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

 

33rd MONTHLY PROGRESS REPORT FOR CONTAMINATED MUD PITS AT SHA CHAU March 2012

 

1.1                                      Background

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 March 2012, the following works were being undertaken at the CMPs:

·         Capping was being undertaken at CMP IVc; 

·         Disposal of contaminated mud was taking place at CMP Va; and

·         The dredging of CMP Vc was in progress.   

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 reporting month of March 2012.

1.3                                      Details of Sampling and Laboratory Testing Activities

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

·       Pit Specific Sediment Chemistry was conducted for CMP Va on 6 March;

·       Impact Water Quality Monitoring during Dredging Operations was conducted for CMP Vc on 13 March; and

·       Water Column Profiling was conducted for CMP Va on 22 March.

A summary of field activities is presented in Annex A.

A summary of monitoring data submitted by the Contractor in this reporting month is presented in Table 1.1.


Table 1.1         Summary of monitoring data submitted by the Contractor for the reporting month

Key Task

Monitoring Component

Date of Results Received from the Contractor

CMP Vc

 

 

Impact Monitoring during Dredging Operations

Water Quality

30 March 2012

 

 

 

1.4                                      Details of Outstanding Sampling and / or Analysis

No outstanding sampling and laboratory analysis remained from March 2012.

1.5                                      Brief Discussion of the Monitoring Results for CMP V

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

 

1.5.1                                Sediment Toxicity Test – February 2012

Sediment Toxicity Tests were undertaken for sediments collected from the Near Field, Reference and Ma Wan stations in February 2012 using three international species (burrowing amphipod Leptocheirus plumulosus, marine benthic polychaete Neanthes arenaceodentata and marine bivalve Crassostrea gigas) and two local species (barnacles Balanus amphitrite and shrimp (Penaeus vannaamei).

Results of the Sediment Toxicity Tests in February 2012 showed that the survival rates of the burrowing amphipods, bivalve, shrimp and barnacles 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 V of the ESC area.

1.5.2                                Routine Water Quality Monitoring of CMP Va – February 2012

The results for the Routine Water Monitoring conducted during February 2012 in the dry season period have been assessed for compliance with the Water Quality Objectives (WQOs) (please see Figure 1.1 for the monitoring locations).  This consists of a review of the Environmental Protection Department (EPD) routine water quality monitoring data for the dry season period (November to March) of 1999-2010 from stations in the Northwestern Water Control Zone, where CMP V is 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 Table 1.2 and 1.3 respectively, with graphical presentation provided in Annex B.

In-situ Measurements

Analyses of results for February 2012 indicated that for all stations (Impact, Intermediate and Reference), levels of pH, Salinity and DO complied with the WQOs (Figure 3, 4 and 6 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 ([1]).  All in-situ water quality measurements showed relatively minor variations between Impact, Intermediate and Reference stations (Figure 1 to 6 of Annex B). 

Laboratory Measurements 

Analyses of February 2012 results indicate that majority of metal concentrations (i.e. Cadmium, Mercury and Silver) were below their limit of reporting at all stations.  Copper, Lead, Nickel and Zinc were detected in samples from all stations while Arsenic and Chromium levels were below the limits of reporting at all stations (Figure 7 and 8 of Annex B).  Concentrations of Copper appeared to be higher in samples obtained from Impact stations compared to those from the Intermediate and Reference stations while concentrations of Lead and Nickel were similar among all stations.  Concentrations of Zinc were slightly higher at the Impact and Intermediate stations.  The higher concentration of Copper recorded at the Impact Station will be further analyzed in the Quarterly Report in order to determine any spatial trend of potential concern (ie increasing Copper concentrations with proximity to the pit).  Levels of 5-day Biochemical Oxygen Demand (BOD5) and Total Inorganic Nitrogen (TIN) were slightly higher at Intermediate station (INF) compared to other stations (Figure 9 and 10 of Annex B).  Concentrations of TSS complied with the WQO (15.60 mg/L for dry season) at all sampled stations (Figure 19 of Annex B) and also complied with the Action and Limit Levels within the reporting month.

