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 HKSAR¡¦s 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 Earth¡¦s crust is generally ~2mg/kg, significantly higher Arsenic
concentrations (median = 14 mg/kg) have been recorded in Hong
Kong ¡¦s 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.