Environmental

Project Name: Vapor Mitigation Research

Project Location: Former Industrial Site in the Midwest

Services Provided:

  • Vapor intrusion
  • Remediation
  • Field services

Trihydro participated in a long-term research project to develop a system to mitigate vapors at a former industrial site in the Midwest. 

Volatile petroleum hydrocarbons were migrating through the vadose zone into an office building located on the former petroleum site.  While there are several approaches for mitigating vapor impacts within a structure (e.g., passive barriers, sub-slab depressurization, building ventilation), the objective of this study was to develop a mitigation system designed to enrich oxygen levels beneath the building and reduce the concentration of volatile petroleum hydrocarbons through intrinsic aerobic biodegradation.  Trihydro also conducted research of advective and diffusive transport mechanisms, as well as the spatial and temporal relationship of oxygen and volatile petroleum hydrocarbon concentrations within the vadose zone.

Trihydro installed an extensive soil gas monitoring system within the office building that included 21 multi-depth sub-slab monitoring locations and 8 near-slab soil gas monitoring wells. Monitoring was conducted using an automated gas chromatography/mass spectrometer and hard-wired oxygen sensors.  As part of this work, Trihydro completed effective diffusion coefficient testing, measurement of the indoor air exchange rate, and estimation of building pressurization. 

In addition, Trihydro installed two horizontal wells beneath the office building.  The wells were first used as a passive means of introducing air into the subsurface and later as injection wells for delivering air beneath the slab.   Air injection created aerobic conditions beneath the slab, allowing for attenuation of volatile petroleum hydrocarbons within the shallow subsurface.  Additional monitoring is being completed to identify the most cost-effective approach for delivery of air while maintaining the oxygen-rich conditions beneath the slab.