Figure 6.1	Location of Water Sensitive Receivers and Water Quality Monitoring Station
Figure 6.2	Identification of Ponds to be Retained or Removed Under the Project

Appendices

Appendix 6.1

Calculation of Pollution Loading of Stormwater During Operational Phase

Glossary

ADWF	Average Dry Weather Flow
BMPs	Best Management Practices
DWF	Dry Weather Flow
EIA	Environmental Impact Assessment
EIAO	Environmental Impact Assessment Ordinance
EIAO-TM	Technical Memorandum on Environmental Impact Assessment Process
EM&A	Environmental Monitoring and Audit
EPD	Environmental Protection Department
LC	Lut Chau
LCNR	Lut Chau Nature Reserve
NSW	Nam Sang Wai
NSW WEA	Nam Sang Wai Wetland Enhancement Area
ProPECC PN	Professional Persons Environmental Consultative Committee Practice Note
SIA	Sewerage Impact Assessment
SPS	Sewage Pumping Station
STW	Sewage Treatment Work
TPB	Town Planning Board
TM-DSS	Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters
uPVC	Unplasticized Polyvinyl Chloride
WCZs	Water Control Zones
WPCO	Water Pollution Control Ordinance
WQI	Water Quality Index
WQOs	Water Quality Objectives
WSRs	Water Sensitive Receivers
YLBS	Yuen Long Barrage Scheme
YLEPP	Yuen Long Effluent Polishing Plant
YLSTW	Yuen Long Sewage Treatment Works
YLTN	Yuen Long Town Nullah

6 Water Quality Impact

6.1 Introduction

6.1.1 This section presents potential water quality impacts associated with the construction and operational phases of the Project. The water quality assessment is based on the criteria and guidelines as stipulated in Annexes 6 and 14 of the EIAO-TM for evaluation and assessment of water quality impact and covers the scope of work described in Section 3.2.1 of the EIA Study Brief of the Project. Mitigation measures are also recommended, when necessary, to avoid or minimise the potential impacts of water quality to acceptable levels as appropriate.

6.2 Environmental Legislations, Standards and Guidelines

6.2.1 The relevant legislation, standards and guidelines used for water quality impact assessment of the Project are described in this section.

Water Pollution Control Ordinance (Cap. 358)

6.2.2 The Water Pollution Control Ordinance (WPCO) (Cap. 358) provides the main statutory framework for the protection and control of water quality in Hong Kong. Under the Ordinance and its subsidiary legislation, the entire Hong Kong waters are divided into ten Water Control Zones (WCZs) and four supplementary WCZs. Each WCZ has a designated set of statutory Water Quality Objectives (WQOs) aimed to protect various water regimes (i.e., inland waters, marine waters, bathing beaches and fish culture subzone etc.) and its users. The location of the Project Site falls within the Deep Bay WCZ and hence the WQOs designated for Deep Bay WCZ are listed in Table 6.1.

Table 6.1: Summary of Water Quality Objectives for Deep Bay WCZ

Parameter	Objectives	Part(s) of Zone
Aesthetic Appearance	Waste discharges shall cause no objectionable odours or discolouration of the water.	Whole zone
	Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other substances should be absent.
	Mineral oil should not be visible on the surface. Surfactants should not give rise to a lasting foam.
	There should be no recognisable sewage-derived debris.
	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.
	Waste discharges shall not cause the water to contain substances which settle to form objectionable deposits.
Bacteria	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.	Secondary Contact Recreation Subzone and Mariculture Subzone
	The level of Escherichia coli should be zero per 100 mL, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.	Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones
	The level of Escherichia coli should not exceed 1 000 per 100 mL, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.	Yuen Long & Kam Tin (Lower) Subzone and other inland waters
	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.	Yung Long Bathing Beach Subzone
Colour	Waste discharges shall not cause the colour of water to exceed 30 Hazen units.	Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones
Colour	Waste discharges shall not cause the colour of water to exceed 50 Hazen units.	Yuen Long & Kam Tin (Lower) Subzone and other inland waters
Dissolved Oxygen	Waste discharges shall not cause the level of dissolved oxygen to fall below 4 milligrams per litre for 90% of the sampling occasions during the year; values should be taken at 1 metre below surface.	Inner Marine Subzone excepting Mariculture Subzone
	Waste discharges shall not cause the level of dissolved oxygen to fall below 4 milligrams per litre for 90% of the sampling occasions during the year; values should be calculated as water column average (arithmetic mean of at least 2 measurements at 1 metre below surface and 1 metre above seabed). In addition, the concentration of dissolved oxygen should not be less than 2 milligrams per litre within 2 metres of the seabed for 90% of the sampling occasions during the year.	Outer Marine Subzone excepting Mariculture Subzone
	The dissolved oxygen level should not be less than 5 milligrams per litre for 90% of the sampling occasions during the year; values should be taken at 1 metre below surface.	Mariculture Subzone
	Waste discharges shall not cause the level of dissolved oxygen to be less than 4 milligrams per litre.	Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone, Indus Subzone, Ganges Subzone, Water Gathering Ground Subzones and other inland waters of the Zone
pH	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.	Marine waters excepting Yung Long Bathing Beach Subzone
	Waste discharges shall not cause the pH of the water to exceed the range of 6.5–8.5 units.	Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones
	The pH of the water should be within the range of 6.0–9.0 units.	Other inland waters
	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.	Yung Long Bathing Beach Subzone
Temperature	Waste discharges shall not cause the natural daily temperature range to change by more than 2.0°C.	Whole zone
Salinity	Waste discharges shall not cause the natural ambient salinity level to change by more than 10%.	Whole zone
Suspended Solids	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
Suspended Solids	Waste discharges shall not cause the annual median of suspended solids to exceed 20 milligrams per litre.	Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone, Ganges Subzone, Indus Subzone, Water Gathering Ground Subzones and other inland waters
Ammonia	The un-ionized ammoniacal nitrogen level should not be more than 0.021 milligram per litre, calculated as the annual average (arithmetic mean).	Whole zone
Nutrients	(a) Nutrients shall not be present in quantities sufficient to cause excessive or nuisance growth of algae or other aquatic plants.	Inner and Outer Marine Subzones
	Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.7 milligram per litre, expressed as annual mean.	Inner Marine Subzone
	Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.5 milligram per litre, expressed as annual water column average (arithmetic mean of at least 2 measurements at 1 metre below surface and 1 metre above seabed).	Outer Marine Subzone
Five-Day Biochemical Oxygen Demand	Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 3 milligrams per litre.	Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones
Five-Day Biochemical Oxygen Demand	Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 5 milligrams per litre.	Yuen Long & Kam Tin (Lower) Subzone and other inland waters
Chemical Oxygen Demand	Waste discharges shall not cause the chemical oxygen demand to exceed 15 milligrams per litre.	Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones
Chemical Oxygen Demand	Waste discharges shall not cause the chemical oxygen demand to exceed 30 milligrams per litre.	Yuen Long & Kam Tin (Lower) Subzone and other inland waters
Toxins	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 toxicant interactions with each other.	Whole Zone
Toxins	Waste discharges shall not cause a risk to any beneficial uses of the aquatic environment.	Whole Zone
Phenol	Phenols shall not be present in such quantities as to produce a specific odour, or in concentration greater than 0.05 milligrams per litre as C₆H₅OH.	Yung Long Bathing Beach Subzone
Turbidity	Waste discharges shall not reduce light transmission substantially from the normal level.	Yung Long Bathing Beach Subzone

Technical Memorandum Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS)

6.2.3 The “Technical Memorandum Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters” (TM-DSS) provides a guidance on effluent discharges based on the type of receiving waters (i.e., foul sewers, storm water drains, inland and coastal waters). This standard controls the physical, chemical and microbial quality of effluents. Any sewage generated from the proposed construction and operation activities shall comply with the standards for effluents discharged into the foul sewers, inland waters and coastal waters of Deep Bay WCZ as presented in the TM-DSS.

ETWB TCW No. 34/2002 Management of Dredged / Excavated Sediment

6.2.4 The Environment, Transport and Works Bureau Technical Circular (Works) No. 34/2002 sets out the procedure for seeking approval to dredge/excavate sediment and the management framework for marine disposal of such sediment, including guidelines for the classification of sediment based on their contaminant levels.

ProPECC PN 2/23 Construction Site Drainage

6.2.5 Apart from the statutory requirements, the “Professional Persons Environmental Consultative Committee Practice Note” (ProPECC PN) provides guidelines for the handling and disposal of construction site discharges. The ProPECC PN2/23 “Construction Site Drainage” also specify good practices for dealing with different types of discharge from construction sites. These include surface runoff, groundwater, boring and drilling water, wheel washing water, bentonite slurry, water for testing and sterilisation of water retaining structures and water pipes, wastewater from the act of acid cleaning, etching and pickling, concrete batching and precast concrete casting, building construction and site facilities. All practices provided in the ProPECC PN2/23 shall be followed as practicable as possible so as to reduce the water quality impact during the construction and operational phases of the Project.

ProPECC PN 1/23 Drainage Plans Subject to Comment by the Environmental Protection Department

6.2.6 This practice note provides guidance on discharges to storm drains and foul sewers, and recommendations on the design of drainage systems for different locations including open areas, covered areas, slopes, pools, roads and carparks. Reference designs are provided for petrol interceptors, grease traps, septic tanks and soil soakaway systems. This guidance should be followed for preparation of drainage plans submitted to the Buildings Authority under the Building (Standards of Sanitary Fitments, Plumbing, Drainage Works and Latrines) Regulations 40(1), 40(2), 41(1) and 90.

Town Planning Board Guidelines No.12C

6.2.7 The Town Planning Board Guidelines No.12C (TPB PG-No.12C) supplement a guidance on the application for developments within Deep Bay area under Section 16 of the Town Planning Ordinance. According to the TPB PG-No.12C, developments within the Deep Bay Wetland Buffer Area shall not cause net increase in pollution load to Deep Bay. Item (ix) of Appendix E of the EIA Study Brief also mentioned that all effluents generated from the Project Site shall require appropriate collection, treatment and disposal to ensure that there is no additional pollution loading to Deep Bay, and hence protect the marine water quality and inland water quality of Deep Bay WCZ. The Project Site falls within the Deep Bay area and is subject to the TPB PG-No. 12C under Section 16 of the Town Planning Ordinance.

ETWB TCW No. 5/2005 Protection of Natural Streams/Rivers from Adverse Impacts arising from Construction Works

6.2.8 The Environment, Transport and Works Bureau Technical Circular (Works) No. 5/2005 provides an administrative framework to better protect all natural streams/rivers from the impacts of construction works. The procedures promulgated under this Circular aim to clarify and strengthen existing measures for the protection of natural streams/rivers from government projects and private developments.

6.3 Description of the Environment

6.3.1 The Project Site is situated in the lower part of the Kam Tin River catchment, which receives water from surrounding hillsides including Tai Mo Shan, Kai Kung Leng and Tai Lam Country Park. Both NSW and LC are low-lying areas that were historically converted into fishponds and are surrounded by tidal rivers (Shan Pui River on the west side and Kam Tin River on the east side) and other wetland habitats. A small number of ponds at NSW are hydrologically connected to Shan Pui River, and one pond at LC has an inter-tidal sluice. The rest of the NSW and LC sites are not hydrologically connected to the surrounding rivers and rely solely on rainfall as water source for the fishponds, hence some of the unmanaged ponds are intermittently wet grassland habitat.

Baseline Water Quality

6.3.2 The intertidal rivers surrounding the Project Site are difficult to access, and there is no regular water quality monitoring data available for this area. The EPD’s water quality monitoring stations near the Project Site are upstream of LC (FVR1) around 1.1 km away, and upstream of Nam Sang Wai (YL3 and YL4 around 1.5 km away, and KT1 and KT2 around 2.7 km away). A summary of the water quality at these sites for the period between 2019 – 2023 is presented in Table 6.2.

6.3.3 The WQO compliance rate at FVR1 was 73% in 2023 and is graded as ‘Fair’ under the Water Quality Index. However, YL3 and YL4 were both graded as ‘Bad’ in 2023 and the overall WQO compliance rate for EPD stations within Yuen Long Creek was 36% in 2023. The two monitoring stations (KT1 and KT2) at Kam Tin River were graded as “Fair” and “Bad”, respectively in 2023.

