Organo-silane (OS) surface modification works by chemically altering the surface of silica based materials and rendering them hydrophobic (waterproof). Limited research is present in the literature addressing the use of OS modified soils as an infiltration barrier. The goal of this research is to develop the relationships between varying degrees of hydrophobicity, varying levels of soil compaction, and water infiltration resistance for materials including Ottawa sand and coal fly ash (CFA). Initial testing was performed to determine key geotechnical engineering properties of the selected materials. Next, a range of treatment levels were established to achieve varying levels of hydrophobicity for two separate OS chemicals. OS modified material was then prepared to varying degrees of hydrophobicity and compacted to field relevant density levels. The hydraulic head required to overcome the infiltration resistance was determined, and therefore the hydraulic head below which no infiltration will occur. Additionally, saturated hydraulic conductivity and soil-water characteristic curve testing was performed. Water entry pressures of hydrophobic sand were found to range from 0 to 14 cm of H2O, and water entry pressures of hydrophobic CFA were found to range from 0 to 542 cm of H2O. Positive correlations were established between compaction, degree of hydrophobicity, and water entry pressure. Soil hydrophobicity was found to have little effect on the saturated hydraulic conductivity. Results indicate that hydrophobic soils are a viable option as an infiltration barrier, but additional research is recommended to address durability and field application.