaimed land. It should be noted that the Contract
does not cover the construction of the submarine cables connecting the Project
Site and Lantau Island as indicated in Figure 1.1.
The construction and operation of the IWMF
Phase 1 (hereafter referred to as the Project) is a Designated Project (DP)
under Schedule 2 of the Environmental Impact Assessment (EIA) Ordinance
(Cap. 499). The EIA Report of the Project (EIA-201/2011) was approved on 17
January 2012, and the Environmental Permit (EP) of the Project was issued on 19
January 2012 (EP-429/2012) and a variation of the EP on 14 October 2016
(EP-429/2012/A). A Further Environmental Permit FEP-01/429/2012/A was granted
to KSZHJV on 27 December 2017.
Figure 1.1 Location in Project Site
Extracted from Figure 1 of
FEP-01/429/2012/A.
The construction of the seawall,
reclamation and breakwater will require marine ground treatment works. KSZHJV
has re-examined the construction sequence of the seawall, reclamation and
breakwater and calculated the water quality impact from different stages of
construction activities. The change of construction sequence and its corresponding
assessment on water quality impact are described in Section 2 and 3.
According to a recent field trial conducted
under Expansion of Hong Kong International Airport into a Three-Runway System
Project (), reduction of sediment dispersion of
at least 80% can be achieved using double layers of silt curtain. This reduces
the contribution of SS to the nearby WSRs.
With the deployment of
two double layers silt curtain in the vicinity of the identified coral located
at indirect impact site as an enhanced environmental mitigation measures,
KSZHJV shall apply for the change of filling rates as stipulated in Conditions 2.5,
2.18, 2.23, Table 1 and Figure 5 of the Further Environmental Permit
FEP-01/429/2012/A.
Due to rough sea
condition at Shek Kwu Chau and relatively new marine ground treatment method
used in this project, the progress of dredging, DCM works, rock filling to form
rubble mound, installation of block work seawall and caisson installation
encountered about 2 - 3 months delay.
Hong Kong currently
solely relies on landfills to dispose of its municipal solid waste (MSW). As
the amount of MSW generated has been increasing considerably in the past
decades, the existing landfills are anticipated to reach their capacities in
the next few years. To reduce the bulk size of such waste substantially, and to
recovery resources as far as possible, the Government's "Hong Kong: Blueprint
for Sustainable Use of Resources 2013-2022" proposes that Hong Kong will
adopt a variety of new waste-related technologies solution. The IWMF Phase 1 is
designed to adopt advanced incineration as the core technology to treat mixed
MSW treatment, with a maximum treatment capacity of 3,000 tonnes per day. The
timely completion of the IWMF Phase 1 will help in alleviating the waste
problem in Hong Kong and benefit the society as a whole. Facing
the problem of scarcity
of landfill space in Hong Kong, the early start of reclamation is beneficial to
our Society as a whole.
Therefore, it was
proposed to have a minor amendment of the construction sequence. Reclamation
works will commence prior to the complete enclosure of caisson and block work
seawall. Temporary double layers silt curtain shall be installed at the eastern
side of Artificial Island as a preventive measure. This temporary arrangement
will last for about 2 3 months. The construction sequence will back to
original EP requirement after substantial completion of seawall.
1.2
Objectives of this Document
The objectives of this Supporting Document to revise dredging and filling rate are:
1.
To describe the overall
construction sequence and change to the minor amendment of construction
sequence for the marine ground treatment works and reclamation works;
2.
To identify various
scenarios which may have environmental impact;
3.
To evaluate the potential
environmental impact associated with the identified scenarios, recommend
appropriate work rates and additional mitigation measures (if necessary);
4.
To review the dredging and filling rate as
stipulated in Conditions 2.5, 2.18, 2.23, Table 1 and Figure 5 of the Further
Environmental Permit FEP 01/429/2012/A.
1.3
Structure of this Document
The structure of the remaining document is:
Section 2: Review of Dredging
Rate and Filling Rate Under Updated Construction Sequence
This
section reviews the maximum dredging rate and filling rate after the
implementation of updated construction sequence. As the key environmental
impact associated with the proposed change is water quality, it further
elaborates on the worst case scenario in terms of potential water quality impact
for detailed evaluation in Section 4.
Section 3: Evaluation of Potential Environmental Impact
associated with the Proposed Change
This section evaluates the potential environmental impacts
associated with the proposed changes was evaluated. Water quality is identified
as the key environmental impact of the proposed change, the assessment was
presented in a separate section (Section 4).
Section 4: Water Quality Impact Assessment
This
section provides a detailed evaluation of the potential water quality impact
associated with the proposed change to construction sequence. The approach adopted
in the approved EIA Report was used in the assessment and the appropriate works
rates at various works fronts were determined based on the findings of the
assessment. Additional mitigation measures were recommended, if required.
2
Review of DREDGInG RATE AND FILLING RATE UNDER
UPDATED Construction Sequence
This section outlines the construction
sequences for reclamation described the latest construction sequence. In
addition, the maximum dredging rate and filling rate shall be submitted to
Director of Environmental Protection for approval after implementing the
enhanced environmental mitigation measures such as installation of two double
layers silt curtain in the vicinity of coral colonies in the indirect impact
site.
2.1
UPDATED Construction Sequence
Construction sequence for ground treatment
and hence seawall structures, reclamation filling and breakwaters will be further
divided into 5 stages with Stage 4A is a newly added Stage to replace original
Stage 4.
Ÿ
Stage 1 - Ground Treatment at Seawall Area Only
Localised dredging,
as shown in Table 2.1, and rock filling operations will be carried out at the northeast
seawall, and geotextile and sand blanket, at a maximum rate as shown in Table
2.2, will be laid at the remaining seawall area requiring DCM. The perimeter
seawall area is defined as Area A (see Figure 1 in Annex A).
Ÿ
Stage 2 - Ground Treatment at Seawall and Reclamation
Area
Localised dredging and
rock filling operations will be continuously carried out at the northeast seawall;
and DCM and rock filling operations will be carried out at the remaining seawall
of Area A. Geotextile and sand blanket will be laid within reclamation area as Area
B after completion of those in Area A (see Figure 2 in Annex A).
Ÿ
Stage 3 - Seawall Construction, Ground Treatment
at Reclamation Area and Breakwater
Localised dredging and rock filling operations will be carried out
at the northeast seawall or at the northern breakwater; precast seawall structure
will be installed at the northeast seawall; DCM operation will be continuously
carried out at the remaining seawall of Area A; ground treatment by PVD will be
installed within Area B; geotextile and sand blanket will be laid at the remaining
breakwater location after completion of those within the reclamation area (see Figure
3 in Annex A).
Ÿ Stage 4A - Reclamation Filling, Installation of precast
seawall, Installation of block work seawall and Ground Treatment at Breakwater
After substantial completion of seawall (except
approximately 50m opening and approximately 200m silt curtain located at the
eastern side of artificial island), marine filling will be carried out within Area
B (reclamation area) and precast seawall structure and block work seawall will
be continuously installed at Area A (Vertical Seawall and Seawall A and Seawall
B). Ground Treatment such as DCM operation and laying of Grade 200 rock to form
rock mound will be carried out in Area B (Breakwater A and B) in parallel (see Figure
4A in Annex A).
Marine filling works within reclamation area
will only be commenced when the installation of block work seawall near the
shoreline have been completed for 310m. In other words, the installation of
block work seawall between Vertical Seawall Chainage S_CH0 and Vertical Seawall
Chainage S_CH310 shall be completed. In addition, the precast caissons at
Seawall A between Chainage SB_CH250 and SB_CH580 and at Seawall B between
Chainage Q_CH0 and Q_CH388 shall be completed. The locations of the Vertical
Seawall Chainage and Seawall A and Seawall B in Area A are shown in Figure 7.
Ÿ
Stage 5 - Reclamation Filling and Breakwater
Construction
After substantial completion of seawall (except approximately 50m
opening), marine filling will be carried out within reclamation area; and
precast seawall structure will be installed at breakwater in parallel (see Figure
5 in Annex A).
Table 2.1 Comparison of Calculated
Suspended Sediment Elevation under Mitigated Dredging Scenario in the Approved
EIA and the VEP Supporting Document
|
Distance from the Nearest Coral (m)
|
Maximum Allowable Production Rate (m3/day)
|
Sediment Loss (kg/s)
|
Maximum SS Elevation at Coral (mg/L)
|
|
Dredging Assumed in Approved EIA Report
|
|
Above
100
|
380
|
0.04398
|
2.5
|
|
Possible Localised Dredging under the Design proposed
by KSZHJV
|
|
16
- 50
|
60
|
0.00694
|
2.5
|
|
50
100
|
190
|
0.02199
|
2.5
|
Extracted from Table 2.2 of VEP Supporting Document.
