6. Water Quality. 6-1
6.1 Introduction. 6-1
6.2 Water Quality Parameters. 6-1
6.3 Monitoring Equipment 6-1
6.4 Measurement and Laboratory Analysis. 6-3
6.5 Monitoring Locations. 6-4
6.6 Baseline
Water Quality Monitoring. 6-4
6.7 Impact
Water Quality Monitoring. 6-5
6.8 Event
and Action Plan. 6-5
List of Appendices
Appendix
1 Implementation Schedule of
Recommended Mitigation Measures
List of Figures
Figure
6.1 Water Sensitive Receivers
at Sung Shan New Village
Figure
6.2 Water Sensitive Receivers
at Tai Wo
Figure
6.3 Water Sensitive Receivers
at Lin Fa Tei
Figure
6.4 Water Sensitive Receivers
at Ha Che
Figure
6.5 Water Quality Monitoring
Location at Sung Shan New Village
Figure
6.6 Water Quality Monitoring
Location at Tai Wo
Figure
6.7 Water Quality Monitoring
Location at Lin Fa Tei
Figure
6.8 Water Quality Monitoring
Location at Ha Che
6.1.1
The
water quality assessment in the EIA Report identified that the key issue would
be related to excavation works for the construction phase of the proposed drainage
improvement works. To minimize potential impacts on water quality during the drainage
construction, the excavation would be carried out in dry condition (even in wet
season) by diverting the stream flow from upstream by a temporary drainage
channel with a temporary sheet piles, earth bund or barrier, so that the works area
will remain dry for later excavation and widening works. The locations of the
representative WSRs are shown in Figures 6.1 to 6.4.
6.1.2
A
monitoring programme is recommended for both baseline conditions and during the
construction phase to detect any deterioration of water quality, as well as to ensure
the performance of the proposed mitigation measures.
6.2.1
The
water quality parameters, as presented in Table
6.1 shall be monitored to ensure the
drainage water quality and to detect any water quality deterioration situations
in order to take actions on time.
Table 6.1 Water Quality Parameters to Be Monitored
|
Parameter
|
Type of Analysis
|
|
Dissolved Oxygen
(DO)
|
In situ measurement
|
|
(mg L-1
and % saturation)
|
|
Temperature (℃)
|
|
pH value
|
|
Turbidity (NTU)
|
|
Salinity (ppt)
|
|
Water Depth (m)
|
|
Suspended Solids
(SS) (mg L-1)
|
Laboratory analysis
|
6.2.2
These
parameters are selected for monitoring on the following basis:
·
To reflect the background
water quality near and within the working area; and
·
To reflect the nature of the
construction activities.
6.2.3
In
addition to the water quality parameters, relevant data shall also be measured,
such as monitoring location / position, time, saturation, weather conditions
and any special phenomena and work underway at the construction site.
6.3.1
Water
quality monitoring equipment with the following specifications shall be
supplied and maintained by the ET.
Dissolved Oxygen and Temperature
Measuring Equipment
6.3.2
The
instrument should be portable, weatherproof dissolved oxygen measuring instrument
with cable, sensor, comprehensive operation manuals, and applicable to use a DC
power source. It should be capable of measuring:
·
DO level in the range of 0 –
20 mg /L and 0 – 200% saturation; and
·
Temperature of 0-45℃.
6.3.3
It
should have a membrane electrode with automatic temperature compensation
connected with a cable. Sufficient stocks of spare
electrodes and cables should be available for replacement where necessary.
(e.g. YSI model 59 meter, YSI 5739 probe, YSI 5795A submersible stirrer with
reel and cable or an approved similar instrument).
pH
6.3.4
pH
meter (e.g. Hanna - HI 9024 or equivalent) should be used to measure pH value
of water samples in situ. It should be readable to 0.1 pH in a range of 0 to 14.
Standard buffer solutions of at least pH 7 to pH 10 shall be used for
calibration of the instrument before and after use.
