Executive Summary
1 introduction
1.1 Purpose of the
Report
1.2 Structure of the
Report
2 Project
Information
2.1 Background
2.2 Marine
Construction Works Undertaken during Reporting Week
2.3 Status of
Environmental Approval Documents
3 Water Quality Monitoring
Requirements
3.1 Monitoring
Locations
3.2 Monitoring Parameters
and Frequency
3.3 Monitoring
Equipment and Methodology
4 Impact
Monitoring Results
4.1 Data Collected
During Mid-Ebb and/or Mid-Flood Tidal Conditions
4.2 Continuous
In-Situ Measurement Data
5 Environmental
Non-CONFORMANCES
5.1 Summary of
Environmental Exceedance
5.2 Summary of
Environmental Complaint
5.3 Summary of
Environmental Summons and Prosecution
6 Future
Key Issues
6.1 Key Issues For
The Coming Week
6.2 Monitoring
Schedule For The Coming WEEK
7 Conclusions
Table
2.1 Summary of Marine Works Undertaken During
the Reporting Week
Table 2.2 Summary of Environmental Licensing,
Notification, Permit and Reporting Status
Table.3.1 Co-ordinates of Starting Points and Ending
Points for Zone A (HK Grid)
Table 3.2 Co-ordinates of All Monitoring Stations in
Zone A (HK Grid)
Table 3.3 Monitoring Frequency and Parameters for
Impact Monitoring
Table 3.4 Action and Limit Levels of Water Quality
for Zone A
Table 3.5 Event Action Plan for Water Quality
Table 4.1 Summary of Exceedances occurring during
the Reporting Week
Figure
2.1 The
Route of the Proposed Cable System
Executive Summary
The construction works for
the VSNL Intra Asia Submarine Cable System – Deep Water Bay commenced on 16 March 2009. This is the seventh Weekly Impact Monitoring Report presenting the impact water
quality monitoring conducted during the period from 31 July to 6 August 2009 in
accordance with the EM&A Manual.
Summary of Construction Works
undertaken during the Reporting Period
The
barge “Challenger II” had been anchored in Deep Water Bay since 24 July, when
marine works commenced. During the
reporting period cable repair operations continued, with initial and final
splicing of the cable, re-laying of the cable on the sea bed and installation
of some split pipes. Marine works
were temporarily suspended in the afternoon on 3 August due to a typhoon
warning, and due to this weather did not resume again until 5 August.
Water Quality
For the impact monitoring, six monitoring events were
scheduled between 31 July and 6
August 2009.
Aside from the 4 August, when a typhoon warning stopped marine works,
monitoring events at all designated monitoring stations were performed on
schedule, ie five events took place on 31 July, 1 August, 3 August, 5 August
and 6 August 2009.
Environmental Non-conformance
Daily exceedances of Action and Limit Levels for
dissolved oxygen were recorded during the reporting period. Depth-averaged turbidity was in general compliant with the Action and Limit
Levels aside from on 1 August, when Station S3 recorded an Action Level
exceedance. Depth-averaged
suspended solids exceeded Action Levels on one day (1 August, at Station B1)
and both Action and Limit Levels on one day (6 August, at Station B1). Results of detailed investigations into
these exceedances indicated that none of them were attributed to the Project
construction works.
No complaints were received during the reporting week.
No environmental
summons/prosecution were received during the reporting week.
Future Key Issues
During the coming week, the repair of the cable will
continue including jetting works and installation of articulated pipes.
1
introduction
ERM-Hong Kong, Limited (ERM) was appointed
by Tata Communications (Bermuda) Ltd (formerly Videsh Sanchar Nigam
Limited (VSNL)) as the Monitoring Team (MT) to implement
the Environmental Monitoring and Audit (EM&A) programme for the VSNL Intra
Asia Submarine Cable System – Deep
Water Bay
(thereinafter called the (‘Project’)).
1.1
Purpose of the
Report
This is the seventh Weekly Impact
Monitoring Report, which
summarises the impact monitoring results and audit findings for the EM&A
programme during the reporting period from 31 July to 6 August 2009.
