LIST
OF TABLES
Table 2.1 Scale
of Proposed Project
Table 2.2 Tentative
Construction Schedule
LIST OF FIGURES
Figure
1.1 General Location Plan of the Project
Figure
2.1 General
Layout Plan
Figure
2.2 Schematic
Diagram for Dry Weather Flow Interception System
1.1.1
This Executive Summary summarizes the
results of the Environmental Impact Assessment (EIA) for Improvement of Yuen
Long Town Nullah (Town Centre Section) (the Project). The EIA has been prepared
in accordance with the requirements of the Environmental Impact Assessment
Ordinance (EIAO) and the EIA Study Brief (ESB-260/2013).
1.2.1
The existing Yuen Long Town Nullah
(YLTN) was constructed in mid 1960s to alleviate the flooding risks in the
Northwest New Territories and is one of the oldest drainage systems in Hong
Kong. Most of the nullah sections were
originally natural water courses, which have been straightened and
modified. The nullahs now primarily
consist of channelized concrete bedding and embankments.
1.2.2
With the increasing aspirations for a
better living environment, the local residents of Yuen
Long are requesting the Government to improve the early design of the YLTN,
which is considered no longer in line with the changing townscape of Yuen
Long. In addition, odour
from the nullah due to the polluted dry weather flow is causing nuisance to the
nearby residents.
1.2.3
In January 2007, the Drainage Services
Department (DSD) of the Government of the Hong Kong Special Administrative
Region (HKSARG) commissioned Black & Veatch Hong Kong Limited (B&V) to
carry out a feasibility study on “Rehabilitation of Yuen Long Town Nullahs” to
investigate various options for improving the design and environmental
conditions of the YLTN. The Study
recommended intercepting the polluted dry weather flow to the nullah for
treatment in the existing Yuen Long Sewage Treatment Works (YLSTW) to alleviate
the odour nuisance.
1.2.4
In relation to the findings of the
feasibility study, B&V was further commissioned by DSD in August 2010 to
conduct “Agreement No. CE 6/2010 – Improvement of Yuen Long Town Nullah (Town
Centre Section) – Investigation” to investigate the improvement of the town
center section of YLTN between On Lok Road and Ma Tong Road of Yuen Long.
1.2.5
According to the latest design, the
Project mainly comprises provision of a dry weather flow (DWF) interception
system, including construction of DWF interceptors along the Town Centre
Section of YLTN and a new pumping station with an average capacity of
approximately 18,000 m3/day. The scope of works of the Project is
shown in Figure 1.1.
1.3.1
A Project Profile (PP-485/2013) was submitted to
the Director of Environmental Protection (DEP) on 7 March 2013. The DEP issued
an EIA Study Brief (ESB-260/2013) on 3 April 2013 for this EIA Study.
2.1.1
The improvement works for the Town Centre
Section of the YLTN mainly comprises of the following items and the
general layout 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 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. 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 system.
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
DWF from West Nullah (3,600 m3/day) will be intercepted to proposed u-channel/pipe
but not treated in YLEPP. Instead, it will be conveyed to existing desilting
basin 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. This existing low flow pumping station is located at the downstream at
Shan Pui Ho Road East.
2.1.6
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.
2.1.7
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. 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.
2.1.8 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 to be
obtained before the commencement of construction:
·
Construction of a DWF pumping station with capacity of 18,000
m3/day within residential area. [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
Under this Project, the polluted DWF to the nullah will be
intercepted and treated in the YLEPP. Upon completion of the DWFI system under
the Project, the residents living along the Town Centre Section of YLTN will be
immediately benefited from the elimination of odour
problem due to polluted DWF. In addition, by intercepting the polluted DWF for
proper treatment, the downstream ecologically sensitive Shan Pui River and
Inner Deep Bay will be benefited by the improved water quality.
2.4.1
The “Without-Project” scenario considers not implementing the
recommended improvement of YLTN. More polluted DWF generation is expected due
to population growth and development in Yuen Long. If the proposed Project is not implemented,
more polluted DWF will be discharged to the nullah resulting in further
worsening of water quality and odour problems as well
as deterioration of the nullah appearance.
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
3.1.1
The potential sources of air quality impacts
associated with the construction and operation of the Project have been
identified and the potential impacts were evaluated.
