2 Consideration of Alternatives
2.1
Introduction
The EIAO Study Brief issued
for this Project requires (Clause 3.3.1) that the Study evaluates and
reviews the possible use of the CDF option as compared to the proposed CAD
option for minimising the potential environmental impacts. The EIAO
Study Brief also states that the EIA Report should present a consideration of
different contaminated mud disposal options and disposal sites with regard to
the findings of the Strategic Assessment and Site Selection Study for
Contaminated Mud Disposal (Agreement CE 105/98). In order to
fulfil the requirements of the EIAO Study Brief the comparison is
presented below in Section 2.2 with information on which contaminated
mud disposal options and disposal sites were examined and details of the
recommended way forward ([1]).
The EIAO Study Brief further
states that the EIA Report should provide clear and objective comparison of the
environmental benefits and disbenefits of different possible project locations
within the scheme boundary (ie the Study Area presented in Figure 1.1a).
The EIA Report should compare the main environmental impacts of different
locations within the Study Area and provide reasons for selecting the project locations,
and the part environmental factors played in the selection. In order to
fulfil the requirements of the EIAO Study Brief the processes by which
the two facilities within the Airport East and East of Sha Chau areas were
identified are presented in Section 2.3.
2.2
Strategic Assessment & Site
Selection Study for Contaminated Mud Disposal
2.2.1
Introduction
The Civil Engineering Department
(CED) initiated a study in 1998 entitled the Strategic Assessment and Site Selection
Study for Contaminated Mud Disposal (Agreement CE 105/98) with the
purpose of providing a preliminary, strategic assessment of potential
contaminated dredged material management options and to recommend a suitable
site or sites for the preferred options. The study was the first stage of
planning a new facility (or facilities) to succeed CMP IV.
2.2.2
Disposal
Options
As part of the study several
contaminated mud disposal options including contained aquatic disposal (CAD),
confined disposal facility (CDF), upland disposal, and disposal outside of Hong
Kong waters were considered in terms of three initial screening criteria:
·
implementation at the required scale either in Hong Kong or elsewhere;
·
appropriate given the characteristics of Hong Kong's contaminated
dredged material; and
·
consistent, if implemented, with all applicable Hong Kong legislation,
regulations and policies.
This initial screening was designed
to eliminate disposal options which are unsuitable or impractical for Hong Kong
regardless of siting considerations. The information below was originally
prepared in 1999 and has been updated to reflect:
·
applicable new technical guidance issued since 1999; and,
·
new project experiences.
Findings
Concerning Contained Aquatic Disposal (CAD) Options
CAD options may involve use of
excavated borrow pits, or may involve purpose-built excavated pits. CAD
sites are those which involve filling a seabed pit with contaminated mud and
capping it with uncontaminated material such that the original seabed level is
restored and the contaminated material is isolated from the surrounding marine
environment (Figure 2.2a).
The concept of CAD was considered as early as 1977 when the United States Army
Corps of Engineers (USACE) conducted an inventory of subaqueous borrow pits
across the US. Since then the CAD alternative has seen an expanding use
worldwide. Several case studies of CAD projects are summarized in the recent
guidance by the International Navigation Association Environmental Working
Group (PIANC)([2]) showing the range of scale and
placement methods for these projects. CAD is actively being considered as
an option for a number of additional projects worldwide.
Hong Kong's experience with CAD
facilities is substantial and given the extensive track record of monitoring,
can be considered as one of the most comprehensively documented programmes in
the world. Given the success of CAD facilities in Hong Kong, as evidenced
by the results of monitoring studies and other related assessments, it is
likely that new CAD facilities engineered using similar principles would be
equally environmentally acceptable and cost effective.
The main environmental issues to
consider when proposing particular sites for CAD are the dispersive
characteristics of the site and its proximity to sensitive receivers. If
materials are placed in the CAD through simple bottom dumping from barges,
sediment plumes will form and may disperse toward areas of high ecological
value or beneficial use, such as beaches or fish culture zones.
Consequently, selection of sites in areas of low current is seen as highly
beneficial. Loss of materials during and after placement (but before
capping) can be managed through disposal rates, controlled disposal procedures
and adopting lower backfill heights. CAD options must also be designed as
effective containment sites for retention of contaminants taking into account long-term
processes such as, erosion, bioturbation or pore water release. This can
be achieved through cap design of the appropriate materials and thickness.
Existing seabed pits have no
inherent advantages over a purpose-built pit in ease of operation or
effectiveness of containment. However, existing pits would not require
initial excavation, and disposal of excavated sediment, and thus would be
preferable.
Use of either existing and
purpose-built seabed pits as a disposal option for contaminated dredged
material has already been implemented at the required scale and found to be
suitable for Hong Kong sediments. Assuming pre-treatment ([3]) can
stabilise contaminants sufficiently to allow confined marine disposal, CADs may
serve either as a Type 2 option, or with pre-treatment, as a Type 3 option ([4]).
Findings
Concerning Confined Disposal Facilities (CDF)
Confined Disposal Facilities (CDFs)
are nearshore or island diked containment structures which serve to isolate
contaminated dredged material, but extend up to and possibly above sea level (Figure 2.2b). Large
scale CDFs have been developed in the Netherlands and elsewhere for both highly
and moderately contaminated dredged material.
