6                           WATER QUALITY

6.1                       Introduction

6.1.1.1              This section presents a water quality impact assessment of the Project, identifying the water quality issues, assessing the potential impacts and recommending mitigation measures where required.

6.1.1.2              As described in Section 3, the selected alignment of Trunk Road T2 comprises a dual 2-lane highway of about 3.0 km connecting the Central Kowloon Route (CKR) and Tseung Kwan O – Lam Tin Tunnel (TKO-LTT).  Approximately, 2.7km of the Trunk Road T2 will be in the form of tunnel with about 2.1km of the tunnel being submarine, to be formed using the Tunnel Boring Machine (TBM) approach.

6.1.1.3              As the TBM method will be used to construct the tunnel, no dredging, reclamation or filling in the marine environment will be involved. The proposed barging point, due to its previous use as a marine berth, will not require any dredging, marine works or disturbance of the seabed for its operation. The indicative alignment and the location of works area involved are illustrated in Figure 3.8.  However, water quality impacts from land based operations during the construction and operational phases may occur.  The potential water quality pollution sources are identified in Sections 6.4 and 6.5 for the construction and operational phases, respectively.

6.2                       Environmental Legislation, Standards and Guidelines

6.2.1                   Environmental Impact Assessment Ordinance (Cap. 499)

6.2.1.1              The proposed Trunk Road T2 is a Designated Project under Schedule 2 of the Environmental Impact Assessment Ordinance (EIAO).  Under Section 16 of the Ordinance, the Environmental Protection Department (EPD) issued the Technical Memorandum on Environmental Impact Assessment Process (TM-EIAO) which specifies the assessment methods and criteria for the EIA.  This study will follow the TM-EIAO to assess the potential water quality impacts that may arise during the construction and operational phases of the Project.  Annexes 6 and 14 of the TM-EIAO stipulate the “Criteria for Evaluating Water Pollution” and “Guidelines for the Assessment of Water Pollution” respectively.

6.2.2                   Water Pollution Control Ordinance (Cap. 358)

6.2.2.1              The Water Pollution Control Ordinance (WPCO) is the principal legislation governing marine water quality in Hong Kong.  Under the provisions of this Ordinance and its subsidiary legislation, Hong Kong’s waters have been divided into a series of 10 Water Control Zones (WCZs). In each WCZ, Water Quality Objectives (WQOs) have been specified to protect the specific beneficial uses and conservation goals of each of the WCZs.

6.2.2.2              Within the water quality assessment area stated in the Study Brief, there are 15 water quality monitoring stations regularly monitored as part of the EPD’s Routine Monitoring Programme. As noted above, due to the absence of construction works within the marine environment or permanent structures that would protrude above the seabed and potentially affect water flows, any run-off impacts should be contained to within the Victoria Harbour Water Control Zone. The water quality data from the stations within Victoria Harbour WCZ nearest to the Trunk Road T2 project area will be used to define the existing water quality, as detailed in Section 6.3 below.

6.2.2.3              Within the Victoria Harbour (VH) WCZ where the Project is located, there are no bathing beaches, secondary contact recreational areas or fish culture zones. However, such areas are found in the Western Buffer (WB) and Eastern Buffer (EB) WCZs.  There is a secondary contact recreational area at the western coast of Junk Bay.  Given the project will not cause any disturbance to the seabed, impacts from land based activities are, therefore, expected to be confined to the immediate waters surrounding the South Apron and Cha Kwo Ling shoreline in the VH WCZ and  impacts to the WB WCZ and EB WCZ are not predicted.  Notwithstanding, Table 6.1 lists all the WQOs in the marine environment for the three WCZs.

Table 6.1    Water Quality Objectives

Water Quality Objectives

WB WCZ

VH WCZ

EB WCZ

Aesthetic Appearance

    There should be no objectionable odours or discolouration of the water.

P

P

P

    Tarry residues, floating wood, articles made of glass, plastic, rubber or any other substances should be absent.

P

P

P

    Mineral oil should not be visible on the surface.

P

P

P

     Surfactants should not give rise to a lasting foam.

P

P

P

    There should be no recognisable sewage derived debris.

P

P

P

    Floating, submerged and semi-submerged objects of a size likely to interfere with the free movement of vessels, or cause damage to vessels, should be absent.

P

P

P

    The water should not contain substances which settle to form objectionable deposits.

P

P

P

Bacteria

    The levels of E. coli should not exceed 180 counts per 100 ml at bathing beaches, calculated as the geometric mean of all samples collected from March to October inclusive. Samples have to be taken at least 3 times a month at intervals of between 3 and 14 days.

P

 

 

    The levels of E. coli should not exceed 610 counts per 100 ml at secondary contact recreation sub-zones, calculated as the geometric annual mean.

P

 

 

    The levels of E. coli should not exceed 610 counts per 100 ml at fish culture sub-zones, calculated as the geometric annual mean.

P

 

P

Dissolved Oxygen

    The depth averaged concentration of dissolved oxygen should not fall below 4 mg/l for 90% of the sampling occasions during the whole year

P

P

P

    The concentration of dissolved oxygen (bottom) should not be less than 2 mg/l within 2m of the seabed for 90% of the sampling occasions during the whole year.

P

P

P

    At fish culture subzones, the depth averaged concentration of dissolved oxygen should not fall below 5 mg/l for 90% of the sampling occasions during the whole year

P

 

P

pH

    The pH of the water should be within the range 6.5-8.5 units.

P

P

P

    Human activity should not cause the natural pH range to be extended by more than 0.2 units.

P

P

P

Temperature

    Human activity shall not cause the natural daily temperature range to change by more than 2.0°C.

P

P

P

Salinity

    Human activity shall not cause the natural ambient salinity to change by more than 10%.

P

P

P

Suspended Solids

    Human activity should neither cause the natural ambient level to be raised by more than 30% nor give rise to accumulation of suspended solids which may adversely affect aquatic communities

P

P

P

Ammonia

    The un-ionised ammoniacal nitrogen level should not be more than 0.021 mg/l calculated as the annual average (arithmetic mean).

P

P

P

Nutrients

    Nutrients should not be present in quantities sufficient to cause excessive or nuisance growth of algae or other aquatic plants; and

P

P

P

    Without limiting the generality of the above point, the level of inorganic nitrogen should not exceed 0.4 mg/l expressed as the annual water column average.

P

P

P

Toxins

    Toxic substances in the water should not attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms, with due regard to biologically cumulative effects in food chains and to interactions of toxic substances with each other.

P

P

P

    Human activity shall not cause a risk to any beneficial use of the aquatic environment. 

P

P

P

WB WCZ = Western Buffer Water Control Zone; VH WCZ = Victoria Harbour Water Control Zone; EB WCZ = Eastern Buffer Water Control Zone.

6.2.3                   Water Supplies Department Water Quality Criteria

6.2.3.1              Besides the WQO set under the WPCO, the Water Supplies Department (WSD) has also specified a set of seawater quality objectives for water quality at their flushing water intakes as detailed in Table 6.2 below.

Table 6.2    WSD Standards at Flushing Water Intakes

Parameter (mg/L, unless otherwise stated)

WSD Target Limit

Colour (Hazen Unit)

< 20

Turbidity (NTU)

< 10

Threshold Odour Number (odour unit)

< 100

Ammoniacal Nitrogen

< 1

Suspended Solids

< 10

Dissolved Oxygen

> 2

Biochemical Oxygen Demand

< 10

Synthetic Detergents

< 5

E.coli (no. / 100 ml)

< 20,000

6.2.4                   Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems

6.2.4.1              Discharges of effluents are 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) sets limits for effluent discharges.  Specific limits apply for different areas and are different between surface waters and sewers.  Any effluent from the Project must comply with the standards for effluents discharged into the four sewers, inshore water or marine waters of the Victoria Harbour WCZ.

