7
SEWERAGE
AND SEWAGE TREATMENT IMPLICATIONs
7.1.1
This Sewerage and Sewage Treatment Implications
(S&STI) is prepared according to Section 3.4.7 and Appendix D2 of the EIA
Study Brief No. ESB-274/2014 which specify the requirements for S&STI. The
sewage and sewerage assessment follows the criteria and
guidelines for evaluating and assessing impacts on the public sewerage, sewage
treatment and disposal facilities as stated in section 6.5 in Annex 14 of the
Technical Memorandum on Environmental Impact Assessment Process.
7.1.2 As the Project is part of Kai Tak Development (KTD), it is necessary to review the approved EIA Report for KTD in relation to this Project and to identify and determine whether an updated S&STI is required.
7.1.3
The
Project is located on the west side of Kai Tak
North Apron. It is separated by existing Kai Tak Tunnel and the new road D2.
The location plan is shown in Figure 7-1-1.
7.1.4
The
Project consists of the following buildings:
l Main
Stadium
l
Public Sports Ground,
including ancillary areas such as retail area
l
Indoor Sports Centre,
including ancillary areas such as retail area
l
Hotel block, including
ancillary areas such as retail area
l
Office block, including
ancillary areas such as retail area
7.1.5
The
master layout plan of the Project is shown in Figure 7-1-2.
7.2.1
According
to EIA of KTD, the sewerage in KTD is separated
into two systems, the eastern sewerage collects sewage from the eastern
catchment and discharge into Kwun Tong Preliminary Treatment Works (KTPTW)
while the sewage from northwest catchment discharges into
To Kwa Wan Preliminary Treatment Works (TKWPTW) as shown in Figure 7-2-1. The sewage from the Project is part of the northwest catchment that
discharges into TKWPTW and ultimately into Stonecutter Island Sewage Treatment
Works via deep tunnels.
7.2.2
The
Project is a new development in KTD, a new sewerage system will be designed to
suit. Six nos. of separate foul water discharge points FDP1 to FDP6 are
proposed by the project team of MPSC and agreed with CEDD to discharge the
sewer from the Project into the sewerage system in Kai Tak Development as
follows,
l A
sewer on the north of Kai Tak Tunnel collecting sewage from FDP1 to FDP4
successively for Public Sports Ground and Indoor Sports Centre then joining a
750mm twin pipe leading to Pumping Station PS2 at the junction of Road L6 and
Road D2, hereinafter called Sewer No. 1.
l A
600mm sewer collecting sewage from FDP5 for the Main Stadium and a 300mm sewer
collecting sewage from FDP6 for Hotel Block and Office Block, both discharge
into a 750mm diameter sewer along Road D2 which subsequently discharges into
Pumping Station NPS, hereinafter called Sewer No. 2.
CEDD is responsible for implementation of Sewer
No. 1 and Sewer No. 2.
7.2.3
The
sewerage layout plan is shown in Figure 7-2-2.
7.3.1
The
design parameters of the Project are shown in Table 7-1.
Table 7-1 Design
Parameters of the Project
Use |
GFA (m2) |
No. of Hotel Rooms |
No. of Seats in Sports Facilities |
Main Stadium |
- |
- |
50,000 |
Public Sports Ground |
- |
- |
7,000 |
Indoor Sports Centre |
- |
- |
5,400 |
Hotel Area |
16,000 |
300 |
- |
Office Area |
16,000 |
- |
- |
Retail Area |
57,000 |
- |
- |
7.3.2 The population and employment data within the Project are based on employment figures provided by LCSD (prepared in 2014) and HAB (prepared in 2015).
7.3.3 The population in the Project are classified in seven types as follow:
l Spectators
in Main Stadium, Public Sports Ground and Indoor Sports Centre
l Permanent
employees in Main Stadium, Public Sports Ground and Indoor Sports Centre
l Temporary
employees in Main Stadium, Public Sports Ground and Indoor Sports Centre
l Residents
in Hotel Area
l Employees
in Hotel Area
l Employees
in Office Area and Retail Area
l Visitors
in Retail Area
7.3.4 The employment figure for Main Stadium in the Project is pro-rated based on the event of Hong Kong Sevens 2014 in Hong Kong Stadium, as advised by LCSD in 2014. There were 21 permanent employees working in Hong Kong Stadium, with capacity of 40,000 seats. Therefore, the proposed rate for the Main Stadium is 21/40,000 for permanent employee. Based on past statistics, about 4,100 temporary employees worked in Hong Kong Stadium, with capacity of 40,000 seats, during the period when Hong Kong Sevens 2014 was held with breakdown as shown in Appendix 7.1. Therefore, the rate of 4,100/40,000 for temporary employee working in the Main Stadium is assumed.
