CO2 efflux-based quantification of natural zone depletion rate of LNAPL gas phase at a large petrochemical site

In this study, the CO2 efflux at the ground surface was measured using a dynamic closed chamber method to evaluate the NSZD rate in light non-aqueous phase liquid (LNAPL) source zone at a large petrochemical site. The results show that the average CO2 efflux associated with contaminant degradation was estimated at 0.59µmol/(m2.s), corresponding to a total petroleum hydrocarbon mineralization rate of 31.1t TPH/year in the study area of 100,000m2, falling within the range of NSZD rates reported at other sites. The result showed that there was active NSZD of petroleum hydrocarbon in source zone. NSZD rates were affected by temperature and atmospheric pressure. Therefore, to provide a more accurate estimate of the average NSZD rate and to evaluate long-term trends, seasonal measurements are required. The annual carbon emissions of NSZD were estimated at 85t at this site, accounting for 19% of the carbon emissions under risk control site. Obviously, the carbon emissions caused by NSZD should be included in the carbon emissions accounting of a contaminated site, which will provide valuable insights into NSZD rate assessment and calculation of carbon emissions. © 2024 Chinese Society for Environmental Sciences. All rights reserved.