1
intorduction
The Hong Kong Civil
Engineering and Development Department (CEDD) have commissioned ERM-Hong Kong, Ltd (ERM) supported by
Mr Peter Whiteside (Independent Consultant), Halcrow
China Ltd (HCL) and Professor Wen-Xiong Wang (Independent
Auditor) of the Hong Kong University of Science and Technology (HKUST), to
undertake the Environmental Monitoring
and Audit for Contaminated Mud Pit at Sha Chau (2009-2013) – Investigation (hereafter referred as
“the Study”). This
Study, awarded under Agreement No. CE 4/2009 (EP), commenced
on 8th July 2009.
Since December 1992, the East of Sha Chau area has been the site
of a series of dredged contaminated mud pits (CMPs)
designed to provide confined marine disposal capacity for contaminated mud
arising from the HKSAR’s dredging and reclamation
projects. The latest group of pits,
CMP IVa, b & c began receiving contaminated mud
from construction projects on 1 December 1997. CMP IVa was
full by March 2000 (7.0 Mm3 of contaminated mud), CMP IVb was full by May 2002 (12.5 Mm3 of
contaminated mud). CMP IVc is presently in operation for backfilling by
contaminated sediments.
As required by the Environment Protection Department
(EPD), an environmental monitoring and audit programme was carried out to
monitor the operation of the CMP IV under the Project “Management and Capping
of Contaminated Mud Pit IV at East of Sha Chau”. In this
connection, an environmental monitoring and audit programme which encompassed
water and sediment chemistry, fisheries assessment, tissue and whole body
analysis, sediment toxicity and benthic recolonisation
studies have been continuously carried out since the operation of CMP IV. A review of the collection and analysis
of such environmental data from the monitoring programme demonstrated that
there had not been any adverse environmental impacts resulting from disposal
activities ().
Capacity to dispose of contaminated mud is
currently predicted to be exhausted by 2010 with the completion of backfilling
of CMP IVc at East of Sha Chau. When CMP IVc is full, a new environmentally acceptable disposal
capacity for essential arisings will be
required. A capacity of 8 Mm3
has been estimated as being needed to provide disposal capacity up to
2015. The assignment Strategic Assessment and Site Selection
Study for Contaminated Mud Disposal (Agreement CE 105/98) recommended a
Contained Aquatic Disposal facility (CAD - capped seabed pit such as those
already used at East of Sha Chau)
at Airport East ().
The results and recommendations of CE 105/98 were presented to the
Advisory Council on the Environment (ACE) on 23 July 2001 (ACE Paper 4/2001). The study recommended that an EIA be
carried out.
The
results of the EIA indicated that a series of four seabed pits be constructed
at East of Sha Chau to meet
continuing contaminated sediment demands ()
(Figure 1.1). This recommendation and
the EIA supporting it were endorsed by ACE on 11 July 2005 and the EIA was
subsequently approved by the Director of Environmental Protection (DEP) without
conditions on 1 September 2005 (AEIAR-089/2005).
An Environmental Permit (EP-312/2008) for the Disposal
of Contaminated Sediment – Dredging, Management and Capping of Sediment
Disposal Facility at Sha Chau
(hereafter referred as “the Project”) was issued by the Environmental
Protection Department (EPD) to the CEDD, the Permit Holder, on 9 September 2008
and varied on 28 November 2008 (EP-312/2008/A).
Under the requirements of Condition 3 of the EP (EP-312/2008), an EM&A programme as set
out in the Environmental Monitoring and
Audit Manual (EM&A Manual) is required to be implemented during
construction and operational phases of the Project. In accordance with the EM&A Manual, baseline monitoring of
water quality for dredging activities to form the new contaminated mud disposal
facility (CMP V) is required for the Project.
