5 Water Quality Impact

5.1 Introduction

5.1.1 This section presents an environmental assessment of potential water quality impacts associated with the construction and operation phases of the Project. Potential Impacts are identified, and appropriate mitigation measures are also recommended to minimise potential adverse impacts and to ensure the acceptability of any residual impact on the surrounding environment.

5.2 Environmental Legislation, Policies, Plans, Standards and Criteria

5.2.1 The criteria for evaluating water quality impacts in this EIA Study include:

· Technical Memorandum on Environmental Impact Assessment Process (Environmental Impact Assessment Ordinance) (EIAO-TM);

· Water Pollution Control Ordinance (WPCO);

· Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters;

· Hong Kong Planning Standards and Guidelines (HKPSG);

· Water Supplies Department (WSD) Water Quality Criteria; and

· Practice Note for Professional Persons (ProPECC), Construction Site Drainage (PN 1/94).

5.2.2 River bottom sediment classification is described in Section 6 of this EIA Report.

Environmental Impact Assessment Ordinance (EIAO), Cap. 499, S.16

5.2.3 This Project is a Designated Project requiring an EIA and an environmental permit under Schedule 2, Part I, I.1 of the EIAO. The EIAO-TM is issued by EPD under Section 16 of the EIAO. EIAO-TM sets out the principles, procedures, guidelines, requirements and criteria for an EIA process. Relevant sections in the EIAO-TM provide the details of assessment criteria and guidelines related to the water quality assessment, including:

Annex 6 – Criteria for Evaluating Water Pollution; and

Annex 14 – Guidelines for Assessment of Water Pollution.

Water Pollution Control Ordinance (WPCO), Cap. 358

5.2.4 The Water Pollution Control Ordinance (Cap. 358), in existence since 1980, is the major legislation relating to the protection and control of water quality in Hong Kong. According to the Ordinance and its subsidiary legislation, Hong Kong waters are subdivided into ten water control zones (WCZs). Each WCZ has a designated set of statutory Water Quality Objectives (WQOs) based on their beneficial uses. The proposed Project is located within the Port Shelter WCZ and the corresponding WQOs are listed in Table 5.1.

Table 5.1 Summary of Water Quality Objectives for the Port Shelter WCZ

Parameters	Objectives	Sub-Zone
Offensive Odour, tints	Not to be present	Whole zone
Colour	Not to exceed 50 Hazen units, due to waste discharges	Inland waters
Visible foam, oil scum, litter	Not to be present	Whole zone
E. coli	Not to exceed 610 per 100mL, calculated as the geometric mean of all samples collected in one calendar year	Secondary Contact Recreation Subzone and Fish Culture Subzones
	Not to exceed 180 per 100mL, calculated as the geometric mean of all samples collected from March to October inclusive in one calendar year.	Bathing Beach Subzones
Dissolved Oxygen (DO) within 2 m of the seabed	Not less than 2 mg L^-1 for 90% of samples	Marine waters including Fish Culture Subzones
Depth-averaged DO	Not less than 4 mg L^-1 for 90% of samples	Marine waters except Fish Culture Subzones
	Not less than 5 mg L^-1 for 90% of samples	Fish Culture Subzones
Dissolved Oxygen	Not less than 4.0 mg L^-1	Inland waters
pH	To be in the range of 6.5 - 8.5 units, change due to human activity not to exceed 0.2 units.	Inland water in Ho Chung (A) Sub-zone. Marine waters except Bathing Beach Subzones
	To be in the range of 6.0 – 9.0 units, change due to human activity not to exceed 0.5 units	Bathing Beach Subzones
Salinity	Change due to human activity not to exceed 10% of ambient	Whole zone
Temperature	Change due to human activity not to exceed 2^oC	Whole zone
Suspended solids	Not to raise the ambient level by 30% caused by human activity	Marine waters
	Annual median not to exceed 25 mg L^-1 due to human activity	Inland waters
Ammonia (NH3-N)	Annual mean not to exceed 0.021 mg L^-1 as unionised form	Whole zone
Nutrients	Shall not cause excessive or nuisance growth of algae or other aquatic plants.	Marine waters
Nutrients	Annual mean depth-averaged inorganic nitrogen not to exceed 0.1 mg L^-1	Marine waters
BOD5	Not to exceed 5 mg L^-1	Inland waters
Chemical Oxygen Demand	Not to exceed 30 mg L^-1	Inland waters
Phenol	Shall not be present in such quantities as to produce a specific odour, or in concentrations greater than 0.05 mg per litre as C6H5OH	Bathing Beach Subzones
Dangerous substances	Should not attain such levels as to produce significant toxic, effects in humans, fish or any other aquatic organisms.	Whole zone
	Human activity should not cause a risk to any beneficial use of the aquatic environment.	Whole zone
Turbidity	No changes in turbidity or other factors arising from waste discharges shall reduce light transmission substantially from the normal level.	Bathing Beach Subzones

Source: Statement of Water Quality Objectives (Port Shelter Water Control Zone).

Technical Memorandum

5.2.5 The Technical Memorandum (TM) on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters, issued under Section 21 of the WPCO (Cap.358, S.21), defines acceptable discharge limits to different types of receiving waters (foul sewers, storm water drains, inland and coastal waters). The limits control the physical, chemical and microbial quality of effluents. Under the TM, effluents discharged into inland waters are subject to different standards for particular volumes of discharge. The discharge standard varies with the type of use of the downstream water. The inland waters are classified into four groups. The inland water bodies within the Project area are used for irrigation and general amenity and secondary contact recreation, which should be classified as Groups B and D inland waters. Any new effluent discharge during the construction phase would be required to comply with the terms and conditions of a discharge licence (standards shown in Table 4 and Table 6 of the TM), issued by EPD, under the WPCO.

Hong Kong Planning Standards and Guidelines

5.2.6 The Hong Kong Planning Standards and Guidelines (HKPSG), Chapter 9 (Environment), provides additional information on regulatory guidelines against water pollution for sensitive uses such as aquaculture and fisheries zones, bathing waters and other contact recreational waters.

5.3 Description of the Environment

Marine Water Quality Monitored by EPD

5.3.1 The EPD marine water quality monitoring data routinely collected in the Port Shelter WCZ were used to demonstrate the marine water quality in the WCZ. EPD monitoring stations PM2, PM3, PM6 and PM7 are located in the vicinity of the Project (Figure 5.1). A summary of the published EPD monitoring data for the year of 2001 is presented in Table 5.2

Table 5.2 Summary Statistics of 2001 Marine Water Quality in the Port Shelter WCZ in the Vicinity of the Project

