3 WATER QUALITY

3.1 INTRODUCTION

The following Section provides details of the water quality monitoring to be undertaken by the ET during the installation of the gas pipelines to verify the distance of sediment plume dispersion and to identify whether the potential exists for any indirect impacts to occur to ecological sensitive receivers.

3.2 SAMPLING METHODOLOGY

3.2.1 Parameters Measured

The parameters to be measured in situ are:

* dissolved oxygen (DO) (% saturation and mg L-1)

* temperature

* turbidity (NTU)

* salinity (0/00)

The only parameter to be measured in the laboratory is:

* suspended solids (SS) (mg L-1)

In addition to the water quality parameters, other relevant data shall also be measured and recorded in field logs (Annex C), including the location of the sampling stations and pipeline jetting machine at the time of sampling, water depth, time, weather conditions, sea conditions, tidal state, current direction and speed, special phenomena and work activities undertaken around the monitoring and works area that may influence the monitoring results.

3.2.2 Equipment

For water quality monitoring, the following equipment shall be supplied and used by the contractor:

* 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 35 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 35 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.

* 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.

* 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.

3.2.3 Sampling / Testing Protocols

All in situ monitoring instruments shall be checked, calibrated and certified by a laboratory accredited under HOKLAS or any other international accreditation scheme before use, and subsequently re-calibrated at-monthly intervals throughout all stages of the water quality monitoring. Responses of sensors and electrodes shall be checked with certified standard solutions before each use. The turbidity meter shall be calibrated to establish the relationship between turbidity readings (in NTU) and levels of SS (in mg L-1) where possible.

For the on-site calibration of field equipment, the BS 1427: 1993, Guide to Field and On-Site Test Methods for the Analysis of Waters shall be observed. Sufficient stocks of spare parts shall be maintained for replacements when necessary. Backup monitoring equipment shall also be made available so that monitoring can proceed uninterrupted even when equipment is under maintenance, calibration etc. Water samples for SS measurements shall be collected in high density polythene bottles, packed in ice (cooled to 4o C without being frozen), and delivered to a HOKLAS laboratory as soon as possible after collection.

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.

3.2.4 Laboratory Analysis

All laboratory work shall be carried out in a HOKLAS accredited laboratory. Water samples of about 1,000 mL shall be collected at the monitoring and control stations for carrying out the laboratory determinations. The determination work shall start within the next working day after collection of the water samples. The analyses shall follow the standard methods as described in APHA Standard Methods for the Examination of Water and Wastewater, 19th Edition, unless otherwise specified (APHA 2540D for SS) with a detection limit of 1 mg L-1 or less.

The submitted information should include pre-treatment procedures, instrument use, Quality Assurance/Quality Control (QA/QC) details (such as blank, spike recovery, number of duplicate samples per-batch etc), detection limits and accuracy. The QA/QC details shall be in accordance with requirements of HOKLAS or another internationally accredited scheme.

3.2.5 Monitoring Locations, Frequency and Actions - Pilot Test

Introduction

In order to verify the modelling predictions in the EIA Report a pilot test will be established during jetting works at either the Tai Po landing point or on the HKSAR waters boundary, dependent on where jetting commences. The pilot test will consist of intensive water quality monitoring on the first three days of the jetting operation. For this intensive monitoring, the area covered will be 400 m either side of the pipelines alignment.

Stations

Three sets of monitoring stations will be arranged perpendicularly to the jetting alignment with respect to the three days monitoring. Monitoring locations will be fixed throughout the whole day of monitoring. The locations of the stations are illustrated in Figure 3.2a, the same protocol should be used at the HKSAR boundary should jetting works commence there first.

Should the works commence at Tai Po the monitoring will also examine the effect of the jetting operations on water quality at the WSD intake, which is 230 m from the pipelines alignment. During the pilot test the silt curtain, detailed in Figure 3.4a should not be used, instead a silt screen should be placed around the WSD intake. The details of the silt screen should be agreed in advance of the pilot test with WSD and EPD. The station representative of the WSD intake should be located outside the silt screen.

As there are no sensitive receivers in proximity to the alignment at the HKSAR boundary no additional stations will be examined other than those within 400 m from the jetting works.