1.2
Structure of the
Report
The structure of the report is as follows:
Section 1 : Introduction
Details the background, purpose and structure of the
report.
Section
2 : Project Information
Summarises background and scope of the project, the construction works
undertaken and the status of Environmental Permits/Licenses during the
reporting period.
Section 3 : Water Quality Monitoring Requirements
Summarises the monitoring parameters, monitoring programmes, monitoring
methodologies, monitoring frequency, monitoring locations, Action and Limit
Levels, and Event / Action Plans.
Section 4 : Impact
Monitoring Results
Summarises the monitoring
results obtained in the reporting period.
Section 5 : Environmental Non-conformance
Summarises any monitoring exceedances, environmental complaints and environmental
summons within the reporting period.
Section 6 : Future Key Issues
Summarises
the monitoring schedule for the next week.
Section 7 : Conclusions
Presents the key findings of
the impact monitoring results.
2
Project Information
2.1
Background
Tata
Communications (Bermuda) Ltd (formerly Videsh Sanchar Nigam Limited (VSNL)) proposes to install a submarine
telecommunications cable, which will run from Deep
Water Bay
and through southeast Hong Kong offshore
waters. The cable landing site will
be at the western edge of Deep
Water Bay
beach at an existing cable landing manhole location. From Deep Water Bay, the cable will extend southwards
towards the East Lamma Channel.
Near to Round
Island, the cable will
turn approximately parallel to the East Lamma Channel passing to the south of
Po Toi Island. The cable will then
run eastward close to the boundary of HKSAR waters and then out beyond Hong
Kong territorial waters into the South China Sea. At the southeast offshore waters, it
will be necessary to install a grout mattress to protect the cable where it
crosses Hong Kong Electric Co., Ltd’s (HKE) gas pipeline. A map of the proposed cable route is
presented in Figure 2.1.
In
August 2007, a Project Profile (PP) included an
assessment of the potential environmental impacts associated with the
installation of the submarine cable circuit was prepared and submitted to the
Environmental Protection Department (EPD) under section 5.(1)(b) and 5.(11) of the Environmental Impact Assessment
Ordinance (EIAO) for application for Permission to apply directly for an
Environmental Permit (EP). The
Environmental Protection Department, subsequently issued an Environmental
Permit (EP-294/2007) and Further Environmental Permit (FEP-01/294/2007). Amendments to the permitting
requirements were incorporated into the Environmental Permit to address
potential environmental impacts associated with cable crossings over the HKE’s
gas pipeline in southeast Hong Kong
waters. Under the requirements of Condition 3 of the EP, an EM&A
programme as set out in the Environmental
Monitoring and Audit Manual (EM&A Manual) is required to be
implemented. In accordance with the
EM&A Manual, impact monitoring of
water quality is required for the Project.
Baseline
Monitoring was conducted near Deep
Water Bay
(ie Zones A and E) between 27 February 2009 and 9 March 2009 and the results
were presented in the Baseline Water
Quality Monitoring Report Part A.
Baseline monitoring for the Po Toi section of works was undertaken from
27 February 2009 to 13 March 2009 and the Baseline
Water Quality Monitoring Report Part B presented the results of
the monitoring data for Zones B to D near Po Toi Island.
Impact
Monitoring has been carried out at Deep
Water Bay
(ie Zone A) since 25 March 2009.
The barge “CB Networker” completed the cable installation works in Hong Kong waters on 2 June 2009 and the water quality
monitoring was suspended subsequently.
A cable fault has recently been identified in the
previously laid submarine telecommunications cable in Zone
A. Hence, the marine works of this
Project have been resumed on 24 July 2009 to locate the cable fault and replace
the cable. This report presents
results of the data from monitoring stations in Zone A during cable repair
works. Results of the impact monitoring
data will therefore be compared against the results of the Baseline Environmental Monitoring Part A.
