9. Sewerage and Sewage Treatment Implications

308875/ENL/ENL/03/07/D May 2014 P:\Hong Kong\ENL\PROJECTS\308875 3rd runway\03 Deliverables\07 Final EIA Report\Ch 9 - SS Treatment.doc

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Expansion of Hong Kong International Airport into a Three-Runway System Environmental Impact Assessment Report

9.1 Introduction

9.1.1.1 This section presents the assessment of impacts on the public sewerage, sewage treatment and

disposal facilities associated with the project, according to the requirements as specified in

Section 3.4.7 and Appendix D2 of the Study Brief (ESB-250/2012).

9.1.1.2 Additional sewage flow will be generated by the project. This section describes the assessment of

impacts associated with the additional sewage flow arising from operation of the project to the

existing / planned sewerage system in North Lantau including the sewerage catchments of Siu

Ho Wan Sewage Treatment Works, and the recommended appropriate mitigation measures to

mitigate any forecasted shortfalls in the sewerage system as a result of the project.

9.1.1.3 It should be noted that the construction phase sewage issues of the project, i.e., sewage

generated by the construction workforce, are addressed separately in Chapter 8.

9.2 Methodology of Sewerage Impact Assessment

9.2.1 Assessment Approach and Methodology

9.2.1.1 The assessment has been undertaken in accordance with the criteria and guidelines for

evaluating and assessing impacts on the downstream public sewerage, sewage treatment and

disposal facilities which would convey and collect the sewage flow from the airport as stated in

Section 6.5 in Annex 14 of the EIAO Technical Memorandum. The following approach and

methodology have been adopted to assess the impact on the existing / planned public sewerage

system and sewage treatment capacity arising from the project:

� Carry out a desktop study to collect relevant information for the assessment.

� Investigate and review the capacity of the existing and planned public sewerage networks and

sewage treatment facilities in North Lantau.

� Review the maximum sewerage flows (i.e., maximum development flows) to be generated by

the project in different phases.

� Study the need and assess the impacts of discharging sewage arising from the project to the

existing / planned public sewerage systems in Tung Chung and Siu Ho Wan Sewage

Treatment Works (SHWSTW).

� Formulate measures to mitigate any forecasted shortfalls in the sewerage system as a result

of the project and provide recommendations on the design, operation and maintenance

requirements for the proposed sewerage system.

9.2.2 Design Reference

9.2.2.1 A desktop study was carried out to collect the relevant background information for the

assessment as summarised below:

� Revised Final Technical Paper (TP7) on Broad Engineering Assessment on Development

Scheme Options under Agreement No. CE 32/2011 (CE) Planning and Engineering Study on

the Remaining Development in Tung Chung – Feasibility Study (or the Tung Chung New Town

Extension);

9. Sewerage and Sewage Treatment Implications


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� Drainage Record Plans within the vicinity of the North Lantau from Drainage Services

Department (DSD);

� Sewage flow generated from the Hong Kong International Airport (HKIA) in different phases;

� Proposed Development Layout Plan of the project;

� Planning Study Report under Agreement no. CE 35/2006 for Kai Tak Development

Engineering Study cum Design and Construction of Advance Works – Investigation, Design

and Construction;

� Final Study Report of the Agreement No. CE32/2010 (CE) Site Formation and Associated

Infrastructural Works for Proposed Development of Columbarium, Crematorium and Related

Facilities at Sandy Ridge Cemetery – Feasibility Study;

� Final Study Report of the Agreement No. CE 1/97 for the Remaining Development in Tung

Chung and Tai Ho Comprehensive Feasibility Study

� Environmental Impact Assessment Report under the Agreement No. CE 60/96 for the

Northshore Lantau Development Feasibility; and

� The Technical Note on the Compilation of 2009-based Territorial Population and Employment

Data Matrices (TPEDM).

9.2.3 Design Standard Guideline

9.2.3.1 The assessment of the existing/planned downstream public sewerage networks and sewage

treatment facilities in North Lantau have been carried out based on the following standards,

guidelines, manuals and reports:

� The Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning Version 1.0

published by EPD (GESF); and

� Sewerage Manual – Part 1 published by DSD (SM1).

9.3 Existing and Planned Sewerage Condition

9.3.1 Existing Sewerage Network of the Airport

9.3.1.1 The existing sewerage network at the airport comprises gravity sewers, grey water pipelines, 11

nos. of sewage pumping stations and associated rising main which are maintained by AAHK. All

the sewage flow within the existing airport is collected locally and conveyed to a pumping station

(Pumping Station No. 1) to discharge all the sewage flow from the airport into the public

sewerage system through a public sewage manhole no. FMH7042035 and then transferred to the

Siu Ho Wan Sewage Treatment Works (SHWSTW). As such, there is no sewage outfall at the

existing airport. The existing sewerage system of the airport is shown in Drawing No.

MCL/P132/EIA/9-001.

9.3.1.2 There is an existing grey water system at the airport to collect and convey grey water from

terminal building kitchens, washroom sinks, and aircraft catering and cleaning activities to a grey

water treatment facility. The capacity of the existing grey water treatment facility is 6,000 m3/day.

The grey water is treated with a portion used for landscape irrigation. The remaining treated grey

water (i.e., surplus of treated grey water) is currently overflowed to the sewerage system within

the airport and then conveyed to the pumping station to discharge into public sewerage system in


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North Lantau Island. It is understood that no untreated grey water is currently discharged to the

sewerage system as the capacity of existing grey water treatment facility has not yet been

reached.

9.3.1.3 The existing sewerage system was designed and maintained in accordance with the standards

and guidelines published by DSD. The existing sewerage network is currently maintained and

operated by AAHK.

9.3.2 Planned Sewerage Network for the Third Runway Development

9.3.2.1 For the proposed airport expansion, the planned sewage discharge scheme is to construct a new

sewerage system to collect the extra sewage flow from the project and then convey it to the

existing public sewerage manhole no. FMH7042035 for discharge via the existing sewerage

system in the airport.

9.3.2.2 The existing sewerage system within the airport island will be further reviewed during the detailed

design stage and, if necessary, upgraded to ensure the extra sewage flow can be properly

conveyed to the public sewerage system in North Lantau. It is anticipated that the capacities of

the existing sewage pumping stations (PS1, PS2 and PS12f) are not able to handle the increased

flow volume collected from the network after Year 2023. The pumping stations are required to be

upgraded to increase its capacity to cope with the future flow.

9.3.2.3 In addition to the possible modification of the existing sewerage system, a new sewage pumping

station will be needed to serve the additional sewage capacity requirements of the third runway

expansion. The new sewage pumping station will be designed with spare capacity and at least

one standby pump will be provided to minimise the risk of service disruption due to accidental

pump failure. In the event of total pumping failure or burst sewer, the contingency will be to

transport the sewage by trucks to SHWSTW. With the standby pumping capacity and contingency

plan in place, emergency sewage overflow system will not be required and there will be no

emergency discharge of sewage from the airport into the marine environment. Based on these

provisions, there will be no discharge of sewage effluent from HKIA into the marine environment,

and no adverse water quality impact due to sewage disposal is anticipated.

9.3.2.4 The planned sewerage system will be designed in accordance with all the relevant standards and

guidelines published by DSD. The planned and existing sewerage network are maintained and

operated by AAHK in accordance with the Sewerage Manual published by DSD. In addition to

continuing the odour control arrangements currently undertaken by AAHK, maintaining the design

maximum retention time of the planned pumping station to not more than 2 hours, monitoring the

(hydrogen sulphide) H2S level once the 3RS is in operation and adoption of active septicity

management measures that can effectively contain any future septicity problems will be included

in the design for the planned 3RS sewerage system. With the inclusion of active septicity

management measures as part of the design, maintenance and operation of the planned

sewerage system, no adverse impacts in respect of septicity and odour from the HKIA new

sewerage system are anticipated.

