4 WATER QUALITY ASSESSMENT

4.1 INTRODUCTION

This Section describes the impacts on water quality associated with the construction and operation of the submarine pipelines supplying gas from the LNG Receiving Terminal in Shenzhen to the Towngas Gas Production Plant in Tai Po. Computer modelling of sediment dispersion has been used to determine the impacts of jetting and dredging trenches for the submarine pipelines. The purpose of the assessment is to evaluate the acceptability of predicted impacts to water quality from the construction and operation of the gas pipelines. Impacts have been assessed with reference to the relevant environmental legislation and standards.

4.2 LEGISLATIVE REQUIREMENTS AND EVALUATION CRITERIA

The following relevant pieces of legislation and associated guidance are applicable to the evaluation of water quality impacts associated with the Project.

* Water Pollution Control Ordinance (WPCO); and

* Environmental Impact Assessment Ordinance (Cap. 499. S.16), Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM), Annexes 6 and 14.

Apart from the above statutory requirements, the Practice Note for Professional Persons, Construction Site Drainage (ProPECC PN 1/94), issued by ProPECC in 1994, also provides useful guidelines on the management of construction site drainage and prevention of water pollution associated with construction activities.

EIAO-TM

Annexes 6 and 14 of the EIAO-TM provide general guidelines and criteria to be used in assessing water quality issues.

The EIAO-TM recognises that, in the application of the above water quality criteria, it may not be possible to achieve the WQO at the source as there are areas which are subjected to greater impacts (which are termed by EPD as the mixing zones) where the initial dilution of a pollution input takes place. The definition of this area is determined on a case-by-case basis. In general, the criteria for acceptance of the initial dilution area is that it must not impair the integrity of the water body as a whole and must not damage the ecosystem or impact marine sensitive receivers (including migratory pathways of important species, beaches, breeding grounds or other beneficial uses).

Water Pollution Control Ordinance

Under the WPCO, Hong Kong waters are divided into 10 Water Control Zones (WCZs) each of which has a designated set of statutory Water Quality Objectives (WQOs) designed to protect the marine environment and it's users. The proposed route for the pipelines is located within the Tolo Harbour and Channel WCZ (which is divided into three sub-zones, Harbour, Buffer and Channel) and the Mirs Bay WCZ. The applicable WQOs associated with the WCZs are provided in Table 4.1.

Table 4.1 Water Quality Objectives

Parameter		Tolo Harbour and Channel WCZ						Mirs Bay WCZ
		Harbour		Buffer		Channel
Suspended Solids (SS)		No criteria established						SS should not be raised above ambient levels by in excess of 30% nor cause the accumulation of SS, which may adversely affect aquatic communities
Dissolved Oxygen (DO)	2 m of the bed	Not less than 2 mg L^-1		Not less than 3 mg L^-1	Not less than 4 mg L^-1			Not less than 2 mg L^-1 for 90% of the samples
	Other depths	The DO levels should not be less than 4 mg L^-1for the rest of the water column						The depth averaged DO should not be less than 4 mg L^-1 for 90% of the samples
	FCZ	At Fish Culture Zones the DO levels should not be less than 5 mg L^-1
Nutrients (measured as inorganic nitrogen)		No criteria established						Nutrients should not reach levels sufficient to cause excessive algal growth and annual mean depth averaged inorganic nitrogen should not exceed 0.3 mg L^-1
Unionised Ammonia (NH3-N)		No criteria established						The annual mean depth averaged unionised ammonia should not exceed 0.021 mg L^-1
Chlorophyll-a:		Chlorophyll-a should not exceed the following concentrations (calculated as a running arithmetic mean of 5 daily measurements for any location and depth).						None
		20 mg L^-1(mg/m^3)	10 mg L^-1 (mg/m^3)				6 mg L^-1 (mg/m^3)
Toxicants		Toxicants are not to be present at levels producing significant toxic effect

WQO's are also provided for temperature, pH and E. coli. However, as the installation of the pipeline will only result in disturbance of seabed sediments, which will not change temperature or pH and will not discharge sewage related bacteria to the WCZs, the criteria for these parameters are not considered applicable to this Project and are not discussed further.

Suspended Sediment Impacts

The WQO for suspended solids in marine waters of the Mirs Bay WCZ states that:

Waste discharges shall neither cause the natural ambient level to be raised by 30% nor give rise to accumulation of suspended solids which may adversely affect aquatic communities

There is, however, no quantitative WQO for suspended solids in the Tolo Harbour and Channel WCZ.

Analysis of EPD routine water quality data for the year 2000(1) for three monitoring stations in the Mirs Bay WCZ along the proposed route of the pipelines (Stations MM3, MM17 and MM5) has determined that the 90th percentile suspended solids concentrations range between 1.0 mg L-1 at the water surface to 9.8 mg L-1 near the sea bed, with 90th percentile depth average values between 2.4 mg L-1 and 4.1 mg L-1. These values would give an allowable increase in suspended sediment concentrations according to the WQO from the construction of the pipelines of 0.3 mg L-1 to 2.9 mg L-1 at the water surface and sea bed respectively, and up to 1.2 mg L-1 for depth average concentrations. These values are very low, and during any construction monitoring programme would be difficult to detect.

In view of the low background concentrations in the north eastern waters of Hong Kong an alternate assessment criterion of allowable increases in suspended solids concentrations of 10 mg L-1 has been adopted in previous projects. These projects included the EIAs for sand dredging at the proposed Eastern Waters Marine Borrow Area (2) and for uncontaminated mud disposal at the exhausted East Tung Lung Chau MBA (3). In addition, a 10 mg L-1 criterion was used as the limit level in the EM&A programme for suspended sediment impacts to coral areas during sand dredging at the West Po Toi MBA(4).

It is particularly relevant to make use of this assessment criterion for this Study because these previous projects were primarily concerned with the potential for impacts to ecologically sensitive areas (ie areas of high coral coverage, fish spawning areas, fish culture zones), which is the main concern with regard to suspended sediment impacts. This criterion will be adopted for both the Tolo Harbour and Channel WCZ, where there is currently no WQO for suspended solids.

This approach will thus allow a consistent assessment criterion to be applied throughout the length of the pipelines. It is proposed that the criterion be adopted for different layers in the water column, ie surface, middle and bed will be assessed separately, because it is to be expected that there will be significant vertical variations in suspended solids concentrations throughout the water column as a result of the construction works.

The increases in suspended sediment concentration due to the construction works will result in increased rates of sediment deposition onto the seabed. A suitable assessment criterion has been derived to ensure that there are no adverse impacts to benthic organisms (discussed below in Section 4.3.3).

4.3 BASELINE CONDITIONS AND WATER QUALITY SENSITIVE RECEIVERS

4.3.1 Hydrodynamics

The route for the proposed submarine gas pipeline passes through two hydrodynamically distinct areas, Tolo Harbour and Mirs Bay. Tolo Harbour is a long narrow tidal inlet, which expands to form a large bay at the landward end, into which a number of rivers and streams discharge, notably the Shing Mun River. Tidal currents are generally low, 0.1 to 0.2 ms-1, within Tolo Harbour, particularly towards the landward end. Along the outer, channel section, of the harbour the tidal currents are generally aligned parallel with the channel, while in the bay at the landward end large circulation patterns form. As a result of the low current speeds the flushing rate of the harbour is low and residence times for the waters are long. Wave activity within Tolo Harbour is not significant as the waters are sheltered by the surrounding hills and because waves from the open sea are not able to propagate up the harbour, due to the narrow seaward entrance.

In contrast, Mirs Bay is an area of open sea, which is exposed to the oceanic waters to the south. Tidal currents along the route of the proposed submarine pipeline within Mirs Bay are fairly low, with maximum speeds on large spring tides of approximately 0.25 ms-1. Further to the south, the tidal currents increase under the influence of the offshore oceanic current. The area is exposed to wave activity propagating up Mirs Bay from the south, such waves are characterised as being long period swell waves. During the dry season the north east monsoon winds may generate larger, shorter period waves within Mirs Bay.