6.3.4 The approved EIA report for Yuen Long Effluent Polishing Plant (AEIAR-220/2019) carried out water quality monitoring at Shan Pui and Kam Tin rivers adjacent to the project between Feb – May 2017. The key results are presented in Table 6.3 and Table 6.4 and the monitoring stations’ locations (SP1 to SP9 and KT1) are indicated in Figure 6.1. Baseline water quality monitoring for the Yuen Long Effluent Polishing Plant was conducted between 1 December 2020 and 26 December 2020. The key results of the baseline water quality monitoring data have also been presented in Table 6.5 to illustrate more recent water quality near the Project Site. Compared to EPD’s water quality monitoring station results, the water quality immediately surrounding the Project Site is similar to YL3, YL4 and KT2 in terms of dissolved oxygen, similar to YL3, YL4 and KT1 in terms of ammonia-nitrogen levels, but more similar to FVR1 in terms of biochemical oxygen demand, while its suspended solids load is notably higher than the EPD upstream stations. If graded under EPD’s WQI, the water quality at Shan Pui and Kam Tin rivers adjacent to the project would likely achieve a borderline ‘Fair’ to ‘Bad’ grading, due primarily to the low dissolved oxygen and high ammonia-nitrogen results.

Table 6.2: Water Quality at EPD’s River Monitoring Stations (2019 – 2023)

Parameters	YL3					YL4
Parameters	2019	2020	2021	2022	2023	2019	2020	2021	2022	2023
Dissolved Oxygen (mg/L)	2.8	2.3	3.2	3.5	2.5	3.4	2.0	2.6	3.1	3.2
Dissolved Oxygen (mg/L)	(1.1 - 6.2)	(1.7 – 6.2)	(2.3 - 4.5)	(1.9 - 6.3)	(1.9 - 6.9)	(1.7 - 6.3)	(1.1 - 3.4)	(1.6 - 3.7)	(1.8 - 6.7)	(1.5 - 5.5)
pH	7.2	7.4	7.3	7.3	7.2	7.2	7.4	7.3	7.2	7.3
pH	(6.9 - 7.7)	(6.8 - 7.9)	(7.0 - 7.9)	(7.0 - 8.7)	(6.9 – 7.6)	(7.0 - 7.5)	(6.4 - 7.7)	(7.0 - 7.8)	(7.1 - 7.6)	(7.0 – 7.5)
Suspended Solids (mg/L)	35.5	24.0	32.5	24.5	29.0	54.0	50.0	27.0	17.0	24.5
Suspended Solids (mg/L)	(18.0 – 170.0)	(2.7 – 67.0)	(11.0 – 140.0)	(6.6 – 75.0)	(5.0 – 160.0)	(11.0 – 87.0)	(27.0 – 330.0)	(13.0 – 57.0)	(7.2 – 87.0)	(2.4 - 150.0)
5-Day Biochemical Oxygen Demand (mg/L)	30.5	51.0	56.5	57.0	55.5	92.0	120.0	110.0	87.0	71.0
5-Day Biochemical Oxygen Demand (mg/L)	(7.0 – 86.0)	(19.0 – 120.0)	(27.0 – 130.0)	(9.1 – 90.0)	(14.0 – 140.0)	(8.8 – 170.0)	(99 - 240)	(25.0 – 230.0)	(23.0 – 140.0)	(51.0 - 120.0)
Chemical Oxygen Demand (mg/L)	54	47	61	69	57	120	99	110	68	47
Chemical Oxygen Demand (mg/L)	(16 - 180)	(20 - 110)	(13 - 270)	(14 - 150)	(10 - 160)	(7 - 210)	(47 - 260)	(51 - 180)	(38 - 130)	(27 - 140)
Oil & Grease (mg/L)	1.9	1.3	1.4	1.6	1.3	4.8	6.7	3.7	2.5	1.7
Oil & Grease (mg/L)	(<0.5 – 4.3)	(<0.5 – 4.6)	(<0.5 – 15.0)	(<0.5 - 2.4)	(<0.5 - 5.4)	(0.9 – 7.6)	(0.7 – 16.0)	(0.6 – 6.9)	(0.6 - 5.2)	(0.6 - 6.3)
E. coli (counts/100mL)	500,000	680,000	1,200,000	860,000	1,304,789	1,700,000	2,200,000	1,600,000	1,200,000	1,166,470
E. coli (counts/100mL)	(90,000 – 1,700,000)	(460,000 – 1,200,000)	(700,000 – 2,500,000)	(330,000 – 2,400,000)	(230,000 - 7,600,000)	(260,000 – 4,200,000)	(810,000 – 7,900,000)	(660,000 – 3,000,000	(260,000 – 2,800,000)	(500,000 – 2,900,000)
Faecal Coliforms (counts/100 mL)	1,200,000	1,600,000	2,100,100	1,500,000	2,134,931	3,700,000	7,500,000	3,500,000	2,300,000	2,219,503
Faecal Coliforms (counts/100 mL)	(160,000 – 4,900,000)	(1,000,000 – 3,200,000)	(900,000 – 3,000,000)	(550,000 – 3,700,000)	(590,000 - 9,600,000)	(820,000 – 8,900,000)	(1,500,000 – 30,000,000)	(1,800,000 – 6,400,000)	(750,000 – 6,400,000)	(800,000 - 5,000,000)
Ammonia-Nitrogen (mg/L)	5.600	6.800	8.500	5.850	5.000	5.400	7.050	6.500	5.100	5.000
Ammonia-Nitrogen (mg/L)	(1.400- 15.000)	(2.100 – 16.000)	(3.600 – 11.000)	(1.100 – 14.000)	(1.100 – 19.000)	(0.500 – 10.000)	(3.700 – 13.000)	(2.700 - 7.300)	(0.770 - 7.100)	(1.200 - 7.100)
Nitrate-Nitrogen (mg/L)	0.006	0.005	0.004	0.010	0.006	0.006	0.004	0.002	0.004	<0.002
Nitrate-Nitrogen (mg/L)	(<0.002 – 0.690)	(<0.002 – 1.000)	(<0.002 - 0.450)	(<0.002 - 0.690)	(<0.002 – 0.640)	(<0.002 – 0.380)	(<0.002 – 0.027)	(<0.002 - 0.014)	(<0.002 - 0.310)	(<0.002 - 0.014)
Total Kjeldahl Nitrogen (mg/L)	8.60	9.50	18.50	7.70	8.60	9.35	12.00	13.00	8.20	7.20
Total Kjeldahl Nitrogen (mg/L)	(2.50 – 41.00)	(3.00 – 21.00)	(15.00 – 20.00)	(1.90 – 20.00)	(1.90 - 25.00)	(1.10 – 14.00)	(5.10 – 24.00)	(12.00 – 19.00)	(<1.70 – 13.00)	(3.10 - 11.00)
Orthophosphate Phosphorus (mg/L)	0.465	0.520	0.550	0.500	0.395	0.265	0.455	0.380	0.280	0.405
Orthophosphate Phosphorus (mg/L)	(0.160 – 1.700)	(0.049 – 2.100)	(0.310 – 1.400)	(0.095 – 1.200)	(0.100 - 3.100)	(0.027 – 0.600)	(0.032 – 1.300)	(0.053 – 0.590)	(0.005 – 0.510)	(0.013 - 0.910)
Total Phosphorus (mg/L)	0.82	1.30	1.60	0.89	0.94	0.86	1.25	1.20	0.82	0.71
Total Phosphorus (mg/L)	(0.33 – 4.50)	(0.52 – 0.28)	1.30 – 2.60)	(0.33 – 2.10)	(0.17 – 4.10)	(0.13 – 1.40)	(0.64 – 3.50)	(1.00 – 1.70)	(0.23 - 1.50)	(0.20 - 1.40)
Sulphide (mg/L)	0.07	0.07	0.07	0.05	0.10	0.13	0.20	0.18	0.07	0.10
Sulphide (mg/L)	(<0.02 – 0.16)	(<0.02 – 0.17)	(0.04 – 0.31)	(<0.02 – 0.16)	(<0.02 – 0.24)	(<0.02 – 0.32)	(0.04 – 0.50)	(0.05 – 0.36)	(<0.02 – 0.15)	(<0.02 - 0.30)
Aluminium (mg/L)	<50	<50	<50	<50	<50	64	<50	<50	<50	<50
Aluminium (mg/L)	(<50 – 768)	(<50 – 163)	(<50 - <50)	(<50 – 73)	(<50 - <50)	(<50 – 264)	(<50 – 514)	(<50 - <50)	(<50 - <50)	(<50 - <50)
Cadmium (mg/L)	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1
Cadmium (mg/L)	(<0.1 – 0.2)	(<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)
Chromium (mg/L)	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
Chromium (mg/L)	(<1 – <1)	(<1 - <1)	(<1 - <1)	(<1 – 4)	(<1 - 1)	(<1 - <1)	(<1 - <1)	(<1 - 2)	(<1 - <1)	(<1 - <1)
Copper (mg/L)	4	3	2	2	2	3	3	3	2	2
Copper (mg/L)	(1 – 7)	(2 – 6)	(1 – 5)	(1 – 8)	(1 – 4)	(2 – 7)	(1 – 4)	(2 – 6)	(2 – 3)	(1 – 3)
Lead (mg/L)	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
Lead (mg/L)	(<1 – 2)	(<1 – 1)	(<1 - <1)	(<1 - <1)	(<1 - 2)	(<1 – 2)	(<1 – 2)	(<1 - <1)	(<1 - <1)	(<1 - <1)
Zinc (mg/L)	17	10	12	12	<10	18	12	10	12	10
Zinc (mg/L)	(<10 – 51)	(<10 – 28)	(<10 – 24)	(<10 – 33)	(<10 – 20)	(<10 – 45)	(<10 – 17)	(<10 – 24)	(<10 – 41)	(<10 – 20)
Flow (m³/s)	1.065	0.754	0.217	0.812	0.480	0.268	0.218	0.217	0.146	0.168
Flow (m³/s)	(0.258 – 3.768)	(0.483 – 1.758)	(0.141 – 0.429)	(0.624 – 1.352)	(0.264 - 1.008)	(0099 – 0.656)	(0.147 – 0.421)	(0.141 - 0.429)	(0.098 - 0.222)	(0.132 - 0.468)

Parameters	KT1					KT2
Parameters	2019	2020	2021	2022	2023	2019	2020	2021	2022	2023
Dissolved Oxygen (mg/L)	5.9	5.1	4.0	5.4	5.9	4.0	4.5	2.4	3.7	3.8
Dissolved Oxygen (mg/L)	(3.6 - 7.0)	(3.5 - 6.8)	(2.0 - 6.5)	(3.1 - 7.0)	(1.8 – 7.2)	(1.8 - 7.6)	(1.4 - 7.0)	(1.4 - 4.0)	(1.1 - 6.9)	(1.2 - 7.4)
pH	7.5	7.5	7.5	7.4	7.5	7.4	7.6	7.5	7.4	7.6
pH	(7.1 - 7.8)	(7.2 - 8.7)	(7.2 - 8.1)	(7.1 - 7.9)	(7.3 – 7.9)	(7.2 - 7.7)	(7.3 - 8.0)	(7.4 - 7.7)	(7.2 - 8.0)	(7.3 - 7.9)
Suspended Solids (mg/L)	12.0	7.9	7.5	8.8	9.4	23.5	22.0	24.0	35.0	15.5
Suspended Solids (mg/L)	(6.5 - 24.0)	(2.6 - 39.0)	(2.5 - 53.0)	(1.5 - 27.0)	(5.9 - 110.0)	(12.0 - 50.0)	(8.4 - 140.0)	(3.6 - 120.0)	(3.8 - 58.0)	(5.3 - 75.0)
5-Day Biochemical Oxygen Demand (mg/L)	8.8	8.5	7.2	10.0	8.5	16.0	14.0	27.0	21.0	15.0
5-Day Biochemical Oxygen Demand (mg/L)	(3.7 - 19.0)	(3.7 - 20.0)	(3.7 - 34.0)	(5.2 - 14.0)	(4.1 - 29.0)	(4.7 - 37.0)	(6.8 - 130.0)	(7.3 - 160.0)	(3.2 - 150.0)	(5.2 - 53.0)
Chemical Oxygen Demand (mg/L)	17	18	21	20	23	31	33	58	52	26
Chemical Oxygen Demand (mg/L)	(12 - 29)	(8 - 28)	(14 - 70)	(12 - 65)	(13 - 46)	(4 - 100)	(11 - 180)	(14 - 200)	(9 - 170)	(14 - 120)
Oil & Grease (mg/L)	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	1.1	0.6
Oil & Grease (mg/L)	(<0.5 – 0.9)	(<0.5 – 0.7)	(<0.5 - 1.4)	(<0.5 – 0.8)	(<0.5 - 1.3)	(<0.5 – 2.3)	(<0.5 - 1.6)	(<0.5 - 2.9)	(<0.5 - 2.4)	(<0.5 - 5.1)
E. coli (counts/100mL)	56,000	46,000	46,000	41,000	32,475	51,000	110,000	120,000	110,000	65,187
E. coli (counts/100mL)	(19,000 – 280,000)	(20,000 – 80,000)	(13,000 – 250,000)	(5,000 – 340,000)	(8,000 – 150,000)	(14,000 – 340,000)	(56,000 – 420,000)	(39,000 – 1,600,000)	(24,000 – 1,700,000)	(28,000 – 190,000)
Faecal Coliforms (counts/100 mL)	160,000	150,000	160,000	150,000	157,082	110,000	280,000	240,000	270,000	215,166
Faecal Coliforms (counts/100 mL)	(54,000 – 400,000)	(61,000 – 370,000)	(47,000 – 600,000)	(52,000 – 470,000)	(78,000 – 510,000)	(36,000 – 490,000)	(100,000 – 2,100,000)	(79,000 – 2,400,000)	(62,000 – 1,900,000)	(74,000 – 970,000)
Ammonia-Nitrogen (mg/L)	3.450	4.500	6.600	4.100	3.450	7.050	5.800	9.800	7.800	7.200
Ammonia-Nitrogen (mg/L)	(1.000 - 13.000)	(1.300 - 12.000)	(2.300 - 12.000)	(0.670 – 10.000)	(0.910 – 15.000)	(0.830 - 10.000)	(1.900 - 13.000)	(4,800 – 36,000)	(0.480 – 25,000)	(1.200 - 14.000)
Nitrate-Nitrogen (mg/L)	0.760	1.100	0.820	0.870	1.200	0.150	0.170	0.007	0.200	0.380
Nitrate-Nitrogen (mg/L)	(0.280 - 1.700)	(0.660 - 2.000)	(0.054 - 1.700)	(0.410 – 3.300)	(0.018 – 3.000)	(<0.002 – 0.900)	(0.006 - 1.200)	(<0.002 - 0.480)	(<0.002 - 0.560)	(<0.002 - 1.000)

