5.
Water Quality Impact
5.1
Legislations, Standards, Guidelines and Criteria
5.1.1
General
5.1.1.1
The relevant legislations,
standards, guidelines and criteria applicable to the
Project for the assessment of water quality impacts include:
·
Environmental Impact Assessment
Ordinance (EIAO) (Cap. 499);
·
Water Pollution Control
Ordinance (WPCO) (Cap. 358);
·
Technical Memorandum on
Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland
and Coastal Waters (TM-DSS);
·
Hong Kong Planning Standards
and Guidelines;
·
ProPECC PN 1/94 “Construction Site Drainage”;
·
ProPECC PN 5/93 “Drainage Plans Subject to Comment by the Environmental
Protection Department”;
·
Environment, Transport and
Works Bureau (ETWB) Technical Circular (Works) No. 5/2005: Protection of
Natural Streams/Rivers from Adverse Impacts Arising from Construction Works;
and
·
Water Supplies Department’s
(WSD) Target Values of Sea Water Quality for Flushing Supply at Intake Point of
Salt Water Pumping Station.
5.1.2
Environmental Impact Assessment Ordinance
(EIAO) (Cap. 499)
5.1.2.1
EIAO (Cap. 499) provides the
major statutory framework for the Environmental Impact Assessment (EIA) in Hong
Kong. Under Section 16 of the
EIAO, EPD issued the Technical Memorandum on Environmental Impact Assessment
Process (EIAO-TM) which specifies the assessment methods and criteria for EIA
process. Annexes 6 and 14 of the EIAO-TM stipulate the “Criteria for Evaluating
Water Pollution” and “Guidelines for Assessment of Water Pollution”
respectively.
5.1.3
Water Pollution Control
Ordinance (WPCO) (Cap. 358)
5.1.3.1
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, the entire
Hong Kong waters are divided into ten Water Control Zones (WCZs) and four
supplementary WCZs. Each WCZ has a designated set of statutory Water Quality
Objectives (WQOs). The WQOs set limits for different parameters that should be
achieved in order to protect specific beneficial uses and conservation goals of
each of the zones.
5.1.3.2
The Project is situated within
the North Western WCZ and the water quality objectives
for the North Western WCZ are summarized in Table 5.1.
Table
5.1 WQOs for North Western WCZ
|
Water Quality Objectives (WQO)
|
Part or Parts of Zone
|
|
Aesthetic Appearance
|
|
·
Waste discharges shall cause no objectionable
odours or discolouration of the water.
·
Tarry residues, floating wood, articles made of
glass, plastic, rubber or 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.
|
·
Whole Zone
|
|
Bacteria
|
|
·
The level of Escherichia coli should not
exceed 610 per 100mL, calculated as the geometric mean of all samples
collected in a calendar year
|
·
Secondary Contact Recreation Subzones
|
|
·
The level of Escherichia coli should not
exceed 180 per 100 mL, calculated as the geometric mean of all samples
collected from March to October inclusive. Samples should be taken at least 3
times in one calendar month at intervals of between 3 and 14 days.
|
·
Bathing Beach Subzones
|
|
·
The level of Escherichia coli should be less than 1
per 100 mL, calculated as the running median of the most recent 5 consecutive
samples taken at intervals of between 7 and 21 days.
|
·
Tuen Mun (A) and Tuen Mun
(B) Subzones and Water Gathering Ground Subzones
|
|
· The level of Escherichia coli should not
exceed 1 000 per 100 mL, calculated as the running median of the most recent
5 consecutive samples taken at intervals of between 7 and 21 days.
|
· Tuen Mun (C) Subzone and other inland
waters
|
|
Colour
|
|
· Waste discharges shall not cause the
colour of water to exceed 30 Hazen units.
|
·
Tuen
Mun (A) and Tuen Mun (B) Subzones and Water Gathering Ground Subzones
|
|
· Waste discharges shall not cause the
colour of water to exceed 50 Hazen units.
|
·
Tuen
Mun (C) Subzone and other inland waters
|
|
Dissolved Oxygen
|
|
· 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 calculated as the water column
average (arithmetic mean of at least 3 measurements at 1 metre below surface,
mid-depth, and 1 metre above seabed). In addition, the concentration of
dissolved oxygen should not be less than 2 mg/L within 2 metres of the seabed
for 90% of the sampling occasions during the year.
|
· Marine Waters
|
|
· Waste discharges shall not cause the
level of dissolved oxygen to be less than 4 mg/L.
|
· Tuen Mun (A), Tuen Mun (B) and Tuen Mun
(C) Subzones, Water Gathering Ground Subzones and
other inland waters
|
|
pH
|
|
· 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 Bathing Beach
Subzones
|
|
· The pH of the water should be within the
range of 6.0-9.0 units.
|
· Other Inland Waters
|
|
· 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.
|
· Bathing Beach Subzones
|
|
· Waste discharges shall not cause the pH of
the water to exceed the range of 6.5–8.5 units.
|
· Tuen Mun (A), Tuen Mun (B) and Tuen Mun
(C) Subzones and Water Gathering Ground Subzones
|
|
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
|
|
Suspended Solids
|
|
· 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
|
|
· Waste discharges shall not cause the
annual median of suspended solids to exceed 20 mg/L.
|
· Tuen Mun (A), Tuen Mun (B) and Tuen Mun
(C) Subzones and Water Gathering Ground Subzones
|
|
· Waste discharges shall not cause the
annual median of suspended solids to exceed 25 mg/L.
|
· Other Inland Waters
|
|
Ammonia
|
|
· The un-ionised ammoniacal nitrogen level
should not be more than 0.021 mg/L calculated as the annual average
(arithmetic mean).
|
· Whole Zone
|
|
Nutrients
|
|
· Nutrients shall not be present in quantities
sufficient to cause excessive or nuisance growth of algae or other aquatic
plants.
|
· Marine Waters
|
|
· Without limiting the generality of
objective (a) above, the level of inorganic nitrogen should not exceed 0.3
mg/L, expressed as annual water column average (arithmetic mean of at least 3
measurements at 1 m below surface, mid-depth and 1 m
above seabed).
|
· Castle Peak Bay Subzone
|
|
· 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 3
measurements at 1 m below surface, mid-depth and 1 m
above seabed).
|
· Marine Waters excepting Castle Peak Bay
Subzone
|
|
5-Day Biochemical Oxygen Demand
|
|
· Waste discharges shall not cause the 5-day
biochemical oxygen demand to exceed 3 mg/L.
|
· Tuen Mun (A), Tuen Mun (B) and Tuen Mun
(C) Subzones and Water Gathering Ground Subzones
|
|
· Waste discharges shall not cause the 5-day
biochemical oxygen demand to exceed 5 mg/L.
|
· Other Inland Waters
|
|
Chemical Oxygen Demand
|
|
· Waste discharges shall not cause the
chemical oxygen demand to exceed 15 mg/L.
|
· Tuen Mun (A), Tuen Mun (B) and Tuen Mun
(C) Subzones and Water Gathering Ground Subzones
|
|
· Waste discharges shall not cause the
chemical oxygen demand to exceed 30 mg/L.
|
· 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.
· Waste discharges shall not cause a risk
to any beneficial use 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.
|
· Bathing Beach Subzones
|
|
Turbidity / Light Penetration
|
|
· Waste discharges shall not reduce light
transmission substantially from the normal level.
|
· Bathing Beach Subzones
|
5.1.4
Technical Memorandum on Standards
for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal
Waters (TM-DSS)
5.1.4.1
Under Section 21 of the WPCO
(Cap. 358), TM-DSS was issued to control the physical, chemical, and microbial
quality of effluent discharges into foul sewers, stormwater drains, inland and
coastal waters. Specific limits apply for different areas and are different
between surface waters and sewers, and the limits vary with the rate of
effluent flow. Under the TM-DSS , any effluents discharged from the Project must comply
with pollutant concentration standards defined by EPD and are specified in
license conditions for any new discharge
5.1.5
Hong Kong Planning Standards
and Guidelines (HKPSG)
5.1.5.1
Chapter 9 of HKPSG outlines the
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 provision of environmental facilities,
design, layout, phasing, and operational controls to minimise adverse
environmental impact. It lists out environmental factors influencing land use
planning and recommends buffer distances for land uses.
5.1.5.2
Section 5 under Chapter 9 of HKPSG provides broad
guidelines on water quality which includes the principal framework for planning
against water pollution. The overall
objectives for planning against water pollution are:
·
Achieving and maintaining the
quality of inland waters, coastal waters, marine waters and groundwaters so
that they can be used for their legitimate purposes;
·
Providing adequate public
sewerage, wastewater treatment and disposal facilities for all wastewaters; and
·
Putting in place and enforce
water pollution control legislation aimed at safeguarding the health and
welfare of the community.
5.1.5.3
With reference to the
aforementioned part of HKPSG, a list of potentially polluting and sensitive
uses is summarized below in Table 5.2.
Table 5.2 Potential Polluting
Sources and Water Sensitive Uses
|
Potential Polluting Sources
|
Water Sensitive Uses
|
|
· Industry and agriculture (including livestock
keeping and slaughterhouses);
· Sewage disposal (including sewage from private
residential developments);
· Civil engineering works (including all building
works, well boring, ground investigation, dredging, reclamation, excavation
of fill, man-made lagoons etc.); and
· Transport facilities.
|
· Bathing;
· Aquaculture and fisheries;
· Agriculture;
· Residential and recreational development;
· Typhoon shelters, marinas and boat parks;
· Water gathering grounds;
· Nature reserves;
· Sites of Special scientific Interest;
· Marine parks/marine reserves;
· Coastal protection areas;
· Conservation areas; and
· Fish spawning grounds.
|
5.1.6
ProPECC PN 1/94: “Construction Site Drainage”
5.1.6.1
Professional Persons
Environmental Consultative Committee Practice Note (ProPECC
PN) 1/94 on construction site drainage provides guidelines for the handling and
disposal of construction discharges.