4.3.2 Water Quality

Tolo Harbour and Channel

This water body is reported as having a gradient of improving water quality from the inner Harbour Subzone through to the outer Channel subzone (Table 4.2)(5). Salinity varies throughout the year from around 24 ppt in the wet season (summer) to 33 ppt in the dry season (winter) (depth averaged). Temperature also shows seasonal variations with lower values during the winter (16oC) than the summer (30oC) (depth averaged). The data indicate that stratification (a combination of a widespread thermocline and more localised haloclines as a result of outflow from the Shing Mun River and freshwater runoff from the surrounding hillsides) occurs in the summer months represented by lower dissolved oxygen (DO) concentrations in the lower part of the water column in the Tolo Buffer and Channel areas. The presence of stratified conditions has lead to non-compliance with the bed layer DO WQO at stations TM6 and TM8. As mentioned above, there is no WQO for suspended solids for the Tolo Harbour and Channel. The EPD data indicate that average levels are generally between 2 and 7 mg L-1 although peaks of up to 56.0 mg L-1 have been recorded in Tolo Channel.

Mirs Bay

The water quality conditions in Mirs Bay are considered to be very good by EPD with low turbidity, BOD, E. coli and nutrient levels and a high level of oxygenation (Table 4.2). In contrast to the Tolo Harbour and Channel, the salinity in Mirs Bay is less affected by the summer rains as the values range from 29 to 34 ppt. As the conditions in Mirs Bay are more oceanic, the water column is well mixed and largely unaffected by stratification. However, it is noted that in 1994 the inner Mirs Bay area experienced a large-scale hypoxia event, which was linked to widespread stratification of the water column. The EPD data indicate that no non-compliances with the WQOs were reported at the three stations along the alignment. The suspended solids levels varied from < 1 to 12 mg L-1 with averages of around 2 mg L-1 (Table 4.2).

Sediment Quality

EPD collects sediment quality data as part of the marine water quality monitoring programme. There are four monitoring stations in the vicinity of the proposed route for the pipelines in the Tolo Harbour and Channel WCZ and three relevant monitoring stations in the Mirs Bay WCZ. Data for these stations have been published in the latest marine water quality monitoring report and are presented in Table 4.3. The published data represents the range of values obtained in the period 1996 to 2000. In order to maintain a degree of conservatism in the modelling results only the maximum values will be used.

The routine EPD sediment quality monitoring data do not include values for TBT. The values for metals, PAHs and PCBs may be compared to the relevant sediment quality criteria specified in Environment Transport & Works Bureau Technical Circular No 34/2002 Management of Dredged/Excavated Sediment (ETWBTC 34/2002), in order to determine whether the concentrations of these parameters is a cause for concern. The sediment quality criteria are presented in Section 5.

Table 4.2 EPD Routine Water Quality Monitoring Data in the Vicinity of the Project Area

WQ Parameter	Tolo Harbour TM2	Tolo Harbour TM3	Tolo Harbour TM4	Tolo Buffer TM5	Tolo Buffer TM6	Tolo Channel TM7	Tolo Channel TM8	Mirs Bay MM3	Mirs Bay MM17	Mirs Bay MM5
Temperature (^oC)	23.6 (16.4 – 29.8)	23.5 (16.5 – 29.8)	23.4 (15.9 – 30.6)	23.8 (16.3 – 31.1)	22.9 (15.6 – 30.1)	23.1 (15.6 – 30.1)	22.4 (15.1 – 30.1)	22.7 (15.7 – 30.0)	22.4 (15.7 – 28.7)	22.5 (15.6 – 30.0)
Salinity (ppt)	29.1 (23.1 – 31.5)	30.5 (25.7 – 32.9)	30.4 (25.6 – 33.3)	30.2 (26.1 – 32.9)	31.1 (27.5 – 33.9)	31.1 (28.0 – 33.9)	31.7 (29.1 – 34.2)	31.7 (28.5 – 34.1)	31.9 (30.9 – 33.3)	32.0 (30.0 – 34.2)
Dissolved Oxygen (mg L^-1)	6.0 (5.0 – 10.1)	5.9 (4.5 – 10.4)	6.3 (5.1 – 10.3)	5.9 (5.6 – 9.9)	5.1 (2.7 – 11.4)	5.8 (3.8 – 9.3)	4.30 (2.3 – 9.5)	5.1 (4.1 – 9.3)	5.2 (3.0 – 8.3)	5.3 (4.6 – 8.1)
Dissolved Oxygen Bottom (mg L^-1)	6.2 (5.5 – 10.1)	5.8 (4.5 – 8.7)	6.2 (5.1 – 7.8)	6.3 (6.2 – 9.0)	2.9 (2.7 – 7.0)	4.1 (3.8 – 7.3)	2.8 (2.3 – 7.3)	4.8 (4.1 – 8.1)	4.9 (3.0 – 8.3)	5.0 (4.6 – 8.0)
5-Day Biochemical Oxygen Demand (mg L^-1)	2.4 (0.3 – 4.5)	1.8 (0.2 – 4.0)	1.9 (0.6 – 3.7)	1.8 (0.6 – 3.6)	1.6 (0.1 – 3.7)	1.5 (0.1 – 3.5)	1.0 (0.1 – 3.6)	0.9 (0.1 – 2.9)	1.2 (0.5 – 3.5)	1.0 (0.1 – 3.2)
Suspended Solids (mg L^-1)	6.8 (2.4 – 28.0)	3.3 (0.8 – 27.0)	2.7 (1.1 – 8.4)	4.1 (0.9 – 38.0)	2.0 (0.7 – 6.2)	4.7 (0.7 – 56.0)	2.0 (0.6 – 6.6)	2.2 (0.5 – 12.0)	2.0 (0.5 – 4.8)	2.1 (0.5 – 12.0)
Total Inorganic Nitrogen (mg L^-1)	0.212 (0.030 – 0.740)	0.083 (0.020 – 0.210)	0.081 (0.010 – 0.220)	0.052 (0.010 – 0.160)	0.073 (0.020 – 0.210)	0.064 (0.010 – 0.210)	0.073 (0.010 – 0.180)	0.0647 (0.0200 – 0.2000)	0.06 (0.03 – 0.10)	0.0586 (0.0200 – 0.1600)
Unionised Ammonia (mg L^-1)	0.00514 (0.00100 – 0.01700)	0.00356 (0.00100 – 0.01000)	0.00325 (0.00100 – 0.00800)	0.00217 (0.00100 – 0.00500)	0.00233 (0.00100 – 0.00600)	0.00219 (0.00100 – 0.00600)	0.00181 (0.00100 – 0.00500)	0.0018 (0.0010 – 0.0040)	0.002 (0.001 – 0.003)	0.0014 (0.0010 – 0.0030)
Chlorophyll a (mg L^-1)	14.2 (2.4 – 31.0)	11.2 (1.0 – 47.0)	10.8 (1.3 – 38.0)	7.3 (2.3 – 21.0)	5.9 (0.3 – 16.0)	7.1 (0.7 – 65.0)	3.2 (0.5 – 16.0)	3.2 (0.2 – 13.0)	4.0 (1.2 – 14.2)	2.5 (0.2 – 9.7)
E. coli (cfu 100mL^-1)	124.2 (12.0 – 5200.0)	8.3 (1.0 – 800.0)	7.4 (1.0 – 220.0)	5.1 (1.0 – 56.0)	2.2 (1.0 – 49.0)	1.2 (1.0 – 4.0)	1.1 (1.0 – 4.0)	1.2 (1.0 – 27.0)	1 (1 – 2)	1.1 (1.0 – 14.0)

Notes:

1. Data presented are depth averaged, except as specified.

2. Data presented are annual arithmetic mean except for E. coli, which are geometric means and dissolved oxygen, which are 10th percentile.

3. Data enclosed in brackets indicate the ranges.

4. Shaded cells indicate non-compliance with the WQOs.

Table 4.3 Summary of Sediment Quality Data for the Tolo Harbour and Channel WCZ and the Mirs Bay WCZ

Parameter	Tolo Harbour and Channel WCZ				Mirs Bay WCZ
	TS2	TS3	TS4	TS5	MS17	MS4	MS5
COD (mg kg^-1)	28,000	24,000	24,000	23,000	21,000	17,000	16,000
Total Carbon (% w/w)	1.2	0.9	1.0	1.1	1.0	0.8	0.9
Ammonia Nitrogen (mg kg^-1)	21	23	15	24	28	18	21
TKN (mg kg^-1)	740	640	820	890	690	640	640
Total Phosphorous (mg kg^-1)	250	190	240	270	240	260	290
Total Sulphide (mg kg^-1)	360	390	420	360	53	89	93
Arsenic (mg kg^-1)	13.0	12.0	9.8	9.7	10.0	7.4	8.7
Cadmium (mg kg^-1)	0.6	0.6	0.5	0.3	0.1	0.1	0.1
Chromium (mg kg^-1)	34	30	81	40	42	44	62
Copper (mg kg^-1)	71	97	38	26	19	18	22
Lead (mg kg^-1)	100	110	81	62	52	48	49
Mercury (mg kg^-1)	0.17	0.10	0.09	0.12	0.17	0.18	0.14
Nickel (mg kg^-1)	23	16	46	27	30	33	39
Silver (mg kg^-1)	<1.0	<1.0	<1.0	<1.0	<1.0	<1.0	<1.0
Zinc (mg kg^-1)	230	270	190	140	120	120	110
Total PCBs (µg kg^-1)	46	52	27	26	5	<5	<5
Low Molecular Wt PAHs (µg kg^-1)	21	31	32	46	8	13	14
High Molecular Wt PAHs (µg kg^-1)	64	71	132	112	96	84	70

A comparison of the data in Table 4.3 with the sediment quality criteria (Section 5 - Table 5.1) shows that the LCEL and UCEL values have been exceeded at a number of stations for a range of parameters. The parameters and stations where these critical values have been exceeded are shown in Table 4.4.

