This Section provides details of the water quality
monitoring to be undertaken by the ET during the construction and operation of the
active pits. Water quality modelling carried
out for the EIA indicates that the potential water quality impacts associated
with the dredging, backfilling and capping works at the active pits will be within acceptable levels and no adverse water
quality impacts are expected.
However, the monitoring programme is designed to verify the predictions
of the EIA and ensure compliance with the WQOs.
The main objective of this component of the study is to
determine the impacts on water quality caused by the dredging operations,
disposal activities and capping works.
Three separate components of water quality monitoring are
necessary.
·
Routine Water Quality Monitoring - conducted to examine the
effects of overall operation of the active
pits on the level of compliance with the water quality objectives (WQOs)
for the NWWCZ;
·
Dissolved Metal Testing - conducted to examine the
levels of contaminants in plumes arising from the backfilling operations; and,
·
Water Column Profiling - conducted to examine in situ the effects of dredging,
backfilling and capping operations on water quality parameters within the water
column.
The impact hypothesis for this work component has been
defined based on the predictions from the EIA regarding impacts from the
construction of the proposed
contaminated mud disposal facilities, the associated contaminated mud
disposal operations and the objectives for the study.
Dredging, disposal
(backfilling) and capping operations do not result in any exceedances of Northwestern
Water Quality Control Zone Water Quality Objectives.
As a consequence of performing three separate tasks for
assessing the impacts of dredging works, disposal operations and capping
activities on water quality, three null hypotheses will be tested:
Routine Water Quality
Monitoring
H0 There are no differences in the level
of compliance with the appropriate WQOs for the NWWCZ as a result of the
overall operation of the active contaminated mud disposal facility.
Dissolved Metal Testing
H0 There are no differences between the
concentrations of contaminants in water samples collected in areas downcurrent
of the active contaminated mud disposal facility as compared to areas upcurrent
of the facility during backfilling operations.
Water Column Profiling
H0 There is no change in the level of
compliance with the NWWCZ WQOs of samples taken from the plume arising from
dredging, backfilling and capping activities (EIA predicted location).
The design for this component of the programme allows
impacts to water quality as a result of the overall operation of the active facility to be assessed. Replicate water samples shall be
collected at specific sites (fixed locations as indicated on Figures 3.4a and
3.4b) which should be located in three areas at increasing distances from
the active facility: near field, mid field and far field/reference. The samples should be collected at
eight times during the year, twice in the dry season, twice during the wet
season and twice in each of the two transitional seasons. The approach will ensure that the
impact of temporal changes on the hydrodynamic conditions in the area is
considered in the sampling.
The number of samples to be collected and the sampling frequency
shall be confirmed in advance of the commencement of the disposal activities
and agreed with EPD based on the detailed design of the facility. In principle, reference stations should
be located in areas that are free from the influence of sediment plumes
resulting from the operation of the facility. For standardisation purposes, consideration of selecting
reference sites at similar locations to the EM&A programmes for the East
Sha Chau CMP IV is proposed (Figures 3.4a and 3.4b). The approach to be adopted for the
sampling shall ensure that the impacts on the hydrodynamic conditions in the
area resulting from the overall operation of the disposal facility are
thoroughly considered.
Dissolved metal stations shall be located at fixed stations
within the predicted trajectories of the plume. Samples shall be collected from two dissolved metal stations
located on a transect running up-current (flood tide) and five down-current
(ebb tide) of the active pits. The
total number of dissolved metal stations and the spacing between sampling
stations should be confirmed in advance of the commencement of the disposal
activities and agreed with EPD based on the detailed design of the disposal
facility. Making reference to the
previous sampling protocol developed for the East Sha Chau CMP monitoring
programmes is recommended when devising the sampling protocol for this Project.
In order to increase the likelihood of sampling within the plume
trajectory and hence increase the ability to detect potential impacts to water
quality, the location of the dissolved metal transect should be determined in
the field on each sampling occasion depending on the current direction and the
location of backfilling at the time of sampling (if backfilling is
concurrent). The position of the
dissolved metal stations shall be determined in the field on each sampling
occasion depending on two factors: the current direction; and the location of
backfilling at the time of sampling (if backfilling is concurrent).
