Contents
6 Sewerage and sewage treatment implications
6.2 Design Standards and Guidelines
6.3 Methodology and Design Parameters
6.6 Existing and Planned Sewerage Infrastructure
6.2 Design Standards and Guidelines
6.2.1 The assessment is based on the following standards, guidelines and reference for the sewerage design:-
6.3 Methodology and Design Parameters
Objectives
6.3.1 The objectives of the sewerage impact assessment are summarized as follows:-
Unit Flow Factors
6.3.2 Design sewage flows have been estimated on the number of living quarters / population and the Design Unit Flow Factors (UFF). The UFF for Domestic Flow and Commercial and Institutional Flow have been adopted in accordance with Table T-1 and Table T-2 of the GESF. The category of the components and the UFF adopted in the assessment are shown in Table 6.1 below.
Table 6.1.1 – Unit Flow Factors for Domestic and Commercial Flow
|
Component |
Category/ Use |
UFF (m3/head/day) |
|
Domestic Flow |
Residential – R1 |
0.19 |
|
Residential – R2 |
0.27 |
|
|
Commercial Flow (Note) |
Transport, Storage & Communication |
0.18 |
|
Wholesale & Retail |
0.28 |
|
|
Restaurants & Hotels |
1.58 |
|
|
Community, Social & Personal Services |
0.28 |
|
|
Other |
School Student |
0.04 |
Note: The unit flow factor of commercial employee 0.08m3/h/d is added into the Commercial Flow Factor.
Catchment Inflow Factors
6.3.3 The Catchment Inflow Factors (Pcif) cater for the net overall ingress of water or waste water to the sewerage system. They are catchment-dependent and applicable to major sewerage facilities of a catchment. They are not applicable to new catchments which are deemed to be free from misconnections and pipe defects. Therefore, the Pcif are not applicable in estimating the total flows from the new development areas.
6.3.4 For the sewerage system in North District, Pcif of 1.00 will be adopted in accordance with Table T-4 of the GESF.
Peaking Factors
6.3.5 Peaking factors cater for seasonal / diurnal fluctuation and normal amount of infiltration and inflow. The peaking factors shall be in accordance with Table T-5 of GESF and are shown in the Table 2.2.
Table 6.1.2 – Peaking Factors for Various Population Ranges
|
Population Range |
Peaking Factor (including stormwater allowance) for facility with existing upstream sewerage |
Peaking Factor (excluding Stormwater allowance) for facility with new upstream sewerage |
|
(a) For sewers |
||
|
<1,000 |
8 |
6 |
|
1,000 – 5,000 |
6 |
5 |
|
5,000 – 10,000 |
5 |
4 |
|
10,000 – 50,000 |
4 |
3 |
|
>50,000 |
Max (7.3/ N0.15, 2.4) |
Max (6/ N0.175, 1.6) |
Notes: N is the contributing population in thousands
Latest Development Proposal
6.4.1 The proposed development could accommodate approximately 12,000 nos. of flats with an estimated population of 33,600.
Retail and Other Non-domestic Facilities (GFA)
6.4.2 With reference to the Commercial and Industrial Floor Space Utilization Survey (CIFSUS) conducted by Planning Department (PlanD), the number of workers per 100m2 of “Retail”, “Community” and “Restaurant” trade group is 3.5, 3.3 and 5.3 respectively.
Welfare Facilities
6.4.3 The number of staff for the social welfare facilities is estimated with reference to the CIFSUS by PlanD and the “Notional Staffing Establishment” published by Social Welfare Department (SWD).
School
6.4.4 Kindergarten – 24-classrooms kindergartens were proposed in the proposed housing development. With reference to “Kindergarten Administration Guide” published by Education Bureau, it is assumed 20 students per class.
6.4.5 Special School – A special school is proposed at the northern tip of the proposed development. As scale of the special school development is still under planning, for conservative, scale of a 30-classrooms primary school has been adopted for preliminary assessment. Taking reference to “Code of Aids for Primary School” published by Education Bureau, it is assumed 20 students per class.
6.5.1 The proposed development area is approximately 10 hectares, with a population intake of about 12,000. Welfare and educational uses are also planned for the proposed development.
6.5.2 The total estimated sewage flows generated by the proposed special school and housing development is approximate 8578.9 m3/d. Breakdown of the estimated sewage flow are summarized in Table 6.3.1 below.
