2
comparison
of Black Point terminal alternatives
The
following section presents a comparison of the alternatives for the Black Point
terminal. The section has been divided into
a discussion of the following:
·
Consideration of Different Layouts and
Design Options; and
·
Consideration of Alternative Construction
Methods.
Based on
the above considerations, the Environmental Impact Assessment (EIA) of the preferred
Black Point terminal scenario is presented in subsequent sections.
2.1
Consideration of Different Layouts and Design Options
In
accordance with Clause 3.6.4 of the
EIA Study Brief (ESB-126/2005), this
section presents considerations of the different layouts and design options
that have been assessed as part of the overall assessment of alternatives for
the Black Point terminal. The
methodology, criteria and findings are presented.
The
assessment was conducted to investigate the environmental considerations of
each layout and design option and to examine the engineering aspects for
each. The assessment thus considers both
the difficulties of the construction and operation of each facility as well as
the associated potential environmental impacts.
2.1.1
Layout
Options
The basic
requirements of a LNG receiving terminal in Hong Kong have been described in
detail in Part 1 - Section 3. Justifications for Black Point being
considered as one of two sites for a LNG receiving terminal in Hong Kong have been
presented in Part 1 – Section 4.
Several
terminal layout options on Black Point have been considered. As there is limited flat land at Black Point
to accommodate the necessary infrastructure, the method of providing sufficient
land, either by reclamation or excavation of the existing headland has been
considered. In addition, due to the
outline of the coastline, there are options for locating the LNG carrier
berth. These provide differences in
dredging requirements but similar approach and berthing issues.
Three
layouts have been selected for further assessment in order to provide a
comprehensive assessment of different layouts and design options. The layouts present, as best possible, a wide
range of engineering options and subsequent environmental considerations for
the construction and operation of the Black Point terminal. Each of the layouts has been prepared so that
the distances between the facilities within the LNG terminal show broad
compliance with EN1473. The three layouts are presented below in
terms of the general design and construction methods.
Option 1 – Base Case
Layout
Option 1 - Base Case is derived from a combination of reclamation and
excavation (Figure
2.1). The purpose of this
combination is to maintain a balance between the cut and fill quantities, and
to create cost effective and sustainable site formation. The area of excavation for the site is
limited to provide sufficient land area initially for two tanks to enable them
to be founded directly on rock which will permit the use of pad/raft
foundations thus negating the need for deep foundations. The steep rock face behind will also screen
the two tanks from any visual sensitive receivers. A platform at a level of +6mPD will be formed
by excavation into the existing hillside.
Land will be reclaimed immediately to the northwest of the Black Point
headland to accommodate the third tank and the terminal facilities.
The LNG
carrier jetty will be located to the northwest of the reclaimed land. Although the jetty is close to the
Option 2 – Full Reclamation
Layout
Option 2 - Full Reclamation is derived such that no excavation is undertaken in
the Black Point peninsula (Figure 2.2). All the land needed for the three LNG tanks
and terminal facilities will be provided by reclamation at the end of the Black
Point peninsula. The platform level will
be at +6mPD. The tanks will be located
nearer to the existing hillside as the rock head is shallower which facilitates
foundation construction. As in Option 1,
the LNG carrier jetty will be located to the northwest of the reclaimed
land.
Option 3 – Full Excavation
Layout
Option 3 - Full Excavation would require no reclamation into the sea such that
the required land is generated by excavation only into the Black Point
headland. In order to create a platform
of sufficient area at a level of +6mPD to house the three tanks and all the
terminal facilities a cutting up to 30m in height will be required. By cutting into the headland the facility is
expected to be more visible from views to the south.
The LNG
carrier jetty will be located to the west of the Black Point site.
Engineering Works Criteria
In order
to satisfy each of the terminal requirements described in Part 1 - Section 3, it is necessary to undertake site formation,
dredging and reclamation works at each of the layout options at Black
Point. A summary of the key engineering
works criteria for each layout option are summarised in Table 2.1.
Table 12.1 Summary of Engineering Works Criteria
(based on conceptual indicative site layouts)
|
Engineering
Criteria |
Option 1 (Base Case) |
Option 2 (Full Reclamation) |
Option 3 (Full Excavation) |
|
Site Area (ha) |
32.0 |
31.5 |
35.0 |
|
Volume of Dredging for Reclamation (106m³) |
0.63 |
0.65 |
0 |
|
Volume of Dredging for Approach Channel & Turning
Basin (106m³) |
2.49 |
2.49 |
1.40 |
|
Volume of Excavation Disposed (106m³) |
0 |
0 |
14 |
|
Volume of Fill Imported (106m³) |
1.90 |
3.43 |
0 |
|
Length of Natural Coastline Affected (m) |
600 |
580 |
0 |
|
Length of Seawall (m) |
1,120 |
1,160 |
0 |
|
Length of Trestle (m) |
100 |
100 |
180 |
The
layouts described above have been considered in terms of a technical comparison
and assessment of the engineering works followed by a comparison of the
potential for environmental impacts through construction and operation. Each of these assessments
is presented below, followed by a summary of the overall findings. On the basis of these assessments, the
preferred layout and design option for the Black Point terminal is identified.
2.1.2
Engineering
Assessment
Overall
Engineering Assessment Criteria
The key
engineering assessment criteria have been established to enable a quantitative
comparison of the three layout options to be scored and ranked in accordance
with their relative merits and demerits.
As each of these assessment criteria do not have an equivalent impact on
the overall construction of the terminal facility, a relative importance factor
has been applied to each as shown in Table
2.2.
