The main advantage of in situ treatments is that they allow ground water to be treated without being brought to the surface, resulting in significant cost savings. In situ processes, however, generally require longer time periods, and there is less certainty about the uniformity of treatment because of the variability in aquifer characteristics and because the efficacy of the process is more difficult to verify.

Physical/chemical treatment uses the physical properties of the contaminants or the contaminated medium to destroy (i.e., chemically convert), or separate the contamination. Passive treatment walls separate and destroy the contaminant from in situ ground water. Air sparging, directional wells, dual phase extraction, fluid/vapor extraction, and hot water or steam flushing/stripping are separation techniques.

Available in situ physical/chemical treatment technologies include air sparging, bioslurping, directional wells, dual phase extraction, thermal treatment, hydrofracturing, in-well air stripping, and passive/reactive treatment walls. These treatment technologies are discussed in Section 4. Completed in situ physical/chemical treatment projects for ground water, surface water, and leachate are shown in Table 3-13 and additional information on completed demonstration projects are shown on the FRTR Web Site. Physical/chemical treatment is typically cost effective and can be completed in short time periods (in comparison with biological treatment). Equipment is readily available and is not engineering or energy-intensive. Treatment residuals from separation techniques will require treatment or disposal, which will add to the total project costs and may require permits.