Laboratory tests for flux evaluation

The USACE has applied a refined version of an existing sediment flux

model (Boyer et al. 1994) for capping evaluations, and more refinements

to the model are planned to account for a comprehensive treatment of all

pertinent processes. But in absence of such a tool, analytical models such

as that in Appendix B should be used in calculating long-term contaminant

loss for capped deposits as long as conservative assumptions are used in

the calculations.

Laboratory tests for flux evaluation

Several testing approaches have been applied to define cap thicknesses

and the sediment parameters necessary to model their effectiveness in

chemical isolation. Laboratory tests may be used to define sediment-

specific and capping-material-specific values of diffusion coefficients and

partitioning coefficients. But no standardized laboratory test or procedure

has yet been developed to fully account for advective and diffusive proc-

esses and their interaction.

The USACE developed a first-generation capping effectiveness test in

the mid-1980s as part of the initial examination of capping as a dredged

material disposal alternative. The test was developed based on the work

of Brannon et al. (1985, 1986), Gunnison et al. (1987a), and Environ-

mental Laboratory (1987). Louisiana State University has conducted labo-

ratory tests to assess diffusion rates for specific contaminated sediments

to be capped and materials proposed for caps (Wang et al. 1991). Diffu-

sion coefficients for long-term modeling of diffusive transport of contami-

nants from contaminated sediment into cap material have also been

measured using diffusion tubes (DiToro, Jeris, and Clarcia 1985). Envi-

ronment Canada has performed tank tests on sediments to investigate the

interaction of capping sand and compressible sediments, and additional

tests are planned in which migration of contaminants due to consolidation-

induced advective flow will be evaluated (Zeman 1993). The USACE has

also developed leach tests to assess the quality of water moving through a

contaminated sediment layer into groundwater in a confined disposal facil-

ity environment (Myers and Brannon 1991). This test is being applied to

similarly assess the quality of water potentially moving upward into a cap

due to advective forces.1

Results of laboratory tests conducted with samples of the contaminated

sediments to be capped and the proposed capping sediments should yield

sediment-specific and capping-material-specific values of diffusion coeffi-

cients, partitioning coefficients, and other parameters needed to model

long-term cap effectiveness. Model predictions of long-term effectiveness

using the laboratory-derived parameters should be more reliable than pre-

dictions based on so-called default parameters. More detailed descrip-

tions of test procedures for evaluation of capping effectiveness are

presented in Appendix C.

Personal Communication, 1995, Tommy E. Myers, U.S. Army Engineer Waterways

Experiment Station, Vicksburg, MS.

Chapter 7 Dredged Material Cap Design