This knowledge can be used to accurately install pathways (e.g., wells) to effect contaminant re-
moval. The flow through these pathways can then be controlled using an intelligent valving system (Photo 3.2a) or enhanced by wind or solar-powered pumping sys-
tems (Photo 3.2b) to optimize the performance of the technology.

Technology Needs

One of the most significant prob-
lems affecting DOE sites is subsur-
face contamination by chlorinated solvents. These solvents tend to accumulate in the finer sediments of the unsaturated zone, where they serve as a continuing source of contamination to the water in the aquifers below. Barometric pumping technology is applicable

to the removal of residual volatile contaminants in the unsaturated zone. In using the baseline tech-
nology (active soil vapor extrac-
tion) to remove contamination in the unsaturated zone, a point of diminishing returns is reached where a residual remains that is resistant to the active extraction process. At this point the baseline technology becomes progressively less cost-effective because of the expense of running the active ex-
traction equipment (i.e., vacuum blowers) over a long period of time. Barometric pumping tech-
nology is complementary to active vapor extraction. When the point of diminishing returns (because of mass transfer limitations) using active vapor extraction process is reached, the residual contaminant can be removed effectively and