Agreement No. CE 4/2009 (EP)
Environmental Monitoring and Audit
for Contaminated Mud Pit at Sha Chau
(2009-2013) - Investigation
42nd MONTHLY PROGRESS REPORT FOR CONTAMINATED MUD PITS AT SHA
CHAU December 2012
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 December 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
· 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 December 2012.
1.3
Details of Sampling and Laboratory Testing Activities
1.3.1
The following monitoring
activities have been undertaken for CMP V in December 2012:
· Cumulative
Impact Sediment Chemistry was
conducted for CMP Va on 3 December 2012;
· Pit
Specific Sediment Chemistry was
conducted for CMP Va on 7 December 2012;
· Impact
Water Quality Monitoring during Dredging Operations was conducted for CMP Vd on 14 December
2012; and
· Water
Column Profiling was
conducted for CMP Va on 19 December 2012.
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 analysis of Pit Specific Sediment Chemistry and
Cumulative
Impact Sediment Chemistry 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 December 2012
|
Monitoring
activities |
Date
of Monitoring |
Monitoring
results presented in this report? |
|
Cumulative Impact Sediment
Chemistry Monitoring for CMP Va |
3 Dec 2012 |
No. Laboratory analysis yet to be
completed during preparation of this monthly report. |
|
Pit Specific Sediment
Chemistry Monitoring for CMP Va |
8 November 2012 7 Dec 2012 |
Yes No. Laboratory analysis yet to be
completed during preparation of this monthly report. |
|
Impact Water Quality
Monitoring during Dredging Operations of CMP Vd |
14 Dec 2012 |
Yes |
|
Water Column Profiling for
CMP Va |
19 Dec 2012 |
Yes |
1.5.2
Pit Specific
Sediment Chemistry of CMP Va
– November 2012
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 November 2012.
Concentrations of Arsenic exceeded the Lower Chemical Exceedance Level (LCEL) at Pit-Edge (NEDA and NEDB) and
Near-Pit (NNDA) stations while concentrations of Chromium, Mercury and Zinc
exceeded the LCEL at Active Pit station (NPDB) (Figures 1-2 of
Annex C). Concentrations of Copper, Nickel and
Silver exceeded the UCEL at Active Pit Station (NPDB). 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 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. In addition, the Active Pit stations are
located within CMP Va which was receiving
contaminated mud during the reporting period. As such, the exceedances
of LCEL/UCEL for Chromium, Copper, Mercury, Nickel, Silver and Zinc which were
recorded at the Active Pit station only is not considered as indicating any
dispersal of contaminated mud from CMP Va.
1.5.4
For organic contaminants, Total Organic Carbon (TOC)
concentration was similar amongst all stations (Figure 3 of Annex
C). Tributyltin
(TBT) concentration was the highest at Active Pit station NPDB when compared to
other stations (Figure
4 of Annex B). Low Molecular Weigh Polycyclic Aromatics
Hydrocarbons (Low MW PAHs) and Total Polychlorinated Biphenyls (PCBs)
concentrations were below the limit of reporting except at Active Pit station
NPDB (Figure 5
and 6 of Annex B). High MW PAHs concentrations were below
the limit of reporting at all stations except at both Active Pit stations NPDA
and NPDB (Figure
5
of Annex B). Total DDT and 4,4’-DDE
were below the limit of reporting at all stations.
1.5.5
As described in Section 1.5.3, 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.
1.5.6
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.
1.5.7
Impact Water
Quality Monitoring during Dredging Operations of CMP Vd – December 2012
1.5.8
Impact Water Quality Monitoring during Dredging
Operations of CMP Vd was
conducted on 14 December 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). Where water depth is less than 6m
the mid-depth station was omitted.
If water depth is less than 3m, only the mid-depth station was
monitored.
1.5.9
Monitoring results are presented
in Table
B1 of Annex
B. Levels
of Dissolved Oxygen (DO), Turbidity and Suspended Solids (SS) generally
complied with the Action and Limit Levels set in the Baseline Monitoring
Report ([3]).
1.5.10
Levels of Turbidity exceeded the
Action Level in the downstream station DS5 during mid-flood tide. Station DS5 is located even further away
from the works area of CMP Vd than other downstream
stations (ie DS1-4) (please refer to Figure 1.2
for the indicative locations of the monitoring stations). The compliance of Action and Limit
Levels at other downstream stations would indicate that the recorded exceedance is unlikely to be caused by the dispersal of
suspended sediments from the dredging operations at CMP Vd. In
addition, high turbidity level was occasionally recorded during the baseline
monitoring of the EM&A programme.
The high turbidity level is thus considered to be sporadic events and
characteristic of water quality in this area of Hong Kong.
1.5.11
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).
1.5.12
Water Column
Profiling for CMP Va –
December 2012
In-situ Measurements
1.5.13
Water Column Profiling was
undertaken at a total of two sampling stations in December 2012. The
water quality monitoring results for December 2012 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
dry 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. Graphical
presentation of the monitoring results is provided in Annex C.
1.5.14
Analyses of results for December
2012 indicated that levels of Salinity, pH and DO complied with the WQOs at
both Upstream and Downstream stations (Figures 7 - 9 of Annex C). DO and Turbidity complied with the
Action and Limit Levels set in the EM&A Manual ([4]).
Laboratory Measurements for Suspended Solids (SS)
1.5.15
Analyses of data obtained in
December 2012 indicated that the SS levels at both Upstream and Downstream
stations complied with the WQO (Figure 10 of Annex C). In addition, SS levels at all stations
complied with the Action and Limit Levels set in the EM&A Manual.
1.5.16
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
1.6.1
The following monitoring
activities will be conducted in the next monthly period of January 2013 for CMP
V:
· Pit
Specific Sediment Chemistry for
CMP Va;
· Demersal Trawling 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 Vd.