Frequency

Monitoring should be conducted hourly of turbidity and every 3-hour on suspended solids (SS) for correlation (the methods for taking and analysing the samples should be as presented above).

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 6 m the mid-depth station may be omitted. If water depth is less than 3 m, only the mid-depth station will be monitored. Duplicate water samples shall be taken and analyzed at all monitoring stations.

Reporting

The turbidity monitoring results should be submitted on a daily basis and the SS results should be submitted within 24 hours of collection by the ET Leader to EPD, AFCD and WSD for review.

Actions

The results of the pilot test will be utilised to indicate how the jetting works are performing in comparison to the modelling predictions presented in the EIA. The results will act essentially as an early warning tool to advise the Contractor how the jetting machine is performing. Should the results indicate that the modelling predictions are being exceeded then the Contractor will be able to take remedial action, such as reductions in jetting speed, in order to ensure that exceedances of the appropriate Action and Limit levels for the Impact Monitoring do not occur in the more environmentally sensitive areas within Tolo Channel.

In order to guide the Contractor, ET Leader and IEC as to whether the jetting machine is performing according to the predictions in the EIA the following protocols should be adopted when analysing the results.

Commencement at Tai Po

Step 1 Analyse the results for the 3 days of monitoring to determine the range of SS values recorded at the WSD intake. The data analysis should focus on bed layer results as these are most relevant to the impact assessment on the key sensitive coral sites.

Step 2 The recorded values should then be compared with the predictions which are as follows:

* WSD Intake Bed Layer Dry Season (Jetting) = 20.68 mg L-1 (max elevation above ambient).

* WSD Intake Bed Layer Wet Season (Jetting) = 3.41 mg L-1 (max elevation above ambient).

As SS measurements are recorded in the laboratory as ( 1 mg L-1 the above values have been rounded up/down to 21 and 3 mg L-1 respectively.

Step 3 If the SS elevations are less than the values presented above then no further actions are required as a result of the pilot test. If the SS elevations are greater than the predictions over three consecutive monitoring events on any one day then the percentage deviations should be determined. For example if the pilot test takes place during the wet season and three consecutive elevations of 4 mg L-1 are recorded then the performance of the jetting machine can be seen to differ consistently by + 33 % from the EIA predictions. The data from the other monitoring stations should be examined to determine whether the jetting machine is the cause of the exceedance. If the station at the WSD intake is recording higher values than the station closest to the jetting machine then it may indicate that other factors have caused the exceedance at the WSD intake.

Step 4 Based on the findings of Step 3 the Contractor in conjunction with the ET Leader and IEC should decide on appropriate reductions to the jetting rate.

Commencement at the HKSAR Boundary

As there are no sensitive receivers in close proximity to the pipelines alignment no sensitive receiver stations can be monitored as can be done at Tai Po. Instead the analysis of results should focus solely on the pilot test stations (ie those presented in Figure 3.2a).

Step 1 Analyse the results for the 3 days of monitoring to determine the range of SS values recorded at the monitoring stations. The data analysis should focus on bed layer results at the stations located 400m from the jetting machine as these are most relevant to the impact assessment on the key sensitive coral sites.

Step 2 The recorded values should then be compared against the coral tolerance criterion of an elevation of 10 mg L-1 above ambient.

Step 3 If the SS elevations are less than the coral tolerance criterion then no further actions are required as a result of the pilot test. If the SS elevations are greater over three consecutive monitoring events on any one day then the percentage deviations should be determined. For example if the pilot test indicates that the 400m stations record three consecutive elevations of 12 mg L-1 then the performance of the jetting machine can be seen to differ consistently by + 20 % from the EIA predictions. The data from the other monitoring stations should be examined to determine whether the jetting machine is the cause of the exceedance. If the 400m stations record higher values than the stations closer to the jetting machine then it may indicate that other factors have caused the exceedances.

Step 4 Based on the findings of Step 3 the Contractor in conjunction with the ET Leader and IEC should decide on appropriate reductions to the jetting rate.