Table 4.4 Summary of Exceedance of Critical Values for Sediment Quality

Parameter	Stations where LCEL Exceeded	Stations where UCEL Exceeded
Arsenic	TS2, TS3	None
Cadmium	None	None
Chromium	TS4	None
Copper	TS2, TS3	None
Lead	TS2, TS3, TS4	TS3
Mercury	None	None
Nickel	TS4	TS4
Silver	None	None
Zinc	TS2, TS3	None
Total PCBs	TS2, TS3, TS4, TS5	None
Low Molecular Wt PAHs	None	None
High Molecular Wt PAHs	None	None
TBT

Sediments that have contaminant concentrations below the LCEL would not be considered to pose a threat to the marine environment and would be classified as being suitable for open sea disposal. Thus, it would not be necessary to use computer modelling to predict the release of contaminants from such sediments to the marine waters of the Study Area. Therefore, the release of only the following parameters will be simulated for different areas.

* Tolo Harbour and Channel WCZ, Harbour Subzone (Stations TS2 and TS3) - Arsenic, Copper, Lead, Zinc, Total PCBs;

* Tolo Harbour and Channel WCZ, Buffer Subzone (Station TS4) - Chromium, Lead, Nickel, Total PCBs; and

* Tolo Harbour and Channel WCZ, Channel Subzone (Station TS5) - Total PCBs.

For the Harbour Subzone, the larger of the two values at Stations TS2 and TS3 will be used as input to the water quality model. No exceedances were observed at the Mirs Bay stations along the alignment. TBT is not monitored by EPD, so background data for the assessment has been taken from ERM 1999(6). The discussion of impacts from release of contaminants during dredging/jetting is presented in Section 4.6.1 (Table 4.11).

4.3.3 Water Quality Sensitive Receivers

The sensitive receives that may be affected by changes in water quality during the installation of the submarine pipelines are listed in the Study Brief, discussed below and presented on Figure 4.3a. For each of the sensitive receivers, established threshold criteria or guidelines have been identified and the method of reviewing these sensitive receives (either through discrete points or contour plots) during the water quality modelling has been described. The shortest distances from the water quality sensitive receivers presented in Figure 4.3a (over the sea) to the pipeline route are detailed in Table 4.5.

Table 4.5 Shortest Distance to Sensitive Receivers

Specification	Name	Shortest Distance (m)
Marine Parks	Hoi Ha Wan (MP1)	600
	Yan Chau Tong (MP2)	4,240
	Tung Ping Chau (MP3)	1,200
Sites of Special Scientific Interest	Ting Kok (SSSI1)	2,670
	Kei Ling Ha Mangal (SSSI2)	3,200
Fish Culture Zones	Yim Tin Tsai (F1)	1,160
	Yim Tin Tsai East (F2)	1,050
	Yung Shue Au (F3)	3,600
	Tap Mun (F4)	4,000
	Sham Wan (F5)	6,500
Corals	Pak Sha Tau (C1)	520
	Lo Fu Wat S (C2)	700
	Lo Fu Wat N (C3)	600
	Lai Chi Chong (C4)	1,160
	Wong Wan Tsui (C5)	380
	Fung Wong Fat (C6)	430
	Gruff Head (C7)	600
	Wong Chuk Kok S (C8)	680
	Wong Chuk Kok (C9)	550
	Wong Chuk Kok N (C10)	810
	Chek Chau S (C11)	1,350
	Chek Chau N (C12)	1,400
	Tung Ping Chau (C13)	1,230
Beach	Sha Lan (B1)	2,730
	Lung Mei (B2)	3,060
	Hoi Ha Wan (B3)	3,820
Intakes	Water Supplies Department (WSD) (I1)	230
	Chinese University (I2)	880

Fish Culture Zones

There are several fish culture zones (FCZ) located within the northeastern waters of Hong Kong which are considered to be sensitive receivers. The FCZs within the area of expected influence of the Project include Yim Tin Tsai, Yim Tin Tsai (East), Yung Shue Au, Lo Fu Wat, Tap Mun, Kau Lau Wan, Sham Wan, Wong Wan, O Pui Tong and Sai Lau Kong. The only WQO that is specific to FCZs is for dissolved oxygen, which is set at no less than 5 mg L-1. In addition to dissolved oxygen there is a general water quality protection guideline for suspended solids (SS), which has been proposed by AFCD. The guideline requires that SS levels remain below 50 mg L-1. With regard to the water quality modelling, the FCZs were included as discrete points for evaluation in the assessment against the above criteria and guideline.

Fisheries Protection Areas

The waters of Tolo Channel and Long Harbour have been proposed by AFCD to be designated as a Fisheries Protection Area (FPA). Therefore, impacts to fisheries within Tolo Harbour and Channel were assessed and are discussed separately in the Fisheries Impact Assessment (Section 7).

To date there are no legislative standards for FPAs in Hong Kong. However, guideline values have been identified for fisheries and selected marine ecological sensitive receivers as part of the recent study for AFCD, Consultancy Study on Fisheries and Marine Ecological Criteria for Impact Assessment (CSFMEC)(7). The AFCD study recommends a maximum SS concentration of 50 mg L-1 (based on half of the no observable effect concentrations). Although a maximum concentration value is recommended, the study acknowledges that site-specific data should be considered on a case-by-case basis. With regard to the water quality modelling, impacts to these and other transitory or mobile sensitive receivers were not plotted as discrete points, rather, an assessment of potential impacts was undertaken through a review of the modelling contour plots and is discussed separately in the Fisheries Impact Assessment (Section 7).

Marine Ecological Resources

The following Marine Ecological Resources have been identified as water quality sensitive receivers.

Marine Parks

The three designated Marine Parks located within the Project area include:

* Hoi Ha Wan Marine Park (situated on the boundary of the Tolo Channel subzone and Mirs Bay WCZ);

* Tung Ping Chau Marine Park (situated within the Mirs Bay WCZ); and,

* Yan Chau Tong Marine Parks (situated within the Mirs Bay WCZ).

The marine parks were established for the purpose of marine nature conservation, outdoor recreation, education, tourism and scientific studies. Within the marine parks of Hoi Ha Wan, Tung Ping Chau and Yan Chau Tong there are marine ecological sensitive receivers, including coral communities and mangroves which are valued in Hong Kong. There is no specific legislative water quality criteria for Marine Parks, rather, the water quality at these sensitive receivers is typically compared with the WQO. However, criteria have been previously established for coral communities in Hong Kong which, in the absence of applicable WQOs, could be adopted for these sensitive receivers. The Marine Parks will be plotted as discrete points at their marine water boundary closest to the proposed pipelines for evaluation in the water quality assessment.

Artificial Reef Deployment Sites

There are a total of three proposed and gazetted Artificial Reef Deployment Sites (ARD) within the Project area:

* Yan Chau Tong ARD site (situated within the Yan Chau Tong Marine Park);

* Hoi Ha Wan ARD site (situated within the Hoi Ha Wan Marine Park); and,

* Long Harbour ARD site (Figure 2.2a).

The ARD sites are proposed as a fisheries resource enhancement tool to encourage growth and development of a variety of marine organisms. There is no specific water quality criterion for the ARD sites; rather, the water quality impacts associated with a Project are measured presently against compliance with the WQO. The two ARD sites located within the Designated Marine Parks will be covered under the discrete points established for the Marine Parks. The two marine park ARDs are closer to the proposed pipeline route than the Long Harbour ARD, so the latter will be assessed using the contour plots.

