Chapter    Title                                                                                                                           Page

5.1              Introduction________________________________________________________________ 5-1

5.2              Environmental Legislation, Standards and Guidelines_______________________________ 5-1

5.3              Assessment Area, Water Sensitive Receivers and Description of the Environment__________ 5-4

5.4              Assessment Methodology_____________________________________________________ 5-9

5.5              Identification, Prediction and Evaluation of Environmental Impact______________________ 5-10

5.6              Mitigation of Adverse Environmental Impact_______________________________________ 5-14

5.7              Evaluation of Residual Impact_________________________________________________ 5-19

5.8              Environmental Monitoring and Audit_____________________________________________ 5-19

5.9              Conclusion_______________________________________________________________ 5-19

 

Tables

Table 5.1__ Water Quality Objective for the Deep Bay WCZ_ 5-1

Table 5.2__ Marine Water Quality in Deep Bay Water Control Zone in 2008_ 5-5

Table 5.3:__ Summary of River Water Quality Monitoring Data at Several Sections of Shenzhen River (2006-2007) 5-6

Table 5.4:__ Summary of River Water Quality Monitoring Data at River Ganges and River Indus (2008) 5-7

Table 5.5:__ Summary of Results of Water Quality Sampling at River Indus, River Ganges and Kong Yiu Channel 5-9

 

Figures

Figure 5.1       Location of Water Control Zone

Figure 5.2       Locations of Key Water Sensitive Receivers

Figure 5.3       Location Plan of the Interception between Proposed Connecting Road Alignment and Existing Stream

 

 

5.1               Introduction

This section presents the assessment of the potential water quality impacts associated with the construction and operation phases of the proposed Boundary Control Point and associated facilities, according to section 3.4.5 of the Study Brief (ESB-199/2008) and Annexes 6 and 14 of the Technical Memorandum to the EIAO. Mitigation measures, where necessary, have been recommended accordingly to reduce the identified water quality impacts to an acceptable level.

5.2               Environmental Legislation, Standards and Guidelines

5.2.1           Environmental Impact Assessment Ordinance

The Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) is issued by the Environmental Protection Department under Section 16 of the EIAO. It specifies the assessment method and criteria that needs to be followed in the EIA. Reference sections in the EIAO-TM provide the details of the assessment criteria and guidelines that are relevant to the water quality impact assessment, including:

¡      Annex 6 Criteria for Evaluating Water Pollution

¡      Annex 14 Guidelines for Assessment of Water Pollution

5.2.2           Water Pollution Control Ordinance

The Water Pollution Control Ordinance (WPCO) (Cap.358) provides the major statutory framework for the protection and control of water quality in Hong Kong. According to the Ordinance and its subsidiary legislation, the whole Hong Kong waters are divided into ten Water Control Zones (WCZs). Water Quality Objectives (WQOs) were established to protect the beneficial uses of water quality in WCZs. Specific WQOs are applied to each WCZ. The Project is located within the Deep Bay WCZ and its corresponding WQOs are listed in Table 5.1, which would also be used as the basis for assessment of water quality impacts in this EIA study.

Table 5.1       Water Quality Objective for the Deep Bay WCZ

Parameters

Objectives

Sub-Zone

Offensive Odour,  Tints

Not to be present

Whole zone

Colour

Not to exceed 30 Hazen units

Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones

 

Not to exceed 50 Hazen units

Yuen Long & Kam Tin (Lower) Subzone and other inland waters

Visible foam, oil scum, litter

Not to be present

Whole zone

E. coli

Not to exceed 610 per 100 mL, calculated as the geometric mean of the all samples taken in 1 calendar year

Secondary Contact Recreation Subzone and Maricultural Subzone

 

Should be zero per 100 mL, calculated as the running median of the most recent 5 consecutive samples taken at intervals between 7 and 21 days

Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones

 

Not to exceed 1000 per 100 mL, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals between 7 and 21 days

Yuen Long & Kam Tin (Lower) Subzone and other inland waters

 

Not to exceed 180 per 100 mL, calculated as the geometric mean of all samples collected from March to October inclusive in one calendar year. Samples should be taken at least 3 times in a calendar month at intervals of between 3 and 14 days

Yung Long Bathing Beach Subzone

Depth-averaged DO

Not less than 4.0 mg L-1 for 90% of samples

Outer Marine Subzone excepting Mariculture Subzone

Dissolved Oxygen (DO) within 2 m of the seabed

Not less than 2.0 mg L-1 for 90% of samples

Outer Marine Subzone excepting Mariculture Subzone

Dissolved Oxygen

Not less than 4.0 mg L-1 for 90%of the sampling occasions during the year, values taken at 1m below surface

Inner Marine Subzone excepting Mariculture Subzone

 

Not less than 5.0 mg L-1 for 90%of the sampling occasions during the year, values taken at 1m below surface

Mariculture Subzone

 

Not less than 4.0 mg L-1

Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone, Indus Subzone, Ganges Subzone, Water Gathering Ground Subzones and other inland waters of the Zone

pH

To be in the range of 6.5 - 8.5, change due to waste discharge not to exceed 0.2

Marine waters excepting Yung Long Bathing Beach Subzone

 

Not to exceed the range of 6.5 – 8.5 due to waste discharge

Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones

 

To be in the range of 6.0 - 9.0

Other inland waters

 

To be in the range of 6.0 – 9.0 for 95% of samples. Waste discharge shall not cause the natural pH range to be extended by more than 0.5 units

Yung Long Bathing Beach Subzone

Salinity

Change due to waste discharge not to exceed 10% of ambient

Whole zone

Temperature

Change due to waste discharge not to exceed 2 oC

Whole zone

Suspended solids

Waste discharge not to raise the natural ambient level by 30% nor cause the accumulation of suspended solids which may adversely affect aquatic communities

Marine waters

 

Annual median not to exceed 20 mg L-1 due to waste discharges

Yuen Long & Kam Tin (Upper and Lower) Subzones, Beas Subzone, Ganges Subzone, Indus Subzone, Water Gathering Ground Subzones and other inland waters

Unionized Ammonia

Annual mean not to exceed 0.021 mg L-1 as unionised form

Whole zone

Nutrients

Not to be present in quantities that cause excessive growth of  algae or other aquatic plants

Inner and Outer Marine Subzones

 

Annual mean depth-averaged inorganic nitrogen not to exceed 0.7 mg L-1

Inner Marine Subzone

 

Annual mean depth-averaged inorganic nitrogen not to exceed 0.4 mg L-1

Outer Marine Subzones

BOD5

Not to exceed 3 mg L-1

Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones

 

Not to exceed 5 mg L-1

Yuen Long & Kam Tin (Lower) Subzone and other inland waters

Chemical Oxygen Demand

Not to exceed 15 mg L-1

Yuen Long & Kam Tin (Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water Gathering Ground Subzones

 

Not to exceed 30 mg L-1

Yuen Long & Kam Tin (Lower) Subzone and other inland waters

Toxic substances

Should not attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms.

