• Adding parameters with double multiplicity

• Parameters with Double Multiplicity in AMBER are parameters indexed over two namesets
• The Sorption Coefficient describes the extent to which a contaminant is retained on the solid phase in a saturated (usually) porous medium.
• Retardation means that the contaminant is transported more slowly than the fluid. Sorption is a key process determining the amount of retardation.

This video covers sections 7.4.3 and 7.4.4 of the User Guide.