2.2
Marine
Construction Works Undertaken during Reporting Week
During the reporting period, the cable repair
barge “Challenger I” continued cable repair works. A summary of the major works undertaken
during the reporting period is shown in Table
2.1.
Table 2.1 Summary
of Marine Works Undertaken During the Reporting Week
|
Date
|
Works Area
|
Activity
|
|
31 July 2009
|
Zone A
|
De-burial and recovery of cable. Start initial splicing of cable.
|
|
1 August 2009
|
Zone A
|
Completion of initial cable splice. Re-laying of
cable. Recovery of further section of cable and removal of some split
pipes. Start of final splicing of
cable.
|
|
2 August 2009
|
Zones A
|
Finalisation of final splicing and cable
testing. Diver inspection. No jetting or water pumping works.
|
|
3 August 2009
|
Zones A
|
Deployment of final splice/final bight to the
water. Work suspended in the
mid-afternoon due to typhoon warning.
Barge ‘Challenger I’ demobilized from Deep Water
Bay to To Kwa Wan
typhoon shelter.
|
|
4 August 2009
|
Zones A
|
Work suspended due to typhoon warnings.
|
|
5 August 2009
|
Zone A
|
Re-mobilization of ‘Challenger I’ barge to Deep Water
Bay. Installation of split pipes in the
late afternoon..
|
|
6 August 2009
|
Zone A
|
Further installation of split pipes.
|
2.3
Status of
Environmental Approval Documents
A
summary of the relevant permits, licences, notifications and/or reports on
environmental protection for this Project is presented in Table 2.2.
Table 2.2 Summary
of Environmental Licensing, Notification, Permit and Reporting Status
|
Permit / Licence / Notification / Report
|
Reference
|
Validity Period
|
Remarks
|
|
Environmental Permit
|
(EP-294/2007)
|
Throughout the construction period
|
Granted on 23 November 2008
|
|
Further Environmental Permit
|
(FEP-01/294/2007)
|
Throughout the construction period
|
Granted on 9 July 2008
|
|
EM&A Manual
|
-
|
Throughout the construction period
|
Approved by EPD on 12 March 2009
|
|
Baseline Water Quality Monitoring Report (Part A)
|
-
|
Throughout the construction period for Zones A and
E
|
Approved by EPD on 1 April 2009
|
|
Baseline Water Quality Monitoring Report (Part B)
|
-
|
Throughout the construction period for Zones B to D
|
Approved by EPD on 30 April 2009
|
|
Pre Installation Geophysical Survey Report
|
-
|
Throughout the construction period for the Grout
Mattress Installation
|
Accepted by AFCD and EPD on 7 July 2009
|
3
Water Quality Monitoring
Requirements
3.1
Monitoring
Locations
In accordance with the EM&A Manual,
during all marine works relating to the cable, water quality sampling was
undertaken at stations situated around the cable works at Deep Water Bay (ie Zone A). This meant water quality sampling was
undertaken throughout the reporting period at the following stations.
·
S1
and S2, situated at the two Seawater Intake Points in Deep Water Bay. They are within 500 m west/northwest of
the cable alignment at Deep
Water Bay
for monitoring the effect of cable laying works in the area;
·
S3, a
Sensitive Receiver used to monitor the water quality condition of the Coastal Protection Areas
at Middle Island;
·
B1,
an Impact Station used to monitor the effect of the construction activities on Deep Water
Bay Beach;
·
R1, a
Control Station for S1, S2, S3 and B1 at Deep Water Bay which is not supposed to be
influenced by the cable repair works due to its remoteness from the cable
construction works;
The
co-ordinates of Zone A and the above monitoring
stations are listed in Table.3.1 and Table 3.2, respectively.