It should be noted that the Contractor is not obliged to reduce jetting rates based on the results of the pilot test but is strongly advised to review their working methods and take remedial measures. If remedial measures (ie reduction in jetting rates) are not implemented following a demonstration of poorer than expected performance of the jetting machine then it can be expected that exceedances of either Action or Limit levels will occur in the subsequent monitoring zone (ie Zone D if works commence at Tai Po or Zone B if works commence on the HKSAR boundary). Actions associated within exceedances of Action and Limit levels are discussed in Section 3.3 below.

3.2.6 Monitoring Locations & Frequency - Baseline & Post-Project Monitoring

Monitoring locations during the baseline work have been set up so that representative water quality data are gathered from the key areas along the pipelines alignment. The key areas are those referred to as Zones A, B, C and D where many sensitive receivers are present.

The following Table 3.1 presents a summary of the monitoring stations:

Table 3.1 Baseline and Post-project Monitoring Stations

Station Code	Nature of Station	Location	Coordinates X (HK Grid)	Coordinates Y (HK Grid)
A1	Control Station	Centre Island	840701.71	832767.91
A2	Control Station	Inner Tolo Harbour	837040.38	834316.23
A3	Impact Station	Fish Culture Zone	839270.90	834848.23
A4	Impact Station	Excavation site (WSD Intake)	837507.55	834575.95
B1	Control Station	Hoi Ha	851764.08	838090.46
B2	Gradient Station	Tolo Channel	846733.08	836317.45
B3	Control Station	Mirs Bay	852845.94	841657.46
B4	Control Station	Sham Chung Kok	846234.67	834058.42
C1	Impact Station	Tung Ping Chau Marine Park	861708.50	845987.19
C2	Control Station	North of route alignment	858576.76	846793.81
D1	Impact Station	Pak Sha Tau	843974.84	834766.98

Baseline monitoring prior to commencement of excavation works (for Zone A) and prior to jetting (for Zones A, B, C and D), Impact Monitoring (during works) and Post-project Monitoring (after completion of works) will be conducted at the fixed sampling stations shown in Figures 3.2b and c (and Table 3.1).

The baseline water quality monitoring will be undertaken three days per week at all fixed stations within Zones A, B, C and D, 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 post-project monitoring will comprise sampling on three occasions within a one week time period after completion of the three sets of works (ie excavation at Tai Po, Jetting in HKSAR waters, and Dredging in Mainland waters), at the same location as the Baseline Monitoring Stations during mid flood and mid ebb tides.

3.2.7 Monitoring Locations & Frequency - Impact Monitoring

The monitoring station locations have been established to determine the distance of sediment plume dispersion during installation of the pipelines and to identify potential impacts to ecological sensitive receivers.

During the pipeline installation works, water quality sampling will be undertaken in four areas along the pipelines route (within Zones A, B, C and D) as shown in Figure 3.2b. Duplicate water samples shall be taken and analyzed at all monitoring stations.

Zone A

This zone is located close to the landing point at Tai Po and will be monitored for two separate activities. The first activity will be excavation works at the Tai Po seawall and this will include control stations close to Centre Island (A1) and one within Inner Tolo Harbour (A2). Impact stations are located close to the WSD intake on the Tai Po seafront (A4) and at the Yim Tin Tsai Fish Culture Zone (FCZ) (A3) (Figure 3.2b). The second activity will be the jetting works within 2km of the Tai Po seawall. The same stations will be monitored. During jetting the stations will be monitored daily within a 3 hour window of 1.5 hour before or after mid-flood and mid-ebb tides. During seawall excavation works the stations will be monitored 3 days per week, at mid- flood and mid-ebb tides. The interval between two sets of monitoring should not be less than 36 hours.

Zone B

Zone B is to be monitored during jetting works in Tolo Channel. Stations for water quality monitoring have been established at each of the locations where ecological monitoring will take place as presented below in Table 3.2 and presented on Figure 3.2c.

