4.1.1.1
Potential water pollution
sources during the construction phase have been identified as construction site
run-off, direct disturbance to water courses, sewage from the workforce,
potential risk of contamination from materials, chemicals and bentonite slurry.
In order to protect water quality in the downstream section of the Ngong Ping Stream within the Lantau
North Country Park and the water gathering grounds, mitigation measures have
been recommended and residual impacts are not predicted. However, in light of the sensitive nature of
the downstream section of the
4.2.1.1
In
accordance with the recommendations of the EIA, construction phase water
quality EM&A is required. Water
quality parameters comprising: (i) suspended solids
(SS); (ii) turbidity in Nephelometric Turbidity Units
(NTU); (iii) dissolved oxygen (DO) in mg/L; and (iv) pH, shall be measured by the
Environmental Team (ET) (see Section 1 for a description of the ET and duties)
at locations which are within the potential influence of construction works at
least three times per week to ensure that any deteriorating water quality could
be readily detected and timely action be taken to rectify the situation. The first parameter, SS, shall be determined
in the laboratory, with the other parameters measured in-situ using direct
reading instrumentation.
4.2.1.2
In
association with the water quality parameter measurements, relevant data shall
also be measured, including the monitoring location/position, time, water
depth, water temperature, salinity, DO saturation, weather conditions if
appropriate, and any special phenomena and work underway at the construction
site. A sample
monitoring record sheet is shown in Appendix C.
4.3.1
Dissolved Oxygen and Temperature Measuring Equipment
4.3.1.1
The dissolved oxygen and temperature measuring
equipment will be as follows:
a) The instrument shall be a portable, weatherproof dissolved oxygen measuring instrument complete with cable and use a DC power source. It shall be capable of measuring:-
- a dissolved oxygen level in the range of 0-20 mg/l and
0-200% saturation; and
-
a
temperature of 0-45 degree Celsius.
b) It shall have a membrane electrode with automatic temperature compensation complete with a cable. Sufficient stocks of spare electrodes and cables shall be available for replacement where necessary (e.g. YSI model 59 meter, YSI 5739 probe, YSI 5795A submersible stirrer with reel and cable or an approved similar instrument).
4.3.2
Turbidity Measurement Instrument
4.3.2.1
The
instrument shall be a portable, weatherproof turbidity-measuring instrument
complete with comprehensive operation manual. The equipment shall use a DC
power source. It shall have a photoelectric sensor capable of measuring
turbidity between 0-1000 NTU and be complete with a cable (e.g. Hach model 2100P or an approved similar instrument).
4.3.3.1
The
equipment for measuring suspended solids shall be as follows:
a) For fresh water sampling within the water courses, a 500ml clean plastic beaker shall be used.
b) Water samples for suspended solids measurement shall be collected in high density polythene bottles, packed in ice (cooled to 4oC without being frozen) and delivered to the laboratory within 24 hour of collection.
4.3.4.1
A portable
salinometer capable of measuring salinity in the
range of 0-40 practical salinity unit shall be provided for measuring salinity. The meter shall be able to
display the equivalent conductivity in mS/cm in real
time and both salinity and conductivity shall be recorded.
4.3.5
pH Measuring Equipment
4.3.5.1
A portable pH meter capable of
measuring a range between 0.0 and 14.0 shall be provided to measure pH under
the specified conditions (e.g. Orion Model 250A or an approved similar
instrument).
4.3.6
Calibration of Equipment
4.3.6.1
All in-situ
monitoring instrument shall be checked, calibrated and certified by an environmental
laboratory accredited under HOKLAS or any other international accreditation
scheme before use, and subsequently re-calibrated at 3 monthly intervals throughout all stages of the water quality monitoring.
Responses of sensors and electrodes shall be checked with certified standard
solutions before each use. Wet bulb calibration for a DO meter shall be carried
out before measurement at each monitoring location.
4.3.6.2 For the on site calibration of field equipment, the BS 1427:1993, "Guide to Field and on-site test methods for the analysis of waters" shall be observed.
4.3.7.1
Sufficient stocks of spare
parts shall be maintained for replacements when necessary. Back-up monitoring equipment shall also be
available so that monitoring can proceed uninterrupted even when some equipment
is under maintenance, calibration, etc.