Table 2.2 Composition of Filling Materials
and Filling Rates at Different Locations (for filling below +2.5mPD) in FEP-01/429/2012/A
|
Area
|
Area
Code
|
Maximum Filling
Rate (m3/day)
|
|
Public
Fill
|
Sand
|
|
Filling of reclamation area between
250m and 400m away from the nearest coral community (or between 50m and 200m
away from opening for marine access)
|
A
|
300
|
4,000
|
|
Filling of reclamation area more
than 400m away from the nearest coral community (or more than 200m away from
opening for marine access)
|
B
|
1,000
|
3,300
|
Extracted from Table 1 of FEP-01/429/2012/A.
In order to
increase the flexibility of the construction programme, it is recommended to provide
the maximum dredging rate when only dredging work shall be conducted.
To reduce the
burden of public fill, it is also recommended to use public fill as filling
materials below +2.5mPD. Unless the unavailability supplies of public fill from
Fill Banks at TKO Area 137 and TM Area 38, it is proposed to use public fill below
+2.5mPD for reclamation purpose.
Therefore,
the maximum filling rate of different scenarios shall be proposed to Director
of Environmental Protection and seek for their approval. Different scenarios
shall be described in details in Section 4.
2.2
Reasons to Proposed Change
EIA report of the captioned project was
conducted more than 10 years ago. In the last 10 years, several severe typhoon
had directly hit Hong Kong and may cause some coral colonies recorded in the
EIA report not updated. Therefore, coral mapping along the shoreline of Shek
Kwu Chau was conducted in January 2019 so as to ensure collect the latest
information of the coral colonies along the shoreline of Shek Kwu Chau. The
locations and species of coral colonies found during the mapping in January 2019
were presented in Section 2.3. In addition, the size of coral colonies,
the percentage of mortality, bleaching and sediment shall be mentioned in the coral
mapping report and such report shall be submitted to EPD and AFCD for record
and the mapping information in January 2019 shall be served as baseline. One
post-construction survey on the mapped coral colonies was also proposed to
ensure the dredging and filling works shall not affect the mapped coral
colonies.
In addition, more boreholes information was
collected from site investigation works since the commencement of the
Contracts. The extent of the dredging can be finalized based on the updated
information.
With due consideration of the latest coral
mapping results and the finalized design of block work seawall, there are room
for revising dredging rate and filling rate after installation of two double
layers silt curtain at the indirect impact site.
The proposed changes can reflect the
maximum allowable dredging rate and filling rate after installation of two double
layers silt curtain in the vicinity of coral colonies at the indirect impact
site.
As dredging activities and filling
activities could both contribute the raise of suspended solids in the nearby
Water Sensitive Receivers, the original dredging rate and filling rate as
stipulated in the Further Environmental Permit No.: FEP 01/429/2012/A assumed
that the dredging work and filling works to be conducted concurrently. It will
allow more programme flexibilities when considering the construction activities
to be conducted separately as another scenario.
It is also noted that public fill shall
predominant be used for filling materials at below +2.5mPD unless the supplies
of public fills from Fill Banks at TKO Area 137 and TM Area 38 are unavailable.
To get the best compaction effect afterwards, sand fill and public fill shall
not be conducted simultaneously. It is therefore required to have a table
showing the maximum allowable filling rate for public fill and sand fill
separately as the original maximum filling rate as shown in Table 1 of
FEP-01/429/2012/A assumed that filling of sand fill and public fill conducted
at the same time.
Due to rough sea
condition at Shek Kwu Chau and relatively new marine ground treatment method
used in this project, the progress of dredging, DCM works, rock filling to form
rubble mound, installation of block work seawall and caisson installation
encountered about 2 - 3 months delay.
Hong Kong currently
solely relies on landfills to dispose of its municipal solid waste (MSW). As
the amount of MSW generated has been increasing considerably in the past
decades, the existing landfills are anticipated to reach their capacities in
the next few years. To reduce the bulk size of such waste substantially, and to
recovery resources as far as possible, the Government's "Hong Kong:
Blueprint for Sustainable Use of Resources 2013-2022" proposes that Hong
Kong will adopt a variety of new waste-related technologies solution. The IWMF
Phase 1 is designed to adopt advanced incineration as the core technology to
treat mixed MSW treatment, with a maximum treatment capacity of 3,000 tonnes
per day. The timely completion of the IWMF Phase 1 will help in alleviating the
waste problem in Hong Kong and benefit the society as a whole. Facing
the problem of scarcity
of landfill space in Hong Kong, the early start of reclamation is beneficial to
our Society as a whole.
Therefore, it is
proposed that reclamation works will be commenced prior to the completion of
installation of caisson and block work seawall. Temporary double layers silt
curtain shall be installed at the eastern side of Shek Kwu Chau as a preventive
measure to the nearby coral colonies. This temporary arrangement will only last
for about 2 3 months. The construction sequence will back to original EP
requirement after substantial completion of seawall.
With the implementation
of the temporary arrangement, the filling rate of public fill and sand fill
will be reduced in order to ensure no adverse impact to the water quality
nearby.
For stage 4A and 5,
opening of marine access at the Western Side of the artificial island has
already relocated further away from the location of coral colonies and approved
in the previously approved Supporting Document to minimize the impact on them
due to dredging and filling activities. For stage 4A, the newly proposed double
layers silt curtain located at the eastern side of artificial island is fixed
between the installed caissons at the seawall area prior to the complete
installation of caisson.
It should be noted that there is no new
type of construction activities and the marine filling for reclamation area would
still be conducted within the substantially completed seawall in general.
2.3
CORAL MAPPING RESULTS
Coral mapping along the shoreline of Shek
Kwu Chau was conducted in January 2019. A total of 52 nos. of coral colonies
were mapped in the survey and tabulated in Table 2.3 and Table 2.4.
The status of all mapped coral colonies were defined as either Abundant or
common in Hong Kong. The location of coral colonies as stated in Table 2.4 were
rounded off from the GPS coordinates as recorded by the diver during coral
mapping in January 2019.
Table 2.3 Summary Table of Coral
colonies mapped in January 2019
|
Scientific name
|
No. of individuals
|
Status in Hong Kong
|
|
Coral
|
|
|
|
Psammocora superficialis
|
36
|
Abundant
|
|
Goniopora stutchburyi
|
16
|
Common
|
|
2 species
|
52 individuals
|
|
Table 2.4 Location and Species of
Coral Colonies mapped in January 2019
|
Coral
No.
|
Coral
Species
|
Coordinates*
|
|
Easting
|
Northing
|
|
01
|
Psammocora superficialis
|
816351
|
806029
|
|
02
|
Psammocora superficialis
|
816355
|
806024
|
|
03
|
Psammocora superficialis
|
816446
|
805966
|
|
04
|
Psammocora superficialis
|
816443
|
805960
|
|
05
|
Psammocora superficialis
|
816449
|
805955
|
|
06
|
Goniopora stutchburyi
|
816455
|
805948
|
|
07
|
Goniopora stutchburyi
|
816462
|
805941
|
|
08
|
Psammocora superficialis
|
816462
|
805934
|
|
09
|
Psammocora superficialis
|
816469
|
805930
|
|
10
|
Psammocora superficialis
|
816475
|
805927
|
|
11
|
Goniopora stutchburyi
|
816551
|
805888
|
|
12
|
Psammocora superficialis
|
816556
|
805888
|
|
13
|
Psammocora superficialis
|
816582
|
805883
|
|
14
|
Psammocora superficialis
|
816588
|
805884
|
|
15
|
Goniopora stutchburyi
|
816594
|
805886
|
|
16
|
Goniopora stutchburyi
|
816592
|
805880
|
|
17
|
Psammocora superficialis
|
816733
|
805828
|
|
18
|
Psammocora superficialis
|
816739
|
805826
|
|
19
|
Psammocora superficialis
|
816738
|
805820
|
|
20
|
Goniopora stutchburyi
|
816741
|
805815
|
|
21
|
Psammocora superficialis
|
816744
|
805808
|
|
22
|
Psammocora superficialis
|
816748
|
805803
|
|
23
|
Psammocora superficialis
|
816770
|
805754
|
|
24
|
Goniopora stutchburyi
|
816778
|
805752
|
|
25
|
Psammocora superficialis
|
816782
|
805745
|
|
26
|
Psammocora superficialis
|
816788
|
805740
|
|
27
|
Psammocora superficialis
|
816831
|
805697
|
|
28
|
Psammocora superficialis
|
816835
|
805694
|
|
29
|
Goniopora stutchburyi
|
816839
|
805687
|
|
30
|
Goniopora stutchburyi
|
816849
|
805671
|
|
31
|
Psammocora superficialis
|
816872
|
805652
|
|
32
|
Psammocora superficialis
|
816855
|
805664
|
|
33
|
Goniopora stutchburyi
|
816884
|
805652
|
|
34
|
Psammocora superficialis
|
816890
|
805638
|
|
35
|
Goniopora stutchburyi
|
816893
|
805633
|
|
36
|
Psammocora superficialis
|
816890
|
805620
|
|
37
|
Psammocora superficialis
|
816894
|
805618
|
|
38
|
Psammocora superficialis
|
816895
|
805613
|
|
39
|
Psammocora superficialis
|
816913
|
805595
|
|
40
|
Psammocora superficialis
|
816927
|
805575
|
|
41
|
Goniopora stutchburyi
|
816930
|
805572
|
|
42
|
Goniopora stutchburyi
|
816943
|
805558
|
|
43
|
Psammocora superficialis
|
816957
|
805553
|
|
44
|
Psammocora superficialis
|
816968
|
805548
|
|
45
|
Psammocora superficialis
|
816992
|
805543
|
|
46
|
Psammocora superficialis
|
816996
|
805543
|
|
47
|
Goniopora stutchburyi
|
817002
|
805541
|
|
48
|
Psammocora superficialis
|
817057
|
805564
|
|
49
|
Psammocora superficialis
|
817062
|
805567
|
|
50
|
Psammocora superficialis
|
817056
|
805557
|
|
51
|
Goniopora stutchburyi
|
817060
|
805560
|
|
52
|
Goniopora stutchburyi
|
817065
|
805562
|
Note:
* - The coordinates of coral colonies were
rounded off from GPS coordinates as recorded by diver during coral mapping in
January 2019 and shall be indicative only.
