Long‐Term Groundwater Monitoring Results at Large, Sudden Denatured Ethanol Releases

Abstract

Hundreds of groundwater samples were collected at E95 (95% ethanol, 5% gasoline) train derailment spills in Balaton and Cambria, Minnesota and South Hutchinson, Kansas. Most samples were analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX), ethanol, methane, acetate, terminal electron acceptors, and field parameters. At each site, maximum groundwater ethanol concentrations at percent levels were restricted to the release area and downgradient ethanol transport was not detected. A shallow, anaerobic groundwater zone characterized by the absence of dissolved oxygen, low nitrate (less than 1 mg N/L), high Fe+2, and high dissolved methane (more than 10,000 μg/L) and BTEX formed and spread downgradient from each release area. BTEX appeared to be persistent. Methane appeared to be generated within the capillary fringe and very shallow groundwater and migrate laterally. Methane's high oxygen demand promotes anaerobic conditions within the shallow groundwater. Estimated and measured methane soil gas concentrations exceeded the lower explosive limit. Long‐term monitoring at South Hutchinson and Cambria using 1 to 5‐foot (0.3 to 1.5 m) well screens straddling the capillary fringe and the shallow water table effectively demonstrated the presence of high ethanol (∼1%) and benzene (more than 250 μg/L) concentrations 5 years after the release. The wells appear impacted by long‐term ethanol inputs from the vadose zone where ethanol has persisted for years after the initial release. Toxicity, volatile fatty acids, excess hydrogen production, and/or exudate coatings could be responsible for ethanol's preservation. High acetate and hydrogen concentrations at South Hutchinson indicated that fermentation was actively occurring in the very shallow groundwater and/or in the lower capillary fringe. Short‐screened (1 to 5 feet; 0.3 to 1.5 m) nested wells were pivotal to improving our understanding of ethanol's behavior.

Increased fermentation activity and persistent methanogenesis in a model aquifer system following source removal of an ethanol blend release

“…However, such a high concentration (>1% v:v) would likely occur for only high ethanol content fuels and would be confined to the capillary fringe near the source zone where a non-aqueous phase liquid (NAPL) phase exists Barker, 2011, 2013b;Stafford et al, 2009;Stafford and Rixey, 2011). Concentrations of dissolved ethanol in groundwater impacted by ethanol-blended fuels are usually lower than 10,000 mg/L (Corseuil et al, 2011;da Silva and Corseuil, 2012;Freitas and Barker, 2013a;Spalding et al, 2011). Since the active zone for biodegradation is usually located within the dissolved plume (especially at the plume edge) rather than in the NAPL phase source zone, information on how ethanol concentrations lower than 10,000 mg/L affect microbial activities is of more practical significance to assess the environmental behavior of ethanol-blended fuel releases.…”

“…The persistence of dissolved methane was also reported in several field studies. At a site impacted by an accidental fuel ethanol spill, the ethanol concentration decreased from~20,000 mg/L to below detection limit (0.1 mg/L) within the first 3 years, but 20 mg/L of dissolved methane was still detected even 6 years after the spill (Sihota et al, 2013;Spalding et al, 2011). At an experimental site impacted by a pulse injection of Brazilian gasoline which contains 24% (v:v) of ethanol, oversaturated dissolved methane (>24 mg/L) was continuously detected in the groundwater even 6.5 years after the spill, while ethanol disappeared 4 years after the spill (Corseuil et al, 2011).…”

“…Whereas several studies have quantified the formation of ethanol metabolites following discrete or continuous release of ethanol blends (Capiro et al, 2008(Capiro et al, , 2007Corseuil et al, 2011;Feris et al, 2008;Ma et al, 2011;Mackay et al, 2006;Nelson et al, 2010;Spalding et al, 2011), previous studies have overlooked how the system responds following source removal, which is usually the first step to remediate a contaminated site. This motivated us to investigate changes in the concentrations of ethanol and its anaerobic metabolites (i.e., acetate, propionate, butyrate, butanol, and methane) following the shut-off of a continuous release of an ethanol blend solution in a model aquifer system.…”

Comparison of Source Zone Natural Attenuation Rates At Crude Oil and Ethanol–Blended Fuel Release Sites

“…Elevated EtOH concentrations can be expected to result directly following large volume, highly concentrated EtOH-augmented fuel releases, such as fuelgrade ethanol (DFE; 95% EtOH, 5% gasoline; Spalding et al 2011). For these scenarios, the combination of initial toxicity (EtOH is toxic above~6%) coupled with the mass of labile carbon for resilient and/or opportunistic microbes once EtOH falls below toxicity thresholds pose unique challenges for risk assessment and site management.…”

Succession of microbial functional communities in response to a pilot-scale ethanol-blended fuel release throughout the plume life cycle

“…Stage 3 followed the removal of ethanol from the continuous release, resulting in continuous exposure to 50 mg/L benzene and 50 mg/L toluene continues for 8 months. This mimicked the earlier removal of ethanol than BTEX at contaminated sites (Corseuil et al, 2011;Freitas and Barker, 2013;Freitas et al, 2011aFreitas et al, , 2011bMackay et al, 2006;Spalding et al, 2011). Stage 4 was the return to initial conditions (benzene and toluene removed from the tank influent), when clean water flowed through the aquifer material for 4 months.…”