5                         WATER QUALITY IMPACT ASSESSMENT

5.1                    Background

5.1.1.1        This section presents the water quality impact assessment for the construction and operation of the Project in accordance with the EIA Study Brief and, in particular, the Appendix D “Requirements for Water Quality Impact Assessment” of the EIA Study Brief.

5.1.1.2        A description of the project can be found in Section 2 of this report, including the drainage design, alignments, construction methodologies and operation maintenance of the drainage system.

5.1.1.3        In accordance with the EIA study brief, the Study Area for the water quality impact assessment shall include all areas within 500m from the project site boundary, including the Ngong Ping Stream.  The Study Area and major sensitive watercourses in the area is shown in Figure 5.1. Project specific water quality surveys have been conducted between 2011 and 2012 to characterise the baseline water quality and pollution loadings of the existing drainage system, including the natural streams and channelised watercourses.

5.2                    Environmental Legislation, Standards and Guidelines

5.2.1              General

5.2.1.1        The following legislation and guidelines are applicable to the evaluation of water quality impacts associated with the construction and operation of the Project. These were, also, considered in formulating the testing scheme:

·         Water Pollution Control Ordinance (WPCO) (Cap.358);

·         Environmental Impact Assessment Ordinance (EIAO) (Cap.499), Technical Memorandum of Environmental Impact Assessment (EIAO-TM), Annexes 6 and 14;

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

·         Practice Note for Professional Persons, Drainage Plan (ProPECC PN 5/93); and

·         Practice Note for Professional Persons, Construction Site Drainage (ProPECC PN 1/94), which provides useful guidelines on the management of construction site drainage and prevention of water pollution associated with construction activities.

5.2.1.2        The Study Area is within the water gathering grounds for the Shek Pik Reservoir (Figure 5.2) and waters collected from these gathering grounds may be finally discharged into the reservoir.

5.2.2              WPCO and Inland Water Quality Objectives

5.2.2.1        The Water Pollution Control Ordinance (Cap. 358) (WPCO) represents the major legislation relating to the protection and control of water quality in Hong Kong.  According to the Ordinance and its subsidiary legislation, Hong Kong waters are divided into ten Water Control Zones (WCZs).  Corresponding Water Quality Objectives (WQOs) are stipulated for different water regimes (marine waters, inland waters, bathing beaches subzones, secondary contact recreation subzones and fish culture subzones, and water gathering ground subzones) in the WCZs based on their beneficial uses.  The majority part of the study area is located in the North Western WCZ while a small portion is in the Southern Supplementary WCZ (Figure 5.1).  The WQOs for the North Western and Southern Supplementary WCZs are shown in Table 5.1  and 5.2, respectively.

5.2.2.2        The WQOs of particular relevance to the Ngong Ping upland water gathering ground include E. coli, dissolved oxygen (DO), pH, temperature, salinity, suspended solids,  ammonia, 5-day biochemical oxygen demand (BOD5) and chemical oxygen demand (COD). 

Table 5.1      Water Quality Objectives for North Western Water Control Zone (NWWCZ)

Water Quality Objectives

Part or Parts of Zone

A.

AESTHETIC APPEARANCE

 

 

(a) Waste discharges shall cause no objectionable odours or discolouration of the water.

Whole zone

 

(b) Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other substance should be absent.

Whole zone

 

(c) Mineral oil should not be visible on the surface. Surfactants should not give rise to a lasting foam.

Whole zone

 

(d) There should be no recognisable sewage-derived debris.

Whole zone

 

(e) 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.

Whole zone

 

(f) Waste discharges shall not cause the water to contain substances which settle to form objectionable deposits.

Whole zone

B.

BACTERIA

 

 

(a) The level of Escherichia coli should not exceed 610/100 mL, calculated as the geometric mean of all samples collected in a calendar year.

Secondary Contact Recreation Subzones

 

(b) The level of Escherichia coli should be less than 1/100 mL, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.

Tuen Mun (A) and Tuen Mun (B) Subzones and Water Gathering Ground Subzones

 

(c) The level of Escherichia coli should not exceed 1000/100 mL, calculated as the running median of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.

Tuen Mun (C) Subzone and other inland waters

 

(d) The level of Escherichia coli should not exceed 180/100 mL, calculated as the geometric mean of all samples collected from March to October inclusive. Samples should be taken at least 3 times in one calendar month at intervals of between 3 and 14 days.

Bathing Beach Subzones

C.

COLOUR

 

 

(a) Waste discharges shall not cause the colour of water to exceed 30 Hazen units.

Tuen Mun (A) and Tuen Mun (B) Subzones and Water Gathering Ground Subzones

 

(b) Waste discharges shall not cause the colour of water to exceed 50 Hazen units.

Tuen Mun (C) Subzone and other inland waters

D.

DISSOLVED OXYGEN

 

 

(a) Waste discharges shall not cause the level of dissolved oxygen to fall below 4 mg per litre for 90% of the sampling occasions during the whole year; values should be calculated as water column average (arithmetic mean of at least 3 measurements at 1 m below surface, mid-depth and 1 m above seabed). In addition, the concentration of dissolved oxygen should not be less than 2 mg/L within 2 m of the seabed for 90% of the sampling occasions during the whole year.

Marine waters

 

(b) Waste discharges shall not cause the level of dissolved oxygen to be less than 4 mg/L.

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones, Water Gathering Ground Subzones and other inland waters

E.

pH

 

 

(a) The pH of the water should be within the range of 6.5-8.5 units. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.2 unit.

Marine waters excepting Bathing Beach Subzones

 

(b) Waste discharges shall not cause the pH of the water to exceed the range of 6.5-8.5 units.

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground Subzones

 

(c) The pH of the water should be within the range of 6.0-9.0 units.

Other inland waters

 

(d) The pH of the water should be within the range of 6.0-9.0 units for 95% of samples collected during the whole year. In addition, waste discharges shall not cause the natural pH range to be extended by more than 0.5 unit.

Bathing Beach Subzones

F.

TEMPERATURE

 

 

Waste discharges shall not cause the natural daily temperature range to change by more than 2.0 degrees Celsius.

Whole zone

G.

SALINITY

 

 

Waste discharges shall not cause the natural ambient salinity level to change by more than 10%.

Whole zone

H.

SUSPENDED SOLIDS (DO)

 

 

(a) Waste discharges shall 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.

Marine waters

 

(b) Waste discharges shall not cause the annual median of suspended solids to exceed 20 mg/L.

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground Subzones

 

(c) Waste discharges shall not cause the annual median of suspended solids to exceed 25 mg/L.

Other inland waters

I.

AMMONIA

 

 

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

Whole zone

J.

NUTRIENTS

 

 

(a) Nutrients shall not be present in quantities sufficient to cause excessive or nuisance growth of algae or other aquatic plants.

Marine waters

 

(b) Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.3 mg/L, expressed as annual water column average (arithmetic mean of at least 3 measurements at 1 m below surface, mid-depth and 1 m above seabed).

Castle Peak Bay Subzone

 

(c) Without limiting the generality of objective (a) above, the level of inorganic nitrogen should not exceed 0.5 mg/L, expressed as annual water column average (arithmetic mean of at least 3 measurements at 1 m below surface, mid-depth and 1 m above seabed).

Marine waters excepting Castle Peak Bay Subzone

K.

5-DAY BIOCHEMICAL OXYGEN DEMAND (BOD5)

 

 

(a) Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 3 mg/L.

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground Subzones

 

(b) Waste discharges shall not cause the 5-day biochemical oxygen demand to exceed 5 mg/L.

Other inland waters

L.

CHEMICAL OXYGEN DEMAND (COD)

 

 

(a) Waste discharges shall not cause the chemical oxygen demand to exceed 15 mg/L.

Tuen Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground Subzones

 

(b) Waste discharges shall not cause the chemical oxygen demand to exceed 30 mg/L.

Other inland waters

M.

TOXINS

 

 

(a) Waste discharges shall not cause the toxins in water to attain such levels as to produce significant toxic, carcinogenic, mutagenic or teratogenic effects in humans, fish or any other aquatic organisms, with due regard to biologically cumulative effects in food chains and to toxicant interactions with each other.

Whole zone

 

(b) Waste discharges shall not cause a risk to any beneficial use of the aquatic environment.

Whole zone

N.

PHENOL

 

 

Phenols shall not be present in such quantities as to produce a specific odour, or in concentration greater than 0.05 mg/L as C6H5OH.

Bathing Beach Subzones

O.

TURBIDITY

 

 

Waste discharges shall not reduce light transmission substantially from the normal level.

Bathing Beach Subzones

Notes:    For WQOs with different criteria for different usage, the criterion that is more relevant to this study is highlighted.

 

Table 5.2      Water Quality Objectives for Southern Supplementary Water Control Zone (SSWCZ)

 

Water Quality Objectives

Part or Parts of Zone

A.

AESTHETIC APPEARANCE

 

 

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

Whole zone

 

(b) Tarry residues, floating wood, articles made of glass, plastic, rubber or of any other substance should be absent.

Whole zone

 

(c) Mineral oil should not be visible on the surface. Surfactants should not give rise to a lasting foam.

Whole zone

 

(d) There should be no recognisable sewage-derived debris.

Whole zone

 

(e) 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.

Whole zone

 

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

Whole zone

B.

BACTERIA

 

 

The level of Escherichia coli should be less than 1/100ml, calculated as the geometric mean of the most recent 5 consecutive samples taken at intervals of between 7 and 21 days.

Whole zone

C.

COLOUR

 

 

Human activity should not cause the colour of water to exceed 30 Hazen units.

Whole zone

D.

DISSOLVED OXYGEN

 

 

The level of dissolved oxygen should not be less than 4 mg/L.

Whole zone

E.

pH

 

 

Human activity should not cause the pH of water to exceed the range of 6.5 – 8.5 units.

Whole zone

F.

TEMPERATURE

 

 

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

Whole zone

G.

SALINITY

 

 

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

Whole zone

H.

SUSPENDED SOLIDS

 

 

Human activity should not cause the annual median of suspended solids to exceed 20 mg/L.

Whole zone

I.

 

AMMONIA

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

 

Whole zone

J.

5-DAY BIOCHEMICAL OXYGEN DEMAND (BOD5)

 

 

The 5-day biochemical oxygen demand should not exceed 3 mg/L.

Whole zone

K.

CHEMICAL OXYGEN DEMAND (COD)

 

 

The chemical oxygen demand should not exceed 15 mg/L.

Whole zone

L.

TOXIC SUBSTANCES

 

 

(a) 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.

Whole zone

 

(b) Human activity should not cause a risk to any beneficial uses of the aquatic environment.

Whole zone

 

5.2.3              Technical Memorandum on Standards for Effluents Discharges (TM-DSS)

5.2.3.1        In addition to the WQOs, the discharge of effluent is, also, 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 beneficial use of the water bodies.  The limits vary with the rate of effluent flow.  Standards for effluents discharged into the inland waters for Group A (Group A inland waters generally include all waters in water gathering grounds and within the boundaries of country parks) and Group B usage are summarised in Table 5.3 and 5.4, respectively.

