Contents

Executive summary

1 Introduction

2 Monitoring Methodology

2.1 Monitoring Frequency and Locations

2.2 Monitoring Parameters

3 Water Quality Performance Limits

3.1 Action and Limit Levels

3.2 Alert Levels

4 Monitoring Results

5 Conclusion

Appendix

A. Graphical Presentations of Water Quality Monitoring Results

Tables

Table 2.2: Locations of Water Quality Monitoring Stations  3

Table 3.1: Calculated Action and Limit Levels  5

Table 4.1: Calculated Initial Alert Levels  6

Table 5.1: Summary of DO Exceedances  7

Figures

Figure 2.1: Water Quality Monitoring Locations

Executive summary

The Project “Improvement Dredging for Lamma Power Station Navigation Channel” commenced on 18 February 2020. This is the second quarterly Water Quality Monitoring report for the Project. This report presents the results of impact monitoring on marine water quality for the Project from May to July 2020.

During this reporting period, a total of 40 days of marine water quality monitoring was carried out. The water quality monitoring results for all parameters, except dissolved oxygen (DO), obtained during the reporting period were within the corresponding Action and Limit Levels for sensitive receiver stations and within the Alert Levels for near stations as stipulated in the EM&A programme. Some of the DO (surface, middle and bottom layers) triggered the relevant Action or Limit Levels, and the corresponding investigations concluded that the cases were not related to the Project. To conclude, the dredging activities in the reporting period did not cause adverse impact to all water quality sensitive receivers.

1 Introduction

On 10 October 2017, the Environment Impact Assessment (EIA) Report (Register No.: AEIAR-212/2017) for the “Improvement Dredging for Lamma Power Station Navigation Channel” (the Project) was approved and an Environmental Permit (EP) (No. EP-535/2017) was issued for the construction and operation of the Project. Mott MacDonald Hong Kong Limited was commissioned by The Hongkong Electric Company, Limited to carry out the water quality monitoring works of the Project during the construction phase.

The purpose of the Project is to provide and maintain safe clearance for ocean-going marine vessels delivering coal to Lamma Power Station (LPS) via the Lamma Power Station Navigation Channel (the “Channel”), through the dredging of naturally accumulating sediment from the seabed. In order to meet the requirements for continued safe passage, the construction phase of the Project involves improvement dredging of the Channel to a target dredge depth[1] of -16.5 mPD.

The construction phase of the Project commenced on 18 February 2020. This Water Quality Monitoring Report summarizes the water quality monitoring as part of the EM&A programme for the Project for the months of May, June and July 2020.

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[1] While the Project aims to dredge to a target depth of -16.5 mPD, some overdredge may occur due to the limited precision control of dredging depths in practice.

2 Monitoring Methodology

2.1 Monitoring Frequency and Locations

The water quality monitoring was conducted three days per week during the reporting period at mid-flood and mid-ebb tides. The monitoring was conducted at a total of 18 water quality monitoring stations, comprising ten SR stations, five near stations and three control stations. Details of the monitoring locations are shown in Figure 2.1 and Table 2.2. It should be noted that the location of SR8 provided in Table 2.2 is approximate due to changing location of fish rafts under different tidal and wind condition. Water quality monitoring at SR8 was conducted at the nearest safely accessible location to the Fish Culture Zone.

Table 2.2: Locations of Water Quality Monitoring Stations

ID	Station	Easting	Northing	Remarks
SR1	HK Electric Power Station Intake	829194	808600	Monitored for SS only
SR2	Hung Shing Yeh Beach	830200	808700	Monitored during bathing season only (March to October inclusive)
SR3	Lo So Shing Beach	830450	807300	Monitored during bathing season only (March to October inclusive)
SR4	Marine Ecological Habitat at Pak Kok	829600	811630
SR5	Marine Ecological Habitat at Shek Kok Tsui	828560	811100
SR6	Marine Ecological Habitat at Ha Mei Wan	829760	805520
SR7	Marine Ecological Habitat at Southwest of Lamma	829590	804520
SR8	Fish Culture Zone at Lo Tik Wan	831265	809115
SR9	Fish Culture Zone at Sok Kwu Wan	831600	807765
SR10	Fish Culture Zone at Cheung Sha Wan	819160	810780
A1	Near station for Zone 1	828543	809573	For monitoring potential impacts to SR5 and SR4 during flood tide
A2	Near station for Zone 2	829053	807945	For monitoring potential impacts to SR1 and SR2 during flood tide
A3	Near station for Zone 3	829187	807100	For monitoring potential impacts to SR3 during both flood and ebb tide
A4	Near station for Zone 4 (east)	829427	805520	For monitoring potential impacts to SR6 during ebb tide
A5	Near station for Zone 4 (south)	829267	805134	For monitoring potential impacts to SR7 during ebb tide
C1	Control Station 1	828000	813500
C2	Control Station 2	825000	808000
C3	Control Station 3	829000	802000

2.2 Monitoring Parameters

For the 10 SR stations (SR1 to SR10) and three control stations (C1 to C3), monitoring of DO, DO%, pH, temperature, turbidity, salinity, water depth and SS were undertaken. For monitoring of the five near stations (A1 to A5), only the in-situ parameters (DO, DO%, pH, temperature, turbidity, salinity and water depth) were recorded. Other relevant data were also recorded, including monitoring location, time, tidal stage, weather condition and sea condition.

3 Water Quality Performance Limits

3.1 Action and Limit Levels

The Action and Limit levels are summarized in Table 3.1.

