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

 

38th MONTHLY PROGRESS REPORTFOR CONTAMINATED MUD PITS AT SHA CHAU August 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 August 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 August 2012.

1.3                                      Details of Sampling and Laboratory Testing Activities

1.3.1                                The following monitoring activities have been undertaken for CMP Va in August 2012:

P          Sediment Chemistry after a Major Storm Event was conducted for CMP Va on 1 and 22 August 2012;

P          Pit Specific Sediment Chemistry was conducted for CMP Va on 10 August 2012;

P          Water Column Profiling was conducted for CMP Va on 13 August 2012,

P          Demersal Trawling was conducted for CMP Va on 15 and 16 August 2012

P          Routine Water Quality Monitoring was conducted for CMP Va on 20 August 2012;

P          Sediment Toxicity Test was conducted for CMP Va on 24 August 2012;

P          Cumulative Impact Sediment Chemistry was conducted for CMP Va on 27 August 2012, and

P          Impact Water Quality Monitoring during Dredging Operations was conducted for CMP Vd on 29 August 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 August 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 August 2012 will be presented in this monthly report.

Table 1.1         Monitoring activities in August 2012

Monitoring activities

Date of Monitoring

Monitoring results presented in this report?

Sediment Chemistry after a Major Storm Event for CMP Va

1 and 22 August 2012

Yes

Pit Specific Sediment Chemistry Monitoring for CMP Va

10 August 2012

Yes

Water Column Profiling for CMP Va

13 August 2012

Yes

Demersal Trawling for CMP Va

15 and 16 August 2012

Yes

Routine Water Quality Monitoring for CMP Va

20 August 2012

Yes

Sediment Toxicity Test

24 August 2012

Yes

Cumulative Impact Sediment Chemistry Monitoring for CMP Va

27 August 2012

Yes

Impact Water Quality Monitoring during Dredging Operations of CMP Vd

29 August 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                                Sediment Chemistry after a Major Storm Event of CMP Va V 1 August and 22 August 2012

1.5.4                                Samplings for Sediment Chemistry after Major Storm Events were conducted on 1 August and 22 August 2012 after the visit of Tropical Storms Vincente and Kai-tak, which led to the issue of Typhoon Signal No. 10 on 23 & 24 July 2012 and Typhoon Signal No. 8 on 16 August 2012 respectively.  A total of nine monitoring stations were being sampled.  The tracks of Vincente and Kai-tak are shown in Figures 1.1 and 1.2.

Figure 1.1       Track of Typhoon Vicente from 20 to 25 July 2012 (Source: Hong Kong Observatory)

Figure 1.2       Track of Typhoon Kai-tak from 12 to 18 August 2012 (Source: Hong Kong Observatory)

Track of Kai-tak (1213) for 12 - 18 August 2012

1.5.5                                Concentrations of all metals, except Arsenic, were below the Lower Chemical Exceedance Limit (LCEL) (Figures 1-2 and 5-6 of Annex B) on both 1 and 22 August 2012.  Concentrations of Arsenic in sediments exceeded LCEL (12 mg/kg) at most of the stations, but remained below Upper Chemical Exceedance Limit (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 storm events and disposal operations at CMP Va but rather as a result of naturally occurring deposits. 

1.5.6                                Overall, there appeared to be no evidence of showing the failure of CMP Va in retaining disposed mud or causing contamination of sediments after the major storm events in August 2012.

1.5.7                                Pit Specific Sediment Chemistry of CMP Va V August 2012

1.5.8                                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 August 2012 were below the LCEL, with the exception of Arsenic (Figures 8 and 9 of Annex B).  Concentrations of Arsenic exceeded the LCEL at Pit-Edge (NEDB) and Near-Pit (NNDA) stations in August 2012.  As discussed in Section 1.5.5 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. 

