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

 

42nd MONTHLY PROGRESS REPORT FOR CONTAMINATED MUD PITS AT SHA CHAU December 2012

 

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 HKSAR’s dredging and reclamation projects.  In December 2012, the following works were being undertaken at the CMPs:

·       Capping was being undertaken at CMP IVc;

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

·       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 December 2012.

1.3                                      Details of Sampling and Laboratory Testing Activities

1.3.1                               The following monitoring activities have been undertaken for CMP V in December 2012:

·       Cumulative Impact Sediment Chemistry was conducted for CMP Va on 3 December 2012;

·       Pit Specific Sediment Chemistry was conducted for CMP Va on 7 December 2012;

·       Impact Water Quality Monitoring during Dredging Operations was conducted for CMP Vd on 14 December 2012; and

·       Water Column Profiling was conducted for CMP Va on 19 December 2012.

 

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 analysis of Pit Specific Sediment Chemistry and Cumulative Impact Sediment Chemistry 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 December 2012

Monitoring activities

Date of Monitoring

Monitoring results presented in this report?

Cumulative Impact Sediment Chemistry Monitoring for CMP Va

 

3 Dec 2012

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

 

Pit Specific Sediment Chemistry Monitoring for CMP Va

 

8 November 2012

 

7 Dec 2012

Yes

 

 

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

 

Impact Water Quality Monitoring during Dredging Operations of CMP Vd

 

14 Dec 2012

Yes

Water Column Profiling for CMP Va

19 Dec 2012

Yes

1.5.2                                Pit Specific Sediment Chemistry of CMP Va – November 2012

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 November 2012.  Concentrations of Arsenic exceeded the Lower Chemical Exceedance Level (LCEL) at Pit-Edge (NEDA and NEDB) and Near-Pit (NNDA) stations while concentrations of Chromium, Mercury and Zinc exceeded the LCEL at Active Pit station (NPDB) (Figures 1-2 of Annex C).  Concentrations of Copper, Nickel and Silver exceeded the UCEL at Active Pit Station (NPDB).  Whilst the average concentration of Arsenic in the Earth’s crust is generally ~2mg/kg, significantly higher Arsenic concentrations (median = 14 mg/kg) have been recorded in Hong Kong’s 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 stations are located within CMP Va which was receiving contaminated mud during the reporting period.  As such, the exceedances of LCEL/UCEL for Chromium, Copper, Mercury, Nickel, Silver and Zinc which were recorded at the Active Pit station only is 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 C).  Tributyltin (TBT) concentration was the highest at Active Pit station NPDB when compared to other stations (Figure 4 of Annex B).  Low Molecular Weigh Polycyclic Aromatics Hydrocarbons (Low MW PAHs) and Total Polychlorinated Biphenyls (PCBs) concentrations were below the limit of reporting except at Active Pit station NPDB (Figure 5 and 6 of Annex B).  High MW PAHs concentrations were below the limit of reporting at all stations except at both Active Pit stations NPDA and NPDB (Figure 5 of Annex B).  Total DDT and 4,4’-DDE were below the limit of reporting at all stations.

1.5.5                               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.

1.5.6                               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.


1.5.7                               Impact Water Quality Monitoring during Dredging Operations of CMP Vd – December 2012

1.5.8                                Impact Water Quality Monitoring during Dredging Operations of CMP Vd was conducted on 14 December 2012.  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 1.2).  Monitoring was also conducted at the 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 is less than 6m the mid-depth station was omitted.  If water depth is less than 3m, only the mid-depth station was monitored.

1.5.9                               Monitoring results are presented in Table B1 of Annex B.  Levels of Dissolved Oxygen (DO), Turbidity and Suspended Solids (SS) generally complied with the Action and Limit Levels set in the Baseline Monitoring Report ([3]).

1.5.10                           Levels of Turbidity exceeded the Action Level in the downstream station DS5 during mid-flood tide.  Station DS5 is located even further away from the works area of CMP Vd than other downstream stations (ie DS1-4) (please refer to Figure 1.2 for the indicative locations of the monitoring stations).  The compliance of Action and Limit Levels at other downstream stations would indicate that the recorded exceedance is unlikely to be caused by the dispersal of suspended sediments from the dredging operations at CMP Vd.  In addition, high turbidity level was occasionally recorded during the baseline monitoring of the EM&A programme.  The high turbidity level is thus considered to be sporadic events and characteristic of water quality in this area of Hong Kong. 

1.5.11                           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).


1.5.12                            Water Column Profiling for CMP Va – December 2012

In-situ Measurements

1.5.13                           Water Column Profiling was undertaken at a total of two sampling stations in December 2012.  The water quality monitoring results for December 2012 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 dry season period (November to March) of 1999-2010 from stations in the Northwestern Water Control Zone, where the CMPs are located.  For Salinity, the average value obtained from the Upstream station was used for the basis as the WQO.  Graphical presentation of the monitoring results is provided in Annex C.

1.5.14                           Analyses of results for December 2012 indicated that levels of Salinity, pH and DO complied with the WQOs at both Upstream and Downstream stations (Figures 7 - 9 of Annex C).  DO and Turbidity complied with the Action and Limit Levels set in the EM&A Manual ([4]).

Laboratory Measurements for Suspended Solids (SS)

1.5.15                           Analyses of data obtained in December 2012 indicated that the SS levels at both Upstream and Downstream stations complied with the WQO (Figure 10 of Annex C).  In addition, SS levels at all stations complied with the Action and Limit Levels set in the EM&A Manual.

1.5.16                           Overall, the results indicated that the mud disposal operation at CMP Va did not appear to cause any deterioration in water quality during this reporting 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 January 2013 for CMP V:

·       Pit Specific Sediment Chemistry for CMP Va;

·       Demersal Trawling for CMP Va;

·       Routine Water Quality Monitoring for CMP Va;

·       Water Column Profiling for CMP Va; and

·       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

([3])        ERM (2009)  Baseline Monitoring Report.  Environmental Monitoring and Audit for Contaminated Mud Pit at Sha Chau (2009-2013) – Investigation. Agreement No. CE 4/2009(EP).  Submitted to EPD in September 2009.

([4])    ERM (2009).  Draft Second Review of the EM&A Manual.  Prepared for CEDD for EM&A for Contaminated Mud Pit at Sha Chau (2009-2013) – Investigation Agreement No. CE 4/2009 (EP).