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Agreement No. CE 59/2020 (EP) Environmental Monitoring and Audit for Disposal Facility to the East of Sha Chau (2021- 2026) – Investigation |
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Monthly EM&A Report for Contaminated Mud Pits to the East of Sha
Chau – July 2025 |
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August 2025 |
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Civil Engineering and Development
Department |
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Mott MacDonald 3/F Manulife Place 348 Kwun Tong Road Kwun Tong Kowloon Hong Kong T +852 2828 5757 mottmac.hk |
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Issue and Revision Record
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Revision |
Date |
Originator |
Checker |
Approver |
Description |
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A |
Aug 2025 |
Various |
Sunny Chan |
Thomas Chan |
Revision A of Submission |
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B |
Aug 2025 |
Various |
Sunny Chan |
Thomas Chan |
Revision B of Submission |
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Document reference: |
423134 | 06/05/52 | B |
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Information class: |
Standard |
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This document is issued for the party which
commissioned it and for specific purposes connected with the above-captioned
project only. It should not be relied upon by any other party or used for
any other purpose. We accept no responsibility for the
consequences of this document being relied upon by any other party, or being
used for any other purpose, or containing any error or omission which is due
to an error or omission in data supplied to us by other parties. This document contains confidential
information and proprietary intellectual property. It should not be shown to
other parties without consent from us and from the party which commissioned
it. |
Contents
1.3 Details of Sampling and Laboratory
Testing Activities
1.4 Details of Outstanding Sampling or
Analysis
2
Brief Discussion of Monitoring Results for ESC CMP V
2.2 Water Column Profiling of ESC CMP Vb – in
July 2025
2.2.2 Laboratory Measurements for
Suspended Solids (SS)
2.3 Routine Water Quality Monitoring of ESC
CMPs – in July 2025
2.4 Pit Specific Sediment Chemistry of ESC
CMP Vb – in July 2025
2.5 Sediment Chemistry after a Major Storm of
ESC CMP V – in July 2025
3.1 Activities Scheduled for the Next
Reporting Period
Tables
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Works Schedule for ESC CMP V Works Schedule for ESC CMP V |
Figures
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Routine
& Capping Water Quality Sampling Stations (Flood-Tide) for ESC CMPs |
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Appendices
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1
Introduction
1.1
Background
The
Civil Engineering and Development Department (CEDD) is managing a number of
marine disposal facilities in Hong Kong waters, including the Contaminated Mud
Pits (CMPs) to the East of Sha Chau (ESC) for the disposal of contaminated
sediment, and various open-sea disposal grounds located to the South of Cheung
Chau (SCC), East of Tung Lung Chau (ETLC) and East of Ninepins (ENP) for the
disposal of uncontaminated sediment.
Environmental
Permits (EPs) (Ref. No. EP-312/2008/A) was issued by the Environmental
Protection Department (EPD) to the CEDD, the Permit Holder, on 28 November 2008
for the Project - Disposal of Contaminated Sediment – Dredging, Management and
Capping of Sediment Disposal Facility at Sha Chau.
Under
the requirements of the EP, EM&A programmes which encompass water and
sediment chemistry, fisheries assessment, tissue and whole body analysis,
sediment toxicity and benthic recolonisation studies as set out in the EM&A
Manuals are required to be implemented. EM&A programmes have been
continuously carried out during the operation of the CMPs at ESC. A review of
the collection and analysis of such environmental data from the monitoring
programme demonstrated that there had not been any adverse environmental impacts
resulting from disposal activities.[1],[2] The current programme will assess the
impacts resulting from dredging, disposal and capping operations of CMP V.
A
proposal on the change of number of sample replication of water quality and
sediment monitoring as well as combination of routine water quality monitoring
and water quality monitoring during capping operation was submitted to EPD and
agreed by EPD on 3 December 2020. The proposed changes have been effective for
the EM&A activities since December 2020. In early 2022, after implementing
the Phase 1 optimisation for at least one year, a further data review was
conducted. The monitoring data has been reviewed and demonstrated that the data
robustness and representativeness are maintained. Therefore, a technical note
presenting the data review results served as a supplementary information was
submitted to EPD and presented that Phase 2 optimization of sample replication
of water quality and sediment monitoring for the Project will be implemented in
2022. EPD expressed no comment on the review and note the implementation of
Phase 2 optimization of sample replication on 18 May 2022, and thus this
optimization has been effective for the EM&A activities since July 2022.
