Ramboll vapor instrusion experts have published new research that challenges USEPA guidance.
In a recent article, Principal Stephen Song and Senior Consultant Barry Schnorr suggest that the USEPA’s recommended approach for assessing vapor intrusion is far too conservative, and that factoring in climate variability could result in more accurate assessments.
In “Accounting for climate variability in vapor intrusion assessments,” the authors demonstrate the derivation of site-specific residential sub-slab attenuation factors that may be used in screening-level vapor intrusion assessments as an alternative to USEPA’s generic value of 0.03. The article, published in Human and Ecological Risk Assessment: An International Journal, presents Ramboll-developed simulation results based on temperature and wind speed data for 20 US cities representing a range of climates from southern Alaska to Hawaii. The simulations show that the most airtight, energy-efficient houses have an attenuation factor that ranges from 0.001 for the warmest climate zone to 0.004 for the coldest climate zone. The authors have concluded that the sub-slab attenuation factor for conventional residential buildings is likely to be less than 0.003 most of the time, results that fall far below the USEPA’s conservative recommendation.