Table 5.3      Standards for Effluents Discharged into Group A Inland Waters

Flow rate

(m3/day)

≦10

＞10

and

≦100

＞100

and

≦500

＞500

and

≦1000

＞1000

and

≦2000

Determinant

pH (pH units)

6.5-8.5

6.5-8.5

6.5-8.5

6.5-8.5

6.5-8.5

Temperature (℃)

35

35

30

30

30

Colour (lovibond units) (25mm cell length)

1

1

1

1

1

Conductivity (ms/cm at 20 ℃)

1000

1000

1000

1000

1000

Suspended solids

10

10

5

5

5

Dissolved oxygen

≧4

≧4

≧4

≧4

≧4

BOD

10

10

5

5

5

COD

50

50

20

20

10

Oil & Grease

1

1

1

1

1

Boron

2

2

1

0.5

0.5

Barium

2

2

1

0.5

0.5

Iron

2

2

1

0.5

0.5

Arsenic

0.05

0.05

0.05

0.05

0.05

Total chromium

0.05

0.05

0.05

0.05

0.05

Mercury

0.001

0.001

0.001

0.001

0.001

Cadmium

0.001

0.001

0.001

0.001

0.001

Selenium

0.01

0.01

0.01

0.01

0.01

Copper

0.2

0.2

0.2

0.2

0.1

Lead

0.1

0.1

0.1

0.1

0.1

Manganese

0.5

0.5

0.5

0.5

0.5

Zinc

1

1

1

1

1

Other toxic metals individually

0.1

0.1

0.1

0.1

0.1

Total toxic metals

0.3

0.3

0.2

0.2

0.15

Cyanide

0.05

0.05

0.05

0.05

0.02

Phenols

0.1

0.1

0.1

0.1

0.1

Hydrogen sulphide

0.05

0.05

0.05

0.05

0.05

Sulphide

0.2

0.2

0.1

0.1

0.1

Fluoride

1

1

1

1

0.5

Sulphate

800

600

500

400

200

Chloride

800

500

500

200

200

Total reactive phosphorus

1

0.7

0.7

0.5

0.5

Ammonia nitrogen

1

1

1

1

0.5

Nitrate + nitrite nitrogen

15

15

15

10

10

E. coli (count/100 ml)

＜1

＜1

＜1

＜1

＜1

Notes:

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

2.         The identified beneficial use of Group A inland waters is for abstraction for potable water supply.

 

Table 5.4      Standards for Effluents Discharged into Group B Inland Waters

Flow rate

(m3/day)

≦200

＞200

and

≦400

＞400

and

≦600

＞600

and

≦800

＞800

and

≦1000

＞1000

and

≦1500

＞1500

and

≦2000

＞2000

and

≦3000

Determinant

pH (pH units)

6.5-8.5

6.5-8.5

6.5-8.5

6.5-8.5

6.5-8.5

6.5-8.5

6.5-8.5

6.5-8.5

Temperature (℃)

35

30

30

30

30

30

30

30

Colour (lovibond units)

1

1

1

1

1

1

1

1

(25mm cell length)

 

 

 

 

 

 

 

 

Suspended solids

30

30

30

30

30

30

30

30

BOD

20

20

20

20

20

20

20

20

COD

80

80

80

80

80

80

80

80

Oil & Grease

10

10

10

10

10

10

10

10

Iron

10

8

7

5

4

3

2

1

Boron

5

4

3

2.5

2

1.5

1

0.5

Barium

5

4

3

2.5

2

1.5

1

0.5

Mercury

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

Cadmium

0.001

0.001

0.001

0.001

0.001

0.001

0.001

0.001

Selenium

0.2

0.2

0.2

0.2

0.2

0.1

0.1

0.1

Other toxic metals individually

0.5

0.5

0.2

0.2

0.2

0.1

0.1

0.1

Total Toxic metals

2

1.5

1

0.5

0.5

0.2

0.2

0.2

Cyanide

0.1

0.1

0.1

0.08

0.08

0.05

0.05

0.03

Phenols

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

Sulphide

0.2

0.2

0.2

0.2

0.2

0.2

0.2

0.2

Fluoride

10

10

8

8

8

5

5

3

Sulphate

800

800

600

600

600

400

400

400

Chloride

1000

1000

800

800

800

600

600

400

Total phosphorus

10

10

10

8

8

8

5

5

Ammonia nitrogen

5

5

5

5

5

5

5

5

Nitrate + nitrite nitrogen

30

30

30

20

20

20

10

10

Surfactants (total)

5

5

5

5

5

5

5

5

E. coli (count/100ml)

100

100

100

100

100

100

100

100

Notes:

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

2.         The identified beneficial use of Group B inland waters is for irrigation.

 

5.2.4              ProPECC Notes

5.2.4.1        The Practice Note for Professional Persons on Construction Site Drainage (ProPECC PN 1/94) was issued by the EPD to provide environmental guidelines for handling and disposal of construction site discharges.  It provides good practice guidelines for dealing with various types of discharge from a construction site.  Practices as outlined in the ProPECC PN 1/94 should be followed during the construction phase in order to minimise the water quality impact due to construction site drainage.  Moreover, other ProPECC Notes including the ProPECC PN 5/93 Drainage Plan (subject to Comment by the Environmental Protection Department) would also be considered.

5.2.5              Protection of the Water Gathering Grounds

5.2.5.1        The proposed works is within the Water Services Department’s (WSD) water gathering grounds (Figure 5.2).  In order to protect the water quality of the water gathering grounds and associated reservoir, the proposed works shall also comply with the relevant restriction imposed by WSD (see Appendix D3). 

5.3                    Sensitive Receivers

5.3.1.1        The main water body within 500m of the Study Area is the Ngong Ping Stream. The upper section of the Ngong Ping Stream is within the Ngong Ping Site of Special Scientific Interest (SSSI) and this section of the stream is also listed as an Ecologically Important Streams/Rivers (EIS) under ETWB TC(W) No. 5/2005.  The lower section of the Ngong Ping Stream is within the Lantau North Country Park (Figure 5.1).  Thus, the upper and lower sections of the Ngong Ping are considered as water quality sensitive receivers.  In addition, as the site is contained within the Ngong Ping Water Gathering Grounds, these would, also be considered as a water quality sensitive receiver.

5.3.1.2        In addition, as per the Study Brief, the following areas of ecological or conservation value shall also be considered in the water quality impact assessments:

(a)  Lantau North Country Park (LNCP) – the proposed new underground box culvert at the northern side of the Ngong Ping 360 Terminal and Columbarium is within the LNCP;

(b)  Lantau South Country Park (LSCP) – none of the proposed works infringed into the LSCP. The alignment section closest to the LSCP is about 400m apart; and

(c)  Conservation Area – A large portion of the areas between the country parks and the existing development are zoned as the Conservation Area under the Ngong Ping OZP (S/I-NP/6).

5.4                    Existing Drainage System

5.4.1              Background

5.4.1.1        The existing drainage system is described in detail in Section 2 and a brief summary is presented below. The catchment of Ngong Ping area covers part of Nei Lak Shan, Lantau Peak, Po Lin Monastery, Ngong Ping Terminal and local village area with total area of about 1.4km2 (Appendix A1).  The direction of water flow for the main watercourses is from the eastern uphill area to the western downhill area (i.e., east to west). At the core area of the Ngong Ping development, the existing watercourses consist of seven portions, including two box culverts underneath the Po Lin Monastery, a 1650mm diameter twin-pipe and the Ngong Ping stream and gabion channel adjacent to the Ngong Ping 360 (see Figure 2.1), as listed below:

·        Portion A – A natural stream near water storage tank at the North of Po Lin Monastery in the conservation area;

·        Portion B – A box culvert underneath Po Lin Monastery;

·        Portion C – A box culvert located at the south of Po Lin Monastery;

·        Portion D – A 1650mm diameter drainage twin-pipe;

·        Portion E – Ngong Ping Stream between the 1650mm diameter twin-pipe and the gabion channel next to Ngong Ping 360 Terminal;

·        Portion F - Gabion channel near Ngong Ping 360 Terminal; and

·        Portion G - Natural stream of Ngong Ping Stream at the downstream of Portion F gabion channel in the Lantau North Country Park.

5.4.1.2        The runoff from the sub-catchment of Nei Lak Shan is collected by the box culvert underneath the Po Lin Monastery (Portion B) and the runoff from the sub-catchment of the Lantau Peak is collected by the box culvert located to the south of the Po Lin Monastery (Portion C).  The collected runoff is discharged into the 1650mm diameter twin-pipe (Portion D). The runoff is then conveyed westward, through the existing watercourse near the local village area (Portion E) and passing through the embanked gabion channel (Portion F) and natural stream (Portion F) near Ngong Ping 360 Terminal before being discharged downhill along the downstream section of Ngong Ping Stream.

5.4.2              Flooding Incidents and Flooding Risk Analysis

5.4.2.1        Flooding incidents have been previously recorded in a few locations within the Study Area (see Figure 2.2). The 2008 Drainage Study included a detailed hydraulic modelling  assessment of the existing drainage system.  

5.4.2.2        Based on a 50 years design return period (see Section 2), with the existing drainage system, the hydraulic modelling predicted flooding at several locations including the northern side of the Po Lin Monastery, natural stream near Lin Ping Drive and the Y-junction near Ngong Ping 360 and Columbarium area. While the interim mitigation measures described in Section 2 provide some immediate relief to certain flooding hotspots, long terms measures to improve the total drainage system of Ngong Ping are required.  Hence, the Project needs to be implemented to protect the Po Lin Monastery, the Ngong Ping 360 Terminal, the local villagers and the local habitats..

5.5                    Baseline Pollution Loading

5.5.1.1        Prior to the operation of the Ngong Ping Sewage Treatment Works (STW), the sewage treatment facilities at Ngong Ping included grease traps and soakaway septic tanks which were found to be inadequate and significant quantities of sewage were being directly discharged into the local streams. It was under this setting that the Ngong Ping STW and associated sewerage infrastructures was constructed in late 2005 in order to improve the local sewage treatment standard and the water quality of local watercourses.

5.5.1.2        Historically, while observations over a long period of time indicated that the watercourse ecosystem was stressed by the effects of pollution primarily from domestic sources, there were no quantitative records of the water quality.  The EPD has an established network of river water quality monitoring programme, however, the nearest one to the Ngong Ping Stream is the Tung Chung River which is in a different catchment. The EPD’s monitoring results for downstream section of Tung Chung River, therefore, cannot adequately reflect the status of the uphill Ngong Ping Stream.

5.6                    Project Specific Baseline Water Quality Monitoring Programme

5.6.1              Survey Objectives

5.6.1.1        The EIA Study Brief defines the following particular objectives with respect to baseline water quality:

(a)     collection and review of background information on the existing water system(s) and their respective catchments, and sensitive receivers which may be affected by the Project during construction and operational stage;

(b)     characterization of water quality of the related water system(s), their respective catchment and sensitive receivers, which may be affected by the Project during construction and operational stages, based on existing best available information or appropriate site survey/tests; and

(c)     establishment and provision of an emission inventory on the quantities and characteristics of these existing and likely future pollution sources in the study area. Field investigation and laboratory tests shall be conducted as appropriate to fill in any relevant information gaps.

5.6.1.2        In order to meet these requirements and obtain the necessary baseline condition of the watercourses in the Study Area, a project specific water quality monitoring programme was carried out between September 2011 and March 2012, with a further wet season survey in August 2012.

5.6.2              Water Quality Monitoring Stations

5.6.2.1        With reference to the proposed alignment and topography, seventeen (17) sampling points in the Study Area were proposed as indicated in Figure 5.3.  The 17 locations cover both upstream (upstream reference (UR) and upstream impact (UI) stations) and downstream (downstream reference (DR) and downstream impact (DI)) locations and include important sites like Lantau North Country Park (W8 and W9), the Ngong Ping Site of Special Scientific Interest (SSSI) (R1, R4 and R6) and the conservation area (R2 and W10). The nature of these monitoring stations with respect to the proposed project is presented in Table 5.5.  These stations also coincided with the freshwater aquatic ecology survey (see Section 6) so that the data can be referenced in ecology impact assessment.  

Table 5.5      Baseline Water Quality Monitoring Stations

ID

Location

Nature

Remark

R1

Ngong Ping Stream in the Ngong Ping SSSI, about 350m to the east of the Tian Tan Buddha Statue

Upstream reference station (UR). Natural section of Ngong Ping Stream (EIS).

Seasonal stream that dried up in the dry season. Far from the proposed works.

R2

A natural stream about 50m to the east of PLM water storage tank

Upstream reference station (UR).  Natural stream in the conservation area.

Upstream of the proposed Intake A (Works Section 1).