Table 21.2 Overall Engineering Assessment Criteria
|
Engineering
Assessment Criterion |
Relative Importance Factor |
|
Construction of site formation works |
0.30 |
|
Construction of site reclamation works |
0.30 |
|
Construction of approach channel and turning basin |
0.20 |
|
Marine navigation |
0.10 |
|
Construction of facility foundations |
0.10 |
|
Total |
1.00 |
The
rationale for the relative importance factor is given below.
·
It was considered logical for the sum of
the relative importance factors to add up to unity. In this manner each relative importance
factor also directly represents the percentage importance to the whole process.
·
The major engineering works for each of the
layout options is considered to be the construction of the site formation and
reclamation. These assessment criterions
are, therefore, given an equally high relative importance factor of 30% each.
·
The next major engineering works for the
layout options is the construction of the approach channel and turning
basin. This assessment criterion is, therefore,
assigned a reasonable importance factor of 20%.
·
Black Point is located adjacent to the
existing traffic fairway that will be used for construction boats and barges
for the import and export of materials to the site. Similarly marine craft will be employed for
the dredging of the approach channel.
The larger the reclamation area, the greater encroachment into the
existing waterway north of the jetty for the turning basin. Since the approach to the site will be
relatively similar for each of the layout options, a relatively low importance
factor of 10% is, therefore, assigned to this criterion.
·
The construction of the facility
foundations and the receiving terminal facility itself will generally employ
conventional construction techniques which will be generally similar to all
sites with minor differences resulting from accessibility and specific location
constraints. A relatively low weighting
of 10% is, therefore, applied to the importance factor for these criteria.
Parameters for Each Engineering
Assessment Criterion
In order
to make a quantitative assessment of the relative advantages and disadvantages
of each layout for each of the engineering assessment criterion defined in Table 2.2, a set of engineering
parameters reflecting the main tasks to be undertaken under each activity has
been developed. Each parameter carries a
weighting to represent the relative significance and impact on the overall
engineering assessment criterion. It was
considered logical for the sum of the relative weighting factors to add up to
unity. In this manner each relative
weighting also directly represents the percentage importance to the whole
process. The parameters used in the
evaluation of the sites for each engineering assessment criterion is detailed
in Tables 2.3 to 2.7.
Construction of Site Formation Works
The
engineering assessment criterion for site formation considers nine main
parameters.
Table 21.3 Engineering Assessment Parameters Used for
Construction of Site Formation Works
|
Engineering
Assessment Criterion |
Parameter |
Relative Weighting |
|
Construction of site formation works |
Volume of excavation in soil |
0.05 |
|
Volume of excavation in rock |
0.25 |
|
|
Volume of soil to be disposed of |
0.20 |
|
|
Volume of rock to be disposed of |
0.05 |
|
|
Impact on construction programme |
0.10 |
|
|
Slope stabilisation measures required |
0.10 |
|
|
Slope maintenance |
0.05 |
|
|
Future slope hazard |
0.05 |
|
|
Blasting risks |
0.15 |
|
|
Total |
1.00 |
The rationale
for the selection of each relative weighting factor in Table 2.3 is given below.
·
The most difficult and time consuming
activity is usually the excavation of rock material which generally comprises
very good quality granite material. The
excavation of this material will require significant effort using blasting and
heavy mechanical equipment for which stringent engineering controls will be
required. The excavation works are also
generally intimately linked with the construction of the storage tanks, which
have a long construction time and are therefore critical path activities. As such, the rock excavation has a
significant impact on the programme. The
highest weighting of 25% is, therefore, assigned to this parameter.
·
The excavation of soil is a relatively easy
and quick task utilising mechanical equipment and, therefore, only a low
weighting of 5% is assigned. The volume
of soil excavation is also generally small.
·
The disposal of the soil material is given
a high weighting of 20% as it will need to be taken to one of the Public Fill
facilities, which should be avoided if possible. High scores are, therefore, awarded to sites
which limit disposal of soil and make the best use of the material which will
be apparent with a high weighting.
·
The disposal of rock is given a low
weighting of 5% as it will likely be reused for construction in
·
As the site formation works impact directly
on the construction programme a medium 10% weighting factor is considered
appropriate to favour the sites which can be constructed in the shortest
duration.
·
Blasting will need to comply with extensive
and stringent regulation requirements. Incorporation of these measures will
lengthen the construction programme; therefore, a medium level relative
weighting of 15% is applied to these works to favour the sites that do not
require blasting.
·
The slope stabilisation works associated
with the facility will need to comply with the regulation requirements which
are reasonably stringent and can be extensive for large slopes. The amount of stabilisation works are,
therefore, best reduced as far as possible.
A medium relative weighting factor of 10% is therefore applied to these
works.
·
Slope maintenance and slope hazards are
both events that will be under the control of the LNG facility during
operation. These can, therefore, be
reasonably managed and as such a low weighting of 5% has been assigned to each.
Construction of Site Reclamation
Works
The
engineering assessment criterion for reclamation considers ten main parameters
as shown in Table 2.4.
