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

4th MONTHLY PROGRESS REPORT FOR CONTAMINATED MUD PITS AT SHA CHAU - October 2009

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.  CMP IVc is presently in operation for backfilling by contaminated mud and is anticipated to reach its capacity in 2010.  A series of four newly constructed seabed pits at the East of Sha Chau area, CMP Va-d, will be provided for the disposal of contaminated mud after CMP IVc is full.  Dredging operations are now taking place to construct CMP Va.  The environmental monitoring and audit (EM&A) programme for the CMPs at the East of Sha Chau area presently covers disposal operations at CMP IVc and dredging operations at CMP V.

1.2                                      Reporting Period

This Monthly Progress Report covers the monitoring period from July to October 2009.

1.3                                      Details of Sampling and Laboratory Testing Activities

Sampling for Impact Monitoring during Dredging Operations of CMP V was conducted on 8 October 2009.  Data for laboratory analysis of samples collected in July 2009 for Sediment Chemistry after a Major Storm Event and Water Column Profiling for CMP IV were received from the Contractor on 15 October 2009.  A summary of field activities are presented in Annex A.

1.4                                      Details of Outstanding Sampling and / or Analysis

Water Column Profiling for CMP V was not conducted in this sampling month as there were no dredging activities on the scheduled sampling day due to maintenance of the dredger.  Data from the Contractor that remain outstanding include concentrations of Total Polycyclic Aromatic Hydrocarbons (PAHs) and Tributyltin (TBT) in sediment samples and TBT in interstitial water samples for Pit Specific Sediment Chemistry and Cumulative Impact Sediment Chemistry.  In addition, data for Particle Size Distribution of the sediment samples for July 2009 sampling for Sediment Chemistry after a Major Storm Event remain outstanding from the Contractor. 

1.5                                      Brief Discussion of the Monitoring Results

For CMP IV, monitoring results for Water Column Profiling, Sediment Chemistry after a Major Storm Event and Demersal Trawling for July and August 2009 as well as Routine Water Quality Monitoring, Benthic Macro-Infauna & Taxonomic Identification, Pit Specific Sediment Chemistry and Cumulative Impact Sediment Chemistry for August 2009 are presented below.  Further for CMP V, monitoring results are presented for Impact Monitoring during Dredging Operations for October 2009.  Detailed results will be discussed in the relevant Quarterly Reports.

1.5.1                                Water Column Profiling for CMP IV during July 2009

Results of Water Column Profiling for July 2009 show that salinity, pH and Dissolved Oxygen (DO) all compiled with the Water Quality Objectives (WQOs) at both Upstream and Downstream stations (Figures 2 to 4 of Annex B).  However, levels of Total Suspended Solids (TSS) exceeded the WQO at both Upstream and Downstream stations (Figure 1 of Annex B). 

1.5.2                                Water Column Profiling for CMP IV during August 2009

Results of Water Column Profiling for August 2009 show that salinity and pH complied with the WQOs at both Upstream and Downstream stations (Figures 6 and 7 of Annex B).  However, levels of DO and TSS at both the Upstream and Downstream stations did not comply with the WQOs (Figure 5 and 8 of Annex B).

1.5.3                                Routine Water Quality Monitoring for CMP IV during August 2009

In-situ Measurements

Levels of pH, DO and Salinity complied with the WQOs at all stations during Routine Water Quality Monitoring in August 2009 (Figures 9, 12 and 13 of Annex B).  All in-situ water quality measurements showed relatively minor variations between Impact, Intermediate and Reference stations (Figures 9 to 14 of Annex B).

Laboratory Measurements

Concentrations of Arsenic, Cadmium, Chromium, Mercury and Silver were all below the limits of detection.  Whereas, Copper, Lead, Nickel and Zinc were detected in water samples and their concentrations were relatively similar among the Impact, Intermediate and Reference stations (Figure 15 of Annex B).  Similarly, concentrations of Total Inorganic Nitrogen and Ammoniacal-Nitrogen showed only minor differences between the Impact, Intermediate and Reference stations (Figure 16 of Annex B).  Levels of TSS complied with the WQO (10.0mg L-1) at the Intermediate station, however, exceedances of the WQO were observed at both the Impact and Reference stations (Figure 17 of Annex B).  Levels of BOD5 were below detection limits at all stations. 

1.5.4                                Sediment Chemistry after a Major Storm Event for CMP IV (Molave)

Sampling for Sediment Chemistry after a Major Storm Event was conducted on 22 July 2009 after the visit of Tropical Cyclone Molave, which led to the issue of No. 8 Gale or Storm Signal on 18 July 2009 and No. 9 Gale or Storm Signal on 19 July 2009.  The track of Molave is shown in Figure 1.4.1. 