Parameters	KT1					KT2
Parameters	2019	2020	2021	2022	2023	2019	2020	2021	2022	2023
Total Kjeldahl Nitrogen (mg/L)	4.05	5.90	12.50	5.45	4.70	8.40	8.20	19.00	9.00	8.50
Total Kjeldahl Nitrogen (mg/L)	(1.80 - 15.00)	(1.40 - 12.00)	(7.70 - 14.00)	(1.80 - 12.0)	(1.80 - 17.00)	(1.50 - 14.00)	(2.20 - 25.00)	(11.00 - 44.00)	(1.90 - 31.00)	(1.80 - 20.00)
Orthophosphate Phosphorus (mg/L)	0.475	0.670	0.880	0.770	0.600	0.785	0.900	1.600	0.830	0.925
Orthophosphate Phosphorus (mg/L)	(0.300 - 1.700)	(0.320 - 1.200)	(0.530 - 2.600)	(0.260 – 1.300)	(0.280 - 2.800)	(0.190 - 1.700)	(0.360 - 2.500)	(1.100 - 2.700)	(0.180 - 2.400)	(0.260 - 1.600)
Total Phosphorus (mg/L)	0.66	0.99	1.75	1.20	0.86	1.25	1.50	2.80	1.40	1.30
Total Phosphorus (mg/L)	(0.46 - 2.00)	(0.58 - 1.50)	(1.20 - 3.00)	(0.40 – 1.60)	(0.38 – 3.50)	(0.32 - 2.40)	(0.61 - 4.30)	(1.70 - 4.50)	(0.44 - 3.80)	(0.38 - 2.90)
Sulphide (mg/L)	<0.02	<0.02	<0.02	<0.02	<0.02	0.04	0.03	0.04	0.05	0.03
Sulphide (mg/L)	(<0.02 – 0.06)	(<0.02 - 0.03)	(<0.02 - 0.12)	(<0.02 - 0.04)	(<0.02 - 0.06)	(<0.02 – 0.27)	(<0.02 - 0.17)	(<0.02 - 0.18)	(<0.02 - 0.11)	(<0.02 - 0.11)
Aluminium (mg/L)	<50	<50	<50	<50	<50	<50	<50	<50	<50	<50
Aluminium (mg/L)	(<50 - 409)	(<50 - 256)	(<50 - <50)	(<50 - <50)	(<50 - 110)	(<50 - 442)	(<50 - 51)	(<50 - <50)	(<50 - 70)	(<50 - <50)
Cadmium (mg/L)	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1
Cadmium (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)
Chromium (mg/L)	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
Chromium (mg/L)	(<1 - <1)	(<1 - 3)	(<1 - <1)	(<1 - <1)	(<1 - <1)	(<1 - <1)	(<1 - <1)	(<1 - <1)	(<1 - <1)	(<1 - 2)
Copper (mg/L)	3	2	2	2	2	2	2	1	1	2
Copper (mg/L)	(2 - 7)	(2 - 3)	(2 - 4)	(1 - 7)	(<1 - 3)	(<1 - 4)	(1 - 3)	(<1 - 2)	(<1 - 4)	(<1 - 4)
Lead (mg/L)	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
Lead (mg/L)	(<1 - <1)	(<1 - <1)	(<1 - <1)	(<1 - <1)	(<1 - <1)	(<1 - <1)	(<1 - <1)	(<1 - <1)	(<1 - <1)	(<1 - <1)
Zinc (mg/L)	14	<10	<10	<10	<10	12	<10	<10	<10	<10
Zinc (mg/L)	(<10 – 26)	(<10 - 18)	(<10 - 17)	(<10 - 25)	(<10 - 20)	(<10 - 34)	(<10 - 19)	(<10 - 11)	(<10 - 25)	(<10 - 30)
Flow (m³/s)	1.411	0.510	0.462	0.462	0.353	1.394	0.711	0.290	0.414	0.282
Flow (m³/s)	(0.324 - 8.979)	(0.238 - 1.786)	(0.259 - 1.153)	(0.244 – 17.587)	(0.086 – 16.788)	(0.238 - 4.454)	(0.139 – 1.494)	(0.193 – 1.451)	(0.186 - 15.984)	(0.080 - 11.926)

Parameters	FVR1
Parameters	2019	2020	2021	2022	2023
Dissolved Oxygen (mg/L)	4.9	5.6	7.5	6.4	5.4
Dissolved Oxygen (mg/L)	(3.2 - 9.6)	(3.7 - 9.7)	(4.4 - 11.0)	(3.3 - 10.4)	(3.7 - 11.7)
pH	7.3	7.4	7.6	7.4	7.4
pH	(7.1 - 8.2)	(6.8 - 8.7)	(7.2 - 8.4)	(6.9 - 8.6)	(7.1 - 8.5)
Suspended Solids (mg/L)	29.5	24.0	29.0	19.0	11.5
Suspended Solids (mg/L)	(17.0 - 100.0)	(12.0 – 57.0)	(12.0 – 77.0)	(1.2 - 83)	(6.8 - 22.0)
5-Day Biochemical Oxygen Demand (mg/L)	6.3	5.0	8.6	10.0	6.9
5-Day Biochemical Oxygen Demand (mg/L)	(2.8 - 9.2)	(3.6 – 15.0)	(5.2 – 12.0)	(5.5 – 16.0)	(3.0 - 13.0)
Chemical Oxygen Demand (mg/L)	22	24	28	29	30
Chemical Oxygen Demand (mg/L)	(3 - 45)	(14 - 35)	(21 - 44)	(23 - 66)	(9 - 70)
Oil & Grease (mg/L)	<0.5	<0.5	<0.5	<0.5	<0.5
Oil & Grease (mg/L)	(<0.5 - <0.5)	(<0.5 – 0.8)	(<0.5 - <0.5)	(<0.5 – 0.7)	(<0.5 - <0.5)
E. coli (counts/100mL)	13,000	16,000	33,000	51,000	25,146
E. coli (counts/100mL)	(2,800 – 1,800,000)	(5,100 – 51,000)	(1,700 – 580,000)	(5,900 – 1,100,000)	(2,900 – 120,000)
Faecal Coliforms (counts/ 100 mL)	39 000	54,000	120,000	120,000	71,882
Faecal Coliforms (counts/ 100 mL)	(11,000 – 1,800,000)	(13,000 – 200,000)	(18,000 – 1,100,000)	(17,000 – 1,400,000)	(14,000 – 440,000)
Ammonia-Nitrogen (mg/L)	1.400	1.300	1.400	1.100	1.450
Ammonia-Nitrogen (mg/L)	(0.370 - 2.900)	(0.920 - 2.100)	(0.610 - 2.900)	(0.320 - 2.900)	(0.450 - 2.800)
Nitrate-Nitrogen (mg/L)	0.760	0.470	0.430	0.470	0.760
Nitrate-Nitrogen (mg/L)	(0.270 – 1.600)	(0.300 – 0.810)	(0.230 - 1.000)	(0.095 - 1.500)	(0.340 - 1.200)
Total Kjeldahl Nitrogen	2.45	2.20	3.30	3.00	2.40
Total Kjeldahl Nitrogen	(1.20 - 4.50)	(1.90 - 3.50)	(3.20 - 5.40)	(2.00 – 4.50)	(0.92 - 4.00)
Orthophosphate Phosphorus	0.285	0.350	0.350	0.260	0.275
Orthophosphate Phosphorus	(0.110 - 0.460)	(0.200 - 0.520)	(0.220 - 0.590)	(0.130 – 0.470)	(0.095 - 0.530)

Parameters	FVR1
Parameters	2019	2020	2021	2022	2023
Total Phosphorus	0.46	0.59	0.60	0.55	0.45
Total Phosphorus	(0.26 - 0.70)	(0.39 - 0.78)	(0.44 - 0.92)	(0.35 - 0.71)	(0.12 - 0.73)
Sulphide (mg/L)	0.02	<0.02	0.02	<0.02	<0.02
Sulphide (mg/L)	(<0.02 - 0.04)	(<0.02 - 0.03)	(<0.02 - 0.04)	(<0.02 - 0.04)	(<0.02 - 0.04)
Aluminium (mg/L)	<50	<50	<50	<50	<50
Aluminium (mg/L)	(<50 - 213)	(<50 - 159)	(<50 - <50)	(<50 - <50)	(<50 - <50)
Cadmium (mg/L)	<0.1	<0.1	<0.1	<0.1	<0.1
Cadmium (mg/L)	(<0.1 - <0.1)	(<0.1 - <0.1)	(<0.1 - <0.1)	(<0.1 - <0.1)	(<0.1 - <0.1)
Chromium (mg/L)	<1	<1	<1	<1	<1
Chromium (mg/L)	(<1 - 2)	(<1 - 2)	(<1 - 2)	(<1 - 1)	(<1 - 1)
Copper (mg/L)	2	2	2	2	2
Copper (mg/L)	(<1 - 3)	(1 - 5)	(<1 - 3)	(<1 - 2)	(<1 - 2)
Lead (mg/L)	<1	<1	<1	<1	<1
Lead (mg/L)	(<1 - 3)	(<1 - <1)	(<1 - <1)	(<1 - <1)	(<1 - <1)
Zinc (mg/L)	19	13	<10	11	10
Zinc (mg/L)	(10 - 32)	(<10 - 39)	(<10 - 20)	(<10 - 20)	(<10 - 20)
Flow (m³/s)	NM	NM	NM	NM	NM

Source: EPD - Environmental Protection Interactive Centre (River Water Quality Data) https://cd.epic.epd.gov.hk/EPICRIVER/river/?lang=en (accessed in November 2024)

Notes: 1. Data presented are in annual medians of monthly samples except for E. coli which is in annual geometric means

2. Figures in brackets are annual ranges

3. Values at or below laboratory reporting limits are presented as laboratory reporting limits

Table 6.3: Water Quality Monitoring Data from Yuen Long Effluent Polishing Plant EIA (Dry Season - Feb to Mar 2017)

