The high cost of landfilling and the potential uses of waste foundry sands have prompted research into their beneficial reuse. Roadways have a high potential for large volume usage of the foundry sands. A laboratory testing program was conducted on soil-foundry sand mixtures amended with cement and lime to assess their applicability as highway subbase materials. The mixtures were compacted in the laboratory at a variety of moisture contents and compactive efforts and subjected to unconfined compression, California bearing ratio, and hydraulic conductivity tests. The environmental suitability of the prepared mixtures was evaluated by analyzing the effluent collected during hydraulic conductivity tests. Finally, required subbase thicknesses were calculated using the laboratory-based strength parameters. The results of the study show that the strength of a mixture is highly dependent on the curing period, compactive energy, lime or cement presence, and water content at compaction. The resistance of foundry sand-based specimens to winter conditions is generally better than that of a typical subbase reference material. Laboratory leaching tests indicated that if these mixtures later come in contact with water that has been discharged directly to the environment (e.g., drainage through asphalt pavement), the quality of water will not be affected.