In principle, water samples shall be collected from stations
located on a transect running up-current and down-current of the active
pit. The first down-current
station and the first up-current station of the dissolved metal station
transect shall be positioned on the edge of the disposal facility at the most
appropriate position depending on the factors mentioned above. The remainder of the up-current or down-current
stations shall be positioned at appropriate distances apart from the respective
first up-current or down-current station along the transect.
The following methodology shall be adopted for monitoring at
dissolved metal stations:
·
contact
the CEDD barge at the start of each survey on every sampling occasion to
determine the backfilling schedule for that particular day and to determine the
likely location of backfilling at the proposed time of sampling.
·
undertake
Water Column Profiling to determine current direction.
·
determine
a suitable location for the dissolved metal station transect (with the
down-current station should be located on the down current edge, and first
up-current station should be located on the up-current edge, of the East of Sha Chau Facility according to
the current direction and the position of backfilling at the time of sampling.
·
collect
samples from the dissolved metal stations located on a transect running
up-current and down-current of the active pit.
The above measures shall ensure that water samples are
collected from locations directly down-current of the active pits (to determine
whether contaminants are being dispersed outside the boundary of the pit), and
up-current of the active pit (to determine background concentrations of
contaminants).
A one hour survey shall be conducted at regular intervals
(eg monthly) at one station located either in the flood or ebb tide plume
depending on the current direction, in order to provide enough time (at least
one hour) to identify the optimum sampling location for the dissolved metal
testing component. Water column
profiling shall be conducted at mid-depth.
Baseline monitoring shall be conducted at all Routine
Monitoring Stations in the vicinity of the active facility (Figures 3.4a and
3.4b) and in reference areas (EPD Water Quality Monitoring Stations NM1, 2,
3, 5 and 6) for a period of one month prior to the commencement of marine works
in order to gather representative water quality data for the EM&A.
The baseline water quality monitoring shall be
undertaken three days per week at all stations within a 3 hour window of 1.5
hours before or after mid-flood and mid-ebb tides for four weeks prior to
construction works commencing. The
interval between 2 sites of monitoring shall not be less than 36 hours.
Each station
will be sampled and measurements will be taken at three depths, 1 m below the
sea surface, mid depth and 1 m above the seabed. Where water depth is less than 6m the mid-depth station may
be omitted. If water depth is less
than 3m, only the mid-depth station will be monitored. Duplicate water samples shall be taken and
analyzed.
The ET shall be responsible for undertaking the baseline
monitoring and submitting the results within 10 working days from the completion
of the baseline monitoring work.
Impact monitoring during dredging and capping operations of
the active pits shall be
conducted at mobile stations around the facility where their location is dependent
on the location of either the dredging or capping activities. These mobile stations should be located
at an appropriate distance between each other along the up-current or
down-current transect for the dredging or capping area. The positioning of the Impact
Monitoring stations shall follow the same rationale as that described above for
the Dissolved Metal Stations. The
precise location of the mobile stations shall be determined on each sampling
occasion by the contractor conducting the monitoring, after contacting CEDD
barge on site to determine the programme and location for dredging and
capping. Sufficient number of
sampling stations shall be identified for taking samples to ensure a
representative set of sampling data is collected. The number of samples to be collected
and the sampling frequency shall be confirmed in advance of the commencement of
the disposal activities and agreed with EPD based on the detailed design of the
facility.
The hierarchy of sampling design should allow for the
application of nested analysis of variance to statistically test any changes or
trends in the dataset. Under the
nested design, differences shall be tested between sites in a particular area
and between the three areas (ie near field, midfield and farfield). Once a time series of data has been
gathered temporal changes in water quality parameters can be analysed for
significant differences. In
addition, the data gathered shall be examined against the water quality
objectives for the NWWCZ to determine if the relevant water quality objectives
have been exceeded.
The data gathered during this programme shall be plotted and
examined for apparent impacts to water quality or contaminant dispersion in the
plumes arising from the backfilling activities. These data shall be compared with the predictions in the
EIA.
The data gathered shall be examined against the water quality
objectives for the NWWCZ to determine if the relevant water quality objectives
have been exceeded.
Should increases be detected in the level of contaminants in
dissolved metal samples, or exceedances of the NWWCZ WQOs be detected, a review
of the other monitoring parameters shall be undertaken. This shall focus on sampling stations
in the vicinity of the water quality stations where increases are detected to
see if these can be attributed to contaminant spread from the active pits. If so, consideration will be given to revising the facility
operations plan.