1.5.9                                For organic contaminants, Total Polychlorinated Biphenyls (PCBs), 4,4-Dichlorodiphenyldichloroethylene (4,4-DDE) and total Dichlorodiphenyl-trichloroethane (DDT) were below the limit of reporting at all stations in August 2012.  Levels of Low and High Molecular Weight Polycyclic Aromatics Hydrocarbons (Low and High M.W. PAHs) were higher than the limit of reporting at Active Pit stations (NPDA and NPDB) and Pit-Edge station (NEDB) in August 2012.  Total Organic Carbon (TOC) concentration was similar amongst all stations (Figure 10 of Annex B).  Tributyltin (TBT) concentration was the highest at Pit-Edge station NEDB in August 2012 when compared to other stations (Figure 11 of Annex B). 

1.5.10                            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.

1.5.11                            Cumulative Impact Sediment Chemistry for CMP Va V August 2012

1.5.12                            Monitoring locations for Cumulative Impact Sediment Chemistry for CMP Va are shown in Figure 1.4.  A total of nine monitoring stations were being sampled.

1.5.13                            Analyses of results for the Cumulative Impact Sediment Chemistry Monitoring indicated that the concentrations of all metals, except Arsenic, were below the LCEL (Figures 12 and 13 of Annex B).  Concentrations of Arsenic in sediments from all stations, except Near Field (RNB), exceeded the LCEL.  As presented in Section 1.5.5 above, the slight exceedances of LCEL for Arsenic do not necessarily indicate any adverse impacts to sediment quality caused by disposal operations at CMP Va.  Generally, there were only minor differences in metal concentrations amongst the stations.

1.5.14                            The concentration of TOC was higher at the Mid Field station RMA than at other stations (Figure 14 of Annex B).  TBTs were recorded in sediment samples at Near Field (RNA), Mid Field (RMA and RMB), Capped Pit (RCA) and Ma Wan Stations (Figure 15 of Annex B).  Total DDT, 4,4-DDE, Total PCBs, Low and High M.W. PAHs were below the limit of detection at all stations. 

1.5.15                            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.

1.5.16                            Sediment Toxicity Test V August 2012

1.5.17                            Sediment Toxicity Tests were undertaken for sediments collected from the Near Pit, Reference and Ma Wan stations (as shown in Figure 1.5) in August 2012 using three international species (burrowing amphipod Leptocheirus plumulosus, marine benthic polychaete Neanthes arenaceodentata and marine bivalave Crassostrea gigas) and two local species (barnacles Balanus amphitrite and shrimp Penaeus vannaamei).  A total of five stations were being sampled.

1.5.18                            Results of the Sediment Toxicity Tests in August 2012 showed that the survival rates of the burrowing amphipod, bivalve, shrimp and barnacle as well as the total dry weight of the benthic polychaete were not significantly different between animals exposed to the sediments taken from Near Pit, Reference and Ma Wan stations.  Therefore, there did not appear to be any evidence of adverse impacts to sediment toxicity due to the mud disposal operations at the CMP Va of the ESC area.

 

1.5.19                            Impact Water Quality Monitoring during Dredging Operations of CMP Vd V August 2012

1.5.20                            Impact Water Quality Monitoring during Dredging Operations of CMP Vd was conducted on 29 August 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 1.6).  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).

1.5.21                            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 Average Turbidity Level at station DS2 during mid-flood tide.  The single case of exceedance recorded at station DS2 is not likely to be caused by the dredging operations at CMP Vd since the turbidity levels well complied with the Action level at stations closer to dredging operations at CMP Vd (ie DS1 and DS2). 

1.5.22                            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.  

1.5.23                            Routine Water Quality Monitoring for CMP Va V August 2012

1.5.24                            The results for the Routine Water Monitoring conducted in the wet season have been assessed for compliance with the Water Quality Objectives (WQOs) (please see Figure 1.7 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 reference stations was used for the basis as the WQO.  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

1.5.25                            Analyses of results for August 2012 indicated that for all stations (Impact, Intermediate and Reference), levels of pH and DO complied with the WQOs (Figures 16-18 of Annex B).  Levels of Salinity complied with WQO at all stations, except at Intermediate station (Figure 19 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 17, 18, 20 of Annex B). All in-situ water quality measurements showed relatively minor variations between Impact, Intermediate and Reference stations (Figures 16 to 20 of Annex B). 