The environmental impacts of CDFs
relate primarily to the degree of contaminant containment in the adopted CDF
design. In general, designs with greater control over contaminant pathways
will have higher associated costs of construction, operation and
maintenance. Features such as installing a liner to gather leachate,
implementing a system to treat leachate and effluent, and/or controlling
placement using an enclosed pipeline system can be used to mitigate contaminant
release to the environment. The impacts of constructing a CDF, such as
building seawalls/dikes and sourcing these materials, can be mitigated.
However, these impacts are likely to be of greater magnitude than impacts
associated with CAD construction, and thus the effectiveness and cost of the
proposed mitigation becomes a key issue.
The size of a CDF
with sufficient volume to accommodate the projected arisings in Hong Kong (8 Mm3)
would be large and may be difficult to site along the coast. However,
once filled and capped, a CDF could provide a beneficial use in the form of
habitat creation, recreation or other low-load uses. All CDF options are
considered appropriate for Hong Kong sediments based on the ranges of material
types, which have been disposed under similar operations in the Netherlands,
the United States and Japan. As a result of this screening, nearshore and
island CDFs were considered as suitable for both Type 2 and Type 3
disposal.
Findings Concerning Upland Options
Suitability of Landfill Disposal:
Information available at the time of the study indicated that dewatering and
solidifying sediments would allow landfill criteria (Toxic Characteristics
Leaching Procedure and water content) to be met. However, as a moderately
contaminated sediment (Type 2) disposal option, the use of an existing landfill
was deemed impractical because the large quantities requiring disposal would
result in an unacceptable reduction of capacity. Although utilising an
existing landfill only as a highly contaminated sediment (Type 3) disposal
option would place a smaller demand on capacity, any reduction of capacity is
undesirable.
Suitability of Existing/Planned
Waste Treatment Facilities: Hong Kong’s Chemical Waste Treatment Centre and
the proposed Sludge Treatment Facility were considered to provide sufficient
capacity only for materials requiring Type 3 disposal and their use for
treatment of dredged material would comply with Hong Kong's legal and policy framework.
However, neither facility's technology was considered appropriate for materials
that are contaminated with high levels of inorganics (ie metals), which is
typically the case in Hong Kong. Therefore, selection of this option was
not recommended.
Suitability of Developing a New
Dedicated Facility: Development of a new dedicated upland
containment facility for contaminated materials could be accomplished on the
appropriate scale and could be designed specifically for Hong Kong
sediments. Nevertheless, given Government's stated preference for use of
existing facilities, the apparent suitability of many existing options, and the
large land requirement for a new upland facility, this option was not
recommended as suitable.
Recommendation
of Preferred Option(s)
To summarise the screening process
presented above, the following list presents the options considered as
components of Hong Kong's future contaminated dredged material disposal
strategy:
·
CAD or Capped Seabed Pit - Existing Pit (Types 2 and 3) ([5]);
·
CAD or Capped Seabed Pit - Purpose-built Pit (Types 2 and 3) ([6]);
·
Nearshore Confined Disposal Facility (Types 2 and 3) ([7]); and
·
Island Confined Disposal Facility (Types 2 and 3) ([8]).
Implementation of the CDF option in
Hong Kong would not only require identification of a suitable site but also
formulation, and perhaps testing, of an appropriate design. The CDF’s
ability to meet all applicable engineering and environmental criteria would
need to be demonstrated before full-scale operations are initiated.
Beneficial after use could serve as both Type 2 and Type 3 options.
Based on the initial assessment
presented above, it appears that the preferred option is CAD for Type 2 and
Type 3 disposal. Hong Kong's experience in handling contaminated
materials using CAD is among the most extensive and well documented in the
world and provides a sound engineering and environmental basis for continuing
with this option. CAD facilities have operated successfully in Hong Kong
for over 10 years and the experience gained through refinement of their design
and operation, and the results of the environmental monitoring and audit
programme, could be easily built upon to provide the foundation of a future
strategy, assuming suitable sites can be located. Section 1.3
contains further details of the review of environmental data gathered at the
East of Sha Chau CMP Facility.
2.2.3
Hong
Kong Wide Site Selection
Identification
of Available Areas
A preliminary site search envelope
was developed to exclude unsuitable areas associated with existing, potential
and future incompatible uses. This included marine traffic constraints,
depth constraints, future reclamations, and buffer zones (around fish culture
zones, known areas of high coral abundance/diversity, gazetted Marine Parks and
Reserves, underwater cables, pipelines and tunnels, and gazetted beaches).
Evaluation of
viable disposal options resulted in an estimate of the area required for a
small facility (where water depth is between 5m and 20m) of 2.4 km2
and of large facility (where water depth is greater than 20m) of 7.3 km2.
A total of 20 potentially available areas, which had the potential to site a
contaminated mud disposal facility, were identified within Hong Kong waters (Figure 2.2c).
