Emission Control Project at Castle Peak Power Station "B" Units

Water Quality Objective	North Western WCZ	Deep Bay WCZ
A. AESTHETIC APPEARANCE
a) Waste discharges shall cause no objectionable odours or discolouration of the water.	Whole zone	Whole zone
b) Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other substances should be absent.	Whole zone	Whole zone
c) Mineral oil should not be visible on the surface. Surfactants should not give rise to a lasting foam.	Whole zone	Whole zone
d) There should be no recognisable sewage-derived debris.	Whole zone	Whole zone
e) Floating, submerged and semi-submerged objects of a size likely to interfere with the free movement of vessels, or cause damage to vessels, should be absent.	Whole zone	Whole zone
f) Waste discharges shall not cause the water to contain substances which settle to form objectionable deposits.	Whole zone	Whole zone
B. BACTERIA
a) The level of Escherichia coli should not exceed 610 per 100 mL, calculated as the geometric mean of all samples collected in one calendar year. b) The level of Escherichia coli should not exceed 180 per 100 mL, calculated as the geometric mean of all samples collected from March to October inclusive in one calendar year. Samples should be taken at least 3 times in a calendar month at intervals of between 3 and 14 days.	Secondary Contact Recreation Subzone Bathing Beach Subzone	Secondary Contact Recreation Subzone and Mariculture Subzone Yung Long Bathing Beach Subzone
D. DISSOLVED OXYGEN
a) Waste discharges shall not cause the level of dissolved oxygen to fall below 4 mg per litre for 90% of the sampling occasions during the year; values should be taken at 1 metre below surface. b) Waste discharges shall not cause the level of dissolved oxygen to fall below 4 mg per litre for 90% of the sampling occasions during the year; values should be calculated as water column average. In addition, the concentration of dissolved oxygen should not be less than 2 mg per litre within 2 metres of the seabed for 90% of the sampling occasions during the year. c) The dissolved oxygen level should not be less than 5 mg per litre for 90% of the sampling occasions during the year; values should be taken at 1 metre below surface.	- Marine Waters (water column average specified as arithmetic mean of at least 3 measurements at 1 metre below surface, mid-depth and 1 metre above seabed)	Inner Marine Subzone excepting Mariculture Subzone Outer Marine Subzone excepting Mariculture Subzone (water column average specified as arithmetic mean of at least 2 measurements at 1 metre below surface and 1 metre above seabed) Mariculture Subzone
E. pH
a) The pH of the water should be within the range of 6.5 - 8.5 units. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.2 units. b) The pH of the water should be within the range of 6.0 - 9.0 units for 95% of samples. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.5 units.	Marine waters excepting Bathing Beach Subzones. Bathing Beach Subzones.	Marine waters excepting Yung Long Bathing Beach Subzone Yung Long Bathing Beach Subzone
F. TEMPERATURE
Waste discharges shall not cause the natural daily temperature range to change by more than 2.0 ^oC.	Whole zone	Whole zone
G. SALINITY
Waste discharges shall not cause the natural ambient salinity level to change by more than 10%.	Whole zone	Whole zone
H. SUSPENDED SOLIDS
a) 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.	Marine waters	Marine waters
I. AMMONIA
The un-ionized ammoniacal nitrogen level should not be more than 0.021 mg per litre, calculated as the annual average (arithmetic mean).	Whole zone	Whole zone
J. NUTRIENTS
a) Nutrients shall not be present in quantities sufficient to cause excessive or nuisance growth of algae or other aquatic plants. b) Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.3 mg per litre, expressed as annual water column average (arithmetic mean of at least 3 measurements at 1m below surface, mid-depth and 1m above seabed). c) Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.7 mg per litre, expressed as annual mean. d) Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.5 mg per litre, expressed as annual water column average.	Marine waters Castle Peak Bay Subzone - Marine waters excepting Castle Peak Bay Subzone (water column average specified as arithmetic mean of at least 3 measurements at 1m below surface, mid-depth and 1m above seabed)	Inner and Outer marine Subzones - Inner Marine Subzone Outer Marine Subzone (water column average specified as arithmetic mean of at least 2 measurements at 1 metre below surface and 1 metre above seabed)
M. TOXINS
a) Waste discharges shall not cause the toxins in water to attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms, with due regard to biologically cumulative effects in food chains and to interactions of toxic substances with each other. b) Waste discharges shall not cause a risk to any beneficial uses of the aquatic environment.	Whole zone Whole zone	Whole zone Whole zone
N. PHENOLS
Phenols shall not be present in such quantities as to produce a specific odour, or in concentration greater than 0.05 mg per litre as C₆H₅OH.	Bathing Beach Subzones	Yung Long Bathing Beach Subzone
O. TURBIDITY
Waste discharges shall not reduce light transmission substantially from the normal level.	Bathing Beach Subzones	Yung Long Bathing Beach Subzone

Parameter	Assessment Criterion (µg L^-1)	Ambient Concentration ^a (µg L^-1)	Allowable Increase (µg L^-1)
Arsenic	25.0	1.8	23.2
Cadmium	2.5	0.1	2.4
Chromium	15.0	0.5	14.5
Copper	5.0	0.9	4.1
Lead	25.0	0.5	24.5
Mercury	0.3	0.1	0.2
Nickel	30.0	1.4	28.6
Silver	2.3	0.5	1.8
Zinc	40.0	6.2	33.8
Total PCBs	0.03 ^b	-	-
Total PAHs	3.0 ^b	-	-
TBT	0.1 ^b	-	-
Alpha-BHC	0.0049 ^c	-	-
Beta BHC	0.017 ^c	-	-
Gamma BHC	0.16 ^b	-	-
Delta-BHC	- ^d	-	-
Heptachlor	0.053 ^b	-	-
Aldrin	1.3^b	-	-
Heptachlor epoxide	0.053 ^b	-	-
Alpha Endosulfan	0.034 ^b	-	-
p, p'-DDT	0.13 ^b	-	-
p, p'-DDD	0.00031 ^c	-	-
p, p'-DDE	0.00022 ^c	-	-
Endosulfan sulfate	89 ^c	-	-
Notes: (a) The ambient concentrations were obtained from the monitoring works at the East Sha Chau CMP IVa and IVb (1997-2000). (b) The water quality criteria were derived from the USEPA water quality criteria. The Criteria Maximum Concentration (CMC) is an estimate of the highest concentration of a material in surface water to which an aquatic community can be exposed briefly without resulting in an unacceptable effect. CMC is used as the criterion of the respective compounds in this study. (c) No saltwater criteria for this chlorinated pesticide were defined by USEPA. The water quality criterion to protect human health for the consumption of aquatic organisms is provided for reference. (d) No water quality criteria for delta-BHC were defined by USEPA.

Water Quality Parameter	Station DM5	Station NM3	Station NM5
Temperature (°C)	23.7	23.4	23.5
	(14.4 - 31.1)	(15.6 - 29.7)	(15.5 - 30.3)
Salinity (ppt)	26.5	29.1	27.7
	(1.4 - 34.3)	(7.4 - 33.9)	(4.1 - 33.6)
pH	8.0	8.0	8.0
	(6.2 - 8.7)	(6.3 - 8.4)	(7.3 - 8.7)
Dissolved Oxygen (mg L^-1)	5.9	5.8	5.8
	(2.6 - 10.0)	(2.2 - 8.8)	(2.3 - 9.2)
Dissolved Oxygen, Bottom (mg L^-1)	5.7	5.6	5.5
	(2.6 - 10.0)	(2.2 - 8.6)	(2.3 - 8.8)
5-day Biochemical Oxygen Demand (mg L^-1)	0.9	0.7	0.8
	(0.1 - 4.9)	(0.1 - 2.6)	(0.1 - 4.1)
Suspended Solids (mg L^-1)	13.3	10.0	13.0
	(1.1 - 130.0)	(1.2 - 71.0)	(1.6 - 210.0)
Total Inorganic Nitrogen (mg L^-1)	0.67	0.43	0.56
	(0.14 - 2.46)	(0.02 - 1.75)	(0.03 - 2.30)
Unionised Ammonia (mg L^-1)	0.007	0.005	0.006
	(0.000 - 0.067)	(0.000 - 0.025)	(0.000 - 0.027)
Chlorophyll-a (mg L^-1)	2.3	2.4	2.6
	(0.2 - 49.0)	(0.2 - 25.0)	(0.2 - 28.0)
E. coli (cfu 100mL^-1)	400	510	520
	(4 - 41,000)	(1 - 180,000)	(4 - 28,000)
Notes: (a) Data presented are depth-averaged, except as specified. (b) Data presented are arithmetic mean except for E. coli, which are geometric mean values. (c) Data enclosed in brackets indicate the ranges. (d) Shaded cells indicate non-compliance with the WQOs.

Water Quality Parameter	Sha Chau and Lung Kwu Chau Marine Park
Temperature (°C)	24.1	24.3	24.1	24.3
Salinity (ppt)	24.7	23.9	25.1	25.1
pH	7.9	8.1	7.9	8.1
Dissolved Oxygen (mg L^-1)	6.2	5.8	6.2	5.8
Suspended Solids (mg L^-1)	20.3	9.7	37.2	10.0
Secchi Depth (m)	1.1	0.8	1.2	0.7
BOD (mg L^-1)	0.2	0.2	0.2	0.2
Ammonia Nitrogen (µg L^-1)	0.050	0.029	0.071	0.030
Unionized Ammonia (µg L^-1)	0.29	0.34	0.29	0.33
Nitrite Nitrogen (µg L^-1)	1.50	3.77	1.38	3.68
Nitrate Nitrogen (µg L^-1)	1.38	0.54	1.31	0.56
Total Inorganic Nitrogen (µg L^-1)	2.26	3.98	2.37	3.81
Total Kjeldahl Nitrogen (mg L^-1)	5.18	14.82	5.13	16.21
Total Nitrogen (mg L^-1)	0.27	0.06	0.13	0.05
Orthophosphate Phosphorus (µg L^-1)	0.74	0.10	0.65	0.09
Total Phosphorus (mg L^-1)	1.02	1.16	1.02	1.10
Silica (mg L^-1)	2.59	2.59	2.09	2.78
Chlorophyll-a (µg L^-1)	1.90	1.07	1.81	1.09
Phaeo-pigment (µg L^-1)	343	54	201	58
E. coli (CFU/100 mL)	1298	117	1070	114
Faecal Coliforms (CFU/100 mL)	24.1	24.3	24.1	24.3
Notes: (a) Data from AFCD (2005). Marine Park Water Quality Report (Web site: www.afcd.gov.hk) (b) Data presented are depth averaged, except as specified. (c) Data presented are annual arithmetic mean except for E. coli, which are geometric means and dissolved oxygen, which are 10^th percentiles.

