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 HKSAR¡¦s 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 Kong¡¦s 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.