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Gasoline oxygenates have been used in gasoline primarily to improve octane, reduce vehicular emissions and comply with the oxygen requirements of the 1990 Clean Air Act Amendments. While there are many different gasoline oxygenates the ones most commonly used in US gasolines are methyl tert-butyl ether (MTBE) and ethanol (EtOH). Tert-butyl alcohol (TBA) is both a trace component found in fuel grade MTBE, and is also a metabolite of MTBE biodegradation. API groundwater research has focused on understanding the fate, transport and remediation of these compounds, with special focus on the factors influencing their biodegradation.

This page is a portal to technical information on fuel oxygenates in soil and groundwater.  Reports and presentations on API-sponsored research are provided for various aspects of risk-based decision-making.

Technical Protocol for Evaluating the Natural Attenuation of MtBE

May 7, 2007 - This technical protocol addresses data collection, evaluation, and interpretation procedures that consider the physical, chemical and biological properties of MtBE and other oxygenates and degradation byproducts.  A tiered approach is provided that can be used by stakeholders to interpret several lines of evidence to evaluate natural attenuation on a site-specific basis.  Several resources are provided to support an MNA evaluation, including:
  • a review of basic scientific principles relevant to the evaluation of MtBE  natural attenuation, including biodegradation and physicochemical attenuation mechanisms;
  • a discussion of data that can be used to assess MtBE (and other oxygenates or degradation byproducts) natural attenuation
  • technical references for relevant chemical properties, analytical methods, and field sampling techniques
  • guidance for data quality assurance and interpretation, including statistical analysis; and
  • guidance on the presentation of natural attenuation data/information to facilitate regulatory and other stakeholder review and acceptance of MNA remedies.
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MTBE and TBA Biodegradation

September 25, 2006 - For the last several years, Dr. Mike Hyman has researched the diversity of pathways of aerobic MTBE and TBA oxidation(metabolism vs cometabolism).  His work has helped identify the enzymes responsible for initiating these processes at the molecular level and led to a better understanding of how distinct microbial processes can contribute to MTBE and TBA degradation in gasoline-impacted groundwater. Click below to download Dr. Mike Hyman's Physiological and Enzymatic Diversity of Aerobic MTBE Biodegradation Processes from the Second European MTBE Conference in Barcelona, Spain.

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Research in Progress

May 9, 2007 - API has several oxygenate-related publications scheduled for completion in 2007 including:
  • Use of Compound Specific Isotope Analyses (CSIA) as an In-situ Indicator of MtBE Biodegradation

  • Technical Manual on the Design and Operation of Ex-Situ Biological Treatment of Oxygenate Impacted Groundwater


Strategies for Characterizing Subsurface Releases of Gasoline Containing MTBE

Solute Plume Migration: Assessment Significance
and Implications for Characterization and Monitoring of "Diving Plumes"

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Groundwater Remediation Strategies Tool

Analytical Methods

Papers and websites on analytical methods for detecting various oxygenates

TBA Hazard Narrative

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The following API Soil and Groundwater Research bulletins cover provide basic information about oxygenate behavior in groundwater:

Answers to Frequently Asked Questions About Ethanol Impacts to Groundwater:
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Ten Frequently Asked Questions About MTBE in Water:
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Fate and Transport

Laboratory studies on the behavior of subsurface fuel releases:

The Impact of Gasohol and Fuel-Grade Ethanol on BTX and Other Hydrocarbons in Ground Water:
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Dissolution of MTBE from a Residually Trapped Gasoline Source:
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Small Releases

Modeling studies to evaluate the potential for groundwater impacts from small mass or volume releases from fuel storage systems: 

Evaluation of Small-Volume Releases of Ethanol-Blended Gasoline at UST Sites:
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Simulation of Transport of Methyl Tert-Butyl Ether (MTBE) to Groundwater from Small-Volume Releases of Gasoline in the Vadose Zone:
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Maximum Potential Impacts of Tertiary Butyl Alcohol (TBA) on Groundwater from Small-Volume Releases of Ethanol-Blended Gasoline in the Vadose Zone:
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Evaluation of Potential Vapor Transport to Indoor Air Associated with Small-Volume Releases of Oxygenated Gasoline in the Vadose Zone:
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