TABLE OF CONTENT

8 Sewerage and Sewage Treatment Implication. 8-1

8.1 Introduction. 8-1

8.2 Description of Environment 8-1

8.3 Design Guidelines and Standards. 8-1

8.4 Sewage Estimation and Impact Assessment 8-1

8.5 Conclusion. 8-6

LIST OF TABLES

Table 8.1 Residents in the Concerned Sewerage Catchment (to FMH4046332)

Table 8.2 Residents in the Sewerage Catchment (to FMH4046336)

Table 8.3 Employees in the Sewerage Catchment (to FMH4046332)

Table 8.4 Employees in the Sewerage Catchment (to FMH4046336)

Table 8.5 Students and Staffs in the Concerned Sewerage Catchment (to FMH4046332)

Table 8.6 Students and Staffs in the Concerned Sewerage Catchment (to FMH4046336)

Table 8.7 Summary of Capacity for Concerned Pumping Stations

Table 8.8 Summary of Capacity for the Relocated Sha Tin Sewage Treatment Works (STSTW)

LIST OF FIGURES

Figure 8.1 Layout Plan for Proposed Dry Weather Flow Interceptor (DWFI) System for Tai Wai Nullah (Sheet 1 of 3)

Figure 8.2 Layout Plan for Proposed Dry Weather Flow Interceptor (DWFI) System for Tai Wai Nullah (Sheet 2 of 3)

Figure 8.3 Layout Plan for Proposed Dry Weather Flow Interceptor (DWFI) System for Tai Wai Nullah (Sheet 3 of 3)

LIST OF APPENDIX

Appendix 8.1 Hydraulic Performance of Existing Sewers

8 Sewerage and Sewage Treatment Implication

8.1 Introduction

8.1.1.1 This section presents the assessment on potential sewerage and sewage treatment impacts on the downstream public sewerage, sewage treatment and disposal facilities arising from the Project, which has been conducted in accordance with the criteria and guidelines as stated in Section 6.5 of Annex 14 of the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) as well as the requirements given in Clause 3.4.9 and Appendix G of the EIA Study Brief (No. ESB-320/2019).

8.2 Description of Environment

8.2.1.1 Tai Wai Nullah is located within the catchment of Sha Tin Sewage Treatment Works (STSTW). The land uses within the Project boundary are mainly residential and commercial uses, partly industrial uses, and some recreational areas.

8.3 Design Guidelines and Standards

8.3.1.1 The design guidelines and standards adopted in the sewerage and sewage treatment assessment are:

· DSD Sewerage Manual Part 1 (2013 Version);

· DSD Sewerage Manual Part 2 (2013 Version);

· DSD Technical Circulars and Practice Notes;

· EPD Guideline for Estimating Sewage Flows for Sewage Infrastructure Planning Version 1.0 (Report No. EPD/TP 1/05); and

· Environmental Impact Assessment Ordinance (EIAO), Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM), Annex 14 Section 6.5.

8.4 Sewage Estimation and Impact Assessment

8.4.1 Dry Weather Flow Intercepting System

8.4.1.1 Due to possible ageing drainage systems, individual direct discharge and possible expedient connection made in the past to Tai Wai Nullah, number of water quality pollution incidents have been reported and there still remains a portion of polluting sources. Hence, a dry weather flow interceptor (DWFI) system is proposed to improve the water quality in the nullah.

8.4.1.2 With the proposed DWFI system, polluted dry weather flows from drainage outlets would be intercepted by two dry weather flow channels, running along both sides of the nullah bed (see Section 2). The dry weather flow will be carried downstream eventually joining the nearby existing sewerage system. The dry weather flow then follows the existing sewage route to existing sewage pumping stations and eventually reaching the relocated Sha Tin Sewage Treatment Works. Proposed alignment of DWFI system is shown in Figure 8.1 to Figure 8.3.

