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

 

39th MONTHLY PROGRESS REPORT FOR CONTAMINATED MUD PITS AT SHA CHAU September 2012

 

1.1                                      Background

1.1.1                                Since 1992, the East of Sha Chau 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 September 2012, 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      The dredging of CMP Vd was in progress.

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

1.2                                      Reporting Period

This Monthly Progress Report covers the monitoring period of September 2012.

1.3                                      Details of Sampling and Laboratory Testing Activities

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

¡P       Impact Water Quality Monitoring during Dredging Operations was conducted for CMP Vd on 5 September 2012;

¡P       Pit Specific Sediment Chemistry was conducted for CMP Va on 6 September 2012; and

¡P       Water Column Profiling was conducted for CMP Va on 24 September 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 and laboratory analysis remained from September 2012. 

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.  All monitoring data collected for CMP V in September 2012 will be presented in this monthly report.

Table 1.1         Monitoring activities in September 2012

Monitoring activities

Date of Monitoring

Monitoring results presented in this report?

Impact Water Quality Monitoring during Dredging Operations of CMP Vd

5 September 2012

Yes

Pit Specific Sediment Chemistry Monitoring for CMP Va

6 September 2012

Yes

Water Column Profiling for CMP Va

24 September 2012

Yes

1.5.2                                Brief discussion of the monitoring results is presented in this section.  Detailed discussion will be presented in the corresponding Quarterly Report.

1.5.3                                Pit Specific Sediment Chemistry of CMP Va ¡V September 2012

1.5.4                                Monitoring locations for Pit Specific Sediment Chemistry for CMP Va are shown in Figure 1.1.  A total of six monitoring stations were being sampled.  Concentrations of metals at all stations in September 2012 were below the Lower Chemistry Exceedance Level (LCEL), with the exception of Arsenic (Figures 1 and 2 of Annex B).  Concentrations of Arsenic exceeded the LCEL at Active Pit (NPDA), Pit-Edge (NEDA, NEDB) and Near-Pit (NNDA) stations in September 2012.  It is important to note that relatively high natural levels of Arsenic are present in Hong Kong¡¦s marine sediments.  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. 

 

1.5.5                                For organic contaminants, Total Polychlorinated Biphenyls (PCBs), Total DDT and 4,4¡¦-DDE were below the limit of reporting at all stations in September 2012.  Total Organic Carbon (TOC) concentration was similar amongst all stations (Figure 3 of Annex B).  TBT concentration was the highest at Active Pit station NPDB in September 2012 when compared to other stations (Figure 4 of Annex B).  Low and High Molecular Weight Polycyclic Aromatics Hydrocarbons (Low and High M.W. PAHs) were higher than the limit of reporting at the Active Pit station NPDB and Near-Pit station NNDA for September 2012.

1.5.6                                It should be noted that the Action Pit stations are located within CMP Va which were receiving contaminated mud during the reporting month.  Therefore, the higher concentrations of contaminants recorded at the Action Pit stations alone are not considered as indicating any dispersal of contaminated mud from CMP Va and thus not considered as indicating any unacceptable environmental impacts from the mud disposal operations.  Nevertheless, detailed analysis will be presented in the Quarterly Report to reveal any trend of increasing sediment contaminant concentrations towards CMP Va.

1.5.7                                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.

1.5.8                                Impact Water Quality Monitoring during Dredging Operations of CMP Vd ¡V September 2012

1.5.9                                Impact Water Quality Monitoring during Dredging Operations of CMP Vd was conducted on 5 September 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).

1.5.10                            Monitoring results are presented in Table C1 of Annex C.  Levels of Dissolved Oxygen (DO), Turbidity and Total Suspended Solids (TSS) generally complied with the Action and Limit Levels set in the Baseline Monitoring Report ([1]). 

1.5.11                            Levels of Turbidity and TSS exceeded the Limit and Action Levels in the downstream station DS3 during the mid-flood tide, respectively.  Station DS3 is located even further away from the works area of CMP Vd than DS1 and DS2, and the compliance of Action and Limit Levels at other downstream stations (i.e. DS1, 2, 4 and 5) outside the works area would indicate that there is no evidence of any unacceptable adverse water quality impacts arising from the dredging operations of CMP Vd (please refer to Figure 1.2) for the indicative locations of the monitoring stations).

1.5.12                            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).

1.5.13                            Water Column Profiling for CMP Va ¡V September 2012

In-situ Measurements

1.5.14                            Water Column Profiling was undertaken at a total of two sampling stations in September 2012.  The water quality monitoring results have been assessed for compliance with the Water Quality Objectives (WQOs) set by EPD.  This consists of a review of the Environmental Protection Department (EPD) routine water quality monitoring data for the wet season period (April to October) of 1999-2010 from stations in the Northwestern Water Control Zone, where 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 B.

1.5.15                            Analyses of results for September 2012 indicated that levels of Salinity, pH and Dissolved Oxygen (DO) all complied with the WQOs at both Upstream and Downstream stations (Figures 5 ¡V 7 of Annex B).  DO and Turbidity complied with the Action and Limit Levels set in the EM&A Manual ([2]).

Laboratory Measurements for Total Suspended Solids (TSS)

1.5.16                            Analyses of data obtained in September 2012 indicated that the TSS levels at both Upstream and Downstream stations exceeded the WQO (Figure 8 of Annex B).  However, TSS levels measured in September 2012 complied with the Action and Limit Levels set in the EM&A Manual.

1.5.17                            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 programmes will be conducted for CMP V in the next monthly period of October 2012:

¡P          Pit Specific Sediment Chemistry for CMP Va;

¡P          Routine Water Quality Monitoring 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

A summary of the Study Programme is presented in Annex D.

 


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

([2])    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) ¡V Investigation Agreement No. CE 4/2009 (EP).