The
latest sampling schedule is provided in Appendix
A.
The
present EM&A programme under Agreement No. CE 59/2020 (EP) covers the
dredging, disposal and capping operations of the ESC CMP V (see Appendix
A for the EM&A programme.) Detailed works schedule for ESC CMP V is
shown in Table 1.1. In July 2025, the following
works were undertaken:
● Capping
operations at ESC CMP Vd.
Table
1.1: Works Schedule for ESC CMP V
%20Jul%202025_Rev%20B_files/Table1-1%20Works%20Schedule%20for%20ESC%20CMP%20V.JPG){kind=link}
1.2
Reporting Period
This Monthly EM&A Report for Contaminated Mud
Pits to the East of Sha Chau – July 2025 covers the EM&A
activities for the reporting period of July 2025 (from 1 to 31 July 2025).
1.3
Details of
Sampling and Laboratory Testing Activities
The
following monitoring activities were undertaken for ESC CMP V during the
reporting period:
● Water Column Profiling of ESC CMP Vb;
● Routine Water Quality Monitoring of
ESC CMPs;
● Pit Specific Sediment Chemistry of ESC
CMP Vb;
● Demersal Trawling for ESC CMPs; and
● Sediment Chemistry after a Major Storm
of ESC CMP V.
1.4
Details of
Outstanding Sampling or Analysis
No
outstanding sampling remained for the reporting month (July 2025). The
following analyses are in progress and will be presented in the corresponding
quarterly report:
● Species identification of the biota
samples collection from Demersal Trawling for ESC CMPs in July 2025.
2
Brief Discussion of Monitoring
Results for ESC CMP V
2.1
Introduction
This
section presents a brief discussion of the results obtained from the following
monitoring activities for ESC CMP V during the reporting period:
● Water
Column Profiling of ESC CMP Vb;
● Routine
Water Quality Monitoring of ESC CMPs;
● Pit
Specific Sediment Chemistry of ESC CMP Vb;
● Demersal Trawling for ESC CMPs; and
● Sediment Chemistry after a Major Storm
of ESC CMP V.
2.2
Water Column
Profiling of ESC CMP Vb – in July 2025
Water
Column Profiling was undertaken at a total of two sampling stations (Upstream
and Downstream stations) on 4 July 2025. The monitoring results have been
assessed for compliance with the Water Quality Objectives (WQOs) set by
Environmental Protection Department (EPD). This consists of a review of the EPD
routine water quality monitoring data for the wet season period (April to
October) of 2015 – 2024 from stations in the North Western Water Control Zone
(WCZ), where the ESC CMPs are located.[3]
For Salinity, the averaged value obtained from the Reference (Upstream) station
was used for the basis as the WQO. Levels of Dissolved Oxygen (DO) and
Turbidity were also assessed for compliance with the Action and Limit Levels
(see Table B1 of Appendix
B for details).
2.2.1
In-situ Measurements
Analyses
of results for July 2025 indicated that levels of Salinity, pH and DO complied
with the WQOs at both Downstream and Upstream stations in July 2025. (Table
B2 of Appendix
B). Levels of DO and Turbidity at all stations complied with the
Action and Limit Levels (Tables B1 and B2 of Appendix
B).
2.2.2
Laboratory Measurements for Suspended Solids (SS)
Analyses
of results for July 2025 indicated that the SS level at both Upstream and
Downstream stations complied with the WQO and the Action and Limit Levels. (Tables
B1 and B2 of Appendix
B).
Overall,
the monitoring results indicated that the mud disposal operation at ESC CMP Vb
did not appear to cause any deterioration in water quality during this
reporting period.