Table 12.4 Engineering Assessment Parameters Used for
Construction of Site Reclamation Works
|
Engineering
Assessment Criterion |
Parameter |
Relative
Weighting |
|
Construction of site reclamation works |
Area of reclamation |
0.10 |
|
Volume of dredging material |
0.20 |
|
|
Total volume of fill material required |
0.05 |
|
|
Total volume of imported fill (sand + rock) |
0.20 |
|
|
Length of natural coastline |
0.15 |
|
|
Length of artificial coastline |
0.05 |
|
|
Length of seawall required |
0.10 |
|
|
Construction time for dredging and filling |
0.05 |
|
|
Time for consolidation after construction |
0.05 |
|
|
Need for ground improvement |
0.05 |
|
|
Total |
1.00 |
The
rationale for the selection of each relative weighting factor is given below.
·
The most significant activities are the
dredging of soft material beneath and the importation requirements for
subsequent filling works. For the latter
case a lower amount of imported material is considered better as it indicates
that a better balance is being made with the excavated materials from the site
formation works. A high weighting of 20%
is, therefore, assigned to these parameters.
·
As the volume of imported material has
already been considered, the total volume of fill material required is less
important if the majority is sourced from within the site, therefore, only a 5%
weighting is assigned.
·
The length of natural coastline affected by
the reclamation is a measure of the extent of the engineering works on the
natural areas of
·
The length of artificial coastline affected
by the reclamation is considered to be less of an effect and a 5% weighting is,
therefore, applied.
·
The length of seawall and the area of
reclamation are indicators of the extent of the reclamation. For these parameters a medium weighting of
10% is deemed appropriate.
·
The time for construction, time for
consolidation and the need for ground improvement are important but less
significant engineering issues. A lower
weighting of 5% is, therefore, assumed for these parameters.
Construction of Approach Channel and
The
engineering assessment criterion for the construction of the approach channel
and turning basin considers five main parameters as shown in Table 2.5.
Table
12.5 Engineering Assessment Parameters Used for
Construction of Approach Channel and
|
Engineering
Assessment Criterion |
Parameter |
Relative Weighting |
|
Construction of approach channel and turning basin |
Total length of approach channel + turning basin |
0.20 |
|
Volume of dredging |
0.35 |
|
|
Rock excavation in dredged zone |
0.20 |
|
|
Impact on existing utilities |
0.15 |
|
|
Siltation & maintenance
dredging |
0.10 |
|
|
Total |
1.00 |
The
rationale for the selection of each relative weighting factor is given below.
(i) For
approach channel and turning basin the most significant activity is the
dredging works. A high weighting of 35% is
therefore assigned to this parameter.
(ii) The
length of the approach channel and the extent of rock excavation will affects the programme and
progress of the overall dredging works and are therefore each assigned a high
to medium weighting of 20%.
(iii)
The impact on existing utilities is
considered to be localised and secondary effects on the overall dredging works
and is therefore assigned a medium weighting of 15%.
The siltation/maintenance for the approach channels are factors
that affects the long-term operation for which a low to medium weighting of 10%
is considered appropriate.
Marine Navigation
The
engineering assessment criterion for marine navigation considers four main
parameters as shown in Table 2.6.
Table
21.6 Engineering Parameters and Associated
Relative Weighting Used for the Assessment of Marine Navigation
|
Engineering
Assessment Criterion |
Parameter |
Relative Weighting |
|
Marine navigation |
Marine traffic |
0.50 |
|
Grounding potential |
0.10 |
|
|
Striking berth by LNG Carrier |
0.10 |
|
|
Striking of the moored carrier by passing traffic |
0.30 |
|
|
Total |
1.00 |
The
rationale for the selection of each relative weighting factor is given below:
·
Although
historically, LNG carriers have had an excellent safety record, the main
hazards are the potential for collision with the carrier while in transit to
the jetty or from passing traffic striking the carrier while moored. The probability for such occurrences and
consequences will be dependent upon traffic density and discipline of shipboard
personnel complying with underway regulations.
As these are the main considerations a weighting of 0.5 and 0.3 are
awarded for Marine Traffic and the striking of the moored carrier by passing
traffic respectively.
·
The consequence of grounding and striking
of the marine berth is significantly lower than the above considerations,
therefore, a lower but equal weighting of 10% is assigned to each.
Construction of Facility Foundations
The
engineering assessment criterion for the facility foundation considers three
main parameters as shown Table 2.7.
Table
12.7 Engineering Assessment Parameters Used for
Construction of Facility Foundation
|
Engineering Assessment
Criterion |
Parameter |
Relative Weighting |
|
Construction of facility foundations |
Terminal facility structures |
0.30 |
|
Jetty piling works |
0.50 |
|
|
Water front access |
0.20 |
|
|
Total |
1.00 |
The rationale
for the selection of each relative weighting factor in Table 2.7 is given below.
·
The most difficult foundation construction
works for the proposed site is the construction of the marine piling works for
the jetty structures as it will be undertaken over water. A weighting of 50% is, therefore, assigned to
these works.
·
The land based foundation construction
works for the terminal facility structures and the water front access areas are
considered to be slightly easier and therefore a weighting factor of 30% and
20% are awarded, respectively. The
slightly higher weighting is given to the terminal facility works as the
quantity is significantly greater.
2.1.3
Site
Comparison Scoring System
Parameters and Relative Weighting for
Each Engineering Assessment Criterion
In order
to make a quantitative assessment of the relative advantages and disadvantages
of each site for each of the engineering assessment criterion defined above, a
set of engineering parameters reflecting the main tasks to be undertaken under
each criterion have been developed. As
with the Assessment Criteria, each parameter carries a relative weighting to
represent the significance and impact on the overall engineering assessment
criterion that also add up to unity.