Whole zone

 

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

Whole zone

Phenol

Not to be present to produce a specific odour, or in concentration greater than 0.05 mg L-1 as C6H5OH

Yung Long Bathing Beach Subzone

Turbidity

Not to reduce light transmission substantially from normal level due to waste discharges

Yung Long Bathing Beach Subzone

Source: Statement of Water Quality Objectives (Deep Bay Water Control Zone).

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

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. The limits vary with the rate of effluent flow. Sewage from the proposed construction activities would be discharged into inland waters and therefore should comply with the standards for effluent discharged into inland waters, as shown in Table 6 of the TM-DSS.

5.2.4           No Net Increase Requirement

Effluent treatment is required prior to discharge into the water courses in the Deep Bay Area, in order to meet the criteria of “no net increase in pollution load requirement” as specified in the Town Planning Board Guidelines No. 12B. The underlying principle is to protect the important habitats and wildlife of the Deep Bay region.

5.2.5           Practice Note for Professional Persons on Construction Site Drainage

A practice note for professional persons was issued by the EPD to provide guidelines for handling and disposal of construction site discharges. The Practice Note for Professional Persons on Construction Site Drainage (ProPECC Note PN 1/94) provides good practice guidelines for dealing with various types of discharge from a construction site. Practices outlined in ProPECC Note PN 1/94 should be followed as far as possible during construction to minimize the water quality impact due to construction site drainage.

5.3               Assessment Area, Water Sensitive Receivers and Description of the Environment

5.3.1           Assessment Area

According to Clause 3.4.5.2 of the EIA Study Brief, water quality impact assessment has been carried out in the Deep Bay Water Control Zone and all areas within 500m from the Project ‘works’ boundary including Shenzhen River, River Ganges, River Indus, Kong Yiu Channel and other stream courses and associated water systems in the vicinity impacted by the Project.

Location of water control zone is shown in Figure 5.1.

5.3.2           Water Sensitive Receivers

Key water sensitive receivers that may potentially be affected include:

¡      Shenzhen River (WSR1)

¡      Kong Yiu Channel (WSR2)

¡      River Ganges (WSR3)

¡      River Indus (WSR4)

¡      Ma Wat Channel (WSR5)

¡      Streams at Kau Lung Hang (WSR6)

¡      Upstream of Man Uk Pin Stream (WSR7)

Figure 5.2 shows the location of key water sensitive receivers.

5.3.3           Description of the Environment / Baseline Conditions

5.3.3.1         Marine Water Quality

Pollution flows into the Deep Bay from the catchments and rivers on both the Hong Kong and Shenzhen sides has resulted in poor water quality especially in Inner Deep Bay. Marine water quality in Deep Bay WCZ in 2008 is detailed in Table 5.2. In 2008, the water quality of Deep Bay remained poor, in particular in the Inner Deep Bay, which was characterised by high organic and inorganic pollutants and low DO. The 5-day biochemical oxygen demand (BOD5), suspended solids (SS) and nitrogenous nutrients showed a distinct increase gradient from the outer Deep Bay to the inner part. While three monitoring stations in the outer bay met the WQOs for DO and NH3, the whole Deep Bay WCZ failed to meet the TIN objective. Of all the monitoring stations, only DM1 and DM2 in the inner bay failed to meet the WQO for UIA, which is toxic to marine organisms.

 

 

Table 5.2       Marine Water Quality in Deep Bay Water Control Zone in 2008

Parameter

Inner Deep Bay

Outer Deep Bay

WPCO WQO

(in marine waters)

DM1

DM2

DM3

DM4

DM5

Temperature (oC)

24.6

(16.7 - 31.5)

24.5

(16.7 - 31.0)

24.4

(16.0 - 30.1)

24.1

(15.9 - 29.5)

23.9

(15.8 - 28.9)

Change due to waste discharge not to exceed  2 oC

Salinity

17.0

(4.4 – 24.4)

18.1

(3.6 - 26.0)

21.2

(6.6 - 29.4)

22.5

(11.4 - 30.0)

25.6 

(14.5 - 31.8)

Change due to waste discharge not to exceed 10% of natural ambient level

Dissolved Oxygen (DO)

(mg/L)

Depth average

3.8

(0.2 – 7.1)

5.3

(1.6 - 10.2)

6.4

(2.7 - 10.4)

6.6

(3.3 - 9.9)

6.7

(3.5 – 11.1)

Not less than 4 mg/L for 90% of the samples

Bottom

Not measured

Not measured

Not measured

6.1

(3.1 – 10.9)

6.0

(3.5 - 8.0)

Not less than 2 mg/L for 90% of the samples

Dissolved Oxygen (DO)

(% Saturation)

Depth average

69

(23 - 128)

88

(37 - 201)

97

(53 - 183)

85

(48 - 124)

85

 (60 – 108)

Not Available

Bottom

Not measured

Not measured

Not measured

82

(46 - 142)

82

(50 - 105)

Not Available

pH

7.4

(6.2 – 8.3

7.6

(6.6 - 8.4)

7.8

(6.7 - 8.6)

7.8

(6.8 - 8.3)

7.8

(7.0 – 8.5)

6.5 - 8.5, change due to waste discharge not to exceed 0.2 from natural range

Secchi disc Depth (m)

0.5

(0.1 - 1.0)

0.5

(0.1 – 1.1)

0.7

(0.1 – 1.3)

0.8

(0.1 – 1.4)

1.1

(0.5 – 1.8)

Not Available

Turbidity (NTU)

36.8

(18.2 – 68.1)

26.0

(15.9 - 41.0)

16.0

 (12.2 – 21.4)

16.9

(11.3 - 24.3)

13.4

(11.0 – 15.8)

Not Available

Suspended Solids (SS) (mg/L)

41.5

(14.0 – 110.0)

22.9

(11.0 – 51.0)

11.2

(4.9 - 20.0)

11.6

(5.0 - 20.5)

7.0

(3.8 - 14.6)

Waste discharge not to raise the natural ambient level by 30% nor cause the accumulation of suspended solids which may adversely affect aquatic communities

5-day Biochemical Oxygen Demand (BOD5) (mg/L)

3.5

(1.1 – 7.1)

2.9

(1.0 – 8.2)

1.4

(0.5 – 4.0)

0.9

(0.5 - 2.2)

0.7

(0.2 – 2.2)

Not Available

Ammonia Nitrogen (NH3-N) (mg/L)

2.88

(1.20 – 6.30)

2.47

(1.90 - 3.60)

0.55

(0.05 - 1.40)

0.46

(0.16 - 1.51)

0.24

(0.10 - 0.48)

