This Section presents an
evaluation of the potential water quality impacts from the decommissioning and construction
of the Project, and the results were assessed with reference to the relevant
environmental legislation, standards and criteria. As there is no cooling water discharge
associated with the operation of the Project, water quality issues during the
operation phase are not expected.
Evaluation of the potential water quality impacts during operation phase
is not required in the EIA Study Brief.
The following legislation and relevant guidance or
non-statutory guidelines are applicable to the evaluation of water quality
impacts associated with the decommissioning
and construction
of the Project:
§ Water
Pollution Control Ordinance (WPCO);
§ Technical
Memorandum for Effluents Discharged into Drainage and Sewerage Systems, Inland
and Coastal Waters (TM- ICW);
§ Environmental
Impact Assessment Ordinance (EIAO) and the Technical Memorandum on EIA Process
(EIAO-TM), Annexes 6 and 14; and
§ Practice
Note for Professional Persons, Construction Site Drainage (ProPECC PN1/94).
The Water
Pollution Control Ordinance (WPCO) is the primary legislation for the
control of water pollution and water quality in Hong Kong. Under the
WPCO, Hong Kong waters are divided into 10 Water Control Zones
(WCZs). Each WCZ has a designated set of statutory Water Quality
Objectives (WQOs).
The
proposed Project is located in the Southern WCZ. The applicable WQOs for Southern WCZ are
presented in Table 5.1.
Table 5.1 Summary of Water Quality Objectives for Southern WCZ
|
|
Water
Quality Objective |
Southern
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 substances 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 contain substances which settle to form objectionable deposits. |
Whole zone |
|
B |
BACTERIA |
|
|
a) |
Annual geometric mean not to
exceed 610 cfu/100mL |
Secondary Contact Recreation
Subzone & Fish Culture Zones |
|
b) |
Annual geometric mean not to
exceed 180 cfu/100mL |
Bathing Beach Subzones |
|
C |
DISSOLVED OXYGEN |
|
|
a) |
Depth average not less than 4 mg
L-1 for 90% of samples; and Bottom value not less than 2 mg L-1
for 90% of samples. |
Marine waters excepting Fish
Culture Subzones |
|
b) |
Depth average not less than 5 mg
L-1 for 90% of samples; and Bottom value not less than 2 mg L-1
for 90% of samples. |
Fish Culture Subzones |
|
c) |
Not less than 4 mg L-1
due to waste discharge |
Inland waters of the Zone |
|
D |
pH |
|
|
a) |
To be in the range 6.5 - 8.5,
change due to waste discharge not to exceed 0.2 |
Marine waters excepting Bathing
Beach Subzones; Mui Wo (A), Mui Wo (B), Miu Wo (C), Mui Wo (E) and Mui Wo (F)
Subzones. |
|
b) |
To be in the range 6.0 - 9.0 |
Mui Wo (D) Sub-zone and other
inland waters. |
|
c) |
To be in the range 6.0 - 9.0 for
95% of samples; change due to waste discharge not to exceed 0.5 |
Bathing Beach Subzones |
|
E |
TEMPERATURE |
|
|
|
Change due to waste discharge
not to exceed 2°C |
Whole zone |
|
F |
SALINITY |
|
|
|
Change due to waste discharge
not to exceed 10% of natural ambient level |
Whole zone |
|
G |
SUSPENDED SOLIDS |
|
|
a) |
Waste discharge not to raise the
natural ambient level by 30% nor cause the accumulation of suspended solids
which may adversely affect aquatic communities |
Marine waters |
|
b) |
Waste discharges not to cause
the annual median to exceed 20 mg L-1. |
