6
water quality Impact
6.1.1
This
section presents an assessment of the potential water quality impacts
associated with construction and operation of the Project. Recommendations for mitigation measures
were provided to minimize the identified water quality impacts.
Environmental Impact
Assessment Ordinance (EIAO)
6.2.1
The
Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) was
issued by Environmental Protection Department (EPD) under Section 16 of the
EIAO. It specifies the assessment
method and criteria that are to be followed in an EIA Study. Reference sections in the EIAO-TM
provide the details of assessment criteria and guidelines that are relevant to
the water quality impact assessment, including:
·
Annex
6 – Criteria for Evaluating Water Pollution; and
·
Annex
14 – Guidelines for Assessment of Water Pollution.
Water Quality Objective
Table 6.1 Summary of
Water Quality Objectives for Deep Bay WCZ
|
Parameters
|
Criteria
|
Subzone
|
|
Aesthetic appearance
|
Waste discharges shall cause no objectionable odours or
discolouration of the water.
|
Whole Zone
|
|
|
Tarry residues, floating wood, articles made of glass, plastic,
rubber or of any other substances should be absent.
|
|
|
|
Mineral oil should not be visible on the surface. Surfactants should
not give rise to a lasting foam.
|
|
|
|
There should be no recognisable sewage-derived debris.
|
|
|
|
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.
|
|
|
|
Waste discharges shall not cause the water to contain substances
which settle to form objectionable deposits.
|
|
|
Bacteria
|
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)
|
|
|
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
|
|
|
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
|
|
|
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)
|
|
Dissolve Oxygen (DO) within 2 m of the seabed
|
The level of dissolved oxygen should not be less than 2 mg/L for 90%
of the sampling occasions during the whole year.
|
Outer Marine Subzone excepting Mariculture Subzone
|
|
Dissolved Oxygen (DO)
|
The level of dissolved oxygen should not be less than 4 mg/L for 90% of
the sampling occasions during the whole year, taken at 1 metre below surface.
|
Inner Marine Subzone excepting Mariculture Subzone
|
|
|
The level of dissolved oxygen should not be less than 4 mg/L for 90%
of the sampling occasions during the whole year, calculated as water column
average.
|
Outer Marine Subzone excepting Mariculture Subzone
|
|
|
The level of dissolved oxygen should not be less than 5 mg/L for 90%
of the sampling occasions during the whole year, taken at 1 metre below
surface.
|
Mariculture Subzone
|
|
|
The level of dissolved oxygen should not 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
|
Human activity 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
|
|
|
Human activity 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 ℃.
|
Whole Zone
|
|
Salinity
|
Waste discharges shall not cause the natural ambient salinity level
to change by more than 10%.
|
Whole Zone
|
|
pH
|
To be in the range of 6.5-8.5, change due to human activity not to
exceed 0.2 units.
|
Marine waters excepting Yung Long Bathing Beach Subzone
|
|
|
To be in the range of 6.5-8.5.
|
Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone,
Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones
|
|
|
To be in the range of 6.0-9.0.
|
Other inland waters
|
|
|
To be in the range of 6.0-9.0 for 95% of samples, change due to human
activity not to exceed 0.5 units.
|
Yung Long Bathing Beach Subzone
|
|
Suspended Solids (SS)
|
Waste discharges shall neither cause the natural ambient level to be
raised by 30% nor give rise to accumulation of suspended solids which may
adversely affect aquatic communities.
|
Marine waters
|
|
|
Human activity 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
|
|
Un-ionized ammonia (UIA)
|
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 Subzone
|
|
|
(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 Subzone
|
|
5-Day Biochemical Oxygen Demand (BOD5)
|
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
|
|
|
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)
|
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
|
|
|
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
|
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
|
|
|
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 Effluents Discharge Standards
6.2.3
Discharges
of effluents are subject to control under the WPCO. The Technical Memorandum on Standards
for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal
Waters (DSS-TM), issued under Section 21 of the WPCO, gives guidance on
permissible effluent discharges based on the type of receiving waters (foul
sewers, storm water drains, inland and coastal waters). The limits control the physical, chemical
and microbial quality of effluent.
Any sewage from the proposed construction and operational activities
must comply with the standards for effluent discharged into the foul sewers and
coastal waters of the Deep Bay WCZ provided in the DSS-TM.
Practice Notes
Professional Persons Environmental
Consultative Committee Practice Note 1/94 Construction Site Drainage
6.2.4
The
Practice Note for Professional Persons ProPECC PN
1/94 “Construction Site Drainage” published by EPD provides good practice
guidelines for dealing with ten types of discharge from a construction
site. These include surface runoff,
groundwater, boring and drilling water, bentonite slurry, water for testing and
sterilisation of water retaining structures and water
pipes, wastewater from building construction, acid cleaning, etching and
pickling wastewater, and wastewater from site facilities. Guidelines given in ProPECC
PN 1/94 should be followed as far as possible during construction to minimize
the water quality impact due to construction site drainage.
Professional Persons Environmental
Consultative Committee Practice Note 5/93 Drainage Plans subject to Comment by
the Environmental Protection Department (ProPECC PN
5/93)
6.2.5
EPD
has issued a Professional Persons Environmental Consultative Committee Practice
Note 5/93 Drainage Plans (ProPECC PN 5/93) to provide
reference in preparing drainage plans for various types of wastewater
that would arise from the proposed Project. Guidelines for handling such wastewater
should be closely followed where appropriate.
Technical Circular
6.2.6
Environment,
Transport and Works Bureau Technical Circular (ETWB TC) (Works) No. 5/2005
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 ETWB TC (Works) No. 5/2005 should be followed
as far as possible to protect the inland watercourses at or near the Project
area during the construction phase.
Hong Kong Planning
Standards and Guidelines
6.2.7
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.
Requirement of No Net Increase
in Pollution Load to Deep Bay
6.2.8
As
stated in Town Planning Board Guideline No.12B, the pollution loads of concern
should be offset by equivalent reduction of current loads for new discharge
into Deep Bay. The "Requirement
of No Net Increase in Pollution Load" aims to provide protection to
the inland and marine water quality of the Deep Bay WCZ. The pollutions entering Deep Bay have
exceeded the assimilative capacity of the water body. Further increasing the pollution loads
to the water body is therefore environmentally undesirable.
Assessment Area
Marine Water
6.3.2
Marine
water monitoring data collected by EPD in 2022 are summarised in Table 6.2 for DM1, DM2 and DM3 respectively, and the respective locations of
these monitoring stations are illustrated in Figure No. C1603/C/NOL/ACM/M53/301. Descriptions of the
baseline water quality conditions provided in the subsequent section are based
on the EPD’s report Marine Water Quality Hong Kong in 2022.
6.3.3
In 2022, the overall WQO compliance rate for the
Deep Bay WCZ was 67%, 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 TIN levels exceeding the respective TIN WQOs, a noticeable
long-term decrease in TIN levels since mid-2000s has been seen.