7.3.5 The employment figures for Public Sports Ground and Indoor Sports Centre in the Project are estimated by HAB in 2015, based on the employment figures of Tseung Kwan O Sports Ground and Queen Elizabeth Stadium respectively. According to 2015 employment figures of Tseung Kwan O Sports Ground with 5,000 spectators, the permanent and temporary employees are 30 and 250 respectively. Applying these ratios to Public Sports Ground, the permanent and temporary employees will be 40 (7,000 x 30/5,000, round off to the nearest 5) and 350 (7,000 x 250/5,000) respectively. Based on 2015 employment figures of Queen Elizabeth Stadium with 3,500 spectators, the permanent and temporary employees are 35 and 36 respectively. Applying these ratios to the Indoor Sports Centre, the permanent and temporary employees will be 55 (5,400 x 35/3,500, round off to the nearest 5) and 55 (5,400 x 36/3,500, round off to the nearest 5) respectively.
7.3.6 The total population of Retail Area in the Project (including employee and visitor) is estimated based on the GFA of Retail Area in the Project, which is 57,000 m2. According to Building (Standards of Sanitary Fitments, Plumbing, Drainage works and Latrines) Regulation 5. (5)(a), the total number of persons in any building shall be determined at the rate of one person for every 9m2 of usable floor area (UFA), i.e. 9 m2 UFA/person. Assuming normal commercial development with floor area efficiency of 70%, i.e. 1 sq m gross floor area (GFA) is equivalent to 0.7 sq m UFA, the total number of persons in any building shall be determined at the rate of one person for every 13 m2, i.e. 13 m2 GFA/person (≈ 9 m2 UFA/70%). Therefore, the total population of Retail Area in the Project (including employee and visitor) is estimated based on about 4,385 (≈ 57,000/13).
7.3.7 The population of employee in Retail Area in the Project is estimated based on the GFA of Retail Area in the Project, which is 57,000 m2. Assuming 1 worker/25 m2 GFA, the population of employee in Retail Area in the Project is 2,280 (= 57,000/25). This assumption is based on the layout and size of individual shops while the total population is governed by the development density. Therefore, the population of visitor in Retail Area in the Project would be 2,105 (= 4,385 – 2,280). Noting that the ratio of employees and visitors may change with different layout and nature of the Retail Area, but the total population remains constant.
7.3.8 The estimated population of the Project is summarized in Table 7-2.
Table 7-2 Population
Estimation of the Project
Use
|
Types
of Population
|
Quantities
|
Rate
|
Estimated
Population
|
Remarks
|
||||
No.
of seats in sports facility
|
GFA
(m2)
|
No.
of Hotel Rooms
|
Sports
facility
|
Office
Area & Retail Area
|
Hotel
Area
|
||||
Main
Stadium
|
Spectator
|
50,000
|
-
|
-
|
-
|
-
|
-
|
50,000
|
-
|
Permanent
employee (1)
|
-
|
-
|
21/
40,000
|
-
|
-
|
30
|
Estimated by the employment
figures of Hong Kong Stadium
|
||
Temporary
employee (1)
|
-
|
-
|
4,100/
40,000
|
-
|
-
|
5,125
|
|||
Public
Sports Ground
|
Spectator
|
7,000
|
-
|
-
|
-
|
-
|
-
|
7,000
|
-
|
Permanent
employee (1)
|
-
|
-
|
30/
5,000
|
-
|
-
|
40
|
Estimated by HAB in 2015, based on
the employment figures of Tseung Kwan O Sports Ground
|
||
Temporary
employee (1)
|
-
|
-
|
250/
5,000
|
-
|
-
|
350
|
|||
Indoor
Sports Centre
|
Spectator
|
5,400
|
-
|
-
|
-
|
-
|
-
|
5,400
|
-
|
Permanent
employee (1)
|
-
|
-
|
35/
3,500
|
-
|
-
|
55
|
Estimated by HAB in 2015, based on
the employment figures of Queen Elizabeth Stadium
|
||
Temporary
employee (1)
|
-
|
-
|
36/
3,500
|
-
|
-
|
55
|
|||
Hotel
Area
|
Resident
|
-
|
-
|
300
|
-
|
-
|
2
x 80%
|
480
|
Assume 2 people/room with 80%
occupancy
|
Employee
|
-
|
-
|
-
|
1
|
300
|
Assume 1 worker/
room
|
|||
Office
Block
|
Employee
|
-
|
16,000
|
-
|
-
|
1/20
|
-
|
800
|
Assume 1 worker/
20m2 GFA
|
Retail
Area
|
Employee
|
-
|
57,000
|
-
|
-
|
1/25
|
-
|
2,280
|
Assume 1 worker/
25m2 GFA
|
Visitor
|
-
|
-
|
-
|
-
|
-
|
2,105
|
(57,000/13 – 2,280)
|
||
TOTAL
|
74,020
|
-
|
7.4.1
As
described in Section 7.3.3, there are seven types of population in the Project.