2.4
Post construction Monitoring SURVEY
After the construction of eco-shoreline and
all marine works, one post construction monitoring survey shall be carried out
to check the conditions of all mapped coral colonies as recorded in coral
mapping in January 2019.
The coral mapping area in the post
construction monitoring survey shall be the same as those mapping areas in
January 2019. The parameters to be monitored for coral colonies in the post
construction monitoring survey shall be the same the parameters to be monitored
for coral colonies in indirect impact site and control site. The parameters to
be monitored are tabulated in Table 2.5.
Table 2.5 Parameters of coral
colonies shall be monitored in post construction monitoring survey
|
Coral
#
|
Species
|
Size
(cm) Max. Diameter/
Height
|
Mortality
(%)
|
Bleaching
(%)
|
Sediment
(%)
|
|
Baseline
|
Completion
|
Baseline
|
Completion
|
Baseline
|
Completion
|
|
|
|
|
|
|
|
|
|
A post construction monitoring survey
report shall be submitted to EPD and AFCD for the record.
3
Evaluation of Environmental
IMpacts associated with the Proposed Change
The
environmental impacts (with respect to the environmental aspects assessed in
the approved EIA Report) associated with the proposed change in construction
sequence are evaluated in this section. The key environmental impact associated
with the proposed change will be water quality and the detailed assessment is
present in Section 4.
3.1
Air Quality Impact
As discussed in Section
2.2, there is no new type of marine construction activities and the
proposed change to the minor amendment of construction sequence will not
increase the number of construction plant and the overall duration for the
construction of the marine works. The associated air quality impact associated
with the operation of the marine construction plant is anticipated to be
reduced as compared with those predicted in the approved EIA Report and VEP
Supporting Document.
Hence, no adverse air
quality impact due to the proposed change is anticipated.
3.2
Noise Impact
As discussed in Section
2.2, there is no new type of marine construction activities and the
proposed change to the minor amendment of construction sequence will not
increase the number of construction plant and the overall duration for the
construction of the marine works. The overall sound power level generated from
the operating plants is anticipated to be similar as compared with those
predicted in the approved EIA report and VEP supporting document.
Hence, no adverse noise
impact due to the proposed change is anticipated.
3.3
Waste Management Implications
As discussed in Section
2.2, there is no new type of marine construction activities and the
proposed change to the minor amendment of construction sequence will not
increase the number of construction plant and the overall duration for the
construction of the marine works. The quantity of waste to be generated from
the work force and maintenance of the marine construction plant during the
construction of the reclamation is anticipated to be similar as compared with
those predicted in the approved EIA Report and VEP Supporting Document.
Hence, no adverse waste
impact due to the proposed change is anticipated.
3.4
Ecological Impact
As discussed in Section
2.2, there is no new type of marine construction activities and the
proposed change to the construction sequence will not increase the number of
construction plant and the overall duration for the construction of the marine
works. The indirect impacts from air emission, construction noise and general
disturbance on terrestrial ecological resources, namely White-bellied Sea Eagle
(Haliaeetus leucogaster) nested on the Shek Kwu Chau Island are
anticipated to be similar as comparing with that predicted in the VEP
Supporting Document.
It should be noted that
most of the corals that may be impacted by the Project have been translocated.
Potential water quality impact associated with the proposed change to
construction sequence on the nearest non-translocatable coral has been assessed
in Section 4. With the implementation of applicable mitigation measures
stated in the approved EIA and VEP Supporting Document as well as additional
mitigation measures (additional layer of silt curtain at sand blanket laying
area and double layer of silt curtain between sediment sources and
non-translocatable coral and installation of fixed double layers of silt
curtain at the eastern side of Shek Kwu Chau), no unacceptable water quality
impact (due to elevation of suspended solids) on the non-translocatable coral
is predicted due to the marine works.
The proposed change to
the minor amendment of construction sequence will not increase the overall
number of construction plant to be used at any one time. Hence, the proposed
change will have similar impact to the marine mammal comparing with that
predicted in the VEP Supporting Document.
As the proposed change
to minor amendment of construction sequence will not change the footprint of
the reclamation and breakwater, it is anticipated that the potential impact on
benthic organisms will be the same as that predicted in the VEP Supporting
Document and hence no adverse impact is anticipated.
Overall, the potential
impact on terrestrial and marine ecological resources due to the proposed
change is expected to be limited and the level would not be worse than that
predicted in the VEP Supporting Document. The existing mitigation measures
required under the approved EIA, including avoidance of works in peak seasons,
using quieter construction methods and plant, implementation of marine mammal
exclusion zones and watching plan, etc. are considered appropriate and sufficient,
and no additional mitigation measure for ecology is required.
3.5
Fisheries Impact
As discussed in Section
4, the water quality impact associated with the proposed change to
construction sequence is expected to be no worse than of that predicted in the
VEP Supporting Document.
As the proposed change
to minor amendment of construction sequence will not change the footprint of
the reclamation and breakwater, there
will be no change to the loss of
fishing ground as that predicted in the VEP Supporting Document.
Therefore, the proposed
change will not cause adverse fisheries impact. No additional mitigation
measure for fisheries is required.
3.6
Health Impact
The proposed change to minor
amendment of construction sequence will not affect the findings and recommendations
of operation phase health impact assessment predicted in the approved EIA
Report and VEP Supporting Document.
3.7
Landscape and Visual Impact
The nature and location
of the marine construction activities will not change due to the proposed change
to minor amendment of construction sequence. The proposed change will not
increase the overall number of construction plant to be used at any one time. The
proposed change will not affect any landscape resources at the south-west of
Shek Kwu Chau. It is therefore not anticipated to have any significant change
to the findings and recommendations of the landscape and visual impact
assessments of the approved EIA Report and VEP Supporting Document.
No unacceptable
landscape and visual impact will be expected and no additional mitigation
measure is required.
3.8
Impact on Cultural Heritage
The proposed change
will not affect reclamation footprint. Therefore, it is expected that there
will be no change to the potential impact on underwater cultural resources and
no additional mitigation measure is required.
3.9
Summary
The
potential environmental impacts (air, noise, waste, marine ecology, fisheries,
health impact, and landscape and visual) due to the proposed change to minor
amendment of construction sequence have been reviewed.
It is
concluded that with the implementation of the mitigation measures recommended
in the approved EIA and VEP Supporting Document and the additional mitigation
measures for water quality (see Section 4), no adverse environmental
impact is anticipated and the impacts will not be worse than those predicted in
the approved EIA Report and VEP Supporting Document.
The
water quality impact assessment is discussed in Section 4.
4
Water Quality Impact
Assessment
Elevation of suspended
solids (SS) from marine works including dredging, sand blanket laying and marine
filling are considered as the major water quality issue under this Project. Marine
filling within reclamation area has been evaluated in the approved EIA Report
and the VEP Supporting Document. The potential water quality impact arising
from concurrent activities of marine ground treatment works including DCM
operation, dredging and sand blanket laying, will be of major concern.
As discussed in the
VEP Supporting Document, no water quality impact would be expected from the DCM
operation as shown by a number of overseas studies and the recent field DCM trial
conducted by the Airport Authority Hong Kong. Therefore, the potential water quality
impact associated with the DCM operation will not be considered in this assessment.
Other marine
works, such as rock filling, installation of pre-cast seawall and installation
of PVD, are not expected to result in notable release of SS into the water
column, and are therefore not included in this assessment.
4.1
Assessment Criteria and Nearest Water Sensitive Receivers
(WSRs)
The assessment criterion
of 2.5 mg/L SS elevation would be adopted. This criterion was established based
on the 30% tolerance value of 90th-percentile SS level for EPD Marine
Water Quality Monitoring Station SM13 in wet season of 2007-2010. This is the same
assessment criterion adopted in the approved EIA Report as well as the VEP Supporting
Document.
There were a number
of coral colonies identified in the approved EIA Report and they were the nearest
WSRs to the Project site. Translocation of the coral to be impacted by the Project
was recommended in the approved EIA Report and was conducted in March 2018. Several
groups of non-translocatable coral colonies within indirect impact site (shown as
blue spots in Figure 6A, 6B and 6C of Annex A) are considered as the
critical WSR for this assessment.
