TABLE OF CONTENTS

5             Water Quality Impact. 5-1

5.1           Introduction. 5-1

5.2           Environmental Legislations, Standards and Guidelines. 5-1

5.3           Description of Environment 5-4

5.4           Identification of Water Sensitive Receivers. 5-9

5.5           Identification of Environmental Impacts. 5-10

5.6           Assessment Methodology. 5-11

5.7           Prediction and Evaluation of Environmental Impacts. 5-11

5.8           Mitigation of Environmental Impacts. 5-13

5.9           Cumulative Impacts. 5-18

5.10         Evaluation of Residual Impacts. 5-19

5.11         Environmental Monitoring and Audit 5-20

5.12         Conclusion. 5-20

 

 

LIST OF TABLES

Table 5.1              Summary of Water Quality Objectives for Watercourses in Tolo Harbour and Channel WCZ

Table 5.2              WSD’s Target Seawater Quality Objectives at Flushing Water Intakes

Table 5.3              Baseline Water Quality Condition for Tolo Harbour and Channel WCZ in 2020

Table 5.4              Baseline Water Quality Condition for Shing Mun River and its Tributaries in 2020

Table 5.5              Summary of Representative Water Sensitive Receivers

 

LIST OF FIGURE

Figure 5.1             Locations of Water Sensitive Receivers and EPD Monitoring Stations

 

 

 

5                 Water Quality Impact

5.1             Introduction

5.1.1.1      This section presents the assessment on potential water quality impacts arising from construction and operation of the Project, which has been conducted in accordance with the criteria and guidelines as stated in Annexes 6 and 14 of the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) as well as the requirements given in Clause 3.4.6 and Appendix D of the EIA Study Brief (No. ESB-319/2019). 

 

5.2             Environmental Legislations, Standards and Guidelines

5.2.1          Environmental Impact Assessment Ordinance (EIAO)

5.2.1.1      Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) was issued by EPD under Section 16 of the EIAO.  The EIAO-TM specifies assessment methodologies and criteria that are to be followed in an EIA Study.  Sections relevant to water quality impact assessment comprise:

l  Annex 6 – Criteria for Evaluating Water Pollution

l  Annex 14 – Guidelines for Assessment of Water Pollution

5.2.2          Water Quality Objectives (WQOs)

5.2.2.1      The Water Pollution Control Ordinance (WPCO) provides the major statutory framework for the protection and control of water quality in Hong Kong.  According to the Ordinance and its subsidiary legislation, Hong Kong waters are divided into ten Water Control Zones (WCZs).  Corresponding statements of Water Quality Objectives (WQOs) are stipulated for different water regimes (marine waters, inland waters, bathing beaches subzones, secondary contact recreation subzones and fish culture subzones) in each WCZ based on their beneficial uses.  WQOs for the watercourses in Tolo Harbour and Channel WCZ relevant to this assessment are listed in Table 5.1.

Table 5.1        Summary of Water Quality Objectives for Watercourses in Tolo Harbour and Channel WCZ

Parameters

Criteria

Subzone

Aesthetic Appearance

Waste discharges shall not cause the water to contain substances that settle to form objectionable deposits;

Whole Zone

Waste discharges shall not cause the water to contain substances that float as debris, scum, oil or other matter to form nuisances;

Waste discharges shall not cause water to contain substances that produce objectionable colour, odours, taste or turbidity;

Waste discharges shall not cause water to contain substances that injure or are toxic or produce adverse physiological responses in humans, animals or plants; or

Waste discharges shall not cause water to contain substances that are conductive to undesirable aquatic life or a nuisance to aquatic life. 

E. coli

Should not exceed 1000 cfu per 100 mL, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.

Inland Waters in Shing Mun (A, C, D, E, H, I) subzones, Tai Po (B, C) subzones and other watercourses.

Should not exceed 0 cfu per 100 mL, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.

Inland Waters in Shing Mun (B, F, G) subzones, Lam Tsuen (C, D) subzones and Tai Po subzone A. 

Colour

Waste discharge shall not cause the colour of water to exceed 30 Hazen units.

Inland Waters in Shing Mun (B, F, G) subzones, Lam Tsuen (C, D) subzones and Tai Po subzone A. 

Waste discharge shall not cause the colour of water to exceed 50 Hazen units.

Inland Waters in Shing Mun (A, C, D, E, H, I) subzones, Tai Po (B, C) subzones and other watercourses. 

pH

To be in the range of 6.0 – 9.0

Inland Waters in Shing Mun (D, E, I) subzones and other watercourses.

To be in the range of 6.5 – 8.5

Inland Waters in Shing Mun (A, B, C, F, G, H) subzones, Lam Tsuen (C, D) subzones and Tai Po (A, B, C) subzones. 

Temperature

Not to exceed ± 2 ℃ daily temperature range due to waste discharge

Whole Zone

Suspended solids (SS)

Waste discharges shall not cause the annual median of suspended solids to exceed 25 milligrams per litre.

Inland Waters in Shing Mun (D, E, I) subzones and other watercourses.

Waste discharges shall not cause the annual median of suspended solids to exceed 20 milligrams per litre.

Inland Waters in Shing Mun (A, B, C, F, G, H) subzones, Lam Tsuen (C, D) subzones and Tai Po (A, B, C) subzones. 

Dissolve Oxygen (DO)

Not less than 4 mg/L or 40% saturation at any time. 

Whole Zone

5-day biochemical oxygen demand (BOD5)

Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 5 milligrams per litre.

Inland Waters in Shing Mun (A, C, D, E, H, I) subzones, Tai Po (B, C) subzones and other watercourses

Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 3 milligrams per litre.

Inland Waters in Shing Mun (B, F, G) subzones, Lam Tsuen (C, D) subzones and Tai Po subzone A. 

Chemical oxygen demand (COD)

Waste discharges shall not cause the chemical oxygen demand to exceed 15 milligrams per litre.

Inland Waters in Shing Mun (B, F, G) subzones, Lam Tsuen (C, D) subzones and Tai Po subzone A. 

Waste discharges shall not cause the chemical oxygen demand to exceed 30 milligrams per litre.

Inland Waters in Shing Mun (A, C, D, E, H, I) subzones, Tai Po (B, C) subzones and other watercourses

Ammoniacal nitrogen

The un-ionised ammoniacal nitrogen level should not be more than 0.5 milligram per litre at any time.

Whole Zone

Toxins

Waste discharges shall not cause the toxicants in water to attain such a level as to produce significant toxic 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

Source:   Statement of Water Quality Objectives for Watercourses (Tolo Harbour and Channel Water Control Zone)

 

5.2.3          Water Supplies Department Water Quality Criteria for Flushing Water Intakes

5.2.3.1      The Water Supplies Department (WSD) has specified a set of target seawater quality objectives for their flushing water intakes.  The list is shown in Table 5.2 below.  These target objectives will be applied at the points of seawater abstraction along the coastlines of Tolo Harbour for flushing purpose.

