Table of contents

 

 

EXECUTIVE SUMMARY.. 1

Introduction. 1

Water Quality. 1

1      INTRODUCTION.. 3

Background. 3

Purpose of the Report 3

Project Organizations. 3

2      Water Quality Monitoring.. 4

Monitoring Requirements. 4

Monitoring Parameters. 4

Monitoring Equipment 4

Monitoring Locations. 4

Monitoring Frequency and Duration. 5

Monitoring Methodology, Calibration Details and QA/QC Procedures. 5

Results and Details on Influencing Factors. 6

Action and Limit Levels. 7

3      CONCLUSIONS AND RECOMMENDATIONS.. 11

Conclusions. 11

 

 

lIST OF TABLES

 

Table 1           Action and Limit Levels for Water Quality

Table 1.1        Key Project Contacts

Table 2.1        Water Quality Monitoring Parameters

Table 2.2        Water Quality Monitoring Equipment

Table 2.3        Locations of Water Quality Monitoring Stations

Table 2.4        Frequency and Parameters of Water Quality Monitoring

Table 2.5        Water Quality Baseline Monitoring Results during Mid-Ebb

Table 2.6        Water Quality Baseline Monitoring Results during Mid-Flood

Table 2.7        Guidelines for Establishment of Action and Limit Levels proposed in the Work Procedure

Table 2.8        Proposed Action and Limit Levels for Water Quality             

Table 2.9        Past Wet Season Data at EPD’s Monitoring Stations SM5, SM19 and MM5

Table 2.10     Calculated Action and Limit Levels for Water Quality

 


lIST OF FIGUREs

 

Figure 2.1      Location of Monitoring Stations (Lamma Section)

Figure 2.2      Locations of Monitoring Stations (Ping Chau Section)

 

 

lIST OF APPENDIces

 

A                     Copy of Calibration Certificate of Monitoring Equipment

B                     Water Quality Monitoring Results and Graphical Presentations (DOSM, DOB, TUR & SS)

C                     Quality Control Reports for Laboratory Analysis

D                     Baseline Monitoring Schedule

 

 


List of Abbreviation

 

 

DO

Dissolved Oxygen

EIA

Environmental Impact Assessment

EM&A

Environmental Monitoring and Audit

ET

Environmental Team

GPS

Global Positioning System

GRS

Gas Receiving Station

HEC

Hong Kong Electric Co. Ltd

HOKLAS

The Hong Kong Laboratory Accreditation Scheme

LNG

Liquefied Natural Gas

QA/QC

Quality Assurance / Quality Control

SS

Suspended Solids

                       

 

 

 


EXECUTIVE SUMMARY

Introduction

 

1.        This Baseline Environmental Monitoring and Audit (EM&A) Report is prepared by Cinotech Consultants Limited (ET-Cinotech) for the post-trenching works for the project “Lamma Project Station Extension – Supply and Installation of Submarine Gas Pipeline” (the Project).  This report presents the baseline environmental monitoring works performed at the sensitive receivers including Ping Chau, southern Po Toi and Lamma between 31st May and 2nd June 2005.

Water Quality

 

2.        The baseline water quality monitoring was conducted at fourteen designated monitoring stations at the three sensitive zones which are identified in the EIA Report, including Ping Chau, southern Po Toi and Lamma three days per week for a period of one week between 31st May and 2nd June 2005.  Salinity, dissolved oxygen (DO), turbidity and suspended solids (SS) were monitored in accordance with the Work Procedure.

 

3.        Data collected was reviewed and analyzed.  Details of the methodology, locations and results are presented in the report.  The monitoring results show that the water quality in the concerned water body is good.  No major pollution sources were identified during the baseline monitoring.  However, the baseline water quality data may not be representative to present the ambient conditions due to the small sample size (only three days of water samples) and limitation in tidal range selection (tidal range less than 0.5 m on one of the sampling events).

 

4.        As a result, the EPD long-term monitoring data were used to establish the Action and Limit Levels (Table I) for the relevant parameters during impact monitoring throughout post-trenching period.

