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

 

45TH MONTHLY PROGRESS REPORT FOR CONTAMINATED MUD PITS AT SHA CHAU MARCH 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 March 2013, the following works were being undertaken at the CMPs:

P       Capping was being undertaken at CMP IVc;

P       Disposal of contaminated mud was taking place at CMP Va; and

P       Dredging of CMP Vd was in progress.

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 March 2013.

1.3                                      Details of Sampling and Laboratory Testing Activities

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

P      Pit Specific Sediment Chemistry was conducted for CMP Va on 12 March 2013;

P      Impact Water Quality Monitoring during Dredging Operations for CMP Vd were conducted on 16 March 2013; and

P      Water Column Profiling was scheduled to be undertaken on 26 March 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 March 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 March 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.

Table 1.1        Monitoring activities in February / March 2013

Monitoring activities

Date of Monitoring

Monitoring results presented in this report?

Pit Specific Sediment Chemistry Monitoring for CMP Va

 

1 Feb 2013

 

12 Mar 2013


Yes

 

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

 

Cumulative Impact Sediment Chemistry Monitoring for CMP Va

7 Feb 2013

Yes

 

 

 

Impact Water Quality Monitoring during Dredging Operations of CMP Vd

16 Mar 2013

Yes

 

 

 

Water Column Profiling for CMP Va

 

26 Mar 2013

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

1.5.2                                Pit Specific Sediment Chemistry of CMP Va V February 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 February 2013.  Concentrations of Arsenic exceeded the Lower Chemical Exceedance Level (LCEL) at Pit Edge stations NEDA and NEDB and Near Pit stations NNDA and NNDB.  Concentrations of Copper, Mercury and Zinc exceeded the LCEL at Active Pit station NPDA while concentrations of Silver exceeded the Upper Chemical Exceedance Level (UCEL) at Active Pit station NPDA (Figures 1-2 of Annex B).  It is also observed that the variations of metal concentrations at Active Pit Stations 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 slight 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 is located within CMP Va which was receiving contaminated mud during the reporting period.  As such, the exceedances of LCEL/UCEL for Copper, Mercury, Silver and Zinc which were recorded at Active Pit station NPDA only are not considered as indicating any dispersal of contaminated mud from 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), High Molecular Weight Polycyclic Aromatics Hydrocarbons (High MW PAHs) and Low Molecular Weigh Polycyclic Aromatics Hydrocarbons (Low MW PAHs) concentrations were higher at Active Pit stations NPDA when compared to other stations (Figures 4 and 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. As described in Section 1.5.3, the higher concentrations of contaminants (including metals and organic contaminants) recorded at the Active Pit 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.

1.5.6                                Cumulative Impact Sediment Chemistry for CMP Va V February 2013

1.5.7                               Monitoring locations for Cumulative Impact Sediment Chemistry for CMP Va are shown in Figure 1.2.  A total of nine monitoring stations were being sampled.

1.5.8                                Analyses of results for the Cumulative Impact Sediment Chemistry Monitoring indicated that the concentrations of all metals, except Arsenic, were below the LCEL in February 2013 (Figures 6 and 7 of Annex B).  Concentrations of Arsenic in sediments from all stations, except for Near Field station RNB, exceeded the LCEL.  As discussed in Section 1.5.3 above, relatively high natural levels of Arsenic are present in Hong Kongs marine sediments and hence the slight exceedances of the LCEL for the Arsenic do not necessarily indicate any adverse impacts to sediment quality caused by disposal operation at CMP Va.

1.5.9                                The concentration of TOC was similar amongst stations (Figure 8 of Annex B).  TBTs were recorded in sediment samples from all stations except Near Field station RNB and Capped Pit station RCB with a higher concentration recorded in Ma Wan station (Figure 9 of Annex B).  Concentrations of Total DDT, 4,4-DDE, Total PCBs, Low and High MW PAHs were below the limit of detection at all stations. 

1.5.10                           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.

1.5.11                           Impact Water Quality Monitoring during Dredging Operations of CMP Vd V March 2013

1.5.12                            Impact Water Quality Monitoring during Dredging Operations of CMP Vd was conducted on 16 March 2013.  On the survey day, sampling was conducted during both mid-ebb and mid-flood tides at two Reference (Upstream) stations upstream and five Impact (Downstream) stations downstream of the dredging operations at CMP Vd (Figure 1.3).  Monitoring was also conducted at Ma Wan station.  At each station, in-situ measurements of water quality parameters as well as water samples were taken from three depths in the water column (ie surface: 1 m below sea surface, mid-depth and bottom: 1 m above the seabed).  Where water depth was less than 6 m, the mid-depth station was omitted.  If water depth was less than 3 m, only the mid-depth station was monitored.

1.5.13                           Monitoring results are presented in Table C1 of Annex C.  Levels of Dissolved Oxygen (DO), Turbidity and Suspended Solids (SS) complied with the Action and Limit Levels set in the Baseline Monitoring Report ([3]).

1.5.14                           Overall, there appears to be no unacceptable water quality impacts causing by the dredging operations at CMP Vd and no additional measures are thus considered required except for those stated in the Environmental Permit (EP-312/2008).

1.6                                      Activities Scheduled for the Next Month

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

P       Pit Specific Sediment Chemistry for CMP Va;

P       Water Column Profiling for CMP Va; and

P       Impact Water Quality Monitoring during Dredging Operations for CMP Vd.

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 D.


 



([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