Confined disposal facility characterization for beneficial reuse of dredged material: a case study to demonstrate a structured approach to sampling and data analysis

摘要

Purpose Confined disposal facilities (CDFs) are widely used for disposal of navigation dredged material, but many are running out of capacity. Removal of dredged material for beneficial use offers potential for sustainable operations, but requires characterization with a high degree of confidence. Few data are available to inform characterization efforts in these artificial depositional environments; thus, a CDF case study was used to demonstrate a structured approach to sampling and data analysis. Materials and methods Selected data analysis procedures were applied to data collected from a CDF, with the objective of illustrating the utility of these procedures in (1) maximizing information obtained from limited data and (2) assessing the adequacy of the data in terms of estimating parameters of interest. In this case, the data were used to estimate the abundance of the desired fraction (sand), the contaminant levels in the sand and residual fractions, and the uncertainty of the parameters measured. From the outcome of this analysis, a stepwise approach to CDF characterization and data analysis was developed. Results and discussion The available dataset proved sufficient to estimate the distribution of sand in the CDF, although estimate reliability was constrained by the small number of samples and the lack of samples along the western facility boundary. Soot, organic carbon, and oil and grease were statistically significant regressors for many contaminants of concern; however, data were too limited and variable to permit prediction of contaminant concentrations in unanalyzed samples on the basis of the sorptive phases. A contour surface of benzo(a)pyrene concentration was generated to illustrate the utility in identifying areas of the CDF that may be problematic with respect to meeting regulatory criteria or guidelines for beneficial use; such areas may require additional processing to remove more highly contaminated fractions. Conclusions Of the graphical data analysis techniques evaluated, the most useful were: the aerial site view showing sample locations and per cent sand; the ternary diagram comparing sample characteristics; the contour map and the sand isopach map, representing aerial variation of sand thickness; and the depiction of contaminant concentrations as a contour surface. The predictive capability of the data was limited, but may have been aided with the addition of density fractionation and a larger dataset.