Sites of Special Scientific Interest/Special Areas

There are numerous Sites of Special Scientific Interest (SSSI) within the Project area, the majority of which are geological in nature. Only marine related SSSIs are considered as sensitive receivers for this Project including:

* Ting Kok (mangrove);

* Kei Ling Ha Mangal (mangrove);

* Hoi Ha Wan (corals); and

* Tung Ping Chau (corals).

Within the Project area there is a designated 'Special Area', Ma Shi Chau, due to geological features. Therefore, this site has not been considered to be a sensitive receiver. The potential for water quality impacts at SSSIs was measured against the Project's compliance with the WQO. The SSSIs that are considered to be marine sensitive receivers will be plotted as discrete points in the water quality model for evaluation in the water quality assessment.

Coral Communities

There are several areas of known coral communities in the vicinity of the pipeline route including Chek Chau, Fung Wong Fat, Wong Wan Tsui, Wong Chuk Kok Tsui, Hoi Ha Wan and Tung Ping Chau. Dive surveys were undertaken as part of this assessment to confirm other potential coral communities that should be considered as sensitive receivers. There are no established legislative criteria for water quality at coral communities; however, information on hard coral tolerances to SS indicate that a 20% reduction in annual growth rate corresponds to a 30% increase in average long-term background SS levels(8). In several studies, including those in the eastern waters of Hong Kong, an elevation criterion of 10 mg L-1 has been adopted as the critical value above which impacts to corals may occur(9)(10)(11)(12)(13). This criterion is utilised in this EIA assessment for determining the acceptability of impacts hard corals, soft corals and black corals. The criterion is considered to be protective of impacts to soft and black corals as these species are usually found in deeper water, that is often more turbid with lower light intensity, than hard corals. This is because hard corals require light for the zooxanthellae within their tissues to photosynthesise. Soft and black corals do not usually contain zooxanthellae and are therefore often found in much deeper and darker waters. This information is supported by the documented presence of soft and black corals in parts of Hong Kong waters than experience higher average turbidity and SS levels than areas where hard corals are recorded, eg the area in proximity to the Lamma Power Station (14), Green Island (15) and the Lamma Island (16).

The coral communities were plotted as discrete points for evaluation in the water quality assessment.

Impacts to hard coral communities have also been assessed with regard to sediment deposition. Hard or hermatypic corals are susceptible to increased rates of deposition, with the species sensitivities to sedimentation being determined largely by the particle-trapping properties of the colony and ability of individual polyps to reject settled materials. Horizontal platelike colonies and massive growth forms present large stable surfaces for the interception and retention of settling solids while vertical plates and upright branching forms are less likely to retain sediments. Tall polyps and convex colonies are also less susceptible to sediment accumulation than other growth forms. It is also acknowledged that sensitivities to sediment loads can also vary markedly between species within the same genus(17).

Information presented by Pastorok and Bilyard (1985)(18) has been regarded as the primary text when discussing the effects of sedimentation on corals. Pastorok and Bilyard have suggested the following criteria:

* 10 - 100 g m-2 day-1 slight to moderate impacts

* 100 - 500 g m-2 day-1 moderate to severe impacts

* > 500 g m-2 day-1 severe to catastrophic impacts

Fringing and inshore reefal environments, however, are known to experience sedimentation events in exceedance of the 500 g m-2 day-1 criterion and support flourishing coral communities(19). It is clear from the above that the adoption of strict criteria for impact assessment based on Pastorok & Bilyard's system of assessment for open water communities may well be overly protective in an environment such as Hong Kong. However, using a precautionary approach, it is proposed to adopt a value of 100 g m-2 day-1 as the assessment criterion for deposition, which is at the lower end of the range for moderate to severe impacts specified above, for the purposes of this Study. This criterion has been utilised in Hong Kong (Eastern Waters, West Po Toi) before and deemed to be sufficiently protective during EM&A (20) (21). It should be noted that exceedance of this value should trigger further assessment and should not be deemed to imply that damage would necessarily occur. The results from EM&A programmes in Hong Kong that have adopted 10 mg L-1 and 100 g m-2 day-1 have indicated that no adverse impacts to corals have occurred.

Non-Gazetted Bathing Beaches

There are three non-gazetted bathing beaches within Tolo Harbour and Channel, which have been identified in the Study Brief as sensitive receivers, these include Sha Lan, Lung Mei and Hoi Ha Wan. Water quality impacts are determined based on the compliance with the WQO. Bathing beaches have been plotted as discrete points for evaluation in the water quality assessment. The closest beach to the pipelines alignment is Sha Lan at a distance of approximately 2.3 km.

Seawater Intakes

The Tai Po Industrial Estate WSD seawater abstraction point and the Chinese University of Hong Kong (CUHK) seawater intake are located within the vicinity of the Project and are considered to be sensitive receivers. The WSD seawater intake is positioned within 3 m of the water surface. WSD maintain a set of water quality standards for abstracted seawater, which state that the allowable suspended solids concentration at the intake is to be less than 10 mg L-1. Water quality standards have also been set for no less than 2 mg L-1 for dissolved oxygen, less than 1 mg L-1 for ammoniacal nitrogen, less than 10 NTU for turbidity, and less than 10 mg L-1 for 5 day BOD. Analysis of the EPD routine water quality data at Stations TM3 and TM4, which are the closest to the two WSD intakes (22), has indicated a maximum suspended sediment concentration in the surface layer of 5.4 mg L-1. The SS criterion applied to the water intakes is 10 mg L-1 in total, including baseline levels. (Baseline value for the intakes will be taken from EPD's data for TM3, ie 3.3 mg L-1.)

With regard to the CUHK seawater intake, the seawater intake has been established for their recently relocated Marine Science Laboratory, situated within the Pak Shek Kok Science Park.

A summary of the assessment criteria to be applied for each sensitive receiver for this Project is presented in Table 4.6.

Table 4.6 Summary of Assessment Criteria for Water Quality Sensitive Receivers

Sensitive Receiver	Specific Assessment Criteria	Value
Fish Culture Zone (FCZ)	Dissolved oxygen Suspended Solids	No less than 5 mg L^-1 No more than 50 mg L^-1
Fisheries Protection Areas (FPA)	Suspended Solids	No more than 50 mg L^-1
Marine Parks, Artificial Reefs, SSSIs and Non-gazetted Bathing Beaches	Water Quality Objectives	See Table
Coral Communities (Hard, Soft and Black)	Sediment Deposition Suspended Solids	100 g m^-2 day^-1 No more than 10 mg L^-1 above ambient
Seawater Intakes	Suspended Solids Dissolved Oxygen Ammoniacal Nitrogen 5 day BOD	No more than 10 mg L^-1 No less than 2 mg L^-1 No more than 1 mg L^-1 No more than 10 mg L^-1

4.4 POTENTIAL SOURCES OF IMPACT

4.4.1 Construction Phase

The main impacts to water quality arising from this project relate to disturbances to the seabed during the construction period. As discussed in Section 3 the pipelines will be laid primarily using the injection jetting technique. The only sections to be dredged in Hong Kong waters is a section in Mirs Bay across the Yantian Fairway. The pipelines will be protected at certain sections along the alignment with a protective rock armour cover. The jetting, dredging and to an extent the backfilling will result in the loss of sediments and backfill material into the water column where they will add to the suspended sediment load.

The jetting process results in a fluidised mixture of water and sediment being formed close to the seabed. The concern with regard to water quality would be if these suspended sediments were to be transported away from the works area to impact the surrounding waters and nearby sensitive receivers. In practice, the levels of SS diminish rapidly as the sediment plume disperses.

Along a certain section of the submarine pipeline route in Mirs Bay, the pipeline will be armoured to prevent damage by vessels dropping their anchors. Along this section a trench will be dredged and the pipeline lowered into the trench. The trench will then be backfilled with rock materials to provide adequate protection from damage. The potential impacts to water quality from this operation will be the same as those for dredging the approach to Cheng Tou Jiao, Shenzhen. There will be no impacts to water quality from backfilling the trenches with rock because this material is granular (ie does not contain fine cohesive sediments) and does not contain contaminants.

Associated with the elevated suspended sediment concentrations from both jetting and dredging, is the potential release of contaminants to the water column. As the sediment is suspended its oxygen demand will be exerted on the water column, if either the oxygen demand is high or the suspended sediment concentrations are high then the resulting decreases in dissolved oxygen could be unacceptable. The seabed sediments contain nutrients, mainly in the form of nitrogen compounds. These nutrients may be released to the water column once the sediments are suspended, causing increases in concentrations of nutrients in the receiving waters. This may then in turn increase the risk of greater algal growth and possibly algal blooms. Any increase in nutrient concentrations would be of most concern in Tolo Harbour, because this area is already subject to high rates of algal growth and the risk of algal blooms is higher as a consequence. Other compounds, such as metals, may desorb from the suspended sediments and dissolve into the receiving waters. Such contaminants in marine waters would be of concern if concentrations reached threshold levels (such as those defined by EU water quality criteria).

