6. Water Quality Impact Assessment

6.1 Introduction

6.2 Relevant Legislations, Standards & Guidelines

6.3 Assessment Methodology

6.4 Study Area and Water Sensitive Receivers (WSRs)

6.5 Baseline Water Quality Conditions

6.6 Water Quality Impact Assessment

6.7 Mitigation Measures

6.8 Cumulative Impact

6.9 Evaluation of Residual Impact

6.10 Environmental Monitoring and Audit Requirements

6.11 Summary

List of Figures

Figure 6.1	Water Sensitive Receivers at Sung Shan New Village
Figure 6.2	Water Sensitive Receivers at Tai Wo
Figure 6.3	Water Sensitive Receivers at Lin Fa Tei
Figure 6.4	Water Sensitive Receivers at Ha Che
Figure 6.5	EPD’s Monitoring Station

List of Appendices

Appendix 6-1	Baseline Water Quality Monitoring Result
Appendix 6-2	Supplementary Baseline Water Quality Monitoring Result

6. Water Quality Impact Assessment

6.1 Introduction

6.1.1. This section addresses the potential water quality impacts associated with both the construction and operation phases of the Project. Mitigation measures have been recommended to reduce/minimize the potential water quality impacts to acceptable levels as appropriate.

6.1.2. The water quality impact assessment is based on the criteria and guidelines stated in Annexes 6 and 14 of the EIAO-TM for evaluation and assessment of water quality impact, and covered the scope of work outlined in section 3.4.4 of the EIA Study Brief for this Project.

6.2 Relevant Legislations, Standards & Guidelines

6.2.1. In carrying out the assessment, reference was made to the following relevant Hong Kong legislations/standards/guidelines governing water pollution control:

Environmental Impact Assessment Ordinance (EIAO);

Water Pollution Control Ordinance (WPCO) (Cap. 358) & Water Quality Objectives (WQOs);

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

Practice Note for Professional Persons (ProPECC) PN 1/94, “Construction Site Drainage”; and

Hong Kong Planning Standards and Guidelines.

Environmental Impact Assessment Ordinance (EIAO)

6.2.2. EIA and an environmental permit are required for this Project under Item I.1(b) of Part I, Schedule 2 of the EIAO - A drainage channel or river training and diversion works which discharges or discharge into an area which is less than 300m from the nearest boundary of an existing or planned (i) site of special scientific interest; (ii) site of cultural heritage; (iii) marine park or marine reserve; (iv) fish cultural zone; (v) wild animal protection area; (vi) coastal protection area; or (vii) conservation area. This Project is classified as a Designated Project (DP) as the drainage channel or river training and diversion works discharges or discharge into an area which is less than 300m from the nearest boundary of an existing conservation area.

6.2.3. The EIAO provides a legislative framework to safeguard the environment by reducing and minimizing adverse environmental impacts from designated projects in Hong Kong.

6.2.4. Annexes 6 and 14 of the EIAO Technical Memorandum on Environmental Impact Assessment Process (TM) specify the general and project-specific criteria, and guidelines for water quality impact assessment.

Water Pollution Control Ordinance (Cap. 358) & Water Quality Objectives (WQOs)

6.2.5. The entire Hong Kong waters are divided into ten Water Control Zones (WCZs) and four supplementary WCZs under the WPCO (Cap. 358). Each WCZ has a designated set of statutory Water Quality Objectives (WQOs) designed to protect the water environment and its users. The Project is located in the Deep Bay WCZ and the corresponding WQOs are summarised Table 6‑1 below.

Table 6‑1 Water Quality Objectives for Deep Bay WCZ

Parameters	Objectives	Sub-Zone
Offensive Odour, Tints	Not to be present	Whole zone
Visible foam, oil scum, litter	Not to be present	Whole zone
Dissolved Oxygen (DO) within 2 m of the seabed	Not less than 2.0mg/L for 90% of samples	Outer Marine Subzone excepting Mariculture Subzone
DO within 1 m below surface	Not less than 4.0mg/L for 90% of samples	Inner Marine Subzone excepting Mariculture Subzone
	Not less than 5.0mg/L for 90% of samples	Mariculture Subzone
Depth-averaged DO	Not less than 4.0mg/L for 90% of samples	Outer Marine Subzone excepting Mariculture Subzone
	Not less than 4.0mg/L	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
5-Day Biochemical Oxygen Demand (BOD5)	Not to exceed 3mg/L	Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones
	Not to exceed 5mg/L	Yuen Long & Kam Tin (Lower) Subzone and other inland waters
Chemical Oxygen Demand (COD)	Not to exceed 15mg/L	Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground
	Not to exceed 30mg/L	Yuen Long & Kam Tin (Lower) Subzone and other inland waters
pH	To be in the range of 6.5 – 8.5, change due to waste discharges not to exceed 0.2	Marine waters excepting Yung Long Bathing Beach Subzone
	To be in the range of 6.5 – 8.5	Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones
	To be in the range of 6.0 –9.0	Other inland waters
	To be in the range of 6.0 –  9.0 for 95% samples, change due to waste discharges not to exceed 0.5	Yung Long Bathing Beach Subzone
Salinity	Change due to waste discharges not to exceed 10% of ambient	Whole zone
Temperature	Change due to waste discharges not to exceed 2°C	Whole zone
Suspended solids (SS)	Not to raise the ambient level by 30% caused by waste discharges and shall not affect aquatic communities	Marine waters
	Not to cause the annual median to exceed 20mg/L	Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone, Ganges Subzone, Indus Subzone, Water Gathering Ground Subzones and other inland waters
Unionized Ammonia (UIA)	Annual mean not to exceed 0.021mg/L as unionized form	Whole zone
Nutrients	Shall not cause excessive algal and other aquatic plants growth	Inner and Outer Marine Subzones
Total Inorganic Nitrogen (TIN)	Annual mean depth-averaged inorganic nitrogen not to exceed 0.7mg/L	Inner Marine Subzone
	Annual mean depth-averaged inorganic nitrogen not to exceed 0.5mg/L	Outer Marine Subzone
Bacteria (E. coli)	Not exceed 610per 100ml, calculated as the geometric mean of all samples collected in one calendar year	Secondary Contact Recreation Subzones and Mariculture Subzones
	Should be zero per 100 ml, calculated as the running median of the most recent 5 consecutive samples taken between 7 and 21 days.	Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones
	Not exceed 180per 100ml, calculated as the geometric mean of the 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 14days.	Yung Long Bathing Beach Subzone
	Not exceed 1000 per 100ml, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21days	Yuen Long & Kam Tin (Lower) Subzone and other inland waters
Colour	Not to exceed 30 Hazen units	Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones
	Not to exceed 50 Hazen units	Yuen Long & Kam Tin (Lower) Subzone and other inland waters
Turbidity	Shall not reduce light transmission substantially from the normal level	Yuen Long Bathing Beach Subzone
Phenol	Quantities shall not sufficient to produce a specific odour or more than 0.05mg/L as C6H5OH	Yuen Long Bathing Beach Subzone
Toxins	Should not cause a risk to any beneficial uses of the aquatic environment	Whole Zone
	Should not attain such levels as to produce toxic carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms.	Whole Zone

Technical Memorandum on Effluents Discharge Standard (TM-DSS)

6.2.6. Apart from the WQOs, Section 21 of the WPCO also specifies the limits to control the physical, chemical and microbial parameters for effluent discharges into drainage and sewerage system at both inland and coastal waters under the Technical Memorandum for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS).

6.2.7. The discharge limits vary with the effluent flow rates. Sewerage from the Project should comply with the standards for effluent discharged into inland water. Group B and C inland water standards in TM-DSS are adopted and the effluent discharge standards are presented in Table 6‑2 and 6-3 below.

Table 6‑2 Standards for Effluents Discharged into Group B Inland Waters

Parameter	Flow Rate (m^3/day)
	<= 200	> 200 and <= 400	> 400 and <= 600	> 600 and <= 800	> 800 and <= 1000	> 1000 and <= 1500	> 1500 and <= 2000	> 2000 and <= 3000
pH (pH units)	6.5-8.5	6.5-8.5	6.5-8.5	6.5-8.5	6.5-8.5	6.5-8.5	6.5-8.5	6.5-8.5
Temperature (°C)	35	30	30	30	30	30	30	30
Colour (lovibond units) (25mm cell length)	1	1	1	1	1	1	1	1
SS	30	30	30	30	30	30	30	30
BOD	20	20	20	20	20	20	20	20
COD	80	80	80	80	80	80	80	80
Oil & Grease	10	10	10	10	10	10	10	10
Iron	10	8	7	5	4	3	2	1
Boron	5	4	3	2.5	2	1.5	1	0.5
Barium	5	4	3	2.5	2	1.5	1	0.5
Mercury	0.001	0.001	0.001	0.001	0.001	0.001	0.001	0.001
Cadmium	0.001	0.001	0.001	0.001	0.001	0.001	0.001	0.001
Selenium	0.2	0.2	0.2	0.2	0.2	0.1	0.1	0.1
Other toxic metals individually	0.5	0.5	0.2	0.2	0.2	0.1	0.1	0.1
Total Toxic metals	2	1.5	1	0.5	0.5	0.2	0.2	0.2
Cyanide	0.1	0.1	0.1	0.08	0.08	0.05	0.05	0.03
Phenols	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.1
Sulphide	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2
Fluoride	10	10	8	8	8	5	5	3
Sulphate	800	800	600	600	600	400	400	400
Chloride	1000	1000	800	800	800	600	600	400
Total phosphorus	10	10	10	8	8	8	5	5
Ammonia nitrogen	5	5	5	5	5	5	5	5
Nitrate + nitrite nitrogen	30	30	30	20	20	20	10	10
Surfactants (total)	5	5	5	5	5	5	5	5
E. coli (cfu/100ml)	100	100	100	100	100	100	100	100

Notes: All units in mg/L unless otherwise stated; all figures are upper limits unless otherwise indicated.

