Hydrogeologic setting, water budget, and analysis of groundwater exchange at Crystal Lake, a glacial lake in McHenry County, Illinois

A study of the hydrology and hydrologic budget of Crystal Lake was performed between the months of May 2005 and April 2006 to better understand the groundwater flow system near the lake. Crystal Lake is in a glaciated setting and is fed by groundwater from a shallow sand and gravel aquifer. Hydraulic head data indicate that Crystal Lake is a flow-through lake, with groundwater entering in the north and discharging to the south. Stable isotope data support this conclusion. The change in weekly net groundwater flows provides some detail on transient groundwater flow. Large weekly and monthly net groundwater flows inversely correlated with periods of heavy precipitation suggesting that heavy precipitation and surface inflow raises the lake water level, reducing the groundwater gradient into the lake. If evapotranspiration is greater than precipitation over a long term period, the groundwater flow into the lake would play an important role in lake stability.