3.
Environmental Impact Assessment
3.1.
The EIA report has provided an
assessment of the potential environmental impacts associated with the
construction and operation of the Project.
The study has been undertaken in accordance with the Technical Memorandum
on Environmental Impact Assessment Process (EIAO-TM) and the Study Brief. The following key areas were addressed in
the EIA Study:
·
Air
quality impacts
·
Noise
impacts
·
Water
quality impacts
·
Sediment
contamination
·
Solid
waste
·
Ecological
impacts
·
Fisheries
impacts
·
Visual
and landscape impacts
3.2.
The findings of the assessments for
the above environmental issues are summarised in the following sections. Cultural heritage aspects of the Project
were addressed separately from the EIA Report.
3.3.
Representative air sensitive receivers
(ASRs) were identified in the EIA Study and are shown in Figure 3.1.
3.4.
During construction phase, no adverse
construction dust impact would be expected at all ASRs in the vicinity of the
study area, except at ASR A24 (football court located next to the proposed
Pumping Station P2). In order to
achieve the air quality objectives (AQO), it is recommended to install 2m high
solid fences around the construction site of Pumping Station P2. With the implementation of the mitigation
measure, no exceedance of 1-hour TSP guideline level and 24-hour TSP AQO limit
would be anticipated at the ASRs.
Notwithstanding this, the implementation of the Air Pollution Control
(Construction Dust) Regulation and the inclusion of good site practices
were also recommended.
3.5.
During operation phase, all pumping
stations, sequence batching reactor (SBR) feed pump station and sludge
dewatering room would be all enclosed and the outlet air from these facilities
would be properly treated by deodorization facilities with 99.5% odour removal
efficiency before discharge via vent pipes.
With the implementation of all these measures, the predicted odour
concentration at the representation ASRs would comply with the EIAO-TM
criteria. Hence, no unacceptable
impacts were predicted.
3.6.
Representative noise sensitive
receivers (NSRs) were identified and are shown in Figure 3.2. Construction
noise impacts from the construction activities such as sewer alignment
construction, pumping stations and STW construction, and the operation noise
impacts from the pumping stations were identified as key environmental issues
for this Project. The potential noise impacts arising from the Project have
been assessed and evaluated.
3.7.
During the construction phase, the
unmitigated noise levels at most of the NSRs would experience noise level
exceeding the noise criteria stated in the EIAO-TM. To alleviate the noise impact, noise mitigation measures
including the adoption of good site practices, quieter equipment and
restriction on the number of plant operating as well as other possible
mitigation measures including erecting of noise screening structures and manual
working were recommended. With the
recommended mitigation measures, no exceedance of the noise criteria was
predicted at all NSRs, except short-term residual impact during sewer
construction. Having considered that
the construction of the sewer is unavoidable as it is an integral element of
the Project and the short duration of the sensitive receivers experiencing the
impacts, the residual impacts were considered acceptable.
3.8.
During operation phase, no adverse
noise impact arising from the operation of the pumping stations are predicted,
except Pumping Station P1a. To
alleviate the noise impact, it is recommended to install a silencer at air
discharge point of the deodouriser at Pumping Station P1a. With the recommended mitigation measures
applied, no exceedance of both daytime and nighttime noise criterion would be
anticipated.
Construction Phase
3.9.
To minimize the potential water
quality impacts from the submarine outfall construction, the Horizontal
Directional Drilling (HDD) technique would be adopted. By using the HDD technique, only minor
dredging works would be required at a location of around 480m from the
coast.
3.10.
The sensitive receivers identified
within the Study Area include the gazetted fish culture zone (FCZ) at Picnic
Bay and secondary contact recreation subzone at Mo Tat Wan, which are located
more than 300 m and 500 m from the proposed dredging works respectively. With the use of closed grab dredger, 2-layer
silt curtains and reduction in dredging rate, the elevations in suspended
sediment (SS) concentration generated from the dredging activities at these
sensitive receivers would comply with the Water Quality Objective (WQO).
3.11.