Table.3.1 Co-ordinates
of Starting Points and Ending Points for Zone A (HK
Grid)
|
Zone
|
Starting Point
|
Ending Point
|
|
Easting
|
Northing
|
Easting
|
Northing
|
|
A
|
837029.763
|
811601.699
|
836367.572
|
810545.975
|
Table 3.2 Co-ordinates
of All Monitoring Stations in Zone A (HK Grid)
|
Station
|
Nature
|
Corresponding Control Station
|
Easting
|
Northing
|
|
S1
|
Seawater
Intakes
|
R1
|
836538.669
|
811528.535
|
|
S2
|
Seawater
Intakes
|
R1
|
836195.047
|
810956.409
|
|
S3
|
Coastal
Protection Areas
|
R1
|
836677.103
|
810666.744
|
|
B1
|
Gazetted
Beach
|
R1
|
837241.114
|
811498.400
|
|
R1
|
Control Station
|
-
|
835951.109
|
809052.535
|
3.2
Monitoring
Parameters and Frequency
The
impact water quality monitoring was conducted in accordance with the
requirements stated in the EM&A
Manual. These are presented
below.
3.2.1
Monitoring Parameters
Parameters measured in situ were:
·
dissolved oxygen (DO) (%
saturation and mg L-1);
·
temperature (°C);
·
turbidity (NTU); and
·
salinity (‰).
The only parameter measured
in the laboratory was:
·
suspended solids (SS) (mgL-1).
In addition to the water
quality parameters, other relevant data were measured and recorded in field logs,
including the location of the sampling stations, water depth, time, weather
conditions, sea conditions, tidal state, special phenomena and work activities
undertaken around the monitoring and works area that may influence the
monitoring results.
3.2.2
Monitoring Frequency
Impact Monitoring at S1, S2, S3, B1 and R1 took
place when the cable repair works were undertaken within 500 m (Zone A) of
monitoring stations S1, S2, S3 and B1, which was throughout the reporting
period. .
Impact
monitoring was carried out during the barge operating hours, normally covering
both mid-flood and mid-ebb tidal conditions, until water quality monitoring was
not required.
In-situ
and SS data of the control and impact stations within the impact zone were
collected daily during mid-flood and mid-ebb tidal states (Table 3.3), unless the mid-ebb tide and/or the mid-flood tide were
not occurring during the monitoring period. In addition, continuous in-situ measurements were taken at the
impact monitoring stations, ie B1 & S1-3, at 30- to 60- minute intervals
(subject to the weather conditions and travelling time between stations) within
Zone A. The monitoring frequency
and parameters for Impact Monitoring are summarised in Table
3.3.
Table 3.3 Monitoring
Frequency and Parameters for Impact Monitoring
|
Zone
|
Station Type
|
Monitoring Station
|
Monitoring Frequency
|
Monitoring Parameter
|
|
Mid-ebb Tide / Mid-flood Tide
|
30- to 60- Minute Interval
|
|
A
|
Control
|
R1
|
Daily when cable installation works undertaken in
Zone A
|
Temperature, Turbidity, Salinity, DO, SS
|
-
|
|
Impact
|
S1, S2, S3 and B1
|
Temperature, Turbidity, Salinity, DO
|
3.3
Monitoring
Equipment and Methodology
3.3.1
Monitoring Equipment
Dissolved Oxygen, Temperature, Salinity, Turbidity Measuring Equipment
The instrument was a portable, weatherproof multi-parameter measuring
instrument (YSI 6820) complete with cables, multi-probe sensor, comprehensive operation
manuals, and was operable from a DC power source. It was capable of measuring:
·
dissolved oxygen levels in
the range of 0 – 50 mg L-1; and 0-500% saturation;
·
temperature of -5 to 50 °C;
·
turbidity levels between
0-1000 NTU (response of the sensor was checked with certified standard
turbidity solutions before the start of measurement); and,
·
salinity in the range of
0-40 ppt (checked with 30 ppt Salinity solutions before the start of the
measurement).
Water Depth Gauge
The water depth gauge affixed to the bottom of the water quality
monitoring vessel was used.
Current Velocity and Direction
Current velocity and direction was estimated by conducting float
tracking.
Positioning Device
A Global Positioning System (GPS) was used (C-Navigator World DGPS, GPS
72A) during monitoring to ensure the accurate recording of the position of the
monitoring vessel before taking measurements. The use of DGPS was used for positioning
device, which was well calibrated at an appropriate checkpoint.