4.2
Assessment Methodology
The same near field
sediment dispersion modelling adopted in the approved EIA Report as well as the VEP Supporting Document
was used. Predicted SS elevation at the WSR was estimated by the following formulae:
_files/image004.png)
where C(x)
= concentration of SS at distance x from the source;
q = sediment loss rate (kg/s);
D = water depth (m);
x = distance from source (m);
ω = diffusion velocity (m/s).
Applicable values in
the approved EIA Report were adopted in this assessment, namely water depth D =
10 m and diffusion velocity ω = 0.01 m/s.
4.3
Determination of Appropriate Work Rates and Mitigation
Measures
Appropriate works rates
for the proposed filling and dredging works as well as mitigation measures were
determined for each major stage of marine works based on plant arrangement, and
assessment method and criterion described in Sections 4.1 and 4.2.
Water Quality Mitigation
Measures to be considered
In view of the short
distance from the nearest coral sites, a number of mitigation measures have been
recommended in the approved EIA Report or VEP Supporting Document to minimise the
potential water quality impact from the marine construction works. These measures
are listed in Table 4.1 and are
taken into considerations in the assessment. Furthermore, additional mitigation
measures have been considered and taken into account in the assessment and are
also included in Table 4.1 below.
Table 4.1 Consideration of Relevant Water Quality
Mitigation Measures
|
Mitigation Measures for the Current Ground
Treatment and Reclamation Proposal
|
Existing Measures Recommended in the EIA
/ EP / VEP?
|
Effect
|
Reference
|
|
No dredging shall be carried out within 16m
to the nearest non-translocatable coral colony/ colonies.
For area between 16m and 50m away from the
nearest non-translocatable coral community, the maximum daily dredging rate shall
not exceed 60 m3; for area between 50m and 100m away from the nearest
non-translocatable coral community, the maximum daily dredging rate shall not
exceed 190 m3; and for area more than 100m away from the nearest non-translocatable
coral community, the maximum daily dredging rate shall not exceed 380 m3.
Each grab shall be enclosed by a frame-type
silt curtain.
|
Yes
|
The combined effect of limited dredging rate
and the use of frame-type silt curtain will limit the
maximum SS elevation from the dredging operation to be at or below 2.5 mg/L, which
is the assessment criterion adopted in the approved EIA Report and VEP Supporting
Document.
|
·
EP Conditions 2.18-2.20
·
Approved EIA Section 5b.7.3.26-29
·
VEP Supporting Document Section 2.2.3.12-15.
|
|
Translocation of coral colonies which are
very close to the Project site / directly impacted
|
Yes
|
·
The non-translocated coral colonies are further
away from the Project site and would be less impacted by the potential change
in water quality from marine construction.
·
The remaining coral colonies which are not translocated
are shown in Figures 6A as blue patch.
|
·
EP Conditions 2.12
·
Approved EIA Section 5b.8.1.9.
|
|
|
|
|
|
|
The sand blanket laying work will be undertaken
using the controlled method such as grab dredger or bottom placement method by
trailer suction hopper dredger, sand spreading pontoon or sprinkler barges, etc.)
to discharge the sand material near the seabed.
In addition, silt curtains will be deployed
to enclose the sand blanket laying area ().
|
Existing measurement plus additional
measure (two double layers of silt curtain)
|
Both measures minimise the potential loss
of fine and disturbance to seabed, thus reducing water quality impact.
|
VEP Supporting Document Section 3.2.2.5-7.
|
|
|
|
|
|
|
Two double layers
of silt curtain will be installed in between Project site and the nearby coral
colonies
|
No; Proposed as an additional measure
|
According to a recent field trial conducted
under Expansion of Hong Kong International Airport into a Three-Runway System
Project (), reduction of sediment dispersion of
at least 80% can be achieved using one double layers of silt curtain. This reduces
the contribution of SS to the nearby WSRs.
According to the EIA report from Tuen Mun
Chek Lap Kwok Link, the combined reduction of fine content of the filling
materials when deploying different types of silt curtain concurrently can be
assumed by multiplying both loss reduction factor of individual type of silt
curtain system.
|
Pilot test report under Expansion of Hong
Kong International Airport into a Three-Runway System Project
EIA report of Tuen Mun Chek Lap Kwok
Link
|
|
|
|
|
|
|
Finish the part of seawall close to coral
colonies first to allow the seawall structure to protect coral from suspended
solids
|
No; Proposed as an additional measure
|
While it may not fully qualified as
leading seawall, the seawall structure is known to be effective in
controlling sediment dispersion. The effect of seawall is not taken into
account in the assessment calculation for this Study though.
|
Approved EIAs of Expansion of Hong Kong
International Airport into a Three-Runway System and Hong Kong Boundary
Crossing Facilities
|
|
Conduct sand blanket laying at far corner
from the nearest coral first while localized dredging proceed close to the
nearest coral
|
No; Proposed as an additional measure
|
The proposed arrangement would avoid
concurrent works close to the nearest coral. This means the actual work
arrangement would not reach the worst cases assessed in the subsequent
sections.
|
-
|
|
|
|
|
|
|
For stage 4A, install a double layers silt
curtain at the eastern side of the artificial island.
|
No; Proposed as an additional measure
|
The constructed seawall together with the
newly installed double layers silt curtain at the eastern side of artificial
island can effectively controlled the dispersion of sediment.
|
|
|
|
|
|
|
|
For Stage 4A and 5, install Type 6 silt
curtain as per approved Silt Curtain Deployment Plan during infilling of
Grade 200 and Grade 75 rock into caisson
|
Yes; Approved Silt Curtain Deployment Plan
|
The proposed arrangement acts as an
enhancement measures to control dispersion of plumes during infilling of
caisson.
|
Approved Silt Curtain Deployment Plan
|
|
Conduct one post construction monitoring survey for the mapped
coral colonies
|
No; Proposed as an additional measure
|
To record the conditions of the mapped coral colonies after
filling and dredging activities and the completion of construction of
eco-shoreline
|
|
|
|
|
|
|
Sediment loss rate from dredging, sand
blanket laying and marine fill by using sand fill and marine fill by using
public fill are calculated as follow in Table 4.2.
Table 4.2 Calculation of Sediment Loss Rate
from Construction Activities
|
Construction Activities
|
Working Hour per day
|
Unit Loss Rate (Unmitigated)
|
Loss Rate (Unmitigated)
|
Reference
|
|
Dredging
|
|
|
|
|
|
60 m3/day (for 16 - 50 m from
nearest coral)
|
12
|
20 kg/m3
|
60 m3/day ÷ 12 hr/day ÷ 3600
s/hr × 20 kg/m3 = 0.0278 kg/s
|
Approved EIA
|
|
190 m3/day (for 50 - 100 m
from nearest coral)
|
12
|
20 kg/m3
|
190 m3/day ÷ 12 hr/day ÷ 3600
s/hr × 20 kg/m3 = 0.0880 kg/s
|
Approved EIA
|
|
380 m3/day (for >100 m from
nearest coral)
|
12
|
20 kg/m3
|
380 m3/day ÷ 12 hr/day ÷ 3600
s/hr × 20 kg/m3 = 0.1759 kg/s
|
Approved EIA
|
|
600 m3/day (for >24 m from
nearest coral)
|
12
|
20 kg/m3
|
600 m3/day ÷ 12 hr/day ÷ 3600
s/hr × 20 kg/m3 = 0.2778 kg/s
|
Approved EIA, with the implementation of
additional mitigation measures as approved in the Supporting Document Rev. C
|
|
700 m3/day (for >24 m from
nearest coral)
|
12
|
20 kg/m3
|
700 m3/day ÷ 12 hr/day ÷ 3600
s/hr × 20 kg/m3 = 0.3241 kg/s
|
Approved EIA, with the implementation of
additional mitigation measures as approved in the Supporting Document Rev. C
|
|
1900 m3/day (for >24 m from
nearest coral)
|
12
|
20 kg/m3
|
1900 m3/day ÷ 12 hr/day ÷ 3600
s/hr × 20 kg/m3 = 0.8796 kg/s
|
Approved EIA, with the implementation of
additional mitigation measures as approved in the Supporting Document Rev. C
|
|
Sand Blanket Laying
(Sand fill)
|
|
1000 m3/hr (reference)
|
12
|
-
|
2.551 kg/s
|
Approved EIA of Expansion of Hong Kong
International Airport into a Three-Runway System (AEIAR-185/2014) (1)
|
|
850 m3/hr
|
12
|
-
|
2.551 kg/s × 850 m3/hr ÷ 1000 m3/hr = 2.1684 kg/s
