7.1
Introduction
The modification works and
operation of the
7.2
Legislation
and Standards
The regulatory requirements
and standards to protect water quality are as follows:
·
Water Pollution Control
Ordinance (WPCO) (Cap. 358);
·
Environmental Impact Assessment
Ordinance (Cap. 499. S.16), Technical Memorandum on Environmental Impact
Assessment Process (EIAO-TM), Annexes 6 and 14;
·
Technical Memorandum
Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland
and Inshore Waters (TM);
·
Practice Note for
Professional Persons on Construction Site Drainage (Prop PECC PN 1/94); and
·
7.2.1
Water Pollution Control
Ordinance (WPCO)
The WPCO is the legislation
for the control of water pollution and water quality in
In accordance with the WPCO, the Study Area is located inside
the
Table 7.1 Water Quality Objectives for
|
Water Quality Objectives |
|
|
A. AESTHETIC APPEARANCE |
|
|
(a) Waste discharges shall cause no
objectionable odours or discolouration
of the water. |
Whole Zone |
|
(b) Tarry residues, floating wood, articles
made of glass, plastic, rubber or of any other substance should be absent. |
Whole Zone |
|
(c) Mineral oil should not be visible on the
surface. Surfactants should not give rise to lasting foam. |
Whole Zone |
|
(d) There should be no recognisable
sewage-derived debris. |
Whole Zone |
|
(e) Floating, submerged and semi-submerged objects of a size likely
to interfere with the free movement of vessels, or cause damage to vessels,
should be absent. |
Whole Zone |
|
(f) Waste discharges shall not cause the
water to Whole Zone contain substances which settle to form objectionable
deposits. |
Whole Zone |
|
B. BACTERIA |
|
|
The
level of Escherichia coli should not exceed 1000 per 100 ml, calculated as the
geometric mean of the most recent 5 consecutive samples taken at intervals of
between 7 and 21 days. |
Inland
waters |
|
C. COLOUR |
|
|
Waste
discharges shall not cause the colour of water to
exceed 50 Hazen units. |
Inland
waters |
|
D. DISSOLVED
OXYGEN (DO) |
|
|
(a) Waste
discharges shall not cause the level of DO to fall below 4 mg L-1 for 90% of the sampling
occasions during the whole year; values should be calculated as water column
average (arithmetic mean of at least 3 measurements at 1 m below surface,
mid-depth and 1 m above seabed). In addition, the concentration of DO should
not be less than 2 mg L-1
within 2 m of the seabed for 90% of the sampling occasions during the whole
year. |
Marine
waters |
|
(b) Waste
discharges shall not cause the level of DO to be less than 4 mg L-1. |
Inland
waters |
|
E. pH |
|
|
(a) The pH of the water should be within the
range of 6.5-8.5 units. In addition, waste discharges shall not cause the
natural pH range to be extended by more than 0.2 unit. |
Marine
waters |
|
(b) Waste discharges shall not cause the pH of
the water to exceed the range of 6.5-8.5 units |
Inland
waters |
|
F. TEMPERATURE |
|
|
Waste
discharges shall not cause the natural daily temperature range to change by
more than 2.0oC. |
Whole Zone |
|
G. SALINITY |
|
|
Waste
discharges shall not cause the natural ambient salinity level to change by
more than 10%. |
Whole Zone |
|
H. SUSPENDED SOLIDS (SS) |
|
|
(a) Waste discharges shall neither cause the
SS concentration to be raised by 30% nor give rise to accumulation of SS
which may adversely affect aquatic communities. |
Marine
waters |
|
(b) Waste discharges shall not cause the annual
median SS to exceed 20 mg L-1. |
Inland
waters |
|
I. AMMONIA |
|
|
The
un-ionized ammonia nitrogen level should not be more than 0.021 mg L-1,
calculated as the annual average (arithmetic mean). |
Whole Zone |
|
J. NUTRIENTS |
|
|
(a) Nutrients
shall not be present in quantities sufficient to cause excessive or nuisance
growth of algae or other aquatic plants. |
Marine waters |
|
(b) Without
limiting the generality of objective (a) above, the level of inorganic
nitrogen should not exceed 0.4 mg L-1, expressed as annual water
column average (arithmetic mean of at least 3 measurements at 1 m below
surface, mid-depth and 1 m above seabed). |
Marine waters |
|
K. 5-DAY
BIOCHEMICAL OXYGEN DEMAND (BOD5) |
|
|
Waste discharges shall not cause
the BOD5 to exceed 5 mg L-1. |
Inland
waters |
|
L. CHEMICAL
OXYGEN DEMAND (COD) |
|
|
Waste discharges shall not cause
the COD to exceed 30 mg L-1. |
Inland
waters |
