13.1 Environmental
Designs Recommended and Environmentally Friendly Options Considered
13.2 Key Environmental Problems Avoided
13
SUMMARY OF ENVIRONMENTAL OUTCOME
13.1 Environmental Designs Recommended and Environmentally Friendly Options Considered
Environmental Enhancement Project by Nature
13.1.1
The proposed sewerage works in Po Toi O is an
environmental enhancement project by nature. Through replacement of
septic tanks/soakaway systems (STS) by a public sewerage system, hygiene and
associated odour nuisance from routine desludging will be eliminated. In
addition, the provision of sewerage is a
preventive measure to avoid potential environmental problems due to
insufficient desludging or structural defect of the STS. This can also relieve
villagers’ burden to maintain their STS (e.g. desludging).
13.1.2
Sewage will be properly collected and treated by
membrane bioreactor process (MBR) up to the effluent discharge standard of Port
Shelter Water Control Zone. Treated effluent will be discharged via a submarine
outfall at a diffuser installed at seabed in outer Po Toi O Bay, which will be
at least 326m, 185m and 100m away, respectively, from the nearest fish culture
zone, a coral-lined rocky shore and an amphioxus habitat.
Various Green Measures in the Project (Mainly
by Avoidance and Minimization of Potential Impacts)
Green Measures in Sewerage System Design
·
Minimization of loss of ecologically sensitive
habitats by locating the STP on a cut slope (disturbed shrubland) and laying gravity sewers and rising mains along
existing footpaths as far as possible from developed area;
·
Avoidance of destruction
of coral-lined rocky shore and major amphioxus habitat by locating the treated effluent discharge location over 100m away from
the coral-lined shore and species of conservation importance (amphioxus);;
·
Minimization of
fisheries impact by discharging the
treated effluent at about 326m away from the fish culture zone;
·
Maximizing effluent
dispersion by placing the diffuser
on seabed at >10m depth and at outer Po Toi O bay where current flows are
fast;
·
Minimization of the
footprint of the STP by constructing most of
the STP structure underground and adopting a less land demanding sewage
treatment technology (MBR);
·
Minimization of odour
and noise nuisance by keeping a sufficient
buffer distance between the STP and village houses;
·
Minimization of visual
impact by embedding the STP
into the existing cut slope;
·
Maintenance of visual
entity with surrounding undisturbed landscape by provision of appropriate façade treatment (e.g. adopting recessive
colours on STP wall that blend in with the natural tones of the landscape
backdrop), compensatory tree planting and vertical greening;
·
Avoidance of impact on
built heritage resources (e.g. Grade 3 historic
building Hung Sing Temple) by laying gravity sewers and rising mains over 5m
away from its footprint;
Green Measures in Construction Design
·
Avoidance of open dredging to minimize
water quality, marine ecological and fisheries impacts by adopting (1)
horizontal directional drilling for submarine outfall below seabed and (2)
enclosed dredging within a cofferdam for the diffuser;
·
Avoidance of concurrent construction activities by designing a
separate works programme for noisy works (carrying out rock breaking works for
STP prior to laying of gravity sewer and rising mains and drilling for
submarine outfall). Also, adopting three workfronts during pipe laying in
village, each of short section and at least 100m away from each other.
Green Measures in Operation Design
·
Improvement of
environmental hygiene and removal of associated odour nuisance in the Po Toi O
area by eliminating the need
of desludging STS;
·
Avoidance
of emergency discharge of raw sewage into waterbodies by a number of design features or arrangements in
case of emergency plant failure,
such as notification to the operator by a supervisory control and
data acquisition (SCADA)
system, provision of standby equipment in the STP, provision of sufficient
capacity of emergency storage of incoming sewage and provision of tankers for
continuous removal of sewage to other STP for treatment.
·
Minimization
of odour nuisance from STP by
provision of an odour removal system with
99.5% efficiency in the STP;
·
Minimization
of noise disturbance from STP by
storing noisy plant equipment underground.
13.2 Key Environmental Problems Avoided/Minimized
13.2.1 A summary of the key environmental problems avoided/minimized for each aspects in this Project is listed in Table 13-1 below:
Table 13-1 Key Environmental
Problems Avoided/Minimized
Aspects |
Key Environmental Problems
Avoided/Minimized |
Air Quality |
Benefits of Environmental Protection Measures
Recommended Construction phase -
Minimization of air quality impact (TSP, RSP and
FSP emission) by adopting dust control measures stipulated in the Air
Pollution Control (Construction Dust) Regulation (e.g. watering of exposed
grounds and proper stockpiling). Operational phase -
Minimization of air quality impact (odour) by
pointing exhaust from the deodorizer of the STP upward to allow maximum
dispersion. -
Minimization of air quality impact (odour) by
proper maintenance of deodorizer to ensure that the overall H2S
(i.e. odour source) removal efficiency of 99.5% or higher. Environmentally Sensitive Areas and Estimated
Population Protected Existing
residential village buildings, recreation area and temple in the vicinity of
the Project Site (within work boundary in Figure 1-1). Compensation Included N/A |
Noise |
Benefits of Environmental Protection Measures
Recommended Construction phase -
Avoidance of concurrent construction activities by designing separate work programme
for noisy works (carrying out rock breaking works for STP prior to laying of
gravity sewer and rising mains and drilling for submarine outfall). Also,
adopt three workfronts during pipe laying in village, each of short works
section and at least 100m away from each other. -
Minimization of noise disturbance by implementing
mitigation measures such as adoption of good site practice, use of quieter
PMEs and mobile noise barrier. Operational phase -
Minimization of noise disturbance by storing most
noisy plant equipment underground. Environmentally Sensitive Areas and Estimated
Population Protected Existing
residential village buildings in the vicinity of the Project Site. Compensation Included N/A |