R3

Watercourse about 80m upstream of the proposed box culvert (Works Section 5)

Upstream reference station (UR).

The watercourse was completely dry throughout the study period. No sampling can be undertaken.

R4

Ngong Ping Stream, about 190m further upstream of R1

Upstream reference station (UR). Natural section of Ngong Ping Stream (EIS).

Additional upstream station. The stream was dry in the dry season.

R5

A small watercourse to the southeast of PLM

Upstream reference station (UR). A small season stream.

Additional upstream station. The stream was dry in the dry season.

R6

Ngong Ping Stream, about 160m downstream of R1.  Immediately before the twin pipe at Portion D.

Upstream reference station (UR). Natural section of Ngong Ping stream.

Additional upstream station.  Far from the proposed works.

W1

A small natural stream right next to the west of PLM water storage tank. Immediate adjacent to the C&C works at Woks Section 1.

Upstream impact station (UI), next to village houses.

Indication of upstream water quality close to existing settlement.

W2

A small natural stream next to 慈德苑

Upstream impact station (UI), next to village houses. About 10m upstream of the works area WA1.

Indication of upstream water quality close to existing settlement.

W3

A stream  to the west of Lin Ping Drive (Portion E)

Downstream impact station (DI), next to village houses. About 40m downstream of Intake B. 

Indication of downstream water quality close to existing settlement.

W4

Watercourse about 110m to the south east of眾善蓮苑. About 10m upstream of the box culvert at Works Section 5.

Upstream impact station (UI), next to village houses.

The watercourse was dry in the dry season.

W5

Watercourse about 40m to the south west of眾善蓮苑. About 15m upstream of the box culvert at Works Section 5.

Upstream impact station (UI), next to village houses.

The watercourse was completely dried thorough the study period. No sampling can be undertaken.

W6

A natural stream to the west of Lin Ping Drive (Portion E). About 40m downstream of Intake B. 

Downstream impact station (DI), next to village houses.

Indication of downstream water quality close to existing settlement.

W7

Gabion channel to the north of Waking with Buddha. At about Outfall A.

Downstream impact station (DI), next to village houses.

Indication of downstream water quality close to existing settlement.

W8

Downstream section of Ngong Ping Stream, about 40m to the south west of the Columbarium. About 25m from jacking pit JP2.

Downstream reference station (DR).

Indication of natural stream water quality downstream of existing settlement.

W9

Downstream section of Ngong Ping Stream, immediate north of the Columbarium.

Downstream reference station (DR). At about Outfall B.

Indication of natural stream water quality downstream of existing settlement.

W10

Watercourse about 300m downhill of the Tan Buddha Statue

Upstream reference station (UR).

The watercourse was completely dry throughout the study period. No sampling can be undertaken.

W12

Ngong Ping STW storm drain outfall.

Upstream reference station, (UR) for discharge from developed area. 

Indication of upstream water quality from Ngong Ping STW.

Notes:

1.             Refer to Figures 2.9a-2.9g for the locations of works section and works area. PLM = Po Lin Monastery; STW = sewerage treatment works.

2.             Please refer to Figure 5.3 for location of the monitoring stations.

3.             Grey shading: monitoring of the station planned but could not be undertaken as the area had dried up or did not have adequate amounts of water flow. 

 

5.6.2.2        While seventeen (17) sampling points were planned to be surveyed, like many of the local uphill streams, some of the watercourses at Ngong Ping were found to be mostly seasonal streams and, generally, did not have sufficient water flows most of the time. Therefore, ultimately only fourteen (14) stations could be monitored despite efforts to increase the sampling success by arranging the sampling to be undertaken immediately after rainfall events and minor adjustments to the actual sampling location based on the site conditions.

5.6.3              Water Quality Monitoring Parameters

5.6.3.1        The followings factors were considered in determining the water quality parameters to be monitored and tested for the baseline survey:

(a)     Nature and purpose of this survey described above;

(b)     Relevant water quality objectives (WQO);

(c)     General land use of the area which is predominantly a mix of agricultural and residential type although more commercial activities are introduced recently. There being, however, no industrial activities in the area;

(d)    Other water quality sampling and monitoring study of similar nature. In this regard, reference is made to the EIA report for Drainage Improvement in Northern Hong Kong Island - Hong Kong West Drainage Tunnel (Register No.: AEIAR-099/2006, approved in April 2006) in which similar stream water quality survey and monitoring was undertaken in March and May 2004; and

(e)     Natural geology of Lantau Island in which arsenic in soils may be naturally high.

5.6.3.2        At each sampling point, duplicate measurements of the following in-situ parameters were taken (Table 5.6). The water depth of each sampling point was, also, recorded. These parameters describe the basic physical chemical properties of the water. The total residual chlorine (TRC) indicates the release of chlorine bleach disinfectant from domestic and commercial sources.

Table 5.6      Summary of In-situ Measurement Parameters

Parameter

WQO

Range

Accuracy

Unit

QA/QC

Salinity

-

0 – 40

± 0.5%

Part per thousand (ppt)

Duplicate reading with ≤25% difference, recalibration

Temperature

-

0 – 45

± 0.2

oC

Duplicate reading with ≤25% difference, recalibration

Dissolved oxygen (DO)

>4

0 – 20

± 0.2

mg/L

Duplicate reading with ≤25% difference, recalibration

Turbidity

-

0 – 1000

± 5%

reading in NTU

Duplicate reading with ≤25% difference, recalibration

pH

6.5 – 8.5

2 – 12

± 0.2

pH unit

Duplicate reading with ≤25% difference, recalibration

Total Residual Chlorine (TRC)

-

0.2 – 4

± 1%

mg/L

Duplicate reading with ≤25% difference, recalibration

 

5.6.3.3        Duplicate water samples were, also, collected for laboratory analysis. The water quality monitoring parameters, relevant benchmark criteria and also the reporting limits are detailed in Table 5.7 below.

Table 5.7      Summary of Laboratory Analysis Parameters and Relevant Benchmark Criteria

No

Parameter

Unit

WQO1

Discharge Limit2

Reporting Limit

Group A3

Group B3

1

Suspended Solids (SS)

mg/L

20

10 / 5

30 / 30

2

2

Oil & Grease (O&G)

mg/L

-

1 / 1

10 / 10

2 (1)5

3

5-day Biochemical Oxygen Demand (BOD5)

mg/L

3

10 / 5

20 / 20

2

4

Chemical Oxygen Demand (COD)

mg/L

15

50 / 10

80 / 20

2

5

Total Organic Carbon (TOC)

mg/L

-

-

-

1

6

Total Kjeldahl Nitrogen (TKN)

mg/L

-

-

-

0.1

7

Nitrate + Nitrite (NOx)

mg/L

-

15 / 10

30 / 10

-

7a

Nitrate NO3

mg/L

-

-

-

0.01

7b

Nitrite NO2

mg/L

-

-

-

0.01

8

Ammonia (NH4)

mg/L

-

1 / 0.5

5 / 5

0.01

8a

Unionised Ammonia (NH3)4

mg/L

0.021

-

-

-

9

Total Phosphorus (TP)

mg/L

-

-

10 / 5

0.01

10

Orthophosphate (OP)

mg/L

-

1 / 0.5

-

0.01

11

E. coli

cfu/100mL

1

<1 / <1

100 / 100

1

12

Chlorophyll-a

ug/L

-

-

-

16

13

Total Surfactant (TSur)

mg/L

-

-

5 / 5

1

13a

Anionic Surfactant

mg/L

-

-

-

0.5

13b

Non-ionic Surfactant

mg/L

-

-

-

0.5

14

Arsenic (As)

ug/L

-

50 / 50

-

1

Notes:

1.   The WQO refer to applicable the Water Gathering Ground subzone, whole zone or inland waters of NWWCZ and/or SSWCZ whichever is more stringent.

2.   The discharge limit refers to the Technical Memorandum Standards For Effluent Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters (TM-DSS). Group A refer to inland water Group A for abstraction for portable water supply. Group B refer to inland water Group B for irrigation.

3.   The x/x represents the higher and lower allowed concentrations in the discharge standard and in general the higher the flows, the lower is the allowable concentrations.

4.   The WQO is based on unionised ammonia (NH3), but laboratory only provide analysis of total ammonia (NH4). The NH3 can be calculated from the in-situ measured temperature and pH. For typical summer water of 20°C and pH of 7.4, the NH4 level need to be > 2 mg/L to cause exceedance in NH3 and a reporting limit of 0.01 mg/L for NH4 is considered sufficient. A lower temperature reduces the fraction of NH3.

5.   Reporting limit without accreditation is indicated in the parentheses.

6.   HOKLAS accredited method for marine water applied.

 

5.6.3.4        Suspended solids (SS) measure the amount of insoluble materials in the water. Organic pollution of river water is measured by 5-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD) and total organic carbon (TOC). The potential for river eutrophication was measured by the nitrogen nutrient (ammonia-nitrogen (NH4), nitrogen oxides (NOx; = NO2 + NO3) and total Kjeldahl nitrogen (TKN)), phosphorus nutrient (orthophosphate (OP) and total phosphorus (TP)) and the plant pigment chlorophyll-a. The oil and grease (O&G) and surfactants (i.e., detergent) measure domestic and commercial pollution. Escherichia coli indicate faecal contamination from domestic sewage and animal waste.

5.6.3.5        The laboratory testing works was performed by ALS Technichem (HK) Pty Ltd. which provides HOKALS accredited testing services for all the required parameters. The HOKLAS endorsed laboratory procedures were followed including the relevant quality assurance and quality control requirements (e.g., method blanks, batch duplicates and reference material for every batch of 20 samples). Full details of the water quality monitoring proposal are presented in Appendix D1.

5.6.4              Water Quality Monitoring Programme

5.6.4.1        The water quality stations were monitored monthly between September 2011 to March 2012 and again in August 2012, covering both the wet and dry season periods. Where possible, the monthly sampling events were conducted after rainfall events to increase the success rate of the sampling works (i.e., the number of stations sampled).  The sampling dates and stations monitored are summarised in Table 5.8 below.

 

 

 

Table 5.8      Summary of Sampling Programme

Station(1)

Wet Season

Dry Season

21-Sep-11

18-Oct-11

6-Aug-12

31-Dec-11

19-Jan-12

23-Feb-12

13-Mar-12

R1

ü

ü

ü

-

-

-

-

R2

ü

ü

ü

ü

ü

ü

ü

R4

-

-

ü

-

-

-

-

R5

-

-

ü

-

-

-

-

R6

- (2)

ü

ü

ü

ü

-

-

W1

ü

ü

ü

ü

ü

ü

ü

W2

ü

ü

ü

ü

ü

ü

ü

W3

ü

ü

ü

ü

ü

ü

ü

W4

-

-

ü

-

-

-

-

W6

ü

ü

ü

ü

ü

ü

ü

W7

ü

ü

ü

-

-

-

ü

W8

ü

ü

ü

ü

ü

ü

ü

W9

ü

ü

ü

ü

ü

ü

ü

W12

- (2)

ü

ü

ü

ü

ü

ü

Total No. of Stations

9

11

14

9

9

8

9

Total No. of Samples

18

22

28

18

18

16

18

Notes:

1.    Only the stations with sufficient water flow to allow monitoring to be undertaken are shown in the table.

2.    Not included in the initial round of monitoring.

 

5.6.5              Water Quality Monitoring Results

5.6.5.1        Six of the planned monitoring stations (R3, R4, R5, W4, W5 and W10) were noted to be completely dried up or with minimal amounts of surface water during the monitoring period between September 2011 to March 2012 and three stations were dry or without sufficient water (R3, W5 and W10) in August 2012.  Based on the observations of overgrown vegetation and deposits of fallen plant materials, it was evident that these sections of the watercourses were highly seasonal and did not have flow for the majority of the time.  In respect of the 14 stations with a reasonable amount of water, the average water depth was noted to be 23cm and ranged between 5 –59cm (Table 5.10).  In general, higher water depths were recorded in the wet season and this is not unexpected given that many of the small hill streams in Hong Kong are seasonal streams.