9.3.2.5 Due to the scale of the project, there will be an interim operation phase after completion of the

land formation whereby the existing South Runway and the new third runway will be in operation

while the existing North Runway will be closed for construction. The new airside fire station and

the new air traffic control tower will commence operation during the interim period, however, the


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new sewerage system for the third runway facilities would be under construction. Therefore, the

sewage arising from these two facilities during that period will be temporarily collected by a pump

sump and transported to the DSD’s sewerage treatment facilities by the licensed sewage

collection contractors at least seven times per day. The estimated sewage load from these new

facilities would be approximately 130 m3/day, therefore, no adverse impacts to the existing

sewerage system will be caused by this interim arrangement. Upon completion of the new

sewerage system for the third runway area, all sewage flow generated within the HKIA will be

collected and conveyed via the sewerage network to the SHWSTW.

9.3.2.6 Based on the current scheme design, an additional grey water treatment plant with a handling

capacity of 700 m3/day is proposed. More information about the additional treatment plant is

given in Chapter 8.

9.3.3 Existing Sewerage Network of Tung Chung

9.3.3.1 The existing sewerage network conveying the sewage flow from the airport to Tung Chung

comprises local gravity sewers between the airport discharge manhole and the Tung Chung

Sewage Pumping Station (TCSPS) rising main connecting TCSPS and SHWSTW. The locations

of these sewerage infrastructures are shown in the Drawing No. MCL/P132/EIA/9-002.

9.3.3.2 The size of the existing gravity sewers conveying the sewage flow from the airport to TCSPS

ranges from 1,050 to 1,500 mm in diameter as shown in Drawing No. MCL/P132/EIA/9-003. The

sewage catchment of the gravity sewers mainly cover residential establishments, commercial

establishments and visitors in Tung Chung areas.

9.3.3.3 The TCSPS is currently served by a single rising main of 1,200 mm in diameter and 6 km in

length, which conveys the sewage generated from the airport and Tung Chung to SHWSTW. As

advised by DSD, the existing capacity of the installed pumpsets at TCSPS is about 1,840 L/s, and

the existing TCSPS has 3 nos. spare dry wells reserved for the additional pumpset installation to

cater the future sewage flow.

9.3.4 Planned Sewerage Network in Tung Chung

9.3.4.1 The Planning Department (PlanD) and the Civil Engineering and Development Department

(CEDD) have jointly commissioned a consultancy study under the Agreement No. CE 32/2011 –

Planning and Engineering Study on the Remaining Development in Tung Chung. The study has

identified the development potential and opportunities for extension of the Tung Chung New

Town to the east and west, which may require a new sewerage network to support the

development. The overall implementation programme for the proposed Tung Chung New Town

Extension (TCNTE) will be established after the reclamation scale and infrastructure

requirements have been determined. According to CEDD, the reclamation and infrastructure

works of the project will be carried out in phases starting from 2018 with the anticipated first

population intake in 2023/24. Also, subject to the approval of EPD, CEDD is investigating the

feasibility of conveying sewage collected from TCNTE to the existing TCSPS and then pumped to

SHWSTW for sewage treatment. However, the associated sewerage network within the Tung

Chung area for sewage collection from TCNTE is still under planning and will be confirmed at the

later stage of their study.


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9.3.4.2 To enhance the operation reliability of the sewerage system, a consultancy study on the

construction of an additional rising main from TCSPS to SHWSTW is currently being carried out

by DSD under the Agreement No. CE 6/2012 – Construction of additional sewage rising mains

and rehabilitation of the existing sewage rising main between Tung Chung and Siu Ho Wan –

Investigation, Design and Construction. According to the latest sewerage impact assessment

report from DSD, twin 1,200 mm diameter rising main will be adopted for conveying the planned

sewage flow from Tung Chung and the airport to the SHWSTW. It is planned to commence the

construction in 2015 and complete the works by end 2022.

9.3.5 Existing/Planned Sewage Treatment Works in North Lantau

9.3.5.1 The sewage flow generated from North Lantau, including Tung Chung, the airport and Hong Kong

Disneyland, is currently discharged to SHWSTW for treatment prior to discharge to the sea

through an existing submarine outfall of 1,840 mm in diameter. The SHWSTW has been

expanded and upgraded to Chemically Enhanced Primary Treatment (CEPT) since March 2005.

The CEPT facilities include six sedimentation tanks, a flocculation and mixing tank, a sludge

dewatering house, sludge buffer tanks, deodorization facilities and chemical dosing facilities. The

allowable treatment capacity of these facilities is 180,000 m3/day with a peak flow of 3,750 L/s. At

the time of preparing this assessment, no further upgrading work for SHWSTW has been

confirmed.

9.4 Assumptions and Parameters Adopted for Assessment

9.4.1 Assessment Scenarios

9.4.1.1 The assessment of impacts due to the project on the public sewerage system in North Lantau has

been carried out for both baseline condition and ultimate design condition of the project as

summarised in Table 9.1. Where appropriate, assessment for the interim scenario has also been

carried out to identify the intermediate timeframe when the existing sewerage system will become

saturated and recommend the appropriate measures to mitigate the impacts on the existing

public sewage system in North Lantau arising from the project.

Table 9.1: Assessment Scenarios

Scenario Year Description

2012 Baseline Condition

2038 Ultimate Design Condition for 3RS (i.e., 15 years after the planned commencement of operation of the 3RS in 2023)

9.4.2 Global Unit Flow Factors (GUFF) – Gravity Sewers in Tung Chung

9.4.2.1 Estimation of the sewage flow in the affected gravity sewers in Tung Chung has been undertaken

according to the methodology as specified in GESF. Appropriate Global Unit Flow Factors (GUFF)

for domestic and commercial/institutional activities have been selected for estimating sewage

flows in the sewerage catchments according to GESF respectively, as presented in Table 9.2.

9.4.2.2 With reference to the Final Study Report of the Agreement No. CE32/2010 (CE) Site Formation

and Associated Infrastructural Works for Proposed Development of Columbarium, Crematorium

and Related Facilities at Sandy Ridge Cemetery – Feasibility Study, a GUFF of 0.010


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m3/day/person is adopted for estimating the sewage flow generated from visitors within the study

area of the project.

Table 9.2: Adopted Global Unit Flow Factors (GUFF) for Gravity Sewers in Tung Chung

Category Unit (per) GUFF (m3/day) Data Source

Domestic (catchment specific)

Private Housing and Public Housing person 0.230 GESF

Commercial/Institutional

Employed Population employee 0.080 GESF

Commercial Activities - General employee 0.200 GESF

Institutions/ Schools employee 0.040 GESF

Visitors for Cable Car Terminal person 0.010 Final Report of Agreement No. CE32/2010

9.4.3 Global Unit Flow Factors (GUFF) – Sewage Treatment Works & Pumping

Station

9.4.3.1 Estimation of the sewage flow to the affected sewage treatment works and pumping station in

Tung Chung and North Lantau has been undertaken according to the methodology as specified in

GESF. Appropriate GUFF for domestic, commercial, industrial and institutional activities have

been selected in accordance with GESF, as shown in Table 9.3.

