This Section presents a
summary of the key potential environmental outcomes associated with the
construction and operation of the proposed South Brothers Facility. The purpose of the assessment was to
thoroughly evaluate the South Brothers Facility in terms of predicted impacts
to water quality from dredging, backfilling and capping of the pits and also
concurrent activities. It should
be noted that the facility is proposed to be developed in close proximity to
the existing East of Sha Chau facility which have been demonstrated to
operation in an acceptable manner as indicated by the findings of an intensive
EM&A programme.
Computer modelling was used to
simulate the loss of sediment to suspension during dredging, backfilling and
capping operations. The assessment
concluded that any sediment disturbed by the works would settle rapidly back
onto the seabed and the suspended sediment elevations would be of short
duration. This indicates that
there would be little transport of suspended sediment away from the pits and
that the sediment would not impact upon sensitive receivers. In general, the sediment plumes
generated by the works remain in open waters.
No residual
environmental impacts, in terms of exceedances of applicable standards were
predicted to occur as a result of the dredging, backfilling and capping of the
South Brothers Facility, provided that the recommended mitigation measures are
implemented. An EM&A programme
has been devised to confirm that the works would be environmentally acceptable.
Through the application of criteria
utilised in previous EIAs in Hong Kong, impacts arising from the proposed
dredging, backfilling and capping operations at the South Brothers Facility are
predicted to be within acceptable levels (as defined by the WQOs) and are not
expected to cause adverse impacts to marine sensitive receivers of either high
or medium ecological value (habitats or species). The loss of the subtidal habitats present within the pit
boundaries is considered to be acceptable, as the habitats are of low ecological
value. Furthermore, recolonisation
of the capped pits by infaunal organisms and epibenthic fauna is expected to
occur following the completion of capping operations. Impacts to marine mammals are likely to be avoided, as
sightings of the Indo-Pacific Humpback Dolphin, Sousa chinensis, are
infrequent in the waters of the proposed South Brothers Facility in comparison
to other waters in the north and west of Lantau.
The residual impacts occurring as a
result of the construction and operation of the South Brothers Facility are
confined to the loss of the low ecological value subtidal habitats present
within the pit boundaries. The
residual impacts are considered to be acceptable as the habitats are of low
ecological value and because infaunal organisms and epibenthic fauna are
expected to recolonise the sediments.
Water quality modelling of the
cumulative impacts of projects planned to be constructed simultaneously has
been conducted. The findings
indicated that no adverse impacts would be expected to water quality sensitive
receivers when compared the allowable increases as defined by the WQO. Unacceptable cumulative impacts as a
result of concurrent project construction and operational activities are,
therefore, unlikely to occur and hence cumulative impacts to marine ecology are
not anticipated.
To protect against unacceptable
impacts to marine ecological resources, an EM&A programme has been designed
to specifically detect and mitigate any unacceptable impacts to marine
ecological resources.
Reviews
of existing information on commercial fisheries resources and fishing
operations located within the Study Area have been undertaken. Information from a study on fishing
operations in Hong Kong and the AFCD Port Surveys indicate that fisheries
production values in the vicinity of the South Brothers Facility vary but are
medium to low.
The
construction and operation of the South Brothers Facility may give rise to
fisheries impacts from disturbances to benthic habitats, changes in water quality
and contaminant release.
Disturbances to benthic habitats are predicted to be confined within the
pit boundaries of the South Brothers facility, and recolonisation of sediments
is expected to occur following completion of works. As changes in water quality are minimal and transient,
adverse impacts to fisheries resources are not predicted to arise. Assessment of contaminant release has
indicated that the minimal concentrations will be minimal and well within the
relevant criteria.
While
no special mitigation measures are required for fisheries resources, mitigation
measures recommended to reduce impacts to water quality are also expected to
mitigate any impacts to fisheries resources.
The carcinogenic risk assessment has
indicated that risks associated with consumption of seafood were below the
acceptability criterion for both the South Brothers and the Background
areas. Results of the hazard assessment
indicated that risks associated with consumption of seafood were below the
acceptability criterion for both the South Brothers and the Background areas.
In addition, it does not appear that
Indo-pacific Humpback dolphin prey organisms are predicted to bioaccumulate
contaminants to higher concentrations than in prey of the same species from
nearby reference locations. These
results indicate that the disposal of contaminated sediments at the proposed
South Brothers Facility is not predicted to contribute to an increased risk of
harm to Indo-pacific Humpback dolphins.
Noise impact associated with the
dredging, backfilling and capping works at the South Brothers Facility have
been assessed. It has been assumed
that 2 grab dredgers will be deployed on-site for dredging work and 1 barge for
the backfilling or capping activity.
Since restricted hours construction activities may be required, the
prediction results were compared against the EIAO-TM daytime
(non-restricted hours) and the evening (1900 – 2300) and night-time (2300 –
0700) restricted hours criteria.
The results indicated that the
criteria for daytime and evening works will comply with the criteria at all
representative NSRs. To enable
dredging works to be conducted at night-time, it would be necessary to operate
only one grab dredger at any one time.
The predicted noise level at N6 under this scenario would be 50dB(A) and
would comply with the night-time criterion.
It is recommended that night-time
dredging by 2 dredgers at Pit C shall be avoided if the planned residential
developments at Kei Tau Kok reclamation area are occupied in the years 2011 to
2012. If the planned developments
are not occupied prior to the dredging activities within Pit C, no restriction
will be imposed for night-time dredging.
The review of the literature
indicated that the region adjacent to the South Brothers Facility had been
occupied for over 4,000 years and had been a focal point for Chinese and
international maritime trade. On
this basis there is the potential for the area to include sites and objects of
archaeological and historical significance; however, a review of charts has
identified no shipwreck records.