5.6.5.2        A total set of 138 in-situ measurements were undertaken and the same number of water samples were collected from the 14 stations for laboratory analysis. Sixty-eight (68) measurements/samples were taken in the three wet season months, that is 23 samples per month on average, and seventy (70) measurements/samples were taken in the four dry season months, equating to 17.5 samples per month on average. Table 5.9 presents the compliance statistics of the measured results compared to the relevant benchmark criteria, as discussed above. A summary of the water quality monitoring results is presented in Table 5.10 – 5.12 below and the full results are presented in Appendix D2. 

Table 5.9      Non-compliance Statistics of Baseline Water Samples

Parameter(1)

Criteria

Unit

Wet Season

Dry Season

Overall

Number

%

Number

%

Number

%

DO

≥42

mg/L

12

18%

14

20%

26

19%

pH

6.5-8.52

pH Unit

18

26%

6

9%

24

17%

SS

<53

mg/L

11

16%

8

11%

19

14%

O&G

<13

mg/L

5

7%

0

0%

5

4%

BOD5

<32

mg/L

2

3%

13

19%

15

11%

COD

<103

mg/L

7

10%

21

30%

28

20%

NOx

<103

mg/L

0

0%

0

0%

0

0%

NH4

<0.53

mg/L

2

3%

6

9%

8

6%

NH3

<0.0212

mg/L

0

0%

0

0%

0

0%

TP

<53

mg/L

0

0%

0

0%

0

0%

OP

<0.53

mg/L

4

6%

8

11%

12

9%

E. coli

<12,3

cfu/100mL

68

100%

65

93%

133

96%

TSur

<53

mg/L

0

0%

0

0%

0

0%

As

<503

µg/L

0

0%

0

0%

0

0%

Notes:

1.       As = Arsenic; BOD5 = Biochemical Oxygen Demand; COD = Chemical Oxygen Demand; DO = Dissolved Oxygen; NH3 = Unionised Ammonia; NH4 = Ammonia Nitrogen; NOx = Nitrogen Oxides; O&G = Oil & Grease; OP = Orthophosphate; SS = Suspended Solids; TSur = Total Surfactants; TP = Total Phosphorus.

2.       WQO

3.      TM-DDS. Group B standard applies if it is not a criterion for Group A usage.

 

 

Table 5.10    Summary of Baseline Water Quality Monitoring In-situ Results and Suspended Solids

 

Water Depth

Dissolved Oxygen (DO)

pH

Salinity

Temperature

Turbidity

Suspended Solids (SS)

Total Residual Chlorine (TRC)

Unit

cm

mg/L

pH Unit

psu

°C

NTU

mg/L

mg/L

RL

-

0.1

0.1

0.1

0.1

0.1

2

0.2

Criteria

-

≥ 4

6.5 - 8.5

-

-

-

5

-

%>RL

-

100%

100%

22%

100%

99%

12%

31%

R1 (n=6)

16 (15 - 19)

3.2 (1.4 - 4.6)

6.0 (5.5 - 6.5)

<0.1

21.9 (20.5 - 23.4)

11.3 (3.0 - 19.7)

5 (<2 - 8)

<0.2

R2 (n=14)

21 (15 - 25)

6.9 (4.0 - 8.2)

6.3 (5.5 - 7.4)

<0.1

17.8 (13.2 - 23.1)

2.3 (<1 - 4.0)

1 (<2 - 1)

<0.2

R4 (n=2)

50 (50 - 50)

3.5 (3.5 - 3.5)

5.2 (5.2 - 5.2)

<0.1

23.7 (23.7 - 23.7)

5.5 (5.0 - 6.0)

1 (<2 - 1)

<0.2

R5 (n=2)

25 (25 - 25)

1.1 (1.1 - 1.1)

6.1 (6.1 - 6.1)

<0.1

22.7 (22.6 - 22.8)

4.5 (4.0 - 5.0)

1 (<2 - 1)

<0.2

R6 (n=8)

27 (16 - 35)

5.2 (3.7 - 5.9)

7.0 (5.5 - 8.1)

<0.1

18.3 (13.9 - 23.3)

13.6 (3.0 - 30.0)

8 (<2 - 20)

<0.2

UR (n=32)

23 (15 - 50)

5.2 (1.1 - 8.2)

6.3 (5.2 - 8.1)

<0.1

19.3 (13.2 - 23.7)

7.2 (<1 - 30.0)

3 (<2 - 20)

<0.2

UR_STW
(W12) (n=12)

27 (15 - 33)

10.0 (8.7 - 12.2)

7.5 (7.0 - 8.3)

0.3 (0.2 - 0.4)

20.2 (15.6 - 26.7)

4.4 (2.0 - 9.2)

2 (<2 - 5)

<0.2

W1 (n=14)

23 (11 - 30)

7.2 (0.7 - 9.6)

6.8 (6.1 - 7.5)

0.1 (<0.1 - 0.3)

18.3 (13.8 - 23.6)

4.2 (2.0 - 11.0)

2 (<2 - 8)

<0.2

W2 (n=14)

17 (11 - 23)

8.0 (7.2 - 9.2)

6.8 (6.3 - 7.9)

<0.1

18.3 (13.5 - 22.6)

3.2 (2.0 - 5.0)

2 (<2 - 5)

<0.2

W4 (n=2)

10 (10 - 10)

2.2 (2.2 - 2.2)

6.7 (6.7 - 6.7)

0.2

26.2 (26.2 - 26.2)

2.0 (2.0 - 2.0)

2 (<2 - 2)

<0.2

UI (n=30)

19 (10 - 30)

7.3 (0.7 - 9.6)

6.8 (6.1 - 7.9)

0.1 (<0.1 - 0.3)

18.9 (13.5 - 26.2)

3.6 (2.0 - 11.0)

2 (<2 - 8)

<0.2

W3 (n=14)

22 (5 - 35)

5.7 (3.8 - 7.3)

7.0 (6.7 - 7.6)

0.1 (<0.1 - 0.1)

19.6 (15.0 - 23.7)

9.5 (2.6 - 37.0)

5 (<2 - 26)

<0.2

W6 (n=14)

19 (12 - 28)

4.0 (1.8 - 6.5)

7.0 (6.6 - 7.4)

0.1 (<0.1 - 0.1)

19.3 (14.1 - 24.1)

4.7 (2.8 - 7.0)

4 (<2 - 9)

<0.2

W7 (n=8)

18 (10 - 30)

5.5 (4.6 - 6.0)

6.9 (6.6 - 7.6)

0.1 (<0.1 - 0.1)

21.3 (14.0 - 24.3)

4.2 (2.0 - 7.0)

2 (<2 - 7)

<0.2

DI (n=36)

20 (5 - 35)

5.0 (1.8 - 7.3)

7.0 (6.6 - 7.6)

0.1 (<0.1 - 0.1)

19.8 (14.0 - 24.3)

6.4 (2.0 - 37.0)

4 (<2 - 26)

<0.2

W8 (n=14)

31 (15 - 59)

6.6 (5.5 - 8.1)

7.1 (6.8 - 7.7)

0.1 (<0.1 - 0.1)

20.0 (14.9 - 25.1)

9.5 (3.0 - 26.0)

4 (<2 - 11)

<0.2

W9 (n=14)

27 (15 - 47)

6.9 (3.6 - 8.3)

7.1 (6.6 - 7.8)

0.1 (<0.1 - 0.2)

19.4 (13.9 - 25.1)

18.9 (1.4 - 116.0)

8 (<2 - 54)

<0.2

DR (n=28)

29 (15 - 59)

6.8 (3.6 - 8.3)

7.1 (6.6 - 7.8)

0.1 (<0.1 - 0.2)

19.7 (13.9 - 25.1)

14.2 (1.4 - 116.0)

6 (<2 - 54)

<0.2

Total

23 (5 - 59)

6.3 (0.7 - 12.2)

6.8 (5.2 - 8.3)

0.1 (<0.1 - 0.4)

19.5 (13.2 - 26.7)

7.4 (<1 - 116.0)

4 (<2 - 54)

<0.2

Notes:

1.     Values are expressed as arithmetic mean (min- max), unless all samples were below detection. For samples that are below detection, the value is substituted with ½ RL for calculation of arithmetic mean. Shaded cell = mean value exceed the relevant criterion.

2.     UR = Upstream Reference Stations (R1, R2 and R6); UR_STW = Upstream Reference Station STW (W12); UI = Upstream Impact Stations (W1 and W2); DI = Downstream Impact Stations (W3, W6 and W7); DR = Downstream Reference Stations (W8 and W9).

3.     RL = Reporting Limit; n = number of samples.

Table 5.11    Summary of Baseline Water Quality Monitoring Results – Pollution Indicators

 

Oil and Greases (O&G)

Biochemical Oxygen Demand (BOD5)

Chemical Oxygen Demand (COD)

Total Organic Carbon (TOC)

E. coli

Total Surfactants (TSur)

Arsenic (As)

Unit

mg/L

mg/L

mg/L

mg/L

cfu/100mL

mg/L

µg/L

RL

1

2

2

1

1

1

1

Criteria

1

3

10

-

<1

5

50

%>RL

10%

18%

83%

75%

96%

0%

48%

R1 (n=6)

1 (<1 - 1)

2 (<2 - 3)

15 (5 - 30)

6 (3 - 11)

145 (19 - 390)

<1

6 (<1 - 15)

R2 (n=14)

1 (<1 - 1)

1 (<2 - 1)

4 (<2 - 14)

1 (<1 - 6)

320 (<1 - 2000)

<1

1 (<1 - 1)

R4 (n=2)

1 (<1 - 1)

1 (<2 - 1)

11

5 (5 - 5)

59 (49 - 69)

<1

1 (<1 - 1)

R5 (n=2)

1 (<1 -2)

1 (<2 - 1)

4 (3 - 4)

1 (<1 - 2)

62 (52 - 71)

<1

1 (<1 - 1)

R6 (n=8)

1 (<1 - 1)

1 (<2 - 2)

5 (<2 - 13)

2 (2 - 3)

833 (30 - 2000)

<1

1 (<1 - 1)

UR (n=32)

1 (<1 - 2)

1 (<2 - 3)

7 (<2 - 30)

3 (<1 - 11)

383 (<1 - 2000)

<1

2 (<1 - 15)

UR_STW
(W12) (n=12)

1 (<1 - 1)

1 (<2 - 1)

6 (4 - 10)

3 (<1 - 4)

311 (<1 - 1800)

<1

2 (<1 - 6)

W1 (n=14)

1 (<1 - 1)

2 (<2 - 6)

6 (<2 - 31)

2 (<1 - 9)

710 (<1 - 3900)

<1

1 (<1 - 2)

W2 (n=14)

1 (<1 - 1)

1 (<2 - 1)

2 (<2 - 4)

1 (<1 - 2)

553 (80 - 1800)

<1

1 (<1 - 1)

W4 (n=2)

1 (<1 - 1)

1 (<2 - 1)

20 (20 - 20)

9 (8 - 9)

440 (410 - 470)

<1

2 (2 - 2)

UI (n=30)

1 (<1 - 1)

1 (<2 - 6)

5 (<2 - 31)

2 (<1 - 9)

619 (<1 - 3900)

<1

1 (<1 - 2)

W3 (n=14)

1 (<1 - 1)

5 (<2 - 11)

14 (3 - 36)

5 (1 - 12)

5623 (630 - 32000)

<1

1 (<1 - 2)

W6 (n=14)

1 (<1 - 1)

4 (<2 - 11)

14 (3 - 47)

5 (2 - 15)

2596 (60 - 13000)

<1

1 (<1 - 2)

W7 (n=8)

1 (<1 - 1)

1 (<2 - 1)

5 (<2 - 7)

2 (1 - 3)

353 (30 - 720)

<1

2 (<1 - 5)

DI (n=36)

1 (<1 - 2)

3 (<2 - 11)

12 (<2 - 47)

5 (1 - 15)

3275 (30 - 32000)

<1

1 (<1 - 5)

W8 (n=14)

1 (<1 - 1)

1 (<2 - 1)

7 (3 - 12)

3 (1 - 4)

560 (34 - 3000)

<1

2 (<1 - 4)

W9 (n=14)

1 (<1 - 1)

1 (<2 - 1)

6 (4 - 8)

3 (2 - 4)

1051 (10 - 10000)

<1

2 (1 - 3)

DR (n=28)

1 (<1 - 1)

1 (<2 - 1)

6 (3 - 12)

3 (1 - 4)

805 (10 - 10000)

<1

2 (<1 - 4)

Total

1 (<1 - 2)

2 (<2 - 11)

8 (<2 - 47)

3 (<1 - 15)

1268 (<1 - 32000)

<1

2 (<1 - 15)

Notes:

1.     Values are expressed as arithmetic mean (min- max), unless all samples were below detection. For samples that are below detection, the value is substituted with ½ RL for calculation of arithmetic mean. Shaded cell = mean value exceed the relevant criterion.

