Figure D-5. Desorption isotherm illustrating nonconstant and constant partitioning

Figure D-5. Desorption isotherm illustrating nonconstant and constant

partitioning

organic carbon (DOC) concentrations in the aqueous phase, mobilizing metals

and organic contaminants bound to the colloidal matter (Brannon et al. 1991).

For these reasons, the type of desorption isotherm shown in Figure D-5 is

referred to as a DOC-facilitated desorption isotherm. Since the relationship of q

versus C is not a one-to-one correspondence for DOC-facilitated desorption

isotherms, q as a function of C cannot be developed from the isotherm.

The shear velocity at particle surfaces affects colloid release from sediment

particles under the influence of decreasing ionic strength. The shear velocities

developed by agitation during batch testing are infinitely large compared to the

low shear velocities developed as water percolates through dredged material in a

CDF. Colloidal mass release in a batch test, therefore, is not representative of

colloidal mass release in a CDF under the influence of decreasing ionic strength.

In addition, batch testing requires a liquid-solids separation step that alters the

size distribution of colloids that are included in the dissolved phase. Thus, in a

batch test, neither the mass nor the size distribution of colloidal release to pore

Appendix D Leachate Testing Procedures