Turbidity Measurement Instrument
6.3.5
The
instrument should be a portable, weatherproof turbidity-measuring instrument
with a comprehensive operation manual. The equipment should use a DC power
source. It should have a photoelectric sensor capable of measuring turbidity
between 0-1000 NTU and be equipped with a cable (e.g. Hach model 2100P or an
approved similar instrument).
Suspended Solids
6.3.6
A
water sampler should comprise a transparent PVC cylinder, with a capacity of
not less than 2 litres, and should be effectively sealed with latex cups at
both ends. The sampler should 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 (e.g. Kahlsico Water
Sampler or an approved similar instrument).
6.3.7
Water
samples for suspended solids measurement shall be collected in high density
polythene bottles, packed in ice (chilled to 4°C without being frozen), and
delivered to the laboratory as soon as possible after collection.
Water Depth detector
6.3.8
A
portable, battery-operated echo sounder should be used for determining 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.
Monitoring Position Equipment
6.3.9
A
hand-held or boat-fixed digital Global Positioning System (GPS) or other
equivalent instrument of similar accuracy shall be provided and used during
water monitoring to ensure the water sampling locations are correct during
water quality monitoring work.
Water Sampling Equipment
6.3.10
A
transparent PVC or glass cylinder, which has a volume of not less than 2 litres
and can be sealed at both ends with cups, should be equipped with a positive
latching system. During the water sampling, a messenger is released to trigger
the closure of the water sampler at suitable water depth.
6.3.11
All
in-situ monitoring instruments should be checked, calibrated and certified by a
laboratory accredited under HOKLAS or another international accreditation
scheme before use, and subsequently re-calibrated at 3-monthly intervals
throughout all stages of the water quality monitoring. Responses of sensors and
electrodes should be checked with certified standard solutions before each use.
Wet bulb calibration for a DO meter should be carried out before measurement at
each monitoring location.
6.3.12
For
the on-site calibration of field equipment, the BS 127:1993, Guide to Field and
On-Site Test Methods for the Analysis of Water should be observed.
6.3.13
Sufficient stocks of spare parts should be
maintained for replacements when necessary. Backup monitoring equipment shall
also be made available so that monitoring can proceed uninterruptedly even when
some equipment is under maintenance, calibration, etc.
6.4.1
Analysis
of suspended solids shall be carried out in a HOKLAS or another international
accredited laboratory. Water samples of about 1,000 ml shall be collected at
the monitoring stations for carrying out the laboratory SS determination. The
detection limit shall be 1mg/L or better. The SS determination shall follow
APHA 17ed 2540D or equivalent methods subject to approval of EPD.
6.4.2
If
a site laboratory is set up or a non-HOKLAS and non-international accredited
laboratory is hired for carrying out the laboratory analysis, the laboratory
equipment, analytical procedures, and quality control shall be approved by EPD.
The ET Leader shall provide the ER with one copy of the relevant chapters of
the “Standard Methods for the Examination of Water and Wastewater” updated
edition and any other relevant document for his reference.
6.4.3
For
the testing methods of other parameters as recommended by EIA or required by
EPD, detailed testing methods, pre-treatment procedures, instrument use,
Quality Assurance/Quality Control (QA/QC) details (such as blank, spike
recovery, number of duplicate samples per batch, etc.), detection limits and accuracy
shall be submitted to EPD for approval prior to the commencement of monitoring
programme. The QA/QC shall be in accordance with the requirement of HOKLAS or
international accredited scheme. The QA/QC results shall be reported. EPD may
also request the laboratory to carry out analysis of known standards provided
by EPD for quality assurance. Additional duplicate samples may be required by
EPD for inter laboratory calibration. Remaining samples after analysis shall be
kept by the laboratory for 3 months in case repeat analysis is required. If
in-house or non-standard methods are proposed, details of the method
verification may also be required to submit to EPD. In any circumstance, the
sample testing shall have comprehensive quality assurance and quality control
programmes. The laboratory shall prepare to demonstrate the programmes to EPD
or his representatives when requested.