2.     UR = Upstream Reference Stations (R1, R2 and R6); UR_STW = Upstream Reference Station STW (W12); UI = Upstream Impact Stations (W1 and W2); DI = Downstream Impact Stations (W3, W6 and W7); DR = Downstream Reference Stations (W8 and W9).

3.     RL = Reporting Limit; n = number of samples.

Table 5.12    Summary of Baseline Water Quality Monitoring Results – Nutrient Loadings and Chlorophyll

 

Total Kjeldahl Nitrogen  (TKN)

Nitrogen Oxide (NOx)

Ammonia Nitrogen (NH4)

Unionised Ammonia (NH3)

Total Phosphorus (TP)

Ortho-phosphate (OP)

Chlorophyll-a

Unit

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

µg/L

RL

0.1

0.02

0.01

0.001

0.01

0.01

1

Criteria

-

10

0.5

0.021

5

0.5

-

%>RL

77%

96%

80%

33%

90%

68%

23%

R1 (n=6)

0.5 (0.1 - 1.0)

0.41 (0.05 - 0.91)

0.16 (0.05 - 0.36)

0.001 (<0.001 - 0.001)

0.75 (0.05 - 1.83)

0.63 (0.03 - 1.68)

1 (<1 - 2)

R2 (n=14)

0.1 (<0.1 - 0.2)

0.03 (<0.02 - 0.08)

0.02 (<0.01 - 0.07)

0.001 (<0.001 - 0.001)

0.01 (<0.01 - 0.02)

<0.01

0 (<1 - 1)

R4 (n=2)

0.2 (0.2 - 0.2)

0.21 (0.20 - 0.21)

0.10 (0.10 - 0.10)

<0.001

0.01 (0.01 - 0.01)

<0.01

<1

R5 (n=2)

0.2 (0.1 - 0.2)

0.36 (0.35 - 0.36)

0.06 (0.06 - 0.06)

<0.001

0.03 (0.03 - 0.03)

<0.01

<1

R6 (n=8)

0.3 (0.1 - 0.7)

0.25 (0.19 - 0.32)

0.05 (<0.01 - 0.13)

0.001 (<0.001 - 0.001)

0.04 (0.02 - 0.07)

0.01 (<0.01 - 0.02)

2 (<1 - 4)

UR (n=32)

0.2 (<0.1 - 1.0)

0.19 (<0.02 - 0.91)

0.06 (<0.01 - 0.36)

0.001 (<0.001 - 0.001)

0.16 (0.01 - 1.83)

0.12 (<0.01 - 1.68)

1 (<1 - 4)

UR_STW(W12) (n=12)

0.5 (0.2 - 1.2)

3.84 (1.61 - 8.32)

0.05 (<0.01 - 0.12)

0.001 (<0.001 - 0.003)

2.43 (0.96 - 4.64)

2.32 (0.88 - 4.33)

1 (<1 - 2)

W1 (n=14)

0.2 (<0.1 - 1.1)

0.14 (0.03 - 0.43)

0.05 (<0.01 - 0.20)

0.001 (<0.001  - 0.001)

0.02 (0.01 - 0.11)

<0.01

1 (<1 - 3)

W2 (n=14)

0.1 (<0.1 - 0.1)

0.10 (<0.02 - 0.34)

0.01 (<0.01 - 0.02)

0.001 (<0.001  - 0.001)

0.02 (0.01 - 0.03)

0.01 (<0.01 - 0.02)

0 (<1 - 1)

W4 (n=2)

0.6 (0.5 - 0.6)

0.04 (0.04 - 0.04)

0.05 (<0.05 - 0.05)

<0.001

0.04 (0.04 - 0.04)

<0.01

<1

UI (n=30)

0.2 (<0.1 - 1.1)

0.12 (<0.02 - 0.43)

0.03 (<0.01 - 0.20)

0.001 (<0.001 - 0.001)

0.02 (0.01 - 0.11)

0.01 (<0.01 - 0.02)

1 (<1 - 3)

W3 (n=14)

1.1 (0.2 - 2.0)

0.41 (0.22 - 0.80)

0.41 (0.08 - 0.80)

0.003 (0.001 - 0.012)

0.22 (0.05 - 0.50)

0.11 (0.01 - 0.20)

2 (<1 - 6)

W6 (n=14)

1.0 (0.2 - 2.8)

0.29 (<0.02 - 0.58)

0.46 (0.14 - 1.11)

0.002 (0.001 - 0.005)

0.22 (0.05 - 0.52)

0.14 (0.02 - 0.35)

3 (<1 - 10)

W7 (n=8)

0.2 (0.2 - 0.3)

0.50 (0.22 - 0.97)

0.06 (0.01 - 0.11)

0.001 (<0.001 - 0.001)

0.06 (0.04 - 0.08)

0.04 (0.02 - 0.07)

0 (<1 - 1)

DI (n=36)

0.9 (0.2 - 2.8)

0.39 (<0.02 - 0.97)

0.35 (0.01 - 1.11)

0.002 (<0.001  - 0.012)

0.18 (0.04 - 0.52)

0.11 (0.01 - 0.35)

2 (<1 - 10)

W8 (n=14)

0.4 (0.2 - 0.7)

0.72 (0.18 - 1.79)

0.09 (0.04 - 0.18)

0.001 (<0.001 - 0.002)

0.18 (0.07 - 0.43)

0.15 (0.02 - 0.39)

1 (<1 - 2)

W9 (n=14)

0.3 (0.1 - 0.6)

0.60 (0.03 - 1.42)

0.03 (<0.01 - 0.09)

0.001 (<0.001 - 0.001)

0.15 (0.04 - 0.38)

0.12 (0.01 - 0.35)

0 (<1 - 1)

DR (n=28)

0.3 (0.1 - 0.7)

0.66 (0.03 - 1.79)

0.06 (<0.01 - 0.18)

0.001 (<0.001   - 0.002)

0.17 (0.04 - 0.43)

0.13 (0.01 - 0.39)

1 (<1 - 2)

Total

0.4 (<0.1 - 2.8)

0.64 (<0.02 - 8.32)

0.13 (<0.01 - 1.11)

0.001 (<0.001   - 0.012)

0.33 (<0.01 - 4.64)

0.29 (<0.01 - 4.33)

1 (<1 - 10)

Notes:

1.     Values are expressed as arithmetic mean (min- max), unless all samples were below detection, except for E. coil. For samples that are below detection, the value is substituted with ½ RL for calculation of arithmetic mean. Shaded cell = mean value exceeded the relevant criterion.

2.     UR = Upstream Reference Stations (R1, R2 and R6); UR_STW = Upstream Reference Station STW (W12); UI = Upstream Impact Stations (W1 and W2); DI = Downstream Impact Stations (W3, W6 and W7); DR = Downstream Reference Stations (W8 and W9).

3.     RL = Reporting Limit; n = number of samples.

Dissolved Oxygen

5.6.5.3        Overall, 19% of the samples have DO concentrations exceeding the WQO (Table 5.9). The average dissolved oxygen (DO) concentration is 6.3mg/L and above the WQO of 4mg/L (range: 0.7 – 12.2 mg/L; Table 5.10).  The station average of upstream reference (UR) R1 (3.2 mg/L), R4(3.5 mg/L), R5 (1.1 mg/L) and downstream impact (DI) W4 (2.2 mg/L), however, was below the WQO. Individual non-compliances were, also, recorded at other upstream reference (UR), upstream impact (UI), and downstream reference (DR) stations. The results suggested that water bodies in the Study Area were still occasionally stressed in terms of DO.

pH

5.6.5.4        Overall, 17% of the samples have pH exceeding the WQO (Table 5.9).  The average pH was 6.8 pH unit (range: 5.2 – 8.3pH unit; Table 5.10) and within the WQO range of 6.5 – 8.5 pH unit. However, the station average of upstream reference (UR) R1 (6.0 pH unit), R2 (6.3 pH unit), R4 (5.2 pH unit) and R5 (6.1 pH unit) was below the WQO. The acidic samples (low pH) recorded in the natural upstream stations could be related acidic bedrock of the area consisting mainly of volcanic rhyolite lava and tuff (see Appendix A4).

Suspended Solids

5.6.5.5        Overall, 14% of the samples have suspended solids (SS) exceeding the TM-DSS (Table 5.9). The loading of SS was, generally, low and averaged 4 mg/L (range: <2 –54 mg/L; Table 5.10), below the WQO of 20 mg/L and TM-DSS discharge limit of 5 mg/L for Group A usage. However, the station average of upstream reference (UR) R6 (8 mg/L), W9 (8 mg/L) exceeded the TM-DSS.  Individual non-compliances of TM-DSS were, also, recorded at other upstream reference (UR), upstream impact (UI), and downstream impact (DI) stations.

Biochemical Oxygen Demand, Chemical Oxygen Demand and Total Organic Carbon

5.6.5.6        The organic pollution indicators 5-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD) averaged 2 mg/L (range: <2 -11 mg/L) and 8 mg/L (range: <2 - 47 mg/L), respectively. The levels were below the respective WQOs of 3 mg/L for BOD5 and 15 mg/L for COD.  Overall, 11% and 20% of the samples exceeded the BOD5 and COD criteria, respectively (Table 5.9). The average BOD5 of downstream impact (DI) W3 (5 mg/L) and W6 (4 mg/L) stations, also, exceeded the WQO. The average COD of upstream reference (UR) R1 (15 mg/L); upper impact (UI) W4 (20 mg/L) and downstream impact (DI) W3 (14 mg/L) and W6 (14 mg/L), also, exceeded the TM-DSS of 10 mg/L for Group A usage.

5.6.5.7         There is no WQO or TM-DSS for TOC but the averaged TOC level of 3 mg/L (range: <1 - 15 mg/L; Table 5.11), exceeded the TM-DSS COD discharge limit of 10 mg/L for Group A usage.

5.6.5.8        The results indicate the organic loading of the water bodies is generally low (indeed, BOD5 was only detected in 18% of the samples; Table 5.11) but tended to be higher in the downstream impact stations near the developed area.

Pollution Indicators

5.6.5.9        The domestic and commercial pollution indicators of total residual chlorine (TRC; common residual of chlorine bleach), oil and grease (O&G) and total surfactants (commonly from detergents) averaged less than 0.2mg/L (all below detection; Table 5.10), 1 mg/L (range: <1 – 2 mg/L) and <1 mg/L (all below detection; Table 5.11), respectively. There is no WQO for these three parameters. The averaged values were, also, below the relevant TM-DSS criteria for O&G (1 mg/L, Group A) and total surfactants (5 mg/L, Group B), although individual exceedances of O&G were recorded in a few samples in the wet season (overall 4% exceeded the criterion; Table 5.9). These parameters suggested that the impact of domestic and commercial discharges were minimal.

