May 21, 2019

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Chase Holton and Dave Folkes Coauthored a Paper on "Subsurface (Vapor) Intrusion in the Hazard Ranking System" for the American Bar Association

Chase Holton, Ph.D., P.E. and David Folkes, P.E. (Colorado) coauthored a paper entitled "Subsurface (Vapor) Intrusion in the Hazard Ranking System" published by the American Bar Association Section on Environment, Energy, and Resources on May 9, 2019.

Chase is a Senior Environmental Engineer based in Colorado with a focus in contaminant fate and transport, including evaluation and mitigation of the vapor intrusion pathway. His past research work under the Department of Defense's Strategic Environmental Research and Development Program (SERDP) involved the long-term monitoring of groundwater, soil vapor, indoor air, and various environmental factors at vapor intrusion research house Sun Devil Manor was awarded Environmental Restoration Project of the Year in 2011.

Dave is a Senior Principal Environmental Consultant based in Colorado with more than 40 years of experience focused on vapor intrusion evaluation and mitigation and soil and groundwater investigation and remediation.

The mission of the American Bar Association is to serve equally their members, their profession and the public by defending liberty and delivering justice as the national representative of the legal profession.


On May 22, 2017, the U.S. Environmental Protection Agency (EPA) added subsurface intrusion (SsI) to the list of pathways evaluated under the Hazard Ranking System (HRS) rule (EPA, 2017a). The HRS is a numerical scoring framework that the EPA uses under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, also known as Superfund) to assess the relative potential of sites to pose a threat to public health or the environment. The HRS score is determined by evaluation of one or more of the migration and/or exposure pathways. The pathways are scored using three categories, (1) likelihood of exposure/likelihood of release, (2) waste characteristics, and (3) targets. One or more pathways can be scored for a site, and sites with an overall score of 28.5 or higher can be proposed for inclusion on the National Priority List (NPL).

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