ABSTRACT
This chapter focuses on the bottom part of the curve where concentrations change at very slow rates. There are several processes that may contribute to the flattening of this curve, all of them may, in part, affect water quality. These processes include physical processes, chemical processes, and chemical reactions. Risk assessment can be uniquely designed for the specific site. Any unusual paths for human contact, and any design method used to prevent human contact can be incorporated into the risk assessment. The contaminants are sorbed to the soil or aquifer. Depending on the organic content of the soil and the chemical properties of the contaminant, the individual compounds may release to the water at different rates. Several contaminant transport processes may cause residual contamination to be flushed from the aquifer more slowly. Transport processes that may cause this include: diffusion or contaminants within heterogeneous sediments, hydrodynamic isolation, sorption-desorption, and liquid-liquid portioning.