Identification
of Suitable Alternatives
The 20 available areas were examined
to determine which would be suitable for siting the viable options (ie existing
pit CADs, purpose built CADs, island CDFs, and nearshore CDFs). The
resulting alternatives (ie site-option combinations) were subject to further
evaluation in the suitability assessment. The criteria used in the
suitability assessment covered environmental, engineering and planning factors
and included the following:
·
water quality;
·
dispersal characteristics;
·
sediment characteristics;
·
cumulative effects;
·
ecological characteristics;
·
potential environmental benefits;
·
technical uncertainty and risk of failure;
·
placement/berthing;
·
interference with marine traffic and risk of collision;
·
ability to isolate contaminants as a function of cost;
·
ability to receive arisings;
·
cost of construction and management;
·
ease and practicality of use and management;
·
procedural impacts;
·
conflicts with beneficial uses; and
·
degree of compatibility with development plans.
Following this process a total of
thirteen alternatives were considered viable for further evaluation (Section
2.2.4):
·
Existing Pit CAD - The Brothers and East Tung Lung Chau;
·
Purpose Built CAD - Airport East, East Sha Chau, Airport
West, Hei Ling Chau, Shek Kwu Chau and Southern Waters; and
·
Island CDF - Airport East, Airport West, Hei
Ling Chau, Shek Kwu Chau and Southern Waters.
The remaining alternatives were
considered unsuitable for a variety of reasons and were excluded from further
consideration. For example, a number of alternatives were considered to
be unsuitable due to environmental factors, such as potential sediment
contamination (Tolo Channel) or ecological characteristics (NE
Inshore), whereas, other alternatives were excluded due to potential marine
traffic issues (Black Point and Urmston Road), and a number due
to incompatibility with development plans (West Tai O, Fan Lau, Sokos
Islands, Shek Kwu Chau, Outer Port Shelter and NE Offshore),
inability to receive arisings (Southeast Offshore Complex, Eastern Waters and
Tai Long Offshore) or seasonal restrictions on disposal (East Tung
Lung Chau).
2.2.4
Strategy
Selection
Capacity
Each strategy
must be able to accommodate the required 8 Mm3 capacity either
through provision of a single alternative. The East Tung Lung Chau
alternative cannot on its own meet the capacity requirements for a
strategy. The existing pit, though available within the required
timeframe, can hold only 5.75 Mm3 and would have to be combined with
another alternative to be viable. Dual disposal sites are not recommended
as this would increase monitoring and management costs.
An extended (ie deepened) East Tung Lung
Chau pit could accommodate the entire required capacity, but due to likely
seasonal dredging/disposal restrictions could only receive contaminated dredged
materials in the dry season. Consequently, the East Tung Lung Chau
alternative was not recommended.
The Brothers alternative was also
excluded from further consideration as it cannot provide for sufficient
capacity. The Marine Borrow Pits at the Brothers have since been proposed
as a facility for sediments requiring Type 1 Dedicated disposal arrangements ([9]).
Availability
of a CDF
The facility is
expected to be operational from early 2009 and should be designed around the
assumption that up to 8 Mm3 of sediment will require disposal.
Flexibility During Operation:
Although the current planning is that CMP IVc will be operational until early
2009 it is possible that the pit may be filled earlier or later.
Consequently, the new facility should be able to accommodate some degree of
flexibility. Contained Aquatic Disposal (CAD) facilities are more
flexible than Confined Disposal Facilities (CDF), as a series of pits can be
created/expanded within a CAD designated area, allowing for incremental
provision of capacity, as the need arises. In contrast a CDF, because of
its nature (a bunded facility) further expansion (horizontally or vertically),
or “scaling back” is limited and thus the facility’s ability to be modified
according to varying arisings is also limited.
Long Term Option:
CED has completed a study (CE 46/2000) examining the feasibility of
disposing dredged materials with construction and demolition material. An
island facility has been selected under CE 46/2000 and should it go
ahead it would become a competitor with a CDF for public fill (for construction
purpose) and, for a suitable site.
Although CDF is a potential long
term option (for disposal of contaminated sediments), the preferred option for
an new disposal facility would be a CAD facility.
2.2.5
Strategy
Development
Shortlisted
Strategies
Further to the processes described
above, six strategies were identified for further evaluation:
·
Strategy 1: Purpose Built CAD Airport East
·
Strategy 2: Purpose Built CAD East Sha Chau
·
Strategy 3: Purpose Built CAD Airport West
·
Strategy 4: Purpose Built CAD Hei Ling Chau
·
Strategy 5: Purpose Built CAD Shek Kwu Chau
·
Strategy 6: Purpose Built CAD Southern Waters
These six strategies were assessed
to provide an outline design and a preliminary indicative cost estimate.
Specification of
Outline Design
Based on established key design
issues the preliminary outline design for new CAD facilities to accommodate the
initially estimated arisings should be formulated on the general basis of the
existing East of Sha Chau Design.
Capacity:
The total capacity must account for the overall contaminated mud disposal
requirement of 8 Mm3, plus an allowance for cap placement and any
volume changes during material placement.
Depth:
The practical and economic depth limitation will be set by a combination of
site geology (the base of the Holocene mud), the potential area of the pit(s)
and dredging plant limitations.
