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Soil could accept onsite wastewater at rates two to three orders of magnitude higher than the current design loading rates if a clogging mat at the wastewater infiltration surface was limited or not present. The clogging mat controls system design, loading rate and life. Maintaining aerobic conditions at the wastewater infiltration surface could substantially reduce or eliminate clogging. This project is studying soil oxygen supply to the zone of clogging in soil. A model based on a form of Ficks Law for diffusive transport is being applied to oxygen diffusion to the wastewater infiltration surface. Gas filled porosity controlled by soil characteristics of texture, structure, consistence and water content as well as the distance to the supply of oxygen and rate of oxygen consumption control the flux, F, of oxygen. If the oxygen consumption rate exceeds the maximum flux of soil oxygen then the soil infiltration surface will become anaerobic. To maximize delivery of oxygen, soil components should be shallow, narrow and have separated infiltration areas. Using models that incorporate system depth, geometry, and oxygen diffusion coefficients in soil, efficient loading rates can be estimated. Design of wastewater infiltration surfaces should be based on both oxygen transport and hydraulics. In many cases, oxygen transport will be limiting and therefore the basis for design.