6.2.4.2              The limits vary with the rate of effluent flow.  Standards for effluent discharged into the inshore waters and marine waters of the Victoria Harbour WCZ are summarised in Tables 6.3 and 6.4 below, respectively.


Table 6.3     Standards for Effluents Discharged into the Inshore Waters of Victoria Harbour Water Control Zone

Determinant

Flow rate (m3/day)

≦10

＞10 and ≦200

＞200 and ≦400

＞400 and ≦600

＞600 and ≦800

＞800 and ≦1000

＞1000 and ≦1500

＞1500 and ≦2000

＞2000 and ≦3000

＞3000 and ≦4000

＞4000 and ≦5000

＞5000 and ≦6000

pH (pH units)

6-9

6-9

6-9

6-9

6-9

6-9

6-9

6-9

6-9

6-9

6-9

6-9

Temperature (°C)

40

40

40

40

40

40

40

40

40

40

40

40

Colour (lovibond units) (25mm cell length)

1

1

1

1

1

1

1

1

1

1

 

1

1

Suspended solids

50

30

30

30

30

30

30

30

30

30

30

30

BOD

50

20

20

20

20

20

20

20

20

20

20

20

COD

100

80

80

80

80

80

80

80

80

80

80

80

Oil & Grease

30

20

20

20

20

20

20

20

20

20

20

20

Iron

15

10

10

7

5

4

2.7

2

1.3

1

08

0.6

Boron

5

4

3

2.7

2

1.6

1.1

0.8

0.5

0.4

0.3

0.2

Barium

5

4

3

2.7

2

1.6

1.1

0.8

0.5

0.4

0.3

0.2

Mercury

0.1

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

Cadmium

0.1

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

Other toxic metals individually

1

1

0.8

0.7

0.5

0.4

0.25

0.2

0.15

0.1

0.1

0.1

Total toxic metals

2

2

1.6

1.4

1

0.8

0.5

0.4

0.3

0.2

0.14

0.1

Cyanide

0.2

0.1

0.1

0.1

0.1

0.1

0.05

0.05

0.03

0.02

0.02

0.01

Phenols

0.5

0.5

0.5

0.3

0.25

0.2

0.13

0.1

0.1

0.1

0.1

0.1

Sulphide

5

5

5

5

5

5

2.5

2.5

1.5

1

1

0.5

Total residual chlorine

1

1

1

1

1

1

1

1

1

1

1

1

Total nitrogen

100

100

100

100

100

100

80

80

50

50

50

50

Total phosphorus

10

10

10

10

10

10

8

8

5

5

5

5

Surfactants (total)

20

15

15

15

15

15

10

10

10

10

10

10

E. coli (count/100ml)

5000

5000

5000

5000

5000

5000

5000

5000

5000

5000

5000

5000

Table 6.4     Standards for Effluents Discharged into the Marine Waters of Victoria Harbour Water Control Zone

Determinant

Flow rate (m3/day)

≦10

＞10 and ≦200

＞200 and ≦400

＞400 and ≦600

＞600 and ≦800

＞800 and ≦1000

＞1000 and ≦1500

＞1500 and ≦2000

＞2000 and ≦3000

＞3000 and ≦4000

＞4000 and ≦5000

＞5000 and ≦6000

pH (pH units)

6-10

6-10

6-10

6-10

6-10

6-10

6-10

6-10

6-10

6-10

6-10

6-10

Temperature (°C)

45

45

45

45

45

45

45

45

45

45

45

45

Colour (lovibond units) (25mm cell length)

4

1

1

1

1

1

1

1

1

1

 

1

1

Suspended solids

700

600

600

500

375

300

200

150

100

75

60

40

BOD

700

600

600

500

375

300

200

150

100

75

60

40

COD

1500

1200

1200

1000

700

600

400

300

200

100

100

85

Oil & Grease

50

50

50

30

25

20

20

20

20

20

20

20

Iron

20

15

13

10

7.5

6

4

3

2

1.5

1.2

1

Boron

6

5

4

3.5

2.5

2

1.5

1

0.7

0.5

0.4

0.3

Barium

6

5

4

3.5

2.5

2

1.5

1

0.7

0.5

0.4

0.3

Mercury

0.1

0.001

0.05

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

Cadmium

0.1

0.001

0.05

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

Other toxic metals individually

2

1.5

1

0.8

0.6

0.5

0.32

0.24

0.16

0.12

0.1

0.1

Total toxic metals

4

3

2

1.6

1.2

1

0.64

0.48

0.32

0.24

0.2

0.14

Cyanide

1

0.5

0.5

0.5

0.4

0.3

0.2

0.1

0.1

0.08

0.06

0.04

Phenols

0.5

0.5

0.5

0.3

0.3

0.2

0.1

0.1

0.1

0.1

0.1

0.1

Sulphide

5

5

5

5

5

5

2.5

2.5

1.5

1

1

0.5

Total residual chlorine

1

1

1

1

1

1

1

1

1

1

1

1

Total nitrogen

100

100

100

100

100

100

100

100

100

100

100

100

Total phosphorus

10

10

10

10

10

10

10

10

10

10

10

5

Surfactants (total)

30

20

20

20

15

15

15

15

15

15

15

15

E. coli (count/100ml)

5000

5000

5000

5000

5000

5000

5000

5000

5000

5000

5000

5000

 

6.2.5                   Practice Note for Professional Persons on Construction Site Drainage

6.2.5.1              The Practice Note for Professional Persons on Construction Site Drainage (ProPECC Note PN1/94) provides guidelines for the handling and disposal of construction discharges. This note is applicable to the control of site runoff and wastewater generated during the construction phase of the Project.  The types of discharges from construction sites outlined in the ProPECC Note PN1/94 that could be relevant to this project would include:

·           Surface run-off;

·           Boring and drilling water;

·           Wheel washing water; and

·           Wastewater from construction activities and site facilities.

6.2.5.2              Practices given in PN 1/94 shall be followed as far as possible during construction to minimise potential water quality impacts due to construction activities.

6.2.5.3              In addition, other ProPECC Notes including ProPECC PN 5/93 Drainage Plan would, also, be considered.

6.3                       Existing Environment

6.3.1                   Assessment Area

6.3.1.1              The project alignment is located at the waters between Kwun Tong Typhoon Shelter (KTTS) and Cha Kwo Ling (CKL) waterfront within the Victoria Harbour. As defined in the EIA Study Brief, the assessment area shall include the Victoria Harbour (VH) Water Control Zone (WCZ), the Eastern Buffer (EB) WCZ and the Western Buffer (WB) WCZ as declared under the Water Pollution Control Ordinance (WPCO) (Figure 6.1), any areas within a distance of 300m from either side and along the full length of the project boundary and from any Project related work areas (Table 3.1).  This study area may be extended to include other areas if they are found being impacted during the course of the EIA and have a bearing on the environmental acceptability of the Project.

6.3.1.2            However, as detailed in Section 3, the Tunnel Boring Machine (TBM) method has been determined as feasible for the construction of the subsea tunnel and is the most environmental preferred method (Section 2).  As such, the tunnel will not be formed by Immersed Tube (IMT) and based on the TBM method, no marine works that would disturb the seabed or marine waters would be required as a result of the construction of the proposed project.

6.3.1.3              One barging point, located on the southern edge of the South Apron of the ex-Kai Tak Airport (see Figure 3.6), has been proposed to be used for marine transportation of plant and disposal of excavated materials generated from the Project to suitable disposal sites.  However, the planned barging point was previously utilised as a cargo handling area by WSD for the transportation of liquid chlorine and has only recently become idle.  As detailed in Section 3.6, the proposed barging point, due to its previous use as a marine berth, will not require any dredging or marine works for its construction or operation.

6.3.1.4              Notwithstanding the above, potential indirect off-site impacts as a result of construction site runoff and chemical waste spillage (e.g. oil and other pollutants from mechanical equipment), could occur.  However, such impacts would be localised to the waters around the work site, that is Kai Tak Approach Channel (KTAC), Kwun Tong Typhoon Shelter (KTTS) and the Kwun Tong-Cha Kwo Ling Waterfront, all within the Victoria Harbour WCZ and, therefore, these areas form the focus of this water quality assessment.