Table 9.3: Adopted Global Unit Flow Factors (GUFF) for Sewage Treatment Works and Pumping Station

Category Unit (per) GUFF (m3/day) Data Source

Domestic (catchment specific)

Private Housing and Public Housing Person 0.230 GESF

Commercial/Institutional

J2 – Electricity Gas & Water employee 0.250 GESF

J3 – Transport, Storage & Communication employee 0.100 GESF

J4 – Wholesale & Retail employee 0.200 GESF

J9 – Construction employee 0.150 GESF

J10 – Restaurants & Hotels employee 1.500 GESF

J11 – Community, Social & Personal Services

employee 0.200 GESF

School Student person 0.040 GESF

Commercial Employee employee 0.080 GESF

Industrial Activities

J1 – Manufacturing

Industrial Employee employee 0.080 GESF

East Kowloon (overall), Sha Tin, Lantau Island (except Mui Wo)

employee 0.450 GESF

9.4.4 Peaking Factors

9.4.4.1 According to GESF, a peaking factor should be applied in determining the peak flow. As the

service condition of the existing sewerage systems within the study area is not clear, the peaking

factors that include stormwater allowance, which are more conservative, have been adopted in


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this assessment. Based on GESF, the peaking factors adopted for determination of peak flows in

sewers, sewage treatment works and pumping station are based on different population ranges

as shown in Table 9.4:

Table 9.4: Peaking Factors

Population Range Peaking Factor (including stormwater allowance) for Sewers

<1000 8

1,000 – 5,000 6

5,000 – 10,000 5

10,000 – 50,000 4

>50,000

4.2,

3.715.0

NMax

where:

N = contributing population in thousands; and

Contributing population = Calculated total average flow in m3/day divided by 0.27 m3/day

Population Range Peaking Factor (including stormwater allowance) for

Sewage Treatment, Preliminary Treatment Works and Pumping Stations

<1000 4

10,000 – 25,000 3.5

25,000 – 50,000 3

>50,000

4.2,

9.3065.0

NMax

where:

N = contributing population in thousands; and

Contributing population = Calculated total average flow in m3/day divided by 0.27 m3/day

9.5 Sewage Flow Estimation

9.5.1 Existing and Projected Sewage Flow from the Airport

9.5.1.1 The maximum pumping flow rate of 628 L/s as recorded in 2012 for Pumping Station No. 1 (PS1),

which collects all sewage flow of the existing airport for discharge into the public manhole no.

FMH7042035, has been adopted as the existing peak flow to assess the baseline condition of the

downstream sewerage network. The Average Dry Weather Flow (ADWF), including the surplus of

treated grey water, in PS1 in 2012 provided by AAHK is about 18,100 m3 per day.

9.5.1.2 Based on the long term traffic forecast compiled by the International Air Transport Association

(IATA) for AAHK, various growth factors for the air traffic movements (ATM), numbers of

passengers and quantities of cargo from 2012 to 2038 have been estimated for the project.

These growth factors were then applied to the baseline sewage flow in 2012 in order to estimate

the sewage flow of the project during the initial operation year of 2023 and the ultimate design

scenario year of 2038, the results of which are summarised in Table 9.5. As explained in Section

9.3.1, overflow of the surplus treated grey water has been included in the estimates of current

sewage flow and no untreated grey water is currently discharged to the sewerage system. As the

worst case scenario in this assessment, however, it is conservatively assumed that starting from

2016 when the capacity of existing grey water treatment works is predicted to be exceeded, the

untreated grey water would be discharged to the sewerage system. In other words, while it has


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been planned to install an additional grey water treatment facility for the project, the worst case

scenario does not take into account the additional grey water treatment capacity. Details of the

sewage estimation of airport are given in Appendix 9.1.

Table 9.5: Estimated Sewage Flows from the airport Adopted for Assessment

Scenario Year Approximate Total ADWF of the Airport (m3/day)a

Approximate Amount of Untreated Grey Water of the Airport (m3/day)a

Approximate Total ADWF of the Airport under Worst Case Scenario (m3/day)a

2012 (baseline condition) 18,100 - 18,100

2023b 26,700 900 27,600

2038 (ultimate design condition) 40,600 2,900 43,500

Note: a. Approximate values rounded to the nearest hundred. b. The values in 2023 are provided to show the total ADWF arising from the airport during the initial operation under worst case

scenario, but are not for the purpose of assessment.

9.5.2 Existing and Projected Sewage Flow for the Gravity Sewers Leading to TCSPS

9.5.2.1 In order to assess the potential impact on the local gravity sewers between the airport discharge

manhole and TCSPS, sewage flows in the existing sewers have been estimated based on the

population and employment data within the sewage catchment areas of the concerned sewers,

including the catchment of Chung Mun Road Sewage Pumping Station (CMRSPS) and Chung

Yan Road Sewage Pumping Station (CYRSPS). It is identified that the sewerage catchment of

the gravity sewers comprises catchments L, K, M and the airport and the corresponding

catchment and sub-catchment plan are shown in Drawing No. MCL/P132/EIA/9-004 &

MCL/P132/EIA/9-005 respectively.

9.5.2.2 The population and employment data of the concerned catchments have been estimated based

on the assumption that the developments within the catchments are fully utilised. Information

obtained from private sectors and the government departments such as the gross floor area (GFA)

of shopping malls and numbers of flats in private and public housings have been adopted in the

estimation. Due to the lack of employment information in some of the current government facilities

such as Police Station, Fire Station and Tung Chung Municipal Services Building, the planning

data of such facilities used in the relevant previous study, namely, Agreement No. CE 1/97 -

Remaining Development in Tung Chung and Tai Ho Comprehensive Feasibility Study, has been

adopted in this assessment.

9.5.2.3 Based on the aforementioned assumptions and information, the sewage flows in different

catchment areas of the gravity sewers connecting to TCSPS have been estimated, as

summarised in Table 9.6. The locations for individual discharges at the gravity sewers are shown

in Drawing No MCL/P132/EIA/9-003. Details of the sewage flow calculation are given in

Appendix 9.2.

Table 9.6: Estimated Sewage Flows in Different Catchment Areas in 2012

Catchment Area Approximate ADWF in 2012 (m3/day)*

Airport 18,100

K (Existing ADWF of CYRSPS) 8,800

L1 to L13 7,800

M1 to M10 7,200


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Total to TCSPS 41,900

*Note: Approximate values rounded to the nearest hundred.

9.5.2.4 The sewerage catchments represented by the Planning Data Zones (PDZ) system from the 2009-

based TPEDM for the concerned gravity sewers and TCSPS are 245, 246, 266, 282 and 396.

The estimated flow generated in these zones based on the 2009-based TPEDM in Year 2012 and

2038 are summarised in Table 9.7. The total flow of 41,900 m3/day in the relevant catchments (L,

K, M and the airport) in 2012 as estimated by the method mentioned in Section 9.5.2.1 and

9.5.2.2 (see Table 9.6) is found to be close to the total flow of 42,500 m3/day as estimated by

summing up the sewage flows in different PDZs (245, 246, 266, 282, 396 and airport) in the same

year (see Table 9.7). Therefore, the method used to estimate the sewage flow of the gravity

sewers is considered as suitable for assessing the impact of the concerned gravity sewers

between the airport discharge manhole and TCSPS.

Table 9.7: Estimated Sewage Flows of Concerned PDZs for Local Gravity Sewer in 2012 and 2038

Planning Data Zones. Approximate ADWF in 2012 (m3/day)* Approximate ADWF in 2038 (m3/day)*

245, 246, 266, 282 and 396 24,400 37,500

247 (Airport) 18,100 43,500

Total 42,500 81,000


9.5.2.5 As can be seen from Table 9.7, the estimated sewage arising from the concerned PDZs (i.e.,

245, 246, 266, 282 and 396) will be increased by approximately 54 % from 24,400 m3/day in 2012

to 37,500 m3/day in 2038. Therefore, a conservative growth factor of 1.6 has been applied to the

sewage flows in different catchments in 2012 for estimating the corresponding sewage flows in

2038, as summarised in Table 9.8.

Table 9.8: Estimated Sewage Flows in Different Catchment Areasin 2038


Airport 43,500

K (Existing ADWF of CYRSPS) 14,100

L1 to L13 12,500

M1 to M10 11,600

Total to TCSPS 81,700


9.5.2.6 As discussed in Section 9.3.4, details of the proposed TCNTE and the associated sewerage

network are yet to be confirmed. Therefore, this proposed TCNTE has not been considered in the

assessment of local gravity sewers under the ultimate design scenario.