 

Table I           Action and Limit Levels for Water Quality

Parameter (unit)

Water Depth

Action Level

Limit Level

Lamma Island – L-I1 and L-I2

 

 

 

DO

(mg/L)

Surface and Middle

4.7

4

Bottom

4.1

2

Turbidity (NTU)

Depth average

17.2

18.4

SS

(mg/L)

Depth average

10.2

10.7

 

 

 

 

Po Toi – PT-I1, PT-I2 and PT-I3

 

 

 

DO

(mg/L)

Surface and Middle

5.0

5

Bottom

3.3

2

Turbidity (NTU)

Depth average

14.0

21.9

SS

(mg/L)

Depth average

6.7

7.2

Ping Chau – PC-I1, PC-I2 and PC-I3

 

 

 

DO

(mg/L)

Surface and Middle

4.8

4

Bottom

2.9

2

Turbidity (NTU)

Depth average

11.2

13.0

SS

(mg/L)

Depth average

5.7

7.6

Notes:

-       For DO, non-compliance of the water quality limits occurs when monitoring result is lower than the limits.

-       For turbidity and SS, non-compliance of water quality limits occurs when monitoring result is higher than the limits.

 


1               INTRODUCTION

Background

1.1        Hong Kong Electric Holdings Ltd. (HEC) intends to develop a 1,800 MW power station in Hong Kong Special Administrative Region (HKSAR) to meet the forecast increase in electricity demand to cope with the social and economical growth of the HKSAR. The proposed power station will be located at reclaimed land in the south of the existing Lamma Power Station at the western edge of Lamma Island, termed Lamma Power Station Extension.

1.2        The proposed Power Station will use natural gas as fuel to generate electricity. The natural gas will be supplied from Guandong Liquefied Natural Gas (GD LNG) Terminal located at Cheng Tou Jiao of Shenzen PRC via a 20 inches diameter gas submarine pipeline. 

1.3        HEC awarded Saipem Asia Sdn. Bhd. (hereafter called “the Contractor) for the design, engineering, supply of materials, fabrication, testing at works, delivery to site, complete erection including pre-trenching, pipe laying, rock dumping, testing and pre-commissioning at site, preservation during the Defects Liability Period of Submarine Gas Pipeline under to Project titled “Lamma Power Station Extension – Supply and Installation of Submarine Gas Pipeline” (hereinafter called “the Project”). Cinotech Consultants Limited was subsequently commissioned by the Contractor as the Environmental Team (ET-Cinotech) to provide environmental consultancy services and to undertake the Environmental Monitoring and Audit (EM&A) works for the Project.

1.4        The Project works include Pre-Trenching works, Pipe-Lay installation, Post-Lay Trenching (Jetting) and Rock Dumping works related to the installation of 92 km of 20 inches diameter Submarine Gas Pipeline between Guandong Liquefied Natural Gas Terminal (GD LNG) and the receiving point at Gas Receiving Station (GRS) at South-West of Lamma Extension on Lamma Island of Hong Kong – SAR.  An Environmental Permit (EP) has been issued for the Lamma Power Station Extension project.  Variations to the EP requirements have been proposed recently for the Project works and the VEP no. EP-071/2000/C was issued on 18th May 2005. 

1.5        In accordance with the requirements of the EM&A Manual, water quality monitoring should be carried out for the jetting operations for the first two weeks of the construction programme. Further monitoring after the initial two weeks should be carried out if unacceptable impacts are revealed.  In addition, monitoring should be carried out at Ping Chau, southern Po Toi and southern Lamma when jetting operation is conducted in the vicinity of these ecological sensitive areas identified in the EIA report. The original water quality monitoring programme stipulated in the EM&A Manual has been reviewed and updated to cater for the proposed variations of the EP requirements.  The updates include a 3-day intensive water quality programme, which supersedes the original two-week programme.  Baseline and impact monitoring will also be undertaken at the said three sensitive zones defined in the EIA report. 

1.6        A Work Procedure outlining the monitoring and audit programme to be undertaken for the post-trenching works was submitted.  The baseline water quality monitoring was conducted at the three sensitive zones prior to the commencement of the post-trenching works. 

