Recommended Updates to the Soil-to-Groundwater Pathway in the U.S. EPA's 1996 Soil Screening Guidance

As part of a Virtual Student Federal Service internship project, this presentation provides an overview of the history, current use, and recommended improvements of the dilution attenuation factor (DAF) used when calculating soil screening levels (SSL), along with recommendations to address the assumption of an infinite contaminant source when calculating SSLs. This project focuses on the United States Environmental Protection Agency's (U.S. EPA) 1996 Soil Screening Guidance (SSG), which provides guidance for calculating SSLs as implemented in the Regional Screening Level (RSL) and Preliminary Remediation Goal (PRG) calculators. The U.S. EPA's SSG currently utilizes a single default nationwide DAF during the calculation of SSLs when a risk of soil-to-groundwater contaminant migration is present, which may not reflect the significant hydrologic differences across the U.S. Additionally, the SSG's calculation assumes an infinite source of contaminant is present, which may not be an accurate reflection of the conditions at sites. This project examines the history and initial development of the DAF, reviews potential issues with the current use of the DAF, and provides recommendations for improvement to the DAF calculations, including hydrologic region-specific DAFs, and a calculator to correct the infinite source assumption inherent in SSL calculations. The presentation concludes with the limitations of this analysis and recommendations for future work to improve the DAF and SSG.

Alex Valdez
Alex Valdez is a recent graduate of the University of Maryland Global Campus. He graduated with a Master of Science in Environment Management. He received his bachelor’s degree in chemistry from Virginia Tech. He has worked for the Department of Health and Human Services, the Federal Bureau of Investigations, and the U.S. Army.

Seth Whiteaker
Seth Whiteaker is an undergraduate pursuing a B.S. in Ecological Management & Restoration at University of California, Davis. In addition to his internship with U.S. EPA, he studies carbon biogeochemistry and soil information systems with the California Soil Resource Lab. After graduation, he hopes to continue working to protect human and environmental health through a position in state or federal government.

Michael McCarroll
Michael McCarroll is a physical scientist in EPA's Office of Superfund Remediation and Technology Innovation. He works as part of the groundwater team in the Science Policy Branch responding to technical inquiries and providing guidance on science policy. He has a M.S. in Applied Geoscience from the University of Pennsylvania and a B.S. in Environmental Science from Wilkes University.

Moderator:

Jean Balent, U.S. EPA Technology Innovation and Field Services Division (balent.jean@epa.gov or 202-566-0832)
Ms Balent is on the staff of the EPA's Technology Innovation and Field Services Division where she has worked to collect and disseminate hazardous waste remediation and characterization information since 2003. Ms Balent manages the Clean Up Information Network website and actively supports online communication and collaboration resources available to EPA. She formerly worked with the US Army Corps of Engineers Environmental Engineering Division in the Buffalo District. Ms Balent was also a member of the SUNY-Buffalo Groundwater Research Group where she constructed and tested large scale models of groundwater flow. Ms Balent has also conducted research relating to the Great Lakes, environmental remediation, and brownfields re-development. She holds a Bachelor's degree in environmental engineering from SUNY-Buffalo and a Master's degree in Information Technology from AIU.

• Slide Presentation for Seth Whiteaker and Alex Valdez (1.57MB/PDF)

Webinar Slides and References:

• Slide Presentation for Seth Whiteaker and Alex Valdez (1.57MB/PDF)

Additional Resources:

• Superfund Soil Screening Guidance
• Soil Screening Guidance for Radionuclides:
  • User Guide
  • Technical Support Document
• Recommended Updates to the Soil-to-Groundwater Pathway in the U.S. EPA's 1996 Soil Screening Guidance
• Finite Source Correction Factor Calculator

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 July 20, 2023: Recommended Updates to the Soil-to-Groundwater Pathway in the U.S. EPA's 1996 Soil Screening Guidance

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