5
Water Quality
5.1.1 This
section presents the assessment on the potential water quality impacts
associated with the construction and operation of the Project. The water quality impact assessment
has been conducted in accordance with the requirement in Annexes 6 and 14 of
the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM)
and the requirements in Section 3.4.5 and Appendix D of the EIA Study Brief
(ESB-363/2023).
Environmental Impact
Assessment Ordinance (EIAO)
5.2.1
The EIAO-TM was issued by Environmental
Protection Department (EPD) under Section 16 of the EIAO. The EIAO-TM specifies criteria and
assessment methodologies that are to be followed in an EIA Study. Sections relevant to water quality
impact assessment include:
·
Annex 6 - Criteria for
Evaluating Water Pollution; and
·
Annex 14 - Guidelines for
Assessment of Water Pollution.
Water Quality Objectives
5.2.2
Water Pollution Control Ordinance (WPCO)
(Cap. 358) provides the major statutory framework for the protection and
control of water quality in Hong Kong.
According to the Ordinance and its subsidiary legislation, Hong Kong
waters are divided into ten Water Control Zones (WCZs). Corresponding statements of Water
Quality Objectives (WQOs) are stipulated for different water regimes (marine
waters, inland waters, bathing beaches subzones, secondary contact recreation
subzones and fish culture subzones) in each WCZ based on their beneficial uses. The Project Site is located within the
Deep Bay WCZ and the respective WQOs are shown in Table 5.1.
Table 5.1 Summary
of Water Quality Objectives for Deep Bay WCZ
|
Parameters
|
Criteria
|
Subzone
|
|
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.
|
|
|
|
(c)
Mineral
oil should not be visible on the surface. Surfactants should not give rise to
a lasting foam.
|
|
|
|
(d)
There
should be no recognisable sewage-derived debris.
|
|
|
|
(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.
|
|
|
|
(f)
Waste
discharges shall not cause the water to contain substances which settle to
form objectionable deposits.
|
|
|
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.
|
Secondary Contact Recreation Subzone and Mariculture Subzone (L.N.
455 of 1991)
|
|
|
(b)
The
level of Escherichia coli should be zero per 100 mL, calculated as the
running median of the most recent 5 consecutive samples taken at intervals of
between 7 and 21 days.
|
Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus
Subzone, Ganges Subzone and Water Gathering Ground Subzones
|
|
|
(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.
|
Yuen Long & Kam Tin (Lower) 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 in
one calendar year. Samples should
be taken at least 3 times in a calendar month at intervals of between 3 and
14 days.
|
Yung Long Bathing Beach Subzone (L.N. 455 of 1991)
|
|
Dissolved Oxygen (DO)
|
(a)
Waste
discharges shall not cause the level of dissolved oxygen to fall below 4 mg/L
for 90% of the sampling occasions during the year; values should be taken at
1 metre below surface.
|
Inner Marine Subzone excepting Mariculture Subzone
|
|
|
(b)
Waste
discharges shall not cause the level of dissolved oxygen to fall below 4
milligrams per litre for 90% of the sampling occasions during the year;
values should be calculated as water column average (arithmetic mean of at
least 2 measurements at 1 metre below surface and 1 metre above seabed). In addition, the concentration of
dissolved oxygen should not be less than 2 milligrams per litre within 2
metres of the seabed for 90% of the sampling occasions during the year.
|
Outer Marine Subzone excepting Mariculture Subzone
|
|
|
(c)
The
dissolved oxygen level should not be less than 5 mg/L for 90% of the sampling
occasions during the year; values should be taken at 1 metre below surface.
|
Mariculture Subzone
|
|
|
(d)
Waste
discharges shall not cause the level of dissolved oxygen to be less than 4
mg/L.
|
Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone,
Indus Subzone, Ganges Subzone, Water Gathering Ground Subzones and other
inland waters of the Zone
|
|
Colour
|
(a)
Waste
discharges should not cause the colour of water to exceed 30 Hazen units.
|
Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus
Subzone, Ganges Subzone and Water Gathering Ground Subzones
|
|
(b)
Waste
discharges should not cause the colour of water to exceed 50 Hazen units.
|
Yuen Long & Kam Tin (Lower) Subzone and other inland waters
|
|
Temperature
|
Waste discharges shall not cause the natural daily temperature
range to change by more than 2.0°C
|
Whole Zone
|
|
Salinity
|
Waste discharges shall not cause the natural ambient salinity level
to change by more than 10%.
|
Whole Zone
|
|
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 units.
|
Marine waters excepting Yung Long Bathing Beach Subzone
|
|
|
(b)
Waste
discharges shall not cause the pH of the water to exceed the range of 6.5–8.5
units.
|
Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone,
Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones
|
|
|
(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. In addition, waste discharges shall not cause the natural pH range
to be extended by more than 0.5 units.
|
Yung Long Bathing Beach Subzone
|
|
Suspended Solids (SS)
|
(a)
Waste
discharges shall neither cause the natural ambient SS level 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 of SS to exceed 20 mg/L.
|
Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone,
Ganges Subzone, Indus Subzone, Water Gathering Ground Subzones and other
inland waters
|
|
Ammonia
|
The un-ionized ammoniacal nitrogen level should not be more than
0.021 mg/L, calculated as the annual average (arithmetic mean).
|
Whole Zone
|
|
Nutrients
|
(a)
Nutrients
shall not be present in quantities sufficient to cause excessive or nuisance
growth of algae or other aquatic plants.
|
Inner and Outer Marine Subzones
|
|
|
(b)
Without
limiting the generality of objective (a) above, the level of inorganic
nitrogen should not exceed 0.7 mg/L, expressed as annual mean.
|
Inner Marine Subzones
|
|
|
(c)
Without
limiting the generality of objective (a) above, the level of inorganic
nitrogen should not exceed 0.5 mg/L, expressed as annual water column average
(arithmetic mean of at least 2 measurements at 1 m below surface and 1 m
above seabed).
|
Outer Marine Subzones
|
|
5-Day Biochemical
Oxygen Demand (BOD5)
|
(a)
Waste
discharges shall not cause the 5-day biochemical oxygen demand to exceed 3
mg/L.
|
Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone,
Ganges Subzone and Water Gathering Ground Subzones
|
|
|
(b)
Waste
discharges shall not cause the 5-day biochemical oxygen demand to exceed 5
mg/L.
|
Yuen Long & Kam Tin (Lower) Subzone and other inland waters
|
|
Chemical Oxygen Demand
(COD)
|
(a)
Waste
discharges shall not cause the chemical oxygen demand to exceed 15 mg/L.
|
Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus
Subzone, Ganges Subzone and Water Gathering Ground Subzones
|
|
|
(b)
Waste
discharges shall not cause the chemical oxygen demand to exceed 30 mg/L.
|
Yuen Long & Kam Tin (Lower) Subzone and other inland waters
|
|
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 uses of the aquatic
environment.
|
Whole Zone
|
|
Phenol
|
Phenols shall not be present in such quantities as to produce a
specific odour, or in concentration greater than 0.05 mg/L as C6H5OH.
|
Yung Long Bathing Beach Subzone
|
|
Turbidity
|
Waste discharges shall not reduce light transmission substantially
from the normal level.
|
Yung Long Bathing Beach Subzone
|
Source: Statement
of Water Quality Objectives (Deep Bay Water Control Zone)
Technical Memorandum on Standards for
Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal
Waters (DSS-TM)
5.2.3 Discharges
of effluents are subject to control under the WPCO. The DSS-TM, issued under Section 21 of
the WPCO, gives guidance on permissible effluent discharges based on the type
of receiving waters (foul sewers, stormwater drains, inland and coastal
waters). The limits control the physical, chemical and microbial quality of
effluent. Any effluent discharges
from the proposed construction and operational activities must comply with the
standards for effluent discharged into the foul sewers, inland waters and
coastal waters of the Deep Bay WCZs provided in the DSS-TM.
Practice Notes
Professional Persons
Environmental Consultative Committee Practice Note 1/23 Drainage Plans subject
to Comment by the Environmental Protection Department (ProPECC PN 1/23)
5.2.4
ProPECC PN 1/23 issued by EPD provides reference
and guidelines to Authorised Persons in preparing drainage plans for various
types of wastewater that would arise from.
The design of drainage and disposal of various types of effluents should
follow relevant regulations, guidelines and practices as given in the ProPECC
PN 1/23.
Professional Persons
Environmental Consultative Committee Practice Note 2/24 Construction Site
Drainage (ProPECC PN 2/24)
5.2.5
ProPECC PN 2/24 issued by EPD provides some
basic environmental guidelines for handling 10 types of discharge from
construction sites. Types of discharge include surface run-off, groundwater,
boring and drilling water, wastewater from concrete batching and/or precast
concrete casting, wheel washing water, bentonite slurries, water for testing
and/or sterilization of water retaining structures and water pipes, wastewater
from building construction, acid cleaning, etching and picking wastewater,
wastewater from site facilities.
Good practice provided in the ProPECC PN 2/24 should be followed as far
as possible during construction to prevent and minimise the water quality
impact due to construction site drainage.
