2.1.1 The improvement works for the Town Centre Section of the YLTN mainly comprises of the following items and the general location plan is shown in Figure 2.1.
a) Construction of DWF interceptors along and within the YLTN;
b) Construction of continuous u-channels adjacent to either side of the retaining walls;
c) Construction of a DWF pumping station with capacity of 18,000 m3/day; and
d) Laying twin rising mains of approximately 400 m long to convey the intercepted DWF to the Yuen Long Effluent Polishing Plant (YLEPP) (upgraded from the existing YLSTW).
2.1.2 YLTN is concrete-lined with a total length of approximately 12 kilometers dividing into five sections namely Downstream Section, Town Centre Section, Upstream Section, West Nullah and East Nullah.
2.1.3 The DWFI system adopts continuous u-channels/pipes adjacent to either side of the retaining walls to collect and convey the expedient discharges from the drainage outlets. The system was further optimised with external covers, screening the presence of the drainage outlet to minimise visual and odour impact as far as practicable.
2.1.4 The latest Interception Scheme for DWF in YLTN is presented in Figure 2.2. Typical cross sections for the existing and improved nullah are shown in Figure 2.3. The DWFI system will be constructed to intercept the polluted dry weather flow being discharged to YLTN from the Town Centre Section (600 m3/day), East Nullah (16,300 m3/day) and upstream San Hui Nullah (1,000 m3/day). Approximately 60 nos. of existing storm water outfalls within the Town Centre Section will be intercepted by the proposed DWFI system (see Annex 2A). The proposed u-channel will be connected to San Hui Nullah and East Nullah for interception of the existing upstream DWF as shown in Annex 2A.
2.1.5 The DWF from upstream Kung Um Road Nullah (13,100 m3/day) will not be intercepted at the upstream as such to maintain water flow within the Town Centre Section during non-rainy days. The concept of river revitalization and Blue-green infrastructure should be introduced to YLTN in the future nullah beautification works by Barrage Scheme. In the conceptual beautification design of the nullah in Barrage Scheme, flowing water has been incorporated in the design to enhance water-friendliness in the nullah.
2.1.6 The DWF from West Nullah (3,600 m3/day) will be intercepted to proposed pipe. As the water quality of DWF in West Nullah is better than the proposed treatment standards of YLEPP, the DWF from West Nullah is recommended to be intercepted but not to be treated in YLEPP. Instead, in order not to mix up the DWF to be treated, a separate 1000mm pipe is proposed to convey the intercepted DWF from West Nullah to the desilting basin of the existing low flow pumping station and eventually, together with the DWF from upstream Kung Um Road Nullah, pumped across the rubber dam and towards Shan Pui River via the existing low flow pumping station, which conveys DWF on the nullah across the inflatable dam (see Annex 2A). This existing low flow pumping station is located at the downstream at Shan Pui Ho Road East. The selection of DWF for interception and treatment is provided in Section 3.4.1 to 3.4.4.
2.1.7 The DWFI system will convey the first 18,000 m3 of DWF being intercepted each day to the YLEPP for treatment. When the above limit is reached, the exceeded DWF will be overflown directly or as close as possible to the desilting basin of the existing low flow pumping station (LFPS) and mixed with the DWF of Kung Um Road Nullah and West Nullah before being discharged to Shan Pui River through the existing LFPS. The amount on treatment of intercepted DWF by YLEPP was estimated based on the flow survey and water sampling which the branches with poorer water quality are selected to be intercepted and treated. The amount on treatment of intercepted DWF by YLEPP (18,000m3/day) has been agreed with EPD/SIG in 2018 and is not recommended to be increase in order not to transfer extra loading to YLEPP.
2.1.8 The intercepted/diverted DWF will flow by gravity to a proposed DWF pumping station to be constructed downstream near the existing low flow pumping station at Shan Pui Ho Road East. The proposed DWF pumping station will be a single storey building structure about 17 m in length, 10 m in width and 7 m in height. It comprises an underground covered inlet chamber, screen chamber with mechanical screen, wet well, ventilation systems, odour control facilities and various associated facilities. The general layout plan for the DWF pumping station is presented in Annex 2B. Twin rising mains of approximately 400 m long will be laid which will be used to convey the first 18,000 m3 of DWF each day from the pumping station to the existing sewers, located at Wang Lok Street, leading to the YLEPP. The diameter of the rising main is around 600 mm. The volume of DWF being conveyed to YLEPP will be monitored inside the DWF pumping station. When the flow limit (18,000 m3/day) is reached, the pumping operation will stop and penstocks inside the pumping station will be closed to prevent more DWF from entering. Overflow pipes constructed in the first upstream chamber will release exceeded DWF to the desilting basin when the water level inside the chamber rises to the pipe inverts. The DWF will eventually be discharged to Shan Pui River by the existing low flow pumping station.