Parameter	Depth (See Note 1)	EPD Monitoring Station (Monthly)
		PM2	PM3	PM6	PM7
Temperature (^oC)		24.0 (16.2 – 30.7)	23.6 (16.3 – 28.4)	23.7 (16.3 – 28.8)	23.5 (16.4 – 28.2)
Salinity (psu)		31.1 (25.8 – 33.1)	31.4 (28.3 – 33.1)	31.3 (27.4 – 32.8)	31.6 (28.1 – 33.0)
Dissolved Oxygen (DO) (% saturation)		90 (72 – 108)	86 (70 – 116)	88 (65 – 104)	88 (69 – 113)
	Bottom	86 (57 – 113)	76 (30 – 121)	79 (38 – 106)	79 (34 – 115)
DO (mg L^-1)		6.4 (5.0 – 8.2)	6.1 (4.9 – 8.9)	6.2. (4.4 – 8.0)	6.2 (4.5 – 8.7)
	Bottom	6.1 (3.9 – 8.6)	5.5 (2.1 – 9.3)	5.7 (2.6 – 8.2)	5.7 (2.4 – 8.8)
pH value		8.3 (7.9- 8.7)	8.3 (7.9 – 8.7)	8.3 (7.9 – 8.6)	8.3 (8.0 – 8.7)
Turbidity (NTU)		6.2 (4.9-8.3)	6.1 (4.8 – 7.5)	6.4 (4.9 – 9.5)	6.1 (4.9 – 8.3)
SS (mg L^-1)		2.3 (0.9-4.8)	2.1 (0.7 – 4.2)	2.1 (0.8 – 5.4)	1.8 (0.5 – 3.7)
Silica (as SiO2) (mg L^-1)		0.6 (0.2 – 1.1)	0.6 (0.2 – 1.2)	0.6 (0.2 – 1.1)	0.6 (0.1 – 0.9)
BOD5 (mg L^-1)		0.9 (0.3 – 1.8)	1.8 (0.3 – 1.9)	0.8 (0.5 – 1.3)	0.8 (0.3 – 2.2)
Nitrite Nitrogen (mg L^-1)		<0.01 (<0.01 – 0.01)	<0.01 (<0.01 – 0.02)	<0.01 (<0.01 – 0.01)	<0.01 (<0.01 – 0.02)
Nitrate Nitrogen (mg L^-1)		0.02 (<0.01 – 0.09)	0.02 (<0.01 – 0.08)	0.03 (<0.01 – 0.09)	0.03 (<0.01 – 0.10)
Ammonia Nitrogen (mg L^-1)		0.03 (0.02 – 0.06)	0.04 (0.01 – 0.09)	0.04 (0.02 – 0.07)	0.03 (0.01 – 0.07)
Unionised Ammonia (mg L^-1)		<0.001 (<0.001 – <0.010)	0.001 (<0.001 – 0.010)	0.001 (<0.001 – 0.010)	0.001 (<0.001 – <0.010)
Total Inorganic Nitrogen (mg L^-1)		0.05 (0.02 – 0.16)	0.06 (0.02 – 0.15)	0.07 (0.02 – 0.15)	0.06 (0.02 – 0.15)
Total Kjeldahl Nitrogen (mg L^-1)		0.14 (0.08 – 0.22)	0.17 (0.08 – 0.23)	0.13 (0.07 – 0.19)	0.11 (0.06 – 0.18)
Ortho-Phosphate (mg L^-1)		0.01 (0.01 – 0.02)	0.01 (0.01 – 0.02)	0.01 (0.01 – 0.02)	0.01 (0.01 – 0.02)
Total Phosphorus (mg L^-1)		0.02 (0.02 – 0.03)	0.02 (0.02 – 0.03)	0.02 (0.02 – 0.04)	0.02 (0.02 – 0.03)
Chlorophyll-a (µg L^-1)		3.0 (0.6 – 5.9)	2.7 (0.9 – 7.5)	3.0 (1.4 –5.1)	1.8 (0.4 – 4.4)
E. coli (Cfu per 100 mL)		3 (1 – 33)	1 (1 – 3)	2 (1 – 4)	1 (1 – 2)
Faecal Coliform (Cfu per 100 mL)		26 (3 –260)	6 (1 – 33)	9 (1 – 28)	2 (1 – 28)

Notes:

1. Except as specified, data presented are depth-averaged values calculated by taking the means of three depths: Surface, mid-depth, bottom.

2. Data presented are annual arithmetic means of depth-averaged results except for E. coli and faecal coliforms that are annual geometric means.

3. Data in brackets indicate the ranges.

Environmental Trend of Marine Water Quality in Port Shelter

5.3.2 As reported in the EPD Marine Water Quality in Hong Kong in 2001, the water quality in Port Shelter has remained in a good and stable condition since mid-1980s. Some water quality improvements in terms of reduction of E. coli bacteria at PM2 and PM6 and an increase in bottom DO at PM3 were observed. These improvements were likely due to the implementation of pollution control measures such as the enforcement of the WPCO, the upgrading of treatment level of the Sai Kung Sewage Treatment Works and provision of sewerage to unsewered areas.

Inland Water Quality Monitored by EPD

5.3.3 Ho Chung River, Sha Kok Mei Stream and Tai Chung Hau Stream are the three major inland water systems within the Project area (Figure 5.1). A summary of the published EPD monitoring data of monitoring stations PR1, PR2, PR5, PR6, PR7 and PR8 for the year of 2001 is presented in Table 5.3.

Table 5.3 Summary Statistics of 2001 Inland Water Quality in the Port Shelter WCZ in the Vicinity of the Project

Parameter	Unit	Ho Chung River		Sha Kok Mei Stream		Tai Chung Hau Stream
		PR1	PR2	PR5	PR6	PR7	PR8
DO	mg/l	8.1 (5.3-8.9)	8.6 (7.7-9.7)	8.6 (6.5-9.5.)	8.9 (7.4-10.3)	8.9 (8.0-10.2)	8.7 (7.1-10.0)
pH	-	7.1 (6.7-7.8)	7.4 (7.0-7.9)	7.3 (6.7-7.8)	7.5 (7.0-7.9)	7.5 (7.0-9.0)	7.3 (6.9-7.8)
SS	mg/l	4 (2-11)	1 (1-2)	3 (2-5)	5 (1-13)	5 (1-1600)	2 (1-9)
BOD5	mg/l	1 (1-4)	1 (1-1)	1 (1-2)	4 (1-9)	1 (1-4)	1 (1-2)
COD	mg/l	9 (5-14)	4 (2-7)	6 (3-12)	9 (3-19)	6 (2-21)	6 (3-10)
Faecal coliforms	Cfu/ 100ml	26000 (3900- 280000)	2400 (510- 8200)	20000 (5500- 67000)	95000 (49000- 360000)	27000 (12000- 80000)	27000 (10000- 250000)
E.Coli	Cfu/100ml	9100 (12000- 110000)	420 (100- 2900)	6400 (950- 47000)	20000 (6700- 66000)	8400 (3700- 29000)	9800 (6100- 18000)

Notes:

1. Data presented are in annual medians of monthly sample;

2. Figures in bracket are annual ranges;

3. DO: Dissolved oxygen; SS: Suspended solids; BOD₅: 5-day Biochemical Oxygen Demand; COD: Chemical Oxygen Demand.

Environmental Trend of Inland Water Quality in Port Shelter Water Control Zone

5.3.4 As reported in EPD’s “River Water Quality in Hong Kong 2001”, the Water Quality Index grading of the three inland water systems in Port Shelter WCZ ranged from “good” to “excellent”. However, the bacterial level at the downstream ends of the three watercourses remained high due to the likely faecal pollution from unsewered premises.

Inland Water Quality Additional Monitoring Survey

5.3.5 Additional water quality field survey stations were arranged at Ho Chung Channel within areas of the river section not presently covered by the EPD routine monitoring stations. Field surveys and water quality measurement were also carried out at Tai Chung Hau Stream / Pak Kong River and Sha Kok Mei Stream / Sai Kung River, where water quality data were not available from the EPD river water quality monitoring programme. Figures 5.3 to 5.5 show the locations of these water quality monitoring stations.

5.3.6 The water quality parameters were measured and analysed at all designated monitoring stations once per week, for four weeks per month during dry, wet and transitional seasons. After detailed site-visits, it was observed that there was no apparent direct industrial pollution source along the watercourses, and therefore no heavy metal measurement was taken. Tables 5.4 - 5.6 present a summary of the measurement results of the surveys for dry, transitional and wet seasons, respectively.

5.3.7 Overall, the results of the survey indicate that no apparent point or non-point pollution discharge was identified in the three river channels. However, the bacterial levels at these downstream stations are considerably higher than the EPD monitoring stations which are located at the upstream of the rivers. The survey results indicated the likely faecal pollution from the unsewered premises at downstream ends of the three river channels.