The potential water quality impact
arising from the release of contaminants from sediment disturbed during the
dredging works was assessed. It was
predicted that, because of the low level of sediment contamination in the
dredging area, adverse impacts arising from the release of heavy metals,
nutrients, and organic compounds would not be expected.
Operation Phase
3.12. Potential impacts in relation to the discharge of treated effluent
from the outfall for the wet and dry season have been assessed using USEPA
CORMIX2 model. The modelling results
indicate that the predicted concentrations of SS, E. coli, and unionised ammonia would satisfy the Water Quality
Objectives (WQOs), while the predicted total inorganic nitrogen (TIN) levels
would exceed the WQO. The exceedances
of WQO for TIN were attributable to the high background TIN levels. The background level for dry season had
already exceeded the limit by more than twice.
Owing to the high background TIN level, exceedance of the WQO limit for
TIN would be unavoidable even with a very small contribution from the treated
effluent discharge at the submarine outfall.
According to the EPD monitoring data, the predicted TIN levels would
fall within the background variations of TIN concentrations at Picnic Bay. Furthermore, the prediction were
considered to be over-estimated as they were predicted by simply adding the
elevated TIN levels from the effluent to the background levels and were not
taken account of the beneficial effect of eliminating untreated or partially
treated sewage discharges to the Picnic Bay upon the operation of the
Project. The denitrification process in
the STW would remove more than 50% of TIN from the sewage and the treated
effluent would be discharged at a location of more than 560m from the FCZ. Hence, the operation of the Project would
not induce a water quality impact worse than that without the implementation of
the Project. In fact, the proposed
project would improve the water quality of the Picnic Bay by eliminating the
discharge of untreated or partially treated sewage into the coastal area of the
bay.
3.13.
The potential impact from emergency
discharge due to the failure operation of the pumping stations and the STW has
also been assessed using the USEPA CORMIX3 model. In order to minimize the occurrence of emergency discharge as far
as possible, the following mitigation measures and contingencies were
recommended:
·
Standby pump at all pumping stations and the STW in
case of duty pump failure;
·
Standby generator at all pumping stations in case of
interruption of electrical power supply;
·
24-hour temporary storage for all pumping stations in
emergency;
·
Use of Sequencing Batch Reactor (SBR) units as a
storage tank in case of STW failure;
·
No emergency discharge is allowed at Pumping Station P2
and the STW;
·
Automatically shutdown the pumping station at Lo So
Shing in case of Pumping Station P1a failure;
·
Automatically shutdown the upstream pumping stations
(including Pumping Station P1a and Lo So Shing Pumping Station) in case of
Pumping Station P1b failure;
·
Automatically shutdown the upstream pumping stations
(including Pumping Stations P1a and P1b, and Lo So Shing Pumping Station) in
case of Pumping Station P2 failure;
·
Automatically shutdown all pumping stations (including
Pumping Stations P1a, P1b and P2, and Lo So Shing Pumping Station)in case of
STW failure;
·
Implement a telemetry system to ensure prompt action to
be undertaken in an emergency occasion.
3.14. With the implementation of the above measures, an emergency overflow
would be unlikely to occur and the potential water quality impacts would be
minimized in the unlikely event that an overflow does occur. Compared with the long-termed improvement of
water quality of Picnic Bay from the Project and given the recommended measures
minimise the possibility of the emergency discharge, the residual impact would
be considered acceptable.
3.15.
Based on the preliminary design, the
total volume of dredged material was estimated to be approximately 26,000 m3. A review of previous field investigation
data on marine sediment quality reveals that Category H contaminated mud may be
present within the boundary of the study area.
However, the available sediment data were of limited extent and
collected about eight years ago, and hence could not fully represent the
existing sediment quality of the proposed dredged areas of the present
Project. A preliminary sediment
contamination survey was therefore conducted to provide more accurate and
updated information on the baseline sediment quality of the proposed dredged
areas such that recommendations on the appropriate disposal requirements of the
dredged material can be made. The
findings of the sediment contamination survey indicate that the marine
sediments to be dredged for the submarine outfall were classified as Category
L. The dredged sediment would therefore
be suitable for open sea disposal.
3.16.