Table 6‑3 Standards for Effluents Discharged into Group C Inland Waters

Parameter	Flow Rate (m^3/day)
	≤ 100	> 100 and ≤ 500	> 500 and ≤ 1000	> 1000 and ≤ 2000
pH (pH units)	6-9	6-9	6-9	6-9
Temperature (℃)	30	30	30	30
Colour (lovibond units) (25mm cell length)	1	1	1	1
Suspended solids	20	10	10	5
BOD	20	15	10	5
COD	80	60	40	20
Oil & Grease	1	1	1	1
Boron	10	5	4	2
Barium	1	1	1	0.5
Iron	0.5	0.4	0.3	0.2
Mercury	0.001	0.001	0.001	0.001
Cadmium	0.001	0.001	0.001	0.001
Silver	0.1	0.1	0.1	0.1
Copper	0.1	0.1	0.05	0.05
Selenium	0.1	0.1	0.05	0.05
Lead	0.2	0.2	0.2	0.1
Nickel	0.2	0.2	0.2	0.1
Other toxic metals individually	0.5	0.4	0.3	0.2
Total Toxic metals	0.5	0.4	0.3	0.2
Cyanide	0.05	0.05	0.05	0.01
Phenols	0.1	0.1	0.1	0.1
Sulphide	0.2	0.2	0.2	0.1
Fluoride	10	7	5	4
Sulphate	800	600	400	200
Chloride	1000	1000	1000	1000
Total phosphorus	10	10	8	8
Ammonia nitrogen	2	2	2	1
Nitrate + nitrite nitrogen	30	30	20	20
Surfactants (total)	2	2	2	1
E. coli (count/100ml)	1000	1000	1000	1000

Notes: All units in mg/L unless otherwise stated; all figures are upper limits unless otherwise indicated.

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

6.2.8. The Practice Note for Professional Persons (ProPECC Note PN1/94) on construction site drainage provides guidelines on good practice for dealing with discharges from construction sites. This Practice Note is applicable to this study for control of site runoff and wastewater generated during the construction phase of the Project.

6.2.9. The water quality assessment followed this Practice Note to recommend mitigation measures to minimize the potential water quality impact arising from construction activities.

Hong Kong Planning Standards and Guidelines (HKPSG)

6.2.10. Chapter 9 of the Hong Kong Planning Standards and Guidelines (HKPSG) outlines environmental requirements that need to be considered in land use planning. The recommended guidelines, standards and guidance cover the selection of suitable locations for the developments and sensitive uses, provision of environmental facilities, and design, layout, phasing and operational controls to minimize adverse environmental impacts. It also lists out environmental factors influencing land use planning and recommended buffer distances for land uses.

6.3 Assessment Methodology

6.3.1. In accordance with Clause 3.4.4.2 of the EIA Study Brief, the area for water quality impact assessment included all areas within a distance of 500m from the site boundary of the Project. The assessment would be extended to include other areas such as stream courses and associated water systems, ponds in the vicinity being impacted by the Project if found justifiable.

6.3.2. Apart from the identified representative WSRs in Table 6-4 below, other small ponds or streams (e.g. small glens, small tributaries with runoff during rainstorms, etc.) were considered as relatively minor and unlikely to have adverse water quality impact since direct water quality impact is limited to existing main stream only. Moreover, the farmland and cultivation area were also identified as WSRs in this EIA.

6.3.3. The major concerns during construction and operational phases of the Project are the works closed to the Cheung Po River. The provision and adequacy of the existing, committed and planned future facilities to reduce pollution arising from the stormwater drainage system and surface water runoff during both construction and operation of the Project were analysed and proposed.

6.3.4. There will be no marine-based works such as dredging or reclamation. Land-based works will include excavation works of affected streams. However, these excavation works would be within cofferdam or diaphragm walls with no direct contact with waterbodies. The assessment approach is referred to Annex 6 – Criteria for Evaluating Water Pollution and Annex 14 – Guidelines for Assessment of Water Pollution under the TM-EIAO.

6.4 Study Area and Water Sensitive Receivers (WSRs)

6.4.1. The potential affected Water Sensitive Receivers (WSRs) have been identified and included in this water quality impact assessment. The assessment will address the characterize water quality of the water systems and sensitive receivers, which may be affected by the Project based on existing best available information or through appropriate site survey and test.

6.4.2. The Project is located within the Deep Bay WCZ. It is located at the hinterland of Tai Lam, Tai Mo Shan and Lam Tsuen Country Park. Latest Outline Zoning Plan (OZP) including OZP No. S/YL-TT/17 (Tai Tong), S/YL-KTS/15 (Kam Tin South), S/YL-SK/9 (Skek Kong) and S/YL-PH/11 (Pat Heung) were reviewed. The Project is mainly drainage improvement works by stream channelling at Sung Shan New Village (SSNV), Tai Wo (TW), Lin Fa Tei (LFT) and Ha Che (HC), constructing new rectangular channel at Tai Wo and constructing new pipes underneath Kam Sheung Road at LFT and Fan Kam Road at HC.

6.4.3. Representative WSRs include the streams/ponds and farm/cultivation area that may be directly or indirectly affected by the Project. According to the site visit, the villager used the tap water in the village for any irrigation. No water extraction from nearby waterbodies is observed. Table 6‑4 listed the representative WSRs and the location plan is shown in Figures 6.1 to 6.4. Regarding Cheung Po Ecologically Important Stream (EIS) titled “WSR_TW1” in Figure 6.2, the EIS is situated to the south of the proposed works boundary. The natural stream on the south of the proposed channel is quite away. According to site survey, the villager used tap water in village for any irrigation. No water extraction from nearby waterbodies is observed.

6.4.4. Details of the proposed drainage improvement works, including layout plans and sections are shown in Figures 2.1 to 2.5 in the Chapter 2 Project Description. The proposed drainage improvement works would be confined within the working areas/ working locations only. The 500m study area equals to the 500m-buffer zone of entire drainage working limit (area buffering zone), rather than simple 500m-buffer zone of working locations (point buffer zone). The proposed drainage improvement works will be confined within the working locations but not entire drainage areas.

Table 6‑4 Representative Water Sensitive Receivers (WSRs)

Representative WSRs		Existing Status	Potential impact from the Project
Sung Shan New Village (SSNV) in Figure 6.1
WSR_SSNV1	SSNV Stream	Drainage stream near SSNV, upstream to Yuen Long Creek	To be widened
WSR_SSNV2	Pond	Individual pond, disconnected to river systems	Around 70m away from the Project, no direct impact
WSR_SSNV3	Pond	Individual pond, disconnected to river systems	Around 90m away from the Project, no direct impact
WSR_SSNV4	Pond	Individual pond, disconnected to river systems	Around 110m away from the Project, no direct impact
WSR_SSNV5	Stream	Upstream stream from conservation area	Around 210m away from the Project, no direct impact
WSR_SSNV6	Stream	Individual stream, disconnected to river systems of Project area	Around 260m away from the Project, no direct impact
Tai Wo (TW) in Figure 6.2
WSR_TW1	Cheung Po River	Natural stream including a section of Ecologically Important Stream (EIS)	No direct impact at the EIS. However, minor construction works will be undertaken at the connections between the proposed rectangular channel and downstream section of Cheung Po River
WSR_TW2	Pond	Individual pool, disconnected to river systems	Around 140m away from the Project, no direct impact
WSR_TW3	Nullah	Disconnected to existing stream in Project area	Around 190m away from the Project, no direct impact
WSR_TW4	Stream	Tributary stream to Cheung Po River	Around 100m away from the Project, no direct impact
WSR_TW5	Stream	Disconnected stream to Cheung Po River	Around 500m away from the Project, no direct impact
Lin Fa Tei (LFT) in Figure 6.3
WSR_LFT1	Kam Tin River Tributary	Drainage stream near LFT, upstream to Kam Tin River	To be widened
WSR_LFT2	Kam Tin River Tributary	Drainage stream near LFT, upstream to Kam Tin River	To be widened
WSR_LFT3	Stream	Individual stream, disconnected to the Project area	Around 473m away from Project area, no direct impact
WSR_LFT4	Kam Tin River – Kam Shui Nam Road	Major drainage stream	No direct impact, except minor construction works will be undertaken to the connections with the proposed box culvert/conduits underneath Kam Sheung Road
WSR_LFT 5 & 6 & 7 & 8	Pond	Individual pond, disconnected to river systems	No direct impact
Ha Che (HC) in Figure 6.4
WSR_HC1	Ha Che Stream	Drainage stream near HC, upstream to Kam Tin River	To be widened
WSR_HC2	Pond	Individual pond, disconnected to river systems	About 51m away from the Project, no direct impact
WSR-HC3	Pond	Individual pond, disconnected to river systems	About 225m away from the Project, no direct impact
WSR_HC4	Stream	Upstream stream to Ha Che Stream	No direct impact
WSR_HC5	Stream	Downstream stream	No direct impact. However, minor construction works will be undertaken at the connections between the proposed drainage and downstream section
WSR_HC6	Stream	Disconnected stream	About 190m away from the Project, no direct impact

6.5 Baseline Water Quality Conditions

6.5.1. To assess the baseline water quality conditions in the Project area, the most recently data/information will be collected as reference:

Baseline survey results providing accurate baseline conditions of water quality for the Project areas;

Recently published monitoring data collected at the EPD’s river water monitoring stations near the Project area; and

Relevant information from approved EIAs in the vicinity area of the Project, if necessary.

River Water Quality Monitoring by EPD (As Reference)

6.5.2. EPD has carried out routine monitoring of the river water quality at Yuen Long Creek and Kam Tin River. There are existing EPD’s river monitoring stations downstream of the affected streams and within the same river catchment (Figure 6.5). Table 6-5 summarized EPD’s river monitoring data, which represents the baseline water quality downstream of the Study Area as reference.

6.5.3. Yuen Long Creek’s overall compliance rate in 2017 was 53%, as compared with 35% in 2007 and 20% in 1987. For Kam Tin River, the overall compliance rate in 2017 was 60%. In terms of Water Quality Index (WQI), the two upstream stations (YL1 and YL2) recorded “Fair” grading, while the two downstream stations (YL3 and YL4) were graded “Bad” in 2017. Both stations in Kam Tin River (KT1 and KT2) also received WQI grading of “Bad” in 2017.

6.5.4. The residual pollution load in Yuen Long and Kam Tin areas is largely contributed by unsewered villages. The Government is now carrying out a review of the local sewerage programme with a view to developing an action plan to improve the water quality in the above areas. Options include the provision of sewerage facilities for unsewered villages and possible installation of dry weather flow interceptors (DWFIs) where appropriate.

