An assessment of the impact of fuel hydrocarbons and oxygenates on groundwater resources with a methodology for prioritizing regulatory action at leaking underground fuel tank sites

The widespread use of the fuel oxygenate methyl tertiary butyl ether (MTBE), combined with its persistence and mobility in the subsurface environment, have contributed to its dominant presence and frequent detection in groundwater plumes and community water system (CWS) wells in the U.S. Concerns about potential groundwater contamination from MTBE have led several states to consider or enact MTBE bans. However, the environmental consequences of replacing MTBE with another oxygenate (or a group of oxygenates) is largely unknown. This work assessed the potential for groundwater contamination of fuel hydrocarbons (FHCs) and oxygenates by examining their occurrence, distribution, and extent at leaking underground fuel tank (LUFT) sites in the greater Los Angeles region. LUFT sites are particularly important because they represent major point sources of gasoline constituents and the leading cause of FHC and oxygenate groundwater contamination.; This work demonstrated that in the absence of new design and construction of the underground fuel tank (UFT) system that emphasizes detection, repair, and containment, an effective management strategy may involve placing greater emphasis on a UFT program for ensuring adequate compliance with existing regulations. The plume lengths data indicated that under a well managed UFT program, with prompt detection and cleanup of source contaminants associated with failed UST systems, the majority of FHC and oxygenate plumes associated with release(s) from LUFT facilities were relatively “localized.” The adequate compliance with existing UST regulations may decrease the probability of future leakage and allow for prompt response and cleanup of possible sources.; This work also presented a screening methodology for prioritizing regulatory action at FHCs- and oxygenates-impacted LUFT sites. The objective of this work is focused on using model applications as a regulatory screening tool to help organize and synthesize the available field data. This work demonstrated that the screening-model applications can be consistently applied to generate reliable and conservative model predictions (e.g., MTBE plume travel time) when the LUFT field data met the data requirements and model assumptions specific to the screening-model applications.