Innovation in Environmental Solutions

Human Health Risk Assessment 6 Tracking radon movement from subsurface to indoor analogous to migration of volatile vapors To better understand attenuation rates at the site, our team developed an innovative solution to quantify a specific rate of attenuation into each residence. Radon, derived from the natural breakdown of radioactive uranium in soil, rock, and water, was used as a conservative, naturally occurring tracer. The movement of radon from the subsurface into indoor air is analogous to the migration of vapors from a source of volatile constituents through the vadose zone and into a structure. Commercially available radon passive samplers, as well as a real-time, continuous radon gas monitors were tested to determine the best means of quantifying concentration inside and beneath the building slab. Our team selected the real-time radon gas monitor, as this technique provided reliable results and allowed for continuous samples to be collected over specified time frames. Paired samples (indoor air, subslab, and crawlspace) were collected and used to develop attenuation factors for each residence. Ultimately, the radon-based attenuation factor was an important line of evidence in evaluating the vapor intrusion pathway and supported findings that the pathway was incomplete within 47 of the 48 residences. Innovative solution reduces costs, project timeline and client liability Consequently, our client was only required to implement mitigation measures to address potential inhalation risks within a single structure, significantly reducing the costs, project timeline, and the potential liability if this innovative approach had not been implemented by our team.