Cap Thickness
The cap design for existing CAD facilities in Hong Kong (ie East of Sha Chau
CMPs) consists of a 3 - 6 metre clean mud cap. This cap thickness has
been assessed through erosion modelling, pore water flux analysis and with
regard to bioturbation, and has been found to be conservative in nature.
The actual cap thickness to be employed is a site-specific consideration and
best addressed once the site is selected. For the study under CE105/98,
it was assumed the cap would be placed so as to fill the pit to the lip,
therefore, the maximum fill height of contaminated materials would be on the
conservative side to within 6 metres below the lip of the pit.
Side Slopes:
A pit side slope of 1:3 was assumed. It should be noted that
site-specific geology should be examined to determine the appropriate
slope. Areas of firmer sediments may allow for a steeper sided pit - such
as the CMP IV pits at East of Sha Chau.
Timing:
Following the identification of a potentially suitable site, ground
investigations, design and EIA procedures would require approximately 18 to 24
months to complete for a CAD facility. Public consultation and
administrative procedures 12 to 18 months. A further 18 to 24 months may
be required to select the dredging and management contractors and to excavate
the first pit if a new pit. Thus the lead-in time for a new CAD facility
is expected to range from 4.5 to 6 years.
Cost Evaluation
Comparisons of the total and unit costs
for the strategies are presented in Table 2.1. The CAD-based
strategies have unit costs between 32 and 60 HKD per cubic metre. It is
noted that this cost comparison is driven by the construction costs of the
strategies since similar operational and monitoring costs were assumed for
each.
Table 2.1 Comparison of
Preliminary Indicative Total and Unit Costs for Strategies
|
Strategy No. |
Strategy Description |
Total Cost (Million HK$) |
Unit Cost (HK$ m-3) |
Rank (based on cost only) |
|
1 |
Airport East CAD |
417.1 |
52.1 |
5 |
|
2 |
East Sha Chau CAD |
283.1 |
35.4 |
3 |
|
3 |
Airport West CAD |
345.6 |
43.2 |
4 |
|
4 |
Hei Ling Chau CAD |
255.7 |
32.0 |
1 |
|
5 |
Shek Kwu Chau CAD |
276.8 |
34.6 |
2 |
|
6 |
Southern Waters CAD |
481.9 |
60.2 |
6 |
Strategy
Evaluation
The six strategies were evaluated
against environmental, engineering, and planning criteria using a
"+"/"-" system. The categorisation system applies
either positive (“+”) or negative signs (“-“) to reflect the degree of suitability
of the alternative, in terms of the relevant criteria, for contaminated mud
disposal. The categories were as follows:
(++) indicates the
alternative is highly suitable and does not have any apparent drawbacks
(+) indicates the alternative is suitable
although some minor drawbacks may be encountered
(0) indicates the alternative is suitable but
only if special engineering, design or management features are incorporated; if
incorporated, drawbacks associated with the alternative can be overcome
(-) indicates the alternative is somewhat
unsuitable since special engineering, design or management features would be
required yet would not guarantee the success of the alternative
(- -) indicates the alternative is unsuitable since the
cost and/or practicality of the special engineering, design or management
features required to overcome drawbacks would likely be prohibitive or
unacceptable
Alternatives assigned a rating of “-
-“ were considered unsuitable and were excluded from consideration in the
Study.
A relative numerical ranking amongst
the six strategies. The results of this evaluation are presented in Table
2.2.
Strategy 1 - Airport East CAD:
The Airport East CAD strategy was the second most costly of the strategies
largely due to the shallow design of the pits and the resulting requirements
for additional dredging works and capping materials relative to the other
CADs. The design was premised on an estimated base of marine mud of
-20mPD which, if confirmed to be deeper, could serve to mitigate the cost of
the strategy. The Airport East CAD was also characterised as having
potential to indirectly conflict with development plans for the North Lantau
area since the various developments on the future Siu Ho Wan Reclamation will
be constructed on reclaimed land close to the CAD site. Although the site
is located outside of the critical habitat for the Indo-pacific Humpback
Dolphin there is evidence that waters around the Brothers are becoming
increasingly important to the dolphin at certain times of the year.
Consequently, the significance of the Airport East site to the dolphin would
need to be confirmed and updated during this EIA. Furthermore, the water
quality and fisheries impact at Ma Wan, and the cumulative impacts with the
planned and committed infrastructure projects at Tai Ho will also need to be
assessed and confirmed during the EIA stage. Of the six strategies the
Airport East CAD was ranked as most preferred on environmental grounds.
Strategy 2 - Airport West CAD:
The Airport West CAD strategy was the third most costly. Like the Airport
East CAD, the cost of this strategy is primarily driven by an assumed shallow
depth of soft mud which results in a larger footprint and a greater requirement
for capping material than at other sites (eg East Sha Chau and Hei Ling
Chau). The Airport West CAD is in an area frequented by the Indo-pacific
Humpback Dolphin and close to the southwestern border of the Sha Chau and Lung
Kwu Chau Marine Park. The site is also on the border of HKSAR waters and
dispersion of sediment plumes into Mainland waters was considered an
issue. All strategies must be able to comply with the Hong Kong Government's
Water Quality Objectives particularly at the boundary of HKSAR waters, and this
strategy was ranked as suitable in terms of its ability to comply, issues of
intergovernmental jurisdiction could complicate the facility's suitability.
