Summary of long-term groundwater monitoring at Lake in the Hills Fen Nature Preserve, McHenry County, Illinois

This report summarizes the extensive hydrological, geological, and geochemical data collected over the past 22 years. The report also provides a detailed assessment of hydrological and geochemical variations observed. Data collected by others as early as 1986 within and near the preserve are also presented. This report updates information submitted by Locke and Miner to the Illinois Nature Preserves Commission in July 2007. The Lake in the Hills Fen Nature Preserve was dedicated as an Illinois nature preserve in 1990 and is jointly owned by the Village of Lake in the Hills, the Illinois Department of Natural Resources, and the McHenry County Conservation District. The preserve supports rare plant species and diverse ecological communities, including calcareous fens. Since 1998, the Illinois State Geological Survey (ISGS)and the Illinois State Water Survey (ISWS) have collected detailed geological, hydrological, and geochemical information to better understand groundwater conditions that support several fens within the preserve that are close to surface mining operations on adjacent property. The ISGS and ISWS groundwater monitoring program has been unique in several respects, including the frequency, breadth, and length of monitoring. Between February 1998 and December 2020, 350 groundwater sample sets were collected during 48 field visits from 17 monitoring wells within or near the preserve. Samples were analyzed for over 40 different parameters.