4.4
Measurement
and Analysis
4.4.1.1
Analysis of
suspended solids shall be carried out in an environmental testing laboratory HOKLAS
accredited to this parameter or other international accredited laboratory and
the testing report shall be HOKLAS endorsed (or equivalent if the testing is
performed by overseas laboratory). Water samples of about 500ml shall be
collected at the monitoring stations for carrying out the laboratory SS
determination. The SS determination work
shall start within 24 hours after collection of the water samples. The SS determination shall follow TSS-SM25400
or equivalent methods subject to approval of the DEP.
4.4.1.2
The limits of detection for the
in-situ and laboratory measurements that shall be obtained are shown in Table 4.1.
Table 4.1 Detection Limits and Precision for Water
Quality Determinants
|
Determinant |
Reporting limit |
Accuracy |
Precision |
|
Dissolved
Oxygen |
0.1
mg/L |
1% |
25% |
|
Salinity |
0.01
practical salinity unit |
1% |
25% |
|
Temperature |
0.1
degree Celsius |
1% |
25% |
|
pH |
0.01
units |
1% |
25% |
|
Turbidity
(NTU) |
0.1
NTU |
1% |
25% |
|
Suspended
Solids |
2 mg/L* |
2% |
25% |
* testing report shall be HOKLAS endorsed (or equivalent if the testing is performed by overseas
laboratory).
4.4.1.3
For the
testing methods of other parameters as recommended by the EIA or required by the
Environmental Protection Department (DEP), detailed testing methods,
pre-treatment procedures, instrument use, Quality Assurance / Quality Control
(QA/QC) details (such as blank, spike recovery, number of duplicate samples per batch, etc), detection
limits and accuracy shall be submitted to the DEP for approval prior to the
commencement of monitoring programme. It is recommended that a minimum of 5% of
the samples shall be collected and analysed in duplicate for QA/QC
purposes. The QA/QC shall be in accordance
with the requirement of HOKLAS or international accredited scheme. The QA/QC
results shall be reported. The DEP may
also request the laboratory to carry out analysis of known standards provided
by them for quality assurance.
Additional duplicate samples may also be required by the DEP for inter-
laboratory calibration. Remaining
samples after analysis shall be kept by the laboratory for 3 months in case
repeat analysis is required. If in-house
or non-standard methods are proposed, detailed of the method verification may
also be required to submit to the DEP.
In any circumstance, the sample testing shall have comprehensive quality
assurance and quality control programmes.
The laboratory shall be prepared to demonstrate the programmes to the
DEP or his representatives upon request.
4.5.1.1
The water
quality monitoring locations are shown in Figure
4.1 and detailed in Table 4.2 below. A schedule for water quality monitoring shall
be prepared by the ET and approved by the ER, Independent Environmental Checker
(IEC), and DEP prior to the commencement of the monitoring.
Table 4.2 Location of Water Quality Monitoring
Stations
|
Station |
Type |
Easting |
Northing |
Relevant Works Section* |
Remark |
|
WS1-R1 |
Upstream
reference |
808664 |
813130 |
WS1/SA1 |
R2
in EIA |
|
WS1-I1 |
Downstream
impact |
808535 |
813094 |
WS1/SA1 |
|
|
WS1-R2 |
Upstream
reference |
808524 |
813134 |
WS1 |
W2
in EIA |
|
WS1-I2 |
Downstream
impact |
808528 |
813101 |
WS1 |
|
|
WS4-R3 |
Upstream
reference |
808214 |
813003 |
WS4/SA2 |
|
|
WS4-I3 |
Downstream
impact |
808196 |
813042 |
WS4/SA2 |
|
|
WS5-R4 |
Upstream
reference |
808096 |
813076 |
WS5/SA3 |
|
|
WS5-I4 |
Downstream
impact |
808055 |
813115 |
WS5/SA3 |
|
|
WS6-R5 |
Upstream
reference |
807983 |
813158 |
WS6/WA3 |
|
|
WS6-I5 |
Downstream
impact |
807919 |
813155 |
WS6/WA3 |
|
|
WS6-C1 |
Intermediate
Control |
807813 |
813214 |
WS6/SA4 |
W8
in EIA |
|
WS6-R6 |
Upstream
reference |
807727 |
813249 |
WS6/WA4 |
|
|
WS6-I6 |
Downstream
Impact |
807762 |
813285 |
WS6/WA4 |
W9
in EIA |
* Please refer to Figures 2.9a-2.9g
of the EIA Report for the relevant Works Section (WS), and/or designated works
area (WA) and stockpiling area (SA).