5.3.4 Sediment Quality

EPD Sediment Quality Monitoring

EPD collects sediment quality data as part of the marine water quality monitoring programme. There are three relevant monitoring stations in the vicinity of the additional berthing facility, i.e., Stations NS3 and NS4 in the Northwestern WCZ and Station DS4 in the Deep Bay WCZ. The locations of these stations are shown in Figure 5.1.

Data for these stations have been obtained from the EPD are presented in Table 5.7. The data represent the range of values collected in 1996-2005. As with the water quality data, this dataset provides Hong Kong’s most comprehensive long term sediment quality monitoring data and provides an indication of temporal and spatial change in marine sediment quality in Hong Kong.

The values for metals, PAHs and PCBs may also be compared to the relevant sediment quality criteria specified in the Environment Transport & Works Bureau Technical Circular No 34/2002 Management of Dredged/Excavated Sediment (ETWBTC 34/2002).

A comparison of the data with the sediment quality criteria (i.e., Lower Chemical Exceedance Level (LCEL) and Upper Chemical Exceedance Level (UCEL)) shows that the levels of arsenic for Station DS4 have exceeded the LCEL and they are classified as Category M.

Table 5.7 Summary of EPD Sediment Quality Monitoring Data Collected in 1996 - 2005

Parameter	Deep Bay WCZ	North Western WCZ		Sediment Quality Criteria
Parameter	DS4	NS3	NS4	LCEL	UCEL
COD (mg kg^-1)	14,540	15,320	13,635	-	-
COD (mg kg^-1)	(8,800 - 20,000)	(8,400 - 19,000)	(6,700 - 19,000)
Total Carbon (% w/w)	0.6	0.6	0.6	-	-
Total Carbon (% w/w)	(0.3 - 1.3)	(0.4 - 0.8)	(0.3 - 0.8)
Ammonical Nitrogen (mg kg^-1)	6.3	6.7	14.2	-	-
Ammonical Nitrogen (mg kg^-1)	(0.0 - 36.0)	(0.1 - 23.0)	(0.2 - 39.0)
TKN (mg kg^-1)	285	308	275	-	-
TKN (mg kg^-1)	(110 - 820)	(120 - 440)	(160 - 530)
Total Phosphorous (mg kg^-1)	165	178	145	-	-
Total Phosphorous (mg kg^-1)	(77 - 270)	(86 - 250)	(92 - 220)
Total Sulphide (mg kg^-1)	15	23	23	-	-
Total Sulphide (mg kg^-1)	(<0.1 - 76)	(<0.1 - 94)	(<0.1 - 77)
Arsenic (mg kg^-1)	14.4	11.7	12.0	12	42
Arsenic (mg kg^-1)	(7.6 - 19.0)	(6.3 - 14.0)	(9.1 - 18.0)
Cadmium (mg kg^-1)	<0.1	<0.1	<0.1	1.5	4
Cadmium (mg kg^-1)	(<0.1 - 0.2)	(<0.1 - 0.3)	(<0.1 - 0.2)
Chromium (mg kg^-1)	32	34	28	80	160
Chromium (mg kg^-1)	(14 - 50)	(16 - 48)	(20 - 44)

Copper (mg kg^-1)	26	34	23	65	110
Copper (mg kg^-1)	(6 - 64)	(17 - 48)	(17 - 42)
Lead (mg kg^-1)	40	39	39	75	110
Lead (mg kg^-1)	(18 - 68)	(20 - 54)	(29 - 47)
Mercury (mg kg^-1)	0.1	0.1	0.1	0.5	1
Mercury (mg kg^-1)	(<0.05 - 0.2)	(<0.05 - 0.2)	(<0.05 - 0.2)
Nickel (mg kg^-1)	19	20	18	40	40
Nickel (mg kg^-1)	(7 - 31)	(10 - 31)	(13 - 30)
Silver (mg kg^-1)	0.4	0.4	0.4	1	2
Silver (mg kg^-1)	(<0.2 - <1.0)	(0.2 - <1.0)	(<0.2 - <0.5)
Zinc (mg kg^-1)	96	95	96	200	270
Zinc (mg kg^-1)	(36 - 180)	(48 - 120)	(67 - 110)
Total PCBs (µg kg^-1)	18	18	18	23	180
Total PCBs (µg kg^-1)	(18 - 18)	(18 - 18)	(18 - 18)
Low Molecular Wt PAHs (µg kg^-1)	91	92	92	550	3,160
Low Molecular Wt PAHs (µg kg^-1)	(90 - 94)	(90 - 95)	(90 - 99)
High Molecular Wt PAHs (µg kg^-1)	61	80	59	1,700	9,600
High Molecular Wt PAHs (µg kg^-1)	(16 - 254)	(31 - 296)	(21 - 139)
Notes: (a) Data presented are arithmetic mean. (b) Data enclosed in brackets indicate the ranges. (c) The shaded cell indicates exceedance of LCEL. (d) Low Molecular Wt PAHs include acenaphthene, acenaphthylene, anthracene, fluorine and phenanthrene. (e) High Molecular Wt PAHs include benzo[a]anthracene, benzo[a]pyrene, chrysene, dibenzo[a,h]anthracene, fluoranthene, pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, indeno[1,2,3-c,d]pyrene and benzo[g,h,I]perylene.

Sediment Quality Tests for Proposed Dredging Area

In addition to the background data presented above, a marine sediment sampling survey and elutriation tests were conducted within the proposed dredging areas. The purpose of elutriate testing was to investigate the leaching potential for the sediment-bonded pollutants being released into the ambient marine water (in the immediate vicinity of dredging) during dredging activities for the Project.

Vibrocore samples were collected at three locations, V1, V2 and V3, and were taken down to the proposed dredging depth (Figure 2.3). Sampling locations were chosen so that they are representative of the dredging area. The contaminants tested included all of the contaminants stated in Table 1 - Analytical Methodology in Appendix B of ETWBTC No 34/2002 plus PCBs and 12 Chlorinated Pesticides.

The results of the sediment quality tests are presented in detail in the Waste Management Section (Table 6.4 of Section 6) and the results indicate that all measured contaminant levels of the samples are below the Lower Chemical Exceedance Level (LCEL) as defined in ETWBTC No 34/2002. Hence, the sediment is likely to be uncontaminated but further sampling and testing in accordance with the detailed requirements of ETWBTC No. 34/2002 will be required for the actual allocation of sediment disposal site and the application for a dumping permit under the Dumping at Sea Ordinance (Cap 466) prior to the commencement of the dredging activities.

The results of the elutriation test are presented in the following section and in Annex C1. The details of the elutriation tests are provided in Annex D.

The sediment samples were also analysed for particle size distribution. The majority of the sediment in the samples was found to be silt and clay.

5.3.5 Water Sensitive Receivers

The sensitive receivers that may be affected by the effluent discharges associated with the construction and operation of the Project are primarily located along the coastline of the north-west New Territories, with the exception of the marine waters around the Sha Chau and Lung Kwu Chau Marine Park. Sensitive receivers have been identified under the broad categories of gazetted bathing beaches, non-gazetted bathing beaches, water intakes and areas of ecological value. The identified sensitive receivers in each of these categories are as follows, the locations of which are shown in Figure 5.2:

· Gazetted Bathing Beaches: Butterfly Beach and the Tuen Mun Beaches (Castle Peak, Kadoorie, Cafeteria New & Old, Golden, Angler’s, Gemini, Ho Mei Wan, Casam, Lido and Ting Kau);

· Non-Gazetted Bathing Beaches: Lung Kwu Upper, Lung Kwu Lower and Dragon Beach;

· Water Intakes: Shiu Wing Steel Mill, the proposed EcoPark in Tuen Mun Area 38, Castle Peak Power Station Intake, Black Point Power Station Intake, Tuen Mun Area 38 Industries Intake, and Tuen Mun Flushing Water Intake; and

· Areas of Ecological Value: Sha Chau and Lung Kwu Chau Marine Park, the Sha Chau and Lung Kwu Chau and Airport Artificial Reefs (ARs).

Water Quality Sensitive Receivers

The Water Quality Objectives (WQOs) presented in Table 5.1 are considered to be suitable as assessment criteria at the water quality sensitive receivers which include the gazetted bathing beaches, the non-gazetted bathing beaches and water intakes. The assessment criteria has been summarised in Table 5.3. Among the seawater intakes, the WSD and power station sea water intakes have been assessed against the specific standards, in addition to the WQOs. The standards for the WSD abstracted seawater are presented in Table 5.2.

Ecological Sensitive Receivers

The Sha Chau and Lung Kwu Chau AR site and the Airport AR site have been deployed to act as a fisheries resource enhancement tool, to encourage growth and development of a variety of marine organisms, and to provide feeding opportunities for the Indo-Pacific Humpback Dolphin. There is no specific water quality criterion for the AR sites, thus water quality impacts have been assessed with reference to the WQOs criterion for the assessment of impacts to marine life.

5.4 Potential Sources of Impact

Potential sources of impacts to water quality as a result of the project may occur during both the construction and operational phases.

5.4.1 Construction Phase

The major construction activities associated with the proposed project that may cause impacts to water quality involve the following:

· Dredging for the additional berthing facility;

· Construction of the additional berthing facility including the piling works;

· Sewage discharges due to the on-site workforce; and

· Site runoff and pollutants entering the receiving waters and/or water drainage system.

Of the above the main impacts arising from the construction works may relate to disturbances to the seabed and re-suspension of marine sediment. These, in turn, may result in physico-chemical changes to the water column as a result of the release of suspended solids.

5.4.2 Operational Phase

The potential impacts to water quality arising from the operation of the proposed facility have been identified as follows:

· Effluent from the FGD process would likely impact concentrations of sulphate ions; salinity; suspended ash particles and chemical and biochemical oxygen demand.

The treated effluent will be added to the cooling water flows and then discharged via the CPB cooling water outfall, resulting in a small increase (i.e. 0.02 %) in the total flows from the outfall. It should be noted that there would be no effect on the temperature of the cooling water or on the quantities of residual chlorine in the discharge.

5.5 Water Quality Impact Assessment Methodology

The methodology employed to assess the above impacts has been based on the information presented in Section 2.

Impacts due to the dispersion of fine sediment in suspension during the construction of the additional berthing facility have been assessed using computational modelling. Mitigation measures were assumed to be absent.

