14.1.1
A local sewage treatment facility is proposed at Po
Toi O, which is currently served by septic tanks. The sewage treatment plant
will be built on a cut-slope away from residence, with much of the noisy plant
equipment hidden underground within the concrete structure. Gravity sewers and
rising mains will be buried along the footpath between houses.
14.1.2
The proposed facility will collect the sewage from
residence and restaurants and treat to meet the EPD’s effluent discharge
standard. The effluent will be discharged through a submarine outfall at the
outer water of Po Toi O bay. This Project is expected to bring improvement in environmental
hygiene in the Po Toi O area.
14.2.1
Dust generating activities were identified and
evaluated. Based on the best available information at time of preparation of
this EIA, there is no concurrent project in Po Toi O area in the construction
phase of the Project. Given the small scale of the works involved in the
Project, extensive excavation and transportation of dusty material are highly
unlikely. Mitigation measures including watering of on-site construction area
are expected to limit fugitive dust levels to acceptable levels. With proper
implementation of mitigation measures, construction dust emissions impacts are
anticipated to be acceptable. An
EM&A programme will be implemented to ensure construction dust impacts are
controlled to acceptable level.
14.2.2
Due to the limited quantity of excavated soil for
the Project, odour impact during the construction phase of Project is acceptable
if control measures are implemented.
14.2.3
During the operational phase of the Project, all the
potential odour generating facilities would be enclosed by building
structure. The deodorization facility is
designed to be able to achieve an odour removal efficiency of 99.5% for the
exhaust of the sewage treatment plant. During sludge transportation, it is
recommended that the sludge should be carried in enclosed containers to avoid
unacceptable odour nuisance. Membrane and filter in the STP should be regularly
cleaned and replace to maintain the efficiency of sewage treatment and odour
removal. With proper mitigation measures incorporated into the design, odour
impacts arising from the proposed sewage treatment plant will be significantly
reduced, and odour impacts are anticipated to be acceptable.
14.3.1
Construction noise arising from typical types and
numbers of powered mechanical equipment items (PME) for the construction of
sewage treatment plant and rising mains/sewer installation have been assessed.
Based on the effective sound power levels of the PMEs and the notional noise
distance to the noise sensitive receivers, unmitigated construction noise
levels would exceed the 75dB(A) guideline level for the non-restricted hours for
all NSRs. At source mitigation measures have been proposed including the use of
quality plants, use of mobile noise barriers, semi-enclosure, strategic work
scheduling and good site practice. With the proposed mitigation measures, no noise
exceedances is expected at the NSRs.
14.3.2
Most of the noisy equipment items in the sewage
treatment plant would be fully underground or enclosed by concrete structure.
With noise reduction due to distance between the STP and the nearest NSR,
operational noise impact is anticipated to be acceptable.
14.4.1
Major water quality impact is expected from the
release of suspended solids during dredging and backfilling at the proposed
diffuser location during the construction phase. By confining these works
within fully enclosed cofferdam and dredging by closed-grab dredger anchored
outside the cofferdam, no sediment loss and thus significant water quality
impact is expected.
14.4.2
During normal operation of the Po Toi O Sewage
Treatment Works (PTO STW), no substantial change in water quality in Po Toi O bay
is expected. All water quality parameters would comply with the WQO except TIN,
which is attributed to the background level.
·
Delivery of an emergency generator to PTO STP
within 4 hours from plant failure;
·
Provision of dual power by CLP;
·
Provision of a Supervisory control and data
acquisition system (SCADA), which signals to the operation and maintenance
personnel for emergency attendance in case of plant failure;
·
Provision of a standby pump and screen at the PTO
STP;
·
Provision of emergency storage of 4-hr ADWF sewage
retention time;
·
Arrangement of tankers for removing incoming sewage
to other sewage treatment plants for treatment continuously to ensure a
sufficient buffer for emergency storage.
14.4.4
Based on these provisions, emergency discharge is
not expected, and thus no adverse impact on water quality due to emergency
discharge is anticipated.
