Innovation in Environmental Solutions

5 Human Health Risk Assessment Assessing Potential Vapor Intrusion Pathways with Radon Tracing Lack of understanding of attenuation impact on vapor migration The client was required to evaluate human health risks associated with the vapor intrusion pathway per the requirements of a state regulatory agency with limited understanding or guidance regarding evaluation of this exposure pathway. Of particular concern, was the lack of understanding that attenuation has on the migration of vapors across a building foundation. As vapors migrate from beneath the ground into a structure, the concentration of volatile constituents decreases due to dilution with indoor air, as well as restriction of vapor movement across the foundation. Risk assessors use attenuation factors to account for this reduction in volatile constituent concentrations and separate structures with the potential for a completed vapor intrusion pathway from those with background sources inside the structure. These background sources are ubiquitous in indoor air from many sources, including, but not limited to, building products, cleaners, paints, and automotive products. If these background sources cannot be accounted for during an investigation, it may mistakenly appear that a completed vapor intrusion pathway and inhalation risks are present, when in reality, the source of vapors are related to chemicals inside a building and not releases underneath the building. Site foundation results in significant variation of volatile petroleum-related constituents This client’s site, a former refinery, is underlain by fractured bedrock with irregularly distributed light non-aqueous phase liquids and dissolved phase impacts, resulting in considerable lateral and vertical variation in the composition and concentration of volatile petroleum-related constituents. The residential structures to be evaluated included a combination of full or partial basements, full or partial crawlspaces, and slab- on grade structures. The age of the structures spanned several decades, and conditions of the building slabs and foundations varied from dirt floors to brand new concrete slabs. Project at a Glance • Client required to evaluate human health risks associated with petroleum vapor intrusion across 48 residences • Lack of understanding of attenuation rates creates more questions about vapor rates and movement • Former refinery site underlain with bedrock results in considerable lateral and vertical variation in the volatile petroleum-related constituents • Team uses radon to better understand attenuation rates and determine volatile vapor migration • Solution saves time, reduces project costs and dramatically reduces client liability