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

 

40th MONTHLY PROGRESS REPORT FOR CONTAMINATED MUD PITS AT SHA CHAU October 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 HKSARs dredging and reclamation projects.  In October 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 October 2012.

1.3                                      Details of Sampling and Laboratory Testing Activities

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

P       Water Column Profiling was conducted for CMP Va on 8 October 2012;

P       Pit Specific Sediment Chemistry was conducted for CMP Va on 24 October 2012;

P       Impact Water Quality Monitoring during Dredging Operations was conducted for CMP Vd on 25 October 2012; and

P       Routine Water Quality Monitoring was conducted for CMP Va on 26 October 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 October 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 October 2012 will be presented in this monthly report.

Table 1.1         Monitoring activities in October 2012

Monitoring activities

Date of Monitoring

Monitoring results presented in this report?

Water Column Profiling for CMP Va

8 October 2012

Yes

Pit Specific Sediment Chemistry Monitoring for CMP Va

24 October 2012

Yes

Impact Water Quality Monitoring during Dredging Operations of CMP Vd

25 October 2012

Yes

Routine Water Quality Monitoring for CMP Va

26 October 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 October 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 October 2012 were below the Lower Chemistry Exceedance Level (LCEL), with the exception of Arsenic, Copper and Silver (Figures 1 and 2 of Annex B).  Concentrations of Arsenic exceeded the LCEL at Pit-Edge (NEDA, NEDB) and Near-Pit (NNDA) stations while concentrations of Copper and Silver exceeded the LCEL at Active Pit (NPDB) station.  It is important to note that relatively high natural levels of Arsenic are present in Hong Kongs 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.  In addition, the Active Pit station is located within CMP Va which was receiving contaminated mud during the reporting period.  Therefore, the exceedances of LCEL for Copper and Silver which were recorded at the Active Pit station alone is not considered as indicating any dispersal of contaminated mud from CMP Va.

 

1.5.5                                For organic contaminants, Total Polychlorinated Biphenyls (PCBs), Low Molecular Weight Polycyclic Aromatics Hydrocarbons (Low M.W. PAHs), Total DDT and 4,4-DDE were below the limit of reporting at all stations in October 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 October 2012 when compared to other stations (Figure 4 of Annex B).  High Molecular Weight Polycyclic Aromatics Hydrocarbons (High M.W. PAHs) were higher than the limit of reporting at the Active Pit stations NPDA and NPDB for October 2012.

1.5.6                                As described in Section 1.5.4, 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 October 2012

1.5.9                                Impact Water Quality Monitoring during Dredging Operations of CMP Vd was conducted on 25 October 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) complied with the Action and Limit Levels set in the Baseline Monitoring Report ([1]). 

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 V October 2012

In-situ Measurements

1.5.13                            Water Column Profiling was undertaken at a total of two sampling stations in October 2012.  The water quality monitoring results for October 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 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.

1.5.14                            Analyses of results for October 2012 indicated that levels of Salinity, pH and 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)

1.5.15                            Analyses of data obtained in October 2012 indicated that the TSS levels at Upstream station exceeded the WQO (Figure 8 of Annex B).  However, TSS levels at all stations measured in October 2012 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.

1.5.17                            Routine Water Quality Monitoring for CMP Va V October 2012

1.5.18                            The results for the Routine Water Quality Monitoring conducted during October 2012 in the wet season have been assessed for compliance with the WQOs set by EPD as presented in Section 1.5.13 above (please see Figure 1.3 for the monitoring locations).  In-situ monitoring and laboratory results are shown in Table 1.2 and 1.3 respectively, with graphical presentation provided in Annex B.  Monitoring was undertaken at a total of sixteen stations in the reporting month.

In-situ Measurements

1.5.19                            Analyses of results for October 2012 indicated that for all stations (Impact, Intermediate and Reference), levels of pH and DO complied with the WQOs (Figures 9-11 of Annex B).  Levels of Salinity complied with WQO at all stations, except at Ma Wan station (Figure 12 of Annex B).  Levels of DO and Turbidity within the reporting month complied with the Action and Limit Levels set in the EM&A Manual ([3]) (Figures 10 and 13 of Annex B).  All in-situ water quality measurements showed relatively minor variations between Impact, Intermediate and Reference stations (Figures 9 to 13 of Annex B). 

Laboratory Measurements

1.5.20                            Analyses of October 2012 results indicate that concentrations of Cadmium, Mercury and Silver were below their limit of reporting at all stations.  Arsenic, Copper, Lead, Nickel and Zinc were detected in samples from all stations while Chromium levels were below the limits of reporting at Ma Wan Station (Figures 14 and 15 of Annex B).  Concentrations of Arsenic, Copper, Lead and Nickel appeared to be similar amongst all stations while concentration of Zinc was highest at Ma Wan station.  Levels of 5-day Biochemical Oxygen Demand (BOD5), Total Inorganic Nitrogen (TIN) and NH3-N were similar among all stations (Figures 16 and 17 of Annex B).  Concentrations of TSS exceed WQO (12.74 mg/L for wet season) at Intermediate Stations while all of them complied with the Action and Limit Levels at all stations within the reporting month (Figure 18 of Annex B).

Table 1.2     In-situ Monitoring Results for Routine Water Quality Monitoring during October 2012

Stations

Temp

Salinity

Turbidity

pH

Dissolved Oxygen

 

(XC)

 

(NTU)

 

(%)

(mg L-1)

RFE (Reference)

26.83

27.78

6.15

7.85

83.11

5.68

IPE (Impact)

26.73

28.49

4.60

7.92

87.59

5.98

INE (Intermediate)

26.68

28.48

4.62

7.88

89.42

6.11

Ma Wan Station

26.71

31.14

3.75

7.95

88.26

5.94

WQO

N/A

25.00-30.55

N/A

6.5-8.5

N/A

>4

Note: #   Not exceeding 10% of natural ambient level which is the result obtained from the Reference Station.

Table 1.3        Laboratory Results for Routine Water Quality Monitoring during October 2012

Stations

As

(µg/L)

Ag

(µg/L)

Cd

(µg/L)

Cr

(µg/L)

Cu

(µg/L)

Hg

(µg/L)

Pb

(µg/L)

Ni

(µg/L)

Zn

(µg/L)

NH3-N

(mg/L)

TIN

(mg/L)

BOD5

(mg/L)

TSS

(mg/L)

RFE

1.88

<LOR

<LOR

0.81

4.98

<LOR

0.59

2.98

8.40

0.07

0.73

0.82

8.93

IPE

1.95

<LOR

<LOR

0.65

4.43

<LOR

0.93

2.88

10.30

0.05

0.60

1.29

10.68

INE

1.98

<LOR

<LOR

0.64

4.55

<LOR

0.51

2.08

7.38

0.04

0.58

0.94

13.03

Ma Wan Station

1.75

<LOR

<LOR

<LOR

6.25

<LOR

1.44

2.63

15.50

0.04

0.38

0.93

11.75

WQO of TSS

12.74

1.5.21                            Overall, the results indicated that the 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 in the next monthly period of November 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).

([3])   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).