The demolition of the CCPP has the potential to cause adverse water
quality impacts if not properly managed.
This section examines the potential impacts on the nearby water
resources due to discharge of wastewater and surface runoff during
decommissioning of the CCPP. The
impacts are evaluated through a review of the surface water management systems
during demolition processes.
The regulatory requirements and standards to protect water quality are
as follows:
·
Water Pollution
Control Ordinance (WPCO) (Cap. 358);
·
Waste Disposal
Ordinance (Cap. 354);
·
Waste Disposal (Chemical
Waste) (General) Regulation (Cap. 354C);
·
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
·
6.2.1
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 North Western WCZ. The WQOs for the North Western WCZ, which are presented in Tables
6.2a, are applicable as evaluation criteria for assessing compliance of any
effects from the discharges of the Project.
Table 6.2a Water Quality
Objectives for North Western Water Control Zone
|
Water Quality Objectives |
North Western WCZ |
|
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 |
|
|
(a) The
level of Escherichia coli should not exceed 610 per 100 ml, calculated as the
geometric mean of all samples collected in one calendar year. |
|
|
(b) The
level of Escherichia coli should be less than 1 per 100 ml, calculated as the
running median of the most recent 5 consecutive samples taken at intervals of
between 7 and 21 days. |
Tuen Mun (A) and |
|
(c) The
level of Escherichia coli should not exceed 1000 per 100 ml, calculated as
the running median of the most recent 5 consecutive samples taken at
intervals of between 7 and 21 days. |
Tuen Mun (C) Subzone and other inland waters |
|
(d)
The level of Escherichia coli should not exceed 180 per 100 ml,
calculated as the geometric mean of all samples collected from March to
October inclusive. Samples should be taken at least 3 times in one calendar
month at intervals of between 3 and 14 days. |
Bathing Beach Subzones |
|
C. COLOUR |
|
|
(a)
Waste discharges
shall not cause the colour of water to exceed 30 Hazen units. |
Tuen Mun (A) and |
|
(b)
Waste discharges
shall not cause the colour of water to exceed 50 Hazen units. |
Tuen Mun (C) Subzone and other inland waters |
|
D. DISSOLVED
OXYGEN |
|
|
(a) Waste
discharges shall not cause the level of dissolved oxygen to fall below 4 mg per
litre 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 dissolved oxygen should not be less than 2 mg
per litre 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 dissolved oxygen to be less than 4 mg
per litre. |
Tuen Mun (A), Tuen Mun (B) and |
|
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 excepting Bathing Beach Subzones |
|
(b) Waste
discharges shall not cause the pH of the water to exceed the range of 6.5-8.5
units |
Tuen Mun (A), Tuen Mun (B) and |
|
(c) The
pH of the water should be within the range of 6.0-9.0 units. |
Other inland waters |
|
(d) The
pH of the water should be within the range of 6.0-9.0 units for 95% of samples
collected during the whole year. In addition, waste discharges shall not
cause the natural pH range to be extended by more than 0.5 unit. |
Bathing Beach Subzones |
|
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 |
|
|
(a) Waste discharges
shall neither cause the natural ambient level to be raised by 30% nor give
rise to accumulation of suspended solids which may adversely affect aquatic
communities. |
Marine
waters |
|
(b) Waste discharges
shall not cause the annual median of suspended solids to exceed 20 mg L-1. |
Tuen Mun
(A), Tuen Mun (B) and |
|
(b) Waste
discharges shall not cause the annual median of suspended solids to exceed 25
mg L-1. |
Other
inland waters |
|
I. AMMONIA |
|
|
The
ammonia nitrogen level should not be more than 0.021 mg L-1,
