The Monarch-Chesterfield levee system is located approximately 15 miles west of the city of St. Louis, MO, along the Missouri River. The 12-mile system provides flood risk reduction to approximately 4,700 acres of land in Chesterfield Valley including primarily commercial and industrial properties, as well as some residential and agricultural properties. The system was federally authorized, and is locally owned, operated and maintained by the Monarch-Chesterfield Levee District (MCLD). In the 1980s, local community constructed improvements to the existing levee system in order to reduce the risk of flooding for a 100-year flood event (a frequency of 1% chance of occurrence in any given year). Rising floodwaters during the summer of 1993 breached the levee system causing an estimated $200 million in damages. Since then, the U.S. Army Corps of Engineers and the MCLD have constructed improvements under a partnering agreement that reduce the risk of flooding during a 500-year flood event (a frequency of 0.2% chance of occurrence in any given year). Increased land values together with commercial and industrial development have resulted in an estimated property value of $1.35 billion. There are an estimated 55,000 people working, residing or traveling through the leveed area on an average day. Properties within the leveed area include the Spirit of St. Louis Airport, U.S. Customs and Border Protection, emergency response services, sports fields, railroad tracks, Interstate 64/US Route 40, chemical manufacturers, churches, community health services, and several shopping centers: Chesterfield Commons, St. Louis Premium Outlets, and Chesterfield Outlet Mall.