4.1
According to EM&A Manual, impact
water quality monitoring shall be carried out three days per week during the
construction period. The interval between two sets of monitoring will not be
less than 36 hours.
4.2
Replicate in-situ measurements and
samples collected from each independent sampling event shall be collected to
ensure a robust statistically interpretable database.
4.3
Impact water quality monitoring was
conducted two times per monitoring day during mid ebb (within + 1.75
hours of the predicted time) and mid flood tides (within + 1.75 hours of
the predicted time) at three
depths (i.e. 1m below surface,
mid-depth and 1m above seabed, except where the water depth less than 6m,
mid-depth station may be omitted. Should the water depth be less than 3m, only
the mid-depth station was monitored) Dissolved oxygen, Suspended solids (SS),
turbidity, pH, salinity and temperature were monitored in accordance with the
requirements set out in the EM&A Manual.
4.4
The proposal for changing Action and
Limit Levels for water quality monitoring was submitted to EPD on 15 March
2013. No objection was received from EPD according to the letter (ref. (10) in Ax(3) to EP2/G/A/129pt.4) dated 25 March 2013. Therefore, the
updated Action and Limit Levels for water quality monitoring was used for
comparison starting from 25 March 2013.
4.5
Appendix A shows the established Action/Limit
Levels for the water quality monitoring works.
4.6
Impact water quality monitoring was
conducted at 14 monitoring stations under the Contract which are summarized in Table 4.1. The monitoring station is
also shown in Figure 4.
4.7
The Proposal for Change of Marine Water
Quality Monitoring Station was submitted to EPD on 12 July 2017. No objection was received from EPD according to the letter (ref.
(22) in Ax(4) to EP2/G/A/129pt.4) dated 28 July 2017.
Therefore, the updated Water Quality Monitoring Station was used for water
quality monitoring starting from 31 July 2017.
Table 4.1 Location for Marine Water Quality Monitoring Locations
|
Monitoring Stations |
Coordinates |
|
|
Easting |
Northing |
|
|
IS1 |
803474 |
815060 |
|
IS2 |
804851 |
815715 |
|
IS3 |
806502 |
815743 |
|
IS4 |
807008 |
816986 |
|
CS1 |
801784 |
812711 |
|
CS2 |
805849 |
818780 |
|
CS2(A)# |
805232 |
818606 |
|
SR1 |
803126 |
812379 |
|
SR2 |
807856 |
816953 |
|
SR3 |
810525 |
816456 |
|
SR6 |
805837 |
821818 |
|
ST1 |
802677 |
816006 |
|
ST2 |
804055 |
818840 |
|
ST3 |
800667 |
810126 |
|
SRA |
809872 |
817152 |
#Alternative station for CS2 starting
from 31st July 2017, after the approval of the Proposal for Change
of Marine Water Quality Monitoring Station by EPD on 28th July 2017.
Instrumentation
4.8
A multi-parameter meters (Model YSI
6820-C-M) were used to measure DO, turbidity, salinity, pH and temperature.
Dissolved Oxygen (DO)
and Temperature Measuring Equipment
4.9
The instrument for measuring dissolved
oxygen and temperature was portable and weatherproof complete with cable,
sensor, comprehensive operation manuals and use DC power source. It was capable
of measuring:
· a dissolved oxygen level in the range of 0-20 mg/L and 0-200%
saturation; and
· a temperature of 0-45 degree Celsius.
4.10 It has a membrane electrode with automatic temperature compensation
complete with a cable.
4.11 Sufficient stocks of spare electrodes and cables were available for
replacement where necessary.
4.12 Salinity compensation was built-in in the DO equipment.
Turbidity
4.13 Turbidity was measured in situ by the nephelometric
method. The instrument was portable and weatherproof using a DC power source
complete with cable, sensor and comprehensive operation manuals. The equipment
was capable of measuring turbidity between 0-1000 NTU. The probe cable was not
less than 25m in length. The meter was calibrated in order to establish the
relationship between NTU units and the levels of suspended solids. The
turbidity measurement was carried out on split water sample collected from the
same depths of suspended solids samples.
