In 2014, the Illinois State Toll Highway Authority began reconstruction of the Jane Addams Memorial Tollway along Interstate 90, a segment of which is adjacent to Trout Park Nature Preserve in Elgin, Illinois. The preserve contains rare and sensitive fen habitat, several threatened or endangered species, and a remnant stand of northern white cedar. This fen habitat, the associated northern white cedar, and a perennial stream within the preserve rely on persistent groundwater discharge to the land surface. Before reconstruction, several impacts to the hydrology and water quality in the preserve were identified, including decreased groundwater levels due to underground drainage infrastructure and elevated levels of pollutants related to roadway runoff from Interstate 90 and Illinois Route 25, as well as leaky storm sewers within and adjacent to the preserve. To mitigate for these impacts, several changes were made to the drainage network and a concrete barrier wall was installed during reconstruction. Under contract with the Illinois State Toll Highway Authority, the Illinois State Geological Survey monitored surface and groundwater levels and water quality at Trout Park Nature Preserve before, during, and after reconstruction to evaluate the response of groundwater levels and water quality due to the reconfiguration of the storm drainage infrastructure. Results of monitoring show that the reconfiguration of the drainage network immediately resulted in increased groundwater levels along the north margin of the preserve. Although this water level recovery generally persisted after decommissioning of the former sewer lines, over the longer term a localized decrease in groundwater levels was observed at one monitoring location and likely reflects a reduction in surface-water runoff from Interstate 90 to the preserve due to the installation of the barrier wall. Before and after reconstruction, groundwater and surface water at the preserve had elevated levels of dissolved solids, mainly due to high concentrations of sodium and chloride resulting from decades of deicing activities along Interstate 90 and Illinois Route 25. After reconstruction, increased levels of dissolved solids, owing mainly to increased sodium and chloride in groundwater, were observed in two of three ISGS monitoring wells. These increases were likely due in part to rewetting and dissolution of residual legacy road salt along the Tollway apron as local groundwater levels increased. Reduced dissolved solids in the third well likely reflects reduced runoff from Interstate 90 following installation of the barrier wall, but is also attributed to a decrease in water level and no rewetting and dissolution of residual legacy road salt at this location. Decreased levels of dissolved solids were observed at all surface-water monitoring locations after reconstruction and likely reflect the combined effects of a period of increased precipitation after reconstruction and reduced influence from the reconfigured drainage network. The occurrence of metals commonly associated with roadways and observed in water samples from Trout Park Nature Preserve generally decreased after reconstruction, although detections of chromium, manganese, and nickel increased slightly after reconstruction.
|Original language||English (US)|
|State||Published - 2020|
|Name||Open File Series 2020-1|