Objective:
This project will demonstrate the assessment of source zone natural attenuation (SZNA) at two sites—a dense non-aqueous phase liquid (DNAPL)-impacted site and either a light non-aqueous phase liquid (LNAPL)- or mixed DNAPL/LNAPL-impacted site—and develop illustrated guidance for application to other sites. The approach to be demonstrated provides answers to questions typically asked by decision makers such as (1) Is SZNA occurring, and if so, what natural processes are contributing to SZNA? (2) What is the current rate of source zone mass reduction associated with SZNA, and how might this change in the future? (3) What are the longer-term implications of SZNA for future groundwater and vapor migration impacts at the site? (4) Are the SZNA processes and rates sustainable? and (5) What is the projected longevity of the non-aqueous phase liquid (NAPL) source zone (or post-treatment NAPL residual)? Technology Description: The data-driven approach to be demonstrated is consistent with National Research Council recommendations for "multiple lines of evidence" and "footprint" approaches, complements existing guidance for assessing the natural attenuation of dissolved plumes, and incorporates the SZNA screening-level modeling tool development previously supported by the Department of Defense. It builds on the fundamental understanding of SZNA mechanisms and translates those into practicable site-specific guidance. While previous work focused on petroleum hydrocarbons, the approach is easily generalized to both DNAPL and mixed DNAPL/LNAPL sites. The SZNA assessment approach includes three basic levels of data collection and reduction, referred to as Group I, Group II, and Group III data and analyses. Group I will focus on measurements that provide evidence that SZNA is occurring, Group II measurements include additional information necessary to estimate the current overall SZNA rate, and Group III measurements are focused on evaluating the long-term implications of SZNA for temporal changes in source zone residual composition, source zone groundwater quality, and vapor migration impacts. Ultimately, users will identify the questions of interest and then collect the corresponding data. Expected Benefits: This project will develop illustrated guidance on how to assess SZNA and answer site-specific questions of interest to decision makers. This information is needed to place other corrective action options in perspective when making decisions as well as to define end points for other options. (Anticipated Project Completion - 2010) Principal Investigator: Dr. Paul Johnson Arizona State University Ira A. Fulton School of Engineering 699 South Mill Avenue, Room 610 Tempe, AZ 85281 Telephone: (480) 965-9115 Fax: (480) 965-4000 E-mail: paul.c.johnson@asu.edu DoD Liaison: Ms. Erica Becvar HQ AFCEE/TDE 3300 Sidney Brooks Brooks City-Base, TX 78235 Telephone: (210) 536-4314 Fax: (210) 536-5989 E-mail: erica.becvar@brooks.af.mil
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