6.5.5. The E. coli levels at Kam Tin River and Fairview Park Nullah remained high in 2017 with the Kam Tin River’s two stations, KT1 and KT2, recording 160,000 and 140,000 cfu/100mL, respectively. The upstream stations of Yuen Long Creek, YL1 and YL2, had E. coli levels of 81,000 and 72,000 cfu/100mL and the two mid-streams stations, YL3 and YL4, had E. coli levels of 830,000 and 2,300,000 cfu/100mL, respectively.

6.5.6. In summary, the E. coli levels in the major rivers in the Northwestern New Territories were still high largely because of discharge from livestock farms, expedient connections and unsewered villages in the area.

Table 6‑5 EPD’s Water Quality Monitoring Results at Yuen Long Creek and Kam Tin River as at Year 2017

Parameters	Unit	WQO	Yuen Long Creek		Kam Tin River
			YL1	YL2	KT1	KT2
DO	mg/L	≥ 4.0	6.0 (3.6 - 7.8)	6.0 (3.5 - 7.8)	5.4 (3.4 - 7.3)	5.1 (2.7 - 7.5)
pH	-	6.5 – 8.5	7.3 (6.7 - 7.5)	7.4 (6.9 - 7.6)	7.3 (6.7 - 7.5)	7.5 (6.9 - 7.7)
SS	mg/L	≤ 20	7.4 (3.6 - 35.0)	6.3 (2.5 - 12.0)	8.5 (5.2 - 34.0)	17.0 (4.6 - 74.0)
BOD5	mg/L	≤ 3	11.3 (3.7 - 59.0)	6.9 (2.7 - 24.0)	15.5 (4.2 - 53.0)	18.0 (4.9 - 170.0)
COD	mg/L	≤ 15	24 (6 - 57)	33 (16 - 61)	19 (7 - 70)	28 (11 - 180)
Oil & grease	mg/L	-	<0.5 (<0.5 - 1.4)	0.7 (<0.5 - 2.4)	<0.5 (<0.5 - 1.3)	<0.5 (<0.5 - 4.2)
Faecal coliforms	cfu/100 mL	-	210 000 (3 300 - 3 600 000)	130 000 (17 000 - 780 000)	320 000 (79 000 - 1 900 000)	300 000 (33 000 - 950 000)
E. coli	cfu/100 mL	-	81 000 (900 - 390 000)	72 000 (7 000 - 730 000)	160 000 (16 000 - 1 400 000)	140 000 (13 000 - 590 000)
Ammonia nitrogen	mg/L	-	5.750 (0.570 - 17.000)	17.500 (4.000 - 35.000)	5.750 (1.000 - 25.000)	6.900 (1.300 - 19.000)
Nitrate nitrogen	mg/L	-	0.510 (0.006 - 1.100)	0.830 (0.046 - 2.800)	0.555 (<0.002 - 1.200)	0.280 (<0.002 - 1.100)
Total Kjeldahl nitrogen	mg/L	-	6.35 (1.20 - 19.00)	18.50 (4.90 - 35.00)	6.95 (1.90 - 26.00)	7.95 (2.00 - 31.00)
Ortho phosphate	mg/L	-	1.050 (0.006 - 1.800)	2.600 (0.660 - 3.400)	1.125 (0.390 - 3.200)	1.200 (0.380 - 2.600)
Total phosphorus	mg/L	-	1.20 (0.22 - 2.00)	2.95 (0.76 - 3.60)	1.35 (0.51 - 3.90)	1.60 (0.47 - 5.00)
Total sulphide	mg/L	-	<0.02 (<0.02 - 0.04)	<0.02 (<0.02 - 0.22)	0.02 (<0.02 - 0.13)	0.02 (<0.02 - 0.10)
Aluminium	µg/L	-	108 (81 - 670)	76 <50 - 373)	58 (<50 - 205)	96 (51 - 194)
Cadmium	µg/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)
Chromium	µg/L	-	<1 (<1 – 2)	<1 (<1 – 1)	<1 (<1 - <1)	<1 (<1 - <1)
Copper	µg/L	-	5 (2 - 12)	3 (2 - 5)	11 (4 - 45)	6 (2 - 14)
Lead	µg/L	-	1 (<1 - 11)	<1 (<1 - 3)	<1 (<1 - 3)	1 (<1 - 3)
Zinc	µg/L	-	29 (22 - 60)	28 (20 - 58)	35 (25 - 91)	37 (16 - 56)
Flow	L/s	-	230 (110 - 450)	23 (9 - 44)	378 (55 - 880)	334 (105 - 1 440)

Notes:

1. Data presented are in annual medians of monthly samples; except those for faecal coliforms and E. coli which are 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.

4. Equal values for annual medians (or geometric means) and ranges indicate that all data are the same as or below laboratory reporting limits.

1^st Round Baseline Water Quality Survey

6.5.7. With reference to Section 4.3 of the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM), baseline water quality survey is required in order to provide accurate baseline conditions. Section 5.4 of Annex 14 Guidelines for Assessment of Water Pollution of the TM-EIAO further provides specific guidelines of the baseline study for the water quality impact assessment. Field surveys shall be carried out to supplement existing information in situation when existing data are outdated or insufficient for the EIA study.

6.5.8. The likely water quality impact during construction phase will be due to construction site runoff, general construction activities and sewage from workforce. As the above, baseline water quality data are available for the rivers in the Deep Bay Water Control Zone where the study area is located within, as reference. Therefore, for the purpose of the EIA study, description of the baseline river water quality of the receiving aquatic environmental will make reference to the water quality data in the relevant Annual Water Quality Reports published by EPD (as described above). These are considered the best published available information.

6.5.9. As a supplementary data to the EPD published information, field surveys are proposed to obtain the current baseline water quality data for the purpose of the EIA study. Baseline water quality monitoring was conducted at 10 locations along the drainage, ponds and streams in Project area, whose detailed information is summarized in Table 6‑6. Details of the baseline water quality monitoring such as monitoring location plans and monitoring results are provided in Appendix 6-1.

6.5.10. The In-situ measurement parameters include Temperature (in ºC), pH, Turbidity (in NTU), Dissolved Oxygen (in mg/L and %), Salinity (in ppt). The laboratory test parameters include Suspended Solids (SS), BOD₅, E.coli, COD, Ammonia-N (NH₃-N) (in mg/L), Nitrite-N (NO₂-N) (in mg/L), Nitrate (NO₃-N) (in mg/L), Total Kjeldahl Nitrogen (TKN) (in mg/L), Ortho-phosphorus (in mg/L), Total Phosphorus (P) (in mg/L), Cadmium (in µg/L), Chromium (in µg/L), Copper (in µg/L), Lead (in µg/L), Mercury (in µg/L), Nickel (in µg/L), Arsenic (in µg/L), Zinc (in µg/L), and Silver (in µg/L).

6.5.11. Baseline water quality monitoring was carried out 3 times per week, for two consecutive weeks from 11 to 21 October 2016 (19 to 31 October 2016 for TW2A) for wet season and from 22 November to 2 December 2016 for dry season.

6.5.12. In-situ measurements and water samples were taken at 3 water depths of the water column for each monitoring location, i.e. 1m below water surface, mid-depth and 1 m above sea bed, except where the water depth was less than 6 m in which case the mid-depth was omitted and for locations where the water depth was less than 3 m only the mid-depth was monitored.

6.5.13. Prior to each monitoring day, wet bulb calibration was performed for the DO probes. Responses of sensors and electrodes were checked with certified standard solutions before each use. At each sampling depth, two consecutive measurements were taken for salinity, turbidity, pH, DO and temperature. Separate deployment of the monitoring instruments was conducted for any two consecutive measurements. When the difference between the two measurements for DO or turbidity was higher than 25% of the value of the first reading, the reading would be discarded and further measurement would be taken.

6.5.14. Duplicate water samples were collected at each sampling depth for laboratory measurement of SS, BOD₅, COD, E. coli, Ammonia, Nitrite, Nitrate, Total Kjeldahl Nitrogen, Ortho-phosphate Phosphorus, Total Phosphorus and Metals. Samples were stored in high density polythene bottles, packed in ice (cooled to 4°C without being frozen), and delivered to the laboratory on the same day of collection for analysis.

Table 6‑6 Supplementary Baseline Water Quality Monitoring Locations

ID	Description	Waterbodies
HC1	A Kung Tin	Stream
HC2	Sheung Che Tsuen	Stream
HC3	Chuk Hang Tsuen	Pond
LFT1	Lin Fa Tei Stream	Stream
LFT2	Shui Tsan Tin Stream	Stream
LFT3	Lin Fa Tei Pond	Pond
SSNV1	Sung Shan New Village	Stream
SSNV2	Yau Cha Po Tsuen	Stream
TW1	Cheung Po Point 1	Stream
TW2A	Cheung Po Point 2	Stream

6.5.15. The completed record of monitoring results has been provided in Appendix 6.1. Table 6‑7 and Table 6‑8 show the summary of In-situ measurements for wet and dry seasons. Table 6‑9 and Table 6‑10 present the summary of laboratory analysis results for wet and dry seasons. As indicated in the baseline survey report, no activities were observed during the period of baseline monitoring.

6.5.16. The mean level of analysis results at each monitoring location was selected for comparison with the specific WQOs. In summary, the in-situ monitoring results complies well with the WQOs for both the wet and dry seasons.

6.5.17. Relatively high SS concentration at Lin Fa Tei and Ha Che was observed at both wet and dry seasons. This may be caused by relatively high water flow and its carried SS from upstream catchment during wet season, or characteristics of relative mountain/rural areas.

6.5.18. Exceedance of E. coli was observed at all locations except TW1, during both wet and dry seasons. The exceedance may be due to discharge from livestock farms, as well as expedient connections and unsewered villages in the area.

6.5.19. Slight exceedance was observed for BOD₅ and COD at most of the locations. The exceedance may be due to discharge from unsewered area and expedient connections.