Scoring Matrices
Using the
parameters described above, each of the different layout options has been
evaluated and compared against the base case based upon an assessment of the
merits and demerits of each. For this
purpose an options evaluation matrix has been created to compare the Black
Point base case layout against each of the two alternative layouts.
Firstly, a
relative comparison matrix summarising the quantities associated with each
assessment parameter is established within separate matrices for each
engineering construction criterion. The
matrices are presented in Annex 2-A.
Using the relative
comparison matrices an overall score is established for each layout option and
each engineering assessment criterion by assigning a relative score for each
parameter of between 0 and 5 which is dependent upon the relative magnitude or
impact of the parameter value on the works as compared to the base case as
shown in Table 2.8. The base case will receive an average median
score of 3 for each parameter. For the
two option layouts, a higher relative score is given to a site parameter with a
lower impact on the construction works when compared to same parameter of the
base case, and a lower relative score given to a site parameter with a higher
impact on the construction works when compared to the base case. The best layout site will, therefore, achieve
the highest overall score for ease of identification.
Table
12.8 Scoring System Applied to Assessment
Criteria
|
Impact on the Construction
of the Works as Compared with Base Case |
Score |
|
Significantly lower Impact relative to base case |
5 |
|
|
|
|
Slightly lower Impact relative to base case |
4 |
|
|
|
|
Similar Level of Impact to Base Case |
3 |
|
|
|
|
Slightly higher Impact relative to base case |
2 |
|
|
|
|
Significantly higher Impact relative to base case |
1 |
The scores
are tabulated in a relative comparison scoring matrix for each engineering
criterion. A total score for each engineering
criterion is determined from the sum of the weighted individual scores assigned
to each parameter depending upon their relative impact.
The
results of the scoring for each engineering assessment criteria are based on
the summary quantity matrices shown in Annex
2-A.
Overall Engineering Ranking of the
Layout Options
Having
assigned a score to each of the parameters within each of the engineering
assessment criteria, the result is multiplied by the relative weighting given
in Table 2.8 from which a total score
for each site for each engineering assessment criterion is derived. These scores are then normalised to a maximum
value of 5 to enable a quantitative comparison to be made. These values are referred to as ‘normalised
scores’ in Annex 2-A.
These
normalised scores for each engineering works activity matrix are applied to the
overall ranking matrix. The relative
importance factors given in Table 2.2
are applied to each of the normalised scores within the overall ranking matrix
in order to determine an overall score for each option.
Engineering Assessment Results
Having
evaluated each layout option for the Black Point terminal separately with
respect to each engineering assessment criterion, the results of each
individual assessment have been used to produce an overall score for each
option. These scores have then been used
to rank the layouts in order of preference to enable selection of the preferred
option on the basis of the highest score from the engineering assessment. The results for each engineering assessment
criterion have been collated and are listed in Table 2.9.
Table
12.9 Engineering Comparison of Layout Options
at Black Point
|
Engineering
Assessment Criterion |
Relative Importance Factor |
Option 1 (Base case) |
Option 2 (Full Reclamation) |
Option 3
(Full Excavation) |
|||
|
|
|
Score |
FS* |
Score |
FS* |
Score |
FS* |
|
Site Formation |
0.30 |
3.85 |
1.15 |
5.00 |
1.50 |
1.28 |
0.38 |
|
Site Reclamation |
0.30 |
3.00 |
0.90 |
2.15 |
0.65 |
5.00 |
1.50 |
|
|
0.20 |
3.66 |
0.73 |
3.66 |
0.73 |
5.00 |
1.00 |
|
Marine Navigation |
0.10 |
5.00 |
0.50 |
5.00 |
0.50 |
5.00 |
0.50 |
|
Facility Foundations |
0.10 |
5.00 |
0.50 |
4.00 |
0.40 |
3.83 |
0.38 |
|
Total Score |
|
|
3.79 |
|
3.78 |
|
3.77 |
|
Site Ranking |
|
1 |
2 |
3 |
|||
Note: * FS = Factored Score (ie Score x Relative Importance Factor)
On the
basis of the engineering assessment for the construction and operation, the
result of the site layout comparison is as follows:
·
Preferred layout: Option 1 – Base Case
·
Second choice: Option 2 – Full Reclamation
·
Third choice: Option 3 – Full Excavation
Summary of Engineering Assessment
A comparative
engineering study has been made to assess the relative merits and demerits of
possible layouts for the proposed LNG receiving terminal at Black Point. It compared the original base case layout
with two other possible layouts – a full reclamation case, and a full
excavation case. The comparisons have
been made based on the following engineering assessment criteria:
·
Construction of site formation works;
·
Construction of site reclamation works;
·
Construction of approach channel and
turning basins;
·
Marine navigation; and,
·
Construction of the facility foundations.
Several
engineering assessment parameters have been derived for each engineering
criteria and a scoring system applied to each.
An overall score for each site has then been established by applying an
importance factor to each of the assessment criteria.
This
assessment procedure has shown that Option 1 Base Case layout is preferred from
an engineering standpoint. The Base Case
layout is preferred as it achieves the best balance between reclamation and
excavation quantities.
2.1.4
Environmental
Assessment
The three
options for the Black Point terminal layout have been assessed in environmental
terms through an environmental impact scoping and preliminary assessment
exercise (Figures 2.1 to
2.3). This
method allows a high level qualitative comparison of each option through the
application of pre-defined impact terminology.
A description of the methodology is presented below ([1]).
