Natural Source Zone Depletion of Petroleum Hydrocarbon NAPL

Abstract

In the last decade, it has become widely recognized that petroleum found in soil and groundwater in the form of non-aqueous phase liquid (NAPL) is depleted by naturally occurring microbial communities. Losses of petroleum NAPL via natural processes are referred to as natural source zone depletion (NSZD). The natural loss rates of petroleum NAPL are large enough that they can often be the primary component of a site management strategy. Losses of NAPL through NSZD processes provide by-products such as CO2, CH4, and heat. As such, based on consumption of O2, production of CO2 and CH4, generation of heat, or changes in petroleum NAPL chemical composition over time, a variety of methods have been developed to measure NSZD rates. Each method has advantages and limitations. Therefore, care is needed to select the method that best fits site conditions and site- and project-specific data quality objectives.