Section    Title                                                                                                                           Page

6.1              Introduction________________________________________________________________ 6-1

6.2              Assessment Approach and Methodology__________________________________________ 6-1

6.3              Design Assumptions, Parameters and Criteria_____________________________________ 6-2

6.4              Existing Sewerage Conditions__________________________________________________ 6-5

6.5              Estimated Pollutant Loads due to the Project_______________________________________ 6-7

6.6              Proposed Mitigation Measures_________________________________________________ 6-9

6.7              Short Term Measures during Construction Phase__________________________________ 6-13

6.8              Environmental Monitoring and Audit_____________________________________________ 6-13

6.9              Conclusion_______________________________________________________________ 6-13

 

Tables

Table 6.1:__ Population of the proposed LT/HYW BCP on Hong Kong Side_ 6-2

Table 6.2:__ Population of the Proposed Resite of Chuk Yuen Village_ 6-2

Table 6.3:__ Staffing of proposed Administration Building_ 6-3

Table 6.4:__ Design Unit Load Factors_ 6-4

Table 6.5:__ Peaking Factor for Sewers_ 6-5

Table 6.6:__ Population and Estimated Sewage Flow from Existing Chuk Yuen Village_ 6-5

Table 6.7:__ Pollutant Loading of  Existing Chuk Yuen Villages_ 6-6

Table 6.8:__ Performance of Septic Tank 6-6

Table 6.9:__ Pollutant Loading Performance of Septic Tank 6-6

Table 6.10:_ Estimated Sewage Flow from Proposed Chuk Yuen Village Resite_ 6-7

Table 6.11:_ Estimated Sewage Flow from the proposed LT/HYW BCP on Hong Kong Side_ 6-7

Table 6.12:_ Estimated Sewage Flow from the proposed LT/HYW BCP on Hong Kong Side (with 15% of passengers using toilet) 6-8

Table 6.13:_ Pollutant Loads arising from the Raw Sewage of the Proposed Development 6-8

Table 6.14:_ Comparison of MBR Treatment Performance with Discharge Standards_ 6-10

Table 6.15:_ Pollutant Loadings in Treated Effluent (with 10% of passengers using toilet) 6-11

Table 6.16:_ Pollutant Loadings in Treated Effluent (with 15% of passengers using toilet) 6-11

Table 6.17:_ Comparison of Pollutant Loadings_ 6-11

Table 6.18:_ Comparison of Sewage Flow and Pollutant Loadings to be discharged after Effluent Reuse (with 10% of Passengers Using Toilets) 6-12

Table 6.19:_ Standards for Reuse of MBR Treated Effluent 6-12

 

Figures

Figure 6.1          General Layout Plan for BCP

Figure 6.2          General Layout Plan for the Proposed Treatment Process

Figure 6.3          Proposed Landscape at Lower Deck Level Plan for BCP

Figure 6.4          Proposed Landscape at Upper Deck Level Plan for BCP

Appendices                                           

Appendix 6.1     Estimation of Sewage Flow at Existing Site

Appendix 6.2     Estimation of Pollutant Loadings from Existing Site

Appendix 6.3     Estimation of Pollutant Loadings from Proposed Development

Appendix 6.4     Estimation of Pollutant Loadings Discharge to Deep Bay from Proposed Development

Appendix 6.5     Estimation of Pollutant Loadings Discharge to Deep Bay After Reuse

 



6.1               Introduction

This section presents the assessment of the sewerage and sewage treatment impact associated with the construction and operation phases of the proposed BCP and associated facilities, according to section 3.4.6 of the Study Brief (ESB-199/2008). The necessary mitigation measures and proposals for sewage treatment and disposal have been recommended with an objective to achieve compliance with the discharge standards as required by the Environmental Protection Department (EPD). 

6.2               Assessment Approach and Methodology

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 as stated in section 6.5 in Annex 14 of the EIAO Technical Memorandum. The following approach and methodology has been adopted in this sewerage and sewage treatment implications assessment:-

¡           Carry out the desktop study, water sampling, topography survey and site visit to collect the relevant information for the assessment.

¡           Investigate and review the existing/planned sewerage networks and sewage treatment facilities in the vicinity of the development and determine the sewage flow and pollutant loading generated from the existing development.