Impact Scoping
Potential
impacts have been identified using a “Scoping Matrix”. Identified activities and key potential
sources of impacts (i.e., hazards) have been listed down the vertical column of
the matrix while environmental resources or receptors are listed across the horizontal
axis. Each square on the scoping matrix
represents a potential interaction between an activity and an environmental
resource/ receptor (i.e., potential impact).
Resources/ receptors are based on the technical requirements of the EIA
Study Brief (ESB-126/2005).
Due to the
nature of the construction of each layout option, described above in the
engineering assessment, a single scoping matrix has been developed. Although each layout differs in terms of its
design, the functional requirements of the terminal result in similar
interactions between activities and environmental resource/ receptors. Differences appear in the severity of
potential impacts. The scoping matrix is
presented in Table 2.10.
Table
12.10 Impact Scoping Matrix
It should
be noted that the list of activities/hazards is not intended to be exhaustive
but rather an identification of key aspects of both construction and operation
phases of the LNG terminal that have the potential to interact with the
environment and subsequently have the potential to cause environmental
impacts. The list of environmental
receptors/resources is also a focused list of the key aspects of the
environment that are considered vulnerable or important in the context of the
construction and operation of the LNG terminal.
Evaluation of Impacts
In
evaluating the degree of potential impacts, the following factors have been
taken into consideration:
·
Impact Severity: The severity of an impact is a function of a
range of considerations including the following:
o impact
magnitude;
o impact
duration;
o impact
extent;
o legal
and guideline compliance; and,
o characteristics of the
receptor/ resource that is affected.
·
Likelihood of Occurrence: How likely is the impact to occur?
Severity Criteria for Environmental
Impacts
In evaluating the severity of potential environmental
impacts, the following factors have been taken into consideration:
·
Receptor/Resource Characteristics: The nature, importance and sensitivity to
change of the receptors or resources that could be affected;
·
Impact Magnitude: The magnitude of the
change that is induced;
·
Impact Duration: The time period over which
the impact is expected to last;
·
Impact Extent: The geographical extent of the induced
change; and
·
Regulations, Standards & Guidelines:
The status of the impact in relation to regulations (e.g. discharge limits),
standards (e.g. environmental quality criteria) and guidelines.
Impact severity has been categorised using the following
subjective scale:
·
Slight;
·
Low;
·
Medium; and
·
High.
Likelihood of Occurrence
The
likelihood (probability) of the pre-identified events occurring has been
ascribed using the following qualitative scale of probability categories (in
increasing order of likelihood):
A. Extremely
unlikely (e.g. never heard of in the industry);
B. Unlikely
(e.g. heard of in the industry but considered unlikely);
C. Low
likelihood (e.g. such incidents/impacts have occurred but are uncommon);
D. Medium
likelihood (e.g. such incidents/impacts occur several times per year within the
industry); and
E. High
likelihood (e.g. such incidents/impacts occurs several times per year at each
location where such works are undertaken).
Likelihood
is estimated on the basis of experience and/or evidence that such an outcome
has previously occurred. Impacts
resulting from routine/planned events (i.e. normal operations) are classified
under category (E).
Impact Significance
The
significance of each impact is determined by assessing the impact severity
against the likelihood of the impact occurring as summarised in the impact
significance assessment matrix provided in Table
2.11.
Table
12.11 Impact Significance
Significance
criteria for negative/adverse impacts (i.e., relative ranking of importance)
are defined in Table 2.12. It is important to note that impacts are
considered without the implementation of mitigation measures. The need for and appropriate method of mitigation
would be determined on the basis of the impact assessment.
Table 21.12 Significance Criteria
·
Positive
Impacts are classified under a single category; they are then evaluated
qualitatively with a view to their enhancement, if practical.
·
Negligible
or Low Impacts will require little or
no additional management or mitigation measures (on the basis that the
magnitude of the impact is sufficiently small, or that the receptor is of low
sensitivity).
·
Medium
or High Impacts require the adoption
of management or mitigation measures.
·
High
Impacts always require further management or mitigation
measures to limit or reduce the impact to an acceptable level.
Evaluation
of Potential Environmental Impacts
An
evaluation of the above identified potential impacts as a result of the
construction and operation of each of the Black Point terminal options has been
undertaken using the concepts described above.
The results of these evaluations are presented in detail in Annex 2-B. The impact assessment matrices for each of
the three layout options for the Black Point terminal are presented below in Tables 2.13 to 2.15. Key impacts, i.e.
those activities/ hazards, which may have the potential to
result in high impacts to environmental resources/ receptors are
highlighted for each option. Following,
environmental impacts that differentiate between the layout options are
presented.
Table
21.13 Impact Assessment Matrix: Option 1 - Base
Case
Key
potential impacts, ie high impacts that are
considered to be significant and may require further management or mitigation,
associated with the construction and operation of the Black Point terminal
according to the Option 1 – Base Case layout have been identified as the
following:
·
Construction Marine Dredging and Disposal
Impacts to Water Quality; and,
·
Construction Piling Works on Marine
Mammals.
Details on
each of the above are presented in Annex
2-B.
Table
21.14 Impact Assessment Matrix: Option 2 - Full
Reclamation
Key
potential impacts associated with the construction and operation of the Black
Point terminal according to the Option 2 – Full Reclamation layout has been
identified as the following:
·
Construction Marine Dredging and Disposal
Impacts to Water Quality; and,
·
Construction Piling Works on Marine
Mammals.
Details on
each of the above are presented in Annex
2-B.