Table 6.2 Summary Statistics of Marine
Water Quality of Deep Bay WCZ Collected by EPD in 2022
|
|
Inner Deep Bay
|
WPCO WQO
|
|
Parameters
|
DM1
|
DM2
|
DM3
|
(in marine waters)
|
|
Temperature
(°C)
|
24.8
(17.9 - 32.4)
|
25.0
(18.0 - 32.1)
|
24.9
(18.9 - 31.0)
|
Not more than 2℃ in daily temperature range
|
|
Salinity
|
14.9
(0.5 - 23.3)
|
17.0
(0.4 - 25.8)
|
21.6
(5.4 - 29.1)
|
Not to cause more than 10% change
|
|
Dissolved Oxygen
(mg/L)
|
Depth Average
|
6.5
(4.9 - 9.2)
|
6.0
(4.9 - 7.8)
|
6.0
(4.8 - 6.9)
|
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 samples
|
|
|
Bottom
|
N/A
|
N/A
|
N/A
|
Outer Marine Subzone excepting Mariculture Subzone: Not less than 2
mg/L for 90% of samples
|
|
Dissolved Oxygen
(% Saturation)
|
Depth Average
|
85
(63 - 123)
|
80
(66 - 111)
|
82
(71 - 94)
|
Not available
|
|
|
Bottom
|
N/A
|
N/A
|
N/A
|
Not available
|
|
pH
|
7.4
(7.0 - 8.5)
|
7.4
(6.9 - 8.3)
|
7.5
(7.1 - 7.9)
|
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)
|
1.1
(0.9 - 1.6)
|
1.2
(0.9 - 1.5)
|
1.5
(1.2 - 2.2)
|
Not available
|
|
Turbidity
(NTU)
|
85.9
(9.9 - 288.0)
|
90.0
(9.4 - 384.0)
|
46.0
(1.8 - 264.0)
|
Yung Long Bathing Beach Subzone: Not reduce light transmission
substantially from the normal level
|
|
Suspended Solids
(SS) (mg/L)
|
27.6
(7.0 - 58.0)
|
26.2
(4.7 - 65.0)
|
9.3
(2.6 - 22.0)
|
Not more than 30% increase
|
|
5-day Biochemical
Oxygen Demand (BOD5) (mg/L)
|
1.8
(<0.1 - 6.0)
|
1.5
(0.4 - 3.2)
|
0.8
(0.2 - 3.5)
|
Not available
|
|
Ammonia Nitrogen
(NH3-N)
(mg/L)
|
0.538
(0.088 - 1.200)
|
0.379
(0.050 - 1.400)
|
0.182
(0.024 - 0.420)
|
Not available
|
|
Unionised Ammonia
(mg/L)
|
0.008
(0.002 - 0.024)
|
0.007
(<0.001 - 0.043)
|
0.003
(<0.001 - 0.011)
|
Not more than annual average of 0.021mg/L
|
|
Nitrite Nitrogen
(NO2-N)
(mg/L)
|
0.161
(0.094 - 0.420)
|
0.119
(0.067 - 0.200)
|
0.066
(0.025 - 0.130)
|
Not available
|
|
Nitrate Nitrogen
(NO3-N)
(mg/L)
|
1.200
(0.840 - 1.800)
|
1.120
(0.510 - 2.300)
|
0.700
(0.280 - 1.200)
|
Not available
|
|
Total Inorganic
Nitrogen (TIN) (mg/L)
|
1.90
(1.13 - 2.61)
|
1.61
(0.70 - 2.89)
|
0.95
(0.41 - 1.49)
|
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)
|
0.93
(0.46 - 2.10)
|
0.73
(0.37 - 2.10)
|
0.40
(0.19 - 0.82)
|
Not available
|
|
Total Nitrogen
(TN)
(mg/L)
|
2.29
(1.40 - 3.37)
|
1.96
(0.95 - 3.59)
|
1.16
(0.51 - 1.85)
|
Not available
|
|
Orthophosphate
Phosphorus (PO4) (mg/L)
|
0.120
(0.018 - 0.180)
|
0.100
(0.014 - 0.130)
|
0.059
(<0.002 - 0.160)
|
Not available
|
|
Total Phosphorus
(TP) (mg/L)
|
0.26
(0.16 - 0.41)
|
0.22
(0.13 - 0.35)
|
0.12
(0.05 - 0.21)
|
Not available
|
|
Silica (as SiO2)
(mg/L)
|
5.74
(1.70 - 8.90)
|
5.17
(0.96 - 11.00)
|
3.74
(1.30 - 7.40)
|
Not available
|
|
Chlorophyll-a
(μg/L)
|
8.8
(2.1 - 45.0)
|
8.9
(2.1 - 33.0)
|
3.0
(0.8 - 7.5)
|
Not available
|
|
E.
coli
(count/100mL)
|
500
(31 - 4900)
|
170
(3 - 10000)
|
32
(<1 - 430)
|
Secondary Contact Recreation Subzones and Mariculture
Subzone (L.N. 455 of 1991): Not exceed 610 per 100mL
Yung Long Bathing Beach Subzone (L.N.455 of
1991): Not exceed 180 per 100mL
|
|
Faecal Coliforms
(count/100mL)
|
1200
(88 - 24000)
|
430
(9 - 18000)
|
53
(<1 - 900)
|
Not available
|
Notes:
1.
Data source: EPD Marine Water
Quality in Hong Kong in 2022.
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
Table 6.3 Summary Statistics of River
Water Quality of Kam Tin River Collected by EPD in 2022
|
Parameters
|
Kam Tin River
|
WPCO WQO
(in inland waters)
|
|
KT1
|
KT2
|
|
Dissolved Oxygen
(mg/L)
|
5.4
(3.1 - 7.0)
|
3.7
(1.1 - 6.9)
|
Not less than 4 mg/L
|
|
pH
|
7.4
(7.1 - 7.9)
|
7.4
(7.2 - 8.0)
|
Yuen Long & Kam Tin (Upper) Subzone: within the
range of 6.5-8.5
|
|
Suspended Solids
(mg/L)
|
8.8
(1.5 - 27.0)
|
35.0
(3.8 - 58.0)
|
Yuen Long & Kam Tin (Upper) Subzone: Annual
median not to exceed 20 mg/L
|
|
5-Day Biochemical Oxygen Demand (mg/L)
|
10.0
(5.2 - 14.0)
|
21.0
(3.2 - 150.0)
|
Yuen Long & Kam Tin (Upper) Subzone: Not to
exceed 3 mg/L
|
|
Chemical Oxygen Demand (mg/L)
|
20
(12 - 65)
|
52
(9 - 170)
|
Yuen Long & Kam Tin (Upper) Subzone: Not to
exceed 15 mg/L
|
|
Oil & Grease (mg/L)
|
<0.5
(<0.5 - 0.8)
|
1.1
(<0.5 - 2.4)
|
Not available
|
|
E.coli (cfu/100mL)
|
41 000
(5 000 - 340 000)
|
110 000
(24 000 - 1 700 000)
|
Not available
|
|
Faecal Coliforms (cfu/100mL)
|
150 000
(52 000 - 470 000)
|
270 000
(62 000 - 1 900 000)
|
Not available
|
|
Ammonia-nitrogen
(mg/L)
|
4.100
(0.670 - 10.000)
|
7.800
(0.480 - 25.000)
|
Not available
|
|
Nitrate-nitrogen
(mg/L)
|
0.870
(0.410 - 3.300)
|
0.200
(<0.002 - 0.560)
|
Not available
|
|
Total Kjeldahl Nitrogen (mg/L)
|
5.45
(1.80 - 12.00)
|
9.00
(1.90 - 31.00)
|
Not available
|
|
Ortho-Phosphate
(mg/L)
|
0.770
(0.260 - 1.300)
|
0.830
(0.180 - 2.400)
|
Not available
|
|
Total phosphorus
(mg/L)
|
1.20
(0.40 - 1.60)
|
1.40
(0.44 - 3.80)
|
Not available
|
|
Sulphide (mg/L)
|
<0.02
(<0.02 - 0.04)
|
0.05
(<0.02 - 0.11)
|
Not available
|
|
Aluminium (µg/L)
|
<50
(<50 - <50)
|
<50
(<50 - 70)
|
Not available
|
|
Cadmium (µg/L)
|
<0.1
(<0.1 - <0.1)
|
<0.1
(<0.1 - <0.1)
|
Not available
|
|
Chromium (µg/L)
|
<1
(<1 - <1)
|
<1
(<1 - <1)
|
Not available
|
|
Copper (µg/L)
|
2
(1 - 7)
|
1
(<1 - 4)
|
Not available
|
|
Lead (µg/L)
|
<1
(<1 - <1)
|
<1
(<1 - <1)
|
Not available
|
|
Zinc (µg/L)
|
10
(<10 - 25)
|
<10
(<10 - 25)
|
Not available
|
|
Flow (m3/s)
|
0.462
(0.244 - 17.587)
|
0.414
(0.186 - 15.984)
|
Not available
|
Remarks:
1.
