The United States Fish and Wildlife Service, the Illinois Environmental Protection Agency, the Illinois Department of Natural Resources, and the Missouri Department of Natural Resources, have initiated a natural resource damage assessment (NRDA) to address natural resource injuries resulting from the release of oil and hazardous substances at the Sauget Industrial Corridor (SIC) site and adjacent sites in St. Clair County, Illinois.    The goal of the NRDA is to restore natural resources to the condition they would have been in had the pollution not occurred, and to compensate the public for the losses of natural resources up to the time that such restoration is complete. Restoration can be accomplished by directly restoring the injured resource, or by rehabilitating, replacing, or acquiring equivalent resources.   The Trustees formally initiated the assessment with the publication of the Preassessment Screen for the SIC in 2009. In 2013, the Trustees released an Assessment Plan documenting their basis for conducting a damage assessment and setting forth the proposed approaches for quantifying natural resource injuries and calculating damages resulting from those injuries.    This document is a Phase 1 assessment of injuries to groundwater resources in Illinois, including a review of hazardous substance sources and the pathways by which hazardous substances have reached groundwater resources. As specified in the Assessment Plan, this injury assessment is based entirely on existing data collected as part of existing monitoring and remediation programs. The Illinois State Trustees may collect additional data to address data gaps in the future.