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

 

37th MONTHLY PROGRESS REPORT FOR CONTAMINATED MUD PITS AT SHA CHAU July 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 July 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

1.2.1                                This Monthly Progress Report covers the reporting month of July 2012.

1.3                                      Details of Sampling and Laboratory Testing Activities

1.3.1                                The following monitoring activities have been undertaken for CMP V in July 2012 and findings from these activities were presented in the current monthly report:

P       Sediment Chemistry after a Major Storm Event was conducted for CMP Va on 6 July 2012;

P       Impact Water Quality Monitoring during Dredging Operations was conducted for CMP Vd on 7 July 2012;

P       Pit Specific Sediment Chemistry was conducted for CMP Va on 9 July 2012;

P       Routine Water Quality Monitoring was conducted for CMP Va on 13 July 2012;

P       Water Column Profiling was conducted for CMP Va on 14 July 2012, and;

P       Demersal Trawling was conducted for CMP Va on 18 and 19 July 2012.

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

1.4                                      Details of Outstanding Sampling and / or Analysis

1.4.1                                No outstanding sampling and laboratory analysis remained from July 2012.

1.5                                      Brief Discussion of the Monitoring Results for CMP V

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

1.5.2                                Sediment Chemistry after a Major Storm Event of CMP Va V July 2012

1.5.3                                Sampling for Sediment Chemistry after a Major Storm Event was conducted on 6 July 2012 after the visit of Tropical Storm Doksuri, which led to the issue of Typhoon Signal No.8 on 29 & 30 June 2012.  A total of nine monitoring stations were being sampled.  The track of Doksuri is shown in Figure 1.1.

Figure 1.1       Track of Severe Typhoon Doksuri from 26 to 30 June 2012 (Source: Hong Kong Observatory)

 

1.5.4                                Concentrations of all metals, except Arsenic, were below the Lower Chemical Exceedance Limit (LCEL) (Figures 1 and 2 of Annex B).  Concentrations of Arsenic in sediments from all stations exceeded LCEL (12 mg/kg), but remained below UCEL (42 mg/kg).  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.    

1.5.5                                Overall, there appeared to be no evidence showing the failure of CMPs in retaining disposed mud or causing contamination of sediments after the major storm event in July 2012.

1.5.6                                Impact Water Quality Monitoring during Dredging Operations of CMP Vd V July 2012

1.5.7                                Impact Water Quality Monitoring during Dredging Operations of CMP Vd was conducted on 7 July 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).

1.5.8                                Monitoring results are presented in Table C1 of Annex C.  Levels of DO, Turbidity and TSS generally complied with the Action and Limit Levels set in the Baseline Monitoring Report ([1]), except for bottom DO level at station DS 3 during the mid-flood tide.  The single case of exceedance recorded at station DS3 is not likely to be caused by the dredging operations at CMP Vd since the bottom DO levels well complied with the Action level at stations closer to dredging operations at CMP Vd (ie DS1 and DS2). 

1.5.9                                Overall, the results indicated that the dredging operations at CMP Vd did not appear to cause any unacceptable deterioration in water quality during this reporting period.  Therefore, no further mitigation measures, except for those recommended in the Environmental Permit (EP-312/2008), are considered required for the dredging operations of CMP Vd.  


1.5.10                            Pit Specific Sediment Chemistry of CMP Va V July 2012

1.5.11                            Monitoring locations for Pit Specific Sediment Chemistry for CMP Va are shown in Figure 1.3.  A total of six monitoring stations were being sampled.  Concentrations of metals at all stations in July 2012 were below the LCEL, with the exception of Arsenic (Figures 4 and 5 of Annex B).  Concentrations of Arsenic exceeded the LCEL at all stations in July 2012.  As discussed in Section 1.5.4 above, 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. 

1.5.12                            For organic contaminants, Total Polychlorinated Biphenyls (PCBs), Low and High Molecular Weight Polycyclic Aromatics Hydrocarbons (Low and High M.W. PAHs) were below the limit of reporting at all stations in July 2012, except at the Active Pit station NPDB.  Total Organic Carbon (TOC) concentration was similar amongst all stations (Figure 6 of Annex B).  TBT concentration was the highest at Active Pit station NPDB in July 2012 when compared to other stations (Figure 7 of Annex B).  Concentrations of 4,4-DDE were higher than the limit of reporting at the Active Pit station NPDB for July 2012, whereas concentrations of DDT were lower than the limit of reporting at all stations. 

1.5.13                            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.

1.5.14                            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.

1.5.15                            Routine Water Quality Monitoring for CMP Va V July 2012

1.5.16                            The results for the Routine Water Monitoring conducted during July 2012 in the wet season have been assessed for compliance with the Water Quality Objectives (WQOs) (please see Figure 1.4 for the monitoring locations).  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.  In-situ monitoring and laboratory results are shown in Tables 1.1 and 1.2 respectively, with graphical presentation provided in Annex B.  Monitoring was undertaken at a total of ten stations in the reporting month.

