Workshop # 6: State of the Science in Assessing MTBE Degradation II

Michael Taylor, Vita Nuova LLC
Bruce Bauman, American Petroleum Institute

The fate of MTBE in groundwater continues to be a hotly debated subject. Data is limited and not definitive, the appropriate tools are still under development, and the experts are still divided. Much work has been done over past three-five years to begin to define possible chemical and biological pathways of degradation. This workshop will help define what we know and don’t-especially as it relates to new research into anaerobic pathways of degradation. 

This workshop will include EPA, industry and technical community perspectives in the assessment of MTBE degradation. The workshop will focus on several degradation pathways, and data analysis that identify those pathways at your site. New work completed by USEPA/NRMRL, API and Microseeps on MTBE plumes will serve as the basis for discussion of problems and opportunities in demonstrating degradation potential. Analytical, monitoring, and transport issues will be discussed.

EPA and API studies have determined that several impediments exist to properly assessing the potential for degradation including:

Inability to accurately measure fuel oxygenates and other degradation indicators  
Determining the exact pathways MTBE breaks down 
Effective remediation methods

Participants will be invited to present data from MTBE plumes prior to the workshop and experts will apply recent findings to the sites in an interactive format. The workshop will include presentations, discussion and feedback sessions.    

Workshop # 7: Recent  Improvements in the Practice of Risk Assessment as Illustrated through Case Studies

Dennis Paustenbach, Exponent, Menlo Park, CA

The field of risk assessment has evolved at a fairly rapid pace over the past 4-5 years.  Fifteen years ago, it was not uncommon for risk assessments to be conservative descriptions of the plausible risks posed by chemicals, often the approach was dictated by regulatory guidance or criteria.   Today, the approach to characterizing risks is more flexible than in years past.  The reliance on a single categorization scheme or a particular dose-response model is much constrained than 5-10 years ago.  Incorporation of mechanistic information or alternative extrapolation models, for example, is more commonplace. 

The first part will describe recent improvemments in the practice of risk assessment with an emphasis on the changes in procedures that have occurred over the past five years (e.g., new EPA cancer guidelines, children’s health guidelines, monte carlo techniques, aggregate and cumulative risk, etc).    The remaining three parts will present applications of the risk assessment methods to real world problems using the case study method.  The case studies will illustrate how to (1) consider EPA or other regulatory guidance in the hazard identification process, (2) apply methods like monte carlo analysis into the exposure assessment, (3) use the information from benchmark dose or other dose-extrapolation models, and (4) effectively characterize the risks.  The case studies cover a range of topics including the assessment of contaminated soil and groundwater, the possible hazard posed by a consumer products to which children are exposed, and how to conduct a dose-reconstruction for a large production facility.  A few example calculations will be presented.  Participants will receive a copy of the recently published, 1500 page, book “Human and Ecological Risk Assessment:  Theory and Practice” which was edited by the session organizer (Dennis Paustenbach).   The presentations will refer to various chapters in the book.

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