|
Approved EIA of Expansion of Hong Kong International
Airport into a Three-Runway System (AEIAR-185/2014) (1)
|
|
900 m3/hr
|
12
|
-
|
2.551 kg/s × 900 m3/hr ÷ 1000 m3/hr = 2.2959 kg/s
|
Approved EIA of Expansion of Hong Kong
International Airport into a Three-Runway System (AEIAR-185/2014) (1)
|
|
1000 m3/hr
|
12
|
-
|
2.551 kg/s × 1000 m3/hr ÷ 1000 m3/hr = 2.551 kg/s
|
Approved EIA of Expansion of Hong Kong
International Airport into a Three-Runway System (AEIAR-185/2014) (1)
|
|
1080 m3/hr
|
12
|
-
|
2.551 kg/s × 1080 m3/hr ÷ 1000 m3/hr = 2.7551 kg/s
|
Approved EIA of Expansion of Hong Kong
International Airport into a Three-Runway System (AEIAR-185/2014) (1)
|
|
1250 m3/hr
|
12
|
-
|
2.551 kg/s × 1250 m3/hr ÷ 1000 m3/hr = 3.1888 kg/s
|
Approved EIA of Expansion of Hong Kong
International Airport into a Three-Runway System (AEIAR-185/2014) (1)
|
|
1400 m3/hr
|
12
|
-
|
2.551 kg/s × 1400 m3/hr ÷ 1000 m3/hr = 3.5714
kg/s
|
Approved EIA of Expansion of Hong Kong
International Airport into a Three-Runway System (AEIAR-185/2014) (1)
|
|
1500 m3/hr
|
12
|
-
|
2.551 kg/s × 1500 m3/hr ÷ 1000 m3/hr = 3.8265
kg/s
|
Approved EIA of Expansion of Hong Kong
International Airport into a Three-Runway System (AEIAR-185/2014) (1)
|
|
1730 m3/hr
|
12
|
-
|
2.551 kg/s × 1730 m3/hr ÷ 1000 m3/hr = 4.4132
kg/s
|
Approved EIA of Expansion of Hong Kong
International Airport into a Three-Runway System (AEIAR-185/2014) (1)
|
|
2150 m3/hr
|
12
|
-
|
2.551 kg/s × 2150 m3/hr ÷ 1000 m3/hr = 5.4847
kg/s
|
Approved EIA of Expansion of Hong Kong
International Airport into a Three-Runway System (AEIAR-185/2014) (1)
|
|
Marine Fill
(Sand fill)
|
|
|
|
|
|
583.56 m3/hr (reference)
|
12
|
-
|
0.65 kg/s
|
Approved EIA of Development of Integrated
Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
|
1425 m3/hr
|
12
|
-
|
0.65 kg/s × 1425 m3/hr ÷ 583.56 m3/hr
= 1.5872kg/s
|
Approved EIA of Development
of Integrated Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
|
2850 m3/hr
|
12
|
-
|
0.65 kg/s × 2850 m3/hr ÷ 583.56 m3/hr
= 3.1745kg/s
|
Approved EIA of Development
of Integrated Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
|
6000 m3/hr
|
12
|
-
|
0.65 kg/s × 6000 m3/hr ÷ 583.56 m3/hr
= 6.6831kg/s
|
Approved EIA of Development
of Integrated Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
|
9925 m3/hr
|
12
|
-
|
0.65 kg/s × 9925 m3/hr ÷ 583.56 m3/hr
= 11.055kg/s
|
Approved EIA of Development
of Integrated Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
|
12000 m3/hr
|
12
|
-
|
0.65 kg/s × 12000 m3/hr ÷ 583.56 m3/hr
= 13.366kg/s
|
Approved EIA of Development
of Integrated Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
|
19850 m3/hr
|
12
|
-
|
0.65 kg/s × 19850 m3/hr ÷ 583.56 m3/hr = 22.11kg/s
|
Approved EIA of Development of Integrated
Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
|
Marine Fill
(Public fill)
|
|
583.56 m3/hr (reference)
|
12
|
-
|
3.85 kg/s
|
Approved EIA of Development of Integrated
Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
|
240 m3/hr
|
12
|
-
|
3.85 kg/s × 240 m3/hr ÷ 583.56 m3/hr
= 1.5834kg/s
|
Approved EIA of Development
of Integrated Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
|
485 m3/hr
|
12
|
-
|
3.85 kg/s × 485 m3/hr ÷ 583.56 m3/hr
= 3.1998kg/s
|
Approved EIA of Development
of Integrated Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
|
1045 m3/hr
|
12
|
-
|
3.85 kg/s × 1045 m3/hr ÷ 583.56 m3/hr
= 6.8943kg/s
|
Approved EIA of Development
of Integrated Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
|
1675 m3/hr
|
12
|
-
|
3.85 kg/s × 1675 m3/hr ÷ 583.56 m3/hr
= 11.051kg/s
|
Approved EIA of Development
of Integrated Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
|
2090 m3/hr
|
12
|
-
|
3.85 kg/s × 2090 m3/hr ÷ 583.56 m3/hr
= 13.789kg/s
|
Approved EIA of Development
of Integrated Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
|
3350 m3/hr
|
12
|
-
|
3.85 kg/s × 3350 m3/hr ÷ 583.56 m3/hr = 22.102kg/s
|
Approved EIA of Development of Integrated
Waste Management Facilities Phase 1
(AEIAR-163/2012)
|
Note: (1) Quantitative
assessment was conducted for sand filling activities but not for sand blanket
laying in the approved EIA Report. Quantitative assessment for sand blanket
laying was also not conducted in the VEP Supporting Document. Therefore,
reference has been made to the Approved EIA Report of Expansion of Hong Kong
International Airport into a Three-Runway System (AEIAR-185/2014) for the
typical sediment loss rate from sand blanket laying activities.
Calculation Assumption:
1.
Silt removal
efficiencies of cage type silt curtain = 75%
2.
Silt removal
efficiencies of one double layers of floating type silt curtain = 80%
3.
Silt removal
efficiencies of two double layers of floating type silt curtain = (1- 0.2*0.2)
* 100% = 96%
The sediment loss rate of
Marine Fill (sand fill) in reference source is calculated by adopting the
following formula:
3.85kg/s (Sediment loss rate of
marine fill (public fill) = xm3/s * 1900 kg/m3 * 25% * 5%
x = 0.1621m3/s
x = 0.1621 * 3600 = 583.56m3/hr
By adopting the same filling
method and equipment, the sediment loss rate of marine fill (sand fill) =
0.1621 * 1600 * 5% * 5%
= 0.65 kg/ s
Stage 1
In this stage, the concurrent marine works
for the Project include (1) localised dredging and rock filling operation at the
northeast seawall, and (2) sand blanket laying within Area A. In this stage of
work, the work arrangement is the same as stated in the VEP Supporting Document
(with the exception of the proposed two double layers of silt curtain).
Nevertheless, an estimation of maximum allowable rate of sand filling is
provided below as good practice. Both localised dredging and sand blanket laying could result in
release of fines into the water column and subsequently elevation of SS at the
WSRs.
Stage 2
In this stage, the concurrent marine works
for the Project include (1) localised dredging and rock filling operation at the
northeast seawall (), (2) DCM and rock filling operation at the remaining seawall of Area A,
and (3) sand blanket laying within Area B. Among these works, localised dredging and sand blanket laying could
result in release of fines into the water column and subsequently elevation of
SS at the WSRs.
Stage 3
In this stage, the
concurrent marine works for the Project include (1)
installation of precast seawall structure at the northeast seawall, (2) DCM
operation at the remaining seawall of Area A, (3) PVD installation within Area
B, localised dredging and rock filling operation at the north breakwater, and
(4) sand blanket laying at the remaining breakwater. Among
these works, localised dredging and sand blanket laying could results in
release of fines into the water column and subsequently elevation of SS at the
WSRs.
To represent the worst case scenario in Stage
1, 2 and 3, the calculation of the proposed dredging rate and filling rate were
based on the assumption that both dredging and filling work to be carried out
in the location nearest to the sensitive receivers. Hence, the nearest distance
between coral colonies and dredging area is 24m and the nearest distance
between coral colonies and sand blanket laying is 58m.
The proposed work rates for sand blanket
laying are 1,000 m3/hr between 24 m and 250 m away from the nearest coral
colonies, 1,730 m3/hr for sand blanket laying between 250 m and 400
m, and 1,730 m3/hr for sand blanket laying from 400 m onwards if the
dredging volume is kept at 380m3/day.
If the dredging rate changes to 600m3/day, the proposed work rates for sand blanket laying are 900 m3/hr
between 24 m and 250 m away from the nearest coral colony, 1,500 m3/hr
for sand blanket laying between 250 m and 400 m, and 1,500 m3/hr for
sand blanket laying from 400 m onwards.
If the dredging rate changes to 700m3/day, the proposed work rates for sand blanket laying are 850 m3/hr
between 24 m and 250 m away from the nearest coral colony, 1,400 m3/hr
for sand blanket laying between 250 m and 400 m, and 1,400 m3/hr for
sand blanket laying from 400 m onwards.
The corresponding of SS contribution by these two kinds of marine
works in Stage 1 to 3 at the nearest WSR is presented in Tables 4.3 4.5.
The maximum work rates for separate construction activities are shown in Table
4.6 and 4.7.
