4.1.1
With
reference to Section 4.6.2 of the EM&A manual, the baseline water quality
shall be carried out once per day for 3 days per week, for a period of 4 weeks
prior to the commencement of construction works. The interval between two sets
of monitoring shall not be less than 36 hours.
4.1.2
There
shall not be any major construction activities in the vicinity of the stations
during the baseline monitoring.
4.2.1
In
accordance with Section 4 of the EM&A Manual, water quality monitoring
should be carried out at 11 designated monitoring locations (3 stations for
construction phase and 8 stations for operation phase).
4.2.2
A
proposal of relocation of water quality monitoring locations was submitted to
EPD on 22 September 2020 in accordance with Section 4.5.7 of the EM&A
Manual, the monitoring location E2, E3 and E5 are proposed to be relocated by
alternative monitoring location E2a, E3a and E5a. EPD’s approval letter is
given in Appendix I.
4.2.3
The
water quality monitoring locations are shown in Figure 4.
4.2.4
The
coordinates of the monitoring location stated in the EM&A Manual is
summarised in Table 4.1.
4.3
Monitoring Parameters
4.3.1
Parameters
for each monitoring station for both in-situ measurement and laboratory
analysis are summarised in Table 4.2.
4.4.1
The
following equipment and facilities shall be used for the monitoring of water
quality impacts:
Dissolved Oxygen and
Temperature Measuring Equipment
4.4.1.1
The instrument shall be a portable and weatherproof DO
measuring instrument complete with cable and sensor, and use a DC power source.
The equipment shall be capable of measuring:
·
a DO level in the range of 0 – 20 mg L-1 and 0 – 200%
saturation; and
·
a temperature of 0 ‑ 45 degree Celsius.
4.4.1.2
It shall have a membrane electrode with automatic temperature
compensation complete with a cable. Sufficient stocks of spare electrodes and
cables shall be available for replacement where necessary.
4.4.1.3
Shall salinity compensation not be built-in to the DO
equipment, in-situ salinity shall be measured to calibrate the DO equipment
prior to each DO measurement.
Turbidity
Measurement Instrument
4.4.1.4
Turbidity shall be measured in-situ by the nephelometric
method. The instrument shall be portable and weatherproof turbidity measuring
instrument using a DC power source complete with cable, sensor and
comprehensive operation manuals. It shall have a photoelectric sensor capable
of measuring turbidity between 0 - 1000 NTU (for example, Hach model 2100P or
an approved similar instrument). The cable shall not be less than 25m in
length. The meter shall be calibrated to establish the relationship between NTU
units and the levels of suspended solids. The correlation between Turbidity
(NTU) & Suspended Solids (mg/L) which was established in the baseline
monitoring under the project are shown in Appendix A.
Sampler
4.4.1.5
A water sampler is required. It shall comprise a transparent
Polyvinyl Chloride (PVC) cylinder, with a capacity of not less than 2 liters, which
can be effectively sealed with latex cups at both ends. The sampler shall have
a positive latching system to keep it open and prevent premature closure until
released by a messenger when the sampler is at the selected water depth (for
example, Kahlsico Water Sampler or an approved similar instrument).
Water Depth Detector
4.4.1.6
A portable, battery-operated echo sounder shall be used for
the determination of water depth at each designated monitoring station. This
unit can either be hand held or affixed to the bottom of the work boat, if the
same vessel is to be used throughout the monitoring programme.
Salinity
4.4.1.7
A portable salinometer capable of measuring salinity in the
range of 0 - 40 parts per thousand (ppt) shall be provided for measuring
salinity of the water at each monitoring location.
pH
4.4.1.8
The instrument shall consist of a potentiometer, a glass
electrode, a reference electrode and a temperature-compensating device. It
shall be readable to 0.1 pH in a range of 0 to 14. Standard buffer solutions of
at least pH 7 and pH 10 shall be used for calibration of the instrument before
and after use. Details of the method shall comply with American Public Health
Association (APHA), 19th ed. 4500-HTB.
Sample Containers
and Storage
4.4.1.9
Water samples shall be stored in high density polythene
bottles with no preservative added, packed in ice (cooled to 4°C without being
frozen) and delivered to the laboratory and analyzed within 24 hours after
collection. Sufficient volume of samples shall be collected to achieve the
required detection limit.
The container types for holding water samples are
presented in Table 4.3.
