Farallon was engaged to address vapor intrusion concerns at a retail facility formerly used by a dry cleaning tenant. Soil gas sampling revealed tetrachloroethene (PCE) at concentrations exceeding environmental screening levels beneath multiple retail tenant spaces. Subsequent sampling of indoor air revealed inhalation exposures in a bank tenant space that required mitigation. Farallon used real-time temporal-spatial monitoring of volatile organic compound (VOC) concentrations in indoor air using an on-site analytical system to determine the likely vapor intrusion entry points. In addition to VOC monitoring, Farallon measured building differential pressures to document changes in vapor flux during and following modifications made to heating, ventilation, and air conditioning (HVAC). Farallon promptly implemented mechanical HVAC engineering control modifications to reduce PCE concentrations in indoor air that were associated with the observed vapor intrusion conditions. To evaluate and document PCE concentration reductions resulting from these mitigation measures, Farallon conducted additional real-time temporal-spatial monitoring of VOC concentrations in indoor air at multiple tenant work stations without disrupting retail operations.
"The vapor intrusion concerns were addressed to the satisfaction of the tenants and client counsel to enable efforts to focus on site remediation," said Senior Geologist Brian Kahl, who managed the project.