The vadose zone encompasses the unsaturated sediments that lie between the soil surface and the water table. The physical and hydraulic characteristics of the vadose zone dampen the flux of water and contaminants to the water table. While transiting the vadose zone, contaminants such as fertilizers, pesticides, herbicides and industrial chemicals can be delayed or degraded by chemical and biological processes, a fate sometimes referred to as natural attenuation. Thus, the vadose zone controls both the quantity and quality of groundwater resources.
PNNL has extensive experience in characterizing and assessing the vadose zone dating back to the 1960s. We maintain top-notch laboratories to measure the physical and hydraulic properties of soils and vadose zone sediments, and using linkages with other PNNL groups to conduct associated chemical and biological testing. We are experienced at designing and conducting field-scale infiltration and transport tests; remotely monitoring vadose zone variables such as water content, matric potential, and temperature and directly monitoring water contents using boreholes. We also use our laboratory and field expertise to design and test cutting-edge sensors to improve our data-collection abilities. We develop and maintain state-of-the-art modeling systems that include simple analytical models sophisticated numerical flow and transport models, and specialty models written for parallel processing and reactive transport calculations.
Some of PNNL's activities are primarily science-oriented, such as the testing of new theories of water movement. Other actvities are devoted to assisting our clients in making informed decisions by using these laboratory, field and modeling systems to:
- Integrate existing vadose zone information to determine its sufficiency
- Optimize vadose zone characterization activities
- Measure and predict vadose zone water flow velocity and direction
- Measure and predict vadose zone contaminant concentrations and transport rates
- Optimize vadose zone remediation technologies
- Evaluate the immediate impacts of vadose zone remediation technologies
- Verify the performance of surface covers
- Predict the long-term impacts of both remediation and no-action alternatives
- Estimate risk to the public.