3.1
Water quality monitoring was conducted at four monitoring stations. Appendix
A shows the established Action and Limit Levels for water quality.
3.2
Water samples were collected at surface at selected sampling locations
by water sampler. The parameters of Dissolved Oxygen (DO) and Turbidity were
measured in-situ and the Suspended
Solids (SS) were analysed in a Hong Kong Laboratory Accreditation Scheme
(HOKLAS) accredited laboratory. The water quality monitoring equipment deployed
are described in Table 3.1
Table 3.1 Water Quality Monitoring Equipment
|
Equipment |
Model
and Make |
|
DO and Temperature Meter, Salinity Meter
and Turbidimeter |
YSI
Model 6820 CE-C-M-Y |
|
Positioning
Equipment |
Magellan
5000 |
|
Water
Depth Detector |
Eagle
cuda 168 |
|
Water
Sampler |
Kahlsico
Water Sampler 2 L with messenger |
Monitoring Parameters, Frequency
and Duration
3.3
Table 3.2 summarises the monitoring parameters and frequency of impact
water quality monitoring. The monitoring
schedule for the reporting month is provided in Appendix B.
Table 3.2 Water Quality Monitoring Parameters and
Frequency
|
Monitoring
Stations |
Parameter,
unit |
Frequency |
No. of Depths |
|
Control Stations: FC1
& FC2 Impact Stations: FM1 –
FM2 |
Depth,
m Temperature,
oC Salinity,
ppt DO,
mg/L DO Saturation,
% Turbidity,
NTU SS,
mg/L |
Three times per week |
Three (Surface, Mid-Depth and Bottom) |
3.4
As stipulated in the EM&A
requirement, impact monitoring at four designated stations was undertaken during
the construction phase. The monitoring locations are shown in Figure 3.1. The
two impact stations, namely FM1 and FM2, were chosen on their proximity to the
site boundary, which would be under the greatest potential for water quality
impacts. Two control stations, namely FC1 and FC2, were also set up for ebb and
flood tide respectively for reference of the ambient water quality in the
region.
3.5
The following procedures were adopted for DO, temperature, salinity,
turbidity and suspended solids measurement:
Instrumentation
3.6
The in-situ water quality parameters, viz. dissolved oxygen,
temperature, salinity and turbidity were measured by a multi-parameter meter (Model:
YSI6820 CE-C-M-Y).
Operating/Analytical Procedures
3.7
Given that all water monitoring stations had water depths over 6 m, all in-situ
measurements and samplings were conducted at 3 water depths, namely 1 m
below water surface, mid-depth and 1 m from seabed.
3.8
At each sampling depth, duplicate readings of dissolved oxygen content
and turbidity were taken. The probes were retrieved out of the water after the
first measurement and then re-deployed for the second measurement. Where the
difference between the first and second readings of each set was more than 25%
of the value of the first reading, a third measurement would be conducted to
ensure data precision.
3.9
Water samples were collected by water samplers and stored in
polyethylene bottles. Sampling bottles were pre-rinsed with the same water
samples. The sample bottles were then packed into a cool-box kept at 4oC,
and delivered to a HOKLAS accredited laboratory, ALS Technichem (HK) Pty Ltd. for the analysis of suspended solids.
For QA/QC, one duplicate sample from each batch of 20 samples was analysed as
required by the HOKLAS.
Maintenance and Calibration
3.10
Before each round of monitoring, the dissolved oxygen probe of YSI 6820
was calibrated by the wet bulb method.
3.11
The monitoring instruments were checked, calibrated and certified by a laboratory
accredited under HOKLAS before use and subsequently re-calibrated at 3-monthly
intervals throughout all stages of the water quality monitoring. Calibration
records are shown in Appendix G.
3.12
All laboratory work was carried out by ALS Technichem (HK) Pty. Ltd. Water
samples of about 1,000 ml were collected at the monitoring stations for
carrying out the laboratory determinations. The determination works started within
24 hours after collection of the water samples. The analysis followed the
standard methods according to Table 3.3 and as described in APHA Standard
Methods for the Examination of Water and Wastewater.
Table 3.3 Analytical Methods to be applied to Water
Quality Samples
|
Determinant, unit |
Standard Method |
|
Total
Suspended Solids, mg/L |
APHA
20th ed 2540D |
3.13
ALS
Technichem (HK) Pty. Ltd. has comprehensive quality assurance and quality control
programmes. For QA/QC procedures, at least one duplicate sample was analysed
for every batch of 20 samples as required by HOKLAS.
3.14
Water quality monitoring was conducted at the 4 designated monitoring
stations. All monitoring data are provided in Appendix E.
3.15
Monitoring of water quality was conducted on 13 occasions from 1 to 31
August 2006.
3.16
The QA/QC results for laboratory testing in the reporting month were
acceptable. The QA/QC results are summarised in Appendix F.
3.17 The exceedances are summarised in Table 3.4.
Table 3.4 Water Quality Exceedance Summary
|
Tide |
Monitoring
Stations |
Exceedance
Level |
Parameters |
||||
|
Dissolved Oxygen |
Turbidity |
Suspended Solids |
TOTAL |
||||
|
Surface
and Middle |
Bottom |
||||||
|
Mid -Ebb |
FM1 |
Action |
0 |
0 |
0 |
0 |
0 |
|
|
Limit |
0 |
0 |
0 |
0 |
0 |
|
|
FM2 |
Action |
0 |
0 |
0 |
1 |
1 |
|
|
|
Limit |
0 |
0 |
1 |
0 |
1 |
|
|
Mid -Flood |
FM1 |
Action |
0 |
0 |
2 |
1 |
3 |
|
|
Limit |
0 |
0 |
0 |
1 |
1 |
|
|
FM2 |
Action |
0 |
0 |
1 |
0 |
1 |
|
|
|
Limit |
0 |
0 |
0 |
1 |
1 |
|
|
Total |
Action |
0 |
0 |
3 |
2 |
5 |
|
|
Limit |
0 |
0 |
1 |
2 |
3 |
||
Turbidity and Suspended Solids
3.18
A total of eight exceedances (five Action and three Limit Levels) were
recorded. Field observation confirmed that no sediment plume observed from the
Fill Bank. The recorded levels were within the respective baseline data range.
The exceedances were due to natural variation and not Project-related.