Incorporating Natural Source Zone Depletion (NSZD) into the Site Management Strategy

This chapter summarizes three petroleum remediation case study sites that incorporated natural source zone depletion (NSZD) into their site management strategy. The sites include: a light petroleum non-aqueous phase liquid (NAPL) pipeline release in an arid climate that transitioned to an NSZD-based monitored natural attenuation (MNA) remedy after several traditional remedial actions; a former refinery in a temperate climate that incorporated NSZD with phytoremediation; and a former industrial petrochemical facility in a tropical climate with waste dense petroleum hydrocarbon NAPL that transitioned to NSZD after several decades of groundwater extraction and treatment. The narratives provide examples of how NSZD was used as an effective and sustainable/resilient management option. Key points related to the use of NSZD on a broader range of site conditions are highlighted. The importance of acknowledging, accounting, and incorporating NSZD into remedies is emphasized because significant depletion rates are frequently observed to occur at petroleum NAPL release sites. The chapter demonstrates how NSZD can be incorporated into a conceptual site model and the implemented remedy. It provides details on the importance of site risk profile and regulatory framework as well as lines of evidence to support transition to a MNA remedy inclusive of NSZD.