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• un 1995 15PM IEG TECHNOLOGIES No 2615 P 5/1JA 95-WP 103 05 monitoring wells 3IOW1 and 3IPW1, the following average hydraulic parameters are calculated (Earth Technologies Corporation, 1994) • ' HYdraulic conductivity (k) 90 5 SPdlf ((average Site 31 value) Hydraulic gradient (i) 0 007 (December 1994 average condition) • Effective porosity (n.) 272% • Transport velocity (V) 0 31 friday TECHNOLOGY DESCRIPTION The WB technology uses a system of chemical, physical, and biological processes to treat VOC- contanunated groundwater and subsurface sods The UVB system consists of a specially adapted groundwater treatment well, a negative pressure stripping reactor, an aboveground vacuum extraction blower, and an off-gas treatment system if necessary (e g, activated carbon adsorption units)(Figure 2) The UVB treatment well is constructed with two screened zones one section which is placed at the bottom of the treatment interval, and one section which straddles the groundwater interface The borehole annulus between the two screened zones is sealed with bentonite. A packer is installed m the treatment well between the two screened zones to ensure one duectional flow of the groundwater through the treatment well. A pipe is placed through the packer and connected to a pump which provides groundwater from the lower zone to the upper zone where the stripper reactor is situated The upper end of the pipe terminates at the reactor The upper, closed part of the well, is maintained at below atmospheric pressure by a centrifugal blower. The air for the in-situ stnppmg is drawn m through a 3-inch diameter fresh air pipe the upper end is open to the atmosphere, and the lower end terminates m a pinhole plate (diffuser) located in the reactor Soil air is also drawn into the treatment well from the vadose zone through the upper well screen. The negative pressure within the upper part of the well also causes a water level rise within the treatment well The stripper reactor is balanced below the groundwater level within the treatment well and is free- floating to allow for changing water levels The location of the reactor month respect to the water level in the well determines the ratio of au that is drawn from the atmosphere through the air intake pipe, to the air that is drawn into the well from the vadose zone through the upper screen- This also controls the air to water ratio within the stepper reactor since only the air drawn from the surface through the air intake pipe is directed to the pinhole plate in the stripper reactor. Balancing of the system within the well is achieved by installing buoyancy tank; below the pump The zone within the well between the pinhole plate and the water surface is the stripping zone, in which an air bubble flow develops and strips VOCs from the groundwater The rising air bubbles produce an air lift pumping effect, which moves the water, and causes a suction effect at the bottom of the well Stnpped air from the groundwater, and extracted soil gas, is transported up through the casing and blower, for treatment, if necessary, before venting to the atmosphere The upward-streaming, stripped groundwater leaves the we❑ casing through the upper screen section of the treatment well The mass of flowing groundwater leaving the upper screen is counterbalanced by • the flow of groundwater toward the lower screened section, thereby setting up a three-dimensional groundwater circulation cell around the UVB well Contaminated groundwater flows toward the well 3