8.4.2 Estimation of Existing Sewage Flow

8.4.2.1 The DWFI system is proposed to discharge into an existing 900mm dia. sewer between manhole FMH4046338 and FMH4046340. To assess the hydraulic performance of the existing 900mm dia. sewer, existing sewage flow from the concerned sewage catchment was estimated.

8.4.2.2 The sewage flow from the concern sewage catchment comprises several components: residential, commercial, and institution/schools. Population from each of the components were estimated and the average dry weather flow (ADWF) were calculated based on the “Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning” (GESF) by the Environmental Protection Department.

8.4.2.3 The existing development parameters in the concerned sewerage catchment are estimated and summarised in Table 8.1 to Table 8.6.

Table 8.1 Residents in the Concerned Sewerage Catchment (to FMH4046332)

Residential Buildings ^[1]	Population ^[2]	Unit Flow Factor ^[3] (m^3/day)	ADWF (m^3/day)
Ho Sze House	45	0.27	13.9
Lai Shing Mansion	20	0.27	6.1
Cheung Hing Mansion	48	0.27	14.8
Moon Wah Mansion	56	0.27	17.4
Wing Fu Building	45	0.27	13.9
Kam Cheong Building	112	0.27	34.8
Tai On Building	168	0.27	52.2
Tin Po Building	84	0.27	26.1
Tak On Building	224	0.27	69.6
Shu Tak Building	84	0.27	26.1
Wah Mee House	42	0.27	13.0
Rich Mansion	14	0.27	4.3
Chik Fu Mansion	84	0.27	26.1
Lai Ming Building	36	0.27	11.3
Yue Huen House	28	0.27	8.7
On Ting Mansion	53	0.27	16.5
Chik Kin Mansion	56	0.27	17.4
Chik Hong Mansion	112	0.27	34.8
Ka Po House	28	0.27	8.7
Chik Tat House	84	0.27	26.1
Fu Cheong House	42	0.27	13.0
Lung Fung House	36	0.27	11.3
Kai Tak Building	22	0.27	7.0
Hey Yuet Building	56	0.27	17.4
Cheung Fung Mansion	56	0.27	17.4
Ka Chuen House	53	0.27	16.5
On Fu Mansion	28	0.27	8.7
Kut Hing House	42	0.27	13.0
Moon Tong House	25	0.27	7.8
Sui Fung Mansion	56	0.27	17.4
Lin King House	25	0.27	7.8
Kai Yuen Building	14	0.27	4.3
Sui Yuen House	53	0.27	16.5
Lung King Building	28	0.27	8.7
Lung Wah House	17	0.27	5.2
Kam Shan Building	448	0.27	139.1
Yiu Po Mansion	112	0.27	34.8
Yuet On Building	112	0.27	34.8
Hing Shing Building	70	0.27	21.7
Glamour Garden	538	0.27	166.9
Grandeur Garden	2117	0.27	657.3
The Garrison	319	0.27	99.1
Kam Fai Building	98	0.27	30.4
Hong Lok Building	168	0.27	52.2
Mei Lun House	28	0.27	8.7
Chung Pak Lau	42	0.27	13.0
Luen Fat House	67	0.27	20.9
Rich Court	84	0.27	26.1
Yan On Building	45	0.27	13.9
On Hong Building	84	0.27	26.1
On Tai Building	84	0.27	26.1
Grandway Garden Block 2 & 3	1612.8	0.27	500.8
Tai Wai Village	1691.2	0.27	525.1
Sub-total =			3010.7

Notes:

[1] Information on no. of flat of existing residential building is collected from the website of Home Affairs Department https://www.buildingmgt.gov.hk/en/database_of_private_buildings_in_hong_kong/12.htm.

[2] According to statistics on population and households by the Census and Statistics Department, an average domestic household size of 2.8 people was adopted in the population estimation.

[3] Unit Flow Factors were obtained from “Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning” (GESF) by the Environmental Protection Department.