This note is applicable for the control of site run-off and wastewater
generated during the construction phase of the Project.
5.1.6.2
The types of discharges from
construction sites outlined in the ProPECC PN 1/94
include:
·
Surface run-off;
·
Groundwater;
·
Boring and drilling water;
·
Wastewater from concrete
batching and precast concrete casting;
·
Wheel washing 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.
5.1.7
ProPECC PN 5/93: “Drainage Plans subject to Comment by the Environmental
Protection Department”
5.1.7.1
ProPECC PN 5/93 issued by EPD provides guidelines on the environmental
design and pollution control in drainage plans submitted under Building
(standards of Sanitary Fitments, Plumbing, Drainage Work and Latrines) Regulations
40(1), 40(2), 41(1), and 90. Any submitted drainage plans submitted shall be
referred to EPD for comment on whether there may be concerns regarding
pollution control.
5.1.8
Environment, Transport and
Works Bureau (ETWB) Technical Circular (Works) No. 5/2005: “Protection of
Natural Streams/Rivers from Adverse Impacts Arising from Construction Works”
5.1.8.1
The ETWB TC (W) No. 5/2005
provides a framework to better protect all natural streams/rivers from the
adverse impacts of construction works. The procedures promulgated under the
Circular aims to clarify and strengthen existing measures for protection of
natural streams/rivers from both government and private projects/developments.
The guidelines and precautionary mitigation measures given in the Circular should
be followed to the best of abilities to protect inland watercourses at or near
the Project area during the construction phase.
5.1.9
Water Supplies Department’s
(WSD) Target Values of Sea Water Quality for Flushing Supply at Intake Point of
Salt Water Pumping Station
5.1.9.1
The criteria for assessing the
water quality impact on the WSD’s seawater intakes are based on the Target
Values of Sea Water Quality for Flushing Supply at Intake Point of Salt Water Pumping Station (at intake point) issued by the
WSD and are summarized under Table 5.3.
Table
5.3 WSD's Target values of Sea
Water Quality at Intake Point of Salt Water Pumping
Stations
|
Parameter
|
Target Value
|
|
Colour
|
< 20 H.U.
|
|
Turbidity
|
< 10 N.T.U.
|
|
Threshold Odour No.
|
< 100
|
|
Ammoniacal Nitrogen
|
< 1 mg/l
|
|
Suspended Solids
|
< 10 mg/l
|
|
Dissolved Oxygen
|
> 2 mg/l
|
|
Biochemical Oxygen Demand
|
< 10 mg/l
|
|
Synthetic Detergents
|
< 5 mg/l
|
|
E. coli
|
< 20,000 cfu/100
ml
|
5.2
Baseline Conditions
5.2.1
Marine Water
5.2.1.1
The Project is located within the North Western
WCZ, which is located at the western side of Hong Kong and covers the waters
around the North and Western side of Lantau Island, Tuen Mun, Sha Chau, and
Lung Kwu Chau. According to
EPD’s Marine Water Quality of Hong Kong 2021 report, the overall WQO compliance
rate of the North
Western WCZ was 89% in
year 2021. The Dissolved Oxygen (DO) and ammonia-nitrogen (NH3-N) WQOs
were fully met. However, for Total Inorganic Nitrogen (TIN), the WQO was 67%
under the influence of high background levels in the Pearl River Estuary. For
the past 5 years, the WQO compliance rate has fluctuated, and there was an
increase from 72% in Years 2017, to 89% in Years 2018 and 2019, before
declining to 67% in 2020, and eventually rising back to 89% in 2021. The water quality monitoring data from monitoring stations NM2 and
NM3 in 2021 is presented in Table 5.4 below.
Table 5.4 Summary of EPD's Routine Marine Water Quality
Data for North Western WCZ in 2021
|
Parameters
|
North Western
WCZ1,2,3,4,5,6
|
|
NM2
|
NM3
|
|
Temperature
(°C)
|
24.8
|
24.1
|
|
(19.5 - 27.9)
|
(18.1 - 27.6)
|
|
Salinity
(ppt)
|
29.3
|
29.1
|
|
(22.9 - 33.5)
|
(24.0 - 33.4)
|
|
Dissolved Oxygen
(mg/L)
|
Depth
Averaged
|
4.9
|
5.1
|
|
(4.1 – 5.7)
|
(4.1 - 6.4)
|
|
Bottom
|
4.9
|
4.9
|
|
(3.3 – 6.7)
|
(3.5 - 6.9)
|
|
Dissolved
Oxygen (% Saturation)
|
Depth
Averaged
|
70
|
71
|
|
(59 – 82)
|
(60 - 86)
|
|
Bottom
|
69
|
68
|
|
(47 – 90)
|
(51 - 87)
|
|
pH
|
7.5
|
7.6
|
|
(7.2 - 7.9)
|
(7.2 - 8.0)
|
|
Secchi
Disc Depth (m)
|
2.3
|
2.3
|
|
(1.7 - 3.5)
|
(1.5 - 3.0)
|
|
Turbidity
(NTU)
|
6.0
|
12.2
|
|
(2.9 - 11.5)
|
(3.3 - 78.8)
|
|
Suspended
Solids (mg/L)
|
4.9
|
5.1
|
|
(1.6 - 9.4)
|
(1.5 - 9.6)
|
|
5-day Biochemical
Oxygen Demand (mg/L)
|
1.3
|
1.2
|
|
(0.2 - 4.9)
|
(0.3 - 2.8)
|
|
Ammonia
Nitrogen (mg/L)
|
0.090
|
0.089
|
|
(0.038 - 0.167)
|
(0.048 - 0.170)
|
|
Unionised
Ammonia (mg/L)
|
0.001
|
0.002
|
|
(<0.001 - 0.003)
|
(<0.001 - 0.003)
|
|
Nitrite Nitrogen
(mg/L)
|
0.063
|
0.062
|
|
(0.004 - 0.117)
|
(0.004 - 0.123)
|
|
Nitrate
Nitrogen (mg/L)
|
0.280
|
0.315
|
|
(0.047 - 0.617)
|
(0.062 - 0.787)
|
|
Total
Inorganic Nitrogen (mg/L)
|
0.43
|
0.47
|
|
(0.21 - 0.76)
|
(0.21 - 0.93)
|
|
Total Kjeldahl
Nitrogen (mg/L)
|
0.61
|
0.56
|
|
(0.35 - 0.95)
|
(0.46 - 0.70)
|
|
Total
Nitrogen (mg/L)
|
0.78
|
0.76
|
|
(0.59 - 1.11)
|
(0.64 - 0.92)
|
|
Orthophosphate
Phosphorous (mg/L)
|
0.014
|
0.013
|
|
(0.003 - 0.027)
|
(<0.002 - 0.026)
|
|
Total Phosphorous
(mg/L)
|
0.06
|
0.06
|
|
(0.04 - 0.09)
|
(0.03 - 0.09)
|
|
Silica (as
SiO2) (mg/L)
|
1.29
|
1.36
|
|
(0.34 - 2.10)
|
(0.30 - 2.67)
|
|
Chlorophyll-a
(µg/L)
|
4.8
|
5.1
|
|
(0.8 - 15.5)
|
(0.6 - 12.1)
|
|
E.
coli (count/100mL)
|
31
|
25
|
|
(6 - 350)
|
(4 - 290)
|
|
Faecal Coliforms
(count/100mL)
|
59
|
51
|
|
(14 - 610)
|
(10 - 660)
|
Notes: 1. Data
presented are annual arithmetic means of the depth-averaged results except for E.
coli and faecal coliforms which are annual geometric means.
2. Data in brackets indicate the ranges.
3. NM indicates no measurement taken.
4. Values at or below laboratory reporting limits
are presented as laboratory reporting limits.
5. Equal values for annual medians (or geometric means)
and range indicates that all data are the same as or below laboratory reporting
limits.
6. Unless specified otherwise, data presented are
depth-averaged value which are calculated by taking the means of three depths (i.e. surface, mid-depth, and bottom).
5.2.2
Tuen Mun Typhoon Shelter
5.2.2.1
Tuen Mun Typhoon Shelter is
located at Tuen Mun South and at the mouth of Tuen Mun River, which is at the
vicinity of the Project’s assessment area. There are no bacteriological WQOs
for typhoon shelters as their beneficial use are primarily for vessel mooring.
Hence the concerned parameters for typhoon shelter water quality are mainly DO
and NH3-N. Both parameters met the WQO in 2021. In general the long term trend shows an improvement of water
quality in Tuen Mun Typhoon Shelter.
5.2.2.2
The water quality monitoring
data from monitoring stations NT1 of Tuen Muen
Typhoon Shelter is presented in Table 5.5 below.