Technical Circular
5.2.6
Environment, Transport and Works Bureau
Technical Circular (Works) (ETWB TC(W)) No. 5/2005 Protection of natural
streams / rivers from adverse impacts arising from construction works
provides an administrative framework to better protect all natural
streams/rivers from the impacts of construction works. The procedures promulgated under this
Circular aim to clarify and strengthen existing measures for protection of
natural streams/rivers from government projects and private developments. The guidelines and precautionary
mitigation measures given in the Circular should be followed as far as possible
to protect the inland watercourses at or near the government projects and
private developments during the construction phase.
Hong Kong Planning
Standards and Guidelines (HKPSG)
5.2.7
Chapter 9 of the HKPSG outlines environmental
requirements that need to be considered in land use planning. The recommended guidelines, standards
and guidance cover the selection of suitable locations for the developments and
sensitive uses, provision of environmental facilities, and design, layout,
phasing and operational controls to minimise adverse environmental
impacts. It also lists out
environmental factors that influence land use planning and recommends buffer
distances for land uses.
5.3.2
The baseline condition of water bodies in the
assessment area was established based on the routine marine and river water
quality monitoring data collected by EPD. Descriptions of the baseline
conditions provided in the subsequent sections are extracted from EPD’s reports
Marine Water Quality in Hong Kong in 2023 and River Water Quality in
Hong Kong in 2023 which contain the latest information on marine and river
water quality respectively at the time of preparation of this EIA Report.
Marine Water
5.3.3 The
marine water quality monitoring data at EPD’s marine water quality monitoring
stations DM1 and DM2 in 2023 are summarised in Table 5.2. The locations of
the monitoring stations are shown in Figure 5.2.
5.3.4 In
2023, the overall WQO compliance rate for the Deep Bay WCZ was 53%, as compared
with a ten-year average of 47% in 2009-2018. Overall, with the measures under
the Deep Bay Water Pollution Control Joint Implementation Programme taken
progressively by the governments of Hong Kong and Shenzhen, there have been
significant water quality improvements in Deep Bay. In particular, there has
been full compliance of the NH3-N WQO in the past seven years.
Although Deep Bay, as compared with other WCZs, shows higher nutrient levels
with annual depth-averaged total inorganic nitrogen (TIN) levels exceeding the
respective TIN WQOs, a noticeable long-term decrease in TIN levels since
mid-2000s has been seen.
Table 5.2 Summary
Statistics of Marine Water Quality of Deep Bay WCZ Collected by EPD in 2023
|
Parameters
|
Inner Deep Bay
|
WPCO WQO
(in marine waters)
|
|
DM1
|
DM2
|
|
Temperature
(°C)
|
25.6
(19.0 - 31.7)
|
25.5
(19.0 - 31.4)
|
Not more than 2℃ in daily temperature range
|
|
Salinity
|
18.6
(9.7 - 23.3)
|
20.5
(11.5 - 25.5)
|
Not to cause more than 10% change
|
|
Dissolved Oxygen
(mg/L)
|
Depth Average
|
5.2
(3.7 - 7.7)
|
5.4
(3.7 - 7.6)
|
Marine Subzone excepting Mariculture
Subzone: Not less than 4 mg/L for 90% of samples
Mariculture Subzone: Not less than 5 mg/L
for 90% of the sampling occasions during the whole year
|
|
Bottom
|
N/A
|
N/A
|
Outer Marine Subzone excepting Mariculture
Subzone: Not less than 2 mg/L for 90% of the sampling occasions during the
whole year
|
|
Dissolved Oxygen
(% Saturation)
|
Depth Average
|
70
(54 - 112)
|
74
(55 - 111)
|
Not available
|
|
Bottom
|
N/A
|
N/A
|
Not available
|
|
pH
|
7.4
(7.1 - 7.8)
|
7.4
(6.8 - 7.8)
|
Marine Waters excepting Yung Long Bathing Beach
Subzone: 6.5 - 8.5 (±0.2 from natural range)
Yung Long Bathing Beach Subzone: 6.0-9.0
for 95% of samples (±0.5 from natural range)
|
|
Secchi Disc Depth
(m)
|
1.2
(0.9 - 1.6)
|
1.1
(0.8 - 1.5)
|
Not available
|
|
Turbidity
(NTU)
|
27.2
(6.0 - 52.2)
|
29.1
(7.2 - 55.7)
|
Yung Long Bathing Beach Subzone: Not reduce
light transmission substantially from the normal level.
|
|
Suspended Solids (SS) (mg/L)
|
28.3
(15.0 - 61.0)
|
35.5
(15.0 - 72.0)
|
Not more than 30% increase
|
|
5-day Biochemical Oxygen Demand (BOD5) (mg/L)
|
1.0
(0.5 - 1.8)
|
1.0
(0.1 - 2.5)
|
Not available
|
|
Ammonia Nitrogen (NH3-N)
(mg/L)
|
0.397
(0.170 - 0.810)
|
0.282
(0.076 - 0.860)
|
Not available
|
|
Unionised Ammonia
(mg/L)
|
0.006
(0.001 - 0.012)
|
0.004
(<0.001 - 0.016)
|
Not more than annual average of 0.021 mg/L
|
|
Nitrite Nitrogen
(NO2-N) (mg/L)
|
0.118
(0.043 - 0.350)
|
0.094
(0.035 - 0.280)
|
Not available
|
|
Nitrate Nitrogen
(NO3-N) (mg/L)
|
0.883
(0.580 - 1.300)
|
0.764
(0.250 - 1.100)
|
Not available
|
|
Total Inorganic Nitrogen (TIN) (mg/L)
|
1.40
(0.83 - 1.82)
|
1.14
(0.60 - 2.04)
|
Inner Marine Subzone: Not more
than annual mean of 0.7 mg/L
Outer Marine Subzone: Not more
than annual water column average of 0.5 mg/L
|
|
Total Kjeldahl Nitrogen (TKN) (mg/L)
|
0.76
(0.40 - 0.98)
|
0.64
(0.31 - 1.00)
|
Not available
|
|
Total Nitrogen (TN)
(mg/L)
|
1.76
(1.24 - 2.20)
|
1.50
(0.97 - 2.18)
|
Not available
|
|
Orthophosphate Phosphorus (PO4) (mg/L)
|
0.123
(0.069 - 0.170)
|
0.119
(0.049 - 0.320)
|
Not available
|
|
Total Phosphorus (TP) (mg/L)
|
0.20
(0.14 - 0.27)
|
0.19
(0.14 - 0.35)
|
Not available
|
|
Silica (as SiO2)
(mg/L)
|
5.38
(1.90 - 10.00)
|
4.43
(1.00 - 11.00)
|
Not available
|
|
Chlorophyll-a
(μg/L)
|
3.5
(1.7 - 6.0)
|
5.5
(1.4 - 13.0)
|
Not available
|
|
E. coli
(count/100 mL)
|
310
(24 - 3,300)
|
380
(21 - 80,000)
|
Secondary Contact Recreation Subzones
and Mariculture Subzone (L.N. 455 of 1991): Not exceed 610 per 100 mL
Yung Long Bathing Beach Subzone
(L.N.455 of 1991): Not exceed 180 per 100 mL
|
|
Faecal Coliforms
(count/100 mL)
|
640
(44 - 10,000)
|
730
(40 - 220,000)
|
Not available
|
Remarks:
1. Data source: EPD Marine Water
Quality in Hong Kong in 2023.
2. Except as specified, data presented
are depth-averaged values calculated by taking the means of three depths:
surface, mid-depth and bottom.
3. Data presented are annual
arithmetic means of depth-averaged results except for E.coli and faecal
coliforms that are annual geometric means.
4. Data in brackets indicate the
ranges.
Inland Water
5.3.5
There is no EPD’s river water quality monitoring
station situated within the 500 m assessment area. The closest EPD’s river
water quality monitoring stations are at Kam Tin River (KT1 and KT2) and
Fairview Park Nullah (FVR1). The locations of these monitoring stations and the
monitoring results are shown in Figure 5.2
and Table 5.3
respectively.
5.3.6
The overall WQO compliance rate at Kam Tin River
in 2023 was 55%. Both monitoring stations (i.e. KT1 and KT2) at Kam Tin River
were graded as “Fair” and “Bad” Water Quality Index (WQI) respectively in
2023. The monitoring station at
Fairview Park Nullah (i.e. FVR1) recorded a WQO compliance rate of 73% in
2023. Its WQI grading remained
“Fair” in 2023.
