1    PROJECT DESCRIPTION

 

1.1    The Project

 

The Project is classified as a Designated Project by virtue of Item C (Reclamation, Hydraulic and Marine Facilities, Dredging and Dumping), Item C.10 (A Marine Dumping Area) and C.12 (A Dredging Operation Exceeding 500,000 m3) of Part I of Schedule 2 under the Environmental Impact Assessment Ordinance (Cap. 499) (EIAO).

 

The works that are the subject of the EIA Study include the construction and operation phases of the Project.  The key components of the Project include the following:

 

i.               Dredging of a series of seabed pits within the proposed South Brothers Facility Boundary (Part 1, Figure 2.4a);

ii.              Backfilling each dredged pit with contaminated mud that has been classified as requiring Type 2 disposal in accordance with ETWBTC 34/2002; and,

iii.            Capping each backfilled pit with uncontaminated mud and/or public fill effectively isolating the contaminated mud from the surrounding marine environment.

 

1.2    Project Design

 

Despite the proven acceptability and close proximity of the existing facility at CMP IV, the purpose of the assessment was to thoroughly evaluate the South Brothers Facility in terms of acceptability of predicted impacts to water quality from dredging, backfilling and capping of the pits and also concurrent activities.

 

This Section describes an engineering design for the proposed South Brothers Facility, which is based on maximising disposal capacity, ensuring continuity in use of the site, and ensuring that environmental impacts are environmentally acceptable and no greater than those associated with existing CMP operations.  The information presented in this section is taken from the preliminary design and will be refined at the detailed engineering design stage.

 

The Project involves the sequential disposal of contaminated mud into a series of dredged pits, provisionally titled Pits A, B, and C.  The sequential construction and operation of the pits has been used to develop scenarios for sediment transport modelling, assess marine traffic issues and identify key environmental issues for water quality, ecology, fisheries, human health, noise and heritage assessments.

 

1.3    Backfill Levels

 

Previous purpose-dredged contaminated mud disposal facilities at the East of Sha Chau area have had backfill levels to 3m below original seabed.  Recently, however, the very large disused sand borrow pits now used as CMP IV have an allowed backfill level up to 6m.  This greater depth was deemed necessary because of the greater surface area of material that would be subject to exposure to the effects of storm waves.

 

In contrast to the above, the South Brothers Facility is located in a shallow water area that experiences low energy hydrodynamics.  The relatively sheltered location would also protect contaminated mud placed within the pits from storm or excessive wave action.  In addition, the preliminary smaller, shallower pit design would minimise exposure of contaminated mud thus reducing the potential for dispersion outside of the pit boundary.  As a result of these design features, the same backfill level design of 3m below original seabed level has been employed in the design of the South Brothers Facility.

 

1.4    Cap Thickness

 

Caps at previous CMPs in the East of Sha Chau Area have consisted of 3 m layer of uncontaminated mud placed by controlled bottom dumping from barges.  Additional clean mud has been added later to compensate for long-term consolidation of the contaminated mud.  Such practice has been employed in the design of the South Brothers Facility.  The rationale for the design of the cap design ([1]) ([2]) is to keep the contaminated material beyond the reach of bioturbation and to protect it against storm erosion.

The potential for damage and breaching of the cap due to anchorage has been considered, but the shallow water of the South Brothers Facility restricts the size of vessel which can anchor in the area which, in turn, restricts the size of anchor and the potential penetration depth.

 

1.5    Construction Programme

 

Once the EIA Report has been formally approved by Government, CEDD will obtain an Environmental Permit (EP) for construction of the Project.  Once the EP has been obtained the first pit is expected to be dredged during 2008 in order to be ready to receive contaminated mud in early 2009.  According to arisings estimates the third pit at the South Brothers Facility will be backfilled during the second half of 2012.  It should be noted that should the rate at which contaminated mud arises change (either increasing or decreasing) then the third pit maybe capped earlier or later than 2015.  The tentative construction programme is presented in Figure 1.1a.  It should be noted that the timeline presents predicted timeframes for each works component. 

 

Figure 1.1a Indicative Works Sequencing at the South Brothers Facility

 

1.6    Concurrent Projects

 

A requirement in the Study Brief is to examine the cumulative effects of other projects concurrent with construction and operations at the South Brothers Facility.  Projects that have been identified as occurring potentially at the same time are detailed below:

·                Disposal at North Brothers

·                Reclamations along North Lantau Coastline

-               Potential New Town Extension at Tung Chung East and Tung Chung West

-               Lantau Logistics Park

-               Potential Theme Park

-               Reclamations at Yam O

·                Permanent Aviation Fuel Facility (PAFF)

·                Highway Projects

-               Tuen Mun to Chek Lap Kok link

-               North Lantau Highway Connection to the Hong Kong - Zhuhai - Macao Bridge

·                Sewage Discharges

-               Siu Ho Wan Sewage Treatment Work (STW) 

-               Pillar Point Sewage Treatment Work (STW)

 

The significance of the above Projects to the proposed South Brothers Facility is discussed in more detail in the Water Quality Impact Assessment (Part 2, Section 2).

 

 


([1])                Premchitt J and Evans NC (1993)  Stability of spoil and cap materials at East Sha Chau contaminated mud disposal area.  Special Project Report No. SPR 2/93.  Geotechnical Engineering Office, CED, Hong Kong. 

 ([2])                Geotechnical Engineering Office, Civil Engineering Department, Information Note, May 1996.