The simulation of operational impacts on water quality has also been performed by means of computational modelling. The models have been used to simulate the effects of discharges on water quality.

Full details of the scenarios examined in the modelling works are presented in the following sections. As discussed previously, the water quality sensitive receivers in the vicinity of the proposed works are presented in Figure 5.2 and the points at which the modelling data has been analysed are shown in Figure 5.3 and summarised in Table 5.8. These modelling output points are considered representative as any sensitive receivers beyond these points would be expected to have lower impacts.

Table 5.8 Water Quality Modelling Output Points

Type	Description	ID	Evaluation Criteria
*Water Quality Sensitive Receivers*
Gazetted Bathing Beach	Butterfly Beach	B3	Water Quality Objectives (WQO)
	Tuen Mun Beaches	B4	Water Quality Objectives (WQO)
Non-Gazetted Bathing Beach	Lung Kwu Sheung Tan Beach	B1	Water Quality Objectives (WQO)
	Lung Kwu Beach	B2	Water Quality Objectives (WQO)
Water Intakes	Black Point Power Station	I1	Water Quality Objectives (WQO) and Power Station Specified Water Quality Criteria
	Castle Peak Power Station	I2	Water Quality Objectives (WQO) and Power Station Specified Water Quality Criteria
	Industrial Intakes and Proposed EcoPark at Area 38	I3	Water Quality Objectives (WQO)
	Tuen Mun WSD	I4	WSD Water Quality Criteria
	Shiu Wing Steel Mill	I5	Water Quality Objectives (WQO)
*Marine Ecological Sensitive Receivers*
Marine Park	Sha Chau and Lung Kwu Chau Marine Park	MP1 ^{a, c} MP2 ^{a, c} MP3 ^{a, c}	Water Quality Objectives (WQO)
*Other Modelling Output Points for Assessment Purpose*
Marine Water Stations	EPD Monitoring station	DM5 NM3 ^{b, c} NM5	Water Quality Objectives (WQO)
	Urmston Road Station	UR1 UR2 UR3 UR4 ^{b, c}	Water Quality Objectives (WQO)
Notes: (a) MP1, MP2 and MP3 indicate the boundary of the Sha Chau Marine Park. They are surrogate points for assessing pollutant dispersion trend at the artificial reefs at Sha Chau. (b) UR4 and NM3 indicate the waters at the Urmston Road which are the closest locations to the Airport. They are surrogate points for assessing pollutant dispersion trend at the artificial reef site at the Airport. (c) If the results for these modelling points indicate no unacceptable impacts to occur due to the Project, it is assumed that those sensitive receivers beyond the modelling points will not be adversely affected.

5.5.1 Uncertainties in Assessment Methodology

Quantitative uncertainties in the hydrodynamic modelling and suspended sediment plumes should be considered when making an evaluation of the modelling predictions. For hydrodynamic modelling these are considered to be negligible for the following reasons:

· The computational grid of the model is sufficiently refined to provide precise simulation results;

· The model has been calibrated and verified in order to provide reliable predictions for the study area; and

· The simulations comprise a sufficient spin up (or initial start up) period of 6 days so that initial conditions do not affect the results.

In carrying out the suspended solids assessment, worst case assumptions have been made in order to provide a conservative assessment of environmental impacts. These assumptions are as follows.

· The assessment is based on the peak dredging rates. In reality, these will only occur for short periods of time;

· The calculations of loss rates of sediment to suspension are based on conservative estimates for the type of plant and method of working.

Such allow a conservative approach to be applied to the water quality modelling and should be considered when drawing conclusions from the assessment.

The following uncertainties, however, have not been covered in the modelling:

· Instantaneous vessel access;

· Ad hoc marine traffic; and

· Near-shore scouring of marine sediment.

5.6 Construction Phase Water Quality Impact Assessment

5.6.1 Modelling Details

The Western Harbour Model was developed by WL|Delft Hydraulics and applied in this Study. The model has been previously set up to cover the whole of the marine waters of the North West New Territories and was most recently used in the assessment of the potential mud disposal areas at East of Sha Chau and South Brothers ([18]).

Hydrodynamics

The first phase of the modelling involved setting up a detailed hydrodynamic model of the area around the CPPS.

The spin-up period equals one spring-neap-cycle is approximately 14 days. The time step used in the model is 1.5 min. The computation simulation periods for the model are as follows.

	Dry	Wet
Start:	08 February 2007 18:00	25 July 2007 23:00
Stop:	23 February 2007 18:00	09 August 2007 23:00

The flow rate of Pearl River discharges have been assumed as shown below.

	Dry	Wet
Humen:	1245 m³s^-1	7442 m³s^-1
Jiaomen:	527 m³s^-1	4732 m³s^-1
Hongqili:	128 m³s^-1	1535 m³s^-1
Hengmen:	136 m³s^-1	2805 m³s^-1
Deep Bay:	2.5 m³s^-1	16 m³s^-1

The existing hydrodynamics data were interpolated onto the refined grid (Figure 5.4) used in the Delft-3D-WAQ module to provide necessary input data for the refined grid simulations. The refinement grid improved resolution (less than 75m) at the areas of interest. This methodology has been successfully applied to simulations using the water quality model in previously approved EIAs in Hong Kong. A detailed discussion of the numerical implementation of the interpolation process is presented in Annex C2.

Hydrodynamic data have also been obtained using coastline and bathymetry for a time horizon representative of the construction period of the facility (i.e., 2007 onwards) (Figure 5.5).

Scenarios

During dredging activities required for the additional berthing facility, a quantity of fine sediment will be lost to suspension which may be transported away from the works area, forming suspended sediment plumes. The formation and transport of such sediment plumes have been modelled with the Delft-3D-WAQ module which simulated the process of sediment transport, deposition and erosion for plumes generated during dredging. The basis of the model is the advection-diffusion transport. All sediment particles are transported by the flow (advection) and turbulent mixing (diffusion), and additional processes will be included for modelling various water quality parameters.

As the dredging area is small, the use of a closed grab dredger is considered to be most suitable. The dredger will commence at the utmost southeast of the dredging area moving along the route as indicated in Figure 5.6, covering the whole trajectory (approximately 1.5 km) in around 12 days. It was assumed the most conservative case that the sediments would be released during neap tide (taking into account applicable working hours).

The assumptions made with regards to modelling grab dredging operations are detailed in Table 5.9.

Table 5.9 Assumptions for the Grab Dredging Operations

Parameter	Assumption
Hopper capacity of each vessel	700 m³
Minimum Grab size	8 m³(closed grab)
Total number of dredgers to be deployed on site	1
Estimated quantity of the dredged sediment	80,700 m³
Typical daily dredging rate	3,500 m³ day^-1
Maximum daily dredging rate	5,200 m³day^-1
Maximum loss rate	20 kg m^-3day^-1
Loss rate per second	1.81 kg s^-1
Duration of the dredging works	maximum 6 weeks
Working time	16 hours per day, 6 days per week

Although it is acknowledged that a larger grab would result in less sediment being released and, therefore, lower loss rates, it is considered appropriate for the conservative nature of the assessment to assume an 8 m³ grab will be used. Typical and maximum daily dredging rate is assumed to be 3,500 m³ day^-1 and 5,200 m³ day^-1. To consider the most conservative case, a loss rate of 20 kg m^-3 is assumed, which equates to a sediment release rate of 1.81 kg s^-1.

Based on the above information, the detailed hydrodynamic model was used to simulate two scenarios which are defined below. Each of the scenarios was simulated for 15 day spring-neap tidal cycles in the dry and wet seasons.

· Scenario 1: Baseline case, corresponding to the current conditions with the existing discharges in the vicinity of the CPPS (including BPPS and CPPS); and

· Scenario 2: Additional Berthing Facility Construction case, including the dredging for the additional berthing facility.

The area proposed to be dredged for the additional berthing facility is presented in Figure 2.3. The dredged area covers approximately 30,000 m². The final dredging level has been taken to be approximately -8.2 mPD.

5.6.2 Prediction and Evaluation of Impacts

As the results of the hydrodynamic model were used to drive the water quality model, these are not discussed in detail.

Dredging for the Additional Berthing Facility

Suspended Solids

Impacts from the dispersion of fine sediment in suspension from the construction of the additional berthing facility have been simulated using computer modelling. The maximum and mean elevations of depth-averaged SS for each scenario are presented in Table 5.10. Results are presented as predicted levels of suspended sediment at each of the sensitive receivers.

Modelling results indicate that SS elevations will be compliant with the WQO for all sensitive receivers in both seasons (Table 5.10).

Table 5.10 Predicted SS Elevations above Ambient due to the Grab Dredging Operations

