Peer Reviewed: Will Ethanol-Blended Gasoline Affect Groundwater Quality?

Powers, Susan E.; Rice, David W.; Dooher, Brendan P.; Alvarez, Pedro J. J.

doi:10.1021/es012247h

Cited by 60 publications

(24 citation statements)

References 7 publications

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“…The fuel to water ratio in a spill scenario determines the ethanol concentration in the aqueous phase, and hence, the impact of the cosolvency effect. In a 2001 review, Powers et al [41] concluded that "Unless there is a neat ethanol spill, aqueous phase ethanol concentrations (are) unlikely to exceed 10% in contaminated sites. Therefore, it is unlikely that cosolvent-related increases in BTEX concentrations will be significant relative to other processes that affect field-scale concentrations following a spill of ethanol-blended gasoline.…”

Section: Phase Separationmentioning

confidence: 99%

Phase equilibria of ethanol fuel blends

French

Malone

2005

Fluid Phase Equilibria

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Section: Phase Separationmentioning

confidence: 99%

Phase equilibria of ethanol fuel blends

French

Malone

2005

Fluid Phase Equilibria

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“…Likely release scenarios include E85 (85% ethanol; 15% gasoline v/v) leaking from underground storage tanks at service stations and fuel grade (denatured) ethanol (95% ethanol; 5% gasoline) spills during transport or after reaching bulk terminals. Although some attention has been given to the impacts of ethanol on the natural attenuation of benzene, toluene, and xylenes (BTX) plumes (Powers et al 2001a,b; da Silva and Alvarez 2002; Deeb et al 2002; Molson et al 2002; MacKay et al 2006), little is known about how physical–chemical processes influence the concentration of hydrocarbons in pore water near a source of a fuel ethanol spill.…”

Section: Introductionmentioning

confidence: 99%

Pore Water Characteristics Following a Release of Neat Ethanol onto Pre‐existing NAPL

Stafford¹,

Cápiro²,

Alvarez³

et al. 2009

Groundwater Monitoring Rem

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Neat ethanol (75.7 L) was released into the upper capillary zone in a continuous‐flow, sand‐packed aquifer tank (8.2 m3) with an average seepage velocity of 0.75 m/day. This model aquifer system contained a residual nonaqueous phase liquid (NAPL) that extended from the capillary zone to 10 cm below the water table. Maximum aqueous concentrations of ethanol were 20% v/v in the capillary zone and 0.08% in the saturated zone at 25 and 30 cm downgradient from the emplaced NAPL source, respectively. A bench‐scale release experiment was also conducted for a similar size spill (scaled to the plan area). The concentrations of ethanol in ground water for both the bench‐ and pilot‐scale experiments were consistent with advective–dispersive limited mass transfer from the capillary to the saturated zone. Concentrations of monoaromatic hydrocarbons and isooctane increased in the pore water of the capillary zone as a result of both redistribution of residual NAPL (confirmed by visualization) and enhanced hydrocarbon dissolution due to the cosolvent effect exerted by ethanol. In the tank experiment, higher hydrocarbon concentrations in ground water were also attributed to decreased hydrocarbon biodegradation activity caused by preferential microbial utilization of ethanol and the resulting depletion of oxygen. These results infer that spills of highly concentrated ethanol will be largely confined to the capillary zone due to its buoyancy, and ethanol concentrations in near‐source zone ground water will be controlled by mass transfer limitations and hydrologic conditions. Furthermore, highly concentrated ethanol releases onto pre‐existing NAPL will likely exacerbate impacts to ground water, due to NAPL mobilization and dissolution, and decreased bioattenuation of hydrocarbons.

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“…Ethanol is a favourable bacterial growth substrate that can be easily metabolized, and bacteria that can feed on ethanol are more ubiquitous in the environment than those that degrade BTX compounds (Powers et al ., 2001a,b). However, ethanol toxicity studies with indigenous organisms in soil matrices have shown that concentrations above 10 g l −1 inhibit bacterial growth (Ingram and Buttke, 1984) and concentrations exceeding 40–100 g l −1 exert a bactericidal effect (Ingram and Buttke, 1984; Hunt et al ., 1997; Araujo et al ., 1998).…”

Section: Introductionmentioning

confidence: 99%

Microbial community response to a release of neat ethanol onto residual hydrocarbons in a pilot‐scale aquifer tank

Cápiro

Silva

Stafford

et al. 2008

Environmental Microbiology

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The microbial community response to a neat ethanol release (E100, 76 l) onto residual hydrocarbons in sandy soil was evaluated in a continuous-flow 8 m(3) pilot-scale aquifer tank, simulating a release at a bulk fuel terminal. Microbial genotypic shifts were assessed using quantitative real-time PCR analysis. High ethanol concentrations in the capillary fringe at potentially toxic levels, exceeding 100,000 mg l(-1), were tolerated by the microbial community. The high biochemical oxygen demand exerted by ethanol rapidly induced anaerobic conditions, and both methane production (up to 1.2 mg l(-1)) and growth of putative methanogenic Archaea (up to 10(6) gene copies per g of soil) were observed in shallow groundwater and soil samples 75 cm down gradient from the source. Aerobic conditions returned after ethanol was flushed out of the system, approximately 45 days after the spill (less than 7.5 pore volumes flushed). Total Bacteria growth coincided with ethanol migration and availability, which was restricted to a relatively thin layer at the capillary fringe and water table interface. The concentrations of bacteria harbouring the aerobic catabolic genes dmpN (coding for phenol hydroxylase) and to dC1 (coding for toluene dioxygenase) increased (up to 100x) down gradient from the source, likely as a result of both fortuitous growth on ethanol and on aromatic hydrocarbons mobilized by ethanol. Growth of hydrocarbon degraders was corroborated by denaturing gradient gel electrophoresis analysis showing proliferation of Azospirillum and Brevundimonas spp., which are bacteria commonly associated with microaerophilic hydrocarbon degradation. Nevertheless, the relative abundance of hydrocarbon-specific degraders (as a fraction of total Bacteria) decreased as other bacteria grew to a higher extent. Overall, the observed growth of hydrocarbon degraders suggests a potential enhancement in aerobic natural attenuation in shallow aquifers after ethanol and its degradation by-products are degraded or flushed from sites impacted by ethanol-blended fuels.

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Peer Reviewed: Will Ethanol-Blended Gasoline Affect Groundwater Quality?

Cited by 60 publications

References 7 publications

Phase equilibria of ethanol fuel blends

Phase equilibria of ethanol fuel blends

Pore Water Characteristics Following a Release of Neat Ethanol onto Pre‐existing NAPL

Microbial community response to a release of neat ethanol onto residual hydrocarbons in a pilot‐scale aquifer tank

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