This Section of the EIA Report
presents the findings of an assessment of the impact of construction and
operation of the proposed East of Sha Chau 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 Bay;
·
Mudflats and horseshoe crab habitat at Tai Ho Bay; and
·
Sha Chau and Lung Kwu Chau Marine Park
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 East of Sha Chau Facility are as follows:
Suspended Solids
Impacts to water quality through
both grab and trailer disposal backfilling operations have been discussed in Part
3, Section 2. Through detailed
water quality modelling it has been identified that backfilling operations will
cause an increase in suspended solid concentrations in the water column. Due to the greater loss rates
associated with trailer disposal backfilling works, predicted concentrations
calculated for these works have been used in the assessment as they thus
represent a worst-case scenario.
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 3, 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. It is thus expected that unacceptable impacts to marine
mammals arising from elevated SS levels will not occur.
Sha Chau and Lung Kwu Chau
Marine Park: The Sha Chau and Lung Kwu Chau Marine
Park is located approximately 2 km from the East of Sha Chau Facility at its
nearest point. As discussed in Part
1, Section 4 the Marine Park is considered as a marine ecological sensitive
receiver to the facility due to its high ecological value. The maximum depth averaged elevations
of SS concentrations at the Marine Park as a result of backfilling operations
are predicted to be 2.2 mg L-1 and 1.6 mg L-1 in the dry and wet
seasons, respectively. The WQOs are thus not exceeded
as a result of backfilling operations.
In terms of deposition of sediments, the
maximum deposition of SS within the Marine Park due to backfilling operations
has been determined to be no greater than < 25 g m-2 day-1. Corals, which have been identified in
the Marine Park (Part 1, Section 4), have been documented in previous
studies in Hong Kong as having a tolerance threshold ranging between 100 g m-2
day-1 ([1]) and 200 g m-2 day-1 ([2]).
As these predicted deposition rates are below these thresholds, corals
within the Marine Park are not expected to be impacted by backfilling
operations at the East of Sha Chau Facility.
As a result, the marine habitats within the Sha Chau and Lung Kwu
Chau Marine Park are not predicted to be adversely affected by backfilling
operations at the East of Sha Chau Facility.
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 East of Sha Chau
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 East of
Sha Chau Facility and whether the proposed operations are likely to adversely
affect the dolphins.
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 East of Sha Chau 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[3]. Dredging and large vessel traffic
generally results in mostly low frequency noise typically in the range of 0.02
- 1 kHz[4]
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, continued 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 ([5]). 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 ([6]). 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 East of
Sha Chau Facility proposes to employ a cap of 3 m of uncontaminated mud (Part
3, 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 East of Sha Chau
Facility. The results of this
assessment are presented in Part 3, Section 5 and in Annex C.
Impacts to the marine ecological resources
and sensitive receivers potentially arising from dredging operations at the
East of Sha Chau Facility are as follows:
Loss of Habitat
The construction of the East of Sha
Chau Facility will result in the loss of approximately 106 ha of soft bottom
seabed. Although this habitat will
be temporarily removed filling and capping works associated with the East of
Sha Chau 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 ([7]) ([8]). 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.
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 3, Section 4), it is thus expected that unacceptable impacts to marine mammals
arising from elevated SS levels will not occur.
Sha Chau and Lung Kwu Chau Marine Park: The results of the water quality modeling indicate that
dredging operations do not appear to increase SS concentrations within the
Marine Park as no detectable concentrations have been identified.
In terms of deposition of sediments, the
maximum deposition of SS within the Marine Park due to dredging operations has
been determined to be no greater than 63 g m-2 day-1. As these predicted deposition rates are
below accepted coral tolerance thresholds, corals within the Marine Park are
not expected to be impacted by dredging operations at the East of Sha Chau
Facility.
As a result, the marine habitats within the Sha Chau and Lung Kwu
Chau Marine Park expect not to be adversely affected by dredging operations at
the East of Sha Chau Facility.
As discussed above under Part 3, 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 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 East of
Sha Chau Facility are as follows:
Changes in water quality as a result
of capping operations have been discussed in Part 3, 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 East of Sha Chau
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 3, Section 4), it is thus expected that unacceptable impacts to marine mammals
arising from elevated SS levels will not occur.
Sha Chau and Lung Kwu Chau
Marine Park: The results of the water
quality modeling indicate that capping operations do not appear to increase SS
concentrations within the Marine Park as no detectable concentrations have been
identified.
In terms of deposition of sediments, the
maximum deposition of SS within the Marine Park due to capping operations has
been determined to be no greater than 24 g m-2 day-1. As these predicted deposition rates are
below accepted coral tolerance thresholds, corals within the Marine Park are
not expected to be impacted by capping operations at the East of Sha Chau
Facility.
As a result, the marine habitats within the Sha Chau and Lung Kwu
Chau Marine Park expect not to be adversely affected by dredging operations at
the East of Sha Chau Facility.
As discussed above under Part 3,
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 East of Sha Chau Facility. The closest habitat of high ecological value, Sha Chau and
Lung Kwu Chau Marine Park, is located 2 km from the site and no unacceptable
impacts have been predicted to occur.
·
Species: Organisms of ecological interest
reported from the literature include the Indo-Pacific Humpback Dolphin. Impacts are 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 East of Sha Chau
CMPs is 106 ha. The low ecological
value benthic assemblages within the areas of the proposed CMPs will be directly
lost during the operation of the facility but are expected to become
re-established within a few years following capping (see Reversibility).
·
Duration: Construction of the East of Sha Chau CMP
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
East of Sha Chau 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 East of Sha Chau 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 East of Sha Chau Facility through the following measures:
·
Adoption of Current 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 ([9]). As all dredging, backfilling and
capping operations proposed for the East of Sha Chau Facility have been designed
to follow the current practices, no adverse unacceptable impacts are expected
to occur.
·
CMP
Design: The East
of Sha Chau CMPs have been designed as four separate shallow 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 East of Sha Chau 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.
·
Avoid
Indirect Impacts to Ecologically Sensitive Habitats: The site for the East of Sha Chau
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 East of Sha Chau Facility in an area of relatively high
hydrodynamic energy, suspended sediments lost outside the boundary of the pits
have been predicted to disperse rapidly and settle in relatively open water.
·
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 East of Sha Chau Facility following the completion of
backfilling operations ([10]). As such, it is anticipated that
subtidal assemblages similar to those currently present will settle on and
recolonise the capped East of Sha Chau Facility returning it to pre-dredging
conditions.
Impacts to marine ecological
sensitive receivers during the operation of the East of Sha Chau 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 East of Sha Chau 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 ([11]).
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 East of Sha Chau
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 3, Section 2 a number of planned projects have the
potential to result in cumulative impacts with the construction and operation
of the proposed East of Sha Chau 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 East of Sha Chau 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 East of Sha Chau Facility.
The proposed East of Sha Chau
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 East of Sha Chau 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 are 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.
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
East of Sha Chau 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 East of Sha Chau 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.