Sensitive Receivers	Depth	Evaluation Criteria (mg L^-1)		Suspended Solids Concentration (mg L^-1)
		Evaluation Criteria (mg L^-1)		Mean		Max
		Dry	Wet	Dry	Wet	Dry	Wet
B1	Surface	6.6	6.9	0.0	0.1	0.2	1.1
B1	Middle	6.6	6.9	0.1	0.1	0.6	1.3
B1	Bottom	6.6	6.9	0.1	0.1	1.0	1.6
B1	Depth-averaged	6.6	6.9	0.1	0.1	0.6	1.3
B2	Surface	6.6	6.9	0.0	0.0	0.1	0.1
B2	Middle	6.6	6.9	0.0	0.0	0.2	0.1
B2	Bottom	6.6	6.9	0.0	0.0	0.3	0.1
B2	Depth-averaged	6.6	6.9	0.0	0.0	0.2	0.1
B3	Surface	6.6	6.9	0.0	0.0	0.0	0.0
B3	Middle	6.6	6.9	0.0	0.0	0.1	0.0
B3	Bottom	6.6	6.9	0.0	0.0	0.1	0.0
B3	Depth-averaged	6.6	6.9	0.0	0.0	0.1	0.0
B4	Surface	6.6	6.9	0.0	0.0	0.0	0.0
B4	Middle	6.6	6.9	0.0	0.0	0.0	0.0
B4	Bottom	6.6	6.9	0.0	0.0	0.0	0.0
B4	Depth-averaged	6.6	6.9	0.0	0.0	0.0	0.0
I1	Surface	726.4	741.2	0.0	0.0	0.2	0.0
I1	Middle	726.4	741.2	0.0	0.0	0.2	0.0
I1	Bottom	726.4	741.2	0.1	0.0	0.4	0.4
I1	Depth-averaged	726.4	741.2	0.0	0.0	0.2	0.1
I2	Surface	742	741	1.2	0.5	7.7	4.5
I2	Middle	742	741	1.7	1.4	16.4	8.9
I2	Bottom	742	741	1.5	2.6	16.9	12.7
I2	Depth-averaged	742	741	1.5	1.6	11.9	8.2
I3	Surface	6.6	6.9	0.1	0.1	1.1	0.9
I3	Middle	6.6	6.9	0.1	0.2	1.1	1.7
I3	Bottom	6.6	6.9	0.1	0.1	1.0	0.5
I3	Depth-averaged	6.6	6.9	0.1	0.1	1.0	0.9
I4	Surface	13.6	13.6	0.0	0.0	0.0	0.0
I4	Middle	13.6	13.6	0.0	0.0	0.1	0.1
I4	Bottom	13.6	13.6	0.0	0.0	0.1	0.1
I4	Depth-averaged	13.6	13.6	0.0	0.0	0.1	0.1
I5	Surface	6.6	6.9	0.1	0.1	1.2	0.9
I5	Middle	6.6	6.9	0.2	0.2	1.7	1.8
I5	Bottom	6.6	6.9	0.1	0.1	1.1	0.6
I5	Depth-averaged	6.6	6.9	0.2	0.2	1.2	1.2
MP1	Surface	28	28	0.0	0.0	0.1	0.0
MP1	Middle	28	28	0.0	0.0	0.1	0.0
MP1	Bottom	28	28	0.0	0.0	0.1	0.1
MP1	Depth-averaged	28	28	0.0	0.0	0.1	0.0
MP2	Surface	28	28	0.0	0.0	0.1	0.0
MP2	Middle	28	28	0.0	0.0	0.1	0.1
MP2	Bottom	28	28	0.0	0.0	0.2	0.1
MP2	Depth-averaged	28	28	0.0	0.0	0.1	0.1
MP3	Surface	28	28	0.0	0.0	0.1	0.0
MP3	Middle	28	28	0.0	0.0	0.1	0.0
MP3	Bottom	28	28	0.1	0.0	0.2	0.2
MP3	Depth-averaged	28	28	0.0	0.0	0.1	0.1
DM5	Surface	6.6	6.9	0.0	0.0	0.1	0.0
DM5	Middle	6.6	6.9	0.0	0.0	0.2	0.0
DM5	Bottom	6.6	6.9	0.1	0.0	0.3	0.3
DM5	Depth-averaged	6.6	6.9	0.0	0.0	0.2	0.1
NM3	Surface	6.6	6.9	0.0	0.0	0.4	0.4
NM3	Middle	6.6	6.9	0.1	0.0	0.3	0.2
NM3	Bottom	6.6	6.9	0.1	0.0	0.2	0.3
NM3	Depth-averaged	6.6	6.9	0.1	0.0	0.2	0.1
NM5	Surface	6.6	6.9	0.0	0.0	0.0	0.0
NM5	Middle	6.6	6.9	0.0	0.0	0.4	0.2
NM5	Bottom	6.6	6.9	0.1	0.0	0.3	0.2
NM5	Depth-averaged	6.6	6.9	0.0	0.0	0.2	0.1
UR1	Surface	6.6	6.9	0.0	0.0	0.1	0.0
UR1	Middle	6.6	6.9	0.0	0.0	0.2	0.1
UR1	Bottom	6.6	6.9	0.1	0.1	0.4	0.3
UR1	Depth-averaged	6.6	6.9	0.0	0.0	0.2	0.1
UR2	Surface	6.6	6.9	0.0	0.0	0.0	0.0
UR2	Middle	6.6	6.9	0.0	0.0	0.2	0.1
UR2	Bottom	6.6	6.9	0.1	0.1	0.4	0.3
UR2	Depth-averaged	6.6	6.9	0.0	0.0	0.2	0.1
UR3	Surface	6.6	6.9	0.0	0.0	0.2	0.5
UR3	Middle	6.6	6.9	0.0	0.0	0.3	0.1
UR3	Bottom	6.6	6.9	0.1	0.0	0.2	0.1
UR3	Depth-averaged	6.6	6.9	0.0	0.0	0.2	0.1
UR4	Surface	6.6	6.9	0.0	0.0	0.3	0.5
UR4	Middle	6.6	6.9	0.1	0.0	0.4	0.1
UR4	Bottom	6.6	6.9	0.1	0.0	0.2	0.2
UR4	Depth-averaged	6.6	6.9	0.1	0.0	0.3	0.1

The contour plots of the suspended solids are also presented in Annex C3. The maximum depth-averaged SS plots for both seasons suggest that plumes over 10 mg L^-1 are likely to be confined to the works area and will not reach the closest northward WSR, ie Lung Kwu Tan Beach. Although they will reach the closest southward WSR, ie Castle Peak Power Station Intake A, the 10 mgL^-1 is predicted to be well below the SS criterion for this intake.

Due to the relatively limited spread of SS and no exceedances of the WQOs or tolerance criterion at sensitive receivers, no unacceptable elevations of SS would be expected to occur.

Sediment Deposition

Contour plots (Annex C3) of sediment deposition as a result of dredging operations indicate that the majority of sediment settles either within, or within relatively close proximity, to the CPPS. Table 5.11 summarises the predicted sediment deposition rate due to the grab dredging operations. The highest sedimentation rate was 110 g m^-2 d^-1 during the wet season at I2, i.e. Castle Peak Power Station intake, which is the closest to the working site. For other intakes, the sedimentation rate is predicted to be < 4 g m^-2 d^-1. In consideration of the short duration of the dredging works (approximately 12 days), the sediment deposition is unlikely cause any unacceptable impacts to the intakes.

For those sensitive receivers farther away from the CPPS representing the ARs, i.e. MP1-3, UR4 and NM3, the sedimentation rate is predicted to be < 1 g m^-2 d^-1 which is far below 50 g m^-2 d^-1 (the criterion used in this Study for the artificial reef). Hence, it is expected that the sediment deposition at those ARs at Sha Chau and the Airport will be minimal. Sediment deposition is, therefore, not expected to affect any nearby submarine utilities or ecological sensitive receivers.

Table 5.11 Predicted Sediment Deposition Rate due to the Grab Dredging Operations

Sensitive Receivers	Sedimentation Rate (g m^-2 d^-1)
Sensitive Receivers	Dry	Wet
B1	4	4
B2	1	0
B3	1	0
B4	0	0
I1	0	0
I2	62	110
I3	2	3
I4	0	0
I5	4	3
MP1	0	0
MP2	0	0
MP3	0	0
DM5	0	0
NM3	0	0
NM5	0	1
UR1	0	1
UR2	0	1
UR3	0	0
UR4	0	0

Dissolved Oxygen Depletion

The degree of oxygen depletion exerted by a sediment plume is a function of the sediment oxygen demand of the sediment, its concentration in the water column and the rate of oxygen replenishment.

The impact of the sediment oxygen demand (SOD) on dissolved oxygen concentrations has been calculated based on the following equation ([19]):

DO_Dep = C * SOD * K * 10^-6

where DO_Dep = Dissolved oxygen depletion (mg L^-1)

C = Suspended solids concentration (mg L^-1)

SOD = Sediment oxygen demand (mg kg^-1)

K = Daily oxygen uptake factor (set as 1 ([20]))

An SOD of 15,000 mg kg^-1 has been used in a recent approved EIA([21])which made reference to EPD Marine Monitoring data. This value was considered as a suitably representative value for sediments in the North Western Waters. In the same EIA, K was set to be 1, which means instantaneous oxidation of the sediment oxygen demand. This was a more conservative prediction of DO depletion than this study since oxygen depletion is not instantaneous and will depend on tidally averaged suspended sediment concentrations.

It is worth noting that the above equation does not account for re-aeration which would tend to reduce impacts of the SS on the DO concentrations in the water column. The proposed analysis, which is on the conservative side, will not, therefore, underestimate the DO depletion.

The calculated results (Table 5.12) showed that the predicted oxygen depletion at the WSRs is less than 0.3 mg L^-1, except at I2, i.e. Castle Peak Power Station Intake. By comparing the predicted depletion values with the allowable deduction in DO, the dissolved oxygen at those WSRs is expected to be compliance with the WQOs. The sediment plumes predicted in the model are thus unlikely to deteriorate dissolved oxygen conditions in the receiving waters. For Castle Peak Power Station Intake, there is no specific DO criterion set for the intake and hence the DO depletion will not affect the intake system.

SS elevations induced by the marine works within the Study Area as a whole will remain compliant with the WQOs. The subsequent effect on dissolved oxygen within the surrounding waters is, therefore, predicted to be minimal and unacceptable impacts to marine ecological resources including the Indo-Pacific Humpback Dolphins are not expected to occur.

Table 5.12 Predicted Dissolved Oxygen Depletion due to Increase in SS Concentrations