The Mainland authorities have
designated the waters adjacent to the western limit of Hong Kong waters (next
to the Sha Chau and Lung Kwu Chau Marine Park) as a nature reserve for the
protection of the dolphin population. This new development suggests that
designating a CAD facility at Airport West, which borders the nature reserve,
would be incompatible with the objectives of the Mainland authorities for the
area. Consequently, this site is not favoured as the preferred location
for a CAD facility.
Strategy 3 - East Sha Chau CAD:
The East Sha Chau CAD strategy was ranked third in terms of cost, but was
considerably more cost-effective, than Airport East, Airport West and Southern
Waters, and would benefit from the ongoing management and monitoring scheme for
further cost-effectiveness. The site may be constrained in several
important ways including its location within critical habitat for the
Indo-pacific Humpback Dolphin, its proximity to the Sha Chau and Lung Kwu Chau
Marine Park, and the presence of a navigational fairway for high speed jetfoils
near the site. However, existing disposal operations at CMP IV have been
designed to minimise adverse impacts to these existing uses of the marine
environment, and extensive monitoring and assessment conducted in the area has
confirmed the environmental acceptability of the disposal operations ([10])
([11]) ([12]) ([13]) and
Section 1.3. Another benefit associated with the East Sha Chau CAD
strategy is that it represents a continuing use of an existing disposal
area. If this strategy is adopted, the requisite number of new pits can
be contained within the existing gazetted area thereby obviating the need for
new gazettal proceedings and avoiding potentially protracted delays in bringing
the site on line. There is capacity within the existing gazetted area for
further expansion if needed.
Strategy 4 - Hei Ling Chau CAD:
Hei Ling Chau CAD was the least costly purpose built CAD strategy. Due to
the depth of soft mud at the site, the facility design can be deeper than at
other sites. This feature allows for less construction and a smaller
volume of cap material, and minimises the environmental footprint at the
site. The site is not known for frequent sightings of either the
Indo-pacific Humpback Dolphin or the Finless Porpoise, nor does it encroach
upon spawning or nursery grounds. It is also located away from existing
and potential Marine Parks. The main drawbacks associated with the Hei
Ling Chau CAD strategy were its proximity to the Cheung Sha Wan Fish Culture
Zone (FCZ) and the lack of expansion potential at the site should arisings
unexpectedly increase and the facility be required to accommodate greater
volumes. The Hei Ling Chau CAD site is already constrained by the
recently opened typhoon shelter. Although siting the facility at Hei Ling
Chau was considered feasible at this stage, should detailed engineering design
work or marine traffic studies establish the facility cannot be located
adjacent to the typhoon shelter, it would need to be moved to the northwest
within the site and thus closer to the Cheung Sha Wan FCZ. While a number
of operational mitigation measures could be implemented to prevent impacts to
the FCZ, mariculturists have advocated a 2-3 km buffer zone between FCZs and
uncontaminated mud disposal sites, and would thus be expected to object
strongly to the strategy. It should be noted also that a Planning Department
study has indicated that the water areas to the east and northeast of Chi Ma
Wan are recommended for an “Inshore Water Protection/Recreation Area”.
Since the completion of Agreement CE 105/98 the site has been earmarked
for development of a prison. Consequently, this site is not favoured as
the preferred location for the facility.
Strategy 5 - Shek Kwu Chau CAD:
This site was originally excluded from further consideration in the
alternatives assessment stage of the strategy selection as a result of AFCD’s
original intention to deploy Artificial Reefs in the area. Since then
AFCD has deferred plans to deploy Artificial Reefs in the area between Shek Kwu
Chau and Cheung Chau. Consequently, this site is again available for
consideration as a suitable CAD facility. In terms of cost-effectiveness
the site was ranked second. The strategy was ranked in the top three for
all of the three groups of factors. The main drawbacks associated with
the Shek Kwu Chau CAD strategy were its proximity to the Cheung Sha Wan Fish
Culture Zone (FCZ) and the lack of expansion potential at the site, as it is
bounded on the northern and southern sides by fairways, should arisings
unexpectedly increase and the facility be required to accommodate greater
volumes. While a number of operational mitigation measures could be
implemented to prevent impacts to the FCZ, mariculturists have advocated a 2-3
km buffer zone between FCZs and uncontaminated mud disposal sites, and would
thus be expected to object strongly to the strategy.
Strategy 6 - Southern Waters CAD:
This strategy was considered to be the least preferred of the shortlisted
strategies. Marine Department has indicated that the strategic planning
for a West Lamma Channel would conflict with the Southern Waters CAD. The
plans for the channel are still in the conceptual stage but this is an issue
that could render the site unsuitable for a CAD facility. This site is
not favoured as the preferred location for a new CAD facility.
