5
WATER POLLUTION
5.1
Introduction
5.1.1.1
This section describes
the requirements for the monitoring and audit of water quality impacts from the
Project during the construction phase. No monitoring of water quality would be
required during the operation phase of the STF as there would be no discharge
of wastewater effluent from the on-site wastewater treatment plant.
5.1.1.2
The water quality
assessment undertaken in the EIA Study concluded that the identified water
quality impacts could be minimized by implementing the recommended mitigation
measures for the construction works, such as control measures on site runoff
and drainage from the works areas to minimise construction run-off and to carry
out proper site management and good housekeeping practices. The EIA
Report concluded that the release of PFA leachate due
to the foundation construction would not be likely to accelerate. Marine
water quality monitoring was recommended during the foundation piling of the
STF to confirm the assessment results. As such, no unacceptable residual
water quality impact would be expected.
5.1.1.3
Regular site
inspections were recommended to be undertaken to inspect the construction
activities and works areas and also the status on the implementation of the
recommended mitigation measures. In addition, water quality monitoring of
the Tsang Kok Stream was recommended during site
formation, foundation piling of the STF, and construction of the access road in
order to ensure no adverse water quality impact to the stream.
5.1.1.4
Discharges of drainage
water from the works areas would be required to comply with the terms and
conditions of a discharge licence, issued by EPD, under the Water Pollution
Control Ordinance (WPCO). It may be a stipulation of the WPCO licence to
require the Contractor to monitor the quality / quantity of the discharge to
show compliance with the conditions of the licence. Such monitoring would
not form part of the EM&A programme.
5.2
Water Quality Parameters
5.2.1.1
Dissolved oxygen (DO),
turbidity, suspended solids (SS) level and pH should be monitored at designated
water quality monitoring stations in the Tsang Kok
Stream during the construction works. DO, turbidity and pH should be
measured in situ whereas SS should be determined by laboratory analysis.
5.2.1.2
With regard to the
potential marine water quality impact from PFA leachate,
heavy metals including cadmium, chromium and aluminium, which have the greatest
tendency to leach from the lagooned PFA into the
seawater, should be monitored during the foundation piling.
5.2.1.3
Other relevant data
should also be recorded, including monitoring location / position, time, water
depth, temperature, weather conditions and any special phenomena or work
underway at the construction site.
5.2.1.4
The proposed water
quality monitoring schedule should be faxed to EPD on or before the first day
of the monitoring month. EPD should also be notified immediately for any
changes in schedule by fax. A monitoring record sheet is presented in Appendix 5.1 for reference.
5.3
Monitoring Equipment
5.3.1
Dissolved Oxygen and Temperature Measuring
Equipment
5.3.1.1
The instrument should
be a portable and weatherproof DO measuring instrument complete with cable and
sensor, and use a DC power source. The equipment should be capable of
measuring:
l a DO level in the range of 0 ‑
20 mg/L and 0 ‑ 200% saturation; and
l
a temperature of 0 ‑ 45 degree
Celsius.
5.3.1.2
It should have a
membrane electrode with automatic temperature compensation complete with a
cable.
5.3.2
Turbidity Measurement Instrument
5.3.2.1
The instrument should
be a portable and weatherproof turbidity-measuring instrument using a DC power
source. It should have a photoelectric sensor capable of measuring
turbidity between 0 - 1000 NTU (for example, Hach
model 2100P or an approved similar instrument).
5.3.3
pH Measurement Instrument
5.3.3.1
The instrument should
consist of a potentiometer, a glass electrode, a reference electrode and a
temperature-compensating device. It should be readable to 0.1pH in a
range of 0 to 14. Standard buffer solutions of at least pH 7 and pH 10
should be used for calibration of the instrument before and after use.
5.3.4.1
A water sampler is
required. It should comprise a transparent PVC cylinder, with a capacity
of not less than 2 litres, which can be effectively sealed with latex cups at
both ends. The sampler should have a positive latching system to keep it
open and prevent premature closure until released by a messenger when the
sampler is at the selected water depth (for example, Kahlsico
Water Sampler or an approved similar instrument).