Table 5.3 Summary
Statistics of River Water Quality of Kam Tin River and Fairview Park Nullah
Collected by EPD in 2023
|
Parameters
|
Kam Tin River
|
Fairview Park Nullah
|
WPCO WQO
(in inland waters)
|
|
KT1
|
KT2
|
FVR1
|
|
Dissolved Oxygen
(mg/L)
|
5.9
(1.8 - 7.2)
|
3.8
(1.2 - 7.4)
|
5.4
(3.7 - 11.7)
|
Not less than 4 mg/L
|
|
pH
|
7.5
(7.3 - 7.9)
|
7.6
(7.3 - 7.9)
|
7.4
(7.1 - 8.5)
|
Yuen Long & Kam Tin (Upper) Subzone: within the
range of 6.5-8.5
Other inland water: within the
range of 6.0-9.0
|
|
Suspended Solids
(mg/L)
|
9.4
(5.9 - 110.0)
|
15.5
(5.3 - 75.0)
|
11.5
(6.8 - 22.0)
|
Yuen Long & Kam Tin (Upper)
Subzone, other inland waters: Annual median not to exceed 20 mg/L
|
|
5-Day Biochemical Oxygen Demand
(mg/L)
|
8.5
(4.1 - 29.0)
|
15.0
(5.2 - 53.0)
|
6.9
(3.0 - 13.0)
|
Yuen Long & Kam Tin (Upper) Subzone: Not to
exceed 3 mg/L
Other inland waters: Not to
exceed 5 mg/L
|
|
Chemical Oxygen Demand (mg/L)
|
23
(13 - 46)
|
26
(14 - 120)
|
30
(9 - 70)
|
Yuen Long & Kam Tin (Upper) Subzone: Not to
exceed 15 mg/L
Other inland waters: Not to
exceed 30 mg/L
|
|
Oil & Grease (mg/L)
|
<0.5
(<0.5 - 1.3)
|
0.6
(<0.5 - 5.1)
|
<0.5
(<0.5 - <0.5)
|
Not available
|
|
E.coli (cfu/100 mL)
|
32,475
(8,000 - 150,000)
|
65,187
(28,000 - 190,000)
|
25,146
(2,900 - 120,000)
|
Other inland water: running
median of most recent 5 consecutive samples shall not to exceed 1000 per 100
mL
|
|
Faecal Coliforms (cfu/100 mL)
|
157,082
(78,000 - 510,000)
|
215,166
(74,000 - 970,000)
|
71,882
(14,000 - 440,000)
|
Not available
|
|
Ammonia-Nitrogen
(mg/L)
|
3.450
(0.910 - 15.000)
|
7.200
(1.200 - 14.000)
|
1.450
(0.450 - 2.800)
|
Not available
|
|
Nitrate-Nitrogen
(mg/L)
|
1.200
(0.018 - 3.000)
|
0.380
(<0.002 - 1.000)
|
0.760
(0.340 - 1.200)
|
Not available
|
|
Total
Kjeldahl Nitrogen (mg/L)
|
4.70
(1.80 - 17.00)
|
8.50
(1.80 - 20.00)
|
2.40
(0.92 - 4.00)
|
Not available
|
|
Ortho-Phosphate
(mg/L)
|
0.600
(0.280 - 2.800)
|
0.925
(0.260 - 1.600)
|
0.275
(0.095 - 0.530)
|
Not available
|
|
Total Phosphorus
(mg/L)
|
0.86
(0.38 - 3.50)
|
1.30
(0.38 - 2.90)
|
0.45
(0.12 - 0.73)
|
Not available
|
|
Sulphide (mg/L)
|
<0.02
(<0.02 - 0.06)
|
0.03
(<0.02 - 0.11)
|
<0.02
(<0.02 - 0.04)
|
Not available
|
|
Aluminium (µg/L)
|
<50
(<50 - 110)
|
<50
(<50 - <50)
|
<50
(<50 - <50)
|
Not available
|
|
Cadmium (µg/L)
|
<0.1
(<0.1 - <0.1)
|
<0.1
(<0.1 - <0.1)
|
<0.1
(<0.1 - <0.1)
|
Not available
|
|
Chromium (µg/L)
|
<1
(<1 - 1)
|
<1
(<1 - 2)
|
<1
(<1 - 1)
|
Not available
|
|
Copper (µg/L)
|
2
(<1 - 3)
|
2
(<1 - 4)
|
2
(<1 - 2)
|
Not available
|
|
Lead (µg/L)
|
<1
(<1 - <1)
|
<1
(<1 - <1)
|
<1
(<1 - <1)
|
Not available
|
|
Zinc (µg/L)
|
<10
(<10 - 20)
|
<10
(<10 - 30)
|
10
(<10 - 20)
|
Not available
|
|
Flow (m3/s)
|
0.353
(0.086 - 16.788)
|
0.282
(0.080 - 11.926)
|
NM
|
Not available
|
Remarks:
1. Data source: EPD River Water
Quality in Hong Kong in 2023.
2. Data presented are in annual
medians of monthly samples; except those for faecal coliforms and E. coli which
are in annual geometric means.
3. NM indicates no measurement
taken.
4. Figures in brackets are
annual ranges.
5. cfu – colony forming unit.
6. Values at or below laboratory
reporting limits are presented as laboratory reporting limits.
5.4.1
The WSRs that have a bearing on water quality
identified within the 500 m assessment area were identified and are listed in Table 5.4
below, with their locations shown in Figure 5.1.1 to Figure 5.1.6.
Table 5.4 List
of Water Sensitive Receivers
|
ID
|
Description
|
Nature
|
Approx. Distance to Project Site
|
Remarks
|
|
Watercourse
|
|
W1
|
Ngau Tam Mei Drainage Channel
|
Modified Watercourse
|
Partially
within Project Site
|
Section within the Development
Area will be retained, diverted and revitalised, while the section outside the Development Area
but within the Project Site will not be affected by the proposed works.
|
|
W2,
W9
|
Branches of Ngau Tam Mei Drainage Channel
|
Natural Watercourse
|
Partially within Project Site
|
Will be partially removed and diverted.
|
|
W2a
|
Branches of Ngau Tam Mei Drainage Channel
|
Modified Watercourse
|
Partially within Project Site
|
Will be
partially removed and diverted.
|
|
W3,
W5
|
Branches of Ngau Tam Mei Drainage Channel
|
Natural Watercourse
|
Within
Project Site
|
Will be removed.
|
|
W4,
W9a, W9b
|
Branches of Ngau Tam Mei Drainage Channel
|
Semi-natural Watercourse
|
Within
Project Site
|
Will be removed.
|
|
W8
|
Branch of Ngau Tam Mei Drainage Channel
|
Semi-natural Watercourse
|
Within
Project Site
|
Will be realigned
and revitalised.
|
|
W8a,
W8b, W10
|
Branches of Ngau Tam Mei Drainage Channel
|
Semi-natural Watercourse
|
Partially
within Project Site
|
Will be partially removed and
diverted.
|
|
W3a,
W5a, W7, W8c, W10a
|
Branches of Ngau Tam Mei Drainage Channel
|
Modified Watercourse
|
Within
Project Site
|
Will
be removed.
|
|
W10b
|
Branch of Ngau Tam Mei Drainage Channel
|
Modified Watercourse
|
Partially within Project Site
|
Will be partially removed and
diverted.
|
|
W8d
|
Branch of Ngau Tam Mei Drainage Channel
|
Modified Watercourse
|
155
m
|
-
|
|
W6
|
Watercourse near Lai Yuen
|
Modified Watercourse
|
Within
Project Site
|
Will be removed.
|
|
W11
|
Watercourse near Ngau Tam Mei Ventilation Building
|
Modified Watercourse
|
Partially
within Project Site
|
Will be partially removed and diverted.
|
|
W13
|
Watercourse near Wah On Villa
|
Semi-natural Watercourse
|
278
m
|
-
|
|
W13a
|
Watercourse near Wah On Villa
|
Modified Watercourse
|
19
m
|
-
|
|
W13b
|
Drainage along Sam Tam Road
|
Modified Watercourse
|
31
m
|
-
|
|
W14
|
Downslope watercourse of Kai Kung Leng
|
Semi-natural Watercourse
|
275
m
|
-
|
|
W15
|
Drainage Channel along San Tin Highway
|
Modified Watercourse
|
Partially within Project Site
|
Some sections that will be affected by proposed road works of
this Project will
be temporarily diverted during the construction phase.
|
|
W16,
W17, W18, W30
|
Branches of Ngau Tam Mei Drainage Channel
|
Modified Watercourse
|
49 m
|
-
|
|
W19
|
Watercourse downslope of Ngau Tam Shan
|
Natural Watercourse
|
Partially within Project Site
|
Will be partially removed and diverted.
|
|
W20
|
Watercourse near Ching Yau Road
|
Modified Watercourse
|
6
m
|
-
|
|
W21
|
Watercourse near Ching Yau Road
|
Natural Watercourse
|
38
m
|
-
|
|
W26
|
Watercourse downslope of Ngau Tam Shan
|
Natural Watercourse
|
Partially within Project Site
|
Will be partially removed and diverted.
|
|
W27
|
Watercourse near Ko Hang
|
Modified Watercourse
|
112
m
|
-
|
|
W28
|
Watercourse near Yau Mei San Tsuen
|
Modified Watercourse
|
Partially within Project Site
|
A section that will be affected by
proposed works for cycle track will be temporarily diverted during the
construction phase.
|
|
W29
|
Branch of Fairview Park Nullah
|
Modified Watercourse
|
346
m
|
-
|
|
W31,
W32
|
Watercourses downslope of Ngau Tam Shan
|
Modified Watercourse
|
238 m
|
-
|
|
W33
|
Drainage Channel within/in the vicinity of Tam Mei Barracks
|
Modified Watercourse
|
Partially within Project Site
|
Will be partially removed and diverted.