Table
21.15 Impact Assessment Matrix: Option 3 - Full
Excavation
Key
potential impacts associated with the construction and operation of the Black
Point terminal according to the Option 3 – Full Excavation layout has been
identified as the following:
·
Construction Marine Dredging and Disposal
Impacts to Water Quality;
·
Construction Piling Works on Marine
Mammals; and,
·
Construction Waste Generation and Disposal
on Waste Storage Facilities.
Details on
the above are presented in Annex 2-B.
Environmental Differentiators
A summary of
the key environmental differentiators between the three options is presented
below.
Waste
Generation and Disposal
All
sites will require the excavation of rock from the existing hillsides in order
to provide sufficient flat land to meet the functional requirements of the LNG
terminal. However, both Option 1 and
Option 2 layouts are expected to utilise all excavated material within the
proposed reclamation. In addition, it is
expected that up to 1.90 and 3.43 Mm3 of fill, respectively, will
need to be imported from existing construction and demolition (C&D) waste
storage facilities.
In
contrast to Options 1 and 2, the design of Option 3, the Full Excavation
layout, will result in a surplus of approximately 14 Mm3 of rock
following excavation and construction works.
This material will be exported to allocated waste storage and disposal
facilities and would be considered as a potentially high impact to storage
facilities.
Environmental Assessment Results
The
results of the environmental impact scoping and assessment allows a comparison
of each layout and design option to be presented based on the number of
issues. Each site has been ranked in
order of preference against the other on the basis of the number of impacts
compared to the other two sites, ie the lower number
of impacts the better. On the basis of
these ranks, the average rank has been determined for each option to determine
the order of preference in both the construction and operation phases of the
potential Black Point terminal. The
result of the comparison is presented in Table
2.16.
Table
21.16 Comparison of Layout Options at Black Point
in terms of Environmental Assessment
On the
basis of the environmental assessment for the construction and operation of the
potential Black Point terminal, the result of the layout comparison is as
follows:
·
Preferred layout: Option 1 – Base Case
·
Equal second choice: Option 2 – Full Reclamation or
Option 3 – Full
Excavation
The main
environmental gains of choosing Option 1 is, on balance, a significant reduction
in dredging and excavated volumes when compared to the other options. The changes have resulted in a reduction in
ecological, fisheries and water quality impacts through reduction in
reclamation, dredging and natural coastline loss. The reduction in dredging and excavation will
also have a benefit in reducing off site impacts, such as during disposal of
dredged muds and ease the burden on the limited
capacity remaining at existing marine disposal sites.
Summary of Environmental Assessment
As with
the engineering assessment a comparative environmental study has been made to
assess the relative merits and demerits of possible layouts for the proposed
Black Point terminal. The study compared
the original base case layout with two other possible layouts to identify the
preferred layout of the three. The
comparisons have been made based on the potential for impacts to occur to
resources/ receptors identified under the EIAO-TM
and the technical requirements of the EIA Study Brief (ESB-126/2005).
As it is
not considered appropriate to apply an importance factor to environmental
criteria, potential impacts to resources/ receptors have been firstly
identified through the potential for interaction, followed by a qualitative
assessment of the likely severity of impact.
The
assessment has determined that the Option 1 – Base Case layout is preferred
from an environmental perspective. This
option offers lower excavation requirements as well as a minimal impact to
potential landscape and visual sensitive receivers. The potential for subsequent impacts to the
environment have, therefore, been considered to be lower for this layout
option.
2.1.5
Summary
of Consideration of Different Layouts and Design Options
The above section
has considered different layouts and design options for the Black Point
terminal as part of the overall assessment of alternatives. The assessment has been conducted to
investigate not only the environmental considerations of each layout and design
options, but to include an examination of the engineering aspects. The assessment has thus considered both the
difficulties of the construction and operation of each facility as well as the
potential environmental impacts associated with such.
Both the engineering
and environmental assessments have identified layout Option 1 – Base Case as
the most preferable for the construction and operation of the Black Point
terminal. This option achieves the best
balance between reclamation and excavation quantities. The location of the two LNG tanks in the
Black Point headland also reduces the potential for impacts to landscape and
visual sensitive receivers. The
engineering consequences and subsequent environmental impacts are considered to
be lower for this layout option.
The Base
Case Layout has thus been taken forward as the preferred layout for the Black
Point terminal in the Environmental Impact Assessment.
2.2
Consideration of Alternative Construction Methods
In
accordance with Clause 3.6.5 of the EIA Study Brief (ESB-126/2005), this section presents the consideration of
alternative construction methods and sequence of works that have been assessed
as part of the overall assessment of alternatives for the Black Point
terminal.
The
assessment has been conducted to investigate potential methods and plant for
the construction of the proposed terminal as well as associated
facilities. The objective of the
assessment is to identify the preferred alternative with a view to avoid the
likelihood of unacceptable adverse environmental impacts.
Alternative
construction sequences have been investigated in the EIA ,
specifically in the water quality section (Section
6) in order to avoid localised cumulative effects and to avoid adverse
impacts to the maximum practical extent.
The basic
requirements of a LNG terminal in
On the
basis of these requirements, it is considered that the following are the key
facilities to be constructed, to which alternative methods have been
considered:
·
Reclamation;
·
Seawalls;
·
Jetty; and,
·
Approach Channel and
As the onsite
facilities, such as the LNG storage, regasification
plant, administration office, canteen, ancillary buildings and sewerage
treatment plants etc., will be constructed to best industry standard,
alternatives for construction will not be discussed.