5.3.5
Water Depth Detector
5.3.5.1
A portable,
battery-operated echo sounder should be used for the determination of water
depth at each designated monitoring station. This unit can either be hand
held or affixed to the bottom of the work boat, if the same vessel is to be
used throughout the monitoring programme.
5.3.6
Sample Containers and Storage
5.3.6.1
Water samples for SS
and three heavy metals measurements should be stored in high density polythene
bottles with no preservative added, packed in ice (cooled to 4°C without being
frozen) and delivered to the laboratory and analysed as soon as possible after
collection. Sufficient volume of samples should be collected to achieve
the detection limit stated in Section 5.4.
5.3.7
Monitoring Position Equipment
5.3.7.1
A hand-held or
boat-fixed type digital Differential Global Positioning System (DGPS) with way
point bearing indication and Radio Technical Commission for maritime (RTCM)
Type 16 error message ‘screen pop-up’ facilities (for real-time auto-display of
error messages and DGPS corrections from the Hong Kong Hydrographic
Office), or other equipment instrument of similar accuracy, should be provided
and used to ensure that the water sampling locations are correct during the
water quality monitoring work.
5.3.8
Calibration of In-Situ Instruments
5.3.8.1
The DO meter and turbidimeter should be checked and calibrated before
use. DO meter and turbidimeter should be
certified by a laboratory accredited under HOKLAS or any other international
accreditation scheme, and subsequently re-calibrated at three monthly intervals
throughout all stages of the water quality monitoring. Responses of
sensors and electrodes should be checked with certified standard solutions
before each use. Wet bulb calibration for a DO meter should be carried
out before measurement at each monitoring location.
5.3.8.2
Sufficient stocks of
spare parts should be maintained for replacements when necessary. Backup
monitoring equipment should also be made available so that monitoring can
proceed uninterrupted even when some equipment is under maintenance,
calibration, etc.
5.4
Laboratory Measurement / Analysis
5.4.1.1
Duplicate samples from
each independent sampling event are required by EPD for all parameters.
Analysis of suspended solids and heavy metals should be carried out in a HOKLAS
or other international accredited laboratory. Sufficient water samples
should be collected at the monitoring stations for carrying out the laboratory
determinations. The determination work should start within 24 hours after
collection of the water samples. The analyses should follow the American
Public Health Association (APHA) Standard Methods for the Examination of Water and
Wastewater or an equivalent method subject to the approval of EPD.
Analytical methods and detection limits for SS and heavy metals are present in Table
5.1.
Table 5.1 Analytical Methods to be
applied to Water Quality Samples
|
Parameters
|
Analytical Method
|
Detection Limit
|
|
Suspended Solids
|
APHA
2540D
|
1
mg/L
|
|
Cadmium
|
APHA
20e 3111B
|
0.5
μg/L
|
|
Chromium
|
APHA
20e 3111D
|
1
μg/L
|
|
Aluminium
|
APHA
3500-Al-D
|
20
μg/L
|
5.4.1.2
Additional duplicate
samples may be required by EPD for inter-laboratory calibration.
Remaining samples after analysis should be kept by the laboratory for 3 months
in case repeat analysis is required. If in-house or non-standard methods
are proposed, details of the method verification may also be required to submit
to EPD. In any circumstance, the sample testing should have comprehensive
quality assurance and quality control programmes. The laboratory should
prepare to demonstrate the programme to DEP or his representatives when
requested.
5.5
Monitoring Locations
5.5.1.1
The proposed water
quality monitoring stations are listed in Table 5.2 and shown in Figure 5.1. For the stream
water quality monitoring, two monitoring stations should be set in the stream
course upstream of the works areas which should act as a control stations, and
three impact monitoring stations should be located in Tsang Kok
stream adjacent and downstream of the works areas. In terms of the marine
water quality monitoring conducted during the foundation piling, a control
station should be set in the EPD marine water quality monitoring station namely
DM4 and two impact monitoring stations should be located adjacent to the East Ash
Lagoon in the Deep Bay WCZ.
