Contaminated and Hazardous Waste Site Management

Glossary V

Vacuum Draft Tube: A narrow tube lowered into an extraction well through which a strong vacuum is pulled via a suction pump at ground surface. Fluids (gas, water, and/or free product) are drawn into the draft tube and conveyed to the surface for treatment or disposal. Depending upon the configuration of the extraction system, the inlet of the draft tube may be either above or below the static level of the liquid in the well.

Vacuum Extraction: A technology used to remove VOCs from soils. Vacuum pumps are connected to a series of wells drilled to just above the water table. The wells are sealed tightly at the soil surface, and the vacuum established in the soil draws VOC-contaminated air from the soil pores into the well, as fresh air is drawn down from the surface of the soil.

Vadose Zone: The zone between land surface and the water table within which the moisture content is less than saturation (except in the capillary fringe) and pressure is less than atmospheric. Soil pore spaces also typically contain air or other gases. The capillary fringe is included in the vadose zone.

Validate Time of Sample Receipt (VTSR): The date on which a sample is received at the Contractor's facility, as recorded on the shipper's delivery receipt and Sample Traffic Report.

Validation: Before a mathematical model can be accepted for use, it must be validated, or proven to realistically simulate the processes for which it was designed. Validation is usually completed by comparing model results against a controlled laboratory or field scale experiment.

Vapor Density: The amount of mass of a vapor per unit volume of the vapor.

Vapor Pressure: The partial pressure exerted by the vapor (gas) of a liquid or solid substance under equilibrium conditions. A relative measure of chemical volatility, vapor pressure is used to calculate air-water partition coefficients (i.e., Henry's Law constants) and volatilization rate constants.

Varve: Laminated clays and fine grained sediments of glacial origin deposited in lakes during the retreat of glacial ice. Each lamina or varve has a thicker coarser layer and a finer layer which represent a years seasonal cycle of deposition. Varve is the Swedish word for cycle.

Venturi: A short tube with a constricted throat for determining fluid pressures and velocities by measuring differential pressures generated at the throat as a fluid traverses the tube.

Verification: A mathematical model is verified by comparing the results to a known exact solution, often obtained using an analytical model.

Viscosity: A measure of the internal friction of a fluid that provides resistance to shear within the fluid. The greater the forces of internal friction (i.e. the greater the viscosity), the less easily the fluid will flow.

Viscous Fingering: The formation of finger-shaped irregularities at the leading edge of a displacing fluid in a porous medium which moves out ahead of the main body of a fluid.

Vitrification: The process of electrically melting wastes and soil sludges to bind the waste in a glassy, solid material more durable than granite or marble and resistant to leaching.

Volatile Organic Compounds (VOCs): VOCs are manufactured as secondary petrochemicals. They include light alcohol's, acetone, trichloroethylene, perchloroethylene, dichloroethylene, benzene, vinyl chloride, toluene and methylene chloride. These potentially toxic chemicals are used as solvents, degreasers, paints, thinners and fuels. Because of their volatile nature, they readily evaporate into the air, increasing the potential exposure to humans. Due to their low water solubility, environmental persistence and widespread industrial use, they are commonly found in soil and groundwater.

Volatilization: The process of transfer of a chemical from the aqueous or liquid phase to the gas phase. Solubility, molecular weight, and vapor pressure of the liquid and the nature of the gas-liquid interface affect the rate of volatilization.