Table
2.2 Summary of the Ranking for Each
Shortlisted Strategy
|
Ranking Factor |
CAD Site 4: Airport East |
CAD Site 5: East Sha Chau |
CAD Site 6: Airport West |
CAD Site 10: Shek Kwu Chau |
CAD Site 11: Hei Ling Chau |
CAD Site 12: Southern Waters |
|
Environmental Factors |
|
|
|
|
|
|
|
Water Quality |
++ (1.5) |
0 (5) |
++ (1.5) |
+ (3) |
0 (5) |
0 (5) |
|
Ecological Characteristics |
+ (1.5) |
0 (3.5) |
0 (3.5) |
- (5.5) |
+ (1.5) |
- (5.5) |
|
Dispersal Characteristics |
+ (2.5) |
0 (5) |
0 (5) |
+ (2.5) |
++ (1) |
0 (5) |
|
Sediment Characteristics |
0 (1.5) |
- (4.5) |
- (4.5) |
0 (1.5) |
- (4.5) |
- (4.5) |
|
Environmental Benefits |
0 (3.5) |
0 (3.5) |
0 (3.5) |
0 (3.5) |
0 (3.5) |
0 (3.5) |
|
Cumulative Impacts |
0 (5.5) |
0 (5.5) |
+ (3) |
+ (3) |
++ (1) |
+ (3) |
|
Engineering Factors |
|
|
|
|
|
|
|
Technical Uncertainty/Risk of Failure |
++ (3) |
++ (3) |
++ (3) |
++ (3) |
++ (3) |
0 (6) |
|
Placement/Berthing |
0 (5) |
0 (5) |
+ (2.5) |
+ (2.5) |
++ (1) |
0 (5) |
|
Interference and Risk of Collision |
++ (2) |
- (6) |
++ (2) |
0 (5) |
+ (4) |
++ (2) |
|
Ability to Isolate Contaminants as a function of Cost |
++ (3) |
++ (3) |
++ (3) |
++ (3) |
++ (3) |
+ (6) |
|
Ability to Receive Arisings |
+ (4) |
+ (4) |
+ (4) |
++ (1.5) |
++ (1.5) |
0 (6) |
|
Planning Factors |
|
|
|
|
|
|
|
Cost of Construction and Management |
0 (4) |
0 (4) |
0 (4) |
0 (4) |
0 (4) |
+ (1) |
|
Ease and Practicality of Use and Management |
++ (3) |
++ (3) |
++ (3) |
++ (3) |
++ (3) |
+ (6) |
|
Procedural Impacts |
+ (4) |
++ (1) |
+ (4) |
+ (4) |
+ (4) |
+ (4) |
|
Conflicts with Beneficial Uses |
+ (2.5) |
0 (5) |
0 (5) |
++ (1) |
0 (5) |
+ (2.5) |
|
Degree of Compatibility with Development Plans |
+ (3) |
++ (1.5) |
++ (1.5) |
0 (4) |
- (5.5) |
- (5.5) |
|
Summary of Rankings |
Second most costly, but low dolphin abundance in the area make it environmentally attractive |
Close to existing site considered an advantage, however, potentially not environmentally favourable |
High abundance of dolphins recorded in the area and in the vicinity of Mainland dolphin reserve |
Close proximity to FCZ, lack of future expansion possibilities, close to existing fairways |
Close proximity to FCZ, lack of future expansion possibilities, close to existing typhoon shelter |
Incompatible with potential future development plans in the West Lamma Channel |
Compiling the rankings for environmental
factors results in the following order of preference:
·
Airport East CAD (composite rank = 16)
·
Hei Ling Chau CAD (composite rank = 16.5)
·
Shek Kwu Chau CAD (composite rank = 19)
·
Airport West CAD (composite rank = 21)
·
Southern Waters CAD (composite rank = 26.5)
·
East Sha Chau CAD (composite rank = 27)
Compiling the rankings for engineering
factors results in the following order of preference:
·
Hei Ling Chau CAD (composite rank = 12.5)
·
Airport West CAD (composite rank = 14.5)
·
Shek Kwu Chau CAD (composite rank = 15)
·
Airport East CAD (composite rank = 17)
·
East Sha Chau CAD (composite rank = 21)
·
Southern Waters CAD (composite rank = 25)
Compiling the rankings for planning
factors results in the following order of preference:
·
Shek Kwu Chau CAD (composite rank = 16)
·
East Sha Chau CAD (composite rank = 14.5)
·
Airport East CAD (composite rank = 16.5)
·
Airport West CAD (composite rank = 17.5)
·
Southern Waters CAD (composite rank = 19)
·
Hei Ling Chau CAD (composite rank = 21.5)
Recommendation
Although it was considered that all
of the remaining strategies were acceptable, the strategies at Southern Waters and
Airport West are not discussed further because of the formers relative cost and
technical difficulties in implementation, and the latter’s proximity to a newly
designated nature reserve in Mainland waters.
The CAD strategies at Shek Kwu Chau
and Hei Ling Chau were regarded as similar, and highly ranked, in terms of the
environmental, engineering and planning criteria used in the evaluation.
