Rehab Runner Up

One of the largest utilities in the United States, Miami-Dade Water and Sewer Department (WASD) services a 400-sq mile area, treating and distributing water to 14 municipalities while collecting and treating wastewater from 11 municipalities.

On March 2, 2010, a failure occurred on a 54-in. prestressed concrete cylinder pipe (PCCP) in Miami, requiring immediate repair and replacement. To add insult to injury, a 72-in. PCCP force main also failed in a similar fashion. The failures precipitated a move by WASD to find and implement the best available inspection and repair/replacement technologies to address potentially damaging deficiencies in the buried pipe.

Through a combination of efforts that included contact with peers, interaction with vendors and online research, the engineers at WASD formed a comprehensive team of industry experts in nondestructive evaluation services, engineering consultation and repair/replacement contracting. Pure Technologies was one such expert and is the lead contractor on this ongoing inspection project.

WASD aimed to identify deteriorated pipe sections through non-destructive testing and monitoring, so the utility could implement proactive management and repairs to eliminate PCCP failures. It was also a goal that the program take place with the least inconvenience to customers serviced by WASD.

In a span of 18 months, several successful inspections, including in-line, robotic, manned, structural evaluations and replacements, were performed on almost 75 miles of large diameter water and wastewater PCCP pipelines within the county. Most of the rehabilitation required used little excavation and minimal shutdown of the system by using internal rehabilitation methods, such as carbon fiber layup repair and HDPE liners.

The basic methodology for WASD’s program is: 1) Prioritize pipelines for inspection; 2) Plan for the inspection including hydraulic modeling, valve testing and contingency plans; 3) Inspect the pipeline using either manned, robotic/tethered or free-swimming devices to detect the location of broken prestressing wires and leaks; 4) Perform a structural evaluation based on this data to determine pipes that require rehabilitation; 5) Plan for the rehabilitation; 6) Shut down pipeline for rehabilitation; and 7) Rehabilitate using the best option.

To date, less than 2 percent of all pipes inspected at WASD require rehabilitation. For the water pipelines, a carbon fiber reinforced polymer (CFRP) was used on the pipes requiring rehabilitation as an internal replacement method. CFRP rehabilitation is useful when a pipeline operator is not able to excavate for rehabilitation or the pipe segments are scattered along a lengthy stretch of pipeline. In these cases, the installation of CFRP would be the fastest, least disruptive and most cost-effective repair solution. By using CFRP, WASD does not have to dig, replace or line long pipe segments. On the wastewater side, because the pipeline inspected was heavily distressed, an HDPE liner was used to rehabilitate the pipeline. Again, HDPE is the fastest, least disruptive and most cost-effective solution. Minimal excavation was required to address the wastewater issues.