In-situ Measurements

1.5.17                            Analyses of results for July 2012 indicated that for all stations (Impact, Intermediate and Reference), levels of pH and DO complied with the WQOs (Figures 8-10 of Annex B).  Levels of Salinity exceeded the WQO at all stations, except at Reference station (Figure 11 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 ([2]) (Figures 9, 10, 12 of Annex B).  All in-situ water quality measurements showed relatively minor variations between Impact, Intermediate and Reference stations (Figures 8 to 12 of Annex B). 

Laboratory Measurements 

1.5.18                            Analyses of July 2012 results indicate that majority of metal concentrations (ie Arsenic, Cadmium, Chromium, Mercury and Silver) were below their limit of reporting at all stations.  Copper, Nickel and Zinc were detected in samples from all stations while Lead and Chromium levels were below the limits of reporting at all stations except Ma Wan Station (Figures 13 and 14 of Annex B).  Concentration of Nickel appeared to be similar amongst all stations.  Concentrations of Copper, Lead and Zinc were higher at Ma Wan station.  Levels of 5-day Biochemical Oxygen Demand (BOD5), Total Inorganic Nitrogen (TIN) and NH3-N also appeared to be similar amongst all stations (Figures 15 and 16 of Annex B).  Concentrations of TSS exceed WQO (12.74 mg/L for wet season) at all stations, except at the Reference station while they complied with the Action and Limit Levels at all stations within the reporting month (Figure 17 of Annex B).

Table 1.1     In-situ Monitoring Results for Routine Water Quality Monitoring during July 2012

Stations

Temp

Salinity

Turbidity

pH

Dissolved Oxygen

 

(XC)

 

(NTU)

 

(%)

(mg L-1)

RFE (Reference)

29.26

12.51

5.66

7.55

94.18

6.74

IPE (Impact)

28.47

17.95

4.35

7.46

74.45

5.24

INE (Intermediate)

28.46

17.75

4.23

7.46

73.63

5.19

Ma Wan Station

27.05

23.63

2.95

7.01

57.66

4.02

WQO

N/A

11.26-13.76

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 1.2        Laboratory Results for Routine Water Quality Monitoring during July 2012

Stations

As

Ag

Cd

Cr

Cu

Hg

Pb

Ni

Zn

NH3-N

TIN

BOD5

TSS

RFF

<LOR

<LOR

<LOR

<LOR

1.58

<LOR

<LOR

2.13

12.79

0.02

1.23

1.00

12.33

IPF

<LOR

<LOR

<LOR

<LOR

1.38

<LOR

<LOR

1.92

8.79

0.03

1.03

1.12

16.92

INF

<LOR

<LOR

<LOR

<LOR

1.19

<LOR

<LOR

2.08

10.04

0.03

1.08

0.93

22.29

Ma Wan Station

<LOR

<LOR

<LOR

<LOR

4.25

<LOR

1.56

2.75

51.00

0.03

0.78

1.16

25.13

WQO of TSS

12.74

1.5.19                            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.

1.5.20                            Water Column Profiling for CMP Va V July 2012

In-situ Measurements

1.5.21                            Water Column Profiling was undertaken at a total of two sampling stations in July 2012.  The water quality monitoring results have been assessed for compliance with the WQOs set by EPD as presented in Section 1.5.16 above.  Graphical presentation of the monitoring results is provided in Annex B.

1.5.22                            Analyses of results for July 2012 indicated that levels of Salinity, pH and DO complied with the WQOs at both Upstream and Downstream stations (Figures 18-20 in Annex B).  DO and Turbidity complied with the Action and Limit Levels set in the EM&A Manual ([3]).

Laboratory Measurements for Total Suspended Solids (TSS)

1.5.23                            Analyses of data obtained in July 2012 indicated that the TSS levels at Upstream stations complied with the WQO (Figure 21 in Annex B), but not at Downstream stations.  TSS levels measured in July 2012 complied with the Action and Limit Levels set in the EM&A Manual.

1.5.24                            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.

1.5.25                            Demersal Trawling for CMP Va V July 2012

Abundance and Biomass

1.5.26                            Demersal Trawling was undertaken at a total of six sampling stations in July 2012. The average number of species collected is presented in Table 1.3.  In July 2012, species richness was relatively similar between Impact and Reference stations, except that the lowest mean number of species was recorded in Reference station TNA.

Table 1.3        Summary of the Mean Number of Faunal Species Caught during July 2012 Monitoring

 

Date of Sampling

Impact Stations

Reference Stations

INA       

INB

TNA

TNB       

TSA

TSB

July 2012

48.8

43.8

39.2

50.4

50.8

45.0

1.6                                      Activities Scheduled for the Next Month

1.6.1                                The following monitoring programmes will be conducted in the next monthly period of August 2012:

CMP IV

P       Impact Monitoring during Capping for CMP IVc;

CMP V

P       Pit Specific Sediment Chemistry for CMP Va;

P       Cumulative Impact Sediment Chemistry for CMP Va;

P       Sediment Toxicity Test for CMP Va;

P       Demersal Trawling 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

1.7.1                                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).