Data source: EPD River Water
Quality in Hong Kong in 2022.
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.
Table 6.4 Summary
Statistics of River Water Quality of River Beas Collected by EPD in 2022
|
Parameters
|
River Beas
|
WPCO WQO
(in inland waters)
|
|
RB2
|
RB3
|
|
Dissolved Oxygen
(mg/L)
|
7.3
(6.4 – 9.9)
|
7.9
(4.7 – 13.3)
|
Not less than 4 mg/L
|
|
pH
|
7.3
(6.8 – 7.4)
|
7.4
(7.1 – 8.4)
|
Within the range of 6.5-8.5
|
|
Suspended Solids
(mg/L)
|
4.0
(1.9 – 13.0)
|
19.0
(1.6 – 690.0)
|
Annual median not to exceed 20
mg/L
|
|
5-Day Biochemical Oxygen Demand
(mg/L)
|
5.0
(1.8 – 8.1)
|
6.1
(1.4 – 30.0)
|
Not to exceed 3 mg/L
|
|
Chemical Oxygen Demand (mg/L)
|
12
(5 – 18)
|
15
(4 – 98)
|
Not to exceed 15 mg/L
|
|
Oil & Grease (mg/L)
|
<0.5
(<0.5 – <0.5)
|
<0.5
(<0.5 – <0.5)
|
Not available
|
|
E.coli (cfu/100mL)
|
5 200
(380 – 24 000)
|
9 300
(530 – 57 000)
|
Not available
|
|
Faecal Coliforms (cfu/100mL)
|
25 000
(1 700 – 520 000)
|
38 000
(1 200 – 280 000)
|
Not available
|
|
Ammonia-nitrogen
(mg/L)
|
0.790
(0.120 – 2.600)
|
1.150
(0.130 – 4.100)
|
Not available
|
|
Nitrate-nitrogen
(mg/L)
|
0.550
(0.081 – 0.920)
|
0.655
(0.330 – 1.700)
|
Not available
|
|
Total Kjeldahl Nitrogen (mg/L)
|
1.50
(0.48 – 3.80)
|
2.40
(0.47 – 6.20)
|
Not available
|
|
Ortho-Phosphate
(mg/L)
|
0.110
(0.058 – 0.210)
|
0.110
(0.069 – 0.220)
|
Not available
|
|
Total phosphorus
(mg/L)
|
0.24
(0.10 – 0.53)
|
0.36
(0.14 – 0.94)
|
Not available
|
|
Sulphide (mg/L)
|
<0.02
(<0.02 – <0.02)
|
<0.02
(<0.02 – 0.02)
|
Not available
|
|
Aluminium (µg/L)
|
<50
(<50 - <50)
|
<50
(<50 - <50)
|
Not available
|
|
Cadmium (µg/L)
|
<0.1
(<0.1 - <0.1)
|
<0.1
(<0.1 - <0.1)
|
Not available
|
|
Chromium (µg/L)
|
<1
(<1 - <1)
|
<1
(<1 - <1)
|
Not available
|
|
Copper (µg/L)
|
1
(<1 – 3)
|
1
(<1 – 3)
|
Not available
|
|
Lead (µg/L)
|
<1
(<1 – <1)
|
<1
(<1 – <1)
|
Not available
|
|
Zinc (µg/L)
|
<10
(<10 – 14)
|
<10
(<10 – 16)
|
Not available
|
|
Flow (m3/s)
|
0.265
(0.010 – 33.600)
|
NM
|
Not available
|
Remarks:
1.
Data source: EPD River Water
Quality in Hong Kong in 2022.
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.
6.4.1
Water
sensitive receivers (WSRs) within 500m from the Project site boundary were
identified based on GeoInfo Map, DSD’s Eco-channels
Database Management System (EcoDMS) and Appendix B
Location of Major Flood Control Projects in Northern and Northwestern New
Territories in DSD 2001/02 Annual Report.
The WSRs within assessment area of NOL mainline are listed in Table 6.5, with their indicative locations
presented in Figure Nos. C1603/C/NOL/ACM/M53/302 to
315.
Table 6.5 Summary of Water Sensitive
Receivers within Assessment Area of NOL Mainline
|
ID
|
Water
Sensitive Receiver
|
Within Aboveground Works Site/ Area?
Yes(1)/No
|
To be
Removed or Diverted under the Project?
|
|
Watercourse
|
|
W11
|
Downstream
rivers of mountain in the east of Tsing Long Highway
|
No
|
No
|
|
W12
|
Downstream
rivers of mountain in the west of Tsing Long Highway
|
No
|
No
|
|
W13
|
Ho
Pui Channel
|
Yes for
southern section only
|
No
|
|
W13a
|
Nullah
at Kam Ho Road
|
No
|
No
|
|
W13b
|
Drainage
along Kam Po Road
|
No
|
No
|
|
W13d
|
Modified
watercourse east of Ho Pui Channel
|
No
|
No
|
|
W14
|
Modified
watercourse passing through along farmland west of Tsing Long Highway
|
No
|
No
|
|
W15,
W18
|
Nullah
at Kam Ho Road
|
No
|
No
|
|
W16
|
Downstream
river of Au Tau
|
No
|
No
|
|
W17,
W20
|
Modified
watercourse near Kam Sheung Road
|
No
|
No
|
|
W19
|
Modified
watercourse near Kam Shek Road
|
No
|
No
|
|
W21
|
Kam
Tin River
|
Yes
|
No
|
|
W21a
|
Mo
Fan Heung Stream
|
No
|
No
|
|
W21b,
W21c, W21f, W21g
|
Tributaries
of Kam Tin River
|
No
|
No
|
|
W21d
|
Tributaries
of Kam Tin River
|
Yes
|
Yes, a
section of W21d will be removed and diverted during the construction of
ancillary building, while another section of W21d will be affected by other
project for road works
|
|
W21e
|
Tributaries
of Kam Tin River
|
No
|
No
|
|
W22
|
Yuen
Long Bypass Floodway
|
No
|
No
|
|
W23
|
Modified
watercourse near Mei Fung Road
|
No
|
No
|
|
W24
|
Drainage
along San Tam Road
|
Yes
|
No
(Remark: W24 will be removed and modified as underground drainage by other project)
|
|
W25,
W26, W27, W33
|
Downstream
rivers of Kai Kung Leng
|
No
|
No
|
|
W28,
W31
|
Downstream
rivers of Kai Kung Leng
|
Yes
|
Yes, W28
and W31 will be partially removed and diverted
|
|
W29
|
Modified
watercourse near Pok Wai West Road
|
No
|
No
|
|
W30
|
Ngau
Tam Mei Drainage Channel
|
No
|
No
|
|
W30a,
W30b, W30c, W30e, W30f, W30g
|
Upstream
semi-modified watercourse of Ngau Tam Mei Drainage Channel
|
No
|
No
|
|
W30d
|
Upstream
semi-modified watercourse of Ngau Tam Mei Drainage Channel
|
Yes
|
Yes,
W30d will be partially removed and diverted
|
|
W32
|
Downstream
rivers of Kai Kung Leng
|
Yes
|
Yes, W32
will be partially removed and diverted
|
|
W34,
W52
|
Drainage
along San Tin Highway
|
No
|
No
|
|
W35
|
Drainage
along Castle Peak Road – Tam Mi
|
No
|
No
|
|
W36
|
Semi-modified
watercourse near Wah On Villa
|
No
|
No
|
|
W38
|
Abandoned
meander from the Ngau Tam Mei Drainage Channel
|
No
|
No
|
|
W39
|
Drainage
of Tam Mei Barracks
|
No
|
No
|
|
W40
|
Drainage
of Tam Mei Firing Range
|
No
|
No
|
|
W41
|
Downstream
rivers of Ngau Tam Shan
|
No
|
No
|
|
W42
|
Downstream
river of mountain of Tam Mei
|
No
|
No
|
|
W43
|
Modified
watercourse in Tam Mei
|
No
|
No
|
|
W44
|
Semi-modified
watercourse near Ko Hang
|
No
|
No
|
|
W45
|
Modified
watercourse near Shek Wu Wai San Tsuen
|
Yes
|
Yes, a
section of W45 will be removed and diverted
|
|
W46
|
San
Tin Western Main Drainage Channel
|
Yes
|
Yes, W46
will be partially removed and diverted
|
|
W46a,
W46b
|
Branches
of San Tin Western Main Drainage Channel
|
No
|
No
|
|
W47
|
Modified
watercourse along Kwu Tung Road