2.2.1
Reclamation
The
preferred layout for the Black Point terminal (see Part 3 – Section 2.1) would involve mainly site formation works and
approximately 16 ha of reclamation ([2]). The layout for the preferred Black Point
terminal is presented in Figure 2.1.
Traditionally
the method to construct the reclamation area has been to dredge away all soft
seabed materials under the entire reclamation area. This would be considered as a ‘Fully Dredged
Method’. However, recently in
Partially Dredged Method
For this
method, dredging would be limited to only the area beneath the seawall. The mud is not dredged from beneath the reclamation
area but rather sand fill is placed over the soft mud to initially raise the
ground level to +2.5 mPD after which, public fill is
compacted in layers to the finished level of +6 mPD. There are two key engineering issues to be
considered with this method as follow:
·
The soft marine mud will consolidate
significantly under the weight of the overlying fill. This consolidation may well be up to 3 metres
and will take many years to complete if no additional ground improvement works
are put in place;
·
The initial layers of sand fill need to be
placed very carefully to avoid the generation of mud waves which can
significantly affect the long term performance of the reclamation.
The second
issue is usually rectified by protecting the mud by a layer of geotextile followed by hydraulically placed sand.
Ground
movements due to consolidation settlement have a significant impact on the
operation of the facility. The most
sensitive structures will need to be necessarily piled in order to mitigate
these effects of ground movement.
However, it will not be cost-effective or practical to support all plant
and services at the site on piles. In
these areas ground improvement measures will be essential to reduce ground movements to
acceptable levels. Two commonly used
ground improvement methods suitable for use in reclamation areas include the
following: -
·
Installation of vertical drains together
with surcharge pre-loading; and
·
Vibro-replacement
/ vibro displacement.
In view of
the tight construction programme, cost-effectiveness and the sensitive nature
of cryogenic equipment, the use of vertical drains with surcharge pre-loading
is considered the most suitable method of ground improvement.
Vertical Drains with Surcharge Pre-loading
The
use of vertical drains (often called band drains) for construction of
reclamations has the effect of shortening the drainage paths of the relatively
impermeable marine clay and/or alluvial clay. The consolidation settlement due to the site
formation can therefore be achieved within a shorter period. Drains are typically inserted on a triangular
grid at 1.2 to 1.5m spacing down to the interface between marine
deposits/alluvial clay layer (sometimes penetrated through the alluvium,
depending on its engineering characteristics).
The surcharge preloading serves the following purposes:
-
·
To significantly speed up the
consolidation;
·
If suitable additional surcharging height
or time duration is allowed, it can substantially eliminate the settlement due
to the future imposed load from low rise buildings and other light weight
structures.
The design
height and duration of placement for the surcharge mound will depend upon the
time allowed in the construction programme.
For projects with a tight construction programme such as this, the surcharge
mound would need to be high. It is
currently estimated that the height of the surcharge mound would need to be
approximately 5m above the future formation level of +6mPD, which will achieve
acceptable long-term settlement performance of the reclamation.
The
cryogenic pipelines and facility structures will require very tight settlement
criteria as the movement tolerances are very small. The proposed foundation schemes for the
structures are still under development and thus a detailed settlement / differential
settlement analysis shall be carried out at a later stage.
2.2.2
Seawalls
Dredging
is required to remove the soft material beneath the seawall to ensure that the
seawall is stable and can be built within a optimum timeframe,
thereby reducing the potential for environmental impacts to occur. In addition to the conventional method of
carrying out full dredging of the marine deposits before filling up for the
seawall, two other alternatives are available.
The first alternative
makes use of ground improvement technique, such as Deep Cement Mixing (DCM), to
enhance the strength of the marine deposits before filling up for the
seawall. In DCM, the soft soil is mixed in-situ with an appropriate additive
using an auger or other mixing device.
The additive used is typically cement or lime. No spoil removal is required. A similar technique called Deep Cement Method
was developed in
The second
alternative requires a long counter fill on the seaward side of the seawall to
provide toe stability against slip failure during construction. The use of this method is, however,
considered to be unsuitable for this project as it is likely to lead to significant
ongoing settlement of the sea wall after the LNG terminal is in operation.
On the
basis of the above, neither of the alternative methods is preferred over the
conventional method of dredging beneath the seawall. As such, the conventional method of carrying
out full dredging of the marine deposits before filling up for the seawall is
recommended as the preferred alternative for the construction of the seawalls
for the LNG terminal.
2.2.3
Jetty
A piled
jetty is required for creation of the berthing facility for the LNG carrier at
the Black Point terminal. For large
jetties of this type, piled structures are preferable to blockwork
or closed structure designs as they are less likely to result in adverse
impacts to water quality and subsequently marine ecology, due to the minimal
disturbance to hydrodynamics.
For the
construction of the LNG Jetty, two alternatives are available for the
installation of marine piles. These are
bored or percussive piling methods. A
discussion of each of these methods in terms of the environmental advantages
and disadvantages is presented below.
Bored Piles
Noise
created by bored piling methods tends to be a less intensive continuous noise,
rather than the pulsed high power sounds emitted through percussive piling.([4]). A summary of potential impacts from bored
piling methods are presented below.
·
a large casing must be driven into the
seabed in order to support the boring equipment which will necessitate a longer
construction period
·
socketing
into the bedrock will require the use of a chisel (noise impacts from socketing may be mitigated by using the reverse circulation
drilling method); and,
·
placing
concrete to the bored pile (potential leakage of cementitious
materials from sacrificial casing during this process.)
