6. Noosa River DMP Ver0 (Combined)

                                                                 Noosa River - Sediment Sampling Report
                                             BMT (OFFICIAL)



2.7 Data Analysis and Assessment

Sediment Concentrations
Concentrations of contaminants measured in sediment samples were compared to screening levels as
described in Table 2.1. Those being Table 1A(1) and Table 1B(6) of the NEPM Volume 2, Schedule B1,
in the first instance to determine whether the material is acceptable for placement on land, and
subsequently, Table 2 of NAGD if required to determine potential impact of dredge plumes and
suitability for placement at sea (if required).

Mean concentrations of chemical parameters at the upper 95% confidence level (95% UCL) were
compared against the screening levels described above (in line with Singh et. al. 2010). An assessment
of the material’s suitability for land-based re-use followed the statistical analysis and the data evaluation
procedures in Section 3.4, Volume 5 Schedule B4 of the NEPM. In the event that 95th percentile upper
confidence limits for particular contaminants are exceeded, the next steps would be to follow the
decision tree in Volume 1, Schedule A of the NEPM to determine a site remediation plan or collect
further data describing the nature of contamination.

Data pre-treatment
Analytical values below detection limit were set to one-half of the laboratory Limit of Reporting (LOR) as
per NAGD recommendation to facilitate 95% UCL calculation. Organic contaminant results (organotins)
were normalised to 1% TOC where the measured value is within the range of 0.2-10%. If TOC values
were outside of this range, the highest (10%) or lowest (0.2%) value was adopted as appropriate.
Organic parameters with concentrations below detection limits were not normalised to 1% TOC but
were included at half their LOR.

An assumption in the calculation of the 95% UCL is that the samples are statistically independent.
Therefore, field triplicate samples and laboratory split samples were not included in the 95% UCL
calculation.

Calculation of 95% UCL and Comparison to Screening Levels and other Guideline Values
ProUCL Version 5.1.00 was used to calculate the 95% UCL. For normally distributed data, the
arithmetic mean and standard deviation were calculated, and the 95% UCL was calculated using the
one-tailed Student’s t UCL test. For data that followed a log-normal (or other) distribution, the geomean
was calculated, and the 95% UCL was analysed using non-parametric Jack-Knife analysis as per
NAGD recommendation.

In some cases where only one value of a dataset was recorded above LOR, calculation of the Jack-
Knife UCL was not possible. In these cases, the maximum recorded value of the dataset was
conservatively used instead for comparison against NAGD screening levels and subsequent updates
(Simpson et al., 2013).

If 95% UCL values for all analysed parameters fell below the screening levels or background levels, the
sediment can be considered clean and suitable for unconfined disposal at sea.

Acid Sulfate Soils
The results of the chromium-suite acid sulfate analysis were assessed against the Australian framework
for Acid Sulfate Soil management in coastal systems (Ahern et al. 1998). The risk of acidification was
determined by the acid-base accounting approach (Ahern et al. 2004). Net acidity was calculated from
the results as a measure of the acid producing capacity of the sampled sediment upon complete
oxidation.




A10342 | 005 | 01                                    18                                          14 April 2022