During the dredging works in Mirs Bay it is possible that water quality impacts could occur through accidental spillage during transport of the dredged material to the disposal site. Although these impacts would be expected to be minor as only a portion of the material in the barge would be lost, a series of measures have been recommended in Section 4.7 (and Annex G - Implementation Schedule) that the Contractor will be expected to comply with. Adherence to these specific, good practice measures, will ensure that dredged materials are not lost during transport and that water quality impacts do not occur.

The Project does not entail significant land based works to install the pipelines or construct the Gas Receiver Station. These facilities will be installed and constructed on reclaimed land at Tai Po. The main water quality issues will be to prevent run-off from the site and minimise suspended sediment loads washed out in stormwater as well as control wastewater streams such as temporary sewage facilities.

With respect to the operation of the gas pipelines, no adverse operational water quality impact is envisaged. Operational impacts are discussed further in Section 4.6.3.

4.5 ASSESSMENT METHODOLOGY

4.5.1 Introduction

The assessment methodology is presented in Annex B and has been based on the information presented in Section 3 - Project Description. The simulation of impacts to water quality has been undertaken through application of the DELFT 3D suite of water quality models. The models have been used to simulate the hydrodynamic conditions along the pipeline route, the dispersion of sediment from the jetting and dredging works, and the consequent effects on water quality. The DELFT 3D water quality model has been used to ensure the accuracy of the simulations. The use of the water quality model also allows for the effects of the installation activities on dissolved oxygen and phytoplankton biomass to be simulated.

4.5.2 Scenarios

The scenarios examined in the assessment have included the following:

* Jetting within Tolo Harbour and Channel during the Dry Season;

* Jetting within Tolo Harbour and Channel during the Wet Season;

* Jetting in Mirs Bay during the Dry Season;

* Jetting in Mirs Bay during the Wet Season;

* Trailer Dredging in Mirs Bay during the Dry Season; and,

* Trailer Dredging in Mirs Bay during the Wet Season.

Full details on the scenarios are presented in Annex B, along with the results.

4.5.3 Simulation of Cumulative Impacts

At present there are no planned marine projects that could have cumulative impacts with the construction of the pipelines. At the LNG terminal at Cheng Tou Jiao there will be dredging works for an access channel and turning circle in Mainland waters, but these works will be constructed prior to the works for the pipelines. The Hongkong Electric Company's (HEC) pipeline will pass close to the Towngas pipeline route, but the construction for the HEC pipeline will not occur concurrently with that for the Towngas pipeline due to the limited working area preventing simultaneous works. ERM has, however, conducted an assessment of the water quality impacts of the two projects being constructed simultaneously. The findings are presented in Annex B and indicate that no adverse impacts would be expected.

The Civil Engineering Department is also planning minor reconstruction works for a public ferry on the island of Tung Ping Chau. Although a detailed programme is not available it is possible that the works will overlap with the pipelines installation. However, this is not expected to cause a cumulative impact as the pier reconstruction works are minor in scale and are expected to cause minimal disturbance to water quality that will not extend far beyond the specific works area. There is also a small reclamation being conducted by the Civil Engineering Department at Ma Liu Shiu in Tolo Harbour. The project is due for completion in November 2004 and consequently is not expected to overlap with any of the major marine works for the proposed project.

4.6 WATER QUALITY IMPACT ASSESSMENT

4.6.1 Impacts During Jetting/Dredging

Impacts from the dispersion of sediment in suspension arising from the installation of the pipeline using injection jetting have been assessed using computer modelling.

Suspended Sediment

Impacts from suspended sediment may be caused by the transport of sediment plumes to sensitive areas such as fish culture zones, coral etc. A number of such areas have been defined as sensitive receivers along the pipelines alignment (Figure 4.3a).

Sediment plumes will cause the ambient suspended sediment concentrations to be elevated and the level of the elevation will determine whether the impact is adverse or not. The determination of the acceptability of any elevations is determined based on the criteria defined in Section 4.3.

The modelling simulated the release of sediment during jetting in the wet and dry seasons (at present it is planned that the jetting works will take place during the wet season). The results have been presented as contours of maximum suspended sediment concentrations above ambient at the surface, middle and bed layers of the water column (Annex B). In addition, tables of elevations at the sensitive receivers are presented for surface, middle and bed layers of the water column and, depth averaged in Table 2.1 of Annex B.

Coral Areas

The contour plots of maximum increases in SS concentrations above background are shown in Figures 2.1a to 2.1d in Annex B. The plumes arising from the jetting works are comparable in both seasons as the horizontal spread of the plumes and their confinement to the bed layer are largely similar. The plumes generated during the dredging works are confined to the alignment of the pipelines with concentrations decreasing with distance from the jetting works. The contour plots indicate that at some of the coral sensitive receiver locations, the concentrations of SS in the bed layer may exceed the criterion of 10 mg L-1 elevation. This was examined further by analysing the predictions at each of the coral locations and the time series plots of SS increases over time. The contour plots of the dredging works indicated that the SS plumes were confined to open waters and did not impinge on any coastlines in Hong Kong waters (Mainland waters are discussed below). Sediment deposition predictions at the coral sensitive receivers are discussed below.

The maximum increases in SS concentrations above background at the sensitive coral areas are given in Table 4.7 for both the wet and dry seasons for both construction methods. The results indicate that at all of the 13 coral sensitive receivers the maximum depth averaged SS elevations comply with the tolerance criterion of 10 mg L-1 elevation.

The time series plots (Figure 2.1e - h in Annex B) indicate that elevations of SS occur over very short periods, ie 6 to 12 hours and that concentrations return rapidly back to levels of less than 1 to 2 mg L-1. The significance of these elevations has been discussed in further detail in Section 6, with the conclusion that the impacts to hard, soft and black corals are not expected to be unacceptable due to the short-term nature of the elevations.

Marine Parks, Proposed & Gazetted Artificial Reef Deployment Areas

The contour plots indicate that the sediment plumes from both dredging and jetting do not affect any of the Marine Parks at their boundaries and hence do not affect the artificial reef sites. Concentrations at the boundary points were taken from the modelling results and are presented in Table 4.8 and indicate that the maximum depth averaged SS elevations comply with the Mirs Bay WQO tolerance level of 1.20 mg L-1 (for Yan Chau Tong and Tung Ping Chau). The depth averaged elevation at the boundary of Hoi Ha Wan Marine Park (not covered by the Mirs Bay WQO) was 1.17 mg L-1 which is within the acceptable range (Table 4.8). The results of the modelling exercise indicate that neither the dredging or the jetting works will cause unacceptable elevations in SS within the Marine Park boundaries. Consequently, the sensitive hard corals, soft corals and black corals present within each of the Marine Parks (Tung Ping Chau, Hoi Ha Wan, Yan Chau Tong) will not be adversely impacted by either the dredging (in both Hong Kong and Mainland waters) or jetting operations.

Fish Culture Zones

Plumes of SS dispersed from the construction works do not affect any of the Fish Culture Zone (FCZ) sensitive receivers at concentrations greater than 50 mg L-1 (tolerance threshold for culture fish). The maximum depth averaged SS elevations at each of the FCZs is less than 3 mg L-1, which is well within the acceptable range and is not expected to cause unacceptable impacts (Table 4.8).

Sites of Special Scientific Interest

Two Sites of Special Scientific Interest (SSSIs), Ting Kok and Kei Ling Ha Mangal, have been included in the modelling exercise. Both of these sensitive receivers were designated for the ecologically important mangroves and mud flats located there. As both of these SSSIs are located remotely from the pipelines alignments, impacts were not expected. This statement has been confirmed by the modelling work which indicates that the maximum depth averaged SS elevations at these locations are less than 1 mg L-1 and therefore well within acceptable levels (Table 4.9).

Beaches

Three non-gazetted beaches are located within the area of interest, Sha Lan and Ha Mei (close to the Ting Kok SSSI) and Hoi Ha in the Marine Park. As all of these beaches are located remotely from the pipelines alignments, impacts were not expected. This statement has been confirmed by the modelling work which indicates that the maximum depth averaged SS elevations at these locations are less than 0.1 mg L-1 and can be considered to be undetectable and therefore acceptable (Table 4.9).

