Natural source zone depletion (NSZD) is the new technical term for naturally occurring biodegradation processes that reduce petroleum, nonaqueous-phase liquids (NAPL) from the subsurface. Petroleum NAPL can seep into soil from oil spills or leaks, resulting in potential groundwater contamination and remediation challenges.
While biodegradation is ubiquitous at petroleum release sites, NSZD biodegradation processes are most significant within the source zones of the contaminating petroleum liquids. In this aspect, it is distinctly different from conventional monitored natural attenuation remedies, where contaminant degradation occurs outside the source zone in dissolved plumes.
Early on, CH2M recognized the high value of NSZD science and began working with a prominent research university to deploy new monitoring methods in the field and present new information to regulators, including endorsing its consideration as a viable remedial option and benchmark for other remediation efforts because it is critical to understanding the short- and long-term fate of hydrocarbons.
NSZD processes represents a paradigm shift in the way petroleum NAPL-contaminated sites are managed and remediated. CH2M has collected extensive data demonstrating typical rates of from 200 to 2,000 gal of petroleum that can be naturally degraded per acre of NAPL source zone per year. These rates are often equal to or greater than other active remediation systems, establishing that, in this new paradigm, NSZD monitoring alone or in combination with an active remediation can be used to more-cost-effectively remediate a site, yet still protect human health and the environment.