We have studied ELF waves which were observed during beam-plasma discharge in the large vacuum chamber at Johnson Space Center. Phase delays as a function of radius (obtained from cross-correlation measurements of density fluctuations) along with measurements of frequency and plasma potential, density, and temperature have been compared to a zero-order slab model of nonlocal azimuthal drift wave propagation. The inferred wave phase velocity in the plasma frame after Doppler correction is found to be near one half the electron diamagnetic drift velocity. Although our measurements do not uniquely define a propagation mode, a model of azimuthal drift wave propagation is found to be consistent with our observations.