Table 5.5 Summary of EPD's Routine Marine Water Quality
data for Tuen Mun Typhoon Shelter in 2021
|
Parameters
|
Tuen Mun Typhoon Shelter1,2,3
|
|
NT1
|
|
Temperature
(°C)
|
26.2
|
|
(20.6 - 29.1)
|
|
Salinity
(ppt)
|
26.1
|
|
(20.4 - 31.8)
|
|
Dissolved
Oxygen (mg/L)
|
Depth Averaged
|
4.8
|
|
(4.2 – 5.8)
|
|
Bottom Layer
|
4.7
|
|
(4.0 - 5.2)
|
|
Dissolved
Oxygen (% Saturation)
|
Depth Averaged
|
69
|
|
(58 - 83)
|
|
Bottom Layer
|
67
|
|
(56 - 75)
|
|
pH
|
7.5
|
|
(7.1 - 7.6)
|
|
Secchi
Disc Depth (m)
|
1.7
|
|
(1.4 - 2.4)
|
|
Turbidity
(NTU)
|
6.9
|
|
(4.9 - 12.2)
|
|
Suspended
Solids (mg/L)
|
7.1
|
|
(3.2 - 10.1)
|
|
5-day
Biochemical Oxygen Demand (mg/L)
|
0.9
|
|
(0.5 - 1.3)
|
|
Ammonia
Nitrogen (mg/L)
|
0.098
|
|
(0.036 - 0.200)
|
|
Unionised
Ammonia (mg/L)
|
0.001
|
|
(<0.001 - 0.003)
|
|
Nitrite Nitrogen
(mg/L)
|
0.053
|
|
(0.019 - 0.073)
|
|
Nitrate
Nitrogen (mg/L)
|
0.330
|
|
(0.143 - 0.635)
|
|
Total
Inorganic Nitrogen (mg/L)
|
0.48
|
|
(0.25 - 0.74)
|
|
Total
Kjeldahl Nitrogen (mg/L)
|
0.63
|
|
(0.58 - 0.68)
|
|
Total
Nitrogen (mg/L)
|
0.83
|
|
(0.81 - 0.84)
|
|
Orthophosphate
Phosphorous (mg/L)
|
0.011
|
|
(0.005 - 0.021)
|
|
Total
Phosphorous (mg/L)
|
0.08
|
|
(0.06 - 0.09)
|
|
Silica (as
SiO2) (mg/L)
|
1.25
|
|
(0.63 - 1.95)
|
|
Chlorophyll-a
(µg/L)
|
7.0
|
|
(0.8 - 19.5)
|
|
E.
coli (count/100mL)
|
33
|
|
(8 - 220)
|
|
Faecal
Coliforms (count/100mL)
|
210
|
|
(42 - 990)
|
Notes: 1. Data presented
are annual arithmetic means of the depth-averaged results except for E. coli
and faecal coliforms which are annual geometric means.
2. Data in brackets indicate the ranges.
3. Unless specified otherwise, data presented are
depth-averaged value which are calculated by taking the means of three depths (i.e. surface, mid-depth, and bottom).
5.2.3
Inland Water
Tuen Mun River
5.2.3.1
Tuen Mun River is a major river
located in the western New Territories, which passes through Lam Tei, San Hing Tsuen and Fu Tei in its upstream section, then through the
densely populated Tuen Mun Town in its mid-stream before draining into the Tuen
Mun Typhoon Shelter at its mouth. This river has experienced improvement in its
water quality over the last three decades, with its WQO compliance rate rising
significantly from 42% in 1991 to 85% in 2021. Four of
the six monitoring stations (i.e. TN3
- TN6) are situated at the middle to lower sections of the river, and maintained
a “Good” water quality index (WQI) grading. In 2021, the upstream monitoring
station (i.e. TN2) received a “Fair” WQI grading,
while another upstream monitoring station (TN1) was graded “Bad”, mainly due to
discharges from unsewered rural areas. The water quality monitoring data
from monitoring stations TN1, TN2, and TN6 in 2021 is presented in Table 5.6 below.
Table
5.6 Summary of EPD's Routine
River Water Quality Data for Tuen Mun River in 2021
|
Parameters
|
Tuen Mun River1,2,3,4,5
|
|
TN1
|
TN2
|
TN6
|
|
Dissolved
Oxygen (mg/L)
|
4.4
|
8.0
|
5.4
|
|
(2.0 - 5.9)
|
(4.3 - 12.9)
|
(3.6 - 7.9)
|
|
pH
|
7.6
|
7.9
|
7.5
|
|
(7.4 - 8.2)
|
(7.2 - 9.2)
|
(6.8 - 8.1)
|
|
Suspended
Solids (mg/L)
|
11.0
|
7.6
|
3.7
|
|
(3.0 - 16.0)
|
(3.3 – 6,600.0)
|
(1.6 - 31.0)
|
|
5-Day Biochemical
Oxygen Demand (mg/L)
|
24.0
|
3.9
|
3.0
|
|
(11.0 - 47.0)
|
(2.4 - 66.0)
|
(1.0 - 9.3)
|
|
Chemical
Oxygen Demand (mg/L)
|
32
|
15
|
14
|
|
(20 - 54)
|
(6 - 100)
|
(8 - 23)
|
|
Oil &
Grease (mg/L)
|
0.6
|
<0.5
|
<0.5
|
|
(<0.5 - 1.4)
|
(<0.5 - 2.0)
|
(<0.5 - <0.5)
|
|
E.
coli (counts/100mL)
|
100,000
|
190,000
|
2 200
|
|
(44,000 – 230,000)
|
(49,000 – 1,400,000)
|
(170 – 45,000)
|
|
Faecal
Coliforms (counts/100mL)
|
340,000
|
290,000
|
15,000
|
|
(130,000 – 990,000)
|
(75,000 – 2,000,000)
|
(1,100 – 300,000)
|
|
Ammonia
Nitrogen (mg/L)
|
6.900
|
2.100
|
0.480
|
|
(5.400 - 9.700)
|
(1.200 - 7.800)
|
(0.150 - 0.960)
|
|
Nitrate
Nitrogen (mg/L)
|
0.280
|
1.100
|
0.275
|
|
(<0.002 - 0.710)
|
(0.011 - 7.000)
|
(0.150 - 0.660)
|
|
Total
Kjeldahl Nitrogen (mg/L)
|
11.50
|
9.00
|
1.10
|
|
(8.60 - 13.00)
|
(3.50 - 11.00)
|
(0.76 - 2.20)
|
|
Orthophosphate
Phosphorous (mg/L)
|
0.520
|
0.260
|
0.027
|
|
(0.400 - 0.600)
|
(0.140 - 0.780)
|
(<0.002 - 0.053)
|
|
Total
Phosphorous (mg/L)
|
0.94
|
0.86
|
0.12
|
|
(0.69 - 1.00)
|
(0.39 - 0.96)
|
(0.07 - 0.16)
|
|
Sulphide
(mg/L)
|
0.03
|
<0.02
|
<0.02
|
|
(<0.02 - 0.05)
|
(<0.02 - 0.03)
|
(<0.02 - <0.02)
|
|
Aluminium
(µg/L)
|
<50
|
<50
|
60
|
|
(<50 - 442)
|
(<50 - 140)
|
(<50 - 163)
|
|
Cadmium
(µg/L)
|
<0.1
|
<0.1
|
<0.1
|
|
(<0.1 - <0.1)
|
(<0.1 - <0.1)
|
(<0.1 - <0.1)
|
|
Chromium
(µg/L)
|
<1
|
<1
|
2
|
|
(<1 - 1)
|
(<1 - 3)
|
(<1 - 3)
|
|
Copper
(µg/L)
|
1
|
2
|
4
|
|
(<1 - 2)
|
(<1 - 7)
|
(3 - 6)
|
|
Lead
(µg/L)
|
<1
|
<1
|
<1
|
|
(<1 - <1)
|
(<1 - 2)
|
(<1 - <1)
|
|
Zinc
(µg/L)
|
<10
|
<10
|
10
|
|
(<10 - 36)
|
(<10 - 46)
|
(<10 - 16)
|
|
Flow
(m³/s)
|
0.138
|
0.017
|
NM
|
|
(0.072 - 0.328)
|
(0.006 - 0.059)
|
Notes: 1. Data presented
are annual arithmetic means of the depth-averaged results except for E. coli
and faecal coliforms
which are annual geometric means.
2.
Data in brackets indicate the ranges.
3.
NM indicates no measurement taken.
4.
Values at or below laboratory reporting limits are presented as laboratory
reporting limits.
5. Equal values for annual medians (or geometric means)
and range indicates that all data are the same as or below laboratory reporting
limits.
Channel near Lung Mun Road at Pillar Point
5.2.3.2
There is no EPD inland water
quality monitoring station at the vicinity of Pillar Point to assess the
baseline conditions of the inland waters of that area. Hence, additional water
quality sampling was conducted under this EIA to supplement the inland water
quality information for both wet season (i.e. between
April and October) and dry season (i.e. between November and March). Sampling
was conducted at a frequency of 3 sampling days per week over a 2 week period (i.e. 6 sampling days in total).
5.2.3.3
The water quality parameters
that were measured and sampled were the same as those used by EPD’s river
monitoring stations. In addition, other relevant data (i.e.
monitoring location, time, weather conditions, river conditions etc.) were also
recorded, the samples were then analysed at a Hong Kong Laboratory
Accreditation Scheme (HOKLAS) accredited laboratory. The water quality sampling
results are summarised under Table 5.7 below. In-situ monitoring records
and laboratory analysis results are also presented in Appendix 5.1.