Table 8.2 Residents in the Sewerage Catchment (to FMH4046336)

Commercial Buildings	Nos. of Workers^[1][2]	Unit Flow Factor ^[3] (m^3/day)	ADWF (m^3/day)
Chik Fuk Building	28	0.27	8.7
Chik Tak Building	33.6	0.27	10.4
Shing Ho Building	28	0.27	8.7
Ping Yuen	8.4	0.27	2.6
20 Chik Fu Street	33.6	0.27	10.4
15 - 17 Shing Ho Road	14	0.27	4.3
Chik Sin Building	28	0.27	8.7
Lin Fung House	30.8	0.27	9.6
Kong Yip House	28	0.27	8.7
Lap Wo Building (House)	56	0.27	17.4
Hing Wan House	28	0.27	8.7
King Sing House	28	0.27	8.7
Chik Shun Building	56	0.27	17.4
Kwai Wai Building	56	0.27	17.4
Yung Wun Building	39.2	0.27	12.2
On Shun Mansion A block	84	0.27	26.1
On Shun Mansion B block	56	0.27	17.4
Mei Fung House	2870	0.19	627.1
Mei Tao House	2870	0.19	627.1
Mei Yeung House	2870	0.19	627.1
Mei Ying Court	604.8	0.19	132.1
Mei Tin Estate	18760	0.19	4099.1
Sub-total=			6309.9

Notes:

[1] The total area of commercial building is measured using base map.

[2] The worker density per area is based on Commercial and Industrial Floor Space Utilization Survey (CIFSUS) conducted by the Planning Department.

[3] Unit Flow Factor was obtained from “Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning” (GESF) by the Environmental Protection Department.

Table 8.3 Employees in the Sewerage Catchment (to FMH4046332)

Commercial Buildings	Nos. of Workers ^[1][2]	Type	Unit Flow Factor ^[3] (m^3/day)	ADWF (m^3/day)
Tai Wai MTR Station	703	J3	0.18	145.5
Shops below Grandway Garden Block 1	6	J10	1.58	10.9
Shops below Grandway Garden Block 2&3	8	J10	1.58	14.5
Market near Shatin Public School	58	J4	0.28	18.7
McDonald under Yiu Po Building	21	J10	1.58	38.2
Restaurants under Kam Shan Building	41	J10	1.58	74.5
Restaurants under Tai On Building	48	J10	1.58	87.2
Restaurants under Cheung Hing Mansion	24	J10	1.58	43.6
Restaurants under Kam Fai Building	21	J10	1.58	38.2
Restaurants under Hong Lok Building	65	J10	1.58	118.1
Salon under Tak On Building	6	J11	0.28	1.9
Restaurant under Shu Tak Building	6	J10	1.58	10.9
Restaurant under Chik Fu Building	2	J10	1.58	3.6
Salon under Chik Sing Building	2	J11	0.28	0.6
Restaurant under Chik King Building	4	J10	1.58	7.3
Restaurant under Yuet Fu Building	8	J10	1.58	14.5
Salon under Yuet Fu Building	5	J11	0.28	1.6
Restaurant under Chik Tak Building	14	J10	1.58	25.4
Restaurant under Kai Tak Building	7	J10	1.58	12.7
Restaurant under Lung Fung House	12	J10	1.58	21.8
Salon under Hey Yuet Building	5	J11	0.28	1.6
Restaurant under Cheong Fung Building	13	J10	1.58	23.6
Restaurant under Sui Fung Mansion	5	J10	1.58	9.1
Salon under Kut Hing Mansion	2	J11	0.28	0.6
Restaurant Yun Wun Building	9	J10	1.58	16.4
Restaurant under On Fu Building	23	J10	1.58	41.8
Restaurant under Nin King Building	12	J10	1.58	21.8
Restaurant under Lung King Building	11	J10	1.58	20.0
Restaurants near Shing Ho Road Refuse Point	7	J10	1.58	12.7
Salon near Shing Ho Road Refuse Point	6	J11	0.28	1.9
Clothes washing shop near Shing Ho Road Refuse Point	3	J11	0.28	1.0
Sub-total=				840.4

Notes:

[1] The total area of commercial building is measured using base map.

