Geology, hydrology, water quality, and potential for interbasin invasive-species spread by way of the groundwater pathway near Lemont, Illinois

Invasive species such as Asian carps have the potential to travel in the egg, larval, or fry stages from the Des Plaines River (DPR) to the Chicago Sanitary and Ship Canal (CSSC) by way of the network of secondary-permeability features in the dolomite aquifer between these water bodies. Such movement would circumvent the electric fish barrier on the canal and allow Asian carps to travel unimpeded into Lake Michigan. This potential pathway for the spread of Asian carps and other invasive species was evaluated by the U.S. Geological Survey.

The bed of the DPR appears to be in at least partial contact with the exposed bedrock in most of the area from about 1 mile west of Kingery Highway to Romeo Road (the study area). Areas of exposed bedrock are the most likely places for Asian carps to enter the groundwater system from the DPR. Water levels in the DPR typically are about 7–16 feet higher than those in the CSSC in most of the study area. This difference in water level provides the driving force for the potential spread of Asian carps from the DPR to the CSSC by way of groundwater.

Groundwater flow (and potentially invasive-species movement) is through an interconnected network of permeable vertical and horizontal fractures within the Silurian dolomite bedrock. At least some of the fractures are associated with paleo-karst features. Several investigative techniques identified horizontal permeable fractures at about 546–552 feet above the North American Vertical Datum of 1988 within about 55 feet of the CSSC in the focus area between Lemont Road and Interstate 355. The elevation of the bottom of the CSSC in this area is about 551 feet, indicating that a direct conduit for flow of groundwater to the CSSC may be present. Wells further away from the CSSC in this area do not intercept fractures, so the fracture network may not be continuous between the DPR and the CSSC. These data are consistent with field observations of the secondary-permeability network along the CSSC walls, which indicate that the secondary-permeability features are completely filled with Pennsylvanian sediments within a few feet of the canal wall.

Water-level data indicate the potential for flow from the DPR into the Silurian aquifer in the focus area, then from the aquifer to the CSSC. Water-level data also indicate that the fractures within the aquifer in the focus area are hydraulically well connected to the CSSC but not to the DPR, indicating that flow from the DPR to the groundwater system may not be substantial or rapid.

Water-quality data in the CSSC and the DPR show similar values and trends and are affected by diel and longer term variations in climate and precipitation. However, the values and trends in water quality in the groundwater system tended to be substantially different from those in the DPR and the CSSC, indicating that the DPR and the CSSC do not appreciably recharge the groundwater system. Water-quality and flow data do indicate that groundwater discharges to the CSSC in part of the focus area. The absence of substantial hydraulic interaction between the groundwater and the DPR is supported by the absence of detectable concentrations of the dye tracer added to the DPR in groundwater in the focus area, which indicates that water from the DPR requires more than 2 weeks to move into the monitored parts of the groundwater system under approximately typical hydraulic conditions. The totality of the data indicates that there is minimal potential for the inter-basin spread of Asian carps by way of the groundwater pathway between Romeo Road and Stickney, Illinois.