The unit flow factors are estimated as follow:
Spectators
in Main Stadium, Public Sports Ground and Indoor Sports Centre
l Unit
flow factor of spectator in Main Stadium, Public Sports Ground and Indoor Sports
Centre: According to the Appendix III of the EPD Guidelines for Estimating Sewage Flows for Sewage
Infrastructure Planning (GESF) (2005), the average daily flushing water
consumption is 0.100 m3/person/day based on total land usual
residents of 6.592 million as at mid-2002.
Assuming the average hours of spectators in the sports facility is 3 hr/day and
taking into account traveling time from home to sports facility, around 4
hr/day of a spectator in average is sports facility related. If the average waking
hours of spectators is 16 hr/day, the percentage of sports facility related
waking hours is 4/16
x 100 = 25%. Therefore,
flushing water consumption of spectators in the sports facilities equals 0.025
m3/person/day (= 0.100 x 0.25).
l With
15% additional allowance for fresh water basin and cleaning flows
and 10% for miscellaneous use for meals, the average sports facility-related
water consumption of every spectator equals 0.0316 m3/person/day
approx. (= 0.025 x 1.15 x 1.1)
l Allowing
for infiltration, the recommended unit flow factor of spectators for Main
Stadium, Public Sports Ground and Indoor Sports Centre is 0.032 m3/person/day.
Permanent
Employees in Main Stadium, Public Sports Ground and Indoor Sports Centre
l Unit
flow factor of permanent employee in Main Stadium, Public Sports Ground and
Indoor Sports Centre: According to Table T-2 of GESF (2005) from EPD, the unit flow factor of permanent employee in Main
Stadium, Public Sports Ground and Indoor Sports Centre is 0.280 m3/person/day,
which is the sum of the unit flow factor of employee, 0.080 m3/person/day
and the unit flow factor of activities, J11 Community, Social & Personal
Services / Planning for Future, 0.200 m3/person/day.
Temporary Employees in Main Stadium, Public Sports Ground and Indoor Sports
Centre
l Unit
flow factor of temporary employee in Main Stadium, Public Sports Ground and
Indoor Sports Centre: According to the Appendix III of GESF (2005) from EPD, the average daily flushing water
consumption is 0.100 m3/person/day based on a total land usual
residents of 6.592 million as at mid- 2002, Assuming the average working hours
of temporary employee is 8 hr/day and the average waking hour of temporary
employees is 16.
Therefore, unit flushing water consumption of temporary employee in the sports
facilities equals 0.05m3/person/day. (=0.100 x 8/16)
l With
15% additional allowance for fresh water basin and cleaning flows and 10% for
miscellaneous use for meals, the average sports facility-related water
consumption of every temporary employee is approx. 0.0633 m3/person/day
(= 0.05 x 1.15 x 1.1).
l Allowing
for infiltration, the recommended unit flow factor of temporary employees for
Main Stadium, Public Sports Ground and Indoor Sports Centre is 0.064 m3/person/day.
Residents in
Hotel Area
l Unit
flow factor of resident in Hotel Block: According to Table T-2 of GESF (2005) from EPD, the unit flow factor of resident in Hotel Block is
0.370 m3/person/day assuming R3 Private development
Employees in
Hotel Area
l Unit
flow factor of employee in Hotel Block: According to Table T-2
of GESF
(2005) from EPD, the unit flow factor of employee in Hotel Block is
1.580 m3/person/day, which is the sum of the unit flow factor of
employee, 0.080 m3/person/day and the unit flow factor of
activities, J10 Restaurants & Hotels / Planning for Future, 1.500 m3/person/day.
