2.1.1 The Sha Tin WTW was first
commissioned in 1964. At that time, it
comprised the current South Works and the Administration Building with a
treatment capacity of 364,000 m3/day. To cope with the rapid increase in the territory’s
water demand, the Sha Tin WTW underwent three stages of expansion in 1973, 1976
and 1983 that are collectively called the North Works. The Sha Tin WTW is the largest WTW in Hong Kong with a
treatment capacity of 1,227,000 m3/day, supplying about 30% of
the total water demand of the territory serving over 2 million people.
2.1.2 The present operation of Sha Tin
WTW can only maintain about 1,060,000 m3/day
average output, due to the aging of plant and equipment after more than 40
years of service. The plant therefore
requires major renovation or replacement.
2.1.3 In addition, since the plant was
first commissioned in 1964, the required treated water quality requirements
have also been raised to meet the latest standards. The existing treated water quality standards as specified by WSD, the authority in Hong Kong, is based on the World Health Organization (WHO)’s
Guidelines for Drinking-water Quality 2011, supplemented by additional parameters not included in the
Guidelines.
2.1.4 Access to safe drinking water is
essential to public health. Hong Kong enjoys one of the safest drinking water
supply in the World with the quality complying fully with the World Health
Organization's (WHO) Guidelines for Drinking-water Quality. The Water Supplies
Department (WSD) is committed to providing a safe, clean and reliable water
supply to customers in Hong Kong (HK). Stringent water treatment combined with
comprehensive monitoring control of the treated water quality is essential
steps in safeguarding public health. WSD has monitored the quality of our drinking
water in accordance with the WHO's Guidelines for Drinking-water Quality 2011. Please
refer to Appendix
2.2 for the details of the drinking water quality standards.
2.1.5 The World Health Organization
advocated for the first time in the Third edition of Guidelines for
Drinking-water Quality to develop and implement a preventive Water Safety Plan
(WSP) to provide an effective and proactive mechanism to ensure the safety of
drinking water for the protection of public health. The WSP is based on the
multiple-barrier approach and the Hazard Analysis and Critical Control Points
principle to ensure the safety of drinking water supply. The plan identifies
potential hazards and prevents risks of contamination of drinking water from
source to consumers' taps and comprises key components including: system
assessment, control measures, operational monitoring, verification, management
plans, documentation and surveillance.
2.1.6 In February 2005, a working group
consisting of senior professionals from various operational units in the
Department was set up to develop a WSP for WSD. They assessed systematically
possible risks of contamination within the water supply system, and identified
control measures to minimise the risks. Based on WHO recommendations, the
Department of Health and WSD have agreed on the adoption of a set of guideline
values for chemical and bacteriological parameters as the health-based targets
for the drinking water supply in HK.
2.1.7 In
order to mitigate the risk of reduction in the supply quantity during
reprovisioning of the South Works of the Sha
Tin WTW, and also to achieve a more reliable and balanced territory-wide water supply
system after the reprovisioning works, this
Project only covers the reprovisioning of the South Works, the most aging part
of the plant while maintaining the North Works in continuous operation. In addition, WSD would
first increase the treatment capacity of Tai Po WTW from 250,000 m3/day to
a treatment capacity of 400,000 m3/day (this uprating work forms part of a separate project)
and then 800,000 m3/day in two stages to tie in with the staged demolition of
some of the facilities in the
South Works to allow the Project to proceed.
The reprovisioned capacity of the South Works will be increased from the
original of 364,000 m3/day to 550,000 m3/day.
·
reprovide the South Works of the existing Sha Tin WTW
with a treatment process that can continue
to meet the latest treated water quality standards and enable a more
reliable water supply to the territory;
·
manage to provide a safe, reliable and sustainable
water supply for the users;
·
cope with the possible
tightening on the drinking water quality by the WHO in the future;
·
meet more stringent treated water quality objectives to
be specified by WSD in the future; and
·
use environmentally friendly and cost-effective
methods to achieve the above objectives.
·
coagulation with alum dosing to raw water to encourage
formation of large particles;
·
flocculator-clarifers to provide flocculation and
settle the large particles;
·
filtration to provide additional polishing for
particulates in the clarified water; and
·
primary disinfection using chlorine.
·
hydrated lime for pH control;
·
alum for coagulation;
·
powered activated carbon for tastes and odours
control as necessary; and
·
polyelectrolyte for assistance of
coagulation and flocculation.
·
chlorine for disinfection;
·
hydrated lime
for pH control; and
·
fluoride for dental protection.
2.3.1 The
main benefits of the proposed Project are: provide a safe and reliable water
supply, improve water supply reliability to the territory, improved quality of
life, development of environmentally sustainable design by applying low-carbon
concept and other design features e.g. sustainable landscape design by
incorporating planting native species, sustainable architectural design that
features green building initiatives and energy efficiency. The visitor facilities will attract visitors
by gaining a firsthand experience on the state-of-the-art treatment technologies
and educate the public for water conservation.
2.3.2 The reprovisioned
South Works together with new common facilities for both the South
Works and the North Works will be able to provide enhanced treatment capability. The environmental benefits relative to
existing conditions are elaborated below.
