For F. candida to live in the unconsolidated subsurface, adequately sized pore spaces must be available. Pore-space volumes were estimated for different subsurface depths and locations in the Michigan study area using grain size distribution data from soil borings ( Peterson et al. 2006). Representative individual pore-space volumes were calculated, using a 3D packing model, and the volume of a single F. candida was estimated by measuring the dimensions of thousands of individuals. It was determined that small differences in representative grain size (d10 or d50) can determine feasibility of F. candida occupancy, but above a minimum size, they do not consistently explain the presence or absence of F. candida in the study area locations. Because the tolerances between the size of the organism and the available void space, including pore throats, are so close, any F. candida mobility must be occurring via transport pathways/corridors of anomalously high effective porosity and permeability in the aquifer material