Table 6‑7 Summary of In-situ Monitoring Results for Wet Season

Monitoring Location	pH			Temperature (degree C)			DO (mg/L)			Turbidity (NTU)			Salinity (ppt)			Time taken for the debris to be wash away (s)
	Mean	Max	Min	Mean	Max	Min	Mean	Max	Min	Mean	Max	Min	Mean	Max	Min	Mean	Max	Min
WQOs	6.5 – 8.5			Change due to human activity not to exceed 2 degree			Not less than 4.0 mg/L			Shall not reduce light transmission substantially from the normal level			Change due to human activity not to exceed 10% of ambient			-
HC1	7.38	7.58	7.09	24.58	25.37	23.77	7.94	8.26	7.55	23.8	111.1	3.2	0.05	0.06	0.02	17	38	5
HC2	7.07	7.36	6.89	25.31	26.36	24.43	4.87	8.03	3.12	35.3	124.6	9.1	0.09	0.12	0.03	23	54	5
HC3	7.94	8.81	6.87	27.63	29.48	25.84	11.29	16.72	6.08	34.2	47.7	23.4	0.12	0.15	0.05	NA	NA	NA
LFT1	7.02	7.2	6.85	25.28	25.94	24.4	6.23	7.07	5.57	7.7	28.4	1.5	0.08	0.1	0.06	9	14	4
LFT2	7.12	7.47	6.92	25.17	26.13	24.32	6.05	7.37	5.2	14.9	29.5	9	0.06	0.11	0.01	31	52	4
LFT3	9	9.36	8.52	26.51	27.34	25.71	12.14	15.74	8.87	42.2	50	36.1	0.11	0.12	0.09	NA	NA	NA
SSNV1	7.22	7.51	6.92	26.61	27.99	24.9	5.96	7.49	4.4	8.4	23.4	2.1	0.11	0.19	0.05	20	26	7
SSNV2	6.99	7.32	6.72	26.18	27.55	24.81	5.4	7.5	3.72	8.8	33.9	1.9	0.08	0.17	0.04	25	26	24
TW1	7.01	7.59	6.79	24.27	24.69	23.48	7.98	8.22	7.59	6.4	16.3	3.2	0.04	0.05	0.03	29	44	5
TW2A	6.66	6.9	6.12	24.97	25.8	24.34	7.8	8.8	7.41	6.9	16.9	2.8	0.04	0.04	0.03	17	25	5

Note:

1. ND: Not Detected

2. NA: Not Applicable

3. Value highlighted in red indicated exceedance of WQOs.

Table 6‑8 Summary of In-situ Monitoring Results for Dry Season

Monitoring Location	pH			Temperature (degree C)			DO (mg/L)			Turbidity (NTU)			Salinity (ppt)			Time taken for the debris to be wash away (s)
	Mean	Max	Min	Mean	Max	Min	Mean	Max	Min	Mean	Max	Min	Mean	Max	Min	Mean	Max	Min
WQOs	6.5 – 8.5			Change due to human activity not to exceed 2 degree			Not less than 4.0 mg/L			Shall not reduce light transmission substantially from the normal level			Change due to human activity not to exceed 10% of ambient			-
HC1	7.02	7.24	6.61	20.03	23.35	18.62	8.69	8.91	8.14	10.8	19.9	2.3	0.04	0.06	0	16	28	10
HC2	6.85	7.1	6.54	20.47	23.76	18.88	6.83	7.42	5.72	13	36	4.9	0.11	0.2	0.08	21	29	11
HC3	7.18	8.01	6.75	22.17	24.61	18.96	7.66	11	5.16	16.8	28.5	8.8	0.14	0.16	0.12	NA	NA	NA
LFT1	6.88	7.02	6.72	20.37	23.78	19.04	7.49	8.33	6.51	6.7	16.8	2.9	0.12	0.19	0.07	14	20	10
LFT2	6.85	7.13	6.53	20.44	23.13	19.22	6.75	7.42	6.29	15.7	23.8	9.1	0.09	0.12	0.06	26	39	13
LFT3	8.94	9.6	8.48	20.93	25.39	18.9	11.63	14.27	9.55	42.8	62.1	31	0.1	0.11	0.05	NA	NA	NA
SSNV1	6.67	6.86	6.54	21.4	23.93	19.12	7.17	7.98	6.4	12.2	24.2	4.1	0.08	0.1	0.05	18	23	15
SSNV2	6.53	6.76	6.39	21.12	23.82	19.13	6.42	7.05	5.6	8	17.3	3.5	0.06	0.07	0.03	NA	NA	NA
TW1	6.7	7.12	6.52	19.49	23.38	18	8.96	10.05	8.15	6.3	17.9	3.1	0.04	0.04	0.02	32	44	18
TW2A	6.6	6.89	6.33	19.59	23.32	18.01	8.66	8.98	7.89	7.4	18.4	3.2	0.03	0.05	0	31	52	13

Note:

1. ND: Not Detected

2. NA: Not Applicable

3. Value highlighted in red indicated exceedance of WQOs.

Table 6‑9 Summary of Laboratory Analysis Results for Wet Season

Monitoring Location		HC1	HC2	HC3	LFT1	LFT2	LFT3	SSNV1	SSNV2	TW1	TW2A	WQOs
SS (mg/L)	Mean	71.2	58	53.6	7.1	36.3	94.3	11.5	11.6	7.6	10.3	Not to cause the annual median to exceed 20mg/L
	Max	342	195	72.9	19.4	66.3	157	21.7	36.2	15	24
	Min	4.5	11.2	41.2	2.1	16.6	55.3	4.1	5	2.3	2.8
BOD5 (mg/L)	Mean	1	48	10	2	3	14	5	2	1	2	Not to exceed 3mg/L
	Max	3	149	14	3	5	18	10	4	1	8
	Min	<1	1	2	1	1	9	<1	<1	<1	<1
COD (mg/L)	Mean	8	94	64	10	14	90	16	9	7	9	Not to exceed 15 mg/L
	Max	28	216	91	18	20	121	28	14	17	16
	Min	2	8	27	8	8	57	3	3	2	6
E. coli (CFU /100mL)	Geo-Mean	3593	108153	2440	3763	4209	1325	19692	5005	433	2668	Not exceed 1000 per 100ml for inland waters
	Max	44000	890000	27000	20000	36000	4100	140000	230000	7800	160000
	Min	690	8600	59	78	440	71	450	160	ND	320
NH3-N (mg/L)	Mean	0.088	1.256	3.126	0.916	2.342	0.041	12.488	2.18	0.035	0.043	-
	Max	0.171	2.07	5.05	1.39	6.57	0.067	30	10	0.053	0.063
	Min	0.039	0.075	0.914	0.283	0.38	<0.025	0.294	0.218	<0.025	0.028
NO2-N (mg/L)	Mean	0.008	0.055	0.266	0.226	0.262	<0.002	0.243	0.164	0.005	0.003	-
	Max	0.02	0.304	0.401	0.337	0.546	<0.002	0.547	0.319	0.007	0.005
	Min	<0.002	<0.002	0.048	0.028	0.023	<0.002	0.028	0.013	<0.002	<0.002
NO3-N (mg/L)	Mean	0.192	0.155	0.789	0.921	0.751	<0.002	0.838	0.701	0.102	0.086	-
	Max	0.323	0.414	1.31	1.1	0.982	<0.002	1.09	0.776	0.153	0.133
	Min	<0.002	<0.002	0.311	0.596	0.462	<0.002	0.721	0.597	0.065	0.047
TKN (mg/L)	Mean	0.37	3.81	6.4	1.28	2.91	3.5	12.96	2.55	0.18	0.36	-
	Max	1.06	6.72	10.3	1.67	7.47	4.89	31	10.6	0.46	0.67
	Min	0.17	0.7	2.07	0.77	0.94	2.9	0.42	0.44	0.08	0.13
Ortho- phosphate P (mg/L)	Mean	0.043	0.123	0.343	0.391	0.785	0.006	1.477	0.632	0.034	0.025	-
	Max	0.077	0.495	0.406	0.466	1.8	0.01	2.95	1.18	0.126	0.089
	Min	0.003	0.015	0.305	0.332	0.315	0.002	0.182	0.14	0.013	0.01
Total P (mg/L)	Mean	0.09	0.49	0.85	0.49	1.08	0.28	1.71	0.75	0.06	0.05	-
	Max	0.14	1.08	1.02	0.58	2.14	0.37	3.32	1.36	0.19	0.15
	Min	0.04	0.13	0.56	0.43	0.41	0.24	0.22	0.18	0.03	0.02
Cadmium (µg/L)	Mean	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1	-
	Max	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
	Min	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
Chromium (µg/L)	Mean	1	2	2	1	1	1	<1	<1	<1	<1	-
	Max	2	6	2	1	2	3	<1	<1	<1	<1
	Min	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
Copper (µg/L)	Mean	3	4	33	6	34	30	6	21	5	4	-
	Max	12	7	53	27	60	86	10	50	17	10
	Min	<1	<1	<1	<1	8	9	5	4	<1	<1
Lead (µg/L)	Mean	2	3	5	3	13	12	2	3	2	2	-
	Max	7	8	7	8	28	32	5	7	5	6
	Min	<1	<1	<1	<1	<1	5	<1	<1	<1	<1
Mercury (µg/L)	Mean	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1	-
	Max	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
	Min	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
Nickel (µg/L)	Mean	<1	3	3	2	1	1	2	1	1	1	-
	Max	<1	6	4	3	3	3	2	2	1	2
	Min	<1	<1	2	<1	<1	<1	<1	<1	<1	<1
Arsenic (µg/L)	Mean	<10	<10	<10	<10	<10	<10	<10	<10	<10	<10	-
	Max	<10	<10	<10	<10	<10	<10	<10	<10	<10	<10
	Min	<10	<10	<10	<10	<10	<10	<10	<10	<10	<10
Zinc (µg/L)	Mean	16	47	76	23	98	61	38	39	21	27	-
	Max	33	112	114	47	202	196	83	61	40	110
	Min	<10	<10	<10	<10	31	17	18	10	<10	<10
Silver (µg/L)	Mean	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1	-
	Max	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
	Min	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1

Note:

1. Ave.: (Except E. coli) "Averaged" is calculated by taking the arithmetic means for the reading

2. ND: Not Detected

3. NA: Not Applicable

4. Averaged of E. coli is calculated by taking geometric mean of the readings, all ND sample results (<1) for E. coli is regarded as 1 in calculating the geometric mean.

