Construction of the McCook Reservoir and connecting tunnel system continues; in this photo from November we can see the McCook Reservoir Main Tunnel bifurcation which will eventually be used to control flow to the 10 billion gallon capacity reservoir. This area of the tunnel is split into two rectangular segments to house the control gates. Installing a 33' diameter circular gate is not practical, so the flow is divided in order to use what are still very large, but more practical, rectangular gates. The floor of this portion of the tunnel is approximately 300 feet below the ground surface. The McCook Reservoir and tunnel system is a huge part of the Tunnel and Reservoir Plan (TARP, or “Deep Tunnel”) and will go online in two stages (Stage 1 in 2017 and Stage 2 in 2029). When complete it will provide flood protection benefits for people in 37 communities and improve water quality in the Chicago Area Waterway System (CAWS) and our rivers and streams by preventing combined sewer overflows.The reservoir that is done on the south side won a non-coal mining award. The posting includes a picture of some uplifted sedimentary rock.
Update: They don't say, but I assume these tunnels are also part of the McCook Reservoir construction.