This Section of the EIA Report presents the findings of an
assessment of the impact of construction and operation of the proposed South
Brothers Facility on existing marine ecological resources based on the Project
Description (Part 2, Section 1)
and the findings of the Water Quality Impact Assessment (Part 2, Section 2). A
series of marine ecological sensitive receivers have been identified in the
Study Area from a review of baseline information (Part 1, Section 4) as
follows:
·
Marine
mammals;
·
San
Tau Site of Special Scientific Interest (SSSI);
·
Seagrass
bed in Yam O;
·
Mudflats
and horseshoe crab habitat at Tai Ho Bay; and,
·
Sha
Chau and
The focus of the following assessment will be on impacts to
marine ecological resources and these identified sensitive receivers.
Impacts to the marine ecological resources and sensitive
receivers potentially arising from backfilling operations at the South Brothers
Facility are as follows:
Suspended Solids
In addition, as recent field investigations within Tai Ho
Bay indicate that current velocities are extremely low, it is expected that the
SS entering the bay at the bed layer will settle out very quickly and not reach
the sensitive receivers located further inside the bay ([1]).
Marine Mammals: The Indo-Pacific Humpback Dolphin, Sousa chinensis,
is thought to be an opportunistic feeder with the most important prey species
being demersal fish (such as croakers, Sciaenidae) as well as several pelagic
groups (Engraulids, Clupeids and Trichiurids). Information from the fisheries impact
assessment (Part 2, Section 4)
indicates that indirect impacts are not predicted to adversely impact
fisheries. The consequences of
this are that impacts to marine mammals through loss of food supply (fisheries
resources) are not predicted to occur as impacts to fisheries resources are
regarded as of low severity and acceptable. In addition,
it should be noted that the waters both within and surrounding the South
Brothers Facility do not appear to be an important feeding ground for Sousa
chinensis as sightings are infrequent, particularly in comparison to other
waters in the north and west of Lantau.
It is thus expected that unacceptable impacts to
marine mammals arising from elevated SS levels will not occur.
Sha
Chau and
In terms of
deposition of sediments, the maximum deposition of SS within the
As a result, the marine habitats within
the Sha Chau and
Dissolved
Oxygen
Nutrients
Modelling results have
indicated that the levels of nutrients are not predicted to increase
appreciably from background conditions during the backfilling operations. Algal blooms are not expected through
works and unacceptable impacts to the marine ecological habitats and
populations present in the vicinity of the South Brothers Facility will
not occur.
Disposal of contaminated mud could potentially result in an
increase in marine traffic and underwater noise affecting Sousa chinensis. When considering potential impacts to Sousa
chinensis, the assessment must address whether the dolphin is found in the
waters in and around the proposed South Brothers Facility and whether the
proposed operations are likely to adversely affect the dolphins. Through a review of dolphin sightings,
it appears that dolphins do not commonly frequent these waters, therefore, the
potential for impacts are considered to be low.
In terms of the potential for noise
impacts, small cetaceans are acoustically sensitive, and sound is extremely
important to their survival, thus noise from construction activities are a
potential concern. In addition,
vessel passes during operations of the South Brothers Facility have the potential to
cause behavioural disturbance or harassment. Most dolphins can hear within the range of 1 - 150 kHz
though the peak for a variety of species is between 8 - 90 kHz[4]. Dredging and large vessel traffic
generally results in mostly low frequency noise typically in the range of 0.02
- 1 kHz[5] which
are below the peak range of 8 - 90 kHz reported for dolphins and therefore,
would not cause problems.
Contaminated mud disposal facilities have been in operation
in the East of Sha Chau area for over ten years. Data available on the use of the waters does not appear to
indicate that the operations of these facilities are resulting in behavioural
changes (Part 1, Section 4).
On this basis and the observations that dolphins do not frequent the
waters of the South Brothers Facility, noise and marine traffic associated with
backfilling activities are not expected to have an adverse impact on the
species.
Bioturbation
Bioturbational effects are an important consideration in
assessing the ultimate effectiveness of any contaminated mud disposal pit
because the thickness of the cap layer required to biologically isolate
contaminated sediments is typically greater than that needed to physically
isolate them. If the cap is of
insufficient thickness it is possible that deep burrowing animals can take up
contaminated sediments, thereby providing a route for contaminants to
potentially enter the food chain.
The depth of reworking of sediments in Hong Kong, as
evidenced from sediment profile images, is generally confined for the most part
to the upper 10 cm of sediment and rarely exceeds 15 cm ([6]). However, based on an international and local literature
review conducted as part of the Environmental Impact Assessment for CMP IV at
East of Sha Chau, a 1 m cap was considered to be sufficiently thick to act as
an effective barrier to macrofauna in the East of Sha Chau area ([7]). A highly conservative cap design would require placement of
at least 3 m of uncontaminated material predicted that there would be no
appreciable risk of cap penetration by bioturbating organisms.
As the present design of the South Brothers Facility
proposes to employ a cap of 3 m of uncontaminated mud (Part 2, Section 1),
cap penetration and the subsequent uptake of contaminated material by
bioturbating organisms is not expected to occur.
