The North Texas Municipal Water District began a comprehensive Condition Assessment Program (CAP) project in Fiscal Year 2017 to identify and prioritize inspections and maintenance for our vast wastewater system of infrastructure. The full scope of the project entails conducting multi-sensor inspections of all large-diameter gravity mains, condition inspection of select force mains, and condition inspection of all manholes and condition inspection of all lift stations to develop a baseline score for each asset to then compare in future inspections. The continued work on this program also helps the District maximize cost efficiencies to get the most value out of funds budgeted for our most critical and aging infrastructure.
Gravity pipelines
Each gravity pipeline is inspected using a tool that measures the inside dimensions of the pipeline for comparison to the original specifications. This data is used to grade the pipe segment on a 1 to 5 scale, with 5 representing the worst condition pipes in need of immediate attention. Each inspected asset is assigned a renewal action based on the observed and measured condition of the asset. These actions include replacements, point repair, O&M work, or re-inspection.
Through FY20 of the program, the team inspected approximately 339,585 linear feet (LF) of large-diameter gravity lines with only 18,719 LF (6%) receiving a score of 4 or 5.
Force mains
In FY20, NTMWD inspected 5 miles of force main, pipelines that convey wastewater under pressure, including the Lower White Rock Creek and Lower White Rock Creek Parallel. Force main inspections were completed using two technologies – one that uses an acoustic inspection to identify possible leaks and air pockets along the force main, and another that is an electromagnetic scan of bar wrapped pipe to identify broken reinforcing bars and possible wall loss due to corrosion. These inspections required a closely coordinated effort with the lift station operators to maintain a narrow allowable velocity range.
Manholes
NTMWD is concurrently working to inspect each of our manholes – approximately 1,800. To date, 1,424 manholes have been inspected, and similar to the pipeline inspections, each manhole receives either a replacement, lining, or O&M recommendation based on the observed condition.
In addition to the inspection work, NTMWD is surveying all of the wastewater manholes and the force main valves. As part of this survey process, the District is able to update our geographical information system (GIS) to more accurately reflect the precise location of numerous manholes and force main valves in our database. To date, teams surveyed nearly 1,320 manholes and 141 force main valves.
Positive Discoveries
Expectations at the beginning of the CAP project anticipated finding large-diameter lines in poor condition with significant defects in need of emergency repairs. Instead, most of the lines (greater than 90%) were found to be in relatively good condition with minimal defects. Additional positive results came from the discovery of differences between field verified, GIS records and construction completion renderings (as-builts). Through the inspections, NTMWD identified 50 (and counting) previously unrecorded manholes, recorded significant changes in numerous manhole locations, identified large difference between as-builts and laser-measured diameters, and determined areas requiring routine cleaning, especially around lift stations.
Overall, the benefits directly related to the CAP project have led to an enhanced understanding and knowledge of asset condition, a restoration of capacity through detailed cleaning and debris removal where needed, increased our proactive maintenance, and heightened our GIS accuracy. By conducting these detailed analyses and performing repairs and maintenance when and where they are needed the most, the District is able to save money and manpower.