SEDIMENT SAMPLING AND ANALYSIS PLAN FOR THE BRISBANE RIVER AND OUTER BAR, NOVEMBER 2003
May 2004
Hydrobiology
This report presents the findings of the Port of Brisbane Corporation (PBC)'s November 2003 Sediment Sampling and Analysis Plan (SAP) for the Brisbane River and Outer Bar (Moreton Bay). The SAP is required to be undertaken prior to routine maintenance dredging, which is required to maintain minimum depths of clearance within defined navigational channels.
The overall purpose of this project is to:
1. Test and analyse sediments for a range of chemical and physical properties, including:
heavy metals;
nutrients;
hydrocarbons;
pesticides;
TBT;
other selected contaminants; and
particle size distributions.
2. Compare contaminant levels with accepted sediment quality criteria (e.g. EA (2002) where available) and/or previous SAP results as required.
Ultimately the findings of the SAP are used to assist in the assessment of disposal options for dredged material from shipping channels and berths. Disposal options include onshore reclaimed areas or placement to designated material placement areas within Moreton Bay. It is PBC’s policy to place all material sourced from maintenance dredging onshore. The Corporation continues to undertake SAP studies to identify any potential contaminant issues in advance of dredging to ensure that placement of the material is appropriately controlled.
This study involved the acquisition and analysis (for the parameters described broadly above) of 48 sediment cores in accordance with EA (2002). Of the 48 sample locations, 45 were from areas of the Brisbane River and Outer Bar requiring dredging and three were from upstream reference sites. An overview of sample sites and locations is provided as Drawing 1 of Appendix A.
Trace metal concentrations in this round were found to be comparable with previous SAP studies, with only nickel and mercury exceeding Screening Levels. Nickel has been routinely measured above Screening Level throughout the dredging and reference sites, and is believed to relate to the local geology rather than introduced contamination, as discussed in the 2002 SAP. On review of the nickel and clay content available from previous SAP studies, it is apparent that nickel concentration increases with clay content.
TBT concentrations in this round were found to be broadly comparable with previous SAP studies, exceeding Screening and Maximum Levels at a number of locations. TBT levels were generally elevated in this round compared to the 2002 SAP which suggests that TBT is a recurrent issue for the Brisbane River. TBT levels in the Outer Bar were all found to be below the Screening Level.
A summary of the percentage of sample locations exceeding Screening Levels, for the current and previous SAP studies, for selected parameters (i.e. those having repeatedly exceeded Screening Levels in previous SAP studies) is given in Table 1.1.
In the 2002 SAP, chlordane was found to exceed the Screening Level at all locations analysed for chlordane. Although there were no detections of chlordane in this round, other organochlorine pesticides, i.e. dieldrin and DDT (and its metabolites DDD and DDE) were detected at levels exceeding Screening and Maximum Levels (for total DDT and DDD). Such levels of these OC pesticides have been observed in previous SAP studies, and detections of dieldrin and metabolites of DDT in sediments of South East Queensland have been reported elsewhere.
A single location (Location 2-0 – City Reaches Reference Site) only exceeded Screening Levels for a limited number of the PAH parameters. This is consistent with previous SAP studies which generally only show minor Screening Level exceedances at a limited number of locations. In the 2002 SAP location 7-0 was the only sample found to have a limited number of PAHs exceed Screening Levels.
All sample locations were found to meet HIL-A soil investigation criteria1 for the extensive set of parameters. Furthermore, a statistical comparison of the 95%UCL for contaminants also complied with HIL-A criteria. Therefore the material is likely to be considered suitable for land disposal to reclamation areas on the basis of chemical contaminant levels. It should be noted that the Screening and Maximum Levels specified in EA (2002) are far stricter than the soil investigation levels applied for the placement of dredge spoil on land. The EA (2002) Guidelines are for the consideration of material for placement at sea where a variety of organisms live on or in the sediment. For land disposal, health investigation levels are applied (here comparison is conservatively made with residential development standards being the strictest health investigation levels).
For all samples collected, the net acidity was below the detection levels provided by the laboratory and most importantly was under the action criteria recommended by QASSIT (1998) and Dear et al. (2002). Net acidity was determined following the methods of Ahern et al. (2003). This indicates that although all materials collected and analysed have the potential to generate sulfidic acidity, they also have the potential capacity to neutralise the acid generated. Therefore, the sediment is not considered to be an acid sulphate soil requiring management action. Given that the dredging operation is only to remove sediment which has in-filled navigation channels since prior dredging events, it is considered unlikely that any material with significant acid sulphate soil material will be removed. However, the consideration of management actions to control the risk of acid sulfate soils should be cognisant of the ultimate place of disposal/use of the dredged material.
A number of parameters in the detailed suite were again recorded below detection, supporting the recommendation of Hydrobiology (2003) that PBC consider reducing the testing program for these. Options available to PBC are to:
reduce the number of detailed suite locations;
only undertake detailed suite analysis every two or more years; and/or
reduce the range of parameters examined in the detailed suite significantly.
Of the parameters of the detailed suite the OC pesticides screen should be continued in future SAP studies, given the continued measurements of dieldrin, and DDT (and its metabolites).
A review of historic PSD results indicates a relationship between the clay content of the dredged material and the non-tidal river flows. In 1999 the clay content was significantly lower than subsequent years, following a major release of water from Wivenhoe Dam earlier that year. This may suggest that in the absence of adequate flushing events there is an accumulation of these cohesive sediments and a net input of clay material from Moreton Bay.
We recommend that PSD analyses continue to be undertaken to 2 µm (so that the clay fraction can be ascertained), to aid in the future interpretation of contaminant levels against historic levels.