Sensitive Receivers	Depth	Allowable Effect (mg L^-1)		Dissolved Oxygen Depletion (mg L^-1)
		Allowable Effect (mg L^-1)		Mean		Max
		Dry	Wet	Dry	Wet	Dry	Wet
B1	Surface	N/A	N/A	0.00	0.01	0.03	0.16
B1	Middle	N/A	N/A	0.01	0.01	0.09	0.20
B1	Bottom	-4.7	-2.5	0.02	0.02	0.15	0.24
B1	Depth-averaged	-2.7	-1.1	0.01	0.02	0.09	0.20
B2	Surface	N/A	N/A	0.00	0.00	0.01	0.01
B2	Middle	N/A	N/A	0.00	0.00	0.03	0.01
B2	Bottom	-4.7	-2.5	0.01	0.00	0.05	0.02
B2	Depth-averaged	-2.7	-1.1	0.00	0.00	0.03	0.01
B3	Surface	N/A	N/A	0.00	0.00	0.01	0.00
B3	Middle	N/A	N/A	0.00	0.00	0.01	0.01
B3	Bottom	-4.7	-2.5	0.00	0.00	0.01	0.00
B3	Depth-averaged	-2.7	-1.1	0.00	0.00	0.01	0.00
B4	Surface	N/A	N/A	0.00	0.00	0.00	0.00
B4	Middle	N/A	N/A	0.00	0.00	0.00	0.00
B4	Bottom	-4.7	-2.5	0.00	0.00	0.00	0.00
B4	Depth-averaged	-2.7	-1.1	0.00	0.00	0.00	0.00
I1	Surface	N/A	N/A	0.00	0.00	0.02	0.00
I1	Middle	N/A	N/A	0.00	0.00	0.03	0.01
I1	Bottom	-4.7	-2.5	0.01	0.00	0.06	0.07
I1	Depth-averaged	-2.7	-1.1	0.01	0.00	0.03	0.02
I2	Surface	N/A	N/A	0.18	0.08	1.15	0.67
I2	Middle	N/A	N/A	0.26	0.21	2.47	1.34
I2	Bottom	-4.7	-2.5	0.22	0.39	2.53	1.91
I2	Depth-averaged	-2.7	-1.1	0.23	0.23	1.79	1.24
I3	Surface	N/A	N/A	0.02	0.01	0.16	0.13
I3	Middle	N/A	N/A	0.02	0.02	0.16	0.25
I3	Bottom	-4.7	-2.5	0.02	0.01	0.14	0.08
I3	Depth-averaged	-2.7	-1.1	0.02	0.02	0.15	0.13
I4	Surface	N/A	N/A	0.00	0.00	0.01	0.00
I4	Middle	N/A	N/A	0.00	0.00	0.01	0.01
I4	Bottom	-4.7	-2.5	0.00	0.00	0.01	0.01
I4	Depth-averaged	-2.7	-1.1	0.00	0.00	0.01	0.01
I5	Surface	N/A	N/A	0.02	0.02	0.19	0.13
I5	Middle	N/A	N/A	0.03	0.03	0.25	0.27
I5	Bottom	-4.7	-2.5	0.02	0.02	0.17	0.10
I5	Depth-averaged	-2.7	-1.1	0.02	0.03	0.19	0.18
MP1	Surface	N/A	N/A	0.00	0.00	0.01	0.00
MP1	Middle	N/A	N/A	0.00	0.00	0.01	0.00
MP1	Bottom	-4.7	-2.5	0.00	0.00	0.02	0.02
MP1	Depth-averaged	-2.7	-1.1	0.00	0.00	0.01	0.00
MP2	Surface	N/A	N/A	0.00	0.00	0.01	0.00
MP2	Middle	N/A	N/A	0.00	0.00	0.01	0.01
MP2	Bottom	-4.7	-2.5	0.00	0.00	0.03	0.02
MP2	Depth-averaged	-2.7	-1.1	0.00	0.00	0.02	0.01
MP3	Surface	N/A	N/A	0.00	0.00	0.01	0.00
MP3	Middle	N/A	N/A	0.00	0.00	0.02	0.01
MP3	Bottom	-4.7	-2.5	0.01	0.00	0.03	0.03
MP3	Depth-averaged	-2.7	-1.1	0.01	0.00	0.02	0.01
DM5	Surface	N/A	N/A	0.00	0.00	0.01	0.00
DM5	Middle	N/A	N/A	0.01	0.00	0.03	0.01
DM5	Bottom	-4.7	-2.5	0.01	0.00	0.05	0.04
DM5	Depth-averaged	-2.7	-1.1	0.01	0.00	0.03	0.02
NM3	Surface	N/A	N/A	0.01	0.00	0.06	0.06
NM3	Middle	N/A	N/A	0.01	0.00	0.05	0.03
NM3	Bottom	-4.7	-2.5	0.01	0.00	0.03	0.04
NM3	Depth-averaged	-2.7	-1.1	0.01	0.00	0.03	0.02
NM5	Surface	N/A	N/A	0.00	0.00	0.01	0.00
NM5	Middle	N/A	N/A	0.01	0.00	0.06	0.03
NM5	Bottom	-4.7	-2.5	0.01	0.01	0.05	0.04
NM5	Depth-averaged	-2.7	-1.1	0.01	0.00	0.03	0.02
UR1	Surface	N/A	N/A	0.00	0.00	0.01	0.00
UR1	Middle	N/A	N/A	0.01	0.00	0.04	0.01
UR1	Bottom	-4.7	-2.5	0.01	0.01	0.05	0.05
UR1	Depth-averaged	-2.7	-1.1	0.01	0.00	0.03	0.02
UR2	Surface	N/A	N/A	0.00	0.00	0.01	0.00
UR2	Middle	N/A	N/A	0.01	0.00	0.04	0.02
UR2	Bottom	-4.7	-2.5	0.01	0.01	0.05	0.04
UR2	Depth-averaged	-2.7	-1.1	0.01	0.00	0.03	0.02
UR3	Surface	N/A	N/A	0.00	0.00	0.04	0.07
UR3	Middle	N/A	N/A	0.01	0.00	0.04	0.01
UR3	Bottom	-4.7	-2.5	0.01	0.00	0.03	0.02
UR3	Depth-averaged	-2.7	-1.1	0.01	0.00	0.03	0.01
UR4	Surface	N/A	N/A	0.01	0.00	0.05	0.08
UR4	Middle	N/A	N/A	0.01	0.00	0.06	0.02
UR4	Bottom	-4.7	-2.5	0.01	0.00	0.03	0.02
UR4	Depth-averaged	-2.7	-1.1	0.01	0.00	0.04	0.02
Note: (a) The shaded indicates the potential non-compliance with the WQO.

Nutrients

An assessment of nutrient release during dredging has been carried out in relation to the modelling results of the sediment plume due to unmitigated dredging works and the sediment testing results for the dredging area. In the calculation it has assumed that all TIN and unionised ammonia (NH₃-N) concentrations in the sediments are released to the water. This is the most conservative assumption and will likely result in overestimation of the potential impacts.

The calculated TIN concentrations due to the increase in SS by the dredging works are presented in Table 5.13. As shown and aforementioned, the existing water quality conditions in the vicinity of the CPPS has already breach the WQO for TIN. It is predicted that the dredging works will cause an increase in TIN by 0.1%. The dredging works are thus not attributed significantly to the non-compliance of WQO.

Ammoniacal Nitrogen (NH₄-N) is the sum of ionised ammoniacal nitrogen and unionised nitrogen. Under normal conditions of Hong Kong waters, more than 90% of the ammoniacal nitrogen would be in the ionised form. For the purpose of assessment, a correction (as a function of temperature, pH, and salinity) has been applied based on the EPD monitoring results for station NM5, i.e. temperature of 23.5 degrees Celsius, salinity of 27.7 ppt and pH of 8. From this it derived that NH₃-N constitutes 5% of ammoniacal nitrogen. The results are presented in Table 5.14.

The results show that the increase in NH₃-N concentrations due to the dredging works would be negligible comparing with the ambient concentrations. The total concentrations of NH₃-N at the water quality sensitive receivers are predicted to be well below the WQO criterion of 0.021g L^-1.

Thus it is anticipated that the impacts of the SS elevations due to the dredging works on the nutrient levels are minimal and acceptable.

Table 5.13 Calculated Total Inorganic Nitrogen Concentrations due to Increase in Suspended Solids

Sensitive Receivers	Maximum Depth-averaged SS Concentration (mg L^-1)		Maximum TIN in Sediment (mg kg^-1)	Maximum Increase in TIN (mg L^-1)		Ambient TIN (mg L^-1)	Total TIN (mg L^-1)
	Maximum Depth-averaged SS Concentration (mg L^-1)			Maximum Increase in TIN (mg L^-1)			Total TIN (mg L^-1)
	Dry	Wet		Dry	Wet		Dry	Wet
B1	0.6	1.3	41.2	0.0000240	0.0000552	0.56	0.56	0.56
B2	0.2	0.1	41.2	0.0000092	0.0000033	0.56	0.56	0.56
B3	0.1	0.0	41.2	0.0000032	0.0000012	0.56	0.56	0.56
B4	0.0	0.0	41.2	0.0000002	0.0000008	0.56	0.56	0.56
I1	0.2	0.1	41.2	0.0000089	0.0000054	0.56	0.56	0.56
I2	11.9	8.2	41.2	0.0004906	0.0003396	0.56	0.56	0.56
I3	1.0	0.9	41.2	0.0000399	0.0000368	0.56	0.56	0.56
I4	0.1	0.1	41.2	0.0000025	0.0000024	0.56	0.56	0.56
I5	1.2	1.2	41.2	0.0000513	0.0000488	0.56	0.56	0.56
MP1	0.1	0.0	41.2	0.0000039	0.0000012	0.56	0.56	0.56
MP2	0.1	0.1	41.2	0.0000044	0.0000027	0.56	0.56	0.56
MP3	0.1	0.1	41.2	0.0000050	0.0000022	0.56	0.56	0.56
DM5	0.2	0.1	41.2	0.0000077	0.0000044	0.56	0.56	0.56
NM3	0.2	0.1	41.2	0.0000089	0.0000057	0.56	0.56	0.56
NM5	0.2	0.1	41.2	0.0000083	0.0000045	0.56	0.56	0.56
UR1	0.2	0.1	41.2	0.0000080	0.0000054	0.56	0.56	0.56
UR2	0.2	0.1	41.2	0.0000077	0.0000050	0.56	0.56	0.56
UR3	0.2	0.1	41.2	0.0000075	0.0000033	0.56	0.56	0.56
UR4	0.3	0.1	41.2	0.0000107	0.0000047	0.56	0.56	0.56
Notes: (a) The TIN concentration in sediment is taken from the maximum concentrations among the three sampling stations. (b) The ambient concentration level is derived from the EPD monitoring data at NM5. (c) The shaded cells indicate potential exceedances of the WQO.

Table 5.14 Calculated Unionised Ammonia Concentrations due to Increase in Suspended Solids

Sensitive Receivers	Maximum Depth-averaged SS Concentration (mg L^-1)		Maximum Ammoniacal Nitrogen (NH₄-N) in Sediment (mg kg^-1)	Maximum Increase in Unionised Ammonia (NH₃-N) (mg L^-1)		Ambient NH₃-N (mg L^-1)	Total NH₃-N (mg L^-1)
	Maximum Depth-averaged SS Concentration (mg L^-1)			Maximum Increase in Unionised Ammonia (NH₃-N) (mg L^-1)			Total NH₃-N (mg L^-1)
	Dry	Wet		Dry	Wet		Dry	Wet
B1	0.6	1.3	41.2	0.0000012	0.0000028	0.006	0.006	0.006
B2	0.2	0.1	41.2	0.0000005	0.0000002	0.006	0.006	0.006
B3	0.1	0.0	41.2	0.0000002	0.0000001	0.006	0.006	0.006
B4	0.0	0.0	41.2	0.0000000	0.0000000	0.006	0.006	0.006
I1	0.2	0.1	41.2	0.0000004	0.0000003	0.006	0.006	0.006
I2	11.9	8.2	41.2	0.0000245	0.0000170	0.006	0.006	0.006
I3	1.0	0.9	41.2	0.0000020	0.0000018	0.006	0.006	0.006
I4	0.1	0.1	41.2	0.0000001	0.0000001	0.006	0.006	0.006
I5	1.2	1.2	41.2	0.0000026	0.0000024	0.006	0.006	0.006
MP1	0.1	0.0	41.2	0.0000002	0.0000001	0.006	0.006	0.006
MP2	0.1	0.1	41.2	0.0000002	0.0000001	0.006	0.006	0.006
MP3	0.1	0.1	41.2	0.0000002	0.0000001	0.006	0.006	0.006
DM5	0.2	0.1	41.2	0.0000004	0.0000002	0.006	0.006	0.006
NM3	0.2	0.1	41.2	0.0000004	0.0000003	0.006	0.006	0.006
NM5	0.2	0.1	41.2	0.0000004	0.0000002	0.006	0.006	0.006
UR1	0.2	0.1	41.2	0.0000004	0.0000003	0.006	0.006	0.006
UR2	0.2	0.1	41.2	0.0000004	0.0000003	0.006	0.006	0.006
UR3	0.2	0.1	41.2	0.0000004	0.0000002	0.006	0.006	0.006
UR4	0.3	0.1	41.2	0.0000005	0.0000002	0.006	0.006	0.006
Notes: (a) The maximum NH₄-N in sediment is taken from the maximum concentrations among the three sampling stations. (b) The ambient concentration level is derived from the EPD monitoring data at NM5.

