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.