Parameters	Shan Pui River									Kam Tin River
Parameters	SP1	SP2	SP3	SP4	SP5	SP6	SP7	SP8	SP9	KT1
Dissolved oxygen (mg/L)	3.68	4.25	4.66	4.41	4.18	5.06	4.18	5	4.88	4.3
Dissolved oxygen (mg/L)	(1.50 - 6.11)	(2.75 - 7.90)	(2.03 - 6.96)	(2.99 - 6.62)	(2.57 - 6.88)	(3.02 - 7.27)	(3.07 - 7.12)	(0.58 - 7.74)	(3.14 - 7.13)	(2.22 - 6.85)
pH	7.83	7.72	7.91	7.73	7.71	7.75	7.74	7.75	7.77	7.74
pH	(7.61 - 8.67)	(7.55 - 8.10)	(7.57 - 9.76)	(7.60 - 8.10)	(7.62 - 7.93)	(7.57 - 8.06)	(7.62 - 7.90)	(7.56 - 7.97)	(7.59 - 7.95)	(7.62 - 7.93)
Suspended Solids (mg/L)	47.3	56	71.6	113.3	78.3	143	79.4	179.7	70.9	87.1
Suspended Solids (mg/L)	(23 - 130)	(18 - 220)	(30 - 200)	(30 - 440)	(18 - 290)	(32 - 460)	(20 - 240)	(11 - 1,100)	(20 - 170)	(27 - 450)
5-day Biochemical Oxygen Demand (mg/L)	6.4	5.3	4.4	4.8	4	4.9	4.3	5.5	4.5	5.3
5-day Biochemical Oxygen Demand (mg/L)	(3 - 17)	(2 - 8)	(2 - 7)	(3 - 9)	(2 - 11)	(3 - 7)	(2 - 10)	(3 - 8)	(2 - 11)	(2 - 11)
Chemical Oxygen Demand (mg/L)	17.5	21.8	24	24.3	25.3	20.1	21.2	12.1	32.5	19
Chemical Oxygen Demand (mg/L)	(5 - 33)	(<2 - 50)	(<2 - 88)	(<2 - 54)	(<2 - 35)	(<2 - 28)	(<2 - 29)	(<2 - 24)	(<2 - 72)	(<2 - 35)
Oil & grease (mg/L)	1.8	2	1.8	2.1	1.4	2	1.6	3.5	1.7	1.6
Oil & grease (mg/L)	(1 - 3)	(<0.5 - 3)	(<0.5 - 3)	(<0.5 - 4)	(<0.5 - 2)	(<0.5 - 3.0)	(<0.5 - 2.0)	(<0.5 - 4.0)	(<0.5 - 2.0)	(<0.5 - 3.0)
E. coli (cfu/100mL)	17,808	10,517	12,650	5,242	3,733	5,767	3,342	5,850	2,800	4,350
E. coli (cfu/100mL)	(900 - 80,000)	(2,200 - 42,000)	(1,200 - 50,000)	(1,600 -10,000)	(1,000 - 8,200)	(2,000 - 18,000)	(1,400 - 6,000)	(2,800 - 15,000)	(600 - 6,900)	(2,100 - 8,000)
Ammonia-nitrogen (mg/L)	8.68	8.4	9.56	6.65	5.78	6.94	4.92	7.2	4.78	6.3
Ammonia-nitrogen (mg/L)	(3.30 - 16.00)	(4.40 - 13.00)	(5.50 - 20.00)	(1.30 - 11.00)	(0.40 - 11.00)	(0.70 - 11.00)	(1.50 - 11.00)	(0.70 - 11.00)	(2.30 - 11.00)	(2.80 - 9.10)
Nitrate-nitrogen (mg/L)	0.63	0.70	0.74	0.87	1.02	0.82	1.12	0.82	1.12	1.21
Nitrate-nitrogen (mg/L)	(0.12 - 1.37)	(0.03 - 1.40)	(0.19 - 1.50)	(0.29 - 1.40)	(0.40 - 1.50)	(0.40 - 1.50)	(0.30 - 1.60)	(0.40 - 1.60)	(0.39 - 1.60)	(0.19 - 5.99)
Total Kjeldahl nitrogen (mg/L)	9.19	9.29	10.5	7.77	6.5	7.97	6.06	7.58	5.64	6.87
Total Kjeldahl nitrogen (mg/L)	(3.80 - 17.00)	(4.90 - 15.90)	(6.40 - 20.70)	(2.10 - 12.00)	(0.80 - 13.20)	(0.80 - 13.50)	(2.10 - 11.30)	(1.00 - 12.20)	(2.70 - 12.00)	(3.20 - 9.60)
Ortho-phosphate (mg/L)	0.62	0.54	0.54	0.45	0.43	0.47	0.37	0.5	0.28	0.37
Ortho-phosphate (mg/L)	(0.38 - 0.86)	(0.38 - 0.73)	(0.38 - 0.72)	(0.25 - 0.54)	(0.34 - 0.48)	(0.41 - 0.54)	(0.24 - 0.48)	(0.38 - 0.64)	(0.18 - 0.48)	(0.09 - 0.61)
Total phosphorus (mg/L)	0.74	0.65	0.66	0.53	0.54	0.56	0.49	0.57	0.43	0.57
Total phosphorus (mg/L)	(0.49 - 0.94)	(0.49 - 0.82)	(0.49 - 0.86)	(0.40 - 0.68)	(0.43 - 0.64)	(0.49 - 0.68)	(0.35 - 1.10)	(0.48 - 0.72)	(0.28 - 0.68)	(0.45 - 0.75)
Total sulphide (mg/L)	<0.02	<0.02	<0.02	<0.02	<0.02	<0.02	<0.02	<0.02	<0.02	<0.02
Total sulphide (mg/L)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)
Aluminium (µg/L)	191	750	962	1,056	563	796	562	1,332	548	609
Aluminium (µg/L)	(13 - 910)	(23 -2,500)	(<10 - 5,300)	(41 - 5,200)	(38 - 2,800)	(<10 - 3,300)	(<10 - 1,500)	(<10 - 7,700)	(<10 - 1,100)	(<10 - 2,000)
Cadmium (µg/L)	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2
Cadmium (µg/L)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)
Copper (µg/L)	4	4	4	5	4	5.5	3.8	5.3	7.6	4.3
Copper (µg/L)	(1 - 7)	(1 - 10)	(1 - 9)	(2 - 15)	(2 - 10)	(2 - 25)	(2 - 10)	(2 - 24)	(2 - 28)	(1 - 13)
Lead (µg/L)	2	3	7	8	4	5.2	2.8	8.3	2.3	3.3
Lead (µg/L)	(<1 - 4)	(<1 - 7)	(<1 - 9)	(<1 - 17)	(<1 - 9)	(<1 - 12)	(<1 - 4)	(<1 - 27)	(<1 - 4)	(<1 - 7)
Zinc (µg/L)	38	50	137	65	39	48.9	37.7	45.5	30.5	28.4
Zinc (µg/L)	(15 - 62)	(15 - 100)	(23 - 740)	(23 - 150)	(19 - 92)	(13 - 130)	(14 - 100)	(20 - 190)	(15 - 51)	(11 - 70)

Source: Agreement No. CE 3/2015 (DS) Yuen Long Effluent Polishing Plant – Investigation, Design and Construction - EIA Report (Section 5.3.3, Table 5.5, and Table 5.7)

https://www.epd.gov.hk/eia/register/report/eiareport/eia_2592019/CD%20for%20EPD_HTML/HTML/EIA%20Report/S5_Water.htm (accessed in June 2024)

Table 6.4: Water Quality Monitoring Data from Yuen Long Effluent Polishing Plant EIA (Wet Season - May 2017)

Parameters	Shan Pui River									Kam Tin River
Parameters	SP1	SP2	SP3	SP4	SP5	SP6	SP7	SP8	SP9	KT1
Dissolved oxygen (mg/L)	2	2.37	2.88	2.88	2.29	3.71	2.42	3.49	3.04	2.47
Dissolved oxygen (mg/L)	(0.30 - 4.88)	(0.79 - 3.81)	(1.09 - 5.54)	(0.80 - 5.80)	(0.72 - 4.24)	(0.57 - 7.65)	(0.88 - 4.42)	(0.82 - 7.61)	(1.40 - 5.28)	(0.93 - 4.03)
pH	7.24	7.29	7.34	7.31	7.28	7.39	7.27	7.39	7.32	7.3
pH	(6.89 - 7.50)	(7.19 - 7.41)	(7.23 - 7.49)	(7.07 - 7.62)	(7.17 - 7.39)	(7.20 - 7.65)	(7.16 - 7.38)	(7.21 - 7.66)	(7.25 - 7.42)	(7.21 - 7.42)
Suspended Solids (mg/L)	33.2	50.8	63.3	100.3	35.8	80.9	37	113.6	25.9	34.8
Suspended Solids (mg/L)	(4 - 76)	(14 - 170)	(9 - 370)	(10 - 750)	(6 - 140)	(30 - 320)	(7 - 140)	(24 - 390)	(7 - 62)	(9 - 100)
5-day Biochemical Oxygen Demand (mg/L)	4.3	3.9	3.9	4.2	4	3.7	3.8	4	3.2	4.2
5-day Biochemical Oxygen Demand (mg/L)	(1 - 8)	(<1 - 7)	(2 - 9)	(2 - 8)	(2 - 6)	(2 - 9)	(2 - 6)	(2 - 7)	(1 - 6)	(3 - 6)
Chemical Oxygen Demand (mg/L)	64.1	73.3	74.7	65.5	75.7	96.8	75.3	104.2	74.3	81.3
Chemical Oxygen Demand (mg/L)	(46 - 78)	(46 - 94)	(46 - 180)	(21 - 100)	(31 - 120)	(38 - 290)	(29 - 94)	(38 - 360)	(46 - 120)	(61 - 150)
Oil & grease (mg/L)	1.2	1.4	1.3	1.3	1.4	1.4	1.3	1.9	1.3	1.3
Oil & grease (mg/L)	(0.5 - 2.5)	(0.5 - 2.0)	(0.8 - 3.0)	(0.5 - 2.2)	(0.5 - 3.0)	(<0.5 - 2.8)	(0.8 - 2.8)	(0.5 - 8.5)	(1.0 - 2.2)	(0.8 - 2.2)
E. coli (cfu/100mL)	12,047	8,953	10,807	6,687	6,120	8,248	4,787	8,612	3,197	6,472
E. coli (cfu/100mL)	(1,600 - 79,000)	(3,200 - 46,000)	(2,100 - 51,000)	(600 -28,000)	(1,800 - 21,000)	(2,600 - 52,000)	(710 - 11,000)	(2,100 - 40,000)	(310 - 16,000)	(1,800 - 31,000)
Ammonia-nitrogen (mg/L)	6.2	6.66	6.09	5.36	5.03	5.03	4.6	4.96	4.81	4.64
Ammonia-nitrogen (mg/L)	(3.60 - 9.70)	(2.60 - 8.70)	(2.10 - 10.00)	(2.50 - 8.70)	(3.00 - 7.60)	(2.10 - 7.10)	(2.40 - 6.80)	(3.60 - 6.80)	(2.60 - 7.70)	(2.50 - 6.30)
Nitrate-nitrogen (mg/L)	1.93	1.68	1.79	1.64	1.59	1.57	1.51	1.84	1.37	1.86
Nitrate-nitrogen (mg/L)	(0.18 - 7.17)	(0.19 - 5.72)	(0.27 - 5.87)	(0.28 - 5.69)	(0.28 - 5.69)	(0.45 - 4.88)	(0.34 - 5.37)	(0.34 - 5.39)	(0.34 - 4.49)	(0.36 - 6.67)
Total Kjeldahl nitrogen (mg/L)	7.35	8.19	7.78	6.6	6.13	5.85	5.28	5.65	5.72	5.5
Total Kjeldahl nitrogen (mg/L)	(4.50 - 10.60)	(4.00 - 10.70)	(3.90 - 12.60)	(3.00 - 9.60)	(3.20 - 9.00)	(2.60 - 9.80)	(3.20 - 7.40)	(4.40 - 7.20)	(2.90 - 9.30)	(3.40 - 7.50)
Ortho-phosphate (mg/L)	0.44	0.4	0.43	0.41	0.43	0.45	0.42	0.36	0.36	0.36
Ortho-phosphate (mg/L)	(0.28 - 0.66)	(0.26 - 0.64)	(0.30 - 0.67)	(0.27 - 0.72)	(0.31 - 0.67)	(0.31 - 0.73)	(0.25 - 0.64)	(0.0002 - 0.72)	(0.0002 - 0.65)	(0.0002 - 0.62)
Total phosphorus (mg/L)	0.68	0.59	0.6	0.59	0.63	0.57	0.56	0.6	0.57	0.57
Total phosphorus (mg/L)	(0.43 - 0.79)	(0.37 - 0.85)	(0.29 - 0.69)	(0.36 - 0.79)	(0.41 - 0.85)	(0.36 - 0.78)	(0.38 - 0.72)	(0.43 - 0.69)	(0.20 - 0.82)	(0.40 - 0.66)
Total sulphide (mg/L)	<0.02	<0.02	<0.02	<0.02	<0.02	<0.02	<0.02	<0.02	<0.02	<0.02
Total sulphide (mg/L)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)	(0 - <0.02)
Aluminium (µg/L)	95	113	136	81	106	320	89	417	81	168
Aluminium (µg/L)	(<10 - 390)	(<10 - 440)	(<10 - 700)	(<10 - 210)	(<10 - 460)	(10 - 1,500)	(<10 - 240)	(<10 - 2,200)	(<10 - 300)	(<10 - 880)
Cadmium (µg/L)	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2
Cadmium (µg/L)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)	(0 - <0.2)
Copper (µg/L)	1.3	1.4	1.4	1.3	1.5	2.8	1.3	1.3	1.3	1.7
Copper (µg/L)	(<1 - 3)	(<1 - 4)	(<1 - 3)	(<1 - 3)	(<1 - 3)	(<1 - 16)	(<1 - 2)	(<1 - 2)	(<1 - 2)	(<1 - 4)
Lead (µg/L)	<1	1.2	1.4	3.2	<1	1.5	<1	1.4	<1	1.3
Lead (µg/L)	(<1 - 1.0)	(<1 - 2)	(<1 - 3)	(<1 - 14)	(<1 - 1)	(<1 - 3)	(0 - <1)	(<1 - 3)	(0 - <1)	(<1 - 2)
Zinc (µg/L)	32	131	88	60	28	27.1	25.6	28	20.5	27.8
Zinc (µg/L)	(<10 - 98)	(<10 - 540)	(<10 - 240)	(<10 - 210)	(<10 - 72)	(<10 - 72)	(<10 - 76)	(<10 - 72)	(<10 - 63)	(<10 - 120)