The purpose of this Baseline Monitoring Report is to present baseline marine water
quality at the designated monitoring locations in the Project and reference
areas prior to the commencement of marine dredging works. These levels will be used as the basis
for compliance monitoring during dredging of four seabed pits for the new
facility at Sha Chau. This report presents the monitoring
requirements, methodologies and results of the baseline marine water quality
measurements in accordance with the EM&A
Manual.
The structure of the report is as follows:
Section
1 : Introduction
Details the background, purpose and structure of the
report.
Section 2 : Baseline
Water Quality Monitoring for Dredging Activities
Summarises the
water quality monitoring parameters, monitoring programme, monitoring
methodology, monitoring frequency and monitoring locations.
Section
3 : Baseline Water Quality Monitoring
Results
Presents the monitoring
results and establishes the Action and Limit Levels in accordance with the EM&A Manual.
Section
4 : Conclusions
Concludes the
representativeness of the baseline monitoring results and observations for the
Project.
2
Baseline Water quality
monitoring for Dredging Activities
The following Section
provides details of methodology used in the baseline monitoring of water
quality prior to the
commencement of marine dredging works for the Project.
In accordance with the EM&A Manual, water quality sampling was undertaken at
monitoring stations in the vicinity of the
new facility at Sha Chau
and in reference areas (EPD Water Quality Monitoring Stations NM1, 2, 3, 5 and
6) prior to the commencement of marine dredging works. Locations of the baseline monitoring
stations are shown in Figure 2.1. Co-ordinates of these monitoring
stations are listed in Table 2.1.
Table 2.1 Coordinates
of Water Quality Monitoring Stations for Baseline Water Quality Monitoring for
Dredging Activities
|
Monitoring Stations
|
Eastings
|
Northings
|
|
Far Field Stations
|
|
|
|
ESC-WFA
|
805787
|
827951
|
|
ESC-WFB
|
806066
|
816537
|
|
MW1
|
823604
|
823654
|
|
Near Field Stations
|
|
|
|
ESC-WNAA
|
811830
|
822706
|
|
ESC-WNAB
|
810833
|
822965
|
|
ESC-WNAC
|
810235
|
822756
|
|
ESC-WNAD
|
809557
|
822527
|
|
ESC-WNBA
|
812767
|
821889
|
|
ESC-WNBB
|
811651
|
822278
|
|
ESC-WNBC
|
811043
|
822178
|
|
ESC-WNBD
|
810514
|
821919
|
|
Mid Field Stations
|
|
|
|
ESC-WMB
|
814033
|
821082
|
|
ESC-WMA
|
809577
|
823922
|
|
Reference Stations
|
|
|
|
NM1
|
820256
|
823214
|
|
NM2
|
816015
|
823686
|
|
NM3
|
812527
|
824049
|
|
NM5
|
807707
|
827244
|
|
NM6
|
807584
|
820286
|
Baseline water quality monitoring was conducted in
accordance with the requirements stated in the EM&A Manual, which are presented below.
2.2.1
Monitoring
Parameters
Parameters measured in situ were:
·
Dissolved
Oxygen (mg L-1);
·
Salinity
(‰);
·
pH;
·
Turbidity
(NTU);
·
Temperature
(°C); and
·
Current
Velocity and Direction (ms-1).
Parameters measured in the laboratory
were:
·
Suspended
Solids (SS) (mg L-1);
·
Ammonia
(mg L-1);
·
Nutrients
(TIN mg L-1);
·
5-Day
Biochemical Oxygen Demand (BOD5);
·
Cadmium
(mg L-1);
·
Chromium
(mg L-1);
·
Copper
(mg L-1);
·
Lead
(mg L-1);
·
Mercury
(mg L-1);
·
Nickel
(mg L-1);
·
Silver
(mg L-1);
·
Zinc
(mg L-1); and
·
Arsenic
(mg L-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.
2.2.2
Monitoring
Frequency
Baseline water quality
monitoring was carried out for four weeks, with the frequency of three days per
week. The interval between two sets
of monitoring was not less than 36 hours.
