Fighting Fire with Fire: Hexavalent Chromium Remediation using Hydrogen Sulfide Gas
$30 for members, $35 for non-members, add $5 if reservation is not received by 5pm the Friday before. Online registration will end at noon on the Monday before the event. Walk-ins with no reservation will be charged an extra $10 and be asked to wait until those with reservations are seated.
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Remedial solutions for vadose zone hexavalent chromium (Cr6+) are commonly limited to dig and haul, in-situ stabilization, or soil flushing with liquid phase reductants in various forms. However, excavation and soil mixing are not always feasible and liquid phase amendments may pose significant concerns for mobilization of impacts to groundwater. In-situ gaseous reduction (ISGR) addresses these issues by reducing the Cr6+ impacts through the controlled injection of hydrogen sulfide (H2S) gas. This presentation will detail the design, field-scale implementation, safety protocols and results of one of the first applications of an ISGR remedy for treatment of vadose zone Cr6+.
The project involved remediation of Cr6+ impacts in vadose zone soils beneath a former plating area to residential screening levels such that the property could be sold without use restrictions. Initial characterization demonstrated that Cr6+ had penetrated to 45 feet below grade. Although well above groundwater (located at 95 feet below grade), treatment of the Cr6+ through standard approaches was either infeasible due to the overlying building, or not advisable due to the potential to further mobilize Cr6+ and subsequently impact groundwater. After direct excavation of the accessible impacted soil in the upper 10-feet, an ISGR treatment area was established around the limited area with deeper impacts. An H2S injection/extraction skid was designed and built to inject an inline stream of H2S gas into a nested injection well, while simultaneously extracting from a ring of six soil vapor extraction wells to control and treat excess H2S gas. Detailed monitoring and leak detection protocols were critical for safe operation of the injection system. Following nine weeks of H2S application, post-remediation sampling of the soil within the treatment area showed excellent Cr6+ reduction meeting project remedial goals.
Brian is the Remediation Group Manager for Geosyntec’s San Diego office. He has over 16 years of site assessment and remediation experience, focused on the implementation of in-situ remediation technologies, for hexavalent chromium, chlorinated VOCs, and polychlorinated biphenyls. He has served as the project manager for the investigation, remedial design, remedial action implementation, and closure of many large scale industrial facilities across the Southwest.
Brian started with Geosyntec in 2000, prior to joining Geosyntec, Brian received a BA in Geology from the College of Wooster and an MS in Structural Geology from the University of Wyoming. He is a Professional Geologist/Certified Hydrogeologist in California and a Registered Geologist in Arizona.