4.5.1.2
The status
and locations of water quality sensitive receivers and the monitoring sites may
change after issuing this Manual. If
such cases exist, the ET shall propose updated monitoring locations and seek
approval from the ER, the IEC, and the DEP.
4.5.1.3
When
alternative monitoring locations are proposed, they shall be chosen based on
the following criteria:
a) at locations close to and preferably at the boundary of the site activities as indicated in the EIA report, which are likely to have water quality impacts;
b) close to the sensitive receptors which are directly or likely to be affected;
c) for monitoring locations located in the vicinity of the sensitive receptors, care should be taken to cause minimal disturbance during monitoring; and
d) reference stations which are at locations representative of the project site in its undisturbed condition.
4.5.1.4
Reference stations are
necessary to compare the water quality from potentially impacted sites with the
ambient water quality. Reference
stations shall be located within the same body of water as the impact monitoring
stations but shall be upstream and outside the area of influence of the works
and, as far as practicable, not affected by any other works. The reference
stations for the freshwater sampling are located at appropriate locations upstream
of the proposed construction area], a distance which is close enough to
represent the local aquatic area which may be affected but far enough not be
been influenced by the works.
4.5.1.5
Replicates
(that is, 2 samples) in-situ from each independent sampling event are required for all parameters to ensure a robust
statistically interpretable data set. Similarly, independent replicated sample
shall also be taken for laboratory analysis of the suspended solid.
4.6
Baseline
Monitoring
4.6.1.1
Baseline
conditions for water quality shall be established and agreed with the IEC and
the DEP prior to the commencement of 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 impact, control and
reference monitoring stations. The baseline conditions shall normally be
established by measuring the water quality parameters specified above.
4.6.1.2
The
measurements shall be taken at all designated monitoring stations including
control stations, once per day for a minimum of 3 days per week for 4 weeks
prior to the commencement of the construction works. Measurements shall be taken at each station
at any time. The interval between two
sets of monitoring shall not be less than 36 hours. For ease of comparison and
analysis, all samples should be taken at each station at approximately the same
time.
4.6.1.3
Only one sampling
depth will be required for the stream monitoring, which shall be taken at mid
depth. However, in all cases duplicate water samples shall be collected. Water
samples for suspended solid analysis shall be collected at all the designated
monitoring stations.
4.6.1.4
No
construction activities shall be on-going in the vicinity of the stations
during the baseline monitoring. The ET shall be responsible for undertaking the
baseline monitoring and submitting the results within 10 working days from the
completion of the baseline monitoring work.
4.6.1.5
In
exceptional cases when insufficient baseline monitoring data or questionable
results are obtained, the ET shall seek approval from the IEC and the DEP on an
appropriate set of data to be used as baseline reference.
4.6.1.6
The baseline
monitoring schedule shall be issued to the IEC and EPD at least 1 week prior to
the commencement of baseline monitoring.
4.7
Impact
Monitoring
4.7.1.1 Only one sampling depth will be required for the streams, which shall be collected at mid depth. Replicates (2 samples) in-situ from each independent sampling event are required for all parameters to ensure a robust statistically interpretable data set.
4.7.1.2 In addition, duplicated water samples for suspended solid analysis shall be collected at all the above stations and delivered to the HOKLAS accredited laboratory for analysis. Results for suspended solids shall be received back from the laboratory within 24hour [typical, but need to check] of the receipt of the samples.
4.7.1.3 The Impact Monitoring shall be taken at the designated monitoring stations when construction works in the relevant Works Sections, designated working area (WA) and stockpiling area (SA) as listed in Table 4.2 is ongoing. The monitoring shall be conducted at least 3 times a week and the interval between two sets of monitoring shall not be less than 36 hours. The parameters to be monitored, the monitoring procedures and equipment shall be the same as the Baseline Monitoring. The Impact Monitoring at a particular Works Section shall not be ceased with the ER, IEC and EPD agreement.
4.7.1.4 The Impact Monitoring schedule shall be issued to IEC and EPD at least one month prior to the commencement of Impact Monitoring.
4.8.1.1 Compliance monitoring will need to be undertaken and the monitoring parameters and frequency will be in accordance with the requirements of the relevant Water Pollution Control Ordinance (WPCO) licence.