5. Value highlighted in red indicated exceedance of WQOs.

Table 6‑10 Summary of Laboratory Analysis Results for Dry Season

Monitoring Location		HC1	HC2	HC3	LFT1	LFT2	LFT3	SSNV1	SSNV2	TW1	TW2A	WQOs
SS (mg/L)	Mean	11.2	84.2	30.3	5.9	26.7	72.6	29.5	12.4	5.9	10.6	Not to cause the annual median to exceed 20mg/L
	Max	18.1	339	46.6	11	38.6	94.6	57.4	27.5	15.3	30.6
	Min	2.8	6.4	14.3	1.6	15.6	58.4	7.4	6.4	1.4	3.9
BOD5 (mg/L)	Mean	1	61	7	4	6	20	9	4	1	<1	Not to exceed 3mg/L
	Max	3	255	12	8	13	24	19	10	2	<1
	Min	<1	4	5	2	4	14	3	2	<1	<1
COD (mg/L)	Mean	6	183	39	14	23	87	21	15	5	5	Not to exceed 15 mg/L
	Max	10	649	60	20	35	99	48	34	9	10
	Min	<2	18	29	9	14	77	9	9	3	<2
E.coli (CFU /100mL)	Geo-Mean	10261	242809	1368	42816	22641	3004	51746	19174	1490	1677	Not exceed 1000 per 100ml for inland waters
	Max	30000	910000	7000	250000	85000	6400	200000	220000	3100	3000
	Min	2900	24000	380	3100	7700	1600	8900	1500	820	1100
NH3-N (mg/L)	Mean	0.137	1.531	7.679	3.538	4.593	0.055	2.513	1.738	0.05	0.046	-
	Max	0.175	2.13	9.28	8.65	6.32	0.086	5.98	2.75	0.101	0.056
	Min	0.111	0.993	7.04	1.64	2.2	0.037	1.38	1.34	0.031	0.037
NO2-N (mg/L)	Mean	0.017	0.057	0.114	0.191	0.093	0.002	0.19	0.156	0.003	0.003	-
	Max	0.023	0.115	0.174	0.259	0.119	0.002	0.248	0.219	0.006	0.007
	Min	0.006	<0.002	0.079	0.074	0.058	<0.002	0.152	0.13	<0.002	<0.002
NO3-N (mg/L)	Mean	0.331	0.389	0.476	0.825	0.384	0.003	0.971	0.769	0.061	0.053	-
	Max	0.42	0.616	0.782	1.03	0.543	0.007	1.13	1.12	0.078	0.08
	Min	0.24	<0.002	0.272	0.679	0.252	<0.002	0.82	0.536	0.042	0.033
TKN (mg/L)	Mean	0.45	15.04	9.96	4.55	6.35	3.55	4.29	2.8	0.18	0.17	-
	Max	0.73	65.7	11.7	8.69	8.73	4.83	7.78	4.38	0.34	0.26
	Min	0.26	1.67	8.1	2.88	3.44	2.98	2.51	1.79	0.1	0.09
Ortho- phosphate P (mg/L)	Mean	0.052	0.371	0.531	0.383	1.027	0.004	1.108	0.888	0.01	0.01	-
	Max	0.067	1.22	0.708	0.656	1.35	0.009	1.79	1.43	0.017	0.015
	Min	0.042	0.016	0.28	0.229	0.781	<0.002	0.56	0.596	0.006	0.007
Total P (mg/L)	Mean	0.1	2.1	0.89	0.52	1.47	0.24	1.79	1.18	0.03	0.04	-
	Max	0.13	8.97	0.95	0.85	2.04	0.31	3.24	2.16	0.06	0.06
	Min	0.08	0.21	0.81	0.35	1.08	0.19	0.72	0.76	0.02	0.02
Cadmium (µg/L)	Mean	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1	-
	Max	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
	Min	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
Chromium (µg/L)	Mean	1	1	1	<1	<1	<1	1	1	<1	<1	-
	Max	1	2	2	<1	<1	<1	2	1	<1	<1
	Min	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
Copper (µg/L)	Mean	4	8	6	4	52	7	22	12	2	2	-
	Max	8	26	10	8	85	9	49	30	6	4
	Min	<1	<1	2	2	28	6	16	5	<1	<1
Lead (µg/L)	Mean	2	2	4	2	7	5	2	3	2	2	-
	Max	4	8	7	3	11	8	4	5	4	4
	Min	<1	<1	2	<1	2	3	1	1	<1	<1
Mercury (µg/L)	Mean	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1	-
	Max	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
	Min	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
Nickel (µg/L)	Mean	1	5	2	1	2	1	1	1	1	1	-
	Max	1	14	3	2	2	2	2	2	4	1
	Min	<1	1	<1	<1	<1	<1	<1	<1	<1	<1
Arsenic (µg/L)	Mean	<10	<10	<10	<10	<10	<10	<10	<10	<10	<10	-
	Max	<10	<10	<10	<10	<10	<10	<10	<10	<10	<10
	Min	<10	<10	<10	<10	<10	<10	<10	<10	<10	<10
Zinc (µg/L)	Mean	24	45	56	78	143	39	179	120	32	17	-
	Max	56	112	132	549	197	64	389	274	138	27
	Min	<10	17	28	19	77	21	51	46	<10	<10
Silver (µg/L)	Mean	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1	-
	Max	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
	Min	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1

Note:

1. Ave.: (Except E. coli) "Averaged" is calculated by taking the arithmetic means for the reading

2. ND: Not Detected

3. NA: Not Applicable

4. Averaged of E. coli is calculated by taking geometric mean of the readings, all ND sample results (<1) for E. coli is regarded as 1 in calculating the geometric mean.

5. Value highlighted in red indicated exceedance of WQOs.

2^nd Round Baseline Water Quality Survey

6.5.20. In order to provide the most up-to-date accurate baseline conditions, the 2^nd round of supplementary water quality survey has been carried out on 23 August 2019.

6.5.21. The In-situ measurement parameters include Temperature (in ºC), pH, Turbidity (in NTU), Dissolved Oxygen (in mg/L and %), Salinity (in ppt) and Water Flow (in m³/s). The Laboratory test parameters include Suspended Solids (SS), BOD₅, E.coli, COD, Ammonia-N (in mg/L), Nitrite-N (in mg/L), Nitrate (in mg/L), Total Kjeldahl Nitrogen (in mg/L), Ortho-phosphorus (in mg/L), Total Phosphorus (in mg/L), Cadmium (in µg/L), Chromium (in µg/L), Copper (in µg/L), Lead (in µg/L), Mercury (in µg/L), Nickel (in µg/L), Arsenic (in µg/L), Zinc (in µg/L), Silver (in µg/L).

6.5.22. The supplementary baseline water quality survey was carried out at four designed monitoring locations at streams as presented in Table 6‑11.

Table 6‑11 Supplementary Baseline Water Quality Monitoring Locations (2^nd Round)

Monitoring Locations	Description	Waterbodies
SSNV2	Yau Cha Po Tsuen	Stream
TW1	Cheung Po Point 1	Stream
LFT2	Shui Tsan Tin Stream	Stream
HC2	Sheung Che Tsuen	Stream

6.5.23. The completed monitoring results can be referred to Appendix 6-2 of this EIA.

6.5.24. Table 6‑12 shows the summary of In-situ measurements. Table 6‑13 presents the summary of laboratory analysis results. As indicated in the baseline survey report, no activities were observed during the period of baseline monitoring.

6.5.25. As indicated in Table 6-12, the water flow in Tai Wo and Lin Fa Tei was in small scale (e.g. not measurable in TW, 0.052 m3/s in LFT2). The water flow in SSNV2 was approximate 0.104 m3/s, while 0.653 m3/s was observed in HC2. In general, the water flows in these four locations are relatively small.

6.5.26. The mean level of analysis results at each monitoring location was selected for comparison with the specific WQOs. In summary, the in-situ monitoring results complies well with the WQOs.

6.5.27. It is observed that relatively high SS concentration existed at Ha Che drainage. This is consistent with the observation in the 1^st round survey in 2016. This may be caused by relatively high water flow and its carried SS from upstream catchment, or characteristics of relative mountain/rural areas. The relatively high SS at HC2 is also corresponding to relatively high water flow.

6.5.28. Exceedance of E. coli was observed at all locations. The exceedance may be due to discharge from livestock farms, as well as expedient connections and unsewered villages in the area.

6.5.29. Slight exceedance was also observed for BOD₅ and COD at HC2 and SSNV2. The exceedance may be due to discharge from unsewered area and expedient connections.

6.5.30. Consequently, the 2^nd round supplementary water quality survey shows high similarity with the 1^st round survey. The incompliance of E.coli, BOD₅ and COD is due to the existing residual pollution load in Yuen Long and Kam Tin areas which is largely contributed by unsewered villages.

Table 6‑12 Summary of In-situ Monitoring Results of 2^nd Round Baseline Water Quality Baseline Survey

Monitoring Location		SSNV2		TW1		LFT2		HC2
Date		23-Aug-19
Weather		Cloudy
Time		14:38		13:47		11:10		11:57
River Depth (m)		0.28		0.05		0.16		0.29
River Width (m)		3.5		1.1		2.26		2.1
Replicate		1	2	1	2	1	2	1	2
pH	Value	6.87	6.83	7.41	7.4	7.16	7.15	7.53	7.5
	Mean	6.85		7.41		7.16		7.52
Salinity (ppt)	Value	0.05	0.05	0.06	0.06	0.08	0.08	0.07	0.07
	Mean	0.05		0.06		0.08		0.07
Temperature (ºC)	Value	29.1	29.1	28.67	28.65	28.37	28.38	29	29.1
	Mean	29.10		28.66		28.38		29.05
DO Saturation (%)	Value	66.3	65.8	93.6	94.1	60.4	60.1	78.8	78.7
	Mean	66.1		93.9		60.3		78.8
DO (mg/L)	Value	5.09	5.05	7.24	7.28	4.69	4.67	6.06	6.04
	Mean	5.07		7.26		4.68		6.05
Turbidity (NTU)	Value	18.7	18.8	6.6	6.7	40.3	40.7	54.4	54.5
	Mean	18.8		6.7		40.5		54.5
Water Flow (m^3/s)	Value	0.097	0.111	0.000	0.000	0.050	0.053	0.670	0.635
	Mean	0.104		0.000		0.052		0.653

Notes:

1. Water flow (m³/s) is calculated by multiplying water velocity (in average) (m/s) by river cross-section area (m²).

2. Murky water was observed at LFT2 and HC2. Unexpectedly rapid flow of water was found at HC2.

3. River depth is taken by the average of river depth (m) throughout the cross-section of the river.

Table 6‑13 Summary of Laboratory Analysis Results of 2^nd Round Baseline Water Quality Baseline Survey