Table 5.2        WSD’s Target Seawater Quality Objectives at Flushing Water Intakes

Parameter

(in mg/L unless otherwise stated)

WSD’s Target Water Quality Limit at Flushing Water Intake

Colour (Hazen Unit)

< 20

Turbidity (NTU)

< 10

Threshold Odour Number (odour unit)

< 100

Ammonia Nitrogen (NH3-N)

< 1

Suspended Solids (SS)

< 10

Dissolved Oxygen (DO)

> 2

Biochemical Oxygen Demand (BOD)

< 10

Synthetic Detergents

< 5

E. coli (no./100mL)

< 20,000

 

5.2.4          Technical Memorandum on Effluent Discharge Standard (TM-DSS)

5.2.4.1      Discharge of effluents is subject to control under the WPCO.  The "Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters" (TM-DSS) gives guidance on the permissible effluent discharges based on the type of receiving waters (foul sewers, storm water drains, inland and coastal waters).  The standards control the physical, chemical and microbial quality of effluents.  Any sewage from the proposed construction and operation activities must comply with the standards for effluents discharged into the foul sewers, inland waters and coastal waters of Tolo Harbour and Channel WCZ, as stipulated in the TM-DSS.

5.2.5          Professional Persons Environmental Consultative Committee Practice Notes (ProPECC PNs)

5.2.5.1      A “Professional Persons Environmental Consultative Committee Practice Note” (ProPECC PN) was issued by the EPD to provide guidelines for handling and disposal of construction site discharges in order to control site runoff and wastewater generated during the construction phase of the Project.  Practices given in the ProPECC PN 1/94 should be followed as far as possible during construction to minimise the water quality impact due to construction site drainage.  The ProPECC PN 1/94 provides good practice guidelines for dealing with various types of discharge from construction sites.

5.2.5.2      The ProPECC PN 5/93 "Drainage Plans subject to Comments by Environmental Protection Department" provides guidelines and practices for handling, treatment and disposal of various effluent discharges to stormwater drains and foul sewers.  The design of site drainage and disposal of various site effluents generated within the new development area should follow the relevant guidelines and practices as given in the ProPECC PN 5/93.

5.2.6          Hong Kong Planning Standards and Guidelines (HKPSG)

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

5.2.7          ETWB Technical Circular (Works) No. 5/2005 Protection of Natural Streams/Rivers from Adverse Impacts Arising from Construction Works

5.2.7.1      Environment, Transport and Works Bureau (ETWB) Technical Circular (Works) [ETWB TC(Works)] No. 5/2005 "Protection of natural streams / rivers from adverse impacts arising from construction works" 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 protection of natural streams/rivers from government projects and private developments.  The guidelines and precautionary mitigation measures given in the ETWB TC (Works) No. 5/2005 should be followed as far as possible to protect the inland watercourse at or near the Project area during the construction phase.

 

5.3             Description of Environment

5.3.1          Assessment Area

5.3.1.1      In accordance with Clause 3.4.6.2 of the EIA Study Brief (No. ESB-319/2019), the assessment area for this water quality impact assessment includes areas within 500 m from the boundary of the Project and covers Shing Mun River, Tolo Harbour and Channel Water Control Zone (WCZ) as designated under the Water Pollution Control Ordinance (WPCO).

5.3.1.2      The baseline conditions of the water bodies in the assessment area were established with reference to the routine river and marine water quality monitoring data collected by EPD.  Descriptions of the baseline conditions provided in the subsequent sections are extracted from the EPD’s reports “River Water Quality in Hong Kong in 2020” and “Marine Water Quality in Hong Kong in 2020”.

5.3.2          Marine Water

5.3.2.1      The water quality monitoring results at station closest to the Project, namely TM2 within Harbour Subzone in Tolo Harbour & Channel WCZ, is shown in Table 5.3.  Full compliances with the WQO was recorded at the selected EPD station TM2 for DO (depth average and bottom), chlorophyll-a and E. coli in 2020.

Table 5.3        Baseline Water Quality Condition for Tolo Harbour and Channel WCZ in 2020

Parameters

Harbour Subzone

WPCO WQO

(in marine waters)

TM2

Temperature

(℃)

26.3

(20.6 - 29.8)

Change due to waste discharge not to exceed ±1℃ and not to exceed 0.5℃ per hour at any location

Salinity (ppt)

29.9

(24.8 - 32.8)

Change due to waste discharge not to be greater than ±3 ppt

Dissolved Oxygen (DO)

(mg/L)

Depth Average

6.1

(5.1 - 7.9)

Not less than 4 mg/L in the water column (except for the bottom water within 2 m from the seabed)

Bottom

6.2

(4.5 - 8.3)

Not less than 2 mg/L within 2 m from the seabed

Dissolved Oxygen

(% Saturation)

Depth Average

89

(73 - 112)

Not available

Bottom

90

(70 - 120)

Not available

pH

8.0

(7.7 - 8.3)

Change due to waste discharge not to be greater than ±0.5 from natural range pH units at any time

Secchi Disc Depth

(m)

2.4

(1.6 - 3.4)

Not available

Turbidity

(NTU)

3.1

(1.5 - 5.5)

Not available

Suspended Solids (SS)

(mg/L)

8.1

(1.4 - 17.0)

Not available

5-day Biochemical Oxygen Demand

(BOD5) (mg/L)

1.7

(0.8 - 2.6)

Not available

Ammonia Nitrogen

(mg/L)

0.045

(0.022 - 0.076)

Not available

Unionised Ammonia (UIA)

(mg/L)

0.003

(<0.001 - 0.005)

Not available

Nitrite Nitrogen

(mg/L)

0.004

(<0.002 - 0.010)

Not available

Nitrate Nitrogen

(mg/L)

0.039

(<0.002 - 0.215)

Not available

Total Inorganic Nitrogen (TIN)

(mg/L)

0.09

(0.03 - 0.27)

Not available

Total Kjeldahl Nitrogen

(mg/L)

0.50

(0.22 - 0.81)

Not available

Total Nitrogen

(mg/L)

0.54

(0.29 - 0.82)

Not available

Orthophosphate Phosphorus

(PO4-P) (mg/L)

0.008

(0.002 - 0.026)

Not available

Total Phosphorus

(mg/L)

0.04

(<0.02 - 0.06)

Not available

Silica (as SiO2)

(mg/L)

1.48

(0.50 - 4.15)

Not available

Chlorophyll-a

(µg/L)

5.8

(1.4 - 9.2)

Harbour Subzone: Not to exceed 20µg/L, calculated as a running arithmetic mean of 5 daily measurements for any single location and depth

E. coli

(cfu/100mL)

13

(<1 - 4500)

Not to exceed 610 cfu/100mL for geometric mean of all samples collected in one calendar year

Faecal Coliforms

(cfu/100mL)

76

(6 - 32000)

Not available

Notes:

1.     Data source: EPD Marine Water Quality in Hong Kong in 2020

2.     Unless otherwise specified, data presented are depth-averaged values calculated by taking the means of three depths: Surface, Mid-depth, Bottom.

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

4.     Data in brackets indicate the ranges.

5.     cfu – colony forming unit.

 

5.3.2.2      The monitoring results of key water quality parameters indicate that the overall WQO compliance rate of the Tolo Harbour and Channel WCZ in 2020 was 93%, markedly improved compared to 79% in 2019.  Tolo Harbour consistently complied with the bacteriological WQO for the secondary contact recreation subzone.  Tolo Channel, however, was subject to a natural hydrological phenomenon of water column stratification and associated lower bottom DO level due to restricted water exchange with the open waters.

5.3.2.3      In the mid-1980s, with the implementation of the Tolo Harbour Action Plan, which includes the control of livestock waste, the provision and improvement of sewerage infrastructure, the export of treated sewage effluent from Sha Tin and Tai Po Sewage Treatment Works outside Tolo Harbour for discharging into Victoria Harbour via Kai Tak River, as well as the extension of village sewerage in the catchment area, there has been a steady improvement in water quality in Tolo Harbour in the past three decades.