14.4.5
With proper implementation of mitigation measures,
no insurmountable water quality impact due to this Project is expected.
14.5.1
Ecological sensitive areas recorded in the Study
Area (500m from work boundary) included the Clear Water Bay Country Park. 3
avifauna species of conservation importance were recorded in past studies,
while 6 plants, 11 avifauna, 1 snake and 2 butterfly species of conservation
importance were recorded in recent surveys.
14.5.2
A small area of shrubland (893 m2) on
Conservation Area will be impacted directly due to the establishment of sewage
treatment plant (STP) and road facilities (footpath and public parking spaces).
One common plant species of conservation importance growing on this shrubland
is also expected to be impacted directly.
14.5.3
Small area of woodland in Conservation Area and
developed area (350 m2 & 2,100 m2 respectively) will
also be lost temporarily for the establishment of associated land-based pipes.
In addition, 750 m2 of rocky shore (above high tide level) on
Coastal Protection Area will be lost temporarily for constructing the pipeline
of submarine outfall. Nevertheless, direct impact caused by the establishment
of associated land-based pipes and pipeline of submarine outfall would be
reversible.
14.5.4
All habitats and fauna species of conservation importance
are expected to be impacted indirectly by water quality and/or noise impacts in
construction phase. As in operational phase, noise impact from sewage treatment
works will be limited.
14.5.5
With proper implementation of mitigation measures,
residual impact is expected to be acceptable. Regular site audit would only be
required in construction phase.
14.5.6
The overall impact on terrestrial ecology is considered
as acceptable.
14.6.1
Coral communities were recorded in past study, while
4 avifauna, 1 amphioxus and 19 hard coral species of conservation importance
were found in recent surveys. Besides, a major amphioxus habitat was recorded
in recent surveys.
14.6.2
Although the muddy seabed where the diffuser will be
located on will be lost during construction phase, no species of conservation
importance will be directly affected. There will be permanent loss of 5 m2
in area at the diffuser location. However, impact on the remaining works area
(495 m2) would be reversible. Indirect impact due to water
deterioration will be minimal as dredging works will be confined within fully
enclosed cofferdam. No sediment release into water bodies is anticipated. No cumulative
impact is expected as no project is known to be carried out concurrently with
this Project. The overall construction phase impact is considered low and
acceptable.
14.6.3
As sewage will be collected and treated before
discharge, no substantial change in water quality is expected for normal
operation of the Po Toi O Sewage Treatment Works. No discharge of raw sewage in case of
emergency plant failure is anticipated as mentioned in Section
14.4.3. The overall
operational phase impact on marine ecology is considered low and acceptable.
14.6.4
With proper implementation of mitigation measures,
residual impact is expected to be acceptable. No specific monitoring and audit
programme is required for marine ecology.
14.7.1
Fisheries resources in the Study Area (covering Po Toi O bay, Clearwater
Bay and waters surrounding Steep Island) included the Po Toi O Fish Culture Zone, Artificial Reefs, fishing
ground in eastern waters of Hong Kong including Po Toi O, and spawning and
nursery grounds for commercial fisheries resources in eastern waters of Hong
Kong. In terms of capture fisheries, adult fish production (in weight) in the
Study Area was “relatively low – medium”, while the overall fish (i.e. both
adult fish and fish fry) production (in value) was “relatively medium – high”
among Hong Kong waters.
14.7.2
Although no direct encroachment on Fish Culture Zone
and Artificial Reefs in the Study Area is anticipated, about 1,920 m2
of fishing ground and 500 m2 of benthic spawning ground will be
affected. Except the 5 m2 benthic spawning ground will be lost
permanently, other impacted area will only be affected in construction phase
temporarily (reversible impact). Indirect impact on fisheries resources by the
water quality deterioration will be insignificant. No cumulative fisheries
impact is expected as no project will be carried out concurrently of this
Project.
14.7.3
No substantial change in water quality in Po Toi O
bay is predicted during normal operation of the PTOSTW. No discharge of raw
sewage in case of emergency plant failure is anticipated as mentioned in Section 14.4.3.