|
No
|
No
|
|
W48
|
Modified
watercourse near San Tin Soccer Pitch
|
No
|
No
|
|
W49
|
Modified
watercourse along Mai Po Lung Road
|
Yes
|
No
|
|
W50,
W50a
|
Modified
watercourse along Shek Wu Wai Road
|
No
|
No
|
|
W51
|
Modified
watercourse near Ka Lung Road
|
No
|
No
|
|
W53
|
Drainage
near Chun San Organic Farm
|
No
|
No
|
|
W54,
W54b, W54c, W54d
|
San
Tin Eastern Main Drainage Channel and its upstream natural watercourse
|
No
|
No
|
|
W54a
|
Upstream
natural watercourse of San Tin Eastern Main Drainage Channel
|
Yes
|
No
|
|
W55,
W56
|
Downstream
river of Hadden Hill
|
No
|
No
|
|
W57,
W59
|
Modified
watercourse near Kwu Tung Road
|
No
|
No
|
|
W58
|
Drainage
along Fanling Highway
|
No
|
No
|
|
W60
|
Drainage
along Lok Ma Chau Road
|
No
|
No
|
|
W61
|
Modified
watercourse in Lok Ma Chau
|
No
|
No
|
|
W63
|
Modified
watercourse in Lok Ma Chau
|
Yes
|
No
|
|
W62
|
Downstream
river of Tit Hang Shan
|
No
|
No
|
|
W64
|
Downstream
watercourse of Mount Kirkpatrick
|
No
|
No
|
|
W65,
W65b, W65c, W65d
|
River
Beas and its tributaries
|
No
|
No
|
|
W65a
|
Tributaries
of River Beas
|
Yes
|
N/A(2) (Remark: W65a will be removed by other project)
|
|
W66
|
Modified
watercourse near Sha Po Tsuen
|
Yes
|
Yes, a
short section of W66 will be temporarily diverted during the construction
phase
|
|
W67
|
Modified
watercourse near Castle Peak Road – San Tin
|
No
|
No
|
|
W68
|
Modified
watercourse near Ko Po Tsuen
|
No
|
No
|
|
Ponds
|
|
|
P4-6,
P8-22, P25-40, P42, P46-53, P56-58, P60, P64-68, P70-71, P76-96
|
Ponds
|
No
|
No
|
|
P41,
P43-45, P54-55, P59, P61-63, P69, P72-75
|
Ponds
|
Yes
|
Yes,
P41, P43, P45, P54, P61-63, P69, P74-75 will be partially removed, while the
remaining will be wholly removed
|
|
P23,
P24
|
Ponds
|
Yes
|
Only one
of P24 will be removed, while the remaining will be removed by other project
|
|
PS1
|
Pok
Wai Floodwater Pond
|
No
|
No
|
|
Others
|
|
|
-
|
Conservation
Area (OZP: S/YL-KTS/15; S/YL-KTS/10; S/YL-KTN/10; S/YL-NTM/12)
|
No
|
No
|
|
-
|
West
Rail Compensatory Wetland
|
No
|
No
|
|
-
|
Lam
Tsuen Country Park
|
No
|
No
|
|
-
|
Tai
Lam Country Park
|
No
|
No
|
|
-
|
Wetland
Buffer Area (OZP: S/YL-NSW/8; S/YL-MP/6; S/YL-ST/8)
|
No
|
No
|
|
-
|
Wetland
Conservation Area (OZP: S/YL-KTN/10; S/YL-ST/8)
|
No
|
No
|
Notes:
(1)
In the event of construction
works at watercourse / ponds within the works sites/areas is found unavoidable,
relevant mitigation measures as discussed in Section 6.8 should be strictly followed.
(2)
N/A - Not Applicable.
6.4.2
Water
sensitive receivers (WSRs) within 500m from the boundary of the temporary
explosive magazine site at Tai Shu Ha (Yuen Long) were identified and are
listed below, with their indicative locations shown in Figure No. C1603/C/NOL/ACM/M53/316.
Table 6.6 Summary
of Water Sensitive Receivers within Assessment Area of Temporary Explosive
Magazine Site at Tai Shu Ha
|
ID
|
Water Sensitive Receiver
|
Within Works Site/ Area?
Yes/No
|
To be Removed or Diverted under the Project?
|
|
Watercourse
|
|
W68a – W68e
|
Downstream river of mountains in Tai Lam Country Park
|
No
|
No
|
|
W69 – W75
|
Upstream of Yuen Long Creek
|
No
|
No
|
|
W76
|
Drainage along Tai Shu Ha Road West
|
No
|
No
|
|
Ponds
|
|
P97, P98
|
Ponds near Nam Hang Pai and Nam Hang Tsuen
|
No
|
No
|
|
Others
|
|
-
|
Conservation Area
|
No
|
No
|
|
-
|
Tai Lam Country Park
|
No
|
No
|
6.5.1
The
assessment area includes all areas within 500 m from the Project boundary
including works site and works area, and covers relevant WSRs that have a
bearing on the environmental acceptability of the Project within the Deep Bay
WCZ. The methodology
employed to assess potential water quality impacts associated with the
construction and operation of the Project followed the detailed technical
requirements given in Appendix D of the Study Brief (ESB-346/2021) and was based
on the preliminary design information. No marine dredging works would be
required for this Project.
6.5.2
The
WSRs that may be affected by the Project were identified. Potential sources of water quality
impact that may arise during the construction works and operation activities
were described and quantified, where applicable. All the identified sources of potential
water quality impact were then evaluated and their
impact significance was determined.
The need for mitigation measures to reduce any identified adverse
impacts on water quality to acceptable levels was also determined.
6.6.1
Potential
sources of water quality impact associated with the construction works include:
·
Wastewater
from general construction activities;
·
Construction
site runoff;
·
Groundwater
infiltration and change in groundwater levels;
·
Groundwater
from contaminated areas, contaminated site run-off and wastewater from land decontamination;
·
Demolition
works;
·
Construction
works in close proximity to inland water;
·
Construction
works in Inland Water;
·
Removal
or diversion of watercourses;
·
Removal
or filling of ponds;
·
Accidental
spillage of chemicals; and
·
Sewage
effluent from construction workforce.
General Construction Activities
6.6.2
Wastewater
generated from construction activities, including general cleaning and
polishing, wheel washing, dust suppression and utility installation may contain
high SS concentrations. It may also
contain a certain amount of grease and oil. Potential water quality impacts due to
the wastewater discharge can be minimised with the
implementation of construction and site management practices to ensure that
litter, fuels, and solvents do not enter public drainage systems. It is therefore expected that if the
good site practice suggested in Section 6.8 are followed as far as practicable, the potential water quality impacts
associated with construction activities would be minimal.