·
Treated water quality will be enhanced to meet the latest treated water
quality standards;
·
Regarding the landscape and visual aspect, the Project creates an
attractive environment for users and visitors.
Architectural design of the buildings will include green roofs and
boundary evergreen planting. Elevated walkway
and improved accesses will provide a pleasant aesthetic appearance;
·
In addition to aesthetic considerations, enhancement of the proposed
trees and shrub planting would act as visual screen, noise and dust barriers
separating the plant and the community users in the vicinity; and
·
Concerning sustainability, the Project would adopt the most energy
efficiency mode of operation appropriate to the required water treatment
processes. Renewable energy facilities
will also be installed to reduce the carbon footprint for the
operation phase of the Project.
2.4.2 The
existing Sha Tin WTW was constructed in 1964, currently called the South
Works. The three subsequent stages of
expansion in 1973, 1976 and 1983 formed the North Works. Before development, the land for the existing
area was a typical rural and hilly area generally covered with vegetation. No residential was recorded there. After the last expansion in
1983, the Sha Tin WTW has been modified several times up to
1994, since then the building and facilities have been generally maintained as
the condition at present.
2.5.1 The
Project comprises the following key elements:
(i)
Demolition of the existing facilities of the South
Works and common facilities for both the South Works and the
North Works in phases;
(ii)
Reprovisioning of the South Works; and
(iii)
Construction of new common facilities for both the South
Works and the North Works.
2.5.2 In
order to maintain water supply to the existing users, the operation of the existing
North Works of the Sha Tin WTW would be undisturbed during construction of the
Project. The future North Works
reprovisioning, if it considers necessary at a later stage, will be
outside the scope of this EIA study.
2.5.3 Existing
major facilities and the treatment process of the South Works include:
(i)
South Works Clarifiers
Raw
water from the main inlet distribution channel is distributed to the four
clarifiers. With the aid of dissolved
alum and polyelectrolyte, fine particles in the raw water will coagulate into
larger particles which will subsequently settle as sludge in the clarifiers.
(ii)
South Works Filters
The
clarified water will then flow by gravity to the filters for removal of the
more finely divided particles.
(iii)
South Works Clearwater Tank
The
filtered water flows to the western end of the filter blocks and drops into the
South Works clearwater tank underneath, where post-lime and post-chlorine are
added to provide disinfection and adjustment of pH and alkalinity
of the final treated water. Fluoride is
also added for dental protection. The
treated water is then stored in the clearwater tank.
(iv)
Filtered Water Pumping Station (South Works)
and Power Supply
Treated
water from the South Works clearwater tank is pumped to the distribution
network from this pumping station. Major facilities locations are provided in Figure 2.1.
2.5.4 The
major scope of works for the Project, with reference to section
1.2 of the EIA Study Brief,
includes:
(1) Isolation
and demolition of the existing facilities of the South Works in phases
comprising clarifiers, filter beds with clearwater tank underneath, filtered water pumping
station (South Works), as well as common facilities for both the South Works
and the North Works including chemical house, alum saturation tanks, washwater recovery tanks,
administration building and the dangerous goods (DGs) store;
(2)
Construction
of the new common facilities for both the South Works
and the North
Works including an Administration
Building
cum Mainland East Laboratory with visitor facilities, pre-treatment facilities, Water
Treatment Works Logistics Centre, switchgears and power supply, South Works
Pumping Station
and washwater recovery facilities;
(3) Cut-back
of the existing engineered slope located to the west of the existing clarifiers
for reprovisioning of chemical house to Water Treatment Works Logistics Centre
where Incense Tree (Aquilaria sinensis)
as listed under the Protection of Endangered Species of Animals and Plants
Ordinance (Cap. 586) was identified;
(4) Construction
of new access roads for both
construction and normal operation of the plant;
(5) Reprovisioning
of the South Works as mentioned in section 2.5.1 to the proposed output of
550,000 m3/day; and
(6) Provision
of all other associated civil, geotechnical, mechanical and electrical works.
General layout of
the facilities mentioned above in current operation stage and construction
stage are presented in Figure 2.5 and Figure 2.6 respectively.
2.5.5
Due
to space constraints on the existing site and to allow a more appropriate
chemical delivery time from the chemical house to the various treatment units
in response to the incoming raw water quality, it is proposed to reprovide a
chemical house (named as Water Treatment Works Logistics Centre) to be placed in a central
location of the site. As a result, it is
necessary to cut-back the above mentioned engineered slope. This has been presented
and agreed in-principle with the Sha Tin
District Council in its Development and Housing Committee
(D&HC) meeting held on 3 September 2009.
2.5.6 The
existing staff quarters are proposed to be used as a site office during
construction. No major construction works will be undertaken in this location
but minor refurbishment work to be required.
2.5.7 The reprovisioned South Works
will comprise treatment processes including pre-ozonation, coagulation, mechanical flocculation,
high rate sedimentation, intermediate ozonation, biological
filters, second stage granular media filters, UV disinfection system,
treated water storage and pumping, as well as residual management facilities. The process diagram of the reprovisioned
water treatment processes is shown in Figure 2.4. The general layout of the
reprovisioned facilities is illustrated in Figure 3.1.
