Earthwork associated with highway construction provides an opportunity for high-volume reuse of excess system sands (ESS) discarded by the foundry industry. California bearing ratio (CBR), unconfined compressive strength, and resilient modulus tests were conducted on 13 ESS, one base sand, and two reference materials. Tests were conducted on specimens prepared dry of optimum, wet of optimum, and at optimum water content with standard and modified Proctor compaction effort. Results of these tests were used to identify characteristic engineering properties of ESS, appropriate compaction conditions for ESS when used as subbase, and empirical equations that can be used to predict the engineering properties of ESS based on index properties. Results of the tests indicate that ESS classify as SP, SM, or SP-SM (A-2-4 or A-3 in AASHTO) and should be compacted dry or at optimum water content and, if possible, with higher compactive effort. The CBR of the ESS ranged from 4 to 40 and averaged 20 when compacted with standard effort at optimum water content. Swell during the soaking portion of the CBR tests was small for all ESS. ESS compacted at optimum water content with standard effort had unconfined compressive strengths ranging from 71 to 190 kPa. Resilient moduli of the ESS were similar to that of a reference subbase material but smaller than a reference base material. A power function model in terms of bulk stress described resilient moduli of the ESS well.