|
M. TOXIC
SUBSTANCES |
|
|
(a) Waste discharges
shall not cause the toxic substances in water to attain such levels as to
produce significant toxic, carcinogenic, mutagenic or teratogenic
effects in humans, fish or any other aquatic organisms, with due regard to
biologically cumulative effects in food chains and to interactions of toxic
substances with each other. |
Whole Zone |
|
(b) Waste
discharges shall not cause a risk to any beneficial use of the aquatic
environment. |
Whole Zone |
7.2.2
Technical Memorandum for
Effluent Discharges into Drainage and Sewerage Systems, Inland and Inshore
Waters (TM)
All discharges from the
Project are required to comply with the TM issued under Section 21 of the WPCO. The
TM defines discharge limits for different
types of receiving waters. Under the TM, effluents discharged into the
drainage and sewerage systems, inshore and inshore waters of the WCZs are subject to pollutant concentration standards for
particular discharge volumes. Any
discharges within a WCZ are subject to licence
conditions and the TM acts as a
guideline for setting discharge standards for inclusion in the licence. As the
sewage arising from the proposed construction and operational activities will
be discharged to foul sewer (ie Table 1 of the TM), it should comply with the standards
for effluent discharged into the foul sewers.
The stormwater collected from the site will be
discharged to the stormwater drains and then to the
7.2.3
Environmental
Impact Assessment Ordinance (Cap. 499. S.16),
Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM)
Annexes 6 and 14 of the EIAO and the EIAO-TM provide
general guidelines and criteria to be used in assessing the potential water
quality impacts.
7.2.4
Practice Note for
Professional Persons on Construction Site Drainage (ProPECC
PN 1/94)
The ProPECC
PN 1/94 issued by the EPD provides environmental guidelines and good
practices for the handling and disposal of construction site discharges to
prevent or minimise impacts on water quality.
Whilst the technical circulars are non-statutory,
they are generally accepted as the best guidelines in
7.2.5
Chapter 9 of the HKPSG
provides guidance for including environmental considerations in the planning of
both public and private developments. It
applies both to the planning of permanent or temporary uses which will have
potential to cause significant changes to the biophysical environment or which
are sensitive to environmental impacts. Section
5 in Chapter 9 of the HKPSG provides additional information
on regulatory guidelines against water pollution for sensitive uses such as
aquaculture and fisheries zones, bathing waters and other contact recreational
waters.
7.3
Water
Quality Sensitive Receivers and Baseline Conditions
7.3.1
Existing Conditions
The marine water monitoring data of the nearest EPD
monitoring stations (see Figure 7.1) in 2008 are
summarised in Table 7.2.
Table 7.2 Summary of Water Quality Statistics for
|
Parameter |
EPD
Monitoring Stations (a) |
||
|
|
|
|
|
|
Temperature (oC) |
23.5 (16.3-27.2) |
23.5 (16.3-27.2) |
22.7 (14.8-27.8) |
|
Salinity (ppt) |
30.9 (25.7-32.7) |
30.9 (27.1-32.7) |
31.0 (26.8-33.2) |
|
DO (Surface to
2m above Bottom) (mg L-1) |
5.0 (3.0-6.2) |
5.1 (2.8-7.1) |
5.4 (3.0-7.8) |
|
DO (Bottom)
(mg L-1) |
5.0 (3.0-6.8) |
4.8 (2.5-6.6) |
5.3 (2.7-7.8) |
|
SS (mg L-1) |
5.0 (2.8-8.7) |
5.3 (2.7-7.3) |
4.6 (2.1-6.8) |
|
BOD5 (mg L-1) |
1.2 (0.3-3.5) |
0.8 (0.3-1.3) |
0.8 (0.2-1.5) |
|
Unionised Ammonia (mg L-1) |
0.007 (0.001-0.010) |
0.007 (0.002-0.011) |
0.008 (0.002-0.015) |
|
Total
Inorganic Nitrogen (mg L-1) |
0.39 (0.22-0.71) |
0.38 (0.21-0.62) |
0.40 (0.21-0.57) |
|
Total
Phosphorus (mg L-1) |
0.05 (0.04-0.09) |
0.05 (0.03-0.07) |
0.05 (0.03-0.07) |
|
Chlorophyll a
(µg L-1) |
3.9 (0.3-19.3) |
3.8 (0.5-24.0) |
1.8 (0.6-3.2) |
|
E. coli (cfu 100mL-1) |
4,200 (840-23,000) |
4,500 (990-12,000) |
5,100 (290-41,000) |
|
Note: (a)
Figures in bracket represent the range of monitoring results. |
|||
7.3.2
Water Sensitive Receivers
No inland watercourse such as river or natural stream
is identified within the Study Area. The
nearest water sensitive receivers include the existing stormwater
drain along
The details of the identified Water Sensitive
Receivers (WSRs) are summarised
in Table 7.3 and
their locations are shown in Figure 7.1.