The following suite of parameters shall be measured for each
task as detailed below:
·
Dissolved
Oxygen (mg L-1) (in situ
and laboratory analysis);
·
pH (in situ and laboratory analysis);
·
Suspended
Solids (mg L-1) (laboratory analysis);
·
Ammonia
(mg L-1) (laboratory analysis);
·
Nutrients
(TIN mg L-1) (laboratory analysis);
·
5-Day
Biochemical Oxygen Demand (BOD) (mg L-1)(laboratory analysis); and
·
Turbidity
(NTU) (in situ and laboratory
analysis).
The measurements listed above for the routine water quality
monitoring along with the following inorganic contaminants shall be tested:
·
Cadmium;
·
Chromium;
·
Copper;
·
Lead;
·
Mercury;
·
Nickel;
·
Silver;
·
Zinc;
and
·
Arsenic.
·
Salinity
(ppt) (in situ);
·
Dissolved
Oxygen (mg L-1) (in situ and
laboratory analysis);
·
Suspended
Solids (mg L-1)(laboratory analysis);
·
Turbidity
(FTU) (in situ);
·
Temperature
(oC) (in situ); and
·
Current
Velocity and Direction (m s-1)
(in situ).
The position of the survey vessel shall be positioned to
within 3 m of the designated coordinates at each monitoring station using a
differential Global Positional System (GPS). In situ water
quality (salinity, temperature, DO and SS) and, current velocity and direction,
shall be conducted from the survey vessel using the equipment recommended in Section
3.8. In order to ensure the
reliability and quality of the data, the measuring instrument shall be
calibrated prior to each sampling cruise and the probe of the measuring
instrument shall be maintained at a suitable distance from the seabed to avoid
re-suspension of bottom sediments from skewing the results.
Water quality profiling shall be conducted continuously for
a one-hour period from a fixed point.
After deployment, the probe of the measuring equipment shall be allowed to
equilibrate with the surrounding seawater for approximately 30 seconds. Subsequently, average readings shall be
taken every few seconds to minimise sampling noise arising from the sensitivity
of the equipment. To further
calibrate the in-situ turbidity
measurements, water samples shall be collected for calibrating and converting
to turbidity measurements in the laboratory. In addition to in-situ
water quality monitoring, water samples shall be collected in a water
sampler at mid-depth. Samples
shall be stored in sealed sampling bottles and chilled, and on completion of
the survey shall be transported to the laboratory for immediate analysis. Samples not for immediate analysis
shall be stored at 4 ± 2°C.
The following equipment shall be supplied and used by the
contractor for the water quality monitoring:
·
Positioning
Device -
A Global Positioning System (GPS) shall be used during monitoring to ensure the
accurate recording of the position of the monitoring vessel before taking measurements. The GPS shall be calibrated daily
before each survey period or results reported.
·
Dissolved
Oxygen and Temperature Measuring Equipment - The instrument shall be a
portable, weatherproof dissolved oxygen measuring instrument complete with cable,
sensor, comprehensive operation manuals, and shall be operable from a DC power
source. It shall be capable of
measuring: dissolved oxygen levels
in the range of 0 - 20 mg L-1 and 0 - 200% saturation; and a
temperature of 0 - 45 degrees Celsius.
It shall have a membrane
electrode with automatic temperature compensation complete with a cable of not
less than 20 m in length.
Sufficient stocks of spare electrodes and cables shall be available for
replacement where necessary (for example, YSI model 59 metre, YSI 5739 probe,
YSI 5795A submersible stirrer with reel and cable or an approved similar
instrument).
·
Turbidity
Measurement Equipment
- Turbidity within the water shall be measured in situ by the nephelometric method. The instrument shall be a portable, weatherproof
turbidity-measuring unit complete with cable, sensor and comprehensive
operation manuals. The equipment
shall be operated from a DC power source, it shall have a photoelectric sensor
capable of measuring turbidity between 0 - 1000 NTU and shall be complete with
a cable with at least 20 m in length (Hach 2100P or an approved similar
instrument).
·
Salinity
Measurement Instrument
- A portable salinometer capable of measuring salinity in the range of 0 - 40
ppt shall be provided for measuring salinity of the water at each monitoring
location.
·
Suspended Solid Measurement Equipment - A
water sampler (eg Kahlsico Water Sampler), which is a PVC cylinder (capacity
not less than 2 litres) which can be effectively sealed with latex cups at both
ends, shall be used for sampling.
