Objective:
It is estimated that more than 7,000 Department of Defense (DoD) sites have contaminated groundwater, most of which will require investigation of the vapor intrusion pathway. In this project, investigators will develop and validate Tier 2 procedures for screening vapor intrusion at corrective action sites along with exit criteria indicating no further need for site evaluation. These procedures will use easily obtainable site-specific information to support the application of screening concentrations that are less conservative than the Tier 1 screening concentrations provided in U.S. Environmental Protection Agency and many state vapor intrusion guidance documents. The Tier 2 procedures will fill the current gap in available guidance documents between generic (Tier 1) screening concentrations and detailed site investigations of vapor intrusion. Technology Description: Building on the results obtained from ESTCP project ER-0423, this project will develop and validate Tier 2 vapor intrusion screening procedures and limited-scope Tier 3 investigation methods based on easily measured site-specific characteristics from two key interfaces—the groundwater-soil gas interface and the building foundation. These screening procedures can be used individually or together to provide maximum flexibility for cost-effective evaluation of vapor intrusion at each site. The groundwater-soil gas interface and the building foundation are key interfaces for site specific screening because (1) volatile organic compound (VOC) transport across these interfaces varies significantly between sites (i.e., greater than 100 times), creating large differences in the potential for vapor intrusion impacts, and (2) easily obtained site-specific data can be used to predict the differences in VOC transport across these interfaces. Utilizing existing data sets for well-studied vapor intrusion sites, investigators will develop preliminary Tier 2 screening criteria—based on aquifer characteristics (e.g., confined versus unconfined), building characteristics, and other relevant site characteristics—and focused field investigation methods for sites where required. The existing data set will be supplemented through focused investigations of the key transport interfaces (i.e., groundwater to deep soil gas and building foundations). Detailed measurements of VOC transport across aquifer-confining layers will be conducted at a number of sites across the United States. In addition, building foundation permeability will be characterized through induced depressurization. The enhanced dataset then will be used to refine and validate Tier 2 screening procedures and focused field investigation methods. Expected Benefits: The development of validated Tier 2 vapor intrusion screening procedures and focused Tier 3 investigation methods is likely to significantly reduce the number of DoD sites requiring extensive investigation or presumptive remediation. If this project is able to reduce the number of vapor intrusion field investigations by 50% and reduce the scope of investigation at those sites where an investigation is required, DoD cost savings have the potential to be greater than $65 million. (Anticipated Project Completion - 2011) Principal Investigator: Dr. Thomas McHugh GSI Environmental Inc. 2211 Norfolk, Suite 1000 Houston, TX 77098-4044 Telephone: (713) 522-6300 Fax: (713) 522-8010 E-mail: temchugh@gsi-net.com DoD Liaison: Dr. Sam Brock HQ AFCEE/TDE 3300 Sidney Brooks Brooks City-Base, TX 78235 Telephone: (210) 536-3253 Fax: (210) 536-5989 E-mail: Samuel.Brock@brooks.af.mil
| 