Table 5.7 Water Quality Sampling Results at Channel near
Lung Mung Road at Pillar Point
|
Parameters
|
Channel near Lung Mung Road at Pillar
Point (R1)1,2,3,4,5
|
|
Wet Season
|
Dry Season
|
|
Dissolved
Oxygen (mg/L)
|
9.5 (9.1 - 9.8)
|
8.8
(8.1 - 9.3)
|
|
pH
|
9.5 (8.8 - 9.8)
|
8.2 (8.0 - 8.4)
|
|
Suspended
Solids (mg/L)
|
2.1 (1.3 - 2.7)
|
4.0 (<0.5 - 6.6)
|
|
5-Day
Biochemical Oxygen Demand (mg/L)
|
1.3 (<0.1 - 2.2)
|
2.9 (2.2 - 3.4)
|
|
Chemical
Oxygen Demand (mg/L)
|
10 (6 - 12)
|
18 (13 - 22)
|
|
Oil &
Grease (mg/L)
|
<0.5 (<0.5 - <0.5)
|
<0.5 (<0.5 - 0.9)
|
|
E.
coli (counts/100mL)
|
595 (340 – 1,200)
|
795 (180 – 2,400)
|
|
Faecal
Coliforms (counts/100mL)
|
3,167 (900 – 8,800)
|
2,006 (410 – 4,700)
|
|
Ammonia
Nitrogen (mg/L)
|
6.2 (5.0 - 6.8)
|
40.1 (33.2 - 50.5)
|
|
Nitrate
Nitrogen (mg/L)
|
2.72 (2.32 - 3.09)
|
3.95 (3.59 - 4.16)
|
|
Total
Kjeldahl Nitrogen (mg/L)
|
7.6 (5.3 - 12.3)
|
42.1 (33.9 - 50.8)
|
|
Orthophosphate
Phosphorous (mg/L)
|
0.006 (<0.001 - 0.014)
|
0.008 (0.004 - 0.010)
|
|
Total Phosphorous (mg/L)
|
0.03 (0.02 - 0.03)
|
0.04 (0.01 - 0.07)
|
|
Sulphide
(mg/L)
|
<0.05 (<0.05 - <0.05)
|
<0.05 (<0.05 - <0.05)
|
|
Aluminium
(µg/L)
|
55 (36 - 77)
|
41 (16 - 94)
|
|
Cadmium
(µg/L)
|
<0.1 (<0.1 - <0.1)
|
<0.1 (<0.1 - <0.1)
|
|
Chromium
(µg/L)
|
1.1 (<1.0 - 1.4)
|
1.0 (<1.0 - 1.3)
|
|
Copper
(µg/L)
|
2.4 (1.0 - 6.8)
|
2.5 (1.3 - 4.1)
|
|
Lead
(µg/L)
|
1.0 (<1.0 - 2.9)
|
<1.0 (<1.0 - 1.1)
|
|
Zinc
(µg/L)
|
33 (10 - 140)
|
172 (10 – 1,330)
|
|
Flow
(m³/s)
|
0.1 (0.1 - 0.1)
|
0.1
(0.1 - 0.1)
|
Notes: 1. Data source: Inland water sampling conducted
in October 2022 for wet season.
2. Data
presented are annual arithmetic means of the depth-averaged results except for
E. coli and faecal coliforms which are annual geometric means.
3.
Data in brackets indicate the ranges.
4. Values at or below laboratory
reporting limits are presented as laboratory reporting limits.
5. The
sampling period was conducted over 2 weeks, with 3 sampling days for each week,
hence, there are a total of 6 sampling days for each season.
5.2.4
Beaches
5.2.4.1
Two beaches in Tuen Mun
District (i.e. Butterfly Beach and Castle Peak Beach)
are identified within the assessment area. Summaries of EPD’s routine beach
water quality monitoring data for the past decade (i.e.
Years 2012 to 2022) are presented in Table 5.7.
The beach water quality monitored in Year 2022 for both beaches received a
“Fair” ranking.
Table 5.7 Annual geometric mean E. coli levels for Beaches of Tuen Mun District (Years 2012 to 2022)
|
Beach
|
E. coli counts per 100mL
|
|
2012
|
2013
|
2014
|
2015
|
2016
|
2017
|
2018
|
2019
|
2020
|
2021
|
2022
|
|
|
Butterfly
|
42
|
71
|
38
|
98
|
131
|
81
|
39
|
91
|
129
|
57
|
50
|
|
|
Castle Peak
|
48
|
78
|
91
|
71
|
106
|
65
|
70
|
128
|
112
|
103
|
162
|
|
5.3
Representative Water Sensitive Receivers
5.3.1.1
The assessment area for the water
quality impact assessment shall include areas within 500m from the Project
boundary, and shall cover the North Western WCZ as
stipulated in Clause 3.4.6.2 of EIA Study Brief (ESB-348/2021). The assessment
area was extended beyond the 500m assessment area to cover other locations
including beaches, water pumping stations, and cooling water intakes etc., to
identify other WSRs that may also be affected by the Project and may have a
bearing on the environmental acceptability of the Project. The major groupings
of WSRs are summarised below:
·
Gazetted beaches;
·
Cooling water intakes;
·
WSD flushing water intakes;
·
Typhoon shelters;
·
Country Parks;
·
Rivers;
·
Water gathering ground and
reservoirs; and
·
Secondary Contact Recreation
Subzones.
5.3.1.2
The identified WSRs are summarised
in Table 5.8 and their locations are shown in Figure 5.1.
Table 5.8 Summary of identified WSRs
|
ID
|
WSR
|
|
Gazetted Beaches
|
|
B1
|
Butterfly Beach
|
|
B2
|
Castle Peak Beach
|
|
Cooling Water Intakes
|
|
C1
|
ASD Tuen Mun Hospital Cooling Water Intake
|
|
WSD Flushing Water Intakes
|
|
WSD1
|
WSD Flushing Water Intake Near Butterfly Beach
|
|
Country Park
|
|
CP1
|
Tai Lam Country Park
|
|
Typhoon Shelters
|
|
TS1
|
Tuen Mun Typhoon Shelter
|
|
Rivers
|
|
RIV1
|
Tuen Mun River
|
|
Water Gathering Ground and Reservoirs
|
|
RSV1
|
Lam Tei Irrigation Reservoir
|
|
RSV2
|
Hung Shui Hang Irrigation Reservoir
|
|
WG1
|
Water Gathering Ground
|
|
Secondary Contact Recreation Subzones
|
|
SCZ1
|
Secondary Contact Recreation Subzone 1
|
|
SCZ2
|
Secondary Contact Recreation Subzone 2
|
5.4
Identification and Evaluation of Water Quality Impacts –
Construction Phase
5.4.1
Summary of Key Construction
Activities
5.4.1.1
A review has been conducted on
the construction methodologies given in Section
2. A summary of the construction methodologies for various tunnel
sections is given below. According to the latest design, both Tunnel Boring
Machine (TBM) and Drill-&-Blast (D&B) / Drill-&-Break tunnelling
methods would be adopted:
Table 5.9 Summary of Construction
Methods for Different Alignment Sections
|
Alignment
Section
|
Construction
Method
|
|
Lam Tei
Interchange to Existing Lam Tei Quarry Site
|
At-grade
works
|
|
Lam
Tei to Sam Shing Estate
|
D&B
tunnelling
|
|
Tuen Mun
Typhoon Shelter
|
TBM
tunnelling (underneath seabed)
|
|
Tuen Mun
West (Tuen Mun Area 44 to Pillar Point)
|
TBM
tunnelling (land based)
|
|
Tuen Mun
West (Pillar Point to River Trade Terminal)
|
At-grade
works
|
5.4.1.2
Other than the above tunnel
sections, the construction of the Project also requires the following:
Table 5.10
Construction Elements Required for Construction Works
|
Construction
Elements
|
Location
|
|
Magazine sites for the storage of
explosives
(for shared use
with Route 11)
|
1 no at Lam Tei
1 no at Siu Lam
1 no at Pillar Point
|
|
Barging point
|
1 no at Tuen Mun – Chek Lap Kok Tunnel
(TM-CLKT) Northern Connection
|
|
Temporary works areas
|
1 no at Sam Shing Estate
1 no at Yau Oi Estate
4 nos at TM-CLKT
Northern Connection
2 nos at Pillar
Point
|
5.4.1.3
As discussed in Section
2, while most of the Project would be in the form of tunnel sections,
the Project Profile has not excluded the possibility for Immersed Tube
Tunnelling (IMT) within the Tuen Mun Typhoon Shelter. Obviously, IMT would
inevitably require dredging which would induce higher water quality impacts
during the construction phase.
5.4.1.4
During the subsequent design
stage after the submission of Project Profile and issue of the EIA Study Brief,
the project team has collated more baseline information and considered
different practicable options for the alignment section within the Tuen Mun
Typhoon Shelter. After considering all the issues including engineering,
environmental etc, it is considered more appropriate to adopt a Tunnel Boring
Machine (TBM) to construct the tunnel section within the Tuen Mun Typhoon
Shelter. The environmental benefit of adopting TBM tunnelling is that dredging
would be avoided and hence the associated water quality impacts within the Tuen
Mun Typhoon Shelter are minimised during the construction phase.