Purpose of the Report

1.7        The purpose of this Baseline Environmental Monitoring Report is to set out baseline levels for the water quality at the sensitive receivers in accordance with the Work Procedure.  These baseline levels will be used as the basis for the impact monitoring during the post-trenching stage of the Project.  This report presents the monitoring locations, equipment, period, methodology, results and observations for the water quality measurements during the baseline period.

Project Organizations

1.8        Different parties with different levels of involvement in the project organization include:

·       Project Proponent –Hong Kong Electric Holdings Ltd. (HEC)

·       Contractor – Saipem Asia Sdn. Bhd.

·       Environmental Team (ET-Cinotech) – Cinotech Consultants Limited

 

1.9        The responsibilities of respective parties are detailed in Section 3 of the EM&A Requirements Review (Review) and the project organization chart is presented in Figure 3.1 of the Review. The key contacts of the ET- Cinotech are shown in Table 1.1.

Table 1.1     Key Project Contacts

Party

Name

Role

Phone No.

Fax No.

ET-Cinotech

Dr. Priscilla Choy

Project Manager

2151 2089

3107 1388

Ms. Winniss Kong

Coordinator

2151 2068

3107 1388

Mr. Henry Leung

Monitoring Team Leader

2151 2087

3107 1388

 


2               Water Quality Monitoring

Monitoring Requirements

2.1        Baseline conditions for water quality should be established prior to the commencement of works.  The purpose of the baseline monitoring is to establish ambient conditions prior to the commencement of the works and to demonstrate the suitability of the proposed impact and control monitoring stations. The baseline conditions should be established by measuring all the water quality parameters for salinity, dissolved oxygen (DO), turbidity and suspended solids (SS) in accordance with the work procedure.

Monitoring Parameters

2.2        The following water quality parameters were included in the monitoring programme.

Table 2.1     Water Quality Monitoring Parameters

Phase

Water Quality Parameters

Construction

·    Salinity (ppt)

·    Turbidity (NTU)

·    Dissolved oxygen (DO) (mg/L and % of saturation)

·    Suspended solids (SS) (mg/L)

 

Monitoring Equipment

2.3        The water samplers used for water quality monitoring were Kahlsico Water-Bottle Model 135DW150.  The samplers with associated equipment complied with the specifications stipulated in the work procedure.

2.4        Table 2.2 summarizes the equipment used in the water quality monitoring program.  All the monitoring equipment complied with the specifications stipulated in the work procedure.  Copies of the calibration certificates of are attached in Appendix A.

Table 2.2     Water Quality Monitoring Equipment

Equipment

Model and Make

Qty.

Water Sampler

Kahlsico Water-Bottle Model 135DW 150

2

Multi-parameter Water Quality System

YSI 6820

2

 

Monitoring Locations

2.5        A total of fourteen water quality monitoring locations were selected.  Table 2.3 describes the locations of these monitoring stations.  The locations of the control and impact monitoring stations are shown in Figures 2.1 and 2.2.

Table 2.3  Locations of Water Quality Monitoring Stations

ID

Location / Corresponding Sensitive Zone

Type of Monitoring Station

Co-ordinates

Easting

Northing

L-C1

Lamma Island

Control Station

827183.8

807646.2

L-C2

Control Station

831676.1

802177.5

L-I1

Impact Station

828810.5

806397.2

L-I2

Impact Station

828885.4

803509.1

PT-C1

Po Toi

Control Station

842723.2

803604.7

PT-C2

Control Station

847367.7

801893.2

PT-I1

Impact Station

843897.0

802669.5

PT-I2

Impact Station

843788.9

802085.1

PT-I3

Impact Station

843751.8

801793.7

PC-C1

Ping Chau

Control Station

861173.7

848150.6

PC-C2

Control Station

864446.5

842633.7

PC-I1

Impact Station

862140.0

846255.0

PC-I2

Impact Station

862126.0

845003.0

PC-I3

Impact Station

863196.0

843564.0

 

Monitoring Frequency and Duration

2.6        Table 2.4 summarizes the monitoring period and frequencies of water quality monitoring.

Table 2.4     Frequency and Parameters of Water Quality Monitoring

Station

Parameters

Frequency

No. of depth

L-C1, L-C2, L-I1, L-I2, PT-C1, PT-C2, PT-I1, PT-I2, PT-I3, PC-C1, PC-C2, PC-I1, PC-I2, PC-I3

SS, turbidity, DO and in-situ parameters*

3 times a week for a period of one week in both mid-ebb and mid-flood tides

3 (1m below water surface, mid-depth and 1m above channel bed.)