Table 3.2 Water Quality Monitoring Locations within Zone B

Station	Location	Coordinates X	Y	Corresponding Ecology Monitoring Stations
Controls
B1	Hoi Ha Wan	851764.08	838090.46
B2	Tolo Channel	846759.64	836269.15
B3	Wong Chuk Kok	852845.94	841657.46
B4	Sham Chung Kok	846234.67	834058.42
Impact Stations
LFW1	Lo Fu Wat FCZ	846467.85	836626.30
WQI1	Wong Wan Tsui W	847911.76	837160.55	Impact - I1
WQI2	Wong Wan Tsui E	848527.83	837632.22	Impact - I2
WQI3	Fong Wang Fat	850193.14	838609.27	Impact - I3
WQI4	Gruff Head	851035.42	837906.57	Impact - I4
WQI5	Wong Chuk Kok South West	850809.21	839080.95	Impact - I5
WQI6	Wong Chuk Kok	851728.50	840043.55	Impact - I6
WQI7	Wong Chuk Kok N	852662.22	840751.07	Impact - I7
WQI8	Chek Chau	854582.63	840130.19	Control - C1
Gradient Stations
G1	Wong Wan Tsui W	847961.91	836999.41	Impact - I1
G2	Wong Wan Tsui E	848638.14	837413.60	Impact - I2
G3	Fong Wang Fat	850294.91	838444.86	Impact - I3
G4	Gruff Head	850759.81	838165.91	Impact - I4
G5	Wong Chuk Kok South West	850895.06	838952.03	Impact - I5
G6	Wong Chuk Kok	851934.76	839839.58	Impact - I6
G7	Wong Chuk Kok N	852805.41	840591.89	Impact - I7

The monitoring includes stations at the boundary of the Hoi Ha Wan Marine Park and close to ecologically sensitive coral habitats (eg Chek Chau). In addition to the stations mentioned above, one gradient station should be located between each of the Impact Stations and the jetting machine as depicted on Figure 3.2c.

The jetting machine will be moving within Zone B at a rate of no faster than 1.08 km day-1 and consequently the locations of the water quality monitoring are expected to change on a daily basis as illustrated on Figure 3.2c. The method will be such that the jetting machine approaches the first Kilometre Point (KP presented on Figure 3.2c) either in Mirs Bay (if the jetting machine is approaching from the NE) or in Tolo Channel (if the jetting machine is approaching from the SW) and this triggers water quality monitoring along a section of coastline. As the machine moves along and approaches the next KP the subsequent section of coastline is monitored for impacts to water quality. This process continues until the jetting machine is clear of Zone B. The KPs are set 2 km apart as the water quality modeling indicated that the effects of the jetting machine may extend 1-2 km either side of the jetting machine (as a result of the ebb and flood tides along Tolo Channel).

For the purposes of the first pass a more detailed monitoring protocol has been proposed whereby stations 2 km either side of the jetting machine are monitored. This protocol is presented in Table 3.3. After the 1st pass, monitoring at the coral sites may be reduced to 1km either side of the jetting machine if the monitoring data of the 1st pass indicate no impact when the jetting machine is more than 1km away from the coral sites. The reduction in monitoring must be agreed with EPD, AFCD and the IEC beforehand.

Table 3.3 Sequence of Water Quality Monitoring in the Tolo Channel Section (Zone B)

Location	Sequence of Monitoring	Gradient Stations	Control Stations
2km before/after KP0 E = 846975.82 N = 836107.91	LFW1, WQI1 and WQI2	B2, G1 and G2	B4
KP0 – KP 2 E = 846975.82 N = 836107.91	LFW1, WQI1 and WQI2	B2, G1 and G2	B4
KP2 – KP 4 E = 848675.42 N = 837136.72	WQI1, WQI2, WQI3, WQI4 and WQI5	G1, G2, G3, G4 and G5	B4
KP4 – KP 6 E = 850383.25 N = 838190.23	WQI2, WQI3, WQI4 and WQI5	G2, G3, G4 and G5	B1
KP6 – KP8 E = 851914.13 N = 839490.65	WQI3, WQI4, WQI5, WQI6 and WQI7	G3, G4, G5, G6 and G7	WQI8 and B1
KP8 E = 853432.65 N = 840799.30	WQI6 and WQI7	G6 and G7	WQI8 and B3
2km before/after KP8 E = 853432.65 N = 840799.30	WQI6 and WQI7	G6 and G7	WQI8 and B3

During jetting the stations will be monitored daily within a 3 hour window of 1.5 hour before or after mid-flood and mid-ebb tides.