Source: Agreement No. CE 3/2015 (DS) Yuen Long Effluent Polishing Plant – Investigation, Design and Construction - EIA Report (Section 5.3.3, Table 5.6 and Table 5.8)

https://www.epd.gov.hk/eia/register/report/eiareport/eia_2592019/CD%20for%20EPD_HTML/HTML/EIA%20Report/S5_Water.htm (accessed in June 2024)

Table 6.5: Baseline Water Quality Monitoring Data from Yuen Long Effluent Polishing Plant (Dec 2020)

Parameters	M1	M2	M3	E1	E5a	SP1	KT1
Dissolved oxygen (mg/L)	4.46	3.86	5.01	S&M: 5.08 B: 4.72	S&M: 4.26 B: 5.81	3.56	S&M: 4.43 B: 5.81
Dissolved oxygen (mg/L)	(1.83 - 6.88)	(1.77 - 6.68)	(3.12 - 6.31)	S&M: (2.42 - 8.07) B: (2.31 - 7.85)	S&M: (1.85 - 7.08) B: (5.63 - 5.98)	(1.20 - 6.05)	S&M: (2.22 - 6.82) B: (5.63 - 5.98)
pH	7.25	7.21	7.62	7.28	7.25	7.19	7.26
pH	(6.94 - 8.12)	(7.02 - 8.14)	(7.12 - 8.05)	(7.03 - 8.17)	(6.98 - 8.17)	(7.02 - 7.95)	(7.07 - 8.09)
Salinity (ppt)	9.38	9.36	5.30	11.39	9.23	9.18	9.01
Salinity (ppt)	(7.22 - 11.63)	(7.70 - 11.51)	(0.97 - 10.40)	(7.40 - 21.71)	(7.14 - 11.13)	(7.70 - 11.32)	(5.90 - 11.63)
Temperature (degree C)	19.84	19.89	22.43	19.61	19.79	19.96	19.64
Temperature (degree C)	(16.50 - 22.49)	(16.48 - 22.74)	(19.33 - 26.12)	(16.20 - 22.59)	(16.41 - 22.84)	(16.53 - 22.72)	(15.88 - 22.52)
Turbidity (NTU)	30.6	29.8	46.9	27.9	27.3	31.2	27.4
Turbidity (NTU)	(17.8 - 50.7)	(19.1 - 54.8)	(14.4 - 79.1)	(15.4 - 47.6)	(19.1 - 40.7)	(13.9 - 52.6)	(13.3 - 45.3)
Total Suspended Solids (mg/L)	42	45	58	38	42	47	39
Total Suspended Solids (mg/L)	(24 - 71)	(28 - 120)	(23 - 185)	(26 - 89)	(23 - 64)	(27 - 175)	(19 - 77)
5-day Biochemical Oxygen Demand (mg/L)	N/A	N/A	N/A	2.5	2.7	2.9	3.2
5-day Biochemical Oxygen Demand (mg/L)	N/A	N/A	N/A	(1.5 - 4.5)	(1.5 - 4.5)	(1.5 - 5.0)	(1.5 - 6.0)
UIA (mg/L-N)	N/A	N/A	N/A	0.020	0.027	0.023	0.026
UIA (mg/L-N)	N/A	N/A	N/A	(0.006 - 0.063)	(0.007 - 0.098)	(0.008 - 0.073)	(0.006 - 0.073)
Total Kjeldahl Nitrogen (mg/L-N)	N/A	N/A	N/A	4.1	5.5	5.9	5.5
Total Kjeldahl Nitrogen (mg/L-N)	N/A	N/A	N/A	(1.5 - 7.6)	(2.3 - 15.0)	(2.9 - 12.5)	(1.7 - 14.5)
Total Nitrogen (mg/L-N)	N/A	N/A	N/A	5.1	6.7	6.6	6.4
Total Nitrogen (mg/L-N)	N/A	N/A	N/A	(2.1 - 7.8)	(3.5 - 16.0)	(3.6 - 13.0)	(3.3 - 14.5)
Ammoniacal Nitrogen (mg/L)	N/A	N/A	N/A	2.88	3.93	3.91	3.9
Ammoniacal Nitrogen (mg/L)	N/A	N/A	N/A	(0.60 - 6.23)	(1.09 - 14.00)	(1.60 -11.00)	(0.98 - 13.00)
Total Inorganic Nitrogen (mg/L)	N/A	N/A	N/A	3.9	5.0	4.6	4.8
Total Inorganic Nitrogen (mg/L)	N/A	N/A	N/A	(1.8 - 6.4)	(2.4 - 15.0)	(2.3 - 11.0)	(2.1 - 13.0)
Total Phosphorus (mg/L)	N/A	N/A	N/A	0.54	0.63	0.68	0.69
Total Phosphorus (mg/L)	N/A	N/A	N/A	(0.25 - 0.99)	(0.01 - 1.20)	(0.24 - 1.25)	(0.25 - 1.25)
E. coli (cfu/100mL)	N/A	N/A	N/A	7,243	10,821	19,178	7,247
E. coli (cfu/100mL)	N/A	N/A	N/A	(1,497 - 40,478)	(1,579 - 57,498)	(1,673 - 214,942)	(1,428 - 27,276)

Source: DSD Yuen Long Effluent Polishing Plant - Project Website http://fts.com.hk/dc-2019-10/uploads/2021/05/Baseline%20Monitoring%20Report%20%280120_20_ED_262_05%29.pdf (accessed in June 2024)

Notes:

1) Monitoring Level: S&M – Surface and Middle; B – Bottom

2) For M1, M2, M3, and SP1, the water depth is less than 3m, only value at the middle was taken in the baseline monitoring

3) For E1, the water depth is between 3m to 6m, only value at Surface was taken in the baseline monitoring

4) N/A – Monitoring is not applicable for that water level/parameter

Baseline Sediment Quality

6.3.5 No sediment quality data is available for the rivers adjacent to the Project. The nearest EPD’s sediment quality monitoring station is in Inner Deep Bay (DS1) around 2.6 km away. A summary of the sediment quality at this site for the consolidated period between 2019 – 2023 is presented in Table 6.6.

Table 6.6: Summary of Bottom Sediment Quality in Deep Bay (DS1), 2019 - 2023

Parameters	DS1 (2019 – 2023)
Particle Size Fractionation <63µm (%w /w )	73
Particle Size Fractionation <63µm (%w /w )	(17 - 98)
Electrochemical Potential (mV)	-164
Electrochemical Potential (mV)	(-340 - -74)
Total Solids (%w /w )	48
Total Solids (%w /w )	(43 - 55)
Total Volatile Soilds (%TS)	6.0
Total Volatile Soilds (%TS)	(4.2 – 8.3)
Chemical Oxygen Demand (mg/kg)	20,200
Chemical Oxygen Demand (mg/kg)	(14,000 – 30,000)
Total Carbon (%w/w)	0.7
Total Carbon (%w/w)	(0.5 – 0.9)
Ammonical Nitrogen (mg/kg)	10.10
Ammonical Nitrogen (mg/kg)	(0.63 – 23.00)
Total Kjeldahl Nitrogen (mg/kg)	530
Total Kjeldahl Nitrogen (mg/kg)	(440 – 650)
Total Phosphorus (mg/kg)	310
Total Phosphorus (mg/kg)	(240 – 440)
Total Sulphide (mg/kg)	169.8
Total Sulphide (mg/kg)	(14.0 – 540.0)
Total Cyanide (mg/kg)	0.2
Total Cyanide (mg/kg)	(0.1 - 0.3)
Arsenic	12.3
Arsenic	(5.3 – 18.0)
Cadmium	0.8
Cadmium	(0.5 – 1.3)
Chromium	45
Chromium	(21 – 71)
Copper	63
Copper	(31 – 100)
Lead	53
Lead	(31 – 78)
Mercury	0.22
Mercury	(0.07 – 0.46)
Nickel	26
Nickel	(18 – 40)
Silver	0.6
Silver	(0.4 – 1.1)
Zinc	280
Zinc	(180 – 430)
Total Polychlorinated Biphenyls (PCBs) (µg/kg)	18
Total Polychlorinated Biphenyls (PCBs) (µg/kg)	(18 - 18)
Low Molecular Weight Polycylic Aromatic Hydrocarbons (PAHs) (µg/kg)	130
	(90 – 180)
High Molecular Weight Polycylic Aromatic Hydrocarbons (PAHs) (µg/kg)	320
	(130 – 690)

Source: EPD Marine Water Quality in Hong Kong in 2023

https://www.epd.gov.hk/epd/sites/default/files/epd/english/environmentinhk/water/hkwqrc/files/waterquality/annual-report/marinereport2023.pdf (accessed in November 2024)

Notes:

1. Data presented are arithmetic means; data in brackets indicate ranges.

2. All data are based on the analyses of bulk (unsieved) sediment and are reported on a dry weight basis unless stated otherwise

3. Total PCBs results are derived from the summation of 18 congeners. If the concentration of a congener is below report limit (RL), the result will be taken as 0.5xRL in the calculation.

3. Low and high molecular weight PAHs results are derived from the summation of the corresponding congeners. If the concentration of a congener is below report limit (RL), the result will be taken as 0.5xRL in the calculation.

Water Sensitive Receivers

6.3.6 The Assessment Area for evaluating water quality impact is 500m from the Project boundaries of NSW and LC, which include fishponds / wetlands, rivers, drainage channels in the vicinity of the Project, part of Mai Po Nature Reserve and the Deep Bay Water Control Zone (WCZ). The WSRs are listed in Table 6.7 and locations are shown in Figure 6.1.

Table 6.7: WSRs with Assessment Area

ID	WSR	Type	Existing / Future Activities and Beneficial Uses
R1	Shan Pui River	River	River habitat, conveys stormwater from Yuen Long area, receives treated effluent discharge from Yuen Long Sewage Treatment Works
R2	Kam Tin River	River	River habitat, conveys stormwater from Kam Tin and Yau Tam Mei areas
W1	Mai Po Nature Reserve	Wetland Nature Reserve	Conservation area for wetland habitat, managed fishponds, feeding ground for wintering and migratory birds, and educational centre for visitors
W2	Inner Deep Bay Estuary / Mudflats	Estuary / Mudflats	Intertidal habitat, feeding ground for wintering and migratory birds
W3	Nam Sang Wai Wetlands	Wetlands	Wetland habitat
W4	Intertidal Ponds in Shan Pui River	Intertidal Ponds	Intertidal habitat, feeding ground for wintering and migratory birds
F1	Lut Chau Fishponds	Fishponds	Active fishponds, fish culture activities
F2	Tai Sang Wai Fishponds	Fishponds	Active fishponds, fish culture activities
F3	Fung Lok Wai Fishponds	Fishponds	Active fishponds, fish culture activities
F4	Nam Sang Wai Fishponds	Fishponds	Active and abandoned fishponds, fish culture activities
D1	Drainage Channels in Tai Sang Wai	Drainage Channels	Lowland stream habitat, conveys stormwater to Kam Tin River
D2	Drainage Channels around Lut Chau	Drainage Channels	Lowland stream habitat, conveys stormwater to Shan Pui River

Alteration of Water Courses

6.3.7 Within the Project Site, there are currently a small number of ponds at NSW that are hydrologically connected to Shan Pui River, and one pond at LC has an inter-tidal sluice. Table 6.8 summarises the effects of the Project on the water courses located within the Project Site. The ponds that will be retained or removed under the Project are identified in Figure 6.2.