Water Quality |
Benefits of Environmental Protection Measures
Recommended Construction phase -
Minimization of water quality impact by dredging
within fully enclosed cofferdam or using horizontal directional drilling
(HDD) instead of carrying out open dredging. -
Avoidance of disturbance on watercourse by
placing sand bag along work zones which are close to watercourse. Operational phase -
Minimization of water quality impact by placing
the diffuser in a deeper sea which allows better dispersion of effluent. -
Avoidance of water quality impact on Po Toi O Bay
by not discharging raw sewage into Po Toi O Bay in case of plant failure. Environmentally Sensitive Areas and Estimated
Population Protected Water bodies in
Po Toi O & Clear Water Bay, which include Po Toi O Fish Culture Zone,
coral & amphioxus habitats, Clear Water Bay First & Second Beaches,
Secondary contact recreation sub-zones, and shorelines at the Coastal
Protection Zone at Po Toi O. Compensation Included N/A |
Terrestrial
Ecology |
Benefits of Environmental Protection Measures
Recommended Construction phase -
Avoidance of disturbance on sensitive habitats
(e.g. woodland in Conservation Area) and natural habitats by locating the STP
on a man-made cut-slope. -
Avoidance/minimization of disturbance on other
habitats and protected species in the vicinity of the Project Site by
erecting hoarding around construction site and bright colour fencing around
the protected shrub Diospyros vaccinioides near the work boundary. -
Avoidance of disturbance on freshwater habitat by
placing sand bag along watercourse near work-zone. -
Minimization of impact on all disturbed habitats
(e.g. rocky shore in “Coastal Protection Area” where HDD entry pit is
located) by habitat reinstatement as far as possible after construction
works. Operational phase N/A Environmentally Sensitive Areas and Estimated
Population Protected Habitat,
vegetation and wildlife within the Study Area Compensation Included Compensatory
planting for felled trees of at least 1:1 by number in accordance
with DEVB TCW No. 7/2015, which requires future application to Lands
Department for final approval. |
Marine Ecology |
Benefits of Environmental Protection Measures
Recommended Construction phase -
Minimization of impact on species with
conservation importance (i.e. coral & Amphioxus communities) by locating the
submarine outfall further away from them. -
Minimization of impact on water quality (hence
marine ecology) by dredging within fully enclosed cofferdam or using
horizontal directional drilling (HDD) instead of carrying out open dredging. -
Avoidance of impact on intertidal habitat and the
associated fauna by designing no works area in intertidal zone. Operational phase -
Avoidance of impact on water quality (hence
marine ecology) by not discharging raw sewage into Po Toi O Bay in case of
plant failure. Environmentally Sensitive Areas and Estimated
Population Protected Habitat and
wildlife within the Study Area Compensation Included N/A |
Fisheries |
Benefits of Environmental Protection Measures
Recommended Construction phase -
Minimization of impact on Po Toi O Fish Culture
Zone by locating the submarine outfall further away from the Fish Culture
Zone. -
Minimization of impact on water quality (hence
fisheries resources) by dredging within fully enclosed cofferdam or using
horizontal directional drilling (HDD) instead of carrying out open dredging. Operational phase -
Avoidance of impact on water quality (hence
fisheries resources) by not discharging raw sewage into Po Toi O Bay in case
of plant failure. Environmentally Sensitive Areas and Estimated
Population Protected Fisheries
resources in the Study Area, e.g. Po Toi O Fish Culture Zone Compensation Included N/A |
Waste Management
and Land Contamination |
Benefits of Environmental Protection Measures
Recommended Construction phase -
Minimization of impact due to waste management by
preparing a specific waste management plan by future contractor (required for
public works under ETWB TCW No.
19/2005 Environmental Management on Construction
Sites) and adopting good site practice (e.g. avoiding over-purchase of
construction materials by careful planning). -
Minimization of environmental nuisance by storing
and delivering waste properly (e.g. in enclosed container) to designated
disposal sites. Operational phase -
Minimization of environmental nuisance by storing
and delivering waste (including sludge, worn filters and general refuse)
properly and disposing of at designated facilities (e.g. dispose of sludge to
sludge treatment facilities) by licensed contractor where applicable. Environmentally Sensitive Areas and Estimated
Population Protected Air and water
sensitive receivers near the Project Site and along transportation routes. Compensation Included N/A |
Landscape and
Visual |
Benefits of Environmental Protection Measures
Recommended Construction phase -
Minimization of impact on adjacent landscape by
minimizing temporary works areas as possible. -
Minimization of visual impact by using decorative
mesh screens, construction hoardings and/or temporary noise barriers around
works areas which are in visually unobtrusive colours as possible. Operational phase -
Reinstatement the landscape which are appropriate
to the context, by tree and shrub planting, and vertical greening. Environmentally Sensitive Areas and Estimated
Population Protected Landscape
resources, landscape character areas and visual sensitive receivers
surrounding the Project Site. Compensation Included Compensatory
planting for felled trees of at least 1:1 by number in accordance
with DEVB TCW No. 7/2015, which requires future application to Lands
Department for final approval. |
Built Heritage |
Benefits of Environmental Protection Measures
Recommended Construction phase -
Prevention of direct damage on built heritages
(see below) by machine or dirt by providing protective covering on a movable
fence. -
Prevention of indirect damage by mechanical
vibration and settlement by carrying out vibration and settlement monitoring. Operational phase N/A Environmentally Sensitive Areas and Estimated
Population Protected Hung Shing
Temple (i.e. Grade 3 historic building), historic built structures (e.g. Sir
Ho Tung Recreation Centre), & cultural landscape features (e.g. Earth God
Shrine) Compensation Included N/A |