9.5.3 Existing and Projected Sewage Flow in TCSPS and SHWSTW

9.5.3.1 In order to assess the impact on TCSPS and SHWSTW due to the project, the future sewage

flows handled by TCSPS and SHWSTW are estimated according to the population forecast in the

airport and the sewerage catchments of TCSPS and SHWSTW in different years.


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9.5.3.2 The sewerage catchments represented by the Planning Data Zones (PDZ) system from the 2009-

based TPEDM are shown in Drawing No. MCL/P132/EIA/9-006. The sewerage catchments of

TCSPS and SHWSTW in terms of PDZ are presented in Table 9.9.

9.5.3.3 The unit of person represents the total number of “Residents with Regular Residence in HK”

within the PDZ from the “Technical Note on the Compilation of 2009-based Territorial Population

and Employment Data Matrices (TPEDM).

Table 9.9: Sewerage Catchments of TCSPS and SHWSTW by PDZ (excluding the project area)

Planning Data Zones. Sewerage Catchments of TCSPS Sewerage Catchments of SHWSTW

239 Yes

241 Yes

245 Yes Yes

246 Yes Yes

265 Yes

266 Yes Yes

282 Yes Yes

283 Yes Yes

284 Yes

327 Yes

395 Yes

396 Yes Yes

398 Yes

9.5.3.4 Although the 2011-based TPEDM was issued in July 2013, it is considered more conservative to

estimate the overall sewage flows from PDZs within the sewerage catchments of SHWSTW

based on the 2009-based TPEDM. Therefore, it is proposed to adopt the 2009-based TPEDM for

the sewage flow estimation. Comparison of the key assumptions adopted in the 2009-based and

2011-based TPEDM is presented in Appendix 9.3.

9.5.3.5 The 2009-based TPEDM includes the population forecast in each PDZ in five discrete years,

namely, 2011, 2016, 2021, 2026 and 2031. The population forecasts for years not provided by

the TPEDM between 2012 and 2038 are estimated by either interpolation or extrapolation from

the data of the available years. Moreover, adjustments to 2009-based TPEDM have been made

for the TCNTE and other proposed development within the sewerage catchments of TCSPS and

SHWSTW. The adjustments and assumptions adopted in 2009-based TPEDM are summarised in

Table 9.10. Details of estimating the population forecasts in years between 2012 and 2038 are

shown in the Appendix 9.4.

Table 9.10: Adjustments and Assumptions adopted in TPEDM 2009-based for Proposed Developments

Proposed Developments PDZs Adjustment to PDZ / Assumption adopted

TCNTE 266, 282, 283 & 396

According to the latest assumption provided by the CEDD, the sewage estimation for TCNTE is interpolated from 0 to 39,200 m3/day in between 2023 and 2027. Therefore, the population forecast for TCNTE has been excluded from the concerned PDZs for Year 2023 to 2038. The nil increase has been assumed from Year 2023 to Year 2038 for Residential, Commercial and Educational population.

Public Rental Housing Development 246 Refer to revised population information from Paper No. IDC/2013


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Proposed Developments PDZs Adjustment to PDZ / Assumption adopted

at Tung Chung Area 39 from Islands District Council, the additional population of 3,000 has been included from Year 2018 for the Public Rental Housing Development at Tung Chung Area 39.

Lantau Logistic Park,

Sunny Bay Development,

Proposed Cross Boundary Transport Hub above Siu Ho Wan Depot

239 & 284 No update information has been included for the concerned PDZs. The population assumption for these developments is based on the TPEDM 2009 (Revised Lantau Concept Plan released in May 2007).

9.5.3.6 A domestic (Residential) population is made up of household members who are either Usual

Residents and Mobile Residents with regular residence in Hong Kong within the Planning Data

Zones (PDZ) from the 2009-based TPEDM (i.e. Residents with regular residence in Hong Kong).

The mobile residents and transients other than usual residents present in Hong Kong (i.e. visitor)

is excluded from the domestic population as the GUFF for job type J10 as shown in Table 9.3

already taken into account the sewage flow arising from customers and/or visitors.

9.5.3.7 Based on the population breakdown assigned to PDZ of TPEDM and the appropriate GUFF,

ADWF of individual PDZ that are within the sewerage catchments of TCSPS and SHWSTW are

estimated for the baseline and ultimate design scenario years of 2012 and 2038. Table 9.11

summarises the estimated ADWFs of PDZs and the airport.

Table 9.11: Estimated ADWF for the Relevant PDZs and airport in 2012 and 2038

Planning Data Zones Sewerage Catchments ADWF in 2012 (m3/day) ADWF in 2038 (m3/day)

239 SHWSTW 53 6,271

241 SHWSTW 5,861 5,792

245 TCSPS & SHWSTW 13,132 18,196

246 TCSPS & SHWSTW 10,640 17,682

265 SHWSTW 42 58

266 TCSPS & SHWSTW 107 217

282 TCSPS & SHWSTW 119 179

283 TCSPS & SHWSTW 0 Included in TCNTE

284 SHWSTW 92 3,929

327 SHWSTW 2,805 5,239

395 SHWSTW 108 4,056

396 TCSPS & SHWSTW 365 1,137

398 SHWSTW 2 3,865

TCNTE* TCSPS & SHWSTW 0 39,200

Airport TCSPS & SHWSTW 18,100 43,500

*Note: ADWF arising from TCNTE for Year 2012 and Year 2038 is provided by CEDD

9.5.3.8 Based on the estimated ADWF of the various PDZ and the airport, the total ADWF of TCSPS and

SHWSTW in 2012 and 2038 are calculated, as summarised in the Table 9.12. Details of the total

sewage flow estimation for TCSPS and SHWSTW in 2012 and 2038 are given in Appendix 9.5.

Table 9.12: Estimated ADWF of TCSPS and SHWSTW in 2012 and 2038

Sewage Facilities Approximate ADWF in 2012 (m3/day)*

Approximate ADWF in 2038 (m3/day)*

Tung Chung Sewage Pumping Station (TCSPS) 42,500 120,200


9-12


Sewage Facilities Approximate ADWF in 2012 (m3/day)*

Approximate ADWF in 2038 (m3/day)*

Siu Ho Wan Sewage Treatment Works (SHWSTW) 51,500 149,400

*Note: Approximate values rounded to the nearest hundred

9.6 Assessment of Impact to Existing/Planned Sewerage and Sewage Treatment System

9.6.1 Overview

9.6.1.1 According to the information obtained from AAHK, the project will be in full-scale operation in

2038 and thus the sewage flow in that year will be the ultimate design flow, which has been used

to assess the impacts on the following key components of the sewerage and sewage treatment

system:

� Gravity sewers between the airport discharge manhole and TCSPS;

� TCSPS and the associated rising main; and

� SHWSTW.

9.6.2 Gravity Sewers from Airport Discharge Manhole to TCSPS

Basis of the Assessment

9.6.2.1 To assess the impacts on the existing gravity sewers from the airport discharge manhole,

reference point as shown in Table 9.10, to TCSPS (see MCL/P132/EIA/9-003), the estimated

sewage flows from the airport for the scenario years of 2012 and 2038 (see Table 9.5) as well as

the sewage flows from different catchment areas in 2012 (see Table 9.6) are used as the basis. A

summary of these estimated sewage flows adopted for the assessment is shown in Table 9.13.

Details of the sewage flow calculation are given in Appendix 9.2.

