Ask the Expert: Sigrida Reinis

Q: Can passive venting systems be appropriate even for high risk vapor intrusion sites?

A:  We’ve found that passive systems will work in many cases, supported by substantial amounts of performance data. We’ve successfully convinced regulators of this by using a site-specific, risk-based approach to vapor mitigation system design.

In the past, the standard approach was to back-calculate the maximum contaminant levels treatable with passive systems. This is done by using indoor air standards, manufacturer-provided diffusion coefficient for the contaminant through their vapor barrier membrane, our historical data for the dilution of contaminants occurring in the passive venting layer, and the state’s default value for the attenuation provided by a generic concrete floor slab. Based on data, we have reason to believe these inputs are overly conservative.

More recently, we have begun to collect radon data that enables us to quickly calculate the vapor attenuation provided by a completed vapor intrusion mitigation system. In other words, we will no longer need to rely on manufacturer data and state and federal attenuation factors to assess if a site’s conditions can be appropriately alleviated with a passive vapor intrusion mitigation system. Using this approach, we are moving toward using radon data from completed projects to demonstrate that passive systems can work in a range of conditions.

About Sigrida Reinis, PhD, PE
Sigrida Reinis has 25 years of experience in environmental engineering and construction management, specializing in complex remediation projects, including commercial and residential redevelopment. Reinis has designed vapor mitigations systems for properties to be built on closed landfills and brownfield sites, as well as existing buildings undergoing remediation.