Hydrogeologic Implications Of Surficial Geologic Mapping And Three-Dimensional Modeling Of Glacial Outwash Deposits Within The Woodstock, Il 7.5 Minute Quadrangle

Over pumping groundwater resources of the greater Chicago metropolitan area reversed the regional hydraulic gradient. Lake Michigan currently supplies ancillary water resources to the growing region (Ipe et al., 2002). Legislation currently limits the Chicago metropolitan area\u27s demand on Lake Michigan (Level of Lake Michigan Act). Nevertheless, the population of the Chicago region continues to grow and water demands continue to increase. McHenry County recognizes the importance of understanding their long-term water supply needs. The County is entirely sustained by groundwater (Meyer, 1998), derived from both shallow (\u3c 200 ft. (60 m)) and deep aquifers. Shallow sand and gravel aquifers supply approximately 60% of the 2.31 mil gal/day groundwater demand. Best management practices in Woodstock, IL require a clearer understanding of potential shallow aquifer systems. Poorly understood groundwater flow and recharge in regional glacially derived sand and gravel aquifers demand further investigation. In McHenry County, sediments in these aquifer systems vary from dense till to coarse sand and gravel outwash (Curry, 1997), (Hansel and Johnson, 1996). Groundwater-surface water interactions and shallow-aquifer connectivity to underlying aquifers complicate local groundwater flow systems and make it difficult to estimate hydrogeologic parameters such as gradients, velocities, and storage volumes. Local mapping and modeling studies can provide insight to better estimate such aquifer parameters and help guide local water managers in related groundwater needs questions. For example, an accurate understanding of these aquifer systems within the county will help officials continue to make wise water-policy decisions such as appropriately instating water shortage notices and reasonably managing water supply. This research addresses mapping and modeling efforts to improve understanding of local shallow groundwater processes in McHenry County, Illinois. This project consists of three parts: (1) surficial geologic mapping, (2) three-dimensional subsurface geologic modeling of a shallow sand and gravel aquifer, and (3) three-dimensional aquifer characterization of proximal glacial outwash variability. Previous publications model geological depositional environments with geostatistical methods (Anderson, 1999), not commonly substantiated by quantitative values (Ritzi, 2000). This thesis is one of few attempts to display facies assemblages in geologically feasible geometries and orientations of an ice front outwash plain