calculated as the annual average (arithmetic mean), as unionized form. |
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 0.3 mg per
litre, 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).below
surface, mid-depth and 1 m above seabed). |
|
|
(c) Without limiting the generality of
objective (a) above, the level of inorganic nitrogen should not exceed 0.5 mg
per litre, 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 excepting |
|
K. 5-DAY BIOCHEMICAL OXYGEN DEMAND |
|
|
(a) Waste discharges shall not cause the 5-day
biochemical oxygen demand to exceed 3 mg L-1. |
Tuen Mun (A), Tuen Mun (B) and |
|
(b) Waste discharges shall not cause the
5-day biochemical oxygen demand to exceed 5 mg L-1. |
Other inland waters |
|
L. CHEMICAL OXYGEN DEMAND |
|
|
(a) Waste discharges shall not cause the
chemical oxygen demand to exceed 15 mg per litre. |
Tuen Mun (A), Tuen Mun (B) and |
|
(b) Waste discharges shall not cause the
chemical oxygen demand to exceed 30 mg per litre. |
Other inland waters |
|
M. TOXINS |
|
|
(a) Waste discharges shall not cause the
toxins 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 toxicant interactions with each
other. |
Whole Zone |
|
(b) Waste discharges shall not cause a risk
to any beneficial use of the aquatic environment. |
Whole Zone |
|
N. PHENOLS |
|
|
Phenols shall not be present in such quantities
as to produce a specific odour, or in concentration greater than 0.05 mg per
litre as C6H5OH |
Bathing Beach Subzones |
|
O. TURBIDITY |
|
|
Waste discharges shall not reduce light
transmission substantially from the normal level. |
Bathing Beach Subzones |
6.2.2
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 Technical
Memorandum for Effluents Discharged into Drainage and Sewerage Systems, Inland
and Inshore Waters (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. Any sewage from the
proposed construction and operational activities should comply with the
standards for effluent discharged into the foul sewers or inshore waters of the
North Western WCZs, shown in Tables 1 and 10a of the TM, respectively.
6.2.3
Environmental Impact Assessment Ordinance
(Cap. 499. S.16), Technical Memorandum on Environmental Impact Assessment
Process (EIAO-TM)
Annexes 6 and 14 of
the Environmental Impact Assessment
Ordinance (Cap. 499. S.16), Technical Memorandum on Environmental Impact
Assessment Process (EIAO-TM)
provide general guidelines and criteria to be used in assessing
water quality issues.
6.2.4
Practice Note for Professional Persons on
Construction Site Drainage (ProPECC PN 1/94)
The ProPECC PN 1/94 issued by
the EPD provides some basic environmental guidelines for the handling and
disposal of construction site discharges to prevent or minimise construction
impacts on water quality.
Whilst the technical
circulars are non-statutory, they are generally accepted as best guidelines in
6.2.5
Chapter 9 of the Hong Kong Planning Standards and Guidelines (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.
6.2.6
WPCO Discharge Licence of GICP
The WPCO discharge licence was
issued to GICP in order to restrict the quality and quantity of the effluent of
the on-site Wastewater Treatment Plant (WWTP) discharged into the public sewer
or North Western WCZ. Any discharge from the
GICP to public foul sewer or North Western WCZ should comply with the discharge licence criteria.
6.3
Water Quality
Sensitive Receivers and Baseline
Conditions
6.3.1
Existing Conditions
The GICP has its own on-site WWTP. The existing treatment works adopted the
aerobic digestion treatment process for the treatment of all wastewater
generated from the site including wastewater from the cement production. The design capacity of the WWTP is 76 m3
d-1. The current flow to
the WWTP is about 50 m3 d-1.
