LESSONS LEARNED – 21 SANITARY SEWER FAILURE AT THE TRINITY RIVER

On May 7, 2001, the south bank of the Trinity River, located in northeast Arlington, Texas, approximately 25 miles west of Dallas, Texas, experienced a massive dish failure and slumped into the river bottom. The failure of the embankment washed away approximately 100 feet of a 21-inch sanitary sewer main. This main carries approximately 1.0 MGD of wastewater to the Trinity River Authority Central Wastewater Treatment System. Arlington Water Utilities Department employees responded immediately and confirmed that the sewer main has been severely damaged from the mudslide. Field Operations Repair Crews (“Crews”) were dispatched, surveyed the situation, and determined that by-pass pumping of the sewer flow around the missing pipe was possible. By-pass pumping equipment was located, delivered, and set-up by the Crews. The Crews were able to contain and by-pass approximately 0.8 MGD flow with 8 hours and 100% of the flow the next day.Due to the location, the need for large construction equipment, and the magnitude of the damage, it was determined that the Crews would be unable to complete permanent repairs and assistance from a pre-qualified utility contractor would be required. On Tuesday, May 8, 2001 Water Department staff met to develop a plan for a permanent repair. Staff identified key tasks that would have to be performed by outside contractors and engineering consultants, and using emergency authority contracted with those parties.Action planning, interdivisional cooperation, and communication with outside parties, allowed Arlington Water Utilities, to respond to numerous potential problems associated with this situation. In addition, this circumstance taught some new lessons and caused established procedures to be modified or changed.