Not Available

Unionised Ammonia (UIA) (mg/L)

0.045

(0.003 – 0.156)

0.082

(0.010 - 0.357)

0.014

(0.004 – 0.025)

0.014

(0.002 – 0.038)

0.007

(0.001 - 0.013)

Annual mean not to exceed 0.021 mg/L

Nitrite Nitrogen (NO2-N)  (mg/L)

0.284

(0.190 – 0.420)

0.291

(0.220 - 0.480)

0.178

(0.110 – 0.270)

0.156

(0.069 – 0.285)

0.104

(0.052 – 0.197)

Not Available

Nitrate Nitrogen (NO3-N) (mg/L)

0.528

(0.200 – 1.000)

0.520

(0.310 - 1.100)

0.673

(0.250 – 1.100)

0.633

(0.205 - 1.050)

0.493

(0.123 - 1.000)

Not Available

Total Inorganic Nitrogen (TIN) (mg/L)

3.70

(2.23 – 6.74)

3.28

(2.48 - 4.25)

1.40

(0.82 - 2.56)

1.25

(0.47 - 2.85)

0.83

(0.30 - 1.65)

Annual mean depth-averaged total inorganic nitrogen not to exceed 0.5 mg/L

Total Kjeldahl Nitrogen (mg/L)

3.76
(2.40 – 8.20)

3.34
(2.60 – 4.70)

0.92
(0.47 – 1.80)

0.72
(0.43 – 1.85)

0.44
(0.30 – 0.64)

Not Available

Total Nitrogen (TN) (mg/L)

4.57

(3.43 - 8.64)

4.15

(3.18 - 5.31)

1.77

(1.09 - 2.86)

1.51

(0.70 - 3.19)

1.04

(0.48 - 1.82)

Not Available

Orthophosphate Phosphorus (OrthoP) (mg/L)

0.278

(0.150 - 0.410)

0.240

(0.140 - 0.320)

0.081

(0.018 - 0.150)

0.058

(0.022 - 0.128)

0.035

(0.014 - 0.052)

Not Available

Total Phosphorus (TP) (mg/L)

0.41

(0.24 – 0.66)

0.36

(0.26 - 0.51)

0.13

(0.09 - 0.21)

0.09

(0.07 - 0.16)

0.06

(0.04 - 0.09)

Not Available

Silica (as SiO2) (mg/L)

4.5

(1.1 - 6.6)

4.0

(0.1 - 7.1)

3.1

(0.1 - 6.2)

3.1

(0.7 - 6.6)

2.5

(0.7 - 5.6)

Not Available

Chlorophyll-a (µg/L)

28.5

(1.1 – 58)

41.5

(1.0 – 170.0)

14.0

(1.3 - 77.0)

7.0

(0.7 - 40.0)

5.2

(0.5 - 35.7)

Not Available

E coli (cfu/100 (mL)

1400

(400 – 19000)

680

(91 - 6900)

85

(9 - 570)

330

(64 - 1200)

270

(66 - 780)

Not Available

Faecal Coliforms (cfu/100 mL)

2700

(670 – 28000)

1200

(160 - 11000)

170

(39 - 890)

620

(96 - 2100)

620

(170 - 1400)

Not Available

Source:   Marine Water Quality in Hong Kong in 2008

5.3.3.2         Shenzhen River

The proposed BCP is located at Chuk Yuen, next to the Shenzhen River, which is situated between Hong Kong and Shenzhen as the boundary river and drainage outlets of rivers, including River Indus, River Beas and River Ganges of Hong Kong. Owing to the rapid development in Shenzhen, industrial and domestic discharge led to the highly polluted water quality at Shenzhen River. A three phase project, named Regulation of Shenzhen River was introduced and completed jointly by the Hong Kong Government and the Shenzhen Government in 2006. As part of the environmental requirement, environmental monitoring and audit was carried out for the water quality in Shenzhen River. The findings showed that the river water quality remained poor in 2006 - 2007, with failure to comply with the WQOs for BOD5 and SS at all monitoring stations. The WQOs for DO was met only at Shenzhen River Estuary. Table 5.3 shows a summary of river water quality, sampled in several monitoring stations of Shenzhen River during 2006 to 2007.

Table 5.3:      Summary of River Water Quality Monitoring Data at Several Sections of Shenzhen River (2006-2007)

 

 

Shenzhen River Estuary

Ta Sha Kok

Man Kam To

Ganges River Outlets

Parameter

River WQOs

2006

Jan–May 2007

2006

Jan–May 2007

2006

2006

pH

6.0 – 9.0

6.86

7.25

6.81

6.90

6.71

6.93

DO (mg/L)

≥ 4

4.32

6.99

1.58

3.72

2.71

3.87

BOD5 (mg/L)

≤ 5

9.73

7.32

28.95

25.49

14.26

18.82

SS (mg/L)

≤ 20

43.73

51.87

66.02

41.86

62.30

69.19

Source:   EM&A monitoring data of Shenzhen River Regulation Project Stage III Contract C (Changjiang Water Resources Protection Institute (長江水資源保護科學研究所), 2007)

Remarks: Data for Chemical Oxygen Demand (COD) is not available.

5.3.3.3         River Ganges and River Indus

River Ganges and River Indus are major rivers in the North District, with outlets to Shenzhen River. River Ganges covers an area of 18km2 with its length of 31km[1], and runs from Wo Keng Shan, passes its tributaries at Ping Che and Ta Kwu Ling and reaches Shenzhen River. Also empties into Shenzhen River, River Indus runs from Hung Fa Leng, passing through the north of Sheung Shui and Fanling. Its tributaries include Tan Shan River and Kwan Tei River.

According to the River Water Quality in Hong Kong in 2008, the upstream section of both rivers have high WQO compliance rate, 97% and 98% respectively, and rated with “Excellent” Water Quality Index (WQI). The compliance rate decreased towards downstream, where the mid stream of both rivers are rated with “Good” WQI. The compliance rates of the downstream station were 47% for River Ganges, rated with “Fair” WQI and 33% for River Indus, rated with “Bad”. It is suggested by the report that major pollution source of River Ganges is the remaining livestock farms, industrial establishments and unsewered villages in the catchment, while the downstream of River Indus is subject to backflow from Shenzhen River[2]. Table 5.4 shows the most recent published river water quality monitoring data, which may be used to represent the baseline water quality conditions of Rivers Ganges and Indus.

