| Tert-butyl alcohol (TBA) is an important intermediate product from MTBE (methyl tert-butyl ether) biodegradation and an environmental contaminant that can be found in service station groundwater contaminant plumes. Typically these plumes are anaerobic, under which conditions TBA appears to biodegrade slowly if at all, however TBA has been shown to biodegrade quickly under induced aerobic conditions in situ in small two-well recirculation pilot tests in a low concentration oxygenate plume. This thesis evaluates opportunities for and impediments to using this technology at a more complex site in Northern California, with near-source contamination lingering above regulatory standards. During oxygen remediation strategies, added oxygen can be consumed by 1) target reactions, in this case the biodegradation of TBA and the other contaminants, and 2) non-target reactions, such as aerobic respiration by autotrophic microbes utilizing organic carbon as an electron donor and oxidation of reduced minerals. The objective of this study was to determine if creation of an in situ aerobic treatment zone at the study site was likely to be feasible, and TBA likely to be degraded sufficiently within it, based on results of aerobic microcosms and column experiments to estimate the TBA aerobic biodegradation capacity of native microbes and oxygen demand of site sediment. The results suggest that 1) TBA degrading microbes are present and, when provided with sufficient oxygen, are able to degrade TBA to below regulatory goals, and 2) the demands for oxygen by non-target reactions will likely not prevent the creation of an in situ aerobic treatment zone within which TBA can be degraded below standards. Instead, groundwater reactive transport modeling of a hypothetical recirculation pilot test utilizing Modflow and RT3D indicated that the non-target reactions consumed oxygen slowly enough and dissolved oxygen penetrated sufficiently far into the aquifer to allow timely TBA degradation to occur. In addition, by analysis of sediments from various locations at the site, solid oxygen demand (SOD) was found to correlate roughly with total organic carbon concentrations (TOC) in sediment, in ratios similar to those noted in previous oxidation technology studies, suggesting that TOC may potentially be used to estimate SOD. Although this research addressed fuel oxygenates, it has broader applications, e.g., to situations involving any groundwater contaminant that can be biodegraded aerobically or treated in situ by addition of other oxidizing amendments. |