6.5.1
The proposed monitoring locations are shown in Figure 6.5 to Figure 6.8, and Table
6.2. These stations were
chosen based on the following criteria:
·
At locations close to and at
the boundary of the major site activities as indicated in the EIA report, which
are likely to have water quality impacts;
·
Close to the sensitive
receivers which are directly or likely to be affected;
·
For monitoring locations
located in the vicinity of the sensitive receptors, care should be taken to
cause minimal disturbance during monitoring.
6.5.2
Control stations are necessary to compare the
water quality from potentially impacted sites with the ambient water quality.
The monitoring stations are proposed to monitor the impacts from the
construction site. Control monitoring stations would be located upstream of the
construction section of the river, while impact monitoring stations would be
located downstream of each river.
6.5.3 The
monitoring locations could be adjusted by the ET Leader to suit the exact location of
the construction work site but need to obtain agreement from EPD in advance.
Table 6.2 Water Quality Monitoring
Locations
|
Stream
|
Station
|
Easting
|
Northing
|
Remarks
|
|
SSNV
|
C1
|
821893
|
831782
|
Impact Monitoring Point
|
|
C2
|
822459
|
831470
|
Control Monitoring Point
|
|
C3
|
822422
|
831413
|
Control Monitoring Point
|
|
TW
|
C4
|
825497
|
830664
|
Control Monitoring Point
|
|
C5
|
825486
|
830716
|
Impact Monitoring Point
|
|
LFT
|
C6
|
827232
|
831713
|
Control Monitoring Point
|
|
C7
|
827044
|
832143
|
Control Monitoring Point
|
|
C8
|
826513
|
832075
|
Impact Monitoring Point
|
|
HC
|
C9
|
828304
|
835029
|
Control Monitoring Point
|
|
C10
|
827919
|
834271
|
Impact Monitoring Point
|
6.5.4
Due to a shallow water depth with low flowrates
in rivers, all the monitoring could be located at mid-depth level.
6.5.5
The ET could review the monitoring stations and
the monitoring period in light of the actual
construction activities. However, the ET Leader should report and seek
agreement form IC(E), ER and approval then from EPD for the actual monitoring
periods for each station.
6.6.1
Baseline conditions of water quality shall be
established and agreed with EPD prior to the commencement of works. The
purposes of the baseline monitoring are to establish ambient conditions prior
to the commencement of the construction works and to demonstrate the suitability
of the proposed impact and control monitoring stations. The baseline conditions
should normally be established by measuring the water quality parameters
specified in Table
6.1. The measurements shall
be taken at all designated monitoring stations including control stations for 3
days per week for 4 consecutive weeks, applicable with a period of four weeks
prior to commencement of the works.
6.6.2 There
shall not be any construction activities in the vicinity of the stations during
the baseline monitoring. In the exceptional case when insufficient baseline
monitoring data or questionable results are obtained, the ET should seek
approval from EPD for an appropriate set of data to be used as baseline reference.
Baseline monitoring schedule shall be sent to EPD 1 week prior to the
commencement of baseline monitoring. The interval between 2 sets of monitoring
shall not be lesser than 36 hours.
6.7.1
During the construction process, impact monitoring
shall be carried out 3 days per week. If no exceedances are recorded during the
three-month’s period, the monitoring frequency can then be reduced to once per
week, with sampling /measurement at the designated monitoring stations. The interval
between two sets of monitoring shall not be less than 36 hours except where
there are exceedances. However, the ET Leader should report and seek agreement
form IC(E), ER and approval then from EPD before changing the monitoring
frequency.
6.7.2
All monitoring information including date and
time, weather conditions, operator, identification and description of
monitoring locations, works, progress and construction activities, method,
analytical data and calculation etc., shall be recorded in the monitoring data
sheet. The water quality monitoring schedule shall be sent to EPD on or before
the first day of the monitoring month, EPD shall be notified immediately of any
changes in schedule in written format.