Zone C

Zone C is to be monitored during jetting works within 2 km of the boundary of the Tung Ping Chau Marine Park. One impact station (C1) on the boundary of the Tung Ping Chau Marine Park and one control stations (C2) north of the alignment will be monitored. During jetting the stations will be monitored daily within a 3 hour window of 1.5 hour before or after mid-flood and mid-ebb tides. After the 1st pass, monitoring at the marine park may be reduced to 1km of the jetting machine if the monitoring data of the 1st pass indicate no impact when the jetting machine is more than 1km away from the marine park. The reduction in monitoring must be agreed with EPD, AFCD and the IEC beforehand.

Zone D

Zone D is to be monitored during jetting works 2 km either side of Pak Sha Tau. Two stations will be monitored at Pak Sha Tau (D1) as the impact station and B4 as a Control, as depicted on Figure 3.2a. During jetting the stations will be monitored daily within a 3 hour window of 1.5 hour before or after mid-flood and mid-ebb tides. After the 1st pass, monitoring may be reduced to 1 km of the jetting machine if the monitoring data of the 1st pass indicate no impact when the jetting machine is more than 1 km away. The reduction in monitoring must be agreed with EPD, AFCD and the IEC beforehand.

Tung Ping Chau

Water quality monitoring (as shown on Figure 4.2b) will take place when dredging works on the Mainland side are within 1 km of the HKSAR water boundary (Table 3.4). Monitoring will take place at gradient stations located on the HKSAR boundary, and impact station on the north of Tung Ping Chau and a control station at A Ma Wan within the Marine Park. The Contractor will notify the ET Leader two days before entering the zone marked on Figure 4.2b (1).

Ecological monitoring will also be conducted in this Zone.

Table 3.4 Location of Water Quality Monitoring Stations in Hong Kong for Dredging Activities in Mainland Waters

Station	Location	Coordinates X	Coordinates Y	Corresponding Ecological Monitoring Stations
WQ1	Tung Ping Chau	861694.09	846009.89	Impact – TPC1, TPC2
WQ2	A Ma Wan	862862.17	845175.55	Control – A Ma Wan
WQ3	Boundary East	861760.84	846894.29	N/a
WQ4	Boundary West	861160.11	846961.04	N/a

3.3 WATER QUALITY COMPLIANCE

Water quality monitoring will be evaluated against Action and Limit Levels (Table 3.5). Exceedance of the Action or Limit levels will result in changes to the monitoring and may result in changes to construction operations.