6.3.2                   Water Sensitive Receivers

6.3.2.1              The study area for the water quality impact assessment is delineated within 300m from  the proposed Trunk Road T2 alignment site boundary and barging point (Figure 6.2), which would cover the relevant existing and potential water sensitive receivers (WSRs) as shown in Table 6.5 below and that would have a bearing on the environmental acceptability of the project.  Due to the highly urbanised nature of Kowloon Peninsula, there are no natural streams located within 300m from the alignment. There are, also, no marine biological sensitive receivers such as fish culture zones, shellfish culture grounds, marine parks/reserves or commercial fishing grounds identified within the Victoria Harbour WCZ.   However, a number of seawater abstraction points for flushing and cooling are identified.  The locations of these WSRs are shown in Figure 6.2.

Table 6.5    Relevant Water Sensitive Receivers

WSR No.*

Water Sensitive Receivers (WSRs)

Distance from Project Boundary (m)

WSR 1

Yau Tong WSD Flushing Water Intake

890

WSR 2

Cha Kwo Ling WSD Flushing Water Intake

74

WSR 3

Sai Wan Ho WSD Flushing Water Intake

1241

WSR 4

Quarry Bay WSD Flushing Water Intake

1231

WSR 5

Cooling Water Intake for Yau Tong Bay Ice Plant

170

WSR 6

Kwun Tong Typhoon Shelter

335

WSR 7

To Kwa Wan Typhoon Shelter

630

WSR 8

Tai Wan WSD Flushing Water Intake

1870

WSR 11

Cooling Water Intake for Kai Tak DCS

223

WSR 12

North Point WSD Flushing Water Intake

2167

WSR 13

Provident Centre Cooling Water Intake

2337

WSR 14

City Garden Cooling Water Intake

2551

WSR 15

North Point Gov. Office Cooling Water Intake

1343

WSR 16

Taikoo Place Cooling Water Intake

1337

WSR 17

Shau Kai Wan Typhoon Shelter

1455

Notes *: WSR Nos. 9 and 10 are not used

 

6.3.2.2              WSR2 and WSR6 are the only sensitive receivers located within the 300m Study Area for the water quality assessment.   While WSRs 5, 7 and 11 are at an intermediate distance, within 650m of the Trunk Road T2 project boundary, the remaining WSRs are located along the coastline of Hong Kong Island and are distant from the project.

6.3.3                   Existing Water Quality

6.3.3.1              The existing water quality in the Study Area has been monitored for many years as part of the EPD’s routine monitoring programme. The EPD’s marine water quality monitoring stations within the Victoria Harbour WCZ nearest to the Trunk Road T2 project area include VM1, VM2 and VT4 (inside the Kwun Tong Typhoon Shelter), as shown in Figure 6.2.   A summary of the EPD’s Routine Water Quality Data for these stations for the years 2010 and 2011 (EPD, 2011; EPD, 2012) is given in Table 6.6 below.

Table 6.6     Summary of EPD’s Routine Water Quality Data (VM1, VM2 and VT4) for Victoria Harbour WCZ (Kwun Tong Typhoon Shelter) (2010-2011)

Parameters

Monitoring Station

VM1

VM2

VT4

2010

2011

2010

2011

2010

2011

Temperature (°C)

22.8

(16.5-27.3)

22.2

(15.8-26.4)

23.0

(16.5-27.3)

22.5

(16.1-26.7)

23.8

(18.3-28.3)

22.7

(16.8-26.0)

Salinity (ppt)

32.0

(29.2-33.6)

32.6

(30.0-33.5)

31.7

(29.1-33.7)

32.2

(29.2-33.5)

29.4

(22.9-31.6)

31.3

(30.1-32.2)

Dissolved Oxygen (mg/L)

5.6

(3.3-7.6)

5.5

(3.3-7.5)

5.4

(3.5-6.7)

5.4

(3.8-7.5)

5.2

(2.1-7.5)

3.9

(2.6-5.1)

Bottom Dissolved Oxygen (mg/L)

4.8

(1.1-6.3)

5.5

(2.9-7.6)

4.8

(1.2-6.4)

5.4

(3.5-7.6)

5.9

(2.6-8.4)

3.6

(1.8-6.0)

SS (mg/L)

4.0

(1.4-8.1)

4.5

(2.5-8.5)

3.6

(0.9-7.6)

3.7

(2.1-6.9)

5.0

(1.6-16.7)

2.7

(1.5-4.6)

BOD5 (mg/L)

0.7

(<0.1-1.2)

0.6

(0.2-1.4)

0.9

(<0.1-1.6)

0.8

(0.3-1.4)

1.8

(1.5-2.6)

2.1

(1.0-3.6)

Unionised NH3

(mg/L)

0.003

(<0.001-0.010)

0.002

(<0.001-0.005)

0.004

(<0.001-0.011)

0.004

(0.001-0.008)

0.011

(0.005-0.022)

0.007

(0.003-0.017)

TIN (mg/L)

0.20

(0.09-0.32)

0.22

(0.13-0.36)

0.27

(0.10-0.40)

0.31

(0.20-0.50)

1.03

(0.55-1.81)

1.09

(0.72-1.59)

Ortho-P

(mg/L)

0.020

(0.010-0.036)

0.019

(0.012-0.027)

0.024

(0.011-0.039)

0.027

(0.012-0.036)

0.140

(0.080-0.186)

0.224

(0.116-0.388)

Total P

(mg/L)

0.03

(0.02-0.06)

0.04

(0.03-0.05)

0.04

(0.02-0.05)

0.04

(0.03-0.06)

0.17

(0.10-0.22)

0.26

(0.13-0.41)

Chlorophyll-a (mg/L)

2.8

(0.5-12.2)

1.8

(0.5-5.0)

3.3

(0.5-15.4)

2.3

(0.4-9.1)

13.9

(1.0-26.7)

12.7

(1.0-41.0)

E. coli (cfu/100mL)

710

(180-4400)

120

(7-430)

2000

(420-17000)

710

(60-11000)

820

(330-6000)

1200

(380-8300)

Notes: [1] Data presented are depth averaged (except as specified) and are the annual arithmetic mean except for E. coli (geometric mean); [2] Data in brackets indicate ranges; [3] Underlined indicates occurrence of non-compliance with that parameter of WQO.


6.3.4                   Assessment Methodology

6.3.4.1              The assessment approach was based on the requirements as specified in the EIA Study Brief (ESB-188/2008).  The criteria and guidelines for assessing water quality impacts as stated in Annexes 6 and 14 of the EIAO-TM have been followed. The identification and assessment of water pollution impacts during the construction and operational phases has taken into account the following factors:

·           water quality of the water bodies with the potential to be affected;

·           the hydrology of the aquatic systems; and

·           the supported aquatic ecology.

6.3.4.2              An analysis has been undertaken of the potential impacts on the sensitive receivers taking into account both point and non-point sources of potential water pollutants during the construction and operational phases of the project.  The scope of the assessment extends to direct and indirect impacts on all the water courses potentially affected by the proposed works.  The identified potential pollution sources are discussed in Sections 6.4 and 6.5 for the construction and operational phases, respectively.

6.3.4.3              The aim of the assessment has been to maintain the balance and integrity of the water courses as far as possible through prevention and minimisation of impacts at source in order to:

·           maintain the natural properties of the water body;

·           maintain the hydrological factors;

·           control any discharges to within the relevant Water Quality Objectives;

·           maintain the physical environment as far as practicable;

·           protect aquatic ecology; and

·           protect any beneficial uses.

6.3.4.4              Specific construction methods and configurations, and the operation of the Trunk Road T2 project have been reviewed to identify any alteration of the adjacent water courses, drainage systems, groundwater hydrology and catchment types or areas would occur.

