A horizontal directional drilling contractor was attempting a pilot bore to place a 20-in steel oil pipeline when an inadvertent return incident occurred, suspending operations for 5 weeks. To mitigate any future suspensions, a lost circulation materials (LCM) plan was requested; the material needed to be carefully chosen to ensure that it would have a minimal impact on the environment. Varied particle sizes and concentrations of nutshells, SAFE-CARB ground marble bridging agent, and fibers were proposed, along with a pumping procedure to cure the loss zone.