Table 4.3 Calculation of Cumulative SS
Elevation (Dredging Rate at 380m3/day) Stage 1, 2, and 3
|
Sources
|
Distance from the Nearest WSR (m)
|
Work Rate
|
Sediment Loss Rate - without mitigation at source (kg/s)
|
Mitigation Measure efficiency at Source
|
Sediment Loss Rate - with mitigation at source (kg/s)
|
SS at WSR - without mitigation at WSR (mg/L)
|
Mitigation Measure at WSR
|
SS at WSR - with mitigation at WSR (mg/L)
|
|
Within 250 m away from nearest WSRs
|
|
Localized dredging at the northeast seawall
|
24
|
380 m3/day
|
0.1759
|
75%
|
0.0440
|
10.34
|
96%
|
0.41
|
|
Sand blanket laying within Area A / B (Sand fill)
|
58
|
1,000 m3/hr
|
2.551
|
80%
|
0.5102
|
49.63
|
96%
|
1.99
|
|
|
|
|
|
|
|
|
Total
|
2.40
|
|
Beyond 250 m away from nearest WSRs
|
|
Localized dredging at the northeast seawall
|
24
|
380 m3/day
|
0.1759
|
75%
|
0.0440
|
10.34
|
96%
|
0.41
|
|
Sand blanket laying within Area A / B (Sand fill)
|
250
|
1,730 m3/hr
|
4.4132
|
80%
|
0.8826
|
19.92
|
96%
|
0.80
|
|
|
|
|
|
|
|
|
Total
|
1.21
|
|
Beyond 400 m away from nearest WSRs
|
|
Localized dredging at the northeast seawall
|
24
|
380 m3/day
|
0.1759
|
75%
|
0.0440
|
10.34
|
96%
|
0.41
|
|
Sand blanket laying within Area A / B (Sand fill)
|
400
|
1,730 m3/hr
|
4.4132
|
80%
|
0.8826
|
12.45
|
96%
|
0.50
|
|
|
|
|
|
|
|
|
Total
|
0.91
|
Table 4.4 Calculation
of Cumulative SS Elevation (Dredging Rate at 600m3/day) Stage 1, 2
and 3
|
Sources
|
Distance from the Nearest WSR (m)
|
Work Rate
|
Sediment Loss Rate - without mitigation at source (kg/s)
|
Mitigation Measure efficiency at Source
|
Sediment Loss Rate - with mitigation at source (kg/s)
|
SS at WSR - without mitigation at WSR (mg/L)
|
Mitigation Measure at WSR
|
SS at WSR - with mitigation at WSR (mg/L)
|
|
Within 250 m away from nearest WSRs
|
|
Localized dredging at the northeast seawall
|
24
|
600 m3/day
|
0.2778
|
75%
|
0.0695
|
16.34
|
96%
|
0.65
|
|
Sand blanket laying within Area A / B (Sand fill)
|
58
|
900 m3/hr
|
2.2959
|
80%
|
0.4592
|
44.67
|
96%
|
1.79
|
|
|
|
|
|
|
|
|
Total
|
2.44
|
|
Beyond 250 m away from nearest WSRs
|
|
Localized dredging at the northeast seawall
|
24
|
600 m3/day
|
0.2778
|
75%
|
0.0695
|
16.34
|
96%
|
0.65
|
|
Sand blanket laying within Area A / B (Sand fill)
|
250
|
1,500 m3/hr
|
3.8265
|
80%
|
0.7653
|
17.27
|
96%
|
0.69
|
|
|
|
|
|
|
|
|
Total
|
1.34
|
|
Beyond 400 m away from nearest WSRs
|
|
Localized dredging at the northeast seawall
|
24
|
600 m3/day
|
0.2778
|
75%
|
0.0695
|
16.34
|
96%
|
0.65
|
|
Sand blanket laying within Area A / B (Sand fill)
|
400
|
1,500 m3/hr
|
3.8265
|
80%
|
0.7653
|
10.79
|
96%
|
0.43
|
|
|
|
|
|
|
|
|
Total
|
1.08
|
Table 4.5 Calculation
of Cumulative SS Elevation (Dredging Rate at 700m3/day) Stage 1, 2
and 3
|
Sources
|
Distance from the Nearest WSR (m)
|
Work Rate
|
Sediment Loss Rate - without mitigation at source (kg/s)
|
Mitigation Measure efficiency at Source
|
Sediment Loss Rate - with mitigation at source (kg/s)
|
SS at WSR - without mitigation at WSR (mg/L)
|
Mitigation Measure at WSR
|
SS at WSR - with mitigation at WSR (mg/L)
|
|
Within 250 m away from nearest WSRs
|
|
Localized dredging at the northeast seawall
|
24
|
700 m3/day
|
0.3241
|
75%
|
0.0810
|
19.04
|
96%
|
0.76
|
|
Sand blanket laying within Area A / B (Sand fill)
|
58
|
850 m3/hr
|
2.1684
|
80%
|
0.4337
|
42.19
|
96%
|
1.69
|
|
|
|
|
|
|
|
|
Total
|
2.45
|
|
Beyond 250 m away from nearest WSRs
|
|
Localized dredging at the northeast seawall
|
24
|
700 m3/day
|
0.3241
|
75%
|
0.0810
|
19.04
|
96%
|
0.76
|
|
Sand blanket laying within Area A / B (Sand fill)
|
250
|
1,400 m3/hr
|
3.5714
|
80%
|
0.7143
|
16.12
|
96%
|
0.64
|
|
|
|
|
|
|
|
|
Total
|
1.40
|
|
Beyond 400 m away from nearest WSRs
|
|
Localized dredging at the northeast seawall
|
24
|
700 m3/day
|
0.3241
|
75%
|
0.0810
|
19.04
|
96%
|
0.76
|
|
Sand blanket laying within Area A / B (Sand fill)
|
400
|
1,400 m3/hr
|
3.5714
|
80%
|
0.7143
|
10.08
|
96%
|
0.40
|
|
|
|
|
|
|
|
|
Total
|
1.16
|
Table 4.6 Calculation
of SS Elevation Stage 1, 2 and 3 (Dredging only)
|
Sources
|
Distance from the Nearest WSR (m)
|
Work Rate
|
Sediment Loss Rate - without mitigation at source (kg/s)
|
Mitigation Measure efficiency at Source
|
Sediment Loss Rate - with mitigation at source (kg/s)
|
SS at WSR - without mitigation at WSR (mg/L)
|
Mitigation Measure at WSR
|
SS at WSR - with mitigation at WSR (mg/L)
|
|
Beyond 24 m away from nearest WSRs
|
|
Localized dredging at the northeast seawall
|
24
|
1,900 m3/day
|
0.8796
|
75%
|
0.2199
|
51.69
|
96%
|
2.07
|
|
|
|
|
|
|
|
|
Total
|
2.07
|
Table 4.7 Calculation
of SS Elevation Stage 1, 2 and 3 (Sand fill only)
|
Sources
|
Distance from the Nearest WSR (m)
|
Work Rate
|
Sediment Loss Rate - without mitigation at source (kg/s)
|
Mitigation Measure efficiency at Source
|
Sediment Loss Rate - with mitigation at source (kg/s)
|
SS at WSR - without mitigation at WSR (mg/L)
|
Mitigation Measure at WSR
|
SS at WSR - with mitigation at WSR (mg/L)
|
|
Within 250 m away from nearest WSRs
|
|
Sand blanket laying within Area A / B (Sand fill)
|
58
|
1,250 m3/hr
|
3.1888
|
80%
|
0.6378
|
62.04
|
96%
|
2.48
|
|
|
|
|
|
|
|
|
Total
|
2.48
|
|
Beyond 250 m away from nearest WSRs
|
|
Sand blanket laying within Area A / B (Sand fill)
|
250
|
2,150 m3/hr
|
5.4847
|
80%
|
1.0969
|
24.75
|
96%
|
0.99
|
|
|
|
|
|
|
|
|
Total
|
0.99
|
|
Beyond 400 m away from nearest WSRs
|
|
Sand blanket laying within Area A / B (Sand fill)
|
400
|
2,150 m3/hr
|
5.4847
|
80%
|
1.0969
|
15.47
|
96%
|
0.62
|
|
|
|
|
|
|
|
|
Total
|
0.62
|
Stage
4A (Newly added construction sequence)
After substantial
completion of seawall (except approximately 50m opening and approximately 200m
silt curtain located at the eastern side of artificial island), marine filling
will be carried out within Area B (reclamation area) and precast seawall
structure will be installed at Area A (Seawall A and Seawall B) concurrently. Installation
of remaining block work seawall at Area A shall also be carried out. In
parallel, ground treatment works such as DCM works and laying Grade 200 rock to
form rock mould will be carried out at Area B (Breakwater A and B). The
duration of this stage is about 2-3 months.
In
this stage, concurrent marine works for the Project include (1) marine filling within reclamation area at
Area B; (2) installation of precast seawall structure at remaining seawall
portion at the eastern side of Artificial Island at Area A (Sewall A and
Seawall B); (3) installation of block work seawall at the remaining seawall
portion at the eastern side of Artificial Island at Area A; and (4) Ground Treatment such
as DCM works and laying Grade 200
rock to form rock mound at Area B (Breakwater A and B). As public fill and sand
fill shall both be used for reclamation below +2.5mPD, the maximum filling rate
of sand fill and public fill are tabulated in Tables 4.8 4.9 if two
filling materials are not filled concurrently.
