National Power Rodding (NPR) recently completed a project in the Chicagoland Area. The customer asked NPR to investigate a tunnel shaft that served as a conduit for a 12-inch diameter watermain. The village knew there was water infiltration but was unsure of the source.
The task presented notable complexities, considering the watermain’s substantial depth of 100 feet underground compounded by its passage beneath the Chicago Sanitary and Shipping Canal. This watermain is responsible for feeding fresh water from the south side of the town to the north side, situated approximately 40-50 feet below the riverbed. The only way to reach and inspect the line was through the 6 by 5-foot diameter tunnel shaft, down to a 12-foot arched tunnel running underneath the canal about 400 feet long. The last time the watermain had been inspected was in 1980 by the local fire department with the assistance of trained divers.
When NPR arrived on the scene, they found that both the north and south side shafts were filled with 80 feet of water that would have to be pumped out in order to access the tunnel. Once the shaft and tunnel were dewatered, they discovered that the watermain was still under pressure and free of leaks. Inspections found the leaks were actually in the base and sides of the tunnel due to groundwater infiltration. These leaks would need to be grouted by hand using a grout gun. The NPR team drilled several 2-inch holes in concrete that was 18 inches thick with a 2-foot head on the grout gun to stop the leaks.
Due to the depth of the project and confined space concerns, a number of safety protocols were put in place prior to addressing the tunnel issues. A pre-launch safety plan was drawn up defining everyone’s role, and confined space retrieval equipment was ordered. First, a camera-only test run was initiated. The crew was tethered and lowered down the shaft into the tunnel. Four crew members were working in the tunnel out of a team of twelve people. Rescue and ventilation personnel were on both sides of the river. The crew was equipped with flotation devices, life vests, gas detectors and escape packs. The air quality was monitored, and blower fans were used to provide fresh air. Two cameras were on at all times capturing all work and providing a live feed to the crew above ground.
The project involved a seven-month planning and execution phase, requiring the deployment of seven trucks and a team of twelve crew members. The job itself only took four days to dewater, pre-inspect, stop the infiltration and then do a final inspection of the job. This underscores the critical role of detailed planning in achieving project success and customer satisfaction.