Water Sampling Equipment
Water samples for suspended solids measurement were collected by the use
of a multi-bottle water sampling system (General Oceanics Inc., Rosette Sampler
ROS02), consisting of PVC bottles of more than two litres, which could be effectively sealed with cups at both ends. The water sampler had 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.
3.3.2
Monitoring Methodology
Timing & Frequency
In-situ and SS data were collected daily at both
control and impact stations in Zone A, provided that the monitoring period had
covered the mid-flood tide and/or mid-ebb tide. The water quality sampling was undertaken within a 3 hour window of 1.5
hours before and 1.5 hours after mid-flood and mid-ebb tides. Tidal range for flood and ebb tides was
not less than 0.5 m for capturing representative tides.
Continuous In-situ
measurements were taken at 30- to 60- minute intervals (subject to the weather
conditions and travelling time between stations) for each impact station within
Zone A.
Reference was made to the predicted tides at Waglan Island, which is the
tidal station nearest to the Project site, published on the website of Hong
Kong Observatory(). Based on the predicted
water levels at Waglan
Island, the impact water
quality monitoring was conducted following the schedule presented in Annex A.
Duplicate samples were collected from each of the monitoring events for in
situ measurements and laboratory analysis.
Depths
Each station was sampled and measurements were taken at three depths, 1
m below the sea surface, mid depth and 1m above the sea bed.
Protocols
The multi-parameter measuring instrument (YSI 6820) was checked and calibrated
by an HOKLAS accredited laboratory before use. Onsite calibration was also carried out
to check the responses of sensors and electrodes using certified standard
solutions before each use.
Sufficient stocks of spare parts were maintained for replacements when
necessary, and backup monitoring equipment was made available.
Water samples for SS measurements were collected in high density
polythene bottles, packed in ice (cooled to 4° C without being frozen), and
delivered to an HOKLAS accredited laboratory as soon as possible after
collection.
Laboratory Analysis
All laboratory work was carried out by a HOKLAS accredited
laboratory. Water samples of about
1,000 mL were collected at the monitoring and control stations for carrying out
the laboratory determinations. The
determination work started within the next working day after collection of the
water samples. The analyses
followed the standard methods as described in APHA Standard Methods for the Examination of Water and Wastewater,
19th Edition, unless otherwise specified (APHA 2540D for SS).
The QA/QC details were in accordance with requirements of HOKLAS or
another internationally accredited scheme (for details refer to Annex B).
3.3.3
Action and Limit Levels
The Action and Limit levels for Zone A,
which were established based on the results of Baseline Environmental Monitoring Part A, are presented in Table
3.4.
Table
3.4 Action
and Limit Levels of Water Quality for Zone A
|
Parameter
|
Action
Level
|
Limit
Level
|
|
Dissolved Oxygen (DO) (1)
|
Surface and Mid-depth (2)
|
Surface and Mid-depth (2)
|
|
|
5%-ile
of baseline data for surface and middle layer = 6.59 mg L-1
|
1%-ile
of baseline data for bottom layer = 6.42 mg L-1
|
|
|
|
|
|
|
Bottom
|
Bottom
|
|
|
5%-ile
of baseline data for bottom layers = 6.58 mg L-1
|
1%-ile of baseline for bottom layer = 6.42 mg L-1
|
|
|
|
|
|
Depth-averaged Suspended Solids (SS) (3) (4)
|
95%-ile of baseline data = 7.91 mg L-1
|
99%-ile of baseline data = 8.96 mg L-1
|
|
|
or 120% of control station's SS at the same
tide of the same day
|
or 130%
of control station's SS at the same tide of the same day
|
|
|
|
|
|
Depth-averaged Turbidity (Tby) (3) (4)
|
95%-ile of baseline data
= 5.17 NTU
|
99%-ile of baseline data
= 5.72 NTU
|
|
|
or 120% of control station's Tby at the same
tide of the same day
|
or 130% of control station's Tby at the same
tide 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) The
Action and Limit Levels for DO for Surface & Middle layer were calculated
from the combined pool of baseline surface layer data and baseline middle
layer data.