Table 5.2 Proposed Water Quality Monitoring
Stations
|
Station
|
Description
|
Easting
|
Northing
|
Parameters
|
|
C1
|
Control stations for the Tsang Kok stream
water quality monitoring
|
810639.3
|
831296.8
|
DO,
turbidity, SS, pH
|
|
C2
|
810461.6
|
831243.9
|
|
W1
|
Impact monitoring stations for the Tsang Kok
stream
|
810639.3
|
831296.8
|
|
W2
|
810461.6
|
831243.9
|
|
W3
|
810323.6
|
831196.1
|
|
DM4
|
Control stations for marine water quality monitoring
|
809629.8
|
835150.8
|
cadmium;
chromium; aluminium
|
|
M1
|
Marine water adjacent to the East Ash Lagoon
|
809915.3
|
831971.6
|
|
M2
|
809026.4
|
831676.8
|
5.5.1.2
For the stream water
quality monitoring, measurement should be taken at surface and bottom
layers. For the marine water monitoring stations, sampling shall be taken
at three water depths, namely, 1m below water surface, mid-depth and 1m above
sea bed, except at where the water depth is less than 6m, in which case the
mid-depth station may be omitted. Shall the water depth be less than 3m,
only the mid-depth station will be monitored.
The status and locations of the works activities/areas may change after issuing
this Manual. If such case arises, the ET Leader should propose with
justification for changes to monitoring locations or other requirements of the
EM&A programme, and seek approval from the IEC and deposit the document
with EPD.
5.6
Baseline Monitoring
5.6.1.1
Baseline conditions in
the stream course and marine water should be established and agreed with EPD
prior to the commencement of construction works. The purpose of the
baseline monitoring is to establish ambient conditions prior to the
commencement of the works and to demonstrate the suitability of the proposed
monitoring stations. The baseline conditions should normally be
established by measuring the water quality parameters specified in Section 5.2.
The measurements should be taken at the designated monitoring stations during
mid-flood and mid-ebb tides prior to the commencement of works.
5.6.1.2
Other relevant data
should also be recorded, such as monitoring location / position, time, water
depth, weather conditions and any special phenomena underway near the
monitoring station. There should not be any construction activities in
the vicinity of the stations during the baseline monitoring.
5.6.1.3
In exceptional cases
when insufficient baseline monitoring data or questionable results are
obtained, the ET Leader should seek approval from the IEC on an appropriate set
of data to be used as baseline reference and deposit the document with EPD.
5.6.1.4
Baseline monitoring
schedule should be faxed to EPD one week prior to the commencement of baseline
monitoring.
5.7
Impact Monitoring
5.7.1
Stream Water Quality Monitoring
5.7.1.1
During the course of
site formation and foundation piling of the STF and construction of the access
road, impact monitoring should be undertaken three days per week with sampling
/ measurement at the designated monitoring stations in the Tsang Kok Stream. Upon completion of the above construction
works, the monitoring exercise at the designated monitoring locations should be
continued for four weeks in the same manner as the impact monitoring.
5.7.1.2
Two consecutive
measurements of DO concentration, DO saturation, turbidity and pH should be
taken at the surface and bottom layers at each location. The monitoring
probes should be retrieved out of water after the first measurement and then
redeployed for the second measurement. Where the difference in value
between the first and second readings of DO or turbidity is more than 25% of
the value of the first reading, the reading should be discarded and further
readings should be taken. Water samples for SS measurement should be
collected at the same surface and bottom layers at each location.
5.7.1.3
The water quality
monitoring schedule should be faxed to EPD on or before the first day of the
monitoring month. EPD should be notified immediately of any changes in
schedule by fax.
