CORRECTION OF A SIX MILLION GALLON PER DAY TUNNEL INFILTRATION PROBLEM UNDER A PERFORMANCE-BASED ENERGY SERVICES AGREEMENT

One component of the City of Niagara Falls, New York sewer collection system is the Falls Street Tunnel, a 90-year-old rock tunnel three miles long. A 200-foot stretch of highly fractured rock had been allowing approximately six million gallons per day (mgd) of groundwater infiltration into the tunnel, which comprised about 20 percent of the wastewater treatment plant average flow. The 2 million cost of a repair project and persistent bonding difficulties had delayed corrective efforts. The project was included with other energy conservation work being undertaken for the City under an energy savings contract. A drilling and grouting project was performed to seal the majority of voids and fissures in the surrounding rock. Reduced pumping costs and chemical usage over the next ten years will pay for the cost of the repairs. Payment to the contractor was based upon the extent of leakage reduction, which was back calculated from the projected cost savings. The amount of groundwater successfully excluded was about four mgd. A long-term performance guarantee was provided, as was done for the other energy conservation projects. Additional benefits include improved combined sewer overflow management, process flexibility, longer pump life, and maintenance flexibility.