4.9.1.1 Surveys of the watercourses shall also be undertaken at least once every week. The surveys shall include a description of the stream course, influencing factors, photographs and a map showing areas of project construction works. As an integral part of the surveys, the ET shall assess and report on the effectiveness of the proposed mitigation measures as part of the construction phase EM&A works and implement modifications and improvements as required.
4.10
Event
and Action Plan
4.10.1.1 The water quality criteria, namely Action and Limit levels, are shown in Table 4.3 below. Should the monitoring results of the water quality parameters at any designated monitoring stations indicate that the water quality criteria are exceeded, the actions in accordance with the Action Plan in Table 4.4 shall be carried out.
4.10.1.2
Any noticeable change to water quality
shall be recorded in the survey reports and shall be investigated and remedial
actions shall be undertaken to reduce impacts. Particular attention shall be
paid to the Contractor’s implementation of the
recommended mitigation measures.
Table 4.3 Action and Limit Levels for Water Quality Monitoring
|
Parameters |
Action (mg/L) |
Limit (mg/L) |
|
DO
in mg/L |
5%-ile
of baseline data |
4mg/L or 1%-ile
of baseline |
|
Suspended
Solids |
95%-ile
of baseline data or 120% of upstream control
station of the same day |
99%-ile
of baseline or 130% of upstream control station of the same day |
|
Turbidity
(Tby) in NTU (depth-averaged) |
95%-ile
of baseline data or 120% of upstream control station of the same day |
99%-ile
of baseline and 130% of upstream control station of the same day |
|
pH |
For
value >7, 95%-ile of baseline data or 110% of upstream control station; For
value <=7, 5%-ile of baseline data
or 80% of upstream control station; |
<6.5
or >8.5 |
Notes:
- For DO,
non-compliance of the water quality limits occurs when monitoring result is
lower than the limits.
- For SS,
non-compliance of the water quality limits occurs when monitoring result is
higher than the limits.
- All the figures
given in the table are used for reference only and the DEP may amend the
figures whenever it is considered necessary.
- For pH, non-compliance
of the water quality limits occurs when monitoring result is unusually extreme
(i.e., too high or too low).
4.10.1.3
The
Independent Environmental Checker (IEC) shall be empowered to audit the
environmental performance of construction, and all aspects of the EM&A
programme, validate and confirm the accuracy of monitoring results, monitoring
equipment, monitoring locations and procedures. If any exceedance occurs, the IEC shall follow the actions stated
in the Event and Action Plan in Table 4.4
Table 4.4 Event and Action Plan for Water Quality Monitoring
|
EVENT |
ACTION |
|||
|
ET(1) |
IEC(1) |
ER(1) |
Contractor |
|
|
Action Level being exceeded
by one sampling day |
1. Repeat in-situ
measurement to confirm findings; 2. Identify source(s)
of impact; 3. Inform the IEC and
the Contractor; 4. Check monitoring
data, all plant, equipment and the Contractor’s working methods; 5. Discuss mitigation
measures with the IEC and the Contractor; 6. Repeat measurement
on next day of exceedance. |
1. Discuss
with the ET and the Contractor on the mitigation measures; 2. Review
proposals on mitigation measures submitted by the Contractor and advise the
ER accordingly; 3. Access
the effectiveness of the implemented mitigation measures. |
1. Discuss with the IEC on the proposed mitigation measures; 2. Make agreement on the mitigation measures to be implemented. |
1. Inform the ER and confirm notification of the non-compliance in
writing; 2. Rectify unacceptable practice; 3. Check all plant and equipment; 4. Consider changes of working methods; 5. Discuss with the ES and the IEC and propose mitigation measures
to the IEC and the ER; 6. Implement the agreed mitigation measures. |
|
Action Level being exceeded
by more than one consecutive sampling days |
1. Repeat in-situ measurement to confirm findings; 2. Identify source(s) of impact; 3. Inform the IEC and the Contractor; 4. Check monitoring data, all plant, equipment and Contractor’s
working methods; 5. Discuss mitigation measures with the IEC and the Contractor; 6. Ensure
mitigation measures are implemented; 7. Prepare to increase the monitoring frequency to daily; 8. Repeat measurement on next day of exceedance. |
1. Discuss with the ET and the Contractor on the mitigation
measures; 2. Review proposals on mitigation measures submitted by the
Contractor and advise the ER accordingly; 3. Access the effectiveness of the implemented mitigation measures. |
Discuss with IEC on the
proposed mitigation measures; Make agreement on the