2.5.8 Raw
water from the inlet channel enters the pre-ozonation contactors (Item No.1 in Figure 3.1). Rapid mixers will be located at the
downstream of the pre-ozonation contactors and the following chemicals are
added:
·
hydrated Lime for pH control; and
·
alum for coagulation.
2.5.9 Water
then flows into the flocculation tanks for slower mixing to help the charged particles
to come together to form larger particles (Item No.2 in Figure 3.1). Polyelectrolyte is added to facilitate the
flocculation.
2.5.10 The
larger particles are removed in the high
rate sedimentation tanks (Item No.3 in Figure 3.1) and dropped to
the bottom of the tank.
2.5.11 The
clarified water from the sedimentation tanks is conveyed to the intermediate
ozone contactors (Item No. 4 in Figure 3.1) where natural organic molecules are broken down for
subsequent biological filtration process. Sodium bisulphite will be dosed to react with
the residual dissolved ozone in the water.
2.5.12 Biological
filters
(Item No.5 in Figure 3.1)
are the key parts of the treatment process where ammonia nitrogen and
natural organic matters are removed, and the following
chemicals are added:
·
ammonium sulphate as nutrients for biomass;
·
sodium phosphate as nutrients for biomass; and
·
polyelectrolyte to assist the filtration.
2.5.13 The
water is then filtered through the second stage granular media filters (Item No.7 in Figure 3.1) to provide additional
removal of particles. Polyelectrolyte is added to
facilitate the filtration process.
·
chlorine to provide residual disinfection of treated water
in the distribution system;
·
hydrated Lime for pH control; and
·
fluoride for dental protection.
2.5.15 The
final treated water
is stored in the
clearwater tanks and pumped by the new pumping station (Item No.6 in Figure 3.1)
to existing service reservoirs.
2.5.16 The spent washwater
for periodical cleaning of biological filters and second stage granular media
filters is diverted to the residual management facilities (Items No. 8 and 9 in Figure 3.1)
for further treatment before recycling back to the inlet channel. Water
entering the residual management system passes through the process of dissolved
air floatation (DAF) or other high rate sedimentation process to remove the
light fraction solids. Water is fed with air which adheres to the particles and
floats them to the surface of the tank for removal.
2.5.17 The differences of
treatment processes between the existing and the proposed treatment processes for the reprovisioned South Works
are presented in Table 2.1 below.
|
Existing
Treatment Facilities |
Reprovisioning
Treatment Facilities |
Benefits from the
Reprovisioning |
|
- |
Pre-ozonation |
Reduce chlorine consumption by oxidizing manganese using ozone in lieu
of chlorine. The use of ozone at this
stage of the treatment has the added benefit of reducing taste and odour
problems. |
|
Coagulation |
Enhanced coagulation with rapid mixers |
Provide sufficient mixing for optimized coagulation |
|
Flocculator-clarifiers |
Mechanical flocculation with mixers |
Enhance the efficiency for large particles formation |
|
High rate sedimentation |
Increase the treatment capacity of the sedimentation tanks, therefore reduce
the required construction footprint |
|
|
- |
Intermediate ozonation |
Break down organics in the water to facilitate better process
performance downstream, and reduce chlorine consumption |
|
- |
Biological filter |
Reduce chlorine consumption by removing ammonia using a biological
process |
|
Rapid gravity filter |
Second stage granular media filter |
Provide additional barriers for particles removal |
|
- |
UV Disinfection |
Enhance the removal efficiency for virus and reduce chlorine usage |
|
Chlorination |
Chlorination |
Provide residual disinfection in the distribution system with lower
dosage of chlorine |
|
- |
Residual management for spent filter backwash water |
Enhance water quality of the spent washwater before recycling to the
inlet raw water |
2.6.1 The study areas for some aspects of
the assessment are follows:
·
Noise impact
assessment study area is 300 m from the boundary of the Project site.
·
Water quality impact
assessment study area is 500 m from the boundary of the Project site.
·
Waste management and
land contamination assessment will focus on areas within the boundary of the
Project site.
·
Ecological impact
assessment study area would include areas within 500 m from the site boundary
of the Project site and also any other areas likely to be impacted by the
Project.
·
Landscape impact
assessment would include all areas within 500 m of the boundary of the Project
site, whereas the visual envelope would define the visual impact study area
boundary.
·
Cultural heritage
impact assessment would include areas within 300 m of the boundary of the
Project Site.
·
The
study area for hazard assessment is the 1-km Consultation Zone of Sha Tin WTW
and the chlorine transport route from Sham Shui Kok dock (North Lantau) to Sha
Tin WTW.
(i) Shatin to Central Link –
Tai Wai to Hung Hom Section
The cumulative
impacts arising from above nearby project operating concurrently have been assessed
and are described in the relevant technical section of this EIA report.
Public Consultation during Project Preparation
Public Consultation
during the Course of the EIA
~ End of
Section 2 ~