5.3.3          Inland Water

5.3.3.1      Section of Shing Mun River, and its tributaries including Fo Tan Nullah (FTN) and Siu Lek Yuen Nullah are located within the assessment area, the corresponding water quality monitoring results at stations, namely TR19I, TR17, TR17L and TR23A, are shown in Table 5.4.

5.3.3.2      The water quality at Shing Mun River, a major river which has three main tributaries and runs through the densely populated Sha Tin urban area, showed marked improvement in the past three decades.  The WQO compliance rate of Shing Mun River was 90% in 2020.

5.3.3.3      The E. coli level at Shing Mun River Main Channel (TR19I), the only watercourse currently used for secondary contact recreation activities in Hong Kong, was rated "Low" (i.e. ≤610 counts/100mL) in 2020.  And the Annual Water Quality Index (WQI) was rated “Excellent” in 2020, while it was rated “Good” in 2019.


Table 5.4       Baseline Water Quality Condition for Shing Mun River and its Tributaries in 2020

Parameters

Shing Mun Main Channel

Fo Tan Nullah

Siu Lek Yuen Nullah

WPCO WQO

(in inland waters)

TR19I

TR17

TR17L

TR23A

Dissolved Oxygen (DO)

(mg/L)

6.7

(4.4 - 8.0)

9.7

(8.1 - 10.2)

6.4

(5.0 - 7.2)

6.3

(4.1 - 7.8)

≥ 4 mg/L or 40% saturation (at 15℃)

pH

8.1

(7.6 - 8.9)

9.2

(7.8 - 10.0)

7.9

(7.8 - 8.2)

7.9

(7.8 - 9.5)

within 6.0 - 9.0 for TR19I;

within 6.5 - 8.5 for TR17, TR17L and TR23A

Suspended Solids (SS)

(mg/L)

3.5

(1.4 - 16.0)

3.5

(2.2 - 6.4)

4.8

(0.9 - 13.0)

9.0

(2.5 - 20.0)

Annual median:

≤ 25 mg/L, for TR19I;

≤ 20 mg/L, for TR17, TR17L and TR23A

5-day Biochemical Oxygen Demand

(BOD5) (mg/L)

3.1

(1.7 - 8.5)

3.0

(1.2 - 6.3)

1.8

(0.7 - 5.4)

1.9

(0.9 - 2.1)

≤ 5 mg/L, for TR19I, TR17 and TR17L;

≤ 3 mg/L, for TR23A

Chemical Oxygen Demand (COD)

(mg/L)

13

(8 - 24)

7

(<2 - 12)

9

(6 - 32)

12

(5 - 19)

≤ 30 mg/L, for TR19I, TR17 and TR17L;

≤ 15 mg/L, for TR23A

Oil & Grease

(mg/L)

<0.5

(<0.5 - <0.5)

<0.5

(<0.5 - <0.5)

<0.5

(<0.5 - <0.5)

<0.5

(<0.5 - <0.5)

Not available

E. coli

(cfu/100mL)

140

(40 - 630)

2 800

(130 - 34 000)

2 500

(120 - 22 000)

1 600

(210 - 8 000)

Running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days (or 14 and 42 days):

≤ 1,000 cfu/100mL, for TR19I, TR17 and TR17L;

≤ 0 cfu/100mL, for TR23A

Faecal Coliforms

(cfu/100mL)

2 500

(810 - 56 000)

14 000

(1 400 - 85 000)

12 000

(760 - 120 000)

13 000

(2 500 - 170 000)

Not available

Ammonia Nitrogen

(mg/L)

0.130

(0.058 - 0.230)

0.092

(0.028 - 0.510)

0.190

(0.100 - 0.700)

0.130

(0.070 - 0.280)

≤ 0.5 mg/L

 

Nitrate Nitrogen

(mg/L)

0.130

(0.014 - 0.510)

0.520

(0.380 - 0.970)

0.330

(0.180 - 0.550)

0.330

(0.044 - 0.510)

Not available

Total Kjeldahl Nitrogen

(mg/L)

0.58

(0.22 - 0.92)

0.37

(0.06 - 1.30)

0.58

(0.29 - 1.30)

0.38

(0.20 - 0.58)

Not available

Orthophosphate Phosphorus

(PO4-P) (mg/L)

0.027

(0.014 - 0.047)

0.017

(0.004 - 0.084)

0.022

(0.013 - 0.033)

0.020

(0.013 - 0.036)

Not available

Total Phosphorus

(mg/L)

0.05

(0.04 - 0.40)

0.05

(0.03 - 0.15)

0.07

(0.05 - 0.08)

0.05

(0.04 - 0.07)

Not available

Sulphide

(mg/L)

<0.02

(<0.02 - <0.02)

<0.02

(<0.02 - <0.02)

<0.02

(<0.02 - <0.02)

<0.02

(<0.02 - <0.02)

Not available

Aluminium (Al)

(µg/L)

<50

(<50 - <50)

63(<50 - 194)

<50(<50 - 104)

<50

(<50 - 202)

Not available

Cadmium (Cd)

(µg/L)

<0.1

(<0.1 - <0.1)

<0.1

(<0.1 - <0.1)

<0.1

(<0.1 - 0.2)

<0.1

(<0.1 - <0.1)

Not available

Chromium (Cr)

(µg/L)

2

(2 - 4)

<1

(<1 - <1)

2

(<1 - 3)

2

(<1 - 2)

Not available

Copper (Cu)

(µg/L)

5

(3 - 6)

2

(1 - 6)

5

(2 - 6)

4

(1 - 5)

Not available

Lead (Pb)

(µg/L)

<1

(<1 - <1)

<1

(<1 - <1)

<1

(<1 - <1)

<1

(<1 - <1)

Not available

Zinc (Zn)

(µg/L)

<10

(<10 - 16)

<10

(<10 - 49)

14

(<10 - 26)

11

(<10 - 19)

Not available

Flow

(m3/s)

NM

0.045

(0.015 - 0.090)

NM

NM

Not available

 

Notes:

1.     Data source: EPD River Water Quality in Hong Kong in 2020

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

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

4.     Figures in brackets are annual ranges.

5.     “NM” indicates no measurement taken.

6.     cfu – colony forming unit

 

5.4             Identification of Water Sensitive Receivers

5.4.1.1      In accordance with Clause 3.4.6.2 of the EIA Study Brief (No. ESB-319/2019), the assessment area for this water quality impact assessment includes areas within 500 m from the boundary of the Project and covers Shing Mun River, Tolo Harbour and Channel WCZ as designated under the WPCO and the water sensitive receivers (WSRs) in the vicinity of the Project.  WSRs within the assessment area were identified with reference to Annex 14 of the EIAO-TM.

5.4.1.2      Key inland WSRs within 500 m from the boundary of the Project and representative marine WSR in Tolo Harbour and Channel WCZ were identified and are summarised in Table 5.5 below.  Locations of the identified WSRs are illustrated in Figure 5.1. 

Table 5.5        Summary of Representative Water Sensitive Receivers

ID

Location

Nature

Description

Key Inland WSR within 500 m from the boundary of the Project

WSR1

Shing Mun River

Channelised watercourse

Trapezoidal channel with concrete bank and experienced tidal influence.