Table 3.1: Calculated Action and Limit Levels

Parameters	Action Level		Limit Level
SR1
SS in mg/L	90		100
SR2 to SR7
DO in mg/L	Wet	Dry	Wet	Dry
Surface & Middle	3.1	5.6	2.6	4
Bottom	2.4	5.8	1.9	2
SS in mg/L	9.5 OR 120% of upstream control station(s) at the same tide of the same day, whichever is higher		12.3 OR 130% of upstream control station(s) at the same tide of the same day, whichever is higher
Turbidity in NTU	9.7 OR 120% of upstream control station(s) at the same tide of the same day, whichever is higher		11.8 OR 130% of upstream control station(s) at the same tide of the same day, whichever is higher
SR8 to SR10
DO in mg/L	Wet	Dry	Wet	Dry
Surface & Middle	5	5.6	5	5
Bottom	2.4	5.8	2	2
SS in mg/L	9.5 OR 120% of upstream control station(s) at the same tide of the same day, whichever is higher		12.3 OR 130% of upstream control station(s) at the same tide of the same day, whichever is higher
Turbidity in NTU	9.7 OR 120% of upstream control station(s) at the same tide of the same day, whichever is higher		11.8 OR 130% of upstream control station(s) at the same tide of the same day, whichever is higher

Notes:

1. Wet season: April to September; Dry season: October to March.

2. For DO measurement, non-compliance occurs when the monitoring result is lower than the limits.

3. For parameters other than DO, non-compliance of water quality occurs when the monitoring result is higher than the limits.

4. Depth-averaged results are used unless specified otherwise.

5. SR1 is monitored for SS only.

6. All the figures given in the table are used for reference only and the EPD may amend the figures whenever it is considered as necessary.

3.2 Alert Levels

The Initial Alert levels for water quality at near stations are presented in Table 4.1.

Table 4.1: Calculated Initial Alert Levels

Alert Level	A1	A2	A3	A4	A5
Turbidity (NTU)	30.1	18.4	38.8	32.0	24.3
DO (mg/L) – Depth-average, Dry Season	4	4	4	4	4
	OR 0.1 mg/L less than the same day control, whichever is lower
DO (mg/L) – Bottom, Dry Season	2	2	2	2	2
	OR 0.1 mg/L less than the same day control, whichever is lower
DO (mg/L) – Depth-average, Wet Season	3	3	3	3	3
	OR 0.1 mg/L less than the same day control, whichever is lower
DO (mg/L) – Bottom, Wet Season	0.9	0.9	0.9	0.9	0.9
	OR 0.1 mg/L less than the same day control, whichever is lower

Note: Wet season: April to September; Dry season: October to March.

4 Monitoring Results

Marine water quality monitoring was conducted as scheduled during the reporting period. Graphical presentations of the monitoring results are provided in Appendix A.

The water quality monitoring results for turbidity and SS obtained during the reporting period were within their corresponding Action Levels, Limit Levels and Alert Levels.

For DO, some of the testing results at SR stations triggered the corresponding Action or Limit Levels. The IEC, Engineer and the construction contractor were informed of the exceedances and the Event and Action Plan of the Updated EM&A Manual was initiated. Table 5.1 presents the summary of the DO exceedances at SR stations during mid-ebb and mid-flood tide for the reporting period.

Table 5.1: Summary of DO Exceedances

Date	Parameter(s)	Affected Station(s)	Tide	Exceedance Type
22 May	DO (Surface & Middle)	SR9, SR10	Flood tide	Limit Level
25 May	DO (Surface & Middle)	SR10 SR10	Ebb tide Flood tide	Limit Level Limit Level
27 May	DO (Surface & Middle)	SR8, SR9	Flood tide	Limit Level
8 June	DO (Surface & Middle)	SR10 SR8, SR9, SR10	Ebb tide Flood tide	Limit Level Limit Level
10 June	DO (Surface & Middle)	SR10 SR8, SR9	Ebb tide Flood tide	Limit Level Limit Level
12 June	DO (Surface & Middle)	SR8	Flood tide	Limit Level
15 June	DO (Bottom)	SR6, SR7	Flood tide	Action Level
19 June	DO (Bottom)	SR2, SR4, SR5	Flood tide	Action Level
29 June	DO (Bottom)	SR10 SR5, SR6 SR5 SR10	Ebb tide Ebb tide Flood tide Flood tide	Action Level Limit Level Action Level Limit Level
13 July	DO (Bottom)	SR2, SR10	Ebb tide	Action Level

The investigation findings are summarised below:

● 22, 25 and 27 May and 8, 10, 12, 15, 19 and 29 June 2020 – dredging work was suspended during this period hence the causes are not related to the Project.

● 13 July 2020 – the contractor confirmed that no abnormal operation and spillage occurred and all required mitigation measures were implemented. The investigations found that the exceedance appeared to be due to local factors not related to the Project.

As all investigations concluded that the cases were not related to the Project, no further action was required.

5 Conclusion

Monitoring work for water quality was conducted during the reporting period in accordance with the updated EM&A Manual.

The water quality monitoring results for all parameters, except DO, obtained during the reporting period were within the corresponding Action, Limit or Alert Levels stipulated in the EM&A programme. For DO (surface, middle and bottom layers), some of the results triggered the relevant Action and Limit Levels, and investigations were conducted accordingly. The investigations concluded that the cases were not related to the Project. To conclude, the construction activities in the reporting period did not cause adverse impact to all water quality sensitive receivers.