(3) “Depth-averaged”
is calculated by taking the arithmetic means of reading of all three depths.
(4) For
turbidity and SS, non-compliance of the water quality limits occurs when
monitoring result is higher than the limits.
|
3.3.4
Event and Action Plan
The Event and Action Plan for water
quality monitoring which was stipulated in the EM&A Manual is presented in Table 3.5.
Table 3.5 Event
Action Plan for Water Quality
|
Event
|
Contractor
|
|
Action
Level Exceedance
|
Step 1 - repeat sampling event.
Step 2 – identify source(s) of impact and confirm whether exceedance was due
to the construction works;
Step 3 – inform EPD, AFCD and LCSD and confirm notification of the
non-compliance in writing;
Step 4 - discuss with cable installation contractor the most appropriate
method of reducing suspended solids during cable installation (e.g. reduce
cable laying speed/volume of water used during installation).
Step 5 - repeat measurements after implementation of mitigation for
confirmation of compliance.
Step 6 - if non compliance continues - increase measures in Step 4 and
repeat measurements in Step 5. If
non compliance occurs a third time, suspend cable laying operations.
|
|
Limit Level
Exceedance
|
Undertake Steps 1-5 immediately, if further non
compliance continues at the Limit Level, suspend cable laying operations until
an effective solution is identified.
|
4
Impact
Monitoring Results
For the impact monitoring, six monitoring
events were scheduled between 31 July and 6 August 2009.
Aside from the 4 August, when a typhoon warning stopped marine works,
monitoring events at all designated monitoring stations were performed on
schedule, ie five events took place on 31 July, 1 August, 3 August, 5 August
and 6 August 2009.
4.1
Data Collected During Mid-Ebb and/or Mid-Flood Tidal
Conditions
Daily monitoring
events were scheduled between 31 July and 6 August 2009 at Deep Water
Bay (ie Zone A). The monitoring data taken during the
mid-ebb and/or mid-flood tidal conditions for Zone A are presented in Annex C and compared against the
baseline monitoring results in Figures
C1-C4, Annex C. A summary of the exceedances is
presented in Table 4.1.
Table
4.1 Summary
of Exceedances occurring during the Reporting Week
|
|
|
Exceedance of Action and Limit Levels found at the Impact Monitoring
Stations in Zone A:
|
|
Date
|
Parameter
|
Mid-Ebb Tide
|
Mid-Flood Tide
|
|
31
July 2009
|
DO
(Bottom)
|
S1,
S2, S3
|
n/a
|
|
1
August 2009
|
DO
(Bottom)
|
S1,
S2, S3, B1
|
n/a
|
|
|
DO
(Depth-averaged)
|
S1,
S2, S3, B1
|
n/a
|
|
|
Turbidity
(Depth-averaged)
|
S3*
|
n/a
|
|
|
SS
(Depth-averaged)
|
B1*
|
n/a
|
|
3
August 2009
|
DO
(Bottom)
|
S1,
S2, S3, B1
|
S1,
S3
|
|
|
DO (Depth-averaged)
|
S3,
B1
|
None
|
|
4
August 2009
|
|
n/a
|
n/a
|
|
5
August 2009
|
DO
(Bottom)
|
n/a
|
S1,
S2, S3, B1
|
|
|
DO
(Depth-averaged)
|
n/a
|
S1,
S2, S3, B1
|
|
6
August 2009
|
DO
(Bottom)
|
S1,
S2, S3, B1
|
S1,
S2, S3, B1
|
|
|
DO (Depth-averaged)
|
S1,
S2, S3, B1
|
S1,
S2, S3, B1
|
|
|
SS
(Depth-averaged)
|
None
|
B1
|
Note:
* Action Level but not Limit Level
exceedance
n/a indicates that no sampling was taken
at that tide (due to it falling outside working hours, or due to weather
conditions).
