Abstract

  The flux is a key element in chemical fate and transport (CFaT) water quality models used for rivers, lakes, estuaries and coastal oceans. Theoretically and mechanistically sound process algorithms backed by both laboratory and field data are needed in order to make confident future predictions of metal and organic pollutant in these aquatic systems. These environmental chemodynamics simulation tools are being used to evaluate the effectiveness of several remedial options including monitored natural recovery, capping, dredging, in situ treatment and combinations of these. The flux element in these CFaT models must contain both particles and soluble algorithms for chemical release from the bed. Particle processes (i.e. resuspension and setting) have traditionally been the focus of attention and it has received much study and re-development in the past decade. The recent availability and analysis of large sets of high quality particle and chemical data from several rivers containing PCBs, including the Hudson, has caused a shift in thinking and a re-evaluation of the significance of the soluble release process. This process occurs when flow conditions are unfavorable for any significant particle re-suspension. The objective of this presentation is to propose and demonstrate that a rapid soluble release process exist and to offer an algorithm for quantifying its flux from the bed. Both theoretical and empirical methods will be used. Data obtained from four major rivers show that the soluble release fraction may vary from a few percent to nearly 100% of the PCB release. A numerical ranking of the known and quantifiable individual soluble release processes places in-bed bioturbation first on the list. Coupled with the benthic boundary layer resistance a simple theoretical algorithm is offered as the model for the overall mass-transfer coefficient Kf(cm/h), of the dominant soluble release process. Limited laboratory plus field observations on thirteen PCB congeners across the Thompson Island Pool of the Hudson River display a soluble release chemical signature compatible with proposed theoretical model for Kf. In conclusion, it appears that the proposed bioturbation mechanism allows for the development of a theoretical model sufficient to explain existing data sets. However, alternative models may explain the data as well. Detailed laboratory experiments and further field studies will be needed to satisfy all members of the engineering science community on this soluble release fraction issue.