Mui Wo (A), Mui Wo (B), Mui Wo
(C), Mui Wo (E) and Mui Wo (F) Subzones. |
|
c) |
Waste discharges not to cause
the annual median to exceed 25 mg L-1. |
Mui Wo (D) Sub-zone and other
inland waters. |
|
H |
UNIONISED AMMONIA |
|
|
|
Annual mean not to exceed
0.021 mg L-1 |
Whole zone |
|
I |
NUTRIENTS |
|
|
a) |
Nutrients not to cause excessive
or nuisance growth of algae or other aquatic plants. |
Marine waters |
|
b) |
Annual mean depth-averaged total
inorganic nitrogen not to exceed 0.1 mg L-1 |
Marine waters |
|
J |
5-DAY BIOCHEMICAL OXYGEN DEMAND |
|
|
a) |
Waste discharges not to cause to
exceed 5 mg L-1. |
Inland waters of the zone |
|
K |
CHEMICAL OXYGEN DEMAND |
|
|
|
Waste discharges not to cause to
exceed 30 mg L-1. |
Inland waters of the zone |
|
L |
TOXIC SUBSTANCES |
|
|
a) |
Not to be present at levels
producing significant toxic effect |
Whole zone |
|
b) |
Not to cause a risk to any
beneficial uses of the aquatic environment. |
Whole zone |
The TM-ICW defines acceptable
discharge limits to different types of receiving waters. Under
the TM-ICW, effluents discharged into the drainage and sewerage
systems, inshore and coastal waters of the WCZs are subject to pollutant
concentration standards for specified discharge volumes. These are defined by
the Environmental Protection Department (EPD) and are specified in licence
conditions for any new discharge within a WCZ.
Annexes 6 and
14 of
the EIAO-TM provide general guidelines and criteria to be used
in assessing water quality impacts.
The EIAO-TM recognises
that, in the application of the above water quality criteria, it may not be
possible to achieve the WQO at the point of discharge as there are areas which
are subjected to greater impacts (which are termed by the EPD as the mixing
zones), where the initial dilution of the discharge takes place. The
definition of this area is determined on a case-by-case basis. In
general, the criteria for acceptance of the mixing zones are that it must not
impair the integrity of the water body as a whole and must not damage the
ecosystem.
Apart from
the above statutory requirements, the Practice Note for Professional
Persons, Construction Site Drainage (ProPECC PN 1/94), issued by EPD in
1994, also provide useful guidelines on the prevention of water pollution
associated with construction activities.
In
accordance with Clause 3.4.5.2 of the EIA Study Brief, the Assessment
Area for the water quality impact assessment covers the Southern WCZ under
the WPCO (Figure 5.1). Considering the nature and extent of potential
impacts, water sensitive receivers (WSRs) within and in the vicinity of the
Assessment Area were identified.
Baseline marine water quality of the Assessment Area has been determined
through a review of EPD routine water quality monitoring data collected between
1986 and 2019. This dataset provides
Hong Kong’s most comprehensive long-term water quality monitoring data and
allows an indication of temporal and spatial change in marine water quality in
Hong Kong. Water quality monitoring data
from EPD monitoring stations which are located within or close to the Assessment
Area were used to provide the baseline water quality conditions of the Assessment
Area. The monitoring results from 1986
to 2019 at the selected monitoring stations are summarised in Table
5.2. Locations of these stations
are presented in Figure 5.1.