Notes:

*   In-situ parameters included temperature, salinity and DO saturation.

Monitoring Methodology, Calibration Details and QA/QC Procedures

Instrumentation

2.7        A multi-parameter meter (Model YSI 6820 CE-C-M-Y) was used to measure DO, turbidity, salinity, and temperature.  Digital Global Positioning Systems (DGPS) were used to ensure that the correction locations were arrived prior to measurement and sample collection.

Operating/Analytical Procedures

2.8        At each measurement, two consecutive measurements of in-situ parameters 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 in the value between the first and second readings of each set was more than 25% of the value of the first reading, the reading was discarded and further readings were taken.

2.9        For SS measurement, grab samples were collected.  Water samples of about 1,000 ml were collected and stored in polyethylene bottles.  The sample bottles were packed into an ice-box and delivered to a HOKLAS Laboratory, WELLAB Ltd., for the analysis within 24 hours.

Maintenance and Calibration

2.10    Before each round of monitoring, a zero check in distilled water was performed with the turbidity probe of YSI 6820.  The probe was kept in wet condition and then calibrated with a solution of known NTU.

2.11    Verifications of the DGPS were carried out at a known fixed reference point (survey nail obtained from the Survey and Mapping office of Lands Department).  The position was monitored over a period of 5 minutes.  Deviations of smaller than +/- 5 metres were demonstrated and recorded.

2.12    QA/QC procedures for the suspended solids analyzed in the HOKLAS-accredited laboratory, Wellab Limited are attached in Appendix C.

Results and Details on Influencing Factors

2.13    Baseline water quality monitoring was conducted between 31st May 2005 and 2nd June 2005 in both mid-ebb and mid-flood tides.  The monitoring results and the graphical presentation are shown in Appendix B.  Note that in Appendix B, the “sea condition” is given as indicative information and does not necessarily adhere to any standard sea state descriptions.  In general, “calm” means small or no waves were observed; “rough” includes white-capped sea or rougher; and “moderate” means all conditions in between “calm” and “rough”.

2.14    The results are summarized in Tables 2.5 and 2.6, which show the averages and the ranges of readings recorded during mid-ebb and mid flood tides. 

Table 2.5      Water Quality Baseline Monitoring Results during Mid-Ebb

Sensitive Zones

Stations

Average DO at S&M*, mg/L

(Range)

Average DO at Bottom, mg/L

(Range)

Average Turbidity, NTU

(Range)

Average SS, mg/L

(Range)

Lamma Island

L-C1

7.5

(6.3 – 9.3)

5.6

(5.0 – 6.1)

3.8

(3.5 – 4.2)

4.7

(2.8 – 5.9)

L-C2

7.1

(6.7 – 7.9)

6.1

(6.0 – 6.1)

3.6

(2.0 – 5.1)

3.4

(2.2 – 4.1)

L-I1

7.5

(6.4 – 9.4)

5.7

(5.7 – 5.8)

4.1

(3.1 – 5.0)

5.0

(2.5 – 7.1)

L-I2

7.1

(6.6 – 8.1)

5.8

(5.6 – 6.0)

4.4

(3.6 – 5.3)

3.9

(2.3 – 4.8)

Po Toi

PT-C1

6.8

(6.5 – 7.2)

6.6

(5.5 – 7.3)

1.9

(1.2 – 2.4)

2.9

(2.5 – 3.6)

PT-C2

6.7

(6.1 – 7.2)

5.9

(5.1 – 7.0)

1.4

(1.1 – 1.6)

2.8

(2.1 – 4.2)

PT-I1

7.2

(7.1 – 7.2)