3.1.2
Construction works of the Project
will inevitably generate some fugitive dust, especially during the excavation
of the YLTN. With the sectioning
construction approach, the areas of excavation works should be limited in
scale. Regular water spraying will also
help to control dust nuisance.
3.1.3
Through proper implementation of dust
control measures required under the Air
Pollution Control (Construction Dust) Regulation, construction fugitive
dust will be controlled at source to satisfactory levels.
3.1.4
Maintenance
works for the Project will be small-scale in nature. During the operation phase, the
Project will unlikely cause any unacceptable air quality impacts in terms of dust and odour. In addition, it is
expected that odour nuisance of the YLTN will be
alleviated due to operation of the Project since the polluted DWF originally
discharged into the Project Site will be diverted to the YLEPP. This is being considered as a beneficial
impact of the Project.
3.1.5
With the implementation of the recommended
mitigation measures, it is expected that the residual impacts from the
construction and operation of the Project will not exceed any relevant air
quality criteria. As such no
unacceptable residual air quality impacts are envisaged from the construction
and operation of the Project.
3.1.6
Cumulative air quality impacts associated with
concurrent projects within the Study Area have been considered, no unacceptable
impacts are anticipated.
3.2.1 A construction noise assessment has been undertaken to predict the noise levels at the representative Noise Sensitive Receivers (NSRs) due to the construction of the Project. Practicable mitigation measures, including use of quiet construction plant, noise barriers, noise insulation sheet and scheduling of construction activities, have been recommended. With the implementation of the recommended mitigation measures, the predicted construction noise levels at all NSRs comply with the noise criteria during the daytime period. Therefore, no unacceptable noise impact is expected to arise from the construction activities. Also, cumulative noise quality impacts associated with concurrent projects within the Study Area have been considered, no unacceptable impact is anticipated.
3.2.2 Potential noise impact from the operation of the proposed DWF pumping station has been assessed. The predicted fixed plant noise levels at the representative NSRs due to the operation of the proposed DWF pumping station and the cumulative noise levels with the operation of the existing pumping stations comply with the day-time and night-time noise criteria. No unacceptable residual impact is anticipated.
3.3.1 Potential impacts arising from the proposed construction works are predicted to be largely confined to the specific works areas. With proper implementation of the recommended mitigation measures, in particular the establishment of dry condition for excavation works within the existing nullah and adoption of good construction site practices as recommended in relevant regulatory guidelines, unacceptable water quality impacts are not expected at the identified Water Sensitive Receivers (WSRs).
3.3.2 During the operation phase, the interception of polluted DWF provided by the Project and subsequent treatment at YLEPP is expected to lead to improvement of water quality within the YLTN and at Shan Pui River by reducing the pollution loading of SS and BOD5 and is thus considered to be beneficial.
3.3.3 With regular maintenance works to remove excessive sediments, it is anticipated that the Project will not lead to any unacceptable water quality impacts by altering the sediment deposition and erosion pattern of the Project Site and its downstream area. Unacceptable water quality impacts are also not expected to occur at any identified WSRs due to the small-scale and infrequent maintenance works.
3.3.4 During emergency discharge of the collected DWF to the YLTN (e.g. due to breakdown of the DWF pumping station), water quality of the nullah is predicted to be similar to the existing condition before operation of the Project. In addition, given the low likelihood of the emergency discharge and proper Emergency Response Plan will be in place and implemented, no unacceptable water quality impact is expected to be associated with such discharge.
3.3.5 With proper implementation of the recommended mitigation measures, it is expected that the residual impacts from the construction and operation of the Project will not be significant. As such, no unacceptable residual water quality impacts are envisaged from the construction and operation of the Project.
3.3.6 Cumulative water quality impacts associated with concurrent projects within the Study Area have been considered with no unacceptable impact anticipated.
3.4.1 Wastes generated by the construction activities are likely to include Construction and Demolition (C&D) materials from the construction works, general refuse from the workforce and chemical waste from any maintenance of construction plant and equipment. Approximately 15,252 m3 of C&D materials is expected to be generated. At this stage it has been identified that approximately 29% of C&D material can be reused, thus reducing the need for off-site disposal. A total of approximately 10,828 m3 of surplus C&D materials has to be disposed of at public fill reception facilities.
