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Tackling Manhole Rehab In Laredo
“This bypass carried the main 36 to 42-inch trunk line for all the sewers for the entire city, and responsibility for its operation was entirely on our shoulders,” said Dupré. “This was the most nerve racking part of the entire project, because if the bypass line broke, untreated sewage would flow directly into the Rio Grande River, having state, local, and international repercussions. One month after we completed the project, the Rio Grande and Zacate Creek flooded Had we still been in operation, floodwaters would have taken out the bypass line. We got lucky there!”
Dupré said the second bypass was an internal system of 24-inch diameter pipes of a proprietary design developed by Southern Trenchless that operated at the bottom of manholes, allowing the line to remain in service while manhole repairs were made.
“The internal bypass saved money by eliminating traffic control requirements and lane and driveway closures so work did not impact top-side traffic,” said Dupré. “The city really appreciated that.”
Safety procedures included using a four-way gas monitor to check atmosphere levels for safe entry, Dupré said.
“We used an electric air blower to blow in fresh air supply, he explained. “And we used respirators meeting N95 OSHA standards to the prevent inhalation of solid particles. Each man who enters confined space is secured to a tripod and harness.”
Also part of the work in Laredo was CCTV inspection and cleaning 56,000 linear feet of the city’s main trunk line that started at 24-inches in diameter, grew to 30 inches, then to 36 inches and finally 42 inches.
Dupré said the pipe was at least 60 or 70 years old and had never been cleaned. Most of the cleaning was performed with a Vactor 2100 truck developing 80 gpm of flow. When a wall of super-heavy debris was encountered, a Brenford Sewer Hog was called in. The machine can deliver 350 gpm at 2,000 psi and uses sewer water because a water supply from a fire hydrant cannot keep up with the machine’s demand for water.
Dupré said he, Pedro Santos, and partner Ramon Closner established Southern Trenchless Solutions in January 2010 to serve the needs of Southern Texas which had no company specializing in manhole rehabilitation.
“Before we arrived, rehab crews had to come from Houston, Dallas and other Texas cities,” said Dupré. “It was clear a local rehab specialist was needed.”
Dupré said the company’s mission is broader than providing rehabilitation services, extending to research and developing its own methods, materials and equipment so they can serve the industry nationwide.