|
|
W34
|
Drainage along Kai Kung Leng
|
Modified Watercourse
|
37 m
|
-
|
|
Ponds
|
|
P-W1
|
Ponds at the northwest of the Project Site
|
-
|
33 m
|
-
|
|
P-W2
|
Ponds at the west of the Project Site
|
-
|
87
m
|
-
|
|
P-N1
|
Ponds at the north of the Project Site
|
-
|
53
m
|
-
|
|
P-S1
|
Ponds near Yau
Tam Mei Tsuen
|
-
|
Within
Project Site
|
Will be removed.
|
|
P-S2
|
Ponds near Yau
Tam Mei Tsuen
|
-
|
Within
Project Site
|
Will be removed.
|
|
P-S3
|
Ponds in the vicinity of upstream of Ngau Tam Mei
Drainage Channel
|
-
|
Within
Project Site
|
Will be removed.
|
|
P-S4
|
Ponds near Wah On Villa
|
-
|
240
m
|
-
|
|
P-E1
|
Ponds near Ngau Tam Mei Water Treatment Works
|
-
|
Partially
within Project Site
|
All ponds that fall within or partially within the Project Site
will be removed, while others outside Project Site will not be
affected.
|
|
Other WSRs
|
|
-
|
Wetland
Buffer Area
|
Wetland Buffer Area
|
Partially
within Project Site
|
Partial
area within the Project Site which is currently as footpath and Castle Peak
Road – Tam Mi will be modified.
|
|
-
|
Wetland
Conservation Area
|
Wetland Conservation Area
|
84
m
|
-
|
|
-
|
Lam
Tsuen Country Park
|
Country Park
|
188 m
|
-
|
|
-
|
Conservation
Area
|
Conservation Area
|
21
m
|
-
|
|
-
|
Comprehensive Development and Wetland Protection
Area
|
Other Specified Uses
|
78
m
|
-
|
|
-
|
Wetland Conservation Park
|
Other Specified Uses
|
18
m
|
-
|
|
|
|
|
|
|
|
5.5
Assessment Methodology
5.5.1
As mentioned in Section 5.3.1,
the assessment area includes all areas within 500 m from the Project Site, and
also covers the Deep Bay WCZ as well as the WSRs in the vicinity of the
Project. The assessment methodology of potential water quality impacts
associated with the Project followed the detailed technical requirements given
in Appendix D of the EIA Study Brief and based on the Project information as
presented in Section 2. The criteria and guidelines for evaluating and
assessing water pollution followed Annexes 6 and 14 of the EIAO-TM.
5.5.2
The WSRs that may be affected during the
construction and operational phases of the Project were identified. Potential sources of water quality
impacts that may arise during the construction and operational stages of the
Project were identified and evaluated for determination of their impact
significance. Practical mitigation
measures were recommended as necessary to reduce any identified adverse impacts
on water quality to acceptable levels for both construction and operational
phases.
5.6.1
No marine works would be required for
construction of the Project. Only inland construction works including site
formation, construction of new infrastructures (e.g. roads, passageway,
transportation system, flood retention facilities, sewers and stormwater drains
and sewage pumping station (SPS)), revitalization of the existing Ngau Tam Mei
Drainage Channel (NTMDC), and superstructure works would be involved under the
Project.
5.6.2
The potential sources of water quality impacts
arising from the inland construction works include:
·
General construction
activities such as site clearance works, demolition works and site formation
works;
·
Construction site run-off;
·
Sewage from construction
workforce;
·
Accidental spillage of
chemicals;
·
Construction works in close
proximity of inland waters;
·
Construction works in inland
waters;
·
Removal / diversion of
watercourses;
·
Removal / filling of ponds;
and
·
Groundwater from contaminated
areas, contaminated site run-off and wastewater from land decontamination.
General Construction
Activities
5.6.3
Various types of construction activities,
including general cleaning and polishing, wheel washing, air quality control
and utility installation, may generate wastewater. These types of wastewater contain high concentrations
of SS, as well as certain amount of grease and oil. Debris and rubbish may also be generated
from packaging, construction materials and refuse. Uncontrolled discharge of
site effluents, rubbish and refuse generated from the construction activities
could lead to water quality deterioration.
It is expected that if the good site practice suggested in Section 5.8.2
to Section 5.8.15
are followed as far as practicable, the potential water quality impacts
associated with construction activities would be minimal.
5.6.4
The Project would involve demolition works of
the existing structures for subsequent construction works of the development.
The sewage remaining or washed out from the decommissioned facilities, if any,
should not be discharged without proper treatment. Another key concern from demolition
works would be surface run-off and site effluent. Precipitation that falls on unpaved
areas with the topsoil exposed during the demolition would wash away soil
particles. Such surface run-off and
stormwater overflows with high levels of suspended solids if directly
discharged into the inland waters may lead to water quality impact. Effluent discharge from temporary site
facilities, such as wheel washing facilities at site entrances, should be
controlled to prevent direct discharge to the neighbouring storm drains and
inland waters.
5.6.5
Good site practices should be implemented to
control site run-off, drainage and site effluent from the works areas, and to
prevent run-off and drainage water with high levels of SS from entering the
adjacent waters. With the
implementation of adequate site drainage and provision of sediment removal
facilities as described in Section 5.8.2
to Section 5.8.15
below, it is anticipated that adverse water quality impacts would not
arise.
Construction Site Run-off
5.6.6
Potential pollution sources of site run-off may
include:
·
Run-off and erosion of exposed
bare soil and earth, drainage channels, earth working areas and stockpiles;
·
Wash water from air quality control
sprays and wheel washing facilities;
·
Release of any bentonite
slurries, concrete washings and other grouting materials with construction
run-off or storm water; and
·
Fuel, oil and lubricants from
maintenance of construction vehicles and equipment.
5.6.7
During rainstorms, site run-off would wash away
the soil particles on unpaved lands and areas with the topsoil exposed. The run-off is generally characterised
by high concentration of SS.
Release of uncontrolled site run-off would increase the SS levels and
turbidity in the nearby water environment.
Site run-off may also wash away contaminated soil particles, and
therefore causes water pollution.
5.6.8
Windblown dust would be generated from exposed
soil surfaces in works areas. It is
possible that windblown dust could fall directly onto the nearby water bodies
when a strong wind occurs.
Dispersion of dust within the works areas may increase the SS levels in
surface run-off causing a potential impact to the nearby sensitive receivers.
5.6.9
It is important that proper site practice and
good site management are followed to prevent run-off with high level of SS from
entering the surrounding waters.
With the implementation of Best Management Practices (BMPs) to control
site run-off and drainage water from the construction site, disturbance of
water bodies could be avoided and deterioration in water quality would be
minimal. Recommended measures in
controlling construction site run-off and adopting proper drainage are
described in Section 5.8.2
to Section 5.8.15.
Sewage from Construction
Workforce
5.6.10
During the construction of the Project, the
workforce on site will generate sewage effluent, which is characterised by high
levels of BOD, ammonia and E. coli counts. Potential water quality
impacts upon the local drainage and fresh water system may arise from these
sewage effluent, if uncontrolled.
5.6.11
Temporary sewage generation can be adequately
handled by temporary sanitary facilities, such as portable chemical toilets,
and are not allowed to be discharged directly into storm drains or inland
waters adjacent to the construction site. The number of toilet facilities to be
provided on site should be at a ratio of not less than 1 for every 25 workers,
subject to later detailed design, the capacity of the chemical toilets, and
contractor's site practices. A
licensed contractor should be employed to provide appropriate and adequate temporary
sanitary facilities and be
responsible for appropriate disposal and maintenance. Details are
described in Section 5.8.16
to Section 5.8.17.
5.6.12
Provided that the mitigation measures as
recommended in Section 5.8.16
to Section 5.8.17
are adopted as far as practicable, no adverse water quality impacts are
anticipated.
Accidental Spillage of
Chemicals
5.6.13
The use of engine oil and lubricants and their
storage as waste materials have the potential to create impacts on the water
quality if spillage occurs. Waste
oil may infiltrate into the surface soil layer, or run-off into adjacent
waterbodies, increasing hydrocarbon levels. Groundwater pollution may also be arisen
from the improper use and storage of chemical and petroleum products within the
site areas where groundwater infiltrates into. Infiltration of groundwater may occur at
areas where there are faults and/or fissures in the rock mass. Nevertheless, the potential impacts
could be mitigated by practical mitigation measures and good site practices as
described in Section 5.8.18
to Section 5.8.20.
Construction Works in
Close Proximity of Inland Waters
5.6.14
Construction activities in close proximity of
inland watercourses may pollute the inland water bodies due to potential
release of construction wastes as well as construction wastewater, and the site
run-off are generally characterised by high concentration of SS and elevated
pH. Adoption of good housekeeping
and mitigation measures would reduce the generation of construction wastes and
potential water pollution. The implementation
of measures to control run-off and drainage water are important for the construction
works adjacent to the inland watercourses in order to prevent run-off and
drainage water with high levels of SS from entering the water environment. With the implementation of BMPs and
provision of mitigation measures as specified in ProPECC PN 2/24 and ETWB TC(W)
No. 5/2005 as detailed in Section 5.8.21,
it is anticipated that water quality impacts would be minimal.