6.4                     Construction Phase Impact Assessment

6.4.1                   Identification of Pollution Sources

6.4.1.1              As noted in Section 6.1 above, and detailed in Section 3, based upon the adoption of the TBM tunnelling method, there will be no dredging, no reclamation nor any disturbance to the seabed required for the construction of the Trunk Road T2 subsea tunnel. In addition, use of an existing berth for the barging point will, also, negate the need to disturb the marine environment and, therefore, no construction of a marine working platform or reclamation for barging point is required.  The Trunk Road T2 project would, however, entail land based works to construct the tunnel portals, land based road sections and mucking out of the subsea tunnel spoil, all of which could have the potential for water quality impacts.  The main water quality related issue will be to prevent erosion on site and minimise suspended sediment loads being washed out via the storm water drains, as well as the need to control waste water streams such as cementitious waters, bentonite slurries and general construction refuse.  Control of the construction phase sewage generation could, also, be an issue and toilets will need to be connected to the local sewerage system if possible during construction. 

6.4.1.2              Based on the above, water quality issues during the construction phase may arise due to the following potential pollution sources:

·           Construction site run-off causing the increase in suspended solids levels and possibly oils due to erosion of exposed surfaces, stockpiles and material storage areas, fuel and oil storage and dust suppression sprays;

·           Wastewater due to retaining wall, piling works, tunnelling works and underground construction works including bentonite slurry;

·           Potential Impacts on the groundwater hydrology through pumping and tunnelling, resulting in drawdown and settlement;

·           Sewage effluent from construction workforce;

·            Accidental spillage of chemicals; and

·           Litter from packaging materials and waste construction materials.

6.4.2                   Avoidance and Minimisation of Impacts

6.4.2.1              The proposed alignment and chosen construction methods have already substantially reduced potential water quality impacts by design as summarised below:

·           adoption of the TBM for the subsea tunnel construction which will avoid all direct disturbance to the seabed and marine environment;

·           no works will affect existing watercourses as none are present within the assessment area; and

·           the project boundary and Works Areas have been minimised as far as possible, thereby minimising the extent of excavation works, and, therefore, the potential for construction run-off.

6.4.3                   Construction Run-off

6.4.3.1              Construction run-off may cause physical, biological and chemical effects. The physical effects include potential blockage of drainage channels and increase suspended solids (SS) levels in the Victoria Harbour WCZ.  Local flooding may also occur in heavy rainfall situations. The chemical and biological effects caused by the construction runoff are highly dependent upon its SS level and pH value.  Run-off containing significant amounts of concrete and cement-derived material may cause primary chemical effects such as increasing turbidity and discoloration, elevation in pH, and accretion of solids. A number of secondary effects may also result in toxic effects to water biota due to elevated pH values, and reduced decay rates of faecal micro-organisms and photosynthetic rate due to the decreased light penetration. 

6.4.3.2              The potential construction site run-off comprises surface run-off that may be contaminated and turbid as a result of erosion from site surfaces, drainage channels, earth working areas and stockpiles and/or release of concrete washing and chemical grouting into construction run-off and storm water. Such wastewater may include wastewater resulting from dust suppression sprays and wheel washing of site vehicles at site entrances.  Run-off waters may enter the adjacent marine waters and storm water drainage system and, therefore, effluent discharge from temporary site facilities should be controlled.

6.4.3.3              Approximately 2.1km of the 3.0km Trunk Road T2 alignment will be in the form of subsea tunnel constructed by TBM, substantially reducing the potential for surface water run-off from excavation, works areas and stockpiles.  Perimeter cut-off drains to direct off-site water around the site and all Works Areas, and prevent it becoming contaminated, will be constructed, with internal drainage works and erosion and sedimentation control facilities implemented.  Catch-pits and perimeter channels would be constructed in advance of site formation works and earthworks.

6.4.3.4              Stockpiling areas, located in Works Areas WA3 and WA4 (see Table 3.1 and Figure 3.8), are places that have a higher potential to generate contaminated run-off as there will be open storage of excavated materials over a relatively large footprint and each are located relatively close to the seawall.  The stockpiling of the excavated soil for subsequent backfilling or for off-site disposal is of particular concern as the earthed material can enter the marine waters due to wind erosion or as a result of being wash away by water (from rain or dust control spraying).  Specific mitigation measures for lowering the risk of contaminated site-runoff from these areas will be required.  It is proposed that each of the stockpile Works Areas, WA3 and WA4, will be contained by site hoarding which will be sealed to contain any run-off within the site and a perimeter drainage system applied to collect any run-off such that it can be desilted and treated prior to any discharge. 

6.4.3.5              Overall, the extent of the above ground excavation works and stockpiling areas are not substantial, confined to a compact project area, and the works in both the South Apron and in Cha Kwo Ling will be undertaken on land that is already disturbed. As such, the works are not expected to significantly increase the area of impermeable surfaces which would cause a significant increase in the volume of run-off during any given rainfall event. 

6.4.3.6              However, assuming the run-off is assimilated into the receiving waters within the KTTS or off the Cha Kwo Ling Coastline into the Victoria Harbour within say 100m from the potential discharge location and based on the latest HKO tidal data of Year 2011 recorded at the nearest monitoring station in Quarry Bay, the mean tidal volume (that is, the increase in volume between low tide and high tide) of the area inshore of this 100m line is estimated to be about 50,000m3 at the South Apron and 37,000m3 at Cha Kwo Ling depending on the tide type.  The total run-off from construction works would be expected to be a fraction of this amount and, therefore, large levels of dilution would be expected.  Any suspended solids would, also, be predicted to be dispersed and settle out rapidly.

6.4.3.7              Bearing in mind the dilution rates which would be achieved, the run-off should not result in a significant increase in the concentrations of SS and associated contaminants.  The total contaminant load in the run-off will represent a small increase in the natural contaminant load and should not result in a significant detrimental impact on marine water quality especially when the small rainfall volumes with respect to the tidal volume are taken into account.  Based upon these factors, significant effects on the water quality are not predicted. 

6.4.3.8              Notwithstanding, some specific mitigation measures, together with the implementation of good construction site practices, are recommended, however, to reduce the suspended solid concentrations to a minimum and with the implementation of these measures, adverse water quality impacts on the WSRs as listed in Table 6.5 would not be anticipated.  These land based mitigation measures are detailed in Section 6.4.9 below.

6.4.4                   Wastewater Discharge from Tunnelling and Excavation

6.4.4.1              The tunnel of the Trunk Road T2 Project would mainly be constructed subsea by TBM method, although two sections of cut and cover tunnel will be constructed at the South Apron and within the Cha Kwo Ling Public Cargo Working Area (PWCA).  A section of depressed road is, also, proposed on the South Apron.  The key potential source of water quality impact from these tunnelling and excavation works would be from the dewatering operations resulting from water infiltration.  Wastewater from these tunnelling and excavation works would contain a high content of suspended solids, concrete washings and chemical grouting.  Concrete washings are potentially toxic to aquatic organisms, raising pH of the receiving water bodies and, also, increase the turbidity in a water body.

6.4.4.2              The quantity of wastewater produced daily from the dewatering of the tunnelling works and excavation works would depend on the volume and type of excavation carried out.  The estimated maximum rate of wastewater to be discharged from tunnelling works and excavation during construction for treatment, that is, chemically enhanced sedimentation, before discharge into the storm water drains have been estimated and are shown in Table 6.7 below for the various works sites. 