Table 9.13: Estimated Sewage Flows for Assessment of the Gravity Sewer in 2012

Reference Point

Discharge Manhole

Sewerage Catchment Approximate ADWF (m3/day)

Contributing Population

Peaking Factor

Peak Flow (L/s)

A FMH7042035 Airport 18,100 - 3.0 628

B FMH7042030 L1, L2 & L4 984 3,644 6.0 68

C FMH7043286 L3, L5, L6, L7, L8, L9, L10, L11,L12, L13 & K

15,605

57,797 4.0 717

D FMH7043283 M1 to M10 7,138 26,437 4.0 330

9.6.2.2 According to the latest information provided by the CEDD, the sewage arising from the

development of Tung Chung West and Tung Chung Village, part of TCNTE, is proposed to be

discharged to Point C (Manhole No.FMH7043286) which is from 0 to 10,450 m3/day in between

year 2023 and year 2027. As explained in Section 9.5.2.5, the estimated sewage flows of

concerned catchments L, M and K can be projected by applying the growth factor to the

corresponding sewage flows in 2012 for assessment of ultimate design scenario, as summarised

in Table 9.14.


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Table 9.14: Estimated Sewage Flows for Assessment of the Gravity Sewer in 2038

Reference Point

Discharge Manhole

Sewerage Catchment Approximate ADWF (m3/day)


Peaking Factor

Growth Factor

Peak Flow (L/s)

A FMH7042035

Airport

43,500

-

3.0

1.536 1,510

B FMH7042030 L1, L2 & L4 1,511 5,598 5.0 1.536 87

C FMH7043286 L3, L5, L6, L7, L8, L9, L10, L11,L12, L13 & K

23,970

34,420 3.5 1.536 1,405

Tung Chung West & Tung Chung Valley

10,450

D FMH7043283 M1 to M10 10,964 40,607 4.0 1.536 508

Hydraulic Assessment

9.6.2.3 The hydraulic assessment on the existing gravity sewers from the airport discharge manhole to

TCSPS is carried by the hydraulic model, InfoWorks (CS Version 14.0), as required in the EIA

Study Brief. Details of the modelling results for the existing sewers are presented in Appendix

9.6, and are discussed below.

9.6.2.4 The sewerage model network of the concerned gravity sewers was setup according to the

drainage record plan published by DSD. The ground level for the node of manhole is based on

the information from the Light Detection and Ranging (LIDAR) survey data.

9.6.2.5 The pipe roughness coefficient is specified as an equivalent roughness (ks) used by the

Colebrook-White equation. In this hydraulic assessment, the roughness coefficient or ks value

used for the existing sewer is taken as 6 mm to cater for long term operational conditions of the

sewer.

9.6.2.6 According to SM1, for sewers of diameter up to 900 mm, it should be designed to achieve a self-

cleansing velocity of 1.0 m/s in full pipe condition. The baseline model has been checked against

with this requirement for the scenario of 2 times of ADWF. The overall velocity for the gravity

sewer between airport discharge manhole and TCSPS generally exceed 1.0m/s. Therefore, the

velocity is sufficient to enable the sewage flow to achieve self-cleansing effect on the concerned

sewer, hence, no sediment is assumed in the hydraulic model. The model result for checking of

this requirement is presented in Appendix 9.6.

9.6.2.7 As highlighted in SM1, local head losses arisen at inlets, outlets, bends, elbows, joints, valves,

manholes and other fittings are usually small in relation to the pipeline head losses and are not

normally considered. Therefore, these head losses are not assumed in this hydraulic

assessment.

9.6.2.8 As summarised in Table 9.15, the InfoWorks modelling results show that all the assessed sewers

would not be surcharged (i.e., with surcharge ratios well below one) during the baseline scenario

year of 2012. Therefore, the existing gravity sewers between the airport discharge manhole and

TCSPS are sufficient to receive all the collected sewage flow from its sewerage catchments

including the airport in 2012.


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Table 9.15: Summary of the Hydraulic Modelling Results for the Existing Gravity Sewers in 2012

Sewerage Catchments/ Upstream Manhole

Downstream Manhole

Pipe Diameter (mm)

Hydraulic Modelling Results in 2012

Freeboard at Peak Flow (mm) Surcharge Ratio*

Airport FMH7042035 700 - -

FMH7042035 FMH7042031 1,050 3,135 0.60

FMH7042031 FMH7042032 1,050 3,334 0.64

FMH7042032 FMH7042033 1,050 2,860 0.64

FMH7042033 FMH7042034 1,050 3,112 0.61

FMH7042034

FMH7042030 1,050 3,621 0.60 Catchment L1, L2 & L4

FMH7042030 FMH7042061 1,050 4,217 0.60

FMH7042061 FMH7042060 1,050 3,833 0.59

FMH7042060 FMH7043290 1,050 4,261 0.54

FMH7043290 FMH7043289 1,050 4,274 0.59

FMH7043289 FMH7043288 1,050 4,820 0.59

FMH7043288 FMH7043287 1,050 5,270 0.56

FMH7043287

FMH7043286 1,050 7,931 0.50 Catchment L3, L5, L6, L7, L8, L9, L10, L11,L12, L13 & K

FMH7043286 FMH7043285 1,350 7,459 0.56

FMH7043285 FMH7043284 1,350 7,416 0.50

FMH7043284 FMH7043283 1,350 8,202 0.45

Catchment M

FMH7043283 FMH7000680 (TCSPS)

1,500 8,461 0.67

*Note: Surcharge ratio extracted from the InfoWorks Model Result (i.e. surcharge ratio > 1: the pipe is under surcharge condition)

9.6.2.9 In the ultimate design scenario year of 2038, there will be additional sewage flow of 25,400 (i.e.,

43,500 – 18,100) m3/day from the expanded airport discharging into the gravity sewers when

compared to the baseline scenario year of 2012. The hydraulic assessment results for Year 2038

are summarised in Table 9.16. It can be seen from the Table that some of the existing gravity

sewers would be surcharged from the design flow during the ultimate design scenario (i.e.,

exceeded the “design capacity” of the sewer).

9.6.2.10 The predicted freeboard of those surcharged sewers at peak flow during the ultimate design

scenario year of 2038 is summarized in Table 9.16.

Table 9.16: Summary of the Hydraulic Modelling Results for the Existing Gravity Sewers in 2038


Downstream Manhole

Pipe Diameter (mm)



Airport FMH7042035 700 - -

FMH7042035 FMH7042031 1,050 1,778 2.00

FMH7042031 FMH7042032 1,050 2,150 2.00

FMH7042032 FMH7042033 1,050 1,880 2.00

FMH7042033 FMH7042034 1,050 2,308 2.00

FMH7042034 FMH7042030 1,050 2,954 2.00


9-15



Downstream Manhole

Pipe Diameter (mm)



Catchment L1, L2 & L4

FMH7042030 FMH7042061 1,050 3,761 2.00

FMH7042061 FMH7042060 1,050 3,484 2.00

FMH7042060 FMH7043290 1,050 3,571 0.86

FMH7043290 FMH7043289 1,050 3,742 2.00

FMH7043289 FMH7043288 1,050 4,446 2.00

FMH7043288 FMH7043287 1,050 4,925 0.90

FMH7043287

FMH7043286 1,050 7,367 0.82

Catchment L3, L5, L6, L7, L8, L9, L10, L11,L12, L13, K, Tung Chung West & Tung Chung Valley

FMH7043286 FMH7043285 1,350 6,992 0.96

FMH7043285 FMH7043284 1,350 6,982 0.84

FMH7043284 FMH7043283 1,350 7,754 0.78

Catchment M

FMH7043283 FMH7000680 (TCSPS)

1,500 8,098 0.96


9.6.2.11 In view of the above assessment findings and in accordance with SM1 that for design purposes

the full bore flow at no surcharge shall be taken as the design capacity of a sewer and sewers

under surcharge are not desirable, adequate mitigation measure should be implemented in a

timely manner to eliminate the surcharged condition. AAHK therefore proposed to construct a

new gravity sewer with a diameter of 1,200 mm adjacent to the existing gravity sewer (1,050 mm

in diameter) and then to divert the sewage flow arising from the airport and other sub-catchment

in Tung Chung to the new gravity sewer, as shown in Appendix 9.7. AAHK will consider to study

the feasibility to keep the proposed abandoned sewer (i.e., the existing gravity sewer of 1,050

mm in diameter) in place as a spare sewer with an overflow system for the emergency discharge

subject to future deign of the new gravity sewer by around 2022.