Heavy Metals and Micro-Organic Pollutants

Elutriate tests were carried out to assess the potential of release of heavy metals and micro-organic pollutants from the dredged marine mud. The test results have been assessed and compared to the relevant water quality standard as shown in Table 5.15.

The results show that most dissolved metal concentrations for all samples are below report limits. In addition, all dissolved metal concentrations are found to be well below the water quality standards.

The results also show that all PAHs, PCBs, TBT and chlorinated pesticides are all below reporting limits. This indicates that the leaching of these pollutants is unlikely to occur.

Unacceptable water quality impacts due to the potential release of heavy metals and micro-organic pollutants from the dredged sediment are not expected to occur.

Table 5.15 Comparison between Results of the Elutriation Test of Heavy Metals and Micro-Organic Pollutants and Water Quality Standards

Parameters		Unit	Reporting Limits	Sample at V1	Sample at V2	Sample at V3	Blank Water	Water Quality Standard
Heavy Metals	Arsenic (As)	µg L^-1	1	<1	<1	<1	<1	25.0
	Cadmium (Cd)	µg L^-1	0.5	<0.5	<0.5	<0.5	<0.5	2.5
	Chromium (Cr)	µg L^-1	5	<5	<5	<5	<5	15.0
	Copper (Cu)	µg L^-1	1	1.9	2.1	2	<1	5.0
	Lead (Pb)	µg L^-1	2	<2	<2	<2	<2	25.0
	Mercury (Hg)	µg L^-1	0.2	<0.2	<0.2	<0.2	<0.2	0.3
	Nickel (Ni)	µg L^-1	2	<2	<2	<2	<2	30.0
	Silver (Ag)	µg L^-1	1	<1	<1	<1	<1	2.3
	Zinc (Zn)	µg L^-1	10	<10	<10	<10	<10	40.0
PAHs (Low Molecular Weight)	Naphthalene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Acenaphtylene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Acenaphtene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Fluorene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Phenanthrene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Anthracene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
PAHs (High Molecular Weight)	Benzo(a)anthracene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Benzo(a)pyrene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Chrysene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Dibenz(ah)anthracene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Fluoranthene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Pyrene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Benzo(b)fluoranthene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Benzo(k)fluoranthene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Indeno(1,2,3-cd)pyrene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
	Benzo(ghi)perylene	µg L^-1	0.1	<0.1	<0.1	<0.1	<0.1	-
PCBs	PCB 8	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 18	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 28	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 44	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 52	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 66	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 77	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 101	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 105	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 118	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 126	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 128	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 138	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 153	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 169	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 170	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 180	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	PCB 187	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	Total PCBs	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	0.03
Tributyltin (TBT)	-	µg L^-1	0.015	<0.015	<0.015	<0.015	<0.015	0.1
Chlorinated Pesticides	Alpha-BHC	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	0.03
	Beta BHC	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	3.0
	Gamma BHC	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	0.1
	Delta-BHC	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	0.0049
	Heptachlor	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	0.017
	Aldrin	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	0.16
	Heptachlor epoxide	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	-
	Alpha Endosulfan	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	0.053
	p, p'-DDT	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	1.3
	p, p'-DDD	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	0.053
	p, p'-DDE	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	0.034
	Endosulfan sulfate	µg L^-1	0.01	<0.01	<0.01	<0.01	<0.01	0.13
Note: (a) The concentrations of the pollutants concerned in the blank seawater sample were all found to be below the reporting limits. The concentrations for the target pollutants in the blank seawater sample were therefore not subtracted from the elutriate test results of the respective pollutants.

Construction of the Additional Berthing Facility

About 39,500 m³ of armour rock from the existing seawall will be removed to drive the piles for the additional berthing facility. The same lot of rock will be put back upon completion of the piling works. The duration of the material removal from existing seawall and marine piling works will be approximately 4 weeks and 6.5 weeks respectively. It is anticipated that the short duration works will not cause any unacceptable water quality impacts to sensitive receivers.

Piling works will be required for the additional berthing facility. Some of the piles will be located at the existing sloping seawall. Underneath the seawall, there is a rock fill down to approximately -25 mPD on top of sand down to approximately -34 mPD. Some of the piles will be located aside the existing seawall in order to support the 140-m desk.

Marine piling will be conducted for installation of the hollow cylindrical piles. These cylindrical piles will be driven into position and the soil inside the driven-in piles will be not removed. No soil or sediment excavation would be carried out. Bubble jackets/curtains will also be deployed during the pile driving following common local construction practice. It is expected that the marine piling with deployment of bubble jacket/curtain will cause limited disturbance to the sediments and is unlikely to cause unacceptable impacts to the nearby seawater intakes or other WSRs.

Sewage Discharges

Sewage will arise from the construction workforce and site office’s sanitary facilities. It is estimated that up to 900 construction workers are assumed to be on site at the peak of the construction programme. It is expected that portable toilets will be provided for site workers and the existing sanitary facilities at the CPPS will not be used by any of the site workers. Portable toilet wastewater should be disposed of by a licensed chemical waste collector.

As sewage discharges are not expected to occur, no unacceptable water quality impacts to sensitive receivers are predicted.

Construction Run-off

During land based construction activities for the proposed FGD system and berthing facility, impacts to water quality may occur from pollutants in site run-off which may enter marine waters. Pollutants, mainly suspended sediments, may also enter the receiving waters if pumped groundwater is not adequately controlled.

Design features and methods that will be used to control surface runoff, reduce the potential for erosion, and prevent offsite siltation of any receiving waters will be adopted. Site inspections will be undertaken to ensure the ongoing suitability and good repair of the adopted erosion control measures. In particular, inspections will be undertaken before and after heavy rainfall events. The site runoff will be treated, if required, and checked for compliance with the appropriate standards prior to being discharged.

As construction runoff is expected to be managed through good site practice, no unacceptable impacts to sensitive receivers are predicted.

5.7 Operational Phase Assessment

5.7.1 FGD Effluent

In the LS-FGD process, the flue gas is passed through absorbers that contain slurry of ground limestone in fresh water. The sulphur dioxide is removed by reacting with the limestone (calcium carbonate) to form calcium sulphite. The slurry is then aerated to oxidise the calcium sulphite to form gypsum (calcium sulphate). The resulting gypsum slurry is then treated, resulting in dewatered gypsum and a small quantity of liquid effluent. The resulting effluent may have a small chemical oxygen demand and/or reduced dissolved oxygen concentrations. A portion of the ash within the flue gas is likely to be entrained within the limestone slurry. The ash may contain some metals, the quantities of which will depend upon the constituents of the original fuel coal. The metals of environmental concern that may be contained within the ash include arsenic, cadmium, chromium, copper, mercury, lead and zinc.

The treated FGD effluent will then be discharged through the existing main cooling water discharges of the Castle Peak Power Station “B” (CPB) (Outfall B in Figure 5.7). The existing flow rate from the CPB outfall is 7,119,360 m³ day^-1. The discharge rate of the treated effluent from the Limestone FGD absorber will be 1,440 m³ day^-1, which means that the total discharge from the CPB cooling water outfall will increase to 7,120,800 m³day^-1 (representing a 0.02% increase when compared with the existing flow).

Treatment method of FGD WWTS has to achieve the WPCO TM. The system will comprise primarily settling, precipitation, biological treatment and pH control.

The technology for the reduction of suspended solids, metals concentration, is precipitation of soluble metals and filtration. Precipitation is achieved through the addition of lime / sulfide to precipitate the metals as the insoluble metals hydroxide / sulfide. Biological treatment would be employed for the removal of total nitrogen, chemical and biological oxygen demand. Biological clarifier effluent is treated in a multimedia filter for suspended solids removal. The sludge from the metals precipitation and biological clarifiers is transferred to the thickener. Thickened sludge will be treated in a filter press for sludge dewatering. A polymer is added to the sludge for conditioning to improve dewatering. Filter press filtrate is collected in a sump and transferred to the system for treatment.

It should be noted that there would be no effect on the quantities of residual chlorine in the discharge. It is conservatively assumed that the temperature of the cooling water discharge from CPB will remain unchanged, although there would likely be a small decrease due to the introduction of the small quantity of the treated effluent from the LS-FGD absorber.

The treated effluent from the Limestone FGD absorber will have the following properties, prior to its introduction to the CPB cooling water outfall ([22]):

· Salinity – 0 ppt (fresh water is mixed with limestone to form the absorber slurry);

· Biochemical Oxygen Demand (BOD) – 20 mg L^-1;

· Chemical Oxygen Demand (COD) – 80 mg L^-1;

· Increased concentrations of sulphate ions; and

· Suspended ash particles, which are likely to contain metals.

impacts to WSRs are expected to occur as a result of the operation of the FGD.

Based on the ratio of flows (0.02% of total discharge is represented by the FGD effluent) the final incremental COD in the outfall discharge is 0.016 mg L^-1 and the incremental BOD of 0.004 mg L^-1. It is likely that the oxygen demand will then be dispersed and diluted and then exerted on the marine waters to cause a small dissolved oxygen reduction. It is anticipated that the minor increase in COD and BOD concentrations in the effluent will not cause any unacceptable impacts to the receiving water.

The DO depletion caused by the FGD effluent is predicted to be negligible, the subsequent effect on dissolved oxygen within the surrounding waters is, therefore, predicted to be minimal and adverse impacts to marine ecological resources including the Indo-Pacific Humpback Dolphins are not expected.