Marine filling works within reclamation area will only be
commenced when the installation of block work seawall near the shoreline have
been completed for 310m. In other words, the installation of block work seawall
between Vertical Seawall Chainage S_CH0 and Vertical Seawall Chainage S_CH310
shall be completed. Precast caissons located at Seawall A between Chainage
SB_CH250 and SB_CH580 and located at Seawall B between Chainage Q_CH0 and
Q_CH388 shall also be completed. The locations of vertical seawall chainage,
Seawall A and Seawall B chainage at Area A are shown in Figure 7.
Grade 75 and Grade 200 rock shall be used for to fill up
the caissons. Rock filling inside the caisson will be carried out within 1 to 2
days after placing it into right position. As rock is assumed to have no fine
content, no unacceptable water quality impact will be expected. Nevertheless,
Type 6 silt curtain, as stated in Silt Curtain Deployment Plan, will be
installed around the caisson under filling. It is not anticipated to have
potential laden overflow of suspended solids when the caisson is filled up with
Grade 75 and Grade 200 rock due to heavy rainfall. According to the design, the
top layer of Grade 75 and Grade 200 rock, acts as ballast inside the caisson,
will only be filled up to +1.3mPD. However, the top level of the caisson will
be +3mPD. Sufficient spaces are available inside caissons to contain rainwater.
As the seawalls had
been constructed higher than +2.5mPD, the fine materials are not anticipated to
leak through the constructed seawalls. Prior to complete enclosure of the
caisson at the eastern side of the artificial island, double layers silt
curtain will be erected both at the western side as marine access opening and
at eastern side as fixed installation, as a temporary mitigation measures.
Different filling rates shall be adopted so as to minimize the effect on the
coral colonies next to the shoreline at Shek Kwu Chau.
A scenario is presented
if sand fill and public fill are filled concurrently. Table 4.10 can
present such relationship.
Table 4.8 Calculation of SS Elevation Stage 4A
(Sand fill only)
|
Sources
|
Distance from the Nearest WSR (m)
|
Work Rate
|
Sediment Loss Rate - without mitigation at
source (kg/s)
|
Mitigation Measure efficiency at Source
|
Sediment Loss Rate - with mitigation at
source (kg/s)
|
SS at WSR - without mitigation at WSR (mg/L)
|
Mitigation Measure at WSR
|
SS at WSR - with mitigation at WSR (mg/L)
|
|
Within 250 m away from nearest WSRs
|
|
Marine Fill within Area B (Sand fill)
|
60
|
2,850 m3/hr
|
3.1745
|
80%
|
0.6349
|
59.70
|
96%
|
2.39
|
|
|
|
|
|
|
|
|
Total
|
2.39
|
|
Beyond 250 m away from nearest WSRs
|
|
Marine Fill within Area B (Sand fill)
|
250
|
12,000 m3/hr
|
13.366
|
80%
|
2.6732
|
60.33
|
96%
|
2.41
|
|
|
|
|
|
|
|
|
Total
|
2.41
|
Table 4.9 Calculation of SS Elevation Stage 4A
(Public fill only)
|
Sources
|
Distance from the Nearest WSR (m)
|
Work Rate
|
Sediment Loss Rate - without mitigation at
source (kg/s)
|
Mitigation Measure efficiency at Source
|
Sediment Loss Rate - with mitigation at
source (kg/s)
|
SS at WSR - without mitigation at WSR (mg/L)
|
Mitigation Measure at WSR
|
SS at WSR - with mitigation at WSR (mg/L)
|
|
Within 250 m away from nearest WSRs
|
|
Marine Fill within Area B (Public Fill)
|
60
|
485 m3/hr
|
3.1998
|
80%
|
0.6400
|
60.18
|
96%
|
2.41
|
|
|
|
|
|
|
|
|
Total
|
2.41
|
|
Beyond 250 m away from nearest WSRs
|
|
Marine Fill within Area B (Public Fill)
|
250
|
2,090 m3/hr
|
13.789
|
80%
|
2.7578
|
62.24
|
96%
|
2.49
|
|
|
|
|
|
|
|
|
Total
|
2.49
|
Table 4.10 Calculation of Cumulative SS Elevation
Stage 4A
|
Sources
|
Distance from the Nearest WSR (m)
|
Work Rate
|
Sediment Loss Rate - without mitigation at
source (kg/s)
|
Mitigation Measure efficiency at Source
|
Sediment Loss Rate - with mitigation at
source (kg/s)
|
SS at WSR - without mitigation at WSR (mg/L)
|
Mitigation Measure at WSR
|
SS at WSR - with mitigation at WSR (mg/L)
|
|
Within 250 m away from nearest WSRs
|
|
Marine Fill within Area B
(Sand fill)
|
60
|
1,425 m3/hr
|
1.5872
|
80%
|
0.3174
|
29.85
|
96%
|
1.19
|
|
Marine Fill within Area B (Public fill)
|
60
|
240 m3/hr
|
1.5834
|
80%
|
0.3167
|
29.78
|
96%
|
1.19
|
|
|
|
|
|
|
|
|
Total
|
2.38
|
|
Beyond 250 m away from nearest WSRs
|
|
Marine Fill within Area B
(Sand fill)
|
250
|
6,000 m3/hr
|
6.6831
|
80%
|
1.3367
|
30.17
|
96%
|
1.21
|
|
Marine Fill within Area B (Public fill)
|
250
|
1,045 m3/hr
|
6.8943
|
80%
|
1.3789
|
31.12
|
96%
|
1.24
|
|
|
|
|
|
|
|
|
Total
|
2.45
|
Stage
5
In
this stage, concurrent marine works for the Project include (1) marine filling within reclamation at Area
B, and (2) installation of precast seawall structure at breakwater. As public fill and sand fill shall both be used for
reclamation below +2.5mPD, the maximum filling rate of sand fill and public
fill are tabulated in Tables 4.11 4.12 if two filling materials are
not filled concurrently.
Grade 75 and Grade 200 rock shall be used for to fill up
the caissons. Rock filling inside the caisson will be carried out within 1 to 2
days after placing it into right position. As rock is assumed to have no fine
content, no unacceptable water quality impact will be expected. Nevertheless,
Type 6 silt curtain, as stated in Silt Curtain Deployment Plan, will be
installed around the caisson under filling. It is not anticipated to have
potential laden overflow of suspended solids when the caisson is filled up with
Grade 75 and Grade 200 rock due to heavy rainfall. According to the design, the
top layer of Grade 75 and Grade 200 rock, acts as ballast inside the caisson,
will only be filled up to +1.3mPD. However, the top level of the caisson will
be +3mPD. Sufficient spaces are available inside caissons to contain rainwater.
As the seawalls had been constructed higher
than +2.5mPD, the fine materials are not anticipated to leak through the
constructed seawalls. Therefore, the nearest coral colonies being affected by
shall be located in the vicinity between the seawall and breakwater. The
minimum distance between the marine filling within reclamation at Area B and
the nearest coral colonies shall be over 400m after changing the location of
marine access.
A scenario is presented if sand fill and
public fill are filled concurrently. Table 4.13 can present such
relationship.
Table 4.11 Calculation
of SS Elevation Stage 5 (Sand fill only)
|
Sources
|
Distance from the Nearest WSR (m)
|
Work Rate
|
Sediment Loss Rate - without mitigation at source (kg/s)
|
Mitigation Measure efficiency at Source
|
Sediment Loss Rate - with mitigation at source (kg/s)
|
SS at WSR - without mitigation at WSR (mg/L)
|
Mitigation Measure at WSR
|
SS at WSR - with mitigation at WSR (mg/L)
|
|
Beyond 400 m away from nearest WSRs
|
|
Marine Fill within Area B (Sand fill)
|
400
|
19,850 m3/hr
|
22.11
|
80%
|
4.422
|
62.35
|
96%
|
2.49
|
|
|
|
|
|
|
|
|
Total
|
2.49
|
Table 4.12 Calculation
of SS Elevation Stage 5 (Public fill only)
|
Sources
|
Distance from the Nearest WSR (m)
|
Work Rate
|
Sediment Loss Rate - without mitigation at source (kg/s)
|
Mitigation Measure efficiency at Source
|
Sediment Loss Rate - with mitigation at source (kg/s)
|
SS at WSR - without mitigation at WSR (mg/L)
|
Mitigation Measure at WSR
|
SS at WSR - with mitigation at WSR (mg/L)
|
|
Beyond 400 m away from nearest WSRs
|
|
Marine Fill within Area B (Public Fill)
|
400
|
3,350 m3/hr
|
22.102
|
80%
|
4.4205
|
62.35
|
96%
|
2.49
|
|
|
|
|
|
|
|
|
Total
|
2.49
|
Table 4.13 Calculation
of Cumulative SS Elevation Stage 6
|
Sources
|
Distance from the Nearest WSR (m)
|
Work Rate
|
Sediment Loss Rate - without mitigation at source (kg/s)
|
Mitigation Measure efficiency at Source
|
Sediment Loss Rate - with mitigation at source (kg/s)
|
SS at WSR - without mitigation at WSR (mg/L)
|
Mitigation Measure at WSR
|
SS at WSR - with mitigation at WSR (mg/L)
|
|
Beyond 400 m away from nearest WSRs
|
|
Marine Fill within Area B
(Sand fill)
|
400
|
9,925 m3/hr
|
11.055
|
80%
|
2.211
|
31.2
|
96%
|
1.25
|
|
Marine Fill within Area B (Public fill)
|
400
|
1,675 m3/hr
|
11.051
|
80%
|
2.21
|
31.15
|
96%
|
1.25
|
|
|
|
|
|
|
|
|
Total
|
2.50
|
Summary of Appropriate
Mitigation Measures and Works Rates
A number of mitigation
measures have been recommended in the approved EIA Report, FEP and the VEP Supporting
Document, including control of dredging rate, use of silt curtain during dredging
as well as use of grab dredger or bottom placement method for sand blanket laying. These measures will
be properly implemented during the construction and have been taken into account
in the assessment. In addition, it is recommended to deploy an additional layer
of silt curtain at the sediment source as well as two double layers of silt curtains
between the sediment sources and nearby WSRs to provide additional protection to
these WSRs Implementation schedules of the proposed mitigation measures is
attached in Annex B.