The sampler shall 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. Water
samples for suspended solids measurement shall be collected in high density
polythene bottles, packed in ice (cooled to 4oC without being
frozen), and delivered to the laboratory in the same day as the samples were
collected.
·
Water
Depth Gauge
- A portable, battery-operated echo sounder (Seafarer 700 or a similar approved
instrument) shall be used for the determination of water depth at each
designated monitoring station.
This unit shall 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.
·
Water
Sampling Equipment
- A water sampler, consisting of a transparent PVC or glass cylinder of not
less than two litres which can be effectively sealed with cups at both ends,
shall be used (Kahlsico Water Sampler 13SWB203 or an approved similar
instrument). The water sampler
shall 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.
·
Current
Velocity Measuring Equipment – A Valeport 108 MKIII current meter or a similar approved
instrument shall be used for measuring current velocity and direction. The instrument shall be calibrated
before taking data.
Using chain of custody forms, collected water samples shall
be transferred directly to laboratory for immediate processing of dissolved
oxygen, pH, suspended solids, ammonia, nutrients, BOD5 and
turbidity. Water samples shall be
analysed for pH and BOD within 4 hours of their arrival at the laboratory. All other parameters shall be analysed
within 48 hours of arrival. During
this period samples shall be held at 4 ± 2ºC. Prior to subjecting the sample to
metals analysis, samples shall be filtered to remove solids and colloidal
matter. Filtration shall be
accomplished using acid washed, single-use 0.45 micron membrane filters within
a maximum of 8 hours from sample collection. Where necessary, samples shall undergo further preparation
involving preconcentration which allows lower method detection limits to be
achieved and removes some of the possible sources of interference.
Field logs shall be maintained for all survey work, noting
the date of the survey, equipment used, survey manager and a record of all
activities and observations. Field
logs shall be retained for the duration of the Project and archived on
completion.
In-situ
measured data shall be digitally recorded from the instruments and converted
into Microsoft Excel format, or manually noted. Both disc copy and hard copy shall be retained for the file
records. Any deviation from the
standard procedure shall be noted in the log and the reason for the deviation
recorded. In addition, field logs
shall contain notes of events or activities in the vicinity of the monitoring
location which might give rise to anomalous data being recorded.
The sampling, collection, storage and identification
procedures are described in Section 3.7 of this Manual and the person
who conducts the sampling shall record all data from in-situ testing and
from any analysis carried out on the boat in a Field Log. All samples shall be identified with a
unique date/time/location/depth/sample-type code which shall be attached to the
sample container or written in indelible ink directly on the container. In order to avoid contamination of the
samples, all containers shall be new and unused and of analytical grade
quality. Sources of contamination shall be isolated from the working area (for
example, vessel fuel and exhaust fames) and any sample contaminated by local
material (such as printed circuit boards) shall be discarded and the sampling
repeated. Low level metal analysis
in seawater is easily contaminated through inappropriate handling and sampling
techniques. Site staff involved in
seawater sample collection intended for dissolved metal analysis shall ensure
that they wear non-contaminating disposable gloves if they have previously been
operating or have handled metallic equipment.
All in-situ monitoring instruments shall be checked,
calibrated and certified and subsequently re-calibrated at 3 monthly intervals
throughout all stages of the water quality monitoring, or as required by the
manufactures specification.
Certificate(s) of Calibration specifying the instrument shall be
attached to the monitoring reports.
All samples transferred from one sub-contractor to another
shall be accompanied by Chain of Custody (COC) forms. Any missing or damaged samples require notification to ET
Leader following logging in the laboratory QA system. The number of samples, the parameters to be tested and the
time of delivery should be clearly stated on the COC forms to ensure that
samples are analysed for the correct parameters and suitable time is provided
to the analytical laboratory for provision of resources required in the
analyses.
For details of the contaminants to be tested, the methods to
be used, the accreditation status of laboratory analytical methods, instruments
and procedures to be used, sample preparation information, method detection
limits (MDLs), QA/QC protocols and turnaround times, contractor should refer to
the previous monitoring programme for the ESC CMPIV ([1])
([2]).
The analytical techniques to be adopted for this Project
must conform to HOKLAS (or similar overseas)
accreditation.
Data Quality Objectives (DQOs) have been developed in the
previous monitoring programme for ESC CMPIV ([3])
([4]) to address precision,
accuracy and analyte recovery. The
contractor is recommended to follow the DQOs developed for data analysis.
