Vapor intrusion evaluation for redevelopment of former industrial facilities

Former industrial facilities in our cities are finding new life as they are repurposed for use as nonindustrial commercial or even residential spaces. Often, these buildings are brownfield properties, complicating redevelopment because of past industrial uses that led to soil and/or water contamination at the site. In case site contaminants include volatile chemicals (VCs), concerns about air quality at the site may arise. VCs can vaporize from the subsurface and migrate through soil to outdoor air or into indoor spaces of overlying buildings, where they may accumulate. Vapour intrusion is a relevant problem especially at sites where building modernization and revitalization is to be carried out, as environmental investigations may be complicated by the structure of the built environment, and the contamination may remain undetected. Moreover, upgrading structures to meet building codes and energy conservation requirements can create tight buildings that may enhance the effects of vapor intrusion. For accurately predicting whether indoor air quality is being or will be adversely affected by subsurface contaminations a multiple lines of evidence approach should be used. Many issues can in fact introduce uncertainty in predicting indoor air concentrations related to vapor intrusion, including i) sampling and analytical methods ii) modelling of fate & transport from subsurface into building, iii) indoor/ambient background sources. This work refers about the risk management strategy at a site in Milan (Italy) where soil remediation (excavation and off-site disposal) left a residual volume of soil polluted with petroleum-derived hydrocarbons next to redeveloped buildings. Furthermore, the site was also affected by an extended plume of chlorinated solvents in groundwater from an unknown source, likely external to the site. Indoor air, outdoor air, crawl-space air and soil gas samplings were carried out to collect robust information for evaluating decisions points in the vapor intrusion process. Despite few ambient air and crawl-space measurements resulted in episodic high values, as a general trend, the average outdoor and indoor concentrations did not differ significantly from the background values, suggesting other sources than soil pollution were affecting the quality of the air at the site. Although not strictly necessary in terms of time-averaged health risk, a mitigation system of the residual soil contamination was, however, installed to prevent future uncontrolled exposure.