Based on the above
assumptions, maximum SS elevation predicted at the nearest WSRs for various stages
of the reclamation is expected to be at or below the corresponding SS assessment
criterion of 2.5 mg/L with the following work rates for sand blanket laying
stated in Tables 4.14 4.24.
Table 4.14 Summary of Maximum Allowable Dredging Rate and Filling Rate
(m3/hr and m3/day for 12 hr work day) for Sand Blanket
Laying while carrying out dredging and filling works
concurrently (Constant Dredging rate at 380m3/day)
|
|
Stage 1 - 3
|
|
Shortest
distance to nearest coral (m) Dredging Rate
|
24
|
|
Distance from
Nearest WSR (m) Dredging Rate
|
|
|
|
|
24 - > 400
|
380 m3/day
|
|
Shortest
distance to nearest coral (m) Filling Rate
|
58
|
|
Distance from
Nearest WSR (m) Filling Rate
|
|
|
|
|
< 250
|
1,000 m3/hr
12,000 m3/day
|
|
250 400
|
1,730 m3/hr
20,760 m3/day
|
|
> 400
|
1,730 m3/hr
20,760 m3/day
|
Table 4.15 Summary
of Maximum Allowable Dredging Rate and Filling Rate (m3/hr and m3/day
for 12 hr work day) for Sand Blanket Laying while carrying out dredging and
filling works concurrently (Constant Dredging rate at 600m3/day)
|
|
Stage 1 - 3
|
|
Shortest
distance to nearest coral (m) Dredging Rate
|
24
|
|
Distance from
Nearest WSR (m) Dredging Rate
|
|
|
24 - > 400
|
600 m3/day
|
|
Shortest
distance to nearest coral (m) Filling Rate
|
58
|
|
Distance from
Nearest WSR (m) Filling Rate
|
|
|
< 250
|
900 m3/hr
10,800 m3/day
|
|
250 400
|
1,500 m3/hr
18,000 m3/day
|
|
> 400
|
1,500 m3/hr
18,000 m3/day
|
Table 4.16 Summary
of Maximum Allowable Dredging Rate and Filling Rate (m3/hr and m3/day
for 12 hr work day) for Sand Blanket Laying while carrying out dredging and
filling works concurrently (Constant Dredging rate at 700m3/day)
|
|
Stage 1 - 3
|
|
Shortest
distance to nearest coral (m) Dredging Rate
|
24
|
|
Distance from
Nearest WSR (m) Dredging Rate
|
|
|
24 - > 400
|
700 m3/day
|
|
Shortest
distance to nearest coral (m) Filling Rate
|
58
|
|
Distance from
Nearest WSR (m) Filling Rate
|
|
|
< 250
|
850 m3/hr
10,200 m3/day
|
|
250 400
|
1,400 m3/hr
16,800 m3/day
|
|
> 400
|
1,400 m3/hr
16,800 m3/day
|
Table 4.17 Summary
of Maximum Dredging Rate (m3/day for 12 hr work day) for carrying
out dredging works only
|
|
Stage 1 - 3
|
|
Shortest
distance to nearest coral (m)
|
24
|
|
Distance from
Nearest WSR (m)
|
|
|
24 - > 400
|
1900 m3/day
|
Table 4.18 Summary
of Maximum Filling Rate (m3/hr and m3/day for 12 hr work
day) for Sand Blanket Laying while carrying out filling works by using sand
fill only
|
|
Stage 1 - 3
|
|
Shortest
distance to nearest coral (m)
|
58
|
|
Distance from
Nearest WSR (m)
|
|
|
< 250
|
1,250 m3/hr
15,000 m3/day
|
|
250 400
|
2,150 m3/hr
25,800 m3/day
|
|
> 400
|
2,150 m3/hr
25,800 m3/day
|
Table 4.19 Summary of Maximum Allowable Filling Rate
(m3/hr and m3/day for 12 hr work day) for Reclamation
while filling sand fill and public fill concurrently
|
|
Stage 4A (Sand fill)
|
Stage 4A (Public fill)
|
|
Shortest distance to nearest coral (m)
|
60
|
60
|
|
Distance from Nearest WSR (m) Filling Rate
|
|
|
|
< 250
|
1,425 m3/hr
17,100 m3/day
|
240 m3/hr
2,880 m3/day
|
|
> 250
|
6,000 m3/hr
72,000 m3/day
|
1,045 m3/hr
15,540 m3/day
|
Table 4.20 Summary of Maximum Allowable Filling Rate
(m3/hr and m3/day for 12 hr work day) for Reclamation
while filling sand fill only
|
|
Stage 4A (Sand fill)
|
|
Shortest distance to nearest coral (m)
|
60
|
|
Distance from Nearest WSR (m) Filling Rate
|
|
|
< 250
|
2,850 m3/hr
34,200 m3/day
|
|
> 250
|
12,000 m3/hr
144,000 m3/day
|
Table 4.21 Summary of Maximum Allowable Filling Rate
(m3/hr and m3/day for 12 hr work day) for Reclamation
while filling public fill only
|
|
Stage 4A (Public fill)
|
|
Shortest distance to nearest coral (m)
|
60
|
|
Distance from Nearest WSR (m) Filling Rate
|
|
|
< 250
|
485 m3/hr
5,820 m3/day
|
|
> 250
|
2,090 m3/hr
25,080 m3/day
|
Table 4.22 Summary
of Maximum Allowable Filling Rate (m3/hr and m3/day for
12 hr work day) for Reclamation while filling sand fill and public fill
concurrently
|
|
Stage 5
(Sand fill)
|
Stage 5 (Public
fill)
|
|
Shortest
distance to nearest coral (m)
|
> 400
|
> 400
|
|
Distance from
Nearest WSR (m) Filling Rate
|
|
|
|
>400
|
9,925 m3/hr
119,100 m3/day
|
1,675 m3/hr
20,100 m3/day
|
Table 4.23 Summary
of Maximum Allowable Filling Rate (m3/hr and m3/day for
12 hr work day) for Reclamation while filling sand fill only
|
|
Stage 5
(Sand fill)
|
|
Shortest
distance to nearest coral (m)
|
> 400
|
|
Distance from
Nearest WSR (m) Filling Rate
|
|
|
> 400
|
19,850 m3/hr
238,200 m3/day
|
Table 4.24 Summary
of Maximum Allowable Filling Rate (m3/hr and m3/day for
12 hr work day) for Reclamation while filling public fill only
|
|
Stage 5
(Public fill)
|
|
Shortest
distance to nearest coral (m)
|
> 400
|
|
Distance from
Nearest WSR (m) Filling Rate
|
|
|
> 400
|
3,350 m3/hr
40,200 m3/day
|
Depending
on the distance between the work fronts and the coral colonies, different
dredging rate and filling rates shall be adopted. For carrying out construction
activities in Stages 1 - 3, the allowable dredging and filling rates shall
referred to Tables 4.12 4.18 and Figure 6A. For carrying out construction
activities in Stage 4A, the allowable filling rates shall refer to Tables 4.19
4.21 and Figure 6B. For carrying out construction activities in Stage 5, the
allowable filling rates shall refer to Tables 4.22 4.24 and Figure 6C.
In
general, the dredging and filling rates for Stages 1, 2, 3 and 5 are remained
the same as the previously approved Supporting Document for Reviewing Dredging
Rate and Filling Rate (Rev. C).
Based on
the assessment above, no unacceptable water quality impact associated with the proposed
changes in construction sequence for Stage 4A for the early start of
reclamation works will be expected with the implementation of newly proposed
mitigation measures.
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