Table 4.7 Maximum Increases in Suspended Sediment Concentrations above Ambient (mg L^-1) at Coral Sensitive Receivers

Sensitive Receiver	C1 Pak Sha Tau	C2 Lo Fu Wat S	C3 Lo Fu Wat N	C4 Lai Chi Chong	C5 Wong Wan Tsui	C6 Fung Wong Fat	C7 Gruff Head	C8 Wong Chuk Kok S	C9 Wong Chuk Kok	C10 Wong Chuk Kok N	C11 Chek Chau S	C12 Chek Chau N	C13 Tung Ping Chau
Allowable Elevation (Standard)^(1)	10	10	10	10	10	10	10	10	10	10	10	10	10
Jetting – Dry Season Surface	2.44	0.64	0.52	0.20	0.17	0.05	0.06	0.01	<0.01	<0.01	<0.01	<0.01	<0.01
Middle	3.15	0.75	0.67	0.24	0.27	0.19	0.15	0.07	0.18	0.01	0.01	0.02	0.00
Bed	3.91	0.76	0.78	0.27	1.06	2.69	3.68	2.23	6.16	1.67	1.28	0.37	0.12
Depth Average	3.09	0.72	0.64	0.24	0.46	0.88	1.17	0.69	1.90	0.50	0.39	0.12	0.04
% of Standard	30.9%	7.2%	6.4%	2.4%	4.6%	8.8%	11.7%	6.9%	19%	5%	3.9%	1.2%	0.4%
Jetting – Wet Season Surface	<0.01	<0.01	0.01	<0.01	<0.01	0.06	<0.01	<0.01	<0.01	<0.01	0.00	<0.01	0.01
Middle	0.03	0.03	0.17	0.15	0.10	1.17	0.03	0.04	0.01	<0.01	<0.01	<0.01	0.26
Bed	5.07	1.24	1.25	1.87	2.45	8.73	1.32	2.52	4.55	0.20	0.08	0.23	0.91
Depth Average	1.53	0.38	0.43	0.61	0.77	2.99	0.40	0.77	1.37	0.06	0.03	0.07	0.35
% of Standard	15.3%	3.8%	4.3%	6.1%	7.7%	29.9%	4%	7.7%	13.7%	0.6%	0.3%	0.7%	3.5%
Dredging – Dry Season Surface	0.00	0.00	0.00	0.00	0.00	<0.01	0.00	<0.01	<0.01	0.00	0.00	<0.01	<0.01
Middle	0.00	0.00	0.00	0.00	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	0.02	0.08	<0.01
Bed	0.00	0.00	0.00	0.00	<0.01	<0.01	<0.01	0.02	0.17	0.97	0.31	1.2	0.04
Depth Average	0.00	0.00	0.00	0.00	0.0	0.00	0.00	0.01	0.05	0.29	0.09	0.39	0.01
% of Standard	0%	0%	0%	0%	0%	0%	0%	0.1%	0.5%	2.9%	0.9%	3.9%	0.1%
Dredging - Wet Season Surface	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	<0.01	0.00
Middle	0.00	0.00	0.00	0.00	0.00	0.00	0.00	<0.01	<0.01	<0.01	<0.01	<0.01	0.00
Bed	0.00	0.00	0.00	0.00	<0.01	<0.01	<0.01	<0.01	0.04	0.43	0.22	0.83	0.06
Depth Average	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.01	0.13	0.07	0.25	0.02
% of Standard	0%	0%	0%	0%	0%	0%	0%	0%	0.1%	1.3%	0.7%	2.5%	0.2%

(1) Standard of 10 mg L-1 elevation is for Coral Sensitive Receivers

Table 4.8 Maximum Increases in Suspended Sediment Concentrations above Ambient (mg L^-1) at Marine Parks and Fish Culture Zones

Sensitive Receiver	MP1 Hoi Ha Wan	MP2 Yan Chau Tong	MP3 Tung Ping Chau	F1 Yim Tin Tsai W	F2 Yim Tin Tsai E	F3 Yung Shue Au	F4 Tap Mun	F5 Sham Wan
Allowable Elevation^(1)(2)	1.2	1.2	1.2	<50	<50	<50	<50	<50
Jetting – Dry Season Surface	0.06	0.00	0.00	0.17	1.91	<0.01	0.00	0.00
Middle	0.15	0.00	<0.01	0.31	2.75	<0.01	<0.01	0.00
Bed	3.68	0.00	0.01	2.32	3.74	<0.01	<0.01	0.00
Depth Average	1.17	0.00	0.00	0.86	2.71	0.00	0.00	0.00
% of Standard	97.5%	0%	0%	8.3%	12%	0%	0%	0%
Jetting – Wet Season Surface	<0.01	0.00	<0.01	0.00	<0.01	0.00	0.00	0.00
Middle	0.03	0.00	0.04	<0.01	<0.01	0.00	0.00	0.00
Bed	1.32	0.00	0.09	2.40	0.19	0.00	<0.01	0.00
Depth Average	0.40	0.00	0.04	0.72	0.06	0.00	0.00	0.00
% of Standard	33.3%	0%	3.3%	8%	6.7%	0%	0%	0%
Dredging – Dry Season Surface	0.00	0.00	<0.01	0.00	0.00	0.00	0.00	0.00
Middle	<0.01	0.00	<0.01	0.00	0.00	0.00	0.00	0.00
Bed	<0.01	0.00	2.71	0.00	0.00	0.00	<0.01	0.00
Depth Average	0.00	0.00	0.82	0.00	0.00	0.00	0.00	0.00
% of Standard	0%	0%	68.3%	0%	0%	0%	0%	0%
Dredging - Wet Season Surface	0.00	0.00	<0.01	0.00	0.00	0.00	0.00	0.00
Middle	0.00	0.00	<0.01	0.00	0.00	0.00	0.00	0.00
Bed	<0.01	0.00	1.61	0.00	0.00	0.00	<0.01	0.00
Depth Average	0.00	0.00	0.48	0.00	0.00	0.00	0.00	0.00
% of Standard	0%	0%	40%	0%	0%	0%	0%	0%

(1) For Marine Parks the Water Quality Objective is applied which is 30% above ambient, ie 1.2 mg L-1 (see Section 4.2 for details).

(2) For Fish Culture Zones the standard applied is a total of 50 mg L-1. The baseline values for the FCZs are calculated as 3.3 mg L-1 for F1 and F2, 4.1mgL-1 for F3, 2.0mgL-1 for F4 and F5 (from Table 4.2).

Table 4.9 Maximum Increases in Suspended Sediment Concentrations above Ambient (mg L^-1) at SSSIs, Beaches and Intakes Sensitive Receivers

Sensitive Receiver	SSI1 Ting Kok	SSI2 Kei Ling Ha	B1 Sha Lan	B2 Lung Mei	B3 Hoi Ha Wan	I1 Tai Po IE	I2 Pak Shek Kok
Allowable Elevation^(1)(2)	1.2	1.2	1.2	1.2	1.2	<10	<10
Jetting – Dry Season Surface	0.04	<0.01	<0.01	0.01	0.00	<0.01	0.04
Middle	0.06	<0.01	<0.01	0.02	0.00	0.17	0.05
Bed	0.08	<0.01	0.01	0.03	0.00	20.68	0.76
Depth Average	0.06	0.00	0.00	0.02	0.00	6.25	0.26
% of Standard	5%	0%	0%	1.7%	0%	95.5%	35.6%
Jetting – Wet Season Surface	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Middle	0.00	0.00	0.00	0.00	0.00	<0.01	0.00
Bed	<0.01	0.00	<0.01	<0.01	<0.01	3.41	0.92
Depth Average	0.00	0.00	0.00	0.00	0.00	1.02	0.28
% of Standard	0%	0%	0%	0%	0%	43.2%	35.8%
Dredging – Dry Season Surface	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Middle	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Bed	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Depth Average	0.00	0.00	0.00	0.00	0.00	0.00	0.00
% of Standard	0%	0%	0%	0%	0%	0%	0%
Dredging - Wet Season Surface	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Middle	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Bed	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Depth Average	0.00	0.00	0.00	0.00	0.00	0.00	0.00
% of Standard	0%	0%	0%	0%	0%	0%	0%

(1) For SSSIs and Beaches in Tolo Harbour and Channel there is no Water Quality Objective for SS. Consequently the Mirs Bay WQO allowable elevation of 1.2 mg L-1 has been adopted (ie 1.2 mg L-1).

(2) For intakes the standard applied is a total of 10 mg L-1. The baseline value for the intakes is taken from EPD's data for TM3 (as presented in Table 4.2) of 3.3 mg L-1.