Table 5.4:      Summary of River Water Quality Monitoring Data at River Ganges and River Indus (2008)

Parameter

River WQOs

River Ganges

River Indus

GR1

GR2

GR3

IN1

IN2

IN3

Dissolved Oxygen (mg/L)

≥ 4

6.1

(3.0 – 8.4)

6.4

(2.8 – 8.5)

7.8

(5.0 -10.9)

2.9

(1.8 – 7.2)

8.1

(5.1 - 9.9)

8.5

(7.7 – 10.5)

pH

6.5 – 8.5

7.2

(6.6 – 7.4)

6.8

(3.3 – 7.0)

7.0

(6.4 – 7.4)

7.1

(6.7 – 7.4)

7.3

(7.0 – 9.5)

7.1

(6.9 – 7.6)

Suspended solids (mg/L)

≤ 20

22

(13 -450)

14

(5 - 31)

11

(4 -26)

35

(16 - 88)

6

(5 - 22)

3

(1-7)

5-day Biochemical Oxygen Demand (mg/L)

≤ 3

8

(2 - 52)

4

(1-24)

1

(<1 - 7)

10

(<1 - 31)

3

(<1 - 20)

<1

(<1 - 2)

Chemical Oxygen Demand (mg/L)

≤ 15

25

(8 - 250)

18

(7 - 43)

5

(3 - 9)

25

(5 - 69)

9

(5 - 20)

9

(5 - 18)

Oil & grease (mg/L)

NA

0.6

(<0.5 – 5.3)

0.6

(<0.5 – 1.1)

<0.5

(<0.5 – 0.6)

0.6

(<0.5 – 1.3)

<0.5

(<0.5 – 0.9)

<0.5

(<0.5 – <0.5)

Faecal coliforms (cfu/100mL)

NA

160000

(16000 – 35000000)

22000

(2 – 140000)

5400

(370 – 22000)

470000

(9300 – 5500000)

8000

(720 – 30000)

3600

(30 – 14000)

E. coli (cfu/100mL)

NA

35000

(5000 – 800000)

3000

(<1 – 24000)

340

(37 – 1200)

210000

(5600 – 2700000)

950

(120 – 13000)

650

(10 – 7000)

Ammonia-nitrogen (mg/L)

NA

6.05

(0.41 – 24.00)

1.35

(0.32 – 6.80)

0.10

(0.03 – 0.39)

9.75

(0.20 – 21.00)

0.82

(0.11 – 1.80)

0.08

(0.05 – 0.17)

Nitrate-nitrogen (mg/L)

NA

0.61

(<0.01 – 1.20)

0.66

(<0.01 – 1.10)

0.17

(0.10 – 0.22)

1.30

(<1.00 – 3.00)

1.10

(0.40 – 1.20)

1.15

(0.30 – 1.70)

Total Kjeldahl nitrogen (mg/L)

NA

7.70

(0.81 – 28.00)

2.10

(0.72 – 9.00)

0.24

(0.11 – 0.52)

12.00

(0.64 – 29.00)

1.50

(0.38 – 2.90)

0.35

(0.23 – 0.62)

Ortho-phosphate (mg/L)

NA

1.80

(0.22 – 6.60)

0.53

(0.15 – 1.40)

<0.01

(<0.01 – <0.01)

0.44

(0.11 – 1.20)

0.09

(0.04 – 0.13)

0.15

(0.09 – 0.36)

Total phosphate (mg/L)

NA

2.25

(0.39 – 11.00)

1.10

(0.31 – 2.50)

<0.02

(<0.02 – 0.05)

0.94

(0.23 – 2.10)

0.20

(0.09 – 0.41)

0.24

(0.13 – 0.49)

Total Sulphide (mg/L)

NA

0.02

(<0.02 – 2.00)

<0.02

(<0.02 – 0.66)

<0.02

(<0.02 – <0.02)

0.03

(<0.02 – 0.42)

<0.02

(<0.02 – <0.02)

<0.02

(<0.02 – <0.02)

Aluminium (µg/L)

NA

120

(<50 – 380)

105

(<50 – 350)

<50

(<50 – 90)

165

(140 – 1600)

70

(<50 – 110)

<50

(<50 – 70)

Cadmium (µg/L)

NA

<0.1

(<0.1 – <0.1)

<0.1

(<0.1 – 0.6)

<0.1

(<0.1 – 0.2)

<0.1

(<0.1 – <0.1)

<0.1

(<0.1 – <0.1)

<0.1

(<0.1 – <0.1)

Chromium (µg/L)

NA

<1

(<1 – 2)

<1

(<1 – <1)

<1

(<1 – <1)

6

(<1 – 10)

<1

(<1 – <1)

<1

(<1 – <1)

Copper (µg/L)

NA

4

(2 – 9)

4

(1 – 25)

<1

(<1 – 2)

7

(3 – 9)

3

(1 – 4)

3

(2 – 8)

Lead (µg/L)

NA

3

(<1 – 10)

5

(<1 – 35)

<1

(<1 – 3)

3

(1 – 6)

1

(<1 – 3)

1

(<1 – 2)

Zinc (µg/L)

NA

25

(10 – 170)

40

(20 – 100)

10

(<10 – 40)

30

(20 – 60)

25

(10 – 150)

10

(<10 – 30)

Flow (L/s)

NA

20

(5 – 200)

47

(6 – 222)

30

(15 – 360)

NM

NM

32

(1 – 532)

Source:   River Water Quality in Hong Kong in 2008

Remarks:

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

2.   Figures in brackets are annual ranges

3.   NM – no measurement taken

4.   cfu – colony forming unit

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

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

5.3.3.4         Further Water Quality Survey

Due to the absence of water quality information at Kong Yiu Channel, a water quality survey was conducted at Kong Yiu Channel near the Works Area. To acquire the current baseline water quality at the possibly affected area near River Ganges and River Indus, water samples were also collected at the relevant sections of River Ganges and River Indus near the Works Area in March 2010. The results are summarized in Table 5.5.

Table 5.5:      Summary of Results of Water Quality Sampling at River Indus, River Ganges and Kong Yiu Channel

Parameters

Unit

Sampling Locations

River Indus

River Ganges

Kong Yiu Channel

Temperature

℃

19.14

19.93

19.06

pH

-

6.90

7.09

7.48

DO Saturation

%

92.1

94.4

96.8

DO

mg/L

8.38

8.58

8.75

Turbidity

NTU

23.00

4.20

640.50

Suspended Solids

mg/L

12

5

347

Ammonia as N

mg/L

2.75

0.02

4.6

Nitrite as N

mg/L

0.14

<0.01

0.22

Nitrate as N

mg/L

3.24

0.05

1.61

Total Phosphorus

mg/L

0.6

<0.1

0.6

Biochemical Oxygen Demand

mg/L

4

5

8

Escherichia coli

CFU/100mL

16000

1000

11000

5.3.3.5         Existing Drainage Conditions

The Study Area of the proposed BCP site and connecting road falls within the catchment of Ta Kwu Ling Basin (formerly Ganges Basin) and Sheung Shui Basin (formerly Indus Basin). The proposed BCP site is located in the western side of Kong Yiu Channel and the eastern side of Shenzhen River. It is understood that the surroundings of the proposed BCP site currently may be susceptible to flooding. Drainage works for improving the current flooding condition by upgrading a section of Shenzhen River is being investigated under the DSD project “Regulation of Shenzhen River Stage 4”. 