14.7.4
With proper implementation of mitigation measures on
water quality, residual impact is expected to be acceptable. No specific
monitoring and audit programme is required for fisheries.
14.7.5
The overall impact on fisheries is considered as
acceptable.
14.8.1
During construction phase, major C&D materials will
be composed of rock and soil from slope cutting for STP construction. Other
waste includes chemical waste from maintenance of plant equipment, used
bentonite from drilling works, marine sediment from dredging works and general
refuse from workforce.
14.8.2
Sediment Sampling and Testing Plan (SSTP) has been
submitted to EPD as required under the Study Brief. Sedimentary Quality Tests
of sediment at dredging point showed that the materials were classified as
Category L. According to ETWB TC(W) No.
34/2002 Management of Dredged/Excavated Sediment, Category L materials
shall be disposed at open sea disposal site assigned by the Marine Fill
Committee (MFC).
14.8.3
Operation of sewage treatment plant will generate
sludge, debris from screening, worn filter in deodouring unit and general
refuse from staff.
14.8.4
The waste shall be handled and disposed of properly to
prevent causing damage to the environment, e.g. water pollution, odour nuisance
and hygiene issue. With implementation of the recommended measures and site
practices, impact due to waste management is expected
to be acceptable.
14.8.5
Based on historical aerial photos, land use history,
site inspection and information from EPD and FSD, it is concluded that land
contamination within the work boundary demarcated in Figure 1-1 is highly
unlikely.
14.9.2
Due to the relatively small scale
of the proposed Project, none of the LRs, LCAs or VSRs will experience
substantial residual impacts. The highest residual impact for Landscape
Resources and Landscape Character Areas is only assessed as Slight on Day 1 and Insubstantial at Year 10 (all the other
LR’s and LCA’s experiencing Insubstantial or No residual impact at Year
10). The highest residual impact for Visually Sensitive Receivers is Moderate at Day 1 and Slight at Year 10, (all the other
VSRs experiencing only Slight or Insubstantial residual visual impacts at Day 1 and Insubstantial or No residual visual impacts at
Year 10).
14.9.3
Based on the above assessment, it
is considered that in accordance with the criteria and guidelines for
evaluating and assessing impacts as stated in Annex 10 and 18 of the TM- EIAO,
the overall residual landscape and visual impacts of the proposed Project are acceptable with mitigation during the construction and operation phases.
14.10.1
Po Toi O was a small fishing
village and developed into a seafood and tourism destination. One Grade 3 historic building, Hung Shing
Temple, was identified in the Study Area (50m from work boundary). It has over 350 years history and it is still
commonly worshipped today. Besides Hung
Shing Temple, two built heritages and six landscape features were
identified. They are not exceptionally
historic but could be culturally connected with the local villagers.
14.11.1
Specific mitigation measures are proposed to avoid
and minimize the potential environmental impacts. Also, a number of monitoring
works will be conducted to ensure compliance of environmental criteria. The
information has been presented in the EM&A Manual.
14.12.1
The existing environmental conditions have been
identified through onsite survey, literature review. The environmental impacts
on air quality (dust & odour), noise, water quality, terrestrial and marine
ecology, fisheries, waste, landscape and visual and built heritage induced
during construction and operational phases of this Project were identified,
assessed and evaluated in this EIA Report. Major construction impact will be elevation
in suspended solids during dredging works and noise from pipe laying work along
the narrow alley between residences. However, dredging works will be confined
within cofferdam. Noise impacts are usually short term and no noise exceedance
is expected with proper implementation of mitigation measures. A number of
measures are proposed to avoid emergency discharge of raw sewage in case the
sewage treatment plant fails to operate.
14.12.2
In order to alleviate any identified environmental
impacts, detailed EM&A requirements have been formulated based on the
assessment results. Monitoring works during construction and operational phases
are proposed if the assessment results conclude that significant impact is
anticipated or the receivers should be protected.
14.12.3
Given the scale project scale and beneficial nature
of this Project, the overall environmental impact is considered acceptable.