Table 6.7    Wastewater Discharge from Tunnelling and Excavation during Construction Phase

Works

Maximum Rate of Wastewater Discharge (L/s/m2)

Depressed Road

0.8

Cut and Cover Sections

0.8

TBM Launching and Receiving Shafts

0.8

 

6.4.4.3              In order to limit the potential water infiltration into the TBM launching/receiving pits and excavation works, the following design measures have been proposed:

·           top slab is proposed to be constructed over the cut and cover section during construction with a small access for equipment and materials only.  The top slab of this section of tunnel will be constructed prior to installation of the TBM equipment train with an access opening left in the slab above the centreline of carriageway. A shaft will be constructed from this top slab up to ground level to create a shaft for both spoil removal and equipment delivery for tunnel construction. The remainder of the excavation will be backfilled up to ground level and capped with a concrete slab as the foundation slab for the TBM ancillary works. The shaft walls will project above the surrounding ground level to provide a safety barrier to the edges of the shaft and prevent water flow into the excavation works; and

·           the TBM launching shaft has been minimised to a footprint of 140m x 45m and up to 70m will be backfilled as soon as practicable after the creation of the space below ground to accommodate the TBM and its equipment train, therefore, reducing the potential to generate contaminated run-off from the pit.

6.4.4.4              However, dewatering of the excavation works areas will be required.   All practical measures would be taken to minimise the ingress of rainwater into trenches and excavation works including the use of perimeter drains and catch pits to prevent run-off entering the excavations.  Also, the excavation works will be dug and backfilled in as short sections as practicable.  All rainwater pumped out from the trenches and excavations will be treated via silt removal facilities prior to discharge to the storm water system.  It is considered that impacts would not be significant with the application of good site practices as detailed in Section 6.4.9 below. 

6.4.4.5              Bentonite will be used in the construction of the diaphragm walls used in the cut and cover tunnel sections on the South Apron and at Cha Kwo Ling before the Trunk Road T2 tunnel interfaces with the TKO-LTT project.  Bentonite is non-toxic but highly turbid and could cause damage to aquatic organisms in receiving waters.   Given that the accidental release of bentonite slurry could lead to a higher level of impacts than other site run-off, the material needs to be controlled.  The used bentonite slurry from the diaphragm walls will be collected and transferred to a desander treatment plant for cleaning and subsequent recycling and reuse.  Specific mitigation measures for the control of bentonite fluid are, also, recommended as detailed in Section 6.4.9 below.

6.4.4.6              Proper treatment of the wastewater by chemically-enhanced sedimentation and concrete washings by optimising the pH will be required to prior to disposal if required. 

6.4.4.7                With reference to the findings of the site investigation for land contamination in Section 11 of this EIA report, there would be no contamination of groundwater determined within the project study area.  However, if contaminated groundwater is found during the course of the works, no direct discharge of groundwater from contaminated areas should be adopted.  Any contaminated groundwater should be properly treated in compliance with the requirements of the Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS).  

6.4.4.8                If wastewater treatment is to be deployed for treating the contaminated groundwater, the wastewater treatment unit should deploy suitable treatment processes (e.g. oil interceptor/activated carbon) to reduce the pollution level to an acceptable standard and remove any prohibited substances (such as TPH) to an undetectable range. All treated effluent from wastewater treatment plant shall meet the requirements as stated in TM-DSS and should be discharged into the foul sewers.

6.4.4.9              If groundwater recharging wells are deployed, recharging wells should be installed as appropriate for recharging the contaminated groundwater back into the ground. The recharging wells should be selected at places where the groundwater quality will not be affected by the recharge operation as indicated in the Section 2.3 of TM-DSS. The baseline groundwater quality shall be determined prior to the selection of the recharge wells, and submit a working plan (including the laboratory analytical results showing the quality of groundwater at the proposed recharge location(s) as well as the pollutant levels of groundwater to be recharged) to EPD for agreement.  Pollution levels of groundwater to be recharged shall not be higher than pollutant levels of ambient groundwater at the recharge well. Prior to recharge, any prohibited substances such as TPH products should be removed as necessary by installing the petrol interceptor. The Contractor should apply for a discharge licence under the WPCO through the Regional Office of EPD for groundwater recharge operation or discharge of treated groundwater.

6.4.4.10          The wastewater is proposed for treatment and reuse after sedimentation as far as practicable.  When there is a need for final disposal, the wastewater would be discharged into storm drains with after treatment with silt removal facilities.  Wastewater discharging into storm drains should comply with the standards stipulated in the TM-DSS or should be tankered away for proper disposal. 

6.4.4.11          In respect of the subsea tunnel itself, no dewatering will be required.  The system will be a closed shield and balancing water with slurry so there will be no-inflow and, hence, no need dewatering or waste water generation for treatment.  However, the excavated alluvium spoil will be wet and mixed with bentonite into a slurry.  As noted above, bentonite is highly turbid and could cause damage to aquatic organisms in receiving waters if directly discharged during the extraction of the bentonite or preparation for recycling or disposal. 

6.4.4.12          The excavated alluvium will be sent to the TBM ancillary facilities so that the material can be dried and pressed to remove excess water and to extract the bentonite fluid.  The wastewater will be treated in the slurry treatment plant at the South Apron prior to the cleaned bentonite being returned to the TBM system for re-use and the treated water which should comply with the standards stipulated in the TM-DSS being disposed of into the local drainage network. 

6.4.4.13          Potential impacts from the waste water generated from the tunnelling and excavation works are expected to be controlled to within acceptable levels by the implementation of good site practices.   With implementation of the mitigation measures, adverse water quality impacts on the WSRs as listed in Table 6.5 would not be anticipated. 

6.4.5                   Sewage Effluent

6.4.5.1              Sewage effluents will arise from the sanitary facilities provided for the on-site construction workforce. The characteristics of sewage would include high levels of BOD5, ammonia and E. coli counts.  It is estimated that there will be a temporary workforce of about 500 people during the construction stage.  Therefore, control of construction phase sewage will be an issue and toilets at the site offices will be connected to the local sewerage system which has sufficient capacity given the former airport or cargo operations on the site.  If necessary, chemical toilets will, also, be provided.  Based on the use of the existing sewerage system and the chemical toilets being managed by a licenced Contractor, adverse water quality impacts on the WSRs as listed in Table 6.5 are not predicted.

6.4.6                   Accidental Spillages

6.4.6.1              The use of mechanical plant during construction will inevitably require refuelling, together with fuel, oil and lubricant storage and maintenance areas.  The use of engine oil and lubricants, and their storage as waste materials has the potential to create impacts on the water quality of adjacent water courses if spillage occurs and enters watercourses.  Waste oil may infiltrate into the surface soil layer, or run-off into local water bodies, increasing hydrocarbon levels. As a consequence, there is the risk of spillage and leakage of the runoff into the adjacent Kai Tak Approach Channel (KTAC) and Kwun Tong Typhoon Shelter (KTTS) and during rainfall and from vehicle wheel and sub-frame washing areas for vehicles leaving and entering the site.

6.4.6.2              Specific works areas for material storage and maintenance works have been defined and Works Areas WA1, WA2, WA4 and WA5 are proposed to be used for plant maintenance (see Table 3.1).  The marine waters surrounding these works areas will be sensitive to impacts from plant maintenance activities and mitigation measures, in the form of perimeter drains and temporary oil and silt traps, will be required to limit water quality impacts and maintain the water quality conditions in the marine waters and avoid pollution of the storm water drains.  Recommended mitigation measures are detailed in Section 6.4.9 below.  It is expected that with the implementation of these measures, any adverse impacts will be reduced to within acceptable levels. 

6.4.6.3              Notwithstanding, in order to protect against impacts to the surrounding marine waters of the KTTS and Victoria Harbour in the event of an accidental spillage of fuel or oil, the Contractor will be required to prepare a spill response plan to the satisfaction of AFCD, EPD, FSD, Police, TD and WSD to define procedures for the control, containment and clean-up of any spillage that could occur on the construction site.

6.4.7                   Waste Construction Materials

6.4.7.1              Waste construction materials will include the generation of waste packaging, rubbish from eating areas and waste disposal areas.  Although the impact will be temporary, the additional population may impose significant stress on the quality of water in the surrounding marine environment with the absence of adequate mitigation. The effects of litter and waste construction material can, also, be limited by the use of good site management practices, as detailed in Section 6.4.9 below.

