Vacuum-enhanced recovery of water and NAPL: Concept and field test

Vacuum-enhanced nonaqueous phase liquid (NAPL) recovery has attracted recent attention because it offers a means to increase NAPL recovery rates compared with conventional methods, and to accomplish dewatering, while also facilitating vapor-based unsaturated zone cleanup. A conceptual model is presented that recognized the effects that vacuum-enhanced recovery has on soil water and NAPL, with focus on liquid residing at negative gage pressures and therefore lacking sufficient potential energy to flow into a conventional recovery well or trench. This conceptual model was tested during a 3-week-long pilot study. During phase 1 of the pilot study, conventional recovery (liquid only) was carried out from a well screened at the water table, while during phase 2, dual-phase extraction was performed at the same well. The application of 27 kPa vacuum resulted in an increase in NAPL recovery from negligible (phase 1) to approximately 6.6 1/d (phase 2), with a noncurrent increase in water recovery from approximately 190 to 760 1/d.