This paper documents the importance of membrane processes to surfactant-enhanced subsurface remediation and presents results of a field study on these processes. Surfactants enhanced the contaminant (BTEX) concentrations by one to two orders of magnitude over baseline ground water concentrations. The surfactant stream was decontaminated by air stripping in hollow fiber membranes and concentrated using ultrafiltration. Hollow fiber air stripping was able to avoid foaming problems which will be more common in packed tower air strippers. A 10000 MWCO ultrafilter was able to recover a majority of the surfactant (approaching 80%) despite being hindered by ground water dilution (ground water extraction was four times greater than injection to maintain hydraulic control). A fundamental model of surfactant-reduced stripping efficiency was corroborated by the field results, providing further confidence in the use of this model for design purposes. The high level of surfactant recovery (90%+/-6%) achieved in a relatively low permeability formation (1 ft/day or 3.5x10(-4) cm/s) is also encouraging. These results thus demonstrate the importance of an integrated design to optimize system performance, and illustrate the ability of surfactant-enhanced technologies to expedite subsurface remediation.