[2] The worker density per 100m² is based on Commercial and Industrial Floor Space Utilization Survey (CIFSUS) conducted by the Planning Department.

[3] Unit Flow Factors and Catchment Inflow Factor (Sha Tin Catchment) were obtained from “Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning” (GESF) by the Environmental Protection Department.

Table 8.4 Employees in the Sewerage Catchment (to FMH4046336)

Commercial Buildings	Nos. of Workers ^[1][2]	Type	Unit Flow Factor ^[3] (m^3/day)	ADWF (m^3/day)
Home for the aged	10	J11	0.28	3.2
Mei Lam Shopping Centre	681	J4	0.28	219.3
Mei Lam Cooked Food Stalls	26	J10	1.58	47.2
Mei Tin Community Hall	118	J11	0.28	38.0
Mei Tin Shopping Centre	260	J4	0.28	83.7
Shing Ho Road Refuse Collection Point	2	J3	0.18	0.4
Shops near Mei Chuen House	19	J4	0.28	6.1
Po Fook Memorial Hall	398	J11	0.28	128.2
Fu Shan Crematorium	76	J11	0.28	24.5
Fu Shan Public Mortuary	311	J11	0.28	100.1
Sub-total=				650.7

Notes:

[1] The total area of commercial building is measured using base map.

[2] The worker density per 100m² is based on Commercial and Industrial Floor Space Utilization Survey (CIFSUS) conducted by the Planning Department.

[3] Unit Flow Factors and Catchment Inflow Factor (Sha Tin Catchment) were obtained from “Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning” (GESF) from Environmental Protection Department.

Table 8.5 Students and Staffs in the Concerned Sewerage Catchment (to FMH4046332)

School/ Institution	Nos. of Students ^[1]	Nos. of Staff ^[1]	Unit Flow Factor for Students ^[3] (m^3/day)	Unit Flow Factor for Staff ^[3] (m^3/day)	ADWF (m^3/day)
Sha Tin Public School	273	68	0.04	0.28	34.5
Sub-total=					34.5

Notes:

[1] Number of students and staffs was collected from the websites of kindergarten, primary school, secondary school and special school.

[2] Unit Flow Factors and Catchment Inflow Factor (Sha Tin Catchment) were obtained from “Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning” (GESF) by the Environmental Protection Department.

Table 8.6 Students and Staffs in the Concerned Sewerage Catchment (to FMH4046336)

School/ Institution	Nos. of Students ^[1]	Nos. of Staff ^[1]	Unit Flow Factor for Students ^[3] (m^3/day)	Unit Flow Factor for Staff ^[3] (m^3/day)	ADWF (m^3/day)
Sin Chu Wan Primary School	685	48	0.04	0.28	47.0
Buddhist Wong Wan Tin College	657.6	62	0.04	0.28	50.2
TWGHs Shui Chuen O Primary School	191.8	47.95	0.04	0.28	24.3
The Salvation Army Centaline Charity Fund Kindergarten	247	21	0.04	0.28	18.1
Sub-total=					139.6

Notes:

[1] Number of students and staffs was collected from the websites of kindergarten, primary school, secondary school and special school.

[2] Unit Flow Factors and Catchment Inflow Factor (Sha Tin Catchment) were obtained from “Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning” (GESF) by the Environmental Protection Department.

8.4.2.4 By summing up all the contributing sources in the concerned sewerage catchment mentioned above (Table 8.1 to Table 8.6), the total ADWF that eventually discharges sewer manhole FMH4046336 combined with the upstream flows from FMH4046332 is 10,985.8 m³/day.

8.4.3 Estimation of Dry Weather Flow

8.4.3.1 As mentioned in Section 8.4.1, a DWFI system was proposed as a water quality enhancement measure. It will intercept dry weather flows with substandard water quality that would otherwise be discharged to Tai Wai Nullah from drainage outlets.

8.4.3.2 A water quality survey has been conducted under this Project. The water quality survey consists of two parts. The first part is the visual inspection of all the drainage outlets along the nullah with an aim to identify outlets with substandard water quality and odour issues, which will likely be intercepted by the DWFI system. The second part is the water quality sampling and testing to verify the water quality conditions of selected outlets.

