Innovative Alternatives - City of Twin Falls
Friday, June 19, 2015
Posted by: Gay Dawn Oyler
Finding cost effective and innovative methods to replace aging infrastructure
The City of Twin Falls has approximately 230 miles of sewer pipe buried underground. The age of the pipes ranges from new to over 100 years old, and the condition generally corresponds to the age of the pipe. The Public Works Department developed a Zone Maintenance Program in 2012 that separated the city into eight zones, allowing for a more efficient method of upgrading and maintaining infrastructure. The budget for sewer pipe replacement in Zone Maintenance is approximately $350,000 each year. Based on traditional and current replacement costs, this budget will only allow for approximately 1 mile of pipe replacement each year. But because the design life of gravity sewer pipe is approximately 90 years, the City should be replacing closer to 2.5 miles of pipe annually. Because of the discrepancy in need and resources, the City began investigating less costly alternatives for sewer pipe replacement.
The resulting alternative solution proposed by Public Works is both innovative and cost effective. Cured-In-Place Piping (CIPP) is a method that was developed in England in the 1970s and became widespread in the 1990s when the patented technology entered the public domain. The method involves lining an existing sewer pipe with a flexible fabric pipe injected with resin The lining is then pressurized and heated with steam until it adheres to the walls of the existing pipe and cures. The curing process takes approximately one hour and results in a solid-walled seamless pipe similar to PVC.
The primary advantage of CIPP is that it is a trenchless solution. By avoiding trenching, and subsequent traffic control and surface repair, there are significant cost savings. There are, however, limits to the use of this technology. The size ranges from 8" up to 60", making any lines larger in diameter than 60" ineligible for this solution. This is not an issue at this time, however, as the City does not have any sewer lines larger than 60" in diameter. Additionally, the existing host pipe must be relatively free from sags and any significant decay.
CIPP was used to replace approximately 330 ft. of 8" sewer pipe at the intersection of S. Park Ave and Washington St. South (State Highway 74) in 2014. The CIPP solution cost $12,000; traditional replacement with trenching, traffic control, and surface repairs would have cost in excess of $25,000. Taking the amount of sewer line that needs to be replaced into account, this will result in a significant cost savings to the City over time.
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