2.1.9 The scale of the proposed Project is summarized in Table 2.1.
Table 2.1 Scale of Proposed Project
|
Nature of Work |
Details (Dimensions) of
Works |
|
DWFI
System |
1.
Construction of DWF
interceptors along and within the YLTN; 2.
Construction of continuous
1000 mm × 800 mm u-channels adjacent to either side of the retaining walls; 3. Construction
of a DWF pumping station (17m(L) × 10m(W) × 7m(H)) with capacity of 18,000m3/day;
and 4.
Laying twin rising
mains of approximately 400 m long with 600 mm diameter each. |
2.2.1 The Project consists of the following designated projects under Part I, Schedule 2 of the EIAO and, therefore, requires an Environmental Impact Assessment (EIA) to be undertaken and an Environmental Permit (EP) to be obtained before the commencement of construction and operation:
·
Construction of a DWF pumping station with capacity of 18,000
m3/day. [Item F.3(b): A sewage pumping station with an installed
capacity of more than 2000 m3 per day and a boundary which is less
than 150 m from an existing or planned – (i) residential area; (ii) place of
worship; (iii) educational institution; (iv) health care institution; (v) site
of special scientific interest; (vi) site of cultural heritage; (vii) bathing
beach; (viii) marine park or marine reserve; (ix) fish culture zone; or (x)
seawater intake point.]
·
Construction of DWF interceptors along the YLTN which discharges
to Deep Bay which is less than 300 m from the nearest boundary of Inner Deep
Bay Site of Special Scientific Interest (SSSI), Mai Po SSSI, the Mai Po Inner
Deep Bay Ramsar Site and Conservation Area. [Item
I.1(b): A drainage channel or river training and diversion works which
discharges or discharge into an area which is less than 300 m from the nearest
boundary of an existing or planned (i) site of special scientific interest;
(ii) site of cultural heritage; (iii) marine park or marine reserve; (iv) fish
culture zone; (v) wild animal protection area; (vi) coastal protection area; or
(vii) conservation area.]
2.3.1 The proposed DWF interceptors and u-channels will be located inside the YLTN. Construction of the above elements will involve ground breaking, excavation, pipe laying, backfilling works and final re-instatement by in-situ concreting.
2.3.2 The proposed rising mains for conveying DWF of the DWFI system will be located under the nullah bed or at road side (for section between the DWF pumping station and the connection manhole to YLEPP). There will be no construction works within the YLTN section beyond the inflatable dam. The construction of the above elements will thus involve ground breaking, excavation, pipe laying, backfilling works and final re-instatement by in-situ concreting.
2.3.3 Construction of the DWF pumping station will mainly be conventional building construction consisting of ground breaking, excavation, construction of substructure and superstructure, installation of equipment and landscaping works.
2.4.1 Maintenance works would be necessary for the proposed DWF interceptors and u-channels to repair damages and remove excessive silts, vegetation, debris and obstructions regularly in order to maintain its hydraulic performance and structural integrity. Siltation will generally be allowed to accumulate at the nullah and removal of excess silt would be carried out at locations only if it would impede water flow. Such small-scale maintenance would require only light mechanical equipment such as a small loader and/or a small crane truck. Hand-held equipment will be used for vegetation removal.
2.4.2 The operation of the proposed DWF pumping station will be monitored and controlled by DSD through the SCADA system. Regular inspection will be conducted by DSD on essential equipment in the pumping station, e.g. switchboard, screen, pump and motor. Through regular inspection, abnormality of the equipment will be identified for remedial action to be taken before failure. Maintenance works will be conducted according to the procedures outlined in the pumping station operation manual. Adequate spare parts will be stocked for planned maintenance and urgent repair.
2.5.1
The construction programme for the Project is
tentatively expected to commence in second quarter of 2021 for completion in early
2026. The Project will be constructed in sections as shown in Figure
2.1. The tentative key milestone
dates are tabulated in
Table 2.2 below.
Table 2.2 Tentative Construction Schedule
2.5.2 In order to minimize potential indirect disturbance to the wetland habitats and associated overwintering waterbirds and wetland-dependent species, the construction of rising mains, which is partly within Wetland Buffer Area, will be conducted outside dry season (i.e. November to March).
2.6.1 The following projects to be undertaken concurrently in the vicinity of the Project Site are identified as potential concurrent projects. The potential cumulative impacts due to these projects are presented in Table 2.3 and addressed in the respective sections of this EIA. The locations of these concurrent projects are illustrated in Figure 2.4.
Yuen
Long Barrage Scheme (1)
2.6.2 The project involves construction of barrage at the downstream end of YLTN; construction and modification of parapet walls along Kam Tin River, YLTN, Yuen Long Bypass Floodway (YLBF) and Sham Chung River; drainage works at the intersection of YLTN and YLBF; revitalization of existing concrete YLTN for section between the proposed barrage and Long Ping West Rail; and associated works. With consultation from DSD, the project is tentatively scheduled to commence in end-2021 for completion by end-2029.