WSR2

Fo Tan Nullah

Channelised watercourse

Trapezoidal channel with concrete bank and experienced tidal influence.

WSR3

Siu Lek Yuen Nullah

Channelised watercourse

Trapezoidal channel with concrete bank and experienced tidal influence.

WSR4 / S1[1]

Further upstream of the concrete channel of Fo Tan Nullah

Natural watercourse

High naturalness with large boulders and rocks along both sides, and a constant slow flow.

WSR5 / S2[1]

Man Hang, upstream of Fo Tan Nullah

Natural watercourse

High naturalness with rocks within and along both sides, and a narrow, clear, slow and shallow (<1m) water flow. 

WSR6 / S3[1]

Along Wong Chuk Yeung Street

Natural watercourse

Moderate naturalness with large boulders alongside with rocky substrate and modified bankside, as well as slightly poorer water quality. 

WSR7

Water gathering ground located upstream of Fo Tan Nullah

Water gathering ground

-

Representative marine WSR in Tolo Harbour and Channel WCZ

W1

WSD Flushing Water Intakes at Shatin

Water abstraction for flushing purpose

-

Remark:

[1]    Refer to Section 9.5 on full descriptions and locations of the natural watercourses S1 – S3, i.e. WSR4 – WSR6.

5.4.1.3      The existing water gathering grounds are located outside the boundary of the Project and upstream to the Project site.  That is, the watercourses identified at or near the Project site are running from the water gathering grounds towards the Project site.  No aboveground structure would be constructed within the water gathering grounds.  Thus, the water source of the existing water gathering grounds is not expected to be affected during both construction and operation phases of the Project.

5.4.1.4      The inland water in Shing Mun River and the marine water in Tolo Harbour and Channel WCZ are designated under the WPCO as secondary contact recreation subzone, which can be used for water sports and water recreational activities (e.g. dragon boating, sailing, rowing etc.).  The E. coli bacteria would be the principle parameter for assessing the acceptability of using the inland and marine water for water sports or secondary contact recreation activities with a WQO of not exceeding 610 cfu/100 mL (calculated as the geometric mean of all samples collected in one calendar year).  Apart from the secondary contact recreation subzone, E. coli should not exceed 0 cfu per 100ml for inland waters in Shing Mun (B, F, G) subzones.

 

5.5             Identification of Environmental Impacts

5.5.1          Construction Phase

5.5.1.1      As detailed in Section 2, the proposed revitalisation works involves mainly channel bed modification, improvement of existing walkways, construction of dry weather flow interceptor (DWFI) system, landscaping and miscellaneous, as well as construction of underground water storage tank equipped with submersible water pumps installed under the nullah bed at mid-stream of FTN and underground water pipes for ecological enhancement associated water retention and supplement.  Desilting works at downstream tidal zone of FTN would be carried out at the commencement and prior to the completion of the construction works to remove the silt accumulated at the nullah, in addition to the routine maintenance desilting works of smaller scale undertaken by DSD along FTN and by CEDD along Shing Mun River under existing arrangement.  The Contractor should communicate and coordinate with DSD and CEDD to avoid overlapping of the proposed desilting works at downstream tidal zone of FTN during construction phase with DSD’s or CEDD’s routine maintenance desilting works as far as practicable to minimise the potential water quality impacts.  The potential sources of water quality impact associated with the construction works would include:

·             Wastewater from general construction activities;

·             Construction site run-off;

·             Construction works in close proximity to inland water;

·             Construction works at FTN;

·             Sewage from construction workforce; and

·             Accidental spillage of chemicals.

5.5.1.2      Except for the flow diversion required for the construction works within Fo Tan Nullah as detailed in Section 5.8.1.16, no alteration of watercourses would be required.

5.5.2          Operational Phase

5.5.2.1      Potential water quality impacts associated with the operation phase would include:

·             Non-point source surface run-off / irrigation runoff from the proposed greening elements and landscaping;

·             Routine maintenance works for the drainage and sewerage systems along FTN, including desilting along the nullah and minor maintenance to the DWFI system, by the DSD to remove excessive / accumulated silt, vegetation, debris and obstructions within the channel (similar to the ones undertaken by DSD along FTN under existing arrangement), which may lead to disturbance and re-suspension of river sediments and thereby affecting water quality; and

·             Potential changes in hydrodynamics properties and hydrology.

5.5.2.2      The Project would not change the path of any existing flow or catchment of FTN.  Due to ageing drainage systems and possible expedient connection made in the past, polluted discharges from the existing drainage outlets along FTN were observed.  The proposed DWFI system under the Project is expected to improve the water quality of the FTN by intercepting all of the polluted dry weather flows from the drainage outlets along the nullah and discharging the dry weather flows to the existing sewerage system that would eventually reach the relocated Sha Tin Sewage Treatment Works for treatment.  As detailed in sewerage impact assessment in Section 8, the existing sewerage system has enough capacity to cater for the additional dry weather flow intercepted by the DWFI system.  As detailed in Section 2, the introduction of general constructed wetland systems and provision of emergent wetland planting (e.g. reed and other aquatic herbs) / mangroves to the channel bed as greening and ecological enhancement measures are also expected to beneficial to the water quality of FTN.  No adverse water quality impact would be expected from operation of the proposed DWFI system and ecological enhancement works.

 

5.6             Assessment Methodology

5.6.1.1      The assessment area includes inland waters within 500 m from the boundary of the Project and shall cover Shing Mun River, Tolo Harbour and Channel WCZ as designated under the WPCO and WSRs in the vicinity of the Project.  The methodology employed to assess potential water quality impacts associated with the construction and operation of the Project followed the detailed technical requirements given in Appendix D of the EIA Study Brief and was based on the information presented in Section 2.  The WSRs that may be affected by the Project have been identified.  Potential sources of water quality impact that may arise during the construction and operation stages of the Project were described, including point source discharges and non-point source surface water runoff / irrigation runoff, sewage from workforce and polluted discharge generated from the Project.  All the identified sources of potential water quality impact will be evaluated and their impact significance will be determined.  Practical water pollution control measures will be recommended to mitigate identified water quality impacts.

 

5.7             Prediction and Evaluation of Environmental Impacts

5.7.1          Construction Phase

Wastewater from General Construction Activities

5.7.1.1      Wastewater generated from construction activities, including general cleaning and polishing, wheel washing, dust suppression and utility installation may contain high SS concentrations, as well as a certain amount of grease and oil.  Potential water quality impacts due to uncontrolled wastewater discharge can be avoided if construction and site management practices are implemented to ensure that litter, fuels, and solvents do not enter the water environment.  It is expected that if the good site practice suggested in Section 5.8 are followed as far as practicable, the potential water quality impacts associated with construction activities would be minimal.

Construction Site Run-off

5.7.1.2      Potential pollution sources of site run-off may include:

·             Run-off and erosion of exposed bare soil and earth, drainage channels, earth working areas and stockpiles;

·             Wash water from dust suppression sprays and wheel washing facilities; and

·             Fuel, oil and lubricants from maintenance of construction vehicles and equipment.

5.7.1.3      During rainstorms, site run-off would wash away the soil particles on unpaved lands and areas with topsoil exposed, if any.  The run-off is generally characterised by high concentrations of SS.  Release of uncontrolled site run-off would increase the SS levels and turbidity in the nearby water environment.  Site run-off may also wash away soil particles that were contaminated by the construction activities and therefore cause water pollution.