However, both of these sites are located close to the Cheung Sha Wan Fish
Culture Zone (FCZ) and although a number of operational mitigation measures
could be implemented to prevent impacts to the FCZ, mariculturists have
advocated a 2-3 km buffer zone between FCZs and uncontaminated mud disposal
sites, and could thus be expected to object strongly to either of these
strategies. Aside from mariculturists, the public may not favour a CAD
facility in the vicinity of an FCZ due to the perceived risk of bioaccumulation
of contaminants in the cultured fish. A Planning Department study has
also indicated that the water areas to the east and northeast of Chi Ma Wan are
recommended for an “Inshore Water Protection/Recreation Area”.
As there is considerable uncertainty
in predicting the volume and timing of contaminated sediment arisings, facilities
which can expand to provide additional capacity will provide greater
security. Both of the Shek Kwu Chau and Hei Ling Chau strategies have
limited potential for further expansion because of marine traffic
constraints. Consequently, neither of these strategies are considered as
highly preferred for future study and implementation.
A potential drawback associated with
the East of Sha Chau strategy is its presence within the critical habitat for
the Indo-Pacific Humpback Dolphin which may make any proposals for further
contaminated mud disposal activities controversial. However,
environmental monitoring and auditing programmes of disposal operations at the
East of Sha Chau CMPs over the first eight years (Section 1.3) have
shown no evidence of impacts or unacceptable risks to this species from
disposal operations. The site lies within the existing gazetted area for
mud disposal and would, from a planning perspective, be relatively easy to
implement.
The strategy of developing a purpose
built CAD facility at Airport East was considered the most suitable. A
preliminary assessment based on the monitoring programmes and studies conducted
for the general area has not revealed any insurmountable problems for this
strategy. The site does, however, lie outside of the existing gazetted
mud disposal area, and so after completion of the EIA process, completion of
gazetting would be required under the Foreshore and Seabed (Reclamations)
Ordinance. Consequently, the Dumping at Sea (Exemption) Order should
also be amended to include the new mud disposal area to enable the application
of the Dumping at Sea Ordinance.
The above considerations reveal the
relative advantages of the Airport East CAD as the recommended strategy for
material requiring either Type 2 or Type 3 disposal (although material
requiring Type 3 disposal would be subject to pre-treatment prior to disposal)
and hence it is the recommended strategy. By maintaining operations in
the vicinity of the existing contaminated mud disposal site for Hong Kong, the
Airport East CAD strategy avoids the proliferation of disposal sites and builds
on the existing knowledge base established through over ten years of site
management and environmental monitoring.
As discussed in Section 1.4, ACE
members requested that the East of Sha Chau strategy was also studied as part
of this EIA. The following sub-section discusses how the preferred
locations within each of the Airport East and East of Sha Chau areas were
selected.
2.3
Consideration of Alternatives within
the Study Area
The Airport East and East of Sha
Chau areas have been identified as potentially suitable for a contaminated mud
disposal facility following the detailed site selection process presented in Section
2.2. However, a number of existing and proposed uses within parts of
these two areas were considered to be incompatible with a contaminated mud
disposal facility. These constraints are presented on Figure 2.3a.
The screening criteria listed above
were compiled to produce a composite map which detailed all of those areas that
were not considered for the siting of a contaminated mud disposal facility in
either the Airport East or East of Sha Chau areas. The remaining areas (Figure 2.3b) were further
divided into three potential sites based on natural changes in bathymetry and
separation through the constraint mapping exercise to create potentially usable
areas.
2.3.1
Assessment of Disposal Options
Section
2.2 of this EIAFSS Report
has presented the findings of a previous review of disposal options, which
concluded that a CAD facility at Airport East was taken forward to the EIA
stage. As discussed in Section 1.4 the ACE members have requested
that other disposal options are re-examined to verify that since the review was
completed that options such as CDF are not the preferred solution.
Consequently, the available unconstrained areas at Airport East and East of Sha
Chau were examined to determine whether suitable locations for a CDF could be
identified.
Consideration of the optimum
configurations of CAD and CDF facilities narrowed down the selection to either
a multi-pit CAD or a fully-dredged CDF. The reasons for this refinement
were as follows.
·
A single pit CAD was not favoured as it would require a relatively large
unconstrained area, would not facilitate the use of the material dredged to
form the pit for use as capping material and would be inflexible if disposal
volumes are revised after construction of the CAD.
·
Multi-pit CADs offer flexibility in disposal volumes, offer ease of
siting due to the smaller area requirement and, if more than two pits were
constructed, a proportion of the materials dredged to form the third (and later
pits) could be used as capping material for earlier pits.
·
A fully-dredged CDF would have the advantage that, for a given volume of
material needing disposal, the footprint would be smaller than a part-dredged
CDF.
·
The volume of construction material (such as sand, armour, and capping
material) required for fully-dredged CDFs would be considerably less than that
required for part-dredged CDFs.
As such, the most suitable disposal
options for a new contaminated mud disposal facility in either the Airport East
and East of Sha Chau areas were considered to be either a multi-pit CAD or a
fully-dredged CDF.
2.3.2
Derivation
of Alternatives and Suitability Assessment
From the potentially usable areas in
both the study areas and the two disposal options considered to be appropriate
to act as a new contaminated mud disposal facility, twelve site and disposal
option alternatives were identified (Table 2.3).