2.6.3 The existing low flow pumping station and the inflatable dam will be decommissioned and relocated under the Yuen Long Barrage Scheme.
Elevated
Pedestrian Corridor in Yuen Long Town Connecting with Long Ping Station (2)
2.6.4 In the project (EPC), an elevated pedestrian corridor, in form of a footbridge, along YLTN from West Rail Long Ping Station to the south of the Kau Yuk Road will be constructed. The proposed elevated pedestrian corridor will be connected to at-grade footpath via pedestrian interchanges located along the nullah. With the previous consultation from HyD, the project is tentatively scheduled to commence in first quarter of 2020 for completion in first quarter of 2025.
2.6.5 According to the latest best information provided by HyD, the commencement of construction of the footbridge is subject to the funding approval by LegCo. To be conservative, the EPC project is assumed to be conducted concurrently with the YLTN Project. For the purpose of assessment in this EIA, the programme presented in Section 2.6.4 is adopted.
Housing
Sites in Yuen Long South (3)
2.6.6 The Yuen Long South (YLS) development would release degraded brownfield with development potential and provide about 28,500 new flats to accommodate a total population of about 88,000. The development covers approximately 223.5 ha and is located to the south of Yuen Long New Town. Other than housing development within the PDA, there are also some other supporting infrastructure works (such as public transport interchange, road construction / improvement works, main laying, partial nullah decking and reclaimed water service reservoir) outside the PDA. According to the construction programme in the EIA Report, the project is tentatively scheduled to commence in 2020 for completion in 2038.
Yuen Long Effluent Polishing Plant (YLEPP) (4)
2.6.7 The existing YLSTW will be upgraded into YLEPP in order to cater for future needs in the catchment and improve the water quality of Deep Bay. The capacity of the YLEPP will be increase from 70,000 m3/day (for existing YLSTW) to 150,000 m3/day (Phase 1: 100,000 m3/day; Phase 2: 150,000 m3/day) with upgrading the treatment level from secondary to tertiary. The treatment capacity of YLEPP would be reduced to 35,000 m3/day during the upgrading period in Phase 1 (i.e. Year 2020 – Year 2027). According to the EIA Report of the YLEPP, the construction works are tentatively scheduled to commence in third quarter of 2020 for completion in second quarter of 2027 for Phase 1 and 2030 for Phase 2 the earliest.
2.6.8 The project boundary of the YLEPP is outside the 500m study area of YLTN Project. However, as the first 18,000 m3 of DWF being intercepted each day under the operation of the YLTN Project will be conveyed to the YLEPP for treatment, cumulative sewerage impact is anticipated.
Table 2.3 Evaluation of Cumulative Impacts due to Concurrent Projects
|
Nature of Work |
Project Proponent |
Programme |
Potential Cumulative
Impact |
||
|
Start |
Complete |
Construction Phase |
Operation Phase |
||
|
Yuen
Long Barrage Scheme |
DSD |
2021 |
2029 |
Air
quality, noise, water quality, ecological impact, visual and landscape |
Noise,
water quality, ecological impact, visual and landscape |
|
Elevated Pedestrian Corridor in Yuen
Long Town Connecting with Long Ping Station |
HyD |
2020* |
2025 |
Air
quality, noise, water quality, ecological impact, visual and landscape |
Noise,
water quality, ecological impact, visual and landscape |
|
Housing Sites in Yuen Long South |
CEDD |
2020 |
2038 |
Air
quality, noise, water quality, ecological impact, visual and landscape |
Noise,
water quality, ecological impact, visual and landscape |
|
Yuen Long Effluent Polishing Plant |
DSD |
2020 |
2030 |
Nil |
Water
quality, ecological impact, sewerage |
*The commencement of
construction of footbridge is subject to the funding approval by Legco.
2.7.1 The following consultation activities have been carried out:
·
1st Consultation with Environmental Improvement Committee of Yuen Long
District Council in March 2012
·
2nd Consultation with Environmental Improvement Committee of Yuen Long
District Council in January 2013
·
Joint Public Forum with HyD’s footbridge in April
2013
2.7.2 In general, public are supportive of this Project.
1)
DSD (2018) – Project
Profile for “Yuen Long Barrage Scheme” (PP-564/2018).
2)
HyD (2014) – EIA Report for
“Elevated Pedestrian Corridor in Yuen Long Town Connecting with Long Ping
Station” (AEIAR-200/2016).
3)
CEDD (2017) – EIA Report
for “Housing Sites in Yuen Long South” (AEIAR-215/2017).
4)
DSD (2019) – EIA Report
for “Yuen Long Effluent Polishing Plant” (AEIAR-220/2019).