E. coli

5.6.5.10    The loading of Escherichia coli indicating domestic sewage and animal waste contamination, however, were high and the geometric mean was 1268 cfu/100mL (range: <1 – 32,000 cfu/100mL; Table 5.11), exceeding the WQO and TM-DSS of 1 cfu/100mL. The exceedances were extensive and 96% (Table 5.11) of total samples had reportable colonies of E. coli and, hence, exceeded the criterion. The geometric means of the upstream reference stations R1, R2, R4, R5 and R6 (UR) was 383 cfu/100mL, upstream reference station from Ngong Ping STW station W12 (UR_STW) was 311 cfu/100mL, upstream impact stations W1, W2 and W4 (UI) was 619 cfu/100mL, downstream impact stations W3, W6 and W7 (DI) was 3275 cfu/100mL and downstream reference stations W8 and W9 (DR) was 805 cfu/100mL.  This indicates that the water bodies of the area are still subject to a certain degree of sewerage impact, especially at sections near the centre of the Ngong Ping development. As animal husbandry was not observed in the area, the source of the faecal bacteria should be from local sewage.

Nitrogen

5.6.5.11    The averaged nitrogen nutrients in the form of ammonia-nitrogen (NH4), nitrogen oxides (NOx), and total Kjeldahl nitrogen (TKN) were 0.13 mg/L (range: <0.01 – 1.11 mg/L), 0.64 mg/L (range: <0.02 – 8.32 mg/L) and 0.4 mg/L (range: <0.1 – 2.8 mg/L; Table 5.12), respectively. There values were below the TM-DSS for NH4 (0.5 mg/L) and NOx (10 mg/L), although there were a few individual samples exceeding the NH4 limit (Table 5.9). Overall, 0% and 6% the samples exceeded the TM-DSS criteria for NOx and NH4 (Table 5.9), respectively. The WQO for nitrogen nutrient is 0.021 mg/L unionised ammonia (NH3) and the recorded values ranged between <0.001 – 0.012 mg/L, all below the WQO. As, also, noted in Table 5.12, the highest NOx was recorded at the upstream reference Ngong Ping STW station W12 (UR_STW) with an average of 3.84 mg/L (range: 1.61 – 8.32 mg/L).

5.6.5.12    The nitrogen nutrient of the water bodies is the form of nitrogen oxides (NOx) and the recorded concentrations was higher than the Tung Chung River (2010 annual average = 0.07 mg/L) or Mui Wo River (2010 annual average = 0.31 mg/L) in the Lantau Island.

Phosphorus

5.6.5.13    The averaged phosphorus nutrients in terms of total phosphorus (TP) and orthophosphate (OP) were 0.33 mg/L (range: <0.01 – 4.64 mg/L) and 0.29 mg/L (range: <0.01 – 4.33 mg/L; Table 5.12), respectively.  There values were below the TM-DSS for TP (5 mg/L) and OP (0.5 mg/L) and overall, 9% the samples exceeded the TM-DSS criteria for OP (Table 5.9). As, also, noted in Table 5.12, the highest OP was recorded at the upstream reference Ngong Ping STW station W12 (UR_STW) with an average of 2.32 mg/L (range: 0.88 – 4.33 mg/L) and all samples from the STW exceeded the TM-DSS. As OP level at the downstream reference stations reduced to an average of 0.13 mg/L (range: 0.01-0.39 mg/L; Table 5.12), the effect of the relatively high OP from Ngong Ping STW appeared to be localised.

Chlorophyll

5.6.5.14    As with NOx, the phosphorus nutrient in the water bodies was generally high compared to the Tung Chung River (2010 annual average = 0.15 mg/L) and Mui Wo River (2010 annual average = 0.14 mg/L). Nonetheless, the relatively high nutrient levels were not observed to induce eutrophication (i.e., algal bloom). The plant pigment chlorophyll-a was only detected in 23% of samples and the calculated average was 1 µg/L (range: <1 – 10 µg/L) which would not induce notable water discolouration (Raschke, 1993[1]). 

Arsenic

5.6.5.15    The averaged arsenic concentration was 2 µg/L (range: <1 – 15 µg/L; Table 5.11), although it should be noted that arsenic was only detected in about half of the samples (48%). The averaged and individual values were all below the TM-DSS criteria of 50µg/L.  In generally, only very low levels of arsenic were detected in the samples and the highest were recorded in the upstream reference R1 (6 µg/L) station.

5.6.6              Summary of Baseline Water Quality

5.6.6.1        The project specific baseline monitoring was conducted between September 2011 and March 2012 and again in August 2012, covering both the wet and dry seasons. Fourteen (14) stations at various tributary watercourses in Ngong Ping, which eventually merge into the Ngong Ping Stream at the Y-junction north of the Ngong Ping 360 Terminal, were monitored. A total of 138 samples were measured and analysed for physical and chemical properties and pollution indicators.

5.6.6.2        The results indicated that the water bodies of the Study Area are slightly stressed as reflected by the recorded exceedances of the WQO and TM-DSS criteria for DO, pH, SS, BOD5, COD, O&G, E. coli, nitrogen (as ammonia nitrogen NH4) and phosphorus (as orthophosphate OP) nutrients. The levels of exceedance, however, were marginal and recorded in a small fraction of samples only, except for E. coli. The exceedances were mostly recorded at the downstream impact stations close to the core of the Ngong Ping development.  E. coil exceedances were recorded in 96% of the samples, suggesting a larger scale and persistent sewerage infiltration issue.

5.6.6.3        In general, the water quality of the upstream reference stations was slightly better than the downstream stations, except for R1 in the upstream natural section of Ngong Ping Stream (EIS) within the Ngong Ping SSSI which appeared more stressed than other upstream stations, based on the generally lower DO levels recorded but higher
SS and COD levels at R1 compared with the other UR stations. The water quality of the downstream reference stations was close to the upstream reference stations.  This spatial pattern suggested that the slightly deteriorated water quality in the centre of Ngong Ping development was largely localised.

5.6.6.4        In terms of pollution, the Ngong Ping STW, which is the only identified point source for nitrogen and phosphorus nutrient, would only affect the sections downstream of the Ngong Ping development. The Ngong Ping development is a non-point source for BOD, COD, TOC, E. coli, and nitrogen and phosphorus nutrients.

5.7                    Assessment Methodology

5.7.1.1        The Study Area for the water quality assessment is 500m from the proposed works boundary (Figure 5.1).  Given the small scale of the proposed works as described in Section 2, extension of the study area to include other areas is not necessary and there are no off-site works areas required.

5.7.1.2        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;

·         the supported aquatic ecology; and

·         WSD requirements for the watering grounds.

5.7.1.3        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.

5.7.1.4        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 beneficial uses, which comprise the streams within the Ngong Ping catchment area.

5.7.1.5        As discussed in Section 2, there are no known concurrent projects in the Study Area that may cause cumulative impacts with the Project.

5.8                    Construction Phase Impact Assessment

5.8.1              Identification of Pollution Sources

5.8.1.1        The proposed project is to construct underground drainage system comprising a underground DN1500mm drain pipe at the upstream section (the interception drain), a combined underground box culvert of 2.5m (W) x 2.5m (H) and 3.0m (W) x 2.5m (H) at the middle section (the loop system), and an underground DN1800mm drain pipe at the downstream section (the flood relief drain).

5.8.1.2        The first and last sections ((Works Sections 1 and 3, see Figures 2.9a-2.9g) of the upstream drain pipe and the box culvert (Works Sections 4 and 5) will be constructed by mean of an open cut and cover (C&C) method. Upon site clearance, trench excavation of soil will commence. The second section of the upstream drain pipe (Works Section 2) and the downstream drain pipe (Works Section 6, in the Lantau North Country Park) will be constructed by means of a trenchless technique for which surface excavation is limited to two jacking pits and four receiving pits. The jacking pits are, also, the point of exits for underground excavated soil.  The excavated material will be temporarily placed beside the trench/pit, and will be moved to designated stockpile areas as soon as practicable (see Figures 2.9a-2.9g) and only returned to the trench/pit when it is ready for backfilling.

5.8.1.3        Pre-cast reinforced concrete pipes will be used for the drain pipes construction while the box culvert will be constructed by in-situ casting of concrete.  There will be no concrete batching on-site and the concrete will be brought in as ready mixed concrete. For the pipe jacking works, small amounts of bentonite (about 15 m3) may, also, be used as the lubricant during the jacking process.

5.8.1.4        Based upon the above, the areas of potential impacts to the surface waters during the construction phase will be principally related to:

·         construction site runoff containing elevated suspended solids, oils due to erosion of exposed surfaces, stockpiles and material storage areas, fuel and oil storage and maintenance areas and dust suppression sprays being washed out into adjacent watercourses as construction site runoff;

·         run-off of bentonite contaminated slurry from pipe jacking operations;

·         disturbance to water course banks and stream beds during intake and outfalls construction;

·         litter from packaging materials and waste construction materials; and

·         construction workforce sewage. 

5.8.1.5        While the works boundary encompassed the entire alignment, specific works areas can be identified as listed in Table 2.13.  The relationship between the works area and the specific water quality sensitive receivers are summarised in Table 5.13 below.

Table 5.13    Works Area and Nearby Water Quality Sensitive Receivers

Works Area ID

Location

(Chainage)

Distance to the Nearest Watercourses and Sensitive Use*

SA1

West of the PLM water storage tank

(A0+00)

0m from the natural stream (where sampling point R2 and W1 are located);

0m from conservation area.

WA1 / RP1

Northeast of PLM,  near 慧海淨舍

(A1+05)

23m parallel to a natural stream (where sampling point W2 is located);

~55m from conservation area.

SO and JP1

Northwest of PLM, around between 法嚴精舍 and 覺淨

(A1+60 – A2+00)

55m to a natural stream (where sampling point W2 is located);

~80m from conservation area.

WA2 / RP2

Northwest of PLM, near 常樂林

(A2+90)

100m to a watercourse (where sampling point R3 is located);

~80m from conservation area.

SA2

North end of Lin Ping Drive

(B0+00 – A4+25)

0m from U channel;

~80m from conservation area.

SA3

East of PLM, around between 眾善蓮苑 and Walking with Buddha (與佛同行)

(B1+20 – B2+22)

0m from gabion channel; ~130m from Lantau North Country Park.

WA3 / RP3

North of the Ngong Ping Village

(C0+00)

0m from gabion channel;

0m from Lantau North Country Park.

SA4 / JP2

North of the Ngong Ping 360 Terminal

(C0+35 –  C0+75)

12m from Ngong Ping Stream;

0m from (inside) Lantau North Country Park.

WA4 / RP4

North of the PLM Columbarium

(C1+96)

0m from Ngong Ping Stream;

0m from Lantau North Country Park.

Notes:

1. JP: Jacking Pit; PLM: Po Lin Monastery; RP: Receiving Pit; SA: Stockpile Area; SO: Site Office; WA: Works Area; WS: Works Section.

2. Please refer to Figures 2.9a-2.9g for the locations of Works Sections and Works Areas, Figure 5.3 for the location of sampling points, Table 2.13 for current status of the works area.

* The distance to sensitive uses excludes the water gathering grounds as the entire site is within it.

 

5.8.1.6        The potential impacts associated with these pollution sources are discussed below.  Particular attention has been made to SA1, WA3/RP3 and WA4/RP4 which could affect the conservation area, country park or natural stream, respectively.

5.8.2              Avoidance and Minimisation of Impacts

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

·         No widening / training of the existing natural streams by providing alternate floodway;

·         Works in the existing watercourses is limited to the construction of interfacing intakes (three only) and outfalls (two only); and

·         The adoption of the trenchless construction method will minimise the extent of excavation required and amount of earthworks and, therefore the potential for construction run-off.