Table 5.2 Summary of EPD Routine Water Quality
Monitoring Data from Selected Stations of the Southern WCZ in 1986-2019
|
Parameter |
SM5 |
SM6 |
SM7 |
|
|
Temperature (°C) |
23.6 |
23.3 |
23.5 |
|
|
|
(14.2-29.6) |
(14.0-29.4) |
(14.2-29.8) |
|
|
Salinity (psu) |
31.2 |
31.4 |
30.7 |
|
|
|
(18.8-34.3) |
(22.9-34.3) |
(20.0-34.4) |
|
|
Dissolved Oxygen (mg L-1) - Depth Average |
6.7 |
6.6 |
6.5 |
|
|
|
(4.1-11.7) |
(3.5-10.4) |
(3.4-10.9) |
|
|
Dissolved Oxygen (mg L-1) - Bottom |
6.3 |
5.9 |
6.2 |
|
|
|
(2.0-10.4) |
(0.3-9.6) |
(2.2-11.1) |
|
|
Dissolved Oxygen (% saturation) |
95 |
92 |
91 |
|
|
|
(57-171) |
(50-132) |
(49-157) |
|
|
Dissolved Oxygen (% saturation) - Bottom |
88 |
83 |
86 |
|
|
|
(29-148) |
(4-120) |
(31-166) |
|
|
pH |
8.1 |
8.1 |
8.1 |
|
|
|
(7.6-8.9) |
(7.6-8.9) |
(7.6-8.7) |
|
|
Secchi Disc Depth (M) |
2.3 |
2.4 |
2.2 |
|
|
|
(0.5-6.0) |
(0.5-10.0) |
(0.5-6.0) |
|
|
Turbidity (NTU) |
6.7 |
6.7 |
7.2 |
|
|
|
(0.4-88.8) |
(0.2-32.2) |
(0.4-40.4) |
|
|
Suspended Solids (mg L-1) |
5.9 |
5.7 |
6.8 |
|
|
|
(0.8-23.7) |
(0.8-33.7) |
(0.9-45.3) |
|
|
5-day Biochemical Oxygen Demand (mg L-1) |
0.9 |
0.9 |
1.0 |
|
|
|
(0.1-3.5) |
(0.1-3.7) |
(0.1-4.5) |
|
|
Ammonia Nitrogen (mg/L) |
0.035 |
0.039 |
0.068 |
|
|
|
(0.01-0.18) |
(0.01-0.21) |
(0.01-0.24) |
|
|
Unionised Ammonia (mg/L) |
0.002 |
0.002 |
0.003 |
|
|
|
(0.001-0.018) |
(0.001-0.025) |
(0.001-0.016) |
|
|
Nitrite Nitrogen (mg/L) |
0.023 |
0.024 |
0.034 |
|
|
|
(0.002-0.183) |
(0.002-0.173) |
(0.002-0.207) |
|
|
Nitrate Nitrogen (mg/L) |
0.102 |
0.107 |
0.151 |
|
|
|
(0.003-0.717) |
(0.002-0.628) |
(0.003-0.790) |
|
|
Total Inorganic Nitrogen (mg L-1) |
0.16 |
0.17 |
0.25 |
|
|
|
(0.02-0.95) |
(0.01-0.87) |
(0.01-1.17) |
|
|
Total Kjeldahl Nitrogen (mg/L) |
0.25 |
0.26 |
0.30 |
|
|
|
(0.07-1.30) |
(0.06-1.04) |
(0.09-1.13) |
|
|
Total Nitrogen (mg/L) |
0.37 |
0.39 |
0.48 |
|
|
|
(0.09-1.36) |
(0.10-1.16) |
(0.11-1.34) |
|
|
Orthophosphate Phosphorus (mg L-1) |
0.012 |
0.013 |
0.017 |
|
|
|
(0.003-0.102) |
(0.002-0.047) |
(0.002-0.040) |
|
|
Total Phosphorus (mg L-1) |
0.04 |
0.04 |
0.05 |
|
|
|
(0.02-0.23) |
(0.02-0.23) |
(0.02-0.25) |
|
|
Silica (mg/L) |
0.84 |
0.90 |
1.05 |
|
|
|
(0.08-4.13) |
(0.08-3.76) |
(0.07-3.77) |
|
|
Chlorophyll-a (μg/L) |
4.4 |
4.2 |
5.2 |
|
|
|
(0.3-36.3) |
(0.3-37.3) |
(0.3-31.7) |
|
|
E. coli (cfu/100mL) |
2 |
3 |
13 |
|
|
|
(1-790) |
(1-267) |
(1-2887) |
|
|
Faecal Coliforms (cfu/100mL) |
4 |
5 |
21 |
|
|
|
(1-1667) |
(1-597) |
(1-6102) |
|
|
Notes: (a) Data
presented are depth-averaged values calculated by taking the means of three
depths, i.e. surface (S), mid-depth (M) and bottom (B), except as specified. (b) Data
presented are annual arithmetic means except for E. coli, which are geometric means. (c) Shaded
cells indicate non-compliance with the WQOs. |
||||
Water quality near the Assessment Area is generally good except for WQO
exceedance of Total Inorganic Nitrogen (TIN), which is a result of both the
relatively high contributions from the Pearl River as well as the stringent
criterion for TIN at the Southern WCZ.
