4              Water Quality Monitoring

Monitoring Requirements

 

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.

Monitoring Locations

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.

Monitoring Equipment

 

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:

 

¡P       a dissolved oxygen level in the range of 0-20 mg/L and 0-200% saturation; and

¡P       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¢XC 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

¡P         Temperature(¢XC)

¡P         pH(pH unit)

¡P         turbidity (NTU)

¡P         water depth (m)

¡P         salinity (ppt)

¡P         dissolved oxygen (DO) (mg/L and % of saturation)

¡P         suspended solids (SS) (mg/L)

¡P      3 water depths: 1m below sea surface, mid-depth and 1m above sea bed.

¡P      If the water depth is less than 3m, mid-depth sampling only.

¡P      If water depth less than 6m, mid-depth may be omitted.

¡P      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.

 

Monitoring Methodology

 Instrumentation

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¢XC 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.

Laboratory Analytical Methods

 

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

QA/QC Requirements

 

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¢XC 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.

Maintenance and Calibration

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.

Results and Observations

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.

 

Event and Action Plan 

 

4.41     Should non-compliance of the criteria occur, action in accordance with the Action Plan in Appendix D shall be carried out.