5.4               Assessment Methodology

In accordance with Clause 3.4.5.1 of the EIA Study Brief, the assessment has been carried out in accordance with Annexes 6 and 14 of the Technical Memorandum to the EIAO.

Pollutants from point discharges and non-point sources to surface water runoff, sewage or polluted discharge generated from the proposed BCP and its associated facilities that could affect the quality of surface water runoff and nearby waters were identified. All the identified sources of potential water quality impact were then evaluated and their impact significance determined. The need for mitigation measures to reduce any identified adverse impacts on water quality to acceptable levels was determined.

5.5               Identification, Prediction and Evaluation of Environmental Impact

In accordance with Clauses 3.4.5.3 and 3.4.5.4 (i to xi) of the EIA Study Brief, disruptions to water bodies arising from construction and operation phases of the Project has been identified and analysed.

5.5.1           Construction Phase

Proposed construction activities of the Project include construction of the proposed BCP, the connecting roads, viaducts, tunnels, ventilation buildings and associated facilities.

Potential sources of water quality impact associated with the construction works proposed for the Project have been identified. These include:

¡      Construction site runoff and drainage

¡      Drainage diversion

¡      General construction activities

¡      Sewage effluent from construction workforce

¡      Hydrological impact

5.5.1.1         Construction site runoff and drainage

The surface runoff of construction works areas may contain suspended solids (SS), contaminants and increased loads of sediments. Potential sources of pollution from site drainage include:

¡      Runoff and erosion from site surfaces, drainage channels, earth working areas and stockpiles;

¡      Release of any bentonite slurries, concrete washings and other grouting materials with construction runoff and storm water;

¡      Wash water from dust suppression sprays and wheel wash facilities; and

¡      Fuel, oil, solvents and lubricants from maintenance of construction vehicles and mechanical equipment.

Sediment laden runoff particularly from works areas subjected to excavation or earth works, if uncontrolled, may carry pollutants (adsorbed onto the particle surfaces) into any nearby stormwater drains. Mitigation measures and good site practices should be properly implemented to control construction site runoff and drainage from the works area, and to avoid runoff and drainage water with high levels of SS entering to the nearby stormwater drains.

For the proposed BCP, the surface runoff generated from the site area would be collected and discharged into Shenzhen River adjacent to the Site. The surface runoff generated from the site area of the connecting road will be collected and discharged into its original flow paths into the nearby watercourses adjacent to the Site. Temporary drainage channels will be provided to collect the runoff of the site area during the construction phase.

Discharge during construction phase would be collected by the temporary drainage system installed by the Contractor and treated or desilted on-site before discharge to stormwater drains. The Contractor would also be required to obtain a license from EPD for discharge to the public drainage system. Provided adequate construction site drainage is implemented and sediment removal facilities are provisioned on site, no unacceptable water quality impact is anticipated.

5.5.1.2         Drainage diversion

Drainage diversions would be required for construction of the proposed connecting roads. The associated flow diversion works would involve the application of concrete and other grouting materials, which would become a potential water quality impact if the discharge of sediment and construction waste is uncontrolled.

Temporary drainage channel diversion would be conducted properly prior to the commencement of works to ensure the flow of the drainage channel is not affected and would not be discharged into the works area. Diversion works should be carried out in sections by methods approved by the Engineer to minimize erosion. Dry zone would be provided for excavation works, if any, within the drainage channel so that the conveyance of suspended sediment downstream would be prevented. Before the works begin, dewatering at the working section would be conducted to provide a dry environment for excavation works. With the mitigation measures to prevent construction site runoff and implement drainage diversion, no adverse water quality impact is anticipated due to the re-alignment of drainage channel.

5.5.1.3         General construction activities

On-site construction activities may result in water pollution from the following:

¡      Uncontrolled discharge of debris and rubbish such as packaging, construction materials and refuse

¡      Spillages of liquids stored on-site, such as oil, diesel and solvents etc.

Good construction and site management practices should be observed to ensure that litter, fuels and solvents do not enter the public drainage system and existing streams and rivers.

5.5.1.4         Sewage effluent from construction workforce

Domestic sewage would be generated from the workforce during the construction phase. However, portable chemical toilets will be provided within the construction site. The Contractor would have the responsibility to ensure that chemical toilets are used and properly maintained, and that licensed Contractors are employed to collect and dispose of the waste off-site at approved locations. Therefore no water quality impacts are anticipated.

5.5.1.5         Potential Tunnel water inflow and Groundwater drawdown

The proposed drill and blast tunnelling works would cause potential impacts on the groundwater system. The potential drawdown of groundwater level could alter the degree of settlement and dewatering of surface water features. Drawdown of groundwater level occurs mostly due to inflows of water into the tunnel. The groundwater inflows would be carefully controlled by pre-injection grouting, supplemented by post-injection grouting where necessary to enhance the groundwater inflow control. With the use of pre-injection with post-injection grouting, the groundwater inflows would be limited and under control.

A preliminary geotechnical and hydrological assessment has been carried out to study the potential effect of the construction works on the sensitive receivers above or adjacent to the tunnelling works. The assessment results indicated that, by controlling the groundwater ingress into the tunnel, the groundwater drawdown and corresponding settlement at Lau Shui Heung Reservoir, River Ganges and River Indus can be controlled to insignificant to acceptable levels.During tunnelling works, groundwater ingress pumped out from the tunnel would have a high content of SS. The water pumped out from the tunnel may be contaminated by grouting materials that would be required for the construction of the tunnel. On-site treatment would be required prior to off-site discharge.

Therefore, water quality impact is not be anticipated due to potential groundwater inflows and the contaminated groundwater, if any, would either be properly treated or recharged into the ground in compliance with the requirements as specified in the TM-DSS.

5.5.2           Operation Phase

Potential areas of concern on operation phase water quality impacts of the proposed BCP and associated facilities have been identified. These include:

¡      Surface and stormwater runoff; and

¡      Sewage effluents and sewerage impact.

5.5.2.1         Surface and stormwater runoff

The potential water quality impacts during the operation phase would be the discharges of surface runoff from the proposed BCP and connecting road.

