In recent years, a number of methods have been used to measure the biodegradation of petroleum light non-aqueous 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.

近年来，已使用多种方法测量石油释放地点轻质非水相液体 (LNAPL) 的生物降解，这一过程称为天然源区耗竭 (NSZD)。最常见的是，NSZD 速率是在地质松散和地下水相对较浅（<50 ft. bgs，<15 m bgs）的地点测量的。在这项研究中，我们使用了两种方法（1. 使用碳捕集器测量的二氧化碳通量和 2. 基于地下温度梯度的热通量）来测量夏威夷玄武岩地质和深层地下水 (>300) 石油释放地点的 NSZD 速率英尺 bgs，>100 m bgs）。这两种方法都记录了设施中 NSZD 的发生情况，并且这两种方法产生的 NSZD 率估计值在 2 倍（4600 到 7400 加仑/年；17,000 到 28，通量法为 000 升/年，8600 至 13,000 加仑/年；温度法为 33,000 至 49,000 升/年）。直接在地下水位上方和包气带内较浅深度收集的土壤气体样本表明整个包气带的有氧条件（氧气> 13％）并且没有检测到甲烷。这些结果表明 NSZD 通过 LNAPL 的直接需氧生物降解在该地点发生，而不是在其他地点记录的浅深度间隔的厌氧产甲烷随后甲烷氧化的两步过程。