期刊
JOURNAL OF CONTAMINANT HYDROLOGY
卷 235, 期 -, 页码 -出版社
ELSEVIER
DOI: 10.1016/j.jconhyd.2020.103729
关键词
Aerobic; Biodegradation; LNAPL; Basalt; NSZD
资金
- U.S. Navy under Comprehensive Long-term Environmental Action Navy (CLEAN) [N62742-17-D-1800]
- GSI Environmental Inc. [9400905]
In recent years, a number of methods have been used to measure the biodegradation of petroleum light nonaqueous phase liquids (LNAPL) at petroleum release sites, a process known as natural source zone depletion (NSZD). Most commonly, NSZD rates have been measured at sites with unconsolidated geology and relatively shallow groundwater (< 50 ft. bgs, 15 m bgs). For this study, we have used two methods (1. carbon dioxide flux measured using carbon traps and 2. heat flux based on subsurface temperature gradients) to measure NSZD rates at a petroleum release site in Hawaii with basalt geology and deep groundwater (300 ft. bgs, > 100 m bgs). Both methods documented the occurrence of NSZD at the facility and the two methods yield estimates of the NSZD rate that agreed within a factor of 2 (4600 to 7400 gal/yr; 17,000 to 28,000 L/yr for the flux method and 8600 to 13,000 gal/yr; 33,000 to 49,000 L/yr for the temperature method). Soil gas samples collected directly above the water table and at shallower depths within the vadose zone indicated aerobic conditions throughout the vadose zone (oxygen > 13%) and no detectable methane. These results indicate that NSZD occurs at this site through the direct aerobic biodegradation of LNAPL rather than the two-step process of anaerobic methanogenesis followed by methane oxidation at a shallow depth interval documented at other sites.
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