 

Figure 1.4.1   Track of Tropical Cyclone Molave from 15-19 July 2009 (Source: Hong Kong Observatory)

Concentrations of all metals, except Arsenic, were below the Lower Chemical Exceedance Limit (LCEL) and Upper Chemical Exceedance Limit (UCEL) (Figures 18 and 19 of Annex B).  Concentrations of Arsenic in sediments from all stations exceeded LCEL (12 mg/kg), but remained below UCEL (42 mg/kg). 

Moisture content in the sediments from all stations ranged between 42.2 - 60.6% (Figure 20 of Annex B).  Data for Particle Size Distribution of sediment samples remains outstanding from the Contractor.

1.5.5                                Sediment Chemistry after a Major Storm Event for CMP IV (Goni)

Sampling for Sediment Chemistry after a Major Storm Event was conducted on 7 August 2009 after the visit of Tropical Cyclone Goni, which led to the issue of No. 8 Gale or Storm Signal on 5 August 2009.  The track of Goni is shown in Figure 1.4.2. 

 

Figure 1.4.2    Track of Tropical Cyclone Goni from 1-9 August 2009 (Source: Hong Kong Observatory)

Concentrations of all metals, except Arsenic, were below the LCEL and UCEL (Figures 21 and 22 of Annex B).  Concentrations of Arsenic in sediments from all stations exceeded LCEL (12 mg/kg), but remained below UCEL (42 mg/kg). 

Moisture content in the sediments from all stations ranged between 45.4 - 57.5% (Figure 23 of Annex B).  Sediments were mainly composed of sand (35.9 – 65.1 %) and gravel (25.4 – 30.8 %) materials (Figure 24 of Annex B).

1.5.6                                Benthic Macro-Infauna and Taxonomic Identification

A benthic survey was conducted at the Capped Mud Pit stations and at the Reference stations to the south of Sha Chau in August 2009.  A total of 73 individuals, belonging to eight animal phyla were obtained from the monitoring stations.  Table 1.4.1 summarises the results of the benthic survey.


Table 1.4.1      Summary of Benthic Survey Results during August 2009 Monitoring

Area

Station

No. of individuals

(Total)

Biomass (g)

(Total)

No. of Individuals (Per Station)

Biomass (g) (Per Station)

Average Biomass per individual (mg)

Average Number of Genera

Capped Stations

CPA

3

7

0.23

2.33

0.08

0.03

5

CPB

3

16

9.07

5.33

3.02

0.57

8

CPC

3

8

3.29

2.67

1.10

0.41

6

(Total)

 

31

12.59

10.33

4.20

1.01

19

Reference Stations

RBA

3

14

21.11

4.67

7.04

1.51

8

RBB

3

7

0.32

2.33

0.11

0.05

6

RBC

3

21

12.43

7.00

4.14

0.59

12

(Total)

 

42

33.86

14.00

11.29

2.15

26

Total

18

73

46.45

 

 

 

 

Total number of individuals, total biomass, average biomass per individual and average number of genera were lower at the Capped stations than at the Reference stations.

1.5.7                                Demersal Trawling for July and August 2009

Abundance and Biomass

The average number of species collected during the July and August 2009 sampling is presented in Table 1.4.2.  In the July and August 2009 sampling, species richness was relatively similar between the Impact and Reference stations.  

Table 1.4.2     Summary of the Mean Number of Faunal Species Caught during July and August 2009 Monitoring

Date of Sampling

IMPACT STATIONS

INA        INB

            REFERENCE STATIONS

TNA       TNB        TSA         TSB

Jul 2009

37.2

41.0

38.0

35.8

42.4

38.8

Aug 2009

37.0

40.4

41.2

36.2

36.0

35.2

During July 2009, the number of individuals per station, total biomass per station, mean Catch per Unit Effort (CPUE) and mean Yield per Unit Effort (YPUE) of the catch were higher at the Reference stations TSA and TSB compared to all other stations (Table 1.4.3).  During August 2009, total biomass per station and mean YPUE were higher at the Impact station INA and the Reference station TSA, whereas the number of individuals per station and the mean CPUE were highest at the Reference station TSA compared with all other stations (Table 1.4.3).