Monitoring Location		SSNV2		TW1		LFT2		HC2		WQOs
Replicate		1	2	1	2	1	2	1	2
Suspended Solids (mg/L)	Value	18	17	3	4	11	10	55	54	Not to cause the annual median to exceed 20mg/L
	Mean	18		4		11		55
BOD5 (mg/L)	Value	6.2	6.4	<1	<1	2.1	3	5.7	6.1	Not to exceed 3 mg/L
	Mean	6.3		1.0		2.6		5.9
E.coli (CFU /100mL)	Value	48,000	62,000	1,300	1,400	36,000	39,000	1.20E+06	1.10E+06	Not exceed 1000 per 100ml for inland waters
	Mean	55,000		1,350		37,500		1,150,000
COD (mg/L)	Value	15	16	7	5	15	15	47	48	Not to exceed 15 mg/L
	Mean	16		6		15		48
Ammonia-N (mg/L)	Value	0.84	0.78	0.07	0.06	3.8	3.8	0.79	0.72	-
	Mean	0.81		0.07		3.80		0.76
Nitrite-N (mg/L)	Value	0.15	0.14	0.01	0.01	0.4	0.42	0.1	0.09	-
	Mean	0.15		0.01		0.41		0.10
Nitrate-N (mg/L)	Value	0.53	0.5	0.08	0.06	1.6	1.5	0.44	0.42
	Mean	0.52		0.07		1.55		0.43
Total Kjeldahl Nitrogen (mg/L)	Value	1.8	1.8	0.66	0.64	4.6	4.3	2.9	2.9	-
	Mean	1.80		0.65		4.45		2.90
Ortho-phosphorus (mg/L)	Value	0.29	0.32	0.013	0.009	0.86	0.92	0.14	0.12	-
	Mean	0.305		0.011		0.890		0.130
Total Phosphorus (mg/L)	Value	0.37	0.39	0.1	0.11	1	0.95	0.32	0.27	-
	Mean	0.38		0.11		0.98		0.30
Cadmium (µg/L)	Value	0.23	<0.2	<0.2	0.46	<0.2	<0.2	<0.2	<0.2	-
	Mean	0.2		0.3		0.2		0.2
Chromium (µg/L)	Value	<1	<1	<1	<1	<1	<1	<1	<1	-
	Mean	1		1		1		1
Copper (µg/L)	Value	3	4	1	1	4	3	4	4	-
	Mean	4		1		4		4
Lead (µg/L)	Value	1	1	<1	1	<1	1	<1	<1	-
	Mean	1		1		1		1
Mercury (µg/L)	Value	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	-
	Mean	0.5		0.5		0.5		0.5
Nickel (µg/L)	Value	<1	<1	<1	<1	1	<1	2	2	-
	Mean	1		1		1		2
Arsenic (µg/L)	Value	1	1	4	4	<1	<1	1	1	-
	Mean	1		4		1		1
Zinc (µg/L)	Value	44	36	36	21	50	47	54	44	-
	Mean	40		29		49		49
Silver (µg/L)	Value	<1	<1	<1	<1	<1	<1	<1	<1	-
	Mean	1		1		1		1

Note:

1. Ave.: (Except E. coli) "Averaged" is calculated by taking the arithmetic means for the reading

2. ND: Not Detected

3. NA: Not Applicable

4. Averaged of E. coli is calculated by taking geometric mean of the readings, all ND sample results (<1) for E. coli is regarded as 1 in calculating the geometric mean.

5. Value highlighted in red indicated exceedance of WQOs.

6.6 Water Quality Impact Assessment

Construction Phase

6.6.1. Details of the location and description of the Project, construction methods and sequences of work have been described in Section 2 (Project Description). There will be no marine-based construction activities for the proposed drainage improvement works at the four villages and the general construction activities would be land-based. The sources of impact from the land-based construction activities mainly include:

· De-Watering of Streams and Sediment Removal

· Construction Site Runoff

· General Construction Activities

· Sewage from Workforce

· Widening of Drainage Channels

· Accidental Spillage of Chemicals

Construction Site Runoff

6.6.2. Construction site runoff comprises runoff and erosion from site surfaces, drainage channels, earth working areas and stockpiles. Wash water from dust suppression sprays and wheel washing facilities and fuel, oil, solvents and lubricants from maintenance of construction machinery and equipment also contribute to the pollutant levels of the construction runoff.

6.6.3. The potential water quality impact associated with drainage improvement works will be resulted from the run-off and erosion from site surfaces and earth working areas. Site runoff from construction sites that are subject to earth works might lead to surface erosion and would carry a high level of sediment. Sediment in runoff may be eventually carried to adjacent waterbodies such as streams or ponds near the proposed works.

6.6.4. With the implementation of good site mitigation measures to control site runoff from working areas with practices outlined in ProPECC PN 1/94, and with the provision of sediment removal facilities, no adverse water quality impacts from site runoff are anticipated to occur in the adjacent waterbodies or drainage systems.

General Construction Activities

6.6.5. The key water quality issues associated with the land-based construction activities would include sediment loaded site run-off, potential wash-out from stockpiles, discharges contaminated with fuel, oil or other pollutants and accidental spillage, especially during the rainy season.

6.6.6. General cleaning and polishing, wheel washing and dust suppression would generate wastewater which contains high concentrations of suspended solids (SS). Stormwater runoff from the land-based construction activities may contain high level of suspended solids generated from the proposed excavation works at the four villages. Release of uncontrolled site runoff would increase the SS levels and turbidity in the nearby water environment. It may also contain oil and grease originated from the operation of mechanical equipment.

6.6.7. Chemicals such as spent lubrication oil, grease, etc. could be used in the construction activities. Accidental spillage of these chemicals may lead to soil contamination, which may in turn impact nearby water bodies through site runoff. Provided that mitigation measures are properly implemented to minimise and control accidental spillage (such as provision of petrol interceptors), no water quality impacts are anticipated.

6.6.8. Debris and rubbish such as packaging and used construction materials may enter the nearby surrounding water bodies, potentially reducing its aesthetic quality as it could result in floating refuse.

6.6.9. All site discharges will be pre-treated as necessary in accordance with the WPCO and the conditions of the Wastewater Discharge License. With the implementation of appropriate measures to control run-off and drainage from the construction site (such as provision of silt traps), disturbance of water bodies would be avoided and deterioration in water quality of the nearby water bodies is anticipated to be minimal.

6.6.10. In view of the nature and scale of the proposed drainage improvement works at the four villages, the effects on water quality due to general construction activities are anticipated to be minimal, provided that site drainage would be well maintained and good construction practices would be implemented in accordance with ProPECC PN 1/94 “Construction Site Drainage”.

6.6.11. If in-situ method is used, the potential water quality impacts may include: potential pollutants in batching plant wastewater such as cement, sand, aggregates and petroleum products. These substances can adversely affect the environment by increasing soil and water pH; increasing the turbidity of waterways (turbidity is a measure of the cloudiness of a suspension).

6.6.12. Increased turbidity results in less light entering an aquatic environment. This in turn affects the rate of photosynthesis by plants, and reduces the visibility of aquatic organisms. Turbidity can also clog fish gills, smother bottom feeding flora and fauna and generally decrease the amenity of an area.

6.6.13. The main sources of wastewater from in-situ batching plants may include:

· contaminated stormwater runoff

· dust control sprinklers

· agitator washout station

· agitator charging station

· slumping station

· cleaning and washing.

6.6.14. To ensure that contaminated wastewater is not discharged to surface waters, groundwater or land, the following mitigation measures have been proposed.

· Minimize the area of the site which generates contaminated stormwater runoff.

· Provide a separate dedicated drainage system to discharge clean stormwater from the site.

· Drain all contaminated stormwater and process wastewater to a collection pit for recycling.

· Regularly clean out solids that accumulate in the pit.

· There must be no dry weather wastewater discharges from the site.

· Monitor wet weather discharges for pH and suspended solids. Retain the records.

6.6.15. With effective control and proper management practices, no adverse impacts to water quality are anticipated to occur due to cast in-situ activities.

Sewage from Workforce

6.6.16. Sewage arising from the construction workforce is another source of water pollution. During the construction phase of the Project, portable chemical toilets and sanitary facilities will be installed within construction works areas. Domestic sewage would be generated from the workforce and the Contractor will have the responsibility to ensure that the sanitary facilities are used and properly maintained and that licensed Contractors are employed to collect and dispose of the waste off-site at approved locations.

6.6.17. According to Table T-2 of Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning, the unit flow of the work force is 0.15m³/day/employed population. The sewage is characterized by high levels of biochemical oxygen demand (BOD), ammonia, E. coli and oil / grease.

6.6.18. Sewage arising from the construction workers on site will be collected by temporary sanitary facilities, e.g. portable chemical toilets, and disposed of by a licensed collector. Hence, no adverse water quality impact is anticipated.

Widening of Drainage Channels

6.6.19. As indicated in Section 2, the area for the proposed widening and deepening of channels will be excavated. Upon completion of excavation, fixing of reinforcement bars and concreting would be carried out on site for the structures of the proposed rectangular channels.

6.6.20. During construction phase, there will be potential water quality impact due to the alternation of watercourses. The existing streams at SSNV (WSR_SSNV1), LFT (WSR_LFT1 and WSR_LFT2), and HC (WSR_HC1) will be upgraded/widened.

6.6.21. The channel widening will involve excavation, formation of embankments and temporary diversion of watercourses, which would probably lead to temporary obstruction of flows. In addition, construction activities being carried out along the channels without adequate mitigation measures may likely cause erosion and lead to suspended solids elevation in the waterbody.

6.6.22. To minimize potential impacts on water quality during the channel works for the proposed drainage improvements, the excavation works would be carried out in dry condition. Construction would be strictly carried out by land-based plant. Potential impacts on water quality would be minimised by restricting the excavation works within an artificially enclosed dry section of the river/stream.

6.6.23. De-watering of streams and sediment removal would be conducted during channel widening works. Temporary access and maintenance access along the proposed drainage channel will be constructed prior to all construction works, and due consideration for the overland flow patterns and the drainage connections will be given if flow diversion is necessary. As the alignment of the proposed channel coincides with the existing stream, channel diversions will be required to divert existing flow, in particular when the construction coincides with the wet season (April to September). Relevant requirements and stipulations from ETWB TCW No.5/2005 “Protection of Natural Streams/Rivers from Adverse Impacts Arising from Construction Works" will be complied to better protect the natural watercourses from the impacts of construction works.

