 Guidance from the Pacific Northwest National Laboratory (PNNL) supplements these documents by discussing specific actions and decisions related to SVE optimization, transition, and/or closure.Design and operation of a SVE system is relatively straightforward, with the major uncertainties having to do with subsurface geology/formation characteristics and the location of contamination.As time goes on, it is typical for a SVE system to exhibit a diminishing rate of contaminant extraction due to mass transfer limitations or removal of contaminant mass.