5.8.3              Construction Site Runoff

5.8.3.1        Construction site runoff may cause physical, biological and chemical effects. The physical effects include potential blockage of watercourses and drainage channels and increase of SS levels.  Local flooding risk may be increased in heavy rainfall situations. The chemical and biological effects caused by the construction runoff are highly dependent upon its SS levels and pH values. Runoff containing significant amounts of concrete and cement-derived material may cause primary chemical effects e.g. 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.  Construction site runoff comprises:

·         Surface run-off may be contaminated and turbid water may enter adjacent stream and stormwater drainage system as excavated material is delivered to ground surface;

·         Runoff and erosion from site surfaces, drainage channels, earth working areas and stockpiles, release of concrete washing with construction runoff and stormwater.  Effluent discharge from temporary site facilities should be controlled to prevent direct discharge to the neighbouring drainage system.  Such wastewater may include wastewater resulting from dust suppression sprays and wheel washing of site vehicles at site entrances; and

·         Fuel, oil, solvents and lubricants from maintenance of construction machinery and equipment: 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 courses, increasing hydrocarbon levels;

5.8.3.2        For this project, construction site run-off can be generated from the Site Office, which, also serves as the main storage site and pipe jacking pit JP1.  However, the Site Office is about 55m downstream of the small natural stream and will be enclosed with a site hoarding.  Hence, the construction site run-off from the Site Office can be easily contained.  In addition, perimeter cut-off drains to direct off-site water around the site will be constructed with internal drainage works and erosion and sedimentation control facilities implemented.  The Works Areas (WA1, WA2, WA3 and WA4; Figures 2.9a-2.9g) are mainly for the formation of receiving pits for extraction of pipe-jacking equipment and there will be no stockpiling of materials at these locations.  Furthermore, each Works Area will be in use for a short period of time only, typically less than 2 months, see Figure 2.8b. Thus, the Works Areas will have limited potential to generate contaminated site runoff, while noting that WA3 and WA4 are close to the watercourses and particular care will be needed to manage the sites.   

5.8.3.3        The jacking pit and cut-and-cover trench is normally the place where substantial amounts of site run-off can be generated due to the need for the removal of the infiltrated ground water.  However, the project is located in a highland area and ground investigation works have indicated that the ground water table is low. Thus, infiltration of ground water to the pits/trench (maximum 8m below ground) is not anticipated.  Site run-off from the pit and trench is, therefore, more likely to be generated in the wet season during periods of rain and during watering of the trench and surrounding area to suppress dust generation.  In order to limit the potential environmental impacts, each cut-and-cover trench section has been reduced to about 40m long and works will proceed section by section. The jacking pit, also, has a small footprint of 4m x 8m only. Therefore, the potential to generate contaminated runoff from the pit and trench is considered low. 

5.8.3.4        The stockpiling areas (SA1, SA2, SA3 and SA4; Figures 2.9a-2.9g) 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 adjacent to the existing watercourses (Table 5.13).  The stockpiling of the excavated soil for subsequent backfilling or for off-site disposal is of particular concern as the earthed material can easily get into the watercourses due to wind erosion or as a result of being wash away by water (from rain or dust control spraying). Specific mitigation measures for lowing the risk of contaminated site-runoff from polluting the existing watercourses to an acceptable level is presented in Section 5.8.8.

5.8.4              Bentonite Slurry

5.8.4.1        Some quantities of bentonite (about 15 m3) could be required as a lubricant during the pipe jacking operations.  The jacking pit will have a dual purpose of where the tunnel excavated soil will be removed and, also, where the jacking equipment will be launched from, requiring the use of bentonite.  The jacking pit JP1 is within the Site Office area enclosed with a site hoarding which is also some distance away from any watercourses. The risk of the waste bentonite slurry leakage from JP1 contaminating the adjacent watercourse is low given that the site hoarding will provide containment and the fact that the nearest watercourse is 55m away.  The jacking pit JP2 in Works Section 6 is within the Lantau North Country Park, however, and is only 15m from the natural Ngong Ping Stream.  Thus, bentonite spillage has a higher potential to affect the natural stream and, also, the downstream catchwater, if not properly controlled.

5.8.4.2        During the pipe jacking process, the bentonite slurry could also get into the surrounding environment through the fractured bedrock into the surrounding rocks and sands and travels towards the surface, a phenomena commonly known as frac-outs.  Frac-outs could occur along the alignment to be pipe jacked.  While the pipe jacking in Works Section 2 is relatively far from existing watercourses, the pipe jacking works in Works Section 6 are closest to the Ngong Ping Stream.

5.8.4.3        Bentonite is non-toxic but may be harmful to aquatic life if it is discharged into the water course as a result of the suspended solids that would be produced.  Suspended solids can inhibit respiration of fish or benthic invertebrates and/or the larval stages of pelagic organisms though suffocation or associated lack of oxygen.    

5.8.4.4        Given that accidental spillage of bentonite slurry can lead to a higher level of impacts than other site-runoff, specific mitigation measures have been recommended in Section 5.8.8 to ensure the impacts are reduced to the acceptable levels.

5.8.5              Disturbance to Water Courses

5.8.5.1        The alignment design has reduced disturbance to the existing watercourses to minimum. Based on this, there are only five small works areas, the Intake A interfacing the stream, Intake B interfacing the U channel, Outfall A interfacing the gabion channel, Intake C/RP3 interfacing the gabion channel and Outfall B/RP4 interfacing the Ngong Ping Stream (see Figures 2.9a-2.9g) which will cause direct disturbance to the existing watercourses.

5.8.5.2        For Intake A and Outfall B/RP4, a temporary working platform over the existing stream will be erected first and, subsequently, an impermeable cofferdam will be constructed to separate the works area from the stream. For the Intake B, Intake C/RP3 and Outfall A in the artificial channels, the gabion rip-rap will be lifted off first before a working platform can be erected. Prior to the construction of the cofferdam, sections of the concrete lining will be broken out as well. Therefore, the impact to the watercourse will be mainly physical disturbance associated with the erection and subsequent removal of temporary works and cofferdam over a short period of time.  As the water level of these watercourses is generally low (<40cm, based on the baseline survey), the impacts of such disturbance would unlikely be significant. Where the programme allows, works in these area has been scheduled for the dry season period to minimise works in the rainy period between April and September. Indeed, with the recommended programme (Figures 2.9a-2.9g), the number of months the interfacing works will be undertaken during the rainy period has reduced from 7 months to 3 months only.

5.8.5.3        Given the above, the potential impacts from temporary disturbance to the watercourses are considered insignificant and no specific mitigation measures would be required. Adoption of the relevant guidelines and good site practices for the construction runoff would ensure the potential water quality impacts is minimised. 

5.8.6              Waste Construction Materials

5.8.6.1        The use of mechanical plant during construction will inevitably require refuelling, together with fuel and oil storage and maintenance areas.  As a consequence, there is the risk of spillage and leakage of the runoff into the adjacent water bodies during rainfall and from vehicle wheel and sub-frame washing areas for vehicles leaving and entering the site.

5.8.6.2        In additional to the Site Office, specific works areas (stockpiling area, works area and pits; see Table 5.13) are designated  but in reality works areas will be located all along the works alignment.  Water courses are in the vicinity of the works as indicated in Table 5.13, and activities at SA1, SA2, SA3, SA4, WA1, WA3 and WA4 will mean the surrounding areas will be sensitive to impacts and mitigation measures will be required to limit water quality impacts and maintain the water quality conditions in the surface waters and avoid pollution of the stormwater drains.  Recommended mitigation measures are detailed in Section 5.8.8 below.  It is expected that with the implementation of these measures, any adverse impacts will be reduced to within acceptable levels.  The effects of litter and waste construction material can, also, be limited by the use of good site management practices.

5.8.6.3        However, as the Project is located with the water gathering grounds and also Works Section 6 is within the Lantau North County Park, there is a need to protect the area from spillages of chemical waste and fuels and oils.  As such, all chemical waste, fuels and oils shall be stored at the Site Office (SO), which is outside the Lantau North Country Park and some distance (55m) away from the nearest watercourse and, therefore, presents the least risk of any spillage entering the water gathering grounds or Country Park.  In addition, all maintenance activities which could give rise to chemical waste shall also be undertaken at the Site Office site, as far as possible.

5.8.6.4        In order to protect against impacts to the water gathering grounds and country park, 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.

5.8.7              Sewage Effluent

5.8.7.1        Sewage effluents will arise from the sanitary facilities provided for the on-site construction workforce.  The characteristics of sewage may include high levels of BOD5, ammonia and E. coli.  In respect of lavatory facilities for the workforce, chemical toilets would be required if connection to a sewer is not practicable.  It is estimated there will be a temporary workforce of about 30 people during the construction stage and a temporary site office will also be required. The sewerage from the site office will be connected to the existing sewer networks and treated at the Ngong Ping STW. However, chemical temporary toilets will be required at the various works areas.  The details of the chemical toilets shall be submitted to WSD prior to the construction commencement.

5.8.7.2        While control of construction phase sewage could, therefore, be an issue, the site office will be connected to the existing sewer networks and temporary toilets will be managed by a licensed Contractor.  As such, adverse water quality impacts would not be anticipated on the nearby WSRs.

5.8.8              Construction Phase Mitigation Measures

Construction Site Run-off and General Construction Activities

5.8.8.1        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:

i)                    At the establishment of Site Office (SO), works area (WA1 and WA2) and stockpiling areas (SA1, SA2, SA3 and SA4 (see Figures 2.9a-2.9g)), 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 stormwater to silt removal facilities.  The design of the temporary on-site drainage system will be undertaken by the Contractor prior to the commencement of construction. 

ii)                  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 an appropriate watercourse, through a site/sediment trap. Sediment/silt traps should be incorporated in the permanent drainage channels to enhance deposition rates.

iii)                While ProPECC PN 1/94 requires construction works should be programmed to minimise surface excavation works during rainy seasons (April to September). By the nature of the pipe laying works, it is considered not practicable to avoid excavation works in the wet season as this would substantially affect the overall construction programme. However, for works at areas that directly interface with the existing watercourses, excavation works shall avoid the rainy season as far as possible.

These include Intake A interfacing the stream, Intake B interfacing the U channel, Outfall A interfacing the gabion channel, Intake C/RP3 interfacing the gabion channel and Outfall B/RP4 interfacing Ngong Ping Stream (see Figures 2.9a-2.9g).  For the works in the above listed areas, an impermeable cofferdam or similar barrier to the level above the stream bank shall be erected to completely enclose these areas before any works are undertaken.  This will ensure that any contaminated runoff from the works areas will not get into the ambient watercourses. These barriers shall not be removed until the interfacing works and the relevant upstream connected drains have been completed. 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. 

iv)                Exposed slope surfaces should be covered by tarpaulin or other means during the rainy season.

v)                  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. The detailed design of the sand/silt traps should be undertaken by the contractor prior to the commencement of construction.

vi)                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.

vii)              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 proper waste receiving facilities. As the area is within the water gathering grounds, on-site disposal of silts/grits shall not be allowed.

viii)            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.

ix)                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;

x)                  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, especially for areas located near steep slopes;

xi)                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.

xii)              Oil interceptors should be provided in the drainage system downstream of any oil/fuel pollution sources.  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.

xiii)            Stockpiled material shall be covered by tarpaulin and /or watered as appropriate to prevent windblown dust and surface run off. Measures should be taken to prevent the washing away of construction materials, soil, silt or debris into any drainage system.

xiv)            Major stockpiled areas shall be sited outside of the country parks area (Works Section 6) and away from stream courses as far as practicable.  For the stockpiling area SA4 within the country park area, stockpiling of earthed material shall be minimised and excavated soil from Works Section 6 shall be delivered to the Site Office as soon as possible. Similarly, overnight stockpiling of earthed material along the exposed trench shall be minimised as far as possible and the excavated soil shall be transferred to the designated stockpiling area as soon as possible.

xv)              The Contractor shall comply with WSD’s General Conditions for Working within Water Gathering Grounds as applicable.

xvi)            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 9 of this EIA report.

xvii)          All fuel tanks and chemical and bentonite 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.

