Passive remediation can be appropriate where natural processes and actions such as institutional controls mitigate exposure to contaminated groundwater, achieving remedial action objectives and protectiveness of human health and the environment. Monitored natural attenuation (MNA) is a prevalent passive remediation strategy supported by a regulatory framework and monitoring design guidance. MNA can also be used after active remediation has been completed (e.g., pump-and-treat) as a polishing step to reach ultimate remedial action objectives. However, MNA and existing monitoring guidance primarily target situations where the remedial action objectives are met within a few decades. When timescales for passive remediation extend to many decades, a corresponding change in monitoring strategy is needed to adapt to the extended time scale. This document provides guidance for implementing an extended-scale monitoring (ESM) approach appropriate for long-duration passive remediation. Extended-scale is defined in this document with respect to time (i.e., a long duration of remediation) and a large enough physical scale such that receptors will not be impacted within the remediation timeframe.
Revised: December 2, 2020 |
Published: September 30, 2020