The GICP is located at the seafront of Tap
Shek Kok near the
Table 6.3a Summary
of Water Quality Statistics for North
|
Parameter |
EPD Monitoring Stations (a) |
|
|
Pillar Point (NM3) |
|
|
|
Temperature (oC) |
23.2 (17.3-28.2) |
23.4 (17.3-28.3) |
|
Salinity (ppt) |
30.1 (24.9-33.1) |
28.6 (23.0-33.0) |
|
Dissolved Oxygen (Surface
to 2m above Bottom) (mg L-1) |
5.8 (3.2-9.6) |
5.7 (3.0-9.3) |
|
Dissolved Oxygen (Bottom)
(mg L-1) |
5.5 (2.5-9.7) |
5.4 (2.1-9.2) |
|
Suspended Solids (mg L-1) |
7.4 (3.9-11.7) |
11.1 (4.3-18.7) |
|
5-Day Biochemical Oxygen
Demand (mg L-1) |
1.1 (0.5-1.5) |
1.1 (0.5-2.7) |
|
Unionised Ammonia (mg L-1) |
0.006 (0.001-0.012) |
0.008 (0.001-0.014) |
|
Total Inorganic Nitrogen
(mg L-1) |
0.47 (0.13-0.87) |
0.64 (0.22-1.06) |
|
Total Phosphorus (mg L-1) |
0.05 (0.04-0.08) |
0.06 (0.04-0.08) |
|
Chlorophyll a (µg L-1) |
5.9 (1.0-22.0) |
5.5 (1.3-23.0) |
|
E. coli (cfu 100mL-1) |
430 (45-2,400) |
590 (64-2,200) |
|
Note: (a)
Figures
in bracket represent the range of monitoring results. |
||
6.3.2
Water Sensitive Receivers
The
There are several seawater intakes located
in the vicinity of the Project Site which may be affected by the effluent
discharges associated with the Project.
The details of the identified Water Sensitive Receivers (WSRs) are summarized in Table
6.3b and their locations are shown in Figure 6.3a.
Table 6.3b Water
Sensitive Receivers
|
No. |
WSR |
Approximate Distance from
the Project Site |
|
WSR 1 |
Sha Chau & Lung Kwu Chau Marine Park |
3.2 km |
|
WSR 2 |
Non-gazetted
Lung Kwu Tan Beach |
1.8 km |
|
WSR 3 |
Non-gazetted
Lung Kwu Sheung Tan
Beach |
3.8 km |
|
WSR 4 |
Black Point Power Station Intake |
4.6 km |
|
WSR 5 |
Gazetted |
3.8 km |
|
WSR 6 |
Gazetted beaches in Tuen Mun |
> 6 km |
|
WSR 7 |
Castle Peak Power Station water intake |
500 m |
|
WSR 8 |
Shiu Wing Steel Mill water intake |
Adjacent to the Project Site |
|
WSR 9 |
Area 38 and proposed EcoPark
water intake |
150 m |
|
WSR 10 |
Tuen Mun WSD water intake |
5 km |
6.4
Potential Sources of
Water Quality Impacts
Potential sources of water quality impact associated
with the proposed demolition activities at the works areas have been identified
and include:
·
wastewater from the
cleaning process;
·
site runoff from the
Project Site; and
·
sewage effluent produced by
on-site workforce.
6.5
Water Quality
Impacts Assessment
6.5.1
Wastewater from
Cleaning Processes
The cleaning works will be carried out inside the
cleaning workshop of the MRRF building.
During the cleaning process, wet wiping and vacuum cleaning will be used
to clean the internal lining of the ducting/equipment and remove the loose dust
particles deposited on the surface of the ducts and equipment. Water flushing will not be used to clean
the plant and equipment of the Co-Combustion unit and hence the wastewater
generated from the cleaning works will be minimal.
If necessary, water will be sprayed at the concrete
breaking area to control dust.
Negligible runoff will be generated from this process.
Disposable
protective clothing will be used for the personnel who works inside the
cleaning workshop and the used clothing will be disposed of at the end of each
working day.
All the demolition and cleaning process will be
conducted within the Project Site area which is about 240m from the waterfront
of the GICP site. Prior to the
commencement of the demolition and cleaning works, temporary drainage
channels, earth bunds or sand bag barriers will be constructed or placed to
delineate clean area and potential contaminated area within the Project Site
and to divert the wastewater or contaminated runoff generated from the Project
Site area to the existing underground wastewater storage tank of the MRRF and
clean surface runoff to the existing surface water drainage system of the GICP.