5.4.1.5
The potential water pollution
sources induced from the construction of the Project are identified and
summarised below:
·
Construction run-off and
general construction activities;
·
Tunnelling and underground works;
·
Construction for ventilation
buildings, satellite building and administration building;
·
Sewage due to construction workforce;
·
Construction works in close
proximity of inland water;
·
Groundwater from contaminated
areas and contaminated site run-off;
·
Operation of barging points;
·
Accidental spillage of
chemicals; and
·
Diversion of watercourses
5.4.1.6
For the construction of sub-sea
section of tunnel at Tuen Mun Typhoon Shelter, tunnel boring machine (TBM)
tunnelling will be adopted. The tunnel will be passing within the bedrock
layer, which will not have disturbance on the waterbodies or seabed. Therefore,
adverse water quality on the marine water bodies is not anticipated, and no mitigation
measure would be required.
5.4.2
Construction Run-off and
General Construction
Activities
5.4.2.1
Construction site run-off is
generated from construction activities at work sites and has the potential to
cause adverse water quality impacts. Potential water pollution sources from
construction site run-offs and construction activities may include:
·
Run-off and erosion from site
surfaces, earth working areas and stockpiles;
·
Accidental release of any
bentonite slurries, concrete washing and other grouting materials associated
with construction run-off, stormwater or groundwater dewatering process;
·
Wash water from concrete
washing, dust suppression sprays, equipment and wheel washing facilities;
·
General site cleaning and
polishing; and
·
Chemical spillage such as fuel,
oil, solvents and lubricants from the maintenance of
construction machinery and equipment.
5.4.2.2
In addition, during rainstorm
events, site run-off would wash away soil particles on unpaved lands and areas
with exposed topsoil. Which generally contains high concentrations of SS,
meaning the discharge of uncontrolled site run-off would increase the SS levels
and turbidity of the nearby water bodies. Uncontrolled site run-off may also
contain concrete and cement-derived materials which may increase the turbidity,
discoloration, pH levels of nearby waterbodies. The increased turbidity of
water bodies decreases the amount of sunlight penetration, hence reducing the
rate of faecal bacteria decay and the rate of photosynthesis. However, the
adverse impacts could be minimised with good construction site practices.
5.4.3
Tunnelling and Underground
Works
5.4.3.1
As discussed in Section
5.5.1, the tunnel sections of the Project would be constructed by
either D&B and TBM methods.
Drill-&-Blast (D&B) / Drill-&-Break Tunnelling
5.4.3.2
As discussed in Section
2, the majority of the tunnel section underneath Tai Lam Country Park
would be in granite. The depth of this tunnel section would vary between 43 –
465m below local ground. After considering the latest geological information,
D&B / Drill-&-Break tunnelling is considered the most suitable
construction methodology for this tunnel section underneath Tai Lam Country
Park.
5.4.3.3
The proposed D&B /
Drill-&-Break tunnelling works may result in groundwater infiltration which
may increase construction site run-off and lead to potential groundwater table
drawdown. Any potential drawdown could result in different degrees of
settlement and dewatering of surface waterbodies (i.e.
Lam Tei Irrigation Reservoir, Hung Shui Hang Irrigation Reservoir, and nearby streams),
and hence groundwater in the vicinity may also be depleted. SS would also be a
key concern as infiltrated water could increase the amount of construction site
run-off from the site to nearby drainage systems.
5.4.3.4
However, as this D&B/
Drill-&-Break tunnel section would be in granite and with sufficient depth
below ground, together with the good practices and mitigation measures as
described in Section 5.8, adverse impacts from the change in
groundwater level and SS would be insignificant.
Tunnelling using Tunnel Boring Machine (TBM)
5.4.3.5
As discussed in Section
2, TBM tunnelling would be adopted for the sections within Tuen Mun
Typhoon Shelter, and the section from Tuen Mun Area 44 to Pillar Point. The
section within Tuen Mun Typhoon Shelter would be approximately 10 – 60m
underneath seabed and within bedrock layer, hence only land-based works would
be involved.
5.4.3.6
Potential sources of water
quality impact from these tunnelling works would be the discharge of tunnelling
wastewater from drilling, boring and wash-down. Furthermore, the use of
bentonite and grouting materials for the construction of bored tunnels would
contaminate the water pumped out from the tunnel. Surface run-off may also be
contaminated, and turbid water may enter adjacent watercourses, drainage
systems, and waterbodies located downstream as excavated material is conveyed
to the surface. Water used for the tunnelling works should also be
re-circulated after sedimentation and when the water is due for final disposal,
it should be treated to ensure compliance with the standards stipulated in the
TM-DSS before being discharged into storm drains.
5.4.3.7
TBM
tunnelling may influence the groundwater levels. However, as the works area is
located at coastal areas, the groundwater level would be quickly re-balanced by
the surrounding marine environments. Also, the TBM tunnelling works within Tuen
Mun Typhoon Shelter would take place at the granite layer underneath thick
marine deposit and alluvium layers, the disturbance to the marine deposit and
alluvium layers of Tuen Mun Typhoon Shelter should be minor. For the section
between Tuen Mun Area 44 to Pillar Point, the vertical alignment would also go
through both granitic and volcanic layers.
Therefore, any change of groundwater level caused by the Project would
be insignificant and hence significant changes in underground hydrology,
hydrodynamic regime, sediment erosion, and deposition patterns are not
anticipated.
5.4.3.8
For the operation of TBM at the
vicinity of water sensitive receivers near Tuen Mun Typhoon Shelter,
reservation of adequate soil cover (i.e. sufficient
buffer distance between seabed and underground works area), and/or sealing up
of charted boreholes would be provided to prevent potential accidental seepage
or discharge due to excessive pressure of TBM. Sufficient ground investigation
and soil testing should be carried out to ascertain that adequate soil cover is
achieved, and all charted boreholes should be checked by engineers to ensure
proper seal up prior to the TMB passing. It may cause accidental blowout during
annulus grouting around the completed segment rings at the back of the TBM. The
grouting may penetrate through the voids of the soil above the TBM and reach
the seabed and leak into the sea. However, provided
that there is adequate soil cover, it will prevent the potential of
the blowout from happening.
5.4.4
Ventilation Building, Satellite
Building and Administration Building
5.4.4.1
As discussed in Section
2, there would be a total of 3 ventilation buildings (at Lam Tei, Wah
Fat Playground, and Pillar Point), 1 satellite building (at Lam Tei) and 1
administration building (at Pillar Point) along the entire tunnel section,
which are shown in Figure 2.9. The construction of
these ventilation buildings, satellite building and
administration building would adopt an open cut excavation method and followed
by construction of superstructure and utilities.
5.4.4.2
These buildings are located at
the vicinity of waterbodies including Tuen Mun River, Lam Tei Irrigation
Reservoir, marine waters, and existing drainage systems. Potential impacts may
occur during rainfall events whilst the excavation works are ongoing, as silt
and sandy materials carried by run-off from the excavation may enter nearby
watercourses, increasing their SS content and turbidity. Other pollutants, such
as oil and grease, chemicals, bentonite, and grouting materials, may also be
present in the run-off should it flow over storage or maintenance areas, where
it may increase discoloration, turbidity, chemical and pH levels of the nearby
water bodies. Additionally, the erosion of soil enriched in organic matter may
release excess nutrients into adjacent water bodies, potentially leading to
eutrophication.
5.4.4.3
These impacts would require the
good practices and mitigation measures as described in Section 5.8
to ensure any residual impacts would comply with the statutory requirements.
5.4.5
Sewage due to Construction Workforce
5.4.5.1
Sewage will be generated by
sanitary facilities (i.e. chemical toilets) provided
for the on-site construction workforce. Sewage is characterized by high levels
of BOD5, ammonia and E. coli counts. According to Table T-2
of Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning
(GESF) published by EPD, the unit flow factor (UFF) is 0.23 m3/day/employee
(0.08 m3/day/employee for commercial employee and 0.15
m³/day/employee for employees of construction activities).
5.4.5.2
According to the current
design, there will be a workforce of approximately 450 people which will be
working on site at any one time during the construction phase of the
Project. Hence, a total sewage load of
approximately 103.5 m3/day
will be generated throughout the entire construction phase of approximately 93
months.
5.4.5.3
Adequate chemical toilets
should be provided to avoid direct discharge into any nearby watercourse or
public drains. With these mitigation measures in place, no adverse water
quality impacts are anticipated.
5.4.6
Construction Works in Close Proximity of Inland Water
5.4.6.1
Construction activities may
pollute nearby inland waterbodies near Lam Tei, Siu Lun, and Pillar Point (i.e. Tuen Mun River and other streams, Lam Tei Irrigation
Reservoir, Hung Shui Hang Irrigation Reservoir, streams and water gathering
ground) through the potential release of construction wastes, which are
generally characterised by high concentration of SS and elevated pH. With the implementation of adequate construction site
drainage as specified in the ProPECC PN 1/94
“Construction Site Drainage” and the provision of mitigation measures as
described in the ETWB TC (Works) No. 5/2005 “Protection of natural streams /
rivers from adverse impacts arising from construction works”, no adverse water
quality impacts are anticipated.
5.4.7
Groundwater from Potential Contaminated Areas and Contaminated Site Run-off
5.4.7.1
As discussed in Section
2, the majority of the Project alignment would go through the Tai Lam
Country Park which would have no potential for land contamination. The tunnel
section from Sam Shing to Pillar Point through Tuen Mun Typhoon Shelter would
be mainly within rock layer and hence also has no potential for land
contamination.