Water Intakes

There are two water intakes in the area of interest, at the Tai Po Industrial Estate (approx 230 m from pipelines) and at the Marine Laboratory of the Chinese University (880 m from pipelines). The maximum depth averaged SS elevations at the Marine Laboratory were considered to be undetectable (< 0.01 mg L-1) (Table 4.9). At the Tai Po Industrial Estate the maximum depth averaged SS elevations from the jetting works do not exceed the intake criterion of (10 mg L-1) (Table 4.9).

Although no exceedances are predicted, given the low level of the intake in the water column and the shallow water depth at the site, Towngas has elected as a precautionary measure to install a silt curtain during jetting works within 2 km of the seawall at Tai Po (Figure 4.6a).

Elevations in Mainland Waters

The jetting works will take place up to the boundary of HKSAR waters and then dredging works will proceed to the landing point at the LNG terminal at Cheng Tou Jiao. Three locations have been included in the model representing sensitive receivers on the Shenzhen coastline. The locations of the sensitive receivers were taken from the EIA Report produced for the State Oceanic Administration and include beaches and fisheries areas (23).

The highest maximum depth averaged SS elevations were reported for the PRC1 sensitive receiver of 0.46 mg L-1 in the dry season and 0.17 mg L-1 in the wet season. The depth averaged concentrations at the other sensitive receivers were considered to be undetectable (< 0.1 mg L-1) (Table 4.10) and also do not affect the Marine Park at Tung Ping Chau.

Table 4.10 Maximum Increases in Suspended Sediment Concentrations above Ambient (mg L^-1) in Mainland Waters

Sensitive Receiver	PRC1 mg/l	PRC2 mg/l	PRC3 mg/l
Jetting – Dry Season Surface	0.00	0.00	0.00
Middle	0.00	0.00	0.00
Bed	0.00	0.00	0.00
Depth Average	0.00	0.00	0.00
Jetting – Wet Season Surface	0.00	0.00	0.00
Middle	0.00	0.00	0.00
Bed	0.00	<0.01	0.00
Depth Average	0.00	0.00	0.00
Dredging – Dry Season Surface	0.35	0.18	0.02
Middle	0.47	0.26	0.03
Bed	0.60	0.34	0.03
Depth Average	0.46	0.25	0.03
Dredging - Wet Season Surface	0.00	0.00	0.00
Middle	<0.01	0.00	0.00
Bed	0.57	<0.01	0.00
Depth Average	0.17	0.00	0.00

Fisheries Protection Areas

There are two proposed Fisheries Protection Areas (FPAs) within the Study Area at Long Harbour and in Tolo Channel. Impacts to the FPA in Long Harbour have been avoided through the routing of the pipelines. However, the pipelines pass directly through the Tolo Channel FPA. The elevations of SS within this FPA are confined largely to the pipelines alignment and overall depth averaged values are less than 25 mg L-1. The significance of the results to fisheries resources have been discussed in Section 7.5 with the conclusion that the impacts to the FPA through elevated SS levels are considered to be of low severity and of short duration.

Sediment Deposition

The information presented in the contour plots (Figures 2.1a to 2.1d in Annex B) illustrates that the SS concentrations decrease rapidly from the pipelines alignment. This indicates that the majority of the suspended sediments settle onto the seabed in the immediate vicinity of the works. The modelling exercise produced contour plots of sediment deposition in the study area as a result of the dredging and jetting works (Figures 2.2a to 2.2f in Annex B). The installation works are a moving source so the results have been presented as the maximum amount of deposition (g m-2) at each sensitive receiver. The deposition event will occur over a short period of time (2 - 3 days) so the often used approach in EIAs in Hong Kong of expressing deposition as an average for g m-2 day-1 is not considered appropriate.

The contour plots indicate that sediments from the dredging works in both the dry and wet seasons stay in close proximity to the pipelines alignment where concentrations exceed 200 g m-2 for the event. Sediment does not, however, reach any of the sensitive receivers.

Sediment from the jetting works deposits in a similar fashion to that from the dredging works. Given the high ecological value of some of the coral sensitive receivers (C5 - C10 Section 6) the water quality model was refined to give greater resolution in the NE part of Tolo Channel where these sensitive receivers are located. The resolution of the refined grid is shown on Figures 1.2a - 1.2e in Annex B and has a resolution of 50 m perpendicular to the pipelines route. For the remainder of the pipeline route the existing model was utilised. The sediment deposition contours for the refined model indicated that for C5 to C10 the levels were less than 20 g m-2 during both dry and wet seasons, which is within the coral tolerance threshold of 100 g m-2.

The water quality modelling works have indicated that for both the dry and wet seasons, the construction works can proceed at the recommended working rates without causing unacceptable impacts to water quality sensitive receivers through either elevations of suspended sediment or deposition of sediment.

Water Quality

The loss of sediment to suspension during jetting may have chemical effects on the receiving waters, as the sediment may contain organic and chemical pollutants. The modelling approach has, as described in Section 4.5, simulated the release of nutrients into the water column and examined the subsequent effects on levels of dissolved oxygen, chlorophyll a and nutrients (as total inorganic nitrogen and unionised ammonia). The simulations have also examined the effects of the release (via desorption) of micro-pollutants from the sediment to the water column.

The results of the modelling are presented in Annex B and indicate that neither the dredging nor the jetting works cause unacceptable impacts to water quality. The results indicate that the levels of chlorophyll a, TIN and ammonia do not change appreciably from background conditions and are compliant with the relevant WQOs.

Micro-pollutants

The approach for the modelling of toxic substances involved four steps, which are presented in Annex B. For the purposes of the assessment, for each type of sensitive receiver (eg beaches, SSSI) the one experiencing the highest elevation was selected for further analysis. The results indicated that the predicted dissolved concentrations of each contaminant were below the applicable standards, as illustrated in Table 4.11.

Table 4.11 Predicted Concentrations of Dissolved Contaminants Expressed as a % of the Allowable Standard

	C1- Pak Sha Tau	MP1 - Hoi Ha Wan	F2 - Yim Tin Tsai E	SSSI1 - Ting Kok	B2 - Lung Mei	I1 - Tai Po IE
Arsenic	1.61E-03	6.08E-04	1.13E-03	3.59E-05	1.04E-05	3.25E-03
Chromium	5.81E-01	2.20E-01	4.08E-01	1.30E-02	3.76E-03	1.17E+00
Copper	1.46E+00	5.54E-01	1.03E+00	3.27E-02	9.47E-03	2.96E+00
Lead	1.84E-01	6.98E-02	1.29E-01	4.11E-03	1.19E-03	3.73E-01
Nickel	2.01E-02	7.61E-03	1.41E-02	4.49E-04	1.30E-04	4.06E-02
Zinc	2.40E-01	9.07E-02	1.68E-01	5.35E-03	1.55E-03	4.84E-01
PCBs	1.04E-02	3.92E-03	7.27E-03	2.31E-04	6.70E-05	2.10E-02
TBT	3.96E-05	1.50E-05	2.78E-05	8.84E-07	2.56E-07	8.01E-05

4.6.2 Laying of the Pipelines at the Landing Sites

The potential for impacts to water quality during the trenching activities on land primarily relate to surface water run-off, which will be controlled through the Contractor's good housekeeping practices.

Due to the shallow water depth at the Tai Po Approach, burial of the pipelines will be undertaken by excavation of a trench using a small grab dredger. It is expected that <400 m3 of seabed at the shore approach will be dredged. The dredging operation will take less than one week for each shore approach. Although the seabed material at the shore ends is generally coarse material (sand and gravel), during dredging a portion of the fine sediments will be lost to suspension to the surrounding marine waters and, if advected away from the works area by tidal currents, could lead to the formation of sediment plumes.

An analysis of the potential transport of fine sediments has been conducted (Annex B) and has determined that elevated concentrations of suspended sediments in excess of 10 mg L-1 would not occur at a distance greater than 190 m from the dredging operations. Towngas has decided that a silt curtain will be employed around the dredging operation which will reduce the loss of materials. The layout of the silt curtain is detailed in Figure 4.6a.

Consequently elevated concentrations of suspended sediments in excess of 10 mg L-1 would not occur at a distance greater than 50 m from the dredging operations. As a result, only localised short term adverse impacts to water quality would occur. Impacts to the Fish Culture Zone will not occur through dredging operations as the closest Yim Tin Tsai West, is located more than 1 km away from the pipelines alignment. The closest seawater intake at the Tai Po Industrial Estate is also not predicted to be affected with the implementation of the silt curtain as it is located more than 200 m from the pipelines alignment. The total concentration of SS (ambient plus elevation) at the intake = 8 mg L-1 and is, therefore, considered acceptable (Annex B).

