3.       WATER QUALITY MONITORING

Monitoring Requirements

3.1               Water quality monitoring was conducted at four monitoring stations. Appendix A shows the established Action and Limit Levels for water quality.

Monitoring Equipment

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)

 

Monitoring Locations

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.

 

Monitoring Methodology

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.

Laboratory Analysis

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

QA/QC Procedure

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.

Results and Observations

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 12 occasions from 1 to 31 July 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

2

0

2

 

Limit

0

0

1

0

1

FM2

Action

0

0

1

1

2

 

Limit

0

0

0

0

0

Mid -Flood

FM1

Action

0

0

0

0

0

 

Limit

0

0

0

0

0

FM2

Action

0

0

0

1

1

 

Limit

0

0

3

1

4

Total

Action

0

0

3

2

5

Limit

0

0

4

1

5

 

Turbidity and Suspended Solids

3.18           A total of ten exceedances (five Action and five 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.