Bioaccumulation
Backfilling activities have the potential for contaminant
release from the disposal material during disposal works and from the pits
through processes such as bioturbation of benthic organisms. In order to address these concerns, the
potential for food chain bioaccumulation has been examined through a hazard to
health risk assessment. Based on
bioconcentration factors, determined from an assessment of bioaccumulation
potential (Annex B), the predicted contaminant concentrations in marine
water and sediments have been assessed to calculate the risks to humans and
marine mammals associated with consuming fish and shellfish collected from the
vicinity of the South Brothers Facility.
The results of this assessment are presented in Part 2, Section 5
and in Annex C.
Impacts to the marine ecological resources and sensitive
receivers potentially arising from dredging operations at the South Brothers
Facility are as follows:
Loss of Habitat
The construction of the South Brothers Facility will result
in the loss of approximately 164 ha of soft bottom seabed. Although this habitat will be
temporarily removed filling and capping works associated with the South
Brothers Facility will reinstate the seabed and hydrodynamic regime to their
original condition. This will
mitigate the adverse impacts of removal of the seabed. A review of long term monitoring of benthos
in and around the capped pits at East of Sha Chau has demonstrated that within
a relatively short period of time, recolonisation of sediments by benthic
assemblages occurs returning the site to a pre-dredged state ([8]) ([9]). These studies have shown that initially the capped
backfilled area will be colonised by opportunists and during the early stages
of recovery diversity is expected to be low. However, as more competitive species begin to colonise, the
diversity of the community will increase until it returns to conditions to the
pre-dredged habitat. This
temporary loss of habitat is, therefore, not considered as unacceptable.
Changes in water quality as a result of dredging operations
have been discussed in Part 2, Section 4. Based on this assessment, impacts to marine ecology have
been assessed and are presented below.
In contrast to trailer disposal, discussed above, the worst-case impact
scenarios for dredging works presented below have been based on grab dredging
at the South Brothers Facility, as loss rates are predicted to be higher
through such works in comparison to those predicted for trailer dredging.
Suspended Solids
Marine Mammals: Impacts to marine mammals as a result of elevations of SS
concentrations are generally associated with the potential influence on prey
and, therefore, affect the animals indirectly. As impacts to fisheries resources are not expected to occur
as a result of dredging operations (Part 2, Section 4), it is
thus expected that unacceptable impacts to marine mammals arising from elevated
SS levels will not occur. In
addition, sightings
of Sousa chinensis are infrequent in the waters of the proposed South
Brothers Facility, thus adverse impacts are unlikely.
Sha Chau and
In terms of
deposition of sediments, the maximum deposition of SS within the
As a result, the marine habitats within
the Sha Chau and
As
discussed above under Part 2, Section 3.3.2, habitat disturbance through
increased traffic and noise is not considered to be a concern to the proposed
operations due to existing practices.
As dredging operations are expected to require less marine traffic, such
operations are, therefore, also not expected to cause unacceptable impacts to
marine ecological resources.
Impacts to the marine ecological sensitive receivers
potentially arising from capping operations at the South Brothers Facility are
as follows:
Changes in water quality as a result of capping operations
have been discussed in Part 2, Section 4. Based on this assessment, impacts to marine ecology have
been assessed and are presented below.
As with dredging operations, discussed above, the worst-case impact
scenarios for capping works presented below have been based on barge placement
of uncontaminated mud at the South Brothers Facility.
Suspended Solids
Marine Mammals: Impacts to marine mammals as a result of elevations of SS
concentrations are generally associated with the potential influence on prey
and, therefore, affect the animals indirectly. As impacts to fisheries resources are not expected to occur
as a result of capping operations (Part 2, Section 4), it is
thus expected that unacceptable impacts to marine mammals arising from elevated
SS levels will not occur. In
addition, sightings
of Sousa chinensis are infrequent in the waters of the proposed South
Brothers Facility, thus adverse impacts are unlikely.
Sha
Chau and
In terms of
deposition of sediments, the maximum deposition of SS within the
As a result, the marine habitats within
the Sha Chau and
As discussed above under Part 2, Section 3.3.2,
habitat disturbance through increased traffic and noise is not considered to be
a concern to the proposed backfilling operations due to existing
practices. As capping operations
are expected to require less marine traffic, such operations are, therefore,
also not expected to cause unacceptable impacts to marine ecological resources.
·
Habitat Quality: Direct impacts are predicted to occur only to the low
ecological value benthic habitats identified within the proposed area for the
South Brothers Facility. The closest
habitat of high ecological value is Tai Ho Bay, located approximately 1 km away
from the site at it’s nearest point. No unacceptable impacts have been
predicted to occur.
·
Species: Organisms of ecological interest reported from the literature
include the Indo-Pacific Humpback Dolphin, however, sightings within and in
vicinity of the South Brothers Facility are infrequent. Impacts are therefore not predicted to
occur to this species as water quality perturbations are predicted to be
compliant with the WQOs.
·
Size: The total size of the South Brothers CMPs is 164 ha. The low ecological value benthic
assemblages within the areas of the proposed CMPs will be directly lost during
operation of the facility but are expected to become re-established within a
few years following capping (see Reversibility).