5.7.1.4      Wind-blown dust would be generated from exposed soil surfaces in works areas.  It is possible that wind-blown dust would fall directly onto the nearby water bodies when a strong wind occurs.  Dispersion of dust within the works areas may increase the SS levels in surface run-off causing a potential impact to the nearby sensitive receivers.

5.7.1.5      It is important that proper site practice and good site management should be followed to prevent run-off with high level of SS from entering the surrounding waters.  Best Management Practices (BMPs) in controlling construction site discharges are recommended in Section 5.8 for this Project.  With the implementation of BMPs to control run-off and drainage from the construction site, disturbance of water bodies would be avoided and deterioration in water quality would be minimal.

Construction Works in Close Proximity to Inland Water

5.7.1.6      Construction activities in close vicinity to the inland watercourses may impact water quality due to the potential uncontrolled release of construction waste and wastewater.  Construction waste and wastewater are generally characterised by high SS concentration and elevated pH.  The implementation of adequate construction site drainage and BMPs as described in Section 5.8 and provision of precautionary measures / practices as specified in ETWB TC(Works) No. 5/2005 "Protection of natural streams / rivers from adverse impacts arising from construction works" as detailed in Section 5.8, it is anticipated that water quality impacts would be minimal.

Construction Works at Fo Tan Nullah

5.7.1.7      Construction of the Project would involve channel bed modification, construction of DWFI system along the nullah, and construction of mid-stream submersible water pumps and water pipe along the nullah for water supplement and desilting works at downstream tidal zone.  The existing concrete nullah bed from the section south to Kwei Tei Street down to the section with tidal influence near Fo Tan MTR Station and embankment down to the confluence with Shing Mun River will be resurfaced with layer of vegetation, while greening along the nullah bed and banksides will be provided.  Potential water quality impacts may be generated by uncontrolled discharge of excavated materials, wastewater, spillage and contaminants to the downstream receiving waters.  Construction works within FTN would be divided into sections and constructed in sequence starting from downstream FTN first.  For each section, the construction works within the nullah, including channel bed modification, construction of DWFI system along the nullah, construction of mid-stream submersible water pumps and water pipe along the nullah for water supplement, and desilting works at downstream tidal zone, would be scheduled in dry season when the flow is low.  Site demarcation and flow diversion will be implemented prior to the construction works within channel to ensure that all the construction works would be undertaken in dry conditions and physically separated from the watercourses downstream to avoid potential water quality impacts upon the downstream water quality.  Together with the implementation of precautionary and pollution control measures as detailed in Section 5.8, the potential water quality impacts would be well controlled.

Sewage from Construction Workforce

5.7.1.8      During the construction of the Project, the workforce on site will generate sewage effluent, which is characterised by high levels of BOD, ammonia and E. coli counts.  Based on the DSD Sewerage Manual, the sewage production rate for construction workers is estimated at 0.35 m3 per worker per day.  Potential water quality impacts upon the local drainage and freshwater system may arise from these sewage effluents, if uncontrolled.

5.7.1.9      Temporary sewage generation can be adequately treated by interim sewage treatment facilities, such as portable chemical toilets.  Provided that sewage is not discharged directly into storm drains or inland waters adjacent to the construction site, temporary sanitary facilities are used and properly maintained, and control measures as recommended in Section 5.8 are adopted as far as practicable, it is unlikely that sewage generated from construction workforce would have a significant water quality impact.

Accidental Spillage of Chemicals

5.7.1.10    The use of chemicals such as engine oil and lubricants, and their storage as waste materials has the potential to impact water quality if spillage occurs and enters adjacent water environment.  Waste oil may infiltrate into the surface soil layer, or runoff into the nearby water environment, increasing hydrocarbon levels.  The potential impacts could however be avoided by practical precautionary measures and good site practices (as given in Section 5.8).

5.7.2          Operational Phase

Surface Run-off / Irrigation Run-off

5.7.2.1      Surface run-off / irrigation run-off to be generated from the Project is known as non-point source pollution.  The paved and developed areas, especially the new public open space (e.g. viewing decks) / footpath will increase the quantity of surface runoff.  Irrigation run-off would also be anticipated from the routine maintenance of the proposed planting.  Release of uncontrolled surface / irrigation run-off would increase the suspended solids levels and turbidity as well as fertiliser / pesticides (if required to sustain healthy growth of the proposed plantings) in the nearby waterbodies.  However, impacts upon water quality would be minimal provided that  proper drainage system would be incorporated into the propsed works  to receive surface / irrigation runoff to the drainage system at the planning and design stages.  It is anticipated that with proper implementation of BMPs as recommended in Section 5.8, no adverse water quality impact from non-point source surface / irrigation run-off is expected.

Routine Maintenance Works

5.7.2.2      During the operational phase, similar to the existing practices, regular maintenance works for the drainage and sewerage systems along FTN, including desilting along the nullah and minor maintenance to the DWFI system, would be carried out by the DSD to remove excessive silts, debris and any obstructions to safeguard the hydraulic capacity of the nullah.  The maintenance practices and frequency would be similar to the existing maintenance works undertaken by the DSD.  Such small-scale routine maintenance works would require only light mechanical equipment such as a small loader and/or a small crane truck.  Hand-held equipment will be used for vegetation removal along the nullah. 

5.7.2.3      Maintenance desilting of the nullah should be carried out on an annual basis during dry season (November to March) when the water flow is low, except during emergency situations where the accumulated silt would adversely affect the hydraulic capacity of the nullah or where flooding risk is imminent, or when complaints on environmental nuisance associated with the accumulated silt are received.  Whilst possible changes to water quality may be expected during the removal of excessive silt, vegetation, debris and obstructions within the nullah, such as increases in SS due to disturbance of nullah bed material and subsequently increased sedimentation onto the nullah bed, it is expected that these changes will be short-term and localised within the area of maintenance works and for a short distance downstream due to rapid settling out of any disturbed nullah bed material that no unacceptable adverse water quality impacts to WSRs downstream would be anticipated.  Changes in SS concentrations would be expected to be within the typical ranges experienced under ambient conditions following heavy storms and increased sediment run-off.  Therefore, no unacceptable water quality impacts are anticipated to occur as a result of the small-scale maintenance desilting works.

5.7.2.4      For the minor maintenance works for the DWFI system, it is expected that any maintenance will only be undertaken on an as-needed basis and frequent maintenance (i.e. monthly) will not be required.  Diversion of the dry weather flow to the nearby sewerage system can be adopted during maintenance of DWFI system so that the water quality at FTN would not be adversely affected.  Given the infrequent maintenance requirements and the collected solid wastes will be collected and disposed off-site properly, unacceptable water quality impact is not expected.

Potential Changes in Hydrodynamics Properties and Hydrology

5.7.2.5      During operation of the Project, DWFI system will be in place along the nullah to intercept and convey the flow with polluted discharges from drainage outlets along the nullah to Sha Tin Sewage Treatment Works for treatment, which would inevitably lead to reduced flowrate and amount of freshwater input into FTN and downstream receiving water (Shing Mun River Main Channel).  Due to the natural sloping gradient along FTN as well as and the water retention and replenish designs and ecological enhancement features (e.g. wetland habitats created) within the nullah (see Section 2), average flow rate will remain similar to baseline condition and no unacceptable impacts on hydrodynamics properties and hydrology are anticipated.  In addition, as all the identified natural watercourses within the assessment area are located at the upper catchment of FTN (see Section 8), no changes in hydrodynamic properties or hydrology are anticipated for the watercourses during operational phase of the Project.

