Novel Technology to Promote Mixing in Dead-End Pores Could Improve Pump-and-Treat

Pump-and-treat remediation is the most common method to remediate groundwater contamination. One major bottleneck to current pump-and-treat techniques is that contaminants become trapped in dead-end pores, which are poorly connected to the mean flow of an aquifer. A similar problem is encountered in the removal of surfactants in the manufacture of semiconductor and the removal of oil residue build-up in small ducts. We hypothesized that just similar strategies employed to resolve this problem and clean these cavities could be applied to groundwater remediation. We tested our hypothesis in a series of numerical and laboratory experiments. We considered unwashed and washed media. To elucidate the dead-end pore dynamics of this new flow regime, we performed numerical experiments and used a physical model to obtain a relationship between the hypothesized flow regime and the pore characteristics. We found two mechanisms in this proposed flow regime that improve mixing between the dead-end pores and the well-connected pores in an aquifer. Our dimensional analysis pointed to the change in pressure as the key component in two distinct, new pore-cleaning mechanisms. Depending on the cleanup target, the proposed new flow regime for pump-and-treat remediation may speedup treatment times by a factor of six or more. Whether or not the laboratory speedup factors would hold in the field cannot be established without field-scale experiments. There are public health and financial implications of this research. Furthermore, while we present this in terms of pump-and-treat remediation, this work demonstrates mixing; which indicates this mechanism may be applied to bioremediation to deliver reactants.