Table 6.8: Summary of Alterations on Water Courses Within and Outside the Development Site of the Project Site

	Within the Development Site	Outside the Development Site
Hydrologically connected to water courses outside the Project Site	Ponds will be removed. Existing hydrological connections to water courses outside the Project Site will be lost. The existing flow regime is limited to one-way replenishment of the hydrologically connected ponds by inflow from the Shan Pui River during high tide.	Ponds will be retained and reprofiled. Existing hydrological connections will be retained. The flow regime will be altered as part of the active management of the NSW and LC.
Not-hydrologically connected to water courses outside the Project Site	Ponds will be removed. No effect on watercourses outside the Project Site.	Ponds will be retained and reprofiled. No effect on watercourses outside the Project Site.

6.3.8 Outside of the Project Site, there will be no alterations of existing water courses. Existing ponds act as flood storage and are not a significant source of inflow to surrounding rivers as they are rainfed only. The volume of inflow received by existing ponds that are hydrologically connected to Shan Pui and Kam Tin rivers outside the Project Site are also minimal relative to the capacity of these rivers.

6.4 Identification of Environmental Impacts

Construction Phase

LCNR

6.4.1 At the LCNR, the main construction activities are the following:

● Pond reprofiling – as part of the Conservation and Management Plan for LC, the ponds are proposed to be re-profiled to create a mixture of gently sloping bunds and submerged berms to provide extensive areas of suitably shallow water for foraging waterbirds.

● Bund removal / reprovisioning - Some existing bunds at LC will also be removed in order to merge smaller into larger ponds which are preferred by large waterbirds. The former sluice in the southwest part will also be reprovisioned to create a larger tidal pond habitat.

● Interconnecting uPVC pipes / sluices will be installed in all internal bunds to allow control of water levels and distribution of water across the LCNR.

● Miscellaneous minor improvement works – these include new grasscrete maintenance access paths, perimeter fencing, etc.

NSW WEA

6.4.2 At the NSW WEA, the main construction activities are the following:

● Pond reprofiling – as part of the Conservation and Management Plan for NSW WEA, the ponds are proposed to be re-profiled to create a mixture of gently sloping bunds and submerged berms to provide extensive areas of suitably shallow water for foraging waterbirds.

● Bund removal / reprovisioning - Some existing bunds at NSW WEA will also be removed in order to merge smaller into larger ponds which are preferred by large waterbirds.

● Interconnecting uPVC pipes / sluices will be installed in all internal bunds to allow control of water levels and distribution of water across the NSW WEA.

● Miscellaneous minor improvement works – these include new grasscrete maintenance access paths, perimeter fencing, etc.

Visitor Centre and Public Park

6.4.3 At the visitor centre and public park area, the main construction activities are the following:

● Site formation and construction of a new visitor centre with public toilets and overnight hostel

● Reprovisioning of the existing wooden jetty

● Miscellaneous minor improvement works – these include new access paths, visitor boardwalks, signage installation, utilities, perimeter fencing, etc.

Development Site

6.4.4 At the Development Site in NSW, the main construction activities would encompass the following:

● Site formation

● Construction of residential units, two clubhouses, a commercial centre, an elderly centre and a basement carpark

● Construction of private underground sewage pumping station (SPS) and underground stormwater detention tank

● Installation of public utilities

● Miscellaneous pavement and road surfacing, signage, street furniture and landscaping works

Proposed Bridge

6.4.5 A new bridge over Shan Pui River (connecting the Development Site to Wang Lok Street) will be constructed. The main construction activities are:

● Construction of bridge foundation and superstructure

● New twin rising main mounted on the bridge connecting the new SPS with the existing public sewerage network

● Miscellaneous pavement and road surfacing, signage, street furniture and landscaping works

Summary of Potential Water Quality Impacts

6.4.6 The aforementioned activities may create water quality impacts due to:

● Construction site runoff

● Direct disturbance of waterbodies

● Accidental spillage and leakage

● Sewage effluent generated by the workforce

● General construction activities

Construction Site Runoff

6.4.7 Construction site runoff can contain high loads of suspended solids due to runoff over exposed excavations and earth surfaces. Traces of other pollutants including fuels, oil and grease may also be present due to washing of construction site vehicles and heavy machinery. Such polluted runoff can elevate the turbidity and adversely affect water quality of the surrounding Shan Pui and Kam Tin rivers as well as the existing ponds within the LCNR and NSW WEA.

Direct Disturbance of Waterbodies

6.4.8 Direct disturbance of waterbodies can induce water quality impacts primarily due to direct agitation of settled sediments or disruptions to existing flow patterns leading to changes in erosion and sedimentation. Typically, such direct disturbances result in increased turbidity and suspended solids concentration in the water column, which can disrupt the natural biological processes in the waterbody and can also lead to reintroduction of pollutants bound in the sediment into the water column.

Accidental Spillage and Leakage

6.4.9 Construction activities will require use of various chemicals, fuels and oils, which may be stored onsite. Accidental spillage and/or leakage of such chemicals, fuels and oils may contaminate the ground and get washed into adjacent drainage channels or ponds, causing potentially severe water pollution that is harmful to aquatic life.

Sewage Effluent Generated by the Workforce

6.4.10 Sewage effluent contains high concentrations of pollutants such as faecal coliforms, E. coli, ammonia and organic solids. Untreated sewage that gets discharged into waterbodies will cause odour and deterioration in water quality by introducing pathogens and depleting dissolved oxygen. High ammonia concentration is also directly poisonous to fish.

General Construction Activities

6.4.11 The daily operation of construction sites will generate various stockpiles and wastes. Any refuse and litter that is not properly contained can be windblown into adjacent waterbodies, causing water pollution. Vehicles entering and leaving construction sites can also track mud and dirt onto public roads, which can cause nuisance to other road users and increase the quantity of suspended solids that is washed into roadside drains during rainstorm events.

Operational Phase

LCNR

6.4.12 At the LCNR, the main operational activities include:

● Monthly rotational pond drain down and water transfer between ponds

● Fish stocking activities

● Site maintenance / fishpond management

NSW WEA

6.4.13 At the NSW WEA, the main operational activities include:

● Monthly rotational pond drain down and water transfer between ponds

● Fish stocking activities

● Site maintenance / fishpond management

Visitor Centre and Public Park

6.4.14 At the visitor centre and public park area, the main operational activities include:

● Operation of the new visitor centre and facilities

● Site maintenance

Development Site

6.4.15 At the Development Site in NSW, the main operational activities include:

● Residential use

● Operation of the two clubhouses (with swimming pool), commercial centre, and elderly centre

● Operation of the SPS and stormwater detention tank

● Site maintenance

Proposed Bridge

6.4.16 At the new bridge over Shan Pui River, the main operational activities include:

● Road and pedestrian traffic use

● Road and roadside maintenance

Summary of Potential Water Quality Impacts

6.4.17 The potential water quality impacts associated with operational phase include:

● Discharge of pond drain down water

● Non-point source pollution from surface runoff

● Sewage effluent from the Project’s operation

● Disturbance of water flows/flow regimes in the Shan Pui River

Discharge of Pond Drain Down Water

6.4.18 Freshwater ponds operated within LCNR and NSW WEA will be partly kept free of larger fish and partly stocked with fish for supporting waterbirds to enhance their ecological function and will be actively managed with a rotational drain down cycle. The water quality of the freshwater ponds operated within LCNR and NSW WEA are thus expected to be notably different from the ambient water quality of the surrounding intertidal river system. In particular, it is expected that the pond water will be of typically higher temperature, lower salinity, lower dissolved oxygen and higher biochemical oxygen demand than the surrounding rivers most of the time. Any discharge of the pond water into the surrounding rivers during pond drain down can therefore have an impact on the water quality of the rivers, though it is noted that intertidal estuarine systems generally have relatively high tolerance to fluctuations in temperature, salinity and dissolved oxygen, while the existing baseline water quality at Shan Pui River and Kam Tin River (particularly in relation to suspended solids, nutrients and E.coli) is already poor (based on the water quality monitoring data shown in Table 6.3, Table 6.4 and Table 6.5).

Non-point Source Pollution From Surface Runoff

6.4.19 Non-point source pollution associated with surface runoff arises mainly from paved areas and roads. Vehicles on roads generate small amounts of pollutants such as oils, rubber and metal residues as well as dirt and fine particulates. During rainstorm events, such pollutants will get washed from the roads and paved areas into nearby drains and if uncontrolled, may discharge into the river system and lead to increased turbidity and water quality deterioration over time.

Sewage Effluent From the Project’s Operation

6.4.20 Sewage effluent from operation of the Project will contain high concentrations of faecal components as well as detergents and oil & grease which will cause deterioration in water quality if allowed to discharge directly into the surrounding environment.

Disturbance of Water Flows/Flow Regimes in the Shan Pui River

6.4.21 For the proposed bridge, no piers will be erected in the river. Hence, there will be no impediment to water flows/flow regimes within the Shan Pui River.

6.5 Prediction and Evaluation of Water Quality Impacts

Construction Phase

Construction Site Runoff

6.5.1 Within the LCNR and NSW WEA, the pond reprofiling works and bund removal / reprovisioning works will be the main potential source of polluted runoff to the existing ponds within the site. Runoff into intertidal ponds would also potentially affect Shan Pui and Kam Tin rivers. It is noted that the rivers surrounding the Project are subject to tidal flows from Deep Bay area, hence are naturally relatively high in suspended solids. Nevertheless, discharges into the rivers should be minimised or avoided as far as possible.

6.5.2 During pond reprofiling and bund removal / reprovisioning works, the affected ponds will be hydraulically isolated from surrounding ponds by temporarily blocking off any existing drainage connections and applying sandbags or other temporary bunding materials to prevent ingress of water from outside the working pond. The pond to be reprofiled will need to be dewatered before the reprofiling works. This water will be pumped to surrounding ponds for temporary storage and will not be drained into the surrounding rivers.

6.5.3 In case of heavy rainfall necessitating further dewatering of the affected pond during reprofiling works, the water pumped out from the pond will either be passed to a sedimentation facility or will be pumped to another isolated pond that has been dewatered in advance to act as additional storage, particularly during wet season. Surplus water pumped to the sedimentation / storage facility will be allowed to settle out the suspended solids before discharging to the surrounding ponds or back to the reprofiled pond once reprofiling works are complete.

6.5.4 For the bund removal / reprovisioning works, these would be carried out alongside the associated pond reprofiling works as far as practicable so that the associated runoff would also be hydraulically isolated and stored as part of the working area for the pond reprovision works. In case a section of bund needs to be removed / reprovisioned with its adjacent ponds still operational, then depending on contractor’s arrangements, silt curtains or other isolation methods such as temporary cofferdams may be adopted to prevent the spread of suspended solids without needing to dewater the entire pond.

6.5.5 Outside of the LCNR and NSW WEA and for site formation works at the new visitor centre and public park area, good site management measures including those specified in ProPECC PN2/23 will be adopted to hydraulically isolate the construction works sites and prevent ingress of runoff from outside the construction sites as well as egress of construction site runoff to surrounding areas. Temporary perimeter bunds and drainage channels will be used to divert construction site runoff into the onsite sedimentation facility for treatment. The contractor will apply for a discharge license for effluent from the construction site and treat all runoff and wastewater to the standards specified in the TM-DSS and the discharge license requirements. Treated effluent discharge volume will be minimised by reuse onsite (e.g., for dust suppression and vehicle wheel washing). Measures will be taken to minimise the generation of wastewater onsite and an emergency response plan will be developed to minimise potential water quality impacts under emergency or severe inclement weather conditions.

6.5.6 With the aforementioned practices in place, runoff generated from the construction works areas can be effectively controlled and there would be no adverse impacts to nearby WSRs.

Direct Disturbance of Waterbodies

6.5.7 During construction of the Project, no direct disturbance or alterations to waterbodies (water courses, natural streams, ponds, wetlands, catchment types or areas) outside the Project Boundary is anticipated, as no structures are proposed to be erected within any waterbody surrounding the Project Boundary.

6.5.8 Within the Project Boundary, there are proposed alterations to the existing ponds within the LCNR and NSW WEA which will be reprofiled and bunds will be removed/reprovisioned, however, the existing catchment type and area will stay the same. For those ponds located within the Development Site, there is a proposed change in catchment type as the existing ponds will be backfilled during site formation and will no longer be a waterbody. Existing hydraulic connections between the Development Site and the Shan Pui River will also be blocked off to isolate the construction works area from the surrounding environment. Direct disturbance to these ponds forms part of the Project’s development and water quality will be managed as part of construction site drainage and runoff practices.

