Laboratory batch experiments were conducted to determine the multi-phase distribution of trichloroethylene (TCE) and ortho-xylene (O-X) among a simulated groundwater, air and Bandelier tuff. A range of concentrations were added to water in batch reactors at the beginning of the experiments and their partitioning between water and air was measured. Equilibrium was practically reached within the first hour. Estimated adsorption on tuff was effectively modeled by Linear and Freundlich isotherms. Henry's Law constants were also calculated for both compounds. Equilibrium data indicate that TCE will partition from an aqueous solution to 64-81% in water, 16-23% in vapor phase, and 2-20% in the tuff. O-X will partition differently: 77-94% in the water, 3-19% as vapor, and 1-13% in the tuff. Analytical chemistry techniques included both radioanalysis and gas chromatography mass spectrometry (GC/MS). The study highlights the need for adequate techniques and procedures to ensure mass accountability of volatile compounds in the laboratory.