Geosyntec's Fort Gillem Vapor Intrusion Investigation project received an Honor Award at the 2017 ACEC Georgia Engineering Excellence Awards on February 25, 2017 at the Cobb Energy Performing Arts Centre in Atlanta.
The American Council of Engineering Companies (ACEC) of Georgia and the Georgia Engineering Alliance based the award on the successful and innovative consulting engineering services Geosyntec provided to the Fort Gillem Vapor Intrusion (VI) Investigation.
Fort Gillem is a former United States Army Installation located in Forest Park, Georgia that was active from 1941 to 2011. In July 2014, the Army initiated a VI study to evaluate whether VOCs detected in off-site groundwater monitoring wells could cause a health risk in the indoor air of over 300 off-site buildings, mostly residential, around Fort Gillem.
Multiple lines of evidence show vapor intrusion is not occurring off-site of Fort Gillem. Forensic analysis of data collected during the Fort Gillem Vapor Intrusion Investigation shows that background sources of volatile organic compounds (VOCs) are the primary contributors of VOCs detected in indoor air.
Geosyntec performed site-specific forensic evaluation of the data collected as part of the VI study. The forensic evaluation included a suite of spatial analysis techniques that were used to assess the source(s) of VOCs detected in indoor air, crawlspace air, or sub-slab soil gas samples, including consumer products, VI, and outdoor sources. Geosyntec developed a site-specific forensic evaluation Excel spreadsheet tool to facilitate systematic evaluation of the data, following the approach used by U.S. EPA to evaluate their own VI database. The forensic evaluation tool allowed for simultaneous spatial comparison of dozens of analytes in multiple media and visualization tools to support interpretation of the results. The forensic evaluation tool included Fort Gillem-specific analytical data, screening levels and action levels, applicable generic attenuation factors, and geographical information such as drainage basin area and proximity to installation fence line. The forensic evaluation tool was used in conjunction with the VI conceptual site models (VI-CSMs) developed by Geosyntec to generate conclusions and recommendations at every building within the study area. The robust VI-CSMs and the spreadsheet tool were pivotal in data evaluation but also in communicating and building trust with the Agencies.
To induce building under-pressurization, Geosyntec used Building Pressure Control (BPC) testing to simulate VI in the span of one investigation event at two separate buildings, the first ever test of its kind done in Georgia. BPC is an investigation technique designed to induce VI and then to exclude VI through manipulation of indoor air pressure and collection of indoor air samples under each condition. The test showed that, even under worse-case VI conditions, no target VOC concentrations exceeded indoor air screening levels at the buildings. These findings supported Geosyntec's conclusion that no further action was required with respect to the VI pathway at the buildings.
In May 2016, U.S. EPA concluded that no further action regarding the VI pathway at Fort Gillem was necessary. Geosyntec's approach and diverse methods allowed the Army to complete the investigation at approximately 80% of its cost estimate at the time Geosyntec was hired, and several months ahead of the projected schedule.
- Aerial Photograph of Fort Gillem Aerial Photograph of Fort Gillem
- Geosyntec Performed Secondary Forensic Analysis Geosyntec Performed Secondary Forensic Analysis
- Vapor Intrusion Conceptual Site Model Vapor Intrusion Conceptual Site Model
- Geosyntec Performed Building Pressure Cycle Testing Geosyntec Performed Building Pressure Cycle Testing
Learn more about 2017 Engineering Excellence Award Winners: http://www.acecga.org/pages/EngineeringExcellenceAwards
Register for the Awards Dinner: http://www.acecga.org/events/details/inaugural-georgia-engineering-awards-276
Learn more about Geosyntec's vapor intrusion practice: https://www.geosyntec.com/contaminated-sites-remediation/contaminated-media-investigations-and-assessments/vapor-intrusion
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