Table 6.3.1 Estimated Sewage Flow Generated by the Proposed Development
|
Type |
Population/ No. of Staff |
Unit Flow Factors |
ADWF (m3/d) |
|
Site 1 Residential (R1) |
23,520(1) |
0.19 |
4468.8 |
|
Site 1 Residential (R2) |
10080(1) |
0.27 |
2721.6 |
|
Site 1 Residential – Employee |
120(2) |
0.28 |
33.6 |
|
Kindergarten |
320(3) |
0.04 |
12.8 |
|
Kindergarten - Employee |
39(3) |
0.28 |
10.92 |
|
Special School |
1,040(4) |
0.04 |
41.6 |
|
Special School – Employee |
124(4) |
0.28 |
34.7 |
|
HSMH |
100 |
0.28 |
28.0 |
|
HSMH– Employee |
66(5) |
0.28 |
18.5 |
|
DAC |
100 |
0.28 |
28.0 |
|
DAC – Employee |
34(5) |
0.28 |
9.5 |
|
HMMH |
50 |
0.28 |
14.0 |
|
HMMH– Employee |
19(5) |
0.28 |
5.3 |
|
HSPH |
50 |
0.28 |
14.0 |
|
HSPH– Employee |
37(5) |
0.28 |
10.4 |
|
SHOS(MH) |
30 |
0.28 |
8.4 |
|
SHOS(MH)– Employee |
12(5) |
0.28 |
3.4 |
|
IVRSC |
120 |
0.28 |
33.6 |
|
IVRSC– Employee |
19(5) |
0.28 |
5.3 |
|
NEC |
6 |
0.28 |
1.7 |
|
NEC– Employee |
10(5) |
0.28 |
2.8 |
|
NEC |
6 |
0.28 |
1.7 |
|
NEC– Employee |
10(5) |
0.28 |
2.8 |
|
CCC |
100 |
0.28 |
28.0 |
|
CCC– Employee |
30(7) |
0.28 |
8.4 |
|
RCHE&DCU |
130 |
0.28 |
36.4 |
|
RCHE&DCU– Employee |
101(7) |
0.28 |
28.3 |
|
Carpark |
112(8) |
0.18 |
20.16 |
|
Covered PTI |
228(7) |
0.18 |
41.0 |
|
Non-Domestic - Retail |
1013(9) |
0.28 |
283.6 |
|
Non-Domestic - Community Facilities |
42(9) |
0.28 |
11.8 |
|
Non-Domestic - Restaurant |
386(9) |
1.58 |
609.9 |
|
Total |
8,578.9 |
Note:
(1) The population of the Sites are estimated based on the proposed no. of flats.
(2) Assume there are 12 blocks with 4 security guards and 6 managing staff for each block.
(3) With reference to “Kindergarten Administration Guide” published by Education Bureau, it is assumed 20 students per class with Student : Teacher ratio = 11 : 1.33.
(4) In conservative view for estimation, number of staff in special school has made reference to scale of primary school. Hence, with reference to to “Code of Aids for Primary School” published by Education Bureau, it is assumed 26 students per class with Student : Techer ratio = 26 : 1.93.
(5) The number of staff is referenced to the “Notional Staffing Establishment” published by Social Welfare Department. For facilities with no domestic demands, the number of workers is summed up according to the list and rounded off to the nearest integer. For facilities with domestic demand, the staffing is proportionally estimated with the capacity stated in NSE.
(6) Neighbourhood Elderly Centre (NEC) is a type of community support services at neighbourhood level. Therefore, it is assumed no additional population in relation to NEC.
(7) The number of staff is reference to Figure 9: Worker Density by Industry Group of “Commercial and Industrial Floor Space Utilization Survey” published by Planning Department.
(8) Assume there are 12 blocks with 2 carpark floors per housing block and 4 carpark floors for retail facilities. Assume 3 shift safe-guard and 1 staff per carpark floors.
(9) No. of workers in the restaurant, retail and community facilities is reference to CIFSUS Table 8. Assume the ratio of restaurant - retail & community is 1:4. Assume there is 1 staff per 18.9m2, 28.6m2 and 30.3m2 for restaurant, retail and community respectively.
6.5.3 For planning perspective, an allowance of 2000m3/d sewage flow has been made as per EPD’s advice to cater for other existing and planned developments in the vicinity including nearby villages and low-rise residential buildings.
