This Section
presents an assessment of the potential water quality impacts associated with
the construction and operation of the Project. The key environmental
issues in respect of water quality impacts associated with the Project would be
the proper control of construction site runoff and drainage during site
formation and foundation works for the proposed flyover, slip roads and
associated works. Recommendations
for mitigation measures have been made, where considered necessary, to minimise
the identified water quality impacts to an acceptable level. In accordance with the EIA Study Brief, the Study Area should
include areas within 300 m of the Site Boundary.
6.2
Relevant
Legislation and Guidelines
6.2.1
Water Pollution Control Ordinance (WPCO)
The Water
Pollution Control Ordinance (Cap. 358)
(WPCO), in existence since 1980, is
the major piece of legislation relating to the protection and control of water
quality in
River water quality is ranked according to
its compliance with the WQOs. The annual
compliance of the monthly water quality data with each of the water quality
parameters is indicated by a percentage, with 100% compliance indicating that
all data for twelve consecutive months are compliant with the WQO. For
the Project, the source of pollutants would predominantly be from any
construction runoff that may contain eroded soils. Parameters of concern would therefore be
pH, Suspended Solids (SS), Dissolved Oxygen (DO), Chemical Oxygen Demand (COD)
and Biological Oxygen Demand (BOD).
The WQOs of these parameters for the inland
waters of the Deep Bay WCZ are listed in Table
6.2a.
Table 6.2a Water
Quality Objectives for Inland Waters in Deep Bay WCZ
|
Concerned Parameters |
Water Quality Objectives (WQOs) |
|
|
pH |
Waste discharges shall not
cause the pH of the water to exceed the range of 6.5-8.5 units. |
Yuen Long & Kam Tin
(Upper and Lower); Beas, |
|
The pH of the water
should be within the range of 6.0-9.0 units. |
Other inland waters |
|
|
Suspended solids (SS) |
Waste discharges shall
not cause the annual median of suspended solids to exceed 20 milligrams per
litre. |
Yuen Long & Kam Tin
(Upper and Lower); Beas, |
|
Dissolved oxygen (DO) |
Waste discharge shall
not cause the level of DO to be less than 4 mg/L |
Yuen Long & Kam Tin
(Upper and Lower); Beas, |
|
Chemical oxygen demand
(COD) |
Waste discharges shall not cause the chemical oxygen
demand to exceed 15 milligrams per litre. |
Yuen Long & Kam Tin
(Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water
Gathering Ground Subzones |
|
Waste discharges shall
not cause the chemical oxygen demand to exceed 30 milligrams per litre. |
Yuen
Long & Kam Tin (Lower) Subzone and other inland waters |
|
|
5-day biochemical oxygen
demand (BOD) |
Waste discharges shall not
cause the 5-day biochemical oxygen demand to exceed 3 milligrams per litre. |
Yuen Long & Kam Tin
(Upper) Subzone, Beas Subzone, Indus Subzone, Ganges Subzone and Water
Gathering Ground Subzones |
|
Waste discharges shall
not cause the 5-day biochemical oxygen demand to exceed 5 milligrams per
litre. |
Yuen
Long & Kam Tin (Lower) Subzone and other inland waters |
6.2.2
Technical Memorandum (TM) issued under WPCO
Besides setting the WQOs,
the WPCO controls effluent
discharging into the WCZs through a licensing
system. A Technical Memorandum on Standards for Effluents Discharged
into Drainage and Sewerage Systems, Inland and Coastal Waters was issued
under the WPCO (WPCO-TM) which
gives guidance on the permissible effluent discharges based on the type of
receiving waters (foul sewers, storm water drains, inland and coastal
waters). The limits control the
physical, chemical and microbial quality of effluents. Under the WPCO-TM,
effluents discharged into inland waters are subject to standards for particular
volumes of discharge. The discharge standard will vary with the use of
downstream water. The majority of the inland water bodies within the
Study Area (see Figure 6.2a) are surface
water drains, which are classified as Group D inland waters. Any new
effluent discharge during the construction phase would be required to comply
with the terms and conditions of a discharge licence, issued by EPD, under the WPCO.
6.2.3
Practice Notes
A practice note for professional persons (ProPECC PN) was issued by the EPD to provide
environmental guidelines for handling and disposal of construction site
discharges. ProPECC PN 1/94, entitled “Construction Site
Drainage” provides good practice guidelines for dealing with various types
of discharge from a construction site. Practices outlined in ProPECC PN 1/94 should be followed as far as
possible during construction to minimise the water quality impact due to
construction site runoff.
6.3
Baseline
Conditions and Sensitive Receivers
6.3.1
Baseline
Conditions
The Site is located inland and direct
impacts arising from the Project activities on marine water quality are not
expected. Supports for the flyover and slip roads would not be located within
any watercourses.
The following water bodies are identified
within the Study Area. The
locations of these water bodies are shown in Figure 6.2a:
·
There
is a main stormwater drainage channel, D1, located to
the east of the Site. The drainage
channel runs in a generally northerly direction and eventually joins
·
Another
stormwater drainage channel, D2, with a width smaller
than that of D1 and runs along
·
Two
small stormwater drains, D3 and D4, are located to
the east and west of the Site respectively. Both of the small drains are open
channels. D3 is situated between an
area of agricultural land to the southeast of POR and the southern arm of POR
and it mainly collects the water from the agricultural land. D4 runs across the eastern boundary of
Wong Uk Tsuen.
