Case Study from Trenchless Rehabilitation of 60-Inch Residuals Transfer Main at East Side Water Treatment Plant

A 55-year-old reinforced concrete water pipe, approximately 11,640 linear feet in length and 60-inch in diameter, transfers water treatment residuals from the East Side Water Treatment Plant to three off-site lagoons on the east side of Dallas, TX. Subsequent to the construction of the 60-inch residuals transfer main, five primary lagoons were built on-site at the water treatment plant, thus relegating operation of this main to overflow and wash water transfer to the off-site lagoons. Improvements of the three off-site lagoons has allowed the plant to transfer wash water to the East Fork of the Trinity River. The existing 60-inch residuals transfer main contains seven in-line manholes ranging from 1,200 to 2,000 feet apart, which many of the manholes are inaccessible. A comprehensive study on hydraulic capacity and condition of pipe, by CCTV inspection method, was performed to determine if the pipe can be converted to the new operating conditions of the water treatment plant. The biggest challenge during pipe inspection was limited access to the manholes due to unknown manhole locations, thus only 50% percent of pipeline was inspected. According to ASTM F 1216, the pipe is classified as "partially deteriorated condition." After assessing the condition of the 60-inch residuals transfer main, four renewal and rehabilitation alternatives were proposed. These alternatives include: (1) replace main in the existing alignment by open-cut, (2) open-cut in new alignment, (3) trenchless rehabilitation by cured-in-place method, and (4) trenchless rehabilitation by sliplining. The objective of this study is to investigate advantage and disadvantage of each proposed alternative and perform cost analysis to find the most reliable and cost-effective method.