3-D Geologic Modeling Data
In two field seasons (2008-2009), the ISGS and McHenry County collected 31 continuous lithologic cores to bedrock (17 wireline-mud rotary, 14 rotosonic), which included downhole geophysical logs at each location (gamma ray and electrical resistivity). The ISGS also collected approximately 90 km of 2D geophysical profiles (seismic (51 km) and electrical resistivity (39 km)). The geophysical datasets help geologists further decipher the character of glacial sediments below land surface. These field data have been the key datasets for regional and local geologic interpretation in the County.
Hover over the drill-holes to download a pdf.
Water Well Database
Another primary data source that is often abundant in McHenry County is the historical water well record dataset. The quality of water well records is a common concern when using these data for geologic interpretation, and various approaches are used by geologists to assess the value of those records. The ISGS has incorporated a two-fold approach to address the quality of those records, which includes lithologic standardization and location verification. In McHenry County, approximately 95% of the formation descriptions from well records have been generalized into 17 descriptive lithologies. In addition to lithologic standardization, errors associated with data point locations are important to address. The locations of approximately 80% of the ~22,000 well records in the county have been verified to the best location available (e.g. GPS coordinates, street address, tax parcel). Although expensive and time consuming, well-location correction has been one of the most worthwhile efforts to address data quality, because it has been a critical means to reduce the inherent variability in water well record dataset (e.g. elevation errors associated with mislocated data).