¡           Determine the potential sewage and pollutant loading arising from the proposed development.

¡           Study and assess the need and impacts of discharging sewage to the existing/planning sewerage systems in North East New Territories (NENT).

¡           Investigate and determine the need and the feasibility of having a separate sewage treatment plant within the Assessment Area.

¡           Formulate options to mitigate the sewerage impacts identified and recommend the design, operation and maintenance requirements for the sewage disposal system.

6.2.1           Collected Information

Desktop study, topographical survey, water sampling of Deep Bay and site visit have been undertaken to collect the relevant information for the assessment. The relevant information collected is summarized below:-

¡           The existing/planned sewerage facilities layout plan in NENT

¡           The layout plan for the proposed LT/HYW BCP

¡           The proposed planning data of the Project

¡           Water sampling data at Deep Bay in 2008

¡           Topographic survey plan for the proposed Project

6.2.2           Design Standards, Guidelines and Reference

The sewage flow and pollutant loading generated from the proposed Project are based on the following standards, guidelines and reference for the sewerage and sewage treatment design:-

¡           Sewerage Manual published by Drainage Services Department (DSD)

¡           Guidelines for the Design of Small Sewage Treatment Plant published by EPD

¡           Review of North District and Tolo Harbour Sewerage Master Plans – Final Report in November 2002

¡           Guidelines for Estimating Sewage Flows for Sewerage Infrastructure Planning Version 1.0 by EPD

¡           NENT New Development Areas (NDAs) – Technical Report on Drainage & Sewerage Impact Assessment

¡           Final Report of Planning Study on Liantang/Heung Yuen Wai Cross-boundary Control Point and its Associated Connecting Road in Hong Kong - Feasibility Study under Agreement No. CE42/2006 (TP)

¡           Technical Memorandum –  Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters enacted under the Water Pollution Control Ordinance

6.3               Design Assumptions, Parameters and Criteria

6.3.1           Design Population

The design population of the proposed LT/HYW BCP and Resite of Chuk Yuen Village is summarised in Table 6.1 and Table 6.2 respectively.

Table 6.1:      Population of the proposed LT/HYW BCP on Hong Kong Side

Type

Daily Vehicles1

Daily Passengers1

Car

2000

30000

Bus/Coach

850

Good vehicles

15000

30000

Staff2

-

500

Type

No.

Kitchen Area (m2)

Canteen3

2

25

Note:

1.     All the vehicles and passengers figures are provided by the Shenzhen authority

2.     The total number of staff is based on the data given in the Feasibility Study under Agreement No. CE42/2006 (TP).

3.     The area of the canteen kitchen in the proposed LT/HYW BCP is based on the Feasibility Study under Agreement No. CE42/2006 (TP).

Table 6.2:      Population of the Proposed Resite of Chuk Yuen Village

Development

Type

Population

Resite of Chuk Yuen Village

Modern village

528

Note: The design population of the Village Resite is based on the assumption that there will be 4 persons per floor, 3 floors in each house and ultimately 44 houses in the Resite.

The number of staff of the proposed Administration Building at the Sha Tau Kok Road Section (between north and south tunnels) of the Connecting Road (see Figure 2-1e) is presented in below Table 6.3.

Table 6.3:      Staffing of proposed Administration Building

Development

No. of Staff

Administration Building

157

Note: The no. of staff is adopted from a similar administration building in another project, namely, Agreement No. CE 58/2006 (HY) Central Kowloon Route and Widening of Gascoigne Road Flyover Investigation.

6.3.2           Design Average Daily Flow

Unit Flow Factor of Villagers and Staff

To estimate the average daily flow (ADF), the following global unit flow factors (GUFF) for villagers and staff have been adopted in accordance with the EPD’s Guidelines for Estimating Sewage Flows for Sewerage Infrastructure Planning Version 1.0 and the DSD’s Sewerage Manual respectively:

¡           GUFF of villagers (modern village)  = 0.27 m3/person/day

¡           GUFF of staff = 0.080 m3/person/day

Unit Flow Factor of Passengers

The GUFF of passengers is estimated based on the Feasibility Study under Agreement No. CE42/2006 (TP) by adopting the following assumptions:

¡           The flushing water consumption is 0.1 m3/person/day for a daily use of 16 hours for typical domestic residents, employees and students.