Table 5.4 Summary of Measurement Results for Dry Season (Feb 2003)

Location	Unit	Ho Chung Channel				Pak Kong River						Sai Kung River
Parameter		HC1	HC2	HC3	HC4	PK1	PK2	PK3	PK4	PK5	PK6	SK1	SK2	SK3	SK4
Suspended Solids (SS)	mg/L	7.0	3.3	2.0	<2	32.8	15.5	5.3	15.5	4.7	2.3	4.0	18.8	3.7	3.3
		(4-10)	(3-4)	(<2-2)	(<2-<2)	(3-112)	(2-29)	(3-10)	(3-44)	(3-8)	(2-3)	(2-6)	(2-68)	(2-6)	(2-5)
Colour (Apparent)	PCU	3.0	5.3	<1	<1	30.0	8.0	<1	3.0	1.5	1.0	2.0	<1	1.0	<1
		(2-4)	(5-6)	(<1-<1)	(<1-<1)	(<1-30)	(1-15)	(<1-<1)	(1-5)	(1-2)	(1-1)	(<1-2)	(<1- <1)	(<1- 1)	(<1- <1)
Turbidity	NTU	3.8	8.2	0.8	0.6	5.1	2.1	0.9	6.6	1.5	0.6	0.9	0.5	0.4	0.7
		(0.2- 5.6)	(0.2- 15.9)	(0.4- 1.3)	(0.2- 1.3)	(0.4- 14.5)	(0.4- 5.8)	(0.3- 2)	(0.6- 23.2)	(0.9- 2.3)	(0.2- 1.1)	(0.3- 1.7)	(0.2- 0.8)	(0.2- 0.9)	(0.2- 1.1)
Ammonia as N	mg/L	0.70	0.21	0.02	0.02	0.08	0.10	0.09	0.08	0.07	0.12	0.03	0.03	0.06	0.03
		(0.17- 1.78)	(0.05- 0.36)	(0.02- 0.03)	(0.01- 0.03)	(0.06- 0.11)	(0.05- 0.19)	(0.06- 0.13)	(0.06- 0.1)	(0.05- 0.1)	(0.06- 0.17)	(0.02- 0.04)	(0.02- 0.05)	(0.01- 0.2)	(0.02- 0.05)
Unionised Ammonia	mg/L	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01
		(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)
Nitrate as N	mg/L	4.88	0.24	0.36	0.36	0.87	1.42	1.64	1.58	1.62	1.11	0.47	0.60	0.54	1.67
		(0.14- 19)	(0.18- 0.29)	(0.32- 0.42)	(0.29- 0.44)	(0.37- 1.39)	(1.1- 1.78)	(1.26- 2.01)	(1.06- 1.86)	(0.79- 2.03)	(0.77- 1.61)	(0.18- 0.66)	(0.53- 0.67)	(0.41- 0.67)	(0.54- 2.9)
Nitrite + Nitrate as N	mg/L	0.2	0.3	0.4	0.4	0.9	1.4	1.7	1.6	1.7	1.1	0.5	0.6	0.5	1.7
		(0.07- 0.27)	(0.18- 0.34)	(0.32- 0.42)	(0.29- 0.45)	(0.37- 1.42)	(1.1- 1.82)	(1.29- 2.07)	(1.09- 1.91)	(0.82- 2.1)	(0.78- 1.63)	(0.18- 0.67)	(0.53- 0.67)	(0.42- 0.67)	(0.54- 2.9)
Total Kjeldahl Nitrogen as N	mg/L	1.0	0.5	0.1	0.2	0.3	0.3	0.3	0.6	0.3	0.3	0.2	0.9	0.3	0.2
		(0.6- 2)	(0.34- 0.7)	(0.1- 0.2)	(0.1- 0.4)	(0.2- 0.6)	(0.2- 0.5)	(0.2- 0.4)	(0.2- 1.5)	(0.2- 0.4)	(0.2- 0.4)	(0.2- 0.3)	(0.3- 1.6)	(0.2- 0.4)	(0.2- 0.3)
Total Inorganic Nitrogen	mg/L	0.5	0.4	0.5	0.4	1.2	1.8	2.1	2.0	1.9	1.6	0.7	0.8	0.7	1.9
		(0.24- 0.68)	(0.2- 0.61)	(0.32- 0.66)	(0.29- 0.66)	(0.43- 1.92)	(1.29- 2.46)	(1.65- 2.55)	(1.74- 2.15)	(1.61- 2.16)	(0.95- 2.5)	(0.22- 1.33)	(0.56- 1.34)	(0.43- 1.34)	(0.56- 2.95)
Total Phosphorus	mg/L	0.2	0.4	<0.1	<0.1	0.1	0.1	0.1	0.1	0.1	0.1	<0.1	0.5	<0.1	<0.1
		(0.1- 0.4)	(0.39- 0.4)	(<0.1- <0.1)	(<0.1- <0.1)	(<0.1- 0.1)	(0.1- 0.1)	(0.1- 0.1)	(0.1- 0.1)	(<0.1- 0.1)	(<0.1- 0.1)	(<0.1- <0.1)	(<1- 0.5)	(<0.1- <0.1)	(<0.1- <0.1)
Reactive Phosphorus as P	mg/L	0.2	0.2	0.0	0.0	0.0	0.1	0.1	0.1	0.1	0.0	0.0	0.1	0.0	0.0
		(0.02- 0.39)	(0.02- 0.4)	(0.02- 0.04)	(0.02- 0.02)	(0.03- 0.05)	(0.04- 0.1)	(0.05- 0.09)	(0.05- 0.14)	(0.04- 0.09)	(0.03- 0.06)	(0.02- 0.04)	(0.04- 0.08)	(0.03- 0.04)	(0.02- 0.06)
E. coli	Cfu /100ml	20145.0	22110.0	305.5	390.5	14577.5	14725.0	12625.0	18000.0	15050.0	17500.0	1862.5	2155.0	1912.5	1460.0
		(180- 78000)	(0.03- 86000)	(92- 450)	(4- 1200)	(110- 55000)	(2000- 44000)	(1500- 35000)	(2300- 53000)	(2500- 48000)	(1700- 46000)	(180- 5200)	(920- 4600)	(900- 4400)	(20- 3400)
Fecal Coliform	Cfu /100ml	21705.0	23768.8	455.0	873.5	15540.0	16300.0	16675.0	23825.0	16325.0	27725.0	2120.0	2225.0	2000.0	1473.3
		(220- 84000)	(25- 92000)	(100- 600)	(4- 2900)	(160- 57000)	(2500- 47000)	2200- 40000)	(2600- 54000)	(3000- 51000)	(2300- 54000)	(180- 5200)	(1100- 4600)	(1000- 4400)	(20- 3400)
Chlorophyll a	Mg/m3	5.0	26.0	<5	<5	12.5	<5	<5	<5	<5	<5	<5	5.0	<5	<5
		(<5-5)	(<5-26)	(<5-<5)	(<5-<5)	(10-15)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-5)	(<5-5)	(<5-5)
Oil & Grease	mg/L	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5
		(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-5)	(<5-5)
Chemical Oxygen Demand	mg/L	Nil	Nil	3.0	2.0	20.0	4.0	5.7	11.5	4.0	2.5	2.7	9.0	3.0	3.3
		(<20-<20)	(<2-<20)	(2-4)	(2-2)	(<20-20)	(4-4)	(2-12)	(4-19)	(2-6)	(2-3)	(2-4)	(2-28)	(2-4)	(2-4)
Biochemical Oxygen Demand	mg/L	4.3	4.7	<2	<2	2.0	2.5	2.0	2.0	<2	2.0	<2	<2	<2	<2
		(2-9)	(3-8)	(<2-<2)	(<2-<2)	(<2-2)	(2-3)	(<2-2)	(2-2)	(<2-<2)	(2-2)	(<2-<2)	(<2-<2)	(<2-<2)	(<2-<2)
pH	-	7.2	7.2	6.9	6.9	7.1	7.2	7.1	7.1	7.3	7.3	6.9	6.9	6.9	6.9
		(6.8- 7.6)	(6.5- 7.8)	(6.4- 7.4)	(6.5- 7.3)	(6.9- 7.6)	(7- 7.9)	(6.7- 7.5)	(6.5- 7.8)	(6.8- 8)	(6.9- 7.8)	(6.7- 7.2)	(6.6- 7.1)	(6.5- 7.6)	(6.6- 7.4)
Dissolved Oxygen	mg/L	6.6	7.0	7.4	6.9	7.4	7.4	7.4	6.8	6.8	7.0	6.9	6.9	7.1	7.3
		(6- 7.2)	(5.8- 8.6)	(6.4- 8.8)	(6.2- 7.5)	(6.3- 8.1)	(6.7- 8.2)	(6.6- 8.1)	(5.8- 7.6)	(5.9- 7.4)	(6.5- 7.4)	(6.1- 7.6)	(6.2- 7.6)	(6.5- 7.7)	(6.5- 8.2)
Flow	m^3/s	1.75	1.25	3.83	0.73	6.3	0.5	1	0.38	3.73	0.15	0.7	0.33	0.33	0.5
		(0.8- 2.6)	(0.03- 2.6)	(0.2- 10.6)	(0.3- 1.7)	(1.1- 10.9)	(0.3- 0.7)	(0.2- 3.2)	(0.2- 0.5)	(1.1- 9)	(0.03- 0.3)	(0.03- 1.8)	(0.03- 0.5)	(0.1- 0.7)	(0.3- 1)