BCP

The existing ground at the proposed BCP would be filled and elevated to site formation levels with adequate flood protection. The proposed BCP is situated adjacent to the existing Kong Yiu Channel. The proposed development would generate additional surface runoff due to the construction of additional paved area. The additional runoff would be discharged into Shenzhen River via an internal drainage system. According to the Feasibility Study for the DSD project –  Regulation of Shenzhen River Stage 4, the estimated additional peak discharge generated from the proposed development is about 6.5m3/s under a 1 in 50 year return period storm, which is approximately 2.2% of the peak flow of the existing Shenzhen River near River Ganges. Since the increase in the surface runoff is insignificant and this has also been taken into account by the project – Regulation of Shenzhen River Stage 4, no adverse effect on the existing aquatic organisms or water quality in the drainage system is anticipated. Besides, the existing engineering channel namely, Kong Yiu Channel, would be maintained and thus no adverse effect on the existing channel is anticipated.

The drainage systems of the proposed BCP would be properly planned during the planning and design stages. The drainage of stormwater and surface runoff from the proposed BCP would be collected and directed to the designated stormwater drainage system. Standard designed silt trap or grease trap (if necessary) and oil interceptor would be provided at the Public Transport Interchange (PTI) and vehicles holding area to remove the oil, lubricants, grease, silt and grit from the runoff before discharge. With the proper drainage systems to be provided for collection and treatment of surface and stormwater runoff prior to discharge, no unacceptable impact due to surface and stormwater runoff on water quality is anticipated.

Connecting Road

The connecting road is an approximately 11km long dual-2 lane trunk road, consists of 5.7km tunnel sections and 5.3km road sections. Since tunnel sections are underground structures and fully covered, no additional runoff would be generated. Thus, no adverse impact is anticipated.

Road sections consist of viaduct, at-grade road and depressed road which will cross a few existing rivers listed below which are also indicated in Figure 5.3:

Location A:        Upstream branches of River Ganges near Nga Yiu Ha

Location B:        Upstream branches of River Ganges near Wo Keng Shan

Location C:        Upstream branches of River Indus near Loi Tung

Location D:        Ma Wat Channel at Kau Lung Hang

The connecting road at Location A consists of viaduct and at-grade road with interchange for the connection to village road for Ping Yeung and Nga Yiu Ha.  Drainage systems would be proposed to maintain the existing flow path for the at-grade road. The crossing to River Ganges would be in the form of viaduct with no piers erected within the existing drainage channel/stream courses. Thus, no adverse impacts are anticipated. 

Location B is mainly at-grade road section. Drainage system including channels, pipeline and cross road drains would be proposed to maintain the flow path. Thus, no adverse impacts are anticipated.

Location C is the interchange for the connection to Sha Tau Kok Road and the depressed road. The depressed road would likely affect the existing flow path at the upstream of River Indus, therefore mitigation measure by providing a channel for conveying the runoff into the existing downstream river is required.

There is an interchange for the connection to Fanling Highways at Location D. The interchange would be in form of viaduct with no piers erected within the existing channel. Thus, no adverse impacts are anticipated.

The major watercourses located along the Connecting Road, including Ma Wat Channel, River Indus and River Ganges, are channelized or artificially modified for flood control. The change of drainage system occurred in these channels is mainly due to flooding in wet season. Given that most of the Connecting Road are constructed over viaduct and the proposed piers or abutments of the viaduct would not encroach on the existing river channels, therefore the flow regimes remains unchanged. The only potential change in hydrology is additional water discharge due to the runoff from the Project. With reference to the Drainage Impact Assessment (DIA), the net increase in water level and discharge at the Fanling Highway Connection are less than 20 mm and 1 m3/s respectively, therefore the impact is considered insignificant. The net increase of peak discharge in River Indus is varying between 0.6 m3/s and 1.6 m3/s for different rainstorm return period, comparing the total peak discharge, the resultant additional runoff is insignificant. The resultant additional runoff will not induce significant change in water level in the upgraded channel under Package C. For River Ganges, the peak rainfall runoff is predicted to be less than 1 m3/s. In summary, no significant change in hydrology would occur due to the construction and operation of this Project and therefore no indirect impact on aquatic organisms is anticipated.

5.5.2.2         Sewage effluents and sewerage impact

Sewage and wastewater effluents generated from the staff, food and beverage outlets at the proposed BCP would be connected to the foul sewerage system, which should be properly planned during the planning and design stages. Sewage and sewerage impact assessment has been conducted to identify the sewage and sewerage implication of the Project. It is estimated that average dry weather flow generated from the proposed BCP at Hong Kong side and Resite of Chuk Yuen Village is approximately 185m3/day and 142.56m3/day respectively. The estimations of sewage flow and pollutant loads are detailed in Section 6.

Based on the information collected from the Government and site inspections, the existing sewerage systems in the vicinity of the project site are the small sewerage systems with a series of sewage pumping stations for the collection of the sewage flow from local villages in the areas and leachate from NENT Landfill site and for the subsequent conveyance of the collected sewage flow to Shek Wu Hui Sewage Treatment Works (SWHSTW) for treatment and disposal. These existing village sewerage systems have only been designed to collect the sewage flow from these local villages only and unlikely to cope with the additional flows due to the new developments.

The proposed development would definitely increase the pollutant loading due to the associated sewage discharge. To achieve the design criteria of no net increase in pollutant loading in the nearby water body, any proposed sewerage and sewage treatment facilities should be capable of achieving a high treatment level and delivering disinfected effluent to the nearby water body.

The options of connecting to SWHSTW and the new sewage treatment plant for New Development Areas at North District are considered as not practicable as they are inadequate to cater the additional flow generated from the proposed BCP. Onsite sewage treatment and disposal for the proposed BCP is then considered as necessary to satisfy the no net increase in pollutant policy in the region. The proposed sewage treatment works is to intercept the sewage flows generated from the proposed BCP as well as Chuk Yuen Village Resite (the existing Chuk Yuen Village is currently discharging its effluent via septic tanks and leachfield) to satisfy no net increase requirement (see Section 6 for details of justification).

To cope with the discharge criteria, a high-level sewage treatment plant is required to remove all additional pollutants. In addition, to enhance environmental sustainability, it is recommended to reuse a portion of the treated effluent from the proposed development for irrigation at BCP (see Section 6 for details).

With the proposed sewerage and sewage treatment facilities as well as reuse of treated effluent, no adverse water quality impact is anticipated from sewage and wastewater effluents generated during operation phase.

5.5.3           Cumulative Impacts

Concurrent / planned projects which have been considered for cumulative environmental impact assessment are presented in Section 2. The aforementioned projects would mainly involve land-based construction works, except Regulation of Shenzhen River Stage 4, which would include the training of section of Shenzhen River relevant to the Project, and Drainage Improvements in Northern New Territories – Package C (Remaining Works), which involves improvement of Ping Yuen River through construction of 1.9 km of drainage channel in Ta Kwu Ling. However, with the implementation of the mitigation measures recommended by each project, it is anticipated that there would be no unacceptable cumulative water quality impact.

5.6               Mitigation of Adverse Environmental Impact

In accordance with Clause 3.4.5.4 (xii to xiii) of the EIA Study Brief, proposals for water pollution prevention and mitigation and protection against accidental spillage have been provided.