Table 1.4.3     Summary of CPUE and YPUE during July and August 2009 Monitoring

Date

Stations

Impact / Reference Stations

No. of Individuals per Station

Total Biomass per Station (g)

Mean CPUE#1 per Tow

Mean YPUE#2 per Tow (g)

Jul 2009

INA

Impact

12,196.0

82,073.3

2,439.2

16,414.7

Jul 2009

INB

Impact

11,055.0

71,573.6

2211

14,314.7

Jul 2009

TNA

Reference

10,036.0

63,738.1

2,007.2

12,747.6

Jul 2009

TNB

Reference

11,171.6

73,785.4

2,234.3

14,757.1

Jul 2009

TSA

Reference

18,343.0

104,439.1

3,668.6

20,887.8

Jul 2009

TSB

Reference

24,836.0

215,796.0

4,967.2

43,159.2

Aug 2009

INA

Impact

12,360.0

97,890.8

2,472.0

19,578.2

Aug 2009

INB

Impact

11,363.0

71,961.9

2,272.6

14,392.4

Aug 2009

TNA

Reference

8,896.0

67,743.5

1,779.2

13,548.7

Aug 2009

TNB

Reference

9,422.0

69,373.3

1,884.4

13,874.7

Aug 2009

TSA

Reference

24,240.0

102,574.9

4,848.0

20,515.0

Aug 2009

TSB

Reference

8,771.0

56,648.1

1,754.2

11,329.6

#1 CPUE is calculated by dividing the number of individuals with the trawling time and number of nets (in hour and number of nets)

#2 YPUE is calculated by dividing the weight (g) of fish with trawling effort (in hour and number of nets)

1.5.8                                Pit Specific Sediment Chemistry for CMP IV during August 2009

All metal concentrations at all stations were below the LCEL Sediment Criteria, with the exception of Arsenic (Figures 25 and 26 of Annex B).  Concentrations of Arsenic exceeded LCEL at all stations.  No metal concentrations exceeded UCEL (Figures 25 and 26 of Annex B).  Overall, variation in the concentration of metals among stations was minor (Figures 25 and 26 of Annex B). 

Concentrations of Total DDT and 4,4” DDE were lower than detection limits at all stations except at the Near-Pit stations, where concentration remained relatively low (Figure 27 of Annex B)  Total Organic Carbon concentrations in the sediment were slightly higher at the Active-Pit stations relative to other stations (Figure 28 of Annex B).  Sediments were mainly composed of sand (30.0 – 63.0 %) and gravel (22.0 – 32.5 %) materials (Figure 29 of Annex B).

Concentrations were below detection limit at all stations for Low Molecular Weight (LMW) PAHs, High Molecular Weight (HMW) PAHs and Polychlorinated biphenyls (PCBs).  Results for Total PAHs of the sediment samples remain outstanding from the Contractor.  Further, concentrations of Tributyltin (TBT) in interstitial water and in sediments are also outstanding from the Contractor.

1.5.9                                Cumulative Impact Sediment Chemistry for August 2009

Concentrations of all metals, except Arsenic, were below LCEL (Figures 30 and 31 of Annex B).  Concentrations of Arsenic in sediments from all stations were above the LCEL.  Overall, there were only minor differences in metal concentrations between the stations (Figure 30 and 31 of Annex B).  All metal concentrations remained below UCEL (Figure 30 and 31 of Annex B). 

The concentration of 4,4” DDE was higher at Mid-Field stations and Far-Field station RFA compared to all other stations, which were below detection limits (Figure 32 of Annex B).  Concentrations of Total DDT were below detection limits at all stations except Mid-Field station RMB (Figure 32 of Annex B).  Concentrations of Total Organic Carbon in sediments were relatively similar between stations (Figure 33 of Annex B).  Sediments were mainly composed of sand (31.8 – 56.4 %) and gravel (33.8 – 40.1 %) materials (Figure 34 of Annex B).

Concentrations were below detection limit at all stations for Low Molecular Weight (LMW) PAHs, High Molecular Weight (HMW) PAHs and Polychlorinated biphenyls (PCBs).  Results for Total PAHs of the sediment samples remain outstanding from the Contractor.  Further, concentrations of Tributyltin (TBT) in interstitial water and in sediments are also outstanding from the Contractor.

1.5.10                            Impact Monitoring during Dredging Operations of CMP V – October 2009

Impact Monitoring during Dredging Operations of CMP V was conducted on 8 October 2009.  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 V.  Monitoring was also conducted at the Ma Wan station.  At each station, in-situ measurements of water quality parameters and water samples were taken from three water depth levels of the water column which were surface (1m below sea surface), mid-depth and bottom (1m above the seabed).

Monitoring results are presented in Figures 35 to 38 of Annex B.  Levels of DO, depth-average Turbidity and TSS compiled with the Action and Limit Levels set in the Baseline Monitoring Report ([1]) (Tables B1 and B2 of Annex B). 

1.6                                      Activities Scheduled for the Next Month

Impact Monitoring during Dredging Operations and Water Column Profiling will be conducted for CMP V in the next monthly period.  No sampling works will be conducted for CMP IV.  The sampling schedule for the Monitoring Contract is presented in Annex A. 

1.7                                      Study Programme

A summary of Study programme is presented in Annex C.

 



([1])        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 CEDD.