Appendix B: Model for Chemical Containment by a Cap

Appendix B

Model for Chemical

Containment by a Cap

by Dr. Danny D. Reible,

Louisiana State University1

Introduction

This appendix describes a model for evaluation of chemical flux through a

cap. Through use of this model, the effectiveness of chemical containment of a

cap can be assessed. This model should be applied once remediation objectives

are determined, a specific capping material has been selected and characterized,

and a minimum cap thickness has been determined based on components for

isolation, bioturbation, and consolidation. If the objective of the cap is attain-

ment of a given contaminant flux, the model can be used to estimate the required

cap thickness.

This model assumes that the cap is armored such that erosion of the cap does

not provide the primary means of contaminant migration. Instead, the contami-

nants contained within the pore water of the sediment are available to migrate

into the cap and subsequently into the overlying water. The pore water concen-

tration, Cpw, is always assumed in a state of local equilibrium that is related to the

sediment contaminant loading, 7sed, milligrams contaminant per kilogram dry

obs

sediment, through an observed partition coefficient, Kd , as

obs

7sed Kd

Cpw

(B1)

Thus the initial pore water concentration in the sediment, C0, is given by

7sed

C0 Cpw

(B2)

obs

This appendix is identical to Appendix B of the report entitled "Guidance for In-Situ

Subaqueous Capping of Contaminated Sediments" (Palermo et al. 1996).

Appendix B Model for Chemical Containment by a Cap