The findings of the geophysical
survey covering one third of the South Brothers Site (Pit A) indicated that the
South Brothers Facility has been heavily disturbed by anchoring, trawling and
dredging. Three sub bottom
obstructions were found in the seabed of the South Brothers Project Area. It is possible that the obstructions
are either cultural heritage material of archaeological/historical
significance, or recently dumped material of no archaeological/historical
significance. The likelihood of
the area containing any well-preserved remains is considered minimal. In order to determine the
archaeological potential of these obstructions and ensure that, if they are in
fact of archaeological importance no impacts occur, it is proposed that a
qualified archaeologist conduct a Watching Brief during dredging works. Such a brief is only considered
necessary in the area where the obstructions are located. Full details on the Watching Brief, as
well as the proposed archaeologist, should be submitted to and approved by AMO
prior to the commencement of works.
CEDD is presently
applying funding to undertake a full MAI for the South Brothers Site, the
findings of the remaining two thirds of the South Brothers Site will be
provided to AMO during to the detailed design stage and prior to
construction. The objective of the
full MAI will be to ensure that the proposed development will impose no impact
to marine archaeological resources.
The construction and operation of
the proposed South Brothers Facility has been demonstrated at rates that
maintain environmental impacts to within acceptable levels. Actual impacts during the works will be
monitored through a detailed Environmental Monitoring and Audit (EM&A)
programme. Full details of the
EM&A programme are presented in the EM&A Manual which has been based on
the on-going and previous monitoring programmes conducted at the Contaminated
Mud Disposal Facility at East of Sha Chau. This programme will provide management actions and
supplemental mitigation measures to be employed should impacts arise, thereby
ensuring the environmental acceptability of the South Brothers Facility.
No unacceptable residual impacts are
predicted for the construction and operation of the facility at the South
Brothers site.
The EIA study has facilitated the
integration of environmental considerations into the design process for the
Project. The principal measures
identified are those achieved through pit and dredging design and backfilling
and capping working rates. In
addition, a number of mitigation measures have been identified to minimise the
potential for adverse environmental impacts. The mitigation measures are detailed in full in the
Implementation Schedule (Annex E) and will be implemented by the
Contractor under enforcement by the EPD.
One of the key environmental
outcomes has been the ability to plan, design and ultimately construct the
project so that direct impacts to sensitive receivers are avoided, as far as
practically possible. A detailed
assessment of alternative sites within the Study Area has been conducted. Through this assessment,
environmentally sensitive areas have been protected by the following means.
·
Avoidance of Direct Impacts to Ecologically Sensitive
Habitats: The site
for the South Brothers Facility has been selected based on a review of the
environmental considerations of the area and the most environmentally
preferable site within the Study Area has been selected to avoid direct impacts
to ecologically sensitive habitats and species.
·
Avoidance
of Indirect Impacts to Ecologically Sensitive Habitats: The site for the South Brothers Facility
has been selected so that it is located at a sufficient distance from
ecological sensitive receivers so that dispersion of sediment from dredging,
backfilling and capping operations does not affect the receivers. By locating the South Brothers Facility
in an area of low hydrodynamic energy the horizontal dispersion of suspended
sediment is restricted to a confined area in close proximity to the pit
boundary.
As a result, it is not expected that
the construction and operation of the South Brothers Facility will result in
adverse impacts to environmentally sensitive areas.
A key concern in the final site and
disposal option design was to take steps to ensure that both direct and
indirect impacts through dredging, backfilling and capping operations were
avoided or minimised.
Consequently, the following approaches were adopted.
·
Adoption of Existing Practices: A review of all environmental monitoring
data collected since the commencement of operations at East of Sha Chau
Contaminated Mud Disposal Facility demonstrates that mud disposal activities at
the East of Sha Chau area have remained within environmentally acceptable
levels. As all dredging,
backfilling and capping operations proposed for the South Brothers Facility
have been designed to follow the current practices, no adverse unacceptable
impacts are expected to occur.
·
CMP
Design: The
South Brothers CMPs have been designed as three separate pits which minimises
the exposure time of contaminated mud to the marine environment and
consequently reduces the magnitude of any potential impacts.
·
Adoption
of Acceptable Working Rates: The
modelling work has demonstrated that the selected working rates for the
dredging, backfilling and capping operations will not cause unacceptable
impacts to the receiving water quality.
Consequently, unacceptable indirect impacts have been avoided.
Key environmental problems have been
avoided through the detailed site selection process that, as discussed above,
allowed environmentally sensitive areas and populations to be avoided. In addition, through the employment of
practices that have been demonstrated to be environmentally acceptable, no
environmental problems are expected to occur as a result of the construction
and operation of the proposed South Brothers Facility.
The construction and operation of
the proposed South Brothers Facility will result in the temporary loss of low
ecological value soft bottom habitat.
Following the completion of capping operations, the seabed will be
reinstated and is expected to return to pre-dredging conditions. As a result, compensation areas are not
deemed necessary.
The design of the South Brothers
Facility will involve the dredging of purpose-dredged pits, backfilling with
contaminated mud and subsequent capping with uncontaminated mud to return the
seabed and hydrodynamic regime to their original condition. A review of long term monitoring data
from in and around the existing capped pits at East of Sha Chau has demonstrated
that within a relatively short period of time, recolonisation of sediments
occurs returning the site to a pre-dredged state. The employment of such environmental protection methods in
the design of the South Brothers Facility will, therefore, act as an
environmental benefit.