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 South of The Brothers (SB) and to the East of Sha Chau (ESC) for the disposal of contaminated sediment, and 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. Two Environmental Permits (EPs), EP-312/2008/A and EP-427/2011/A, were issued by the Environmental Protection Department (EPD) to the CEDD, the Permit Holder, on 28 November 2008 and 23 December 2011 for the Dredging, Management and Capping of Contaminated Sediment Disposal Facilities at ESC CMP V and SB CMPs, respectively.
Under the requirements of the two EPs for ESC CMP V and SB CMPs, 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 and SB. 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., The current programme will assess the impacts resulting from dredging, disposal and capping operations of CMP V as well as capping operations of SB CMPs.
A proposal on the change of number of sample replication of water quality & sediment monitoring and 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. 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 May 2021, the following works were undertaken:
● Disposal of contaminated mud at ESC CMP Vb; and
● Capping operations at ESC CMP Vd.
This Monthly EM&A Report for Contaminated Mud Pits to the East of Sha Chau May 2021 covers the EM&A activities for the reporting period of May 2021 (from 1 to 31 May 2021).
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; and
● Pit Specific Sediment Chemistry of ESC CMP Vb.
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; and
· Pit Specific Sediment Chemistry of ESC CMP Vb.
Water Column Profiling was undertaken at a total of two sampling stations (Upstream and Downstream stations) on 5 May 2021. 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 2010 2019 from stations in the North Western Water Control Zone (WCZ), where the ESC CMPs are located. 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).
Analyses of results for May 2021 indicated that levels of Salinity, pH and DO complied with the WQOs at both Downstream and Upstream stations (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).
Analyses of results for May 2021 indicated that the SS levels at both Downstream and Upstream 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.
Routine Water Quality Monitoring of ESC CMPs was undertaken on 6 May 2021. 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 and B4 of Appendix B and Figures 1 to 10 of Appendix C. A total of sixteen (16) monitoring stations were sampled in May 2021 as shown in Figure 2.1
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, Salinity and DO complied with the WQOs at most stations during the reporting period, except for higher levels of Salinity were recorded at Ma Wan station. The higher Salinities recorded at Ma Wan station are likely to be caused by the larger separation distance to Pearl River Delta mouth, which releases a large amount of freshwater runoff in the area during wet season, when compared to the Reference stations.
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 May 2021.
Laboratory analysis of samples obtained during the reporting period indicated that the concentrations of Arsenic, Chromium, Copper, Lead, Nickel and Zinc were detected in the samples at all stations and their concentrations were generally similar across stations, except the concentrations of Zinc were higher at Ma Wan Station (Table B4 of Appendix B; Figure 7 of Appendix C).
For nutrients, concentrations of Total Inorganic Nitrogen (TIN) at the Reference (RFF), Impact (IPF) and Intermediate (INF) stations were higher than the WQO (0.5 mg/L) (Table B4 of Appendix B; Figure 8 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. 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) and Biochemical Oxygen Demand (BOD5) were slightly higher at Ma Wan station in the reporting month (Table B4 of Appendix B; Figure 8 and 9 of Appendix C).
Analyses of results for the reporting period indicated that the SS levels at all stations complied with the wet season WQO (11.8 mg/L) and the Action and Limit Levels (Tables B1 and B4 of Appendix B; Figure 10 of Appendix C).
Overall, results of the Routine Water Quality Monitoring 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 Report to investigate any spatial and temporal trends of potential concern.
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 4 May 2021.
The concentrations of most inorganic contaminants were lower than the Lower Chemical Exceedance Levels (LCELs), except for Arsenic (Figures 11 and 12 of Appendix C). The concentrations of Arsenic were higher than the LCEL at Pit-Edge stations ESC-NECA and ESC-NECB and Active-Pit station ESC-NPCA.
Whilst the average concentration of Arsenic in the Earths crust is generally ~2mg/kg, significantly higher Arsenic concentrations (median = 14 mg/kg) have been recorded in Hong Kongs onshore sediments. It is presumed that the natural concentrations of Arsenic are similar in onshore and offshore sediments, and relatively high Arsenic levels may thus occur throughout Hong Kong. Therefore, the LECL exceedances of Arsenic are unlikely to be caused by the disposal operations at ESC CMP Vb but rather as a result of naturally occurring deposits.
For organic contaminants, the concentrations of Total Organic Carbon (TOC) were higher at Active-Pit station ESC-NPCA during the reporting period (Figure 13 of Appendix C). The concentrations of Low Molecular Weight and High Molecular Weight Polycyclic Aromatic Hydrocarbons (PAHs) were lower than the LECLs at all stations (Figure 14 of Appendix C). The concentrations of Tributyltin (TBT) were higher at Active-Pit stations ESC-NPCA and ESC-NPCB (Figure 15 of Appendix C). The concentrations of 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.
Overall, 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 report to investigate whether there are any unacceptable impacts in the area caused by the contaminated mud disposal.
The following monitoring activities will be conducted in the next reporting period of June 2021 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; and
· Cumulative Impact Sediment Chemistry of ESC CMPs.
A summary of the Study Programme is presented in Appendix D.
 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.
 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.
 Sewell RJ (1999) Geochemical Atlas of Hong Kong. Geotechnical Engineering Office, Government of the Hong Kong Special Administrative Region
 Whiteside PGD (2000) Natural geochemistry and contamination of marine sediments in Hong Kong. In: The Urban Geology of Hong Kong (ed. Page A & Reels SJ). Geological Society of Hong Kong Bulletin No. 6, p109-121