Construction of the Proposed Bridge

6.5.9 The proposed bridge over the Shan Pui River will be constructed without the need for any pier structures located within the river boundary. Hence, there will be no direct disturbance of riverbed sediments and no impediment to water flows/flow regimes in the Shan Pui River during the construction phase. No adverse water quality impact is anticipated during the construction phase.

Accidental Spillage and Leakage

6.5.10 Within the construction works areas for the LCNR and NSW WEA, onsite storage of chemicals, fuels and oils will not be required given the nature of the works being primarily pond reprofiling, bund removal/reprovisioning and minor installations. Nevertheless, given the high sensitivity of the ponds and the site in general, onsite storage of chemicals, fuels and oils will be prohibited within the LCNR and NSW WEA areas. Measures to minimise the risk of leakage from operating equipment and machinery onsite will also be implemented.

6.5.11 Within the Development Site, onsite storage of chemicals, fuels and oils will be restricted to minimal quantities necessary for daily construction activities, and such chemicals and chemical wastes will be properly contained within a locked and impermeable bunded enclosure. Relevant best practice measures on labelling, handling, storage, use, transport and disposal will be implemented to minimise the risk of accidental spills and leaks.

Sewage Effluent Generated by the Workforce

6.5.12 Given the high sensitivity of the Project’s surroundings and the ‘no net increase in pollution load’ requirement for Deep Bay area, any discharge of sewage effluent by the construction workforce (whether treated or untreated) within or surrounding the Project Site is strictly prohibited. Adequate numbers of portable toilets will be provided onsite at conveniently accessible locations, and these will be carefully managed to ensure no accidental leakage into the surroundings. A licensed waste collector will be employed to transport the sewage effluent to a suitable government sewage treatment facility offsite and to maintain the cleanliness and operations of the portable toilets. Training will be provided to construction workers to ensure they are fully aware of the requirements and comply with the proper use of the toilets. Implementation of these measures will prevent adverse water quality impacts associated with sewage effluent discharge.

General Construction Activities

6.5.13 To prevent water quality impacts associated with general construction activities, good housekeeping practices at the construction site is essential. Stockpiles of materials will be appropriately secured and covered when not in use and appropriate refuse bins will be provided to prevent materials and general refuse from becoming windblown. Refuse bins will also be emptied regularly to avoid littering around the bins. Wheel washing facilities will be provided at each site entrance / exit to ensure the wheels and body of the vehicles are free from mud and dirt before leaving the construction site. Additional best practice measures are specified in Section 6.6. Implementation of the measures will prevent adverse water quality impacts associated with general construction activities.

Operational Phase

Discharge of Pond Drain Down Water

6.5.14 As part of the management of the LCNR and NSW WEA, two ponds will be drained each month to provide better foraging for birds and for periodic desilting where necessary. Water from the ponds to be drained will be pumped to adjacent ponds, except for those ponds with existing intertidal connections to the river, which will be naturally drained during ebb tide by keeping the sluice gate open. For all freshwater ponds, no discharge of drain down water will be permitted into the adjacent rivers. As only two ponds will be drained each month, there will be sufficient capacity maintained at the other ponds for retaining the drained water, hence no overflow into surrounding rivers is anticipated. Similarly, any sediment from desilting of ponds will either be reused onsite or disposed to landfill or other licensed waste facility offsite and will not be released into the surrounding water courses outside the Project Boundary.

Non-point Source Pollution From Surface Runoff

6.5.15 Within the LCNR and NSW WEA, there will be no changes to the existing drainage characteristics in line with the “Keep Untouched” approach specified in the TPB submission. Access paths within this area will also be paved with grasscrete, which will retain the permeability of the paths and help to trap pollutant residues while limiting any overland flow.

6.5.16 Within the Development Site, an “On-site Detention” approach will be adopted as per the commitments in the TPB submission. The runoff generated from the residential area will be collected by an internal storm drainage system and conveyed to an underground detention tank (with a capacity of approx. 31,750m³, which is based on the rainfall modelling for 1 in 50-year rainstorm events) for temporary storage. This will aid the settling of suspended solids. After rainstorm events, any surplus that cannot be retained and reused onsite will be discharged to Shan Pui River as a last resort. The tank will also be regularly desilted to remove the settled solids and maintain storage capacity.

6.5.17 Additional measures to minimise the pollutants in runoff from the Development Site include blue-green measures such as effective use of the public open space (recreational grassland area) as bioswales to filter and trap pollutants in the runoff and applying grasscrete or other types of permeable paving to pedestrian areas to increase permeability and reduce runoff potential. Maintenance of the bioswales will be carried out in accordance with the best management practices (BMPs) to be developed as part of the detailed design of the bioswales, which will aim to maintain the efficiency of the bioswale and minimise the potential water quality impacts associated with bioswale maintenance activities. Examples of BMPs include limiting maintenance activities to dry season and requiring vegetation cuttings to be removed from the site.

6.5.18 With consideration of the above proposed mitigation measures, the monthly pollution loading of surface runoff from paved areas due to rainfall is calculated in Appendix 6.1. The month with the highest rainfall-generated runoff is August, with a daily mean runoff of 9.236 mm/day. Taking suspended solids, total nitrogen and total phosphorus as representative key pollutants, the resulting daily mean pollution loading is 1.629 kg/day for suspended solids, 0.302 kg/day for total nitrogen, and 0.016 kg/day for total phosphorus within the Development Site. The first flush runoff flow is the main concern as it carries a higher load of pollutants. The proposed detention tank will effectively capture and prevent direct runoff of first flush discharge to Shan Pui River, which is an effective way to control pollution at source and abate pollutants. In addition, priority will be to retain the runoff onsite by pumping the outflow from the detention tank to designated ponds at NSW WEA and reusing for onsite irrigation. Hence it is expected that under non-extreme rainfall conditions, the runoff collected by the detention tank can be fully retained and reused onsite, and discharge to Shan Pui River would only occur infrequently during prolonged extreme rainfall when the onsite capacity is exhausted.

6.5.19 With the application of these measures, the pollution loading due to surface runoff generated by the Development Site will be adequately controlled and minimised, hence is a minor source and will have an insignificant impact on water quality at Shan Pui River.

Sewage Effluent From the Project’s Operation

Visitor Centre, Commercial Centre and Residential Development

6.5.20 Sewage effluent generated from the operation of the visitor centre, commercial centre and residential development has been estimated in the SIA as part of the TPB submission. As committed in the TPB, all sewage generated by the Project will be collected by the internal sewerage network and pumped to the existing public sewers that will convey the sewage to the existing Yuen Long Sewage Treatment Works (STW). Further details of the sewerage arrangements are provided in Chapter 12.

Clubhouse Facilities

6.5.21 Sewage effluent generated from the operation of the clubhouse facilities, including filter backwashing of the swimming pool has been estimated in the SIA as part of the TPB submission. The backwash volume of the swimming pool will be collected by the internal sewerage network and pumped to the existing public sewers that will convey the sewage to the existing Yuen Long STW. Further details of the sewerage arrangements are provided in Chapter 12. Swimming pool drain down water will be discharged to the underground stormwater detention tank. Prior to drain down, the swimming pool water will be held within the pool for several days to allow natural decay of any remaining residual chlorine, which will prevent release of residual chlorine into the surrounding environment.

Private Underground Sewage Pumping Station

6.5.22 For the private underground SPS, standby pumps and electricity supply conforming to the requirements set out in ProPECC PN 1/23 will be provided to ensure continuous operation during maintenance or mechanical failure. No overflow will be permitted, and in the very unlikely event of needing emergency discharge, a contingency plan will be implemented which will include management measures to prevent discharge of untreated sewage into surrounding rivers and ponds.

6.5.23 With the implementation of the recommended mitigation measures, the chances of any direct discharge of sewage effluent into surrounding rivers or ponds will be adequately minimised, and no adverse water quality impact is anticipated.

Disturbance of Water Flows/Flow Regimes in the Shan Pui River

6.5.24 For the proposed bridge, no piers will be erected within the river. Hence, once the bridge is operational, it will not impede the water flows or flow regimes of the Shan Pui River. No adverse water quality impact is anticipated during the operational phase.

6.6 Mitigation Measures

Construction Phase

Construction Site Runoff

6.6.1 Mitigation measures that will be applied for pond reprofiling and bund removal / reprovisioning works within the LCNR and NSW WEA include:

● Dewatering the affected ponds by pumping the water to surrounding ponds for temporary storage prior to construction activities;

● Hydraulically isolating the working area / ponds during reprofiling and bund removal / reprovisioning by temporarily blocking off any existing drainage connections and applying sandbags or other temporary bunding materials;

● In case of heavy rainfall, water pumped out from the pond will either be passed to a sedimentation facility or will be pumped to another isolated and pre-dewatered pond. Surplus water collected in the sedimentation / storage facility should settle out the suspended solids before discharging to surrounding ponds or used to recharge reprofiled ponds;

● Water from the ponds at LCNR and NSW WEA will not be drained to the surrounding rivers.

6.6.2 At all construction works areas, relevant practices specified in ProPECC PN2/23 will be applied during site construction to minimise surface runoff and erosion, which includes:

● Planning of earthworks (including drains, dykes and embankments) to minimise excavation of soil during wet season and implementation of erosion and sedimentation control facilities to control water discharge from the site during construction;

● Provision and maintenance of sand/silt removal facilities such as sand/silt traps and sediment basins;

● Provision of temporary perimeter bunds and drainage intercept channels to divert construction site runoff into the onsite sedimentation facility for treatment and onsite reuse;

● Covering exposed slope/soil surfaces and open stockpiles by a tarpaulin or other means, as far as practicable, especially during rainstorms. Exposed soil areas to be minimised to reduce potential for increased siltation and contamination of runoff;

● Earthwork final surfaces to be well compacted and subsequent permanent work or surface protection to be immediately performed;

● Provision and maintenance of oil/grease removal facilities at appropriate locations where chance of contamination of runoff is high;

● Adequately cover and temporarily seal manholes to prevent silt and debris getting into the drainage system or foul sewers;

● Provision of onsite sedimentation facility and reuse of treated runoff (e.g., for dust suppression and vehicle wheel washing) to minimise need for offsite discharge;

● Appropriate storage, treatment and disposal of any chemical waste to prevent spillage into watercourses;

● Appropriate treatment, neutralisation and disposal of concrete washings.

6.6.3 The contractor shall apply to EPD for a discharge license and ensure the treated discharge complies with the discharge license issued by EPD and the criteria specified in the TM-DSS.

6.6.4 The contractor shall implement measures to minimise the generation of wastewater associated with construction activities, including:

● Phased construction to minimise the size of the construction area with potential to generate construction site runoff;

● Adopt construction methods that use less water, such as offsite prefabrication;

● Apply polymers, soil binders or temporary paving of haul roads to reduce the need for water spraying for dust suppression;

● Excess concrete should be scraped off the equipment before it is washed to reduce the amount of washout water produced; and

● Adopt high pressure, low volume water spray nozzle for construction vehicle and equipment washing activities.

6.6.5 For emergency situations such as failure of onsite wastewater treatment facilities or severe inclement weather conditions that might cause polluted construction site discharge, the contractor should implement an emergency response plan. The emergency response plan should specify:

● Emergency contacts and persons to be notified during emergency situations;

● Details of the construction site drainage system and treatment facilities;

● Requirements and procedures for routine integrity checking and maintenance of the drainage system and treatment facilities;

● Emergency response and rectification procedures to restore normal operation of the treatment facilities; and

● An event and action plan including additional water quality monitoring.

6.6.6 The emergency response plan should be agreed with EPD prior to commencement of construction works.

Direct Disturbance of Waterbodies

6.6.7 As described in Section 6.5, there will be no direct disturbance of waterbodies outside the Project Boundary during construction phase, hence no specific mitigation measures are required.

Accidental Spillage and Leakage

6.6.8 Onsite storage of chemicals, fuels and oils will be prohibited within the LCNR and NSW WEA areas.

6.6.9 Within the Development Site, chemical spillage during construction will be minimised by the following measures:

● Onsite storage of chemicals, fuels and oils will be restricted to minimal quantities necessary for daily construction activities;

● Suitable containers will be used to hold any chemical wastes to avoid leakage or spillage during storage, handling and transport;

● Chemical waste containers will be suitably labelled, to notify and warn the personnel who are handling the wastes to avoid accidents;

● Storage area will be selected at a safe location on site and secured by locks, and adequate space will be allocated to the storage area;

● Designated storage areas will have pollution prevention facilities e.g., impermeable bunding around the storage area with capacity at least 110% that of the chemicals / chemical wastes stored;

● Vehicles and equipment involved in activities with potential for leakage or spillage will be correctly maintained;

● In case of an accidental spillage of chemicals, immediate clean-up / remedial action to be implemented in order to minimise water quality impacts.