Construction Site Runoff
6.6.3
Surface
runoff generated from the construction site may contain increased loads of SS
and contaminants. 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 dust suppression sprays and wheel washing facilities; and
·
Fuel,
oil and lubricants from maintenance of construction vehicles and equipment.
6.6.4
During
rainstorms, site run-off would wash away the soil particles on unpaved lands
and areas with topsoil exposed, if any.
The run-off is generally characterized by high concentrations of SS. Release of uncontrolled site run-off
would increase the SS levels and turbidity in the nearby streams. Site run-off may also wash away
contaminated soil particles and therefore cause water pollution.
6.6.5
Windblown
dust would be generated from exposed soil surfaces in the works areas. It is possible that windblown dust would
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 runoff causing a potential impact
to the nearby sensitive receivers.
6.6.6
It
is important that proper site practice and good site management be followed to
prevent run-off with high level of SS from entering the surrounding
waters. Best Management Practices
(BMPs) in controlling construction site discharges are recommended for this
Project. With the implementation of
BMPs to control run-off and drainage from the construction site, disturbance of
water bodies would be avoided and deterioration in water quality would be
minimal. Suggested measures to
control construction site run-off and drainage are described in Section 6.8.
Groundwater Infiltration and Change in Groundwater Levels
6.6.7
Construction
of tunnels may result in infiltration of groundwater (Appendix 6.1 refers). The major concern from these
construction activities would be the increase in site runoff and the associated
potential drawdown of groundwater in any soil and aquifer layers. Groundwater infiltration would affect
the construction works and infiltrated water would carry away silt from site
into the site drainage. The water
pumped out from the tunnel may also be contaminated by grouting materials. Consideration should be taken in
underground tunnel design to minimise the infiltration of groundwater and the
potential impacts from the change in groundwater level.
Groundwater from Contaminated Areas, Contaminated Site Run-off and
Wastewater from Land Decontamination
6.6.8
It was
identified that some of the construction works areas would have land
contamination issues. Proper land
contamination remediation and mitigation measures are proposed in Section 6.8.
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.
Excavated contaminated materials will be properly stored, housed and
covered to avoid generation of contaminated run-off. Open stockpiling of contaminated
materials will not be allowed. Any
contaminated site run-off and wastewater from land decontamination activities
will be properly treated and disposed in compliance with the requirements of
the DSS-TM. Mitigation measures for
contaminated site run-off and wastewater from land decontamination are
recommended in Section 6.8.
With proper implementation of the recommended mitigation measures, the
potential water quality impacts arising from the land decontamination works
would be minimised.
6.6.9
Groundwater
pumped out or from dewatering process during excavation works in the
contaminated areas will be potentially contaminated. Any contaminated groundwater will be
either properly treated or properly recharged into the ground in compliance
with the requirements of the DSS-TM.
No direct discharge of contaminated groundwater will be adopted. Mitigation measures and monitoring
requirements for contaminated groundwater discharge/ recharge are recommended
in Sections 6.8.17 to 6.8.19.
With proper implementation of the recommended mitigation measures, no
unacceptable water quality would be expected from the groundwater generated
from contamination areas.
Demolition works
6.6.10
The Project would involve demolition works of some
existing structures for the construction of NOL. The sewage remaining or washed out from
the decommissioned facilities will not be discharged without treatment. Another key concern from demolition
works would be surface runoff and site effluent. Precipitation that falls on unpaved
lands and areas with the topsoil exposed during the demolition would wash away
soil particles. Such surface runoff
and stormwater overflows with high levels of suspended solids if directly
discharged into the marine and inland waters which may lead to water quality
impact. Effluent discharge from
temporary site facilities should be controlled to prevent direct discharge to
the neighbouring marine waters and storm drains. Such wastewater may include wastewater
resulting from wheel washing of site vehicles at site entrances.
6.6.11
Good site practices should be implemented to control
site runoff and drainage and site effluent from the works areas, and to prevent
runoff and drainage water with high levels of suspended solids from entering
the adjacent Deep Bay waters. With
the implementation of adequate site drainage and provision of sediment removal
facilities as described in Section 6.8 below, it is
anticipated that unacceptable water quality impacts would not arise. Surface runoff would be collected by the
temporary drainage system and then treated or desilted on-site before
discharging to the storm water drain.
Effluent from wheel washing would also be treated or desilted on-site
before discharged. A license should
be obtained from EPD for discharge to the public drainage system.
Construction Works in Close Proximity to Inland Water
6.6.12
Construction activities in close vicinity to the
inland watercourses may impact water quality due to the
potential release of construction waste and wastewater. Construction waste and wastewater are
generally characterized by high SS concentration and elevated pH. The
implementation of adequate construction site drainage and Best Management
Practices as described in Section 6.8 and provision of mitigation measures as specified in ETWB TC (Works) No.
5/2005 “Protection of Natural Streams / Rivers from Adverse Impacts Arising
from Construction Works” as detailed in Section 6.8, it is anticipated that water
quality impacts would be minimal.
Construction Works in Inland Water
6.6.13
The construction of temporary
vehicular bridge structures across Ho Pui Channel (W13)
would require the installation of temporary bridge pier. The bridge piers installation would
involve pilling works and construction activities in Ho Pui Channel, which may
lead to elevated suspended solids (SS) levels and dispersion of SS to the
downstream section of the river if in contact with river water. According to the proposed preliminary
design, concrete block cofferdam would be erected
at Ho Pui Channel and thereafter dewatering and temporary filling will be
conducted inside the cofferdam to create a dry working zone for the
construction of temporary deck such that all the piling and construction works
would be isolated from the water.
The piling and installation of cofferdam would be conducted during dry
season as far as practicable.
Concrete block cofferdam will be removed before the coming wet season to
allow river flow avoiding potential overflow onto the riverbanks of Ho Pui
Channel during wet season. Water
pumps would be used to collect any construction site runoff and ingress/seepage
water within the cofferdam. The collected construction site runoff and
ingress/seepage water would be diverted to the on-site wastewater treatment
facilities for treatment to satisfactory levels before discharge. The temporary vehicular bridge will be
demolished upon completion of required construction works.
6.6.15
A portion of Ho Pui Channel (W13) that is close to the
east side of Pat Heung Depot will also be temporary decked and covered during
the construction phase. Potential
water quality impacts may be generated by discharge of construction materials,
wastewater, excavated spoils, spillage and contaminants to the downstream
receiving waters.
6.6.16
A portion of grout block for TBM breakout underneath
Kam Tin River (W21) at the immediate north of the proposed KSR(NOL) Station
would be constructed in Kam Tin River during dry season. During the construction, concrete blocks
would be erected to fence off the works area such that the grouting works would
be conducted within a dry zone and physically
separated from the water. It is therefore
anticipated that the impact on Kam Tin River would be minimal during
construction.
6.6.17
Ground treatment works (i.e.
grouting works) would be carried out at the area near the upstream watercourse
of Eastern Main Drainage Channel in San Tin (W54a) due to the tunneling works crossing the existing
LMCSL tunnels. It is expected that the proposed grouting works would not
have direct impact on the existing stream and the existing stream could be
retained during construction.
6.6.18
Excavated materials (including sediment) may be
generated from the above works.
Mitigation measures for handling and disposal of excavated materials and
sediment as recommended in Section 6.8 should be followed to minimise the potential
environmental impacts arising from the excavated materials. Mitigation measures for protection of
downstream water quality from diversion / removal of watercourses are described
in Section 6.8. With adoption of the recommended
mitigation measures, there should not be significant sediment and contaminant
release to the downstream water.