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.


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

Stations

Temp

Salinity

Turbidity

pH

Dissolved Oxygen

 

(°C)

 

(NTU)

 

(%)

(mg L-1)

RFF (Reference)

16.48

31.69

8.64

7.69

95.85

7.73

IPF (Impact)

16.69

31.27

6.03

7.66

93.05

7.49

INF (Intermediate)

16.64

31.25

5.76

7.62

92.88

7.49

Ma Wan Station

16.35

32.01

6.72

7.68

90.84

7.33

WQO

N/A

28.52-34.86#

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 February 2012

Stations

As

Ag

Cd

Cr

Cu

Hg

Pb

Ni

Zn

NH3-N

TIN

BOD5

TSS

RFF

<LOR

<LOR

<LOR

<LOR

11.04

<LOR

2.54

2.33

13.04

0.12

0.45

1.24

10.13

IPF

<LOR

<LOR

<LOR

<LOR

16.54

<LOR

2.08

2.33

16.58

0.19

0.67

1.30

10.96

INF

<LOR

<LOR

<LOR

<LOR

12.79

<LOR

2.54

2.75

16.25

0.18

0.83

1.74

6.88

Ma Wan Station

<LOR

<LOR

<LOR

<LOR

13.63

<LOR

1.50

2.13

12.00

0.15

0.41

0.76

10.63

1.5.3                                Cumulative Impact Sediment Chemistry – February 2012

Monitoring locations for Cumulative Impact Sediment Chemistry for CMP Va is shown in Figure 1.2.  Analyses of results for the Cumulative Impact Sediment Chemistry Monitoring indicated that the concentrations of all metals, except Arsenic, were below the Lower Chemistry Exeedance Level (LCEL, Figure 12 and 13 of Annex B).  Concentrations of Arsenic in sediments from all stations exceeded the LCEL, except at the Near Field station RNB.  It is important to note that relatively high natural levels of Arsenic are present in Hong Kong’s marine sediments.  Whilst the average concentration of Arsenic in the Earth’s crust is generally ~2mg/kg, significantly higher Arsenic concentrations (median = 14 mg/kg) been recorded in Hong Kong’s onshore sediments ([2]).  It is presumed that the natural concentrations of Arsenic are similar in onshore and offshore sediments ([3]), and relatively high Arsenic levels may thus occur throughout Hong Kong.  Therefore, the slight exceedances of the LCEL for the Arsenic do not necessarily indicate any adverse impacts to sediment quality caused by disposal operation at CMP Va. 

Concentrations of Total Organic Carbon (TOC) and Tributyltins (TBTs) were highest at Ma Wan station compared to Near Field, Mid Field, Far Field and Capped Pit stations (Figure 14 and 15 of Annex B). 

Concentrations of Total Dichlorodiphenyltrichloroethane (DDT) and 4,4”-Dichlorodiphenyldichloroethylene (4,4”-DDE) were found to be highest at Mid Field station RMA (Figure 16 of Annex B).  Total Polychlorinated Biphenyls (PCBs), Low and High Molecular Weight Polycyclic Aromatics Hydrocarbons (Low M.W. PAHs and High M.W. PAHs) were below the limit of reporting at all stations.  Sediments were mainly composed of silt and clay materials (68 – 96%, Figure 17 of Annex B). 

Overall, the contaminated mud disposal operation at ESC did not appear to cause any deterioration in sediment quality of the area.

1.5.4                                Pit Specific Sediment Chemistry Monitoring – February and March 2012

Monitoring locations for Pit Specific Sediment Chemistry for CMP Va are shown in Figure 1.3.  Concentrations of metals at all stations in February and March 2012 were below the LCEL, with the exception of Arsenic (Figure 18 and 24 of Annex B).   Concentrations of Arsenic exceeded the LCEL at all stations in February 2012 while it exceeded the LCEL in all stations except in Pit Edge (NEDA) and Near Pit station (NNDB) in March 2012.  It is important to note that relatively high natural levels of Arsenic are present in Hong Kong’s marine sediments (see Section 1.5.3 above).   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. 