2.3
Routine Water Quality Monitoring of ESC CMPs – in July 2025
Routine
Water Quality Monitoring of ESC CMPs was undertaken on 3 July 2025. The
monitoring results have been assessed for compliance with the WQOs (see Section
2.2 above for details). The monitoring results are shown in Tables B3,
B4 and B5 of Appendix
B and Figures 1 to 11 of Appendix
C. A total of ten (10) monitoring stations were sampled in July 2025 as
shown in Figure
2.1.
2.3.1
In-situ Measurements
Graphical
presentation of the monitoring results (Temperature, DO, pH, Salinity and
Turbidity) is shown in Figures 1 to 6 of Appendix
C. Analyses of results indicated that the levels of pH, and DO complied
with the WQOs at all stations in July 2025, except for higher levels of
Salinity were recorded at Ma Wan station.
The
levels of DO and Turbidity complied with the Action and Limit Levels at all
stations (Table B3 of Appendix
B; Figures 3 and 6 of Appendix
C).
Overall,
in-situ measurement results of the Routine Water Quality Monitoring
indicated that the disposal and capping operation at ESC CMPs did not appear to
cause any unacceptable impacts in water quality in July 2025.
2.3.2
Laboratory Measurements
Laboratory
analysis of samples obtained in July 2025 indicated that the
concentrations of Arsenic, Cadmium, Chromium, Copper, Lead, Mercury, Nickel and
Zinc were detected in the samples at some/ all stations and their
concentrations were generally similar across stations; except the concentration
of Cadmium were only detected at Reference (RFF), Impact (IPF) and Intermediate
(INF) stations; the concentration of Lead were only detected at Impact (IPF)
and Intermediate (INF) stations; the concentration of Silver was only detected
at Impact (IPF) station; and the concentration of Zinc were higher at
Intermediate (INF) station. (Table B4 of Appendix
B; Figure 7 and 8 of Appendix
C).
For
nutrients, concentrations of Total Inorganic Nitrogen (TIN) were higher than
the WQO (0.5 mg/L) at all stations. (Table B5 of Appendix
B; Figure 9 of Appendix
C). It should be noted that due to the effect of the Pearl River, the
North Western WCZ has historically experienced higher levels of TIN. [4]. Therefore, the exceedances of TIN WQO at
these stations are unlikely to be caused by the disposal operation at ESC CMPs.
The concentrations of Ammonia Nitrogen (NH3-N) were below limit of reporting at
Reference (RFF), Impact (IPF) and Intermediate (INF) stations; while the
concentrations of Biochemical Oxygen Demand (BOD5) were similar across all
stations. (Table B5 of Appendix
B; Figure 9 and 10 of Appendix
C)
Analyses
of results for the reporting period indicated that the SS levels complied with
the wet season WQO (12.0 mg/L) and Action and Limit Levels at all stations. (Tables
B1 and B5 of Appendix
B; Figure 11 of Appendix
C).
Based
on the available results of the Routine Water Quality Monitoring which
indicated that the disposal and capping operation at ESC CMPs did not appear to
cause any unacceptable deterioration in water quality during the reporting
period. Detailed statistical analysis will be presented in the Quarterly
EM&A Report to investigate any spatial and temporal trends of potential
concern.
2.4
Pit Specific Sediment Chemistry of ESC CMP Vb – in July 2025
Monitoring
locations for Pit Specific Sediment Chemistry for ESC CMP Vb are shown in Figure
2.2. A total of six (6) monitoring stations were sampled on 2 July
2025.
The
concentrations of most inorganic contaminants were lower than the Lower
Chemical Exceedance Levels (LCELs) at all stations, except for Copper and
Silver at Active-Pit stations. The concentrations of Copper were higher than
the LCEL at Active-Pit stations ESC-NPCA. The concentrations of Silver were
higher than the LCEL at Active-Pit stations ESC-NPCA. (Figures 12 and 13 of
Appendix
C)
Considering
that the higher levels of Copper and Silver occurred within Active-Pit station
only but not at the Pit-Edge and Near-Pit stations, there is no evidence
indicating any unacceptable environment impacts to sediment quality as a result
of the contaminated mud disposal operation at ESC CMP Vb in July 2025.