6.6.19
Temporary diversion of watercourse is anticipated in
modified watercourse near Sha Po Tsuen (W66). Other watercourses including partial
W21d, W24 and W65a will be removed/diverted/modified before the construction of
the Project under other projects.
Partial removal of existing watercourses (namely W21d, W28, W30d, W31,
W32, W45, and W46), would involve diversion of water flow from their existing
routes to the new routes. Potential
sources of impact may include discharge of concrete slurry and other grouting
materials generated by concreting works as well as release of construction
materials, wastewater, excavated sediment, spillage and contaminants to the
receiving waters in the downstream during soil excavation for construction of
new drainage and demolition of the existing watercourses. All these construction works should be
undertaken in dry conditions to avoid and minimise potential water quality
impacts on the downstream water quality.
The tentative works sequence for diversion and removal of watercourse is
described below.
·
Construction
works at watercourse would be undertaken only after flow diversion or
dewatering operation is fully completed to avoid water flow in the works area.
·
Dewatering
of watercourse would be performed by diverting the water flow to new or
temporary drainage. Where
necessary, cofferdams or similar impermeable sheet pile walls should be used to
isolate the works areas from neighbouring waters.
·
Permanent
or temporary drainage for carrying the diverted flow from existing watercourse
to be removed would be constructed and completed before dewatering of that
existing watercourse.
·
Construction
of all the proposed permanent and temporary drainage would be undertaken in a
dry condition prior to receiving any water flow.
6.6.20
Excavated materials (including sediment) may be
generated from the removal and diversion of watercourses. Mitigation measures for handling and
disposal of excavated materials and sediment as recommended in Section 6.8 should be followed to minimise the potential
environmental impacts arising from the excavated materials.
6.6.21
Mitigation measures for protection of downstream water
quality from diversion and removal of watercourses are described in Section 6.8. With adoption of the recommended
mitigation measures, there should not be significant sediment and contaminant
release to the downstream water.
Removal or Filling of Ponds
6.6.22
One pond of P24, P41, P43-45, P54-55, P59, P61-63,
P69, and P72-75 would be affected partially or wholly by the construction
works, while P23 and remaining ponds of P24 would be affected by others for
road works. The associated construction works would include draining the water
in ponds / watercourses 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 dumping of these drained waters
to the nearby watercourse or marine water will not be allowed.
6.6.23
The drained water generated from dewatering of the
ponds to be removed would be temporarily stored as appropriate in storage tanks
or containers for reuse on-site where practicable and any surplus water would
be tankered away for disposal or treated as necessary
before disposal in compliance with the DSS-TM. In order to minimise the potential
impact, dewatering works at ponds would be conducted within dry season as far
as practicable to minimise the quantity of drained water. No direct discharge of drained water
from these construction works will be allowed.
6.6.24
Excavated materials (including sediment) may be
generated from the construction works in ponds. Mitigation measures for handling and
disposal of excavated materials and sediment as recommended in Section 6.8 should be followed
to minimise the potential environmental impacts arising from the excavated
material. Together with the
adoption of the mitigation measures for removal of ponds as recommended in Section
6.8, no unacceptable
water quality impact would be expected.
Accidental Spillage of Chemicals
6.6.25
The use of chemicals such as engine oil and
lubricants, and their storage as waste materials has the potential to impact
water quality if spillage occurs and enters adjacent streams. Waste oil may infiltrate into the
surface soil layer, or runoff into the nearby streams, increasing hydrocarbon
levels. The potential impacts could
however be mitigated by practical mitigation measures and good site practices
as described in Section 6.8.
Sewage Effluent from Construction Workforce
6.6.26
During
the construction of the Project, the workforce on site will generate sewage
effluent, which is characterized by high levels of BOD, ammonia and E. coli counts. According to Section 5.6.10 of the
Construction Industry Council (CIC)’s publication “Reference Materials –
Construction Site Welfare, Health and Safety Measures”, the number of toilet facilities
should be provided at a ratio of not less than one for every 25 workers. Potential water quality impacts upon the
local drainage and fresh water system may arise from
these sewage effluents, if uncontrolled.
6.6.27
Temporary
sewage generation can be adequately treated by interim sewage treatment
facilities, such as portable chemical toilets. The number of the chemical toilets
required for the construction sites would be 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 portable toilets and be responsible for
appropriate disposal and maintenance.
6.6.28
Provided
that sewage is not discharged directly into storm drains or inland waters
adjacent to the construction site, temporary sanitary facilities are used and
properly maintained, and mitigation measures as recommended in Section 6.8 are adopted as far as practicable, it is
unlikely that sewage generated from the site would have a significant impact on
water quality.
6.6.29
The
construction of the Project would have potential impacts on change of
groundwater table. Such
construction activities would include:
·
Cut
& Cover works for tunnels, stations and ancillary buildings i.e. EAPs/EEPs/VBs;
·
Bored
tunnelling works;
·
Mined
tunnelling works;
·
Drill
& blast construction works for adits, tunnels and
ancillary building; and
·
Site
formation works for NTD.
Cut & Cover Works for Tunnels, Stations and Ancillary Buildings
6.6.30
The
excavation for station boxes, cut & cover tunnels (including overrun
tunnels and southern extension, etc.), ancillary buildings (i.e. EAPs/EEPs/VBs) and construction
shaft structures will require temporary dewatering within the excavation to
facilitate the construction of permanent structure. The Contractors should follow the
contract requirement during the design and construction of temporary works to
control the changes in surrounding piezometric pressure head and/or groundwater
level not to exceed the equivalent of 1m head of water from the specified
groundwater level. Mitigation
measures will be required to mitigate any significant drawdown effects (i.e. >1m) to the groundwater table during the temporary
dewatering works. Provided that the
mitigation measures are properly followed, no unacceptable impact in relation
to the groundwater drawdown would be expected. In addition, those permanent structures
would be designed as watertight structures to avoid the long
term groundwater drawdown issue.
Bored Tunnelling Works
6.6.31
For
the bored tunnelling works, the effects on the external groundwater regime are
expected to be small during construction due to the method of construction and
the use of undrained linings. The
bored tunnels will be constructed using a closed face tunnel boring machine
(TBM) to limit water inflow into the tunnel. The cutter head for the machine will be
sealed during excavation to control the water inflow from the cutter face, and
therefore the water inflow from the face is expected to be insignificant. Precast segmental linings will be
installed and back grouted at the tail skin as the TBM advances along the
alignment, the potential inflow of water behind the TBM shield would be small
and adverse impact on groundwater drawdown would not be anticipated. The permanent precast segment linings
will be designed as watertight structures with Ethylene Propylene Diene Monomer
(EPDM) gasket provided between segments to resist the water inflow through the
joints, so that long term groundwater drawdown is not expected.
Mined Tunnelling Works
6.6.32
Mining
works would be conducted to the areas with limited rock cover, soft/mixed
ground and in close proximity to the existing sensitive receivers. In view of high permeability of the
overlying soil materials compared to the relatively impermeable rock stratum
beneath, potential loss of groundwater into the mined tunnel is anticipated and
the groundwater table close to the surface would be affected by the tunnelling
works. Therefore, undrained lining
would be adopted to ensure insignificant effect on the groundwater table above
the rockhead level. Also,
pre-excavation grouting would be adopted as necessary to control the
groundwater inflow to mined tunnelling under mixed ground condition and
minimise the groundwater drawdown.
The permanent lining will be designed as watertight structures to avoid
the long term dewatering of the groundwater.