6.8.1 The
Action and Limit levels for the water quality monitoring are shown in Table
6.3. These thresholds shall
be applied to ensure that any water quality deterioration can be readily detected.
If the monitoring results at any designated monitoring stations indicate that
the water quality thresholds are exceeded, appropriate actions in accordance
with the Event and Action Plan in Table 6.4 shall be carried
out.
Table 6.3 Action and
Limit Levels for Water Quality
|
Parameters
|
Action Level
|
Limit Level
|
|
DO in mg/L
|
< 5%-ile of baseline data
|
< 4mg/L or < 1%-ile of baseline data
|
|
SS in mg/L
|
> 95%-ile of baseline data or >120%
of upstream control station of the same day
|
> 99%-ile of baseline data or 130% of
upstream control station of the same day
|
|
Turbidity in NTU
|
> 95%-ile of baseline data or >120%
of upstream control station of the same day
|
> 99%-ile of baseline data or > 130%
of upstream control station of the same day
|
Notes:
1. For DO, non-compliance of the water quality limits
occurs when monitoring result is lower than the limits.
2. For SS and turbidity, non-compliance of the water quality
limits occurs when monitoring result is higher than the limits
3. All the figures given in the table are used for
reference only and the EPD may amend the figures whenever it is considered as
necessary.
Table 6.4 Event and Action Plan for Water
Quality Monitoring
|
EVENT
|
ACTION
|
|
|
ET(1)
|
IEC(1)
|
ER(1)
|
Contractor
|
|
|
Action Level being
exceeded by one sampling day
|
1. Repeat in-situ
measurement to confirm findings;
2. Identify source(s) of impact;
3. Inform the IEC and the Contractor;
4. Check monitoring data, all plant, equipment and the Contractor’s working
methods;
5. Discuss mitigation measures with the IEC and the Contractor;
6. Repeat measurement on next day of exceedance.
|
1. Discuss with the
ET and the Contractor on the mitigation measures;
2. Review proposals on mitigation measures submitted by the Contractor and
advise the ER accordingly;
3. Access the effectiveness of the implemented mitigation measures.
|
1. Discuss with the
IEC on the proposed mitigation measures;
2. Make agreement on the mitigation measures to be implemented.
|
1. Inform the ER and confirm notification of the
non-compliance in writing;
2. Rectify unacceptable practice;
3. Check all plant and equipment;
4. Consider changes of working methods;
5. Discuss with the ES and the IEC and propose mitigation measures to the IEC
and the ER;
6. Implement the agreed mitigation measures.
|
|
|
|
|
|
|
|
Action Level being
exceeded by more than one consecutive sampling days
|
1. Repeat in-situ measurement to confirm findings;
2. Identify source(s)
of impact;
3. Inform the IEC and
the Contractor;
4. Check monitoring data, all plant, equipment and Contractor’s working
methods;
5. Discuss mitigation
measures with the IEC and the Contractor;
6. Ensure mitigation measures are implemented;
7. Prepare to increase the monitoring frequency to daily;
8. Repeat measurement on next day of exceedance.
|
1. Discuss with the
ET and the Contractor on the mitigation measures;
2. Review proposals on mitigation measures submitted by the Contractor and advise
the ER accordingly;
3. Access the effectiveness of the implemented mitigation measures.
|
1. Discuss with IEC on
the proposed mitigation measures;
2. Make agreement on
the mitigation measures to be implemented;
3. Access the
effectiveness of the implemented mitigation measures.
