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.

 ([3])     Option for treatment/stabilisation prior disposal include, but are not limited to cement mixing, lime mixing, isolation with geotextile bags.

 ([4])     ETWBTC (2002).  Management of Dredged/Excavated Sediment.  Environment, Transport and Works Bureau Technical Circular 34/2002.

 ([5])     CAD facilities can be used as Type 3 options if material is treated prior to placement.

 ([6])     Ibid.

 ([7])     A CDF may serve as a Type 2 option, a Type 3 option (without pre-treatment) or a Type 3 (with pre-treatment).  The requirements for use of a CDF as a Type 3 option (ie whether pre-treatment is required) will depend on the nature of the material to be disposed and the design of the CDF itself.

 ([8])     Ibid.

 ([9])     Mouchel Asia Limited (2002).  Environmental Assessment Study for Backfilling of Marine Borrow Pits at North of the Brothers.  Final Report for the Civil Engineering Department of the HKSAR Government.

 ([10])    ERM (1999a).  Environmental Monitoring and Audit for Contaminated Mud Pit IV at East of Sha Chau - First Annual Programme Review Report, prepared for Civil Engineering Department. 

 ([11])    ERM (1999b).  Environmental Monitoring and Audit for Contaminated Mud Pit IV at East of Sha Chau First Risk Assessment Report, prepared for Civil Engineering Department.

 ([12])    EVS Environment Consultants (1996a).  Implications of fish and dolphin contaminant studies for management of the East Sha Chau contaminated mud disposal facility, prepared for Civil Engineering Department. 

 ([13])    EVS Environment Consultants (1996b).  Contaminated Mud Disposal at East Sha Chau:  Comparative Integrated Risk Assessment, prepared for Civil Engineering Department.

 ([14])    This technique was adapted from that used in ERM 2001 Op cit.