6.4

(5.1 – 7.0)

2.5

(1.3 – 3.7)

4.1

(3.5 – 4.5)

PT-I2

6.7

(6.4 – 7.1)

5.9

(4.7 – 7.1)

2.5

(1.3 – 4.5)

2.6

(1.2 – 3.4)

PT-I3

6.7

(6.4 – 7.1)

6.4

(6.1 – 7.1)

2.1

(1.8 – 2.6)

3.2

(2.7 – 4.0)

Ping Chau

PC-C1

7.1

(6.6 – 7.9)

6.2

(6.1 – 6.4)

2.9

(1.8 – 4.6)

3.2

(2.0 – 4.5)

PC-C2

7.0

(6.8 – 7.3)

6.3

(6.0 – 6.5)

1.5

(1.2 – 1.7)

2.9

(1.9 – 3.6)

PC-I1

7.6

(6.8 – 9.2)

7.2

(6.6 – 8.3)

1.7

(1.2 – 2.1)

3.0

(2.2 – 4.3)

PC-I2

7.1

(6.7 – 7.8)

6.2

(5.8 – 6.4)

3.9

(2.6 – 5.4)

4.0

(2.0 – 6.3)

PC-I3

6.9

(6.6 – 7.6)

6.0

(5.4 – 6.4)

3.1

(2.4 – 4.0)

4.3

(2.7 – 7.2)

* Surface and middle depths

Table 2.6      Water Quality Baseline Monitoring Results during Mid-Flood

Sensitive Zones

Stations

Average DO at S&M*, mg/L

(Range)

Average DO at Bottom, mg/L

(Range)

Average Turbidity, NTU

(Range)

Average SS, mg/L

(Range)

Lamma Island

L-C1

7.0

(6.1 – 7.8)

5.4

(4.7 – 5.8)

5.1

(4.6 – 6.0)

6.7

(5.5 – 7.7)

L-C2

7.4

(6.6 – 8.0)

5.8

(5.2 – 6.1)

3.3

(2.4 – 4.3)

3.2

(3.0 – 3.5)

L-I1

7.3

(6.5 – 8.2)

5.6

(5.2 – 5.9)

4.5

(3.4 –5.4)

6.0

(4.8 – 7.4)

L-I2

6.8

(6.1 – 7.3)

5.4

(4.5 – 6.0)

4.8

(4.3 – 5.1)

4.9

(3.3 – 6.6)

Po Toi

PT-C1

6.5

(6.2 – 7.2)

6.0

(5.1 – 7.2)

2.7

(1.2 – 5.0)

2.5

(1.9 – 2.9)

PT-C2

6.7

(6.2 – 7.1)

6.2

(4.9 – 6.9)

2.0

(1.3 –3.2)

2.5

(1.7 – 3.0)

PT-I1

6.8

(6.4 – 7.1)

5.8

(4.7 – 7.1)

2.5

(1.6 – 3.1)

2.9

(2.3 – 3.8)

PT-I2

6.5

(6.2 – 6.8)

5.7

(4.9 – 6.5)

2.0

(1.4 – 2.9)

2.4

(1.5 – 3.0)

PT-I3

6.5

(5.7 – 7.2)

6.0

(5.2 – 6.6)

2.4

(1.7 – 2.8)

2.6

(1.4 – 3.6)

Ping Chau

PC-C1

6.9

(6.8 – 6.9)

6.2

(6.0 – 6.4)

2.8

(2.3 – 3.6)

3.7

(2.9 – 4.1)

PC-C2

6.3

(5.8 – 6.8)

5.7

(4.5 – 6.6)

1.3

(1.2 – 1.5)

2.8

(1.7 – 3.4)

PC-I1

7.5

(6.5 – 9.3)

7.0

(6.5 – 7.8)

1.2

(0.7 – 1.8)

3.2

(2.0 – 5.1)

PC-I2

7.1

(6.7 – 7.8)

6.2

(6.0 – 6.5)

3.3

(2.0 – 4.0)

4.4

(2.3 – 7.0)

PC-I3

7.2

(6.7 – 7.9)

6.1

(5.5 – 6.5)

2.4

(2.0 – 3.2)

3.6

(2.7 – 5.0)

* Surface and middle depths

 

2.15    No major pollution source and influencing factor was observed during the baseline monitoring period.  However, the baseline water quality data may not be representative to present the ambient conditions due to the small sample size (only three days of water samples) and limitation in tidal range selection (tidal range less than 0.5 m on one of the sampling events).

