7 SEWERAGE AND SEWAGE TREATMENT IMPLICATIONs

7.1 Introduction

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 Sewerage Layout

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 Population and Employment Data

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 (m^2)	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 (m^2)	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/ 20m^2 GFA
Retail Area	Employee	-	57,000	-	-	1/25	-	2,280	Assume 1 worker/ 25m^2 GFA
	Visitor	-		-	-	-	-	2,105	(57,000/13 – 2,280)
TOTAL								74,020	-

Note: (1) The estimated population is rounded up to the nearest 5 unit.

7.4 Sewage Flow Estimation

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 (m^3/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 (m^3/person/day)	Estimated Flow (m^3/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 (m^3/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 Preliminary Sewerage Design

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 (m^3/day)		Projected ADWF (Kwun Tong Catchment/To Kwa Wan Catchment+10% Allowance (m^3/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 Conclusion

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.