Agreement No. CE 4/2009 (EP)
Environmental Monitoring and Audit
for Contaminated Mud Pit at Sha Chau (2009-2013) - Investigation
15th MONTHLY PROGRESS REPORT FOR CONTAMINATED MUD PITS AT SHA CHAU - September 2010
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 2011. 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 Vb. 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 Vb.
This Monthly Progress Report covers the monitoring period of September 2010.
No field sampling activities were scheduled in this monthly period for CMP IVc. For CMP V, sampling for Impact Water Quality Monitoring during Dredging Operations was conducted on 7, 9, 11, 13, 15, 17, 20, 22, 24, 27 and 29 September 2010. A summary of field activities are presented in Annex A.
No outstanding sampling and laboratory analysis remained from September 2010.
Results of Impact Water Quality Monitoring during Dredging Operations for September 2010 are presented for CMP V. Detailed results will be discussed in the relevant Quarterly Reports.
Impact Water Quality Monitoring during Dredging Operations of CMP V was conducted on 7, 9, 11, 13, 15, 17, 20, 22, 24, 27 and 29 September 2010. On each 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 V. 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 B. Generally, levels of Dissolved Oxygen (DO), Turbidity and Total Suspended Solids (TSS) complied with the Action and Limit Levels set in the Baseline Monitoring Report (). However, very occasional exceedances of Action Levels are recorded for Turbidity and TSS (Table B1 of Annex B). Student’s t-tests were then employed to investigate any significant differences in levels of Turbidity and/or TSS between Reference (US1 and US2) and Impacts stations where exceedance(s) of Action Level(s) was/were reported (p-value = 0.05). Results of the statistical analysis show that except for the exceedances recorded at DS1 during the mid-flood monitoring on 27 September 2010, levels of Turbidity and TSS did not show any significant differences between Reference (US1 and US2) and Impact stations. It is thus considered that these exceedances are more likely to be caused by natural background fluctuation in water quality rather than indicating any adverse impacts from the dredging operations of CMP V. It should be noted that the Impact station where exceedances were recorded on 27 September 2010 (ie DS1) is located at the boundary of the works area and the absence of exceedance at other downstream stations (DS2 to DS5) indicates that the sediment plume did not extend beyond the works area. Therefore, it is also considered that the recorded exceedances do not indicate any adverse water quality impacts caused by the dredging works of CMP V.
Impact Water Quality Monitoring during Dredging will be undertaken for CMP V in the next monitoring month for three times per week. No monitoring will be conducted for the disposal operations of CMP IV in October 2010.
The sampling schedule is presented in Annex A.
A summary of the Study programme is presented in Annex C.