For
organic contaminants, the concentrations of Total Organic Carbon (TOC) were
higher at Active-Pit stations ESC-NPCA and ESC-NPCB. (Figure 14 of Appendix
C). The concentrations of Low Molecular Weight Polycyclic Aromatic
Hydrocarbons (PAHs) were higher than LCEL at Pit-Edge station ESC-NECA. (Figure
15 of Appendix
C)
For
High Molecular Weight Polycyclic Aromatic Hydrocarbons (PAHs), the
concentrations were higher than LCEL at Pit-Edge station ESC-NECA. (Figure
15 of Appendix
C)
The
concentration of Tributyltin (TBT), Total Polychlorinated Biphenyls (PCBs),
Total dichloro-diphenyl-trichloroethane (DDT) and
4,4’-dichlorodiphenyldichloroethylene (DDE) were below the limit of reporting
at all stations during the reporting period.
It
is observed that the elevated level concentration of Low Molecular Weight PAHs
and High Molecular Weight PAHs (i.e. higher than LCEL) only occurred at
Pit-Edge station ESC-NECA, but the concentrations of other organic and all
inorganic contaminants were lower than the LCELs at the Pit-Edge stations.
The
slightly elevated level of Low Molecular Weight PAH and High Molecular Weight
PAH at Pit-Edge station are possible induced by external factors rather than
disposal operations. Therefore, there is no evidence indicating any
unacceptable environmental impacts to sediment quality outside the pit area as
a result of the contaminated mud disposal operations at ESC CMP Vb during the
reporting period.
Therefore,
there is no evidence indicating any unacceptable environmental impacts to
sediment quality outside the pit area as a result of the contaminated mud
disposal operations at ESC CMP Vb during the reporting period.
Statistical
analysis will be undertaken and presented in the corresponding Quarterly
EM&A Report to investigate whether there are any unacceptable impacts in
the area caused by the contaminated mud disposal.
2.5
Sediment Chemistry after a Major Storm of ESC CMP V – in July 2025
Sampling
for Sediment Chemistry after a Major Storm Event was conducted at nine (9)
monitoring stations (see Figure
2.3 for the locations of the monitoring stations) on 22 July 2025 after
the visit of tropical cyclone Wipha, which led to the issue of No. 10 Hurricane
Signal on 20 July 2025.The track of Wipha is shown in Figure
2.4.
Figure 2.4: Track of Tropical Cyclone
Wipha (Source: Hong Kong Observatory)
%20Jul%202025_Rev%20B_files/image005.jpg)
Analyses
of results for the Sediment Chemistry after a Major Storm indicated that the
concentrations of all inorganic contaminants were below the LCEL in July 2025. (Figures 16 and 17 of Appendix
C).
Overall,
there appeared to be no evidence showing the failure of ESC CMP V in retaining
disposed mud or causing contamination of sediments after the major storm event
in July 2025.
3
Future Key Issues
3.1
Activities Scheduled for the Next Reporting Period
The following monitoring activities will be conducted
in the next reporting period
of August 2025 for ESC CMP V (see Appendix
A for the sampling schedule):
● Water
Column Profiling of ESC CMP Vb;
● Routine
Water Quality Monitoring of ESC CMPs;
● Pit Specific Sediment Chemistry of ESC
CMP Vb;
● Cumulative Impact Sediment Chemistry
of ESC CMP Vb;
● Sediment Toxicity Tests of ESC CMPs;
and
● Demersal Trawling for ESC CMPs.
3.2
Study Programme
A
summary of the Study Programme is presented in Appendix
D.
[1] ERM (2013) Final Report. Submitted under
Agreement No. CE 4/2009 (EP) Environmental Monitoring and Audit for
Contaminated Mud Pit at East Sha Chau. For CEDD.
[2] ERM (2017) Final Report. Submitted under
Agreement No. CE 23/2012 (EP) Environmental Monitoring and Audit for
Contaminated Mud Pits to the South of The Brothers and at East Sha Chau (2012 -
2017). For CEDD.
[4]
https://www.epd.gov.hk/epd/sites/default/files/epd/english/environmentinhk/water/hkwqrc/files/waterquality/annual-report/marinereport2005.pdf