The dredging works should be carried
out in a controlled manner such that release of sediments into the marine
environment would be minimized. With
the implementation of the recommended mitigation measures, residual water
quality impacts would not be anticipated.
3.17.
Wastes generated by the construction
works would include workforce wastes, maintenance and chemical wastes, and
construction and demolition material.
Provided that the identified waste arisings are handled, transported and
disposed of using approved methods and that the recommended good site practices
are adhered to, adverse environmental impacts would not be expected.
3.18.
Wastes generated during normal STW
operations would include inlet screenings, grit from detritors and dewatered
sludge. It has been proposed that the
sewage sludge generated from the STW would be dewatered on-site and the sludge
cake would be delivered to Sok Kwu Wan refuse transfer station for disposal to
nearby landfill site.
3.19. Construction and operation of the sewage treatment project in Sok
Kwu Wan at Lamma might affect the terrestrial and marine environments. Based on
site investigations there appeared to be no insurmountable ecological impacts
arising from this project. The overall impacts of project construction and
operation on ecology were predicted to be minor.
3.20. Based on the nature of the project and the baseline conditions of
the study area, the impacts of project construction and operation on
terrestrial ecology were predicted to be minor. A small moist area of
shrubland/grassland habitat near Pumping Station P2 which is used by Romer’s
Tree Frog and thus of moderate to high ecological value would not be affected.
Nevertheless, additional measures to control site runoff for protecting the
tree frog site were proposed on a precautionary basis.Impacts on intertidal
habitats would not occur on the sand flat but in a limited area on the rocky
shore and thus were also predicted to be minor. Hard corals of low ecological value (widely distributed in HK,
small in size and having low coral cover (<5%)) were recorded in the shallow
waters of the bay. HDD technique would
be used to avoid direct loss of coral colonies. Construction of a submarine outfall would not involve any
disturbance of the seabed until at a location of around 480m from coastline.
The seabed loss area is of muddy substrate only. No loss of seabed, which is available for hard coral
colonization, would be constituted. No
hard corals would be directly impacted by the HDD or the dredging work, while
silt curtains around the dredging site, use of closed grab dredger and
reduction in dredging rate could prevent indirect impacts on corals.
3.21. Based on results of water quality modelling, during the operational
phase, discharge of the effluent would not adversely affect water quality in
the Study Area. Hence no adverse impacts to marine ecology inducing coral
communities in Sok Kwu Wan would be anticipated.
3.22. Water quality impact arising from the emergency discharge of the
pumping stations and STW are anticipated.
With the implementation of the mitigation measures as described in Water
Quality Impact Assessment, the possibility of an emergency overflow occurring
would and the potential water quality impacts would be minimized.
3.23. With the implementation of the mitigation measures recommended, the
impacts of project construction and operation on ecology are predicted to
remain within acceptable bounds. Due to
the limited scale of the Project, low ecological value of the fauna and flora
recorded, and the minor degree of impacts caused, no ecological monitoring and
audit is proposed.
3.24.
Baseline information on the cultured
and capture fisheries resources and operations within the Study Area were
gathered through desktop study and interviews with mariculturists. These indicate that Sok Kwu Wan has a
capture fishery of above average production for Hong Kong and is a nursery area
for some commercially important species.
The most important and sensitive fisheries resource in Sok Kwu Wan is
the gazetted Fish Culture Zone.
3.25.
The potential impacts to fisheries
sensitive receivers during the construction phase were identified as being the
release of suspended sediment and release of ammonia associated with the
dredging works required for the construction of about 240 m outfall pipeline
and the diffuser section. These dredging works would be conducted no closer
than 300m from the FCZ. With reference to Water Quality Impact Assessment in
Section 5 of the EIA report, it was determined that the release of ammonia from
sediments during the construction phase would comply with the WQO and would not
have any toxic impact to fish in the Study Area. In order to ensure environmental acceptability, it was determined
that mitigation measures to prevent sediment plumes reaching the FCZ would be
required and are the same as those recommended for water quality impacts.
Potential impacts due to construction of the outfall pipeline would be reduced
through the adoption of the HDD construction method.
3.26.
