A number of experiments have been conducted to acoustically image plumes of particulates suspended in the ocean. In many cases the scattering is in the long-wavelength or Rayleigh region. A comprehensive framework was recently developed for calculating the intensity received by a monostatic sonar system due to backscattering in the Rayleigh region from a plume of suspended, nonspherical particulates [D. R. Palmer, J. Acoust. Soc. Am. 99, 1901--1912 (1996)]. This framework is extended to include the possibility that the plume is close to an ocean boundary. The distances of the particulates from the boundary are assumed to be small compared to the wavelength and the boundary surface is assumed to be planar. The scattering amplitude in the presence of a rigid or a pressure-release boundary surface is related to the amplitude in the absence of the surface. As a result the intensity can be averaged over the random orientations of the individual particulates and this averaged intensity can be bounded in terms of the intensity that would be measured if the particulates scattered the acoustic wave as if they were spherical.