Construction Works in
Inland Waters
5.6.15
Permeable
paver block, porous concrete, composite wood and natural granite would be
adopted for the revitalization of the existing NTMDC, subject to the detailed
design. Potential impacts arising from the revitalization works may be
generated by the discharge of construction materials, wastewater, excavation
materials (including sediment) and spillage to the receiving downstream waters.
With the implementation of the BMPs and the provision of mitigation measures
proposed in Section 5.8.21
to Section 5.8.23,
it is anticipated that water quality impacts would be minimal.
Removal / Diversion of
Watercourses
5.6.16
All the watercourses that fall within the
Project Site (except the NTMDC), will be permanently removed under the Project,
while the watercourses that are partially within the Project Site would be
partially removed and diverted to connect with the proposed drainage system
under the Project. The upstream of NTMDC would be realigned and revitalised to
improve the flood resilience and adaptation to climate change of the
Development Area. The removal /
diversion of watercourses would also not induce change in flow regime as the
Project will not cause changes in the catchment area. Details of the
watercourses to be affected by the Project are presented in Table 5.4
above and the locations are shown in Figure
5.1.1 to Figure 5.1.6.
5.6.17
Potential impacts may be generated by the
release of construction materials, wastewater, excavated sediment, spillage and
contaminants to the receiving waters in the downstream (due to soil excavation
for construction of new drainage and removal / diversion of the existing
watercourses). All these
construction works should be undertaken in dry conditions to avoid potential
water quality impacts upon the downstream water quality.
5.6.18
With the implementation of mitigation measures
as recommended in Section 5.8.24
to Section 5.8.26,
it is anticipated that there would be no significant water quality impacts.
Removal / Filling of Ponds
5.6.19
Due to the new developments, most of the
existing ponds within or partially within the Project Site will be removed by
the Project, while few ponds will be removed by other project (i.e. Northern
Link (NOL) Main Line) prior to the commencement of construction works of this
Project. Details of the ponds to be affected by the Project are presented in Table 5.4
above and the locations are illustrated in Figure 5.1.1 to Figure 5.1.6.
5.6.20
The associated construction works would include
draining the water in ponds either before filling up these areas or before
commencement of any excavation and construction works. The water of these ponds
to be drained would probably be sediment-laden and would carry a certain level
of pollutants. Direct discharge of
these drained waters to the nearby watercourses will not be allowed.
5.6.21
Excavated materials (including sediment) may be
generated from the removal / filling of ponds. Mitigation measures for handling
and disposal of excavated materials and sediment as recommended in Section 5.8.27
to Section 5.8.28
should be followed to minimise the associated potential environmental impacts.
5.6.22
Together with the adoption of the recommended
mitigation measures for the removal / filling of ponds as recommended in Section
5.8.27
to Section 5.8.28,
no adverse water quality impact would be expected.
Groundwater from
Contaminated Areas, Contaminated Site Run-off and Wastewater from Land
Decontamination
5.6.23
It is suspected that some of the areas within
Project Site may have land contamination issues, and land decontamination works
would be required at the area(s) confirmed with land contamination issues. Any contaminated material disturbed, or
material which comes into contact with the contaminated material, has the
potential to be washed with site run-off into watercourses. Any wastewater discharge from land
decontamination processes could also adversely affect the nearby water
environment. Proper land contamination remediation and mitigation measures for
contaminated site run-off and wastewater from land decontamination are proposed
in Section 5.8.29
to Section 5.8.31.
With proper implementation of the recommended mitigation measures, the
potential water quality impacts arising from the land decontamination works
would be minimised.
5.6.24
Groundwater pumped out or from dewatering
process during excavation works in the contaminated areas, if any, would be
potentially contaminated. Mitigation measures and monitoring requirements for
contaminated groundwater discharge / recharge are recommended in Section 5.8.29
to Section 5.8.31.
With proper implementation of the recommended mitigation measures, no adverse
water quality would be expected from the groundwater generated from
contamination areas.
5.7
Identification, Prediction and Evaluation of Water Quality Impact During Operational
Phase
5.7.1
The potential sources of water quality impacts
arising from the operational phase of the Project include:
·
Non-point source surface
run-off from new impervious areas;
·
Sewage disposal strategy for the new developments;
·
Revitalisation and greening of drainage channel banks;
·
Sewage
overflow and emergency discharge from the proposed sewage pumping station (SPS);
·
Potential
impact from refuse collection points;
·
Potential
flood risk; and
·
Change in flow
regime and hydrology.
Non-point Source Surface
Run-off from New Impervious Areas
5.7.2
Surface run-off to be generated from the Project
is known as non-point source pollution.
The newly paved roads will increase the quantity of surface run-off. The
presence of oil, grease and grit on their surfaces could be washed into the
nearby drainage system or even into the watercourses (e.g. revitalised NTMDC
and nearby watercourses outside Project boundary) during rainfall event. The
surface run-off may also contain debris, refuse, dust from the roof of buildings
and cleaning agents used for washing streets and building facades, which may
also affect the quality of the nearby receiving water environment, if
uncontrolled.
Greening Area of the
Project
5.7.3
Within the Development Area of approximately 130
ha, currently about 98 ha have already been developed / paved areas (including
brownfield sites / wasteland / village developments), while the remaining area
of about 32 ha consists of greening / unpaved surface (such as plantation,
grassland, shrubland, etc.). Without the Project, the amount of paved / unpaved
area in the future is assumed to be the same as that under the existing
situation.
5.7.4
Based on the HKPSG and general guidelines for
designing public open space, the percentage of greening (such as soft landscape
and tree planting) to be provided for the Development Area is approximately 40%
at open spaces, while there will be approximately 20% to 30% greening at new
government facilities / school / residential development areas following
requirements under DEVB TC(W) 3/2012 Site Coverage of Greenery for
Government Building Projects and Building Department's APP 152 - Sustainable
Building Design Guidelines. Based on these percentages of greening, it is
estimated that a minimum of about 36 ha greening would be provided under this
Project within the area to be developed (i.e. 94 ha paved area).
Non-point Source Pollution
from Surface Run-off
5.7.5
Surface run-off would be generated during the
operation of the Project. The paved area within the Development Area is
expected to be reduced, comparing to the existing situation. Nonetheless, the
surface run-off containing debris and dust, and cleaning agent used during
washing would adversely affect the water quality of the nearby waterbodies.
5.7.6
EPD’s study “Update on Cumulative Water
Quality and Hydrological Effect of Coastal Developments and Upgrading of
Assessment Tool (Update Study)” suggested that only rainfall events of
sufficient intensity and volume would give rise to run-off. It is assumed that only a daily rainfall
of greater than 10 mm per day and a rainfall intensity greater than 2 mm/hour
would give rise to run-off. The
run-off percentage has been calculated based on the 5-year (i.e. 2019 – 2023)
data from the Hong Kong Observatory, while the daily run-off value has been
calculated using the equation below:
Daily run-off value (mm/day) = Averaged daily rainfall (mm/day) ×
Run-off percentage of the month
where
Run-off percentage of the month = (sum of rainfall
for days with total rainfall>10 mm and with maximum rainfall intensity>2
mm/hr) / Total rainfall of the month ×100%
5.7.7
Under the existing situation, the paved surface
within the Development Area is about 98 ha. Upon the completion of the Project,
the total paved surface of the Development Area is around
94 ha. With consideration of the paved area and a run-off coefficient of
1 for paved surface, the highest daily run-off volume generated from the
Project would occur in June with a monthly average value of 13,417 m3/d. As compared to the existing condition of
13,988 m3/d, the operation of Project resulted in a reduction in the
volume of run-off generated from the Development Area. The maximum pollution
loading of stormwater is presented in Table 5.5.
Table 5.5 Pollution Loading
|
Parameters
|
Event
Mean Concentrations for Stormwater Run-off (g/m3)
|
With
Project
|
Without
Project
|
|
Pollution
Loading(1) (kg/d)
|
|
SS
|
43.25
|
580.29
|
604.97
|
|
BOD5
|
22.48
|
301.61
|
314.44
|
|
NH3-N
|
0.20
|
2.68
|
2.80
|
|
Cu
|
0.01
|
0.13
|
0.14
|
|
TP
|
0.20
|
2.68
|
2.80
|
|
PO4-P
|
0.04
|
0.54
|
0.56
|
|
Si
|
3.28
|
44.01
|
45.88
|
|
NOx-N
|
0.40
|
5.37
|
5.60
|
|
TKN
|
1.40
|
18.78
|
19.58
|
Note:
(1) Pollution loading is calculated by multiplying the
event mean concentration of stormwater run-off with the maximum daily run-off
volumes for the with-project and without-project scenarios, which are 13,417
m³/day and 13,988 m³/day, respectively.
5.7.8
Stormwater control measures including BMPs,
various blue-green infrastructure and Storm Water Pollution Control Plan would
be implemented within the Development Area to: (1) control erosion and
sedimentation; (2) control run-off quantity and quality; (3) eliminate
pollutants in point source discharge from drainage outfalls; (4) prevent “first
flush” pollution; and (5) eliminate pollutant discharge in stormwater run-off
from entering the poor flushing water of Deep Bay, as described in Section 5.9.2
to Section 5.9.12. The effects of these stormwater control
measures have not been taken into consideration in the quantification of
non-point source pollution as given above.