Table 5.5 Summary of Measurement Results for Transitional Season (April 2003)

Location	Unit	Ho Chung Channel				Pak Kong River						Sai Kung River
Parameter		HC1	HC2	HC3	HC4	PK1	PK2	PK3	PK4	PK5	PK6	SK1	SK2	SK3	SK4
Suspended Solids (SS)	mg/L	6.3	4.8	4.3	4.7	12.0	14.0	12.5	6.8	6.8	5.8	5.5	7.7	4.3	3.3
		(3-8)	(3-7)	(3-7)	(3-8)	(5-29)	(4-27)	(4-26)	(2-13)	(2-12)	(3-13)	(4-7)	(3-15)	(2-7)	(2-5)
Colour (Apparent)	PCU	7.0	9.5	5.5	9.0	7.5	6.3	8.8	11.0	17.5	9.5	5.0	21.5	6.7	10.0
		(4-10)	(9-10)	(5-6)	(7-11)	(2-20)	(1-18)	(2-20)	(10-12)	(7-28)	(1-32)	(2-10)	(13-30)	(1-11)	(10-10)
Turbidity	NTU	1.8	1.0	0.9	0.7	6.2	6.1	6.0	1.0	2.6	3.4	1.4	1.9	1.3	1.3
		(0.4- 3.5)	(0.2- 1.9)	(0.5- 1.3)	(0.4- 1)	(0.2- 19.3)	(0.4- 18.4)	(0.7- 17.3)	(0.6- 1.4)	(0.6- 8.1)	(0.7- 9.2)	(0.5- 2.9)	(0.3- 4.8)	(0.2- 3.6)	(0.6- 2.6)
Ammonia as N	mg/L	0.50	0.24	0.06	0.06	0.17	0.16	0.14	0.12	0.11	0.09	0.06	0.05	0.05	0.06
		(0.19- 0.8)	(0.04- 0.6)	(0.01- 0.14)	(0.03- 0.09)	(0.08- 0.27)	(0.09- 0.25)	(0.07- 0.21)	(0.09- 0.17)	(0.07- 0.16)	(0.04- 0.17)	(0.03- 0.1)	(0.03- 0.11)	(0.03- 0.11)	(0.02- 0.11)
Unionised Ammonia	mg/L	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01
		(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)
Nitrate as N	mg/L	0.41	0.54	0.51	0.52	1.67	1.56	1.74	1.93	2.33	1.88	0.60	0.69	0.68	2.64
		(0.16- 0.86)	(0.38- 0.86)	(0.34- 0.81)	(0.29- 0.85)	(1.32- 1.89)	(1.35- 180)	(1.32- 1.91)	(1.54- 2.44)	(1.93- 2.65)	(0.49- 2.46)	(0.45- 0.82)	(0.46- 0.94)	(0.49- 0.89)	(2.3- 2.92)
Nitrite + Nitrate as N	mg/L	0.4	0.5	0.5	0.5	1.7	1.6	1.8	2.0	2.4	1.9	0.6	0.7	0.7	2.6
		(0.17- 0.87)	(0.38- 0.88)	(0.35- 0.81)	(0.29- 0.86)	(1.36- 1.93)	(1.35- 1.88)	(1.36- 1.92)	(1.58- 2.55)	(1.99- 2.65)	(0.49- 2.53)	(0.45- 0.82)	(0.46- 0.95)	(0.49- 0.9)	(2.3- 2.92)
Total Kjeldahl Nitrogen as N	mg/L	0.9	0.5	0.5	0.4	0.9	0.7	0.5	0.7	0.5	0.5	0.3	0.4	0.3	0.3
		(0.5-1.2)	(0.3-1.1)	(0.3-0.9)	(0.2-0.5)	(0.5-1.1)	(0.5-0.8)	(0.3-0.8)	(0.3-1.1)	(0.2-1.1)	(0.2-1.2)	(0.2-0.3)	(0.2-0.8)	(0.2-0.4)	(0.2-0.4)
Total Inorganic Nitrogen	mg/L	0.9	0.8	0.6	0.6	1.9	1.8	1.9	2.1	2.5	2.0	0.7	0.7	0.7	2.7
		(0.57- 1.06)	(0.42- 1.05)	(0.4- 0.95)	(0.29- 0.95)	(1.53- 2.19)	(1.49- 2.13)	(1.53- 2.1)	(1.67- 2.72)	(2.1- 2.73)	(0.53- 2.7)	(0.49- 0.87)	(0.49- 1.06)	(0.19- 1.01)	(2.32- 2.98)
Total Phosphorus	mg/L	0.2	0.2	<0.1	0.1	0.2	0.1	0.1	0.2	0.2	0.2	<0.1	0.2	<0.1	<0.1
		(0.1-0.2)	(0.2-0.2)	(<0.1-<0.1)	(0.1-0.1)	(0.1-0.2)	(0.1-0.2)	(0.1-0.2)	(0.1-0.2)	(0.1-0.2)	(0.1-0.2)	(<0.1- <0.1)	(0.2-0.2)	(<0.1- <0.1)	(<0.1- <0.1)
Reactive Phosphorus as P	mg/L	0.0	0.0	0.0	0.0	0.1	0.1	0.1	0.1	0.1	0.1	0.0	0.1	0.0	0.0
		(0.01- 0.09)	(0.02- 0.05)	(0.02- 0.04)	(0.02- 0.03)	(0.07- 0.13)	(0.06- 0.13)	(0.07- 0.13)	(0.07- 0.16)	(0.08- 0.16)	(0.02- 0.15)	(0.02- 0.05)	(0.04- 0.09)	(0.04- 0.05)	(0.02- 0.04)
E. coli	Cfu/ 100ml	17600.0	11387.5	737.5	592.5	34500.0	42250.0	34250.0	47750.0	31650.0	27775.0	5725.0	4150.0	6175.0	654.0
		(3400- 23000)	(950- 20000)	(290- 1300)	(50- 1300)	(22000- 68000)	(11000- 76000)	(12000- 87000)	(30000- 97000)	(8600- 86000)	(1100- 76000)	(1100- 9600)	(1000- 5200)	(1500- 8000)	(3- 2600)
Fecal Coliform	Cfu/ 100ml	29550.0	16625.0	1360.0	874.0	42250.0	50750.0	38750.0	54750.0	36500.0	34300.0	8575.0	6900.0	8200.0	679.8
		(5200- 42000)	(1700- 29000)	(300- 3300)	(56- 2200)	(22000- 93000)	(11000- 100000)	(12000- 99000)	(31000- 120000)	(10000- 100000)	(1200- 96000)	(3100- 12000)	(5600- 8000)	(6600- 8900)	(3- 2700)
Chlorophyll a	mg/m3	<5	<5	15.0	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5
		(<5-<5)	(<5-<5)	(15-15)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)
Oil & Grease	mg/L	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5
		(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)
Chemical Oxygen Demand	mg/L	40.0	3	7.0	4.3	26.5	10.0	9.0	9.7	8.3	13.0	10.3	7.3	5.0	11.0
		(20-60)	(<2-<11)	(3-10)	(4-5)	(13-40)	(6-14)	(6-15)	(6-12)	(4-13)	(12-14)	(9-12)	(6-8)	(3-8)	(3-22)
Biochemical Oxygen Demand	mg/L	5.0	3.0	<2	4.0	4.0	3.0	2.0	2.5	3.0	2.5	<2	<2	2.0	2.0
		(5-5)	(3-3)	(<2-<2)	(4-4)	(4-4)	(3-3)	(2-2)	(2-3)	(2-4)	(2-3)	(<2-<2)	(<2-<2)	(<2-2)	(<2-2)
pH		7.4	7.4	7.4	7.4	7.3	7.4	7.3	7.4	7.5	7.4	7.4	7.4	7.4	7.4
		(7.2-7.6)	(7.2-7.7)	(7.3-7.5)	(7.3-7.6)	(7.2-7.4)	(7.3-7.5)	(7.1-7.4)	(7.2-7.4)	(7.4-7.6)	(7.3-7.4)	(7.4-7.4)	(7.3-7.6)	(7.3-7.5)	(7.3-7.5)
Dissolved Oxygen	mg/L	5.1	6.2	7.4	7.2	6.4	7.5	7.5	8.1	7.4	7.6	6.0	6.4	7.0	7.8
		(4.6-5.7)	(4.7-8.8)	(4.1—9)	(4.6-8.3)	(5.1-7.3)	(7.1-8.3)	(6.1-8.6)	(6.9-8.9)	(7.3-8)	(7.1- 8.32)	(4.1-6.8)	(6.2-6.6)	(6.1-7.6)	(7.1-8.7)
Flow	m3/s	1.25	0.28	0.93	0.35	2.2	0.3	0.28	0.23	0.08	0.13	0.08	0.05	0.75	0.6
		(0.7- 2.6)	(0.1- 0.6)	(0.1- 2.8)	(0.03- 0.7)	(0.5- 6.2)	(0.2- 0.4)	(0.03- 0.5)	(0.03- 0.5)	(0.03- 0.2)	(0.03- 0.3)	(0.03- 0.2)	(0.03- 0.1)	(0.1- 1.4)	(0.1- 1.1)