Employees in
Office Area and Retail Area
l Unit
flow factor of employee in Office Block and Retail Block: According to Table
T-2 of GESF
(2005) from EPD, the
unit flow factor of employee in Office Area and Retail Area is 0.280 m3/person/day,
which is the sum of the unit flow factor of employee, 0.080 m3/person/day
and the unit flow factor of activities, J4 Wholesale & Retail / Planning
for Future, 0.200 m3/person/day.
Visitors in
Retail Area
l Unit
flow factor of visitor in Retail Area: According to the Appendix III of GESF
(2005) from EPD, with a total land usual residents of 6.592 million as at
mid-2002, the average daily flushing water consumption is 0.100 m3/person/day.
Assuming the average hours of visitors in the Retail Area is 1 hr/day and
taking into account traveling time from home to Retail Area in the Project,
around 2 hr/day of a visitor in average is Retail Area related. If the average
waking hours of visitors is 16 hr/day, the percentage of Retail Area related
waking hours is 2/16 x 100 = 12.5%. Therefore, flushing water consumption of
visitors in Retail Area is 0.0125 m3/person/day (=0.100 x 0.125).
l With
15% additional allowance for fresh water basin and cleaning flows and 10% for
miscellaneous use for meals, the average Retail Area-related water consumption
of every visitor is approx. 0.0158 m3/person/day (= 0.0125 x 1.15 x
1.1)
l Allowing
for infiltration, the recommended unit flow factor of visitors for Retail Area
in the Project is 0.016 m3/person/day.
l The
unit flow factors adopted in the sewage flow estimation for the Project
are summarized in Table 7-3.
Table 7-3 Unit Flow Factors Adopted for the
Project
Use |
Unit (per) |
Unit Flow Factors (m3/person/day) |
Main
Stadium |
Spectator |
0.032 |
Permanent
employee |
0.280 |
|
Temporary
employee |
0.064 |
|
Public Sports Ground |
Spectator |
0.032 |
Permanent employee |
0.280 |
|
Temporary employee |
0.064 |
|
Indoor Sports Centre |
Spectator |
0.032 |
Permanent employee |
0.280 |
|
Temporary employee |
0.064 |
|
Hotel Area |
Resident |
0.370 |
Employee |
1.580 |
|
Office Area |
Employee |
0.280 |
Retail Area |
Employee |
0.280 |
Visitor |
0.016 |
7.4.2 Based on the population estimated in Table 7-2 and the unit flow factor described in Section 7.4.1, the estimated sewage flow in the Project is about 3,933.4 m3/day with breakdown as shown in Table 7-4.
Table 7-4 Estimated Sewage Flow from the Project
Use |
Types of Population |
Estimated Population |
Unit Flow Factor (m3/person/day) |
Estimated Flow (m3/day) |
Main
Stadium |
Spectator |
50,000 |
0.032 |
1,600.00 |
Permanent employee |
30 |
0.280 |
8.40 |
|
Temporary employee |
5,125 |
0.064 |
328.00 |
|
Public Sports Ground |
Spectator |
7,000 |
0.032 |
224.00 |
Permanent employee |
40 |
0.280 |
11.20 |
|
Temporary employee |
350 |
0.064 |
22.40 |
|
Indoor
Sports Centre |
Spectator |
5,400 |
0.032 |
172.80 |
Permanent employee |
55 |
0.280 |
15.40 |
|
Temporary employee |
55 |
0.064 |
3.52 |
|
Hotel
Area |
Resident |
480 |
0.370 |
177.60 |
Employee |
300 |
1.580 |
474.00 |
|
Office
Area |
Employee |
800 |
0.280 |
224.00 |
Retail
Area |
Employee |
2,280 |
0.280 |
638.40 |
Visitor |
2,105 |
0.016 |
33.68 |
|
TOTAL (m3/day) |
3,933.40 |
7.4.3
The
estimated average dry weather flow (DWF) of 3,933.40 m3/day or 0.046
m3/sec is comparable with the flow of 0.083 m3/sec
reported in Table 4.18 Projected Peak Flow for Year 2031 and Ultimate Scenario in
the Infrastructure Review Report (Final) Rev 1 (IRR), see Appendix 7.2. Noting that the value reported in IRR includes peaking factor that
ranges from 2.48 to 2.50 as shown in IRR Table 4.17, see Appendix 7.2(i). Back analysis shows that
the DWF from MPSC cited in IRR is 0.033 m3/sec, see Appendix 7.2(ii). Comparing the two flow rates, the increase is about 39%. This
increase is caused by increase in seating capacity of MPSC since IRR.
