Emerging Contaminants Summit

Spring 2020

rothRobert Roth
Senior Environmental Engineer

Mr. Roth is a civil/environmental engineer specializing in soil and groundwater remediation, and landfill remediation/closure. He has 30 years of broad-based environmental experience including site characterization, evaluation of applicable remedial technologies, selection of scientifically-based and proven remedial technologies, bench and pilot studies, concept design, full-scale design, construction oversight, system startup and operations, and site closure. He has successfully managed the design, construction and operations of 40+ soil and groundwater remediation projects for industrial and commercial clients with costs ranging from $50,000 to $12,000,000. Mr. Roth’s expertise has been applied to large complex sites such as Superfund Sites, state priority sites, and other sites including above ground storage tanks, below ground storage tanks, refineries, bulk liquid terminals, international airports, local airports, and numerous types of industrial and commercial facilities. Mr. Roth holds a Doctor of Philosophy and Masters of Science in Environmental Science, and Bachelor of Science in Civil Engineering from Rutgers University. He is currently a senior environmental engineer at Terracon in Wheat Ridge, Colorado.



The Use of Variable-Slot Spacing in Sub-Slab Vapor Collection Laterals to Ensure a Uniform Distribution of Sub-Slab Vacuum and Zone of Vapor Collection Influence in Vapor Mitigation Systems

Vapor intrusion is the migration of volatile organic compounds (VOCs) from contaminated groundwater and/or soil into above buildings. To reduce the risk of exposure to these vapors and their associated adverse health effects, a vapor mitigation system (VMS) can be installed to vent the vapors in the soil below the building to the exterior of the building.  A VMS can be constructed as passive or active. In active VMSs, a vacuum blower is used to extract vapors from the perforated/slotted piping installed beneath the floor slab to collect the vapors that accumulate in the void space in the sub-slab gravel. The perforated/slotted piping used beneath the slab is typically PVC or HDPE pipe which is commercially available with perforation/slots separated by equal distances. However, where long (>50 to 100 feet in length) vapor collection laterals are used in large buildings, VMS monitoring data for many sites show that the vacuum along the longitudinal axis of vapor collection laterals decreases significantly, i.e., the flow of sub-slab vapors into the vapor collection laterals can decrease significantly towards the end of the collection lateral. When this occurs, there is the potential that sub-slab vapors towards the end of a vapor collection lateral may not be captured by the system and pockets of vapors could migrate through floor slab holes, cracks, and pipe penetrations into the interior of the building. To address this issue, VMS design engineers can vary the slot spacing to more equally distribute the vacuum along the longitudinal axis of a vapor collection lateral to ensure a more equal zone of influence beneath a slab. The concept of variable slot spacing is supported by pilot and full-scale monitoring as well as vacuum loss calculations as presented herein.

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