5.7.2
Marine Water Quality Monitoring
5.7.2.1
During the foundation
piling of the STF, impact monitoring should be undertaken three days per week
with sampling / measurement at the designated monitoring stations in the Deep
Bay WCZ. Upon completion of the piling, the monitoring exercise at the
designated monitoring locations should be continued for four weeks in the same
manner as the impact monitoring.
5.7.2.2
Sampling should be taken at three water depths, namely, 1m
below water surface, mid-depth and 1m above sea bed, except where the water
depth be less than 6m, in which case the mid-depth
station may be omitted. Shall the water depth be less than 3m, only the
mid-depth station will be monitored.
5.7.2.3
The water quality
monitoring schedule should be faxed to EPD on or before the first day of the
monitoring month. EPD should be notified immediately of any changes in
schedule by fax.
5.8
Event and Action Plan for Water Quality
5.8.1.1
The water quality
criteria, namely action and limit levels, are shown in Table 5.3.
These criteria should be applied to ensure that any deterioration of water
quality is readily detected and timely action is taken to rectify the
situation. Should the monitoring results of the water quality parameters
at any designated monitoring station exceed the water quality criteria, the
actions in accordance with the Event and Action Plan summarized in Table 5.4
shall be carried out.
Table 5.3 Action and Limit Levels for Water Quality
|
Parameters
|
Action
|
Limit
|
|
DO in mg/L
(mid-depth)
|
£ 5 %-ile of
baseline data
|
£ 4 mg/L
|
|
SS in mg/L (mid-depth)
|
≥ 95 %-ile of baseline data or 120% of
control station’s SS on the same day of measurement
|
≥ 99 %-ile of baseline or 130% of
control station's SS on the same day of measurement
|
|
Turbidity in NTU (mid-depth)
|
≥ 95 %-ile of baseline data or 120% of
control station’s turbidity on the same day of measurement
|
≥ 99 %-ile of baseline or 130% of
control station's turbidity on the same day of measurement
|
|
pH
|
Within the interval of 5 percentile and 95 percentile of baseline data
|
pH £ 6 or pH ≥ 9
|
|
Cadmium
|
≥ 95 %-ile of baseline data
|
≥ 99 %-ile of baseline
|
|
Chromium
|
≥ 95 %-ile of baseline data
|
≥ 99 %-ile of baseline
|
|
Aluminium
|
≥ 95 %-ile of baseline data
|
≥ 99 %-ile of baseline
|
Notes:
1.
For
DO, non-compliance of the water quality limits occurs when monitoring result is
lower than the limits.
2.
For SS
and turbidity, non-compliance of the water quality limits occurs when
monitoring result is higher than the limits.
Table 5.4
Event and Action Plan for Water Quality
|
Event
|
ET
Leader
|
IEC
|
SOR
|
Contractor
|
|
|
¨ Repeat in situ measurement to confirm
findings;
¨ Inform IEC and Contractor;
¨ Check monitoring data, all plant, equipment
and Contractor's working methods;
¨ Discuss mitigation measures with IEC and
Contractor;
¨ Repeat measurement on next day of exceedance.
|
¨ Discuss with ET and Contractor on the mitigation
measures;
¨ Review proposals on mitigation measures submitted by
Contractor and advise the SOR accordingly;
¨ Assess the effectiveness of the implemented
mitigation measures.
|
¨ Discuss with IEC on the proposed mitigation
measures;
¨ Make agreement on the mitigation measures to be
implemented.
¨ Assess the effectiveness of the implemented
mitigation measures.
|
¨ Inform the SOR and confirm notification of
the non-compliance in writing;
¨ Rectify unacceptable practice;
¨ Check all plant and equipment;
¨ Consider changes of working methods;
¨ Discuss with ET and IEC and propose
mitigation measures to IEC and SOR;
¨ Implement the agreed mitigation measures.
