Barrier-controlled monitored natural attenuation.

Three existing technologies (source containment, source reduction, and monitored natural attenuation) are integrated in barrier-controlled monitored natural attenuation (BCMNA)--a new approach for managing plumes of contaminated groundwater and remediating contaminated sites. The basic BCMNA concept uses a low-permeability, nonreactive barrier to release contaminants into an aquifer at a rate that optimizes natural attenuation. A simplified, one-dimensional model of the process is developed, and a hypothetical example of BCMNA is presented for a site contaminated with benzene. The analytical solution is used to demonstrate how contaminant concentrations can be controlled at a downgradient point of environmental compliance by manipulating design variables. BCMNA provides a greater degree of process control and risk reduction than monitored natural attenuation alone. BCMNA also holds promise for reducing remediation costs because (1) barriers can be constructed relatively inexpensively and (2) a cost-effective amount of source reduction can be applied inside the contained area with the BCMNA system remaining in place to safely complete the remediation process after source reduction is terminated. Further numerical modeling and a demonstration project are recommended to address important details and prove the concept.