 

5.8             Mitigation of Environmental Impacts

5.8.1          Construction Phase

Wastewater from General Construction Activities and Construction Site Run-off

5.8.1.1      Control of potential pollution of nearby water bodies during the construction phase of the Project should be achieved by measures to:

·             prevent or minimise the likelihood of pollutants (generated from construction activities) being in contact with rainfall or run-off; and

·             abate pollutants in the stormwater surface run-off prior to the discharge of surface run-off to the nearby water bodies.

5.8.1.2      These principle objectives should be achieved by implementation of the BMPs of mitigation measures in controlling water pollution.  The guidelines for handling and disposal of construction site discharges as detailed in the ProPECC PN 1/94 should be followed, where applicable.  All effluent discharged from the construction site should comply with the standards stipulated in the TM-DSS.  The following measures are recommended to protect water quality of the inland and coastal waters, and when properly implemented should be sufficient to adequately control site discharges so as to avoid water quality impacts.

Construction Site Run-off

5.8.1.3      Surface runoff from construction sites should be discharged into storm drains via adequately designed sand/silt removal facilities such as sand traps, silt traps and sedimentation basins.  Channels or earth bunds or sandbag barriers should be provided on site during construction works to properly direct stormwater to such silt removal facilities.  Perimeter channels should be provided on site boundaries where necessary to intercept storm runoff from outside the site so that it will not wash across the site.  Catchpits and perimeter channels should be constructed in advance of site formation works and earthworks.

5.8.1.4      Silt removal facilities, channels and manholes should be maintained and the deposited silt and grit should be removed regularly, at the onset of and after each rainstorm to prevent local flooding.  Any practical options for the diversion and re-alignment of drainage should comply with both engineering and environmental requirements in order to provide adequate hydraulic capacity of all drains.

5.8.1.5      Construction works should be programmed to minimise soil excavation works in rainy seasons (April to September).  If soil excavation cannot be avoided in these months or at any time of year when rainstorms are likely, for the purpose of preventing soil erosion, temporary exposed slope surfaces should be covered e.g. by tarpaulin, and temporary access roads should be protected by crushed stone or gravel, as excavation proceeds.  Intercepting channels should be provided (e.g. along the crest / edge of excavation) to prevent storm runoff from washing across exposed soil surfaces.  Arrangements should always be in place in such a way that adequate surface protection measures can be safely carried out well before the arrival of a rainstorm.

5.8.1.6      Earthworks final surfaces should be well compacted and the subsequent permanent work or surface protection should be carried out immediately after the final surfaces are formed to prevent erosion caused by rainstorms.  Appropriate drainage like intercepting channels should be provided where necessary.

5.8.1.7      Measures should be taken to minimise the ingress of rainwater into trenches.  If excavation of trenches in wet seasons is necessary, they should be dug and backfilled in short sections.  Rainwater pumped out from trenches or foundation excavations should be discharged into storm drains via silt removal facilities.

5.8.1.8      Open stockpiles of construction materials (e.g. aggregates, sand and fill material) on sites 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.

5.8.1.9      Manholes (including newly constructed ones) should always be adequately covered and temporarily sealed so as to prevent silt, construction materials or debris from getting into the drainage system, and to prevent storm runoff from getting into foul sewers.  Discharge of surface runoff into foul sewers must always be prevented in order not to unduly overload the foul sewerage system.

Boring and Drilling Water

5.8.1.10    Water used in ground boring and drilling for site investigation or rock / soil anchoring should as far as practicable be re-circulated after sedimentation.  When there is a need for final disposal, the wastewater should be discharged into storm drains via silt removal facilities.

Wheel Washing Water

5.8.1.11    All vehicles and plants should be cleaned before they leave a construction site to minimise the deposition of earth, mud, debris on roads.  A wheel washing bay should be provided at every site exit if practicable and wash water should have sand and silt settled out or removed before discharging into storm drains.  The section of construction road between the wheel washing bay and the public road should be paved to reduce vehicle tracking of soil and to prevent site runoff from entering public road drains.

Rubbish and Litter

5.8.1.12    Good site practices should be adopted to remove rubbish and litter from construction sites so as to prevent the rubbish and litter from spreading from the site area.  It is recommended to clean the construction sites on a regular basis.

Acid Cleaning, Etching and Pickling Wastewater

5.8.1.13    Acidic wastewater generated from acid cleaning, etching, pickling and similar activities should be neutralised to within the pH range of 6 to 10 before discharging into foul sewers.

Effluent Discharge

5.8.1.14    There is a need to apply to EPD for a discharge licence for discharge of effluent from the construction site under the WPCO.  The discharge quality must meet the requirements specified in the discharge licence.  All the runoff and wastewater generated from the works areas should be treated so that it satisfies all the standards listed in the TM-DSS.  The beneficial uses of the treated effluent for other on-site activities such as dust suppression sprays, wheel washing and general cleaning etc., can minimise water consumption and reduce the effluent discharge volume.  If monitoring of the treated effluent quality from the works areas is required during the construction phase of the Project, the monitoring should be carried out in accordance with the relevant WPCO licence.

Construction Works in Close Proximity to Inland Water

5.8.1.15    The precautionary measures / practices outlined in ETWB TC (Works) No. 5/2005 "Protection of natural streams / rivers from adverse impacts arising from construction works" should also be adopted where applicable to minimise the water quality impacts on any natural streams or surface water systems.  Relevant precautionary measures / practices from the ETWB TC (Works) No. 5/2005 include but not limited to the following:

·             The use of less or smaller construction plants may be specified in areas close to the watercourses to reduce the disturbance to the surface water.

·             Temporary storage of materials (e.g. equipment, chemicals and fuel) and temporary stockpile of construction materials should be located well away from any water courses when carrying out of the construction works.

·             Stockpiling of construction materials and dusty materials should be covered and located away from any watercourses.

·             Construction debris and spoil should be covered up and / or disposed of as soon as possible to avoid being washed into the nearby water receivers.

·             Proper shoring may need to be erected in order to prevent soil or mud from slipping into the watercourses.

Construction Works at Fo Tan Nullah

5.8.1.16    As detailed in Section 5.7.1.7, construction works within FTN would be divided into sections and constructed in sequence and all construction works within the nullah should be scheduled in dry season when the flow is low.  All the construction works should be undertaken in dry conditions and physically separated from the watercourses downstream.  Precautionary measures in Appendix D of ETWB TC No. 5/2005, such as temporary isolation to other connected watercourse using concrete blocks, sandbag barriers or other appropriate measures, shall be applied.  Site demarcation and flow diversion with physical barriers / temporary drainage will be implemented prior to the construction works within channel to ensure that all the construction works would be undertaken in dry conditions and physically separated from the watercourses downstream to avoid potential water quality impacts upon the downstream water quality.  Physical barriers (such as concrete blocks/sandbags or other appropriate measures) with impermeable liners will be deployed to confine the works area to maintain a dry condition within and  to prevent pollutants running into the downstream waters; and depending on the site conditions, physical barriers or temporary drainage would be established to intercept and divert the upstream flow.  Dewatering of the construction works area shall be conducted prior to the construction works.  Silt removal facilities should be adopted to treat the wastewater from dewatering operations prior to discharge.  Details of the containment structures, flow diversion pathway and water treatment method should be provided by the Contractor to the Engineer for approval before commencement of construction works for the Project.  After completion of the construction works, the works area shall be cleaned up before receiving any water flow or connecting to any existing watercourse.