6.6.24. Works will commence from downstream and proceed to upstream. Diversion of the channel flow is required before excavation works start. Shallow water levels were noted in the existing channels and dewatering will be required in trenches below channel inverts or after heavy rainstorm. Adequate knowledge of subsurface conditions is required before excavation. All excavated materials will be stockpiled outside the existing stream/channel but within the defined works area, and temporarily stabilized to prevent re-entry into the stream/channel. The stockpile should not create adverse drainage impacts and not impede the overland flow patterns. The area next to the proposed channel works shall be fully utilized as temporary workplace and storage of construction plant. Where possible, the excavated materials will be utilized in any backfilling. On balance, it is anticipated that some fill will need to be imported to form the embankments.

6.6.25. The proposed channel will be constructed in segments from downstream to upstream. When the segment under construction requires stream diversion, sheet pile will be installed both upstream and downstream of the existing stream to separate the flow through the bypass channel so that the works area will remain dry for later excavation and widening works. To reduce resumption of private land lots for temporary construction works, where possible, all stream diversion and widening works will be strictly confined within the site boundary.

6.6.26. Construction of embankment will be undertaken after excavation works. Ramps shall also be required to provide a pathway for machinery to utilize the excavated channel bottom for construction and maintenance of the embankment and channel. Lining of channel bank will be followed and the lining material to be used will be fully agreed with DSD.

6.6.27. With good implementation of appropriate working method controls and good management practices, it is anticipated that unacceptable water quality impacts would not arise at the identified WSRs during construction phase. However, monitoring and audit of water quality during the construction phase is recommended.

Proposed Underground Drainage Pipes

6.6.28. The proposed underground drainage pipes would be installed at Kam Sheung Road in Lin Fa Tei and Fan Kam Road at Ha Che.

6.6.29. The proposed underground drainage pipes underneath Kam Sheung Road would be constructed by open trench method, due to its cost effectiveness. The proposed works would be carried out on a section-by-section basis at each active works area to minimize period of nuisance to the nearby WSRs during construction.

6.6.30. The proposed drainage pipes underneath Fan Kam Road in Ha Che would be constructed by trenchless method in order to minimise traffic impact.

6.6.31. For pipe installation works by open trench method, temporary traffic management will be carried out on a section-by-section basis to minimize period of nuisance to the village traffic. Upon the completion of utility survey to ensure no existing utilities would clash with the proposed works, ground excavation will take place between the time periods 7am and 7pm. No construction noise permit would be required. For excavation greater than 1.2m, sheetpiles with struts and walers system will be driven by sheet-piling rig with vibratory hammer. Underground pipes would be laid after the completion of pipe bedding and then backfilled with soil. As the construction duration by open trench method is relatively faster than trenchless method, disturbance to the surrounding environment is expected to be low.

6.6.32. The excavation works by open trench method may cause water quality impact in the aspect of site runoff/erosion from earth working areas. Site runoff from the excavation works might lead to surface erosion and would carry a high level of sediment. Sediment in runoff may be eventually carried to adjacent waterbodies near the proposed site. However, with good implementation of site mitigation measures to control site runoff from excavation areas with practices outlined in ProPECC PN 1/94, and the provision of sediment removal facilities, the adverse water quality impacts from site runoff are not anticipated.

6.6.33. For pipe installation works by trenchless method, jacking pit and receiving pit would be constructed for the trenchless pipe sections. The pipes would be constructed by pipe jacking method. This construction method by trenchless works would minimize water quality impact to the surrounding environment.

6.6.34. In consideration of environmental factors and traffic issues during construction, pipe installation works by open-cut method at Kam Sheung Road in Lin Fa Tei, and trenchless method at Fan Kam Road in Ha Che are preferred.

Accidental Spillage of Chemicals

6.6.35. Accidental spillage and illegal disposal of chemicals within the site area would cause soil contamination. This could have potential to impact the groundwater. It could also impose pollution to nearby channels or waterbodies through leaching to site runoff.

6.6.36. The Code of Practice on Packaging, Labelling and Storage of Chemical Wastes published under the Waste Disposal Ordinance should be used as a guideline for handling chemical wastes. Chemical wastes should be disposed of by following the rules stipulated in the Waste Disposal Ordinance.

6.6.37. With effective control through good operation and management practices, no adverse impacts to water quality are anticipated to occur due to accidental spillage of chemicals from construction activities.

Operation Phase

Hydrology

6.6.38. As indicated in the Drainage Impact Assessment (DIA) report, the associated drainage sub-catchments are highlighted in red in the diagram below.

6.6.39. Compared to the total catchment area of the Yuen Long catchment, each of the village drainage sub-catchments is relatively small. Therefore, it is considered that the flows discharged from the village drainage sub-catchments will have a limited impact to the hydraulic conditions at the trunk drains, located at the downstream of the villages, within the Yuen Long district.

6.6.40. The upgraded/new alignments of the drainage system would provide widened sections to alleviate flooding during heavy rainfalls for the 4 villages.

6.6.41. For instance, in Sung Shan New Village, under a 1 in 10 years return period event, the maximum water levels along the channel at Sung Shan New Village for the future scenarios are lower than those of the existing condition. The proposed drainage improvement works increase the drainage capacity of the existing stream.

General Water Quality

6.6.42. Based on available information of proposed land-uses set out in the approved OZP No. S/YL-TT/17 (Tai Tong), S/YL-KTS/15 (Kam Tin South), S/YL-SK/9 (Skek Kong) and S/YL-PH/11 (Pat Heung), the Project is mainly drainage improvement works at Sung Shan New Village (SSNV), Tai Wo (TW), Lin Fa Tei (LFT) and Ha Che (HC). No potential new pollution source could be identified and expected in vicinity of the drainage.

6.6.43. As such, discharge of non-point sources discharge from run-off into the drainage causing adverse impacts would be similar to existing conditions and not be anticipated during the operation phase.

6.6.44. Quoted from EPD Annual River water quality report (2016) and baseline water quality survey results, the streams are still impacted by discharges from livestock farms, expedient connections in old buildings and unsewered villages in the area. However, the implementation of the Schemes for the Voluntary Surrender of Poultry and Pig Farm Licence has already brought about a reduction of livestock waste loading. The North District Sewerage Master Plan and Yuen Long and Kam Tin Sewerage Master Plan have included plans to provide public sewers to most of the unsewered villages, and the river water quality in the North-western New Territories is expected to gradually improve when these schemes are implemented.

Sediment

6.6.45. As described in the DIA report, the drainage flow (surface runoff) was calculated and driven by design rainfall stipulated in Drainage Services Department Stormwater Drainage Manual (DSD-SDM). The same design rainfall has been applied for both existing and planned scenarios in the hydraulic modelling. Thus, the upstream runoff into the channels shall not be expected to be increased under the same design rainfall.

6.6.46. Therefore, we expect same/similar scale of upstream water volume (i.e. in the unit of “m³”) discharging into the channel. After improvement works, the cross-section is expected to be larger, hence the water flow (i.e. in the unit of “m³/s”) shall be decreased. The drainage velocity will be slightly decreased with implementation of drainage improvement works due to wider cross-sections.

6.6.47. Bottom sediment re-suspension will be alleviated because of the decreased flow. Sediment erosion would be substantially reduced, which lead to reduction of drainage maintenance desilting frequency and minimize the potential water quality impacts which may arise from maintenance desilting activities. Sedimentation rate is a function associated with densities of the particle and water, effective particle diameter and dynamic viscosity (Stokes Law). Thus, the change of flow regime will not change the sedimentation rate significantly.

6.6.48. Based on the analysis above-mentioned, no adverse impact for water quality is anticipated from the operational phase.

6.6.49. In order to avoid adverse pollution from first flush during rainstorm, regular maintenance debris clearances are recommended before rainstorm events. For maintenance desilting works, given the widened channel would reduce the need of desilting frequency, all such maintenance desilting could be scheduled section by section during dry season so as to minimize the water quality impact.

6.6.50. However, if maintenance dredging is necessary, it is suggested that maintenance dredging should be carried out at intervals and in appropriate environment (e.g. confined and dry conditions), such that sediments will not be transported into open waters.

6.6.51. There would be no chemicals or hazardous materials stored / used on-site during operation, as such the likelihood of accidental spillage is not expected. Emergency contingency plan for operation phase is therefore considered not necessary.

6.7 Mitigation Measures

6.7.1. The mitigation measures recommended below should be implemented throughout the construction phase to further minimise the potential water quality impacts. With the implementation of these mitigation measures, adverse water quality impacts are not expected to arise from the Project.

Construction Phase

Construction Site Runoff

6.7.2. The practices outlined in ProPECC PN 1/94 Construction Site Drainage are recommended to be adopted to minimize potential water quality impacts from construction site runoff and other construction activities. Design of mitigation measures should be submitted by the Contractor to the Engineer for approval. The Contractor shall obtain a discharge license under the Water Pollution Control Ordinance and the discharge should comply with the terms and conditions stipulated in the license. The mitigation measures should cover, but not limited to the following Best Management Practices:

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

· Work programmes should be designed to minimize the size of work areas to minimize the soil exposure and reduce the potential for increased siltation and runoff;

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

· Silt removal facilities, channels and manholes should be maintained and cleaned regularly to ensure the proper function;

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

· Careful programming of the works to minimize soil excavation during the rainy season; If excavation of soil cannot be avoided during the wet season (April to September), exposed slope surfaces should be covered by a tarpaulin or other means. Other measures that need to be implemented before, during, and after rainstorms are summarized in ProPECC PN 1/94.

· Earthwork surfaces should be well compacted and the subsequent permanent work or surface protection should be carried out immediately after the final surfaces are formed;

· Wastewater generated from the washing down of mixer trucks and drum mixers and similar equipment should wherever practicable be recycled. The discharge of wastewater should be kept to a minimum;

· To prevent pollution from wastewater overflow, the pump sump of any water recycling system should be provided with an on-line standby pump of adequate capacity and with automatic alternating devices;

· Under normal circumstances, surplus wastewater may be discharged into foul sewers after treatment in silt removal and pH adjustment facilities (to within the pH range of 6 to l0). Disposal of wastewater into storm drains will require more elaborate treatment;

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

· Under adverse weather conditions in dry season such as heavy rainfall, apart from programming the construction works in dry season, other mitigation measures, including but not limited to the use of precast concrete unit and erection of cofferdam with silt curtain to prevent the surface runoff from rainfall events from directly discharging into the watercourses if appropriate, would be adopted. Refer to the assessment on water quality, the impacts of construction works to the drainage channels were assessed to be minor. All surface runoff and sewage from the construction sites would be properly handled in accordance with the Environment, Transport and Works Bureau Technical Circular (Works) No. 5/2005 “Protection of natural streams/rivers from adverse impacts arising from construction works”.