6.4.8                   Construction Phase Mitigation Measures

Construction Site Run-off and General Construction Activities

6.4.8.1              In accordance with the Practice Note for Professional Persons on Construction Site Drainage, Environmental Protection Department, 1994 (ProPECC PN 1/94), construction phase mitigation measures shall include the following:

·           Surface run-off from the construction site, including all Works Areas, will be discharged into storm drains via adequately designed sand/silt removal facilities such as sand traps, silt traps and sedimentation basins. At the establishment of works sites and works areas including the barging point, perimeter cut-off drains to direct off-site water around the site should be constructed with internal drainage works and erosion and sedimentation control facilities implemented.  Channels (both temporary and permanent drainage pipes and culverts), earth bunds or sand bag barriers should be provided to divert the storm water to the silt removal facilities.  The design of the temporary on-site drainage system will be undertaken by the Contractor prior to the commencement of construction and the catch-pits and perimeter channels would be constructed in advance of site formation works and earthworks; 

·           Dikes or embankments for flood protection should be implemented around the boundaries of earthwork areas and Works Areas. Temporary ditches should be provided to facilitate the runoff discharge into an appropriate watercourse, through a site/sediment trap;

·           The design of efficient silt removal facilities should be based on the guidelines in Appendix A1 of ProPECC PN 1/94, which states that the retention time for silt/sand traps should be 5 minutes under maximum flow conditions.  The sizes may vary depending upon the flow rate, but for a flow rate of 0.1m3/s, a sedimentation basin of 30m3 would be required and for a flow rate of 0.5m3/s the basin would be 150m3.  All effluent discharged from the construction site should comply with the standards stipulated in the TM-DSS. The detailed design of the sand/silt traps shall be undertaken by the Contractor prior to the commencement of construction;

·           In accordance with ProPECC PN 1/94, the construction works should be programmed to minimise surface excavation works during rainy seasons (April to September), as far as practicable.  All exposed earth areas should be completed and vegetated as soon as possible after the earthworks have been completed, or alternatively, within 14 days of the cessation of earthworks where practicable.  If excavation of soil cannot be avoided during the rainy season, or at any time of year when rainstorms are likely, exposed slope surfaces should be covered by tarpaulin or other means;  

·           The overall slope of works sites should be kept to a minimum to reduce the erosive potential of surface water flows, and all trafficked areas and access roads should be protected by coarse stone ballast.  An additional advantage accruing from the use of crushed stone is the positive traction gained during the prolonged periods of inclement weather and the reduction of surface sheet flows;

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

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

·           Open stockpiles of construction materials (for example, aggregates, sand and fill material) 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 the year when rainstorms are likely, actions to be taken when a rainstorm is imminent or forecasted and during or after rainstorms, are summarised in Appendix A2 of ProPECC PN 1/94.  Particular attention should be paid to the control of silty surface runoff during storm events;  

·           All vehicles and plant should be cleaned before leaving a construction site to ensure no earth, mud, debris and the like is deposited by them on roads.  An adequately designed and sited wheel washing facilities should be provided at the exit of every construction site 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-washing bay to public roads should be paved with sufficient backfall toward the wheel-washing bay to prevent vehicle tracking of 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, specifically Works Areas WA1, WA2, WA4 and WA5 where plant maintenance is proposed.  Oil interceptors should be emptied and cleaned regularly to prevent the release of oil and grease into the storm water drainage system after accidental spillage.  A bypass should be provided for oil interceptors to prevent flushing during heavy rain;

·           The construction solid waste, debris and rubbish on-site should be collected, handled and disposed of properly to avoid causing any water quality impacts.  The requirements for solid waste management are detailed in Section 11 Waste Management of this EIA report; and

·           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 the nearby WSRs.

6.4.8.2              By adopting the above mitigation measures with best management practices it is anticipated that the impacts of construction site runoff will be reduced to an acceptable level.

6.4.8.3              There is a need to apply to the 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.  Minimum distances of 100m should be maintained between the discharge points of construction site effluent and the existing seawater intakes.  The beneficial uses of the treated effluent for other on-site activities such as dust suppression, 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 WPCO license. 

Tunnelling and Excavation Works

6.4.8.4              Specific mitigation measures for the tunnelling works using TBM, soft ground and mechanical excavation techniques should include the following:

·           The cut-and-cover tunnelling works should be conducted sequentially as far as practicable to limit the amount of construction wastewater generated from the exposed areas during the wet season (April to September);

·           Uncontaminated discharge should pass through settlement tanks prior to discharge;

·           If contaminated groundwater is found during the course of the works, no direct discharge of groundwater from contaminated areas should be adopted.  Any contaminated groundwater should be properly treated in compliance with the requirements of the TM-DSS.  If wastewater treatment is to be deployed for treating the contaminated groundwater, the wastewater treatment unit should deploy suitable treatment processes (e.g. oil interceptor/activated carbon) to reduce the pollution level to an acceptable standard and remove any prohibited substances (such as TPH) to an undetectable range;

·           If groundwater recharging wells are deployed, recharging wells should be installed as appropriate for recharging the contaminated groundwater back into the ground. The recharging wells should be selected at places where the groundwater quality will not be affected by the recharge operation as indicated in the Section 2.3 of TM-DSS;

·           The baseline groundwater quality shall be determined prior to the selection of the recharge wells, and submit a working plan (including the laboratory analytical results showing the quality of groundwater at the proposed recharge location(s) as well as the pollutant levels of groundwater to be recharged) to EPD for agreement. Pollution levels of groundwater to be recharged shall not be higher than pollutant levels of ambient groundwater at the recharge well. Prior to recharge, any prohibited substances such as TPH products should be removed as necessary by installing the petrol interceptor; and

·           The wastewater with high concentrations of SS should be treated such as by settlement in tanks with sufficient retention time before discharge.  Oil interceptors would also be required to remove the oil, lubricants and grease from the wastewater.

Bentonite Slurry

6.4.8.5              In order to prevent any accidental release of bentonite slurry from getting into the surrounding environment, the following specific control measures shall be followed to reduce the risk and impacts of accidental spillage:

·           All bentonite slurry should be stored in a container that resistant to corrosion, maintained in good conditions and securely closed;

·           The container should be labelled in English and Chinese and note that the container is for storage of bentonite slurry only;

·           The storage container should be placed on an area of impermeable flooring and bunded with capacity to accommodate 110% of the volume of the container size or 20% by volume stored in the area and enclosed with at least 3 sides;

·           The storage container should be  Sufficiently covered to prevent rainfall entering the container or bunded area (water collected within the bund must be tested and disposed of as chemical waste, if necessary);

·           An emergency clean up kit shall be readily available where bentonite fluid will be stored or used; and

·           The handling and disposal of bentonite slurries should be undertaken in accordance within ProPECC PN 1/94.  Surplus bentonite slurries used in construction works shall be reconditioned and reused wherever practicable.  Residual bentonite slurry shall be disposed of from the site as soon as possible as stipulated in Clause 8.56 of the General Specification for Civil Engineering Works. The Contractor should explore alternative disposal outlets for the residual bentonite slurry (dewatered bentonite slurry to be disposed to a public filling area and liquid bentonite slurry, if mixed with inert fill material, to be disposed to a public filling area) and disposal at landfill should be the last resort.

Barging Point

6.4.8.6              The proposed barging point at South Apron will not involve marine works like dredging or modifying the submerged portion of the existing seawall.  As such, no direct adverse water quality impacts are anticipated during its construction or operation.  However, mitigation measures as outlined above should be applied to minimise water quality impacts from site run-off and temporary open stockpiles of spoil at the proposed barging point, where appropriate.  Other good site practices include:

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

·           All hopper barges should be fitted with tight fitting seals to their bottom openings to prevent leakage of material;

·           Construction activities should not cause foam, oil, grease, scum, litter or other objectionable matter to be present on the water within the site; and

·           Loading of barges and hoppers should be controlled to prevent splashing of material into the surrounding water.  Barges or hoppers should not be filled to a level that will cause the overflow of materials or polluted water during loading or transportation.  