In situ measurements and water samples were taken during
mid-flood and mid-ebb tidal state on each sampling occasion.
2.3.1
Monitoring
Equipment
Positioning Device
A Global Positioning System
(GPS) was used (C-Nav globally corrected DGPS, GPS 84
datum) during monitoring to ensure the accurate recording of the position of
the monitoring vessel before taking measurements. The instrument calibration was checked
by recording a measured position at a previously coordinated location on shore.
Electronic data logging device
A data logging device capable of storing in situ measurement data was used. The device was able to read and store
the output from all electronic meters used for this project and recorded time
and location as measured by the GPS.
In situ Measurement
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:
·
turbidity levels between 0-1000 NTU (response
of the sensor was checked with certified standard turbidity solutions before
the start of measurement);
·
pH of 0 to 14 units with a resolution of 0.01
unit;
·
dissolved oxygen levels in the range of 0 –
50 mg L-1; and 0-500% saturation;
·
temperature of -5 to 45 °C; and,
·
salinity
in the range of 0-40 ppt (checked with 30 ppt Salinity solutions before the start of the measurement).
Water Depth Gauge
An echo sounder mounted to
the hull of the survey vessel was used to measure water depth.
Current Velocity
Sea water
current velocity was measured using a Workhorse Acoustic Doppler Current
Profiler (ADCP) manufactured by Teledyne RD Instruments. This instrument measured current speed
and direction in 1 m vertical increments below the survey vessel, from just
below the sea surface to just above the seabed.
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.
2.3.2
Monitoring
Methodology
Timing & Frequency
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 be less than 0.5 m for capturing
representative tides.
Reference were made to the
predicted tides at Lok On Pai,
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 Lok On Pai,
the baseline water quality monitoring was conducted between 28 July and 23 August
2009, following the schedule presented in Annex A. It should be noted that on 4 August
2009, monitoring was completed for the mid-flood but not for the mid-ebb tidal window
as the survey was suspended due to adverse weather conditions caused by the
severe tropical storm Goni which led to issue of
Strong Wind Signal No. 3 by the Hong Kong Observatory in the morning of the
survey.
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 1 m above the sea bed. For
stations that were less than 3 m in depth, only the mid depth sample was taken.
Protocols
The multi-parameter
measuring instruments (YSI 6820) were checked and calibrated by an HOKLAS
accredited laboratory before use (see calibration reports in Annex B).
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 were
collected in high density polythene bottles, packed in ice (cooled to 4° C
without being frozen), and delivered to HOKLAS accredited laboratory as soon as
possible after collection for
immediate analysis.
Laboratory Analysis
All laboratory work was
carried out by HOKLAS accredited laboratory. Water samples were collected at the
monitoring and reference stations for carrying out the laboratory
determinations. The determination
work started within the next working day after collection of the water samples.
For SS analysis, the Quality
Assurance / Quality Control (QA/QC) details were in accordance with
requirements of HOKLAS or another internationally accredited scheme (details
refer to Annex C).
3
Baseline Water Quality Monitoring Results
This Section presents the results of the baseline
monitoring of water quality for dredging activities for the Project.
Monitoring data and graphical
presentations are summarised in Annex D. It should be noted that the laboratory
analysis results for ammonia, nutrients (TIN), BOD5, cadmium, chromium,
copper, lead, mercury, nickel, silver, zinc and arsenic will be provided once
the data are available.
No major activities influencing the water quality
were identified during the monitoring period.
The Action and Limit Levels for DO, turbidity and SS were
set in the EM&A Manual and the
proposed Action and Limit Levels were determined as shown in Table 3.1.
The Action and Limit Levels of DO, turbidity and
suspended solids are derived from the baseline monitoring data for all
stations, and the results are presented in Table
3.2.