¡           The sewage flow generated from wash basins is 0.03 m3/person/day for a daily use of 8 hours.

Assuming the average processing time for a passenger is about 2 hours, then the GUFF of passengers, including sewage from both flushing and washing basins, can be estimated as 0.1 x 2/16 + 0.03 x 2/8 or 0.02 m3/person/day.

Unit Flow Factor of Canteen

In accordance with EPD’s Guideline for Design of Small Sewage Treatment Plants, the GUFF of 0.5 m3/m2 of kitchen area/day has been adopted.

6.3.3           Design Pollutant Loadings

The sewage loadings such as suspended solid (SS), biological oxygen demand (BOD), nitrite nitrogen (NO2N)+ nitrate nitrogen (NO3N), ammonia nitrogen (NH3N) and Faecal Coliforms (E. coli) have been identified for use in this assessment to assess the discharge requirements for the proposed development.

NO2N and NO3N are assumed to be in very small amount or zero in raw domestic wastewater at the beginning and it will be increased with time in a series of bacteria reaction. Some of the Total Kjeldahl Nitrogen (TKN) will be changed to the form of NO2N and NO3N and finally discharged into water body (Deep Bay). As NO2N and NO3N are included in the parameter of Total Nitrogen (TN), it can be assumed if the loading of TN discharging into the receiving water body is controlled to less than or equal to that before the proposed development, the loading of NO2N and NO3N discharging into the receiving water body should have no net increase. Therefore, the loading of NO2N and NO3N has been assessed in terms of TN. 

Unit Load Factors for Villagers and Staff

The pollutant loadings of the sewage for villagers and staff are extracted from Table 4 of the Sewerage Manual Part 1 by DSD as summarised in Table 6.4. 

Unit Load Factors for Passenger

Since there is no reference data for passenger sewage characteristics, such characteristics are assumed to be similar to those of the employed population, but the sewage loading of passengers would be less than that of the employed population due to the generally shorter time of stay of passengers. To estimate the unit sewage load factors for passengers, it is assumed that the processing time of each passenger is about 2 hours while the normal working hour of a staff is about 8 hours per days. The unit load factors of passengers should therefore be 1/4 of the unit load factors of staff.  However, a factor of 1/3 instead of 1/4 has been adopted to estimate the unit load factors of passengers to account for the uncertainties in sewage loadings of passengers. The estimated design unit load factors of passengers are summarised in Table 6.4.

Unit Load Factors for Canteens

The pollutant loading factors of canteens are adopted from the Guideline for Design of Small Sewage Treatment Plants published by EPD as summarized in Table 6.4.

Table 6.4:      Design Unit Load Factors

Loading Type

Unit Load Factor

 

Villagers1

Staff1

Passengers2

Canteen3

SS (kg/day/person)

0.04

0.034

0.0113

0.3 kg/kitchen area m2/day

BOD (kg/day/person)

0.042

0.034

0.0113

0.3 kg/kitchen area m2/day

TN (kg/day/person)4

0.0085

0.0067

0.0022

-

NH3N (kg/day/person)

0.005

0.004

0.0013

-

E. Coli. (no./day/person)

4.3x1010

3.5x1010

1.17 x1010

-

Note:

1.      The unit load factors for villagers and staff are based on Table 4 of the Sewerage Manual Part 1 by DSD.

2.      The unit load factors for passengers are estimated as 1/3 of the unit load factors for staff.

3.      The unit load factors for canteen are based on the Guideline for Design of Small Sewage Treatment Plants by EPD.

4.      The total nitrogen (TN) is equal to “TKN + nitrite N + nitrate N” whereas TKN is equal to “organic N + NH3N”. As nitrite N and  nitrate N are assumed to be in very small amount or zero in raw domestic wastewater at the beginning, TN is taken as equal to TKN in the raw sewage.

6.3.4           Peaking Factors

Peaking factors cater for seasonal/diurnal fluctuation and normal amount of infiltration and inflow. The peaking factors which are functions of equivalent population should be in accordance with EPD’s Guidelines for Estimating Sewage Flows for Sewerage Infrastructure Planning Version 1.0 and are shown in Table 6.5.