Sewage and Effluent

6.4.8.7              If chemical toilets and sewage holding tanks are required for handling sewage generated by the construction workforce, a licensed contractor should be employed to provide appropriate and adequate portable toilets and be responsible for appropriate disposal and maintenance. 

Accidental Spillage of Chemicals

6.4.8.8              In order to protect against impacts to the surrounding marine waters of the KTTS and Victoria Harbour in the event of an accidental spillage of fuel or oil, the Contractor will be required to prepare a spill response plan to the satisfaction of AFCD, EPD, FSD, Police, TD and WSD to define procedures for the control, containment and clean-up of any spillage that could occur on the construction site.

6.4.8.9              The Contractor must, also, 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. 

6.4.8.10          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. 

6.4.8.11          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; and

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

6.4.8.12          Given that recommended measures are tried and tested techniques used extensively throughout Hong Kong construction projects, the level of uncertainty of their effective implementation would be small. Notwithstanding, the EM&A programme will be implemented to ensure all mitigation measures are effective.

6.5                     Operational Phase Impact Assessment

6.5.1                 Identification of Pollution Sources

6.5.1.1            During the operational phase, there will be no routine discharge of wastewater or contaminated surface drainage to sea or surface watercourses during the operational phase.  However, the following potential water pollution sources could arise during the operational phase:

·           waste water run-off generated from cleaning and fire operations in the tunnel;

·           run-off from the road surfaces that could be marginally contaminated with pollution from vehicles fuel;

·           sewage from the ventilation buildings offices; and

·           accidental spillage of chemicals during the use of the road.

6.5.2                 Tunnel Run-off

6.5.2.1            During the operational stage, there will be no routine discharge of wastewater or contaminated surface drainage to sea.  Water seepage into the subsea tunnel requiring operational tunnel drainage will be avoided by the use of waterproofing and sealing between the tunnel joints and the tunnel will be constructed to avoid all leakage into the structure.  Waste water will be generated as a result of the use/testing of fire mains and cleaning operations and the tunnel drainage will be able to handle 240m3 per hour.  However, these operations would be very infrequent and undertaken for short durations only and the quantities of waste water produced negligible.  The generated tunnel water will drain into drainage pipes located along the tunnel alignment.  The run-off will be treated via oil interceptors located next to the pump sumps at low points in the tunnel, prior to pumping the water into the local stormwater network at the South Apron for discharge. The discharge of tunnel run-off should comply with the standards shown in the TM-DSS and the provisions stipulated in the WPCO.

6.5.2.2              Based upon these factors, significant effects on the water quality are not predicted.  Notwithstanding, measures to further protect the water quality from tunnel run-off in the form of oil interceptors are recommended, as detailed in Section 6.5.6, will be required

6.5.3                 Surface Road Run-off

6.5.3.1              Surface road run-off may be arise during the operational phase from the at-grade sections of road.  Substances such as dust and lubricant oil deposited and accumulated on the road surfaces will be washed into the drainage system and ultimately into the sea during rainfall.  However, bearing in mind the dilution rates which would be achieved, the road run-off should not result in a significant increase in concentrations of contaminants.  The total contaminant load in the road run-off will represent a small increase in the natural contaminant load and should not result in a significant detrimental impact on marine water quality especially when the small rainfall volumes with respect to the tidal volume are taken into account.  Based upon these factors, significant effects on the water quality are not predicted and no mitigation measures are considered to be required.  

6.5.4                 Sewage

6.5.4.1              The ventilation buildings are not designed for any significant amounts of long term staffing so sewage from the ventilation buildings offices will be minimal, produce less than 7m3 of sewage per day, as detailed in Table 3.2. 

6.5.4.2              For the western ventilation building on the South Apron, the sewage from the facility is proposed to be discharged into the existing sewerage system.  Adequate capacity in the local system to accommodate this amount is available. For the eastern ventilation building at Cha Kwo Ling, the sewage will need to be discharged to a sewage storage tank located adjacent to the facility as the building is located in an area which is much lower than the surrounding Cha Kwo Ling sewerage network and it is not considered practical to provide pumping arrangements for such small quantities.  The sewage in the tank will be managed by a licenced Contractor and would be emptied into a tanker before suitable disposal to the TKO-LTT sewage pumping station.

6.5.4.3              As a result, no significant operational impacts on the marine environment from sewage are expected.

6.5.5                 Accidental Spillage

6.5.5.1            Under normal operating circumstances, significant impacts on water quality are not predicted.  However, while Dangerous Goods (DG) vehicles of Categories 1, 2 and 5 are prohibited from using the tunnel, other tankers/vehicles carrying oil and chemicals will be allowed to use the tunnel.  In the event of an accident with such a tanker on the at-grade sections of road, there is the possibility for the spillage of a large volume of oil or chemicals.  While the road drainage system is proposed to include oil and silt interceptors which will help to collect some of a spill depending upon the amount, in the event that a major spill occurs, a defined response plan is required in order to, not only be able to reopen the road as soon as possible to minimise disruption to traffic, but also to minimise effects on the marine ecological resources and water quality.  All methods of spill clearance should be environmentally acceptable and should not lead to pollution of the marine environment.  The following sections detail the procedures that would be applicable in this situation.

Chemical Spillages

6.5.5.2            For chemical spillages that do not pose fire, explosion or life risks, the spills should be contained, recovered and soaked-up for disposal as chemical waste.  Under no circumstances should chemical spillages be washed into the natural streams, or any other natural or man-made water bodies or carrying systems. 

Oil Spillages

6.5.5.3            In respect of oil spillage, the use of chemical dispersants to break up the oil is not recommended as their use could impact on the surrounding environment and compound the pollution situation.  In addition, the oil spill should be contained in the location of the spill wherever possible.

6.5.5.4            For all spillages, the acceptable method of control is by “absorption” and then removal of the absorbed waste for disposal by special contractors.  Absorption of the oil should be achieved by the use of sawdust or other suitable material. Advice on how to clean-up a chemical spillage if required can be sought from EPD. Contact should be made with EPD’s Chemical Waste Treatment Centre for assistance in disposing of the contaminated sawdust. Source of sawdust for use in case of emergencies can be obtained from Highways Department.

6.5.5.5            The management and maintenance authority for the venue/roads/parts would be responsible for clearing up a spillage in their responsible area, as summarised in Table 6.8.  The emergency call-out procedure in case oil/chemical spillage on roads are:

a)     Police

·           to access the impact of incident and then immediately inform:

-      FSD in case of fire hazard; and

-      TD in case of road closure:

·           to set up a Mobile Command Post to co-ordinate the road closure and clearing up operations.  All parties concerned might then liaise with the Command Post for updated information; and

·           to inform EPD, FEHD and other departments to render assistance if necessary after the immediate traffic and rescue operations completed.

b)     Transport Department

·           to inform HyD’s Emergency Co-ordination Centre;

·           to liaise with the bus companies, MTRCL, relevant ferry operators on emergency public transport arrangements; and

·           to disseminate information of emergency public transport arrangements through GIS.

6.5.5.6            A summary of the key responsibilities of relevant authorities are provided in the following Table 6.8.

Table 6.8     Spill Response Key Responsibilities

Department

Area of Responsibility

FSD

To standby at scene if there is fire hazard

HyD

To be responsible for clearing up chemical spillage on public roads by supplying labour and sawdust

To assist Police in assessing the road re-opening time.