Drill & Blast Tunnels for Adits, Tunnels
and Ancillary Building
6.6.33
Drill
and blast techniques would be proposed for certain tunnel sections and adits in rock formation. Considering the proposed tunnel span
together with the maximum expected groundwater pressure heads in excess of 300m
in sections of the alignment and also this method will generally be adopted
under the competent rock condition where the permeability is anticipated to be
low, a drained tunnel system is the most technically feasible option. The drained tunnel system had been
widely adopted in this situation in Hong Kong and elsewhere around the world
without adverse effect on the environment or water catchments. With regard to the loss of water
into the tunnels this is anticipated to be relatively very small and the water
table close to the surface will not be affected by these subsurface tunnelling
works. This is due to the high
permeability of the overlying soil materials compared to the relatively
impermeable rock stratum beneath.
The drained tunnels will cause only localized pressure relief and
groundwater drawdown in the area immediately surrounding the tunnel. Beyond this localized distance
horizontal natural recharge will ensure insignificant effect on the groundwater
above the rockhead level.
6.6.34
Pre-excavation
grouting would be adopted where necessary as preventive / mitigation measure for
excessive groundwater inflow which lead potential groundwater drawdown, and
also undrained lining may be provided under the poor rock or soft ground
condition to mitigate the long term dewatering
issue.
Site Formation Works for Ngau Tam Mei Depot
Operational Phase
·
Sewage
and wastewater from stations, ancillary buildings and depot operation; and
·
Non-point
source surface runoff from new impervious area.
Sewage and Wastewater Effluents Discharge
6.6.37
Sewage effluent from the staff and passengers at
KSR(NOL), AUT, NTM, SAT and KTU(NOL) Stations and NTD would be connected to the
existing or planned foul sewerage system, subject to the availability of the
planned foul sewerage system at the time of NOL operation. Wastewater from air conditioning system
and cleaning activities would also be discharged to the foul sewer, while
accumulated at the foul water line sumps in railway tunnels will be pumped to
the ground surface via stations/ancillary buildings for discharge to the public
sewerage system. Hence, no adverse
water quality impact would be anticipated to arise from sewage and wastewater
effluents generated during the operation of the stations, ancillary buildings
and depot.
Non-point Source Surface Runoff from New Impervious Area
6.6.38
Surface runoff to be generated from the Project is
known as non-point source pollution.
A small amount of grease and grit may be deposited on the surfaces of
the rail tracks and stabling sidings.
These pollutants could be washed into the nearby drainage system during
rainfall events. Sources of
potential polluted stormwater that may also arise from the stations, NTD and
ancillary buildings include dust from the roof of the structures and cleaning
agents used for washing building façade.
Surface runoff generated from these newly paved areas may also affect
the quality of the nearby receiving water environment, if uncontrolled.
Construction Site Runoff and General
Construction Activities
·
prevent
or minimise the likelihood of pollutants (generated from construction
activities including demolition works) being in contact with rainfall or
runoff; and
·
abate
pollutants in the stormwater surface runoff prior to the discharge of surface
runoff to the nearby water bodies.
6.8.4
Surface
runoff 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 sand bag barriers should be provided
on site during construction to properly direct stormwater to such silt removal
facilities. Perimeter channels
should also be provided at site boundaries where necessary to intercept storm
runoff from outside to 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.
6.8.5
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 local flooding. 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.
6.8.6
Construction
works should be programmed to minimize 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 runoff from washing across exposed soil surfaces. Arrangements should always be in place
such that adequate surface protection measures can be safely carried out well
before the arrival of a rainstorm.
6.8.7
Earthworks
final surfaces should be well compacted and the
subsequent permanent work 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.
6.8.8
Measures
should be taken to minimize 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.
6.8.9
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 1/94
should be closely followed when handling and disposing bentonite slurries.
6.8.10
Open
stockpiles of construction materials (e.g. aggregates,
sand and fill material) on sites should be covered with tarpaulin or similar
fabric.
6.8.11
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 runoff from getting into
foul sewers. Discharge of surface
runoff into foul sewers must always be prevented in order not to unduly
overload the foul sewerage system.
6.8.13
The
following mitigation measures related to the transportation of
the sediment should be implemented, where applicable, to minimize the potential
water quality impact:
·
Loading
of the excavated sediment to the barge should be controlled to avoid splashing
and overflowing of the sediment slurry to the surrounding water.
·
The
barge transporting the sediments to the designated disposal sites should be
equipped with tight fitting seals to prevent leakage and should not be filled
to a level that would cause overflow of materials or laden water during loading
or transportation.
·
Monitoring
of the barge loading should be conducted to ensure that loss of material does
not take place during transportation.
Transport barges or vessels should be equipped with automatic
self-monitoring devices as specified by the Director of Environmental
Protection (DEP).
6.8.14 Discharge licence issued by the EPD for discharge of effluent from the construction site
under the WPCO is needed. The
discharge quality and quantity should meet the requirements specified in the
discharge licence. All the runoff and wastewater generated
from the works areas should be treated so that it satisfies all the standards
listed in the DSS-TM. The
beneficial uses of the treated effluent for other on-site activities such as
dust suppression, wheel washing and general cleaning etc., can minimise water
consumption and reduce the effluent discharge volume. If monitoring of the treated effluent
quality from the works areas is required during the construction phase of the
Project, the monitoring should be carried out in accordance with the relevant
WPCO licence.
Groundwater infiltration and change in
groundwater levels
6.8.15
As
discussed in Section 6.6.30 to 6.6.35, preventive or mitigation measures
during construction period would be required to minimise the potential impact
on groundwater system. Examples of
preventive or mitigation measures are listed below:
·
Adoption
of close mode TBM at ecological sensitive area (e.g.
wetland), if any, to prevent the groundwater ingress to tunnel excavation and
control the ground settlement;
·
Adoption
of robust hydraulic cut-off to control groundwater inflow into the excavation;
·
Provision
of recharge well to mitigate the excessive groundwater drawdown out;
·
Adoption
of ground treatment if necessary to control groundwater inflow into the excavation;
·
For
mined or drill & blast tunnels, adoption of probing ahead before excavation
to identify the geological features and water inflow ahead to determine the
need for pre-excavation grouting and the type of temporary support. In case of excessive groundwater inflow
observed, pre-excavation grouting should be applied as suitable mitigation measure;
·
In
the event of excessive drawdown being observed within the groundwater as a
result of the tunnelling works even after incorporation of the water control
strategies by the pre-grouting measures, post-grouting should be applied as far
as practicable before the lining is cast;
·
Provision
of ground treatment for undrained tunnel (e.g. mined
tunnel in soft and permeable ground) to enhance the properties of ground; and
·
Monitoring
of groundwater level and settlement during the construction.
6.8.16
In
addition, as mentioned in Section 6.6.30 to 6.6.35, preventive or mitigation measures
during operational phase would be required to minimise the potential impact on
groundwater system. Examples of
preventive or mitigation measures are listed below:
·
For
drill & blast tunnels, adoption of undrained lining under the poor rock
condition to mitigate the long term dewatering issue;
·
For
drained tunnel section, provision of an individual groundwater drainage system
within the tunnel to collect the groundwater inflow to
public drainage system; and
·
Provision
of ground treatment for undrained tunnel (e.g. mined
tunnel in soft and permeable ground) to enhance the properties of ground.
Groundwater from Contaminated Areas,
Contaminated Site Runoff and Wastewater from Land Decontamination
6.8.18 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 with reference to Guidance
Note for Contaminated Land Assessment and Remediation and the review
results should be submitted to EPD under the Contamination Assessment Report
(CAR) 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.
Construction Works in Close Proximity to Inland
Water
·
Use
of less or smaller construction plants may be specified in works area close to
the inland water bodies as far as practicable;
·
Temporary
storage of material (e.g. equipment, filling
materials, chemicals and fuel) and temporary stockpile of construction
materials should be located well away from 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;
·
Construction
activities, which generate large amount of wastewater, should be carried out in
a distance away from the watercourses, where practicable;
·
Construction
effluent, site run-off and sewage should be properly collected and / or
treated; and
·
Proper
shoring may need to be erected in order to prevent soil / mud from slipping
into the inland water bodies.
