Comparison of Radiocarbon‐ and Background Location‐Corrections on Soil‐Gas CO2 Flux‐Based NSZD Rate Measurements at Petroleum Impacted Sites. Issue 3 (22nd July 2022)

• Record Type: Journal Article
• Authors: Zimbron, Julio A.
• Is Part Of: Ground water monitoring & remediation. Volume 42:Issue 3(2022)
• Page Start: 116
• Page End: 122
• Publication Date: 2022-07-22
• Subjects: Groundwater -- Periodicals; Groundwater -- Purification -- Periodicals; Wellhead protection -- Periodicals; Hydrogeology -- Periodicals; 553.790286
• DOI: 10.1111/gwmr.12538
• Languages: English
• ISSNs: 1069-3629

Abstract

Abstract: The measurement of contaminant natural source zone depletion (NSZD) rates has become an important tool to manage petroleum contaminated sites. Most NSZD rate measurement methods rely on a balance on the biodegradation by‐products (either carbon or heat). Carbon balance‐based methods stoichiometrically convert measured soil‐gas CO2 flux related to contaminant degradation to equivalent contaminant mass loses. CO2 flux‐based methods require separating the fraction of the total CO2 flux produced by NSZD from the fraction of CO2 flux produced by natural soil processes (due to modern carbon turnover). Two method corrections are available to distinguish the nature of the measured CO2 flux: (1) The background location correction subtracts a measurement from an unimpacted location from measurements collected at impacted locations, and (2) a location‐specific radiocarbon ( 14 C) analysis that differentiates the modern and old carbon fractions of each total CO2 measurement. This work evaluates both correction approaches using 36 measurements at impacted locations from five sites. The 14 C‐corrected data shows that the magnitude and variability of the modern carbon‐related fraction (noise) and the NSZD related fossil fuel signal are similar, suggesting a location‐specific correction is more valid. Only one sparsely vegetated arid site showed close agreement between both corrections ( 14 C‐ and background location). These results highlight the strong effect of the correction method used on NSZD rate measurements, and the importance of considering data quality on the subsequent data management process.