Police

To implement road closure and direct traffic

To coordinate the operations of clearing up

To inform FSD, TD in the first instant and then other departments on an as need basis

Transport Department

To inform HyD

To liaise with bus companies and MTRCL, ferry operators on emergency public transport

To disseminate information of emergency public transport arrangements through GIS

 

6.5.5.7            These measures will reduce the magnitude of any impacts.  Notwithstanding it is possible for some of the spilled material to be discharged into the marine environment via the viaduct drainage system.  However, the spill will decay through a variety of means including evaporation, adsorption onto suspended materials and emulsification.  Adsorption of oils can be effective means for breaking up the spill.  However, the natural process of the spill spreading reduces its thickness and allows the process of wind and wave action in breaking up the spill to increase as well as evaporation and dissolution.  Dispersion of any spill will occur more rapidly in high energy waters which occur along the majority of the viaduct length but in lower flows of the waters in the bays, dispersion could take longer.  Notwithstanding, it is likely that a spill would disperse in region of 3-4 days without any long term effects on water quality (ERM 1995). 

6.5.5.8            Based upon this, the emergency response plan would be considered to be sufficient to reduce any impacts to acceptable levels.

6.5.6                 Operational Phase Mitigation Measures

6.5.6.1            Mitigation measures are only required to mitigate runoff from tunnel during the operational phase.  With the implementation of the following mitigation measures, no residual impact during operational phase is anticipated:

·           The road drainage in the tunnel should pass through oil interceptors to remove oil, and grease before being discharged into the public storm water drainage system;

·           Silt traps and oil interceptors should be cleaned and maintained regularly; and

·           The oily contents of oil interceptors should be transferred to an appropriate disposal facility, or to be collected for reuse, if possible.

6.6                     Residual Impacts

6.6.1.1            The residual impacts refer to the net impacts after mitigation, taking into account the background environmental conditions and the impacts from existing, committed and planned projects.  Residual impacts associated with the construction and operation phases have been assessed but no quantification of residual impacts is required.

6.6.1.2            Significant adverse residual impacts during the construction and operational phases are not anticipated, provided that the above mitigation measures are implemented.

6.6.1.3            The water quality residual impacts are not predicted to significantly affect health or cause loss of life as such unduly affect the welfare of the local community or any agricultural activities, and the environment resources would be protected with the mitigation measures.

6.7                     Cumulative Impacts

6.7.1.1              The potential cumulative impacts due to related concurrent project activities or pollution sources within the assessment area have been assessed. The Trunk Road T2 construction should commence in late 2015 and complete by end of 2020 for commissioning in 2021.  The following concurrent projects in Table 6.9 below have been identified as being relevant from a water quality perspective and a full list of concurrent projects is provided in Appendix 3C.

                   Table 6.9           Potential Concurrent Projects Related to Water Quality

Project

Project Proponent

Construction Programme

Major Works

 Project Involving Marine-based Works

Central Kowloon Route (CKR)

Highways Department (HyD)

2015-2020

Temporary reclamation and dredging

Kai Tak Runway Opening

Civil Engineering and Development Department (CEDD)

2018

Opening and dredging

Cross Bay Link (CBL)

Civil Engineering and Development Department (CEDD)

May 2017 to

August 2018

Dredging and filling

Tseung Kwan O – Lam Tin Tunnel

(TKO-LTT)

Civil Engineering and Development Department (CEDD)

January 2016 to December 2020

Reclamation works for the TKO section, piling works, construction and decommission of two temporary barging points

Projects Involving Land-based Works

Junction Improvement Works

Civil Engineering and Development Department (CEDD)

2019 - 2020

 

Land-based

Extension of Existing Footbridge FB-02

Civil Engineering and Development Department (CEDD)

2019 - 2020

 

Land-based

Proposed Foot Bridge FB-06

Civil Engineering and Development Department (CEDD)

2019 - 2020

 

Land-based

Road L10 and L18

Civil Engineering and Development Department (CEDD)

2019 - 2020

 

Land-based

Centres of Excellence in Paediatrics and Neuroscience and a New Acute Hospital

Hospital Authority (HA)

2013-2017

Land-based

District Cooling System at the Kai Tak Development

EMSD

Mid-2013 - 2016

Land-based

 

6.7.1.2              Based on the Trunk Road T2 proposed construction programme of late 2015 to the end 2020 (Section 3.9), it can be seen that there are potential concurrent projects involving marine works that would be undertaken in parallel with the Trunk Road T2 within the wide study in the wide assessment area comprising Western Buffer, Victoria Harbour and Eastern Buffer WCZs (Table 6.9).

6.7.1.3              As the Trunk Road T2 project would not involved any marine works that would disturb the seabed and induce water quality impacts associated with the elevation of suspended solids nor result in changes to water flows through permanent structures above the seabed, no cumulative impacts on the marine environment associated with the construction or operation of the Trunk Road T2 in parallel to these concurrent projects are predicted. 

6.7.1.4              In terms of land based works, there are several projects within the 300m assessment area, as detailed in Table 6.9, for which construction would be on-going at the same time as the Trunk Road T2 and could, also, result in construction run-off and discharges.   However, each of the projects would involve the provision and implementation of individual mitigation measures and based on the implementation of the Trunk Road T2 mitigation measures as described above, no adverse cumulative water quality impacts associated with the land based works would be anticipated on the WSRs as listed in Table 6.5.

6.8                     Environmental Monitoring and Audit

6.8.1.1            The implementation of good construction works practices as well as the various specific mitigation measures recommended above will be important to prevent the pollution of the marine waters from land based works during the construction phase.  It is, therefore, recommended that construction activities should be subject to a routine audit programme throughout the construction period.  Further details on the scope of this audit are provided in the Environmental Monitoring and Audit (EM&A) Manual.  No operational phase EM&A for water quality is considered required.

6.9                     Summary and Conclusions

6.9.1                 Construction Phase

6.9.1.1            Potential water pollution sources have been identified as construction run-off, wastewater discharge from tunnelling and excavation, contaminated groundwater, sewage effluent, accidental spillages and waste construction materials.  Mitigation measures including providing perimeter drains, sand/silt removal facilities and oil interceptors, covering excavated and construction materials and spill response plans have been recommended to mitigate any adverse water quality impacts. 

6.9.1.2            Based on the implementation of the mitigation measures, no adverse water quality impacts are predicted. Routine audit of the implementation of the mitigation measures is recommended during the construction phase EM&A.

6.9.2                 Operational Phase

6.9.2.1            Operational phase water quality impacts may be associated with tunnel run-off, surface road run-off, sewage from ventilation buildings and accidental spillage.  However, any impacts are considered negligible provided that the recommended mitigation measures are implemented and adverse water quality impacts are not predicted. The residual impacts have been assessed and would be unlikely to induce public health concerns.

6.10                 References

EPD (Environmental Protection Department) (2011). Marine Water Quality in Hong Kong in 2010. Hong Kong SAR Government.

EPD (Environmental Protection Department) (2012). Marine Water Quality in Hong Kong in 2011. Hong Kong SAR Government.

EPD (Environmental Protection Department), Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS). Hong Kong SAR Government.

EPD (Environmental Protection Department), Professional Persons Environmental Consultative Committee Practice Note (ProPECC PN) 1/94 Construction Site Drainage. Hong Kong SAR Government.

EPD (Environmental Protection Department), Professional Persons Environmental Consultative Committee Practice Note (ProPECC PN) 5/93 Drainage Plan. Hong Kong SAR Government.

ERM Hong Kong Ltd (1995). Proposed Aviation Fuel Receiving Facility at Sha Chau: Environmental Impact Assessment, Volume 1, January 1995.

Manusell Consultants Asia Ltd (2007). Agreement No. CE 35/2008 (CE). Kai Tak Development Engineering Study cum Design and Construction of Advance Works – Investigation, Design and Construction.  Dredging Works for Proposed Cruise Terminal at Kai Tak Environmental Impact Assessment Report. Prepared for the Civil Engineering Department, Hong Kong SAR Government. (CTD EIA)

Manusell Consultants Asia Ltd (2008). Agreement No. CE 35/2008 (CE). Kai Tak Development Engineering Study cum Design and Construction of Advance Works – Investigation, Design and Construction.  Kai Tak Development Environmental Impact Assessment Report. Prepared for the Civil Engineering Department, Hong Kong SAR Government. (KTD EIA)