Dr. Julio Zimbron holds a M.Sc. and Ph.D. in Chemical Engineering from Colorado State University. He has 15 years of academic and applied research professional experience. In the last seven years, he has focused on developing innovative ways of estimating the rate of petroleum natural source zone depletion at the field scale.
PLATFORM PRESENTER - NAPL Characterization and Depletion: My Old Friend
New API Guidance on Petroleum Natural Source Zone Depletion
Natural source zone depletion (NSZD) has emerged as an important concept for petroleum environmental remediation. NSZD is a term used to describe the collective, naturally occurring processes of dissolution, volatilization, and biodegradation that result in mass losses of hydrocarbon constituents from the subsurface.
In order to provide interested parties (i.e., site owners, regulators, and practitioners) with a basic understanding of NSZD processes and methods to quantify NSZD mass loss rates, the American Petroleum Institute (API) led an initiative to develop a practical guidance for Quantification of Vapor Transport-related NSZD Processes (API NSZD guidance). The primary objective of the document is to improve NSZD data quality by providing consensus-built, consistent methodology that represents the current state of knowledge and practice.
This presentation will describe the API NSZD guidance, including theory, application, measurement methods, and data interpretation. Three methods are described in detail: i) the gradient method, ii) passive flux traps, and iii) the dynamic closed chamber (DCC). The gradient method is the oldest, and is described in the 2009 ITRC LNAPL-1 technology overview document. The gradient method estimates fluxes of biodegradation gases (e.g., oxygen and methane) within a region of the vadose zone using effective vapor diffusion coefficients and gas concentrations. Two new methods have emerged in recent years - passive flux traps and the DCC method. Both of these methods focus on measuring biodegradation by-product gas flux at the ground surface (i.e., soil gas efflux). The DCC method measures efflux real-time using an automated chamber and gas analyzer system. It can be used to generate single event (snapshot) soil gas flux measurements or set-up to evaluate fluxes over time. The passive CO2 traps measure long-term integrated (average) fluxes over one to three weeks using a temporary receiver pipe and sorbent apparatus.
In addition to a detailed description of specific NSZD quantification methodologies, the API NSZD guidance provides key elements of a monitoring program design, implementation procedures, data evaluation considerations, a case study, and a statement of method limitations. It also identifies areas of emerging research related to petroleum biodegradation, such as new methods to quantify NSZD based on soil temperature measurements and soil thermal flux.