4.4.1.10
Monitoring Position Equipment
A hand-held or boat-fixed type digital Differential
Global Positioning System (DGPS) with way point bearing indication or other
equipment instrument of similar accuracy, shall be provided and used during
marine water monitoring to ensure the monitoring vessel is at the correct
location before taking measurements.
4.4.1.11
Current Velocity and Direction
Valeport Model 106 is proposed for monitoring the
current velocity and direction except at M3 where the vessel cannot be accessed
and River
Surveyor M9 is proposed to be used for current velocity and
direction.
4.4.2
The
equipment employed for the monitoring and sampling and their specifications are
presented in Table 4.4.
4.5.1
All
in-situ monitoring instruments shall be checked, calibrated and certified by a
laboratory accredited under HOKLAS before use and subsequently re-calibrated at
three monthly intervals throughout all stages of the water quality monitoring
programme. Responses of sensors and electrodes shall be checked with certified
standard solutions before each use. Wet bulb calibration for a DO meter shall
be carried out before measurement at each monitoring location.
4.5.2
Sufficient
stocks of spare parts shall be maintained for replacements when necessary.
Backup monitoring equipment shall also be made available so that monitoring is
uninterrupted even when some equipment is under maintenance or calibration etc.
4.6.1
The
position of water monitoring station will be located by the Differential Global
Positioning System (DGPS) or equivalent. The water depth of water monitoring station
will be determined by the echo sounder affixed to the bottom of the monitoring
vessel or a portable echo sounder depth detector.
4.6.2
Once
the location and water depth are confirmed, water samples shall be collected at
3 depths (1m below the surface, mid-depth, and 1m above the seabed) of the
water column at each location, except where water depth is less than 6m, the
mid-depth will be omitted and if the water depth is less than 3m only the
mid-depth station will be monitored. Duplicate marine samples will be collected
in each sampling event. The water samples are decanted from the water sampler
into the water sample bottles. The bottles are labelled, tightly sealed, placed
into a cool-box and packed with ice ready for delivery to the laboratory.
4.6.3
Two
consecutive measurements of water quality data, including pH, salinity,
dissolved oxygen and turbidity will be recorded according to the monitoring
locations. Separate deployment of the monitoring instruments and water samplers
will be conducted for the consecutive measurements or samplings. The monitoring
location / position, time, water depth, sampling depth, tidal stages, weather
conditions, sea condition and any special phenomena or work underway nearby
shall also be recorded. If the difference in value between the first and second
measurement of DO or turbidity parameters is more than 25% of the value of the
first reading, the reading shall be discarded and further readings should be
taken.
Background
4.7.1
Fugro Technical Services Limited (HOKLAS Reg: No.015)
has been appointed to conduct the laboratory measurement or analysis of water
sample in this project. The certificate of
accreditation are shown in Appendix J.
Quality Assurance / Quality Control
4.7.2
The
laboratory incorporates a variety of QA/QC monitoring programme into their
testing system. Where applicable or available, the quality of
the analysis will be monitored by conducting the following QC analysis:
For each
batch of 20 samples:
§
A minimal of 1 laboratory method blank will be
analyzed;
§
A minimal of 1 sample duplicate will be analyzed;
§
A minimal of 1 sample matrix spike will be analyzed.
4.7.3
QA/QC
records is provided in Appendix D.
4.8.1
Baseline
water quality monitoring was conducted at 11 designated monitoring locations
between 1 December 2020 and 26 December 2020. The baseline monitoring schedule
is given in Appendix F.
4.8.2
No major construction activities were observed during the period of
baseline monitoring.
The weather condition in the monitoring period is provided in Appendix
G.
4.8.3
A
summary of the in-situ baseline water quality monitoring results is given in Table 4.5.
Results of laboratory analysis of baseline water quality are presented in Table 4.6.
Detailed water quality monitoring results is provided in Appendix D.
4.9.1
The
Action and Limit Levels in construction phase water quality monitoring were
determined in accordance with the EM&A Manual, as shown in Table 4.7.
Action and Limit Levels are used to determine whether operational modifications
are necessary to mitigate impacts to water quality.
4.9.2
The
Action Levels (AL) and Limit Levels (LL) of water quality are determined from
the baseline monitoring data and are shown in Table 4.8.
4.10
Event
and Action Plan
4.10.1
The
Event and Action Plan for Water Quality are given in Appendix E.