The impact on fisheries sensitive
receivers in the Study Area was also evaluated for the operational phase using
water quality modelling results. Based
on these predictions, discharge of the effluent would not adversely affect
water quality in the Study Area and hence no adverse impacts to fisheries
sensitive receivers would be anticipated.
3.27.
The small increase in TIN levels owing
to effluent discharge was identified as deserving special attention owing to
its high background levels (often exceeding WQO) and the importance of nitrogen
in mediating algal growth (and hence the potential for red tide
formation). However, according to the
EPD monitoring data, the predicted TIN levels would fall within the background
variations of TIN concentrations at Picnic Bay. In addition, the proposed project would improve the water quality
of the Picnic Bay by eliminating the discharge of untreated or partially
treated sewage into the coastal area of the bay. It is anticipated that the small contribution to TIN levels by
effluent discharge would not significantly enhance algal growth, and the
potential impact for inducing red tide in Sok Kwu Wan would not anticipated.
3.28. Emergency discharge from the pumping station or STW would have the
potential to lead to adverse impacts on the FCZ. With the implementation of the mitigation measures as described
in Water Quality Impact Assessment, the possibility of an emergency overflow
occurring and the potential water quality impacts would be minimized.
3.29. In conclusion, with the implementation of the recommended mitigation
measures, it would be expected that the implementation of the Project at Sok
Kwu Wan would be environmentally acceptable for the fisheries perspective.
Landscape Impact Assessment
3.30.
In general, the Project would cause
slight to moderate adverse landscape impact in the construction phase and
negligible to slight/moderate adverse landscape impact in operation phase
before the implementation of mitigation measures. The impacts would be localised at the pipeline alignment along
First Street, the pumping stations and STW.
They are small in scale and thus they will not cause serious landscape
impact. The following table shows the
dimension of the pumping stations and STW above ground level.
|
|
Approximate Dimension (m)
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Refer
to Figure 10.13 in the EIA Report for layout
|
Refer
to Figure 10.13 in the EIA Report for layout
|
|
|
Note: * Height above ground level
3.31. Vegetation loss would be small - 1% (2283 m2) of the
study area. Mitigation measures at
construction phase include minimise damage and protect existing vegetation,
conservation of topsoil for reuse, careful transplant of the identified tree,
short excavation sections and immediate back filling upon completion, and
compensatory planting would alleviate the adverse impact to negligible to
slight adverse. However, at the Exposed
Coastline area, the presence of the sea-borne construction traffic at the
outfall site would disturb the natural context of the coastline, the landscape
impact would be relatively high - slight/moderate adverse. Other than the new ancillary buildings (STW,
3 nos. pumping stations), the impacts at construction phase would be
reversible. Mitigation measures in the
operation phase include architectural and soft landscape finishes to the
ancillary buildings and planting to reformed slope to establish a coherent
context within the overall landscape.
Visual Impact Assessment
3.32. In general, the major visual impact is during construction where the
sewer is at parts adjacent to residential units and to the waterfront
restaurants, which leads to slight/moderate to moderate adverse visual
impact. Mo Tat Wan would have a
moderate adverse impact during construction since it is close to the location
of the outfall affecting its tranquil quality.
If night lighting is required for the marine fleets near Mo Tat Wan, the
light source should be directed away from the residential units. Mitigation measures in construction phase
include short excavation sites and immediate backfilling upon completion of
sections, minimise damage to vegetation along footpath, and use of site
hoarding appropriate to the natural site context to screen trenches. Mitigation measures in operation phase
include architectural and soft finishes to the pumping stations and STW
appropriate to its site context, planting to reformed slope behind the STW, and
appropriate paint finishes to the exposed section of pipeline. Upon implementation of the mitigation
measures, the visual impact in operation phase would be reduced to negligible
to slight.
Evaluation of the Project
3.33.
The major adverse landscape and visual
impacts occur in the construction phase, and these impacts are reversible with
the completion of construction. Since
the major length of the pipeline alignment would be underground and the scale
of the ancillary buildings would be relatively small, the landscape and visual
impact in operation would be limited.
3.34.
Overall in the context of Annex 10 of
the EIAO-TM, the landscape and visual impacts would be acceptable with
mitigation measures.