Natural source zone depletion predicts finite longevity for petroleum products in soil and groundwater

From environmental concerns to economics, managing inadvertent releases of petroleum products in soils and groundwater is a significant concern. Here, estimates of specific petroleum product volumes ranging from 80,000 to 800,000 L/hectare are developed using cryogenic coring techniques at 5 sites. Heat generated from natural petroleum hydrocarbon oxidation at 10 sites provides daily estimates of Natural Source Zone Depletion (NSZD) over 0.43 to 3.07 years. NSZD rates ranging from 4,000 to 20,000 L/hectare/year are relatively constant in time and apparently independent of specific product volumes, soil permeabilities, and depth. A weak correlation between NSZD rates and source zone temperatures suggests that microbially mediated oxidation is controlled by electron transport from electron donors (hydrocarbons) to atmospheric oxygen (terminal electron acceptor). Data-driven regression of daily NSZD rates yields source zone longevity estimates of one to four decades. At two sites with active product recovery, NSZD outperformed recent conventional recovery efforts by 96% and 99%. These findings demonstrate the importance of NSZD as a key remedy component at mature sites, limitations of conventional recovery, and the potential of enhancing NSZD rates. Source zone longevity is a new quantifiable metric, that can support informed decisions for managing petroleum products in soils and groundwater.