mitigation measures to be implemented; Access the effectiveness of
the implemented mitigation measures. |
1. Inform the ER and confirm notification of the non-compliance in
writing; 2. Rectify unacceptable practice; 3. Check all plant and equipment; 4. Consider changes of working methods; 5. Discuss with the ES and the IEC and propose mitigation measures
to the IEC and ER within 3 working days; 6. Implement the agreed mitigation measures. |
|
Limit Level being exceeded by
one consecutive sampling day |
1. Repeat in-situ measurement to confirm findings; 2. Identify source(s) of impact; 3. Inform the IEC, the Contractor and the DEP; 4. Check monitoring data, all plant, equipment and the Contractor’s
working methods; 5. Discuss mitigation measures with the IEC, the ER and the Contractor; 6. Ensure mitigation measures are implemented; 7. Increase the monitoring frequency to daily until no exceedance of Limit Level. |
1. Discuss with the ES and the Contractor on the mitigation measures; 2. Review proposals on mitigation measures submitted by the
Contractor and advise the ER accordingly; 3. Access the effectiveness of the implemented mitigation measures. |
1. Discuss with the IEC, the ES and the Contractor on the proposed
mitigation measures; 2. Request the Contractor to critically review the working methods; 3. Make agreement on the mitigation measures to be implemented; 4. Access the effectiveness of the implemented mitigation measures. |
1. Inform the Engineer and confirm notification of the non-compliance
in writing; 2. Rectify unacceptable practice; 3. Check all plant and equipment; 4. Consider changes of working methods; 5. Discuss with the ES, the IEC and the ER and propose mitigation
measures to the IEC and the ER within 3 working days; 6. Implement the agreed mitigation measures. |
|
Limit Level being exceeded by
more than one consecutive sampling days |
1. Repeat in-situ measurement to confirm findings; 2. Identify source(s) of impact; 3. Inform the IEC, the Contractor and DEP; 4. Check monitoring data, all plant, equipment and Contractor’s
working methods; 5. Discuss mitigation measures with the IEC, the ER and the
Contractor; 6. Ensure mitigation measures are implemented; 7. Increase the monitoring frequency to daily until no exceedance of Limit Level for two consecutive days. |
1. Discuss with ET and Contractor on the mitigation measures; 2. Review proposals on mitigation measures submitted by the
Contractor and advise the ER accordingly; 3. Access the effectiveness of the implemented mitigation measures. |
1. Discuss with the IEC, the ES and the Contractor on the proposed
mitigation measures; 2. Request Contractor to critically review the working methods; 3. Make agreement on the mitigation measures to be implemented; 4. Access the effectiveness of the implemented mitigation measures; 5. Consider and instruct, if necessary, the Contractor to slow down
or to stop all or part of the works until no exceedance
of Limit Level. |
1. Inform the ER and confirm notification of the non-compliance in
writing; 2. Rectify unacceptable practice; 3. Check all plant and equipment; 4. Consider changes of working methods; 5. Discuss with the ES, the IEC and the ER and propose mitigation
measures to the IEC and the ER within 3 working days; 6. Implement the agreed mitigation measures; 7. As directed by the ER, slow down or stop all or part of the
construction activities. |
Note (1): ET – Environmental Team, IEC – Independent
Environmental Checker, ER – Engineer’s Representative
4.11
Water
Quality Mitigation Measures
4.11.1.1
The EIA
report has recommended water quality mitigation measures. The Contractor shall
be responsible for implementation of the following measures. The recommended
mitigation measures are summarised in the Environmental Mitigation
Implementation Schedule provided in Appendix A.
Construction Site Run-off and General Construction
Activities
4.11.2.1 In accordance with the Practice Note for Professional Persons on Construction Site Drainage, Environmental Protection Department, 1994 (ProPECC PN 1/94), construction phase mitigation measures shall include the following:
(i) At the establishment of Site Office (SO), works area (WA1 and WA2) and stockpiling areas (SA1, SA2, SA3 and SA4; (see Figures 2.9a-2.9g of the EIA Report), perimeter cut-off drains to direct off-site water around the site should be constructed with internal drainage works and erosion and sedimentation control facilities implemented. Channels (both temporary and permanent drainage pipes and culverts), earth bunds or sand bag barriers should be provided to divert the stormwater to silt removal facilities. The design of the temporary on-site drainage system will be undertaken by the Contractor prior to the commencement of construction.