Table 3.5 Action and Limit Level for Water Quality

Area/Purpose	Parameter	Action Level	Limit Level
Zone A – Tai Po Landing Area
Zone A – water quality impacts to FCZ and WSD intake	DO in mgL^-1 (Surface, Middle, Bottom)	Data from impact stations (A3 and A4) show a depletion of 30% compared with corresponding data from control stations.	DO levels are <5 mgL^-1at the surface and middle depths or are <2 mgL^-1 for the bottom depth.
Zone A – water quality impacts to FCZ and WSD intake	SS in mgL^-1 (depth-averaged)	Impact stations exceed 95 percentile of baseline data (A1 – A4) or 120% of the control station’s SS at the same tide of the same day	WSD Intake Exceedance of the Limit Value = 10 mg L^-1. FCZ Exceedance of the Limit Value (calculated as mean value from baseline data obtained at all of the stations plus 10 mg L^-1).
Zone A – water quality impacts to FCZ and WSD intake	Turbidity in NTU (depth-averaged)	Impact stations exceed 95 percentile of baseline data (A1 – A4) or 120% of control station’s turbidity at the same tide of the same day	WSD Intake Exceedance of the Limit Value = 10 NTU. FCZ Exceedance of the Limit Value (calculated as mean value from baseline data obtained at all of the stations plus 10 NTU).
Zone B – Jetting within Tolo Channel
Zone B - water quality impacts to FCZ and corals	SS in mgL^-1 (depth-averaged for FCZ, bed layer for corals)	Impact stations exceed 95 percentile of baseline data (stations B1 – B4) or 120% of control station’s SS at the same tide of the same day. If gradient stations report lower SS values than impact stations then action level is not exceeded.	Exceedance of the Limit Value (calculated as mean value from baseline data obtained at all of the stations plus 10 mg L^-1).
Zone B - water quality impacts to FCZ and corals	Turbidity in NTU (depth-averaged for FCZ, bed layer for corals)	Impact stations exceed 95 percentile of baseline data (stations B1 – B4) or 120% of control station’s turbidity at the same tide of the same day. If gradient stations report lower NTU values than impact stations the action level is not exceeded.	Exceedance of the Limit Value (calculated as mean value from baseline data obtained at all of the stations plus 10 NTU^).
Zone B – water quality impacts to FCZ	DO in mgL^-1 (Surface, Middle, Bottom)	Data from impact station (LFW1) shows a depletion of 30% compared with corresponding data from control station (B4). If gradient station (B2) reports higher DO values than LFW1 the action level is not exceeded.	DO levels are <5 mgL^-1at the surface and middle depths or are <2 mgL^-1 for the bottom depth.
Zone C – Jetting in HKSAR water within 2 km of boundary of Tung Ping Chau Marine Park
Zone C - water quality impacts to the Marine Park	SS in mgL^-1 (bed layer)	Impact station (C1) exceeds 95 percentile of baseline data or 120% of control station (C2) SS at the same tide of the same day	Exceedance of the Limit Value (calculated as mean value from baseline data obtained at all of the stations plus 10 mg L^-1).
Zone C - water quality impacts to Marine Park	Turbidity in NTU (bed layer)	Impact station (C1) exceeds 95 percentile of baseline data or 120% of control station (C2) turbidity at the same tide of the same day	Exceedance of the Limit Value (calculated as mean value from baseline data obtained at all of the stations plus 10 NTU^).
Zone D – Jetting works within 2 km either side of Pak Sha Tau
Zone D - water quality impacts to corals	SS in mgL^-1 (bed layer)	Impact station (D1) exceeds 95 percentile of baseline data (B2) or 120% of control station (B2) SS at the same tide of the same day	Exceedance of the Limit Value (calculated as mean value from baseline data obtained at all of the stations plus 10 mg L^-1).
Zone D - water quality impacts to corals	Turbidity in NTU (bed layer)	Impact station (D1) exceeds 95 percentile of baseline data (B2) or 120% of control station (B2) turbidity at the same tide of the same day	Exceedance of the Limit Value (calculated as mean value from baseline data obtained at all of the stations plus 10 NTU^).
Tung Ping Chau Marine Park During Dredging on Mainland side within 1 km of boundary of HKSAR waters (see Figure 4.2b for locations)
Water quality impacts to the Marine Park	SS in mgL^-1 (bed layer)	Impact station (WQ1) exceeds 95 percentile of baseline data (C1 and C2) or 120% of control station ( WQ2) SS at the same tide of the same day. If gradient stations (WQ3 and WQ4) report lower SS values than impact stations then action level is not exceeded.	Exceedance of the Limit Value (calculated as mean value from baseline data obtained at all of the stations plus 10 mg L^-1).
Water quality impacts to Marine Park	Turbidity in NTU (bed layer)	Impact stations exceed 95 percentile of baseline data (C1 and C2) or 120% of control station’s turbidity at the same tide of the same day. If gradient stations (WQ3 and WQ4) report lower turbidity values than impact stations then action level is not exceeded.	Exceedance of the Limit Value (calculated as mean value from baseline data obtained at all of the stations plus 10 NTU^).

Action and Limit levels are used to determine whether operational modifications are necessary to mitigate impacts to water quality arising from excavation work at Tai Po or Jetting works in Tolo Harbour, Channel and Mirs Bay. In the event that the levels defined in Table 3.5, are exceeded, appropriate actions in Table 3.6 should be undertaken and a review of works should be carried out by the Contractor. This may include a combination of the following:

a) a review of operational controls as defined in the EIA;

b) a review of general mitigation measures such as working methods and practices; and

c) inspection of any plant or equipment suspected of contributing to the exceedance.

The Contractor should inform EPD, AFCD and WSD (Zone A only) of any actions taken in response to an Action or Limit Level exceedance that is attributable to the works. In addition, a record of all actions taken during each current month should be kept and forwarded to the Environmental Team, to be included in the EM&A monthly report.