Details of quality control specifications for inorganic
testing should be included in the updated EM&A Manual prior to commencement
of disposal activities.
Precision
Duplicates (1 in every 10 samples) shall be used to
monitoring the precision of the analysis.
Results should be flagged for reference when:
·
In
water samples, for metals with a concentration >4x MDL, the duplicate
results have more than a 15% RPD
·
For
all analytes with concentration <4x MDL, the duplicate results shall be
reported as analysed and no bounds should be quoted
Accuracy
Standard and certified reference material (CRM) shall be
used to monitor accuracy and precision within and between batches: Results should be flagged for reference
if:
·
The
variation of the standard from its true value is more than ± 15% (for mercury: ± 20%).
Recovery
Post digest spikes shall be used to determined the recovery
of determinants in complex sample matrices. Results should be rejected if:
·
Spike
recoveries are more than ± 25% from the theoretical recovery for
water samples. An exceptional case
would be if the sample concentration is greater than four times the spike
value, the spike may be disregarded.
Water quality monitoring will be evaluated against Action
and Limit Levels. The key assessment
parameters are dissolved oxygen and suspended sediment and thus Action and
Limit Levels based on the assessment criteria are identified for these. However turbidity can also provide
valuable instantaneous information on water quality and thus an Action Limit is
also recommended for this parameter to facilitate quick responsive action in
the event of any apparent unacceptable deterioration attributable to the
works. The baseline data will be
taken into account in setting the Action and Limit Levels, however, the
rationale are shown in Table 3.1
Action and Limit levels are used to determine whether
operational modifications are necessary to mitigate impacts to water
quality. In the event that the
levels are exceeded, appropriate actions in Event and Action Plan (Table 3.2) should be undertaken.
Table 3.1 Action and
Limit Levels for Water Quality
|
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 Water
Quality Event and Action Plan
|
Event |
Environmental
Team (ET) |
Contractor |
|
Action
Level |
|
|
|
Exceedance
for one sample |
·
Repeat
in-situ measurement to confirm findings; ·
Identify
the source(s) of impact; ·
Inform
contractor and contractor informs CEDD, EPD and AFCD and confirm notification
of the non-compliance in writing; ·
Check
monitoring data; ·
Discuss
potential mitigation measures if exceedance is attributed to the works with
contractor. |
·
Discuss
potential mitigation measures with ET and agree on mitigation measures to be
implemented if exceedance is attributed to the works; ·
Ensure
mitigation measures are implemented; ·
Assess
the effectiveness of the implemented mitigation measures. |
|
Limit
Level |
|
|
|
Limit
level for one occasion |
·
Repeat
in-situ measurement to confirm findings; ·
Identify
source(s) of impact; ·
Inform
contractor and contractor informs CEDD, EPD and AFCD; ·
Discuss
further mitigation measures if exceedance is attributed to the works with
contractor; ·
Increase
the monitoring frequency to daily if exceedance is attributed to the works
until no exceedance of the Limit Level. |
·
Critical
review of working methods; ·
Check
plant, equipment and working methods; ·
Discuss
further mitigation measures with ET to be implemented if exceedance is
attributed to the works; ·
Ensure
mitigation measures are being implemented; ·
Assess
the effectiveness of the implemented mitigation measures. |
|
|
|
|
|
Limit
Level exceeded on two or more occasions |
·
Identify
source(s) of impact; ·
Inform
contractor and contractor informs, CEDD, EPD and AFCD. |
·
If
exceedance is attributed to the works consider and if necessary reduce works
until no exceedance of Limit Level. |
|
|
|
|
|
Impacts
attributable to works |
·
Inform
contractor and contractor informs, CEDD, EPD and AFCD. |
·
Comprehensive
review of works; ·
Reduce
works; and ·
Suspension
of works. |
([1]) ERM
(2001) Environmental Monitoring and Audit for Contaminated Mud Pit IV at East
Sha Chau: Monitoring and Audit
Manual. Submitted to CED, February
2001.
([2]) Mouchel
(2001) Consultancy for
Environmental Monitoring and Audit for Contaminated Mud Pit IV at East Sha Chau
(2000-2005): Monitoring and Audit
Manual. Submitted to CED, May
2001.
([3]) ERM
(2001) Op cit.
([4])
Mouchel
(2001) Op cit.