The ambient salinity is assumed to be 30.1 ppt, which is derived from the average concentrations near the sea bed and thus represents the higher value, which gives the greater deficit for the worst case. Based on the ratio of flows, the final salinity deficit is thus 0.006 ppt less than the surrounding marine waters. This small salinity deficit is unlikely to cause any adverse impacts to the water quality.

The discharge of the treated effluent discharged into the marine waters should be compiled with the WPCO TM standards and also the effluent standards will be subject to refinement at WPCO licensing stage.

5.7.2 Based on the above, no unacceptable Additional Berthing Facility

A total of about 77 piles, with approximate diameter of 1 m, will stand underneath the deck of the additional berthing facility, which will be constructed parallel and close to the shore. The cross-sectional area of each pile underwater has been estimated to be 0.982 m² with the volume of each pile underwater being 42.2 m³. In view of the small cross-sectional area occupied by the piles and the closeness to the shore, it is not expected that the structure will result in any adverse impact to the hydrodynamic system.

5.8 Construction Phase Water Quality Mitigation Measures

Unacceptable impacts to water quality sensitive receivers have largely been avoided through the adoption of the following measures at the project planning stage.

· Reduction in Indirect Impacts: The proposed works are located at a sufficient distance from water quality sensitive receivers so that the dispersion of sediments from the construction works does not affect the receivers at levels of concern (as defined by the WQO and tolerance criterion).

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

The water quality modelling works, with the assumption of no mitigation measures to be adopted, have indicated that for both the dry and wet seasons, no exceedances of the WQO and the evaluation criterion are predicted to occur during the dredging operation. The impact assessment has also shown that other construction works, if properly controlled, are not expected to cause any unacceptable impacts to the surrounding waters and the sensitive receivers. Hence, the operational constraints and good site practice measures for dredging and construction run-off, presented in the following section, are recommended.

5.8.1 Marine Based Construction Activities

Dredging operations should be undertaken in such a manner as to minimse resuspension of sediments. Specific mitigation and standard good dredging practice measures should therefore be implemented including the following requirements which should be written into the dredging contract. These measures are also summarised in Section 10.2.

· Silt curtains should be deployed around the closed grab dredger to contain suspended solids within the construction site during dredging;

· A daily dredging rate of a closed grab dredger (with a minimum grab size of 8 m³) should be less than 5,200 m³ day^-1, with reference to the maximum rate for dredging, which was derived in the EIA;

· Mechanical grabs should be designed and maintained to avoid spillage and should seal tightly while being lifted;

· Barges or hoppers should have tight fitting seals to their bottom openings to prevent leakage of material;

· Loading of barges or hoppers shall be controlled to prevent splashing of dredged material to the surrounding water;

· Barges or hoppers should not be filled to a level which will cause overflow of materials or pollution of water during loading or transportation;

· Excess material should be cleaned from the decks and exposed fittings of barges or hoppers before the vessel is moved;

· Adequate freeboard should be maintained on barges to reduce the likelihood of decks being washed by wave action;

· All vessels should be sized such that adequate clearance is maintained between vessels and the seabed at all states of the tide to ensure that undue turbidity is not generated by turbulence from vessel movement or propeller wash; and

· The works should not cause foam, oil, grease, litter or other objectionable matter to be present in the water within and adjacent to the works site;

5.8.2 Land Based Construction Activities

Appropriate on-site measures are defined to reduce potential impacts, which will be sufficient to prevent adverse impacts to water quality from land based construction activities. These measures are appropriate for general land based construction activities. All effluent discharge from the construction phase will be subject to control under the WPCO.

Construction Run-off

· At the start of site establishment, perimeter cut-off drains to direct off-site water around the site should be constructed and internal drainage works and erosion and sedimentation control facilities implemented. Channels, earth bunds or sand bag barriers should be provided on site to direct stormwater to silt removal facilities. The design of efficient silt removal facilities should be based on the guidelines in Appendix A1 of ProPECC PN 1/94.

· All the surface runoff or extracted ground water contaminated by silt and suspended solids should be collected by the on-site drainage system and diverted through the silt traps prior to discharge into storm drain.

· All exposed earth areas should be completed as soon as possible after earthworks have been completed, or alternatively, within 14 days of the cessation of earthworks, where practicable. If excavation of soil cannot be avoided during the rainy season, or at any time of year when rainstorms are likely, exposed slope surfaces should be covered by tarpaulin or by other means.

· All drainage facilities and erosion and sediment control structures should be regularly inspected and maintained to ensure proper and efficient operation at all times and particularly following rainstorms. Deposited silt and grit should be removed regularly and disposed of by spreading evenly over stable, vegetated areas.

· Measures should be taken to reduce the ingress of site drainage into excavations. If the excavation of trenches in wet periods is necessary, they should be dug and backfilled in short sections wherever practicable. Water pumped out from trenches or foundation excavations should be discharged into storm drains via silt removal facilities.

· Open stockpiles of construction materials (for example, aggregates, sand and fill material) of more than 50 m³ should be covered with tarpaulin or similar fabric during rainstorms. Measures should be taken to prevent the washing away of construction materials, soil, silt or debris into any drainage system.

· Manholes (including newly constructed ones) should always be adequately covered and temporarily sealed so as to prevent silt, construction materials or debris being washed into the drainage system.

· Precautions to be taken at any time of year when rainstorms are likely, actions to be taken when a rainstorm is imminent or forecasted, and actions to be taken during or after rainstorms are summarised in Appendix A2 of ProPECC PN 1/94. Particular attention should be paid to the control of silty surface runoff during storm events, especially for areas located near steep slopes.

· Oil interceptors should be provided in the drainage system and regularly emptied to prevent the release of oil and grease into the storm water drainage system after accidental spillages. The interceptor should have a bypass to prevent flushing during periods of heavy rain.

· All temporary and permanent drainage pipes and culverts provided to facilitate runoff discharge should be adequately designed for the controlled release of storm flows. All sediment traps should be regularly cleaned and maintained. The temporary diverted drainage should be reinstated to the original condition when the construction work has finished or the temporary diversion is no longer required.

Wastewater from Site Facilities

· Sewage from toilets should be collected by a licensed waste collector.

· Vehicle and plant servicing areas, vehicle wash bays and lubrication bays should, as far as possible, be located within roofed areas. The drainage in these covered areas should be connected to foul sewers via a petrol interceptor.

· Oil leakage or spillage should be contained and cleaned up immediately. Waste oil should be collected and stored for recycling or disposal, in accordance with the Waste Disposal Ordinance.

Storage and Handling of Oil, Other Petroleum Products and Chemicals

· Waste streams classifiable as chemical wastes should be properly stored, collected and treated for compliance with Waste Disposal Ordinance or Disposal (Chemical Waste) (General) Regulation requirements.

· All fuel tanks and chemical storage areas should be provided with locks and be sited on paved areas.

· The storage areas should be surrounded by bunds with a capacity equal to 110% of the storage capacity of the largest tank to prevent spilled oil, fuel and chemicals from reaching the receiving waters.

· The Contractors should prepare guidelines and procedures for immediate clean-up actions following any spillages of oil, fuel or chemicals.

· Surface run-off from bunded areas should pass through oil/grease traps prior to discharge to the stormwater system.

5.9 Operational Phase Water Quality Mitigation Measures

5.9.1 Hydrodynamics

The marine works and structures are expected to have minimal effects on hydrodynamics and water quality. Mitigation measures are not considered to be necessary.

5.9.2 Limestone FGD Absorber Effluent

The high degree of mixing inherent in the coastal margin will result in rapid dilution of the effluent to non-significant concentrations, and therefore mitigation measures are considered unnecessary.

5.9.3 Storage and Handling of Oil, Other Petroleum Products and Chemicals

· Waste streams classifiable as chemical wastes should be properly stored, collected and treated for compliance with the requirements under the Waste Disposal Ordinance or Waste Disposal (Chemical Waste) (General) Regulation.

· All fuel tanks and chemical storage areas should be provided with locks and be sited on paved areas.

· The Contractors should prepare guidelines and procedures for immediate clean-up actions following any spillages of oil, fuel or chemicals.

· Surface run-off from bunded areas should pass through oil/grease traps prior to discharge to the stormwater system.

5.10 Environmental Monitoring and Audit (EM&A)

5.10.1 Construction Phase

Although no unacceptable impacts have been predicted to occur during the operation of dredging works and other associated construction works, monitoring of marine water quality during the construction phase is considered necessary to evaluate whether any impacts would be posed by the dredging operations on the surrounding waters during the construction period of the dredging works. The details of the EM&A programme are presented in Section 10.

5.10.2 Operational Phase

As no unacceptable impacts have been predicted to occur during the operation of the CPB following the installation of additional emissions control facilities, monitoring of marine water quality during the operational phase is not considered necessary.

5.11 Residual Environmental Impacts

No unacceptable impacts have been predicted to occur during the construction phase. Given that impacts to water quality have predicted to be transient and no unacceptable impacts expected to occur, residual environmental impacts during the operational phase are not expected.

5.12 Cumulative Impacts

At present the only committed project that could have cumulative impacts with the construction of the additional berthing facility is the construction of the Permanent Aviation Fuel Facility (PAFF) for the Airport Authority at Castle Peak which is more than 1.5 km away.

By reviewing the EIA study for PAFF ([23]), unacceptable water quality impacts due to the construction works of both projects are not expected. In case any concurrent construction works exist, the cumulative impacts from these two projects are thus expected to be minimal. Referring to the PAFF EIA study, the edge of the mixing zone of the SS elevations caused by the dredging works would not be farther than 500 m away from where the dredger locates. In this Study, the predicted plume of 10 mg L^-1 of maximum depth averaged SS will maximally reach at a point approximately 500m away from the Study dredging area or approximately 1.1 km away from the PAFF dredging area. Thus, the sediment plumes (< 10 mg L^-1) from the two projects are unlikely to overlap each other. It is expected that the construction impacts, if any, due to the dredging works of this Project would be mitigated by implementing the mitigation measures such as deployment of a silt curtain around the grab dredger.

It is noted that there may be a possibility for an overlap of construction schedule between the Project and the potential construction of an Liquefied Natural Gas terminal at South Soko and the associated submarine natural gas pipeline to the Black Point Power Station. Due to the remote distance (greater than 4 km) between these two project works areas, as well as the low severity of water quality impacts as assessed in this Study, cumulative impacts are not likely to occur.

The above-mentioned Liquefied Natural Gas (LNG) terminal project has not been confirmed at the time of the compilation of this Report and therefore appropriate measures should be implemented to avoid cumulative impacts such as the proper scheduling of the Project-related marine works to prevent them from overlapping with those for the LNG project.