None means there was no exceedance for
that parameter
4.1.1
Exceedances for Dissolved Oxygen from 31
July to 6 August 2009
Except for 4 August, when no marine works
and hence no monitoring took place, exceedances of the Action and Limit Levels
for Dissolved Oxygen (DO) were recorded daily throughout the reporting period
for bottom DO (DOB) and on all but one day for depth averaged DO (31 July 2009)
(Table
4.1).
It is observed that DO trends fluctuate
widely. Similar to the results of
the previous months, DOB concentrations at all the monitoring stations appeared
to be lower than the baseline data, with the exception of Station B1 on 31 July. It should be noted however that the DO
levels recorded at all the impact stations were predominantly higher than, if
not comparable to the DO measured at the control station R1. Daily exceedances of Action and Limit
Levels set from baseline data for DOB were observed not only at the impact
monitoring stations but also at the control station. All this implies that the background
levels of DO were also relatively low.
It was concluded in previous weekly
reports that the recent declining trends of dissolved oxygen and daily DO
exceedances could be due to seasonal variation such as stratification occurring
during the summer. Warmer summer
water temperatures speed up the uptake of oxygen through respiration by living
organisms and decomposition of organic matter in the water column and
sediments. As a result, the
replenishment of dissolved oxygen is less than the DO consumption leading to
depletion in dissolved oxygen concentrations during the summer months.
Also, for DO, critical conditions usually
occur within the bottom waters during the summer months when the water column
is stratified, with a warmer surface layer separated from deeper water by a
picnocline, or density gradient.
When the density gradient within the picnocline is high, transport of oxygen
from the aerated surface waters to the lower waters by mixing is significantly
reduced. Dissolved oxygen levels
could also decrease in the bottom layer because photosynthesis and contact with
the air may be significantly reduced.
This phenomenon is supported for the reporting week by the fact that in
general DOB concentrations were lower than DO concentrations measured at the
surface and mid-depth from 31 July to 6
August 2009.
At the beginning of the reporting week,
the weather was sunny and hot (high solar radiation) which would favour the
aforementioned thermal stratification.
Later in the week however a typhoon warning was issued and heavy rain
followed. It is believed that the
thermocline would have been broken up by the heavy rain, leading to mixing of
the oxygen deficient bottom waters and the slightly oxygen-richer surface
waters. The already reduced
oxygen levels could be further depleted through the decomposition of organic
matter washed into the marine waters during the rainstorm. There is the potential for all DO
present in the water to be rapidly removed for satisfying the oxygen demand
resulting in further oxygen depletion throughout the water column in the
subsequent days. This is supported
by the fact that there were exceedances at all Stations for both DOB and DO
depth-averaged in the latter half of the week, while at the start of the week,
some Stations still fell within the Limits.
It is important that although exceedances
of the Action and Limit Levels for DO occurred, no-non-compliances of the Water
Quality Objectives (ie not less than 2 mg/L for 90% of samples for bottom DO
and not less than 4 mg/L for 90% of samples for depth-averaged DO) were
reported.
A
review of the monitoring data compared to the works practices similarly
concluded that all DO exceedances are unlikely to be caused by the Project due
to the fact that the marine works undertaken were diver hand jetting operations
inside an enclosed silt curtain and hence these construction activities were
not expected to cause decreases in the DO levels.
In view of all of the above, the DO
exceedances were considered unlikely to be related to the Project works.
4.1.2
Exceedance for Turbidity on 1 August 2009
An exceedance of the Action Level for Depth-averaged
turbidity was recorded during the mid-ebb tide on 1 August 2009 at Station S3 (Table 4.1). Upon investigation, the exceedance was
considered unlikely to be related to the Project works for the following
reasons:
·
During
the mid-ebb tide, the turbidity level measured at Station S3 was slightly
higher than the Action Level derived from the baseline data but it was well below
120% of the Control Station’s turbidity.
·
At
the time of monitoring, there were no marine construction works being carried
out. A diver did go into the water
to undertake inspection works, but this would have been unlikely to have
disturbed the sea bed.