·
A
group of three fish ponds, F1, are located to the north of the Site and
·
A
number of small rivers/streams, S1 to S4, run into the drainage channel from
the adjacent catchments but all of these are outside the boundary of the
Project.
No water quality data are available for
these water bodies.
6.3.2
Water
Sensitive Receivers
The identified water bodies within the
Study Area are regarded as Water Sensitive Receivers (WSRs). None of the WSRs
are located within the boundary of the Project. The shortest distance
from the boundary of the Project to each of the WSRs
is shown in Table 6.3a.
Table 6.3a Shortest
Distance Between the Water Sensitive Receivers (WSRs) and the Limit of the Works Area
|
WSR |
Description |
Shortest distance from the Boundary of the
Project (m) |
|
D1 |
Stormwater
Drainage Channel |
36.4 |
|
D2 |
Stormwater
Drainage Channel |
133.0 |
|
D3 |
Stormwater
Drainage Channel |
40.8 |
|
D4 |
Stormwater
Drainage Channel |
28.0 |
|
F1 |
Fish Pond |
13.2 |
|
S1 |
Stream |
114.7 |
|
S2 |
Stream |
109.0 |
|
S3 |
Stream |
156.7 |
|
S4 |
Stream |
101.3 |
The Study Area for the water quality impact
assessment is defined by a distance of 300 m from the boundary of the
Project. The WSRs within the Study Area were
identified in Section 6.3.
Construction methods and configurations
and operation of the Project, as presented in Sections 2 and 3, have
been reviewed in terms of their potential to impact water quality. Based on this review, potential sources
of water quality impact that may arise during the construction and operational
phases of the Project have been identified and are presented Section 6.5. All the identified
sources of potential water quality impact were then evaluated and their impact
significance were determined in Section
6.5. If considered necessary, effective and practicable water
pollution and mitigation measures have been recommended in Section 6.6 to assist in reducing any identified adverse impacts on
water quality to acceptable levels.
6.5
Identification
and Evaluation of Environmental Impacts
6.5.1
Construction Phase
Potential sources of water quality impact associated
with the construction of the Project have been identified and include:
·
construction
site runoff and drainage;
·
general
construction activities;
·
sewage
generated by on-site workforce; and
·
piling
activities.
Construction Site Runoff and Drainage
Runoff from the construction works areas
during site clearance and site formation activities may contain increased loads
of sediments, other suspended solids and potentially contaminants.
Potential sources of pollution from site drainage include:
·
runoff
and erosion from exposed soil surfaces, earth working areas and stockpiles;
·
release
of grouting and cement materials with rain wash;
·
wash
water from dust suppression sprays; and
·
fuel
and lubricants from maintenance of construction vehicles and mechanical equipment.
Sediment laden runoff may carry pollutants
(adsorbed onto the particle surfaces) into the nearby WSRs.
Associated effects which may arise include increased suspended solids
concentrations in receiving waters and blockage of stormwater
drains.
Mitigation measures should be implemented
to control construction site runoff and drainage from the works areas, and to
prevent runoff and drainage water with high levels of suspended solids from
entering the nearby WSRs. With the
implementation of adequate construction site drainage and provision of sediment
removal facilities as described in Section
6.6.1, it is anticipated that unacceptable water quality impacts on the WSRs would not arise.
General Construction Activities
On-site construction activities may cause
water pollution from the following:
·
uncontrolled
discharge of debris and rubbish such as packaging, construction materials and
refuse; and
·
spillages
of liquids stored on-site, such as oil, diesel and solvents, which may be
likely to result in water quality impacts if they enter the nearby stormwater drainage channels.
As detailed in Section 6.6.1, good construction and site management practices
should be observed to ensure that litter, fuels and solvents do not enter the
surrounding stormwater drains.
Sewage generated by On-site Workforce
Domestic sewage would be generated from
the workforce during the construction phase. It is expected that the temporary sewage
will be adequately treated by interim sewage collection facilities, such as portable
chemical toilets, which would be installed within the construction site. It is unlikely that sewage generated
from the Site would have significant water quality impact on the WSRs, provided that sewage is not discharged directly to
the adjacent watercourses, and the interim sewage collection facilities are
sufficient and properly maintained.
Piling Activities
Continuous flight auger piling instead of
bored piling will be used for the construction of the bridge pier
foundations. Any groundwater generated
from the piling activities will be collected and directed to sedimentation
facilities for treatment before discharge to meet the relevant WPCO-TM standards.
Cumulative Impacts
Adjacent projects identified to involve
concurrent construction activities during the construction period of the
Project are:
·
Kau Hui Development – Engineering Works in Area
16, Yuen Long, Phase 2 – Extension of Road L3, to be undertaken by Civil
Engineering and Development Department (CEDD); and
·
Proposed
The construction works of CEDD’s project is scheduled to commence in August 2008 and
be completed towards the end of 2010. Excavation works are expected to be
completed before the commencement of construction activities for the Project, ie February 2009.