Percussive Piles
The sounds
emitted from percussive hammer pile driving activities have their highest
energy at lower frequency (20 Hz to 1 kHz) and loud sounds have been identified
to cause (short-term) behavioural reactions such as increased swimming speed in
cetaceans ([5]). Studies in Hong Kong have, however,
determined that with measures such as bubble jackets and bubble curtains,
marine mammal behaviour does not change substantially during percussive piling
operations ([6]).
Based on
the well-proven track record for the successful employment of these measures,
it is proposed that either method be used for the construction of the LNG Jetty
as part of the Black Point terminal.
Detailed assessments of the impacts of both methods are also mentioned
in other sections in this EIA Report.
2.2.4
Approach
Channel and Turning basin
An
approach channel and turning basin will be required as part of the Black Point
terminal in order to allow for the safe transit of the LNG carrier to the
jetty. In order to meet the required
draft of the carrier, both the channel and turning basin will be required to be
dredged to approximately -15 mPD.
There are
two common dredging plants that are employed for the removal of marine
sediments in
Grab Dredgers
A grab
dredger comprises a rectangular pontoon on which is mounted a revolving crane
equipped with a grab. The dredging
operation consists of lowering the grab to the bottom, closing the grab,
raising the filled grab to the surface and discharging the contents into a
barge. Grab dredgers are usually held in
position while working by anchors and moorings but some have a spud or pile,
which can be dropped onto the bottom while the dredger is operating.
Grab
dredgers may release sediment into suspension by the following mechanisms:
·
Impact of the grab on the seabed as it is
lowered;
·
Washing of sediment off the outside of the
grab as it is raised through the water column and when it is lowered again
after being emptied;
·
Leakage of water from the grab as it is
hauled above the water surface;
·
Spillage of sediment from over-full grabs;
·
Loss from grabs which cannot be fully
closed due to the presence of debris;
·
Release by splashing when loading barges by
careless, inaccurate methods; and,
·
Disturbance of the seabed as the closed
grab is removed.
During the
transport of dredged materials, sediment may be lost through leakage from
barges. Dredging permits in
Sediment
is also lost to the water column when discharging material at disposal
sites. The amount that is lost depends
on a large number of factors including material characteristics, the speed and
manner in which it is discharged from the vessel and the characteristics of the
disposal sites.
Trailing Suction Hopper Dredgers
Trailing
Suction Hopper Dredgers (TSHD) are designed to use a
suction mouth at the end of a long pipe.
As the barge moves, the suction hopper trails along and sucks up the
soft seabed sediments. During dredging
the draghead will sink below the level of the
surrounding seabed and the seabed sediments will be extracted from the base of
the trench formed by the passage of the draghead. The main source of sediment release is the
bulldozing effect of the draghead when it is immersed
in the mud. This mechanism means that
sediment is generally lost to suspension very close to the level of the
surrounding seabed.
During
dredging marine sediments are pumped into the vessel’s hopper. Once the hopper is loaded the dredging
operation will be stopped and the vessel will sail to a designated disposal
area. A TSHD is usually positioned by
dynamic positioning, thus they have no anchor wires. In comparison to grab dredgers, TSHDs generally have a higher production rate.
Both Grab
dredgers and Trailing Suction Hopper Dredgers (TSHD) are commonly used in
2.3
Selection of Preferred Scenario
The
preferred scenario/alternative to be taken forward to the EIA stage at Black
Point is Base Case Layout (Option 1).
Full details of the components of the preferred scenario are detailed in
Part 3- Section 3 of this EIA report.
The
selection of the preferred scenario has brought about a series of environmental
and engineering benefits to the Project as presented in Figures 2.4 and 2.5. These benefits have arisen through
modifications to the engineering layout stimulated by issues raised during
consultations with stakeholders in Government, District Councils, Rural
Committees, NGOs and the Advisory Council on the Environment, as well as
through engineering optimisation. The
main environmental gains are:
·
A significant reduction in dredging volumes
from approximately 5 Mm3 to approximately 3 Mm3.
The above
changes have resulted in a reduction in ecological, fisheries and water quality
impacts through reduction in reclamation, dredging and natural coastline
loss. The reduction in dredging will
also have a benefit in reducing off site impacts during disposal of dredged muds and ease the burden on existing disposal sites.
Further
details are presented on Figures 2.4
and 2.5.
Figure 2.4 Base
Case Design Adopted in Pre-EIA Studies
|
|
Base Case Design Adopted in Pre-EIA Studies |
|
Details |
The
layout initially studied included approximately 16 ha of reclamation to accommodate
the LNG terminal facilities. Total
dredging volumes exceeded 5 Mm3. |
|
Layout |
|
|
Issues |
Consultation
with stakeholders such as ESMG members, rural committees, NGOs questioned
whether dredging volumes could be reduced. |
Figure 2.5 Preferred Scenario Design Assessed in
this EIA
|
|
Preferred Scenario Design Assessed in this EIA |
|
Details |
During
the early stages of this EIA, as described in the sections above the CAPCO team
has examined various layouts taking into account: ·
Issues raised
during consultations with ACE, NGOs, fishermen, LegCo
members; ·
Ongoing process,
civil and marine engineering reviews; ·
Updated findings
of environmental baseline surveys. The outcome
of this work has been the production of preferred layout as presented below. |
|
Layout |
|
|
Issues |
The
resultant layout has a reduction in dredging volumes are reduced to
approximately 3 Mm3. These changes
have brought about an overall reduction in water quality, ecological,
fisheries and waste impacts. The
positioning of the tanks has resulted in an improvement in visual impacts. |