For organic contaminants, PCBs, Low M.W. PAHs and High M.W. PAHs were all below the limit of reporting at all stations in February 2012.  Levels of Low M.W. PAHs and High M.W. PAHs were higher than the limit of reporting in only a few samples collected in March 2012 while PCBs were below the limit of reporting in all samples in March 2012.  TOC concentrations were the highest at Active Pit stations (NPDB) in both February and March 2012 when compared to other stations (Figure 20 and 26 of Annex B).  Highest concentrations of TBTs were recorded at Active Pit stations (NPDB and NPDA) in sediment samples collected in February and March 2012, but were not detected in any interstitial water samples (Figure 21 and 27 of Annex B). 

Concentrations of DDT and 4,4”-DDE were higher than the limit of reporting at all stations for both February and March 2012 (Figure 22 and 28 of Annex B).  In February 2012, concentrations of Total DDT and DDE were similar among all stations.  In March 2012, highest level of Total DDT and DDE were recorded at Active Pit stations (NPDA and NPDB).  Sediments were mainly composed of silt and clay (60 - 92%) materials and sand (9 – 39%, Figure 23 and 29 of Annex B).

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.

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.

1.5.5                                Impact Water Quality Monitoring during Dredging Operations of CMP V – March 2012

Impact Water Quality Monitoring during Dredging Operations of CMP V was conducted on 13 March 2012 for CMP Vc.  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 Vc (Figure 1.4).  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).

Monitoring results are presented in Table B1 of Annex C.  Levels of DO, Turbidity and TSS generally complied with the Action and Limit Levels set in the Baseline Monitoring Report ([4]).  Levels of TSS exceeded the Action Level in the downstream station DS1 during the mid-ebb tide.  Station DS1 is located on the edge of the works area of CMP Vc and the compliance of Action and Limit Levels at other downstream stations outside the works area (ie DS2-4) would indicate that there is no evidence of any unacceptable adverse water quality impacts outside the dredging works area of CMP Vc.

Overall, the results indicated that the dredging operations at CMP Vc 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 Vc.

1.5.6                                Water Column Profiling for CMP Va – February and March 2012

In-situ Measurements

The water quality monitoring results for February and March 2012 in the dry season period have been assessed for compliance with the WQOs set by EPD (please refer to Section 1.5.2 for details of setting the WQOs).   Graphical presentation of the monitoring results is provided in Annex B.

Analyses of results for February and March 2012 indicated that levels of Salinity, pH and Dissolved Oxygen (DO) all complied with the WQOs at both Upstream and Downstream stations (Figure 30 to 36 in Annex B).  DO and Turbidity complied with the Action and Limit Levels set in the EM&A Manual ([5]).

Laboratory Measurements for Total Suspended Solids (TSS)

Analyses of data obtained in February and March 2012 indicated that the TSS levels at both Upstream and Downstream stations complied with the WQO for the dry season period (Figure 33 and 37 in Annex B).  TSS levels measured during February and March 2012 complied with the Action and Limit Levels set in the EM&A Manual.

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

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

·       Pit Specific Sediment Chemistry for CMP Va;

·       Routine Water Quality Monitoring for CMP Va; 

·       Water Column Profiling for CMP Va; and

·       Impact Water Quality Monitoring during Dredging Operations for CMP Vc.

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).  Draft Second Review of the EM&A Manual.  Prepared for CEDD for EM&A for Contaminated Mud
      Pit at Sha Chau (2009-2013) – Investigation Agreement No. CE 4/2009 (EP).

([2])    Sewell RJ (1999) Geochemical Atlas of Hong Kong. Geotechnical Engineering Office, Government of the Hong Kong Special Administrative Region

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

 

([5])    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) – Investigation Agreement No. CE 4/2009 (EP).