5.8.1.17    All excavated materials generated from construction works in watercourses and wet areas should be collected and handled in compliance with the Waste Disposal Ordinance.  No direct disposal of the construction wastes or excavated materials into the stormwater drainage system and inland water should be allowed.  The above pollution control measures for handling and disposal of excavated materials should be followed to avoid and minimise the potential environmental impacts arising from the excavated materials. 

5.8.1.18    The pollution control measures for construction works in close proximity to inland water and mitigation measures for general construction activities as recommended in Section 5.8.1.1 to 5.8.1.15 should also be implemented to avoid and minimise any potential water quality impacts from construction within FTN.  Regular site checks should be conducted to ensure no adverse impact to FTN  are induced by the construction activities.

Sewage from Construction Workforce

5.8.1.19    No direct discharge of sewage to the stormwater drains and inland water will be allowed.  Adequate and sufficient portable chemical toilets should be provided in the works areas to handle sewage from construction workforce.  A licensed collector should be employed to clean and maintain the chemical toilets on a regular basis.

5.8.1.20    Notices should be posted at conspicuous locations to remind the workers not to discharge any sewage or wastewater into the surrounding environment.  Regular environmental audit of the construction site should be conducted to provide an effective control of any malpractices and achieve continual improvement of environmental performance on site.

Accidental Spillage of Chemicals

5.8.1.21    Contractor must register as a chemical waste producer if chemical wastes would be produced from the construction activities.  The Waste Disposal Ordinance (Cap 354) and its subsidiary regulations in particular the Waste Disposal (Chemical Waste) (General) Regulation, should be observed and complied with for control of chemical wastes.  The Contractor is also recommended to develop management procedures for chemicals used and prepare an emergency spillage handling procedure to deal with chemical spillage in case of accident occurs.

5.8.1.22    Any service shop and maintenance facilities should be located on hard standings within a bunded area, and sumps and oil interceptors should be provided.  Maintenance of vehicles and equipment involving activities with potential for leakage and spillage should only be undertaken within the areas appropriately equipped to control these discharges.

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

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

·             Chemical waste containers should be suitably labelled, to notify and warn the personnel who are handling the wastes, to avoid accidents.

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

5.8.2          Operational Phase

Surface Run-off / Irrigation Run-off

5.8.2.1      The ProPECC PN 5/93 “Drainage Plans subject to Comments by Environmental Protection Department” provides guidelines and practices for handling, treatment and disposal of various effluent discharges to stormwater drains and foul sewers.  The design of site drainage should follow the relevant guidelines and practices as given in the ProPECC PN 5/93.

Design Measures

5.8.2.2      Exposed surface shall be avoided within the site to minimise soil erosion.  The site shall be either hard paved or covered by landscaping area and plantation where appropriate.

5.8.2.3      The drainage system within the site should be designed to cater for the runoff from 50 year-return-period rainstorm.

Devices / Facilities to Control Pollution

5.8.2.4      Screening facilities such as standard gully grating and trash grille, with spacing which is capable of screening large substances such as fallen leaves and rubbish should be provided at the inlet of drainage system.

5.8.2.5      Road gullies with standard design and silt traps and oil interceptors should be incorporated during the detailed design to remove particles present in stormwater runoff.

Administrative Measures

5.8.2.6      BMPs for storm water discharge and management as detailed below are recommended for the Project to mitigate potential adverse water quality impacts.

5.8.2.7      Good management measures such as regular cleaning and sweeping of road surface / open areas should be followed.  The road surface / open area cleaning should also be carried out prior to occurrence of rainstorm.

5.8.2.8      Good management practices should be adopted to properly manage the water application rate and time during irrigation to minimise chance of run-off.  Use of fertilisers and pesticides, if required, should be properly controlled, e.g. applications prior to forecasted heavy rain event should also be avoided to minimise the potential for run-off of residual fertiliser.  Priority would be given to remove infected/sick plantings over the use of pesticides.  In addition, use of more specific, systemic and biodegradable pesticide in low dosage is more preferred.  The use and handling of fertilisers and pesticides should follow the Pesticide Ordinance and Code of Practice for the Safe and Proper Use of Pesticides in Public Areas by AFCD, Food and Health Bureau (FEHD) and Leisure and Cultural Services Department (LCSD).

5.8.2.9      Manholes, as well as storm water gullies, ditches provided among the development areas should be regularly inspected and cleaned (e.g. monthly).  Additional inspection and cleansing should be carried out before forecasting heavy rainfall.

Routine Maintenance Works

5.8.2.10    During the operational phase, similar to the existing practices, regular maintenance works for the drainage and sewerage systems along FTN, including desilting along the nullah and minor maintenance to the DWFI system, would be carried out by the DSD to remove excessive silts, debris and any obstructions to safeguard the hydraulic capacity of the nullah.  The maintenance practices and frequency would be similar to the existing maintenance works undertaken by the DSD. 

5.8.2.11    The following good site practices would be included in planning for the maintenance works:

·             Maintenance desilting of the nullah should be carried out on an annual basis during dry season (November to March) when the water flow is low, with the exception of during emergency situations where the accumulated silt would adversely affect the hydraulic capacity of the nullah or where flooding risk is imminent, or when complaints on environmental nuisance associated with the accumulated silt are received.  Desilting should be carried out by hand-held or light machinery at low tide.

·             Phasing of the works should be considered to better control and reduce any impacts caused.  Where possible, works should be carried out along half width of the drainage channel in short sections.  A free passage along the drainage channel is necessary to avoid forming stagnant water in any phase of the works.

·             Containment structures (such as sandbags barrier) should be provided for the desilting works area to facilitate a dry or at least confined working area within the drainage channel.

·             The locations for the disposal of the removed materials should be identified and agreement sought with the relevant departments before commencement of the maintenance works.  Temporary stockpile of waste materials should be located away from the channel and properly covered.  These waste materials should be disposed of in a timely and appropriate manner.

·             Effective temporary flow diversion scheme should be implemented and the generated wastes should be collected and disposed off-site properly to avoid adversely affecting the water quality of the drainage system.

 

5.9             Cumulative Impacts

5.9.1          Potential Concurrent Projects

5.9.1.1      A number of potential concurrent projects have been identified and their potential environmental cumulated impacts are discussed in Section 2.8. Based on the latest available information at the time of preparation of this EIA Report, there are six projects potentially be constructed and operated concurrently with the Project, including:

·     Flood walls along Shing Mun River Channel under “Drainage Improvement Works in Sha Tin and Sai Kung;”

·     Sewage rising mains under “Relocation of Sha Tin Sewage Treatment Works to Caverns – Upstream Sewerage and Pumping Stations”;

·     “Revitalisation of Tai Wai Nullah”;

·     “Revised Trunk Road T4”;

·     “Redevelopment of Housing Authority’s (HA) Sui Fai Factory Estate for Residential Use”; and

·     “New Facilities Building of the Hong Kong Sports Institute (HKSI)”.

 

5.9.1.2      Since construction of the projects “Widening of Tai Po Road (Sha Tin Section)” and “Sewerage Works near Kwei Tei Street” would be completed prior to commencement of the Project construction, no cumulative environmental impacts from these two projects would be expected during the construction phase the Project.

