Presented January 8, 2015- Presentation Slides
Assessing Source Zone Natural Attenuation at Chlorinated Solvent Spill Sites by Dr. Paul Johnson
Source zone natural attenuation (SZNA) is often used as a basis for assessing the performance and relative benefits of engineered remediation, and is also a component of the cleanup strategy at most chlorinated hydrocarbon-impacted sites. Thus, there is a need for a well-defined and accepted assessment approach. This ESTCP-funded project demonstrated a data-driven paradigm to assist decision-makers in addressing key questions on whether SZNA is occurring, current SZNA rates and longer-term implications of SZNA. The approach uses multiple lines-of-evidence and macroscopic mass balances, and these lead to confirmation of SZNA and quantification of the total mass loss rate resulting from degradation, dissolved phase transport and volatilization. Application of the approach was demonstrated at three sites through four events per site over a three-year period. The mass loss rates were relatively consistent over time for each site, but varied from site to site, and ranged between 1 to 10 kg/year at two sites and as high as about 600 kg/year at the third site. When applying the generalized method, it is likely that different practitioners will choose the number and locations of samples in different ways. The high spatial density data collected from the demonstration sites in this project were used to examine the effect of different sampling strategies on the quantification of mass loss rates at those sites. This experience and lessons learned from previously published studies on this topic were used as the basis for new proposed heuristic sampling guidelines with the hope is these guidelines can increase sampling efficiency and confidence in the quantification of SZNA rates.
Reconstructing Source Zone Histories Using High Resolution Coring To Improve Monitored Natural Attenuation by Dr. Charles Newell
An important building block of a Monitored Natural Attenuation (MNA) demonstration is the compilation and analysis of historical groundwater monitoring data to "demonstrate a clear and meaningful trend of decreasing contaminant mass and/or concentration over time at appropriate monitoring or sampling points” (USEPA MNA Directive, 1999). However, these data are often limited in duration, sometimes only a few years, reducing our ability to understand if and how much attenuation processes have reduced groundwater concentrations over decadal time scales. This presentation highlighted a recently completed ESTCP demonstration project of an innovative method for reconstructing the “source history” at a site (i.e., the long-term concentration trend over time at any point in the source or plume) by using high-resolution soil coring within low permeability zones (“low-k zones”). Essentially, soil cores in these zones serve a similar role as tree rings in that the cores store information about historic environmental conditions (typically from up to 60 years into the past to the present). For contaminants that have migrated into low-k zones via diffusion and slow advection, a simple spreadsheet-based modeling tool was developed to evaluate the concentration versus depth profile and to determine if there has been long-term changes of contaminant concentrations in groundwater in the in transmissive zones overlying low-k zones. In summary, the method relies on high-resolution sampling of low-K zones and analysis of these data using a public domain spreadsheet model based on the 1-D diffusion equation to understand the general style of long-term temporal record (increasing, stable or decreasing). The results from the ESTCP Source History Methodology provide a new line of evidence for evaluating the viability of MNA at a site based on the information stored in low permeability clays and silts at that site.
Dr. Paul Johnson is a Professor in and the Dean of the Ira A. Fulton Schools of Engineering at Arizona State University in Phoenix, Arizona. He has over 25 years of experience in the remediation field, ranging from theoretical analyses to detailed field-scale studies focused on the design, monitoring, and optimization of soil and groundwater remediation systems and modeling and monitoring related to risk assessment. He has co-authored guidance documents for both industry and regulatory agencies, and has served as advisor to DoD, industry, and EPA. Dr. Johnson was the Editor-in-Chief of the Nation al Ground Water Association's journal Ground Water Monitoring and Remediation from 2003 through 2012 and served on the recent National Research Council Committee on Future Options of the Nation's Subsurface Remediation Effort, the results of which were published in 2013. He has received numerous awards, including NGWA’s Keith E. Anderson Award in 2011 and more recently the Brown and Caldwell Lifetime Achievement Award at the 2014 Battelle Conference. Before joining Arizona State, Dr. Johnson was a senior research engineer for Shell Development in Houston from 1987 through 1994.
Dr. Charles Newell is a Vice President of GSI Environmental, Inc. He is a member of the American Academy of Environmental Engineers, a NGWA Certified Ground Water Professional and an Adjunct Professor at Rice University. He has co-authored five U.S. EPA publications, eight environmental decision support software systems, numerous technical articles, and two books (Natural Attenuation of Fuels and Chlorinated Solvents; and, Ground Water Contamination: Transport and Remediation). His professional expertise includes site characterization, groundwater modeling, non-aqueous phase liquids, risk assessment, natural attenuation, bioremediation, non-point source studies, software development and long-term monitoring. He has taught graduate level groundwater courses at both the University of Houston and Rice University. Dr. Newell has been awarded the Hanson Excellence of Presentation Award by the American Association of Petroleum Geologists, the Outstanding Presentation Award by the American Institute of Chemical Engineers and the 2001 Wesley W. Horner Award by the American Society of Civil Engineers (for his paper titled “Modeling Natural Attenuation of Fuels with BIOPLUME III”). He was recently cited as the Outstanding Engineering Alumni from Rice University in 2008.