·
Station
B1 was closer to the construction barge than S3, but the turbidity level
measured at B1 (4.78 NTU) was lower than that measured at S3 (5.55 NTU). Both stations were downstream of the
construction barge.
4.1.3
Exceedances for Depth-averaged Suspended
Solids on 1 & 6 August 2009
An exceedance of the Action and Limit
Levels for Depth-averaged Suspended Solids (SS) was recorded on one day (6
August) and an exceedances of Action Levels but not Limit Levels on one further
day (1 August). Both exceedances
occurred at Station B1 (Table 4.1).
A review of the monitoring data and work
practices concluded that all SS exceedances are unlikely to be caused by the
Project due to the following:
·
At
the time of monitoring, no marine works were being carried out that were likely
to have disturbed the seabed; in one case, there was no marine works occurring
and in the other, a diver was in the water inspecting newly laid split pipes.
·
The
SS level at Station B1 did not show non-compliance during the previously
measured mid-ebb or mid-flood tide.
·
On 6
August Station B1 was upstream of the marine cable works, while at sampling
Stations downstream of the marine cable works, no SS exceedances were recorded.
·
The
depth-averaged turbidity measured at B1 at the same mid-ebb or mid-flood tide
was within its respective Action and Limit Levels.
It was, therefore, considered that the SS
exceedances were more likely to be caused by localised factors or temporary
tidal influence rather than the Project works.
4.2
Continuous In-Situ Measurement Data
Continuous in-situ measurements were taken at the impact monitoring stations
within the required monitoring zone at 30- to 60- minute intervals (subject to
the weather conditions and travelling time between stations) and the results
and the graphical presentations were included in Annex D.
In general, the water quality in the vicinity
of the Project works was stable and acceptable throughout each sampling day (31
July to 6 August) with the exception of some slight fluctuations in
depth-averaged turbidity.
5
Environmental
Non-CONFORMANCES
5.1
Summary of
Environmental Exceedance
Daily Notification of Exceedances (NOEs)
with detailed investigation reports were issued to EPD and AFCD during the
monitoring period (ie 31 July to 6 August 2009) for recording water quality
monitoring exceedances on dissolved oxygen, turbidity and suspended solids of
the monitoring stations. The
exceedances were examined against the Project works. Results of the detailed investigation
indicated that none of the exceedances were attributed to the Project
construction works.
5.2
Summary of
Environmental Complaint
No complaints were received during the
reporting period.
5.3
Summary of
Environmental Summons and Prosecution
No summons or prosecution on environmental
matters were received during the reporting period.
6
Future
Key Issues
6.1
Key Issues For
The Coming Week
During the following week, the repair of
the cable will continue including jetting works and installation of articulated
pipes.
6.2
Monitoring Schedule For The Coming WEEK
The tentative schedule of water quality
monitoring for the coming week is presented in Annex A. Since marine
works are predicted to be complete by 11 August, the schedule for the coming
week runs from 7 to 11 August. The
water sampling will be conducted at the same monitoring locations as in this
reporting period. However, the
tentative schedule of the water quality monitoring is subject to continued
operational progress and weather constraints.
7
Conclusions
This Weekly Impact Monitoring Report
presents the EM&A work undertaken during the period from 31 July to 6
August 2009 in accordance with the EM&A Manual and the requirements under FEP-01/294/2007.
There were daily exceedances of Action and
Limit Levels for dissolved oxygen, both bottom layer (on all days) and
depth-averaged (on all days except 31 July). There were only two exceedances of
suspended solids, both at Station B1, once on 1 August (Action Level only) and
once on 6 August. Depth-averaged
turbidity was compliant with Action and Limit levels throughout the reporting
period, with the exception of one Action Level exceedance at Station S3 on 1
August. Results of detailed
investigations have indicated that none of the mentioned exceedances were
attributed to the Project construction works.
No complaints and
summons/prosecution were received during the reporting week.
The MT will keep track of the EM&A
programme to verify compliance of environmental requirements and the proper
implementation of all necessary mitigation measures.