Table 6.5:      Peaking Factor for Sewers

Population Range

Peaking Factor (including stormwater allowance) for facility with existing upstream sewerage

Peaking Factor (excluding stormwater allowance) for facility with existing upstream sewerage

<1,000

8

6

1,000-5,000

6

5

5,000-10,000

5

4

10,000-50,000

4

3

>50,000

 7.3 x N0.15 or 2.4, whichever is higher

 6 x N0.175 or 1.6, whichever is higher

Note: N is the contributing population in thousands.

6.3.5           Assessment Criteria for the Sewerage Facilities

It is understood that the site is within a sensitive area where additional pollutant loadings from the proposed residential development is not allowed to be discharged to the existing water body from the environmental view point. Therefore, this “no net increase in pollutant loading requirement”, particularly for the BOD, SS, Nitrite + Nitrate Nitrogen, NH3N and E.Coli. in the nearby water body from the proposed development has been used in assessing the proposals of the sewerage and sewage treatment facilities.

6.4               Existing Sewerage Conditions

6.4.1           Existing Sewerage and Sewage Treatment Facilities

Based on the information collected from the Government and site inspections, the existing sewerage systems in the vicinity of the proposed BCP site are small sewerage systems with a series of sewage pumping stations for collection of the sewage flow from local villages in the areas and leachate from NENT Landfill site and for subsequent conveyance of the collected sewage flow to Shek Wu Hui Sewage Treatment Works (SWHSTW) for treatment and disposal.  Apart from the aforementioned small sewerage system, the existing village systems at some remote village areas are comprised of septic tank and leach field for on-site natural treatment and disposal.

These existing village sewerage systems have been designed to collect the sewage flow from these local villages only. It is considered that the existing systems are unlikely to cope with the additional flows due to the Project.

6.4.2           Estimated Sewage Flow and Pollutant Loading from the Existing Site

The existing local villages, Chuk Yuen South and North Village, in the vicinity of the BCP site are served by their own sewage treatment facilities such as septic tanks/soak away facilities. The sewage flow and pollutant loading from these villages are summarised in Tables 6.6 and 6.7 respectively. Details of the estimation are as shown in Appendix 6.1 and 6.2.

Table 6.6:      Population and Estimated Sewage Flow from Existing Chuk Yuen Village

Development

Type

Population

GUFF (m3/person/day)

ADF

(m3/day)

Existing Chuk Yuen (North)

Modern  village

378

0.24

90.72

Existing Chuk Yuen (South)

Modern  village

102

0.24

24.48

 

 

 

Total

115.2

Note: The global unit flow factor (GUFF) for existing Chuk Yuen villagers is in accordance with Table 2 of Sewerage Manual Part 1, DSD and modern village is assumed.  

Table 6.7:      Pollutant Loading of  Existing Chuk Yuen Villages

Loading Type

Chuk Yuen (North)

Chuk Yuen (South)

Total

SS

15.12

kg/day

4.08

kg/day

   19.20

kg/day

BOD

15.88

kg/day

4.28

kg/day

   20.16

kg/day

TN

3.21

kg/day

0.87

kg/day

4.08

kg/day

NH3N

1.89

kg/day

0.51

kg/day

2.40

kg/day

E. Coli.

16.25 x1012

no/day

4.39 x1012

no/day

20.64 x1012

no/day

 

6.4.3           Design Treatment Performance of Existing Systems

It is understood that the sewage from the existing Chuk Yuen Village (North and South) are treated and disposed by septic tanks in association with a leach field. The performance of the existing treatment facilities (septic tanks) for removal of various pollutant loadings are based on the reference data provided in Chapter 25 of Syed R. Qasim “Wastewater Treatment Plants: Planning, Design and Operation” and is summarized in Table 6.8 below:-

Table 6.8:      Performance of Septic Tank

Loading Type

Range of Removal

Design Removal1

SS

66% - 75%

70%

BOD

40% - 52%

45%

TN

20% - 29%

24%

E. Coli.

3 log – 4 log

3 log

Loading Type

Range of Increase

Design Increase1

NH3N2

178% - 223%

200%

Note:

1.     The design removal and increase percentages of sewage loading are assumed to be the mid-values of the typical ranges of removal and increase.

2.     The amount of NH3N in the effluent of septic tank will be increased after the biological reactions within the septic tank but it will not exceed the amount of TN in the effluent of septic tank as TN=TKN + Nitrate N + Nitrite N and TKN = NH3N + Organic N.   