8.4.3.3 In addition, a flow survey has also been conducted under this Project. Flow sensors have been installed in major drainage outlets and along the main channel.

8.4.3.4 Based on the results from the water quality and flow surveys, outlets that will likely discharge polluted flow into the nullah have been identified, and the dry weather flow targeted for interception was estimated to be roughly 2,850 m³/day.

8.4.4 Sewage from Proposed Toilet near Pok Ngar Villa

8.4.4.1 An additional toilet facility for the visitors in Tai Wai Nullah is located near Pok Ngar Villa. As such, this toilet facility would generate additional sewerage flow that is required to be conveyed to the nearby existing sewerage system. A proposed outlet pipe from the new toilet would be connected to the nearest manhole FMH4039953. The fresh water and salt water consumption combined for the toilet flushing and handwashing basins is estimated to be 10.8m³/day. Checking of the impact to the pipe immediately downstream of FMH4039953 has been carried out. An additional flow percentage of approximately 0.03% from the toilet facility is added to the pipe system downstream of FMH4039953. Considering that the flow from the proposed toilet is small, it is considered to be negligible and would not have adverse impacts on the downstream sewerage network.

8.4.5 Impact Review on Existing Sewerage Network and the Proposed Sewerage Improvement Works

8.4.5.1 To assess the sewerage impact from the additional 2,850 m³/day dry weather flow as mentioned above, the hydraulic performance of the existing 900mm dia. sewer between manhole FMH4046332 and FMH4046340 was reviewed and the results are shown in Appendix 8.1.

8.4.5.2 The assessment results demonstrate that the existing 900mm dia. sewer has enough capacity to cater for the additional flow intercepted by the DWFI system. Under current condition, the percentage utilisation of the concerned sewage system is 83%. The percentage goes up to 89% with the additional dry weather flows, which still leaves roughly 11% spare capacity. No mitigation measures are anticipated.

8.4.6 Impact Assessment on Treatment Capacity of Sha Tin Sewage Treatment Works

8.4.6.1 Table 8.7 and Table 8.8 outline the information on capacity for concerned pumping stations and sewage treatment works of the DWFI system. The planned ultimate flow to STSTW was 339,000 m³/day, which includes 10% for flow uncertainties. In other words, the relocated STSTW shall be able to take up the dry weather flow whose amount is within the 10% flow uncertainties limit.

Table 8.7 Summary of Capacity for Concerned Pumping Stations

Sewage Pumping Stations	Existing Maximum Daily Flow 2017 (m^3/day)	Planned Maximum Daily Flow (m^3/day)	Design Capacity (m^3/day)
P7 Sha Tin Main SPS	173,240	547,000	552,960
ISPS ^[1]	-	708,000	708,000

Note:

[1] Intermediate Sewage Pumping Station (ISPS) will be located within the existing STSTW.

Table 8.8 Summary of Capacity for the Relocated Sha Tin Sewage Treatment Works (STSTW)

Relocated Sha Tin Sewage Treatment Works	Flow (m^3/day)
Planned Ultimate Flow (THEES Review Study)	309,000
Planned Ultimate Flow (Cavern Study) ^[1]	339,000
Design Capacity for the Relocated STSTW	340,000

Note:

[1] Cavern study has an additional 10% for flow uncertainties

8.5 Conclusion

8.5.1.1 To improve the water quality in the nullah, a DWFI scheme is proposed. The intercepted dry weather flow along the nullah was estimated to be 2,850 m³/day. An additional toilet facility for the visitors in Tai Wai Nullah located near Pok Ngar Villa with negligible additional sewage flow has also been proposed. The sewage impact assessment indicated that existing sewerage system has enough capacity to take up the additional dry weather flow intercepted by the DWFI system and proposed toilet facility. Thus, no mitigation measures are anticipated. No adverse sewerage impact arising from the Project is anticipated.