text: For mutually insoluble compounds, Dalton's law states that the partial pressure of a non aqueous phase liquid (NAPL)  is equal to its vapor pressure, and that the NAPL in contact with water will boil when the vapor pressure of water plus the vapor pressure of the VOC is equal to ambient pressure.  When a VOC-steam bubble is formed the composition of the bubble is proportional to the composite’s respective vapor pressures.