·
Duration: Construction of the South Brothers Facility is currently
proposed to commence in 2008 and capping operations complete in 2015. However, it should be noted that this
duration has been based on arising predictions, and as such, should arisings of
contaminated material change a subsequent change in duration could be
expected. It should also be noted
that the water quality modelling has been based on a worst-case dredging/
disposal/capping rate, however, in practice operations may be expected to be
significantly lower. Nevertheless,
under this worst-case scenario increases in SS concentrations in the vicinity
of sensitive receivers as a result of the construction and operation of the
South Brothers Facility are expected to be non detectable, thus, within
environmentally acceptable limits (as defined by the WQOs and tolerance
criteria).
·
Reversibility: Impacts
to the benthic assemblages inhabiting the soft bottom habitats within the areas
proposed for the South Brothers Facility are expected to return to pre-dredging
conditions within a relatively short timeframe once operations have
ceased.
·
Magnitude: No
unacceptable impacts to the ecologically sensitive habitats have been predicted
to occur.
·
Avoidance: Potential impacts should be avoided to the maximum extent
practicable by adopting suitable alternatives;
·
Minimisation: Unavoidable impacts should be minimised by taking
appropriate and practicable measures such as constraints on the intensity of
works operations (eg dredging rates) or timing of works operations; and
·
Compensation: The loss of important species and habitats may be provided
for elsewhere as compensation.
Enhancement and other conservation measures should always be considered
whenever possible.
To summarise, impacts to marine
ecological resources have largely been avoided during the construction
and operation of the South Brothers Facility through the following measures:
·
Adoption
of Existing Practices: A review of all previous environmental
monitoring results since the operation of the East of Sha Chau Contaminated Mud
Disposal Facility has provided statistical analyses that mud disposal
activities at the East of Sha Chau area have remained within environmentally
acceptable levels ([10]). 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 exposure time of contaminated mud to the marine environment
and consequently reduces the magnitude of potential impacts to ecological
resources.
·
Avoid
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 to avoid direct impacts
to ecologically sensitive habitats and species. Specifically, the area where dolphin sightings are less
frequent or have not been recorded in comparison to other areas in the Study
Area has been selected.
·
Avoid 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 at levels of concern (as defined by the WQO). By locating the South Brothers Facility
in shallow area of relatively low hydrodynamic energy, thereby limiting the
potential for material to be lost outside of the pit, the horizontal spread of
suspended sediment is restricted to a confined area within close proximity to
the pit boundary.
·
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 to marine ecological resources have been avoided.
The impact assessment presented above indicates that no
unacceptable impacts to marine ecology are expected to occur. Although soft bottom habitat will be
temporarily lost, it has been demonstrated through long term monitoring of
previous and existing CMPs in the East of Sha Chau area that marine organisms
have recolonised capped South Brothers Facility following the completion of
backfilling operations ([11]). As such, it is anticipated that subtidal assemblages similar
to those currently present will settle on and recolonise the capped South
Brothers Facility returning it to pre-dredging conditions.
Impacts to marine ecological sensitive receivers during the
operation of the South Brothers Facility are predicted to be within
environmentally acceptable levels, as well as those in ecologically important
areas. As such, no marine ecology
specific mitigation measures are required during projects operation.
Residual impacts occurring as a result of the construction
and operation of the South Brothers Facility are the loss of the low ecological
value subtidal assemblages 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. Such recolonisation of capped pits
within the East of Sha Chau area has previously been demonstrated to occur
through long-term monitoring ([12]).
Cumulative impacts to marine
ecological resources may arise from concurrent dredging, backfilling or
development projects in the area.
In addition, cumulative impacts through the combination of dredging,
backfilling and capping operations within the South Brothers Facility have the
potential to occur. Types of
impacts may include physical effects (eg increased suspended sediment
concentrations), water quality effects (eg changes in dissolved oxygen,
nutrients, or contaminant concentrations), and ecosystem effects (eg benthic or
water column habitat disturbance).
Concurrent activities that contribute to one or more of these types of
impacts may result in the following cumulative effects on marine ecology:
·
prolonging
the period of impact;
·
increasing
the intensity of the impact; and,
·
causing
different effects in combination than any one impact would cause independently
(synergy).
As discussed in Part 2,
Section 2 a number of planned projects have the potential to result in
cumulative impacts with the construction and operation of the proposed South
Brothers Facility. Water quality
modelling of the cumulative impacts of these projects being 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. It should be
noted, however, that the assessment has been conducted on maximum operations
without the use of operational controls.
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.
The construction and operation of the proposed South
Brothers Facility has been shown to proceed at rates that maintain
environmental impacts to within acceptable levels. Actual impacts during the works will be monitored by 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.
The proposed South Brothers Facility was studied in detail
through a site and disposal options selection study in order that a preferred
site was selected that avoided direct impacts to habitats or species of high
ecological value. 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 high 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.
In addition, a review of all previous environmental
monitoring results since the operation of the East of Sha Chau Contaminated Mud
Disposal Facility has provided confirmation 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 thus expected to occur.
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.