The WSRs that
may be affected by changes in water quality arising from the Project have been
identified in accordance with the EIAO-TM. For each of
the WSRs, established threshold criteria or guidelines have been utilised for
establishing the significance of impacts to water quality. Note that the only WSRs within the 500 m
Assessment Area for water quality are the seawater intakes for the Lamma Power
Station itself. The nearest bathing
beach at Hung Shing Yeh is about 1.5 km away, while the second nearest is the
Lo So Shing Beach at 2.3 km away. The
nearest marine ecological sensitive receiver is the coral identified at the
northern Hung Shing Yeh, which is about 1.4 km away.
The
locations of the identified WSRs are provided in Figure 5.1. The approximate
shortest distances by sea from the Project are detailed in Table 5.3.
Table 5.3 Water
Sensitive Receivers in the Vicinity of the Project
|
Description |
Location |
Approximate
geodesic distance from project site (km) |
|
Water Sensitive Receivers |
||
|
Gazetted Beaches |
Hung Shing Yeh Beach |
1.5 |
|
Gazetted Beaches |
Lo So Shing Beach |
2.3 |
|
Seawater Intakes |
Lamma Power
Station Intake (North) |
0.3 |
|
Seawater Intakes |
Lamma Power
Station Intake (South) |
0.4 |
|
Marine Ecological Sensitive Receivers |
||
|
Corals |
Northern Hung
Shing Yeh |
1.4 |
Other sensitive receivers within
Southern Water Control Zone beyond the 500 m Assessment Area are considered too
far away to be affected by the Project.
They are therefore not considered in this assessment.
Potential
sources of impacts to water quality arising from the Project may occur during
both the decommissioning/ demolition and construction phases. Each is discussed in turn below.
The decommissioning and demolition
of existing OCGTs will not involve marine, civil or earth works. Therefore, nil or minimal exposed soil would
be expected. Minimal disturbance to
sediment is expected as well. Before the
decommissioning/ demolition, the existing OCGTs will be cleaned to remove
excessive fuel / chemical retained to minimise safety hazard as well as
potential loss to the surrounding. The
wastewater, chemical waste or effluent generated from the cleaning process
would be stored and treated and / or disposed of by licensed contractor. Before removal, such waste
would be properly stored at safe locations following the guideline of relevant Cap. 354C Waste Disposal (Chemical Waste)
(General) Regulation.
The dismantled parts of the existing OCGTs would be stored on impervious
surface and covered to avoid rainfall from carrying residual contaminants to
the surrounding. The dismantled parts
would be removed from site for disposal as soon as practicable to reduce risk
on runoff contamination.
With the implementation of the recommended
measures, no adverse water quality impact is expected from the decommissioning/
demolition phase of the Project.
No marine works, major site
formation or earth works will be required during the construction phase of the
Project. Potential sources of water
quality impact from the land-based construction works include:
§ Sewage
effluent from construction workforce;
§ Runoff
from land-based work sites;
§ Chemical cleaning during pre-commissioning activities.
The
presence of construction workforce would result in increased generation of
sewage from toilets and site kitchen.
Suitable number of chemical toilets would be provided onsite where
necessary to cater for the need of construction workforce. Chemical toilets would be regularly cleaned
and emptied to avoid any environmental nuisance. Wastewater from site kitchen and other
facilities would be properly stored and then collected for disposal by licensed
contractor. No onsite discharge from
these chemical toilets would be allowed.
Therefore, no adverse water quality impact to sensitive receivers is
anticipated.
Based on the latest available information,
the construction works involve mostly aboveground replacement of existing OCGTs
with new OCGTs, and there will be very limited civil / earth works. Civil / earth works required would be the
construction of new 132kV cable trenches, staircase and lift, as well as
reconstruction works inside GTAB which occupies very limited footprint. Also, the existing drainage system of the
LPS, with incorporated pollution removal design, would be retained. Therefore, site runoff is expected to be
controlled and no adverse water quality impact on the nearby bodies of water is
expected.