Table 5.6 Summary of Measurement Results for Wet Season (June 2003)

Location	Unit	Ho Chung Channel				Pak Kong River						Sai Kung River
Parameter		HC1	HC2	HC3	HC4	PK1	PK2	PK3	PK4	PK5	PK6	SK1	SK2	SK3	SK4
Suspended Solids (SS)	Mg/L	6.7	4.7	2.0	<2	3.3	3.8	2.7	3.0	2.8	2.7	4.0	5.0	3.0	4.3
		(3-11)	(4-6)	(<2-2)	(<2-<2)	(3-4)	(2-7)	(<2-3)	(<3-3)	(2-3)	(<2-3)	(2-7)	(<2-8)	(<2-4)	(<2-8)
Colour (Apparent)	PCU	<1	<1	1.0	2.0	1.7	2.0	1.0	1.0	<1	<1	1.0	2.0	1.0	<1
		(<1-<1)	(<1-<1)	(<1-1)	(<1-2)	(<1-2)	(<1-2)	(<1-1)	(1-1)	(<1-<1)	(<1-<1)	(<1-1)	(<1-2)	(<1-1)	(<1-<1)
Turbidity	NTU	0.7	0.5	1.0	0.9	0.8	1.2	1.1	0.7	0.7	0.3	0.6	0.9	0.5	0.7
		(0.5-0.8)	(0.2-0.8	(0.5-1.3)	(<0.1-1.1)	(0.2-1.4)	(0.2-1.6)	(<0.01-1.7)	(0.3-1)	(1-<0.1)	(<0.1-0.4)	(<0.1-0.9)	(<0.1-1.5)	(0.2-0.8)	(0.2-1.0)
Ammonia as N	Mg/L	0.07	0.05	<0.01	0.01	0.06	0.06	0.06	0.05	0.06	0.05	0.03	0.04	0.05	0.04
		(0.01- 0.13)	(0.01- 0.08)	(<0.01- 0.01)	(0.01- 0.01)	(0.03- 0.09)	(0.02- 0.15)	(0.04- 0.12)	(0.04- 0.07)	(0.04- 0.07)	(0.04- 0.06)	(0.01- 0.05)	(0.02- 0.08)	(0.02- 0.12)	(0.02- 0.07)
Unionised Ammonia	Mg/L	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01
		(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)	(<0.01- <0.01)
Nitrate as N	Mg/L	0.3	0.3	0.3	0.3	0.8	0.8	0.8	1.0	1.1	1.1	0.3	0.3	0.3	0.8
		(0.26- 0.44)	(0.26- 0.44)	(0.16- 0.44)	(0.13- 0.46)	(0.57- 1.24)	(0.58- 1.21)	(0.58- 1.23)	(0.71- 1.64)	(0.7- 1.66)	(0.71- 1.64)	(0.18- 0.38)	(0.18- 0.38)	(0.18- 0.36)	(0.23- 1.98)
Nitrite + Nitrate as N	Mg/L	0.3	0.3	0.3	0.3	0.8	0.8	0.8	1.1	1.1	1.1	0.3	0.3	0.3	0.8
		(0.27- 0.44)	(0.26- 0.44)	(0.17- 0.45)	(0.13- 0.46)	(0.58- 1.26)	(0.59- 1.23)	(0.62- 1.26)	(0.72- 1.71)	(0.71- 1.73)	(0.72- 1.71)	(0.18- 0.38)	(0.18- 0.38)	(0.18- 0.39)	(0.23- 2)
Total Kjeldahl Nitrogen as N	Mg/L	0.4	0.3	0.2	0.3	0.6	0.5	0.5	0.7	0.6	0.6	0.5	0.4	0.3	0.4
		(0.2-0.5)	(0.2-0.6)	(0.1-0.3)	(0.2-0.3)	(0.1-0.8)	(0.2-0.7)	(0.2-0.6)	(0.4-1.0)	(0.2-0.8)	(0.4-1.0)	(<0.1-0.6)	(0.2-0.8)	(0.2-0.4)	(0.2-0.5)
Total Inorganic Nitrogen	Mg/L	0.4	0.4	0.3	0.3	0.9	0.8	0.9	1.1	1.2	1.1	0.3	0.3	0.3	0.9
		(0.27- 0.52)	(0.29- 0.45)	(0.17- 0.46)	(0.13- 0.47)	(0.61- 1.35)	(0.62- 1.38)	(0.63- 1.38)	(0.77- 1.75)	(0.78- 1.77)	(0.78- 1.75)	(0.21- 0.39)	(0.2- 0.46)	(0.22- 0.48)	(0.27- 2.07)
Total Phosphorus	Mg/L	<0.1	0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	0.1	0.1	<0.1	<0.1
		(<0.1- <0.1)	(<0.1- 0.1)	(<0.1- <0.1)	(<0.1- <0.1)	(<0.1- <0.1)	(<0.1- 0.1)	(<0.1- <0.1)	(<0.1- <0.1)	(<0.1- <0.1)	(<0.1- <0.1)	(<0.1- 0.1)	(<0.1- 0.1)	(<0.1- <0.1)	(<0.1- <0.1)
Reactive Phosphorus as P	Mg/L	0.02	0.02	0.02	0.02	0.02	0.03	0.04	0.1	0.1	0.1	0.02	0.02	0.01	0.04
		(0.02- 0.02)	(0.02- 0.02)	(0.02- 0.02)	(0.01- 0.02)	(0.01- 0.06)	(0.01- 0.06)	(0.03- 0.07)	(0.03- 0.12)	(0.04- 0.12)	(0.03- 0.12)	(0.01- 0.03)	(<0.01- 0.03)	(<0.01- <0.01)	(0.01- 0.08)
E. coli	Cfu/ 100ml	2797.0	4025.0	1416.0	1487.5	23000.0	13425.0	11025.0	13275.0	20500.0	17000.0	8590.0	6155.0	5385.0	660.0
		(88- 4000)	(2400- 6100)	(64- 3200)	(70- 3900)	(12000- 40000)	(9700- 20000)	(5600- 15000)	(2100- 22000)	(10000- 33000)	(8000- 21000)	(960- 28000)	(420- 21000)	(840- 17000)	(10- 1500)
Fecal Coliform	Cfu/ 100ml	4450.0	6300.0	2602.5	3099.0	72500.0	65750.0	46250.0	22625.0	23750.0	21250.0	10750.0	7100.0	10825.0	967.5
		(300- 6500)	(3500- 8200)	(110- 4700)	(96- 5200)	(14000- 200000)	(12000- 180000)	(15000- 120000)	(2500- 42000)	(15000- 33000)	(19000- 24000)	(2200- 33000)	(700- 21000)	(1200- 32000)	(20- 2000)
Chlorophyll a	Mg/m3	5.0	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5
		(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)
Oil & Grease	Mg/L	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5	<5
		(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)	(<5-<5)
Chemical Oxygen Demand	Mg/L	21.0	6.0	4.5	3.8	10.0	6.3	8.7	7.0	9.0	7.3	5.7	4.5	4.5	5.0
		(2-40)	(6-6)	(3-6)	(2-6)	(6-18)	(2-11)	(6-14)	(6-8)	(5-12)	(6-10)	(4-7)	(3-7)	(4-6)	(4-6)
Biochemical Oxygen Demand	mg/L	<2	<2	<2	<2	<2	<2	6.5	<2	<2	2.0	<2	<2	<2	<2
		(<2-<2)	(<2-<2)	(<2-<2)	(<2-<2)	(<2-<2)	(<2-<2)	(<2-20)	(<2-<2)	(<2-<2)	(<2-2)	(<2-<2)	(<2-<2)	(<2-<2)	(<2-<2)
pH	-	6.6	6.7	6.5	6.6	6.8	6.8	6.8	6.9	6.8	6.9	6.8	6.7	6.6	6.6
		(6.2-7)	(6.5-6.9)	(6.2-6.7)	(6.5-6.8)	(6.3-7.3)	(6.7-7.1)	(6.5-7.1)	(6.8-7.1)	(6.5-7.2)	(6.5-7.2)	(6.5-6.9)	(6.6-7.0)	(6.5-6.7)	(6.1-7)
Dissolved Oxygen	mg/L	6.5	7.3	7.2	8.4	4.5	5.3	4.8	5.0	6.2	5.5	6.0	5.4	5.8	8.5
		(3.8-8.3)	(5-8.6)	(3.4-9.7)	(7.5-9)	(2-7.3)	(3.7-7.6)	(3.6-7.5)	(3.9-6.5)	(5.8-6.5)	(3.9-7.4)	(3.8-7.8)	(3.1-6.6)	(3.9-7.3)	(7.6-9.2)
Flow	m^3/s	2.2	1.4	4.5	0.1	2.5	1.0	0.2	0.03	0.1	0.2	0.1	0.03	0.1	1.1
		(0.1-7.6)	(0.03-4.5)	(0.03-14.7)	(0.03-0.3)	(0.4-4.9)	(0.1-3.2)	(0-0.5)	(0.03-0.1)	(0.03-0.5)	(0.03-0.7)	(0.03-0.2)	(0.03-0.03)	(0.03-0.5)	(0.3-2.3)