5.8.8.2        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.

5.8.8.3        Given that recommended measures are tried and tested techniques which have been implemented on other construction site in Hong Kong, the level of uncertainty of their effective deployment would be small. Notwithstanding, the EM&A programme will be implemented to ensure all mitigation measures are effective.

5.8.8.4        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.  It should particularly be noted that the TM-DSS specifically prohibits the discharge of the following substances into the inland waters:

·        polychlorinated biphenyls (PCB);

·        polyaromatic hydrocarbon (PAH);

·        fumigant, pesticide or toxicant ;

·        radioactive substances ;

·        chlorinated hydrocarbons;

·        flammable or toxic solvents ;

·        petroleum oil or tar;

·        calcium carbide;

·        wastes liable to form scum, deposits or discoloration;

·        sludge or solid refuse of any kind; and

·        detergents in Group A inland waters only. 

5.8.8.5        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 and shall be encouraged.  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. 

5.8.8.6        In addition to compliance with the discharge licence requirement, to prevent bank side erosion, the discharge of site effluents shall be either at existing storm drains or artificial channels. No effluent or treated surface runoff shall be allowed to discharge at natural stream course.

Bentonite Slurry

5.8.8.7        The use of bentonite slurries shall be minimised as far as possible. In addition to the requirement of a peripheral bunds and drainage system for the WA4 and SO, where the bentonite slurries will be used, 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; and

·                     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).

5.8.8.8        In order to reduce the possibility of frac-out, detailed ground investigation shall be undertaken to evaluate the likelihood of frac-out and if necessary advanced ground treatment applied before the commencement of the pipe jacking works. A member of the Contractor’s site staff shall, also, be dedicated to closely monitor the ground surface above the pipe jacking head for any frac-outs release. The pipe jacking works and application of bentonite shall immediately stop if frac-outs are observed. Any frac-out shall be immediately cleaned or bunded to prevent spreading of the bentonite slurry. The Contractor shall immediately notify the Engineer and propose rectification measures to prevent further frac-out to the satisfaction of the Engineer before pipe jacking works resume.  An emergency clean up kit shall be readily available at Works Section 2 and 6 where pipe jacking will be undertaken.   

5.8.8.9        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.

Accidental Spillage of Chemicals

5.8.8.10    The contractor must register as a chemical waste producer if chemical wastes would be produced from the construction activities. The Waste Disposal Ordinance (Cap 354) and its subsidiary regulations in particular the Waste Disposal (Chemical Waste) (General) Regulation should be observed and complied with for control of chemical wastes. 

5.8.8.11    Any maintenance facilities should be located outside Works Section 6 in the Lantau North Country Park. Such 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.  All maintenance activities which may generate chemical waste shall be undertaken in the Site Office area, as far as possible.

5.8.8.12    Disposal of chemical wastes should be carried out in compliance with the Waste Disposal Ordinance. The Waste Disposal Ordinance (Cap 354) and its subsidiary regulations in particular the Waste Disposal (Chemical Waste) (General) Regulation should be observed and complied with for control of chemical wastes.  The 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. 

5.8.8.13    In order to minimise the risk of accidental spillage, the use and storage of oils/chemicals/waste should be limited to absolute minimum volume and are to be removed from sites at the earliest opportunity.   However, all chemical waste, fuels and oils shall be stored at the Site Office (SO), to minimise impact to the Lantau North Country Park and water gathering grounds.

5.8.8.14    In order to protect against 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, HyD, Police, TD and WSD to define procedures for the control, containment and clean-up of any spillage that could occur on the construction site.

5.8.8.15    At all times, the Contractor shall comply with WSD’s General Conditions for Working within Water Gathering Grounds, as applicable.

Sewage Wastewater

5.8.8.16    The sewage of the site office will be connected to the existing sewer networks and be treated at the Ngong Ping STW. Portable chemical toilets and sewage holding tanks are recommended for the handling of the construction sewage generated by the workforce at other works area.  The use of temporary toilets within the water gathering ground, however, is also subject to the approval of Water Services Department. A licensed contractor should be employed to provide appropriate and adequate portable toilets and be responsible for appropriate disposal and maintenance.

Environmental Permit EP-192/2004

5.8.8.17    The Outfall A and Intake C and associated works areas are within the gabion channel, the construction and operation of which was previously governed by the Environmental Permit EP-192/2004.  While the EP was surrendered in May 2007, the currently proposed works at these locations shall, also, comply with the specific conditions of the EP (see Section 2.7 of this Report) as far as possible and in particular avoid works in the rainy period between April and September so as to minimise potential water quality pollution to the lowest possible.

5.9                    Operational Phase Impact Assessment

5.9.1              Identification of Pollution Sources

5.9.1.1        The proposed drainage system will be operated by passive gravity and there is no requirement of any active system such as a pump house. The discharge point of Outfall A is located in the existing gabion channel, with Outfall B within the natural section of Ngong Ping Stream immediately above and next to the cliff area and, as such, no operational wastewater discharges or discharge points will be within the existing watercourse and would not affect the overall amount of water available to Ngong Ping Stream.  Stormwater will only discharge into the newly built drainage system when the water levels raise above a height of 500mm during heavy rainfall periods, as a result of weir walls constructed (or equivalent) at intakes and outfalls.  Hence, there will be no flows in the proposed system for the majority of the time and any discharges from the proposed system will be the same as the ambient water from the existing watercourses. Hence, there would be no discharge of wastewater during the operational phase of the Project.  

5.9.1.2        For the majority of the time, the watercourses in the Study Area will be flowing normally, and the water quality and depth level of the existing watercourses will not be affected by the proposed drainage improvement system.  Similarly, the ground water table of the Study Area will not be affected as the proposed drainage system will not affect the existing flow patterns. The quantity of water flowing into the downstream section of the Ngong Ping Stream will remain the same as the same discharges points of the proposed system remain within the Ngong Ping Stream.  Indeed, the proposed drainage system is design to only re-distribute the stormwater from the Ngong Ping developed areas during heavy rainfall periods. Therefore, there will be no net change in the quality and quantity of the water both in the upstream and downstream sections of the Ngong Ping Stream. 

5.9.1.3        The only operational potential for water quality impacts would be during the maintenance desilting works.  Since the proposed drainage system will not be in operation for most of the time and any stormwater that will flow into the drain will flow by gravity, maintenance works are anticipated to be minimal. As indicated in the layout drawings, Figures 2.7a-2.7e, there will be sand-traps at the intakes which will limit sediment entering the drain pipes and box culvert.  Maintenance desilting works, if required, will be limited to the intakes which are designed to facilitate sedimentation but as a precautionary measure should be carried out during the dry season when flow in the watercourse is low.

5.9.1.4        Maintenance desilting works are typically accomplished either by mechanical removal or hydraulic jetting action. Water jetting, however, can generate small amounts of wastewater which has to be collected at desilting manholes and this could cause downstream impacts, particularly at Intake C which is connected to Outfall B where any wastewater would flow directly get into the natural downstream section of Ngong Ping Stream and the Shek Pik Reservoir catchwater.  As such, it is recommended that hydraulic jetting is avoided during maintenance works.   

5.9.2              Operational Phase Mitigation Measures

5.9.2.1        All intakes and outfalls of the proposed system shall have weir walls constructed to at least 500mm or equivalent to ensure the normal flow of existing watercourses is not interrupted.  Therefore, the flow of the natural streams would not be affected by the upgrading works and secondary impacts associated with reduced flows in the natural streams which could impact water quality or aquatic ecology would not be expected.

5.9.2.2        Since Intake C is within the gabion channel, the construction and operation (maintenance desilting works, if any) of both will comply with the Specific Conditions EP-192/2004 unless otherwise approved by the DEP.

5.9.2.3        In order to avoid wastewater being discharged in the existing watercourses during maintenance works, desilting by hydraulic jetting shall be avoided and mechanical scooping / scraping methods are recommended.  Desilting or maintenance works shall also be undertaken during the dry season when flow in the watercourse is low.  The disposal of the removed silt material shall be properly handled in accordance with the recommendations in Section 9 of the EIA Report.

5.9.2.4        Similarly to the construction phase mitigation measures, all recommended measures are well established and do not involve any new or untested methods. Therefore, the level of uncertainty of success would be small.  Notwithstanding, the EM&A programme will be implemented to ensure all mitigation measures are effective.

5.10                cumulative impacts

5.10.1.1       As discussed in Section 2, there are no known concurrent projects in the Study Area that may cause cumulative impacts with the Project.

5.11                Residual Impacts

5.11.1.1    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.

5.11.1.2    The extent of residual impacts would be localised and of a short duration, confined to the construction phase or any minor maintenance works and would be unlikely to induce public health concern, unduly affect the welfare of the local community or any agricultural activities, and the environment resources would be protected with the mitigation measures. Therefore, adverse residual impacts during the construction and operation phases of this Project would not be anticipated, provided that the above mitigation measures are implemented. 

5.12                Environmental Monitoring and Audit Requirements

5.12.1.1    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 stream water during the construction phase.  It is, therefore, recommended that construction activities should be subject to water quality monitoring and a routine audit programme throughout the construction period.  Further details of the specific EM&A requirements are detailed in Section 10 of this report and in the EM&A Manual under separate cover.  No operational phase EM&A for water quality is considered required.

5.13                Summary and Conclusions

5.13.1.1    Potential water pollution sources during the construction phase have been identified as construction site run-off, direct disturbance to water courses, sewage from the workforce, potential risk of contamination from materials, chemicals and bentonite slurry.   Mitigation measures including the implementation of the construction site practices in accordance with the EPD’s ProPECC PN 1/94 Construction Site Drainage, provision and management of portable toilets on-site and preventive measures to avoid accidental chemical spillages are recommended to mitigate any adverse water quality impacts, based on which adverse residual impacts would not be anticipated and the health and welfare of the community, as well as the environmental resources would be protected.  

5.13.1.2    Weir walls, of at least 500mm in height or equivalent, shall be constructed at all intakes and outfalls as planned to ensure the normal flow of existing watercourse is not interrupted during the operational stage.

5.13.1.3    Since Outfall A and Intake C and the associated works area are within the gabion channel, the construction and operation (maintenance desilting works, if any) of both shall comply with the Specific Conditions of EP-192/2004.

5.13.1.4    In order to avoid affecting the water quality in the downstream section of the Ngong Ping Stream within the Lantau North Country Park which feeds the catchwaters of the Shek Pik Reservoir, the following activities shall be avoided at Works Section 6:

 

·        Storage of chemicals, oils, fuels and waste, including major stockpiles; and

·        Maintenance operations for the construction plant.

5.13.1.5    Also, in order to protect the water gathering grounds, maintenance works on construction plant and storage of chemicals and chemical waste should be undertaken at the Site Office only. Overnight stockpiling of earth material and cements at Works Section 6 in the Lantau North Country Park shall be minimised. All the excavated material from Works Section 6 shall be delivered to the Site Office as soon as possible. All backfilling material and cement required for this Works Section 6 shall be delivered as required and only the quantity required. Any surplus backfill and cement not used shall be returned to the Site Office as soon as practicable.  In addition, in order to protect against an accidental spillage of fuel or oil, the Contractor will be required to prepare a spill response plan.

5.13.1.6    During operation phase, the maintenance operations to desilt the intakes are not expected to results in adverse impacts to water quality.  However, good practice measures have been recommended to minimise any effects.  Hydraulic jetting shall be avoided and the maintenance shall also only be undertaken during the dry season when flow in the watercourse is low.  The disposal of the removed silt material shall be properly handled in accordance with the recommendations in Section 9 of the EIA Report.   


[1] Raschek, R. L. (1993). Proceedings of the 1993 Georgia  Water Resources  Conference,  held April 20  and 21,  1993, at The University of Georgia, Kathryn J.  Hatcher, Editor, Institute of Natural Resources, The University of Georgia,  Athens,  Georgia.