Table 3.1 Determination
of Action and Limit Level of Water Quality for Dredging Activities
|
Parameter
|
Action Level
|
Limit Level
|
|
Dissolved
Oxygen
|
|
|
|
Surface and
Middle
Depth Averaged
|
The depth
average of the impact station readings are <5%ile of baseline data
and
Significantly
less than the reference stations mean DO (at the same tide of the same day)
|
The average of
the impact station readings are <4mg/L
and
Significantly
less than the reference stations mean DO (at the same tide of the same day)
|
|
Bottom
|
The average of
the impact station readings are <5%ile of baseline data
and
Significantly
less than the reference stations mean DO (at the same tide of the same day)
|
The average of
the impact station readings are <2mg/L
and
Significantly
less than the reference stations mean DO (at the same tide of the same day)
|
|
Suspended Solids
|
|
|
|
Depth Averaged
|
The depth
average of the impact station readings are >95%ile of baseline data
and
120% or more of
the reference stations SS (at the same tide of the same day)
|
The depth
average of the impact station readings are >99%ile of baseline data
and
130% or more of
the reference stations SS (at the same tide of the same day)
|
|
Turbidity
|
|
|
|
Depth Averaged
|
The depth
average of the impact station readings are >95%ile of baseline data
and
120% or more of
the reference stations turbidity (at the same tide of the same day)
|
The depth
average of the impact station readings are >99% of baseline data
and
130% or more of
the reference stations turbidity (at the same tide of the same day)
|
Table 3.2 Proposed
Action and Limit Levels of Water Quality for Dredging Activities
|
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 = 3.76 mg L-1
and
Significantly less than the reference stations mean
DO (at the same tide of the same day)
|
1%-ile of baseline data for surface and middle
layer = 3.11 mg L-1
(3)
and
Significantly less than the reference stations mean
DO (at the same tide of the same day)
|
|
|
|
|
|
|
Bottom
|
Bottom
|
|
|
5%-ile of baseline data for bottom layers = 2.96 mg L-1
and
Significantly less than the reference stations mean
DO (at the same tide of the same day)
|
The average of the impact station readings are
<2 mg/L
and
Significantly less than the reference stations mean
DO (at the same tide of the same day)
|
|
|
|
|
|
Depth-averaged Suspended
Solids (SS) (4) (5)
|
95%-ile of baseline data for depth average = 37.88
mg L-1
and
|
99%-ile of baseline data for depth average =
61.92 mg L-1
and
|
|
|
120% of control station's SS at the same
tide of the same day
|
130% of control station's SS at the same
tide of the same day
|
|
|
|
|
|
Depth-averaged Turbidity (Tby) (4) (5)
|
95%-ile of baseline data
= 28.14 NTU
and
|
99%-ile of baseline data
= 38.32 NTU
and
|
|
|
120% of control station's Tby at the same tide of the same day
|
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 layers were
calculated from the combined pool of baseline surface layer data and baseline
middle layer data.
(3)
Given the Action
Level for
DO for Surface & Middle layers has already been lower than 4 mg L-1, it
is proposed to set the Limit Level at
3.11 mg L-1 which
is the first percentile of the baseline data.
(4)
“Depth-averaged”
is calculated by taking the arithmetic means of reading of all three depths.
(5)
For
turbidity and SS, non-compliance of the water quality limits occurs when
monitoring result is higher than the limits.
|
4
Conclusion
Baseline water quality monitoring was conducted
between 28 July and 23 August 2009 at eighteen designated monitoring stations
established for the Project. The
monitoring was carried out 3 days per week, at mid-flood and mid-ebb tides, at
three depths (surface, middle and bottom), for 4 weeks prior to the
commencement of dredging works. No
major activities were noted during baseline monitoring. Water quality monitoring results are,
therefore, representative of the baseline conditions for the Project.
Results have been used to determine Action and Limit
Levels for the dissolved oxygen, suspended solids and turbidity for impact
monitoring to be conducted during dredging of four seabed pits for the new
facility at Sha Chau.