Table 7.3 Water Sensitive Receivers
|
No. |
WSR |
Approximate Distance from
the Project Site |
|
WSR 1 |
Existing stormwater drain along |
Adjacent to the Site |
|
WSR 2 |
|
650m |
|
WSR 3 |
Seawater abstraction points
along the seafront |
650m |
7.4
Potential
Sources of Water Quality Impacts
Potential
sources of water quality impact associated with the modification activities at
the works areas have been identified and include:
·
Site runoff from the Project Site; and
·
Sewage produced by on-site workforce.
During operation phase
of the Project, the sewage generated by the staff, visitors, café and
restaurant have the potential to cause adverse water quality impacts if not
managed properly.
7.5
Water
Quality Impacts Assessment
7.5.1
Construction Phase
Site Runoff and Drainage
Runoff from the construction works areas during
demolition and foundation activities may contain increased loads of sediments,
other suspended solids and potentially contaminants. Potential sources of pollution include:
·
runoff and erosion from exposed soil
surfaces, earth working areas and stockpiles;
·
release of grouting and cement materials with
rain wash;
·
wash water from dust suppression sprays; and
·
accidental
discharge of fuel and lubricants from maintenance of construction vehicles and
mechanical equipment.
Sediment laden runoff may carry pollutants (adsorbed
onto the particle surfaces) into the nearby stormwater
drainage system. Associated effects
which may arise include increased suspended solids concentrations in receiving
waters and blockage of stormwater drains.
Mitigation measures should be implemented to control
construction site runoff and drainage from the works areas, and to prevent
runoff and drainage water with high levels of suspended solids from entering
the identified WSRs.
Most of the modification works will be carried out within the existing
buildings, and the foundation works for the new buildings are related small
scale and will last for a few months.
New building works will not increase the suspended solids concentration
significantly. With the implementation
of adequate construction site drainage and provision of sediment removal
facilities as described in Section 6.6.1, it is anticipated that no
unacceptable water quality impacts on the identified WSRs
would arise.
General Construction Activities
The following on-site construction activities may
cause water pollution:
·
uncontrolled discharge of debris and rubbish
such as packaging, construction materials and refuse; and
·
spillages
of liquids stored on-site, such as oil, diesel and solvents, which will result
in water quality impacts if they enter the nearby stormwater
drainage channels.
As detailed in Section 7.6, good construction and site
management practices will be implemented to ensure that litter, fuels and
solvents do not enter the surrounding stormwater
drains.
Sewage Generated from Workforce
Sewage will arise from the
construction workforce. It is estimated
that a maximum of 200 workers will be working at the site at any one time. The amount of sewage to be generated will be
about 30 m3 per day. The
existing toilet facilities of the CPS will be available to the construction
workforce. The sewage will be discharged
to the public sewer. With respect to the
small volume of sewage to be discharged to the sewer (much lower comparing with
the previous workforce of the CPS (Police Headquarters, prisons, etc)), the
discharge will not cause adverse sewerage impacts. No adverse impact water quality is
anticipated due to the treatment and disposal of sewage generated from the
workforce.
7.5.2
Operation Phase
Sewage from Staff, Visitors, Café and Restaurant Sewage will arise from the
dinning areas, operation staff and visitors of the
7.6
Water
Quality Mitigation Measures
7.6.1
Construction Phase
The impact assessment has indicated that the
modification works, if properly controlled, will not cause adverse impacts to
the existing drainage and sewerage systems.
