Draft Protocol for Controlling Contaminated Groundwater by Phytostabilization

The Air Force is responsible for a large number of sites that contain water-soluble contamination in the vadose zone or in the ground water. The contamination at many of these sites is confined by natural conditions to a relatively shallow depth of the earth's crust (0 to 30 feet maximum, depending upon site characteristics). The contaminants are usually moving in water both within the vadose zone and shallow ground water. In addition, the contaminants are often naturally biodegrading, but the rate of degradation and retardation is not sufficient to prevent continued migration into uncontaminated areas, thereby resulting in ongoing environmental concerns. Contaminants sometimes migrate into deeper aquifers. This protocol does not address contaminants found in deep or confined aquifers; it is restricted to remediation of the numerous, shallow water table sites. Many shallow groundwater bodies are thin, contain a limited amount of water, and have low hydraulic conductivity (referred to as the "K" value in this report). As a result, water may move slowly and well yields may be very small. Several methods are currently employed to remediate shallow groundwater bodies, including: soil vapor extraction, bioventing, biodegradation, flow barriers, in situ passive treatment walls, groundwater removal for treatment by horizontal and vertical wells and drains. The currently used methods rely on relatively homogeneous subsurface conditions and high hydraulic conductivity. The currently used methods are costly. The widely used groundwater capture methods may fail because of low well yields, subsurface heterogeneity, failure to capture all (or even most) of the groundwater body, or may require such a long duration of remediation effort as to make the method impractical. The Air Force needs more effective and less costly remediation methods that do not require homogeneous aquifers and high hydraulic conductivity.