5.6.1           Construction Phase

5.6.1.1         Construction site runoff and drainage

Adequate construction site drainage management measures shall be implemented and maintained by the Contractor to control site runoff and drainage and thereby prevent high sediment loadings from reaching the nearby watercourses.

The site practices outlined in ProPECC Note PN 1/94 should be followed as far as practicable in order to minimise surface runoff and the chance of erosion. The following measures are recommended to protect water quality and when properly implemented should be sufficient to adequately control site discharges so as to avoid water quality impacts:

¡      At the start of site establishment, 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 on site to direct stormwater to silt removal facilities. The design of the temporary on-site drainage system should be undertaken by the Contractor prior to the commencement of construction.

¡      The dikes or embankments for flood protection should be implemented around the boundaries of earthwork areas. Temporary ditches should be provided to facilitate the runoff discharge into stormwater drainage system through a sediment/silt trap. The sediment/silt traps should be incorporated in the permanent drainage channels to enhance deposition rates, if practical.

¡      Sand/silt removal facilities such as sand/silt traps and sediment basins should be provided to remove sand/silt particles from runoff to meet the requirements of the TM standards under the WPCO. The design of efficient silt removal facilities should be based on the guidelines in Appendix A1 of ProPECC Note PN 1/94.  Sizes may vary depending upon the flow rate. The detailed design of the sand/silt traps should be undertaken by the Contractor prior to the commencement of construction.

¡      All drainage facilities and erosion and sediment control structures should be regularly inspected and maintained to ensure proper and efficient operation at all times and particularly during rainstorms. Deposited silt and grit should be regularly removed, at the onset of and after each rainstorm to ensure that these facilities are functioning properly at all times.

¡      Measures should be taken to minimize the ingress of site drainage into excavations. If excavation of trenches in wet periods is necessary, they should be dug and backfilled in short sections wherever practicable. Water pumped out from foundation excavations should be discharged into storm drains via silt removal facilities.

¡      If surface excavation works cannot be avoided during the wet season (April to September), temporarily exposed slope/soil surfaces should be covered by tarpaulin or other means, as far as practicable, and temporary access roads should be protected by crushed stone or gravel, as excavation proceeds. Interception channels should be provided (e.g. along the crest/edge of the excavation) to prevent storm runoff from washing across exposed soil surfaces.  Arrangements should always be in place to ensure that adequate surface protection measures can be safely carried out well before the arrival of a rainstorm. Other measures that need to be implemented before, during and after rainstorms are summarized in ProPECC Note PN 1/94.

¡      The overall slope of the site should be kept to a minimum to reduce the erosive potential of surface water flows.

¡      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 facility should be provided at construction site exit where practicable. Wash-water should have sand and silt settled out and removed regularly to ensure the continued efficiency of the process. The section of access road leading to, and exiting from, the wheel-wash bay to the public road should be paved with sufficient backfall toward the wheel-wash bay to prevent vehicle tracking of soil and silty water to public roads and drains.

¡      Open stockpiles of construction materials or construction wastes on-site 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 be adequately covered and temporarily sealed so as to prevent silt, construction materials or debris being washed into the drainage system and stormwater runoff being directed into foul sewers.

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

¡      Bentonite slurries used in piling or slurry walling should be reconditioned and reused wherever practicable. Temporary enclosed storage locations should be provided on-site for any unused bentonite that needs to be transported away after all the related construction activities are completed. The requirements in ProPECC Note PN 1/94 should be adhered to in the handling and disposal of bentonite slurries.

The following conditions should be complied, if there is any works to be carried out within the water gathering grounds:

¡      Adequate measures should be implemented to ensure no pollution or siltation occurs to the catchwaters and catchments.

¡      No earth, building materials, oil or fuel, soil, toxic materials or any materials that may possibly cause contamination to water gathering grounds are allowed to be stockpiled on site.

¡      All surplus spoil should be removed from water gathering grounds as soon as possible.

¡      Temporary drains with silt traps should be constructed at the site boundary before the commencement of any earthworks.

¡      Regular cleaning of silt traps should be carried out to ensure proper operation at all time.

¡      All excavated or filled surfaces which have the risk of erosion should always be protected form erosion.

¡      Facilities for washing the wheels of vehicles before leaving the site should be provided.

¡      Any construction plant which causes pollution to catchwaters or catchments due to the leakage of oil or fuel should be removed off site immediately.

¡      No maintenance activities which may generate chemical wastes should be undertaken in the water gathering grounds. Vehicle maintenance should be confined to designated paved areas only and any spillages should be cleared up immediately using absorbents and waste oils should be collected in designated tanks prior to disposal off site. All storm water run-off from these areas should be discharged via oil/petrol separators and sand/silt removal traps.

¡      Any soil contaminated with fuel leaked from plant should be removed off site and the voids arising from removal of contaminated soil should be replaced by suitable material approved by the Director of Water Supplies.

¡      Provision of temporary toilet facilities and use of chemicals or insecticide of any kind are subject to the approval of the Director of Water Supplies.

¡      Drainage plans should be submitted for approval by the Director of Water Supplies.

¡      An unimpeded access through the waterworks access road should always be maintained.

¡      Earthworks near catchwaters or streamcourses should only be carried out in dry season between October and March.

¡      Advance notice must be given before the commencement of works on site quoting WSD’s approval letter reference.

5.6.1.2         General construction activities

Construction solid waste, debris and refuse generated on-site should be collected, handled and disposed of properly to avoid entering any nearby stormwater drain. Stockpiles of cement and other construction materials should be kept covered when not being used.

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

5.6.1.3         Sewage effluent from construction workforce

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

5.6.1.4         Potential Tunnel water inflow and Groundwater drawdown

Suitable water ingress control strategies should be adopted as far as practicable during tunnelling works. Probing of the ground ahead of tunnel excavation works can be undertaken to identify zones of potential significant water inflow (e.g. highly fracture rock or high hydrostatic pressure zone) and to determine specific grouting requirements in line with the tunnel in advance. In case of excessive water inflow quantities, grout injection works would be conducted, for sealing a limited area around the tunnel with a grout of a suitable strength for controlling the potential groundwater inflows. The pre-injection grouting would be designed on the basis of probe hole drilling ahead of the tunnel face and can be achieved by systematic and carefully specified protocol of grouting. Pre-grouting ahead of the tunnel face is considered to be the most effective method of controlling groundwater inflow. The pre-injection grouting method would be supplemented by post-injection grouting where necessary to further enhance the groundwater inflow control. Post-grouting would be applied if excessive drawdown within the groundwater was observed as a result of the tunnelling works after excavation and insufficient control of water inflows by pre-grouting measures. Post-grouting can be undertaken before the lining is cast, as such permeability of the tunnel surround can be reduced and water inflows can be limited to acceptable levels. Recharge wells would be installed as necessary outside the excavation areas to maintain the ground water level and prevent excessive settlement. The aforesaid methods for groundwater inflow control are common practices and are widely adopted in tunnelling works.