Construction Works in Inland Water
6.8.21
The
construction method and sequence of the proposed construction works at Ho Pui
Channel (W13) should be carefully designed so that all the construction works
including any excavation would be undertaken within a dry zone and physically
separated from the watercourses downstream.
6.8.22
Impermeable
sheet pile walls or cofferdam walls should be installed to fully enclose the
construction works area (including all the excavation and piling works) in the
watercourse prior to the commencement of any works in watercourse. Dewatering of the construction works
area should be undertaken before the commencement of construction works to
avoid water flow in the construction works area. Silt removal facilities should be used
to clarify the effluent generated from the dewatering operation before discharging
back to the watercourse / drainage system.
Any construction works including excavation and piling activities should
be undertaken in a dry zone surrounded by the impermeable sheet pile walls or
cofferdam walls. All wastewater
generated from the piling activities should be regarded as part of the
construction site effluent, which should be properly collected and treated as
appropriate to meet the standards stipulated in the DSS-TM before
disposal. It is recommended that
the construction works in watercourses should be undertaken in dry seasons,
where practicable, when the water flow is low.
6.8.23
The
mitigation measures for construction site drainage as recommended in Sections
6.8.1 to 6.8.14 and protection measures for construction works near watercourses as
detailed in Section 6.8.20 should also be followed to minimise
the potential water quality impacts from the construction in watercourses.
6.8.24
The pilling works for the temporary vehicular bridge
in Ho Pui Channel should be conducted by phases. The method and sequence of the proposed
bridge works in Ho Pui Channel should be carefully designed so that wastewater
and sediment laden water generated from the pilling works would be confined and
physically separated from the watercourse.
All pilling, the associated construction works in the watercourse should
be fully enclosed by concrete cofferdam/sheet pile. Concrete cofferdam should be constructed
to isolate the construction activities from the river water. The detail design of the concrete
cofferdams will be conducted by the Contractor during the construction phase to
fulfil the requirements in Drainage Services Department (DSD) Technical
Circular No. 1/2017 "Temporary Flow Diversions and Temporary Works
Affecting Capacity in Stormwater System" for DSD approval in order to
formulate feasible options of these temporary structure. Water pumps should be used to collect
any construction site runoff and ingress/seepage water within the concrete
cofferdam. The collected
construction site surface runoff and ingress/seepage water should be diverted
to the on-site wastewater treatment facilities for treatment to satisfactory
levels before discharge. Discharge licence for discharging effluent from the construction site
under the WPCO should be obtained from the EPD. The discharge quality and quantity
should meet the requirements specified in the discharge licence
and follow the DSS-TM.
Removal or Diversion of Watercourses
6.8.25
The
construction works for removal and diversion of watercourses should be
undertaken within a dry zone.
Cofferdams or similar impermeable sheet pile walls should be used as
necessary to isolate the works areas from the neighbouring
waters.
6.8.26
The
tentative works sequence for provision of a dry zone for the construction works
is described as follows.
Construction works at watercourse should be undertaken only after flow
diversion or dewatering operation is fully completed to avoid water flow in the
works area. Dewatering of
watercourse should be performed by diverting the water flow to new or temporary
drainage. Where necessary,
cofferdams or similar impermeable sheet pile walls should be used to isolate
the works areas from neighbouring waters. The permanent or temporary drainage for
carrying the diverted flow from existing watercourse to be removed should be
constructed and completed before dewatering of that existing watercourse. Construction of all the proposed
permanent and temporary drainage should be undertaken in a dry zone prior to
receiving any water flow.
6.8.27
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 and the DSS-TM before
discharge.
6.8.28
The
site practices outlined in the ProPECC PN 1/94
“Construction Site Drainage” and ETWB TC (Works) No. 5/2005 “Protection of
natural streams/rivers from adverse impacts arising from construction works”
should be adopted for the proposed demolition or diversion of watercourses
where applicable.
Removal or Filling of Ponds
6.8.29
Construction
works at the existing ponds should be conducted after dewatering is completed
if practicable. The drained water generated
from the dewatering of these ponds to be removed should be temporarily stored
as appropriate in storage tanks or containers for reuse on-site where practical
and any surplus drained water should be tankered away
for disposal or treated as
necessary before disposal in compliance with the DSS-TM.
6.8.30
It
is recommended to drain ponds by stages to minimise the potential water quality
impact. Dewatering works at ponds
should be conducted within dry season as far as practicable to minimise the
quantity of drained water. No
direct discharge of drained water to the stormwater drainage system or marine
water should be allowed.
Accidental Spillage of Chemicals
6.8.32
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.
Sewage Effluent from Construction Workforce
Operational Phase
Sewage and Wastewater Effluents Discharge
6.8.36
Most
of the sewage and wastewater effluents generated from the operation of
stations, ancillary buildings and depot would be connected to the public
sewerage system and diverted to public sewers, subject to the availability of the planned foul
sewerage system at the time of NOL operation. At some satellite
locations without nearby public sewerage systems (Section 7.6 refers),
sewage generated will be stored at MTR’s Sewage Holding Tanks before being tankered away by MTR’s competent contractor regularly. The sewerage generation of these
satellite locations is anticipated to be minimal as they are unmanned and are
mainly used by limited MTR staff.
No direct discharge of sewage and wastewater effluents into the storm
drains or inland/marine waters will be allowed.
Stormwater Runoff
Design
Measures
6.8.39
The
drainage system should be designed to avoid flooding. The
drainage system will be designed to avoid any case of flooding based on at
least 1 in 50 year return period.
Devices and
Facilities
6.8.40
Screening
facilities such as standard gully grating and trash grille, with spacing which
is capable of screening large substances such as fallen leaves and rubbish
should be provided at the inlet of drainage system.
6.8.41
Silt
traps and oil interceptors should be incorporated as appropriate during the
detailed design to remove particles and oil, where appropriate.
Administrative
Measures
6.10.2
It
is recommended that regular site inspections during the construction phase
should be undertaken to inspect the construction activities and works sites /
areas in order to ensure the recommended mitigation measures are properly
implemented. Details of the audit
requirements are provided in the stand-alone EM&A Manual for the Project.
Construction
Phase
6.11.1 The potential water quality impacts from the construction works are
associated with the construction works in inland water, and in close proximity
to inland water, wastewater generated from general construction activities,
construction site run-off, groundwater infiltration and change in groundwater
levels, groundwater from contaminated areas and contaminated site runoff,
demolition works, accidental spillage of chemicals and sewage effluent from
construction workforce. Provided
that proper site management practices and the mitigation measures including adequate construction site drainage, provision of sediment
removal facilities, practical groundwater control measures and chemical toilets
would be implemented, no adverse water quality impact during construction phase
would be anticipated.
Operational
Phase
6.11.2 The key potential source of water quality impact during operational
phase would be related to non-point source stormwater runoff, sewage and
wastewater effluents from operation of depot, ancillary buildings and stations. Adequate drainage system should be
provided to collect the stormwater runoff.
Most of the sewage and wastewater effluents generated from operation of
depot, ancillary buildings and stations would be connected to the public
sewerage system and diverted to public sewers, subject to the availability
of the planned foul sewerage system at the time of NOL operation. At some satellite
locations without nearby public sewerage systems (Section 7.6 refers),
sewage generated will be stored at MTR Corporation’s Sewage Holding Tanks
before being tankered away by MTR Corporation’s competent contractor regularly.
With proper design of drainage and sewerage systems and implementation
of the recommended mitigation measures. Therefore, no adverse water quality
impact during operational phase would be anticipated.