It is expected that with proper implementation of the recommended
measures, the water quality impact due to the non-point source pollution from
the Development Area would be minimised.
Surface Run-off from Major
Roads
5.7.9
Road run-off may contain minimal amount of oil, grease
and grit that may cause water quality impacts to the receiving waters in Deep
Bay WCZ. Thus, minor non-point source pollution would be expected from the
proposed major roads (e.g. Road D1 and road connection to/from San Tin
Technopole). To minimise the potential impact from road run-off, all the roads
proposed under the Project should be designed with adequate drainage system and
appropriate oil interceptors, as required. It is anticipated that with proper
implementation of BMPs as recommended in Section 5.9.2
to Section 5.9.12,
no adverse water quality impact from non-point source surface run-off is
expected.
5.7.10
With reference to Section 6, the sewage
generated within the Development Area will be conveyed to the proposed on-site
SPS and further conveyed via sewerage connections to the future San Tin
Effluent Polishing Plant (EPP) (by others) and, as possible measures, the existing Nam Sang Wai (NSW) SPS then
ultimately to Yuen Long EPP for proper treatment and disposal in the
Deep Bay catchment. The planned and existing sewerage treatment facilities
would be adequate in handling the sewage generated from the Project. The associated impact arising
from the operation of the San Tin EPP and Yuen Long EPP was evaluated in the
approved San Tin / Lok Ma Chau Development Node EIA report (Register No.:
AEIAR-261/2024) and the Yuen Long Effluent Polishing Plant EIA Report
(AEIAR-220/2019). It is concluded that the provision of the San Tin EPP and
Yuen Long EPP would induce water quality beneficial effect by providing new
sewerage facilities to the existing unsewered areas.
5.7.11
Considering that the sewage generated within the
Development Area would be properly collected, treated and disposed of, no
adverse water quality impact is anticipated.
Revitalisation
and Greening of Drainage Channel Banks
5.7.12
Sections of NTMDC running through the
Development Area will be realigned and revitalised to improve the flood
resilience and adaptation to climate change of the Development Area. Permeable
paver block, porous concrete, composite wood, natural granite would be adopted
for the revitalization of the existing NTMDC, subject to detailed design in
later stage. It is anticipated that
no change to the hydrodynamics and water quality would result from the
revitalisation and greening works during the Project operation.
Sewage
Overflow and Emergency Discharge from the proposed Sewage Pumping Station
5.7.13
A SPS with design capacity of 44,875 m3/day is proposed under the
Project. The location of the SPS is shown in Figure
5.4.
5.7.14
The normal operation of the proposed SPS would
actually have beneficial effect through the enhancement of the efficiency of
the sewerage system. However, there
will also be an emergency bypass of sewage from the proposed SPS discharged to
NTMDC (Figure 5.4 refers)
due to pump failure, power supply failure and damage to pressure main or
flooding, resulting in potential water quality impact.
5.7.15
Emergency bypass culvert will be built to convey
any emergency overflow from the proposed SPS to the NTMDC which joins Kam Tin
River and finally discharges to the Deep Bay. The emergency bypass alignment is
illustrated in Figure 5.4. The
NTMDC, which was channelised in 2005, is a modified watercourse with moderate
ecological value as evaluated in Section 9.
5.7.16
Under the emergency situation, raw sewage from
the proposed SPS will be discharged to the NTMDC leading to Deep Bay. SPS with similar emergency discharge
arrangement was previously assessed under the approved EIA report Upgrading and
Expansion of San Wai Sewage Treatment Works and Expansion of Ha Tsuen Pumping
Station (Register No.: AEIAR-072/2003) (hereinafter referred to as “the
approved EIA report for SW STW”).
The approved EIA report for SW STW assessed the water quality impact due
to an emergency discharge of raw sewage from Ha Tsuen SPS of 246,000 m3/day
for a duration of 12 days. Since
the emergency discharge assessed in the approved EIA report for SW STW would
also enter modified watercourses leading to Deep Bay, which is similar to the
emergency discharge arrangement of this Project, the findings of the approved
EIA report for SW STW can be applied here.
5.7.17
According to the approved EIA report for SW STW,
the emergency discharge from Ha Tsuen SPS would cause an increase in E. coli,
un-ionized ammonia (UIA) and TIN in the receiving waters. The baseline
conditions for TIN and UIA would be recovered in 5 to 8 days after termination
of the emergency discharge. For E. coli, its concentration would
decrease more rapidly and return to the baseline level in a much shorter
period. Since the capacity of the proposed SPS is smaller than that assessed in
the approved EIA report for SW STW, the time required for E. coli, UIA
and TIN to return to the baseline value is expected to be shorter. Based on
past experience, breakdown of SPS could be recovered in only hours, which is
much shorter than the emergency period of 12 days assessed in the approved EIA
report for SW STW. Thus, the actual water quality impact that would result from
the emergency bypass from the proposed SPS could be much smaller than that
predicted in the approved EIA report for SW STW.
5.7.18
Since the potential water quality impact arising
from overflow, if any, from the proposed SPS would be reversible, no long-term
insurmountable water quality impact would be expected from the emergency
overflow from the SPS.
5.7.19
In order to minimise the chance of emergency
sewage discharge, various precautionary measures to be incorporated in the
design of the proposed SPS are recommended in Section 5.9.13.
With incorporation of the recommended preventive measures, the chance of
emergency sewage bypass would be exceptionally rare.
5.7.20
In order to minimise the potential water quality
impact in case of emergency discharge, development of a Contingency Plan in the
detailed design stage is recommended to deal with the remote occurrence of
emergency discharge. An outline of the Contingency Plan is given in Section 5.9.14.
Potential Impact from
Refuse Collection Points (RCPs)
5.7.21
The potential source of water pollution to be
generated from the RCPs would be the potential spillage of pollutants (e.g.
rubbish, dirt, debris, etc.) and associated contaminated surface run-off or
washed water from any floor cleansing activities. Given that the RCPs would be housed or
covered to prevent generation of contaminated rainwater run-off, in addition,
that all contaminated surface run-off or washed water would be collected and
diverted to appropriate treatment facilities for proper treatment before
discharge to the foul sewers, no adverse water quality impact arising from the
operation of RCPs would be expected.
Potential Flood Risk
5.7.22 Two
underground storage tanks as covered tanks are proposed to minimise flood risk
by collecting run-off from the nearby drainage system through gravity flow to
avoid overflow of nearby open drainage channels. The stored run-off would be pumped to
the adjacent drainage channels after heavy rains. The locations of the
underground storage tanks are shown in Figure
5.3. With
implementation of the recommended flood protection measures including the
realignment and revitalization of NTMDC within the Project Site, the potential flooding risk would
be minimised.
Change in Flow Regime and
Hydrology
5.7.23
Due to the proposed developments, the
watercourses within the Project Site (except NTMDC) will be permanently removed
/ diverted / realigned under this Project.
These watercourses are tributaries of NTMDC and some downhill
watercourses. All the watercourses to be removed or diverted are however
considered minor water channels only.
The main drainage channel within the assessment area namely the NTMDC
would be revitalised and remained in the Project Site. The hydraulics of water
flow may be changed due to the removal or diversion of these minor
watercourses, but the impact is expected to be localised and small. No significant change on the flow regime
and hydrology within the assessment area is expected.
5.8
Mitigation
Measures for Construction Phase
5.8.1
Measures as discussed below are recommended to
mitigate the potential water quality impacts from the land-based construction
works during construction phase, and should be incorporated into the Project's contract documents.
General Construction
Activities and Construction Site Run-off
·
prevent or minimise the
likelihood of pollutants (generated from construction activities including demolition works)
being in contact with rainfall or run-off; and
·
abate pollutants in the
stormwater surface run-off prior to the discharge of surface run-off to the
nearby water bodies.
5.8.3
These principle objectives should be achieved by
implementation of the BMPs of mitigation measures in controlling water
pollution. The guidelines for
handling and disposal of construction site discharges as detailed in the
ProPECC PN 2/24 should be followed, where applicable. All effluent discharged from the
construction site should comply with the standards stipulated in the DSS-TM. The following measures are recommended
to protect water quality of the inland waters, and when properly implemented
should be sufficient to adequately control site discharges so as to avoid water
quality impacts.
Construction Run-off
5.8.4
Surface run-off from construction sites should
be discharged into storm drains via adequately designed sand/silt removal
facilities such as sand traps, silt traps and sedimentation basins. Channels or earth bunds or sandbag
barriers should be provided on-site during construction works to properly
direct stormwater to such silt removal facilities. Perimeter channels should be provided at
site boundaries where necessary to intercept storm run-off from outside the
site so that it will not wash across the site. Catchpits and perimeter channels should
be constructed in advance of site formation works and earthworks.
5.8.5
Silt removal facilities, channels and manholes
should be maintained and the deposited silt and grit should be removed
regularly, at the onset of and after each rainstorm to prevent overflows and
localised flooding. Before disposal
of at the public fill reception facilities, the deposited silt and grit should
be solicited in such a way that it can be contained and delivered by dump truck
instead of tanker truck. Any
practical options for the diversion and re-alignment of drainage should comply
with both engineering and environmental requirements in order to provide
adequate hydraulic capacity of all drains.