The tunnel sections of this project are designed as undrained. For undrained lining design of tunnels, water inflow rates in tunnels and water pressure would be determined. The lining of the undrained tunnel has to carry a full hydrostatic load and therefore the full circumference of tunnel would be designed with a waterproofing system to prevent groundwater inflow into the tunnel. The watertight tunnel structure can withstand hydrostatic pressure and the effect on ground water levels during operation phase is regarded as negligible.

The groundwater drawdown and water ingress into the tunnel are predicted using a background permeability approach based on the analysis undertaken using the software SEEP/W 2D.

The Kwan Tei River will come across with the proposed road tunnel. The settlement due to underground excavation is neglected as the rock cover is more than half span of the tunnel. By controlling the groundwater ingress into tunnel to 3.23 litre/second/km, the groundwater drawdown and corresponding settlement can be controlled to an acceptable level.

The Tan Shan River will pass through the proposed road tunnel. The maximum settlement due to underground excavation are 15 mm. By controlling the groundwater ingress into tunnel to 1.36 litre/second/km, the groundwater drawdown and corresponding settlement can be controlled to acceptable level. In comparison with the Measured River Water Quality Data (River Indus IN3) from Environmental Protection Department, the average flow rate of the Tan Shan River is 0.0874 m3/sec, and thus the proposed tunnelling work would only withdraw 0.188% of the river water.

It is predicted that the groundwater drawdown and corresponding settlement at nearby water sensitive receivers would be limited to insignificant and acceptable levels by controlling the groundwater ingress into the tunnel, therefore groundwater monitoring programme on tunnel groundwater ingress only is recommended from the engineering perspective during the construction phase.

5.6.2           Operation Phase

5.6.2.1         Surface and stormwater runoff

With the provision of an adequately designed drainage system to prevent uncontrolled discharges, adverse water quality impact from discharge of surface runoff is not anticipated. The location of proposed BCP would generate additional surface runoff due to the construction of additional paved area. Surface runoff from the proposed BCP will be discharged into the proposed Shenzhen River Stage 4. In order to minimize the pollutants discharging into the Shenzhen River, especially for the first flushes, a dry weather flow intercepting system in the BCP would be probably planned during detail design stage to direct the first flushes to the sewage treatment plant, leaving only the excess surface runoff during heavy rainfall to discharge into the Shenzhen River. As the project – Regulation of Shenzhen River Stage 4 has already taken into account of the change of land use for the proposed BCP in their design, no further mitigation measures are considered necessary.

For the connecting road, no major drainage diversion is required at road sections at locations A, B and D. However, the proper channel/pipeline/cross road pipes to maintain the overland flow path would need to be provided. The interchange and depressed road at location C would affect the local overland flow. Drainage channel would be provided to convey the storm drain and discharge at downstream of River Indus.

5.6.2.2         Sewage effluents and sewerage impact assessment

With the provision of an adequately designed sewerage and sewage treatment facilities to collect and treat the sewage generated from the operation of Project and to reuse a portion of the treated effluent for irrigation at BCP (see Section 6 for details), adverse water quality impact is not anticipated. Hence, no further mitigation measures are considered necessary.

5.7               Evaluation of Residual Impact

In accordance with Clause 3.4.5.4 (xiv) of the EIA Study Brief, residual impacts on the affected water system(s) and the sensitive receivers have been evaluated.

With the implementation of the recommended mitigation measures for the construction and operation phases of the proposed BCP and associated facilities, no residual water quality impact is anticipated.

5.8               Environmental Monitoring and Audit

Adverse water quality impact is not predicted during the construction and operation phase of the Project. Nevertheless, appropriate mitigation measures are recommended in Section 5.6 to minimize potential water quality impacts.

Water quality monitoring is recommended during the course of construction works near Kong Yiu Channel, River Ganges, River Indus, Ma Wat Channel and streams at Kau Lung Hang to obtain a robust, defensible database of baseline information of water quality before construction, and thereafter, to monitor any variation of water quality from the baseline conditions or exceedances of WQOs during construction and to ensure the recommended mitigation measures are properly implemented.

Regular audit of implementation of the recommended mitigation measures during the construction phase at the works areas should also be undertaken during the construction phase to ensure the recommended mitigation measures are properly implemented.

Details of the water quality monitoring and audit programme and the Event and Action Plan are provided in the stand-alone EM&A Manual.

Groundwater monitoring on tunnel groundwater ingress is recommended from the engineering perspective during construction phase. Baseline data would be obtained prior to commencement of construction works.

With the full implementation of the recommended mitigation measures during operation phase, no adverse water quality impact is anticipated. Operation phase water quality monitoring is not considered necessary.

5.9               Conclusion

5.9.1           Construction Phase

The key issue in terms of water quality during the construction phase of the Project would be the potential for release of sediment-laden water from surface works areas and tunnelling works, and the potential for drawdown of groundwater level. 

Deterioration in water quality could be minimised to acceptable levels through implementing adequate mitigation measures such as control measures on sediment release, on site runoff and drainage from the works areas to minimise sediment spillage and construction runoff; pre-injection of grouting prior to tunnelling works supplemented by post-injection of grouting; and on-site treatment of tunnelling wastewater prior to discharge. Proper site management and good housekeeping practices would also be required to ensure that construction wastes and other construction-related materials would not enter the public drainage system and nearby waters. Sewage effluent arising from the construction workforce would also be handled through provision of portable toilets.

With the implementation of these recommended mitigation measures, no unacceptable impacts on water quality from the construction works for the Project are anticipated. Water quality monitoring during the course of construction works at channels and rivers and site inspections during construction phase should be undertaken routinely to inspect the construction activities and works areas to ensure the recommended mitigation measures are properly implemented.

5.9.2           Operation Phase

The operational surface and stormwater runoff would have no adverse water quality impact provided that the recommended mitigation measures are incorporated in the design of the planned drainage system. Sewage arising from the operation of the proposed BCP and associated facilities as well as from the Chuk Yuen Resite will be collected and treated by the recommended sewerage and sewage treatment facilities to fulfil the no net increase in pollutant loading policy. In order to enhance environmental sustainability, reuse of a portion of the treated effluent for irrigation at BCP is recommended (see Section 6 for details).  Thus, no adverse water quality impact during operation phase is anticipated.

 


[1] EPD, (2010). Laws & Regulations, Environmental Compliance, North District, River Ganges. Retrieved on 16 March 2010 from website: http://www.epd.gov.hk/epd/english/laws_regulations/enforcement/river_p08.html   

[2] River Water Quality in Hong Kong in 2008.