|
|
Action level being exceeded
by more than one consecutive sampling day
|
¨ Repeat in situ measurement to confirm
findings;
¨ Inform IEC and Contractor;
¨ Check monitoring data, all plant, equipment
and Contractor's working methods;
¨ Discuss mitigation measures with IEC and
Contractor;
¨ Ensure mitigation measures are implemented;
¨ Prepare to increase the monitoring frequency
to daily;
¨ Repeat measurement on next day of exceedance.
|
¨ Discuss with ET and Contractor on the mitigation measures;
¨ Review proposals on mitigation measures submitted by Contractor and
advise the SOR accordingly;
¨ Assess the effectiveness of the
implemented mitigation measures.
|
¨ Discuss with IEC on the proposed mitigation
measures;
¨ Make agreement on the mitigation measures to be
implemented;
¨ Assess the effectiveness of the implemented
mitigation measures.
|
¨ Inform the SOR and confirm notification of
the non-compliance in writing;
¨ Rectify unacceptable practice;
¨ Check all plant and equipment; Consider
changes of working methods;
¨ Discuss with ET and IEC and propose
mitigation measures to IEC and SOR within three working days;
¨ Implement the agreed mitigation measures.
|
|
Limit level being exceeded
by one sampling day
|
¨ Repeat in situ measurement to confirm
findings;
¨ Inform IEC Contractor and EPD;
¨ Check monitoring data, all plant, equipment
and Contractor's working methods;
¨ Discuss mitigation measures with IEC, SOR and
Contractor;
¨ Ensure mitigation measures are implemented;
¨ Increase the monitoring frequency to daily
until no exceedance of Limit level.
|
¨ Discuss with ET and Contractor on the mitigation
measures;
¨ Review proposals on mitigation measures submitted by
Contractor and advise the SOR accordingly;
¨ Assess the effectiveness of the implemented
mitigation measures.
|
¨ Discuss with IEC, ET and Contractor on the proposed
mitigation measures;
¨ Request Contractor to critically review the working
methods;
¨ Make agreement on the mitigation measures to be
implemented;
¨ Assess the effectiveness of the implemented
mitigation measures.
|
¨ Inform the SOR and confirm notification of
the non-compliance in writing;
¨ Rectify unacceptable practice;
¨ Check all plant and equipment;
¨ Consider changes of working methods;
¨ Discuss with ET, IEC and SOR and propose
mitigation measures to IEC and SOR within three working days;
¨ Implement the agreed mitigation measures.
|
|
|
¨ Repeat in situ measurement to confirm
findings;
¨ Inform IEC Contractor and EPD;
¨ Check monitoring data, all plant, equipment
and Contractor's working methods;
¨ Discuss mitigation measures with IEC, SOR and
Contractor;
¨ Ensure mitigation measures are implemented;
¨ Increase the
monitoring frequency to daily until no exceedance
of Limit level for two consecutive days.
|
¨ Discuss with ET and Contractor on the mitigation
measures;
¨ Review proposals on mitigation measures submitted by
Contractor and advise the SOR accordingly;
¨ Assess the
effectiveness of the implemented mitigation measures.
|
¨ Discuss with IEC, ET
and Contractor on the proposed mitigation measures;
¨ Request
Contractor to critically review the working methods;
¨ Make agreement on
the mitigation measures to be implemented;
¨ Assess the
effectiveness of the implemented mitigation measures;
|
¨ Inform the SOR and confirm notification of
the non-compliance in writing;
¨ Rectify unacceptable practice;
¨ Check all plant and equipment;
¨ Consider changes of working methods;
¨ Discuss with ET, IEC and SOR and propose
mitigation measures to IEC and SOR within three working days;
¨ Implement the
agreed mitigation measures;
¨ As directed by
the SOR, to slow down or to stop all or part of the construction activities.
|
5.9
Mitigation Measures
5.9.1
Introduction
5.9.1.1
Mitigation measures
recommended for the construction and operation phases of the Project are
summarized below.