5.4.7.2
Section
7 has conducted a comprehensive land
contamination study for the entire Project. According to the current findings,
potential contaminated areas are identified at Lam Tei, Sam Shing Hui, and
Pillar Point areas. Proper land contamination remediation and mitigation
measures proposed in Section
7 should be followed. If the groundwater that is pumped out, or from
discharged from the dewatering process during excavation works are located
within potential contaminated areas, the water could also be contaminated. Any
potential contaminated materials which may be disturbed, or any foreign
materials which contacts such contaminated material, could be washed by site
run-off into the drainage system, thereby discharging contaminated water into
the drainage system. Any potential contaminated groundwater or site run-off
should be properly treated and disposed in compliance with the requirements of
TM-DSS.
5.4.8
Operation of Barging Point
5.4.8.1
As discussed in Section
2, the barging points are located at the eastern coastline of TM-CLKT
northern landfall. Given the sufficient water depth, dredging would not be
required. This would
avoid any disturbance to the seabed and hence the associated water quality
impacts.
5.4.8.2
However, activities conducted at the barging
points still have the potential to cause adverse water quality impacts.
Uncontrolled surface run-off generated at the barging point may contain high
concentrations of SS, oil & grease, and chemicals. Additionally, materials
may also be splashed into the surrounding water during the transportation of
spoil using the barging point. These activities may increase the turbidity,
discoloration, pH level of the nearby marine waters. Barges may also increase
the turbidity and SS content of the nearby waters as marine deposits on the
seabed may be disturbed through vessel movements and propeller wash.
5.4.8.3
With the implementation of the
good practices and mitigation measures recommended in Section 5.8.
any residual water quality impacts would comply with the statutory
requirements.
5.4.9
Accidental Spillage of
Chemicals
5.4.9.1
The use of chemicals such as
engine oil and lubricants, and their storage as waste materials has the
potential to cause adverse water quality impacts if spillage occurs and enters
the adjacent water bodies. Waste oil may infiltrate the surface soil layer, or
discharged into the nearby water environment, increasing hydrocarbon levels.
However, adverse impacts can be mitigated by implementing practical mitigation
measures and good site practices.
5.4.10
Diversion of Watercourses
5.4.10.1
Due to engineering constraints
and geological conditions, it is unavoidable that the Project alignment would
require diversion of watercourses to be diverted at some locations, including
Lam Tei, near Wah Fat Playground, and Pillar Point. The diversion of water
courses would involve excavation and construction works. If not properly
controlled, pollutants including excavated materials, chemicals, wastewater or
construction materials may be flushed downstream via the watercourse, This may cause water quality impacts and flooding may occur
in the downstream areas of the diverted or removed watercourses. This requires
the implementation of proper mitigation measures stated in Section 5.8,
to ensure no adverse water quality impacts.
5.5
Identification and Evaluation of Water Quality Impacts – Operational
Phase
5.5.1
General
5.5.1.1
The following potential sources
of water quality impacts are identified for the operational phase of the Project:
·
Road run-off discharged from
paved roads and developments proposed under the Project;
·
Sewage generated by satellite
building and administration building;
·
Tunnel run-off and drainage;
and
·
Wastewater generated from
washing and maintenance operations.
5.5.2
Surface Run-off from Paved
Areas of the Project
5.5.2.1
Surface run-offs would
typically contain pollutants that are deposited onto paved surfaces including
roads, bridges, administration building, satellite building and ventilation
buildings which are then discharged to existing waterways during rainfall and
storms via drainage systems, and are considered as a
non-point source. The key pollutants in concern include sediments, oil and
grease, heavy metals, debris, rubber, and fertilizers.
5.5.2.2
Pollutants such as rubber,
debris, oil and grease and sediments may be generated by road users (i.e. vehicles), and are accumulated on the roads during dry
periods. Most of the accumulation is found in slightly depressed and at-grade
road sections where sediment and silt will be carried and deposited. Pollutants
deposited on the road surface will be washed away from the roads by run-off
generated during rainfall and storms events, where a large proportion of the
rainfall landing on road hard surfaces will reach the surface water drainage
systems.
5.5.2.3
Factors including climatic
conditions and intensity of precipitation, topography, and the degree of
urbanisation has a significant influence on the characteristics of road run‑off.
Following high intensity precipitation, the road surface may be scoured,
resulting in an initial run-off that is referred to as the “first-flush”,
which typically contains a high amount of pollutants, and may include
significant water quality impacts on the water bodies. Subsequent run-offs may
contain lower levels of pollutants. Overall, with the application of adequate
mitigation measures, any water quality impacts can be reduced to an acceptable
level.
5.5.3
Sewage Effluent from the
Proposed Buildings
5.5.3.1
During the operational phase,
the sewage generated from the satellite building near the north ventilation
building at Lam Tei and the administration building near the toll plaza of Tuen
Mun Chek Lap Kok tunnel at Pillar Point, would be a pollution source. Staff and
workers at the satellite building and administration building will generate
sewage through toilet and sanitary facilities. To avoid adverse water quality
impacts, the sewage should not be discharged to waterbodies. Instead, the
sewage should be discharged through public sewers that are connected to public
sewerage systems which are located at the vicinity of the buildings.
5.5.3.2
No toiletry facilities are
proposed for ventilation buildings at Lam Tei, Siu Lun
and Pillar Point. Hence, it is anticipated that no sewage will be generated at
the ventilation buildings. Adverse
impacts are therefore not anticipated.
5.5.4
Drainage of Road Surface and Tunnel Runoff
5.5.4.1
During or after rainstorm
events, rainwater on at-grade roads and viaducts may drain into the drainage
system, and seepage of groundwater into the tunnel may generate tunnel
run-off. These run-off
may contain limited amount of SS, oil and grease. Direct discharge of tunnel run-off into
nearby waterbodies may induce adverse water quality impact and should be
avoided. No adverse water quality impacts are anticipated with the proper
implementation of recommended mitigation measures such as the installation of
silt traps and oil/grit interceptors as described in Section 5.9.
5.5.5
Wastewater Generated from Washing and Maintenance Operations
5.5.5.1
Wastewater will be generated
from washing and maintenance operations associated with work vehicles and the maintenance
activities for the tunnel ventilation system.
Direct discharge of the generated wastewater to the nearby drainage
system and waterbodies will induce adverse water quality impacts and should be
avoided. Instead, the wastewater should be discharged to the sewerage system.
5.5.5.2
Wastewater generated by washing and maintenance operations
associated with the tunnel system, tunnel surface and the ventilation system
may include dusts and undissolved oils, whereas wastewater generated by washing
and maintenance activities of work vehicles usually contains hydrocarbon
pollutants such as petroleum and diesel.
5.5.5.3
No adverse water quality impact
is anticipated with the proper implementation of recommended mitigation
measures such as discharging wastewater to the public sewerage system properly,
as described in Section 5.9.
5.6
Cumulative Impacts from Concurrent Projects
5.6.1.1
The construction of the Project
may potentially overlap with the construction period of other nearby concurrent
projects as identified in Section
2. The identified concurrent projects within the 500m Assessment
Area of the Project may induce cumulative water quality impacts, which are
evaluated and discussed in Appendix 5.2. No
cumulative water quality impacts are anticipated for concurrent projects.
5.6.1.2
Appendix 5.2 also tabulates and evaluates those concurrent projects that are
beyond the 500m Assessment Area of the Project. Given the large separation
distances, the cumulative impacts from the concurrent projects beyond 500m
would not be significant.
5.7
Recommended Mitigation Measures –
Construction Phase
5.7.1
Construction Run-off and General Construction
Activities
5.7.1.1
Best Management Practices
(BMPs) of mitigation measures in controlling water pollution and good site
management, as specified in ProPECC PN 1/94, should
be followed as applicable to prevent run-off with a high level of SS from
entering the surrounding waters. Additionally, all effluent discharged from the
construction site should comply with the standards stipulated in the TM-DSS.
The following mitigation measures are recommended to protect the water quality
of the nearby waterbodies, and should provide
sufficient and adequate control to site discharges to minimise adverse water
quality impacts when properly implemented.
5.7.1.2
All effluent discharged from
the construction site should comply with the standards stipulated in the
TM-DSS. The following measures are recommended to protect the water quality of
the nearby water, and when properly implemented should be sufficient to
adequately control site discharges to avoid water quality impacts:
·
At the start of site
establishment, perimeter cut-off drains to direct off-site water around the
site should be constructed with internal drainage works and erosion and
sedimentation control facilities implemented. Channels (both temporary and
permanent drainage pipes and culverts), earth bunds or sand
bag barriers should be provided on site to direct stormwater to silt
removal facilities. The design of the temporary on-site drainage system will be
undertaken by the contractor prior to the commencement of construction;
·
The dikes or
embankments for flood protection should be implemented around the boundaries of
earthwork areas. Temporary ditches should be provided to facilitate the run-off
activities discharge into an appropriate watercourse, through a silt/sediment
trap. The silt/sediment traps should be incorporated in the permanent drainage
channels to enhance deposition rates;
·
The design of efficient silt
removal facilities should be based on the guidelines in Appendix A1 of ProPECC PN 1/94. The detailed design of the sand/silt traps
should be undertaken by the Contractor prior to the commencement of construction;
·
All areas with exposed earth
should be vegetated as soon as possible after earthworks have been completed.
If excavation of soil cannot be avoided during the rainy season, or at any time
of year when rainstorms are likely, exposed slope surfaces should be covered by
tarpaulin or other means. All drainage facilities and erosion and sediment
control structures should be regularly inspected and maintained to ensure
proper and efficient operation at all times, particularly following rainstorms.