Hence, no additional mitigation measures are required.
Appropriate on-site measures are defined to reduce
potential impacts, which will be sufficient to prevent adverse impacts to water
quality from the construction, demolition and renovation activities. All effluent discharge from the works will be
subject to control under the WPCO.
Site Runoff
Prior to the modification works, perimeter cut-off drains
to direct off-site water around the site will be constructed and internal
drainage works and erosion and sedimentation control facilities
implemented. Channels, earth bunds or
sand bag barriers will be provided on site to direct potential contaminated
runoff to the on-site slit trap before discharged to the stormwater
drains. The design of any slit removal
facilities will be based on the guidelines in Appendix A1 of ProPECC PN 1/94.
·
All drainage facilities and erosion and
sediment control structures will be regularly inspected and maintained to
ensure proper and efficient operation at all times and particularly following
rainstorms. Deposited silt and grit will
be removed regularly and disposed of.
·
Measures will be taken to reduce the ingress
of stormwater into excavation areas. If the excavation of the concrete foundation
is to be carried out in wet season, they will be dug and backfilled in short
sections wherever practicable. Water
pumped out from trenches or foundation excavations will be discharged into stormwater drains via silt removal facilities.
·
Open stockpiles of excavated and demolition
materials will be covered with tarpaulin or similar fabric during
rainstorms. Measures will be taken to
prevent the washing away of residues, chemicals or debris into any drainage
system.
·
Manholes (including newly constructed ones)
will always be adequately covered and temporarily sealed so as to prevent silt,
construction materials or debris being washed into the drainage system.
·
Precautions will be taken when a rainstorm is
imminent or forecasted, and actions to be taken during or after rainstorms are summarised in Appendix A2 of ProPECC
PN 1/94. Particular attention will
be paid to the control of silty surface runoff during
storm events.
·
All temporary and permanent drainage pipes
and culverts provided to facilitate runoff discharge will be adequately
designed for the controlled release of stormwater
flows. All sediment traps will be
regularly cleaned and maintained. The
temporary diverted drainage will be reinstated to the original condition when
the construction work has finished or the temporary diversion is no longer
required.
Wastewater from Site Facilities
·
Vehicle and plant servicing areas, vehicle
washing bays and lubrication bays will, as far as possible, be located within
roofed areas. The drainage in these
covered areas will be connected to foul sewers via a petrol interceptor.
·
Oil leakage or spillage will be contained and
cleaned up immediately. Waste oil will be collected and stored for recycling or
disposal, in accordance with the Waste Disposal Ordinance.
Storage and Handling of Oil, Other Petroleum Products
and Chemicals
·
Waste streams classifiable as chemical wastes
will be properly stored, collected and treated for compliance with Waste Disposal
Ordinance or Waste Disposal (Chemical Waste) (General) Regulation
requirements.
·
All fuel tanks and chemical storage areas
will be provided with locks and be sited on paved areas.
·
The storage areas will be surrounded by bunds
with a capacity equal to 110% of the storage capacity of the largest tank to
prevent spilled oil, fuel and chemicals from reaching the receiving waters.
·
The Contractors will prepare guidelines and
procedures for immediate clean-up actions following any spillages of oil, fuel
or chemicals.
·
Surface runoff from bunded
areas will pass through oil/grease traps prior to discharge to the stormwater system.
The stomwater discharge from the site will be
monitored as part of the routine monitoring under the WPCO licence, if applicable.
Sewage from Workforce
The existing toilet
facilities of the
7.6.2
Operation Phase
As no adverse water quality impacts
are identified during the operation of the
7.7
Residual
Environmental Impacts
With the implementation of the recommended mitigation
measures, no residual impacts are anticipated from the modification works and
operation of the
7.8
Environmental
Monitoring and Audit
With the implementation of the good site practice, no
adverse water quality impact is anticipated during the construction and operation
of the Project.
7.8.1
Construction Phase
Monthly site audits of the
works areas will be carried out during the construction phase to monitor the
environmental performance of the Project and to enable prompt actions to
rectify any malpractice which may give rise to water pollution problem.
7.8.2
Operation Phase
No environmental and monitoring works will be required
for the operation of the
The
anticipated quantities of wastewater to be generated during the Project will be
small. With the implementation of
general good site practices, the construction and operation of the Project will
not cause adverse water quality impact.