Once the pipelines have been laid in the short trenches at the shore approach they will be covered with rock armour and backfilled using the excavated materials. The backfilling materials will be carefully placed into the trenches so that disturbance to the water column is minimised. This operation will be conducted within a silt curtain and adverse impacts to water quality will not occur.

4.6.3 Operation Phase Impacts

The only operational impacts from the gas pipelines would be if repairs were required. The impacts from this would be of reduced severity that those during the construction phase as the work would take place in a specific and confined small area. In the unlikely event that a full rupture of one of the pipelines occurs then that particular section would be isolated and repaired. The repair works would be confined solely to the damaged section. The process would involve uncovering of the affected section using divers with hand jets. Although the sediments would be disturbed the small scale nature of the works and use of hand jets would prevent sediment from being dispersed far from the site and consequently impacts to water quality sensitive receivers would not occur. As discussed in Section 3.2.2 the pipelines are designed to be maintenance free and should they require inspection this will be done using a remotely operated intelligent pipe inspection gauge (PIG). This type of maintenance will occur once every ten years and will be within the gas pipes. Consequently, there will be no need to disturb the seabed sediments during inspection and therefore water quality will not be affected. No further assessment is considered necessary and no mitigation is required.

4.7 WATER QUALITY MITIGATION MEASURES

The water quality modelling works have indicated that for both the dry and wet seasons, the construction works can proceed at the recommended working rates without causing unacceptable impacts to water quality sensitive receivers through either elevations of suspended sediment or deposition of sediment. Changes to other water quality parameters have been demonstrated to be minor, compliant with applicable standards and therefore not of concern.

The impacts from jetting and dredging of the gas pipelines were assessed to be very localised and of short duration. Impacts to water quality sensitive receivers have largely been avoided during the installation of the pipelines through the following measures:

* Pipelines Alignment: A number of alternative pipeline routes were studied and the preferred alignment avoids direct impacts to sensitive receivers.

* Bundle Configuration: As the pipelines will be bundled together and laid in the same trench the amount of sediment disturbed has been reduced and consequently the magnitude of potential impacts to water quality has been reduced.

* Reduction in Indirect Impacts: The alignment chosen for the two pipelines is located at a sufficient distance from water quality sensitive receivers so that the temporary dispersion of sediment from the installation works does not affect the receivers at levels of concern (as defined by the WQO and tolerance criteria). By laying the pipelines in the same trench, the horizontal spread of suspended sediment is restricted to a confined area in the centre of the Tolo Channel. Should the pipelines have been laid in separate trenches the horizontal spread of suspended sediment would have been much larger.

* Installation Equipment: The use of injection jetting along the majority of the route has minimised the severity of perturbations to water quality and hence allowed compliance with the WQOs at the sensitive receivers.

* Adoption of Acceptable Working Rates: The modelling work has demonstrated that the selected working rates for the dredging and jetting works will not cause unacceptable impacts to the receiving water quality.

Aside from the above pro-active measures that have been instituted for the Project, the following operational constraints should be applied. It should be noted that there is no requirement for constraints on timing or sequencing apparent from the assessment, as all scenarios have been demonstrated to be acceptable with the required mitigation measures in place.

* 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 (based on modelled rate in Annex B). 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 4.6a.

* Excavation works at the Tai Po Landing Site should be conducted within a silt curtain established as detailed in Figure 4.6a.

* 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.

4.8 RESIDUAL ENVIRONMENTAL IMPACTS

No residual environmental impacts, in terms of exceedances of applicable standards (ie Water Quality Objectives and marine ecology and fisheries tolerance criterion), were predicted to occur during the construction phase, provided that the mitigation measures, described in Section 4.7 are implemented. The mitigation measures were specified in the form of operational constraints and as a series of 'best practice' methods.

4.9 ENVIRONMENTAL MONITORING & AUDIT

This section summarises details of the environmental monitoring programme and presents technical requirements for monitoring water quality during the laying of the gas pipelines. Monitoring will be required for the following activities:

* excavation works at the Tai Po seawall;

* jetting works within 2 km of the Tai Po seawall;

* jetting works within 2 km of Pak Sha Tau;

* jetting works within Tolo Channel (between Wong Wan Tsui and Wong Chuk Kok Tsui); and,

* jetting works within 1 km of the HKSAR boundary; and

* dredging works on the Mainland side.

Water quality monitoring results will be compared to Action and Limit levels to determine whether impacts associated with the works are acceptable. An Event and Action Plan provides procedures to be undertaken when monitoring results exceed Action or Limit levels. The procedures are designed to ensure that if any significant exceedances occur (either accidentally or through inadequate implementation of mitigation measures on the part of the Contractor), the cause is quickly identified and remedied, and that the risk of a similar event re-occurring is reduced.

Action and Limit levels will be used to determine whether modifications to the operations are required. Action and Limit levels are environmental quality standards chosen such that their exceedance indicates potential deterioration of the environment. Exceedance of Action levels can result in an increase in the frequency of environmental monitoring, modification of operations and implementation of the proposed mitigation measures. Exceedance of Limit levels indicates a greater potential deterioration in environmental conditions and may require the cessation of works unless appropriate remedial actions, including a critical review of plant and working methods, are undertaken. Before works commence one month of baseline monitoring should be undertaken at stations along the pipelines alignment. The full details of the EM&A programme for water quality is presented in the EM&A Manual for this Project.

4.10 CONCLUSIONS

This Section describes the impacts on water quality arising from the construction and operation of the submarine pipelines supplying gas from the LNG receiving terminal in Shenzhen to the Towngas Gas Production Plant in Tai Po. The purpose of the assessment was to evaluate the acceptability of predicted impacts to water quality from the construction and operation of the gas pipelines.

Computer modelling of sediment dispersion has been used to assess construction impacts in terms of the laying of the pipeline, which will be carried out using two methods:

* dredging trenches in the Yantian Fairway and the Shenzhen approach (outside HKSAR waters); and

* jetting for the majority of the pipelines route.

The trench dredging in the Yantian Fairway and the Shenzhen approaches was examined quantitatively. It was determined that the impacts from the dredging would comply with the WQOs and coral tolerance criteria.

Computer modelling was used to simulate the loss of sediment to suspension during the jetting operations. The assessment concluded that any sediment disturbed by the works would settle rapidly back onto the sea bed and the suspended sediment elevations would be of short duration. This means that there would be little transport of suspended sediment away from the jetting operations and that it would not impact upon sensitive receivers. This operation was also determined to be environmentally acceptable.

An EM&A programme was devised to confirm that the assessment of the localised impacts of the jetting operations was accurate and that the operation would be environmentally acceptable.

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(4) ERM (2001). Focussed Cumulative Water Quality Impact Assessment of Sand Dredging at the West Po Toi Marine Borrow Area. Environmental Monitoring and Audit Manual. Updated Manual for HAM Dredging and Marine Contractors.

(5) EPD (2001). Marine Water Quality in Hong Kong 2000.

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(14) ERM-Hong Kong, Limited (1999). EIA for 1,800 MW Gas Fired Power Stations at Lamma Extension. EIA Report for Hongkong Electric Co Ltd.

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(16) ERM-Hong Kong, Limited (1999). Op cit.

(17) Hawker DW & Connell DW (1992). Op cit.

(18) Pastorok RA and Bilyard GR (1985). Effects of sewage pollution on coral-reef communities. Marine Ecology Progress Series 21: 175-189.

(19) Ayling AA and Ayling AK (1987). Is silt run-off affecting corals communities on the Cape Tribulation Fringing Reefs? In; Fringing Reef Workshop, GMRMPA Workshop series 9: 83-86. Ed CL Baldwyn.

(20) Hyder (1997). Sand Dredging and Backfilling of Borrow Pits at the Potential Eastern Waters Marine Borrow Area, EIA Report, CED, 1997.

(21) ERM-Hong Kong, Limited (2001). Focused Cumulative Water Quality Impact Assessment of Sand Dredging at the West Po Toi Marine Borrow Area Final Report.

(22) EPD (2001). Marine Water Quality in Hong Kong in 2000.

(23) SCSMEERI (2002). Cheng Tou Jiao to Tai Po Submarine Pipelines: Shenzhen Section EIA. South China Sea Marine Environmental Engineering Research Institute, State Oceanic Administration (2002).