General Construction Activities

6.7.3. It is important that appropriate measures are implemented to control site runoff with high SS content and drainage from entering the nearby water bodies. Proper site management is essential to minimise surface water runoff and soil erosion.

6.7.4. The guidelines stipulated in the ProPECC PN 1/94 “Construction Site Drainage” issued by the EPD should be followed to minimize the potential water quality impacts. Good housekeeping and stormwater best management practices, as detailed below, should be implemented to ensure that all construction runoff is well controlled in order to minimize the water quality impacts that arise due to the construction works of the Project.

· Flood protection such as dikes or embankments should be provided around the boundaries of earthwork areas. Temporary ditches should be provided as appropriate to facilitate the runoff discharge into drainage system, through a silt/sediment trap. The silt/sediment traps should be incorporated in the permanent drainage channels to enhance deposition rates.

· Construction works should be programmed to avoid surface excavation works during the rainy seasons (April to September). All exposed earth areas should be completed and vegetated as soon as possible after earthworks have been completed. If excavation of soil cannot be avoided during the rainy season, or at any time of year when rainstorms are likely, exposed slope surfaces should be covered by tarpaulin or other means.

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

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

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

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

· All vehicles and plants should be cleaned before leaving a construction site to ensure no earth, mud, debris and the like are deposited by them on roads. An adequately designed and sited wheel washing facilities should be provided at every construction site exit where practicable. Wash-water should have sand and silt settled out and removed at least on a weekly basis to ensure the continued efficiency of the process. The section of access road leading to, and exiting from, the wheel-wash bay to the public road should be paved with sufficient backfall toward the wheel-wash bay to prevent vehicle carrying soil and silty water to public roads and drains.

· Oil interceptors should be provided in the drainage system downstream of any oil/fuel pollution sources as far as possible. The oil interceptors, if any, should be emptied and cleaned regularly to prevent the release of oil and grease into the storm water drainage system after accidental spillage.

· Construction solid waste, debris and rubbish on site should be collected, handled and disposed of properly to avoid water quality impacts.

· All fuel tanks and storage areas should be provided with locks and sited on sealed areas, within bunds of a capacity equal to 110% of the storage capacity of the largest tank to prevent spilled fuel oils from reaching water sensitive receivers nearby.

6.7.5. It is not expected that there will be any service shop and maintenance facilities located within the Project works areas. Maintenance of vehicles and equipment involving activities with potential for leakage and spillage is expected to be carried out off-site and should only be undertaken within areas appropriately equipped to control these discharges.

6.7.6. By adopting the best management practices, it is anticipated that the impacts of general site operation will be reduced to satisfactory levels before discharges. The details of best management practices will be highly dependent to actual site condition and the Contractor shall obtain a discharge license under the WPCO.

Sewage from Workforce

6.7.7. During the period of construction, domestic sewage may be generated in the construction site. In order to prevent domestic sewage from flowing into pond and channel nearby construction site, placing sandbags and sheet piles around the construction site is necessary. Portable chemical toilets and/or sewage holding tanks should be provided for handling the construction sewage generated by the workforce. A licensed contractor should be employed to provide appropriate and adequate portable toilets to cater 0.15m³/day/employed population and be responsible for appropriate disposal and maintenance.

6.7.8. Notices should be posted at conspicuous locations to remind the workers not to discharge any sewage or wastewater into the nearby environment during the construction phase of the Project. Regular environmental audit on the construction site should be conducted in order to provide an effective control of any malpractices and achieve continual improvement of environmental performance on site. It is anticipated that sewage generation during the construction phase of the Project would not cause water quality impact after undertaking all required measures.

6.7.9. With good control of domestic sewage, unacceptable water quality impacts from the workforce sewage are not anticipated to occur.

Widening of Drainage Channels

6.7.10. Due to the characteristics of narrow width and small water flow of the existing channel, the excavation should be carried out in dry condition (even in wet season) by diverting the stream flow from upstream by a temporary drainage channel with a temporary sheetpiles, earth bund or barrier; so that the works area will remain dry for later excavation and widening works.

6.7.11. The temporary drainage channel would be removed when the construction works are completed or the temporary diversion is no longer required. Although flooding of the proposed contaminant section seldom occurs in dry season, the excavation would be considered to suspend when flood water enters the containment and causes leakage of runoffs to stream water.

6.7.12. After dewatering of the streams, the sediments should be allowed to dry before excavation (yet still maintain a moist state to avoid dust nuisance). This will facilitate excavation of the sediments and also minimize the risk of drained water flowing back into watercourses or diversion channels as the sediment is handled. Where time or weather constraints require handling of wet sediment, care should be taken in the removal of sediment and the storage area should be bunded to prevent silty runoff entering watercourses. Given its small quantity, all excavated sediment should be reused on-site as backfilling material.

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

6.7.14. Excavated sediment will likely be temporarily stored on-site for reuse as backfilling material. This should be stored in a bunded area and covered at any time to avoid inadvertent release of silts and suspended solids to nearby water bodies.

6.7.15. Regular monitoring of suspended solids, pH and turbidity should be conducted during excavation works. Any exceedance of water quality in the nearby water bodies caused by inadvertent release of site runoff should be rectified in accordance with EM&A programme for this Project.

Cast in-situ Construction

6.7.16. To ensure contaminated wastewater is not discharged to surface waters, groundwater or land. The suggested mitigation measures include:

· Minimize the area of the site which generates contaminated stormwater runoff.

· Provide a separate dedicated drainage system to discharge clean stormwater from the site.

· Drain all contaminated stormwater and process wastewater to a collection pit for recycling.

· Regularly clean out solids that accumulate in the pit.

· There must be no dry weather wastewater discharges from the site.

· Monitor wet weather discharges for pH and suspended solids. Retain the records.

Accidental Spillage of Chemicals

6.7.17. Illegal disposal of chemicals should be strictly prohibited. Registration to EPD as a CWP (Chemical Waste Producers) is required if chemical wastes are generated and need to be disposed of. Disposal of chemical wastes should be carried out in compliance with the Waste Disposal Ordinance (WDO). The Code of Practice on Packaging, Labelling and Storage of Chemical Wastes published under the WDO should be used as a guideline for handing chemical wastes.

Operation Phase

6.7.18. Maintenance desilting may be necessary for the upgraded channel to remove excessive silts, vegetation, debris and obstruction. Desilting should be carried out during period of low flow (i.e. dry season, from October to March).

6.7.19. Before proceeding with any maintenance desilting works, except for emergency works, the maintenance engineer should check to ascertain if any of the proposed works will be located in or near an environmentally sensitive and/or ecologically important watercourses. Best Management Practices for the planning and execution of desilting and maintenance works on environmentally sensitive watercourses are recommended in the following:

· Maintenance of the drainage should be programmed to annual silt removal when the accumulated silt will adversely affect the hydraulic capacity of the channel (except during emergency situations where flooding risk is imminent). Desilting should be carried out by hand or light machinery during the dry season (October to March) when water flow is low;

· Containment structures (such as sand bags barrier) should be provided for the active desilting works area to facilitate a dry or at least confined working area within the watercourses;

· Where no maintenance access is available for the channel, temporary access to the works site should be carefully planned and located to minimize disturbance caused to the watercourse, adjacent vegetation and nearby sensitive receivers;

· The use of lesser or smaller construction plants should be considered to reduce disturbance to the channel bed where fish habitats are located and to the nearby sensitive receivers; and

· The use of concrete or the like should be avoided or minimized.

6.8 Cumulative Impact

6.8.1. As indicated in Project Profile and relevant information, the proposed drainage improvement works in four villages are planned to commence in 2022 and completion in 2025. The major potential interfacing projects identified at this stage are listed as Table 6‑14 below.

Table 6‑14 Summary of the Potential Interfacing Projects

Potential Interfacing Projects	Construction Period	Affected Location
Agreement No. CE 61/2012 (HY) – Improvement to Fan Kam Road - Investigation	2021 to 2025	Ha Che

6.8.2. Careful programming of the works should be designed to minimize interface with the construction works of Fan Kam Road Improvement Works Project. If interfacing construction works cannot be avoided, containment structures (such as sand bags barrier) should be provided at the interfacing areas. Other measures that need to be implemented before, during, and after rainstorms are summarized in ProPECC PN 1/94. As environmental mitigation measure would also be implemented under the Fan Kam Road Improvement Works Project, close liaison with Fan Kam Road Improvement Works Project is required. Based on the above review, no cumulative impact would be anticipated.

6.9 Evaluation of Residual Impact

6.9.1. With implementation of recommended mitigation measures during both construction and operation phases, it’s anticipated that unacceptable residual impact on water quality would not arise.

6.10 Environmental Monitoring and Audit Requirements

6.10.1. The water quality assessment identified that the key issue in terms of water quality would be related to excavation works during the proposed drainage improvement. Details of the recommended water quality monitoring requirements and regular audit during construction phase are included in the EM&A Manual.

6.11 Summary

6.11.1. Key issues in terms of water quality would be related to excavation works for the construction phase of the proposed drainage improvement works. To minimize potential impacts on water quality during the channel construction, the excavation would be carried out in dry condition (even in wet season) by diverting the stream flow from upstream by a temporary drainage channel with a temporary sheet piles, earth bund or barrier, so that the works area will remain dry for later excavation and widening works.

6.11.2. With implementation of recommended appropriate mitigation measures, the construction works for the proposed drainage improvement works would not be anticipated to result in unacceptable impacts on water quality.

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

6.11.4. During operation of the Project, the drainage improvement works would not produce extra point sources or non-point source pollution loading. The new alignments of the drainage would provide widened sections to alleviate flooding during heavy rainfalls.

6.11.5. In order to avoid adverse pollution from first flush during rainstorm, regular maintenance debris clearances are recommended before rainstorm events. Maintenance desilting may be necessary for the proposed channel to remove excessive silts, vegetation, debris and obstruction. Desilting should be carried out during period of low flow.