Based on the performance of Septic Tank, the effluent quality from septic tank in the existing Chuk Yuen Villages is summarised in Table 6.9 below, which will act as the baseline pollutant loadings currently discharging to the Deep Bay.  Detail of the calculation is shown in Appendix 6.2.

Table 6.9:      Pollutant Loading Performance of Septic Tank

Loading Type

Before Septic Tank

After Septic Tank

SS

   19.20

kg/day

5.76

kg/day

BOD

20.16

kg/day

11.09

kg/day

TN

4.08

kg/day

3.10

kg/day

NH3N

2.40

kg/day

3.10

kg/day

E.Coli.

20.64 x1012

no/day

20.64 x109

no/day

6.5               Estimated Pollutant Loads due to the Project

6.5.1           Estimated Sewage Flow from the Proposed BCP and Chuk Yuen Village Resite

Based on the design population and sewage unit flow factors as mentioned in Section 6.3, the estimated average dry weather flows generated from the proposed LT/HYW BCP at Hong Kong side and Resite of Chuk Yuen Village are 185.00 m3/day and 142.56 m3/day respectively, as summarised in Tables 6.10 and 6.11.

Table 6.10:    Estimated Sewage Flow from Proposed Chuk Yuen Village Resite

Development

Type

Population

GUFF (m3/person/day)

ADF

(m3/day)

Proposed village resite

Modern village

528

0.27

142.56

Note: The GUFF for modern village is based on the EPD’s Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning Version 1.0

Table 6.11:    Estimated Sewage Flow from the proposed LT/HYW BCP on Hong Kong Side

Type

Daily Vehicles

Daily Passengers

GUFF1,2 (m3/person/day)

Percentage of Using Toilet5 (%)

ADF

(m3/day)

Car

2000

30000

0.02

10

60.00

Bus/Coach

850

Goods vehicles4

15000

30000

0.02

10

60.00

Staff

-

500

0.08

100

40.00

Total

 

60500

 

Sub-Total

160.00

 

Type

No.

Kitchen Area (m2)

GUFF3 (m3 per day per m2 of kitchen area)

ADF

(m3/day)

Canteen

2

25

0.5

25

 

 

 

Total

185.00

Note:

1.     The GUFF of passengers is estimated based on the Feasibility Study under Agreement No. CE42/2006.

2.     The GUFF of staff is based on the Sewerage Manual by DSD.

3.     The GUFF of canteen kitchen is based on the Guideline for Design of Small Sewage Treatment Plants by EPD.

4.     The no. of passengers for goods vehicles is assumed as 2 persons (i.e. a driver and a passenger) per vehicle.

5.     The percentage of passengers using toilets is assumed as 10%, which is referenced from the design data of Lok Ma Chau sewage treatment system.

As shown in above table, the 10% of passengers using toilet is adopted based on the previous design data of sewage treatment system in Lok Ma Chau.  Since this percentage of toilet use is a critical parameter to determine the total sewage flow in the future LT/HYW BCP, a sensitivity test of using 15% has been carried out and the results are presented in below Table 6.12 to demonstrate the impact on the sewage flow and pollutant loadings. 

Table 6.12:    Estimated Sewage Flow from the proposed LT/HYW BCP on Hong Kong Side (with 15% of passengers using toilet)

Type

Daily Vehicles

Daily Passengers

GUFF (m3/person/day)

Percentage of Using Toilet (%)

ADF

(m3/day)

Car

2000

30000

0.02

15

90.00

Bus/Coach

850

Goods vehicles

15000

30000

0.02

15

90.00

Staff

-

500

0.08

100

40.00

Total

 

60500

 

Sub-Total

220.00

 

Type

No.

Kitchen Area (m2)

GUFF (m3 per day per m2 of kitchen area)

ADF

(m3/day)

Canteen

2

25

0.5

25

 

 

 

Total

245.00

Notes:      The percentage of passengers using toilets is taken as 15% for the purpose of sensitivity test.

6.5.2           Estimated Pollutant Loads from the Proposed BCP and Chuk Yuen Village Resite

Estimation of the pollutant loads arising from the proposed development is detailed in Appendix 6.3. The following Table 6.13 summarizes the pollutant loads arising from the raw sewage of the proposed development.<