Sampler
4.14 A water sampler, consisting of a transparent PVC or glass cylinder of a
capacity of not less than two litres which can be
effectively sealed with cups at both ends was used. The water sampler has a
positive latching system to keep it open and prevent premature closure until
released by a messenger when the sampler was at the selected water depth.
Water Depth Detector
4.15 A portable, battery-operated echo sounder was used for the determination
of water depth at each designated monitoring station.
pH
4.16 The instrument was consisting of a potentiometer, a glass electrode, a
reference electrode and a temperature-compensating device. It was readable to
0.1pH in a range of 0 to 14. Standard buffer solutions of at least pH 7 and pH
10 were used for calibration of the instrument before and after use.
Salinity
4.17 A portable salinometer capable of recording
salinity within the range of 0-40 ppt was used for
salinity measurements.
Monitoring Position
Equipment
4.18 A hand held Differential Global Positioning System (DGPS) was used
during water quality monitoring to ensure the monitoring vessel is at the
correct location before taking measurements.
Sample Container and
Storage
4.19 Following collection, water samples for laboratory analysis were stored
in high density polythene bottles (250ml/1L) with no preservatives added,
packed in ice (cooled to 4°C without being frozen) and kept in
dark during both on-site temporary storage and shipment to the testing
laboratory. The samples were delivered to the laboratory as soon as possible
and the laboratory determination works were started within 24 hours after
collection of the water samples. Sufficient volume of samples was collected to
achieve the detection limit.
Calibration of In Situ
Instruments
4.20 All in situ monitoring instruments were checked, calibrated and
certified by a laboratory accredited under HOKLAS or other international
accreditation scheme before use, and subsequently re-calibrated at 3 monthly
intervals throughout all stages of the water quality monitoring programme. Responses of sensors and electrodes were checked
with certified standard solutions before each use. Wet bulb calibration for a
DO meter was carried out before measurement at each monitoring event.
4.21 For the on site calibration of field equipment
(Multi-parameter Water Quality System), the BS 1427:2009, "Guide to
on-site test methods for the analysis of waters" was observed.
4.22 Sufficient stocks of spare parts were maintained for replacements when
necessary. Backup monitoring equipment was also being made available so that
monitoring can proceed uninterrupted even when some equipment was under
maintenance, calibration, etc.
4.23 The equipment used for impact water quality monitoring is shown in Table 4.2. All the monitoring equipment complied
with the requirements set out in the EM&A Manual.
Table 4.2 Water Quality
Monitoring Equipment
|
Equipment |
Model and Make |
|
Sonar Water Depth Detector |
Garmin Fishfinder 140 |
|
Monitoring Position Equipment |
KODEN DGPS (KGP913MKIID, GA-08
& BA-03) |
|
Multi-parameter
Water Quality System |
YSI EXO |
|
Water Sampler |
Kahlsico Water-Bottle Model
135DW 150 |
Monitoring
Parameters, Frequency
4.24 Table 4.3 summarizes the monitoring parameters, monitoring period and frequencies
of the water quality monitoring.
Table 4.3 Water Quality
Monitoring Parameters and Frequency
|
Monitoring Stations |
Parameters, unit |
Depth |
Frequency |
|
IS1, IS2, IS3 IS4, CS1, CS2 / CS2(A), SR1, SR2, SR3, SR6, ST1, ST2, ST3, SRA |
·
Temperature(°C) ·
pH(pH unit) ·
turbidity (NTU) ·
water depth (m) ·
salinity (ppt) ·
dissolved oxygen (DO) (mg/L and % of saturation) ·
suspended solids (SS) (mg/L) |
·
3 water depths: 1m below sea
surface, mid-depth and 1m above sea bed. ·
If the water depth is less than 3m, mid-depth sampling
only. ·
If water depth less than 6m, mid-depth may be omitted. |
·
Impact monitoring: 3 days per week, at mid-flood and
mid-ebb tides during the construction period of the Contract |
4.25 Monitoring location/position, time, water depth, sampling depth, pH,
salinity, DO saturation, water temperature, tidal stages, weather conditions
and any special phenomena or work underway nearby were recorded.
4.26 A multi-parameter meters (Model YSI 6820-C-M) were used to measure DO,
turbidity, salinity, pH and temperature.