3.4.2 Provided that these identified wastes arisen are handled, transported and disposed of using approved methods and that the recommended good site practices are strictly followed in terms of the avoidance-minimisation-reuse-recycling-disposal hierarchy, unacceptable environmental impacts are not anticipated during construction of the Project.
3.4.3 The recommended measures can be enforced by incorporating them into the waste management requirements in the Waste Management Plan as part of the Environmental Management Plan. Environmental site audit would be necessary to ensure the implementation of proper waste management practices during construction.
3.4.4 For the operation phase, only silt material and debris are expected to be produced by maintenance works of the DWFI system. Such waste will be removed by manual means and disposed of immediately after the clearance works. Small amount of screenings and chemical waste will be generated during operation and routine maintenance of the DWF pumping station. No unacceptable environmental impacts are anticipated with proper waste management practices.
3.4.5 A review of past and present land uses of the Project Site was conducted. Based on desktop review and site walkover, the presence of contaminated land is not expected.
3.5.1 A literature review and ecological field surveys have been conducted. The ecological resources recorded within the Study Area included ten habitats (agricultural land, channelized watercourse, developed area, shrubland, mangrove, plantation, pond, reedbed, semi-natural watercourse and tidal marsh) of which two occurred in the Project Site (i.e. channelized watercourse and developed area). Total of 1 floral species and 46 faunal species of conservation importance have been identified within the 500m Study Area. Among them, four bird species were recorded within the Project Area.
3.5.2
Given that construction works is temporary in nature and of
relatively small scale, and all the construction works will be confined within
the channelized watercourse and developed area with low ecological values, with
the implementation of the proposed avoidance/mitigation measures such as
scheduling the construction of rising main within WBA outside dry season,
implementation of mitigation measures for water quality control and good site
practices, unacceptable adverse ecological impact is thus not anticipated
during construction.
3.5.3 Unacceptable ecological impacts are also not anticipated during operation of the Project given the small-scale and temporary nature of the maintenance works as well as the small percentage of reduction in freshwater input to Shan Pui River due to the DWF interception. During operation, the ecological sensitives areas and wildlife at downstream could be potentially benefited from the improvement of water quality of Shan Pui River and Inner Deep Bay.
3.6.1 During the construction stage, potential adverse landscape and visual impacts would arise from potential tree removal, ground breaking and excavation, backfilling works and final re-instatement by in-situ concreting. According to the latest design, all trees will be preserved. If tree felling is unavoidable during construction, tree transplanting and/or compensatory planting will be provided.
3.6.2 During the operation phase, only minor maintenance works such as regular clearance of debris inside the drainage channel and repair of damages to the channel bed and sides are expected. No adverse impacts are anticipated.
3.6.3 Specifically regarding visual impacts, the proposed pumping stations are the major visual elements of the proposed development which may visually impact on the surrounding Visual Sensitive Receivers (VSRs).
3.6.4 In order to minimize the potential landscape and visual impacts, mitigation measures including good site practice, erection of decorative screen hoarding and tree preservation during construction phase as well as minimum lighting during night time, green roof, vertical greening and designing structure blending with surrounding environment during operation phase will be implemented. With mitigation measure implementation, all affected Landscape Resources (LRs) and Landscape Character Areas (LCAs) will have slight to insignificant adverse landscape impacts during construction phase. All LRs and LCAs will have insignificant or even no impact during operational phase.
3.6.5 All VSRs will experience from moderate to insignificant visual impacts during construction phase after adoption of mitigation measures. At Year 10 of operation, two VSRs will receive moderate visual impacts arising from the proposed DWF pumping station while the remaining VSRs will receive nil or insignificant visual impacts.
4.1.1 Monitoring of air quality (odour), noise and water quality has been recommended at designated sensitive receivers during the construction phase of the Project. Environmental site audit should be conducted weekly throughout the construction phase to ensure that the proposed mitigation measures are implemented.
5.1.1 The EIA has identified and assessed the potential environmental impacts during the construction and operation of the Project in accordance with the guidelines of the EIAO-TM and the EIA Study Brief. The EIA has concluded that with the implementation of the recommended mitigation measures, no unacceptable environmental impacts are envisaged as a result of the construction and operation of the Project and the Project would be in compliance with the applicable environmental legislation and standards.
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