5.13 Summary and Conclusion

5.13.1 Construction Phase

The water quality modelling works, with the assumption of no mitigation measures to be adopted, have indicated that for both the dry and wet seasons, no exceedances of the WQO and the evaluation criterion are predicted to occur during the dredging operations. The impact assessment has also shown that other land-based construction works, if properly controlled, are not expected to cause any adverse impacts to the surrounding waters and the sensitive receivers.

5.13.2 Operational Phase

No effluent is anticipated from the operation of the SCR system and water quality impact is not expected.

In the LS-FGD process, the gypsum slurry from the absorber unit is treated, resulting in dewatered gypsum and a small quantity of liquid effluent. The resulting effluent may have a small chemical oxygen demand and/or reduced dissolved oxygen concentrations.

The effluent will be treated to comply with the discharge standards stipulated in the Technical Memorandum on Standards for Effluents Discharged Into Drainage And Sewerage Systems, Inland And Coastal Waters issued under the Water Pollution Control Ordinance. It will then be added to the cooling water flows and discharged via the existing sub-marine cooling water outfall of CPB, resulting in a small increase in the total flows from the outfall. The treated FGD effluent would not be expected to have any adverse effect on the temperature of the cooling water or on the quantities of residual chlorine in the discharge. The high degree of mixing inherent in the coastal margin or coastal zone will result in rapid dilution of the effluent to very low concentrations and no unacceptable water quality impact are predicted. The discharge standards should comply with the WPCO TM and will subject to refinement at WPCO licensing stage.. As a result, further mitigation measures are considered unnecessary.

([1]) Hawker DW & Connell DW (1992). Standards and Criteria for Pollution Control in Coral Reef Areas. Chapter 7 of Pollution in Tropical Aquatic Systems. Connell DW & Hawker DW ed. CRC Press.

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

([3]) 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.

([4]) ERM-Hong Kong, Limited (2003) The Proposed Submarine Gas Pipelines from Cheng Tou Jiao Liquefied Natural Gas Receiving Terminal, Shenzhen to Tai Po Gas Production Plant, Hong Kong – EIA Study. For The Hong Kong China Gas Company.

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

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

([7]) ERM-Hong Kong, Limited (2002) EIA Construction of an International Theme Park in Penny's Bay of North Lantau and it's Essential Associated Infrastructres. CEDD, 2002.

([8]) Chester, R (1990). Marine Geochemistry, Unwin Hyman Ltd.

([9]) Her Majesty's Inspectorate of Pollution (HMIP) (1994). Environmental Economic and BPEO Assessment Principals for Integrated Pollution Control.

([10]) Maunsell (2002). EIA for Decommissioning of Cheoy Lee Shipyard at Penny's Bay. For Civil Engineering Department, Hong Kong SAR Government.

([11]) ERM – Hong Kong (1997). EIA for Disposal of Contaminated Mud in the East Sha Chau Marine Borrow Pit. For Civil Engineering Department, Hong Kong SAR Government.

([12]) Maunsell (2001). EIA for Wanchai Development Phase II - Comprehensive Feasibility Study. For Territory Development Department, Hong Kong SAR Government.

([13]) ERM-Hong Kong (2003). Detailed Site Selection Study for a Proposed Contaminated Mud Disposal Facility within the Airport East/East of Sha Chau (Agreement No. CE 12/2002 (EP)) – Environmental Monitoring Data Review. For the Civil Engineering Department, Hong Kong SAR Government.

([14]) United States Environmental Protection Agency (2006). National Recommended Water Quality Criteria.

([15]) Australian and New Zealand Environment and Conservation Council (1992). Australian Water Quality Guidelines for Fresh and Marine Waters.

([16]) Salazar, M.H. and Salazar, S.M. (1996). "Mussels as Bioindicators: Effects of TBT on Survival, Bioaccumulation, and Growth under Natural Conditions" in Organotin, edited by M.A. Champ and P.F. Seligman. Chapman & Hall, London.

([17]) EPD (2005). Beach Water Quality Report in 2004.

([19]) ERM - HK Ltd (1997). EIA for Disposal of Contaminated Mud in the East of Sha Chau Marine Borrow Pit. For Civil Engineering Department of the SAR Government.

([20]) Mouchel (2002). EIA for Permanent Aviation Fuel Facility. For Hong Kong Airport Authority.

([22]) Information supplied by CLP, based on data from the FGD system manufacturer.

([23]) Mouchel (2002). EIA for Permanent Aviation Fuel Facility. For Hong Kong Airport Authority.

Parameter	Criterion
Colour (HU)	< 20
Turbidity (NTU)	< 10
Threshold Odour No.	< 100
Ammoniacal Nitrogen (mg L^-1)	< 1
Suspended Solids (mg L^-1)	< 10 (20 is the upper threshold)
Dissolved Oxygen (mg L^-1)	> 2
5-day Biochemical Oxygen Demand (mg L^-1)	< 10
Synthetic Detergents (mg L^-1)	< 5
E. coli (cfu 100mL^-1)	< 20,000

Parameter	Depth ^(a)	Unit	Water Quality Objective (WQO)	Ambient Level ^{(b) (c) (d)}			Allowable Effect
Parameter	Depth ^(a)	Unit	Water Quality Objective (WQO)	Annual	Dry	Wet	Annual	Dry	Wet
Dissolved Oxygen ^(e)	S	mg L^-1	> 4 mg L^{-1 (f)} > 5 mg L^{-1 (g)}	6.2	6.7	5.8	-2.2 -1.2	-2.7 -1.7	-1.8 -0.8
	M	mg L^-1	-	5.8	6.7	5.1	N/A	N/A	N/A
	B	mg L^-1	> 2 mg L^{-1 (h)}	5.5	6.7	4.5	-3.5	-4.7	-2.5
	DA	mg L^-1	> 4 mg L^{-1 (h)}	5.8	6.7	5.1	-1.8	-2.7	-1.1
Temperature	S	°C	± 2 °C	N/A	N/A	N/A	± 2 °C	± 2 °C	± 2 °C
	M	°C	± 2 °C	N/A	N/A	N/A	± 2 °C	± 2 °C	± 2 °C
	B	°C	± 2 °C	N/A	N/A	N/A	± 2 °C	± 2 °C	± 2 °C
	DA	°C	± 2 °C	N/A	N/A	N/A	± 2 °C	± 2 °C	± 2 °C
Salinity	S	o/oo	10% variation	23.9	30.2	19.2	2.4	3.0	1.9
	M	o/oo	10% variation	28.6	31.4	26.5	2.9	3.1	2.6
	B	o/oo	10% variation	30.4	31.7	29.5	3.0	3.2	2.9
	DA	o/oo	10% variation	27.6	31.1	25.1	2.8	3.1	2.5
Suspended Solids	S	mg L^-1	30% increase	13.9	16.7	12.0	4.2	5.0	3.6
	M	mg L^-1	30% increase	16.0	20.7	14.0	4.8	6.2	4.2
	B	mg L^-1	30% increase	51.0	49.2	51.0	15.3	14.8	15.3
	DA	mg L^-1	30% increase	23.4	27.6	21.4	7.0	8.3	6.4
pH	S	-	6.5 – 8.5 units	8.0	8.0	8.0	± 5	± 5	± 5
	M	-	6.5 – 8.5 units	8.0	8.1	8.0	± 5	± 4	± 5
	B	-	6.5 – 8.5 units	8.0	8.1	8.0	± 5	± 4	± 5
	DA	-	6.5 – 8.5 units	8.0	8.1	8.0	± 5	± 4	± 5
Notes: (a) Depth: S = Surface, M = Middle, B = Bottom, DA = Depth average (b) The ambient level is derived from the routine EPD monitoring data in 1996-2005 for Station NM5. (c) The ambient level is the arithmetic mean value, with exception for SS. (d) The ambient level for SS is the 90^th percentile values for the difference depth layers and depth-average. (e) No surface and middle DO WQO criteria have been specified for the North Western WCZ. (f) The WQO for Inner Marine Subzone excepting Mariculture Subzone of the Deep Bay WCZ (g) The WQO for Mariculture Subzone of the Deep Bay WCZ (h) The WQO for the North Western WCZ and the Outer Marine Subzone excepting Mariculture Subzone of the Deep Bay WCZ

Water Quality Parameter	Sha Chau and Lung Kwu Chau Marine Park
	N Lung Kwu Chau	N Sha Chau	Pak Chau	SE Sha Chau
	(1999 – 2005)	(1999 – 2000)	(1999 – 2005)	(1999 – 2000)
Temperature (°C)	24.1	24.3	24.1	24.3
Salinity (ppt)	24.7	23.9	25.1	25.1
pH	7.9	8.1	7.9	8.1
Dissolved Oxygen (mg L^-1)	6.2	5.8	6.2	5.8
Suspended Solids (mg L^-1)	20.3	9.7	37.2	10.0
Secchi Depth (m)	1.1	0.8	1.2	0.7
BOD (mg L^-1)	0.2	0.2	0.2	0.2
Ammonia Nitrogen (µg L^-1)	0.050	0.029	0.071	0.030
Unionized Ammonia (µg L^-1)	0.29	0.34	0.29	0.33
Nitrite Nitrogen (µg L^-1)	1.50	3.77	1.38	3.68
Nitrate Nitrogen (µg L^-1)	1.38	0.54	1.31	0.56
Total Inorganic Nitrogen (µg L^-1)	2.26	3.98	2.37	3.81
Total Kjeldahl Nitrogen (mg L^-1)	5.18	14.82	5.13	16.21
Total Nitrogen (mg L^-1)	0.27	0.06	0.13	0.05
Orthophosphate Phosphorus (µg L^-1)	0.74	0.10	0.65	0.09
Total Phosphorus (mg L^-1)	1.02	1.16	1.02	1.10
Silica (mg L^-1)	2.59	2.59	2.09	2.78
Chlorophyll-a (µg L^-1)	1.90	1.07	1.81	1.09
Phaeo-pigment (µg L^-1)	343	54	201	58
E. coli (CFU/100 mL)	1298	117	1070	114
Faecal Coliforms (CFU/100 mL)	24.1	24.3	24.1	24.3
Notes: (a) Data from AFCD (2005). Marine Park Water Quality Report (Web site: www.afcd.gov.hk) (b) Data presented are depth averaged, except as specified. (c) Data presented are annual arithmetic mean except for E. coli, which are geometric means and dissolved oxygen, which are 10^th percentiles.

5 Water Quality assessment