Action and Limit Levels

2.16    Guidelines for establishment of the Action and Limit levels for the impact monitoring during the post-trenching works of the Project were provided in the work procedure, as presented in Table 2.7.


Table 2.7       Guidelines for Establishment of Action and Limit Levels proposed in the Work Procedure

Parameter (unit)

Action

Limit

Dissolved Oxygen (mg/L)

(surface, middle, bottom)

Surface and middle

80% of upstream control station at the same tide of the same day

 

Bottom

80% of upstream control station at the same tide of the same day

Surface and middle

4 mg/L except 5mg/L for FCZ

 

 

 

Bottom

2 mg/L

SS (mg/L)

(depth average)

120% of upstream control station’s SS at the same tide of the same day

130% of SS readings at the upstream control station at the same tide of same day and specific sensitive receiver water quality requirements

Turbidity (NTU)

(depth average)

120 % of upstream control station’s turbidity at the same tide of the same day

130% of turbidity at the upstream control station at the same tide of same day

Notes:

1.                       “Depth-average” is calculated by taking the arithmetic means of reading of all three depths.

2.                       For DO, non-compliance of the water quality limit occurs when monitoring result is lower than the limit.

3.                       For SS and turbidity, non-compliance of the water quality limits occur when monitoring result is higher than the limits.

 

2.17    For determination of Action / Limit Levels of DO, turbidity and SS, the control station approach was proposed in the work procedure.  However, based on the baseline water quality monitoring results, the water quality of the control stations, especially that at the Po Toi (PT-C1 and PT-C1) and Ping Chau (PC-C1 and PC-C2) were considered good (with low turbidity and SS levels).  In order to avoid false alarm of the impact of the post-trenching works, it is proposed to adopt the percentile approach of baseline water quality data at the three sensitive receivers including Ping Chau, southern Po Toi and southern Lamma for establishment of Action / Limit Levels.  The proposed Action / Limit Levels for water quality are provided in Table 2.8.

2.18    Given the limitation of the baseline monitoring data as identified in Section 2.15, the EPD long-term monitoring results (DO, turbidity and SS) collected in the years from 1998 to 2003 at Stations SM5, SM19 and MM5 were adopted for the establishment of Action / Limit Levels for the stations at Lamma, Po Toi and Ping Chau respectively. 

2.19    Also, the Action / Limit Levels were computed based on two categories, dry season and wet season.  Since the pipeline jetting works would be carried out in the wet season only, only the Action / Limit Levels for wet season are derived.  The EPD long-term monitoring results collected from May to October in the years of 1998 to 2003 are adopted for the computation for wet season. 

Table 2.8       Proposed Action and Limit Levels for Water Quality

Parameter (unit)

Action

Limit

Dissolved Oxygen (mg/L)

(surface, middle, bottom)

Surface and middle

5%-ile of baseline data

 

Bottom

5%-ile of baseline data

Surface and middle

4 mg/L except 5mg/L for FCZ

Bottom

2 mg/L

SS (mg/L)

(depth average)

95%-ile of baseline data

99%-ile of baseline data

Turbidity (NTU)

(depth average)

95%-ile of baseline data

99%-ile of baseline data

Notes:

1.       “Depth-average” is calculated by taking the arithmetic means of reading of all three depths.

2.                       For DO, non-compliance of the water quality limit occurs when monitoring result is lower than the limit.

3.                       For SS and turbidity, non-compliance of the water quality limits occur when monitoring result is higher than the limits.

 

2.20    A summary of the past data of 1998-2003 at station SM5, SM19 and MM5 is provided in Table 2.9.  Given that major marine works (including the HEC Navigation Channel Improvement and Lamma Power Station Extension Reclamation) were carried out in the vicinity of SM5 since April 2001 until end of 2004, the wet season data at station SM5 between 1998 and 2000 is presented for better illustration of the natural ambient levels.