(ii) Dikes or embankments for flood protection should be implemented around the boundaries of earthwork areas. Temporary ditches should be provided to facilitate the runoff discharge into an appropriate watercourse, through a site/sediment trap. Sediment/silt traps should be incorporated in the permanent drainage channels to enhance deposition rates.
(iii) While ProPECC PN 1/94 requires construction works should be programmed to minimise surface excavation works during rainy seasons (April to September). By the nature of the pipe laying works, it is considered not practicable to avoid excavation works in the wet season as this would substantially affect the overall construction programme. However, for works at areas that directly interface with the existing watercourses, excavation works shall avoid the rainy season as far as possible.
These include Intake A interfacing the stream, Intake B interfacing the U channel, Outfall A interfacing the gabion channel, Intake C/RP3 interfacing the gabion channel and Outfall B/RP4 interfacing Ngong Ping Stream (see Figure 2.9a- 2.9g of the EIA Report). For the works in the above listed areas, an impermeable cofferdam or similar barrier to the level above the stream bank shall be erected to completely enclose these areas before any works are undertaken. This will ensure that any contaminated runoff from the works areas will not get into the ambient watercourses. These barriers shall not be removed until the interfacing works and the relevant upstream connected drains have been completed. All exposed earth areas should be completed and vegetated as soon as possible after the earthworks have been completed, or alternatively, within 14 days of the cessation of earthworks where practicable.
(iv) Exposed slope surfaces should be covered by tarpaulin or other means during the rainy season.
(v) The design of efficient silt removal facilities should be based on the guidelines in Appendix A1 of ProPECC PN 1/94, which states that the retention time for silt/sand traps should be 5 minutes under maximum flow conditions. The sizes may vary depending upon the flow rate, but for a flow rate of 0.1m3/s, a sedimentation basin of 30m3 would be required and for a flow rate of 0.5m3/s the basin would be 150m3. The detailed design of the sand/silt traps should be undertaken by the contractor prior to the commencement of construction.
(vi) The overall slope of works sites should be kept to a minimum to reduce the erosive potential of surface water flows, and all trafficked areas and access roads should be protected by coarse stone ballast. An additional advantage accruing from the use of crushed stone is the positive traction gained during the prolonged periods of inclement weather and the reduction of surface sheet flows.
(vii) All drainage facilities and erosion and sediment control structures should be regularly inspected and maintained to ensure their proper and efficient operation at all times particularly following rainstorms. Deposited silts and grits should be removed regularly and disposed of proper waste receiving facilities. As the area is within the water gathering grounds, on-site disposal of silts/grits shall not be allowed.
(viii) Measures should be taken to minimise the ingress of site drainage into excavations. If the excavation of trenches in wet season is inevitable, they should be dug and backfilled in short sections wherever practicable. The water pumped out from trenches or foundation excavations should be discharged into storm drains via silt removal facilities.
(ix) Manholes (including newly constructed ones) should always be adequately covered and temporarily sealed so as to prevent silt, construction materials or debris being washed into the drainage system and storm runoff being directed into foul sewers;
(x) Precautions to be taken at any time of the year when rainstorms are likely, actions to be taken when a rainstorm is imminent or forecasted and during or after rainstorms, are summarised in Appendix A2 of ProPECC PN 1/94. Particular attention should be paid to the control of silty surface runoff during storm events, especially for areas located near steep slopes;
(xi) All vehicles and plant should be cleaned before leaving a construction site to ensure no earth, mud, debris and the like is deposited by them on roads. An adequately designed and sited wheel washing facilities should be provided at the exit of every construction site where practicable. 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. The section of access road leading to, and exiting from, the wheel-washing bay to public roads should be paved with sufficient backfall toward the wheel-washing bay to prevent vehicle tracking of soil and silty water to public roads and drains.
(xii)
Oil
interceptors should be provided in the drainage system downstream of any
oil/fuel pollution sources. Oil
interceptors should be emptied and cleaned regularly to prevent the release of
oil and grease into the storm water drainage system after accidental
spillage. A bypass should be provided
for oil interceptors to prevent flushing during heavy rain.