5.9.2
Construction Phase
Construction Site Run-off
and Drainage
5.9.2.1
The site practices
outlined in ProPECC PN 1/94 “Construction Site
Drainage” should be followed as far as practicable in order to minimise surface
runoff and the chance of erosion. These practices include the following
items:-
l
At the start of site establishment,
internal drainage works and erosion and sedimentation control facilities should
be implemented. Channels, earth bunds or sand bag barriers should be
provided on site to direct stormwater to silt removal
facilities. The detailed design and installation of the temporary on-site
drainage system should be undertaken by the contractor prior to the
commencement of construction.
l
Before commencing any site formation work,
all sewer and drainage connections should be sealed to prevent debris, soil, sand
etc. from entering public sewers/drains.
l
Boundaries of
earthworks should be surrounded by dykes or embankments for flood protection,
as necessary.
l
Sand/silt removal
facilities such as sand traps, silt traps and sediment basins should be
provided to remove sand/silt particles from runoff to meet the standards of the
Technical Memorandum under the Water Pollution Control Ordinance. 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.
l
Water pumped out from
foundation piles must be discharged into silt removal facilities.
l
During rainstorms, exposed slope/soil
surfaces should be covered by a tarpaulin or other means, as far as
practicable. Other measures that need to be implemented before, during
and after rainstorms are summarized in ProPECC PN
1/94.
l
Exposed soil areas
should be minimized to reduce potential for increased siltation and
contamination of runoff.
l
Earthwork final
surfaces should be well compacted and subsequent permanent work or surface
protection should be immediately performed.
l
Open stockpiles of
construction materials or construction wastes on-site should be covered with
tarpaulin or similar fabric during rainstorms.
l
All vehicles should be cleaned before
leaving the works area to ensure no earth, mud and debris is deposited on
roads. An adequately designed and sited wheel washing bay should be
provided at every site exit. The wheel washing facility should be
designed to minimize the intake of surface water (rainwater). Wash-water
should have sand and silt settled out and removed at least on a weekly basis to
ensure the continued efficiency of the process.
General Construction
Activities
5.9.2.2
Debris and refuse
generated on-site should be collected, handled and disposed of properly to
avoid entering the nearby water bodies and public drainage system.
Stockpiles of cement and other construction materials should be kept covered
when not being used.
5.9.2.3
Oils and fuels should
only be used and stored in designated areas which have pollution prevention
facilities. To prevent spillage of fuels and solvents to nearby water
bodies and public drains, 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 tank. The bund should be
drained of rainwater after a rain event.
Sewage from Construction
Workforce
5.9.2.4
Temporary sanitary
facilities, such as portable chemical toilets, should be employed on-site where
necessary to handle sewage from the workforce. A licensed contractor
would be responsible for appropriate disposal and maintenance of these
facilities.
Release of PFA Leachate from Ash Lagoon into the Aquatic Environment
5.9.2.5
The past monitoring
data showed that the water quality at the location outside the Tsang Tsui Ash Lagoons was not affected by the PFA filling
operation. Although no liner system is installed at the base of the
lagoons, the low permeability values of the marine deposits and alluvium
underneath the PFA layer would limit the seepage of PFA leachate.
The foundation construction of the STF is not likely to accelerate the release
of PFA leachate through the base of the lagoon
site. Marine water quality monitoring is recommended during the
foundation piling of the STF to confirm the assessment results.
5.9.3
Operation Phase
Receiving Area in the STF
5.9.3.1
An adequate number of
drains should be provided at the receiving area of the STF with drain piping
for draining and cleaning all areas of the floor. The floors should be
adequately sloped to floor drains for collection of drainage water during
cleaning. Such floor drains should contain no traps. The drainage
water should be routed to an outdoor vented and trapped manhole for connection
to the on-site wastewater treatment plant.
Wash Down Facilities at
STF
5.9.3.2
Frequent and sufficient
maintenance should be provided for the drainage system, and multiple outlets in
the drainage system should be designed and provided to reduce the likelihood of
drainage blockage.
Temporary Sludge Storage
at STF
5.9.3.3
A detection
device/alarm should be installed to prevent overfilling of temporary sludge
storage tank.