Laboratory Measurements

1.5.26                            Analyses of August 2012 results indicate that majority of metal concentrations (i.e. Cadmium, Mercury and Silver) were below their limit of reporting at all stations.  Copper and Nickel were detected in samples from all stations.  Arsenic was detected at Impact, Intermediate and Ma Wan stations while Lead was detected at Impact and Intermediate stations.  Chromium was only detected at Intermediate stations while Zinc was detected at Reference and Impact stations (Figures 21 and 22 of Annex B).  Concentration of Arsenic, Copper, Lead, Nickel and Zinc appeared to be similar amongst all stations.  Levels of 5-day Biochemical Oxygen Demand (BOD5), Total Inorganic Nitrogen (TIN) and NH3-N also appeared to be similar amongst all stations (Figures 23 and 24 of Annex B).  Concentrations of TSS exceed WQO (12.74 mg/L for wet season) at Intermediate and Impact Stations while all of them complied with the Action and Limit Levels at all stations within the reporting month (Figure 25 of Annex B).


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

Stations

Temp

Salinity

Turbidity

pH

Dissolved Oxygen

 

(XC)

 

(NTU)

 

(%)

(mg L-1)

RFE (Reference)

28.79

21.41

8.42

7.60

73.03

5.01

IPE (Impact)

28.96

21.06

12.79

7.63

73.37

5.03

INE (Intermediate)

28.47

24.05

9.88

7.68

75.38

5.12

Ma Wan Station

29.11

22.21

6.64

7.66

80.40

5.46

WQO

N/A

19.27-23.56

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 August 2012

Stations

As

Ag

Cd

Cr

Cu

Hg

Pb

Ni

Zn

NH3-N

TIN

BOD5

TSS

RFE

1.65

<LOR

<LOR

<LOR

2.13

<LOR

<LOR

2.80

5.73

0.08

0.94

0.70

10.50

IPE

2.08

<LOR

<LOR

<LOR

1.90

<LOR

0.66

2.48

5.45

0.08

0.94

0.64

19.20

INE

2.13

<LOR

<LOR

0.71

1.09

<LOR

0.55

1.98

3.23

0.06

0.72

0.88

13.93

Ma Wan Station

2.13

<LOR

<LOR

<LOR

1.25

<LOR

<LOR

2.13

2.50

0.09

0.86

0.78

9.75

WQO of TSS

12.74

1.5.27                            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.

1.5.28                            Water Column Profiling for CMP Va V August 2012

1.5.29                            Water Column Profiling was undertaken at a total of two sampling stations in August 2012.  The water quality monitoring results have been assessed for compliance with the WQOs set by EPD as presented in Section 1.5.24 above.  Graphical presentation of the monitoring results is provided in Annex B.

In-situ Measurements

1.5.30                            Analyses of results for August 2012 indicated that levels of Salinity, pH and Dissolved Oxygen (DO) all complied with the WQOs at both Upstream and Downstream stations (Figures 26, 27 and 28 of 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)

1.5.31                            Analyses of data obtained in August 2012 indicated that the TSS levels at Upstream and Downstream stations complied with the WQO (Figure 29 of Annex B).  TSS levels measured in August 2012 complied with the Action and Limit Levels set in the EM&A Manual.

1.5.32                            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.

1.5.33                            Demersal Trawling for CMP Va V August 2012

Abundance and Biomass

1.5.34                            Demersal Trawling was undertaken at a total of six sampling stations in August 2012.  The average number of species collected is presented in Table 1.4.  In August 2012, species richness was relatively similar between Impact and Reference stations.

Table 1.4        Summary of the Mean Number of Faunal Species Caught during August 2012 Monitoring

 

Date of Sampling

Impact Stations

Reference Stations

 

INA       

INB

TNA

TNB       

TSA

TSB

August 2012

43.4

45.0

42.4

42.2

47.4

42.4

1.6                                      Activities Scheduled for the Next Month

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

CMP V

P          Pit Specific Sediment Chemistry 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).