(xiii) Stockpiled material shall be
covered by tarpaulin and /or watered as appropriate to prevent windblown dust
and surface run off. Measures should be taken to prevent the washing away of
construction materials, soil, silt or debris into any drainage system.
(xiv) Major stockpiled areas shall be
sited outside of the country parks area (Works Section 6) and away from stream
courses as far as practicable. For the
stockpiling area SA4 within the country park area, stockpiling of earthed
material shall be minimised and excavated soil from Works Section 6 shall be
delivered to the Site Office as soon as possible. Similarly, overnight
stockpiling of earthed material along the exposed trench shall be minimised as
far as possible and the excavated soil shall be transferred to the designated
stockpiling area as soon as possible.
(xv)
The
Contractor shall comply with WSD’s General Conditions for Working within Water
Gathering Grounds as appropriate.
(xvi) The construction solid waste,
debris and rubbish on-site should be collected, handled and disposed of
properly to avoid causing any water quality impacts. The requirements for solid waste management
are detailed in Section 9 of this EIA report.
(xvii) All fuel tanks and chemical and bentonite storage areas should be provided with locks and
sited on sealed areas, within bunds of a capacity equal to 110% of the storage
capacity of the largest tank to prevent spilled fuel oils from reaching the
nearby WSRs.
4.11.2.2
By
adopting the above mitigation measures with best management practices, it is anticipated that the impacts of construction
site runoff will be reduced to an acceptable level.
4.11.2.3
Given
that recommended measures are tried and tested techniques which have been
implemented on other construction site in
4.11.2.4 There is a need to apply to the EPD for a discharge licence for discharge of effluent from the construction site under the WPCO. The discharge quality must meet the requirements specified in the discharge licence. All the runoff and wastewater generated from the works areas should be treated so that it satisfies all the standards listed in the TM-DSS. It should particularly be noted that the TM-DSS specifically prohibits the discharge of the following substances into the inland waters:
· polychlorinated biphenyls (PCB);
· polyaromatic hydrocarbon (PAH);
· fumigant, pesticide or toxicant ;
· radioactive substances ;
· chlorinated hydrocarbons;
· flammable or toxic solvents ;
· petroleum oil or tar;
· calcium carbide;
· wastes liable to form scum, deposits or discoloration;
· sludge or solid refuse of any kind; and
· detergents in Group A inland waters only.
4.11.2.5
The beneficial uses of the
treated effluent for other on-site activities such as dust suppression, wheel washing and general cleaning etc, can minimise water
consumption and reduce the effluent discharge volume and shall be
encouraged. If monitoring of the treated
effluent quality from the works areas is required during the construction phase
of the Project, the monitoring should be carried out in accordance with the
WPCO license.
4.11.2.6 In addition to compliance with the discharge licence requirement, to prevent bank side erosion, the discharge of site effluents shall be either at existing storm drains or artificial channels. No effluent or treated surface runoff shall be allowed to discharge at natural stream course.
Bentonite Slurry
4.11.2.7 The use of bentonite slurries shall be minimised as far as possible. In addition to the requirement of a peripheral bunds and drainage system for the WA4 and SO, where the bentonite slurries will be used, to prevent any accidental release of bentonite slurry from getting into the surrounding environment, the following specific control measures shall be followed to reduce the risk and impacts of accidental spillage:
·
All bentonite
slurry should be stored in a container that resistant to
corrosion, maintained in good conditions and securely closed;
·
The container should be labelled in English and
Chinese and note that the container is for storage of bentonite
slurry only;
·
The storage container should be placed on an area
of impermeable flooring and bunded with capacity to
accommodate 110% of the volume of the container size or 20% by volume stored in
the area and enclosed with at least 3 sides; and
·
Sufficiently covered to prevent rainfall entering the container or bunded area (water collected within the bund must be tested
and disposed of as chemical waste, if necessary).
4.11.2.8 In order to reduce the possibility of frac-out, detailed ground investigation shall be undertaken to evaluate the likelihood of frac-out and if necessary advanced ground treatment applied before the commencement of the pipe jacking works. A member of the Contractor’s site staff shall, also, be dedicated to closely monitor the ground surface above the pipe jacking head for any frac-outs release. The pipe jacking works and application of bentonite shall immediately stop if frac-outs are observed. Any frac-out shall be immediately cleaned or bunded to prevent spreading of the bentonite slurry. The Contractor shall immediately notify the Engineer and propose rectification measures to prevent further frac-out to the satisfaction of the Engineer before pipe jacking works resume. An emergency clean up kit shall be readily available at Works Section 2 and 6 where pipe jacking will be undertaken.