Deposited silt and grit should be removed regularly and disposed of by
spreading evenly over stable, vegetated areas. Considering the scale of the
proposed excavation works, it is not practicable to avoid works during the
rainy season as this would significantly affect the overall construction
programme. However, for works area that is close to watercourses, excavation
works shall avoid the rainy season whenever possible. Excavation works shall be
proceeded section by section to reduce the amount of works are with exposed earth;
·
Measures should be taken to
minimise the ingress of site drainage into excavations. If the excavation of
trenches in rainy seasons are necessary, it should be excavated and backfilled
in short sections wherever practicable. Water pumped from trenches or
foundation excavations should be discharged into storm drains installed with
silt removal facilities;
·
All open stockpiles of
construction materials (i.e. aggregates, sand and fill
material etc.) 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;
·
Manholes (including newly
constructed ones) should always be adequately covered and temporarily sealed to
prevent silt, construction materials or debris from being washed into the
drainage system and storm run-off being directed into foul sewers;
·
Precautions should be taken
during rainy seasons, and actions as summarised in Appendix A2 of ProPECC PN 1/94 should be taken when a rainstorm is
forecasted or imminent,. Particular attention should
be paid to the control of silty surface run-off during storm events;
·
All vehicles and plants should
be cleaned before leaving construction sites to minimise the deposition of
earth, mud, debris and other potentially polluting
particles on roads. An adequately designed and sited wheel washing
facilities should be provided at every construction site’s exit where
practicable. Wash water should have sand and silt settled out and removed at
least on a weekly basis to ensure the continued efficiency of the process. The
section of access road leading to, and exiting from, the wheel-wash bay to the
public road should be paved with sufficient back fall towards the wheel-wash
bay to prevent vehicles from tracking of soil and silty water to public roads
and drains;
·
Oil interceptors should be
provided in the drainage system downstream of any oil/fuel pollution sources.
The oil interceptors should be emptied and cleaned regularly to prevent the
release of oil and grease into the storm water drainage system after accidental
spillage. A bypass should be provided for the oil interceptors to prevent
flushing during heavy rain;
·
Construction solid waste,
debris and rubbish on site should be collected, handled, and disposed of
properly to minimise adverse water quality impacts;
·
Water used for tests to check
for leakages in structures and pipes should be reused for other purposes as far
as practicable. Surplus unpolluted water could be discharged into storm drains;
·
Earthworks final surfaces
should be compacted, and the subsequent permanent work or surface protection
should be carried out immediately after the final surfaces are formed to
prevent erosion of earth caused by rainstorms. Appropriate drainage with
intercepting channels should be provided where necessary;
·
Extracted groundwater from
activities such as water pumped from basement or foundation construction, and
groundwater seepage pumped from tunnel or cavern constructions should be
discharged into storm drains after the removal of silt through silt removal facilities;
·
Water used in ground boring and
drilling for site investigation or rock/soil anchoring should as far as
practicable be recirculated after sedimentation. When there is a need for final
disposal, the wastewater should be discharged into storm drains through silt
removal facilities; and
·
The bentonite 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.
5.7.1.3
The temporary drainage system
during the construction phase could cope with a design return period of 1 in 10
years rainfall as recommended in DSD Technical Circular No. 1/2017 “Temporary
Flow Diversions and Temporary Works Affecting Capacity in Stormwater Drainage
System” and DSD’s practical Notes No. 1/2017 “Design rainfall and profile for
temporary works within the Dry Season”.
5.7.1.4
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.
5.7.1.5
Requirements to be incorporated
in the Project contract document should be established based on the water
quality mitigation measures as mentioned above.
5.7.2
Tunnelling and Underground Works
5.7.2.1
Whilst conducting tunnelling
works, the Contractor should adopt suitable water control strategies, which are
applicable to both TBM tunnelling and D&B tunnelling, as far as
practicable, including:
·
Face confinement (TBM
tunnelling): The confinement pressure to be applied at the TBM front should at
least balance the existing groundwater pressure to ensure no seepage flow will
occur through the TBM face, and hence no groundwater table drawdown throughout
the excavation is anticipated.
·
Probing Ahead (D&B
Tunnelling): The Contractor should undertake rigorous probing of the ground
ahead of tunnel excavation works to identify zones of potential significant
water inflow. The probe drilling results should be evaluated to determine where
grouting is required in line with the tunnel ahead. In zones where significant
water inflow could occur due to discrete, permeable features, grouting should
be applied to reduce overall inflow of groundwater;
·
Pre-grouting (D&B
Tunnelling): Where water inflow quantities are excessive, pre-grouting will be
required to reduce the water inflow into the tunnel, which will be achieved via
a systematic and carefully specified protocol; and
·
In principle, the grout pre-treatment would be designed based on probe
hole drilling ahead of the tunnel face.
5.7.2.2
In the event
of where there is still excessive drawdown of the groundwater table, even after
the implementation of water control strategies, post-grouting should be applied
as far as practicable, which is described below:
·
Post-grouting:
Groundwater drawdown will most likely be caused by inflows of water into the
tunnel that have not been sufficiently controlled by pre-grouting measures.
Should there be groundwater drawdown, post-grouting should be undertaken before
the lining is cast. Whilst post-grouting is unlikely required, it should still
be considered as a contingency measure to further reduce the permeability of
the tunnel to limit groundwater inflow to acceptable levels.
5.7.2.3
The tunnel sections adopting
TBM tunnelling should be constructed using a closed face TBM to limit water
inflow into the excavation face. The cutter head for the machine will be sealed
during excavation and therefore the water inflow from the face will be kept to
a minimum. Precast undrained linings should be installed and back grouted
behind the TBM as it advances along the tunnel alignment to minimize the
potential inflow of water behind the cutter head.
5.7.3
Ventilation Buildings, Satellite Building and Administration Buildings
5.7.3.1
For underground excavations for
the proposed ventilation buildings, satellite building and administration
building which will require temporary dewatering during their construction, the
following mitigation measures are recommended to minimise the potential adverse
effects to the groundwater table during the works:
·
Toe grouting should be applied
beneath the toe level of the temporary/permanent cofferdam walls as necessary
to lengthen the effective flow path of groundwater from outside and thus
control the amount of water inflow to the excavation; and
·
Recharge wells should be
installed as necessary outside the excavation areas. Water pumped from the
excavation areas should be recharge back onto the ground.
5.7.4
Sewage Due to Construction Workforce
5.7.4.1
No sewage discharge to the
drainage system, watercourses, and marine water will be allowed. Adequate and
sufficient portable chemical toilets should be provided in the works areas to
handle sewage generated by the construction workforce. Should there be any
on-site kitchens or canteens, a temporary storage tank should be provided to
collect wastewater. A registered collector should be employed to clean and
maintain the chemical toilets on a regular basis.
5.7.4.2
Notices should be posted at
conspicuous locations to remind the construction workforce not to discharge any sewage or wastewater
into the surrounding environment. Regular environmental audit of the
construction site should be conducted to provide an effective control of any
malpractices and to achieve continual improvement of environmental performances
on site.
5.7.5
Construction Works in Close
Proximity of Inland Water
5.7.5.1
The practices outlined in ETWB
TC (Works) No. 5/2005 “Protection of natural streams/rivers from adverse
impacts arising from construction works” should be adopted where applicable to
minimise the water quality impacts. Relevant mitigation measures from the ETWB
TC (Works) No. 5/2005 are listed below:
·
Construction works close to the
inland waters should be carried out in dry season as far as practicable where
the flow in the surface channel or stream is low;
·
Trenches should be dug and
backfilled in short sections. Measures should be taken to minimize the ingress
of rainwater into trenches;
·
The use of less or smaller
construction plants may be specified in areas close to the water courses 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 during 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; and
·
Proper shoring may need to be erected
in order to prevent soil or mud from slipping into the watercourses.
5.7.5.2
In addition, WSD’s Conditions
for Working within Water Gathering Grounds shall also be complied with. The
conditions are provided in Appendix
5.3.
5.7.6
Groundwater from Contaminated Areas and Contaminated Site Run-off
5.7.6.1
The remediation of contaminated
land should be properly conducted following the recommendations proposed under Section
7.
5.7.6.2
Any excavated contaminated
material and exposed contaminated surface should be properly housed and covered
to avoid generation of contaminated run-off, the open
stockpiling of contaminated materials should not be allowed. Any contaminated
run-off generated under the construction process should be properly collected
and treated as necessary before disposal.
5.7.6.3
The direct discharge of
groundwater from contaminated areas is not allowed. Prior to any excavation
works within 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, the review results should be submitted to EPD for approval. If
the review results indicated that the groundwater generated from the excavation
works would be contaminated, the contaminated groundwater should be either
properly treated or properly recharged into the ground in compliance with the
requirements of the TM-DSS.
5.7.6.4
If a water treatment facility
is deployed on-site to treat the contaminated groundwater, it should be
equipped with suitable instruments (e.g., oil interceptor, activated carbon
etc.) to reduce the pollution level to an acceptable standard and remove to any
prohibited substances (such as total petroleum hydrocarbon) to an undetectable
range. All treated effluent from the wastewater treatment plant shall meet the
requirements as stipulated in the TM-DSS and should be either discharged into
the foul sewers or tankered away for proper disposal.