Operating/Analytical
Procedures
4.27 The monitoring stations were accessed by the guide of a hand-held
Differential Global Positioning System (DGPS) during water quality monitoring
in accordance with the EM&A Manual. The depth of the monitoring location
was measured using depth meter in order to determine the sampling depths.
Afterwards, the probes of the in-situ measurement equipment were lowered to the
predetermined depths (1 m below water surface, mid-depth and 1 m above seabed)
and the measurements were carried out accordingly.
4.28 At each measurement, two consecutive measurements of DO concentration,
DO saturation, salinity, turbidity, pH and temperature were taken. The probes were retrieved out of the
water after the first measurement and then re-deployed for the second
measurement. Where the difference
in the value between the first and second readings of each set was more than
25% of the value of the first reading, the reading was discarded and further
readings were taken.
4.29 Water sampler was lowered into the water to the required depths of
sampling. Upon reaching the pre-determined depth, a messenger to activate the
sampler was then released to travel down the wire. The water sample was sealed
within the sampler before retrieving. At each station, water samples at three
depths (1 m below water surface, mid-depth and 1 m above seabed) were collected
accordingly. Water samples were stored in a cool box and kept at less than 4°C but without frozen and sent to the laboratory as soon as possible. In
addition, field information as described in Section 4.25 was also recorded.
4.30 The testing of all parameters was conducted by CMA Testing and
Certification Laboratories (HOKLAS Registration No.004) and comprehensive
quality assurance and control procedures in place in order to ensure quality
and consistency in results. The testing method, reporting limit and detection
limit are provided in Table 4.4.
Table 4.4 Methods
for Laboratory Analysis for Water Samples
|
Determinant |
Instrumentation |
Analytical Method |
Detection Limit |
|
Suspended Solid (SS) |
Weighing |
APHA 21e
2540D |
0.5 mg/L |
Decontamination Procedures
4.31 Water sampling equipment used during the course of the monitoring programme was decontaminated by manual washing and rinsed
clean seawater/distilled water after each sampling event. All disposal
equipment was discarded after sampling.
Sampling Management and Supervision
4.32 All sampling bottles were labelled with the sample I.D (including the
indication of sampling station and tidal stage e.g. IS1_me_a), laboratory
number and sampling date. Water samples were dispatched to the testing
laboratory for analysis as soon as possible after the sampling. All samples
were stored in a cool box and kept at less than 4°C but
without frozen. All water samples were handled under chain of custody protocols
and relinquished to the laboratory representatives at locations specified by
the laboratory.
4.33 The laboratory determination works were started within 24 hours after
collection of the water samples.
Quality Control Measures for Sample
Testing
4.34 The samples testing were performed by CMA Testing and Certification
Laboratories.
4.35 The following quality control programme was
performed by the CMA Testing and Certification Laboratories for every batch of
20 samples:
² One set of quality control (QC)
samples.
4.36 All in situ monitoring instruments were checked, calibrated and
certified by a laboratory accredited under HOKLAS or other international
accreditation scheme before use, and subsequently re-calibrated at 3 monthly
intervals throughout all stages of the water quality monitoring programme.
4.37 The monitoring results and graphical presentation of water quality at
the monitoring stations is shown in Appendix
B. The monitoring data and the Quality Control reports for the laboratory
analysis could be found in the monthly reports.
4.38 A total of 24 Action Level exceedances and 15 Limit Level exceedances
for Dissolved Oxygen (Surface & Middle), 47 Action Level exceedances and 23
Limit Level exceedances for Dissolved Oxygen (Bottom), 47 Action Level
exceedances and 120 Limit Level exceedances for Turbidity and 330 Action Level
exceedances and 223 Limit Level exceedances for Suspended Solids were recorded
during the construction period of the Contract. The summary of exceedance is
attached in Appendix G.
4.39 According to the ET’s investigation, no direct
evidence demonstrated the exceedances of Action/Limit level for water monitoring
parameters were caused by the Contract during the construction period.
4.40 The impact marine water quality monitoring programme
for all monitoring stations was completed on 23 October 2018.
4.41 Should non-compliance of the criteria occur, action in accordance with
the Action Plan in Appendix D shall
be carried out.