For the jetting works it is expected that performance of the monitoring programme will be reviewed after the first jetting pass has been conducted with a view to stream lining the methodology and re-assessing the need for the Control Stations.

Table 3.6 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 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 EPD, WSD 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^(a); · 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, EPD, WSD and AFCD.	· If exceedance is attributed to the works consider and if necessary slow down (reduce dredging/jetting rate) or to stop all or part of the dredging/jetting activities until no exceedance of Limit Level.
Impacts attributable to works	· Inform contractor and contractor informs, EPD, WSD and AFCD.	· Comprehensive review of dredging/jetting operations; · Reduce dredging/jetting rates; and · Suspension of dredging/jetting operations.

Note:

(a) The critical review of working methods will include examination of: dredging volumes, dredging/jetting rates, and vessel types. Actions will include reducing dredging volumes and dredging/jetting rates, increasing dredging intervals, and, if necessary prohibiting the use of specific vessels.

* WSD should only be informed concerning the works in Zone A.

3.4 WATER QUALITY MITIGATION MEASURES

The impacts from jetting and dredging of the gas pipelines were assessed to be very localised and of short duration. The following operational constraints have been applied:

* The forward speed of the jetting machine should be limited to a maximum of 1.08 km day-1 (67.5 m hr-1 for 16 hours per day) in Tolo Harbour and Channel (as defined by the Tolo Harbour and Channel Water Control Zone) and 1.62 km day-1 in Mirs Bay (67.5 m hr-1 for 24 hours per day) (as defined by the Mirs Bay Water Control Zone).

* A trailer suction hopper dredger should conduct the dredging and only one dredger is allowed to dredge at any one time along the pipelines route.

* The dredging rate for the section within Mirs Bay should not exceed 11,880 m3 hour-1. The hourly rate of dredging may be increased subject to further detailed modelling investigations to be agreed with EPD in advance.

* No overflow is permitted from the trailer suction hopper dredger but the Lean Mixture Overboard (LMOB) system will be in operation at the beginning and end of the dredging cycle when the drag head is being lowered and raised.

* During jetting works within 2 km of the Tai Po Industrial Estate Seawall a silt curtain should be established as detailed in Figure 3.4a.

* Excavation works at the Tai Po Landing Site should be conducted within a silt curtain established as detailed in Figure 3.4a.

* Dredged marine mud shall be disposed of in a gazetted marine disposal area in accordance with the Dumping at Sea Ordinance (DASO) permit conditions.

The following good practice measures shall apply at all times:

* All trailers should be fitted with tight bottom seals in order to prevent leakage of material during transport.

* All trailers should be filled to a level, which ensures that material does not spill over during transport to the disposal site and that adequate freeboard is maintained to ensure that the decks are not washed by wave action.

* After dredging, any excess materials should be cleaned from decks and exposed fittings before the vessel is moved from the dredging area.

* The contractor(s) should ensure that the works cause no visible foam, oil, grease, litter or other objectionable matter to be present in the water within and adjacent to the dredging site.

* The design of the suction heads on suction dredgers should minimise over-break and sedimentation around the head.

* Dragheads should improve suction efficiency, thus reducing suction effect, for silty materials which contain significant quantities of organic material and natural gases.

* Degassing systems should be used to avoid irregular cavitation within the pump.

* The speed of the control pump should be carefully controlled to maximise the concentration where density of the transport mixture is critical.

* Monitoring and automation systems should be used to improve the crew's information regarding the various dredging parameters to improve dredging accuracy and efficiency.

* Control and monitoring systems should be used to alert the crew to leaks or any other potential risks.

* When the dredged material has been unloaded at the disposal areas, any material that has accumulated on the deck or other exposed parts of the vessel should be removed and placed in the hold or a hopper. Under no circumstances should decks be washed clean in a way that permits material to be released overboard.

* All pipe leakages should be repaired promptly and plant should not be operated with leaking pipes.

All dredgers should maintain adequate clearance between vessels and the seabed at all states of the tide and reduce operations speed to ensure that under turbidity is not generated by turbulence from vessel movement or propeller wash.

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(1) The start point of the zone illustrated on Figure 4.2b is 861836 (E), 847941 (N) (HK GRID).