Preserving Casper's Infrastructure: A Large Diameter Pipeline Trenchless Rehabilitation Project-DFI49 Published Technical Paper

DFI49 Published Technical Paper

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The document describes the rehabilitation of Casper, Wyoming’s North Platte Sanitary Sewer Interceptor (NPSSI), a nine-mile wastewater line built in the early 1980s from unlined reinforced concrete pipe. Over time, low flow conditions caused high hydrogen sulfide levels, leading to severe corrosion and structural deterioration. After years of inspection, corrosion modeling, and pilot corrosion-control testing, the City and project team developed a long-term renewal strategy using trenchless technology.<br /><br />The project focused on critical portions of the interceptor and was designed to maintain service, minimize disruption, and control costs. The final rehabilitation scope included 7,600 ft of large-diameter CIPP lining, point repairs, new junction structures, manhole reconstruction and lining, and siphon structure improvements. The work was divided into phases to manage bypass pumping, winter weather, and subcontractor logistics.<br /><br />Construction presented major challenges, including heavy debris, severely degraded pipe with exposed reinforcement, extreme winter temperatures, and utility conflicts. The team developed innovative solutions, such as a floating cleaning/scouring platform and a transitional CIPP liner to bridge an unexpected diameter change from 48 to 54 inches. Another conflict involving a 27-inch utility pipe inside a vault was solved through temporary bypassing and structural redesign.<br /><br />Despite these difficulties, the project was completed on time, with only one time extension and at a final cost slightly under budget. The paper emphasizes lessons learned: invest in thorough inspection, involve all stakeholders, research historical records, anticipate utility conflicts, and plan carefully. The NPSSI rehabilitation is presented as a successful example of restoring critical buried infrastructure for another 100 years of reliable service.

Keywords

North Platte Sanitary Sewer Interceptor

Casper Wyoming

wastewater rehabilitation

trenchless technology

CIPP lining

hydrogen sulfide corrosion

sewer interceptor renewal

bypass pumping

manhole reconstruction

utility conflicts