4.11.2.9 The handling and disposal of bentonite slurries should be undertaken in accordance within ProPECC PN 1/94. Surplus bentonite slurries used in construction works shall be reconditioned and reused wherever practicable. Residual bentonite slurry shall be disposed of from the site as soon as possible as stipulated in Clause 8.56 of the General Specification for Civil Engineering Works. The Contractor should explore alternative disposal outlets for the residual bentonite slurry (dewatered bentonite slurry to be disposed to a public filling area and liquid bentonite slurry if mixed with inert fill material to be disposed to a public filling area) and disposal at landfill should be the last resort.
Accidental Spillage of Chemicals
4.11.2.10 The contractor must register as a chemical waste producer if chemical wastes would be produced from the construction activities. The Waste Disposal Ordinance (Cap 354) and its subsidiary regulations in particular the Waste Disposal (Chemical Waste) (General) Regulation should be observed and complied with for control of chemical wastes.
4.11.2.11
Any maintenance facilities
should be located outside Works Section 6 in the
4.11.2.12 Disposal of chemical wastes should be carried out in compliance with the Waste Disposal Ordinance. The Waste Disposal Ordinance (Cap 354) and its subsidiary regulations in particular the Waste Disposal (Chemical Waste) (General) Regulation should be observed and complied with for control of chemical wastes. The Code of Practice on the Packaging, Labelling and Storage of Chemical Wastes published under the Waste Disposal Ordinance details the requirements to deal with chemical wastes. General requirements are given as follows:
· Suitable containers should be used to hold the chemical wastes to avoid leakage or spillage during storage, handling and transport;
· Chemical waste containers should be suitably labelled, to notify and warn the personnel who are handling the wastes, to avoid accidents; and
· Storage area should be selected at a safe location on site and adequate space should be allocated to the storage area.
4.11.2.13
In order to minimise the risk
of accidental spillage, the use and storage of oils/chemicals/waste should be
limited to absolute minimum volume and are to be removed from sites at the
earliest opportunity. However, all
chemical waste, fuels and oils shall be stored at the Site Office (SO), to
minimise impact to the
4.11.2.14 In order to protect against an accidental spillage of fuel or oil, the Contractor will be required to prepare a spill response plan to the satisfaction of AFCD, EPD, FSD, HyD, Police, TD and WSD to define procedures for the control, containment and clean-up of any spillage that could occur on the construction site.
4.11.2.15 At all times, the Contractor shall comply with WSD’s General Conditions for Working within Water Gathering Grounds, as appropriate.
Sewage Wastewater
4.11.2.16 The sewage of the site office will be connected the existing sewer networks and be treated at the Ngong Ping STW. Portable chemical toilets and sewage holding tanks are recommended for the handling of the construction sewage generated by the workforce at other works area. The use of temporary toilets within the water gathering ground, however, is also subject to the approval of WSD. A licensed contractor should be employed to provide appropriate and adequate portable toilets and be responsible for appropriate disposal and maintenance.
Environmental Permit EP-192/2004
4.11.2.17 The Outfall A and Intake C and associated works areas are within the gabion channel, the construction and operation of which was previously governed by the Environmental Permit EP-192/2004. While the EP was surrendered in May 2007, the currently proposed works at these locations shall, also, comply with the specific conditions of the EP (see Section 2.7 of the EIA Report) as far as possible and in particular avoid works in the rainy period between April and September so as to minimise potential water quality pollution to the lowest possible.
4.11.3.1 The all intakes and outfalls of the proposed system shall have weir walls constructed to at least 500mm to ensure the normal flow of existing watercourses is not interrupted. Since Intake C is within the gabion channel, the construction and operation (maintenance desilting works, if any) of both will comply with the Specific Conditions EP-192/2004 unless otherwise approved by the DEP.
4.11.3.2 In order to avoid wastewater being discharged in the existing watercourses during maintenance works, desilting by hydraulic jetting shall be avoided and mechanical scooping / scraping methods are recommended. Desilting or maintenance works shall also be undertaken during the dry season when flow in the watercourse is low. The disposal of the removed silt material shall be properly handled in accordance with the recommendations in Section 9 of the EM&A Manual.