Compliance with Water Quality Objectives (WQOs)

5.3.8 The river water quality was assessed by compliance with the water quality objectives (WQOs) for inland waters. Five key water quality parameters, namely pH, suspended solids, DO, BOD₅, and COD were used in the assessment of compliance with the WQOs (Table 5.1). The seasonal compliance with WQOs was expressed in percentage terms and was based on the data of the water samples collected during the three hydrodynamic seasons (dry, transitional and wet) (Tables 5.4 to 5.6).

Table 5.7 Summary of the Compliance with the WQOs for the Inland Waters

Location	Ho Chung Channel (% Compliance)			Pak Kong River (% Compliance)			Sai Kung River (% Compliance)
WQOs	Dry	Transition	Wet	Dry	Transition	Wet	Dry	Transition	Wet
pH	93.8	100	100	100	100	100	100	100	100
SS	100	100	100	87.5	87.5	100	93.8	100	100
DO	100	100	93.8	100	100	71.0	100	100	87.5
COD	100	93.8	93.8	100	100	100	100	100	100
BOD5	87.5	100	100	100	100	100	100	100	100

Ho Chung Channel

5.3.9 A high overall compliance rate (> 95%) with the key WQOs was observed in Ho Chung Channel during the three seasons. Only the recorded BOD₅ of samples collected at the downstream stations HC1 and HC2 were observed to exceed the WQO on one occasion in the dry season. However, in the wet season with the increased flow, this phenomenon was not observed.

Pak Kong River

5.3.10 A high overall compliance rate (> 96%) with the key WQOs was observed in Pak Kong River through the three seasons. Scattered high suspended solids (SS) concentrations were observed, likely due to the disturbance of sampling. Low DO concentrations were observed at PK1, PK3 and PK6 respectively. This may be due to the temporary discharge from unsewered premises.

Sai Kung River

5.3.11 The highest overall compliance rate (> 98%) with the key WQOs was observed in Sai Kung River throughout the three seasons. Low DO data was observed at station SK2, which was located closest to the likely unsewered premises.

5.4 Water Sensitive Receivers

5.4.1 The Project is located within the Port Shelter WCZ. In order to evaluate the potential water quality impacts during the construction and operation phases, the proximity of water sensitive receivers (WSRs) to the Project sites (Ho Chung Channel, Pak Kong River and Sai Kung River) were identified. Figure 5.2 shows the water sensitive receivers identified in accordance with the HKPSG and the EIAO (Sha Ha Beach within Sai Kung river area, Hebe Haven and Pak Sha Wan Scout Sea Activities Centre within Pak Kong River area, Marine Cove and the mangrove embayment between Maine Cove and Nam Wai within Ho Chung Channel area).

5.5 Assessment Methodology & Criteria

5.5.1 The Assessment Area for the water quality impact assessment is defined by a distance of 500m from the project boundary of the three proposed river channels.

5.5.2 The water sensitive receivers that may be affected by the construction activities for the drainage improvement works were identified. Potential sources of water quality impact that may arise during the construction and operation phases of the Project were described. This task included identifying pollutants from point discharges and non-point sources to surface run-off. All the identified sources of potential water quality impact were then evaluated and their impact significance determined. The need for mitigation measures to reduce any adverse impacts on water quality to acceptable levels was identified.