9.6.2.12 The sewer upgrading work will be able to provide sufficient design capacity in the sewer in order

to deliver the sewage arising from the project to the TCSPS. The hydraulic assessment for the

upgrading proposal is summarized in Table 9.17 and Appendix 9.7. Design and construction of

the new gravity sewer shall be in accordance with relevant guidelines as set out in the Project

Administration Handbook for Civil Engineering Works, Sewerage Manual published by DSD, DSD

Technical Circular No. 2/2005 and DSD Practice Note No. 1/2010 to ensure smooth delivery and

handing over of the new sewer to DSD for the completion of works.

9.6.2.13 Since the concerned gravity sewer is projected to reach full capacity by 2027, the sewer

upgrading work shall be completed by 2026 (allowing a buffer period of about one year before the

full capacity is reached), with the planning work to commence in 2022 (assuming one year for

planning plus three years for design and construction).


9-16


Table 9.17: Summary of the Hydraulic Modelling Results for the Proposed Gravity Sewers in 2038


Downstream Manhole

Pipe Diameter (mm)



Airport FMH01 700 - -

FMH01 FMH02 1,200 2,652 0.80

FMH02 FMH03 1,200 3,315 0.78

FMH03

FMH04 1,200 3,909 0.71 Catchment L1, L2 & L4

FMH04 FMH05 1,200 3,935 0.65

FMH05 FMH06 1,200 4,060 0.64

FMH06 FMH07 1,200 5,005 0.53

FMH07

FMH7043286 1,200 7,483 0.50

Catchment L3, L5, L6, L7, L8, L9, L10, L11,L12, L13, K, Tung Chung West & Tung Chung Valley

FMH7043286 FMH7043285 1,350 6,998 0.88

FMH7043285 FMH7043284 1,350 7,129 0.78

FMH7043284 FMH7043283 1,350 7,949 0.74

Catchment M

FMH7043283 FMH7000680 (TCSPS)

1,500 8,130 0.92


9.6.2.14 While AAHK undertakes to implement and complete the mitigation works for the affected gravity

sewers by 2026, the discharge of additional sewage will start upon commissioning of the project

and the sewage build up may be at a more rapid rate than that predicted. Therefore, it is

recommended that AAHK should monitor the sewage flow build-up as a part of the environmental

monitoring and audit (EM&A) for the project and start planning construction of the upgrading

works in 2022 or when the sewage flow in the affected gravity sewer exceeds 80% of the design

capacity of the sewer, whichever is earlier, so as to ensure timely completion of the mitigation

works before the flow would exceed the design capacity of the sewer.

9.6.3 Tung Chung Sewage Pumping Station (TCSPS) and the associated Rising Main

9.6.3.1 The potential impact on TCSPS has been assessed based on the estimated sewage flows arising

from the project in 2012 and 2038 as well as the population forecast from the 2009-based

TPEDM within the catchment areas of TCSPS (see Table 9.11). The estimated sewage flow

handled by TCSPS are summarised in Table 9.18 and details of the sewage flow estimation are

given in Appendix 9.5.

Table 9.18: Estimated Sewage Flows Handled by TCSPS in 2012, 2022 and 2038

Scenario Year

Approximate ADWF from Relevant PDZs (m3/day)a

Approximate ADWF from Airport (m3/day)a

Total ADWF (m3/day)


Peaking Factor

Total Peak Flow (L/s)

Existing Design Peak Flow of TCSPS (L/s)

2012 (baseline

24,400 18,100 42,500 157,271 2.8 1,380 1,840


9-17


Scenario Year

Approximate ADWF from Relevant PDZs (m3/day)a


Total ADWF (m3/day)


Peaking Factor


Existing Design Peak Flow of TCSPS (L/s)

condition)

2022b 34,400 23,100 57,500 212,937 2.8 1,832

2038 (ultimate design condition)

76,700 43,500 120,200 444,854 2.6 3,648

Note: a. Approximate values rounded to the nearest hundred. b. While 2022 is not one of the assessment scenarios, the values in 2022 are provided to show that the design peak flow of TCSPS

would be exceeded after that particular year.

9.6.3.2 As shown in Table 9.18, the total peak sewage flow from the airport and the relevant PDZ will

exceed the existing design peak flow of TCSPS (1,840 L/s) during the ultimate design scenario

year of 2038.

9.6.3.3 By estimating the total ADWF and peak flows between 2012 and 2038 , it can be found that the

total peak sewage flow from the airport and the relevant PDZ would exceed the existing design

peak flow of TCSPS after 2022 (i.e., from 2023 onwards), subject to future development of

TCNTE, as presented in Table 9.18.

9.6.3.4 As mentioned in Section 9.3.4, a government project under the Agreement No.CE6/2012 is

currently underway to investigate, design and construct an additional sewage rising main

between TCSPS and SHWSTW to enhance the operation reliability of the sewerage system.

Under the project, it is planned to commence the construction in 2015 and complete the works by

end 2022. According to the latest information from DSD, twin 1,200 mm diameter rising main will

be adopted for conveying the planned sewage flow from Tung Chung and the airport to the

SHWSTW, which is sufficient for the estimated ultimate design sewage flow of 3,648 L/s. [Note:

EPD has agreed to reserve 43,500 m3/day (ADWF) at the TCSPS for the total sewage discharge

from the expanded airport and AAHK will closely liaise with EPD and DSD to ascertain a smooth

interface with the upgrading works for TCSPS.] AAHK will monitor the situation closely and take

appropriate action to handle the excess sewage arising in case there is any programme

mismatch.

9.6.4 Siu Ho Wan Sewage Treatment Works (SHWSTW)

9.6.4.1 The potential impact on SHWSTW has been assessed based on the estimated sewage flows

arising from the project in 2012 and 2038 as well as the population forecast from the 2009-based

TPEDM within the catchment areas of SHWSTW (see Table 9.11). The estimated sewage flows

handled by SHWSTW are summarised in Table 9.19 and details of the sewage flow estimation

are given in Appendix 9.5.

Table 9.19: Estimated Sewage Flows Handled by SHWSTW in 2012, 2026 and 2038

Scenario Year

Approximate ADWF from Relevant PDZ (m3/day)*


Total ADWF (m3/day)a


Peaking Factor


Existing Treatment Capacity of SHWSTW

Peak Flow (L/s)

Daily Flow (m3/day)

2012 33,400 18,100 51,500 190,462 2.8 1,650 3,750 180,000


9-18


Scenario Year

Approximate ADWF from Relevant PDZ (m3/day)*


Total ADWF (m3/day)a


Peaking Factor


Existing Treatment Capacity of SHWSTW

Peak Flow (L/s)

Daily Flow (m3/day)

(baseline condition)

2026b 87,900 30,800 118,700 439,402 2.6 3,606

2038 (ultimate design condition)

105,900 43,500 149,400 553,038 2.6 4,471

Note: a. Approximate values rounded to the nearest hundred. b. While 2026 is not one of the assessment scenarios, the values in 2026 are provided to show that the design peak flow of

SHWSTW would be exceeded after that particular year.

9.6.4.2 It can be seen from Table 9.19 that the estimated total ADWF and peak sewage flow to be

handled by SHWSTW in 2026 would be approximately 118,700 m3/day and 3,606 L/s respectively,

which are within the treatment capacity of the existing SHWSTW. However, the design peak flow

(3750 L/s) of the existing SHWSTW would be exceeded after 2026. The upgrading work for

SHWSTW is considered necessary to cater for the ultimate design peak flow of 4,471 L/s from

the expanded airport and the relevant PDZ in 2038.