With respect to the nature of the works, the wastewater generated from
the demolition works will mainly be inorganic (eg
suspended solids). The wastewater
will then be pumped to the on-site WWTP for treatment. Currently the on-site WWTP has a free
capacity of about 26 m3 d-1. As the anticipated additional flow
of wastewater generated from the demolition works will be limited (less than 2
m3 d-1) and GIC’s process
engineers have confirmed that the treatment of this small additional load will
not have adverse impact on the performance of the WWTP and the effluent
quality. No wastewater will be discharged directly into the adjacent marine
water or any other water bodies in the vicinity of the Project Site. It is therefore expected that the
demolition of the CCPP will not cause adverse water quality impact.
6.5.2
Demolition Site
Runoff and Drainage
During demolition
activities, site run-off may cause pollution if they enter the marine
waters. Pollutant such as residual
ashes and chemicals may enter the
receiving waters if site runoff is not properly managed.
As discussed above
the clean surface runoff from the Project Site will be diverted to the existing
drainage system of the GICP which will lead to the on-site stormwater detention pond. Suspended solids will be settled out in
the pond before discharging into the stormwater
drainage. With respect to the small
scale of the demolition works, small site area, and the site is paved for most
periods of the demolition works, it is anticipated that the surface runoff will
not have a high level of suspended solids.
It will not cause adverse impacts to the performance of the existing
site stormwater detention pond. It should be noted that the total volume
of surface water runoff from the GICP has not been changed due to the CCPP.
As all surface water runoff generated from the
works area will be properly collected, treated and disposed during the
demolition processes, no unacceptable impact to water sensitive
receivers is anticipated.
6.5.3
Sewage Generated
from Workforce
Sewage will arise from the demolition workforce. It is estimated that a maximum of 14
workers will be working at the site at any one time. The amount of sewage to be generated will be about
2.1 m3 per day. The existing
toilet facility of the GICP will be available to the construction
workforce. The sewage will be
discharged to the on-site WWTP. No adverse impact water
quality is anticipated due to the treatment and disposal of sewage generated
from the workforce.
As the sewage
generated from the workforce will be properly treated and the treated effluent
will be discharged through the existing arrangement which is acceptable to the
EPD, no unacceptable water quality impacts to sensitive receivers are
predicted.
6.6
Water Quality
Mitigation Measures
The impact
assessment has indicated that the demolition works, if properly controlled,
will not cause adverse impacts to the surrounding waters and the sensitive
receivers. Hence, no addition
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 demolition activities. These measures are appropriate for
general land based demolition activities.
All effluent discharge from the demolition works will be subject to
control under the WPCO.
Site Run-off
Prior to the
demolition 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 wastewater
to existing underground wastewater storage tank of the MRRF building. The wastewater will then be pumped to the
on-site WWTP for treatment. The
design of any silt 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 site drainage into excavations. If the excavation of 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 storm 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 storm 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 run-off from bunded areas will pass through oil/grease traps prior to
discharge to the stormwater system.
Sewage from Workforce
·
The
existing toilet facility of the GICP will be available to the construction
workforce. The sewage will be
discharged to existing WWTP of the GICP.
The effluent discharge from the site will be monitored as part of the
routine monitoring under the WPCO
licence.
6.7
Residual
Environmental Impacts
With the
implementation of the recommended mitigation measures, no residual impacts are
anticipated from the demolition of the CCPP.
6.8
Environmental
Monitoring and Audit
With the
implementation of the good site practice and the proposed demolition and
cleaning procedures, no adverse water quality impact is anticipated due to the
demolition of the CCPP. All wastewater and site runoff from the
Project Site will be treated using the existing WWTP and stormwater
detention pond of the GICP and the effluent discharge from the site will be
monitored as part of the routine monitoring under the WPCO licence. No additional
environmental monitoring and audit programme is therefore required.
Monthly site
audits of the works areas will be carried out 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.
The anticipated quantities of wastewater to
be generated during the Project will be small and all wastewater will be
treated in the existing on-site WWTP.
With the implementation of general good site practices, the demolition
of CCPP will not cause adverse water quality impact.