5.8.6
Construction works should be programmed to
minimise soil excavation works in rainy seasons (April to September) as far as
practicable. If soil excavation
cannot be avoided in these months or at any time of year when rainstorms are
likely, for the purpose of preventing soil erosion, temporary exposed slope
surfaces should be covered e.g. by tarpaulin, and temporary access roads should
be protected by crushed stone or gravel, as excavation proceeds. Intercepting channels should be provided
(e.g. along the crest / edge of excavation) to prevent storm run-off from
washing across exposed soil surfaces.
Arrangements should always be in place in such a way that adequate
surface protection measures can be safely carried out well before the arrival
of a rainstorm.
5.8.7
Earthworks final surfaces should be well
compacted and the subsequent permanent works or surface protection should be
carried out immediately after the final surfaces are formed to prevent erosion
caused by rainstorms. Appropriate
drainage like intercepting channels should be provided where necessary.
5.8.8
Measures should be taken to minimise the ingress
of rainwater into trenches. If
excavation of trenches in wet seasons is necessary, they should be dug and
backfilled in short sections.
Rainwater pumped out from trenches or foundation excavations should be
discharged into storm drains via silt removal facilities.
5.8.9
Open stockpiles of construction materials (e.g.
aggregates, sand and fill material) on sites should be covered with tarpaulin
or similar fabric during rainstorms.
Measures should be taken to prevent the washing away of construction
materials, soil, silt or debris into any drainage system.
5.8.10
Manholes (including newly constructed ones)
should always be adequately covered and temporarily sealed so as to prevent
silt, construction materials or debris from getting into the drainage system,
and to prevent storm run-off from getting into foul sewers. Discharge of surface run-off into foul
sewers must always be prevented in order not to unduly overload the foul
sewerage system.
5.8.11
If bentonite slurries are required for any
construction works, they should be reconditioned and reused wherever
practicable to minimise the disposal volume of used bentonite slurries. Temporary enclosed storage locations
should be provided on-site for any unused bentonite that needs to be
transported away after the related construction activities are completed. Requirements as stipulated in ProPECC PN
2/24 should be closely followed when handling and disposing bentonite slurries.
Boring and Drilling Water
5.8.12
Water used in ground boring and drilling for
site investigation or rock / soil anchoring should be re-circulated after
sedimentation as far as practicable.
When there is a need for final disposal, the wastewater should be
discharged into storm drains via silt removal facilities.
Wheel Washing Water
5.8.13
All vehicles and plants should be cleaned before
they leave a construction site to minimise the deposition of earth, mud and
debris on roads. A wheel washing
bay should be provided at every site exit if practicable and washwater should
have sand and silt settled out or removed before discharging into storm
drains. The section of construction
road between the wheel washing bay and the public road should be paved with backfill
to reduce vehicle tracking of soil and to prevent site run-off from entering
public road drains.
Rubbish and Litter
5.8.14
Good site practices should be adopted to remove
rubbish and litter from construction sites so as to prevent the rubbish and
litter from spreading from the site area.
It is recommended to clean the construction sites on a regular basis.
Effluent Discharge
Sewage Effluent from
Construction Workforce
Accidental Spillage of
Chemicals
5.8.19
Any service shop and maintenance facilities
should be located on hard standings within a bunded area, and sumps and oil
interceptors should be provided.
Maintenance of vehicles and equipment involving activities with
potential leakage and spillage should only be undertaken within the areas
appropriately equipped to control these discharges.
·
Suitable containers should be
used to hold the chemical wastes to avoid leakage or spillage during storage,
handling and transport.
·
Chemical waste containers
should be suitably labelled, to notify and warn the personnel who are handling
the wastes to avoid accidents.
·
Storage area should be
selected at a safe location on site and adequate space should be allocated to
the storage area.
Construction Works in
Close Proximity of Inland Water
·
Construction works close to
the inland waters should be carried out in the dry season as far as practicable
where the flow in the surface channel or stream is low.
·
The use of less or smaller
construction plants may be specified in areas close to the watercourses to
reduce the disturbance to the surface water.
·
Temporary storage of materials
(e.g. equipment, chemicals and fuel) and temporary stockpile of construction
materials should be located well away from any watercourses when carrying out
of the construction works.
·
Stockpiling of construction
materials and dusty materials should be covered and located away from any
watercourses.
·
Construction debris and spoil
should be covered up and / or disposed of as soon as possible to avoid being
washed into the nearby water receivers.
·
Proper shoring may need to be
erected in order to prevent soil or mud from slipping into the watercourses.
Revitalisation Works at
NTMDC
5.8.22 In
addition to the mitigation measures recommended in Section 5.8.21
above, the following measures should also be followed to minimise the potential
water quality impacts from the revitalisation works at the NTMDC:
·
All the construction works
should be undertaken in dry conditions and physically separated from the
watercourses downstream, for example,
by provision of concrete blocks, sandbag barriers or other
appropriate measures, prior
to the construction works within the NTMDC.
·
Physical barriers (such as
concrete blocks/sandbags or other appropriate measures) with impermeable liners
will be deployed to confine the works area within the NTMDC to maintain a dry
condition within and to prevent pollutants running into the downstream waters;
and depending on the site conditions, physical barriers or temporary drainage
would be established to intercept and divert the upstream flow.
·
Dewatering of the construction
works area within the NTMDC should
be conducted prior to the construction works.
·
Silt removal facilities should
be adopted to treat the wastewater from dewatering operations prior to
discharge.
·
Details of the containment
structures, flow diversion pathway and water treatment method should be
provided by the Contractor to the Engineer for approval before commencement of
construction works within the NTMDC.
·
After completion of the
construction works within the NTMDC, the works area should be cleaned up before
receiving any water flow or connecting to any existing watercourse(s).
Removal / Diversion of
Watercourses
5.8.25
The Contractor should provide a dry zone for all
the construction works to be undertaken in watercourses and stormwater drainage
following the tentative works sequence as described above or using other
approved methods as appropriate to suit the works condition. The flow diversion
works should be conducted in dry season, where possible, when the flow in the
watercourse is low. The wastewater and ingress water from the site should be
properly treated to comply with the WPCO before discharge.
Removal / Filling of Ponds
Groundwater from
Contaminated Areas, Contaminated Site Run-off and Wastewater from Land
Decontamination
5.8.30
No direct discharge of groundwater from
contaminated areas should be adopted.
Prior to any excavation works within the potentially contaminated areas,
the baseline groundwater quality in these areas should be reviewed based on the
past relevant site investigation data and any additional groundwater quality
measurements to be performed should be made reference to Guidance Note for
Contaminated Land Assessment and Remediation. The review results should be
submitted to EPD for examination. If the review results indicated that the
groundwater to be generated from the excavation works would be contaminated,
this contaminated groundwater should be either properly treated or properly
recharged into the ground in compliance with the requirements of the DSS-TM. If
wastewater treatment is to be deployed for treating the contaminated
groundwater, the wastewater treatment unit should deploy suitable treatment
processes (e.g. oil interceptor / activated carbon) to reduce the pollution
level to an acceptable standard and remove any prohibited substances (such as
total petroleum hydrocarbon) to an undetectable range. All treated effluent
from the wastewater treatment plant should meet the requirements as stated in
the DSS-TM and should be either discharged into the foul sewers or tankered
away for proper disposal.
Emergency Response Plan
(ERP) for Construction Site Discharges
·
Provide spare or standby
treatment facilities of suitable capacities for emergency replacement in case
damage or defect or malfunctioning of the duty treatment facilities is observed;
·
Conduct daily integrity
checking of the construction site drainage and treatment facilities to inspect
malfunctions, before, during and after a storm event; and
·
Carry out regular maintenance
or desilting works to maintain effectiveness of the construction site drainage
and treatment facilities before, during and after a storm event.
5.8.33
An ERP should be developed to minimise the
potential impact from construction site discharges under failure of treatment
facilities during emergency situations or inclement weather. The ERP should give the emergency
contacts to mobilise flood retention facilities and stakeholders to be
notified, as well as the details of the proposed construction site drainage
system and the design and operation of duty and standby treatment facilities. The ERP should also provide the
procedures and guidelines for routine integrity checking and maintenance of the
drainage system and treatment facilities as well as the emergency response and
rectification procedures to restore normal operation of the treatment
facilities in case of treatment failure during emergency situation or inclement
weather. An event and action plan
including the water quality monitoring requirement to be conducted during
emergency discharge should be included in the ERP. The ERP should be submitted to the EPD
for approval before commencement of the construction works.
5.9
Mitigation Measures for Operational Phase
5.9.1
Relevant
design, contingency plan and mitigation measures as described below should be
incorporated into the Project's contract documents.
Stormwater Management
Practices and Stormwater Pollution Control Plan
Design Measures to Control
Erosion and Run-off Quantity
5.9.3
Exposed surface should be avoided as far as
practicable within the Development Area to minimise soil erosion. The Development Area, including open
space, roadside amenity strips and central dividers, should be either hard
paved or covered by landscaping area and plantation where appropriate to reduce
soil erosion. Green areas / tree / shrub planting would be introduced within
the Development Area in open space, along roadside amenity strips and central
dividers as far as practicable to reduce soil erosion.