|
1. Inform the ER and confirm notification of the
non-compliance in writing;
2. Rectify unacceptable practice;
3. Check all plant and equipment;
4. Consider changes of working methods;
5. Discuss with the ES
and the IEC and propose mitigation measures to the IEC and ER within 3 working
days;
6. Implement the agreed mitigation measures.
|
|
|
|
|
|
|
|
|
|
Limit Level being
exceeded by one consecutive sampling day
|
1. Repeat in-situ
measurement to confirm findings;
2. Identify source(s) of impact;
3. Inform the IEC, the Contractor and the DEP;
4. Check monitoring data, all plant, equipment and the Contractor’s working
methods;
5. Discuss mitigation measures with the IEC, the ER and the Contractor;
6. Ensure mitigation measures are implemented;
7. Increase the monitoring frequency to daily until no exceedance of Limit
Level.
|
1. Discuss with the ES and the Contractor on the mitigation
measures;
2. Review proposals on mitigation measures submitted by the Contractor and
advise the ER accordingly;
3. Access the effectiveness of the implemented mitigation measures.
|
1. Discuss with the IEC, the ES and the Contractor on the
proposed mitigation measures;
2. Request the Contractor to critically review the working methods;
3. Make agreement on the mitigation measures to be implemented;
4. Access the effectiveness of the implemented mitigation measures.
|
1. Inform the
Engineer and confirm notification of the non-compliance in writing;
2. Rectify unacceptable practice;
3. Check all plant and equipment;
4. Consider changes of working methods;
5. Discuss with the ES, the IEC and the ER and propose mitigation measures to
the IEC and the ER within 3 working days;
6. Implement the agreed mitigation measures.
|
|
|
|
|
|
|
|
|
Limit Level being exceeded
by more than one consecutive sampling days
|
1. Repeat in-situ
measurement to confirm findings;
2. Identify source(s) of impact;
3. Inform the IEC, the Contractor and DEP;
4. Check monitoring data, all plant, equipment and Contractor’s working methods;
5. Discuss mitigation measures with the IEC, the ER and the Contractor;
6. Ensure mitigation measures are implemented;
7. Increase the monitoring frequency to daily until no exceedance of Limit
Level for two consecutive days.
|
1. Discuss with ET and Contractor on the
mitigation measures;
2. Review proposals on mitigation
measures submitted by the Contractor and advise the ER accordingly;
3. Access the effectiveness of the
implemented mitigation measures.
|
1. Discuss with the IEC, the ES and the Contractor
on the proposed mitigation measures;
2. Request Contractor to critically
review the working methods;
3. Make agreement on the mitigation
measures to be implemented;
4. Access the effectiveness of the
implemented mitigation measures;
5. Consider and instruct, if necessary,
the Contractor to slow down or to stop all or part of the works until no
exceedance of Limit Level.
|
1. Inform the ER and confirm notification of
the non-compliance in writing;
2. Rectify unacceptable practice;
3. Check all plant and equipment;
4. Consider changes of working
methods;
5. Discuss with the ES, the IEC and
the ER and propose mitigation measures to the IEC and the ER within 3 working
days;
6. Implement the agreed mitigation
measures;
7. As directed by the ER, slow down or
stop all or part of the construction activities.
|
|
|
|
|
|
|
|
Note (1): ET –
Environmental Team, IEC – Independent Environmental Checker, ER – Engineer’s
Representative
6.8.2
It is recommended that additional mitigation
measures be taken if the monitoring results indicate that the construction
works have caused adverse impacts on water quality to identified sensitive
receivers to rectify the non-compliance to water quality criteria. Construction
programme shall be carefully reviewed to ensure that water quality at locations
of identified sensitive receivers is in compliance with
criteria. Working schedule and mitigation measures should be reviewed by the
Contractor, IC (E), ET Leader and ER. The schedule for construction works may need
to be revised until the adverse impacts to water quality are reduced to an
acceptable level.
6.8.3
The ET Leader should assess the effectiveness
and efficiency of the proposed mitigation measures and/or remedial actions for
on-going construction activities. The
performance of the environmental management system (that is, the overall
EM&A programme) should be reviewed by the ET Leader on a weekly basis. The
findings of this review should be included in the relevant monthly EM&A
reports and quarterly summary reports, together with any recommendations to
improve the performance of the EM&A programme.