5.6 Identification of Environmental Impacts

Construction Phase

5.6.1 Potential sources of water quality impact associated with the construction of the proposed drainage improvement works have been identified and include:

· excavation within watercourses for channel construction;

· construction site runoff and drainage;

· general construction activities;

· sewage effluent generated by on-site workforce; and

· accidental spillage of chemicals in the construction site.

Channel Construction

5.6.2 The construction of the Project is expected to involve excavation, formation of embankments and permanent/temporary diversion of watercourses, which would probably lead to temporary or permanent obstruction of flows. In addition, construction activities being carried out along the streams/rivers without adequate mitigation measures may likely cause scouring and deposition of sediment and lead to an increase of suspended solids levels and depletion of dissolved oxygen in the water body. This may also alter the existing natural processes such as siltation, flows and flow velocity. Potential increases in SS concentrations in the watercourse are likely to affect the water sensitive uses downstream and the receiving water body of the Port Shelter WCZ.

5.6.3 The disposal of any slurry water would need to comply with the TM on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters under the WPCO.

Construction Site Runoff and Drainage

5.6.4 Runoff from the construction works areas may contain increased loads of sediments, other suspended solids and contaminants. Potential sources of pollution from site drainage include:

· runoff and erosion from exposed soil surfaces, earth working areas and stockpiles;

· release of grouting and cement materials with rain wash;

· wash water from dust suppression sprays; and

· fuel and lubricants from maintenance of construction vehicles and mechanical equipment.

5.6.5 Sediment laden runoff may carry pollutants (adsorbed onto the particle surfaces) into the downstream water body. Associated effects which may arise include increased suspended solids concentrations in the receiving waters.

General Construction Activities

5.6.6 On-site construction activities may cause water pollution from the following:

· uncontrolled discharge of debris and rubbish such as packaging, construction materials and refuse; and

· spillages of liquids stored on-site, such as oil, diesel and solvents etc, are likely to result in water quality impacts if they enter the adjacent watercourses.

Sewage Effluents

5.6.7 Domestic sewage would be generated from the workforce during the construction phase. However, this temporary sewage can be adequately treated by interim sewage treatment facilities, such as portable chemical toilets, which can be installed within the construction site.

Operation Phase

5.6.8 Potential negative impacts are identified below:

· Maintenance desilting: desilting would be required to remove any silt, grit or rubbish deposited within the drainage channel.

· Likely change in estuarine water quality due to the change of flow rate, erosion rates and sedimentation patterns.

5.7 Prediction and Evaluation of Impacts

Construction Phase

Channel Construction

5.7.1 To minimise potential impacts on water quality during the channel construction for the proposed drainage improvements to the Sai Kung River, Pak Kong River and Ho Chung Channel, the excavation works at these three rivers would be carried out in the dry condition. Construction would be carried out by land-based plant. Potential impacts on water quality would be minimised by restricting the excavation works to within an artificially enclosed dry section of the river/stream. Containment measures such as bunds and barriers would be used within the river/stream to minimise the impacts upon the downstream water body. Figure 5.6 demonstrates this special construction method for channel with the mitigation measures.

5.7.2 As only minimal disturbance would result to the watercourse during the diversion works at the three rivers, the potential for impacts on water quality within the rivers/streams is expected to be localized and in short-term. It is anticipated that any elevations in suspended solids concentrations during the diversion works would be limited to the bottom depth of the water column during the placement of the bund or barrier and that any re-suspended sediment would settle quickly on the channel bed, close to the area of disturbance. This kind of minimal disturbance would unlikely cause any unacceptable water quality impacts on the downstream water body.

5.7.3 Identified water sensitive receivers in the vicinity of the proposed drainage improvement works (see Figure 5.2) include the beach at Sha Chau (located approximately 500m from the site boundary of the Sai Kung River), the Marina Cove (located approximately 300m from the site boundary of the Ho Chung Channel), the mangrove embayment between Maine Cove and Nam Wai (approximately 250 m from the river mouth of Ho Chung Channel), and the Pak Sha Wan Tam Wah Ching Sea Activity Centre (located approximately 250m from the site boundary of the Pak Kong River). With the implementation of the working method controls as described above and detailed in Section 5.8.2, it is anticipated that unacceptable water quality impacts would not arise at the identified water quality sensitive receivers during the excavation works for the channel construction. As an additional level of protection, monitoring and audit of water quality during the construction stage is recommended.

Resuspension of Sediment and Potential Contaminant Release

5.7.4 Excavation along the streams may disturb deposited bottom sediment. The extent of SS impact would depend on the scale of works along the streams and working methods employed, but is predicted to be minimal since excavation activities would be undertaken within the dry stream channels which enclosed by earth bunds/concrete blocks.

5.7.5 The excavated material from the river channel would comprise soil, sand, gravel and small rocks (for details see Section 6). The chemical testing results discussed in Section 6 indicated that the material on the stream and riverbeds was generally “unpolluted”. Furthermore, potential water quality impact due to the release of pollutants from the riverbed material would not be expected since the excavation works would be carried out in the dry section of the river channel.

Construction Run-off and Drainage

5.7.6 Without mitigation, construction runoff and drainage would likely cause physical, chemical and biological effects to the water bodies in the vicinity. It is important that mitigation measures, as described in Section 5.8.5, should be strictly followed to prevent runoff and drainage water with high levels of SS from entering the adjacent water bodies. With the implementation of mitigation measures, including the installation of silt traps and use of embankments or bunds, it is considered that disturbance to water bodies would be localised and deterioration in water quality would be minimal. Unacceptable impacts on downstream watercourses would not be expected.

General Construction Activities

5.7.7 The effects on water quality from construction activities are likely to be minimal, provided that site boundaries are well maintained and good construction practices described in Sections 5.8.6 and 5.8.7 are well implemented.

Sewage Effluents

5.7.8 It is unlikely that sewage generated from the site would have a significant water quality impact, provided that sewage is not discharged directly to the adjacent water bodies, and chemical toilets are used and properly maintained.

Cumulative Construction Impacts

5.7.9 The “Improvement of Ho Chung Road “ Project is found likely to be undertaken concurrently with this proposed project. However, taking the same mitigation measures as above, no significant cumulative water quality impacts would be expected.

Operation Phase

5.7.10 During operation of the Project, the flood improvement works would not produce extra pollution loading to the flow of the three river systems. The new alignments of the streams would provide widened sections to alleviate flooding within the Sai Kung area during heavy rainfalls. The improved channels/streams would allow greater flow and flushing during the flush periods. The greater flushing will enable organic, nutrients, heavy metals and other dissolved pollutants to be dispersed downstream. However, due to their existing “good” water quality condition (see Table 5.7), this kind of dispersion would not cause any significant water quality impacts on the downstream-end water quality sensitive receivers for the three river systems.

5.7.11 Based on available information including review of proposed land-uses set out in the Pak Kong and Sha Kok Mei OZP (OZP No. S/SK-PK/7), Hebe Haven OZP (S/SK-HH/4) and Ho Chung OZP (S/SK-HC/6), no potential new pollution source could be identified and expected in vicinity of the three rivers. As such, discharge of run-off into the three rivers causing adverse impacts on coastal waters of Hebe Haven, Sha Ha and Inner Port Shelter would not be anticipated during the operation of the project.

5.7.12 In addition, the future alignments of the streams would also likely increase the natural aeration of the widened channel waters that would further improve the DO conditions. After the implementation of the Project, sediment erosion would be substantially reduced. This reduction would reduce the maintenance desilting frequency downstream and minimise the potential water quality impacts which may arise from maintenance desilting activities.

5.7.13 Ad hoc maintenance desilting is likely to cause potential short-term negative local impacts on water quality. However, the water quality impact would be localized and in short-term. As mentioned above, the widened channel would reduce the frequency of desilting and the desilting would be carried out section by section within the channel and in the dry season.