9.6.4.3 In view of the above assessment findings, it is considered that the existing SHWSTW will not be

able to handle estimated peak flows from the project as well as other future development within

the relevant PDZ after 2026. It is understood that the upgrading works of SHWSTW will be

carried out by the relevant government departments before exceeding the capacity, and the

scope and programme of the upgrading works are still under discussion among the relevant

government departments subject to future development within the catchment of SHWSTW

including TCNTE. It is understood that EPD will monitor the sewage flow build-up and coordinate

the necessary upgrading works for the SHWSTW when needed in due course.

9.6.4.4 With the upgrading of SHWSTW to cater for the proposed development within North Lantau such

as TCNTE, the project and other developments of relevant PDZs, there is no need to establish

any central pre-treatment facilities or separate sewage treatment plant for the project.

9.7 Mitigation Measures

9.7.1 Planned Sewerage System within the Expanded Airport Island

9.7.1.1 The planned sewerage system will be designed in accordance with all the relevant standards and

guidelines published by DSD. The planned and existing sewerage network are maintained and

operated by AAHK in accordance with the Sewerage Manual published by DSD. In addition to

continuing the odour control arrangements currently undertaken by AAHK, maintaining the design

maximum retention time of the planned pumping station to not more than 2 hours, monitoring the

H2S level once the 3RS is in operation and adoption of active septicity management measures

that can effectively contain any future septicity problems will be included in the design for the

planned 3RS sewerage system. With the inclusion of active septicity management measures as

part of the design, maintenance and operation of the planned sewerage system, no adverse

impacts in respect of septicity and odour from the HKIA new sewerage system are anticipated.


9-19


9.7.2 Gravity Sewers from Airport Discharge Manhole to TCSPS

9.7.2.1 According to the InfoWorks modelling results, it is predicted that some of the existing gravity

sewers from the airport discharge manhole to TCSPS would be under surcharge condition during

the ultimate design scenario year of 2038.

9.7.2.2 In view of the above assessment findings and in accordance with SM1 that for design purposes

the full bore flow at no surcharge shall be taken as the design capacity of a sewer and sewers

under surcharge are not desirable, adequate mitigation measure should be implemented in a

timely manner to eliminate the surcharged condition. AAHK therefore proposed to construct a

new gravity sewer with a diameter of 1,200 mm adjacent to the existing gravity sewer (1,050 mm

in diameter) and then to divert the sewage flow arising from the airport and other sub-catchment

in Tung Chung to the new gravity sewer, as shown in Appendix 9.7. AAHK will consider to study

the feasibility to keep the proposed abandoned sewer (i.e., the existing gravity sewer of 1,050

mm in diameter) in place as a spare sewer with an overflow system for the emergency discharge

subject to future deign of the new gravity sewer by around 2022.

9.7.2.3 This sewer upgrading work will be able to provide sufficient design capacity in the sewer in order

to deliver the sewage arising from the project to the TCSPS. The hydraulic assessment for the

upgrading proposal is summarized in Table 9.17 and Appendix 9.7. Design and construction of

the new gravity sewer shall be in accordance with relevant guidelines as set out in the Project

Administration Handbook for Civil Engineering Works, Sewerage Manual published by DSD, DSD

Technical Circular No. 2/2005 and DSD Practice Note No. 1/2010 to ensure smooth delivery and

handing over of the new sewer to DSD for the completion of works.

9.7.2.4 Since the concerned gravity sewer is projected to reach full capacity by 2027, the sewer

upgrading work shall be completed by 2026 (allowing a buffer period of about one year before the

full capacity is reached), with the planning work to commence in 2022 (assuming one year for

planning plus three years for design and construction).




recommended that AAHK should monitor the sewage flow build-up as a part of the EM&A for the

project and start planning construction of the upgrading works in 2022 or when the sewage flow in

the affected gravity sewer exceeds 80% of the design capacity of the sewer, whichever is earlier,

so as to ensure timely completion of the mitigation works before the flow would exceed the design

capacity of the sewer.

Potential Secondary Environmental Impacts from the Proposed Upgrading Works

9.7.2.6 The design and construction of new gravity sewer for replacement of the existing sewer is

anticipated to begin in early 2024 and complete by 2026, which would not overlap with the

planned construction period of the 3RS project (i.e., 2015 – 2023). The upgrading work is not of

large scale, comprising a works area of about 550 m in length and 3 m in width, and would

generally involve the following construction activities:

� Break up of road surface

� Excavation of soil material


9-20


� Laying of new sewers

� Steel fixing and concreting of manholes

� Laying of bedding material

� Backfilling and soil compaction

� Reinstatement of road surface

9.7.2.7 Potential environmental impacts from the above construction works include dust emission, noise

impacts from the use of Powered Mechanical Equipment (PME), generation of construction and

demolition (C&D) waste, surface run-off and tree preservation, as discussed below.

9.7.2.8 The breaking of road surface, excavation and backfilling works is expected to generate potential

dust impact. Relevant dust control measures as stipulated in the Air Pollution Control

(Construction Dust) Regulation should be adopted to reduce potential dust impacts. Measures to

be adopted include, but are not limited to, good site management, regular water spraying at

works areas, and covering dusty materials with impervious sheet. Given that the upgrading work

is not of large scale and with the implementation of dust control measures, no adverse

construction dust impacts are anticipated.

9.7.2.9 The use of PME such as generator, breaker and poker for the upgrading work is expected to

generate potential construction noise impacts. Relevant noise mitigation measures as listed in

Professional Persons Environmental Consultative Committee Practice Note (ProPECC PN) No.

1/93 and 2/93 should be adopted to miminise potential noise impacts. In addition, good site

practice such as use of well-maintained plants only and shut down of machines that may be in

intermittent use could also reduce noise level. Given that the upgrading work is not of large scale

and with the implementation of noise mitigation measures, no adverse construction noise impacts

are anticipated.

9.7.2.10 Different types of wastes would be generated during the course of the upgrading work, including

inert C&D materials from road surface breaking and soil excavation; non-inert C&D materials from

site clearance; chemical waste from maintenance and repairing of construction equipment as well

as general refuse from site workers. The inert C&D materials would largely be reused on-site as

backfill materials, with a small surplus amount requiring off-site delivery to the government’s

Public Fill Reception Facilities for beneficial use by other local projects. The non-inert C&D

materials may not be suitable for direct reuse on site due to its non-inert contents, and would

therefore be disposed of at designated landfill site. Given that the upgrading work is not of large

scale, the amount of non-inert C&D materials to be generated is expected to be minimal. A small

amount of chemical wastes may be generated from the maintenance and repairing of

construction equipment, which should be properly handled, stored, labelled and disposed of at

licensed facilities in accordance with the Waste Disposal (Chemical Waste) (General) Regulation

and the “Code of Practice on the Packaging Labelling and Storage of Chemical Wastes”

published by EPD. A limited amount of general refuse would be generated by the construction

workforce, which should be properly collected and disposed of at designated landfill site. Given

that the various waste materials are handled and reused/ disposed of in accordance with the

relevant legislative and recommended requirements, no adverse environmental impact due to

waste arising is expected from the upgrading works.


9-21


9.7.2.11 There would be surface runoff from the works area, which may contain increased loads of

suspended solids (SS) and contaminants. The relevant good site practices as given in the

ProPECC PN 1/94 should be followed to minimise surface runoff and erosion. Given that the

upgrading work is not of large scale and with the implementation of good site practice, no adverse

water quality impact is anticipated.