Sewage Effluent Generated by the Workforce

6.6.10 During construction stage, temporary sanitary facilities, such as portable chemical toilets, will be employed onsite where necessary to handle sewage from the workforce. A licensed contractor will be responsible for regular and appropriate disposal and maintenance of these facilities.

6.6.11 Construction workers will receive training on the requirements for proper use of the portable chemical toilets and prohibited from discharging any sewage effluents into the surrounding areas.

General Construction Activities

6.6.12 Mitigation measures to be implemented for general construction activities include:

● Good housekeeping practices will be implemented within the construction areas such as keeping materials and equipment tidy and covering stockpiles when not in use;

● Provide adequate refuse bins and ensure they are emptied regularly;

● Provide wheel washing facilities at each site entrance / exit and wash all vehicles and their wheels to remove mud and dirt before leaving the construction site;

● Regular checking and maintenance of plant and equipment.

Operational Phase

Discharge of Pond Drain Down Water

6.6.13 No discharge of drain down water from the freshwater ponds to the adjacent rivers will be permitted during operational phase (only the existing ponds with intertidal connections to the river will be allowed to naturally drain during ebb tide). Water from drained ponds will be pumped to and temporarily stored at adjacent ponds within the LCNR and NSW WEA site. Sediment from the desilting of ponds will either be reused onsite (e.g., as material for bund maintenance) or be disposed to licensed waste facility offsite (e.g., landfill).

Non-point Source Pollution From Surface Runoff

6.6.14 Within the LCNR and NSW WEA, permanent grasscrete tracks will be created to allow access for management of the ponds, which will induce minimal runoff.

6.6.15 Within the Development Site, following the “On-site Detention” approach, the following measures will be implemented:

● Runoff within the residential area will be minimised by adopting blue-green measures including bioswales and permeable paving as part of the design of pedestrian and open space areas;

● Operation and maintenance of the bioswales shall follow the BMPs to be developed as part of the detailed design of the bioswales;

● BMPs for stormwater discharge will also be adopted to minimize stormwater pollution arising from the Project. Runoff from roads within the residential area will be drained through a separate drainage system equipped with gullies, oil interceptors and grit traps to remove the pollutants;

● The internal drainage system will convey runoff to an underground detention tank (with capacity of approx. 31,750m³) for temporary storage and settling out of suspended solids;

● The underground detention tank will be regularly desilted to remove the settled solids and maintain storage capacity;

● Outflow from the detention tank will be retained onsite (e.g. pumped to designated ponds at NSW WEA) and used for irrigation where practicable. Surplus outflow from the detention tank will be discharged to Shan Pui River only when the onsite capacity is exhausted.

Sewage Effluent From the Project’s Operation

6.6.16 The estimated average dry weather flow (ADWF) of sewage generated from the Project is 3,059.8 m³/day. As concluded in Chapter 12 of this EIA, the hydraulic model has shown that there is sufficient capacity at the existing sewerage system to receive the additional sewage flow from the Project, hence no adverse sewerage impact from the Project would be anticipated.

Visitor Centre, Commercial Centre and Residential Development

6.6.17 Sewage generated from the visitor centre, commercial centre and residential development would be conveyed to the Project’s private underground SPS, then drained into the government sewer for discharge into the Yuen Long Sewage Treatment Works, which is being upgraded to the Yuen Long Effluent Polishing Plant (YLEPP). The sewage will not enter watercourses.

Clubhouse Facilities

6.6.18 The sewage generated by the staff in the clubhouse and the backwash from the swimming pool will be conveyed to the Project’s private underground SPS for discharge to the YLEPP, for which the backwash volume was calculated and presented in Appendix 12.1. Drain down from the swimming pool will be temporarily held within the pool to ensure natural decay of residual chlorine and tested for no residual chlorine before being discharged to the underground detention tank. The operator shall apply for a discharge license under the WPCO and shall meet the requirements of the licence, as well as conditions in the Environmental Permit of this Project under the EIAO.

Private Underground Sewage Pumping Station

6.6.19 For the private underground SPS, operation activities should follow the requirements set out in DSD’s Sewerage Manual (Part 2 – Pumping Stations and Rising Mains). In addition, the following measures will be implemented:

● Provide and maintain standby pumps with capacity not less than any of the duty pumps and electricity supply to ensure the continuous operation during maintenance or mechanical failure;

● Duty pumps should not operate more than 10 on-off cycles per hour;

● No overflow is permitted under any circumstance;

● A contingency plan should be prepared to cater for emergency scenarios and should be prior agreed with EPD and DSD. The contingency plan should include:

– Management measures in case of unavoidable emergency discharge (such as providing portable toilets onsite to reduce sewage loading into the internal sewerage network, and arrangements for tank away of any surplus raw sewage to the public STW);

– Measures to deal with accidental or unintended leakage of untreated sewage (from incidents such as pipe burst events), including water quality monitoring programme.

Disturbance of Water Flows/Flow Regimes in the Shan Pui River

6.6.20 As described in Section 6.5, there will be no disturbance of water flows or flow regimes in the Shan Pui River during both the construction and operational phases. Therefore, no specific mitigation measures are required.

6.7 Cumulative Impacts

6.7.1 Concurrent projects with potential cumulative water quality impacts are identified and evaluated below.

Yuen Long Barrage Scheme

6.7.2 The Yuen Long Barrage Scheme (YLBS) primarily involves the construction and operation of tidal barrier facilities across Yuen Long Nullah and works within the Nullah itself (to widen and deepen the Nullah). With reference to the approved EIA (AEIAR-228/2021), to mitigate construction phase water quality impacts on the river downstream, a containment structure in conjunction with silt curtain where practicable is proposed to be set up to contain suspended solids during channel excavation and sediment removal works, and the existing flow is proposed to be diverted away from the works area using a diversion channel. Various measures are also recommended for typical construction site runoff and drainage control, which will prevent adverse water quality impact downstream. During operational phase, maintenance measures will also be controlled to limit water quality impact (e.g., by carrying out desilting works in dry season) and temporary flow diversion scheme would also be implemented. Potential water quality impacts to Shan Pui River adjacent to the Project Site (which is downstream of the YLBS) are expected to be minimised with the implementation of the recommended mitigation measures, while the implementation of the YLBS itself is expected to help improve existing water quality via the revitalisation works. Therefore, adverse cumulative water quality impact from YLBS is not expected.

Yuen Long Effluent Polishing Plant

6.7.3 The YLEPP project is an upgrade of the existing Yuen Long Sewage Treatment Works (YLSTW) to cater to future needs in the catchment and improve the water quality of Deep Bay. Construction activities for this project is land based and does not involve any direct disturbance of Shan Pui River. As specified in the approved EIA report (AEIAR-220/2019), mitigation measures will be implemented to control construction site runoff and works in close proximity to the river. During operational phase, measures will also be implemented to minimise the risk of emergency discharge and/or implement temporary diversion of part of the sewage to San Wai STW (where capacity allows) to reduce potential emergency discharge loading to the surrounding rivers. Adverse cumulative water quality impact is not expected with proper implementation of the recommended mitigation measures.

Improvement of Yuen Long Town Nullah (Town Centre Section)

6.7.4 The improvement works for the Town Centre Section of the Yuen Long Town Nullah (YLTN) involves the construction of dry weather flow (DWF) interceptors and associated DWF conveyance facilities to YLEPP. Construction phase activities may generate elevated suspended solids discharge potentially affecting Shan Pui River downstream. Mitigation measures have been specified in the approved EIA (AEIAR-223/2020) which includes site management practices to control runoff and drainage, use of containment structures and diversion channels to hydraulically separate the works areas from the river, and other typical measures for handling spillage / leakage and wastewater discharges. Implementation of these measures will prevent adverse water quality impacts to downstream waterbodies, while during operational phase, the diversion of DWF to YLEPP will substantially reduce existing pollution loadings to Yuen Long Nullah, which is expected to improve water quality downstream at Shan Pui River. Hence no adverse cumulative water quality impact from YLTN is expected.

Proposed Private Residential Development in D.D.115 at Chung Yip Road, Nam Sang Wai, Yuen Long

6.7.5 This project involves approximately eight blocks of private residential development within the 1.5ha site at Chung Yip Road, Nam Sang Wai, under the approved planning application (No. A/YL-NSW/282). No construction and operation details are available on this project at this stage, though it is expected that this project is also required to comply with TPB PG-No.12C with respect to no net increase in pollution load to Deep Bay as part of its construction and operational phase. It is thus reasonably assumed that there will be no adverse water quality impacts arising from this project based on its approved planning application, and hence no adverse cumulative water quality impact is expected.

Northern Metropolis Highway

6.7.6 The 23-km Northern Metropolis Highway comprises of four main road sections, with the proposed alignment for the Tin Shui Wai Section (from Tin Shui Wai to Kam Tin) initially anticipated to intersect the NSW WEA. No construction and operation details are available on this project at this stage, while the alignment is subject to the findings of an Investigation Study to be carried out. Given that this project will be required to carry out an EIA, potential cumulative water quality impacts for the proposed alignment should be addressed under that EIA study.

Sam Po Shue Wetland Conservation Park

6.7.7 The Sam Po Shue Wetland Conservation Park is part of the San Tin / Lok Ma Chau Development Node under the approved EIA (AEIAR-261/2024) and is a planned wetland conservation area with wetland and fishpond enhancement. An Investigation Study is currently ongoing for this project and no construction and operation details are available at this stage, though the approved EIA report for San Tin / Lok Ma Chau Development Node has specified mitigation measures to prevent adverse water quality impacts associated with the project. Thus it can be reasonably assumed that potential water quality impacts associated with the project will be addressed in the Investigation Study and there will be no adverse water quality impacts arising from this project, hence no adverse cumulative water quality impact is expected.

6.8 Evaluation of Residual Impacts

6.8.1 With the implementation of the recommended mitigation measures, no adverse water quality impacts are expected during construction and operational phase, and no residual impacts on water quality is anticipated.

6.9 Environmental Monitoring and Audit Requirements

6.9.1 The potential water quality impacts from the construction works can be controlled by the recommended mitigation measures, while the proposed bridge will be constructed without the need for any pier structures within the river so there will be no direct disturbance of riverbed sediments or impediment to flows in Shan Pui River. No adverse water quality impact is anticipated during the construction phase. Nonetheless, as the Project Site is surrounded by ecologically sensitive areas, regular site inspections and water quality monitoring should be undertaken during construction phase to check that the recommended mitigation measures are properly implemented. A WPCO license should be obtained by the contractor for any construction site discharge, and monitoring of the discharge should be carried out in accordance with the WPCO license conditions.

6.9.2 During the operational phase, sewage effluent generated from the residential development, public park, visitor centre and commercial centre would be conveyed to the Project’s private underground SPS, and then drained into the government sewer for discharge into the YLEPP. The sewage will not enter watercourses. Water quality associated with the LCNR and NSW WEA will be monitored and managed following the Conservation and Management Plan. Operation and maintenance of the bioswales should follow the BMPs to be developed as part of the detailed design of the bioswales. In case of any accidental or emergency discharge or leakage from the proposed private underground SPS, water quality monitoring should be undertaken as part of the contingency plan to be agreed with EPD and DSD.

6.10 Conclusions and Recommendations

6.10.1 The main water quality impact associated with the construction phase is polluted runoff from construction site activities, particularly earthmoving works for the ponds/bunds and site formation of the Development Site. Specific measures have been recommended to hydraulically isolate the works areas from the surrounding waterbodies and to minimise wastewater generated from construction activities. Best practice measures as specified in ProPECC PN1/23, ProPECC PN2/23, ETWB TC (Works) No. 5/2005 will also be adopted and an emergency response plan is recommended to minimise the potential for water quality impacts during emergency situations and inclement weather.

6.10.2 During the operational phase, the management of the LCNR and NSW WEA will follow a “Keep Untouched” approach and there will not be any discharge of pond drain down water into the surrounding rivers, while an “On-site Detention” approach will be adopted at the Development Site to control surface runoff, including blue-green runoff reduction measures such as bioswales and permeable paving, an onsite detention tank and onsite reuse. All sewage generated from the residential area will be conveyed to the existing Yuen Long Sewage Treatment Works, which is being upgraded to YLEPP. A contingency plan for the private underground SPS will be prepared for emergency scenarios, such as arrangements for the tanking away of any surplus raw sewage to the public STW, to prevent the discharge of untreated sewage into surrounding rivers and ponds.

6.10.3 With the implementation of the recommended mitigation measures during the construction and operational phases, no adverse water quality impact is anticipated.