EXECUTIVE SUMMARY

of the I l linois State Geological Survey to conduct a hydrogeologic characterization of the La Grange Wetland Mitigation Bank site near La Grange in Brown County, I l linois. The purpose of this report is to identify the hydrogeologic conditions of the wetland mitigation bank site and to recommend wetland restoration strategies. The I l linois State Geological Survey began collecting data at the site in May 2000. Data presented in this report include, descriptions of geologic materials, on-site precipitation, and water-level measurements from monitoring wells, staff gauges, and data loggers. Factors that indicate favorable conditions for wetland restoration include: hydric soils mapped over most of the site, extensive reversible hydrologic alterations, multiple potential water sources, and prior-converted (drained) wetlands mapped over approximately 50 % of the site. Also, significant portions of the site conclusively satisfied jurisdictional wetland hydrology criteria in 2001, 2002, 2003, and 2004. The area that conclusively satisfied wetland hydrology criteria ranged from 200 ha (493 ac.) in 2001 to 624 ha (1543 ac.) in 2002. The most significant potential water source for restoring wetlands at this site is the I l l inois River. Flood-frequency analysis shows that floods from the I l l inois River would inundate up to 527 ha (1303 ac.) once annually on average during the growing season, and up to 443 ha (1095 ac.) o