The 44-surface-ac. Sylvan Lake is held by a dam that was installed by a mink farmer in the early 1940s. In 1960, the Colorado Division of Wildlife acquired the property, turning it over to the Colorado State Parks system a few years later. The Sylvan Lake dam was considered a Class I, high-hazard dam because of the campsites located downstream from the outlet. During a 1998 inspection, a Colorado Division of Water Resources dam safety engineer discovered pinholes and a 4-in. deflection in the 30-in. corrugated metal dam outlet pipe. Colorado State Parks hired a private consultant, Christopher Manera, P.E., president of Colorado River Engineering, to advise on the best way to fix the problem. Manera’s first task was to conduct a feasibility study. Initial inspections showed that although the pipe was deteriorated, there was no immediate threat of collapse. That gave the team plenty of time to research replacement and rehabilitation alternatives.Over the course of further evaluations, Manera found that-other than replacement of the outlet structure, which would require a complete breach of the dam-the only viable option was trenchless rehabilitation. Trenchless rehabilitation was a less expensive option than replacement. In addition, because Sylvan Lake is a high-elevation reservoir, the construction season lasts a mere four months. “Replacement of the dam would have taken at least two summer seasons,” says Manera.