Abstract: A bioremediation apparatus for removal of volatile organic compounds (VOC's) from a contaminated air stream generated from the subsurface remediation of hydrocarbon contaminated ground water and soil is described. The apparatus includes an above ground multilevel biofilter which holds a biologically active media at each level, the levels forming a stack of interlocked levels in series such that the media in each level does not directly contact the media in the adjacent levels. The biofilter includes, a perforated support plate having a multiplicity of holes, the holes having a maximum diameter sufficiently small to prevent significant amounts of the bioactive media from passing there through and a minimum diameter sufficiently large to prevent clogging, the spacing between adjacent holes being selected to produce an overall ratio of total hole area to total plate area of between from about 20% to about 35%.