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

 

46TH MONTHLY PROGRESS REPORT FOR CONTAMINATED MUD PITS AT SHA CHAU APRIL 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 April 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 April 2013.

1.3                                      Details of Sampling and Laboratory Testing Activities

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

P         Routine Water Quality Monitoring was conducted for CMP Va on 9 April 2013;

P         Water Column Profiling was scheduled to be undertaken on 11 April 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 April 2013.

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

P         Pit Specific Sediment Chemistry was conducted for CMP Va on 23 April 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 April 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 March / April 2013

Monitoring activities

Date of Monitoring

Monitoring results presented in this report?

Pit Specific Sediment Chemistry Monitoring for CMP Va

 

12 Mar 2013

 

23 Apr 2013


Yes

 

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

 

Impact Water Quality Monitoring during Dredging Operations of CMP Vd

16 Apr 2013

Yes

 

 

 

Water Column Profiling for CMP Va

 

11 Apr 2013

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

 

 

 

Routine Water Quality Monitoring for CMP Va

9 Apr 2013

Yes

1.5.2                                Pit Specific Sediment Chemistry of CMP Va V March 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 March 2013.  Most contaminants complied with the Lower Chemical Exceedance Level (LCEL) at all stations except Arsenic.  Concentrations of Arsenic exceeded the LCEL at Pit Edge stations NEDA and NEDB and Near Pit station NNDA (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 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. 

1.5.4                               For organic contaminants, Total Organic Carbon (TOC) concentration was similar amongst all stations (Figure 3 of Annex B).  Tributyltin (TBT) concentration was found to be higher at Active Pit station NPDA and Near Pit station NNDA (Figure 4 of Annex B).  Low Molecular Weigh Polycyclic Aromatics Hydrocarbons (Low MW PAHs) and High Molecular Weight Polycyclic Aromatics Hydrocarbons (High MW PAHs) concentrations were recorded above the limit of reporting at Active Pit stations NPDA and NPDB only (Figure 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.  The Active Pit station is located within CMP Va which was receiving contaminated mud during the reporting period.  Therefore, 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                                Impact Water Quality Monitoring during Dredging Operations of CMP Vd V April 2013

1.5.7                                Impact Water Quality Monitoring during Dredging Operations of CMP Vd was conducted on 16 April 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 1.2).  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.

1.5.8                               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]).

1.5.9                               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).

1.5.10                            Routine Water Quality Monitoring for CMP Va V April 2013

1.5.11                           The results for the Routine Water Quality Monitoring conducted during April 2013 in the wet season 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 (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.  In-situ monitoring and laboratory results are shown in Tables 1.2 and 1.3, respectively, with graphical presentation provided in Annex B.  Monitoring was undertaken at a total of 16 stations in the reporting month (see Figure 1.3).

In-situ Measurements

1.5.12                           Analysis of results for April 2013 indicated that for all stations (Impact, Intermediate, Reference and Ma Wan), levels of pH and DO complied with the WQOs (Figures 6-8 of Annex B).  Levels of Salinity complied with the WQO at all stations, except at Ma Wan Station (Figure 9 of Annex B).   The higher salinity recorded at Ma Wan station is likely to be caused by its greater separation distance from the Pearl River mouth, which is a key source of freshwater inputs in the area, when compared to the Reference stations.  Levels of DO and Turbidity within the reporting month complied with the Action and Limit Levels set in the EM&A Manual ([4]) (Figures 7 and 10 of Annex B).  All in-situ water quality measurements showed relatively minor variations amongst Impact, Intermediate and Reference stations (Figures 6-10 of Annex B).

Laboratory Measurements

1.5.13                            Analyses of April 2013 results indicate that concentrations of Cadmium, Mercury and Silver were below their limit of reporting at all stations.  Arsenic, Copper, Nickel and Zinc were detected in samples from all stations while Chromium and Lead were recorded in samples from Impact stations only.  Concentrations of Arsenic, Chromium, Lead and Nickel appeared to be similar amongst all stations while concentrations of Copper and Zinc were slightly higher at Impact stations (Figures 11 and 12 of Annex B).  Levels of 5-day Biochemical Oxygen Demand (BOD5), Total Inorganic Nitrogen (TIN) and NH3-N were similar amongst all stations (Figures 13 and 14 of Annex B).  Concentrations of SS complied with the WQO (12.74 mg/L for wet season) and Action and Limit Levels at all stations during the reporting month (Figure 15 of Annex B).

1.5.14                            Overall, the results indicated that the disposal operation at CMP Va did not appear to cause any unacceptable deterioration in water quality during this reporting period.


Table 1.2        In-situ Monitoring Results for Routine Water Quality Monitoring of CMP Va in April 2013

Stations

Temp

Salinity

Turbidity

pH

Dissolved Oxygen

 

(XC)

 

(NTU)

 

(%)

(mg L-1)

RFE (Reference)

20.09

27.33

6.14

7.76

89.59

6.92

IPE (Impact)

19.95

28.38

7.70

7.79

91.60

7.05

INE (Intermediate)

19.87

28.69

6.66

7.80

93.07

7.16

Ma Wan Station

19.98

30.40

4.35

7.77

90.71

6.90

WQO

N/A

24.60-30.06#

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 of CMP Va in April 2013

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)

SS

(mg/L)

RFE

1.20

<LOR

<LOR

<LOR

5.55

<LOR

<LOR

3.08

6.33

0.27

0.83

1.22

8.40

IPE

1.43

<LOR

<LOR

0.58

9.35

<LOR

0.94

2.98

12.55

0.24

0.71

1.17

10.68

INE

1.13

<LOR

<LOR

<LOR

9.08

<LOR

<LOR

2.40

8.45

0.22

0.64

0.96

8.50

Ma Wan Station

1.00

<LOR

<LOR

<LOR

7.88

<LOR

<LOR

2.00

9.63

0.17

0.45

1.06

7.25

 

WQO of SS: 12.74mg/L

Note: LOR = Limit Of Reporting

 

1.6                                      Activities Scheduled for the Next Month

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

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

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

 

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