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Chlorinated solvents are prevalent contaminants in groundwater and soils at DoD sites, representing a substantial liability. These sites are characterized by wide ranges of concentrations. In many cases, subsurface environmental conditions and contaminant distributions are complex. Many of these sites also have identifiable dense nonaqueous phase liquid (DNAPL) source zones. These sources are particularly difficult to remediate, resulting in substantial and long-term contaminant plumes. In recent years, concerns have grown over the migration of vapors from these groundwater plumes into surface and sub-surface structures.
Vapor intrusion into buildings is driven by natural processes, including advection, diffusion, biodegradation, and pressure fluctuations caused by wind, temperature, and diurnal cycles. Vapor intrusion also can be associated with manmade processes, such as occupant activities in buildings. This risk pathway is the driver for many corrective action plans and site cleanups.
While the development of methods for assessing and measuring vapor intrusion has been underway for several years, research on the underlying science governing the vapor intrusion pathway has been lacking. Tremendous uncertainty remains regarding how best to assess the vapor intrusion pathway. The monitoring required at sites where vapor intrusion is suspected can be expensive and time-consuming. Temporal and spatial variability can be vast. As a result, interpreting and evaluating the data from vapor measurements is difficult. It is also challenging to predict and measure the fate and transport of vapors in soil.
SERDP research efforts focus on developing a more robust understanding of vapor intrusion and its significance. Researchers are investigating the processes associated with the emission of chemical vapors from dissolved chemical groundwater plumes and entrapped DNAPL sources; their transport and attenuation in heterogeneous vadose zones; and their entry to indoor air. Integrated field-scale, lab-scale, and modeling studies are included.
Demonstration efforts under ESTCP are focused on improving the current sampling methodology and risk assessment approach for vapor intrusion assessments. Spatial and temporal variability in volatile organic compound (VOC) concentrations have a significant impact on vapor intrusion investigations. Vapor intrusion field investigation methods are being studied to support cost-effective evaluation of the vapor intrusion pathway.
Both the development of a greater understanding of the vapor intrusion pathway from chlorinated solvent-contaminated groundwater plumes and the demonstration of improved sampling methodologies will, over time, provide more accurate prediction, monitoring, and management tools. The ultimate goal of these efforts is to provide more cost-effective protection of human health.