Appendix C: Capping effectiveness Tests

Appendix C

Capping Effectiveness Tests

Introduction

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 coefficients,

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 predictions based on

so-called default parameters. At present, there are several tests that have been

applied for this purpose.

Louisiana State University has conducted laboratory tests to assess diffusion

rates for specific contaminated sediments to be capped and materials proposed

for caps. A capping simulator cell was used in which a cap material layer is

placed over a contaminated sediment, and flux due to diffusion is measured in

water that was allowed to flow over the cap surface. Initial tests measured flux

of 2,4,6-trichlorophenol (TCP) through various cap materials. These tests

showed that the breakthrough time and time to steady state were directly depen-

dent on the partitioning coefficient and that cap porosity and thickness were the

dominant parameters at steady state (Wang et al. 1991).1

Environment Canada has performed tank tests on sediments from Lake

Ontario to qualitatively investigate the interaction of capping sand and com-

pressible sediments. The tests were carried out in 3.6- by 3.6- by 3.7-m

observation tanks in which the compressible sediments were placed and allowed

to consolidate; sand was released through the water column onto the sediment

surface. In the initial tests, physical layering and consolidation behavior were

observed. Additional tests are planned in which migration of contaminants due

to consolidation-induced advective flow will be evaluated (Zeman 1993).

References cited in this appendix are listed in the References at the end of the main text.

Appendix C Capping Effectiveness Tests