5.9.2          Construction Phase

5.9.2.1      Based on the tentative construction programme of potential concurrent projects as detailed in Section 2.8, the construction phase of the Project would potentially overlap with that of the flood wall construction under “Drainage Improvement Works in Sha Tin and Sai Kung” during 2024 – 2029, sewage rising mains under the “Relocation of Sha Tin Sewage Treatment Works to Caverns” in 2024, “Redevelopment of Housing Authority’s (HA) Sui Fai Factory Estate for Residential Use” during 2024 – 2029 and “New Facilities Building of Hong Kong Sports Institute” in 2024.  While no confirmed construction programme of these concurrent projects is available at time of the preparation of this EIA, potential water quality impacts from these concurrent projects are expected to be localised and land-based, including construction site runoff, wastewater from general construction activities, accidental spillage and sewage from construction workforce.  With proper implementation of mitigation measures and good site practices, potential water quality impacts to downstream areas in Shing Mun River Channel would be well controlled.  No unacceptable cumulative water quality impacts from these concurrent projects would therefore be anticipated. Nontheless, during the detailed design stage, the contractor of this Project should be requested to closely liaise the contractors of these potential concurrent projects in planning the interfacing works properly to further minimise any potential cumulative impacts.

5.9.2.2      Based on the tentative construction programme of potential concurrent projects as detailed in Section 2.8, the construction of “Revitalisation of Tai Wai Nullah” and construction of bridge piers within Shing Mun River under “Revised Trunk Road T4 in Sha Tin” would overlap with that of the Project during 2024 to 2029 and 2024 to 2025 respectively.  Both concurrent projects are located over 2km from this Project.  For “Revitalisation of Tai Wai Nullah”, potential water quality impacts from this concurrent project are expected to be similar to this Project and localised that significant cumulative water quality impacts would not be expected given the large separation distance. With proper implementation of mitigation measures and good site practices, potential water quality impacts to downstream areas in Shing Mun River Channel would be well controlled.  For the construction of bridge piers within Shing Mun River under “Revised Trunk Road T4 in Sha Tin”, based on the approved EIA report (AEIAR-231/2021), the construction activities for bridge piers would be conducted by phases and all pilling and excavation works in river would be fully enclosed by cofferdam/watertight steel casing and with deployment of silt curtains to completely enclose the cofferdam/watertight steel casing prior to setting up piling works, hence, the potential water quality impacts could be mitigated and controlled by implementing the recommended mitigation measures.  As such, no unacceptable cumulative water quality impacts from these projects would be anticipated.

5.9.3          Operational Phase

5.9.3.1      The operation of flood wall proposed under “Drainage Improvement Works in Sha Tin and Sai Kung” does not constitute any elements that would be water pollution sources and would not generate any new pollution load to the catchment, no cumulative water quality impact would be expected from its operation.

5.9.3.2      The operation of underground rising mains proposed under “Relocation of Sha Tin Sewage Treatment Works to Caverns – Upstream Sewerage and Pumping Stations” does not constitute any elements that would be water pollution sources.  In addition, the planned Intermediate Sewage Pumping Station and upstream sewerage works proposed under the “Relocation of Sha Tin Sewage Treatment Works to Caverns” would have sufficient capacity to take up the addition dry weather flow intercepted by the DWFI system as detailed in Section 8.  Hence, no adverse cumulative water quality impact would be anticipated.

5.9.3.3      For the “Widening of Tai Po Road (Sha Tin Section)”, major sources of water quality impacts were expected to be paved area runoff and accidental spillage of chemicals from loaded vehicles during operational phase.  Based on the approved EIA Report (AEIAR-020/1999), no unacceptable water quality impacts from its operation would be anticipated provided that the recommended mitigation measures are implemented properly.

5.9.3.4      The nature of “Revitalisation of Tai Wai Nullah” is similar to the Project that no adverse water quality impact would be anticipated with the implementation of appropriate precautionary/control measures and good site practices during the operational phase.  Furthermore, water quality and hygiene of the nullahs would be improved by the proposed DWFI system.  

5.9.3.5      For the “Revised Trunk Road T4”, major sources of water quality impacts were expected to be non-point source surface run-off from new paved areas; and hydrodynamic and water quality impact on Shing Mun River during operational phase.  Based on the approved EIA Report (AEIAR-231/2021), no unacceptable water quality impacts from its operation would be anticipated provided that the recommended mitigation measures are implemented properly.

5.9.3.6      For the operation of “Sewerage Works near Kwei Tei Street”, “Redevelopment of Housing Authority’s (HA) Sui Fai Factory Estate for Residential Use” and “New Facilities building of Hong Kong Sports Institute”, provided that the site drainage would be properly designed and adequate sewerage works would be provided for the development in accordance with relevant guidelines (e.g. ProPECC PN 5/93) to avoid direct discharge of sewage and wastewater to the nearby drainage system and inland watercourses.  No unacceptable water quality impact would be anticipated.

5.9.3.7      As neither the Project nor the concurrent projects were anticipated to generate significant water quality impact during the operational phase, adverse cumulative water quality impacts would not be expected.

 

5.10           Evaluation of Residual Impacts

5.10.1.1    With proper implementation of mitigation measures described in Section 5.8, no adverse residual water quality impact is expected in construction and operation phases.

 

5.11           Environmental Monitoring and Audit

5.11.1.1    With proper implementation of the recommended pollution control measures, water pollution from the Project would be avoided and minimised and no adverse water quality impacts would be expectced during the construction and operational phases.  Water quality monitoring is therefore not considered necessary.  Nonetheless, regular weekly site audit during the construction phase is proposed to inspect the construction activities and works area to ensure the recommended pollution control measures are properly implemented.

 

5.12           Conclusion

5.12.1        Construction Phase

5.12.1.1    The key issues of the land-based construction works include construction works at and in close proximity to FTN / inland water, wastewater generated from general construction activities, construction site runoff, sewage from construction workforce and accidental spillage of chemicals.  The potential water quality impacts would be avoided and minimised  by implementing the recommended pollution control measures.  No adverse water quality impact during construction phase would therefore be anticipated. 

5.12.2        Operational Phase

5.12.2.1    The potential sources of water quality impacts during the operational phase would be related to non-point source surface / irrigation runoff, routine maintenance works (maintenance desilting and minor maintenance to DWFI system) and potential changes in hydrodynamics properties and hydrology.  Adequate drainage system with silt traps and oil interceptors should be incorporated into the proposed works to collect the surface / irrigation runoff.  With proper design of drainage system and implementation of the recommended pollution control measures, no adverse water quality impact from non-point source surface / irrigation run-off would be expected.  No adverse water quality impacts would be expected to occur at any identified WSRs due to the small-scale and infrequent routine maintenance works to remove excessive silts, debris and any obstructions for safeguarding the hydraulic capacity of the nullah, which practices and frequencies would be similar to the ones undertaken by DSD along FTN under existing arrangement.  Despite the reduced environmental baseflow at the nullah due to the interception of the flow with polluted discharges by the DWFI system, owing to the natural sloping gradient along FTN and the water retention and replenish designs and ecological enhancement features (e.g. wetland habitats created) within the nullah, average flow rate would remain similar to baseline condition and no unacceptable impacts on hydrodynamics properties and hydrology would be anticipated.  No adverse water quality impact during the operational phase would therefore be anticipated.