 

Table 2.9       Past Wet Season Data at EPD’s Monitoring Stations SM5, SM19 and MM5

Year

1998-2000

1998-2003

Stations

SM5 (Lamma)

SM5 (Lamma)

SM19

(Po Toi)

MM5

(Ping Chau)

DO at S&M*, mg/L

Average

 

6.8

7.0

6.2

6.1

Maximum

10.6

11.9

8.0

8.0

Minimum

4.5

4.2

4.6

4.0

5%-ile

4.7

4.7

5.0

4.8

1%-ile

4.5

4.3

4.7

4.2

DO at Bottom, mg/L

Average

 

5.8

5.9

4.9

5.0

Maximum

7.0

9.1

7.4

7.9

Minimum

3.5

3.5

2.8

1.6

5%-ile

4.1

4.2

3.3

2.9

1%-ile

3.6

3.7

2.8

2.0

Turbidity, NTU

Average

 

7.8

8.3

8.4

6.3

Maximum

18.7

18.7

23.6

13.2

Minimum

1.2

1.2

1.1

2.6

95%-ile

17.2

15.1

14.0

11.2

99%-ile

18.4

18.0

21.9

13.0

SS, mg/L

Average

 

4.9

5.8

4.1

2.3

Maximum

10.9

20.7

7.3

7.9

Minimum

0.8

0.8

1.1

0.5

95%-ile

10.2

12.2

6.7

5.7

99%-ile

10.7

18.6

7.2

7.6

* Surface and middle depths

 

2.21    Following the criteria set out in Table 2.8, the Action and Limit Levels for water quality impact monitoring have been established as Table 2.10.  In addition, based on the data summarized in Table 2.9, elevated SS levels at SM5 are observed between 2001 and 2003.  The elevated SS levels may be related to the said marine projects.  As a result, the data at SM5 between 1998 and 2000 is adopted for deriving Action and Limit Levels at sensitive receivers at Lamma.  For the sensitive receivers at Po Toi and Ping Chau, the data between 1998 and 2003 are adopted.

Table 2.10     Calculated Action and Limit Levels for Water Quality (Wet Season)

Parameter (unit)

Water Depth

Action Level

Limit Level

Lamma Island – L-I1 and L-I2

 

 

 

DO

(mg/L)

Surface and Middle

4.7

4

Bottom

4.1

2

Turbidity (NTU)

Depth average

17.2

18.4

SS

(mg/L)

Depth average

10.2

10.7

 

 

 

 

Po Toi – PT-I1, PT-I2 and PT-I3

 

 

 

DO

(mg/L)

Surface and Middle

5.0

5

Bottom

3.3

2

Turbidity (NTU)

Depth average

14.0

21.9

SS

(mg/L)

Depth average

6.7

7.2

Ping Chau – PC-I1, PC-I2 and PC-I3

 

 

 

DO

(mg/L)

Surface and Middle

4.8

4

Bottom

2.9

2

Turbidity (NTU)

Depth average

11.2

13.0

SS

(mg/L)

Depth average

5.7

7.6

Notes:

-       For DO, non-compliance of the water quality limits occurs when monitoring result is lower than the limits.

-       For turbidity and SS, non-compliance of water quality limits occurs when monitoring result is higher than the limits.

 


3               CONCLUSIONS AND RECOMMENDATIONS

Conclusions

3.1        Environmental monitoring works were performed on 31st May, 1st and 2nd June 2005 in accordance with the work procedure.

3.2        During the baseline water quality monitoring period, no observable pollution source was identified in the vicinity of the monitoring stations.  However, the baseline water quality data may not be representative to present the ambient conditions due to the small sample size (only three days of water samples) and limitation in tidal range selection (tidal range less than 0.5 m on one of the sampling events).

3.3        The EPD long-term monitoring data were used to establish the Action and Limit Levels for the relevant parameters during impact monitoring at sensitive receivers throughout post-trenching period.