7.4.4
The
population and sewage flow is expected to be steady upon commissioning of this
Project. The estimated projected flow after ten years should be the same.
7.5.1
The
pipe roughness is specified as an equivalent sand roughness (ks) used by the
Colebrook-White equation. For the hydraulic assessment of the new sewers inside
KTD, the roughness coefficient to be used in this Preliminary Sewerage Design
is 0.6 mm for vitrified clay pipes and 1.5 mm for precast concrete pipes based
on CEDD’s “Kai Tak Development - Stage 4 Infrastructure at Former North Apron
Area Sewerage Design”, Contract No. KL/2012/03 which is confirmed in Appendix 7.4.
7.5.2
Preliminary
estimation of Sewer No. 1 shows that the sewer
line is adequate to collect sewage from the Public Sports Ground and Indoor
Sports Centre to the PS2, including catchment for the 750 mm twin pipe.
Preliminary sewerage calculation is included in Appendix 7.3.
7.5.3
Preliminary
estimation of Sewer No. 2 shows that the sewer line is adequate to collect
sewage from the Main Stadium, Hotel and Office Block to NPS, including the
rising mains from PS2 and PS1. Preliminary sewerage calculation is included in Appendix 7.3.
7.5.4 The additional sewage from the Project is 3,933.40 m3/day, or 0.046 m3/sec will be discharged into TKWPTW and subsequently delivered to Stonecutter Island Sewage Treatment Works via deep tunnels. According to latest estimated figures from IRR, the estimated average dry weather flow (ADWF) for KTD and To Kwa Wan Catchment Area to TKWPTW in both Year 2031 and the ultimate scenario are summarized in Table 7-5. The projected peak flow for Year 2031 and ultimate scenario, excluding and including MPSC are summarized in Table 7-6, the peaking factor (PF) is based on EPD guideline for contributing population equals calculated average flow divided by 0.27. It gives contributing population of 14,568 that gives PF = 3.5. The projected peak flow from MPSC, based on estimated ADWF of 3,933.40 m3/sec gives peak flow of 13,767 m3/day or 0.159 m3/sec. The total projected peak flow including MPSC at ultimate scenario is 8.71 m3/sec.
Table 7-5 Average Dry Weather Flows for Year 2031
and Ultimate Scenarios
To Kwa Wan Preliminary Treatment Works |
Projected ADWF (m3/day) |
Projected ADWF (Kwun Tong Catchment/To Kwa
Wan Catchment+10% Allowance (m3/day)) |
||
Year 2031 |
Ultimate |
Year 2031 |
Ultimate |
|
Kai Tak Development |
27,478 |
27,478 |
27,478 |
27,478 |
To Kwa Wan Catchment |
227,374 |
238,743 |
250,111 |
262,617 |
Total |
254,852 |
266,221 |
277,589 |
290,095 |
Table 7-6 Projected Peak
Flows for Year 2031 and Ultimate Scenarios in To Kwa Wan Preliminary Treatment
Works, in m3/sec
|
Year 2031 |
Ultimate |
Year 2031 |
Ultimate |
Remark |
Kai Tak Development |
0.79 |
0.79 |
0.79 |
0.79 |
Peak flow
based on IRR |
To Kwa Wan Catchments |
6.58 |
6.90 |
7.19 |
7.53 |
|
MTR – SCL |
0.02 |
0.02 |
0.02 |
0.02 |
|
DWFI (NPS) |
0.21 |
0.21 |
0.21 |
0.21 |
|
Total,
excluding MPSC |
7.60 |
7.92 |
8.21 |
8.55 |
|
MPSC |
0.16 |
0.16 |
0.16 |
0.16 |
PF=3.5 |
Total,
including MPSC |
7.76 |
8.08 |
8.37 |
8.71 |
|
According to IRR, the current design capacity of TKWPTW is 9.32 m3/sec, there is no adverse impact to TKWPTW as the projected flow is still less than the capacity of TKWPTW. The sewerage impact to Stonecutter Island STW is insignificant.
7.5.5
There is no significant sewerage impact because
the sewerage system in the whole KTD including the Project are newly planned,
designed and constructed at about the same time. The sewer line connecting MPSC
to this sewerage system are relatively short that discharged into pumping
stations.
7.6.1 Based on the above review, no adverse sewerage and sewage impact caused by the Project is anticipated.
7.6.2 No further detailed assessment or Info Work Modelling is required.