5.7.14 The water levels in the channel are predicted to be lower than existing condition due to channel widening. The lowering of water levels and the low flow during dry season would enhance sedimentation. Considering the low existing SS concentration of the streams (see Tables 5.4, 5.5 and 5.6), this pattern would unlikely cause a significant impact on the water quality of the streams.

Cumulative Operation Impacts

5.7.15 The “Improvement of Ho Chung Road “ Project is found likely to be interacted with this proposed project. However, no significant water operational impact would be expected from “Improvement of Ho Chung Road” considering that it is only a small local village road improvement project. Hence, apart from the operational water quality impacts identified above, no cumulative operational impact would be expected.

5.8 Mitigation Measures

5.8.1 Proposed mitigation measures for containing and minimising water quality impacts are summarised below.

Construction Phase

Channel Excavation Works

5.8.2 The excavation works for the earth channel construction would be carried out along sections of the three streams. Due to the characteristics of narrow width and small water flow of the original channel, the excavation can be carried out in dry condition (even in wet season) by diverting the stream flow from upstream by a temporary drainage channel or narrowing the river/stream with a temporary earth bund or barrier. Figure 5.6 shows the schematic design of the special construction method involving the temporary drainage division. This could effectively isolate the excavating section from the stream water. Containment measures such as bunds and barriers should be used within the river/stream to prevent water from entering the excavation area. The temporary drainage channel would be backfilled when the construction works are completed or the temporary diversion is no longer required. Although flooding of the proposed contaminant section seldom occurs during the dry season, the excavation would consider to temporarily stop when flood water enter the containment causing leakage of runoffs to stream water.

5.8.3 To further minimise the leakage and loss of sediments during excavation, tightly sealed closed grab excavators should be employed in river sections where material to be handled is wet. Where material is dry and in non-river sections, conventional excavations can be used.

5.8.4 This method of channel excavation is feasible and practical as proposed by the Project Engineer and will be specified in the contract document for implementation.

Construction Run-off and Drainage

5.8.5 The site practices outlined in ProPECC PN 1/94 “Construction Site Drainage” should be followed as far as practicable in order to minimise surface runoff and the chance of erosion, and also to retain and reduce any suspended solids prior to discharge. These practices include the following items:

· Before commencing any site formation work, all sewer and drainage connections should be sealed to prevent debris, soil, sand etc. from entering public sewers/drains.

· Temporary ditches should be provided to facilitate run-off discharge into appropriate watercourses, via a silt retention pond.

· Boundaries of earthworks should be marked and surrounded by dykes or embankments for flood protection, as necessary.

· Sand/silt removal facilities such as sand traps, silt traps and sediment basins should be provided to remove sand/silt particles from runoff to meet the requirements of the Technical Memorandum standards under the WPCO. The design of silt removal facilities should be based on the guidelines provided in ProPECC PN 1/94. All drainage facilities and erosion and sediment control structures should be inspected monthly and maintained to ensure proper and efficient operation at all times and particularly during rainstorms.

· Water pumped out from foundation excavations should be discharged into silt removal facilities.

· Careful programming of the works to minimise surface excavations for the drainage improvement works during the wet season. If excavation of soil cannot be avoided during the wet season, exposed slope surfaces should be covered by a tarpaulin or other means. Other measures that need to be implemented before, during, and after rainstorms are summarized in ProPECC PN 1/94.

· Exposed soil areas should be minimised to reduce potential for increased siltation and contamination of runoff.

· Earthwork final surfaces should be well compacted and subsequent permanent work should be immediately performed.

· Open stockpiles of construction materials or construction wastes on-site should be covered with tarpaulin or similar fabric during rainstorms.

General Construction Activities

5.8.6 Debris and refuse generated on-site should be collected, handled and disposed of properly to avoid entering the adjacent watercourses. Stockpiles of cement and other construction materials should be kept covered when not being used.

5.8.7 Oils and fuels should only be used and stored in designated areas which have pollution prevention facilities. To prevent spillage of fuels and solvents to the river/streams, all fuel tanks and storage areas should be provided with locks and be sited on sealed areas, within bunds of a capacity equal to 110% of the storage capacity of the largest tank. The bund should be drained of rainwater after a rain event.

Sewage from Construction Workforce

5.8.8 Temporary sanitary facilities, such as portable chemical toilets, should be employed on-site where necessary to handle sewage from the workforce. A licensed contractor would be responsible for appropriate disposal and maintenance of these facilities.

Operation Phase

5.8.9 Desilting of the three river channels should be carried out during periods of low flow (i.e. dry season, from November to March).

Accidental Spillage of Chemicals on Site

5.8.10 In case of the occurrence of accidental spillage of chemicals, it is required to take immediate actions to control the release of chemicals into the nearby water bodies. It is recommended that the contractor of the project should develop an emergency plan to deal with accidental spillage of chemicals in the construction site. The contractor shall submit for approval of the Director 3 sets of emergency spillage action plan for the Project before commencement of operation of the project. The emergency spillage action plan should ensure that any accidental spillage will be dealt with immediately and will not impact on any water bodies. The plan shall be verified by the Environmental Manager before submission. Measures covered by other pollution control Ordinances shall not be included in the emergency spillage action plan.

5.8.11 Good site practices would avoid the accidents to occur. Areas for chemical storage should be securely locked and kept as far from the drainage systems or stream courses as possible. The storage area should have an impermeable floor and bunding of capacity to accommodate 110% of the volume of the largest container or 20% by volume of the chemical waste stored in that area, whichever is the greatest, to minimise the impacts from any potential accidents.

5.8.12 Disposal of chemical wastes should be carried out in compliance with the Waste Disposal Ordinance. The Code of Practice on the Packaging, Labelling and Storage of Chemical Wastes published under the Waste Disposal Ordinance details the requirements to deal with chemical wastes. General requirements are given as follows:

· Suitable containers should be used to hold the chemical wastes to avoid leakage or spillage during storage, handling and transport;

· Chemical waster containers should be suitably labelled to notify and warn the personnel who are handling the wastes to avoid accidents;

· Storage area should be selected at a safe location on site and adequate space should be allocated to the storage area.

5.9 Residual Environmental Impact

5.9.1 With the full implementation of the recommended mitigation measures for the construction and operation phases of the proposed Project, no unacceptable residual impact on water quality is anticipated.

5.10 Environmental Monitoring and Audit Requirements

5.10.1 The water quality assessment in the EIA Report identified that the key issue in terms of water quality would be related to excavation works for the earth channel construction of the proposed drainage improvement works. Details of the recommended water quality monitoring requirements and regular audit during construction phase are included in Section 11 of this report and the stand-alone EM&A Manual.

5.11 Conclusions

5.11.1 The key issue in terms of water quality would be related to excavation works for the construction phase of the proposed drainage improvement works in Sai Kung. To minimise potential impacts on water quality during the channel construction, working method controls have been recommended for the three river channels in Sai Kung River, Pak Kong River and Ho Chung Channel. In particular, excavation works for the earth channel at each river would be carried out in dry condition by diverting the stream flow from upstream of the site and containment measures would be used within the channel to prevent water from entering the excavation area.

5.11.2 Other potential sources of water quality impact comprised construction site runoff and drainage; debris, refuse and liquid spillages from general construction activities; and sewage effluents from the construction workforce. Minimisation of water quality deterioration could be achieved through implementing adequate mitigation measures such as control measures on site runoff and drainage from the works areas to minimise construction run-off. Proper site management and good housekeeping practices would also be required to ensure that construction wastes and materials would not enter the downstream water courses. Sewage effluent arising from the construction workforce would also require appropriate treatment through provision of portable toilets. With the implementation of these recommended mitigation measures, the construction works for the proposed drainage improvement works would not be anticipated to result in unacceptable impacts on water quality.

5.11.3 Water quality monitoring and audit would be carried out to detect any deterioration of water quality during the construction phase.