Transport of sequentially decaying reaction products influenced by linear nonequilibrium sorption

Predicting the migration of sequentially degrading reaction products is imp ortant for the accurate analysis of subsurface treatment walls and other en vironmental systems. Recently, it has also been realized that consideration of rate-limited sorption may be necessary to quantify the transport of con taminants in reactive treatment walls. In this paper, analytical and semian alytical solutions are developed for the one-dimensional transport of a par ent compound and three sequentially decaying reaction products influenced b y nonequilibrium sorption. The solutions are based on the Laplace transform ation technique and incorporate a different sorption distribution coefficie nt and mass transfer rate for each reaction product. Two types of exit boun dary conditions are considered: semi-infinite and finite zero-gradient. The developed solutions are used to simulate the migration of trichloroethylen e and its reaction products in a zero-valent iron treatment wall. The effec t of nonequilibrium sorption on the time to reach steady state is investiga ted, and it is shown that a zero-valent iron treatment wall may exhibit a s ignificant transient period. However, concentrations reach 80% of the stead y state values within the first 100 pore volumes. It is also shown that neg lecting dispersion may lead to nonconservative predictions of the effluent contaminant concentrations.