Innovation in Environmental Solutions

7 Human Health Risk Assessment Protecting Construction Workers in a Trench Scenario Construction Workers Face Inhalation Risk in Sub-grade Utility Install Our client approached our team with the desire to expedite redevelopment of approximately 80 acres of a former marketing terminal located in southwest Ohio. While many of the potential exposure pathways were addressed via a combination of engineering controls (e.g. capping, vapor mitigation systems) and administrative controls (e.g. environmental covenants, deed restrictions), there was significant concern regarding the safety of construction workers during horizontal redevelopment activities, particularly those workers installing sub-grade utilities in trenches. The so called “trench scenario” is typically evaluated by estimating exposure concentrations to determine potential inhalation risk for construction workers. The exposure concentration is calculated by combining a vadose zone model to estimate transport of vapors from the source into the trench, with a box model to estimate the exposure point concentration following mixing of the volatile constituents with atmospheric air in the trench. There are two primary assumptions: (1) the trench dimensions and (2) the air exchange rate within the trench. Industry best practices and professional judgement can be employed to constrain the modeled trench dimensions; however, default air exchange rates have not been developed for trenches. Regulatory agencies typically recommend using air exchange rates based on historical studies of air flow between tall buildings in an urban setting. Field Study Leads to Better Modeling and Risk Estimations We designed a field study which allowed us to directly measure trench air exchange rates to better constrain modeling to provide more realistic estimates of inhalation risk to construction workers during horizontal redevelopment. Project at a Glance • Concerns of construction worker safety pauses installation of sub-grade utility in trenches at SW Ohio project • Trench-scenario evaluated to identify inhalation risks of volatile compound • Team designed field study to measure trench air exchange rates to better constrain modeling and provide realistic estimates of risks to workers • Carbon dioxide used as tracer • Study reduces risks to workers, reduces costs and expedites redevelopment