5.9.4
All the watercourses, except the existing NTMDC
which will be retained and revitalised, within the Project Site will be removed
or diverted. The drainage system should be designed to avoid flooding based on
the 1 in 50-year return period in accordance with Stormwater Drainage Manual
(5th Edition) published by DSD.
Devices / Facilities to
Control Pollution
5.9.5
Screening facilities such as standard gully
grating and trash grille, with spacing which is capable of screening off large
substances such as fallen leaves and rubbish should be provided at the inlet of
drainage system.
5.9.6
Road gullies with standard design and silt traps
and oil interceptors should be incorporated during the detailed design to
remove particles present in stormwater run-off.
5.9.7
Evergreen tree species, which in general
generate relatively smaller amount of fallen leaves, should be selected where
possible in landscaping design.
Administrative Measures
5.9.8
Good management measures such as regular
cleaning and sweeping of road surface / open areas is suggested. The road surface / open area cleaning
should also be carried out prior to occurrence of rainstorm.
5.9.9
Manholes, as well as stormwater gullies and
ditches provided among the Development Area should be regularly inspected and
cleaned (e.g. monthly). Additional inspection and cleansing should be carried
out before forecasted heavy rainfall.
5.9.10
For maintenance of stormwater drainage
system, reference should be made to ETWB TC (Works) No. 14/2004 Maintenance
of Stormwater Drainage Systems and Natural Watercourses where
applicable. This Circular sets out
the departmental responsibilities for the maintenance of stormwater drainage
systems and natural watercourses in government and private lands. Any required maintenance or desilting
work (e.g. removal of any silt, grit or rubbish deposited in the inland water
system) should be carried out during periods of low flow in dry season to
minimise impacts on downstream water quality and sediment suspension.
Blue-green Infrastructure
to Control Sedimentation and Run-off Quantity
5.9.11
Various blue-green infrastructures have been
proposed under this Project to reduce the drainage loading to the drainage
system. They include:
·
Rainwater harvesting should be
implemented within the Development
Area,
where possible, to collect rainwater from building roofs, podiums, walkway
canopies and other built structures for reuse as an alternative water source
e.g. irrigation. The system should
meet the prevailing DSD Practice Note No. 4/2022 Guidelines on Water
Harvesting.
·
Porous paving materials should be used, where
practical,
to increase stormwater infiltration, improve groundwater recharge and reduce flooding from surface
run-off.
·
Green roofs would be proposed
with vegetation to absorb rainwater and reduce site run-off.
Stormwater Pollution
Control Plan
Sewage Overflow and
Emergency Discharge from Sewage Pumping Station
·
A standby pump and screen
should be provided to cater for breakdown and maintenance of the duty pump in
order to avoid emergency discharge.
·
Backup power supply in the
form of dual / ring circuit power supply or generator should be provided to
secure electricity supply.
·
An alarm should be installed
to signal emergency high water level in the wet well.
·
An emergency storage tank /
spare volume of wet well should be provided for the proposed SPS to cater for
breakdown and maintenance of duty pump.
·
Regular maintenance and
checking of plant equipment should be undertaken to prevent equipment failure.
·
A telemetry system to the
nearest manned station / plant should be provided so that swift action can be
undertaken in case of malfunction of the unmanned facilities.
·
A bar screen (with clear
spacing of approximately 25 mm) should be provided to cover the lower half of
the opening of any emergency sewage bypass which can prevent the discharge of
floating solids into receiving waters as far as practicable while ensuring
flooding at the facilities would not occur event if the screen is blocked.
·
Locations of water bodies or
WSRs in the vicinity of the emergency discharges.
·
A list of relevant government
departments to be informed and to provide assistance in the event of emergency
discharge, including key contact persons and telephone numbers.
·
Reporting procedures required
in the event of emergency discharges.
·
Procedures listing the most
effective means in rectifying the breakdown of the SPS in order to minimise the
discharge duration.
Control of Operational
Site Effluents
5.9.15
The practices outlined in ProPECC PN 1/23 should
be adopted where applicable for handling, treatment and disposal of operational
stage effluent. Drainage outlets provided in covered areas, such as covered
electricity substation, covered podiums and other roofed areas, should be
discharged to foul sewers.
5.9.16
Drainage serving the Project’s covered Transport
Interchange Hub, Public Transport Terminus and RCPs should be connected to foul
sewers. Sedimentation facilities, petrol interceptors or other appropriate
wastewater treatment system should be provided to treat the wastewater or
surface run-off generated in these facilities as necessary to meet the
discharge standards as stipulated in the DSS-TM prior to the discharge of these
effluents to the public sewers.
5.10.1
With proper mitigation measures deployed during
the construction and operational phases, no residual water quality impact is
anticipated.
5.11.1
The construction
of the Project tentatively commence in 2027 for completion by 2036. The Project
would potentially overlap with the construction periods of other nearby
concurrent projects as identified in Section 2. Nevertheless, with
implementation of the adequate mitigation measures, BMPs and effective site
management for individual projects, cumulative water quality impacts during
construction phase are not anticipated.
5.11.2
In particular,
the proposed NTM Station and NTD under NOL Main Line are located within the
Development Area. The NOL Main Line is a Schedule 2 designated project and the
potential water quality impacts arising from its operation were evaluated in
the approved NOL EIA report (Register No.: AEIAR-259/2024). Since all sewage
effluent (e.g. from staff and passengers, etc.), wastewater and washed water
generated from the operation of NOL Main Line will be properly collected and
discharged to the public sewerage system, and no wastewater discharge to the
watercourses or nearby water environment would occur, it is concluded that
there would be no adverse cumulative water quality impact anticipated during
the operation of the Project.
5.12.1
Considering that the proposed revitalisation
works would be carried out at NTMDC and its branches, baseline and construction
phase water quality monitoring at NTMDC is recommended to be carried out.
Details of the recommended water quality monitoring requirements are provided
in the stand-alone EM&A Manual for the Project.
5.12.2
A WPCO licence should be obtained if there would
be construction drainage discharge.
Self-monitoring and reporting should be carried out for monitoring the
construction drainage discharge in accordance with the requirements of WPCO
licence.
5.12.3
It is also recommended that regular site
inspection during the construction phase should be undertaken to inspect the
construction activities and works areas in order to ensure the recommended
mitigation measures are properly implemented.
5.13
Environmental
Acceptability of Schedule 2 Designated Projects
Construction and Operation of new District
Distributor Road (Road D1) (DP1)
5.13.1 With proper implementation of the
recommended mitigation measures and BMPs for the construction activities as
described in Section 5.8, as well as the mitigation measures
and BMPs to reduce pollution arising from the surface water run-off during the
operational phase as described in Section 5.9, no adverse water quality impact would be resulted from the
construction and operation of the proposed roads.
Revitalisation of NTMDC and River Diversion Works
(DP2)
5.13.2 With proper implementation of the
recommended mitigation measures and BMPs for construction activities in close
proximity of or in watercourses and by avoiding polluted site run-off from
entering the revitalised drainage channel water during construction phase,
along with BMPs to reduce pollution arising from the surface water run-off
during the operational phase (as detailed in Section 5.8), no adverse water quality impact would result from the proposed
revitalisation works.
Construction Phase
5.14.1
Water quality impacts from the construction
works are associated with the general construction activities, construction
site run-off, sewage effluent from construction workforce, accidental spillage
of chemicals, construction works in close proximity of / in inland waters,
removal / diversion of watercourses, removal / filling of ponds, groundwater
from contaminated areas, contaminated site run-off and wastewater from land
decontamination. The site practices as outlined in the ProPECC PN 2/24 and the
ETWB TC(W) No. 5/2005 are recommended to be implemented in order to minimise
the potential water quality impacts from the construction activities. Proper
site management and good site practices are also recommended to ensure that
construction and demolition wastes and other construction-related materials
would not enter the nearby watercourses. Sewage effluent arising from the
construction workforce would be handled through provision of adequate portable
toilets. Water quality monitoring and regular site inspection will be
implemented during the construction phase to ensure that the recommended
mitigation measures are properly implemented. With the implementation of the
recommended mitigation measures, the construction works for the Project would
not result in adverse impacts on water quality.
Operational Phase
5.14.2
All sewage generated from the Project will be
discharged to the public sewerage system and diverted to San Tin EPP, and when
necessary, to the Yuen Long
EPP for proper treatment via the proposed SPS. To avoid emergency bypass
to the maximum extent as far as practicable, various precautionary measures
have been proposed for incorporation in the design of the SPS. Also, a
Contingency Plan is recommended to be developed for dealing with the remote
occurrence of emergency discharge. Hence, the possibility of sewage overflow
would be remote and the associated adverse water quality impact would be
minimised.
5.14.3
Another source of potential impact during the
operational phase will be non-point source run-off from impervious areas.
Stormwater control measures including adequate stormwater drainage system with
suitable pollutant removal devices, blue-green infrastructure and BMPs are
recommended for the Project to minimise the non-point source pollution. The removal of watercourses would have
minimal impact on hydrology and flow regime. With proper implementation of the recommended
mitigation measures, it is anticipated that the water quality impacts
associated with the non-point source discharge from road surfaces and developed
areas would be minimised.