Table 2.3 Site and
Disposal Option Alternatives
|
Study Area |
Usable Area |
Disposal Option |
Alternative |
|
Airport East |
South Brothers 1 |
Multi-pit CAD |
SB1/CAD |
|
|
|
Fully-dredged CDF |
SB1/CDF |
|
|
South Brothers 2 |
Multi-pit CAD |
SB2/CAD |
|
|
|
Fully-dredged CDF |
SB2/CDF |
|
|
Tung Chung 1 |
Multi-pit CAD |
TC1/CAD |
|
|
|
Fully-dredged CDF |
TC1/CDF |
|
East of Sha Chau |
East of Sha Chau 1 |
Multi-pit CAD |
ESC1/CAD |
|
|
|
Fully-dredged CDF |
ESC1/CDF |
|
|
East of Sha Chau 2 |
Multi-pit CAD |
ESC2/CAD |
|
|
|
Fully-dredged CDF |
ESC2/CDF |
|
|
West Brothers 1 |
Multi-pit CAD |
WB1/CAD |
|
|
|
Fully-dredged CDF |
WB1/CDF |
Discussions have been held with
various parties, including the Hong Kong Government and the Hong Kong Airport Authority
on the preliminary results of this site selection process. The outcome of
the discussions has been the removal from further consideration of the usable
area north of Tung Chung and east of the Airport Platform. The Chek Lap
Kok Airport is expected to take on a strong role as an aviation hub in the
Pearl River Delta. Consequently, it was considered important, by the
Airport Authority and the Hong Kong Government, that the location of the
proposed mud disposal facility should not hamper the Airport’s potential for
expansion. Hence the usable area was excluded and is not discussed
further in this report.
An evaluation of each of the
remaining ten alternatives based on engineering, environmental and planning
considerations was conducted ([14]).
After
consideration of all of the criteria, a summary of the ranking assigned to
each alternative was compiled.
As for previous applications of this technique in Hong Kong, it was not
considered to be appropriate to merely sum positive and negative rankings, as
by that method, sites rating a (- -) could be carried forward even though they
have potentially prohibitive drawbacks in some respects. Consequently,
CED’s more preferred alternatives were considered to be those that had
comparatively more “+ +” than other rankings. Where an equal number of “+
+” was observed the preference would defer to the next rating ie “+” and so
on. The outcome of this process is shown in Table 2.4 which
indicated that SB2/CAD and ESC1/CAD are the two preferred facilities in the
Airport East and East of Sha Chau areas respectively for further study.
Table
2.5 Summary of the Ranking Process
|
Alternative |
++ |
+ |
0 |
- |
- - |
Rank |
|
SB1/CAD |
10 |
8 |
3 |
2 |
0 |
2 |
|
SB1/CDF |
7 |
7 |
3 |
6 |
0 |
3 |
|
SB2/CAD |
12 |
9 |
3 |
0 |
0 |
1 |
|
SB2/CDF |
6 |
10 |
3 |
4 |
0 |
4 |
|
ESC1/CAD |
12 |
9 |
1 |
1 |
0 |
1 |
|
ESC1/CDF |
0 |
0 |
0 |
0 |
1 |
Not suitable* |
|
ESC2/CAD |
12 |
7 |
3 |
1 |
0 |
2 |
|
ESC2/CDF |
0 |
0 |
0 |
0 |
1 |
Not suitable* |
|
WB1/CAD |
11 |
8 |
2 |
2 |
0 |
3 |
|
WB1/CDF |
6 |
8 |
4 |
5 |
0 |
4 |
|
Note: * Alternative not considered suitable due to irregular and expensive design requirements. |
||||||
It is important to note, however, that
although the ranking of SB2/CAD seems to be higher than ESC1/CAD, the
Airport East and East of Sha Chau areas are considered to be independent of
each other at this stage in the study. In the next stage of the study, an
EIA will be conducted on SB2/CAD (Part 2) and on ESC1/CAD (Part 3)
and this will allow a comparison to be made and the overall preferred site and
disposal option to be recommended (Part 4).
2.4
Selection of Preferred Scenario
Airport
East
The preferred alternative to be taken
forward to the EIA stage is a multi-pit CAD facility in site South Brothers 2
(SB2). A preliminary layout for such a facility is shown in Figure 2.4a, along with
indicative dimensions. As can be seen from the figure three potential
pits have been presented.
East
of Sha Chau
The preferred alternative to be
taken forward to the EIA stage is a multi-pit CAD facility in site East of Sha
Chau 1 (ESC1). A preliminary layout for such a facility is shown in Figure 2.4b, along with
indicative dimensions. As can be seen from the figure four potential pits
have been presented.
([1]) The
information is taken from various reports prepared under CE 105/98 though
mainly the Final Strategy Development Report prepared by ERM and dated
2001.
([2]) PIANC
(2002) Guidelines for Marine, Nearshore, and Inland Confined Disposal
Facilities, Report of the Working Group No 5 of the permanent Environmental
Committee, Permanent International Association of Navigation Congresses,
Brussels, Belgium.
([5]) CAD
facilities can be used as Type 3 options if material is treated prior to
placement.
([14])
This technique was adapted from that used in ERM 2001 Op cit.