Agreement No. CE 4/2009 (EP)
Environmental Monitoring and Audit
for Contaminated Mud Pit at Sha Chau (2009-2013) - Investigation

 

48TH MONTHLY PROGRESS REPORT FOR CONTAMINATED MUD PITS AT SHA CHAU JUNE 2013

1.1                                      Background

1.1.1                               Since 1992, the East of Sha Chau (ESC) area has been the site of a series of dredged contaminated mud pits (CMPs) designed to provide confined marine disposal capacity for contaminated mud arising from the HKSARs dredging and reclamation projects.  In June 2013, the following works were being undertaken at the CMPs:

P      Capping was being undertaken at CMP IVc; and

P      Disposal of contaminated mud was taking place at CMP Va.

1.1.2                               The Environmental Monitoring and Audit (EM&A) programme for the CMPs at the ESC area presently covers the above operations.

1.2                                      Reporting Period

1.2.1                                This Monthly Progress Report covers the monitoring period of June 2013.

1.3                                      Details of Sampling and Laboratory Testing Activities

1.3.1                               The following monitoring activities have been undertaken for CMP V in June 2013:

P      Pit Specific Sediment Chemistry was conducted for CMP Va on 6 June 2013;

P      Cumulative Impact Sediment Chemistry was conducted for CMP Va on 14 June 2013;

P      Water Column Profiling was scheduled to be undertaken on 18 June 2013.  However, there was no dumping activity at CMP Va while the monitoring team was on-site.  As such, in-situ measurements and water sampling were not undertaken for Water Column Profiling in June 2013.

1.3.2                               A summary of field activities are presented in Annex A.

1.4                                      Details of Outstanding Sampling and / or Analysis

1.4.1                               No outstanding sampling remained and laboratory analyses of Pit Specific Sediment Chemistry conducted in May and June 2013 were yet to be completed during preparation of this monthly report. 

1.5                                      Brief Discussion of the Monitoring Results for CMP V

1.5.1                               Table 1.1 summarises the monitoring results that are presented in the current monthly report.  Brief discussion of the monitoring results is presented in this section.  Detailed discussion will be presented in the corresponding Quarterly Report.

Monitoring activities

Date of Monitoring

Monitoring results presented in this report?

Pit Specific Sediment Chemistry Monitoring for CMP Va

 

23 Apr 2013

 

14 May 2013


 

 

6 June 2013

Yes. 

 

No.  Laboratory analysis yet to be completed during preparation of this monthly report.

 

No.  Laboratory analysis yet to be completed during preparation of this monthly report.

 

Cumulative Impact Sediment Chemistry Monitoring for CMP Va

 

14 June 2013

No.  Laboratory analysis yet to be completed during preparation of this monthly report.

Water Column Profiling for CMP Va

 

18 June 2013

No.  In-situ measurements and water sampling were not undertaken as there was no dumping activity on the monitoring day.

Table 1.1        Monitoring activities in April to June 2013

1.5.2                                Pit Specific Sediment Chemistry of CMP Va V April 2013

1.5.3                               Monitoring locations for Pit Specific Sediment Chemistry for CMP Va are shown in Figure 1.1.  A total of six monitoring stations were sampled in April 2013.  Most contaminants complied with the Lower Chemical Exceedance Level (LCEL) at all stations except for Arsenic, Copper, Mercury and Silver.  Concentrations of Arsenic exceeded the LCEL at Pit Edge station NEDB and Near Pit stations NNDA and NNDB (Figures 1-2 of Annex B).  Concentrations of Copper and Mercury exceeded LCEL at Pit Edge station NEDA while concentration of Silver exceeded LCEL and Upper Chemical Exceedance Level (UCEL) at Active Pit station NPDB and Pit Edge station NEDA, respectively.  It is observed that the variations of metal concentrations at Active Pit Stations and Pit Edge station NEDA were much larger (ie greater standard deviation) when compared to other stations.  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 ([1]).  It is presumed that the natural concentrations of Arsenic are similar in onshore and offshore sediments ([2]), and relatively high Arsenic levels may thus occur throughout Hong Kong.   Therefore, the exceedances of the LCEL for Arsenic are unlikely to be caused by the disposal operations at CMP Va but rather as a result of naturally occurring deposits.  In addition, the Active Pit station NPDB and Pit Edge station NEDA are located within and near the boundary of the CMP Va which was receiving contaminated mud during the reporting period.  As such, the exceedances of LCEL/UCEL for Copper, Mercury and Silver which were recorded at the two stations only are not considered as indicating any dispersal of contaminated mud from CMP Va.  Nevertheless, detailed analysis will be presented in the Quarterly Report to reveal any trend of increasing sediment contaminant concentrations towards CMP Va.

1.5.4                               For organic contaminants, Total Organic Carbon (TOC) concentration was similar amongst all stations (Figure 3 of Annex B).  Tributyltin (TBT) concentration was found to be higher at Active Pit station NPDB and Near Pit station NNDA (Figure 4 of Annex B).  Low Molecular Weigh Polycyclic Aromatics Hydrocarbons (Low MW PAHs) and High Molecular Weight Polycyclic Aromatics Hydrocarbons (High MW PAHs) concentrations were recorded above the limit of reporting at Active Pit station NPDB and Near Pit station NNDA only (Figure 5 of Annex B).  Total Polychlorinated Biphenyls (PCBs), Total Dichloro-diphenyl-trichloroethane (DDT) and 4,4-Dichloro-diphenyl-dichloroethylene (4,4-DDE) were below the limit of reporting at all stations.  The Active Pit station NPDB and Near Pit station NNDA is located within and near the boundary of CMP Va which was receiving contaminated mud during the reporting period.  Therefore, the higher concentrations of contaminants (including metals and organic contaminants) recorded at the two stations only are not considered as indicating any dispersal of contaminated mud from CMP Va.  Nevertheless, detailed analysis will be presented in the Quarterly Report to reveal any trend of increasing sediment contaminant concentrations towards CMP Va.

1.5.5                               Overall, there is no evidence indicating any unacceptable environmental impacts to sediment quality as a result of the contaminated mud disposal operations at CMP Va during this monthly period.  

1.6                                      Activities Scheduled for the Next Month

1.6.1                               The following monitoring activities will be conducted in the next monthly period of July 2013 for CMP V:

P       Pit Specific Sediment Chemistry for CMP Va;

P       Water Column Profiling for CMP Va; and

P       Demersal Trawling for CMP V.

1.6.2                               The sampling schedule is presented in Annex A.

1.7                                      Study Programme

1.7.1                               A summary of the Study Programme is presented in Annex C.


 

 



([1])    Sewell RJ (1999) Geochemical Atlas of Hong Kong. Geotechnical Engineering Office, Government of the Hong Kong Special Administrative Region

([2])    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