6.5.4 For the remaining portion of PDA, it is proposed to conserve the areas as far as practicable. Therefore, one of the development proposals is to develop the Sub-Area 2 to 4 into the areas with “Other Specified Uses” annotated “Recreation cum Conservation”. However, as the detailed land uses for Sub-Areas 2 to 4 cannot be confirmed at this stage, an ADWF of 200m3/day is assumed for 3,200 visitors per day to cater for the additional sewage flow generated by land users and visitors.
6.5.5 Summarizing the estimation in this section, total 8,778.9 m3/day sewage flow would be generated from the PDA.
6.6 Existing and Planned Sewerage Infrastructure
Existing Sewage Treatment Works and Planned Upgrading Works
6.6.1 Shek Wu Hui Sewage Treatment Works (SWHSTW) is a secondary sewage treatment works which serves Fanling, Sheung Shui and neighbouring areas with a design capacity of 105,000 m3/day. The planned upgrading and expansion works of the existing SWHSTW in three successive stages to meet the future development needs are tabulated as follows:-
Table 6.4.1 Planned Shek Wu Hui Sewage Treatment Works Upgrading Works
|
Expansion Stage |
Treatment Capacity (m3/day) |
Tentative Year of Completion |
|
Main Works Stage 1 |
140,000 |
2025 |
|
Main Works Stage 2 |
160,000 |
2029 |
|
Main Works Stage 3 |
190,000 |
2034 |
Existing Land Use and Sewage Generation
6.6.2 In view of the business nature of existing Fanling Golf Course (FGC), it is assumed that the existing sewage generated due to the population within the PDA is negligible.
6.6.3 Currently, there is an existing sewer connection point at manhole FTH1000895 at the north of the PDA. The nearest sewer would be the DN225 sewer running along Fan Kam Road which connects to the DN300/375/450/750 sewers in between Choi Po Court and Choi Yuen Estate. The sewer finally connected to the DN1800 running along San Wan Road to SWHSTW. The existing sewerage infrastructure is shown in Drawings Nos. CE17/SIA/001/021 to CE17/SIA/001/026.
6.7.1 New PVC Lined Precast Concrete sewers connecting from PDSA to existing DN1800 sewer along the cycling track of San Wan Road are proposed. Tapping point to the development is proposed in the housing site along the side of Ping Kong Road. New DN750 sewers are proposed to be laid primarily along Ping Kong Road, Po Kin Road, Fan Kam Road, Tai Tau Leng Interchange, cycling track between Choi Po Court / Choi Yuen Estate and Choi Yuen Road up to the cycling parking area at Choi Yuen Road. Two sections of sewers are proposed to be laid by trenchless construction method. The first trenchless section of DN750 sewer to be installed in Choi Yuen Road is underneath an existing stormwater box culvert. The second trenchless section of DN900 sewer is underneath the existing running lines of the East Rail Line.
6.7.2 To receive the additional sewage flow generated from the PDSA, the existing DN1350 sewer between manhole no. FMH1004752 and FMH1004667 is proposed to be upgraded to DN1800.
6.7.3 The proposed sewerage scheme including upgrading works is shown in Drawings Nos. CE17/SIA/001/031 to CE17/SIA/001/034.
6.7.4 Nonetheless, in order to prevent putting stress on the existing main trunk along San Wan Road, an alternative option to construct a separate DN900-1050 new sewer along San Wai Road up to Shek Wu Hui Sewage Treatment Works has been explored. The proposed alignment is shown in Drawings Nos. CE17/SIA/001/041 to CE17/SIA/001/042. This option should be further review in detailed design stage.
6.7.5 Based on the calculation result, the existing and proposed sewers were found to have adequate capacity to cater for the sewage flow from the proposed development.
6.8.1 The capacity of existing and planned sewerage infrastructure has been reviewed based on the latest available information.
6.8.2 The latest development parameters of the proposed development have been utilized for calculation.
6.8.3 Total 8,778.9m3/day sewage flow would be generated from the PDA in which 8,578.9m3/day would be generated from Sub-Area 1 and 200m3/day is assumed sewerage flow for future development in Sub-Area 2 to 4.
6.8.4 New sewers were proposed to connect with the existing trunk alongside San Wan Road. Only manageable impact to the downstream sewerage networks is anticipated.