9.7.2.12 There are no registered Old and Valuable Trees (OVTs) in the vicinity of the upgrading works

area, however, roadside trees are observed. As stated in Technical Circular (Works) No. 10/2013

Tree Preservation, trees should be preserved as far as practicable. A detailed tree survey should

be carried out and a Tree Preservation and Removal Proposal (TPRP) should be prepared during

detailed design stage. The aforementioned technical circular should be strictly followed.

9.7.2.13 In addition to the above recommended mitigation measures, guidelines as given in the Technical

Circular (Works) No. 19/2005 – Environmental Management of Construction Sites, should also be

followed where appropriate. With implementation of good site practices and the recommended

mitigation measures, the proposed gravity sewer upgrading work is not anticipated to cause

adverse secondary environmental impacts.

9.7.3 Tung Chung Sewage Pumping Station (TCSPS) and the associated Rising Main

9.7.3.1 Based on the assessment findings, the total peak sewage flow from the airport and the relevant

PDZ would exceed the existing design peak flow of TCSPS in 2023, subject to future

development of TCNTE.

9.7.3.2 A government project under the Agreement No.CE6/2012 is currently underway to investigate,

design and construct an additional sewage rising main between TCSPS and SHWSTW to

enhance the operation reliability of the sewerage system. Under the project, it is planned to

commence the construction in 2015 and complete the works by end 2022. According to the latest

information from DSD, twin 1,200 mm diameter rising main will be adopted for conveying the

planned sewage flow from Tung Chung and the airport to the SHWSTW, which is sufficient for the

estimated ultimate design sewage flow of 3,648 L/s. [Note: EPD has agreed to reserve 43,500

m3/day (ADWF) at the TCSPS for the total sewage discharge from the expanded airport and

AAHK will closely liaise with EPD and DSD to ascertain a smooth interface with the upgrading

works for TCSPS.] AAHK will monitor the situation closely and take appropriate action to handle

the excess sewage arising in case there is any programme mismatch.

9.7.4 Siu Ho Wan Sewage Treatment Works (SHWSTW)

9.7.4.1 It has been assessed that the existing treatment capacity of SHWSTW (180,000 m3/day) is

sufficient to handle the predicted total sewage flow in 2038 (i.e., 149,400 m3/day). However, the

existing design peak flow of SHWSTW (3,750 L/s) would be exceeded after 2026. It is understood

that SHWSTW will be upgraded by the relevant government departments to cater for the sewage

treatment demand arising from future developments within the relevant sewerage catchment

areas including the expanded airport and TCNTE. It is understood that EPD will monitor the

sewage flow build-up and coordinate the necessary upgrading works for the SHWSTW when

needed in due course.


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9.8 Environmental Monitoring and Audit

9.8.1.1 With the implementation of the recommended mitigation measures, the existing public sewerage

system would be upgraded to cater for the maximum development flows arising from the project.

In order to monitor the sewage flow build-up for the project to ensure timely completion of the

mitigation works for the affected gravity sewer before the flow would exceed the sewer design

capacity, it is recommended to implement a regular sewage flow monitoring programme.

9.8.1.2 Moreover, in order to ensure the additional sewage generated from the 3RS project would not

impose adverse impacts in respect of sewage septicity and odour issues on the existing

sewerage networks including the public sewerage system, it is recommended to implement a H2S

monitoring system for the sewerage system of the 3RS.

9.8.1.3 Details of the above monitoring works are given in the EM&A Manual.

9.9 Conclusion

9.9.1.1 Under the worst case scenario, the project will generate a total sewage flow of 43,500 m3/day

during the ultimate design scenario year of 2038 when the project will be in full-scale operation.

On this basis, the impacts arising from the project on the existing sewerage and sewage

treatment system have been assessed.

9.9.1.2 The planned sewerage system for 3RS will be designed in accordance with all the relevant

standards and guidelines published by DSD. The planned and existing sewerage network are

maintained and operated by AAHK in accordance with the Sewerage Manual published by DSD.

In addition to continuing the odour control arrangements currently undertaken by AAHK,

maintaining the design maximum retention time of the planned pumping station to not more than

2 hours, monitoring the H2S level once the 3RS is in operation and adoption of active septicity

management measures that can effectively contain any future septicity problems will be included

in the design for the planned 3RS sewerage system. With the inclusion of active septicity

management measures as part of the design, maintenance and operation of the planned

sewerage system, no adverse impacts in respect of septicity and odour from the HKIA new

sewerage system are anticipated.

9.9.1.3 According to the hydraulic assessment results, the existing gravity sewers from the airport

discharge manhole to TCSPS would reach full capacity by 2027. AAHK therefore proposed to

construct a new gravity sewer with a diameter of 1,200 mm adjacent to the existing gravity sewer

(1,050 mm in diameter) and then to divert the sewage flow arising from the airport and other sub-

catchment in Tung Chung to the new gravity sewer, as shown in Appendix 9.7. AAHK will

consider to study the feasibility to keep the proposed abandoned sewer (i.e., the existing gravity

sewer of 1,050 mm in diameter) in place as a spare sewer with an overflow system for the

emergency discharge subject to future deign of the new gravity sewer. This sewer upgrading

work will be able to provide sufficient design capacity in the sewer in order to deliver the sewage

arising from the project to the TCSPS. The sewer upgrading work shall be completed by 2026

(allowing a buffer period of about one year before the full capacity is reached), with the planning

work to commence in 2022 (assuming one year for planning plus three years for design and

construction).


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recommended that AAHK should monitor the sewage flow build-up as a part of the EM&A for the

project and start planning construction of the upgrading works in 2022 or when the sewage flow in

the affected gravity sewer exceeds 80% of the design capacity of the sewer, whichever is earlier,

so as to ensure timely completion of the mitigation works before the flow would exceed the design

capacity of the sewer.

9.9.1.5 Based on the assessment findings, the total peak sewage flow from the airport and the relevant

PDZ would exceed the existing design peak flow of TCSPS in 2023, subject to future

development of TCNTE. A government project under the Agreement No.CE6/2012 is currently

underway to investigate, design and construct an additional sewage rising main between TCSPS

and SHWSTW to enhance the operation reliability of the sewerage system. Under the project, it is

planned to commence the construction in 2015 and complete the works by end 2022. According

to the latest information from DSD, twin 1,200 mm diameter rising main will be adopted for

conveying the planned sewage flow from Tung Chung and the airport to the SHWSTW, which is

sufficient for the estimated ultimate design sewage flow of 3,648 L/s. [Note: EPD has agreed to

reserve 43,500 m3/day (ADWF) at the TCSPS for the total sewage discharge from the expanded

airport and AAHK will closely liaise with EPD and DSD to ascertain a smooth interface with the

upgrading works for TCSPS.] AAHK will monitor the situation closely and take appropriate action

to handle the excess sewage arising in case there is any programme mismatch..

9.9.1.6 In view of the assessment findings, it is considered that the design capacity of the existing

SHWSTW is sufficient to handle the estimated total ADWF from the project and the relevant PDZ

during the ultimate design scenario year of 2038. However, it is estimated that the design peak

flow of SHWSTW would be exceeded after 2026. It is understood that SHWSTW will be upgraded

by the relevant government departments to cater for the sewage treatment demand arising from

future developments within the relevant sewerage catchment areas including the expanded

airport and TCNTE. It is understood that EPD will monitor the sewage flow build-up and

coordinate the necessary upgrading works for the SHWSTW when needed in due course.

9.9.1.7 With implementation of the upgrading works for the gravity sewer, TCSPS and SHWSTW, there

is no need to establish any central pre-treatment facilities or separate sewage treatment plant for

the project. Provided the upgrading of the gravity sewer, TCSPS and SHWSTW will be

completed by respectively 2026, end 2022 and 2026, no interim sewage treatment facilities will

be required for the project.

Documents

9. Sewerage and Sewage Treatment Implications