The potential for cumulative water quality impacts arising from the
concurrent construction activities is considered limited. Should any activities
overlap, it is expected that the associated cumulative impacts would be minor
with no unacceptable adverse impacts anticipated to occur.
The construction period of Sun Hung Kai’s
project will last for approximately one year and will be completed on or before
2010. As this project is of a
relatively small scale and a short duration, no adverse cumulative water
quality impacts are expected to result from its concurrent implementation with
the Project.
With the implementation of mitigation
measures to control construction site runoff and drainage, potential impacts on
water quality would be controlled to within the boundary of the Project.
6.5.2
Operational Phase
The only identified potential source of impact
on water quality during the operational phase would be runoff from the road
surfaces. A surface water drainage system would be provided to collect
the road runoff. It is recommended that standard HyD
road gullies be installed along the drainage system to trap silt and grit in
the first flush of runoff.
Proposed mitigation measures for
containing and minimising water quality impacts are summarised below.
6.6.1
Construction Phase
Construction Site Run-off and Drainage
Good site practices outlined in ProPECC PN 1/94 should be followed as far as practicable to
minimise surface runoff and the chance of erosion, and also to retain and
reduce any suspended solids prior to discharge. These practices include
the follows:
·
Silt
removal facilities such as silt traps or sedimentation facilities should be
provided to remove silt particles from runoff to meet the requirements of the WPCO-TM standard. The design of
silt removal facilities should be based on the guidelines provided in ProPECC PN 1/94. All drainage facilities and erosion
and sediment control structures should be inspected monthly and maintained to
ensure proper and efficient operation at all times and particularly during
rainstorms.
·
Careful
programming of the works to minimise surface excavations for the Project during
the wet season. If excavation of soil cannot be avoided during the wet
season, exposed slope surfaces should be covered by tarpaulin or other
means. Other measures that need to be implemented before, during, and
after rainstorms are summarised in ProPECC PN 1/94.
·
Exposed
soil surfaces should be protected by paving or fill material as soon as
possible to reduce the potential of soil erosion.
·
Open
stockpiles of construction materials or construction wastes on-site of more
than 50m3 should be covered with tarpaulin or similar fabric during
rainstorms. These materials should not be placed near water courses.
·
A
Drainage Management Plan (DMP) should be prepared by the Contractor and
submitted to EPD before the commencement of any construction works to detail
the procedures for control of construction site runoff. No site run-off
or drainage should be allowed enter the nearby WSRs.
General Construction Activities
·
Debris
and refuse generated on-site should be collected, handled and disposed of
properly to avoid entering the nearby WSRs.
Stockpiles of cement and other construction materials should be kept covered
when not being used.
·
Oils
and fuels should only be used and stored in designated areas which have
pollution prevention facilities. All fuel tanks and storage areas should
be provided with locks and be sited on sealed areas, within bunds of a capacity
equal to 110% of the storage capacity of the largest container or 20% by volume
of the chemical waste stored in that area, whichever is the greater. The
bund should be drained of rainwater after a rain event.
Sewage generated from On-site Workforce
·
Temporary
sanitary facilities, such as portable chemical toilets, should be employed
on-site. A licensed contractor would be responsible for appropriate
disposal and regular maintenance of these facilities.
Piling Activities
·
Silt
removal facilities such as silt traps or sedimentation facilities should be
provided to remove silt particles from groundwater to meet the requirements of
the WPCO-TM standard. The
design of silt removal facilities should be based on the guidelines provided in
ProPECC PN 1/94. All drainage facilities and
erosion and sediment control structures should be inspected and maintained on a
regular basis to ensure proper and efficient operation at all times and
particularly during rainstorms.
6.6.2
Operational
Phase
It is recommended that the standard HyD road gullies be installed along the road drainage
system to trap any silt and grit in the first flush of runoff.
6.7
Residual
Environmental Impact
With the full implementation of the
recommended mitigation measures for the construction and operational phases of
the Project, no unacceptable residual impacts on water quality are
expected. It is recommended that regular site audits of the
implementation of the recommended mitigation measures be undertaken during the
construction phase.
6.8
Environmental Monitoring and Audit
The impact assessment has evaluated that
there would be no water quality impacts on the WSRs
within the Study Area. As a result, it is considered that environmental
monitoring of water quality is not required. Nevertheless, regular site inspection is
recommended to ensure that the recommended mitigation measures are properly
implemented.
6.9.1
Construction
Phase
No WSRs were
identified within the limits of the works area. Water quality impacts are negligible and
minimal during the construction phase of the Project provided that good site
practices and housekeeping are implemented. No water quality monitoring is thus
considered necessary during the construction phase.
6.9.2
Operational
Phase
For the operation of the Project, the only
source of water quality impact would be runoff from the road surface. A surface water drainage system should
be provided to collect the road runoff and to facilitate drainage of runoff
during rainstorms. With the provision
of an appropriate road drainage system, no adverse water quality impacts are
anticipated. No operational water
quality monitoring is considered necessary.