Chemicals will be used in the construction of
the new OCGTs which carry risk of spillage.
These chemicals are also currently used within the LPS and also used by
the existing OCGTs for maintenance.
There would be no significant change in the usage and associated risk
levels for use in the new OCGTs. Appropriate
clean up kits would be provided onsite to facilitate any required clean up
action in case of any spillage. Also,
existing spill control arrangement and response plan in the LPS would be
implemented during the construction phase of this Project. In view of routine use of chemicals with
existing control measures, the above are considered sufficient to control any
potential spillage of chemicals onsite during construction phase. No adverse water quality impact from spillage
of storage chemicals is expected.
Wastewater,
chemical waste and effluent from cleaning of the existing OCGTs would be
collected, stored for proper disposal by licensed contractor. Dismantled parts of the existing OCGTs would
be removed from the site as soon as practicable. Before their removal, these parts would be
placed at impervious surface and be protected from rain.
Standard
site practices outlined in ProPECC PN
1/94 “Construction Site Drainage”
will be followed as far as practicable in order to reduce surface runoff, and
also to retain and reduce any SS prior to discharge. These practices include the following:
§ Silt
removal facilities such as silt traps or sedimentation facilities will be
provided where necessary to remove silt particles from runoff to meet the
requirements of the TM standard under the WPCO. The design of silt removal facilities will be
based on the guidelines provided in ProPECC
PN 1/94. All drainage facilities and
erosion and sediment control structures will be inspected on a regular basis
and maintained to confirm proper and efficient operation at all times and
particularly during rainstorms.
Deposited silt and grit will be removed regularly.
§ Appropriate
surface drainage will be designed and provided where necessary.
§ The
precautions to be taken at any time of year when rainstorms are likely together
with the actions to 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.
§ Oil
interceptors will be provided in the drainage system where necessary and
regularly emptied to prevent the release of oil and grease into the storm water
drainage system after accidental spillages.
§ Temporary
and permanent drainage pipes and culverts provided to facilitate runoff
discharge, if any, will be adequately designed for the controlled release of
storm flows.
§ The
temporary diverted drainage, if any, will be reinstated to the original
condition when the construction work has finished or when the temporary
diversion is no longer required.
§ Appropriate
numbers of chemical toilets shall be provided by a licensed contractor where
necessary to serve the construction workers over the construction site to
prevent direct disposal of sewage into the water environment.
The construction of the Hong Kong Offshore LNG
Terminal is currently in progress and the associated land-based works at the
Lamma Power Station Extension (LMX) may coincide with the decommissioning/
demolition and construction works of the Project. In addition, the construction of the proposed
L12 and L13 at LMX may also take place during the decommissioning/ demolition
and construction phases of the Project. These
land-based construction works at LMX are relatively minor and would require limited
excavation only, with site runoff expected to be relatively low and well
controlled. No other land-based
construction works in the vicinity of the Project are expected during the
decommissioning/ demolition and construction phases of the Project. Adverse cumulative water quality impact is
not anticipated during the decommissioning/ demolition and construction phases
of the Project.
No adverse residual water quality impact is anticipated from the decommissioning/
demolition and construction of the Project.
No adverse
water quality impact is anticipated during the decommissioning/ demolition and
construction phases of the Project with appropriate mitigation measures in
place. However, it is recommended to
conduct regular environmental site inspections during the decommissioning/
demolition and construction phases to ensure that mitigation measures as
recommended in Section 5.5 are properly implemented.
The
only nearby WSRs identified within the 500 m Assessment Area are seawater
intakes of the LPS itself. Limited water
quality impact is expected in view of the nature of the project and therefore
these nearby WSRs (as well as those further away) are not expected to be
impacted. Standard mitigation measures
and good site practices are however recommended as good practices. Water quality monitoring for decommissioning/
demolition and construction phases is not required.