5.7.6.5
If the deployment of a
treatment facility to treat the contaminated groundwater is not feasible,
groundwater recharging wells should be installed as appropriate to recharge the
contaminated groundwater back onto the ground. The recharging wells should be
selected at places where the groundwater quality will not be affected by the
recharge operation as stipulated in TM-DSS. The baseline groundwater quality
should be determined before selecting the recharge wells and a working plan
should be submitted to EPD for agreement. Pollution levels of the recharged
groundwater shall not be higher than pollutant levels of ambient groundwater at
the recharge well. Groundwater monitoring wells should be installed near the
recharge points to monitor the effectiveness of the recharge wells and to
ensure that no there is no increase of groundwater level and the transfer of
pollutants beyond the site boundary. Prior to the recharge, oil
and grease, if any, should be removed as necessary by installing an oil
interceptor. The Contractor should apply for a discharge licence under the WPCO
through the Regional Office of EPD for groundwater recharge operation or the
discharge of treated groundwater.
5.7.6.6
All exposed earth areas should
be completed and vegetated as soon as possible after earthworks have been
completed. If excavation of soil cannot be avoided during the rainy season, or
at any time of year when rainstorms are likely, exposed slope surfaces should
be covered by tarpaulin or other means. All drainage facilities and erosion and
sediment control structures should be regularly inspected and maintained to
ensure proper and efficient operation at all times and particularly following
rainstorms. Deposited silt and grit should be removed regularly and disposed of
by spreading evenly over stable, vegetated areas. For works area that is close
to watercourses, excavation works shall avoid the rainy season as far as
possible, and excavation works shall be proceeded section by section.
5.7.7
Operation of Barging Point
5.7.7.1
To minimise the adverse water
quality impacts of the surface run-off generated by the operation of the
barging point, the mitigation measures recommended under Section
5.7.1 should be followed. To minimise the potential adverse water
quality impact due to the transportation of spoil using the barging point, the
following good site practices should be strictly followed:
·
Loading of barges and hoppers
should be controlled to prevent the splashing of material into the surrounding
water. Barges or hoppers should not be filled to a level that will cause the
overflow of materials or polluted water during loading or transportation; and
·
All vessels should be sized so
that adequate clearance is maintained between vessels and the seabed in all
tide conditions, to minimise that undue turbidity is not generated by
turbulence from vessel movement or propeller wash.
5.7.8
Accidental Spillage of Chemicals
5.7.8.1
The Contractor must be
registered as a chemical waste producer if chemical wastes are produced from
the construction activities. The Waste Disposal Ordinance (Cap. 354) and its
subsidiary regulations, in particular the Waste Disposal (Chemical Waste)
(General) Regulation (Cap. 354C), should be observed and complied with for the
control of chemical wastes. The Contractor is also recommended to develop
management procedures for the chemicals used and prepare an emergency spillage
handling procedure to deal with chemical spillage in case of an accident occurs,
a contingency plan for any accidental spillage and heavy rainfall event should
also be devised.
5.7.8.2
Any services and maintenance
facilities should be located on hard standings within a bunded area, sumps and
oil interceptors should be provided. Activities with the potential for
accidental leakage and spillage of chemicals, including the maintenance of
vehicles and equipment should only be undertaken within areas that are
appropriately equipped to control the discharges from these potential
accidents. The service and maintenance, and any chemical storage areas should
not be positioned near watercourses as a safeguard measure.
5.7.8.3
Disposal of chemical wastes
should be carried out in compliance with the Waste Disposal Ordinance. The Code
of Practice on the Packaging, Labelling, and Storage of Chemical Wastes
published under the Waste Disposal Ordinance details the requirements to deal
with chemical wastes. General requirements are given as follows:
·
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; and
·
Storage area should be
selected at a safe location on-site and adequate space should be allocated to
the storage area.
5.7.9
Diversion of Watercourses
5.7.9.1
During diversion of
watercourses, precaution measures should be implemented to prevent adverse
water quality impact to the surrounding environment and downstream areas. Good
site practices as described in ETWB TC(Works) No. 5/2005 “Protection of natural
streams/rivers from adverse impacts arising from construction works” and ProPECC PN1/94 “Construction Site Drainage” should be
implemented. The following major measures include:
·
Cofferdams or
impermeable structures should be installed as appropriate to isolate the water
flow from the construction works area;
·
Dewatering or flow
diversion shall be conducted prior to the construction works to prevent water
overflow to the surrounding area;
·
Watercourse removal and
flow diversion should be conducted in dry season as far as practicable when the
water flow is low;
·
Water drained from the
watercourse shall be diverted to new/temporary drainage for watercourse
diversion; and
·
Any excavated
land-based sediment from the diversion of watercourse shall be properly stored
at bunded areas away from any watercourses and covered with tarpaulin before
transporting out of the site.
5.8
Recommended Mitigation Measures –
Operational Phase
5.8.1
Surface Run-off from Paved Areas of the Project
5.8.1.1
Surface run-off is identified
as a source of water pollution. The paved and developed areas, especially the
new roads, tunnels will increase the quantity of surface run-off. The presence
of oil, grease and grit on the paved surfaces could be washed into the nearby
drainage systems, or nearby watercourses during rainfall.
5.8.1.2
To minimise the adverse water
quality impacts, the road drainages should be equipped with adequate silt traps
and oil interceptors. Regular washing of the roads and paved areas are also
recommended to prevent the accumulation of pollutants. To maintain the
equipment’s efficiency, contents collected in silt traps and oil interceptors
should be cleared regularly, and transferred to an appropriate disposal
facility, or to be collected for reuse if possible. Considering the recommended
mitigation measure, the adverse water quality impact generated by surface
run-off is kept to a minimum.
5.8.2
Sewage Effluent from the Proposed Buildings
5.8.2.1
Sewage effluent generated
should be discharged to the existing sewerage networks identified through
public sewer at the vicinity of the proposed satellite building and
administration building, the sewerage system at these buildings should be
connected properly whilst ensuring that the public networks have a sufficient
capacity to handle the sewerage load generated. Toilets and other sanitary
facilities should be cleaned and maintained on a regular basis.
5.8.3
Drainage of Road Surface and Tunnel Runoff
5.8.3.1
Tunnel run-off is identified as
a non-point water pollution sources. To minimise the adverse water quality
impacts, the discharge of road drainage channels should pass through treatment
facilities (i.e. silt traps and oil/grit interceptors)
to remove oil, grease and sediment content before the run-off is discharged to
the public storm drainage system. The treatment facilities including silt traps
and oil interceptors should be cleaned and maintained regularly to ensure their
continued effectiveness. Oily contents of the oil interceptors should be
transferred to an appropriate facility, or where possible, reused. With the
proper implementation of the recommended mitigation measures, no adverse water
quality impacts are anticipated.
5.8.4
Wastewater Generated from Washing and Maintenance Operation
5.8.4.1
Wastewater generated by washing
and maintenance activities of ventilation systems should be collected and
treated via an activated carbon filter before being discharged, whereas
wastewater generated by washing and maintenance activities associate with work
vehicles should be collected and treated by petrol interceptors before being
discharged. A Licensed Chemical Contractor should be employed to collect and
dispose of spent lubrication oil generated from vehicle maintenance activities
in compliance with the Waste Disposal Ordinance. No direct discharge of wastewater into the
inland water will be allowed. Instead, wastewater should be discharged to
public sewerage system.
5.9
Residual Impacts
5.9.1.1
With the full implementation of
the recommended mitigation measures for the construction phase of the proposed
Project, no unacceptable residual impacts on water quality are anticipated. It
is recommended that regular audit of the implementation of the recommended
mitigation measures be carried out during the construction phase.
5.9.1.2
With the full implementation of
the recommended mitigation measures for the operational phase of the proposed
Project, no unacceptable residual impacts on water quality are anticipated.
5.10
Environmental Monitoring and Audit (EM&A)
5.10.1.1
With the proper implementation
of the recommended mitigation measures, no unacceptable water quality impacts
are expected during the construction phase of the Project. Detailed approaches
and methodology for water quality monitoring during the construction phase are
detailed in a separate EM&A Manual.
5.10.1.2
For the construction phase of
the Project, EM&A monitoring is recommended for the land-based works to
assess the potential water quality impacts on the waterbodies at the vicinity,
both baseline monitoring before the commencement of works, and post-project
monitoring is recommended. TMB tunnelling would be adopted for the section within
Tuen Mun Typhoon Shelter which would be approximately 10 - 60m underneath
seabed and within bedrock layer, hence marine water quality monitoring is
considered not required. In addition, it is recommended that regular site
inspections are undertaken, to ensure that the recommended mitigation measures
are properly implemented during construction activities and in the works areas.
5.10.1.3
As no adverse water quality
impact is anticipated for the operational phase of the Project, no EM&A
activities are required.
5.11
Conclusion
5.11.1.1
The key water quality impacts
associated with the Project which could impact the nearby waterbodies and water
sensitive receivers is mainly associated with the construction phase of the
Project, which includes general construction activities, construction site
run-off, tunnelling and underground works, sewage from construction workforce,
construction works in close proximity of inland water, groundwater from
contaminated areas and contaminated site run-off, and the accidental spillage
of chemicals. With the proper implementation of recommended mitigation
measures, no adverse water quality impacts would be anticipated during the
construction phase of the Project.
5.11.1.2
During the operation phase of
the Project, the major sources of potential adverse water quality impact
include road run-off discharged from paved roads and developments proposed
under the Project, and the sewage generated by the proposed satellite building
and administration building. With proper implementation of the recommended
mitigation measures, no adverse water quality impacts would be anticipated
during operational phase.